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A GUIDE TOPOLYOLEFIN

EXTRUSION COATING

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Table of Contents Page

What Are Polyolefins?.............................................................................................. 2Effect of Molecular Structure and Composition on Properties and Processability .... 2How Polyolefins Are Made ....................................................................................... 6Polyolefins for Extrusion Coating ............................................................................. 7LyondellBasell Works Closely with Processors ................................................................. 8

Shipping and Handling Polyolefin Extrusion Coating Resins .................................... 8The Extrusion Coating Process .............................................................................. 8

Resin Handling/Conditioning ................................................................................ 8Blending with Colorants and Additives ................................................................... 10Substrate Handling and Surface Preparation ......................................................... 10

The Extrusion Coating Machine ............................................................................. 15Start-Up of An Extrusion Coating Line ................................................................... 34

Guidelines for Start-Up ....................................................................................... 35Shut-Down Procedures for Extrusion Coating Line ............................................... 36Optimizing the Extrusion Coating Process ........................................................... 36Process Variables Affecting Properties of Extrusion Coatings .............................. 37Appendix 1: Common Coating Problems and Their Causes ................................ 39Appendix 2: Formulas for the Extrusion of Polyolefins ......................................... 41Appendix 3: Cleaning the Extruder and Its Parts .................................................. 42Appendix 4: Metric Conversion Guide ................................................................... 43Appendix 5: Abbreviations ............................................................................................ 45Appendix 6: Glossary ........................................................................................... 47Appendix 7: Test Methods Applicable to Polyolefin Extrusion Coating

Resins and Their Substrates ............................................................ 51Appendix 8: Trade Names for Products of LyondellBasell Chemicals ........................... 53Index ................................................................................................................... 54

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What Are Polyolefins?

Polyolefins are thermoplasticresins polymerized from petroleum-based gases. The two principal gasesare ethylene and propylene. Ethylene isthe raw material for making polyethyl-ene (PE) and ethylene copolymerresins and propylene is the mainingredient for making polypropylene(PP) and propylene copolymer resins.Polyolefin resins are classified asthermoplastics, which means that theycan be melted, solidified and meltedagain. This contrasts with thermosetresins which, once molded, cannot bereprocessed. Most polyolefin resins forextrusion coating are sold in pelletform. The pellets are about 1/8 inchlong and 1/8 inch in diameter, usuallysomewhat translucent and white incolor. Polyolefin resins sometimescontain additives, such as thermalstabilizers, or are compounded withcolorants, antistatic agents, UVstabilizers, etc.

Effect of Molecular Structure andComposition on Properties andProcessability

Three basic molecular propertiesaffect most of the properties essentialto high quality extrusion coatings.These molecular properties are:

• Average Molecular Weight

• Molecular weight Distribution

• Crystallinity or Density

These molecular properties aredetermined by the materials used toproduce polyolefins and the conditionsunder which resins are manufactured.The basic elements from whichpolyolefins are derived are hydrogenand carbon atoms. For polyethylenes,these atoms are combined to form theethylene monomer, C

2H

4, i.e., two

carbon atoms and four hydrogen atoms(Figure 1). In the polymerizationprocess, the double bond connectingthe carbon atoms is broken. Under theright conditions, these bonds combinewith other ethylene molecules to formlong molecular chains (Figure 2). Theresulting product is polyethylene resin.

H H

C = C

H H

Figure 1. Ethylene monomermolecular structure

Figure 5. Crystalline (A) andamorphous (B) regions inpolyolefin.

H H H H H H H H H H

C C C C C C C C C C

H H H H H H H H H H

Figure 2. Polyethylene molecularchain.

Figure 3. Polyethylene chain withside branches.

Ethylene copolymers, such asethylene vinyl acetate (EVA) andethylene n-butyl acrylate (EnBA) aremade by the polymerization of ethyleneunits with comonomers, such as vinylacetate (VA) and normal butyl acrylate(nBA),

Polymerization of monomerscreates a mixture of molecular chainsof varying lengths. Some are short,others enormously long containingseveral hundred thousand monomerunits. For polyethylene, the chains havenumerous side branches. For every100 ethylene units in the molecularchain, there are one to ten short or longbranches, radiating three-dimensionallyaround the polymer chain (Figure 3).Chain branching affects many polymerproperties, including density, hardness,flexibility and transparency, to name afew. Chain branches also becomepoints in the molecular network whereoxidation may occur. In someprocessing techniques where hightemperatures are reached, the resultingoxidation can adversely affect thepolymer’s properties.

DensityPolyolefin resins are a mixture of

crystalline and amorphous structures.Molecular chains in crystalline areasare arranged somewhat parallel to eachother. In amorphous areas they arerandom. This mixture of crystalline andamorphous regions (Figure 4) isessential to the extrusion of goodextrusion coatings. A totally amorphouspolyolefin would be grease-like andhave poor physical properties; a totallycrystalline polymer would be very hardand brittle.

HDPE resins have molecularchains with comparatively few sidechain branches. Therefore, the chainsare packed closely together. The resultis crystallinity up to 95%. LDPE resinshave, generally, a crystallinity rangingfrom 60 to 75%, and LLDPE resinshave crystallinity from 60 to 85%.

Density Ranges for PolyolefinExtrusion Coating Resins

• LDPE resins range from 0.915 to0.925 grams per cubic centimeter(g/cm³).

• LLDPE resins have densitiesranging from 0.910 to 0.940 g/cm³.

• MDPE resins range from0.926-0.940 g/cc.

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• HDPE resins range from 0.941 to0.955 g/cc.

• The density of PP resins rangefrom 0.890 to 0.915 g/cc.

Higher density, in turn, influencesnumerous properties (Table 1). Withincreasing density some propertiesincrease in value. However, increaseddensity also results in a reduction ofsome properties, e.g., stress crackingresistance and low temperaturetoughness.

Molecular WeightAtoms of different elements, such

as carbon, hydrogen, etc., havedifferent atomic weights. The atomicweight of carbon is 12, and ofhydrogen, 1. Thus, the molecularweight of the ethylene unit is the sum ofits six atoms (2 carbon + 4 hydrogen) or28. Every polyolefin resin consists of amixture of large and small chains, i.e.,chains of high and low molecularweights. The molecular weight of thepolymer chain is generally in thethousands. The average of these iscalled, quite appropriately, the averagemolecular weight.

As average molecular weightincreases, resin toughness increases.The same holds true for tensile strengthand environmental stress crackingresistance (cracking brought on when apolyolefin object is subjected tostresses in the presence of liquids suchas solvents, oils, detergents, etc.).However, because of increasing meltviscosity, drawdown becomes moredifficult as average molecular weightincreases.

Melt ViscosityMelt viscosity for polyethylene

resins is expressed by melt index, aproperty tested under standard condi-tions of temperature and pressure. Meltindex (MI) is inversely related to theresin’s average molecular weight: asaverage molecular weight increases, MIdecreases. Generally, a polyolefin resinwith high molecular weight has a lowMI, and vice versa.

Melt viscosity is an extremelyimportant property since it reflects theflow of molten polymer. The resin’s flow,when melted, increases with increasingMI. Therefore, polyolefins with a lowerMI require higher extrusion tempera-tures. However, pressure can alsoinfluence flow properties. Two resinsmay have the same MI but different

high-pressure flow properties. There-fore, MI (Table 2) must be used inconjunction with other yardsticks, suchas molecular weight distribution, tomeasure the flow and other propertiesof resins. Generally, polyolefin extrusioncoating resins are characterized ashaving medium, high and very highviscosity.

Molecular Weight DistributionThe relative distribution of large,

medium and small molecular chains inthe polyolefin resin is important to itsproperties. When the resin is made upof chains close to the average length,the resin is said to have a “narrow

molecular weight distribution” (Figure5). “Broad molecular weightdistribution” polyolefins have a widervariety of chain lengths. In general,resins with narrow molecular weightdistributions have greater stresscracking resistance and better opticalproperties. Resins with broad molecularweight distributions generally havegreater impact strength and betterprocessability.

ComonomersPolyolefins made with one basic

type of monomer are calledhomopolymers. However, manypolyolefins, consisting of two or more

Table 1: General Guide to the Effects of Polyolefin PhysicalProperties on their Mechanical Properties and Processing.

As Melt Index As DensityCharacteristic Increases Increases

Chemical Resistance Stays the Same Increases

Clarity Increases Increases

Elongation at Rupture Decreases Decreases

Extrusion Speed Increases Increases

Drawdown Increases Increases

Flexibility Stays the Same Decreases

Gloss Increases Stays the Same

Heat Resistance Stays the Same Increases(softening point)

Impermeability to Gases/Liquids Stays the Same Increases

Low Temperature Flexibiity Decreases Decreases

Melt Viscosity Decreases Increases

Mechanical Flex Life Decreases Decreases

Stress Crack Resistance Decreases Decreases

Tensile Strength at Break Decreases Increases

Resistance to Blocking Decreases Increases

Stress Cracking Resistance Decreases Decreases

Tensile Strength at Rupture Decreases Increases

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Table 2: Polyolefin Extrusion CoatingResins

Resin Melt Index Ranges*

LDPE 3 to 15 LLDPE 3 to 15 HDPE 5 to 15 EVA 5 to 40

* Melt Index describes the flow behaviorof a resin at a specified test temperature(190°C, 374°F) and under a specifiedweight (2,160g). Resins with a highermelt index flow more easily in the hot,molten state than those with a lower meltindex.

Table 3: Typical Additives Used withPolyolefin Extrusion Coating Resins.

Additive Primary Benefit

Antistats Static buildupresistance

Fragrances Add attractivecolor, e.g. floral

Slip/Antiblock Improved Agents coating-to-

coating slip

monomers, are called copolymers.Some extrusion coating grades ofLLDPE, LDPE and HDPE are madewith comonomers. These side chaingroups provide specific additionalproperties to the resin. The commoncomonomers used with LLDPE andHDPE are butene and hexene. VinylAcetate (VA) is another comonomerused with ethylene to make extrusioncoating grades, producing ethylenevinyl acetate (EVA).

Small amounts of VA are oftenadded to polyethylene to produce aresin which extrudes much likepolyethylene but yields toughercoatings of lower stiffness andpotentially higher clarity. A wide range

of properties are possible depending upon the proportion of VA incorporated in the resin and the synthesis conditions used to make the modified resins.

Modifiers, Additives andTie-Layers

Numerous chemical modifiers and additives can be compounded with polyolefin extrusion coating resins(Table 3) In some grades, chemical modifiers, such as thermal stabilizers and antistatic, antiblocking and slip agents, are added during resin manufacture. However, most extrusion coating converters prefer to let down additive concentrates into the polyolefins as part of the extrusion process. NOTE: the use of additives in extrusion coating may affect adhesion and heat seal properties in the final copolymer product. Contact the LyondellBasell technical service representative or your LyondellBasell sales representative for more information.

Tie-layers, such as LyondellBasell's PLEXAR® resins, are polyolefin-based resins which bond one type of polyolefin to a different material or to another polyolefin during coextrusion, coating or lamination. Tie-layers are specifically designed for use with barrier materials such as nylon(polyamide-PA), polyester (PET), polyvinylidene chloride (PVDC) and ethylene vinyl alcohol (EVOH).

Figure 5. Schematic representationof molecular weight distribution.

Figure 6: Diagram of the polyethylene production process from liquified petroleum gas (LPG) to solidpolyethylene pellets.

EthyleneEthane

Natural GasPipeline

ExtractionUnit

FractionationUnit

Cracking andPurification

FurtherPurification

Polyethylene

Propane ButaneLiquified Petroleum Gases

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Figure 7. Linear Low Density Reactor at LyondellBasell's Morris, IL, plant

Figure 7a. LyondellBasell's plant at Clinton, IA, where high and low density polyethylene and PLEXAR tie-layers are produced.

Figure 8. Process diagaram for LDPE production in an autoclave reactor.

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How Polyolefins Are Made

High-purity ethylene and propylene gases are the basic feedstocks for making polyolefins (Figure 6). These gases can be a petroleum refineryby-product or they can be extracted from ethane-propane liquefied gas mixtures coming through pipelines from gas fields. High efficiency in the ethane/propane cracking and purification results in very pure ethylene and propylene. This high purity is one of the key reasons LyondellBasell's polyolefin extrusion coating resins excel among commercially available LDPE, LLDPE, HDPE and ethylene copolymers. LyondellBasell Chemicals can produce polyolefins by more polymerization technologies and with a greater range of catalysts than any other supplier(Figure 7 - 11).

LDPETo make LDPE resins (Figure 8),

LyondellBasell uses high pressure, high temperature polymerization reactors. Ethylene gas, pumped into the reactors is combined with an initiator to synthesize LDPE. The LDPE formed flows to a separator where unused gas is removed. Next, the LDPE passes to a compounding extruder where additives can, if needed, be incorporated prior to pelletizing.

HDPELyondellBasell produces HDPE for

extrusion coating using a solution process in a three-stage reactor system. The multi-reactor technology provides precise control of molecular weight and molecular weight distribution, which impact processability and physical properties. With this technology the polymer is produced in solution at high temperatures. Downstream separation includes catalyst removal fromthe product that results in low catalyst residuals. The removal of catalyst residuals results in very low gel products. A schematic of the process is shown in Figure 9.

LLDPELyondellBasell uses the gas-phase

(GP) process to produce LLDPE (Figure 10). The LLDPE processe is quite different from the LDPE process, but similar to the HDPE process. The major

Figure 10. Process diagram for LLDPE production in a gas-phasereactor.

Figure 9. HDPE solution process.

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difference from the LDPE process is that low pressure, low temperature polymerization reactors are used. Another difference is that the ethylene is copolymerized with a butene or hexene comonomer in the reactor. A final distinction is that the polymer exits the reactor in granular form and the granules are compounded with additives in a finishing extruder and pelletized. HDPE resins also can be made in these reactors.

PolypropyleneFor making polypropylene (PP),

LyondellBasell uses a vertical, stirred fluidized-bed, gas-phase reactor(Figure 11). LyondellBasell was the first PP supplier in the United States to use gas-phase PP technology. This process is more energy efficient and produces a more uniform product than other PP manufacturing processes.

Polyolefins for Extrusion Coating

In extrusion coating, resin is melted and formed into thin hot film, which is coated onto a moving, flat substrate such as paper, paperboard, metal toil or plastic film. The coated substrate then passes between a set of counter rotating rolls that press the coating onto the substrate to ensure complete contact and adhesion.

Extrusion laminating, also called sandwich laminating, is a process related to extrusion coating. However, in extrusion laminating, the extrusion coated layer is used as an adhesive layer between two or more substrates. A second layer is applied to the extrusion coating while it is still hot and then the sandwich is pressed together by pressure rolls. The extrusion coated layer may also serve as a moisture barrier.

Substrates that can be coated with polyolefins include paper, paperboard biaxially-oriented polypropylene(BOPP), biaxially-oriented nylon (BON), polyester and other plastic films, metal foil, fabrics and glass fiber mat.

Resins for Extrusion CoatingLyondellBasell offers a wide range of

resins for extrusion coating, including

PETROTHENE® low density polyethylene (LDPE), linear low density

Figure 11. Process diagram for polypropylene production.

polyethylene (LLDPE), and ALATHON®

high density polyethylene (HDPE) and

ULTRATHENE® ethylene vinyl acetate(EVA) copolymer.

Properties of Substrates Coatedwith Polyolefins

The basic reasons for applying apolyolefin extrusion coating to a flexiblesubstrate are to:

• Provide moisture barrier to eitherkeep moisture out of packagedgoods or to keep moisture in

• Increase tear, scuff and punctureresistance

• Gain a heat sealable surface

• Provide grease, oil and chemicalresistance

• Provide adhesion between multiplesubstrates

• Improve package appearance

Applications for PolyolefinExtrusion Coated Products

Some important applications forpolyethylene-coated substrates are:

• Food board used to make cartonsfor packaging milk, liquid,powdered and solid foods,chemicals, fertilizers and resins

• Food pouches, such as those usedfor sugar and powdered food

• Multiwall bags, such as are usedfor shipping foodstuffs, chemicals,fertilizers, and plastic resins

• Lumber and steel overwrap• Moisture barriers• Cheese wrap• Document sealing• Medical packaging• Liners for cartons, corrugated

shipping containers, fiber drums,etc.

• Vacuum-forming materials forblister packaging and other specialtypes of packaging

• Book or booklet covers• Military packaging

Other Products from LyondellBasell offers an extensive range of polyolefin resins, engineering resins and polyolefin-based tie-layer resins not only for extrusion coating, but also for film extrusion, injection molding,

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blow molding, sheet and profile extrusion, wire and cable coating, hot melt coatings and adhesives, powder coating, blending and compounding and flame retardant applications. LyondellBasell also produces several chemicals, including vinyl acetate monomer, ethyl alcohol, ethyl ether and methanol, Information on all these products also can be obtained from your LyondellBasell sales representative.

LyondellBasell Works Closely withProcessors

As mentioned previously, LyondellBasell offers a wide range of polyolefin resins for extrusion coating. Working on new developments in extrusion coating as well as assisting customers with current problems and application projects is a section of our Technical Service and Development Department, part of LyondellBasell's Cincinnati Technology Center. The Cincinnati Technology Center is a state-of-the-art facility that brings together all of LyondellBasell's basic and applied research efforts under one roof. Production level plastics processing machinery is also located there, including a full-scale extrusion coater with three extruders capable of five-layer coextrusion coatings for use in product evaluation, product development and polymer and product testing.

LyondellBasell can also produce polyolefin resins with different perfor-mance capabilities by modifying the resins’ three basic molecular properties via changes in reactor conditions and by adding comonomers, modifiers and additives. Processors can work closely with their LyondellBasell sales representative and technical service representative to determine which PETROTHENE, ALATHON or ULTRATHENE resin best meets their extrusion coating needs.

