Release liners a fresh review

Principles of a Release Liner
● Silicones define base materials for Release Liner
● Papers: the most important bases for Release Liner
● Key applications and value chain for Release Liner
● Labels
● Graphic Arts
● Fibre Composites

What is a Release Liner
A Release Liner is a carrier for self adhesive products;
it comprises a substrate in web form with a surface on which adhesives don’t stick.
o Substrate in web form
o Not sticking surface

Silicone
Properties &
Factors Influencing
Release Anchorage
Low Surface
Energies
Solid Surface
Silicone Factors
Influencing
Sensitive
Cost
Polymerisation
Effective
Physical
state /
solid/liquid

Framework for Release Liners
Variables
All are interlinked
Silicone
Properties
Carrier
Coating
Technology

Release Liner base materials: properties
❑ Almost all Release Liners carry a silicone layer
❑ Silicone is by far the most expensive material in such liners
❑ Therefore all efforts are taken to minimize the coat weight necessary
to about 0.3 to 1 g/m² = 1 µm
❑ To generate silicone hold-out the substrate (paper) is made with a surface
as much tight and as smooth as possible
❑ With various substrates tightness and smoothness are achieved by:
Avoid catalyst poisoning by using chemically very clean base papers / films.

Release liners based on super
calendared papers:

Release liners based on clay coated papers:

Release liners based on super calendared papers:

A release liner generally consists of a thin-layer of release coating applied to a carrier
substrate as illustrated in the label construction of Figure 1.
This design is an essential feature of a typical PSA construction.
There are many different PSA constructions available depending on the application.
These include pressure sensitive tapes, labels, double backed tape, and so forth.
Release agents are substances that control or eliminate the adhesion between two surfaces.
Release liners are simply carriers for the PSA that prevent it from sticking to itself and
provide a method of dispensing and application.
Certain products and even industries could not have been developed to their current level
of importance without the availability of modern release coatings and liners.
Importance of Release

PSAs may be constructed as either a one sided or two sided product.
With a one sided product such as pressure sensitive tape, the tape backing may also serve
as the release mechanism.
With two sided products such as transfer film or double sided tape, a separate liner is
required. The PSA product construction can vary significantly.
Figure 2 represents a complex PSA construction. The multi-functional nature of the liner
and its value to the end-user is readily apparent.
Construction of a typical pressure sensitive label
Figure 1: Construction of a typical pressure sensitive label
Importance of Release

Release liners serve several very useful functions.
They are used as a carrier sheet onto which the adhesive can be cast.
They protect the adhesive during storage and transit and also during various converting and assembly
processes so that unintended blocking does not occur.
Liners provide a functional support during die cutting and printing.
For example, liners can serve as a printing substrate for advertising, product instructions, product
identification, etc.
The liner also provides a lay-flat characteristic that prevents curling.
This is an important attribute in graphics and other applications.
Most importantly liners must perform these functions without damaging the adhesive or compromising its
subsequent performance properties.
Release liners represent an enabling technology that allows one to deliver and apply a PSAproduct to bond
two materials together.
Manufacturers and processors use release coatings and liners in a wide variety of general handling
operations, such as calendaring, casting, embossing, extrusion, forming, laminating, packaging, and labeling.
Arguably the most import applications are PSAtape, transfer film, and label release.

The optimal selection of a release liner can be a significant factor that impacts greatly on productivity. PSA
products need to be designed not only to meet the required end use specifications, but also to maximize
speed, efficiency, and reliability of the entire adhesive application process. Poorly chosen release liners can
result in expensive downtime due to problems such as the following.
o The release liner fails to protect the adhesive
o The liner releases prematurely
o Machines must be set to a slower speed because of poor liner reliability and performance

It should provide an adequate release.
The release level should be sufficiently low to provide an easy unwind without unduly stretching the
adhesive film or it's backing, but it should be high enough to prevent flagging when the PSA product is
wound in a roll.
The release should be slow at a low peel angle and rapid and easy
at 90 degree and higher angles, normally used for unwind.
The level of release should be reproducible.
This requires that the release level is not very sensitive to the amount of release agent used.
The release liner must be specifically designed to perform in a particular product and production process to
which it will be subjected.
For all applications, liners must stay in place until the appropriate time during assembly. They then must
remove easily with the application of a consistent force.
The release liner must at least meet the following minimum requirements.

The release agent should be firmly anchored and should not transfer to the adhesive surface, causing a
decrease in tack and inherently poor adhesion when applied.
The release coating should be resistant to aging and the unwind should not change much with prolonged
aging.
There usually are additional requirements for specific application.
For example, masking tape requires that the release coating have a good solvent resistance and that the
paint adhere reasonably well to the release coating.
Otherwise, the paint chips may fall off and remain adhered to the freshly painted surface.

The selection of a proper liner material will depend on the application and the type of PSA product being
constructed.
A number of essential questions will require answering before proper selection can be made. Table 1
summarizes the type of forethought that is required in this process.
A properly designed liner will function reliable in high speed and automated processes, enabling significant
gains in productivity.
Release liners on automated assembly lines are usually made of film to avoid tearing during the removal.
Film liners are also preferred for most electronics applications, because the fibers introduced with paper
liners can cause contamination.

What is the price vs. performance limit and which properties can be sacrificed for lower price?
Is environmentally acceptable disposal of the liner after its use a requirement?
Is product identification or color important?
Will the liner be removed during the initial assembly procedure or remain intact until removed by the end-
user?
How important is dimensional stability and the liner having a lay-flat characteristic?
Will the liner be die-cut or printed? If so, what are the particulars of these processes (e.g., thermal printing,
type of die-cut operation, etc.)?
Is a heavyweight liner required to give the product stiffness, or would a lightweight liner be better to allow
conformation to the substrate surface?
Should the liner offer easy release, or will a higher release strength ensure that it will stay in place during
all processing conditions?

The release of a pressure sensitive adhesive from a liner is a
very complex phenomenon.
There are a number of factors that contribute to the release
level of a liner and to the difficulty that is generally
experienced in selection of an appropriate liner product.
These are indicated in Table 2.
2. the end user's application process. At a minimum this
includes an understating of the types of sub-processes (e.g.,
dispensing, printing, die-cutting, etc.) that will be employed,
the sequence of events, the force and speed of each sub-
process, and the environmental conditions that will exist
during adhesive storage and application.
Nature of the adhesive
Chemical type
Thickness
Modulus
Diluents
Nature of the base liner
Roughness
Porosity
Sizing or plasticizers used
Surface energy
Nature of the release coating
Chemical composition
Coating weight
Film continuity
Degree of cure
Crosslink density
Modulus
Nature of the PSA product prior to release
Age of the liner / coating
Thickness and modulus of the product
Mode of adhesive applications
Conditions of storage (e.g. temperature and humidity)
Stripping operation
Speed
Angle of removal
Physical dimensions
Ambient conditions (e.g., temperature and humidity)
Table 2: Factors Affecting Release Level
In order to provide an optimized product with both an
adhesive and liner system that acts in concert, the
manufacturer of the PSA product must completely
understand the
1. the functional requirements of the adhesive itself and

A variety of release liners are used in PSA products.
They range from coated paper to plastic films.
They all have certain advantages and disadvantages and must be chosen in concert with the needs of
the specific application.
The various types of liners that are generally used are described in Table 3.
The surface to which the release coating is applied should be reasonably nonporous to hold the release
coating on the surface and to prevent the flow of soft pressure sensitive adhesive into the pores and
roughness of the surface, causing an increase in the unwind force.
Backside coating, which might or might not have the release characteristics, is often used on fabric
and paper surfaces to provide a smooth and impermeable surface for release.
Types of Release Liner

