polypropylene design guide dow chemical

Polypropylene Technical Center

Design Guide An intensive look at chemical resistance and plastic part design for parts made with DOW Polypropylene Resins.

Molding Guide Technical information for producing parts made with DOW Polypropylene Resins.

Technology Primer Learn about typical characteristics of polypropylene resins as well as shrinkage predictions and data.

Troubleshooting Guide A step-by-step guide for troubleshooting with polypropylene resins.

Safety and Handling ConsiderationsInformation on safely handling and disposing of polypropylene resins.

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Design Guide

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Polypropylene Design Guide

Nominal Wall Thickness

Rib, Boss and Gusset Design

Radii and Fillet Design

Draft Angle Design

Undercuts

Integral Hinges

This section reviews how to design with DOW Polypropylene Resins to assure long-term functional performance without sacrificing the product moldability of the polypropylene part. Although designing with polypropylene and other thermoplastics can be complex, following these fundamental design principles will assist in minimizing problems during molding, and in final part performance.

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Nominal Wall ThicknessRib, Boss and Gusset Design


Draft Angle Design

Undercuts

Integral Hinges

Nominal wall thickness is one of the major factors to consider when designing with polypropylene. Nominal wall thickness has a major effect on the shrinkage of polypropylene parts, because it can take a long time for the semicrystalline polymer chains to stop contracting (typically it takes as much as 48 hours, and sometimes longer, to reach the final dimensions of a polypropylene part).

When molding thick parts in polypropylene, it is found that the thicker the part, the greater the shrinkage, because more heat is retained in the thicker part to keep the semicrystalline polymer chains moving. Therefore, parts designed with polypropylene need to be designed with as constant a nominal wall thickness as possible, because varying part thickness from thick to thin varies shrinkage and creates problems such as stressed and warped parts.

Two additional problems caused by thick walls are longer cooling cycles that reduce part productivity, and sink marks which can hurt part aesthetics. If a varying nominal wall thickness is needed when designing a polypropylene part, transitions can be made which are less drastic than an abrupt variation in nominal wall thickness. Proper Design of Nominal Wall Thickness for Polypropylene shows the proper design of nominal wall thickness for polypropylene with varying nominal wall thickness and several transition schemes for improving part design.



Design Guide: Nominal Wall Thickness



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Rib, Boss and Gusset DesignRadii and Fillet Design

Draft Angle Design

Undercuts

Integral Hinges

Ribs and bosses are used extensively to strengthen parts when designing polypropylene, but also can present unusual flow problems in filling a polypropylene part. This section reviews how to design these features into a polypropylene part.

Ribs and Bosses Ribs are longitudinal protrusions on a plastic part that may be used for a number of purposes. They may be used to add strength to a part or to add a decorative feature to a part design. Finally, a rib may be used to minimize warpage in a part.

Bosses can be defined as protruding, hollowed-out posts on a part that aid in the assembling of one plastic part with another piece. Because they are frequently used to fasten members (by use of inserts, self-tapping screws, drive pins, expansion inserts, cut threads ,and plug and force fits) between the plastic part and the mating part, they are subjected to different forces, strains, and stresses not typically found in other sections of the plastic part.

Both ribs and bosses can create different effects on the way a part flows. Typically, a rib or a boss is made in the cavity or core section of a mold, but cannot be made by a combination of both. Note that the venting of ribs and bosses can be difficult and affect the appearance and/or filling of the part. If a rib design is very thin, an intermittent thick section on which an ejector pin is placed to remove gases, can facilitate part filling.

Adding ribs to a part should not create a non-uniform wall thickness. Hollowing out the back of the rib will provide added strength and ultimately reduce material costs because material is removed. If long,thin bosses are needed, gussets should be positioned on the side to improve flow, adding strength to the boss.

Ribs must be designed in the correct proportions to avoid defects such as short shots. If the design allows, they should be radiused. Rather than using one large rib and risk voids or sink marks, it is better to use a number of smaller ribs. Recommended Rib Design for DOW Polypropylene Resins illustrates the proper proportions to use when designing a rib structure for polypropylene. All dimensions listed are based on the dimension of the nominal wall thickness. It is also recommended that the rib thickness at the intersection of the nominal wall not exceed one-half of the nominal wall to prevent rib read-through problems that affect part aesthetics.

Parts requiring a high gloss, sink-free surface will require an even smaller rib thickness at the nominal wall.

Gussets Gussets are reinforcing plates used with both ribs and bosses to further support and improve their structural integrity. Positioning of ribs and gussets has a significant effect on the fill pattern of a mold. If ribs and gussets are positioned in the line of flow, both can act as an internal runner and improve part filling. Poorly located ribs and gussets can act as a flow restrictor and create poor flow, causing trapped gas and burning of the part. Example of Gusset Design illustrates proper design of gussets.

Avoid designing stand-alone bosses. It is recommended to connect these bosses to a wall or rib with the use of a connecting rib, as shown in Recommended Design of a Boss Near a Wall . If this is not feasible, design the boss with gussets, as shown in Recommended Design of a Boss Away from a Wall (with Gussets) . Recommended Dimensions for a Boss Near a Wall (with Rib and Gussets) and Recommended Dimensions for a Boss Away from a Wall (with Gusset) show calculations used in determining dimensional proportions for designing bosses at or away from a wall.



Design Guide: Rib, Boss and Gusset Design



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Radii and Fillet DesignDraft Angle Design

Undercuts

Integral Hinges

Radii and fillet design is critical in the design and functionality of polypropylene parts. In all plastic molded parts, molded-in stresses are formed which, in some cases, can cause a part to prematurely fail during its use. Plastic material will flow around these sharp corners, but upon cooling, stresses will be formed as the material shrinks into the sharp corner, creating a microscopic notch. It is possible to relieve some of these stresses by using post-molding operations, such as annealing. However, stresses will still remain in the part. An area where high stresses frequently occur is in sharp corners, and it is here that weaknesses in the parts' design are found.

With the addition of radii and fillets on inside and outside corners, materials will flow around these areas easier and, upon cooling, will not shrink into a sharp corner, giving the part improved structural integrity and reduced stress concentrations. This also allows for easier part ejection, which also reduces part stress. It is recommended that for a 90 ° radius, the inside corner should range from 0.25% to 0.75% of the nominal wall thickness. The outside corner of the radius should range from 0.25% to 0.75% of the nominal wall thickness of the part to maintain uniform wall thickness around the corner. Sink marks will occur if the outside wall is not radiused. Radius Recommendations for DOW Polypropylene Resins illustrates proper radius design for polypropylene.



Design Guide: Radii and Fillet Design


Draft Angle Design

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Draft Angle DesignUndercuts

Integral Hinges

Draft angle design is also an important factor in designing with polypropylene. Due to its higher shrinkage than amorphous materials, parts may have a greater tendency to shrink onto a core, creating higher contact pressure on the core surface and increasing normal friction between the part and the core, making part ejection difficult. Therefore, properly designed draft angles will greatly assist in part ejection from the mold, reduce cycle time, and improve productivity. Draft angles should be used on interior or exterior part walls in the direction of draw. A minimum 1° draft angle per side is recommended for DOW Polypropylene Resins with parts having no textured surfaces. Textured surfaces need additional draft to easily release the part, and eliminate drag marks or scuffing of the part surface. Draft Angle Comparison - ABS vs. Polypropylene and Effect of Texturing on Ejector Force for Polypropylene illustrate a comparison of draft angles for polypropylene and ABS, and the effect of texturing on the ejector force for polypropylene.



Design Guide: Draft Angle Design


Undercuts

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Draft Angle Design

UndercutsIntegral Hinges

Undercuts are typically used in articles such as enclosures. If an undercut is required in an enclosure design, it is recommended to design the undercut with a lead angle of 25° to allow the enclosure to be stripped easily from the mold. Radii recommended for this application range from 0.010 to 0.015in (0.25 to 0.40 mm).

Internal Undercut Design Recommended for DOW Polypropylene Resins shows a design for an undercut. The size of the undercut is indicated by the designation "Umax." The Umax, in terms of percentage, is determined by the outer diameter minus the inner diameter divided by the outer diameter multiplied by 100. It is strongly suggested that Umax does not exceed 5%, otherwise, permanent damage can occur to the part. Umax is an indication of the allowable percentage rate of deformation of the undercut.



