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Alternative Liners for

Label Applications

presented at the

FINAT Technical Seminar,

Barcelona, Plaza Hotel

14 16 March 2001

Technology Adapting to New Demands

by

Dr. Winfried Hamann

degussa.

Goldschmidt Industrial Specialties

Technical Service Release Liner Business

[email protected]

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Based on the evaluations of professional market analysts and our own ex-

perience in the market over the years, the global demand for self-adhesive

materials will still increase in the years to come. North-America, Europe,

and Asia will be the biggest players, with approximately three-quarters of

the total release liner consumption. Label manufacturers will remain the top

user of release liner materials; they will cover more than 50% of the world

production of release liners.

Pressure-sensitive self-adhesive materials

Looking into the European market for self-adhesive materials, PS labelstockapplications are clearly dominating over the feminine hygiene and tape

sector. For the label manufacturer, the glassine and super calandered kraft

(SCK) liners are the most important release liner for PS materials in roll ap-

plications. These substrates are also often used in tape or special applica-

tions, whereas in the field of hygiene and building/insulation, these materi-

als are of minor interest.

The physical/mechanical properties of the glassines and SCKs are tailor-

made for the various steps of processing: siliconising, adhesive coating,

die-cutting, and dispensing. The release properties are important for the

converting of the PS laminate and for manual or automatic dispensing. Un-

acceptable variations in the thickness of the release liner may cause prob-

lems during the die-cutting process and the matrix stripping. So, decades of

development and optimisation have lead to a high-tech product, which is

superfluous after having released the label to its final destination.

Self-adhesive Materials (1999) - Europe

Label

Hygiene

Tape

Building/Insulation

Others

Glassine / SCK Paper

65%10%

7%

4%

14%

Source: AWA Alexander Watson Associates BV

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Cost ShareTherefore, the release components, i.e. silicone and silicone base paper,

must not be expensive. Looking at the cost structure of a standard paper

label, you will find that more than one third of all material costs is caused by

the release base paper.

Therefore, there is an ongoing trend towards lighter basis weight papers.

Decades ago, the typical glassine paper for roll labels started at a thickness

of 75 g/m. Today, the standard weight for a glassine release liner is

62 g/m. Going to an even lower basis weight could cause problems in

processability and converting. There is always a compromise between cost

and technical properties.

In the past years, when the market for self-adhesive products became more

and more competitive and cost-driven, the variety of release liners in-

creased to meet exactly the performance requirements and not to be over-

Cost share of a classical paper laminate (materials)

Release linersubstrate

42%

16%5%

37%

SiliconeAdhesive

Paper face stock

Raw material costs

face 80gsm 1 /kg 0,08 /m

adhesive 1,50 /kg 0,03 /m

silicone 10 /kg 0,01 /m

glassine 62 gsm 1,40 /kg 0,07 /m

(37 %of the total laminate construction)

Classical PS self-adhesive laminate on roll

l Paper face stock

l Pressure sensitive adhesive

l thermally curing silicone

l glassine type release liner

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qualified. On the other hand, down-sizing the number of raw materials, sim-

plification of product lists, and focussing on standard products are key-

words to stay competitive in the international market.

Release Liner Substrates

Within the European release liner market, paper substrates continue to ac-

count for the bulk demand. SCK paper and glassine are the dominating

base substrates with a predicted constant share for the upcoming years.

Clay-coated and machine finished papers are used in the label industry for

sheet materials, and in hygiene applications. It is said that the demand forthis group of base papers will slightly decrease. Poly-coated krafts, which

are strong in Asia, will decrease over time, due to the fact that they are

composed of two materials and are not easily recyclable.

Synthetic base release liners are steadily increasing their share in different

market segments, particularly in labels, tapes, and hygiene applications.

Filmic release liners offer a bundle of new opportunities and a big potential

for improvements on the production and converting side, and for new ap-

plications.