Shipping and Handling Polyolefin Extrusion Coating Resins

Keeping polyolefin resins clean is of utmost importance. Contaminated resins can produce poor products. Polyolefin resins are shipped to processors in rail cars, hopper trucks, 1,000-and 1,500 pound polyethylene lined corrugated boxes and 50-pound bags. Strict quality control throughout resin manufacture and subsequent

handling, through delivery to theprocessor, ensure the cleanliness of theproduct. When bulk containers aredelivered, the processor must useclean, efficient procedures forunloading the resin. Maintenance of thein-plant material handling system alsois essential. When bags and boxes areused, care must also be taken whenopening the containers, as well ascovering them as they are unloadedand used.

CAUTION: It is not recommendedthat reground resin or trim be used forextrusion coating. Gels, adhesionproblems and taste and odor concernscan result from the use of regrindmaterial

The Extrusion Coating Process

There are four basic stages in theextrusion coating process:

1. Resin handIing/conditioning2. Substrate handling and surface

preparation3. Extrusion coating4. Coated substrate takeoff

Resin Handling/ConditioningThe production of high quality

extrusion coated substrates requiresparticularly close attention to preventingresin contamination during production,storage, loading and shipment. Sincepolyolefin resins are non-hygroscopic(they absorb virtually no water), they donot require drying prior to being meltedin the extruder.

Resin Transfer SystemOne of the best ways to improve

polyolefin resin utilization is to eliminatecontaminants from transfer systems.Whenever a polyolefin resin is trans-ferred by a current of air, the possibilityof contamination exists. Dust, fines andother polyolefin detritus left behind inthe transfer system can plug filters orother components, resulting in thestarvation of the extruder. Occasionally,large clumps of polyolefins fromprevious transfers, sometimes called“angel hair” and “streamers,” mayaccumulate in a silo and plug the exitport. All of these problems can result inextruder down-time, excessive scrapand the need to spend time and moneyto clean silos, transfer lines and filters.

Many transfer systems consist ofsmooth bore piping that conveys theresin from hopper cars to storage silosor holding bins. Some systems alsomay be designed with long radiusbends. A polyolefin pellet conveyedthrough a transfer line travels at a veryhigh velocity. As the pellet comes incontact with the smooth pipe wall, itslides and slows down due to friction.The friction, in turn, creates sufficientheat to raise the pellet’s surface to theresin’s melting point. As this happens, asmall deposit of molten polyolefin is lefton the pipe wall. This deposit solidifiesalmost instantly. Over time, thesedeposits lead to a build-up called “angelhair.”

As the pellets continuously come incontact with the pipe wall, such asalong the curved outside surface of along radius bend, the deposits ofpolyolefin become almost continuousand streamers are formed. Eventually,the angel hair and streamers aredislodged from the pipe wall and findtheir way into the extrusion process, thestorage silo or the transfer filters. Thesize and number of streamers formedincrease with increased conveying airtemperature and velocity and are alsogreater with smooth bore piping thanwith other kinds of handling systems.

Since smooth piping is a leadingcontributor to angel hair and streamers,the logical solution is to roughen theinterior wall of the piping. This rough-ness will cause the pellets to tumbleinstead of slide along the pipe, thusdecreasing the formation of streamers.However, as the rapidly movingpolyolefin pellets come in contact withan extremely rough surface, smallparticles break off, and fines or dust arecreated. Two specific finishes formaterials handling systems haveproven to be the best performers andgive the longest life:

• A sand blasted finish of 600 to 700RMS roughness. This finish is theeasiest to obtain; however, due toits sharp edges, it initially createsdust and fines until the edgesbecome rounded with use.

• a finish achieved by shot blastingthe piping with a #55 shot of 55-60Rockwell Hardness to produce a900 RMS roughness. Variations ofthis surface finish are commonlyknown as “hammer finished”

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surfaces. The shot blasting allowsdeeper penetration and increaseshardness, which in turn leads tolonger surface life. The roundededges obtained minimize the initialproblems encountered with dustand fines. They also reduce metalcontamination concerns associatedwith the sandblasted finish.

Whenever a new transfer system isinstalled or when a portion of anexisting system is replaced, the interiorsurfaces should be treated either bysand or shot blasting. The initial cost ofhaving this done is far outweighed bythe prevention of future problems.

Eliminating long radius bendswhere possible also is important(Figure 12). Long radius bends areprobably the leading contributor tostreamer formation. When pipe withlong bends is used interior walls shouldbe sand or shot blasted as describedabove. The use of self-cleaningstainless steel “tees” in place of longbends prevents the formation ofstreamers along the curvature of thebend (Figure 13) by causing the pelletsto tumble instead of slide. Some loss ofefficiency within the transfer systemoccurs when this method is used,however. By making sure that sufficientblower capacity is available, therequired transfer rate can bemaintained and clogging of the transferlines prevented.

The transfer piping should berotated 90° periodically. Resin pelletstend to wear grooves in the bottom ofthe piping as they are transferred. Thegrooves contribute to the formation oftines and streamers. Regardless of thetype of equipment used or the materialstransferred, the transfer system shouldbe maintained and kept clean, Periodicwashing of silos and holding binsreduces the problem of fines and dustbuildup. Other steps used to eliminatecontamination include:

• Cleaning all filters in the transfersystem periodically.

• Ensuring that the suction line is notlying on the ground when thesystem is started. This preventsdebris or gravel from entering thesystem.

• Placing air filters over hopper carhatches and bottom valves duringunloading to prevent debris ormoisture from contaminating theresin.

Figure 12. Interior surfaces of longradius blends should be roughenedto minimize “angel hair” andstreamer formation in transfersystems.

Figure 13. Eliminate long radiusblends where possible by using self-cleaning stainless steel “tees”instead. These “tees” prevent theformation of streamers along thecurvature of the bend.

Figure 14. Gravimetric blending units accurately measure components inpolyolefin extrusion.

Courtesy of HydReclaim Corp.

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• Initially purging the lines with airand then with a small amount ofproduct prior to filling storage silosor bins. Let blowers run severalminutes after unloading to cleanthe lines. This reduces the chanceof cross-contamination of product.

Information regarding transfersystems and types of interior finishesavailable can be obtained from mostsuppliers of material handlingequipment. Complete systems can besupplied which, when properlymaintained, will efficiently conveycontamination-free product.

Blending With Colorants andAdditives

On-the-machine blending unitsconsist of multiple hoppers which feed

Figure 16. Schematic drawing of tension control equipment for the unwind-ing substrate. The arrows indicate the motions of the driven tension rolls,idlers, substrate and the direction of the outward pressure on the rolls.

different resin compound ingredients(Figure 14). Colorant or additiveconcentrates and base resin arecombined using either volumetric orweight-loss feeding (gravimetric)techniques, the latter usually moreaccurate. Microprocessor controlsmonitor the amount of materials fed intoa mixing chamber. Recipes can bestored in the control unit for instantrecall.

Central blending units also can beused when much higher throughput isneeded than possible with on-themachine blenders. Transfer to theextruder is by a central vacuum loadingsystem.

Substrate Handling and SurfacePreparation

The extrusion coating processstarts with feeding the substrate to the

coating rolls from a “pay-off” roll(unwind) or reel (Figure 15). As thesubstrate comes off the pay-off roll, thediameter of this roll decreases. Withoutsome compensating force, usually webtension, the decreasing diameter of thepull-off roll would manifest itself innon-uniform tension in the unrollingsubstrate. Without uniform tension, thecoating is inconsistent.

Web tension is the amount of pullon the moving substrate per unit of itswidth. Web tension, measured inpounds per inch of width per milthickness (lbs/in. width/mil), varies withthe type of substrate used (see Table4, Figure 16).

Figure 15. Schematic diagram of an extrusion coating line.

Courtesy of Black Clawson

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Table 4: Typical Web Tensions forExtrusion Coating

Substrate Tensionlbs/in (mil)

Aluminum Foils 0.5 - 1.5 Cellophane 0.5 - 1.0 Acetate Film 0.5 Nylon Film 0.15 - 0.5 Paper (15-80 lb/ream) 0.5 - 2.5 Paperboard (8-30 pt.) 3.0 - 11.0 Polyester Film 0.5 - 1.0 Polyethylene Film 0.25 - 0.3 Polypropylene Film 0.25 - 0.3 Polystyrene Film 1.0 Polyvinylidene Film 0.05 - 0.2 Vinyl 0.05 - 0.2

Source: TAPPI

To compensate for slack, automaticweb tension control must be providedfor the unrolling substrate. Unwinderroll designs include the following types(Figure 16): single roll, non-indexingdual roll, roll frame, dual width turretrollstand, phantom shaft andcantilevered rollstand.

Two types of roll braking are usedwith unwinders: surface braking andcenter braking. In surface braking, a rollis forced against the substrate roll as itunwinds. The two rolls thus turn inopposite directions. In center braking, a

friction brake on the unwind spindleacts as a tension control.

To change from a nearly emptysubstrate roll to a new, full roll withoutinterruption (or with only a slight slow-down) “flying-splice” equipment isrequired (Figure 17). The flying-spliceset-up can be fully automatic. In sometypes of flying-splice unwindequipment, the ball bearings for thecore shafts for both substrate rolls (therunning one and the new one) aremounted on two tracks on top of theside frames of the unroll stand. Whenmost of the substrate on the running rollhas come off, this roll moves forward bya handwheel. Then the new, full roll islowered into its bearings on the stand.Heavy lifting equipment is needed forthis operation. The old roll, its diameterdecreasing as it runs out, is stillunreeling during this process.

Glue is applied along the leadingedge of the substrate on the new roll.The driving rings are moved against thebottom of the new roll as it is broughtup to the required rotating speed. Now,the new roll of substrate is movedagainst a bumper roll over which thesubstrate from the old roll is traveling.The glue connects the new roll’sbeginning edge with the tail of theexpiring old roll. Concurrently, a cut-offknife cuts the expiring web from the oldroll. The extrusion coater now is fedfrom the new roll and the almost empty

Figure 17. Flying Splice Unwind System

Courtesy of TAPPI

core of the old roll is lifted off the stand.Flying-splice equipment permits

long, continuous runs at high speeds.On smaller equipment, connecting thewebs of the new and the expiring rollscan be done by attaching a separatestrip of substrate with adhesive on oneside onto the beginning of the new roll.The rolls are then moved together.When the adhesive adheres to the tailof the expiring roll, this roll of substrateis cut. In extrusion laminating, thesecond substrate feeds into the nipover the chill roll from a second unwindroil.

PrecoatersPrior to extrusion coating, sub-

strates often pass through a precondi-tioning and/or pretreater station(s) toenhance adhesion. Generally, thepriming/surface treatment unit islocated in-line, just after the substrateunwinding unit and close to theextrusion coating station. Occasionallysubstrate preconditioning occursoff-line.

The three methods generally used toprecondition substrates are chemicalpriming, flame treatment and coronadischarge treatment. The choice of pre-conditioning method depends largelyon the type of substrate to be extrusioncoated. Metal foils almost alwaysrequire pretreatment, mainly to ensurea clean surface. Some plastic films

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need pretreatment, often a combinationof both corona discharge and chemicalprimer. Corona treatment of the filmsurface is used to improve theadhesion of the chemical primer to thefilm.

The extruded polymer web can alsobe treated via an in-line ozonator toenhance adhesion to a pretreatedsubstrate (Figure 18).

PrimersPrimers serve two main purposes:

to clean and decontaminate thesubstrate surface and to enable twodifferent surfaces to adhere to eachother through dipole interaction,hydrogen bonding, covalent bonding,van der Waals forces or a combinationof these effects.

Primers should not be confusedwith tie-layers, which are extrudedadhesives. Tie-layers are applied at theextrusion coating stage of the processand not as a preconditioning treatment.

Primers commonly used inextrusion coating are listed in Table 5.

Priming equipment comes in manydesigns and sizes (Figure 19),including reverse roll coaters, offsetgravure coaters, smooth roll coaters,kiss coaters, knife coaters, air-bladecoaters wire-wound rods and meteringrollers. The choice of type and sizeusually depends on the substrates tobe coated, the viscosity of the primer

Courtesy of TAPPI

Figure 18. Ozone air is generated in a remotely located ozonechamber and carried through flexible hose to the appicator whichdistributes the ozone air evenly over the entire width of the extrudate.

Primer Adhesion Performance Chemical Performance

Heat Moisture ChemmicalTo Paper To Foil To Film Resistance Resistance Resistance

Shellac P E P P P P Orgganic Titanate G G G F F F Urethane VG E E E E E Polyethylene Imine VG G E E P P Ethylene Acrylic Acid E E F F E G Polyvinylidene Chloride E F E G VG F

E = Excellent; VG = Very Good; G = Good; F = Fair; P = Poor Source: TAPPI Manual, “Extrusion Coating of Paper and Paperboard — Equipment and Materias”

Table 5: Primers Used in Extrusion Coating

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and system line speed. Thin substratesand thin coatings require a smoothroller, not a high capacity coater, suchas the gravure roller or wire-wound rod.It the line speed is high, a largediameter roller is needed to prevent theprimer from being “thrown” by thecentrifugal force generated by a smallerroller running at a high speed.

The coating pan, from which theroller picks up primer, should be readilyaccessible for quick replacement orcleaning. The pan can be replenishedeither by a pumping system ormanually. The pan can be eliminatedentirely if reverse angle dual bladeapplicators are installed (Figure 20).With this device, liquid primer ispumped into the applicator and excessreturned to a closed supply tank.

Continuous monitoring systemsaccurately control primer application.These units work on the principle ofinfrared spectroscopy, opticalreflectance or electron absorbance.

When primer or lacquer is appliedto the substrate, the web must passthrough a drying tunnel before going tothe extrusion coating stage. A volatilesrecovery system is essential here toprevent vapors from escaping. Variousdryer designs are available, e.g., archdryers, U-type dryers, counterflowdryers, belt dryers, air-flotation dryers,roller-support dryers and drum dryers.

In these dryers, volatilecomponents of the primer areevaporated by hot air or infraredheaters. Ovens should be equippedwith a system for recovering volatiles sonone are released to the atmosphere orthe extrusion coating shop.

Flame TreatmentIn flame treatment, which is primarilyused for heavy paper and paperboard,the substrate is lightly oxidized toenhance its adhesion to the polyolefinextrusion coating. This type ofequipment is simple in design, easy tooperate and relatively inexpensive.Flame treatment is also said to preventpinholes, which can occur with animproperly adjusted corona treater.

Corona TreatmentCorona treatment of plastic

substrate involves high voltage, highfrequency electricity discharged froman electrode into an ionizing air gap(generally about 0.060 in.), where itpasses through the substrate to an

Courtesy of TAPPI

Courtesy of TAPPI

Figure 20. Reverse Angle Dual Blade Applicatiors for Priming

Figure 19. Chemical Priming Stations

14


Figure 22. Coextrusion Coating Line with Bare Roll Corona Pre-treat and Post-treat Stations


Figure 23. Multiple Extruders for Coextrusion Coating

Courtesy of TAPPI

Figure 21. Corona Treatment

15

electrically grounded metal roll (Figure21). This treatment increases thesurface tension (measured in dynes/cm) of the substrate to at least 10dynes/cm higher than the tension of theextrusion coating. A method ofmeasuring the surface tension is the“Wetting Test” (ASTM D 2578).

The power of the corona treater(W/ft²) required to obtain the neededlevel of surface tension varies with thetype of plastic substrate. For LDPE, itcan be as low as 0.5 W; for high-slipHDPE or PP, 10 W may be needed.

Two of the more widely usedcorona treatment electrodes areceramic and quartz. Ceramic elec-trodes are particularly effective anddurable. The generators used in coronatreatment produce high voltage andextreme care must be taken in theiroperation. Further, corona dischargeproduces ozone, a corrosive and toxicgas. The treater station, therefore,should be made of materials thatwithstand ozone, such as stainlesssteel or aluminum, and proper ventila-tion systems must be installed toprotect workers.

Courtesy of TAPPI

Figure 24. The Extruder and its Parts

THE EXTRUSION COATINGMACHINE

To coat a substrate with a polyolefin(Figures 15 and 22), the resin is firstsubjected to heat and pressure insidethe barrel, or cylinder, of an extruder.The now molten resin is then forced bythe extruder screw through the narrowslit of the extrusion coating die. The slitis straight, and thus, melt emerges asthin film.

This molten film is drawn down fromthe die into the nip between two rollsbelow the die —-the driven, water-cooled chill roll and a rubber-coveredpressure roll. Here, while coming intocontact with the faster moving substrateon the rubber-covered pressure roll, hotfilm is drawn out to the desiredthickness, or gauge. The hot film isthen forced onto the substrate as bothlayers are pressed together betweenthe two rolls, Pressure is generallybetween 50 to 100 lb/linear in. (136 to271 kPa/linear cm). The combination of

substrate and polyolefin coating is thenrapidly cooled by the chill roll.

Coextrusion systems designed formaking multilayer extrusion coatingshave two or more extruders feeding acommon die assembly. The number ofextruders depends on the number ofdifferent materials comprising thecoextruded film. For example, athree-layer coextrusion consisting of abarrier material core and two outerlayers of the same resin requires onlytwo extruders. A five-layer coextrusionconsisting of a top layer of LDPE, atie-layer resin, a barrier resin, atie-layer and a EVA copolymer layer,requires four extruders, as the twotie-layers come from the same extruder(Figure 23).

Tie-layers often are used in thecoextrusion coating of multiple layerconstructions where polymers or othermaterials would not bond otherwise.The tie-layers are applied betweenlayers of these materials to enablemaximum adhesion. Atypical multilayerfilm construction might be LLDPE/tie-layer/EVOH barrier/tie-layer/EVA.

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LyondellBasell produces PLEXAR tie-layer resins designed for use with specific substrates and coatings, e.g., EVOH/BOPP, EVOH/HDPE, EVOH/PS, nylon/PET, etc.