Design Guide: Undercuts


Integral Hinges

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Draft Angle Design

Undercuts

Integral Hinges

Due to its toughness and ductility, polypropylene allows designers to use a concept that cannot easily be used with many engineering thermoplastics: the living, or integral, hinge. This type of hinge can be found in applications such as small containers where the living hinge connects the lid to the body of the container. Automotive applications, such as glove box bins and doors, have begun to incorporate the living hinge design. There are two basic types of integral hinges used in injection molded polypropylene parts: the molded-in hinge, and the die-formed hinge.

Molded-in hinges The molded-in hinge is the more widely used concept in polypropylene design because it can be molded by conventional injection molding techniques. In molded-in hinges, optimum performance is found with the polypropylene polymer orientation transverse to the center axis point of the hinge. This is obtained by material flowing across, and not along, the hinge area at a high velocity at high material melt temperatures. This also helps the molder achieve improved cycles and increased productivity. Filling too slow, using low melt temperatures, or non-uniform flow through the hinge, may result in delamination of the hinge and its premature failure.

Recommended Living Hinge Feature for Polypropylene illustrates a proper hinge design, which can be altered to meet required performance criteria. Again, note that radii are used for improved flow of material across the hinge. Also, the radiused section allows for bending at the smallest cross section of the hinge area. Land lengths of the top of the hinge can range from 0.050 to 0.090 in (1.3-2.3 mm),with 0.060 in(1.5 mm)as an optimum. Hinge thickness can also range from 0.010 to 0.020 in (0.25-0.50 mm), depending on whether the application requires a stiffer closing mechanism. Because a living hinge has a tendency to loop, or gather, above the upper plane of the hinge, a clearance of between 0.005-0.010 in (0.13-0.25 mm) should be allowed. An offset radius should be provided to align the two matching sections that the living hinge connects. Approximately 0.030 in (0.8 mm) minimal offset should be used. The radius of the hinge is recommended at 0.030 in (0.8 mm) to allow for the minimum thickness of the hinge to be located at the center, and to facilitate moldability.

Die-formed hinges Molded-in hinges are used quite extensively in smaller parts, such as electrical connectors or small, hand-held containers. However, for larger parts or more complex-designed parts, a hinge may be cold formed, or coined, into a surface mechanically. In this case, polymer flow may not be considered as critical as it is for molded-in hinges. In forming a die-formed hinge, a die is used to compress a slot onto a flat surface. This die is heated and allows the material to move away from the die upon contact. The cross-section of the part is compressed to form the thin wall section of the hinge. This is shown in Die-Formed Hinge Method. The time it takes to form the hinge under die pressure is approximately 10 seconds. The male section of the die should be heated between a range of 250°F to 290°F (121°C to 143°C). The area supporting the part during the die forming operation can be either rigid, such as steel, or flexible, such as a rigid elastomer or rubber.



Design Guide: Integral Hinges


Recommended Rib Design for DOW Polypropylene Resins

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Center: Design Guide: Ribs, Boss and Gusset Design

Recommended Rib Design for DOW Polypropylene Resins


Example of Gusset Design1

1 Source: Designing with Thermoplastics, The Dow Chemical Company, 1992




Example of Gusset Design


Recommended Design of a Boss Near a Wall (with Ribs and Gussets)1





Recommended Design of a Boss Near a Wall


Recommended Design of a Boss Away from a Wall (with Gussets)1




Center: Design Guide: Draft Angle Design

Recommended Design of a Boss Away from a Wall (with Gussets)


Recommended Dimensions for a Boss Near a Wall (with Rib and Gussets)1





Recommended Dimensions for a Boss Near a Wall (with Rib and Gussets)


Recommended Dimensions for a Boss Away from a Wall (with Gusset)1





Recommended Dimensions for a Boss Near a Wall (with Gusset)


Radius Recommendations for DOW Polypropylene Resins



Center: Design Guide: Radii and Fillet Design: Radius

Recommendations for DOW Polypropylene Resins


Draft Angle Comparison - ABS vs. Polypropylene1

1 Source: Paul A. Tres, Polypropylene Product Design and Processing, 1996-97.



Center: Design Guide: Draft Angle Design Draft Angle

Comparison - ABS vs. Polypropylene


Effect of Texturing on Ejector Force for Polypropylene1




Center: Design Guide: Draft Angle Design Effect of

Texturing on Ejector Force for Polypropylene


Internal Undercut Design Recommended for DOW Polypropylene Resins



Center: Design Guide: Undercuts Internal Undercut

Design Recommended for DOW Polypropylene Resins


Recommended Living Hinge Feature for Polypropylene1




Center: Design Guide: Integral Hinges Recommended

Living Hinge Feature for Polypropylene


Die-Formed Hinge Method1




Center: Design Guide: Integral Hinges Die-Formed

Hinge Method


Proper Design of Nominal Wall Thickness for Polypropylene



Center: Design Guide: Nominal Wall Thickness:

Proper Design of Nominal Wall Thickness for Polypropylene


Molding Guide

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Polypropylene Molding Guide

The Molding Guide will aid the parts fabricator and tool builder with technical information needed to produce parts made with DOW Polypropylene Resins.



Center: Molding Guide


Gate Design

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Many types of gate designs can be molded from polypropylene. Gates discussed in this section include:

Edge gates

Fan gates

Drop gates

Tunnel gates

Ring gates

Diaphragm or disk gates

Sprue gates

Tab gates

Edge Gates Edge gates are used most often in large part design, and also where thin walls are used in the part. One of the advantages of edge gates is that of all the gate designs, it provides the widest molding window due to lower shear rates. Edge Gates illustrates a suggested edge gate

design for polypropylene. A straight land is used with this gate design in order to facilitate part trimming. To avoid high shear, a minimum of 0.035 in (0.90 mm)length for the straight land is suggested.

Fan Gates Fan gates are also widely used in designing polypropylene parts. Fan gates provide reduced pressures and clamp tonnage over other conventional gate designs, and are excellent for relatively short flow lengths. Fan gates also allow for a wide process window, and reduce overpacking issues because the pressure through is lower than found with a tunnel gate. Problems in using fan gates include the inability to trim off the gate because a larger area must be trimmed through. Increased scrap may also be found due to the difficulty in trimming off fan gates. Fan Gates shows a suggested fan gate design.

Drop Gates Drop gates, otherwise known as pin point gates, are used primarily in single or multi-cavity three plate tools, or where multi-gates are used in a part design. Typically, drop gates are used in parts with a thin nominal wall thickness, but with a large surface area. A big advantage of drop gates is that they are self-degating, with no need to use a special degating tool to remove the gate. Drop Gates shows a drop gate

design for polypropylene.

Tunnel Gates Tunnel gates for polypropylene are typically used for smaller parts weighing less than 2 lbs. (900 grams) and for parts with short flow distances. Also, this type of gate is optimum for thin wall parts. This gate is used to convey material below a parting line of the mold into a cavity. An advantage of this type of gate is ease of ejection of the part from the runner system. A disadvantage is a narrower process window due to high shear rates, which can potentially degrade most plastic materials. The cross section of the gate is either round or elliptical in shape. A gate diameter of no more than 0.085 in (2.15 mm) is typically used for polypropylene. Tunnel Gates shows a typical

tunnel gate for polypropylene.

Ring Gates Ring gates are commonly used in molding around cylindrical cores, such as syringes. The material flows around a core pin and flows down to fill the pin evenly. Advantages of this gate are the prevention of trapped air that can cause weld lines, and reduction of the core pin shift phenomenon which can result in extreme variations in wall thickness of the material around the core. See Ring Gates.

Diaphragm or Disk Gates Diaphragm or disk gates are the opposite of ring gates in that the material flows from a cylindrical core to its perimeter. These gates are used mostly for single-cavity tools in fabricating single-shaped parts, such as cylindrical-shaped parts, that have small or medium sized internal diameters. These gates improve flow around a core, and also improve the core pin shift phenomenon when molding tube-shaped parts. Diaphragm or Disk Gates provides an illustration and an equation for minimizing core pin shifting using a gate.

Sprue Gates Sprue gates are found in large parts made in a single-cavity tool, such as a copier enclosure. Typically, the gate is located at the center of the part to allow for even flow through the part. A reverse taper is placed at the end of a sprue gate to remove the part from the mold upon ejection, and to act as a cold slug well to capture the coldest material coming from the end of the nozzle of the barrel, and prevent it from entering the runner system. Variations of the reverse taper also include ring pullers and Z-pullers. Sprue Gates shows a sprue gate design

and an equation for determining the correct sizing for a sprue gate.

Tab Gates Tab gates usually extend from the runner system directly into the molded part, and can be the same thickness as the molded part. This type of gate is used with larger parts, such as enclosures. It is suggested that the thickness of the tab gate be no more than 60%of the part's nominal wall, in order to degate the part without using a gate removal apparatus. See Tab Gates shows a typical tab gate design.