Linerless Pressure Sensitive Materials

Some years ago a new idea for pressure sensitive labels was introduced to

the traditional label market, linerless labels. This concept was sparked by

looking that way pressure sensitive adhesive tapes are manufactured, and

Materials for Release Liners (1999) - Europe

Glassine / SCK

Clay-coated Paper

Other Papers

Poly-coated Paper

Film22%

11%

7%

10%

50%


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applying the technique to labels. By adding a release coat directly over the

printed label, one would be able to apply adhesive to the backside, wind it

into a roll, and dispense it like a tape, all without the need for a separate

liner.

Linerless labels are printed using conventional methods on narrow web

presses, using either thermal sensitive or classical graphic base paper.

Curing and adhering the release coating on top of the ink is the key point for

this new technology. UV curable silicone acrylates are used successfully for

this purpose.

One of the most obvious and most significant distinctions of linerless labels

is that they produce no waste in the application process. For end users, the

absence of the silicone coated liner represents savings, adds to inventory

space, removes a safety hazard in the plants, and presents an environ-

mental benefit.

One of the limitations of the linerless labels is the shape. Since there is no

liner, one label is attached directly to the next; shapes are limited to squares

Linerless Labels on roll

paper substrate

printedinformation

release coatingover print

adhesive coatingon backside

micro-perforation

Linerless Labels

Pros

no liner - simplified manu-

facturing process

no liner - raw material savings

no waste in the application

process

adds to inventory space

Cons

shape limitations -

squares and rectanlges

investment in new equipment

for manufacturing and

end-use

loss of flexibility due to

printing prior siliconising

no transport of single labels

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or rectangles. Cutting the labels takes place during application; machinery

used to apply the labels use various methods of cutting, e.g. scissors or tear

bars.

Graphical base papers

The development of the classical silicone base papers over the past dec-

ades has resulted in highly technical and specialised substrates, tailor-

made for the thermally curable release coatings and the subsequent con-

verting processes. Special focus has been put on the composition of ingre-

dients used in the glassine and clay-coated papers to prevent inhibiting thesilicone curing reaction. This is the reason why many of the less expensive

machine and cast-coated graphical papers, used as facestock materials,

failed as silicone base papers for thermally cured coatings. For the UV cur-

able silicone acrylates, which are not sensitive to potential thermal inhibitors

in the paper surface, that does not matter. Curing is not affected by traces

of heavy metal compounds, amines, sulfur compounds etc.

There is a wide variety of graphical papers in the market, normally used for

label facestocks. Some of them have the potential to replace the traditional

silicone base substrates, although there are differences in the mechanical-

physical properties in comparison to the conventional clay-coats.

Graphical Papers

Pros

low cost compared to classical

clay-coated silicone base paper

double-side siliconising possible

Cons

changed mechanical-physical

properties

adjustments of siliconising

and converting equipment

higher silicone coat weight

compared to clay coats

lack of experience in

siliconising, laminating, and

converting

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We tried some of these potential substitutes successfully in terms of proc-

essibility on our narrow web lab coater. We found that they need approx.

30-50% more silicone than normally used on typical silicone base papers,

caused by poor holdout.

On the other hand the savings on cost for the alternative paper overcom-

pensate the high silicone coat weight. By using UV curable silicones there is

no significant thermal impact during the siliconising process. Rehumidifica-

tion is not necessary. Of course, the graphical paper must withstand the

stress while adhesive coated and converted.

These are new areas to be explored and will require unconventional think-

ing and some commitment, but the rewards will be greater than the effort

invested.

Again, you will have to break with decades of experience and standard

properties of conventional silicone base papers. All parties involved in the

process chain will have to demonstrate flexibility and standing power to

bring this idea to success.

Filmic Release Liners

Today, there are already important applications for filmic release liners,

which is no surprise because approximately 10% of the total release liner

production is on filmic substrates.