HopperThe hopper feeds polyolefin resins

into the teed section of the extruder. On top of the hopper, generally there is an automatic loader that periodically feeds the resin into the hopper. Some designs may also have hopper blenders, which can feed and proportion resin, colorants and additives to the extruder. Two types of automatic hopper feeding systems are common:

1. Volumetric feeders refill the hopperon a schedule based on theextrusion system’s output.

2. Gravimetric feeders, also referredto as weight-loss feeders, directlyteed resin into the extruder feedthroat. These feeders weighmaterials fed to the extruder from aweigh hopper and determine the

Figure 25. Extruder Cross Section with Polymer Melting Stages

rate at which the material isconsumed. Gravimetric feedersensure that the resin in the feedsection of the screw remains thesame. With volumetric feeders,resin pellets tend to become morecompact in the screw area whenthe hopper is full. If a computer isconnected to the system, the actualmaterial consumption rate can becompared against set pointsspecified, statistical analysisperformed and adjustments made,as necessary, to maintain specifiedoutput. When a deviation isdetected, the control systemcorrects by changing the screwspeed.

ExtruderThe extruder (Figure 24), generally

the single screw-type, mounted on topof a carriage, consists of:

• A Gear Box

• A Drive Motor

• A Barrel that encloses a constantlyturning, flighted auger screw andseveral heaters (induction orresistance)

• A Cooling System (either water orair) on the outside of the barrel

• Many Thermocouples to measureand control zone temperatures viaa control instrument

• A Valved Adapter with a screenpack through which the melt isdirected into a flat die

• A Melt Thermocouple andbackpressure transducer forindicating process conditions

The extruder drive provides thepower needed to rotate the screw. Forextrusion coating, a DC SCR(silicon-controlled rectifier) drive is mostwidely used. The drive power requiredgenerally ranges from 5 to 7.5 kW/lb-hr(3 to 4.7 kWkg-hr). A typical 4½-in.diameter extruder has a 200 hp drive; a6-in. extruder has a 400 hp drive.

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The extruder drive provides thepower needed to rotate the screw. Forextrusion coating, a DC SCR(silicon-controlled rectifier) drive is mostwidely used. The drive power requiredgenerally ranges from 5 to 7.5 kW/lb-hr(3 to 4.7 kWkg-hr). A typical 4½ inchdiameter extruder has a 200 hp drive; a6 inch extruder has a 400 hp drive.

The screw in an extruder rotates ata speed of 5 to 300 rpm, which is farbelow the maximum output speeds ofthe drive systems, which can be as highas 1,750 rpm. Therefore, a gearreducer is used to supply the neededtorque from the drive. The gearing usedis helical, double helical, herringbone ora variation of these three. A typical ratiofrom drive motor to extruder screw is7.6:1 for polyethylene extrusion coating.

BarrelExtruder barrels are lined with

wear-resistant bimetallic liners, such astungsten carbide. With such liners, thelife of the barrel, under continuous use,can range from 5 to 20 years,Generally, the downstream end of thebarrel has a rupture tube or diskdesigned to fail if pressure in the barrelincreases beyond a safety limit.

HeatersHeat to soften the resin on its way

through the barrel is provided internally,by frictional forces from the mixing andcompressing action of the screw andexternally by heaters. The adapter anddie head are also heated to preventloss of heat from the melt. Bandheaters are the most common types ofelectric heater used. They respondrapidly, are easy to adjust and requireminimum maintenance. As shown inFigure 25, the heater bands aredistributed along the barrel length inzones (typically, there are three to sixindependent zones, each with its ownheating control). About 25 to 45 Watt/in²(4 to 7 Watt/c\m²) of barrel surfacegives adequate heat. Resistanceheating is usual for electric heaters onextruders, although induction heating isoccasionally used.

Each of the independent electricalheating zones are regulated by acontroller. A temperature drop in onezone may indicate a defective heater-,a rise may point to a hot spot causedby a damaged screw rubbing on thebarrel lining or another problem.Today’s modern extruders usecomputer-aided controllers, which can

be programmed for specificapplications on the line, to maintainrecipes and to print reports.

If the heating capacity of theextruder is inadequate, heaters will beturned on most of the time. To facilitatethe detection of heat failure, someextruders are equipped with an alarmsystem, which warns of heat loss or ablown fuse in the extruder or die.(NOTE: At high output rates, 90% ofheat energy should be supplied by thedrive and 10% by the barrel heaters forgood, uniform melting of the polymer.)

Heater failures occurring duringoperation may not be detected sincethe frictional heat generated by theextruder can be sufficient to maintainthe operating temperature. When anextruder is shut down, the heatcontrollers should be checked beforestarting a new production run.

Barrel CoolingAir blowers, located along the

barrel length, can be run to lower barrel

temperature. Blowers also permit rapidbarrel cooling when the extruder is shutdown. Air cooling is a maintenance-freesystem, although water cooling is alsoused to adjust barrel temperatures.Temperature-control led watercirculates through tubes within theheater bands and a heat exchangerremoves heat from the water before it isrecirculated. Scale build-up and leakshowever, often plague this system. Alsowith water cooling, control solenoidscan malfunction, causing temperaturezone control problems.

ThermocouplesThermocouples, inserted deep into

the barrel wall in the various heatingzones and in some cases even into themelt, monitor processing temperatures.Temperature controllers receive signalsfrom the thermocouples to regulate theband heaters and cooling devices.Thermocouples should be regularlychecked to detect loose fittings and

Channel Section Depth Functions

Feed Deep Cool resin pellets are movedforward into hotter barrelzones

Compression or Transition Decreasing Air carried along slips back tothe feed section. Resin iscompressed, melted andmixed.

Metering Shallow Sufficient back pressure iscreated to make the melthomogeneous (uniform)

Table 6: Functions of the three Sections of a Single-Stage Extrusion Screw

Extruder Size Die Width

3½ in. (89 mm) 24 to 48 in. (61 to 122 cm)4½ in. (114 mm) 36 to 60 in. (91.5 to 152.5 cm)6 in. (152 mm) 54 to 128 in. (137 to 325 cm)8 in. (203 mm) to 160 in. (406.5 cm)

Table 7: Common Extruder Sizes and Die Widths

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other problems. Automatic processcontrols work only when thermocouplesare tightly seated in the barrel wall.

ScrewThe screw rotates within the

hardened liner of the barrel. Thestandard single-stage screw generallyhas three sections (Table 6). Channeldepth is shallower in each progressivesection. As the screw rotates, the screwflights force the resin in the channelsforward. As the channels become moreshallow, the resin is heated, melted,thoroughly mixed and compressed(Figure 25).

Variables in the design ofsingle-stage screws include:

• The pitch of the flight (steady,increasing or decreasing)

• Number of flights per section

• Pitch of the root diameter(constant, tapered or tapered andconstant)

• Design of the screw head.

Extruder sizes are designated bytheir cylinder bore diameter in inches orcentimeters. Table 7 lists extrusioncoating die sizes used with the mostcommon extruder sizes.

Extrusion coating lines normallyuse wide dies and speeds up to 3,000ft/min. (915 m/min.) to be economical.Large volumes of resin, usually 300 to3000 lb. (135 to 1,350 kg) commonlypass through the die each hour.Therefore, extruders with large barreldiameters, from 4½ to 8 in. (114 to 203mm), are generally used.

Screws are specified by theirlength-to-diameter (UD) ratios andcompression ratios. Since highertemperatures are needed for extrusioncoating than for any other polyolefinprocessing technique, extruders usedfor coating and laminating should havea barrel length-to-diameter ratio of atleast 24:1 to provide adequate heating.Generally, 30:1 UD barrels are usedtoday; in some cases, the ratio is ashigh as 32:1 UD. A long barrel andscrew permit:

a. More thorough mixing andtherefore, more intensive internalheating of the resin.

b. A greater number of electricheaters for external heating placedalong the barrel.

Courtesy of TAPPI

Figure 26. Mixing Screw

Figure 27. BarrierScrew

Courtesy of TAPPI

The compression ratio is the ratioof the channel volume of one screwflight in the feed section to that of onescrew flight in the metering section. Acompression ratio of about 4:1 issuggested for polyolefin extrusioncoating.

High compression forces result inhigh internal heating and good mixingof the melt. Additionally, these forcesefficiently push any traces of air carriedforward with the melt back and outthrough the hopper. Air in the melt cancause bubbles, and at hightemperatures, may cause the resin tooxidize in the barrel.

Extruder screws can be cored forwater cooling. A cool screw can preventbridging in the feed section that mightbe caused by premature melting of theresin. Also, cooling can improve resinmixing, but can reduce output at agiven screw speed. Screw temperatureis automatically controlled (80° - 180°F;25° - 80°C) by a temperature controllerwhich adjusts the amount of waterflowing through the screw. If the screwoverheats, it loses its pumping capacity.Newer screw designs, however, do notuse water cooling.

Screws for polyolefin extrusioncoating are practically always run“neutral,” i.e., without cooling by watercirculating through an axial bore about

4 to 5 flights past the resin feed inlet inthe hopper section. However, coolingthe screw may make it a little moreversatile by increasing its effectivecompression ratio. Certain extrusioncoating resins, such as ionomers andEVA, require screw cooling.

In addition to single-stage screws,there are many multi-stage designs,such as mixing screws (Figure 26). Forsome materials, such as LLDPE, coloradditives and HDPE, additional mixingis required. Mixing screws differ fromgeneral-purpose screws in that theyhave an additional mixing section. Themixing section generally has severalrows of raised rectangular rods or pinsdesigned for either dispersive ordisruptive mixing. Other kinds of mixingscrews have two mixing sections: oneat the end of the metering section andone at the end of the compressionsection.

Barrier type screws (Figure 27) areanother type of multi-stage screw. Alsodesigned for improved mixing, thesescrews generally have the same threeinitial sections as general-purposescrews with a dispersive mixing sectionat the end of the metering section. Allbarrier screw designs have the samemodification: an additional flight, calledthe barrier flight, in the transitional

19

section of the screw. There are twoseparate channels in the barrier flight: asolids channel and a melt channel. Themore shallow solids channel is locatedon the pushing side of the barrier flight.The deeper melt channel is located onthe trailing edge of the opposite side.The cross-sectional area of the solidschannel is uniformly reduced over thelength of the barrier section while themelt channel is correspondinglyincreased. The barrier flight has a radialclearance larger than the clearance ofthe main flight. This allows the melt inthe solids channel to flow over thebarrier flight into the melt channel whilethe solids are retained, unable to passover the small clearance. This removalof the melt film helps expose moresolids to the extruder barrel surface,thus increasing the rate of melting.While barrier screws can offersignificant advantages over mixingscrews and general purpose screws,their design is based on experiment.Computer models are developed forbarrier screws, as they have been forsome other types of screws.

Breaker PlateAfter travelling along the screw

length, the melt passes through ascreen pack and supporting breakerplate and then, through the adapter tothe die. The round breaker plate

Courtesy of Rapidac Machine Co.

Figure 28. Valve Assembly

(Figure 28) is located between the endof the barrel and the head adapter,usually fitting into both, but sometimesonly into the adapter. This fittingensures that no melt can leak out. Thethick plate breaker is pierced by a largenumber of equally spaced holes, 1/16to 1/8 in., (1.6 to 3.2 mm) in diameter,and is held in place by a sturdy ring.

A spare breaker plate should alwaysbe available in case the one in usebreaks or is replaced along with thescreen pack. An extra breaker platemay mean less downtime, because theused one does not have to be cleanedbefore operations can resume.

The screen pack (Figure 28),located in the breaker plate, consists ofa number of stainless steel screens.The screen mesh is the number ofopenings per one inch of screen. Thescreen pack serves primarily as a filterfor foreign matter, although it alsoimproves pigment dispersion if pigmenthas been added. Higher back pressurein the screw metering zone, which canimprove extrusion coating quality butlower output, may be obtained by apack of many fine screens.

Melt temperature can be raisedslightly by using a very heavy screenpack (more or finer screens) which, byincreasing pressure, generatesadditional frictional heat and results inimproved coating quality. However,

excessive pressures (>2500 psi, butthis can vary with the type of resinextruded) may indicate screen packsneed to be changed.

There is no “typical” screen pack.Different packs are best suited fordifferent jobs. Fine-meshed (dense)screens should be located betweencoarse screens, such as a 20-80-20screen pack. Always use stainless steelscreens. Never use copper screensalthough they cost less. Copper is toosoft for such a high-pressureapplication and may oxidize andcontaminate the resin. Extruders with avalved adapter need only use a singlescreen; a 24 x 110 stainless steelscreen is recommended under theseconditions.

Automatic screen changers, whichhave either a continuous screen bandor a rotary unit that indexes whenexposed sections plug, can be usedwith extrusion coating machines. Theindexing occurs without interrupting themelt flow.

Pressure ValvesPressure valves provide control of

the barrel pressure, which has apowerful effect on the melt temperature.Pressure valves provide good backpressure control and take this functionaway from the die design and screenpack arrangement. Two types ofpressure valves are common:

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1. The internal pressure valve (Figure29) is a movable stem that can beadjusted forward or backward toincrease or decrease pressure.Moving the valve stem varies thesize of the orifice opening betweenthe end of the stem and thepolymer flow pipe.

2. Some stems are located on a sideof the polymer flow pipe, andpressure is regulated by the landarea created by the depth of thestem’s insertion into the polymerflow pipe.

Gear PumpsGear pumps (Figure 30), also

called melt pumps, can be attachedbetween the end of the extruder andthe die head to increase melt quality.For continuous multilayer extrusioncoating, these pumps can deliver astable, surge-free melt output andprovide excellent layer uniformity.These benefits are particularlyimportant for the extrusion of thinbarrier layers and adhesive tie-layers.

The DieThe extrusion coating die is

attached to the valved adapter via adown spout or connecting pipe. A gooddie design provides smooth melt flowand minimizes the chance that anyparticles can be held up andoverheated. The functions of the die areto:

1. Force the melt into a thin film2. Maintain the melt at a constant

temperature3. Meter the melt at a constant

pressure and rate to the die land foruniform film gauge.

Basic parts of a die include:

• Body• Mandrel or Jaws• Heaters• Lands

The die lands generate resistanceto the melt flow and build upbackpressure in the die and adapter. Ifthe land length is too short, the meltflow out of the die may be uneven. Thedie lips, or jaws, can be adjusted tochange the die opening to controlgauge uniformity (Table 8). Some diedesigns have as little as 0.098" die landarea and have excellent gauge control.

Figure 30. Gear pumps, also called melt pumps, lead to improvedfilm gauge uniformity by preventing surges in melt output.

Courtesy of Luwa Corp.

Courtesy of TAPPI

Figure 29. Pressure Control Valve

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The key is in the machining quality ofthe die lips.

Die temperature and resintemperature at the die lands (melttemperature) are usually quite high inextrusion coating, up to 625°F (330°C).It is important to keep melt tempera-tures uniform. An extrusion coating diealways has a number of heating zones,each no more than eight inches (20 cm)wide. For uniform coating gauge, thetemperature along the die should notvary by more than 2°F (1°C). Dieheaters are automatically controlled.For extrusion coating, there are twobasic types of die designs:

• “Coat-hanger” dies (Figure 31)• “T-slot” dies (Figures 32, 32A and

32B)

In the coat-hanger design, the diemanifold, which generally has ateardrop or half teardrop cross section,distributes the incoming melt flowacross a steadily widening area. Thearea ahead of the land streamlines themelt into a film. If this die is “deckled”(see Deckling Systems, page 22, thefilm edge bead is greater than it is witha T-slot die because of the good resinflow to the end of the die from thecoat-hanger design.

The T-slot design uses a largevolume, circular or teardrop—shapedmanifold to minimize melt flowresistance to the die ends. This type ofdie is normally used with high melt flowresins. With this type of die, theformation of film edge beads is lessthan it is with “coat-hanger” dies.

With both types of dies, a die lipgives the melt its proper cross-sectionalthickness and width. Two basic types ofadjustable die lips are common: slidingor flexible. The flexible, adjustable lip(Figure 33) design uses evenly spacedadjustment screws (about one inchapart) across the full die width. Themore rigid sliding, adjustable lip (Figure34) also uses evenly spacedadjustment screws, but about twoinches apart.

With both the flexible and thesliding adjustable die lips, two basictypes of screws are used: “push/pull” or“push-only.” The push/pull screw, oftenused with sliding, adjustable designs,allows the lip to be either forced openor closed. The push-only screw,generally used with the flexible,adjustable lip design, only allows the lipto be closed. To open the lip, the screw

Figure 32. Coat Hanger and T-Slot Dies

Figure 31. Schematic cross section on a “coat hanger” type die.

Table 8: Recommended Die Gap Openings

Die Gap Opening, Coating Weights,in. lb/ream*

0.020 <30.030 3 - 420.040 42 - 700.050 >70

* A Ream = 3,000 ft²

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Figure 32A. “Jyohoku” Edge Bead-Free T-Slot Die


Figure 32A. “Jyohoku” Edge Bead-Free T-Slot Die

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is backed off, which enables the springaction of the steel lip and the force ofthe melt to open the die.

The die lip screws can be manuallyadjusted or automatically controlled. Anautomatic control includes amicroprocessor interfaced with a filmgauge sensor. The screws’ lengths arethermally expanded or contracted, thusclosing or opening the die lip whereadjustment is needed.

Deckling SystemsExtrusion coating die widths maysurpass 150 inches. However,increasing die width means increasingsystem sensitivity. Deckling systems,mechanical devices affixed to bothsides of the die lip, can be used toreduce the width of an extrusioncoating. Deckling designs include:

• Fixed external, which are notadjustable while the line is running

• Adjustable external, which areusually driven by a rack and piniongear, permitting adjustment whilethe line is running

• Adjustable internal

Maintenance is very importantwhen using deckling: resin builds upand oxidizes behind the deckling.Periodically the coating line must bestopped and the die cleaned toeliminate this problem.