Center: Molding Guide: Gate Design


Edge Gates



Center: Molding Guide: Gate Design: Edge Gates


Fan Gates



Center: Molding Guide: Gate Design: Fan Gates


Drop Gates



Center: Molding Guide: Gate Design: Drop Gates


Tunnel Gates



Center: Molding Guide: Gate Design: Tunnel Gates


Ring Gates



Center: Molding Guide: Gate Design: Ring Gates


Diaphragm or Disk Gates



Center: Molding Guide: Gate Design: Diaphragm or

Disk Gates


Sprue Gates



Center: Molding Guide: Gate Design: Spruce Gates


Tab Gates



Center: Molding Guide: Gate Design: Tab Gates


Runner Design

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Cold Runner Design Different runner designs can be used when molding polypropylene parts. These include full round runners, standard trapezoidal runners, and modified trapezoidal runners.

Full Round Runners Full Round Runners are found to be the best at holding pressures because

the center of flow away from the mold surface cools last. Also, because the center cools last, the cooling rate is slower in comparison to other runner systems. Of all the runner systems used, full round runners offer the smallest surface relative to the cross section of the runner. This type of runner allows the plastic material in the center to move more rapidly. Machining of full round runners is relatively easy in that standard size end mills can be used to machine out full round runner systems. However, while full round runners are very efficient, machining is more expensive because the runner must be cut into both mold halves.

Trapezoidal Runners Trapezoidal Runners offer a lower-cost alternative to machining full round runners because machining is only performed on one mold half.

The trapezoidal runner offers a higher volume-to-surface area than full round runner systems. This runner system should be designed with a taper of 2° to 5° per side, with the depth of the trapezoid equal to its base width.

Modified Trapezoidal Runners Another runner system recommended for polypropylene is the Modified Trapezoidal Runner System . It has the features of a standard

trapezoidal runner system, but includes a radiused base. This provides ease of part ejection, and is also easy to machine.

Other Runner Design Considerations There are several other factors to be considered in designing runners for polypropylene. Minimum runner diameter, or the equivalent cross-sectional area, leading into a gate should be 0.250 in (6.35 mm).This runner should never have a diameter less than the thickest section of the plastic part to be molded. The runner should be large enough to minimize pressure loss, yet small enough to not adversely affect cycle time.

Balanced runner systems are highly recommended to promote simultaneous filling of multi-cavity, or multi-gated molds. Other, less balanced, runner systems can be used for the sake of economics. In such cases, balancing can be assisted by stepping down the runners in the direction of flow, or by adjusting gate sizes.



Center: Molding Guide: Runner Design


Full Round Runner Design



Center: Molding Guide: Runner Design: Full Round

Runners


Trapezoidal Runner Design



Center: Molding Guide: Runner Design: Trapezoidal

Runners


Modified Trapezoidal Runner Design



Center: Molding Guide: Runner Design: Modified

Trapezoidal Runners


Gate Location

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Use the following guidelines when molding parts using DOW Polypropylene Resins:

● Gates should be located so the flow of the resin is from the thickest to the thinner sections of the part.

● Create as balanced a flow as possible within the mold cavity to avoid overpacking of the cavity, which may lead to variations in the mold shrinkage (warpage) of the final part.

● Reduce as many weld lines as possible, or alter flow to place them in areas where they will not affect the structural integrity or the aesthetics of the part.

● Place gates in areas where the material can flow smoothly and uniformly through the mold cavity.● For integral hinges, locate gating to provide a smooth, even flow across the hinge web to prevent a premature hinge failure; an

optimum location is beyond the hinge centerline and away from the hinge.



Center: Molding Guide: Gate Location


Vent Location

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Using vents offers a number of advantages to the molder. These include:

● Improving weld line strength and appearance● Reducing pack and hold pressures in filling the part● Preventing gate overpacking● Reducing part weight

In all cases, all cavities molding DOW Polypropylene Resins must be sufficiently vented so that air trapped inside the cavity is evacuated from the tool. If no venting, or insufficient venting is used, burn marks caused by "dieseling" in the cavity will occur. Also, weak weld lines, where part integrity is sacrificed, and incomplete or short shots will be found in the part. The best areas for locating venting are:

● At the last section of the tool to be filled● Where converging melt fronts meet to form knit or weld lines● Near bosses, ribs, and other types of projections from the nominal wall

Vent Size and Vent Location Requirements for Molding Polypropylene Parts gives suggested vent sizes for tools molding with DOW

Polypropylene Resins. Other methods which also can be used in providing proper venting include grinding a flat on one side of the ejector pin, and using a porous metal insert in the area of the part where converging melt fronts are found forming gas or trapping air.



Center: Molding Guide: Vent Location


Vent Size and Vent Location Requirements for Molding Polypropylene Resins

Vent size requirements

Width As needed to properly vent, but not flash part

Depth 0.001-0.002 in (0.025-0.050 mm) average – .015 in (.381 mm)

Length of vent land 0.040-0.050 in (1.02-1.27 mm)

Vent location requirements

Locate vents: At last section of mold or part to be filled

Where converging melt fronts meet to form knit or weld lines

In the area of surface projections, such as bosses, ribs, and gussets

In blind spot areas, such as ribs



Center: Molding Guide: Vent Location:Vent Size and

Vent Location Requirements for Molding Polypropylene Resins


Cooling and Mold Steels

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Mold temperature control is one of the biggest factors to consider when molding polypropylene due to the potential for shrinkage and warpage when fabricating polypropylene parts. From a productivity standpoint, even though cooler mold temperatures lead to reduction in cycle time, cooler tooling for molding polypropylene may lead to dimensional stability problems and excessive residual stresses. This in turn, leads to problems such as differential shrinkage and part warpage.

For faster cycles in molding polypropylene, the optimum is to design a cooling system that provides uniform cooling of the part, minimizes residual stresses, and reduces shrinkage and warpage. See Guidelines for Laying

Out Cooling Channels in Polypropylene Tools . It is also suggested to use bubbler cooling for long cores as well as thin core projections.

Another suggestion is to use highly conductive metal inserts in areas where these core projections are found.

In existing tools, other considerations include increasing the rate of coolant flow-through, reducing coolant temperature, and removing rust and scale buildup in cooling lines, which may adversely affect the cooling efficiency of the tool. To maximize cooling rate, the cooling fluid to be used, whether it is water or an ethylene glycol/water mixture, should flow turbulently. Turbulent flow provides as much as three to five times more heat transfer than laminar, or non-turbulent, flow.

Mold temperature control is also critical when molding polypropylene parts. Chiller capacities of 1 ton for every 35 lbs. of polypropylene to be processed per hour are typically used for fabricating polypropylene parts.

In molding integral hinges, it is recommended to set up a separate cooling line and control near the thin sections of the integral hinge. Mold temperatures between 150-170°F (66-77°C) may be needed in these areas. Polypropylenes can be molded in a variety of materials, such as aluminum, beryllium copper, and various steel materials. Selection of mold materials can also be critical in molding polypropylene.

For example, Thermal Conductivity of Various Mold Materials and Other Materials shows that a tool made in beryllium copper offers three to

four times the heat transfer in comparison to a tool steel mold. This does not mean that using a beryllium copper mold will give a cycle time four times as fast as stainless steel tooling. Beryllium copper molds are capable of molding some thin wall parts significantly faster. Consideration must also be given to the length of the production run, where steel materials are known to last longer in comparison to beryllium copper and other metals.



Center: Molding Guide: Cooling and Mold Steels


Guidelines for Laying Out Cooling Channels in Polypropylene Tools



Center: Molding Guide: Cooling and Mold Steels

Guidelines for Laying Out Cooling Channels in Polypropylene


Thermal Conductivity of Various Mold Materials and Other Materials

Mold Material Thermal Conductivity (Btu./Ft.–°F Hr) at 212°F (100°C)

Copper (pure) 222

Aluminum 100

Brass (60-40) 70

Kirksite 62

Beryllium copper 62

Tool steel (P-20) 21

Tool steel (H-13) 12

Stainless steel 10

Water 0.39

Air 0.14

Polypropylene 0.07

Source: Rosato, Donald V. and Dominick V., Injection Molding Handbook, 1995.



Center: Molding Guide: Cooling and Mold Steels:

Thermal Conductivity of Various Mold Materials and Other Materials


Multi-Cavity Tool Design

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Multi-cavity tools may be needed for molding polypropylene depending on machining size, part production size, delivery requirements, and mold costs. If a multi-cavity tool is needed, the biggest factor to consider is the balancing of the runner system.