Graphical Papers

Grammage [g/m]Thickness [m]

Tensile strength [N/15mm] MD

CD

Elongation [%] MD

CD

Smoothness [Bekk-s] FS

BS

Stiffness [mN] MD

CD

IGT [mm] FS

Silicone coat weight [g/m]

Ref. A B C

80 90 87 8482 72 73 80

85 85 80 86

40 32 54 42

2,9 2,1 2,1 1,8

7,5 5,5 5,5 6,5

600 1100 2200 900

25 750 420 30

62 67 54 72

35 45 32 58

128 135 140 145

1,1 1,4 1,6 1,5

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Although glassine paper is the standard substrate for reel materials in

Europe, filmic liners based on polypropylene (PP) and polyester (PET) arecompetitive alternatives, fuelled by cost and physical properties. In the

cosmetic and hygienic fields, the no-label-look has been established as an

alternative for direct printing on glass bottles and flacons. The crystal clear

appearance of the adhesive coated label demands a glossy and perfect re-

lease liner substrate; PP or PET are the ideal candidates for that applica-

tion.

Filmic liners are also preferred in tape applications with high technical re-

quirements, e.g. duo- and triple constructions with double-side release

coatings and differential release values. Diaper tapes are a well-known fil-

mic release liner application. In the medical field, super clear PET materials

imply a sterile and proper impression; so, PET liners are often used for

wound care and other medical products. Polyethylene (PE) and PP films

are the favourite substrates for packaging of sticky goods because of their

tensile strength and elasticity. Coated with a special adhesive for low adhe-

sion force, LDPE films are often used as protective films for high gloss sur-

faces in the electronic and automotive industry.

During the last five years biaxally oriented polypropylene (boPP) liners have

gained more and more importance in the European label industry, replacing

part of the dominating glassine papers. Furthermore, the markets for hy-

giene, building/insulation, and tape applications contribute to the two digit

growth of PP liners.

Typical applications for filmic release liners

labels replacement of glassine liners

no-label-look materials

packaging materials

hygiene tapes (multi-functional)

medical applications

industrial tapes (double-side coated)

self-adhesive tapes

for protection of high gloss surfaces

for sticky goods (bitumen, hotmelt)

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The advantages of a PET film over PP are its high optical transparency and

the tensile strength. Although it is more expensive than a boPP liner, PET iswell established in the label market followed by health and medical applica-

tions.

Properties

Comparing the properties of paper and synthetic liners, you will see that

there are some pros for the filmic substrates, which may help to combat the

ongoing pressure on prices and decreasing profits.

Polyester film for release liners (1999) - Europe

15%

12%

6%

10%6%

51%

Label

Health/Medical

Tape

Building/Insulation

Covering

Others


Polypropylene film for release liners (1999) - Europe

25%

14%

11%

5% 5%

40%

Label

Hygiene

Building/Insulation

Tape

Health/Medical

Others


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A significant difference between paper and filmic substrates is the lack ofexperience in processing and handling the synthetic materials. The switch

to a new liner material often requires rebuilding technical equipment, and in

some cases reconfiguring some aspects of converting devices.

Savings

A promising approach to reduce the ongoing price pressure could be the re-

placement of a traditional paper liner. About one third of the cost, of e.g. a

PS laminate, is caused by the backing material, as already mentioned.

By using synthetic release liner materials, it is possible to save a consider-

able amount of the material cost of a PS laminate. Using 12 PET as a re-

placement of a 57 glassine paper would be a very challenging effort. In

close co-operation with your partners in the manufacturing chain, it should

Paper substrate Filmic substrate

Tensile strength OK OK

Transparency limited crystal clear - opaque

Thickness 40 - 200 g/m 12 - 150

Smoothness smooth - rough very smooth - rough

Silicone coat weight 0,8 - 1,5 g/m 0,4 - 1,0 g/m

Die-cuttibility OK, well known new; challenging

Dimension stability curl, shrinkage shrinkage possible

Humidity sensitive non-sensitive

Recyclability possible possible

some typical properties

Replacement of paper liner by filmic substrate

Cost savings by using filmic release liners

Release liners (raw material)

glassine 62 gsm 0,07 /m (100%)

boPP 30 0,06 /m ( 86%)

PET 36 0,12 /m (171%)

PET 12 0,05 /m ( 71%)(from entire laminate 13%)

42%

16%5%

37%

Release linersubstrate

Silicone

Paper face stock

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be possible to prepare this way of innovation step-by-step for the benefit of

all parties involved.