A recent requirement placed on all release liners is that they be recyclable once used. It is generally
considered that all spent liners (paper, film, polycot, etc.) are recyclable.
However, there are issues regarding segregation of material by type, packaging requirements, and
quantity that will enter into a successful recycling program.
Film liners represent the greatest potential for growth over the next three to five years, especially in high-
volume, fast moving applications.
However, paper liners will continue to enjoy the majority of the market due to their lower cost, caliper,
and technology enhancements via silicone release coatings.
Kraft liners can exhibit problems with dimensional stability under changing temperature or humidity
pieces.
strength than Kraft papers due to the brittle nature of the clay.
for all forms of die cutting.
high tear strength, high speed rotary cutting and hot-wire cutting. The production of static electricity from the
Type Description Characteristics
Kraft paper
Release coating is applied on one or both
sides of densified Kraft paper
An economical option, suited for general-purpose applications and rotary die cutting. Not for kiss cutting.
conditions.
Board
Made of paper with a heavy weight and a
caliper of 12-14 mils
The large caliper maximizes kiss-cutting performance and allows easy removal of small parts and waste
Clay-coated paper Paper coated on one or both sides with clay
Provides high temperature performance and better humidity resistance (dimensional stability). Lower tear
Poly-coated paper
Base paper with extruded polyethylene or
polypropylene film on one or both sides and
sometimes coated with a silicone release agent
A versatile option. Resistant to tearing and to wrinkling or "cockling" when exposed to humidity. Can be used
Film
Produced from low or high density
polyethylene, polypropylene, and polyester
Most expensive liner. Provides excellent humidity resistance (dimension stability). Liner will provide the
smoothest coating of adhesive possible. Do not produce "paper dust" during slitting and conversion. Offers
liner is a concern.
Table 3: Types of Liners Commonly Employed in PSA Products

Types of Release Coatings
Many types of release coatings have been used on liners over the years.
The first release coatings for pressure sensitive tapes were polymers such as shellac, starch, casein, and
nitrocellulose.
These older release coatings did not exhibit good release characteristics but functioned primarily by
preventing the adhesive from penetrating the pores of the liner.
In more recent times, PVC resin, polyvinyl butyral, polyvinyl alcohol, vinyl acetate copolymers, and
acrylic resins have all been applied as release coatings for PSA products. Several of the more widely
used release coatings are summarized in Table 4.
When a liner consists of a release coating applied to a substrate (e.g., Kraft liners), the release coating is
applied over the substrate from a dilute solution or dispersions.
Many modern release liner manufacturers now use UV curing coatings, which have no VOCs or
environmental constraints.
Light coatings are generally sufficient.

coating. Could effect performance of the pressure sensitive adhesive if the coating attaches to
release characteristics. Generally copolymer of alkyl acrylate and acrylic acid, nitrocellulose,
are attached to C14 -C18 fatty acids.
subst ra tes. Use d si m i l arly t o t he c hrom i um c om pl e xes.
Type C h a r a c t e r i s t i c s
Si l i c one s
Most widely used release coating of PSA products. Exhibit easy release at low peel rates. Can
be applied as solventless, solvent borne, or water borne systems. Low surface energy makes
silicone coatings ideal for all types of liners including polymeric film.
Wa x e s
Generally used as additive to film forming polymer coatings to improve release.
Effectiveness is based on their incompatibility and ability to migrate to the surface of the
the adhesive.
Long chain branched
p o l ym e r s
Polymers with long side chains are waxy compound exhibiting good coating performance and
and vinyl chloride.
Polyvinyl carbamates Generally used as a release agent on film backings (e.g., cellophane film).
C h r o m i u m c o m p l e x e s
Provides good release characteristics and water repellenc y to paper. Chromium complexes
Fl uoroc a rbon
c o p o l ym e r s
Have very low surface tension to provide for easy release characteristics. Expensive.
Am i ne s
Long chain alkyl substituted amines have good release properties especially on paper
Tabl e 4: Com m onl y Appl i e d Re l e a se Coa t i ngs for Pre ssure Se nsi t i ve Produc t s

Silicone Chemistry
Siloxane polymers have many attractive attributes including low surface energy, low glass transition
temperature, thermal stability, and a low viscosity at relatively high molecular weights.
Silicone polymers used for release liner coatings start with polydimethylsiloxane (PDMS) backbone
base polymers. Base polymers have pendant or end-blocked functionalities.
In thermally-cured systems, hydroxyl groups (condensation reaction, Figure 1) or vinyl groups
(addition reaction, Figure 2) react with silane functionalized PDMS in the presence of heat and an
organometallic catalyst (Sn, Pt, or Rh).
These reactions may take place in the presence or absence
of solvents.
In solvent-based systems,
common solvents include
heptane, methyl ethyl ketone, toluene, and
isopropanol.
Full cure is achieved in a few seconds up to a few days.

Radiation-cured silicones incorporate two basic
systems: epoxy chemistry with a cationic curing
mechanism (Figure 3)
and
acrylate chemistry with a free radical curing
mechanism (Figure 4).
Both reaction types occur without the need for a heat
source.
UV light can be used as an energy source for
both types of chemistry, while e-beam is restricted to
free radical chemistry.

UV-cured systems with cationic chemistry involve a cycloaliphatic epoxide functionalized PDMS and
require a photo initiator.
Upon irradiation, the cationic photo initiator reveals a strong acid which in turn
initiates a ring opening reaction for polymerization of the epoxides to polyethers.
A diaryliodonium salt with a metal halide counterion is typically used as a photo initiator .
UV light may also be used an energy source for free radical polymerization.
This system involves acrylate functionalized PDMS and also requires the use of a photo initiator.
UV light irradiates the photo initiator to generate free radicals and curing proceeds via free radical
polymerization of the acrylates.
E-beam cured systems involve acrylate functionalized PDMS and proceed via a free radical
polymerization reaction.
E-beam systems provide a higher amount of energy than UV and initiate the
free radical reaction without the need for a radical initiator.

In free radical polymerization of acrylates, the intermediate free radicals may be quenched by oxygen,
so an inert atmosphere is required to ensure the reaction drives to completion.
Cationic polymerization does not require inerting.
However, in cationic polymerization systems cure can be inhibited by moisture, so direct coating onto paper
is a limitation.
Direct-coated applications utilizing cationic chemistry are sometimes possible with prior treatment of the
paper to reduce or eliminate the availability of water.

Why Radiation Instead of Thermal?
The most significant advantage of the use of radiation-cured silicone coatings for release liners is that
complete cure is achieved quickly without the use of heat.
From a liner manufacturer’s perspective, this means that a radiation curing coating machine may be constructed
with a much smaller footprint due to the absence of lengthy ovens needed to provide enough heat for thermally-
cured liner coatings.
Thermally-cured silicone systems also impose limitations and complications in the use of certain
substrates.
The heat required for thermally-cured coatings is more than many filmic substrates can
withstand while maintaining dimensional stability.
Substrates for thermal systems are generally limited to papers, polyester, and some polypropylenes.
There are some tin-cured systems on polyethylene, although low oven temperatures and slow line speeds are
required.

The use of radiation-curable coatings opens the door for the use of a much larger variety of substrates.
These coatings may be applied to nearly any temperature sensitive substrate such as
✓ lower gauge polyester,
✓ polypropylenes,
✓ polyethylene,
✓ polystyrene,
✓ polyvinyl chloride,
✓ nylon,
in addition to the substrates mentioned above.
The heat required in thermal systems also drives moisture out of paper. Moisture control in direct coated
Papers is crucial for lay-flat and dimensional stability.
A certain amount of moisture is required for Control of liner curl and cockling or the development of
bagginess over time due to uneven adsorption of moisture in water-starved sheets.
Implementation of moisturization units and careful tuning of process parameters are often required where
these properties are critical to the end use application of the liner, adding cost and complexity.