Balancing is achieved by varying the size and shape of the cold or hot runners so that the pressure filling each part is identical. It is suggested not to balance tooling by varying gate size, because this does not affect tool balancing as much as runner size and shape.

The ideal tool balancing for polypropylene should provide flow to each gate under identical process conditions, such as temperature and pressure.

Unbalanced tooling will result in such problems as:

● Part overpacking● Part warpage● Differential shrinkage● Part embrittlement● Dimensional inconsistencies● Part sticking to the tool



Center: Molding Guide: Multi-Cavity Tool Design


Hot Runner Systems

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Hot runner tooling is used for polypropylene in large-sized, multi-gated parts, such as automotive interior trim and automotive instrument panels. Hot runner tooling differs from cold runner tooling by extending the molding machine's melt chamber, or barrel, and acting as an extension of the machine's nozzle. A hot runner system maintains all, or a portion, of the polymer melt at approximately the same temperature and viscosity as the polymer in the plasticating barrel.

Hot runners offer the following advantages in comparison to cold runner systems:

● Elimination of scrap from the runner, resulting in less regrind● Less sensitivity to the requirements of balanced runners● Reduction in material shear● Increased consistency in the volume of the polymer per part● Reduced molding cycles● Improved part surface aesthetics● Decreased tool wear

A disadvantage of hot runners is increased cost in the system because the tool design becomes more complex both in manufacturing and operation.

The heated manifold acts as an extension of the machine nozzle by maintaining a completely molten polymer from the nozzle to the tool gate. To accomplish this, the manifold is equipped with heating elements and controls that keep the melt at the desired temperature. Installing and controlling the heating elements is difficult. It is also difficult to insulate the rest of the mold from the heat of the manifold so the required cyclic cooling of the cavity is not affected.

Another concern is the thermal expansion of the mold components. This is a significant detail of the mold design, and requires strict attention to ensure the maintenance of proper alignment between the manifold and the cavity gates.

When designing runner systems for hot runner tooling, it is suggested to use generously radiused runner systems to prevent dead spots. Also, each nozzle contains a capillary to act as a valve to prevent plastic material leakage. Heating elements positioned around the nozzles provide proper temperature control. When thick walled parts are molded, the long pressure time may necessitate the use of nozzles with needle valves, as capillaries tend to freeze up quickly.



Center: Molding Guide: Hot Runner Systems


Screw and Check Ring Designs

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Screw designs When determining screw design requirements for molding polypropylene, the typical design used is a single-stage, general purpose type with an L/D (length to diameter) ratio of 16:1 to 24:1,and a compression ratio between 2.5:1 and 3.0:1. It is not necessary to use a two-stage screw design with a vented barrel. For further improvement of color mixing and improved melt homogeneity, a barrier type screw or Energy Transfer (E.T.)1 screw can be used. Energy Transfer Design with a Spiral Mixer for Polypropylene M.I. 20-

50 illustrates an E.T. screw design with a spiral mixer for polypropylene materials with a melt flow rate between 20-50 grams (0.7-1.75 oz)/10

min. Energy Transfer Design for Polyproylene M.I. 5-20 shows an E.T. screw design for polypropylenes with a melt flow rate of 5-20 grams

(0.175-0.7 oz)/10 min.

Check ring designs Most check ring designs can be used with polypropylene materials. The most common is the sliding ring type, shown in Most Common Check

Ring Design - Sliding Ring Type . Other types include air-operated or hydraulic shut-off valves, ball check valves, Spirex 2 spring check

valves, the Dray DNRV check valve, the Glycon 3 Piece Free Flow N.R.V. Valve, and the Glycon Repeater 1 Poppet-type Valve.

1 Trademark of Glycon Inc. 2 Trademark of Spirex Inc.



Center: Molding Guide: Screw and Check Ring Designs


Energy Transfer Design with a Spiral Mixer for Polypropylene M.I. 20-50



Center: Molding Guide: Screw and Check Ring

Designs: Energy Transfer Design with a Spiral Mixer for

Polypropylene M.I. 20-50


Energy Transfer Design for Polypropylene M.I. 5-20




Designs: Energy Transfer Design for Polypropylene M.I.

5-20


Most Common Check Ring Design Sliding Ring Type




Designs: Most Common Check Ring Design - Sliding

Ring Type


Injection Molding Process Conditions

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DOW Polypropylene Resins can be molded in standard injection molding equipment, and do not need drying, under normal conditions, because they are not hygroscopic. However, some filled grades of polypropylene may require drying because some of the fillers used are hygroscopic. The following sections will discuss other process variables, such as cylinder temperatures, screw dimensions, clamping forces, injection pressures, hold time, booster time, mold cooling time, and ejection time.

Injection Molding Processing Temperatures See Typical Mold and Melt Temperature Ranges for DOW Polypropylene Resins. Improper barrel temperatures can cause a number of

problems for polypropylenes. Excessive temperatures can cause flashing and burning. Shrinkage problems also may occur, leading to problems such as sink marks, warpage, excessive shrinkage, and formation of voids. Brittle parts can also be caused by either excessively high or excessively low process temperatures. Low process temperatures can also cause weld lines, flow marks, an aesthetically poor surface finish, delamination of the part surface, and incompletely filled parts. Barrel Profile Settings provides a guide to barrel profile settings.



Center: Molding Guide: Injection Molding Process

Conditions


Typical Mold and Melt Temperature Ranges for DOW Polypropylene Resins

Dow PolyPropylene RESiN type

Melt temperature ranges (Max-Min/Target)

Mold temperature ranges

°F °C Range, °F Range, °C Target, °F Target, °C

1-4 MFR - Homopolymer1-4 MFR - Copolymer

445-475/460 230-250 70-120 15-50 100 25


445-475/460 220-250 70-120 15-50 100 25


445-475/460 200-240 70-120 15-50 100 25

<25 MFR - Homopolymer<25 MFR - Copolymer

385-420/405 200-240 70-120 15-50 100 25




Conditions: Typical Mold and Melt Temperature Ranges

for DOW Polypropylene Resins


Barrel Profile Settings




Conditions: Barrel Profile Settings


Coloring of Polypropylene

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Coloring of polypropylene materials can be done using several different techniques. These include:

● Pre-colored resin● Mixing natural colored resin in a tumbler mixer and adding dry

pigments or color concentrates before adding into the injection-molding machine.

● Using automated mixing and proportioning of pigments or color concentrates with natural resin pellets set up to continuously feed the mixture into an injection molding machine.

Improved economics can be found by adapting to in-house coloring capabilities. Color Concentrate Types Used for Polypropylene lists

different types of color concentrates typically used for polypropylene with their advantages and disadvantages.



Center: Molding Guide: Coloring of Polypropylene


Color Concentrate Types Used for Polypropylene

Type of Color Concentrate

Description Advantages Disadvantages

Dry Color ● Pigment Supplier develops blends of pigments formulated to provide a color match.

● Pigments are developed with a specified amount of natural resin to obtain a desired color.

● Lower cost in comparison to pre-colored resins and color concentrates.

● Natural resin can be used in bulk as base for coloring.

● Blending operation needed to mix materials.

● Molder responsible for final color.

● Material handling of dry colors can create housekeeping issues such as contamination of equipment and work area.

● Cleaning of residual dry color pigment systems from blending equipment and mold machine hoppers.

Solid Color Concentrates

● High loading of pigments are predispersed in a resin carrier.

● Concentrates are formulated to give a specified color match when blended with a predetermined amount of natural resin.

● Let-Down ratio used to determine solid color to natural resin mix (example: 50:1, 50 parts natural resin, 1 part color concentrate).

● Lower cost than pre-coloring.

● Can store bulk quantities of natural resin.

● Can quickly and efficiently change colors in process operation.


● Blending operation added at the machine.

● Mixing nozzles may need to be added to improve mixing, in some cases.

Liquid Color Systems

● High loading of pigments are predispersed in a liquid carrier.

● Let-down ratios of 100:1 are typical.

● Metering takes place at the machine throat or at the nozzle.

● Efficient, low cost method. Blending operation of resin and color eliminated. Improved dispersion of coloring media due to use of liquid carrier.

● Cleaning of equipment can be difficult.


● Compatibility of liquid carrier and natural color resin an issue.