Forward-thinking manufacturers, converters and printers will undertake the

hardware investment to run the attractive alternatives because of their focus

on long-term return on investment.

Radiation Curable

Some of the alternative synthetic release liner substrates are sensitive to

temperature where the conventional thermal curing silicones would fail be-

cause of damage to the liner substrate. For years now, novel, radiation

curing silicone systems in the market allow silicone to cure under very mild

conditions. These EB and UV curable silicones are best suited for sili-

conising filmic substrates or thermal sensitive paper materials.

In the early 1980s, the idea of radiation curing silicone to form a release

coating was a novelty. The first commercial products for release coatings

were based on the principal of curing through the acrylate sites. The curing

of the acrylate groups was activated by radicals. Already at that time Gold-

schmidt AG was the driving force for the development of radiation curing

technology.

Goldschmidt AG was (and still is) a pioneer in this field, having started with

its 1st generation of radiation curable TEGORC Products in 1983.

Innovative self-adhesive laminate on roll

l Paper face stock

l Pressure sensitive adhesive

l UV/EB curable RC silicone

l filmic release liner (boPP/PET)

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Silicone Acrylates

With continuous feedback from the market, Goldschmidt AG developed a

variety of chemical modifications and improvements over the past sixteen

years. After extensive development time and up-scaling these products to

standard materials, we were able to improve three important properties:

At the end of 1998, Goldschmidt announced and demonstrated the 4th gen-

eration of high performance silicone acrylates with outstanding properties.

This latest range of TEGO RC Silicone Acrylates includes the novel prod-

ucts RC 902, RC 715, and RC 709.

A very wide range of release values can be generated by blending different

types of RC Silicone Acrylates. In our product range (the new) RC 902

stands for easy release applications, e.g. for typical PSA label laminates.

You can increase the release level almost continuously by adding RC 715,

RC 706, RC 709, and finally pure RC 711 for tight release applications .

Since the introduction of this RC silicone system it has been well accepted

by various customers for many different applications. In addition, Gold-

l Better Cure - higher line speed

l Lower Viscosity - better processibility

l Adhesive Compatibility - improved ageing

TEGO RC Silicones - improved 4th Generation

Wide range of release values

easy release to controlled release

controlled release

controlled to tight release

controlled to tight release for

differentials

tight release

TEGO RC 902

TEGO RC 715

TEGO RC 706

TEGO RC 709

TEGO RC 711

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schmidt has given public proof of the processability and the capability to

meet the most demanding requirements for future growth.

High Speed

Speed of cure is one of the essential keypoints of our RC technology. In

contrast to the thermal silicone systems, the maximum cure speed does not

depend on the type or the gauge of the substrate to be coated. The reactiv-

ity of the RC silicone formulation is the dominating factor for the maximum

speed of cure. Using a UV lamp (arc type) with a UV power of 120 W/cm a

standard formulation of silicone acrylates, RC 902 and RC 709 can be

cured at 200 m/min.

Because of higher functionality, and therefore higher release level, the de-

gree of cure of RC 715 and RC 706 is excellent up to 300 m/min per lamp

(120 W/cm). Pure RC 711 for very tight release values can be cured as fast

as 400 m/min with just one UV lamp.

Recently Goldschmidt AG, together with two leading companies in the PSA

market, successfully demonstrated the improved properties of the 4th

gen-

Practical Proof

l High Speed UV Siliconising (Kroenert / Hamburg)

l Film-on-Film Laminating (Kroenert / Hamburg)

l Inline coating at Black Clawson (Fulton / NY)

Cure Speed of TEGO RC Products

one 120 W/cmArc Lamp

with 2 % A12 or15 % PC 750

with min. 30 %RC 711

All blends includingRC 902 or RC 709

All blends includingRC 715 or RC 706

RC 711 only

200 m/min.