To minimize the formation of edgebead when the extrusion coating isapplied to the substrate (Figure 35),bead control rods can be attached tothe deckling system. The ends of theserods come in contact with the edge of

Courtesy of TAPPI

Figure 33. Flex-Lip Design

the extruded film to restrict beadformation. Bead formation can begreatly reduced, if not totally eliminated,with a “T-slot” die incorporating aspecial deckle design with a split innerdeckle (upper and lower) and edgecontrol rod (Figure 36).

Coextrusion CoatingIn coextrusion coating, some

additional equipment is required, butthe result is a sophisticated multilay-ered package. Coextrusion coating canbe an economical alternative to tandemand multi-pass extrusion coating andextrusion lamination. Specifically,coextrusion coating:

• Reduces production timecompared to multiple passes andlaminations

• Reduces raw material costs• Improves adhesion between layers

because the adhesion layer can berun hotter than the seal layers

• Reduces layer thickness comparedto monolayer extrusions

• Maintains melt strength becausethinner, lighter layers of individualpolymers can compare favorablywith an individual monolayer withthe same thickness as the sum ofthe multilayers.

• Eliminates odor by using a reducedmelt temperature for the surfacelayer

• Improves heat seal by decreasingthe extrusion temperature of thesealing surface layer

• Improves the strength of the “meltcurtain”, so that a seal layer and atie-layer can support a polymerwith little melt strength, such as abarrier resin

• Reduces pin holes and improvesfracture resistance

• Reduces scrap

Coextrusion EquipmentEquipment is selected based upon

the resins to be used and the structuresto be produced. Coextrusion diechoices include:

• Dual manifold dies are designed sothat the melt curtains combineeither internally or externally. Dualmanifold dies are usually usedwhen two polymers with greatdifferences in extrusion melttemperature or melt viscosity are tobe coextruded. Each side of the diecan be separately heated.

Figure 34. Fixed-Lip Design

Courtesy of TAPPI

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Courtesy of TAPPI

Figure 35. Edge Beads

Figure 36. Bead Reduction Die


• Dual manifold dies come as singleexit dies, which combine thepolymer internally just before theexit, or as dual slot dies. Single exitdies, the preferred choice, providebetter adhesion and melt curtaindraw strength. Dual slot dies areused when the viscosities of thepolymers are so different that meltpressure and melt temperaturevariables prevent an even flow ofboth curtains from the die lips. Meltcurtain surging and melt fractureson the polymer interface can result.With dual slot dies (Figure 37),each layer can be individuallyadjusted by changing the separateslot die lip adjusting bolts.

• Keyhole dies are often preferredfor the extrusion coating of highmelt flow resins where manydeckle changes are made.

• Coat-hanger dies are used for theextrusion coating of low melt flow(highly viscous) resins, becausethis die enables better melt flow toits ends. Good flow to the ends ofthe die can be a problem whenhigh melt flow resins are extrudedand when the die has to bedeckled-in for narrow webcoatings.

Transfer PipingMelt flowing from the extruder to a

multilayer die or coextrusion combiningadapter passes through piping. Thispiping must be kept as short aspossible in length and as large aspossible in diameter to minimize itsimpact on the melt passing through.

Combining AdapterThe combining adapter is the

technology most often used forcoextrusion coating. This method canbe used with all manifold dies, providedthe entrance port is correct for theselected adapter design. The selectionof the optimum design for the adapter,as well as for the extruder, valveadapter, feedblocks, feed piping anddies is based upon the rheology of thepolymers to be coextruded. Knowledgeof rheology and the visoelasticproperties of the polymers alsooptimizes their processability. Contactyour polymer supplier for moreinformation about polymer melt flowproperties when designing any newcoextrusion structure.

25

Courtesy of Egan Machinery Division, John Brown, Inc.

Figure 37. Designs of Manifold Dies

Figure 39. Multimanifold Die

Courtesy of TAPPI

Figure 38. Coextrusion Coating Feedblockand Monolayer Die

Courtesy of Peter Cloren Co., Inc.

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Coextrusion Coating FeedblockFor the extrusion of multilayer

extrusion coatings (coextrusions),feedblocks stack melt layers from twoor more extruders (Figure 38), basedon the principles of polymer meltrheology. The feedblock can beadapted to layer multiplying devices tofurther increase the number of layers.The multilayered melt stream is thenfed to a single-manifold die exit.

Multimanifold CoextrusionCoating Dies

Multilayer (coextruded) coatingsalso can be made using multimanifolddies (Figure 39), of which there aremany designs on the market. Basically,the multimanifold die has multiple coat-hanger or T-slot dies that feed thedifferent melt streams to either a singleor dual flexible, adjustable die lip. Thistype of coextrusion die is much morecomplicated than the feedblock type.

The Coating Rolls

Pressure RollThe hot film flowing from the die

meets the uncoated substrate as itpasses between a pressure roll and achill roll. For best adhesion, the hot filmshould contact the substrate just beforeit reaches the nip that is only ¼ to 3/8in. (6.5 to 9.5 mm) above-as indicatedin Figure 40. The pressure roll, a largeidler roll with a thick, hard rubbercovering, forces the substrate againstthe extruded coating and eliminates theair between the two layers. Twopneumatically loaded cylinders providepressure, one on each side of the roll.The hardness of the rubber coveringthe pressure roll varies according to thesubstrate being coated. In general, therecommended hardness is 80 to 90Shore A. If textiles or soft paperboardare the substrate, very hard rubbercoverings are used. The pressure roll ismounted such that the nip between itand the chill roll can be opened upmore than six inches (15 cm) to makethreading substrate during start-upeasier. The ability to open the nipquickly and widely is important in anemergency as well.

The design of the coating station isvery important. The nip roll must beelevated above the chill roll center lineand the back-up pressure roil. Thisposition allows for better clearance ofthe die relative to the chill roll and theincoming substrate; extends the service

Courtesy of TAPPI

Figure 40. Coating Station (set air gap range for 5” minimum to15” maximum)

Air Gap, inches Line Speed, (FPM)

7.0 up to 7008.5 700 - 1,20010.0 1,200 to 1,80012.0 1,800 and above

Table 9: Air Gap Opening vs. Coating Line Speed

life of the fluoropolymer tapes; andincreases adhesion to the incomingsubstrate (Figure 40).

The position of the coating stationis adjustable so that the size of the airgap can be changed relative to the die.The air gap size has a decisiveinfluence on the degree of adhesionbetween the polymer and the substrate.With polyethylene extrusion coating, arule of thumb Is 11 each one-inchincrease in air gap length has the sameeffect on adhesion as a 10°F increasein melt temperature.

Cooling the pressure roll surfacecan prevent the hot film from sticking,especially with thin coatings of lessthan one mil (25 microns). Awater-cooled metal idler roll may be runagainst the pressure roll for thispurpose. For some extrusion coating

applications, such as fabric coatings,the cooling roll may rotate in a tray filledwith cold water. If this set-up is used, adoctor roll or other device preventswater carry-over from the tray onto thesubstrate. The pressure roll can also becooled internally. However, the poorheat conductivity of the rubber coveringthe roll prevents really effective coolingof the surface, but helps the rubbercover adhere to the metal core.Pressure rolls of large coaters mayhave both external and internal watercooling.

The pressure roll covering sleeve isgenerally made from a silicone rubber,neoprene rubber, chlorosulfonatedpolyethylene rubber (Hypalon*) or afluoropolymer. Unlike neoprene rolls,silicone-covered rolls do not have to bereground after “wrap-arounds”

27

(wrapping of torn, coated substratearound the pressure roll).Silicone-covered rolls are alsopreferred for very porous substrates,such as cloth, non-woven material ortissue paper and because of theiredge-trim release. High temperaturesubstrate preheating also is possiblewhen the pressure roll covering ismade from silicone rubber.

On the other hand, silicone rubbercoverings are not as hard, resilient ordurable as coverings made fromneoprene or chlorosulfonatedpolyethylene rubber. The latter alsohave good release and can be cleanedeasily. Fluoropolymer-covered rollshave the best release of all the typesmentioned, but are expensive anddifficult to maintain.

Chill RollThe chill roll has three functions:

1. In less than one revolution, itsolidifies the coating and cools it to

Courtesy of TAPPI

Figure 41. Extrusion Lamination Machine and Trim Slitting Station

a temperature low enough topermit the coated substrate to berewound.

2. Its speed controls the coatingthickness (or coating weight) bydrawing down the melt film fromthe die. Speed also controls theeconomy of the extrusion coatingprocess.

3. The chill roll surface determines, toa large degree, the surfacesmoothness of the coating. If ahigh-gloss coating is required, thechill roll surface must be highlypolished. For a dull coatingsurface, the chill roll may have amatte finish. The surface of the rollcan also be embossed for specialeffects.

The chill roll is usually a chrome-plated, twin-shell steel drum with anouter shell and an inner bodycontaining spiral grooves for coolingwater. Periodically, the rolls must bereconditioned; new, flat, highly polishedsurfaces applied to the outer surface;

and the inner channels cleaned. Somechill roll designs use a replaceableouter shell for quick changes todifferent surface finishes.

Good alignment of the chill roll, inrelation to the failing melt and thepressure roll, is very important (Figure41). Whenever the coated substratewrinkles, especially in thin-gaugecoatings, the position of the die, thelead-in roll, the chill roll or the pressureroll must be carefully adjusted.

A typical system for a closed-circuitchill roll cooling system is shown inFigure 42. Chill roll water temperature(68°F in Figure 41) ranges between62° and 80°F (17° to 27°C). The chillroll surface temperature must notexceed 150°F (65°C). The mostfavorable chill roll cooling watertemperature for a given resin andcoating speed should be carefullydetermined and closely monitored,keeping variances less than ± 2°F(1°C).

The chill roll temperature can beadjusted by the flow rate and the

28

temperature of the cooling waterpassing through the roll. A flow rate of350 gal/min. of cooling water (12 to 15ft/sec) through the chill roll per 1,000 lb/hr of polyethylene extruded isnecessary for good cooling andsubstrate release.

Condensation can form on chillrolls, particularly when ambienttemperatures are well above roomtemperature, adversely affectingextrusion coating quality. Special,internally-cooled chill rolls which resistcondensation even when the roll isstopped are available (Figure 43). Thistype of chill roll has an internal cylinderwith a permanently sealed, capillarywick structure that encloses a heattransfer fluid. Inside the capillarystructure, there are channels for coolingwater. When the hot film contacts theroll surface, it releases heat that causesthe fluid in the capillary system tovaporize. The condensed fluid migratesto the center of the roll by centrifugalforce. Here, cooling water absorbs thethermal energy and condenses thevapor. The roll’s rotation facilitates theheat transfer.

The coated substrate can be runaround two or more chill rolls to lowerits temperature. The heat removed bythe second, third, etc. roll dependsupon take-off speed, melt temperatureand the temperature of the first roll. Thecooling water temperature of these rollsshould gradually reduce the coating’stemperature to that desired for windup.

Peel RollA peel roll or stripper roll is required

to remove the coated substrate fromthe chill roll (Figure 44). The location ofthe peel roll is very important for bothproper release and good adhesion. Thepeel roll should be placed as close tothe chill roll as possible, only 0.5 to 1inch away for a hard-surface roll anddirectly touching the chill roll if arelease cover, such as silicone orfluoropolymer rubber, is used. However,the peel roll must be positioned (“a” to“b” in Figure 44) far enough away sothat the chill roll surface temperaturedecreases before it passes againthrough the coating nip. If the chill rollsurface does not cool adequately, linespeeds can not be maintained. Also,poor adhesion may result under theseconditions as the polymer may stick tothe chill roll and pull away from thesubstrate.

Courtesy of TAPPI

Figure 43. An Internally Cooled Chill Roll

Courtesy of TAPPI

Figure 42. Closed Circuit Chill Roll Cooking System

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Feed RollersAfter coming off the chill roll, the

coated substrate passes through aseries of feed rollers before it is woundup by the take-off equipment. Inaddition to guiding the web topost-coating operations andmaintaining proper web tension, theserollers perform other functions. Forexample, rollers with a herringbonepattern ingrained on them can laterallyspread the coated substrate andremove wrinkles; rollers with circulargrooves can remove surface air flowingalong with the web; pivoting or steeringrollers can realign the web; and slightlybowed rollers can laterally tighten theweb.

Surface TreatersIf polyolefin-coated surfaces are to

be printed or an adhesive applied, theyfirst must be treated. Electronictreatment is preferred. Ink andadhesive do not adhere to untreatedpolyolefin surfaces. Treatment is bestdone in-line, i.e., within the extrusioncoating set-up. A treatment stationbetween the chill roll and the slitter rollor right after the trimming step iscommon. When polyolefins contain slipor antiblock additives, treatment musttake place in-line before the additive“blooms” to the surface of the coating.

Edge Bead Trim SlittersAs the polyolefin melt leaves the

extrusion coating slot die and is drawndown in thickness from about 20 to 30mils to about one mil, the width of themolten web also narrows. Thisphenomenon is called “neck-in.” Theamount of neck-in depends on:

• Grade of resin extruded• Speed of the operation• Temperature of the melt• Length of the air gap

With neck-in, a bead usually formsat the edge of the web, thicker than theaverage coating thickness across theweb. The amount of beading dependsupon the coating thickness relative tothe thickness of the substrate.Lightweight coatings on thicksubstrates are not as susceptible tobeading as are heavyweight coatingson thin substrates. In most cases, thisbead must be trimmed off before theweb is rewound. The build-up of edgebeading can cause flared edges on the

Figure 44. Proper Cooling Recovery Set-Up

rolls, to the extent that the edges tear.Consequently, most extrusion coatershave trim slitters between the coatingunit and the rewinder (Figure 45). Thethree most common types of slittersare:

1. Score cutters, consisting of ahardened wheel with a V-shapededge that is pressed against ahardened-steel backing roll. Theweb passes between the wheeland the roll.

2. Shear slitters, consisting of a pairof driven, overlapping sharpenedor beveled blades in a scissors-type arrangement.

3. Razor blade slitters, consisting ofdisposable razor blades positionedagainst the moving web as itpasses either between two closelyspaced idler rolls or against agrooved back-up roll.

The type of slitter used depends onthe type of substrate coated. Scoreslitters are often used for film,cellophane, paper and foil laminates.Shear slitters are used on paper boardand heavy paper. Trim from the slittersis usually carried away in an air streamvia a suction manifold located near theslitter station. The velocity of the air inthe trim manifolds must be greater than

Figure 45. Edge Bead Trim Slitters

Courtesy of TAPPI

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Figure 46. Vortex Cooling Needle

Courtesy of Exair

the line speed of the coater.If an “overcoat” of polyolefin is appliedto the substrate, i.e., the coatingextends past the edges of thesubstrate, the excess coating adheresto the pressure roll. Fluoropolymer tapeis sometimes used to mask thepressure roll at the edges of thesubstrate. A few precautions arenecessary for best results. When linespeeds are very low and the pressureroll is warming up, as occurs when rollsare changed on the unwind stand, the“overcoat” may stick to thefluoropolymer tape.

Silicone grease or spray may beused in extrusion coating as a releaseagent at start-up to prevent the polymerfrom adhering to the nip roll. However, itis recommended that silicone materialsbe eliminated from extrusion coating.Silicone cannot be used if the reverseside of the substrate is also to becoated, since the silicone will preventadhesion on the edge of the secondcoating. Silicone should not be usedwhen the coated substrate is to beused for packaging food products.[NOTE: Silicone should only be used asa last resort since it can causeproblems which outweigh the benefits.]

A better solution is to use VortexTube Air Jets, which blow cold air at thebottom of the pressure roll (nip roll) tocool the fluoropolymer tape. Thiscooling prevents the edge bead fromadhering to the tape and increases thelife of the tape (Figure 46).

Courtesy of TAPPI

Figure 47. Slitting the Web

The fluoropolymer tape must bereplaced periodically because ofblistering. An operator normally canchange the two tapes on the pressureroll in a few minutes, so there is littleloss of production time when thesubstrate width is changed. Someextrusion coating lines usefluoropolymer belts that can bereplaced even more quickly.

When substrates less than 10 mill(0.25 mm) thick are coated, thefluoropolymer tape may mark or imprint

the coating. To prevent this, place thetape on the pressure roll so that itcomes just inside the edges of thesubstrate for no more than 0.125 inch.Handling this kind of material obviouslyrequires superior edge guiding.

An undercut pressure roll is onethat is recessed exactly to the edge ofthe substrate so that the hot polyolefinbead does not stick to the roll. Usingundercut pressure rolls means that aseparate pressure roll for eachsubstrate width must be readily

31

available, and production runs must belong enough to make this techniqueeconomical.

A single coated web also may be slitinto two or more separate webs (Figure41 and 47). After slitting, the substratepasses over a series of bowed rollersthat separate the webs slightly beforethey are wound up.

Recycling SystemThe edge trim from the extrusion

coating operation is conveyed from thecoater through pneumatic trim disposaltubes to a granulator (Figure 48). If thetrim is substrate-free, i.e., it is onlypolyolefin film, it may be sold as scrap.It should not be reused in extrusioncoating because changes in thepolymer properties as well asprocessing characteristics such as gels,neck-in, draw-down, odor, etc., arelikely.

Coating Weight/ThicknessMonitors

Two types of devices are used tomeasure coating weights:

• Nuclear sensors• Infrared sensors

Nuclear sensors are usually locatedjust ahead of the point where thesubstrate passes into the coatingstation and where the coated webmoves to the windup equipment(Figure 49). Nuclear gauges, alsocalled “beta gauges,” measure the netcoating weight on the substrate byfocusing a beam of radiation throughthe web and onto a detector. Theradiation absorbed by the web isinversely related to the weight per unitof web. Since the measurements aretaken both before (base) and after(gross) coating, it is possible todetermine the net coating weight(thickness).