Radiation-curable coatings are notably fast and complete cure can be achieved at very fast line speeds
without the need of a catalyst.
Line speeds are typically limited by machine constraints or misting at the coater head, instead of minimum
oven dwell times, as with thermally-cured coatings.
Tin-catalyzed thermally-cured systems sometimes suffer from post cure of several days resulting in dramatic
shifts in release force at the point of use compared to that measured directly off the coater.
Platinum-cured systems typically do not suffer from the post cure seen with tin systems, but may be subject
to catalyst poisoning from plastic additives and cross contamination, which can prevent complete cure.
Because of the absence of a catalyst, UV acrylate systems are far less sensitive to contamination.
Electron beam vs Ultraviolet Radiation
E-beam
Radiation curing technology for silicone coatings began with E-beam as an energy source, starting in the
1980s.
E-beam curable silicone systems consist of an acrylate functionalized siloxane polymer backbone cured by
free radical polymerization (Figure 4

Energy needed for this reaction is provided from an electron accelerator.
Free radical polymerization proceeds extremely fast and does not require the addition of a photo initiator
because of the amount of energy provided by the electron beam.
E-beam cured coatings can provide a wide range of release force, and very tight release forces can be
achieved (400+ g/in-width, measured with rubber-based Tesa 4651 test tape).
One disadvantage of E-beam coatings
is their propensity to develop increasing adhesion to some aggressive acrylic adhesives over time.
For this reason, E-beam coatings are generally recommended for rubber-based adhesives and should be
evaluated on a case-by-case basis for acrylic adhesives.

Ultraviolet
Since the inception of radiation curable coatings, UV has gradually taken a strong lead as the go-to
method of commercialized silicone coating liners cured without heat.
Because UV light can be used as the energy source for both types of curing chemistries (Figure 3 and Figure
4), UV curable systems can realize most of the benefits of e-beam cured coatings with few disadvantages.
The notable difference in these 2 systems is the requirement of a photo initiator when UV light is used.
However, a strong advantage of UV-cured coatings is that they are compatible with a wide variety of
adhesives and are not restricted from use with acrylic adhesives.
Traditionally, mercury vapor lamps have been used as a UV light source. Mercury lamps emit a broad
spectrum of light without the ability for tuning to narrower wavelength bands.
For the purposes of free radical initiation, mercury lamps yield 70-75% of radiation in non-useful
wavelengths, including enough high energy infrared light to produce a significant amount of heat.

Recent work has resulted in the development of light emitting diodes as UV light sources.
LED light sources benefit from the ability to fine tune their emission spectrum; typically in a 20-40 nm range.
This concentration of energy output allows for more efficient machine operation by delivering a sufficient
dose of radiation at the target wavelength without the emission of radiation at wavelengths not needed, which
in turn requires less power input.
A notable benefit of this is the much cooler operating temperatures. LEDs also benefit
from a much longer lifetime than mercury vapor lamps (20,000 h vs. 2,000 h).

Summary
Radiation-cured silicone coatings offer several advantages over their thermally-cured counterparts.
These types of chemistry provide efficient, fast cure and allow for the use of many substrates not
available with the use of traditional thermally-cured coatings.

Films made from a variety of low surface energy polymers have also been found to be useful as backings as
well as release liners.
For example, oriented polypropylene film tape can be constructed by corona discharge treating one side to
which the adhesive is applied.
Asufficiently low release level is obtained on the other side without release coating if a polar acrylic is used.
However, if a styrene block copolymer is used a release coating may be required.
Other film release liners include polyethylene, polypropylene, fluorocarbon polymers, and polyester.

Silicones are, by far, the most widely used materials for pressure sensitive release applications.
They provide uniform, thin coatings that exhibit easy release at low peel rates.
The good release characteristics of silicone are related to its low surface energy (22-24 dyne/cm) compared
to most organic adhesives (40-50 dynes/cm).
This provides sufficient adhesion between the silicone and the PSA to keep the adhesive in place, yet not
enough adhesion to prevent easy parting of the liner from the PSA during application.

The three basic types of silicone release coatings used in the PSA industry can be classified by the form in
which they are applied to the liner: solvent borne, water borne, and solvent-free. These are characterized in
Table 5.
The major component of a cured silicone release coating is polydimethylsiloxane.
Crosslinking of the silicone coating is necessary for it to resist penetration by the PSA. Without crosslinking,
the adhesive could diffuse into the flexible siloxane polymer chain.
Crosslinking also provides a coating with the physical characteristics required of a release liner (strength,
elongation, etc.).
Type Solvent Cure Rate Release Comments
Fast to slow Easy to tight Dull to glossy, good anchorage
Medium to slow Easy to medium Some coatings require post cure
Fast to medium Easy to tight Glossy coatings, premium release
Table 5: Comparison of Silicone Release Coating Systems

UV and EB curing of silicone release coatings seem to be the major driver in release coatings today.
This is due to their very fast cure, low energy consumption, and ability to be easily modified to meet
specific release requirements.
These materials can be applied to both paper and polymeric film based liners.
A significant benefit of UV and EB cured release coatings is that significant heat is not required for cure
and as a result they can be applied to heat sensitive substrates such as plastic film.
Significant activity has occurred in the thermally cured silicone release segment of this market.
The high cost of platinum catalysts have been addressed by Dow Corning and Wacker who has developed
proprietary polymer and crosslinkers that enable lower platinum usage.
These new products also feature lower temperature cures and higher speed coating application.
Solvent less silicone release coatings are the most important type.
These have been developed to address environmental pollution / health problems, solvent cost, and
productivity issues related to solvent and water borne systems.
This class of coatings includes thermal, ultraviolet (UV), and electron beam (EB) curing.

Cationic curing can take place without an inert atmosphere in the coating unit. However, the coating will
undergo post curing after it leaves the UV unit.
Clay coated papers cannot be used as liners with cationic cured coatings as they produce poisoning effects
from the alkaline components.
The curing of these coating is also negatively affected by high humidity conditions.
Each of these systems has its advantages and disadvantages.
The radical polymerization of the acrylate groups is much faster than the cationic polymerization, so that
faster processing speeds are possible.
Their main disadvantage is the need to use nitrogen blanketing to eliminate the presence of oxygen, which
will terminate the polymerization process.
There are two UV curable silicone release systems widely used:
Silicone acrylate (cures by a free radical mechanism)
Epoxy silicone (cures in the presence of cationic initiators).

EB curing is the subject of much activity since it provides certain advantages that offset the higher cost of
the curing equipment.
UV radiation is usually associated with some heat energy output, but EB is a completely room temperature
process that does not require a post cure.
Electron beam curing also provides improved anchorage of the release coating to many different substrates.
With EB curing there is no need to cure the coatings under an inert atmosphere.
The intensity of EB radiation, however, may be so strong that it could affect the base liner properties.
Similar to UV curing, EB curing has achieved commercial status.
The types of coatings that are used with EB curing processes are acrylate functional, epoxy functional, or
thiolene based.
Acrylate materials are most widely used and provide very fast cure at dosages in the region of 1-5
Megarads.

For Self ive
A y
WaterWater
Solvent less
SolventSolvent
Based onBased on
Silicone
The Types and the Chemistry
Release Coating
Adhes Tapes
ver crucial component

Platinum UV
Cure
Platinum UV
Cure
Platinum Cure
Platinum CureNow Outdated / Banned Platinum CureTin Cure
WaterSolvent lessSolvent
Based on
Silicone

Coating Substrate for
Transfer Coating
Release Liner Double side
Release Liner Single side Back sizing / Controlled
Release on backside
ApplicationsApplications
Silicone

Recommended for Single
Generally not Suitable /
sided Tapes requiring
Higher Self Adhesion Force
Not Suitable / Recommended
for Transfer Coating
LimitationsLimitations
Silicone

A
Adhesive
Release Coating is Possible
inline with Adhesive Coating
Faster Coating speeds , do not
require curing
Recommended for Reverse
Printed Tapes / Printing is
possible after Release coat
100% Transfer of Coated Recommended for Self
Adhesive Tapes with higher
SelfAdhesion Values
Very Low Release Values Relatively High Release Force
Advantagesdvantages
Silicone

Silicone
More about Silicone Coating
NOW

he age
Transfer coating allows us to produce Adhesive coated with almost any substrate ,
very Thin or very Thick , Very delicate to very rigid , extremely porous to absolutely
non porous
Let us see how this is possible ?
Transfer Coating is a method of Transferring Dry Adhesive Film from Silicone liner
to the Main Substrate.
What is Transfer Coating ?
Silicone coated Liner : Paper or Film
Allows Transfer Coating
T MainAdvant of Silicone based Release Coating