Center: Molding Guide: Coloring of Polypropylene:

Color Concentrate Types Used for Polyproylene

Use of Regrind

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Rejected parts, as well as runners, gates, sprue, and flash material for molding parts, may be returned to the molding operation as regrind. However, reground polypropylene materials should be handled differently than virgin material (from a property point of view). Depending on the severity of the molding conditions used to make first-pass parts, the reground material may exhibit a higher melt flow rate, discoloration, and show a reduction in physical properties in comparison to virgin material. Mechanical properties adversely affected by this include flexural modulus or stiffness, tensile strength and elongation, and impact properties. A starting point of 25%of regrind in a mix with virgin material is generally used. This may be changed by the molder pending performance and appearance of the final molded part made from the regrind/virgin material mix.



Center: Molding Guide: Use of Regrind


Post-Molding Operations

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This section discusses operations performed on a polypropylene plastic part after the molding operation is completed. This section also covers machining, fastening and joining, and decorating polypropylene parts.

Machining Polypropylene materials machine very well, and can be processed on any standard machine shop equipment, such as lathes, milling machines, saws, and drilling equipment. See Machining Guide for Polypropylene.

Fastening and Joining Methods A number of fastening and joining techniques can be used to bond and fasten polypropylene parts. Fastening and Joining Techniques for

Polypropylene lists several fastening and joining techniques with recommendations and restrictions for their use.

Decorating Polypropylene can be decorated using a number of methods. Decorating Techniques for Polypropylene lists several decorating methods

used in fabricating polypropylene parts.



Center: Molding Guide: Post-Molding Operations


Machining Guide for Polypropylene

Machine Process Guidelines and Recommendations

Chasing (Thread Cutting) ● Excellent threads can be machined into polypropylene. ● Both fine and coarse threads can be machined with excellent results.

Drilling and tapping ● Standard drill sizes and standard machine taps can be used with polypropylene. ● Use of high speed drills and tool travel control are recommended.

Milling and shaping ● Standard milling and shaping tools can be used with polypropylene. ● Both processes can produce good to excellent finishes. ● Excess burnish or burrs can be removed easily.

Sawing ● Table saws, jigsaws, and band saws can be used on polypropylene. ● Caution must be taken, because too much friction can cause material to melt. ● Sufficient tooth clearance is needed to avoid melting the material.

Turning ● Polypropylenes can be turned on any conventional lathe used for metal fabrication. ● Grind tool turning bits to specifications used for wood turning. ● Use high speeds and a sharp cutting tool.



Center: Molding Guide: Post-Molding Operations:

Machining Guide for Polypropylene


Fastening and Joining Techniques for Polypropylene

Fastening and Joining Process

Characteristics of Process Limitations and Recommendations for Process

Heated tool welding ● Similar to hot plate welding, except material is in sheet form.

● Soldering iron-type heaters used.

● Excessive flash may occur if high pressures are applied or high temperatures are used.

Hot plate welding ● Use of a hot plate to soften surfaces.● Parts are joined together after contact

surfaces are melted.● Parts are cooled after being joined.

● Poor bonding can occur if too little pressure is used to join parts. This is a result of material being moved aside upon applying pressure to mating surfaces.

● Too much heat can also cause part flashing.

Hot gas welding ● Hot gas gun used with nitrogen gas to minimize oxidative degradation of the polypropylene.

● Weld rod, made of same material, is used.

● Standard milling and shaping tools can be used with polypropylene.

● Both processes can produce good to excellent finishes.

● Excess burnish or burrs can be removed easily.

Spin welding ● Utilizes frictional heat during spinning process.

● One part is stationary, the other rotating at a high speed in contact with stationary part.

● Spinning motion stopped once parts are bonded.

● Cooling time needed after bonding completed.

● Restricted to circular cross-sections.● Need flash traps in part design to remove

flash.● Considerations for weld strength include

speed of spinning part, pressure applied during process, surface contact time, joint design, and bond cooling time.

Ultrasonic welding ● Mechanical vibration from high-frequency sound waves used.

● Transducer converts electrical energy into mechanical energy in form of high- speed vibrations.

● Heat generated from vibrations bonds two surfaces together.

● Horn design of ultrasonic welder critical to achieving good bonding.

● Plastics modulus determined on transmissions of vibrations.




Fastening and Joining Techniques for Polypropylene

Decorating Techniques for Polypropylene

Decorating Process Description of Process

Hot stamping ● Flexible foil is used to transfer pre-printed design onto the polypropylene part.● Heated metal surface or rubber die presses design onto part.● Part is dried and ready for next production step.● Drying time is less than one second.

Heat transfer decorating ● Process similar to hot stamping, but a pre-printed coating with release paper transfers design onto part.

● Good for multi-color decorating.● Can be easily automated for high volume applications.

In-mold decorating ● Printed film or foil is inserted into an injection mold, either by hand or automatic indexing.● Polypropylene is injected into mold once film or foil has been inserted.● Molten material and film substrate bond together in mold and form integral system.● Good for multi-color decorating.

Printing ● Surface treatment needed to print onto polypropylene surfaces due to low surface energy and chemical functionality.

● Etching of surface needed. Methods used to etch include corona discharge, flame treatment, and chemical treatment.

● Screen printing most widely used in polypropylene. Inks used include quick drying inks, flame dry inks, and hot inks.

Painting ● Surface cleanliness essential for aesthetics and performance.● Surface pretreatment – e.g., adhesion-promoting primer, flame, plasma, or corona treatment

required for good adhesion.




Decorating Techniques for Polypropylene


Technology Primer

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Polypropylene Technology Primer

What is Polypropylene?

Polypropylene vs. ETP

Typical Characteristics

Shrinkage Prediction

Shrinkage Data for Impact Copolymer with 20 MFR


In many industries today there is a major emphasis on reducing part and manufacturing costs, and improving productivity in an effort to stay globally competitive.

Many engineering thermoplastics, such as polycarbonate, polycarbonate blends, nylon, and polyesters, continue to be used in a wide variety of applications. However, because of the emphasis on cost reduction, other lower-cost materials are being given a closer examination as possible replacements for engineering thermoplastics, without sacrificing part performance. One material playing a key role due to its properties and cost advantages is polypropylene.



Technology Primer



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What is Polypropylene?Polypropylene vs. ETP





Producing a polymer begins with its basic building block: the monomer. A monomer is an individual molecule. Either by reacting under the effect of heat and/or pressure, the monomer grows to form one long chain of monomers called a "polymer," from the Greek "poly," meaning many, and "mer," meaning units.

Polypropylene is a long chain polymer made from propylene monomers. See Propylene

Monomer and Polypropylene Polymer . After exposing the propylene to both heat and

pressure with an active metallic catalyst, the propylene monomers combine to form a long polymer chain, called "polypropylene." Several different polymerization methods are used to produce polypropylene.

Depending on the catalyst and the polymerization method used, the molecular configuration can be altered to produce three types of polypropylene:

● Atactic● Isotactic● Syndiotactic

Atactic, Isotactic and Syndiotactic Polypropylene shows examples of each type of polypropylene.

Polymer CharacteristicsAtactic polymers are characterized by their tacky, amorphous behavior and low molecular weights. They provide the same effect as a plasticizer, by reducing the crystallinity of the polypropylene. A small amount of atactic polymers in the final polymer can be used to improve certain mechanical properties. This provides properties to the final polymer, such as improved low temperature performance, elongation, processability and optical properties, but sacrifices flexural modulus or stiffness, and long-term heat aging properties. From a commercial viewpoint, isotactic polypropylene is the most important. In comparison to atactic and syndiotactic, isotactic polypropylene is the most stereo-regular structure of polypropylene. From this, a higher degree of crystallinity is achieved. As a result, many of polypropylene 's mechanical properties and processability are heavily determined by the level of isotacticity and thus crystallinity.

Although the increased crystallinity of polypropylene makes the material less tough than polyethylene, it also provides polypropylene with a higher flexural modulus, and tensile properties much higher than polyethylene. This allows polypropylene to be used as a replacement for engineered thermoplastics, such as ABS.

Syndiotactic polypropylene has just recently become a commercial reality.



Center: Technology Primer: What is Polypropylene?


Comparing Polypropylene to Engineering Thermoplastics

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Polypropylene vs. ETPTypical Characteristics




The basic difference between polypropylene and many engineering thermoplastics (ETPs)such as polycarbonate, polycarbonate/ABS blends and polystyrene, is that polypropylene is a semicrystalline polymer, whereas most ETPs are classified as amorphous polymers. The following section explains the difference between semi-crystalline and amorphous polymers, and how this makes polypropylene different from ETPs.