300 m/min.

400 m/min.

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eration of RC Silicone Acrylates to a public audience. In close co-operation

with one of the major builders of coating lines, MAX KROENERT GmbH

and the innovator of inerted UV curing systems, ELTOSCH GmbH, we

coated three different substrates for various self adhesive applications with

a standard easy release formulation based on RC 902 at extraordinary high

line speeds.

All the substrates were run through the pilot line at 600 m/min without any

problems. A state of the art inerted UV unit, built by Eltosch, cured the easy

release coating. With just three lamps of 200 W/cm each, we achieved ex-

cellent curing and good anchorage on the three release liner materials.

We finished the demonstration trials with the boPP responsible LDPE sub-

strate for running at 900 m/min.

The UV output of three arc lamps of 200 W/cm each, was sufficient run at

speeds of 900 m/min. Subsequent adhesion values were in the eighties and

High Speed UV Siliconising

TEGO RC Silicone for Easy Release application

Substrates for siliconising

TEGO RC 902 70 parts

TEGO RC 711 18 parts

TEGO

PC 750 15 parts

boPP 30 UCB Films

LDPE 25 Nordenia Gronau

clay-coated paper 80 g/m Cartiere BOSSO

Curing conditions

Machine parameters

Speed 600 - 900 m/min

coating width 1020 mm

corona treatment 3 kW

UV output 3 x 200 watts/cm

residual oxygen 25 - 45 ppm

nitrogen consumption approx. 300 m/h


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nineties with no smear and no rub-off. Also, inerting was not a problem at

that high speed. The nitrogen consumption was approximately 300 m/h.

It could be that a line speed of 900 m/min is not of interest for every cus-

tomer. Nevertheless, the 4th generation of TEGO RC Silicone Acrylates has

been proven to be capable of withstanding these extreme conditions. In-

erting, which is occasionally still a reason for future customers to hesitate in

silicone acrylate chemistry, was fully capable at these high speeds. In the

end, this demonstration confirmed that siliconising at moderate speeds and

for combined in-line coating silicone acrylates offer a high security level for

the processing and the properties of the final product.

No-Label-Look

In a second trial, we demonstrated that the manufacturing of no-label-look

material is not a problem with RC silicones. From market response, it is un-

derstood that the shrinkage of the coated release liner during the adhesive

drying process is a critical point.

Some results (LDPE and boPP film)

LDPE 25 600 m/min

ctwght 1,1 g/m

subsequent adhesion 87 %

release (tesa7475/7476) 4 / 42 cN/in

LDPE 25 900 m/min

ctwght 1,1 g/m



boPP 30 600 m/min

ctwght 0,9 g/m



boPP 30 900 m/min

ctwght 0,8 g/m




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Therefore, we siliconised some boPP films (30 and 50) with the standard

RC formulation for easy release properties. These trials were also per-

formed on the KROENERT Technicum line in Hamburg. Since in-line adhe-

sive coating is not an option on this line, we applied a PS acrylate emulsion

in a second pass onto the siliconised filmic release liner. The face stock

material for the no-label-look laminate was a transparent 75 PP film. The

adhesive was applied onto the release carrier by means of a multi-pressure

gravure system (coat weight 15-18 g/m).

The drying process of the adhesive took place in four oven segments with a

length of 3 meters each at a speed of 100-200 m/min. We optimised the

temperature profile of the air flotation dryer to find the best compromise of

machine speed, adhesive coat weight, residual humidity, and the shrinkage

of the boPP liner.

We were successful in producing a clear laminate at 150 m/min. There was

no shrinkage of the boPP film at temperatures of up to 135C; which proves

that finding the best temperature setting for the adhesive dryer segments is

a critical point. It was demonstrated that using solventless RC silicones and

known adhesive technology, is a proven way to face and meet the chal-

lenging requirements of future products and applications.