Slot Die
Floating Knife
Comma
Gravure / Gravure + Myer Bar
Sketch of Coating and Lamination Machine suitable for
Transfer Coating by

is
he
1 st
Unwind
Coating
Zone
2 ed
Unwind
Rewind
GRAVURE COATING & LAMINATION
Have a look at the most common four methods of Transfer Coating Below
What common in all these methods ?
What is t special advantage of these methods ?

is
he
Unwind
1 stCoating
Zone
2 ed
Unwind
Rewind
COMMA COATING AND LAMINATION

is
he
Zone
Coating 2 ed
Unwind
Rewind1 st
Unwind
FLOATING KNIFECOATING AND LAMINATION

is
he
SLOT DIE AHESIVE COATING & LAMINATION
Coating
Zone
1 st
Unwind
Rewind 2 ed
Unwind

The on
he
e ethod
Hence the Substrate is not exposed to the wetAdhesive at all.
The Substrate comes in contact with theAdhesive Dry Film only
at the Lamination Zone .
What are th Advantages of this m ?
T Substrate to be converted into aAdhesive Coated Product is
mounted at Unwind Station no. 2
Comm factor is that
The coating is done on Silicone coated Liner : Mounted at Unwind
station no. 1
Yes ,
you are Right

the od
he
Minimum snaps or wastage
Very ThickDelicateFlexibleRigid
Ability to handle number of Main
Substrate
Thick FoamNon Woven /
Film
FabricsMetal Foil
Very Quick Change overs , in case of
change in t Main Substrate
Uniform Coating Nip : Hence Uniform
Coating Thickness of Adhesive
Advantages of this meth ? are

Non
no
Silicone coatings
w
Let us see more about
Non Silicone

What is it
s
wound Adhesive Tape
Transparent
Printed
Electrical
Yellow
is called a Adhesion to self
Packaging
BOPP
Brown
PET
Insulation
The Tape adheres to its own backside
and hence a force is required to pull or
peel of the tape from the roll. This force
BOPP
Packaging
BOPP
Packaging
All
These
Tape
Are
self Wound
&
they need
a very
Important
Property
inbuilt
“ Called as
Adhesion
to
self ”
This is a very Important property especially of a Single side or self
Adhesion to Self
?

our
s
e
Non Silicone Coating on Backside
Silicon Coating on Backside
No Coating on Backside
We will study
3 variation now as follows
Now let us try and understand
How
coating on backside of the substrate
can change the behavi of self wound Tape

iations
s
The Tape adheres to its own backside and hence a force is required to pull or peel of the tape
from the roll. This force is called a Adhesion to self . In case of Packing or Insulation Tapes
this force will be almost 75-80% of the peel adhesion strength of the tape .for example if the
peel strength is say 650-700 grams/ 25 mm width ,then
The adhesion to self will be nearly 500 to 550 grams/ 25 mm
& this forc unwin p off necessary for some tapes like above
No Coating on Backside
We will study
3 var now as follows

iations
ne
the
e tape ill t g on
Now imagine the backside of the substrate is coated with Silicone ?
What will be Adhesion to self .
Suppose the peel strength is say 650-700 grams/ 25 mm width ,then
The adhesion to self , in this case will drop down nearly 25 to 50 grams/ 25 mm
& so what will be the inbuilt problem here ?
Th w star unwindin it own the moment the tape end is hold . This could cause lots of
problems on the assembly line , packaging line , because you need certain amount of resistance to
unwind or peel off
Silico Coating on Backside
We will study

iations
the
e ape ill not g on
Now imagine the backside of the substrate is coated with non Silicone ?
What will be Adhesion to self .
Suppose the peel strength is say 650-700 grams/ 25 mm width ,then
The adhesion to self , in this case will drop down nearly 150 to 250 grams/ 25 mm
& so what will be the inbuilt advantage here ?
Th t w unwindin it own the moment the tape end is hold . But at the same time the tape
peel off will be much more easier than the first case , where there was no coating at all on the back
side .
Non Silicone Coating on Backside
We will study

They are also used domestically for bake ware, ice cube trays, and easily cleaned surfaces. Abhesive coatings
are employed for deicing surfaces such as airplane wings, ship structures, and windshields. Abhesives are
formulated into anti-graffiti and "self-cleaning" paint coatings. Abhesives are also used to prevent
microorganism growth and salt formation on marine or outdoor seacoast structures. In the medical industry,
abhesive's are used for providing non-stick and bio-resistant surfaces for medical devices such as catheters.
The applications for abhesive's are nearly as numerous and as commercially important as they are for
adhesives. The most recognizable abhesive's are used as mold release surfaces and as liners for pressure
sensitive tapes and labels. However, abhesive's are also used to protect general plastic processing equipment
such as used for casting, extrusion, laminating, and molding.
Introduction
"Abhesives" are films or coatings that are used to prevent or greatly decrease adhesion. An abherend is a
surface that discourages adhesion. Abhesive materials are also often referred to as mold-release agents, non-
stick surface coatings, parting agents, or antistick agents. Abhesion is exactly the opposite of adhesion, and
the requirements for a good abhesive are reverse that which is necessary for a good adhesive to function.

This is an important concept for the polymer scientist or engineer since manufacturers of polymeric products
frequently tackle release problems and also because an efficient and profitable solution to a release problem is
often a polymer.
However, the main purpose of this review will be to explain the material and surface science fundamentals
required for an abhesive to function.
A variety of materials and processes have been developed to provide surfaces that function as abhesive's.
Many of these will be described in this article, and several new abhesive's will be discussed.

Therefore, surface treatments that enhance adhesion do so by removing weak boundary
layers, changing surface topography, changing the chemical nature of the surfaces, and
modifying the physical structure of the surface.
Important criteria in adhesion include the surface topology, surface tension and energy,
wetting, and thermodynamic work of adhesion.
Adhesion occurs through a combination of the following mechanisms: mechanical
interlocking, interdiffusion, adsorption (surface reaction), and electrostatic attraction
In order to understand how abhesive's work, one must first understand the mechanism of
adhesion and the factors that affect it.
Mechanisms Abhesion

of
Since many of the factors causing adhesion are of a chemical nature, a good abhesive
must also be chemically inert toward the two materials whose adhesion are to be
prevented.
o A barrier to mechanical interlocking
o Prevention of interdiffusion
o Poor adsorption and surface reaction
o Low surface tension and thermodynamic work of separation
o Limited or no electrostatic attraction
o Incorporation of a weak boundary layer.
Abhesion requires just the opposite. For maximum adhesion, or resistance to adhesion,
the surface should exhibit the following characteristics.
Mechanisms Abhesion

Sacrificial Abherends require only that the abhesive material fill the pores or smooth-out the roughness of a
surface (e.g., an inert powder on a rough metal surface). Sacrificial Abherends generally remain attached to
both surfaces after release, and they must be applied to a surface every time it is to be protected. On the
other hand, permanent Abherends will last through many cycles of release.
Permanent Abherends require that the abhesive material have good spreading tendency on the material to be
protected and a surface that exhibits poor spreading tendency to the material which adhesion is to be
prevented. The permanent abherend must be a good coating material (i.e., easily applied, uniformly spread
over the surface to be protected, and relatively permanent during all expected processes).
Thus, there are several ways in which abhesive's can be classified. The most popular classifications are
permanent (corresponding to 1 above) and sacrificial (corresponding to 2 above). Several examples of each
are readily evident in the household environment. The coating on a non-stick baking pan is an example of
permanent abherend. Flour, grease, or oil used for non-stick baking are examples of sacrificial Abherends.
Abhesion, therefore, occurs via one of two primary modes:
(1) prevention of adhesion to the abhesive coating layer, or
(2) an easily separable coating or cohesively weak boundary layer.

Another factor to be considered in choosing an abhesive is volatility. Water would be a good abhesive, but
because it vaporizes at relatively low temperatures, water could not be used as a mold release in many high
temperature applications.
An important factor in choosing an abhesive is temperature dependence. A material could act as an abhesive
at room temperature and as an adhesive at elevated temperatures. Thermoplastic polyethylene coatings are
good examples of this. Polyethylene is relatively inert with a low surface energy, non-stick surface in its
solid state, but it has good adhesive properties in the molten state.