Amorphous polymers Amorphous polymers consist of polymer molecules having no regular conformation. Amorphous Polymer Conformation vs. Semi-crystalline Polymer Conformation shows the

conformation of a typical amorphous polymer and a semicrystalline polymer.

Upon heating amorphous polymers, the tangled polymer chains become active and begin moving past each other to disentangle themselves. This results in softening of the polymer and, ultimately, to polymer flow. As molecular activity increases, the material becomes more fluid. After polymer flow is achieved, the molten polymer is fabricated or shaped into a defined plastic part. Upon cooling, rigidity returns to the polymer and molecular movement decreases.

Semi-crystalline polymers In semi-crystalline polymers, because of their stereo-regularity, ordered molecular configurations are built into the chain structure. These ordered areas are crystals that form when the polymer is cooled from its molten state. When the polymer is heated once again, the crystal domains remain unchanged until the polymer reaches its melting point. This point is referred to as the crystalline melting point of the polymer.

Once these materials reach the melting point, the polymer behaves like an amorphous polymer in that the molecular configurations become random. Another factor, the degree of crystallinity, is not only affected by the chemical structure, but by the process conditions used to manufacture the plastic part. The rate of cooling is the process variable having the greatest effect on the degree of crystallinity.

Using the polymers in parts fabrication The previous sections describe the basic difference between amorphous and semi-crystalline polymers. How this applies to making polypropylene parts, and how this differs from fabricating amorphous parts, is explained here.

High crystallinity imparts improved chemical resistance in comparison to amorphous polymers. Therefore, polypropylenes can be exposed to a wide variety of agents without failure in comparison to amorphous polymers. Part shrinkage for polypropylene is higher than for amorphous polymers. This is due to better packing of the molecular chains in the crystalline regions. Differences in cooling lead to differences in crystallinity and thus differences in shrinkage. Therefore, controlling process variables, such as mold temperature and cooling time, plays a major role in determining mold shrinkage for semi-crystalline materials such as polypropylene.

In semi-crystalline polymers, crystals will form more completely in areas where they are the most densely packed. A crystallized area is rigid and strong, where an amorphous area is tougher and more flexible. This results in better creep, heat, and stress crack resistance, as well as increased shrinkage for polypropylene in comparison to amorphous polymers. However, since amorphous areas are tougher and more flexible, the low temperature resistance properties are improved for amorphous polymers in comparison to polypropylene. Properties of

Crystalline vs. Amorphous Polymers provides a comparison of the mechanical properties of both crystalline and amorphous polymers.



Center: Technology Primer: Polypropylene vs. ETP


Typical Characteristics of Polypropylene

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Typical CharacteristicsShrinkage Prediction



Polypropylene, like many other thermoplastics, has its own set of unique characteristics. Typical Characteristics of Polypropylene shows some key characteristics of polypropylene.

Polypropylene has a lower density, ranging from approximately 0.880 to 0.920 grams per cubic inch, in comparison to engineering thermoplastics and high density polyethylene (HDPE), thus allowing for potential weight reductions. DOW Polypropylene Resins have excellent heat resistance and can be used in continuous environments as high as 220°F (104°C).

DOW Polypropylene Resins are also highly resistant to chemical attack from solvents and chemicals in very harsh environments. Contact with some chemicals, such as liquid hydrocarbons, chlorinated chemicals, and strong oxidizing acids, can cause surface crazing and material swelling.

In general, polypropylene is not susceptible to environmental stress cracking, and it can be exposed under load in the toughest environments. Resistance to weathering may be limited without the use of ultraviolet light absorbers, or stabilizers. Polypropylenes are subjected to degradation when exposed to certain conditions of ultraviolet radiation. Due to its higher crystallinity, polypropylene has excellent moisture barrier properties and good optical properties. Higher crystallinity improves stiffness, but reduces impact strength.

Polypropylenes do not need drying prior to molding as opposed to most engineering thermoplastics because polypropylenes are not hygroscopic. Processors can then use material out of the container rather than adding an initial step for drying the material. Lastly, the excellent fatigue resistance and flexural modulus of polypropylene allow the material to be used for molded-in hinges.

Designations for DOW Polypropylene Resins Dow Plastics† produces a number of DOW Polypropylene Resins for use in end-use applications. Proper material selection is a critical factor to consider in designing or processing a part made with DOW Polypropylene Resins. In order to assist you in your material selection, the Resin Designation Key shows resin designations for DOW Polypropylene Resins.



Center: Technology Primer: Typical Characteristics


Shrinkage Prediction for DOW Polypropylene Resins

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Shrinkage PredictionShrinkage Data for Impact Copolymer with 20 MFR


The links below provide information on how to predict shrinkage for designing and molding plastic parts made from DOW Polypropylene Resins. The data details how part thickness affects shrinkage and also provides general guidelines to the molder and designer on how process variables affect final part dimensions, and gives general guidelines for controlling part shrinkage.

Part Thickness Shrinkage vs. Parts Thickness illustrates how part thickness affects mold shrinkage in DOW

Polypropylene Resins. This graph shows data for a part with dimensions of 2.625 in by 2.625 in (65.6 mm by 65.6 mm).

Choose from the following to learn more about shrinkage: Shrinkage Data for Impact Copolymer with 20 MFR




Center: Technology Primer: Shrinkage Prediction


Shrinkage Data for a Typical DOW Polypropylene Resins Resin, Impact Copolymer with 20 MFR

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Shrinkage Data for Impact Copolymer with 20 MFRShrinkage Data for Impact Copolymer with 35 MFR

The effects of injection speed, mold temperature, melt temperature, and average cavity pressure on mold shrinkage is shown for parts with dimensions of 4 in (100 mm) by 12 in (300 mm) at a thickness of 0.100 in (2.5 mm). (See Shrinkage Data Charts for a Typical DOW

Polypropylene Resins Resin, Impact Copolymer with 20 MFR.)



Center: Technology Primer: Shrinkage Data for a

Typical DOW Polypropylene Resins Resin, Impact Copolymer with 20 MFR



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The effects of injection speed, mold temperature, melt temperature, and average cavity pressure on mold shrinkage is shown for parts with dimensions of 4 in (100 mm) by 12 in (300 mm) at a thickness of 0.100 in (2.5 mm). (See Shrinkage Data Charts for a Typical DOW Polypropylene Resins Resin, Impact Copolymer with 35 MFR.)




Typical DOW Polypropylene Resins Resin, Impact Copolymer with 35 MFR


Amorphous Polymer Conformation vs. Semi-crystalline Polymer Conformation




Amorphous Polymer Conformation vs. Semi-crystalline Polymer Conformation


Properties of Crystalline vs. Amorphous Polymers

Mechanical Property Crystalline Polymer Amorphous Polymer

Examples: Polypropylene, Polyethylene, Nylon, PBT, PET

Examples: Amorphous Polymer Polycarbonate, PC Blends, ABS, Polystyrene, TPU, SAN, PPO

Chemical Resistance Higher Lower

Shrinkage Higher Lower

Warpage Higher Lower

Tensile Strength Higher Lower

Tensile Modulus Higher Lower

Elongation Lower Higher

Creep Resistance Higher Lower

Flow Higher Lower

Maximum Exposure Temperature Higher Lower

Density Higher Lower

Source: Rosato, Donald V. and Dominick V., Injection Molding Handbook, 1995.




Properties of Crystalline vs. Amorphous Polymers


Typical Characteristics of Polypropylene



Center: Technology Primer: Typical

Characteristics: Typical Characteristics of

Polypropylene


Resin Designation Key

PP TYPE(1 Digit)

GRADE TYPE(3 Digits)

MELT FLOW(2 Digits)

ADDITIVES(Up to 4 Digits)

C ImpactR RandomH HomopolymerT TPOD Developmental

100 ... 199 Extrusion / BM300 ... 399 Films / Coatings500 ... 599 Fibers700 ... 799 Injection Molding

00 MFR<1.002 MFR 2.0-2.910 MFR 10.0-10.935 MFR 35.0-35.999 MFR>99

R Controlled RheologyN Nucleator / ClarifierS SlipA AntistatU UV StabilizerG Non-gas fadingHP High PerformanceZ Other Additives

Homopolymer PP / Injection Molding - Houseware / 15 MFR / Antistat & Antiblock -- H7xx-15BAImpact Copolymer PP / Sheet-Packaging / 0.5 MFR / Antistat & Mold Release -- Clxx-00AZ



Center: Technology Primer: Typical

Characteristics: Resin Designation Key


Shrinkage vs. Part Thickness



Center: Technology Primer: Shrinkage

Prediction: Shrinkage vs. Part Thickness






Typical DOW Polypropylene Resins Resin, Impact

Copolymer with 20 MFR: Shrinkage Data for a Typical

DOW Polypropylene Resins Resin, Impact Copolymer with 20 MFR



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Polyolefins: Polypropylene Technical


Typical DOW Polypropylene Resins Resin, Impact

Copolymer with 35 MFR: Shrinkage Data for a Typical

DOW Polypropylene Resins Resin, Impact Copolymer with 35 MFR


Propylene Monomer and Polypropylene Polymer




Propylene Monomer and Polypropylene Polymer


Atactic, Isotactic and Syndiotactic Polypropylene




Atactic, Isotactic and Syndiotactic Polypropylene


Troubleshooting Guide for Injection Molding Polypropylene

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Polypropylene Troubleshooting Guide

Troubleshooting guidelines are provided for injection molding polypropylene parts. The guide lists the problem, the cause of the molding problem, and the solutions for resolving the particular molding problem. Any one or combination of these solutions can be used to identify and solve molding issues when molding polypropylene parts.