Film-on-Film Laminating

Release l iners: PP films 30-50 (from UCB and Nordenia Gronau)

Face stock material: PP film 75 (from Nordenia Gronau)

Adhesive: acrylic dispersion for plastic face stock, permanent

Adhesive coating: multi-pressure gravure, coat weights 15-18 g/m

Drying: 4 segments 3 m length, air temp. 70-130C,coating speeds 150 - 200 m/min,residual water < 1% shrinkage < 1%

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In-Line Coating

A further trial that proves practical maturity of UV silicones was demon-

strated by tandem coating trials of UV silicones and emulsion acrylics at

BLACK CLAWSON Research & Technical Centre in Fulton/NY. Since UV

capacity can be added to a coating line at a lower cost than installing an

oven makes UV a practical solution for many companies. UV machines take

up less space, and require lower capital investment than other curing proc-

esses. Fast cure speeds and no post cure of RC silicone acrylates allows a

company to design a process with tandem coating in mind

The trials were designed to test a range of parameters including release

level, adhesives, substrates, and face stock. Substrates for the release liner

were three general types, including 30 polypropylene and 25 and 36

polyester. Silicones were chosen to give four different release levels with

easy, medium, controlled, and tight release properties. The two supplied

adhesives were both clear drying acrylic dispersions. Both polyester and

polypropylene (white/clear) were used as face stocks for the trial runs.

Inline coating trials

Substrate, silicone, adhesive

Substrates

- release liners three different types, e.g.

boPP 30, PET 25 and 36

- facestock PET and PP (clear/white)

Silicones four different formulations, based on

RC902, RC711, RC709, and

PC750

Adhesives two permanent acrylic dispersions

Trial conditions

UV output 1 x 240 watts/cm

Speed 125 m/min

Coating width 457 mm

Coating heads

- silicone differential offset gravure

- adhesive reverse g ravure (transfer coating)Coat weights

- silicone 0,9 g/m

- adhesive 15 g/m

Inline coating trials

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One row of FUSION UV bulbs was utilised with the machine speed kept

constant at approximately 125 m/min. This speed was limited due to adhe-

sive drying capacity. The silicone coating was done on a three roll offset

gravure coating station, and adhesives were applied to the release liner with

a reverse gravure coater. The achieved coat weights were approximately

0,9 g/m for the release coating and averaged 15 g/m for the adhesives. To

date, the results are very promising; release for all samples remains stable,

and there is no interaction between the silicones and the adhesives. The

pure transparent synthetic laminates are highly clear and suited for no-

label-look materials.

Future

In the future, new technologies for siliconising, adhesive coating, convert-

ing, and final applications will have a strong impact on the label, tape, and

release liner business. It is expected that the pressure on prices will con-

tinue and therefore profits will drop.

It has been shown at customers and machine manufacturers that UV sili-

cone technology opens the door for using alternative release liners in to-

days standard PS products. UV silicone technology is capable of saving

money by replacing more expensive release liner substrates, and gives ac-

cess to new applications and additional business.

Outlook and Message

l

save cost in standard label applications by the useof alternative release liners

l make use of specific physical properties of filmic

substrates for new applications

l participate in future growth of the attractive

alternatives for classical release liners

l take the challenge and break with conventions to be

prepared for the highly competitive label market

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Today, e.g. filmic release liners already have a two digit growth; some com-

panies are on the learning curve for handling and processing alternative

backings. In some years from now the substrates themselves and the tech-

nologies involved will be further developed and they will be industrial stan-

dards with benefits of optimised properties, better technical understanding

and know-how, and world-wide experience.

Release liner production requirements for label applications are constantly

increasing and changing. It is more important than ever before that all play-

ers in the production chain, including suppliers of raw materials and final

users, work closely together for the benefit of everyone.

pub_2001-03_finat_wh_e

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