The term is the interfacial tension of the solid material in equilibrium with a fluid vapor, is the surface
tension of the fluid material in equilibrium with its vapor, and is the interfacial tension between the solid
and liquid materials. Complete, spontaneous wetting occurs when = 0 deg, or when the material spreads
uniformly over a substrate to form a thin sheet.Acontact angle of 0 deg occurs with a pure water droplet on
a clean, glass slide. Therefore, for complete spontaneous wetting, cosine > 1.0 or when:
Wetting can be determined by contact angle measurements. It is governed by the Young equation which
relates the equilibrium contact angle, , made by the wetting component on the substrate to the appropriate
interfacial tensions:
Two solid materials generally do not adhere to each other because wetting does not take place and there is
no penetration or interdiffusion of one material into the other. When wetting is minimal, the secondary van
der Walls bond forces that provide the majority of molecular adhesion are not large, the work of adhesion is
minimal, and the surface has the properties of a good abherend.
Theory

A simple view of the relationship of wetting and adhesion is provided by Figure 1. Here the contact angle of
a drop of a liquid on a surface of different critical surface tension is shown. The expected bond strengths
would increase as the contact angle decreases. Therefore, best abhesive scenario is when the contact angle is
greatest.
Thus, most common adhesive liquids readily wet clean metal surfaces ( > 100 dyne/cm), ceramic surfaces,
and many high-energy polymeric surfaces. However, common adhesives do not wet low energy surfaces
such as polyethylene and fluorocarbons. The fact that good wetting requires the adhesive to have a lower
surface tension than the substrate explains why organic adhesives, such as epoxies ( about 40 dyne/cm),
have excellent adhesion to metals, but offer weak adhesion on many untreated polymeric substrates, such as
polyethylene, polypropylene, and the fluorocarbons ( < 30 dyne/cm).
Wetting is favored when the substrate surface tension, , or its critical surface energy, , is high, and the
surface tension of the wetting liquid, , is low (i.e., wetting is favored when > ). Low energy polymers,
therefore, easily wet high-energy substrates such as metals. Conversely, polymeric coatings and polymeric
substrates having low surface energies will not be readily wet by other materials and are useful for
applications requiring nonstick, passive surfaces.
Theory

end
Many commercial abhesive's are of proprietary composition. These products can be formulations of more than
one type of abhesive with modifiers or additives, such as emulsifiers, biocides, solvents, etc., incorporated into
the final product.
There are many materials that can be used as abhesive's. These are generally classified chemically as shown in
Table 1. They can be supplied in many different forms such as fluids, waxes, greases, emulsions, dry films,
and solid powders.
Types ofAbher Materials

Two solid materials generally do not adhere to each other because wetting does not take place and there is
no penetration or interdiffusion of one material into the other.
When wetting is minimal, the secondary van der Walls bond forces that provide the majority of molecular
adhesion are not large, the work of adhesion is
Theory
Water would be a good abhesive, but because it vaporizes at relatively low temperatures, water could not be
used as a mold release in many high temperature applications.
Another factor to be considered in choosing an abhesive is volatility.
Polyethylene is relatively inert with a low surface energy, non-stick surface in its solid state, but it has good
adhesive properties in the molten state.
A material could act as an abhesive at room temperature and as an adhesive at elevated temperatures.
Thermoplastic polyethylene coatings are good examples of this.
An important factor in choosing an abhesive is temperature dependence.

oil
Chemical Class Chemical Subdivision Specific Examples
Waxes
Petroleum waxes Paraffin wax, microcrystalline wax
Vegetable waxes Carnaubawax
Animal waxes Lanolin
Synthetic waxes Polyethylene wax
Fatty acid metal soaps
Metal stearates Magnesium stearate, zinc stearate
Others Calcium ricinoleate
Long chain alkyl derivatives
Fatty ester synthetic waxes
Diethylene glycol monostearate, hydrogenated castor
Fatty acids Stearic acid, oleic acid
Fatty amides Ethylenebis(stearamide), oleyl palmitamide
Natural products
Cellulose derivatives Cellophane, cellulose acetate
Polysaccharides Sodium alginate
Inorganic materials
Silicates Talc
Clay Kaolin, mica
Other Silica, graphite
Silicones Polydimethylsiloxane, polyalkylmethylsiloxane
Fluorocarbons Polytetrafluoroethylene
Synthetic polymers Other fluoropolymers Poly(fluoroacrylates), poly(fluoroethers)
Polyolefins Polyethylene, polypropylene
Other Polyvinyl alcohol
Fluorinated compounds Fluorinated fatty acids and alcohols Perfluorolauric acid
Table 1: Chemical Classification of Abhesives 2

This is an added advantage while processing further to adhesive coating. Non silicones generally do not
require any Thermal curing , and hence can be coated at lower temperatures. These
coatings are therefore coat able inline with adhesive coating.
This does not mean that non Silicone coatings is a answer to all self wound tapes. While choosing a
most suitable release coat , one has to take into consideration , The peel strength values of the product ,
as well as the Tensile strength and percentage of elongation of the substrate.
Secondly , all most all Silicone coatings are thermally cured at processing temperature above 90 deg C.
Most importantly , it is really impossible to coat and cure silicone coatings inline with adhesive coating.
The only exception to this could be UV cured silicones , which cured at room temperature. However
this option is relatively ruled out owing to the cost of manufacture. They are very expensive.
Now on the other hand , Non silicone coatings are meant for controlled release with release values of 50
grams to 200 grams depending upon the requirement , as well as the backing substrate.
Silicone release coated film or paper will provide a too easy release while unwinding a self wound
Adhesive tape. Many a times this could be a unwanted property , considering the further conversion or
application methods.
Let us now compare the Release properties of Silicone based Coating and Non Silicone based.
Silicone based release coatings are meant for , very easy release , or the release values as low as , 0 to
say 70 grams/25 mm width. In other words a

s lease
There are many materials that can be used as abhesive's. These are generally classified chemically as
shown in Table1.
They can be supplied in many different forms such as fluids, waxes,
greases, emulsions, dry films, and solid powders. Many commercial abhesive's are of proprietary
composition. These products can be formulations of more
than one type of abhesive with modifiers or additives, such as emulsifiers,
Type of Non Silicone Re Coatings
The unwind force or the adhesion to self values should be lower than the tensile strength values for a
particular substrate. This is true in particular , when we consider films like Poly ethylene , PVC , Poly
propylene or various paper as backing substrate. The unwind force higher than the tensile strength , could
result into elongation of films like PE, PVC , PP , and snapping of paper based tapes. The elongation of
films will cause

dyne/cm
Paraffin wax 23
Polyethylene 25-36
Polymethylsiloxane film 24
Polyvinyl fluoride 28
Polytetrafluoroethylene 18.5
Perfluorolauric acid monolayer 6
Petroleum lubricating oil 29
Table 2: Surface Tensions of VariousAbherend Substrates
Silicone oil 21
Fluoroethylene propylene 16
Polyvinylidene fluoride 25
Polymethylsiloxane fluid 20
Polypropylene 29-34
Fatty acid monolayer 24
Abherend
Surface Tension,
Carnauba wax 38
References:
1. Pocius, A. V., Chapter 6, Adhesion and Adhesive Technology, Hanser Publishers, New York, 1997.
2. Encyclopedia of Polymer Science and Engineering, Volume 14, Second Edition, John Wiley & Sons, New York,
1988.
3. "Abherends", Adhesion and Bonding, N.M. Bikales, ed., John Wiley & Sons, New York, 1971.