Troubleshooting Guide:



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Problem Cause Solution

Brittle Parts Degradation of PP Material ● Reduce Barrel Temperatures● Reduce Material Residence Time in Barrel● Check Barrel-To-Shot Ratio

High Level of Molded-In Stresses ● Increase Barrel Temperatures● Adjust Injection Speed (Moderate to Slower Speed)

Material Contamination ● Check Color Concentrates Used, as well as Base Resin● Check Material Handling System, such as Material Feed Lines and Hopper for

Contaminant Materials

Poor Part Design ● Remove Sharp Corners and Use Radiused Corners● Move Weld Lines Away from Areas Where Strength is Critical



Troubleshooting Guide: Brittle Parts



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Excessive Shrinkage Cooling Time Too Short or Poor Part Cooling

● Increase Cooling Time

Pack Pressure Too Low ● Increase Pack Pressure or Pack Time

Mold Temperature Too High ● Reduce Mold Temperature Resin● Check Cooling Lines for Scale or Rust Build-Up and Clean Out

Build-Up● Relocate Cooling Lines, or Use Bubblers in Areas Where Cores

are Used

Material Melt Temperature Too High ● Reduce Barrel Temperature● Check for Overriding Barrel Temperature Controls● Reduce Back Pressure

Runners and Gates Too Small ● Enlarge Runners and Gates to Reduce Pressure While Keeping Runner and Gate System Balanced

Poor Part Design ● Eliminate Wall Thickness Variations, and Design for Consistent Nominal Wall



Troubleshooting Guide: Excessive Shrinkage



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Flashing Parts Injection Pressures Too High ● Reduce Injection Pressures

Clamping Pressures Too Low ● Increase Clamping Pressures● Check Die Height Adjustment Setting on Injection Molding Machine

Material Temperature Too High ● Reduce Barrel Temperature● Check for Overriding Barrel Temperature Controls● Reduce Back Pressure

Obstruction on Mold Surface Preventing Mold from Closing Completely

● Clean off Mold Surface and RemoveObstructions Such as Dirt, Runners,Sprues, Metal Parts or Fines, or Other Foreign Materials



Troubleshooting Guide: Flashing Parts



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Flow Marks Melt Temperature Too Cold ● Increase Barrel Temperature● Increase Back Pressure

Injection Speed Too Slow ● Adjust Injection Speed (Moderate to Fast)

Mold Temperature Too Low ● Increase Mold Temperature

Poor Mold and/or Part Design ● Move Weld Lines Away from Areas Where Strength is Critical● Polish Cavity and Core Surfaces



Troubleshooting Guide: Flow Marks



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Gas Burn Marks (Dieseling) Injection Speed Too High ● Reduce Injection Speed

Barrel Temperature Too High ● Reduce Barrel Temperature● Reduce Back Pressure

Poor/Inadequate Venting In Mold ● Adjust Existing Vent Size



Troubleshooting Guide: Gas Burn Marks (Dieseling)



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Gloss Too Low Injection Speed Too Slow ● Adjust Injection Speed (Moderate to Fast)

Melt Temperature Too High ● Reduce Barrel Temperature and/or Back Pressure

Mold Temperature Too Low ● Increase Mold Temperature

Packing Pressure and/or Packing Time Too Low ● Increase Packing Pressure and/or Packing Time

Poor Mold Surface ● Polish Mold Surface



Troubleshooting Guide: Gloss Too Low



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Gloss Too High Injection Speed Too High ● Reduce Barrel Temperatures● Reduce Material Residence Time in Barrel● Check Barrel-To-Shot Ratio

Melt Temperature Too High ● Reduce Mold Temperature

Packing Pressure and/or Packing Time Too High

● Reduce Packing Pressure and/or Back Pressure

Mold Surface Highly Polished ● Texture Mold Surface● Reduce Mold Temperature

Mold Not Properly Balanced ● Mold Series of Short Shots and Check Flow Pattern of Each Shot● Perform Mold Filling Analysis Utilizing 2-D or 3-D Mold Filling

Software

Machining Capacity Undersized ● Check Cylinder Size Versus Shot Size Needed for Part and Determine Barrel-to-Shot Ratio

● Check Volumetric Requirements of Machine and Heating Capacity of Machine

Worn Check Rings ● Replace Worn Out Check Rings



Troubleshooting Guide: Gloss Too High



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Nozzle Drool Barrel Temperatures Too High ● Reduce Barrel Temperatures and/or Back Pressure

Hot Runner Manifold and/or Barrel Drop Temperatures Too High

● Check for Overriding Temperature Controls● Reduce Manifold Temperatures in Hot Too High Runner System● Reduce Hot Tip Temperatures in Hot Runner Systems● Utilize Valve Gating in Mold

Cycle Time Too Short ● Increase Cycle Time

Screw Decompression Off ● Set Screw Decompression "On"



Troubleshooting Guide: Nozzle Drool



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Part Sticking in Cavities Excessive Mold Packing ● Reduce Packing Pressure and/or Packing Time● Increase Barrel Temperatures and Decrease Injection Pressure

Insufficient Cooling ● Increase Cycle Time

Poor Condition of Mold ● Utilize High-Lubricity Mold Coatings or Finishes● Polish Mold Surfaces● Remove Hang-Up Areas Such as Undercuts● Increase Draft Angles● Modify Core to Increase Friction to Allow Part to Stick on Core Side of Tool● Relocate Gates from Near Projections, Such as Ribs, Bosses, Holes, etc.



Troubleshooting Guide: Part Sticking in Cavities



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Part Sticking on Cores Excessive Mold Packing ● Reduce Packing Pressure and/or Packing Time● Increase Barrel Temperatures and Decrease Injection Pressure

Cycle Time Too Long ● Reduce Cycle Time

Poor Conditions of Mold ● Utilize High-Lubricity Mold Coatings or Finishes● Draw Machine Cores (Machine in Direction of Flow)● Increase Draft Angles● Remove Hang-Up Areas Such as Undercuts● Modify or Improve Ejector Pin Set Up or System



Troubleshooting Guide: Part Sticking on Cores



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Poor Color Dispersion Incompatible Color Concentrate ● Change to Compatible Color Concentrate

Barrel Temperatures and/or Back Pressures Too Low

● Increase Barrel Temperatures and/or Back Pressure

Poor Mixing in Machine Barrel ● Replace Standard Machine Screw with Improved Mixing Screw, Such as Barrier Type Screw

● Use Static Mixer or Mixing Nozzle● For Dry Color Mixing, Achieve Good Mix of Color and Base

Material



Troubleshooting Guide: Poor Color Dispersion



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Poor Knit or Weld Lines Barrel Temperatures Too Low ● Reduce Barrel Temperatures● Reduce Material Residence Time in Barrel● Check Barrel-To-Shot Ratio

Mold Temperatures Too Low ● Increase Barrel Temperatures● Adjust Injection Speed (Moderate to Slower Speed)

Injection Time Too Short ● Check Color Concentrates Used, as well as Base Resin● Check Material Handling System, such as Material Feed Lines

and Hopper for Contaminant Materials

Poor Mold and/or Part Design ● Move Weld Lines Away from Areas Where Strength is Critical● Use Overflow Tabs at Weld Line Location● Increase Wall Thickness, or Add Ribs and Increase Flow Length

After Weld Line Area

Incorrect Grade of Polypropylene ● Use Un-nucleated Grade of Polypropylene



Troubleshooting Guide: Poor Knit or Weld Lines



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Rough Part Surface Barrel Temperatures Too Low ● Increase Barrel Temperatures and/or Back Pressure Mold Temperatures Too Low

