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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
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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%
Source: AWA Alexander Watson Associates BV
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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
Source: AWA Alexander Watson Associates BV
Polypropylene film for release liners (1999) - Europe
25%
14%
11%
5% 5%
40%
Label
Hygiene
Building/Insulation
Tape
Health/Medical
Others
Source: AWA Alexander Watson Associates BV
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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
High Speed UV Siliconising
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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
subsequent adhesion 83 %
release (tesa7475/7476) 6 / 47 cN/in
boPP 30 600 m/min
ctwght 0,9 g/m
subsequent adhesion 94 %
release (tesa7475/7476) 6 / 45 cN/in
boPP 30 900 m/min
ctwght 0,8 g/m
subsequent adhesion 95 %
release (tesa7475/7476) 8 / 56 cN/in
High Speed UV Siliconising
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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.