The location of the two nuclearsensors and the interval betweenreadings must be carefully coordinatedso that the sensors measure the samearea on the web. The nuclear sensorreadings can be used to adjust the dieopening manually or automatically.

Infrared (IR) sensors operate onthe principle that all materials have theirown characteristic absorption bands inthe near-infrared spectrum. The IRunits function in one of two modes:

Courtesy of TAPPI

Figure 49. Coating Weight and Thickness Monitors

Courtesy of TAPPI

Figure 48. Extrusion Coating Scrap Recycle System

• Transmission: the signals passthrough a transparent web to adetector

• Reflectance: the signals reboundoff an opaque web and into adetector.

Two wavelength measurementsgenerally are used: a referencewavelength that is not absorbed by theweb; and a measurement wavelengththat is absorbed by the web. Thedetector measures the signals andforms a ratio proportional to the weightof the web.

IR measuring equipment is simplerto operate and less expensive thannuclear sensors and it also canmeasure multilayer materials. However,pigments can adversely affect IR

readings (black pigment totally absorbsthe near-IR spectrum and whitepigment, i.e., titanium dioxide, has ascattering effect). A matte finish alsocan diffuse the IR beam. Differentsubstrates can yield different IRreadings. These disadvantages of near-IR sensors can be minimized by usingfull-spectrum infrared (FSIR) measuringdevices instead.

Both nuclear and infrared sensorsshould be built so that no ionizingradiation or infrared radiation reachesthe operator.

Takeoff and Windup EquipmentThe extrusion coated substrate

usually is wound tightly onto acardboard tube, called a core althoughmetal cores also are used. The core is

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turned by a winder. Full coatedsubstrate rolls are replaced by emptycores without interruption if multiplewindup stations are available.

WindersWinders are characterized by:

• The type of take-up roll drive:surface, center or center/surfaceassist

• The type of roll changing: manual,semi-automatic or fully automatic

• The type of roll stand configurationstacked, face-to-face orback-to-back.

Some winders run shaftless andthe web is wound directly on the core.However, most commercial extrusioncoating winders have air shafts toinflate rubber bladders attached toexpandable metal shafts that fit insidethe cardboard cores. The air-supportedmetal shaft permits different corediameters to be used and enables thecore to resist the pressure of the webwinding. This second benefit isparticularly important when separateweb widths are wound on a commoncore without interleaving. A lay-on rolloften is part of this take-off assemblyalong with a pneumatically-actuatedslitting knife for cutting the web into twoor more narrower webs.

Surface winders (Figure 50) have adriven drum that fits flush against theface of the windup roll. Several surfacewinder configurations are available, butbasically their operation is the same:the rotating drum forces the roll to turnand thus, wind up the web. The roll isheld against the rotating drum bygravity or pneumatically. The webremains in uniform contact with thedrum by means of a tensioning device.A lay-on roll forces air out from underthe web as it is drawn onto the roll.Surface winders are often used whenroll diameters exceed 40 inches, butnot all polyolefin coatings are handledbest by surface winding.

In center winders (Figure 51),torque is applied directly to the winduproll shaft. To keep tension constant, acenter winder must slow down at a rateinversely proportional to the constantlyincreasing diameter of the roll. Manycenter winders incorporate lay-on rollsto force air out from under the web or toensure optimum flat contact. Rolls ofextrusion coated substrate, wrapped

Courtesy of TAPPI

Figure 50. Single Drum Winder Automatic Transfer

Courtesy of TAPPI

Figure 51. Center Winder

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onto cores held by chucks inserted inboth ends, are formed under constanttension.

Surface or center assist windershave center drives added to the shaft ofa surface winder. This type of winderseparates winding tension from webpositioning requirements and rollhardness.

Gap winding, or proximity winding,is a modification of the center windingtechnique that is especially effective fortacky polyolefin coatings. An air gap ofabout a 0.25 inch is maintainedbetween the surface roll and thebuilding roll. Each roll has atension-controlled drive. As the webbuilds up on the roll, this roll isgradually moved away.

Taper tensioning, a gradualreduction of web tension, generally isused when the ratio of the final roll isgreater than six times the diameter ofthe core (the “build-up ratio”). In tapertensioning, the dancer roll assembly orthe strain gauge roll is controlled. Forextensible or soft polyolefin coatedwebs, taper tensioning eliminates rolldefects such as crowning and wrinkling.

The flying-splice unwind, used forcontinuous long runs (Figure 52), callsfor large unwind rolls of many

Courtesy of TAPPI

Figure 52. Flying Splice System Unwind

thousands of linear feet of coatedsubstrate. The diameter of a finishedroll is many times that of its core. As theroll builds up in diameter, its rotationalspeed must be reduced because thelinear speed of the coated substratecoming from the coater remains thesame. For splicing at the rewind, glueor tape is generally used, just as it wasat the unwind.

Edge-guide equipment is essentialwhen a flying-splice set-up is used atthe unwind station. Either mechanical,pneumatic or photo-electric sensingelements are placed at the edges of thesubstrate. Whenever the web movesout of line, the sensing elementsactuate a device that adjusts theposition of the web. A similar set-up issometimes used to detect breaks in thesubstrate, sound an alarm andsimultaneously open the nip to preventdamage to the pressure roll by the hotmelt.

Automatic roll changers deflate airshafts, remove the full roll, place the rollon a cart or the floor, install emptycores into the ready position and inflatethe bladders in the metal shafts. Rollchangers are particularly useful forhigh-speed applications that requirerelatively small roll diameters.

Turret winders are designed torotate a full roll away from the lay-onroll and index a new core into thewinding position. With automatic turretwinders, the spindles are separatelymotor-driven to match the speedrequired for the automatic cutoff of theweb at high speeds.

ControlsMany elements affect production

and quality in an extrusion coatingsystem. Microcomputer controls answerthe complex problem of controlling themany variables involved (Figure 53).These closed loop systems monitorresin feed, substrate feed andconditioning, temperatures, pressures,screw speed, line speed, coatinggauge, output, etc., and makeadjustments when values drift outsidepreset limits. VDT monitors displayoperating conditions, and managementinformation systems software providehard-copy reports, such as shift reports,monthly reports and/or job summaries.A microcomputer also can be set up torun a coating operation using valuesfrom a previous run, stored in thememory. The microcomputer also is akey element of statistical processcontrol (SPC) and statistical quality

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control (SQC) programs. Real-timeSPC systems alert operators when theextrusion coating process is drifting outof its control limits and indicatepotential sources of problems.

Start-Up of An ExtrusionCoating Line

Safety FirstExtrusion coating can become a

hazardous operation if proper safetyprecautions are not followed.

• The extrusion equipment should bekept clean and well maintained atall times.

• Remove any water around theextrusion coating line to preventslipping accidents.

• Good housekeeping is essential.• Loose pellets on and around the

extruder can cause accidents.• “NO SMOKING” signs must be

enforced.• Allow only trained and qualified

personnel in the operating areas.• Make sure all high voltage areas

are identified and suitablygrounded.

• Keep areas around the extrusioncoating line clear of boxes, barrelsand other impediments.

• Obtain and read the MSDS for allmaterials used in the extrusioncoating process.

• Wear proper protection (clothing,eyewear, safety shoes, etc.) asrequired by the NSDS orequipment manufacturer.

• Make sure proper ventilationsystems are installed andoperating when solvents are used;corona or another treatmentmethod is operating; or anotherprocedure is underway whichrequires such systems.

HeatHigh temperatures are used in

extrusion coating. Always use heatprotective gloves, safety glasses andprotective clothing. Signs on theextruders should indicate specific hotareas on the machines. Since flametreatment is used on many lines, fireand personal protection is required.

Figure 53. Sophisticated microprocessor controls monitor the extrusion coating line at LyondellBasell's Cincinnati Technology Center.

ElectricitySigns on the extruders should also

warn about electric shock hazard areason the machines. Keep water awayfrom these areas. Periodically check allelectrical devices and connections.

VentilationAdequate ventilation is a must

when working with hot resins. Hightemperatures in the die may result indecomposition products. Carefullyfollow the recommended handling andprocessing conditions provided bymaterials suppliers.

Machinery MotionConsiderable mechanical

movement occurs during the extrusioncoating operation. Avoid wearing tiesand other loose-fitting clothing sinceloose items can get caught by themoving equipment. Make sure allpeople working near the extrusion lineknow where the EMERGENCYSHUT-OFF BUTTON is located.NEVER disengage any of the safetymechanisms on the extrusion line. DONOT OPERATE equipment withprotective guards removed. Installwarning signs where necessary.

Heavy ComponentsMany of the components of an

extrusion coating line are extremelyheavy. Use appropriate liftingequipment when changing and/oradjusting these components. Safetyshoes (ANSI 2-87) are required.

Prior to start-up, check to see thatall safety devices are in place andoperational. Walk around the machineto be certain that there are noobstructions to the machine’smovement and that no one is workingtoo close to the line. The extrudershould be backed away from thepressure and chill roll unit.

Be sure to have the followingavailable before start-up:

• Safety glasses for everyoneassisting in the start-up (at leasttwo operators are needed).

• Loose fitting, heavy-duty workgloves

• A large metal container (drool pan)for collecting melt produced duringthe start-up and shut-downprocedures.

• Soft metal tools for use in removingplastic from the die area and forcleaning the die lips and die gap.

35

• A sharp safety cutting knife for usein cutting the web on the winduprolls and for preparing the newsubstrate rolls for extrusioncoating. The knife must retractwhen not in use.

Guidelines For Start-UpA wide range of extruders can be

used with polyolefins. Therefore, thefollowing procedures for start-up andshut-down are provided only as ageneral guide. The operating manualfor the specific extruder should beclosely followed.

1. Turn on the cooling systems for thehopper and the screw,

2. Turn on all the heaters in stages.(Table 10)

3. Put drool pan under die.4. When the die temperatures have

reached at least 500°F (260°C),start the screw drive motor at theminimum speed. Gradually raisethe speed to 18 to 20 rpm.

5. If the screw does not rotate, thebarrel heaters have not been onlong enough. Turn off the extruderdrive and wait 10 to 15 minutes forthe heaters to bring the polymer toa molten state.

6. As the screw rotates, watch thescrew load: if it exceeds 100% orthe maximum amperage, reducethe screw RPM (i.e., speed).

7. Now purge and clean the die. Usea drool pan until the melt comingout the die appears to be cleanand consistent. Now the extruder isready for the coating operation.

8. Adjust the back pressure valve toincrease the work being done onthe resin to reach the desired melttemperature. [NOTE: Never set anyheater above the desired melttemperature.]

9. Adjust the deckling to roughlyobtain the desired coating width.

10. Run the screw speed back to theminimum. Stop the extruder longenough to carry out the next sixsteps, which should not take longerthan three minutes.

11. Remove the drool pan.12. Move the extruder into the final

coating position, i.e., just above thenip of the pressure and chill rolls(the nip should be in the openposition).

13. With the substrate in the line fromthe unwind to windup, start the linedrive in tread speed.

Main Objectives Substrates

Paper & Metal BOPPCloth Paperboard Foil Film

Adhesion X X X X Clarity X X X X Heat Sealing X X X X

Operating Conditions Recommended

Let melt fall against X X X X the pressure roll slightly above the nip

Minimum melt temp- X X X X erature compatible with good adhesion

Cool Chill Roll — X X X X 60°F to 80°F (21°C to 27°C)

Table 11. Operating Recommenations for Various Substrates

Table 10: Temperature Profile for LDPE Extrusion Coating

Initially After 1 Hour After 1½ Hour

Barrell Zone #1 300°F 350°F 350°F Barrell Zone #2 450°F 525°F 550°F Barrell Zone #3 500°F 575°F 600°F Barrell Zone #4 500°F 575°F 610°F Barrell Zone #5 500°F 575°F 610°F Adapter 500°F 57\5°F 610°F All Die Zones 500°F 575°F 610°F

Check with your resin supplier for specific recommendations for other polymers

36

14. Close the nip.15. Start the extruder screw again and

bring the screw and the line up tothe running speeds.

16. Check operating temperatures.They should be at the desiredlevels. Adjust the back pressurevalve to achieve the desired melttemperature.

17. Adjust the windup tension so thatthe take-off is firm and at thecorrect tension for the substrate.

18. Set the edge trimmers to thedesired width. Bring the slitters incontact with the coated substrate.

19. Feed the edge trim into the trimdisposal system.

20. Raise the line speed to the desiredlevel.

21. Make all quality checks after theline and extruder have settled out,and complete final adjustments.

Shut-Down Guidelines forExtrusion Coating Lines

For shut-down, follow these steps:

1. Decrease the line speed to 50 fpm(15 mpm) or less and decrease thescrew speed to the minimum.

2. Turn off the screw.3. Move the extruder back from the

nip area.4. Stop the line drive.5. Put drool pan under the die.6. Restart the screw and drool the

extruder.7. Purge the extruder with purge

compound only if needed. Do notlet the screw run “dry.” Shut downthe extruder only with clearpolyethylene or purge compound.

8. Clean the die lands and seal dielips with a Pogo stick or othermechanism, and stop the extruder.Make sure the die opening issealed to prevent oxidation.

Optimizing the ExtrusionCoating Process

After starting up an extrusioncoating line, various steps can be takento optimize its operation.

Line SpeedOne method of reducing the cost of

extrusion coating is by increasingcoating speeds. The surface speed ofthe chill roll is, of course, limited by thedrawdown properties of the meltcoating. Too high a speed may causetear-offs and voids (holes) in thecoating. These problems can best beprevented by using polyolefin resinswith unusually high uniformity andexcellent drawdown strength.

High coating speeds are notalways required or even desirable. Linespeed, i.e., chill roll speed along withextruder screw speed, controls coatingthickness (coating weight). Coatingweight depends on the requirements ofthe finished product. Line speeds rangewidely from 50 to 3,000 feet (15 to 915m) per minute. The slowest speeds areused to lay on heavier coatings or,occasionally, where maximum adhesionis a prime requirement. In highervolume, thin-coating work, the extrusioncoater may be run at high line speedsup to 3,000 ft./min. (915 m/min.).

AdhesionA coating which can easily be

peeled off is worthless. Good adhesionis, therefore, the most importantconsideration in extrusion coating. Abetter bond between substrate andcoating also means better heat sealstrength. Good adhesion of the coatingto the substrate depends upon anumber of factors, including the type ofsubstrate, type of priming, resin flow,stock temperature, coating speed andcoating weight (see Table 11).

Porous substrates, such as paperor cloth, have a natural tendency tohold onto a coating because of thepenetration of the hot melt into thesubstrate. This kind of adhesion iscalled a physical or mechanical bond.

Most smooth, non-porous sub-strates, such as metal foils, plastic filmsor even glassine, have no physicalmeans of clinging to a coating. Theytend to resist adhesion, and thesubstrate and coating must be chemi-cally bonded. To obtain a chemicalbond, a trace of oxidation on thepolymer surface is necessary. Suchoxidation requires:

• A high melt temperature• An adequate drawdown distance or

“air gap” between the point where

the hot melt leaves the die and thepoint where it solidifies, that is, thechill roll/pressure roll nip.

An adequate air gap, although itcools the web (which impairsadhesion), is needed simply to giveoxidation time to occur. When coatingporous substrates, oxidation plays arole also, although to a lesser degree.The recommended gap between dieand nip is seven to nine inches (18 to23 cm). It may be less for some poroussubstrates or where very goodadhesion is not desirable. The air gapcan be adjusted by raising or loweringthe extruder or the chill roll assembly.

The hot film can be treated withozone just before it is pressed againstthe substrate to help increase bondstrength and line speeds and reduceextrusion temperatures. However,ozone is corrosive and toxic inconcentrated amounts. The treaterstation should be made of materialsthat withstand ozone attack, such asstainless steel or aluminum andadequate ventilation is essential.

Preheating the substrate before itreaches the pressure roll promotesadhesion of the coating to some porousmaterials, such as kraft paper,paperboard or cloth. Preheating makesthe surface more receptive to themolten film. Preheating also helpsremove moisture. However, preheatingcannot dry a really wet, porous web.Adhesion to a wet substrate is alwayspoor. A wet substrate should beoven-dried before it is fed into thecoater. To preheat, pass the substrateover a steel drum that is internallyheated by steam or electricity to about350°F to 375°F (176°C to 190°C).

Resin flow properties affect theadhesion of polyolefin resins to poroussubstrates since the ability of a resin topenetrate the substrate’s surfacedepends on the viscosity of the moltenweb, as well as the porosity of thesubstrate. Higher melt index resins,with their lower viscosities, adherebetter to porous substrates than dolower melt index resins.

Any factor that reduces the amountof oxidation of the hot polyolefin webreduces its adhesion to the substrate.Low coating speed and high coatingweights tend to promote adhesionbecause more time is available foroxidation to occur. As thinner coatings

37

are extruded, they cool more betweenthe die lip and the roll nip. Hence,adhesion may be poorer. The lower thecoating weight, the higher the air gaprequired to obtain good adhesion.Conversely, the higher the coatingweight, the lower the required air gap.Too low a chill roll temperature alsoimpairs adhesion.

A high, well controlled, resintemperature in the die and at the pointwhere the resin first contacts thesubstrate are essential for goodadhesion. High melt temperatures(600°F [315°C] or higher) are requiredto chemically bond a polyolefin coatingto paper, for example.

Although high melt temperature isa critical factor in extrusion coating,high temperatures can adversely affectthe coated substrate’s sealability. Hightemperatures in the die may also resultin odor and smoke during production.Negative pressure ventilation systemsare essential (see Table 12).