Now let’s have a look at the most common method of Non Silicone Release Coating
What is special advantage of these methods ?
SLOT DIE CASTING
SLOT DIE AHESIVE COATING & LAMINATION
KISS ROLL + MYER COATING &
LAMINATION
FLOATING KNIFE COATING AND LAMINATION
COMMA COATING AND LAMINATIONGRAVURE COATING & LAMINATION

a
ve in olvents ,
olve
,Do not dissol S water or Polymers
& hence the same do not get transferred to any other
The coated Adhesive forms a firm bond with the liner ,
substrate that come in contact after applying Nip
Pressure
The coated Adhesive forms a Film , & the same
gets transferred to any other substrate that come
in contact after applying Nip Pressure
The coating once fully cured
used in the Adhesive Formulation
The coating never cures. Hence the solvent is just
evaporated and the solids in the solution remain on the
surface. The solids on the surface diss back in the
Solvents or Polymers used in theAdhesive
Formulation
Based on Crosslinking Reaction ( Thermal
Process )
Based on simple drying & No Cross linking
Silicone
Here is valid reason for the same
Why Non Silicone Coated liner is not suitable for Transfer Coating ?

um
Able to coat in line , along with adhesive.
cost effective
Should not interfere with the PS Adhesive , or lower the peel adhesion , due to
unwanted pick up of the release coating by adhesive
very low coat weight
Non curing type , no chemical reaction or Cross linking is involved.
The Non Silicone Release coating should be Quick drying.
Just to s up

The term RC Silicones stands for Radiation Curing Silicones. Release liners made with UV curable silicones
are growing in popularity. For the last 25 years, Evonik has been an expert in UV curable silicone release
systems for the PSA (pressure sensitive adhesive) market.
TEGO® RC Silicones are functional silicone polymers. The functional groups are firmly linked to the
silicone backbone. The products are 100% polymeric materials and contain no solvents.
UV curing requires the addition of a photoinitiator (PI).
There are two UV curable silicone release systems on
the market.
Both are solventless and produce release coatings
without the use of heat, but differ in their underlying
chemistry.

The term RC Silicones stands for Radiation Curing Silicones. Release liners made with UV curable silicones
are growing in popularity. For the last 25 years, Evonik has been an expert in UV curable silicone release
systems for the PSA (pressure sensitive adhesive) market.
TEGO® RC Silicones are functional silicone polymers. The functional groups are firmly linked to the
silicone backbone. The products are 100% polymeric materials and contain no solvents.
The first is based on silicone acrylate and cures via a
free radical mechanism, whilst the other release system
uses epoxy silicones and cures in the presence of a
cationic photo-catalyst.
Evonik offers both free radical and cationic curing
silicones.
This guide has been prepared as an aid for line
supervisors and operators when using RC Silicones
from Evonik. It covers

Mixing of Tego® Rc Silicones
It is best to keep silicones separated from all other coating materials. We recommend that the silicones are
handled in a specially marked, separate area. Always wear personal protective gear: rubber gloves and eye
goggles. In order to avoid spills of silicone on the floor, it is advisable to cover the floor with cardboard or
paper. Note: spilled silicone will make any surface extremely slippery.
The silicones can be measured by their weight or volume. Variations of 1 – 2% silicone in a blend will not
have a big influence on release properties. However, the photoinitiator or photocatalyst should be added
more accurately, e. g. 2.0 +/- 0.2%.
To use RC Silicones, merely blend the appropriate amounts of RC Silicones needed for the desired release.
Add the photoinitiator or photocatalyst as the last component to avoid having this small addition remaining
on the bottom of your bucket and not mixed properly. Mix until the blend is homogeneous in color.
The recommended mixing equipment is depending on the daily volumes used.
For smaller amounts of silicone up to 30 kgs, a drilling machine with a stirrer may be good enough.
For higher volumes we would recommend more professional mixing equipment.

However, there are no special requirements to blend TEGO® RC Silicones since they are easily mixable
with each other.
The different RC products have different colors. The color does not affect the quality of the RC product.
With most recipes, the mixed silicones will turn turbid after blending. The turbidity of
the silicone blend will disappear completely during the UV curing process. The silicone coating will
become transparent.
The turbidity is due to the fact, that some of the RC Silicones are not soluble into each other. They are
miscible,but will separate on standing. The time for separation is dependent on temperature, the silicone
formulation and component ratio.
If the mixture is left undisturbed, separation may occur within a few hours. Therefore, continuous stirring
in the holding tanks at the process line is advisable. After longer stand-still or storage, separated silicone
formulations can be easily remixed.
Also the one-component products as well as the ones containing fillers will separate on standing, although
this needs a much longer time. Therefore, these products should be stirred prior to use. The entire content
of the drum must be stirred well before removing any material. To facilitate this, for these products extra
headspace has been left in the drums. Refer to the corresponding technical data sheet before use of the
product.

Silicones At The Coater Head
Blended silicones should be transported to the coater head in a closed container or tank. We recommend
that the holding tank is located next to the coater head or coating station and is equipped with a stirrer.
This helps to keep the blend mixed during the production period. In order to get air bubbles out of the
silicone blend, the RC Silicones should be circulated between the coater head and holding tank. RC
Silicone blends range in viscosity from 150 to 3000 mPa*s.
Some silicone lines are not equipped to handle viscosities at the upper end of this range. High or
inconsistent coat weights and poor coverage may result. Lowering the viscosity is possible by
heating free radical curing silicone and coating head to 60°C (140°F), which will reduce the viscosity into
the range of 150 to 1000 mPa*s. At 60°C (140°F) or below, there will be no risk of gelation on the coater
head, but the blend will need to remain agitated in order to prevent separation.
To reduce the viscosity further, you can add special reactive UV curable diluents to the free radical
silicones. These diluents should have a good silicone solubility to avoid fast separation. ▸ ▸ ▸
The addition of 5 to 10% dodecyl acrylate or multifunctional acrylates is possible. At this addition level, the
release properties are influenced to a small but noticeable amount only. However the compatibility of these
reactive diluents has to be tested thoroughly with the adhesives of the final application.

Cationic UV silicone formulations often show lower viscosities than comparable silicone acrylates. To
avoid gelation on the coater head, they should not be heated to more than 30°C (85°F). Nevertheless it is
advisable to control the temperature of the coating head in the range between 20 and 30°C (70 to
85°F).
This ensures that the system is not heated up by friction during longer production runs and therefore
enables constant coat weights and uniform coating quality.
Coating Technologies
TEGO® RC Silicones can be applied with all current coating techniques such as 5-roll-coater, offset
gravure and flexo.
5-roll-coater
For high speed coating and the best coating quality, TEGO® RC Silicones can be applied with a smooth
multi roller coating head. Smooth filmic substrates can be siliconized with a silicone coat weight of 0.6 to
0.8 g/m². Rough substrates and paper may require higher silicone coat weights for full coverage.
Offset Gravure Coater
Another common method to apply silicones is offset gravure coating. Smooth filmic substrates can be
siliconized with a silicone coat weight of 0.8 to 1.2 g/m². Again, rough sub strates and paper may need a
slightly higher silicone coating weight for a sufficient surface coverage.

Silicone Coating with smooth application
( Rubber ) Roller
Silicone Coating with worn application (
Rubber ) Roller

Rubber Rollers
The most used roller materials are
✓ EPDM Ethylene-Propylene-Diene Rubber
✓ PUR Polyurethane Rubber
The preferred hardness of the applicator for silicone coating both on paper is Shore A 55 – 75. Softer rollers
have a better recovery compared to harder rollers.
The preferred hardness of the dosage roll of 5-roll-coater heads is Shore A 75 – 80. The cleaning solvents
must be compatible with the rubber roller material you use. If rubber rollers are cleaned with unsuitable
solvents, the rubber will swell. Repeated swelling and shrinking can reduce the diameter and flexibility by
extracting plasticizers and fillers.
The silicone can migrate into the rubber and become sticky, which decreases the life span of the roller and
harms the coating quality. We recommend isopropanol for cleaning. For PUR, however, you should consult
with the manufacturer, which solvents are recommended.
The surface smoothness of the rubber does have a huge influence on coating quality. Both microscope pictures
above (50 times magnification) show silicone coatings made with Shore A 60 applicator EPDM rollers: Left a
coating made with a very smooth roller, right a coating employing a roller with a worn surface.