Mold Temperatures Too Low ● Increase Mold Temperatures

Injection Speed Too Slow ● Increase Injection Speed to Moderate to Fast

Insufficient Venting ● Adjust Existing Vent Size● Add Additional Vents to Mold● Utilize Porous Metal Inserts

Poor Mold Surface ● Polish Mold Surface



Troubleshooting Guide: Rough Part Surface



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Short Shots Shot Size Too Low ● Increase Shot Size

Injection Time Too Short ● Increase Injection Time

Low Injection Pressure Too Low ● Increase Injection Pressure

Barrel Temperatures and/or Back Pressure Too Low

● Increase Barrel Temperatures and/or Back Pressure

Gates, Runners, or Sprues Undersized ● Open Gates, Runners, and Sprue in Mold

Nozzle or Gates Obstructed ● Remove Foreign Matter from Nozzle and Gates

Insufficient Venting ● Adjust Existing Vent Size● Add Additional Vents to Mold● Utilize Porous Metal Inserts

Melt Flow of Polypropylene Material Too Low

● Utilize Higher-Flow Polypropylene Resin


Software



Troubleshooting Guide: Short Shots


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Sink Marks Packing Pressure and/or Packing Time Too Low

● Increase Packing Pressure and/or Packing Time

Barrel Temperatures Too High ● Reduce Barrel Temperatures

Gates of Mold Too Small ● Open Gates of Mold

Improper Location of Gates ● Locate Gates in Thick Walled Sections Instead of Thin Wall Areas

Nominal Wall Too Thick ● Reduce Wall Thickness● Use Foaming Agent to Expand Out Sink Areas

Wall Too Thick at Ribs and Bosses ● Reduce Wall Thickness at Ribs and Bosses● Core Out Thick Walled Sections● Use Foaming Agent to Expand Out Sink Areas



Troubleshooting Guide: Sink Marks



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Splay Moisture in Material ● Dry Material, if Needed

Contamination in Material ● Remove Contaminated Material● Check Material Handling System, Such as Material Feed Lines, and

Hopper for Contaminant Materials

Moisture Accumulating on Mold ● Set Mold Temperatures Above Dew Point

Hang Up, or Flow Disruption in Fill Path of Mold

● Reduce Injection Speed to Moderate to Slow● Reduce Barrel Temperatures and/or Back Pressure

Packing Pressure and/or Packing Time Too Low

● Increase Packing Pressures and/or Packing Time


Software



Troubleshooting Guide: Splay



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Voids Moisture in Material ● Dry Material, if Needed

Contamination in Material ● Remove Contaminated Material● Check Material Handling System, Such as Material Feed Lines, and Hopper for

Contaminant Materials

Insufficient Venting ● Adjust Existing Vent Size● Add Additional Vents to Mold● Utilize Porous Metal Inserts● Polish Mold Surface

Improper Gate Location ● Locate Gates in Thick Walled Sections Instead of Thin Wall Areas

Injection Speed Too Fast ● Reduce Injection Speed to Moderate to Slow



Troubleshooting Guide: Voids


Safety and Handling Considerations

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Polypropylene Safety & Handling Considerations

Hazards and Handling Precautions

Combustibility

Disposal

Environment

Product Stewardship

Customer Notice

Material Safety Data (MSD) sheets for DOW Polypropylene Resins are available from Dow Plastics, a business group of The Dow Chemical Company. MSD sheets are provided to help customers satisfy their own handling, safety, and disposal needs, and those that may be required by locally applicable health and safety regulations, such as OSHA (U.S.A.), MAK (Germany), or WHMIS (Canada).

MSD sheets are updated regularly, therefore, please request and review the most current MSD sheet before handling or using any product. The links at the right provide general comments and apply only to DOW Polypropylene Resins as supplied.

Various additives and processing aids used in fabrication and other materials used in finishing steps have their own safe use profile and must be investigated separately.



Center: Safety and Handling



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Hazards and Handling PrecautionsCombustibility

Disposal

Environment

Product Stewardship

Customer Notice

DOW Polypropylene Resins have a very low degree of toxicity and under normal conditions of use should pose no unusual problems from ingestion, eye, or skin contact. However, caution is advised when handling, storing, using or disposing of these resins, and good housekeeping and controlling of dusts are necessary for safe handling of product. Workers should be protected from the possibility of contact with molten resin during fabrication.

Handling and fabrication of plastic resins can result in the generation of vapors and dusts. Dusts resulting from sawing, filing, and sanding of plastic parts in post-molding operations may cause irritation to eyes and the upper respiratory tract. In dusty atmospheres, use an approved dust respirator. Pellets or beads may cause a slipping hazard. Good general ventilation of the polymer processing area is recommended. Processing may release fumes which may include polymer fragments and other decomposition products. Fumes can be irritating. At temperatures exceeding melt temperature, polymer fragments can occur.

Good general ventilation may be necessary for some operations. Use safety glasses. If there is a potential for exposure to particles which could cause mechanical injury to the eye, wear chemical goggles. If vapor exposure causes eye discomfort, use a full-face respirator. No other precautions other than clean body-covering clothing should be needed for handling DOW Polypropylene Resins. Use gloves with insulation for thermal protection, when needed.



Center: Safety and Handling: Hazards and Handling

Precautions


Combustibility

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CombustibilityDisposal

Environment

Product Stewardship

Customer Notice

DOW Polypropylene Resins will burn and, once ignited, may burn rapidly under the right conditions of heat and oxygen supply. Do not permit dust to accumulate. Dust layers can be ignited by spontaneous combustion or other ignition sources. When suspended in air, dust can pose an explosion hazard. Dense black smoke is produced when product burns. Toxic fumes are released in fire situations.

Fire fighters should wear positive-pressure, self-contained breathing apparatus and full protective equipment. Water or water fog are the preferred extinguishing media. Foam, alcohol resistant foam ,carbon dioxide, or dry chemicals may also be used. Soak thoroughly with water to cool and prevent re-ignition.



Center: Safety and Handling: Combustibility


Disposal

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Combustibility

DisposalEnvironment

Product Stewardship

Customer Notice

DO NOT DROP INTO ANY SEWERS, ON THE GROUND,OR INTO ANY BODY OF WATER. For unused or uncontaminated material, the preferred options include sending to a licensed recycler, reclaimer,incinerator, or other thermal destruction device.

For used or contaminated material, the disposal options remain the same, although additional evaluation is required (see, for example,in the U.S.A.,40 CFR, Part 261,"Identification and Listing of Hazardous Waste "). All disposal methods must be in compliance with Federal,State/Provincial, and local laws and regulations.

As a service to its customers, Dow can provide lists of companies which recycle, reprocess, or manage chemicals or plastics, and companies that manage used drums. Contact the nearest Dow Customer Service Center for further details.



Center: Safety and Handling: Disposal


Environment

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Combustibility

Disposal

EnvironmentProduct Stewardship

Customer Notice

Generally speaking,in the environment, lost pellets are not a problem except under unusual circumstances – when they enter the marine environment. They are inert and benign in terms of their physical environmental impact, but if ingested by waterfowl or aquatic life, they may mechanically cause adverse effects. Spills should be minimized, and they should be cleaned up when they happen. Plastics should not be discarded into the ocean or any other body of water.



Center: Safety and Handling: Environment


Product Stewardship

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Combustibility

Disposal

Environment

Product StewardshipCustomer Notice

The Dow Chemical Company has a fundamental concern for all who make, distribute, and use its products, and for the environment in which we live. This concern is the basis of our Product Stewardship philosophy, by which we assess the health and environmental information on our products and then take appropriate steps to protect employee and public health and the environment. Our Product Stewardship program rests with every individual involved with Dow products from initial concept and research to the manufacture, sale, distribution, and disposal of each product.



Center: Safety and Handling: Product Stewardship


Customer Notice

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Combustibility

Disposal

Environment

Product Stewardship

Customer Notice

Dow encourages its customers and potential users of Dow products to review their applications for such products from the standpoint of human health and environmental quality. To help ensure that Dow products are not used in ways for which they were not intended or tested, Dow personnel will assist customers in dealing with ecological and product safety considerations. Your Dow sales representative can arrange the proper contacts. Dow literature, including Safety Data Sheets, should be consulted prior to the use of Dow products. These are available from the nearest Dow Customer Service Center.



Center: Safety and Handling: Customer Notice


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EUR 260-12801 1003

polypropylene design guide dow chemical

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