Table 12: Main Factors Affectingthe Bond Between Resins andSubstrates

• Substrate Type and Surface

• Coating (Melt Temperature)

• Air Gap

• Resin Flow Properties (MeltIndex)

• Coating Speed

• Coating Thickness

• Preheating of Substrate

• Nip Pressure

• Primer

• Corona or Flame Pretreatingof the Substrate

• Ozone Treating of theExtrudate

Voids, Holes and TearsVoids in the extrusion coating are

generally caused by volatilecomponents in the polymer melt or thesubstrate. Too high a temperatureanywhere in the extruder may breakdown the polyolefin into volatile,vaporizing agents that cause bubblingand result in voids. Rapid changes intemperature, humidity or both, betweenthe storeroom and extrusion shop maycause moisture to condense on the

resin pellets. When the moisture ispresent in such quantities that it cannotbe vented back out the hopper, itevaporates and may cause voids.Substrates may also absorb moisturebefore coating, which leads to voids.Voids may occur when oxidized resinparticles collect in the die.

Pinholes can result if fibers fromthe substrate penetrate very thinextrusion coatings. Flame treating canprevent pinholes. Holes, edge tears,breaks and other defects can alsoindicate that operating conditions needto be changed. One of the followingsolutions or a combination may preventthese defects:

• Keep the resin dry and tree fromforeign matter.

• Keep the barrel, screw, screenpack and die clean. Do not let thisequipment become soiled withdegraded resin or foreign matter.

• Adjust the die properly to keep thegauge uniform and eliminate thinareas.

• Prevent surging. Keep thetemperature along the die uniform.

• Keep the resin feed throat cool(around 80°F [27°C]).

• Use only virgin resins that are freeof fines, and prevent contaminationfrom entering resin feed system.When changing resins, theextruder and die must be purgedwith the incoming resin longenough to assure that nopreviously used polymer is in thedie (15 to 30 minutes).

Neck-InWhen the hot film is drawn down

onto the cool chill roll, it exhibits “neck-in,” or shrink at the edges (see Figure35, page 23) Neck-in is the differencebetween the hot melt width at the dieface and the coating width on thesubstrate. The smaller the drawdowndistance between die and chill roll (airgap) and the narrower the die openingis set, the less neck-in. However, forgood adhesion of the melt web to thesubstrate, the air gap must have acertain minimum length, so someneck-in must be expected. Increasedneck-in can be caused by:

• Deckling —-but there is no way toeliminate neck-in due to decklingsince it is not practical to have aseparate die for each substratewidth.

• Too high a melt temperature.• Too great a die speed: decrease

the die setting and decreaseneck-in.

• Too slow a coating speed: increasecoating speed and decreaseneck-in slightly.

• A resin with too high a melt indexor density: decrease melt index,density or both and decreaseneck-in. An optimum combinationof these two properties musteventually be determined forsuccessful coating.

Wherever there is neck-in,“beading” also takes place (see Figure35, page 23). Beading is a thickening ofboth edges of the coating film. If thebeaded edges are not trimmed, thenthe final roll of coated substrate sags inthe middle because of the thickness ofthe ends. The sagging can result inbreaking edges, wrinkling anddifficulties in converting the roll later.Special internal deckling can be used tovirtually eliminate beading (Figure 36,page 23) and loss of resin.

Coating Thickness (Gauge)Variances in the thickness (gauge)

of the coating generally are due toproblems in the die. If the die and dielips are not clean, thin bands can occurin the coating. Problems with dieheaters can also cause temperaturestriations that result in gauge bands.

Uneven extrusion (non-uniformflow) from the die is called surging.Surging may result in non-uniformcoating gauge, “applesauce” defectsand voids in the coating. Table 13provides some possible reasons forsurging.

Process Variables AffectingProperties of ExtrusionCoatings

Various steps can be taken tooptimize the performance of extrusioncoated substrates.

Barrier PropertiesThickness uniformity is the most

important processing factor affectingbarrier properties. With very thincoatings, blemishes and imperfections(pinholes, fisheyes, etc.) reduce barrierproperties. Furthermore, some

38

Table 13: Reasons for Surging and Their Causes

Problem Possible Causes of Surging

Variations in Melt Temperature The screw is too hot in the feedsection so that the resin stickstogether at the feed throat,causing bridging.

Variations in Resin A poorly designed screw.

A barrel heater is burned out orfaulty, causing variationsn inelectric heating (or an instru-ment is faulty)

The resin is improperly mixedbecause the barrel is too short.

Bridging when the screw fee istoo hot.

The motor belt is slipping.

Die surfaces obstruct smoothmelt flow.

The screw fabrication could beat fault.

additives and colorants also can reducea coating’s barrier properties. Resindensity also determines barrierproperties.

ClarityThe main factor affecting clarity is

the choice of resin. However, the clarityof an extrusion coating improves withincreasing processing temperaturesand faster cooling. Clarity is alsoaffected by the chill roll used. A highgloss or mirror pocket chill roll yields ahigher clarity coating. A matte-finishchill roll results in a coating with lowclarity.

ESCRVarying processing variables has

little or no effect on ESCR. Resinchoice is the most important factor.LLDPE resins have excellent ESCR.

Gauge UniformityThe problem of poor gauge

uniformity in extrusion coating is quitecommon. Variations in gauge of less

than ±10% are not considered aproblem. Variations exceeding this levelrequire corrective steps. Non-uniformmelt temperature may result innon-uniform extrusion coating gaugeand other defects.

Hot polymer forms a flow channelthat can cause gauge bands. When thegauge bands are adjusted, a newgauge band is created on either side ofthe original one, since the hot melt flowmust go somewhere. The source of thehot melt flow must be identified andcorrected before uniform coatingthickness can be attained

Overheated melt may come out ofthe die too fluid, resulting in a coatingthat is difficult to cool and peel off thechill roll. Poor mixing may also result innon-uniform extrusion coatingthickness. It is essential to periodicallymeasure gauge on a cut piece ofcoated substrate or with a built-inelectronic gauge-measuring andrecording device.

GlossExtrusion coating gloss improves

with increasing operating temperatures.Gloss is also affected by the chill rollthat is used. A high gloss or mirrorpocket chill roll yields a glossiercoating. A matte-finish chill roll reducesthe gloss of the coating.

Heat SealabilityVarious factors can adversely

affect heat sealability. If the air gap istoo great, melt temperatures too high orcorona treatment excessive, oxidationoccurs and affects the coating’s heatsealability. Additives (antistats, slipagents, dispersion agents) also reducethe coating’s heat sealability.

SlipPolyolefin coated substrates to be

made into bags or pouches must notblock, i.e., coated sides must not stickto each other. Slip prevents blockingfrom occurring. Slip is affected by suchprocessing factors as coatingtemperature, chill roll temperature andsurface and treatment, A high coatingtemperature and a highly polished chillroll, while having beneficial effects onadhesion and coating gloss, definitelycontribute to blocking. A matte chill rollimproves slip properties considerably.Increased chill roll temperatureincreases slip and decreases blockingto a degree. If a substrate is to have aglossy coating, a polyolefin resincontaining a slip additive should beused. These additives however, canresult in some loss of adhesion.

StiffnessThe main factor affecting stiffness

is the resin choice (higher densityresins yield stiffer films). Processconditions in the barrel and screw canaffect the stiffness or “feel” of the film.

StrengthThe most important factor

controlling strength (including tear,puncture and tensile) is the choice ofresin. Naturally however, blemishes andimperfections (pinholes, fisheyes, etc.)reduce strength properties.

ToughnessThe main factor affecting

toughness is the resin choice. Extrusioncoating toughness generally is bestwith the more difficult to process resins,i.e., the low MI, high molecular weightgrades.

39

Coating Problems Possible Causes

Poor Clarity Extrusion temperature too lowInadequate coolingRough finish on the chill rollUnsuitable resin

Wrinkles on the Windup Roll Gauge variations caused by die or cooling defectsInsufficient or unequal coolingInadequate tension control at the rewindIdler rollers not in train

Coating-Film Structure Defects such as Extrusion temperature too low or high Applesauce Poor mixing

Poor screw design

Coating-Film Defects such as Gels and Fisheyes Poor mixingFlaking away of oxidized polymer caused by a dirty screw

and/or barrelInsufficient purging after changing resinsContaminated resin due to lack of cleanliness in the shop,

mixing the resin with scrap or reground polymerFaulty start-up or shut-downResin hang-upHot hopper inlet sectionPoor resin quality

Streaks in Coating Inadequate mixingForeign matter held up in dieImpurities in the die landsScratches in the die landsBurrs in the idler rollsIdler rolls not turning

Wide Coating Thickness Variations Non-uniform temperature at the die openingNon-uniform cooling across the meltNon-uniform flow at the die opening (probably caused by surging)Non-uniform die gap opening

Poor Winding Non-uniform gaugePoor rewind tension controlExcess slip additive in the resinInadequate rewind equipmentToo much blockingInadequate cooling of the coated substrate before windupChill roll too highly polishedOvertreatmentImproper wind-up tensionImproper idler roll alignment

Adhesion, Ppoor or Spotty Bonds Low melt temperatureImproper air gapHeater malfunctionSubstrate surface not prepared; corona treatment or primer

requiredChill roll temperature too high or lowUse of silicone spraysIncorrect nip roll impression

AAAAAppendix 1:ppendix 1:ppendix 1:ppendix 1:ppendix 1:Common CoaCommon CoaCommon CoaCommon CoaCommon Coating Prting Prting Prting Prting Proboboboboblems and lems and lems and lems and lems and TTTTTheir Causesheir Causesheir Causesheir Causesheir Causes

40

AAAAAppendix 1:ppendix 1:ppendix 1:ppendix 1:ppendix 1: (Contin (Contin (Contin (Contin (Continued)ued)ued)ued)ued)Common CoaCommon CoaCommon CoaCommon CoaCommon Coating Prting Prting Prting Prting Proboboboboblems and lems and lems and lems and lems and TTTTTheir Causesheir Causesheir Causesheir Causesheir Causes

Coating Problem Possible Causes

Coating Film Defects

Applesauce Extrusion temperature too high or lowPoor mixingResin contamination; improper purging technique

Gels Insufficient purging after resin changeContaminated resin: transfer lines not cleaned or storage boxes not coveredOver-oxidized polymer as a result of high melt temperaturesOverheated hopper feed section; water cooling passages clogged

Edge Tear Improper die designDie temperature ends too lowDeckle settings too wide or narrowDeckle seal strip improperly set up

Gauge Bands Heater malfunction; melt temperature variationDirty dieDie gap opening not uniformMelt temperature too highImproper melt back pressure control

Pinholes Rough substrateLow polymer coatingGelsHigh tension settings on line drivesDirty or damaged idler rollers

Voids Wet polymer; moisture pickup due to quick temperature changes orresin handling

GelsMelt temperature too highDirty die

Surging Hot hopper inlet section from poor water circulationImproper screw designImproper process conditions

Draw Resonance Improper air gapMelt temperature too highWrong resin used for jobImproper die gap

Oxidation Improper air gapMelt temperature too highImproper purging technique; possible resin contaminationShut-down procedure problems: screw turned off too soonHigh treater settings on barrel down stream zones

Curtain Tear-Outs or Breaks Improper die gapMelt temperature too lowLow back pressureLow coating thicknessImproper deckle set-up

Heat Sealability Problem Over-oxidation: high melt temperature or improper air gap settingExcessive corona treatmentAdditives or excessive use of silicone sprays, resulting in surface contamination

41

AAAAAppendix 2:ppendix 2:ppendix 2:ppendix 2:ppendix 2:FFFFFororororormmmmmulas fulas fulas fulas fulas for the Extror the Extror the Extror the Extror the Extrusion ofusion ofusion ofusion ofusion of P P P P Polololololymerymerymerymerymersssss

1. Output, lbs/hr

(FPM) Width, in.) (basic weight) 600

FPM = line speedbasic weight = gauge desiredWidth = die opening

2. Output, lbs/RPM

lbs./hr RPM

3. Horsepower

(volt) (amp) 750

4. Outputs, lbs/hp

lbs/hr HP

5. RPM

lbs/hr lbs.RPM

42

AAAAAppendix 3:ppendix 3:ppendix 3:ppendix 3:ppendix 3:Cleaning the ExtrCleaning the ExtrCleaning the ExtrCleaning the ExtrCleaning the Extruder and Its Puder and Its Puder and Its Puder and Its Puder and Its Pararararartststststs

A definite periodic cleaningschedule should be established forthe extrusion coating line. The timeinterval between thorough cleaningcan best be determined byexperience. Standard operatingprocedures should be developed forspecific machines operated underspecific conditions in the shop. Thefollowing are general guidelines only.

How to Clean the ExtruderOver long periods of operation, a

layer of oxidized polymer slowlybuilds up on the inside barrel walls,the screw and the die. Eventually, thisdegraded resin will begin to flake off.This in turn results in coating defects,such as gels or yellow-brown oxidizedparticles. Such defects cause thecoating to have a poor appearance,especially in very thin coatings.

The following disassembly stepsare suggested prior to cleaning theextruder:

1 . Refer to the MSDS on thematerials run most recently tolearn about potential hazards ifdecomposition occurs.

2. Let the extruder run with resin,without further feeding, until thescrew can be seen when thehopper is uncovered. Do not letthe screw run “dry”.

3. Turn off all electricity and watercooling.

4. Move the extruder away from thewindup equipment and removeanything else in line with thescrew while the machine is stillhot. Wear protective gloves. Makesure that the hazards of volatileand other resin decompositionproducts are eliminated.

5. Disconnect electrical and waterlines.

6. Remove the die. Use heavy-dutycarrying equipment, an overheadcrane or fork lift truck.

7. Remove the barrel cover and theadapter from the barrel.

8. Remove the breaker plate andscreens from the adapter.

9. Push the screw forward with arod from the back end of thebarrel and remove it. Now, youhave access to all the extruderparts to be cleaned orexchanged.

To clean the screw, first use a copperor brass knife (putty knife) to removemost of the molten resin adhering tothe screw. Do not use a steel blade.Next, clean the screw with copper orbrass wool. Use a silicone greaseand/or nonchlorinated scouringpowder to remove stubborn resin. Butuse the silicone grease sparingly;residual silicone can cause problemsin extrusion coating for days. Finally,coat the screw with a thin layer ofcastor oil.

To clean the barrel, run a brassbrush at the end of a long handlethrough the barrel to remove anyresin build-up. Lubricate the barrelwith a thin layer of castor oil. To cleanthe adapter, also use copper or brasstools. Clean the collar. Clean andlubricate the seat of the adapter. Theface of both the adapter and thebarrel must be clean in order to makea good seal on reinstallation. To cleanthe breaker plate, it is necessary toburn away the oxidized polymer witha Bunsen burner. The polymer maybe clinging to or possibly clogging theplate. Specially designed cleaningovens or fluidized baths may also beused for cleaning breaker plates orsmall parts.

To clean the extrusion coatingdie, remove the fixed die lips whilethey are hot. If the die lands areseparate from the lips, remove them.Scrape the lands, the manifold andthe fixed and adjustable lips free ofresin with a brass or wooden “knife.”Use only copper or brass tools forcleaning all the parts. Finish thecleaning with a copper-wool cloth orbrush. Polish the curved surfaces ofthe manifold with a very fine grit

polishing cloth, and hone themanifold’s flat surface to remove anymars or scratches. Reassemble allthe parts. Set the opening betweenthe die lands to the desired width witha feeler gauge or shim made of brassor some “soft” metal which does notmark the lands. The recommendeddie gap opening is 0.030 inch (0.008mm).

To clean the pressure rolls, use acloth saturated with ethyl or isopropylalcohol. Make sure to work in a wellventilated area. If there are minorscratches or nicks in the pressure roll,it must be refinished, which can bedone with a coarse emery cloth,followed by polishing with a piece offelt. Repairs of more significantdamage, such as cracks, surfacehardening, gouges, etc., requireremoval of the roll and regrincling orresurfacing.

To clean the chill roll, also use anethyl or isopropyl alcohol -saturatedcloth. Make sure to work in a wellventilated area. Take special care notto mar the chill roll surface in any way.Check the surface to make sure that itis perfectly flat. Periodically, the chillroll must be reconditioned: a new, flat,highly polished surface applied andthe cooling water channels cleaned.Chill roll manutacturers generally offerthis service. A replacement chill rollshould be available while the currentroll is sent out for reconditioning.