Silicones And Printing Operations
If you keep the workplace clean and the silicones confined, RC Silicones can be used in the same production
area, even on the same production machinery as printing inks or overprint varnishes.
It is important to avoid silicone contamination of the printing stations or the printing inks.
Silicone contamination can cause print failures, such as pinholes or orange peel effects.
Silicone Coverage and Release Properties
A high-quality silicone coating requires good coverage of the substrate. Uncoated areas, pinholes, and
exposed paper fibers will increase the release value and give poor release stability over time.
In general, we can expect similar release values on all substrates when coating the same release blend.
Air bubbles and foam in the silicone can have an influence on the silicone coverage. This occurs most often
with offset gravure coaters, but also happens with 5-roll coaters. We recommend circulating the silicones
between the holding tank and coater.
This allows the silicones to de aerate. With open pan or 5-roll coaters, it may be useful to discharge these air
bubbles by means of a moving bar. This will avoid the formation of areas with high foam/air bubbles, which
may transfer to the web and cause stripes in the machine direction. ▸ ▸ ▸

Prerequisites For Consistent
Release Values
very good silicone coverage
no interfering additives or migratory (“blooming”)
components in the substrate
good silicone anchorage
same surface roughness of the substrates

5-roll coating system
Extremely slight and precise coating weights are adjustable
Coating weight can be increased or reduced, up to 50%, by changing one cylinder
velocity during machine run
Accurate repeatability through high precision mechanical stops with micro-adjustments
Specifications
Production speed up to 1500m/min (4900ft/min)
Coating width >3000mm possible
High precision cross profile over the whole web width of 2% which is guaranteed by
using a special cylinder technology with a patented deflection compensated impression
roll
Applications
solvent less coatings with 100% solids
thermal curing
UV curing
EB curing

5-roll coating head for solventless, 100% solids coatings.
The coating head is designed for a production speed of up to 1500 m/min.,
with a coating width of 1700 mm and is equipped with a patented roll deflection
compensating system.
This coating method is especially suitable for low coating weights with high quality
requirements in regard to the coverage and coating weight tolerances at high
production speed.
The precision presetting mechanism ensures highest accuracy in repeatability of
production parameters.

5-roll coating system
Extremely low and precise coating weights are adjustable
Coating weight can be increased or decreased, up to 50%,
by changing one-cylinder velocity during machine run
Accurate repeatability through high precision mechanical stops with
micro-adjustments

Roller No Type Speed
R 1 Steel Gravure 1
S 1 Silicone / EPDM
Rubber
10
R 2 Stainless Steel 30
S 2 Silicone / EPDM
Rubber
99
R 3 Stainless Steel 100
Roller Details

Corona Treatment
In-line corona treatment just before siliconizing is always
recommended when using free radical RC Silicones. It can
also help to improve the anchorage of cationic curing
silicones.
Corona treatment forms hydroxyl, carboxyl, and free radical
groups, which are important for anchorage of the RC
Silicones.
Corona treatment also influences the spreading behavior of the silicones. High surface tension is not a guarantee for
good silicone anchorage, rather it is the presence of reactive molecules.
As they disappear quickly, in-line corona treatment is recommended even on high level pre-treated substrates.
With most types of film, in-line corona treatment is recommended for good silicone anchorage. Some PET films
generate very high surface tension, and may need only a little or no in-line treatment. On clear films, a good in-line
corona treatment will help to coat a transparent silicone coating without blemishes.

Flame treatment or extremely high corona treatment of a plastic film can cause low molecular weight
polymers to be formed on the film surface, which can cause anchorage problems.
With rough substrates, such as some clay coated papers, in-line treatment may not be necessary. When
using a pre-treated substrate for single side siliconizing, please make sure to in-line treat and siliconize on
the pre-treated side.
If the non-treated side is silicone coated and wound onto a roll, the silicone coated side of the substrate and
the pretreated side (backside) will be in contact.
This contact will influence the release properties and may result in undesirable release values. This is a
time-dependant effect and may take months to become noticeable.

Corona Treatment For Double-sided
Release Coatings
When coating the second pass of a double-sided release
coating, it is important to make sure that the in-line corona
treatment is not affecting the first silicone coating.
Backside corona treatment can happen with some corona treaters. It is generally caused by a thin layer of
air trapped between the treater roll and the film.
Even a small amount of backside corona treatment can increase the release value of the first pass silicone
coating. Usually, back side treatment does not happen uniformly across the web, thus results in stripes or
spots.
To avoid backside corona treatment, use a corona treater with a lay-on roll, a tight wrap angle, and a clean,
smooth treater roll.
This will help minimize the amount of air being trapped behind the substrate.
When a double-side silicone coating is made with differential release, it is advisable to run the tight release
side first.

UV Power Demand And Cure Speed
Speed of cure is one of the essential points of our RC technology. Due to the cold curing there is little heat
stress to the substrate.
Contrary to the thermal silicone systems, the maximum cure speed does neither depend on the type or the
gauge of the substrate to be coated nor on the silicone coat weight. UV lamps are available with outputs of 80
- 240 W/cm depending on the working width.
Standard medium pressure mercury lamps are widely used in the UV printing industry. These Hg-lamps have
strong emission bands at 250 - 300 nm, which fits best into the absorption spectrum of the commonly used
photo initiators and photocatalysts.
The cure speed of free radical curing silicones is very fast.

Their UV power demand for a complete cure is very low.
One bank of 120 W/cm (300 W/in) lamps can be sufficient to cure at 200 m/min (660 ft/min).
Some of our silicone acrylates cure even much faster.
As the UV bulbs and reflectors have a reduced UV output over time, it is recommended to overdose a little, e.
g. to 160 W/cm (400 W/in) at 200 m/min.
The properties of the release coating will not be affected by a higher UV output applied during the curing
process.
The reaction speed of cationic curing silicones is mainly influenced by the substrate used and by the silicone
formulation and therefore can show strong variations. Hence, cationic curing silicones often require more UV
power than free radical curing silicones.

One bank of UV arc lamps with 120 W/cm should be enough to run line speeds up to 100 m/min.
The shape of the reflector has a major influence on cure speed.
Trials have shown, that a diffused UV light reaches a higher cure speed compared to focused UV light.
Perhaps due to this, we have seen a higher cure speed of both UV silicone systems with standard arc lamps
compared to microwave powered lamps.
The latter always have a focused reflector system.
Best results for free radical curing have been seen with standard medium pressure mercury lamps (so called
H-lamps, not doped). For cationic curing, Gallium doped mercury bulbs, so called D-bulbs, may be of some
advantage.

Suitability Tests
Before using any new silicone formulation, it is recommended to check whether the final product meets all
given requirements.
After coating and curing, it is necessary to check whether the cured silicone has the desired performance.
This includes
o coverage of the silicone coating on the substrate
o full cure of the silicone coating
o silicone anchorage
o compatibility of the release coating against the adhesives via release ageing tests at low and high
temperatures Post-irradiation may cause a property change in the final product.
If the final product is subject to
o electron beam or Gamma irradiation for e. g. sterilization purposes or
o a secondary UV exposure e. g. when curing UV printing
o inks on label stock with a clear face stock, the influence on the final product should be tested.

Changing Between Different RC Blends
If you use different mixtures of RC Silicones of one and the same system (just free-radical or just cationic
curing products), they will not influence each other in curing properties but might have an influence on
release properties.
If you change from a blend of easy release to a blend of tight release, it will be necessary to clean the coater
head carefully.
Small amounts of an easy release blend can reduce the release of a tight release blend considerably.
If you want to produce low and very high release values on the same production line, we recommend
having a separate stirrer, holding tank, and piping for each blend.
The coating order for production should be to coat tight release blends first,
followed by lower release blends.
However, if you are not sure, clean the coater head very carefully in order to
avoid any production failures

Using Tego® Rc Silicones And Other Types Of
Silicones On The Same Machine
Thermal, cationic and free radical silicone systems are not compatible with each other; thus contamination of
one of the other systems will not cure within the main silicone system.
Any residuals of different silicone types left on the coater head, in the holding tank, or in the piping, will remain
uncured in the final silicone coating. This will cause release and subsequent adhesion values to decrease.
Therefore, strictly avoid cross-contamination of different silicone systems as the curing mechanisms are not
compatible with each other.
When changing between silicone systems, it is important to clean all parts very carefully.
There may be silicones, especially in the piping and mixing container, which are not easy to be removed
completely.
Therefore, we recommend having separate silicone mixing
devices available for each silicone system you use.