43

AAAAAppendix 4:ppendix 4:ppendix 4:ppendix 4:ppendix 4:Metric ConMetric ConMetric ConMetric ConMetric Convvvvvererererersion Guidesion Guidesion Guidesion Guidesion Guide

To Convert From To Multiply By

Areasquare inches square meters 645.16square millimeters square inches 0.0016square inches square centimeters 6.4516square centimeters square inches 0.155square feet square meters 0.0929square meters square feet 10.7639

Densitypounds/cubic inch grams/cubic centimeter 7.68grams/cubic centimeter pounds/cubic inch 0.000036pounds/cubic foot grams/cubic centimeter 0.016grams/cubic centimeter pounds/cubic foot 62.43

Energyfoot-pounds Joules 1.3558Joules foot-pounds 0.7376inch-pound Joules 0.113Joules inch-pounds 8.85foot-pounds/inch Joules/meter 53.4Joules/meter foot-pounds/inch 0.0187foot-pounds/inch Joules/centimeter 0.534Joules/centimeter foot-pounds/inch 1.87foot-pounds/square inch kilo Joules/square meter 2.103Joules/square meter foot-pounds/square inch 0.4755

Lengthmil millimeter 0.0254millimeter mil 39.37inch millimeter 25.4millimeter inch 0.0394

Outputpounds/minute grams/second 7.56grams/second pounds/minute 0.1323pounds/hour kilograms/hour 0.4536kilograms/hour pounds/hour 2.2046

Powerkilowatts horsepower(metric) 1.3596horsepower (metric) kilowatts 0.7376voltage/mil millivolts/meter 0.0394millivolts/meter voltage/mil 25.4

44

To Convert From To Multiply By

Pressurepounds/square inch (psi) kilopascals (kPa) 6.8948kilopascals (kPa) pounds/square inch (psi) 0.145pounds/square inch (psi) bar 0.0689bar pounds/square inch (psi) 14.51

Temperature°F °C (°F-32)/1.8)°C °F 1.8°C+32inches/inch F meters/meter,C 1.8meters/meter,C inches/inch,F 0.556

Thermal ConductivityBtu-in/hr, sq. ft.,°F W/(m-°K) 0.1442W / (m-°K) Btu-in/hr,sq ft, °F 6.933

Thermal Expansioninches/inch,°F meters/meter,°C 1.8meters/meter, °C inches/inch, °F 0.556

Viscositypoise Pa-sec. 0.1Pa-sec poise 10

Volumecubic inch cubic centimeter 16.3871cubic centimeter cubic inch 0.061cubic foot cubic meter 0.0.83cubic yard cubic meter 0.765

Weightounce gram 28.3495kilogram ounce 0.03527pound kilogram 0.4536kilogram pound 2.2046ton (US) ton (metric) 0.972ton (metric) ton (US) 1.1023

Coating Weightgrams/meter² pounds/3,000 ft² 0.614

AAAAAppendix 4:ppendix 4:ppendix 4:ppendix 4:ppendix 4: (Contin (Contin (Contin (Contin (Continued)ued)ued)ued)ued)Metric ConMetric ConMetric ConMetric ConMetric Convvvvvererererersion Guidesion Guidesion Guidesion Guidesion Guide

45

AAAAAppendix 5:ppendix 5:ppendix 5:ppendix 5:ppendix 5:

AbAbAbAbAbbrbrbrbrbreeeeeviaviaviaviaviationstionstionstionstionsACS American Chemical SocietyAPC Automated process controlASTM American Society for Testing and MaterialsBOPP Biaxially oriented polypropyeneBtu British thermal unitDB Dinkelberry. Caused by leaking die end plates, deckles or

other extruder matting surfaces.deg Degree (angle)E Modulus of elasticityEAA Ethylene acrylic acid copolymerEEA Ethylene-ethyl acrylate copolymerelong ElongationEMAA Ethylene methyl acrylic acid copolymerEnBA Ethylene-n-butyl acrylateESCR Environmental stress cracking resistanceEVA Ethylene vinyl acetate copolymerEVOH Ethylene vinyl alcohol copolymerFDA Food and Drug Administrationflex FlexuralFPA Flexible Packaging AssociationFR Flame retarantg GramGP General purposeHALS Hindered amine light stabilizerH/C Hopper CarHDPE High density polyethyleneHMW High molecular weightimp ImpactIR InfraredJ JouleK Kelvinkpsi 1,000 pounds per square inchL/D Length to diameter ratio of screwlbf Pound-forceLDPE Low density polyethyleneLLDPE Linear low density polyethyleneMD Machine directionMDPE Medium density polyethyleneMl Melt indexMIL Military, as in Military Standard (MIL STD)mod Modulusmol% Mole percentMU Greek muMVTR Moisture vapor transmission rateMW Molecular weightN NewtonOPP Oriented polypropylenePA PolyamidePBT Polybutylene terephthalatePE PolyethylenePET Polyethylene terephthalatePP Polypropylene

46

pphr Parts per hundred resin, parts per hourppm Parts per millionpsi Pounds per square inchPVdc PolyvinylideneRH Relative humidityrpm Revolutions per minuteSCR Silicon controlled rectifiersp gr Specific gravitySPC Statistial process controlSPE Society of Plastics EngineersSPI The Society of the Plastics IndustrySQC Statistia quality controlTAPPI Technical Association of the Pulp and Paper IndustryTD Transdirectionalten TensileTg Glass transition temperature (crystalline polymers)T/L TruckloadTm Melt temperature (amorphous polymers)TPO Thermoplastic olefinUHMW-HDPE Ulta-high molecular weight HDPEult UltimateUV UltravioletVAM Vinyl acetate monomerWVTR Water vapor transmission rateyld Yield

AAAAAppendix 5:ppendix 5:ppendix 5:ppendix 5:ppendix 5: (Contin (Contin (Contin (Contin (Continued)ued)ued)ued)ued)

AbAbAbAbAbbrbrbrbrbreeeeeviaviaviaviaviationstionstionstionstions

47


GLGLGLGLGLOSSAROSSAROSSAROSSAROSSARYYYYY

Air Gap: The vertical distance betweenthe die lips and the nip to chill rollcontact point.Applesauce: Rough wavy appearanceon the surface of the polymer curtain,sometimes called Orange Peel. Itoccurs when the plastic has not beenuniformly homogenized.Aging: Change of a material with timeunder defined environmentalconditions, leading to improvement ordeterioration of properties.Air Jet: Device used to cool andstabilize the polymer edge.Alloy: Composite material made byblending polymers or copolymers withother polymers or elastomers underselected conditions, e.g.,polypropylene-rubber blends.Amorphous Phase: Devoid ofcrystallinity; no definite order. Atprocessing temperatures a plastic isnormally amorphous.Angle of Repose: Minimum angle forthe hopper wall design. It is equivalentto the angle formed when the resin isplaced in a pile on a flat surface.Annealing: Holding a material at anelevated temperature below its meltingpoint to permit stress relaxation withoutdistortion of shape.Antiblock: Additive that prevents anundesired adhesion between touchinglayers of a material, such as occursunder moderate pressure duringstorage or use.Antioxidant: Substances that preventor slow down oxidation of polymersexposed to air.Antistatic Agent: Additives thatminimize static electricity in polymers.Arrowheads: Imperfections in filmresembling “arrowheads”.Auto-oxidation: Self-sustainedoxidation of a polyolefin after initialexposure to some oxidizing agent, suchas molecular oxygen.Average Molecular Weight: Mostsynthetic polymers are a mixture ofindividual chains of many differentsizes, hence a molecular weight forsuch a mixture is an average molecularweight.

Beta Gauge: Gauge consisting of twofacing elements, a “ß”-ray-emittingsource and a “ß-ray detector. When asheet material (substrate) is passedbetween the elements, the “ß” -raysabsorbed are a measure of the densityor thickness of the sheet.Beta Scission: Abstraction of hydrogenfrom the polymeric backbone, causingchain breakage, resulting in a markedreduction in melt viscosity.Bleed: To give up color when in contactwith water or a solvent. Also, theundesired movement of certainmaterials to the surface of a finishedarticle or onto an adjacent material.Blister: Raised area on the surface of acoated substrate or molded plasticcaused by the pressure of gases insidethe area’s independently hardenedsurface, sometimes created byentrapped air between a substrate andthe coating,Blocking: Undesired adhesionbetween touching layers of material,which can occur if the materials areunder moderate pressure duringstorage or use.Blooming: Movement of an additive tothe surface of the finished article.Blowing Agents: Chemical additivesthat generate inert gases when heatedand cause the polymer to assume acellular structure.Branched: In the molecular structure ofpolymers, this refers to side chainsattached to the main chain,Breaker Plate: Perforated plate locatedin an extruder head. It often supportsscreens that prevent foreign particlesfrom entering the die.Bulk Density: Mass per unit volume ofa powdered or pelletized material asdetermined in a reasonably largevolume.Burning Rate: Tendency of polymers toburn under given conditions.Chill Roll: Cored roll, usuallytemperature controlled by circulatingwater, which cools the web beforewinding. In extrusion coating, either apolished or matte-surfaced chill roll maybe used, depending on the desiredfinished coating.Clarity: The transparency of a coating.Clearance: Controlled distancebetween parts of an object.

Coat-hanger Die: Extrusion slot dieshaped internally like a coat hanger toimprove distribution of the melt acrossthe full width of the die.Coating Weight: Weight of coating perunit area.Color Concentrate: Color pigmentcompounded with a base resin andthen let down at a specific ratio with thepolymer being extruded to achieve acorrect end concentration.Compression Ratio In an extruderscrew, the ratio of the channel volumein the first flight at the hopper to that ofthe last flight at the end of the screw.Conditioning: Subjecting a material toa stipulated treatment so it responds ina uniform way to subsequent testing orprocessing. The term is frequently usedto refer to the treatment given tospecimens before testing.Copolymer: Polymeric system thatcontains two or more monomeric units.Polymer that has a functional chemicalgroup added for improved properties.Examples are EnBA, tie-layers, EAAadhesive polymers, EVA, EMA, EMAA.Creep: Dimensional change with timeof a material under load, following theinitial instantaneous elasticdeformation.Crosslinking: Formation of primaryvalence bonds between polymermolecules, resulting in a markedincrease in melt viscosity. A method ofdegradation by which molecules jointogether resulting in an increased highmolecular weight proportion. Many gelsare actually highly crosslinked material.Crystallinity: Molecular structure inpolymers denoting stereo regularity andcompactness of molecular chains.Normally can be attributed to theformulation of solid crystals in thepolymer with a definite geometric form.Curling: Condition in which a coatedsubstrate rolls in the machine ortransverse direction and sometimes inboth directions.Deckle Rods: Small rod or adjustabledevice inserted or attached at each endof an extrusion coating die, used tocontrol the width of the polymer as itleaves the die lips.Delamination: Separation of dissimilarmaterials into layers.Deliquescent: Capable of attractingmoisture from the air.

48

Density: Weight per unit volume of asubstrate expressed in grams per cubiccentimeter, pounds per cubic foot, etc.Die Adapter: Extrusion die part thatconnects the die to the barrel adapter.Die Gap: Distance between the die lips,forming the die opening, through whichthe polymer flows, typically 0.020" to0.040" (0.508mm to 1.016mm).Die Lines: Vertical marks on the filmextrudate caused by damage to the dielips or contamination on the die lips’land areas.Dinkelberrys: Drippings from deckles,mating surfaces on dies and adaptors,etc.Dielectric Constani: Ratio of thecapacitance of an assembly of twoelectrodes separated by a dielectricmaterial to the assembly’s capacitancewhen the electrodes are separated byair.Dielectric Strength: Electric voltagegradient at which an insulating materialis broken down, given in volts per mil ofthickness.Dispersion: Finely divided particles ofa material suspended in anothersubstance.Doctor Roll, Doctor Bar, DoctorBlade: Device regulating the amount ofliquid material on the rollers of aspreader or applicator,Drawdown Ratio: Ratio of thethickness of the die opening to the finalthickness of the product.Drawdown Limit: The complete andinstantaneous breaking or tearing of themolten film curtain across its entirewidth.Draw Resonance: A different form ofextrudate drawdown failurecharacterized by instability of themolten film edge or loss of thicknessuniformity across the width of the filmcurtain. The thickness changes movefrom side to side and are not confinedto one area of the die.Edge Bead: A buildup of polymer alongthe edges of the web resulting fromneck-in of the molten polymer curtainas it exits the extrusion coating die.



Edgebead Reduction: A wire rod orshaped mechanism inserted above thefinal die lip lands from each end of theextrusion coating die. This devicereduces or eliminates edge bead.Edge Tear, Edge Weave: Weaving orpartial tearing of the melt curtain alongits edges.Elasticity: Property of a material thatallows it to recover its original size andshape after deformation.Elongation: Increase in length of amaterial under stress.Embossing: To create impressions of aspecific pattern in plastic film.Environmental Stress Cracking:Susceptibility of a thermoplastic tocrack or craze under the influence ofchemical treatment and/or mechanicalstress.Ethylene Vinyl Acetate: A copolymer ofethylene and vinyl acetate having manyof the properties of polyethylene, butexhibiting increased flexibility,elongation and impact resistance.Extrudate: Product or materialdelivered by an extruder, such as film,pipe, and the web coating of paper orfilms, etc.Extrusion: Forcing a heated plasticthrough a shaping orifice to produce acontinuous flow.Extrusion Coating: Coating of asubstrate by extruding a thin film ofmolten polymer and pressing it onto thesubstrate.Film: Sheeting with a thickness lessthan 0.010 inch.Fisheye: Fault in transparent ortranslucent polymer film or sheet, whichappears as a small globular mass.Caused by contamination or incompleteblending.Flame Treating: Treating inertthermoplastic materials so they arereceptive to inks, lacquers, adhesives,etc. The material is heated in an openflame to promote oxidation on thesurface. Paperboard is usually flametreated to promote adhesion of themolten polymer curtain to its surface.Flammability: Measure of the extent towhich a material supports combustion.Flow: Fluidity of a plastic.Gauge: Thickness of a single layer offilm expressed in mils (0.001 inch = 1mil).Gels: A film defect characterized byround or oblong clear spots, so hardthey can be felt.

Gel Flurry: Sporadic appearance ofgels in a large area of a film extrudate.Gel Streaks: Groups of gels aligned inthe direction of flow in film.Glass Transition: Change in anamorphous polymer or in amorphousregions of a partially crystalline polymerfrom a viscous or rubbery condition to ahard and relatively brittle one.Gloss: Measure of the ability of amaterial to reflect incident light. It is afunction only of the surface of thematerial.Hardness: Resistance of a plastic tocompression and indentation. Amongthe most important methods of testingthis property are Brinell Hardness,Rockwell Hardness and ShoreHardness.Haze: Degree of cloudiness in apolymerHeat Sealing: Joining plastic surfacesby simultaneous application of heat andpressure to areas in contact. Heat maybe supplied conductively or inductively.Homopolymer: Polymer consisting ofonly monomeric species.Hopper: Conical feed reservoir intowhich polymer is loaded and fromwhich it falls into the extruder.Hot Gas Welding: Joiningthermoplastics by softening thematerials with a jet of hot air andpressing together the softened points. Athin rod of the same material is used tofill the gap in some applications.Hydroscopic: Tendency to absorbmoisture.Impact Strength: Ability of a material towithstand shock loading.Land: Bearing surface along the top ofthe flights of a screw in an extruder orthe surface of an extrusion die parallelto the direction of melt flow.Light Resistance: Ability of a plastic toresist fading after exposure to sunlightor ultraviolet light,L/D Ratio: Ratio of the extruder lengthto its barrel diameter.Masterbatch: Plastic compound thatincludes a high concentration of anadditive or additives, i.e.; colorpigments, slip, antiblock, etc.Melt Flow Rate: Amount, in grams, of athermoplastic forced through the orificeof an extrusion plastometer underconditions described in ASTM D 123-F9(condition L) at 230°C. Normally usedfor polypropylene.

49

Melt Fracture: Instability in the meltflow through a die starting at the entryto the die. It leads to surfaceirregularities of the finished product.Melt Index: Amount, in grams, of athermoplastic which can be forcedthrough the orifice of an extrusionplastometer under conditions describedin ASTM D1238-F9 (condition E) at190°C. Normally used for polyethylene.Melt Strength: Strength of a polymerwhile in a molten state.Moisture Vapor Transmission Rate:Rate at which water vapor permeatesthrough a plastic film at a specifiedtemperature and relative humidity.Molecular Weight Distribution:Measure of the frequency of occurrenceof the different molecular weight chainsin a homologous polymeric system. Theratio of the weight average molecularweight to the number averagemolecular weight is sometimes used asan indication of the breadth of thedistribution.Monomer: Molecule that can react toform a polymer.Neck-In: Contraction of the moltenpolymer curtain as it leaves the die. Thedifference between the die openingwidth and the finished coating widthbefore trimming off the edge bead.Nips: Rolls in various locations alongthe length of the coating line includingthe nips in the coating stations (priming,extrusion) etc,Orange Peel: Surface defect in filmresembling the skin of an orange.Orientation: Aligning the crystallinestructure of polymers to produce ahighly uniform structure accomplishedby cold drawing or stretching duringfabrication.Permeability: Rate of diffusion of avapor, liquid, or solid through a barrier.Pigment: Solid, insoluble additiveproviding opacity or color.Poise: Unit of viscosity.Polytillends: Mechanical mixture of twoor more polymers, for examplepolypropylene and rubber.Polyethylene: Thermoplasticcomposed mainly of ethylene.

AAAAAppendix 6:ppendix 6:ppendix 6:ppendix 6:ppendix 6: (Contin(Contin(Contin(Contin(Continued)ued)ued)ued)ued)


Polymer: High molecular weightorganic compound, natural or synthetic,with a structure represented byrepeating small units.Polypropylene: Tough, lightweight,rigid plastic made by the polymerizationof propylene gas in the presence of anorganometallic catalyst at relatively lowpressures and temperatures.Purging: Cleaning one color or type ofmaterial from the barrel of an extruderby forcing it out with a new material or apurge compound, if needed.Quench: The shock cooling ofthermoplastics from the molten state.Recycle: Ground material from edgetrimmings or drool which, after mixingwith certain amount of virgin material, isreused in some extrusion operations(blow molding, injection molding, filmand sheet extrusion).Rheology: Study of the flow ofpolymers on a macroscopic andmicroscopic level.Rockwell Hardness: A test for plasticsmeasuring resistance to indentation byusing a diamond or steel ball underpressure to deform the test specimen.Rubber Roll Marks: A repeatimpression made on the coated surfacewhen contamination particles are stuckon a nip roll (rubber roll). After eachrevolution, the contaminant leaves amark on the substrate.Shear Rate: Overall velocity of thecross section of a channel at whichmolten polymer layers are gliding alongeach other or along a channel in alaminar flow.Shear Strength: Ability of material towithstand shear stress or the stress atwhich a material fails to shear.Shear Stress: Stress development in apolymer melt when the layers in a crosssection are gliding along each other oralong a wall of the channel in a laminarflow.Sheet: Flat section of a thermoplasticat least 10 mils thick, with its lengthconsiderably greater than its width.Shrinkage: Contraction of a moltenmaterial upon cooling.Slip Additive: Modifier that acts asinternal lubricant which blooms to thesurface of the plastic during andimmediately after processing. Theadditive coats the surface and reducesthe coefficient of friction.

Specific Heat: Amount of heat requiredto raise a unit mass by one degree oftemperature under specified conditions.Stabilizer: Ingredient used in theformulation of some polymers to assistin maintaining the physical andchemical properties of the compoundedmaterials, for example, heat and UVstabilizers.Surface Treatment: Treating a polymerto render the surface receptive to inks,lacquers, and adhesives. Also used torender the surface of paper, paperboardand film substrates receptive topolymer adhesion. Also refers toprocesses such as chemical, flame andelectronic treating.Surging: Unstable pressure build-up inan extruder leading to variablethroughput and waviness of theextrudate.Synergism: Use of stabilizers or slipadditives in a polymer when thecombination of two or more stabilizersimproves the stability of a polymer to agreater extent than would be expectedfrom the additive effect of eachstabilizer alone.T-Die: Center-fed, slot extrusion die,which in combination with the dieadapter (down-spout), resembles aninverted “T.”Tear Strength: Ability to resist tearing.Temperature Profile: Temperaturesalong the extruder, adapter, down-spoutand die. Usually described by zonesstarting at the feed zone andprogressing to the die lips,Tensile Strength: Pulling stress inpounds per square inch required todeform a given specimen. The originalarea of the coating is usually used incomputing strength, rather than thenecked-in area.Thermal Stability: Ability of a polymerto maintain its initial physical andchemical properties at elevatedtemperatures.Treating: Preparing a substrate foradhesion of a polymer. Preparing apolymer surface to retain inks,adhesives, etc.UV Absorbers: Any chemicalcompound which, when mixed with athermoplastic, selectively absorbsultraviolet rays and retards polymerdegradation.

50

Ventilation: Blower devices used toremove smoke and fumes from aroundextrusion coating lines and the extruderdie.Viscosity: Internal friction or resistanceto flow of a liquid. The ratio of shearingstress to rate of shear.Viscosity of Common Liquids inPoise at 25°CWater 0.01Kerosene 0.10Motor Oil SAE 10 1.0Castor Oil 10.00Glycerin 10.00Corn Syrup 100.0Molasses 1000.0Polymers (typical) 10,000 to

100,000(at 200°C)

Void: Bubble or hole in film, caused bygels, hang-up in die lips and moisture inresin.

AAAAAppendix 6:ppendix 6:ppendix 6:ppendix 6:ppendix 6: (Contin(Contin(Contin(Contin(Continued)ued)ued)ued)ued)


51


TEST METHODS TEST METHODS TEST METHODS TEST METHODS TEST METHODS APPLICABLE APPLICABLE APPLICABLE APPLICABLE APPLICABLE TTTTTO POLO POLO POLO POLO POLYYYYYOLEFIN EXTROLEFIN EXTROLEFIN EXTROLEFIN EXTROLEFIN EXTRUSION COUSION COUSION COUSION COUSION COAAAAATINGTINGTINGTINGTINGRESINS RESINS RESINS RESINS RESINS AND AND AND AND AND THEIR SUBSTRATHEIR SUBSTRATHEIR SUBSTRATHEIR SUBSTRATHEIR SUBSTRATESTESTESTESTES

Property ASTM Method TAPPPI Method

Abrasion Resistanceof Paperand Paperboard T476of Plastic Materials D 1242

Adhesion of Polyethyleneto Porous Substrates T539to Nonporous Substrates T540

Air Permeabilityof Paper and Paperboard T547

Blocking Resistanceof Paper and Paperboard D 918

Brittleness, Low Temperatureof Plastic Film D 746

Burst Strengthof Paperboard and Linerboard D 774 T807of Paper D 774 T403

Chemical Resistanceof Adhesive Bonds D 896of Plastic Film D 1239

Coefficient of Frictionof Packaging Paper T542Density of Plastic Film D 1505 or D 792

Dielectric Constant of Plastic Film D 150Dissipation Factor of Plastic Film D 150

Elongation of Plastic Film D 882Environmental Stress Cracking Resistance

of Plastic Film D1693Flexural Modulus of Plastic Film D790Folding Endurance of Paper T423Gloss (spectral)

of Paper and Paperboard T480of Plastic Film D 2457

Grease Resistanceof Flexible Packaging Materials T507

Hardness of Plastic Film, Rockwell D 785Shore D 2240

Haze of Plastic Film D 1003Heat Seal Strength of Plastic Film F 88Impact Strength, falling dart of Plastic Film D 1709/AMelt Index D1238Oxygen Permeability of Plastic Film D 3985Printability of Polyolefin Film Surfaces T698Rheological Properties Using Capillary

Rheometer D 3985Specific Gravity D 792Stiffness of Paper T451

of Paperboard T4891% Secant modulus of Plastic Film D 638

52

Surface Resistivity of Plastic Film D 257Surface Tension

of Paper Substrate D 724 T458of PE and PP D 2578 T698

Tear Resistanceof Plastic Film D 1922of Paper T414

Tensile Strengthof Plastic Film D 882of Paper and Paperboard D 828 T404

Thermal Conductivity C l 77Vicat Softening Point D 1525Volume Resistivity of Plastic Film D 257Water Absorption of Plastic Film D 570Water Vapor Transmission Rate

of Paper and Paperboard T448of Flexible Packaging Materials E 96 T448of Flexible Barrier Materials D 1434

Wetting Tension of Polyolefin Film Surfaces T698Wetting Tension of Polyolefin film and T552

coated surface via the Mayer rod technique


TEST METHODS TEST METHODS TEST METHODS TEST METHODS TEST METHODS APPLICABLE APPLICABLE APPLICABLE APPLICABLE APPLICABLE TTTTTO POLO POLO POLO POLO POLYYYYYOLEFIN EXTROLEFIN EXTROLEFIN EXTROLEFIN EXTROLEFIN EXTRUSION COUSION COUSION COUSION COUSION COAAAAATINGTINGTINGTINGTINGRESINS RESINS RESINS RESINS RESINS AND AND AND AND AND THEIR SUBSTRATHEIR SUBSTRATHEIR SUBSTRATHEIR SUBSTRATHEIR SUBSTRATESTESTESTESTES

Property ASTM Method TAPPPI Method

53

AAAAAppendix 8:ppendix 8:ppendix 8:ppendix 8:ppendix

HDPE Polyethylene ResinsEthylene vinylsilane compounds for wire and cableThermoplastic Polyolefin ResinsFunctionalized PolyolefinsPowdered polyethylene resinsPolyethylene and polypropylene resinsTie-layer resins

Alathon® Aquathene™ Flexathene® Integrate™ Microthene® Petrothene® Plexar® Ultrathene® Ethylene vinly acetate (EVA) copolymer resins

54

IndeIndeIndeIndeIndexxxxxAAbbreviations, 45Additives, 2, 4, 5 blending, 10Adhesion optimizing, 36 problems with, 39Aging, 47Air blowers, barrel cooling and, 17Air gap, 47 adhesion and, 36Air jet, 47Alarm system, for heat failure, 17Alloy, 47Amorphous phase, 47Angel hair, 8Angle of response, 47Annealling, 47Antiblock, 47Antioxidant, 47Antistatic agents, 2, 47Applesauce, 37, 40, 47Area, metric conversion guide for, 43Arrowheads, 47Atactic substances, 47Automatic roll changers, 33Automatic screen changers, 19Auto-oxidation, 47Average molecular weight, 47

BBarrel, 17 cleaning, 47 cooling, 17Barrier properties, 37Barrier-type screws, 18Bead control rods, 23Beading, 29Bends, long radius, eliminating, 9Beta gauge, 47Beta scission, 47Bimetallic liners, of barrels, 17Bleed, 47Blister, 47

Blocking, 47 resistance to, 3Blooming, 47Blowing agents, 47Branched chains, 2, 47Breaker plate, 17, 47“Build-up ratio,” 33Bulk density, 47Burning rate, 47Butene, 4

CCarbon atoms, 2Center braking, 11Center winders, 32Central blending units, 10Chain branching, 2, 47Chemical bonding, 36Chemical priming, 11Chemical resistance, 37Chill rolls, 27, 47 cleaning, 42Cincinnati Technology Center, 8Clarity, 4, 38, 47 problems with, 39Cleaning, of extruder, 42Clearance, 47Coat-hanger dies, 21, 47Coating pan, 13Coating thickness, 37 variations in, 39Coating weight, 47 metric conversion guide for, 43 monitoring, 31Coextrusion coating feedblock, 26Coextrusion equipment, 23Colorants, 47 blending, 10Color concentrate, 47Combining adapter, 24Comonomers, 3Compression, 47Compression ratio, of extruder screw, 18Condensation, on cooled chill rolls, 27Conditioning, 47Contamination, eliminating in resin transfer, 9Continuous monitoring systems, primer application and, 13

55

Control(s), 33Controller, 17Cooling of barrel, 17 of extruder screw, 18 of chill roll, 27 of pressure roll, 27Copolymer, 47Corona discharge treatment, 11Creep, 47Crosslinking, 47Crystallinity, 47 density and, 2Curling, 47Curtain tear-outs or breaks, 40

DDeckle rods, 47Deckling systems, 23Delamination, 47Deliquescent, 47Density, 2, 48 metric conversion guide for, 43Die(s), 20 cleaning, 42 coat-hanger, 24, 47 coextrusion, 23 dual manifold, 23 dual slot, 24 heating zones of, 21 keyhole, 24 multimanifold coextrusion coating, 26 single exit, 24Die adapter, 48Die gap, 48Dielectric constant, 48Dielectric strength, 48Die lines, 48Die lips, 20Dinkelberrys, 48Dispersion, 48Doctor roll/bar/blade, 48Drawdown, 3Drawdown limit, 48Drawdown ratio, 48Draw resonance, 40, 48

Dryers, for priming, 13Dual manifold dies, 23Dual slot dies, 24Dust, 8

EEdge bead, 48 minimizing formation of, 21 reduction of, 48Edge bead trim slitters, 29Edge-guide equipment, 33Edge tear, 37, 40Elasticity, 48Electricity, 34Electrodes, for corona treatment, 15Elongation, 48 at rupture, 3Embossing, 48Energy, metric conversion guide for, 43Environmental stress cracking resistance

(ESCR), 3, 38, 48Ethylene, 2,Ethylene copolymers, 2Ethylene vinyl acetate (EVA), 4, 48Extrudate, 48Extruder(s), 16 cleaning, 42 number of, 15Extrusion, 48 speed of, 3Extrusion coated products, applications for, 7Extrusion coating, 48Extrusion coating line

shut-down, 36start-up, 34

Extrusion laminating, 7

FFeeders

gravimetric, 16volumetric, 16

Feed rollers, 29Film, 48Fines, 8Fisheyes, 39, 48Flame treatment, 11, 13, 48Flammability, 48Flexibility, 3

IndeIndeIndeIndeIndex (Continx (Continx (Continx (Continx (Continued)ued)ued)ued)ued)

56

Flexible die lip, 23Flow, 48Flow properties, adhesion and, 36Fluoropolymer tape

to mask pressure roll, 29 preventing marking or imprinting of

coating by, 30 replacement of, 30Flying-splice unwind, 111, 33Formulas, for extrusion of polymers, 41Fragrances, 4

GGap winding, 33Gas phase (PG) process for

HDPE resin manufacture, 6 LDPE resin manufacture, 6Gas phase reactor

for manufacture of polypropylene, 7Gauge,48 uniformity of, 37 variations in, 39Gauge bands, 40Gear pumps, 20Gear reducer, 17Gel(s), 39, 40, 48Gel fIurry, 48Gel streaks, 48Glass transition, 48Gloss, 3, 38, 47Gravimetric feeders, 16

H“Hammer finished” surfaces, 8Handling, 8Hardness, 48 Rockwell, 49Haze, 48Heat, 34Heaters, 17Heat failure, alarm system for, 17Heating zones, of die, 21Heat resistance, 3Heat sealing, 38, 48 problems with, 40Hexene,4


High density polyethylene (HDPE) resins, 4 density of, 2, 3 manufacture of, 6Holes, 37Homopolymers, 4, 48Hopper, 16, 48Hot gas welding, 48Hydrogen atoms, 2Hydroscopic substances, 48

IImpact strength, 48Impermeability, 3Infrared (IR) sensors, 31In-line ozonator, 12

KKeyhole dies, 24

LLand, 48Lay-on roll, 32L/D ratio, 48Length, metric conversion guide for, 43Lifting, of heavy equipment, 34Light resistance, 48Linear low density polyethylene (LLDPE) resins, 4 density of, 2 manufacture of, 7Line speed, 36 Low density polyethylene (LDPE) resins, 4 density of, 2

manufacture of, 7

MMachine motion, 34 Masterbatch, 48Mechanical bonding, 36Mechanical flex life, 3Medium density polyethylene (MDPE) resins, density

of, 2Melt flow rate, 48Melt fracture, 49Melt index (MI), 3, 49Melt pumps, 20

57

Melt strength, 49Melt temperature, 21 adhesion and, 36Metal foils, pretreatment of, 11Metric conversion guide, 43Microcomputer controls, 33Mixing screws, 18Modifiers, 4Moisture vapor transmission rate, 49Molecular structure, polyolefin properties and

processability, 2Molecular weight, 3Molecular weight distribution, 3, 49Monomers, 49 polymerization of, 2Multimanifold coextrusion coating dies, 26Multi-stage screws, 18

NNeck-in, 29, 37, 49Nips, 49Nuclear sensors, 31

OOn-the-machine blending units, 10Orange peel, 49Orientation, 49Output, metric conversion guide for, 43Oxidation, 40

adhesion and, 36 requirements for, 36Ozone adhesion and, 45 corrosiveness of, 36 produced by corona, 15

PPay-off roll, 10Peel roll, 28Permeability, 49PETROTHENE resins, 7Physical bonding, 36Pigment, 49Pinholes, 37, 40Piping, 18 roughening interior walls of, 8Plastic films, pretreatment of, 12


PLEXAR resins, 7, 16Poise, 49Polyblends, 49Polyethylene, 2, 49Polymer(s), 49

formulas for extrusion of, 41Polymerization, 2Polyolefins, 2 for extrusion coating, 7 manufacture of, 6 molecular structure and composition of, 2-6Polypropylene (PP), 49 density of, 2 manufacture of, 7Power, metric conversion guide for, 43Precoaters, 11Pressure, metric conversion guide for, 44Pressure rolls, 26 cleaning, 42 undercut, 31Pressure valves, 20Priming, 12 chemical, 11 equipment for, 12Propylene, 2, 6Proximity winding, 32Pumps, gear (melt), 20Purging, 49Push-only screw, 23Push/pull screw, 23

QQuench,49

RRazor blade slitters, 29Real-time SPC systems, 34Rear strength, 49Recycling, 49Recycling system, 31Reflectance mode, of infrared sensor, 31Reground resin shipping and handling, 8Resin handling/conditioning, 8Resin toughness, 3Resin transfer system, 8Rheology, 48

58

Rockwell Hardness, 49Roll braking, 11Rubber roll marks, 49

SSafety, extrusion coating line start up, 34Sandwich laminating, 7Score cutters, 29Screen plate, 19Screws, of extruder, 16 cleaning, 42 types of, 18 , 23Shear rate, 49Shear slitters, 29Shear strength, 49Shear stress, 49Sheet, 49Shipping, 8Shrinkage, 49Shut-down of extrusion coating line, 36Silicone, of pressure roll covering sleeve, 27Silicone grease, as release agent, 30Single exit dies, 24Single-stage screws, 18Sliding die lip, 21Slip, 38Slip additive, 49Slip/antiblock agents, 4Slurry process for HDPE resin manufacture, 6 for LDPE resin manufacture, 6Specific heat, 49Stabilizer, 49Start-up, of extrusion coating line, 34Statistical process control (SPC), 34Stiffness, 38Streaks, 39Streamers, 8Strength, 38Stress cracking resistance, 3, 39Substrate, priming, 11Substrate(s)

handling, 10porous and non-porous, 36precoating, 11properties of, 7

Surface braking, 11Surface treatment, 10, 29, 49

IndeIndeIndeIndeIndex (Continx (Continx (Continx (Continx (Continued)ued)ued)ued)ued)Surface winders, 32Surging, 37, 40, 49Synergism, 49

TTakeoff, 32Taper tensioning, 33Tears, 37Temperature, metric conversion guide, 43Temperature profile, 49Tensile strength, 3, 49Thermal conductivity, metric conversion guide for, 44Thermal expansion, metric conversion guide for, 44Thermal stability, 49Thermocouples, 18Thermoplastics, 2Thermoset resins, 2Tie-layers, 4, 12, 15Toughness, 38Transfer piping, 18, 24Transmission mode, of infrared sensor, 31Treating, 49T-slot die, 21Turret winders, 33

UULTRATHENE copolymers, 7Undercut pressure roll, 31Unwinder rolls, 11UV absorbers, 49

VVentilation, 34Ventilation blower, 49Vinyl acetate (VA), 4Viscosity, 3, 49 metric conversion guide for, 44Voids, 37, 40, 50Volume, metric conversion guide for, 44Volumetric feeders, 16Vortex Tube Air Jets, 30

WWater

barrel cooling with, 17 cooling of extruder screw by, 18 Web tension, 10

59

Weight, metric conversion guide for, 44"Wetting Test" 15Winders, 32 center, 32

surface, 32turret, 33

Winding problems, 39Windup equipment, 32 wrinkles on, 39Wrinkles, on windup roll, 39


6664/0715

LyondellBasell IndustriesP.O. Box 3646Houston, TX 77252-3646United States

www.LYB.com

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Adsyl, Akoafloor, Akoalit, Alathon, Aquamarine, Arcopure, Arctic Plus, Arctic Shield, Avant, CRP, Crystex, Dexflex, Duopac, Duoprime, Explore & Experiment, Filmex, Flexathene, Hifax, Hostacom, Hostalen, Ideal, Integrate, Koattro, Lucalen, Lupolen, Metocene, Microthene, Moplen, MPDIOL, Nexprene, Petrothene, Plexar, Polymeg, Pristene, Pro-Fax, Punctilious, Purell, Sequel, Softell, Spheripol, Spherizone, Starflex, Tebol, T-Hydro, Toppyl, Tufflo and Ultrathene are registered in the U.S. Patent and Trademark Office.

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