Silicone acrylate polymerization is initiated by the formation of free radicals, which are formed by UV
irradiation of the photo initiator. Free radicals are chemical species that have a free electron but no charge.
They exist everywhere, including in human bodies.
They react quickly with other free radicals, acrylates, and oxygen. In fact, they react so quickly with oxygen
that they would react with oxygen molecules rather than the acrylate groups of the TEGO® RC
Silicone acrylates, preventing the silicones from curing.
Therefore, it is imperative to ensure as much as possible the absence of air-borne oxygen in the curing
chamber for the reaction in order to achieve the required release characteristics.
The proportion of oxygen remaining on the surface of the substrate as well as at any place in the inerted
chamber should not exceed 50 ppm. The inert gas recommended for the process is nitrogen
as supplied for general technical applications, with a purity level of 99.996 vol. % (quality 4.6 or 5.0).
Residues are hydrocarbons, oxygen, argon and other noble gases.
For the purging process, the residual oxygen should not exceed 10 ppm. The quality of nitrogen should be
discussed well ahead of time with the supplier. An economical way to purchase nitrogen is a liquid nitrogen
tank with an evaporator.
Both, tank and vaporizer normally are rented on a monthly basis from the nitrogen supplier. The nitrogen tank
will be refilled without interrupting production. Nitrogen tanks and evaporators are available in different sizes
and will be adapted to your needs and requirements.

Nitrogen is extremely safe to use. It makes up approximately 80% of the air we breathe (the remaining
20% is oxygen and other gases), and nitrogen is non-toxic.
By using nitrogen as the inerting gas, special exhaust systems and safety precautions are not needed.
However care must be taken to ensure that outside air is circulated in the working environment.
Nitrogen gas is easily available worldwide and inexpensive.
Carbon dioxide (CO2) has been proposed as an inert gas as well. Unlike nitrogen, CO2 is heavier than
air and would concentrate on the production area floor.
Thus, CO2 is not a safe inert gas and is not recommended for this application.

Nitrogen Consumption
Every substrate has a surface boundary layer of air with an oxygen content of approximately 20 vol. %. If
the substrate passes through a purged reaction chamber, the oxygen will be lost by diffusion.
However, since this diffusion process requires too much time, efficient production would be
seriously hampered. It is, therefore, necessary to accelerate the removal of the boundary layer by the use of
suitable nitrogen jets or nozzles.
The chamber under the UV lamps is specially engineered to remove the boundary layer of air that is carried
along by the moving web.
This is accomplished by using a nitrogen “knife” at the front of the chamber. The “knife” provides a
laminar flow of nitrogen, which effectively removes the boundary layer, like a real knife peeling an apple.
The exit side of the chamber is designed to allow the substrate to pass from the chamber and limit the
amount of nitrogen used.
Good sealing of the chamber is essential to minimize the consumption of nitrogen and prevent air (oxygen)
from getting inside the chamber.

The preconditions for effective inerting and minimum inert gas consumption are as follows:
✓ low reaction chamber volume and good reaction chamber
✓ seals (gaskets)
✓ properly sealed quartz plates
✓ effective barrier nozzle at the entry side
✓ uniform nitrogen distribution in the chamber
✓ carefully conceived oxygen monitoring
✓ good exit-side resistance against nitrogen outflow
✓ certain interlocks and further options
The overall nitrogen consumption depends on the width of the line and the number of UV lamps, thus the
length of the UV unit.

In addition, the line speed influences the nitrogen consumption to a great extent.
In a UV line with a working width of 1600 mm, a well-designed inerting unit will work efficiently on
smooth film substrates with the following quantities of nitrogen:
✓ at 100 m/min approx. 45 – 60 m³/h,
✓ at 200 m/min approx. 60 – 80 m³/h
✓ at 300 m/min approx. 75 – 100 m³/h.
On rougher substrates, replacing the air boundary layer is more challenging than on smooth surfaces. In
such cases, the nitrogen consumption for the inerting of paper substrates is expected to be approx. 20 - 50%
higher.

Siliconizing of Plastic Films
The UV radiation necessary to cure RC Silicones will not increase the web temperature during production
significantly.
Typically a temperature increase of only 5°C (10°F) is seen, depending on the material, thickness and the color
of the film. A broad range of plastic films down to 3 µm PET (polyethylene terephthalate) or 15 µm LDPE
(low density polyethylene) can be coated.
When stopping the line, very thin filmic substrates may get hot due to heat released from the quartz glass
windows. This may require the web to run at very low speed through the line until the window is cooled down.
Free radical RC Silicones will cure on all types of substrates.
However, there are additives in some plastic films that may influence the silicone anchorage to the film,
e. g. plasticizer in PVC (polyvinylchloride) or
slip additives and anti-stats in PP (polypropylene) or
PE (polyethylene) films.

Silicone anchorage (rub-off) with RC Silicones usually does not depend on time.
If the anchorage is good right after coating and curing of the silicones, the rub-off will not change. A bad rub-
off usually stays bad.
There are only few exceptions from this rule: In some rare occasions (mainly on PET) the rub-off may improve
within the first 24 hours after coating. On the other hand, on soft PVC, the plasticizers might be migratable and
cause initially good anchorage to get worse over time.
Some migratory (“blooming”) components of the film can travel through the silicone coating and reduce the
release force or give false subsequent adhesion values.
Silicone coated soft PVC therefore often exhibits low subsequent adhesion values, as low as 55%, although the
silicone coating is fully cured.
If anchorage failure is observed on a particular type of film substrate, a special anchorage additive to the
silicone may help.
With the addition of an additive, good silicone anchorage can be achieved even on most PVC substrates. Please
contact your Evonik technical service team for further details.

Pot Life / Remaining Silicone Acrylates
After The Job
The guaranteed pot life of coater-ready free radical curing
silicones is 72 hours, however, they can easily be stored for
much longer time. Without UV light, free radical TEGO® RC
Silicones will not cure. Store the unused portions of the blends
in either lined drums or pails, or plastic containers. Keeping
the following preconditions in mind pot life can be extended
to several months:
• Prevent exposure to UV light. Use containers that prevent
light from getting through to the silicone.
• Do not store the silicone outside where it can be exposed
to direct sunlight or high temperatures.
• Allow air to get to the silicone blend. The oxygen in the air
prevents the silicone from curing. Allow headspace in the
container, and reopen the container from time to time.
• If the blend will be sitting for a long period, you may want
to stir the pail occasionally. This mixes air into the silicone,
which helps prevent curing.
• Clearly identify the container to avoid confusion.

direct sunlight reaching the silicones, they will not cure inside the tubes. Flushing will be required if you will
be using other materials or silicones after running free radical RC Silicones.
Also, silicone acrylates will not cure on the roller for a production break overnight or for the weekend (as
long as it is not exposed to direct sunlight).
The coating remains liquid and does not plug up the cells. Therefore, there will be no build up on the doctor
blade.
However, the silicones will attract dust and dirt from the production environment. Therefore the rollers
should be protected by a kind of cover against dirt and light during stand still. Of course, before longer
stand-still of the coating line and changes between different coating or silicone systems, the coating system
needs to be cleaned thoroughly.
To clean the coater head, drain the silicone from the coater head and piping into the holding tank. Keep the
silicones in the holding tank or put them into a properly identified container
to store it for future use.
The rollers and the silicone pan or closed chamber system should be cleaned by means of disposable towels
and a suitable solvent such as isopropanol. If you need a thorough cleaning,
stronger solvents like white spirit may be used to clean the roller. Please make sure that all regulations for
the use of solvents are observed and that the solvent would not tend to swell the rubber rollers.

Siliconizing Of Paper Substrates
The standard pulping process for the production of common paper grades is alkaline. Since the mechanism
of cationic polymerization is initiated via an acid, most paper substrates are not suitable to be coated with
cationic Curing silicones.
The residual basic components in the paper will react with the acid formed by the photocatalyst, thus The
curing process will not be initiated properly. There are specialty papers manufactured in acidic pulping
processes. These papers can be used with cationic curing silicones providing the same advantages as free
radical curing UV silicones (excellent paper lay-flat, no re humidification).
Polyolefin coated kraft papers (PEK) are coated with a thin layer of plastic film to prevent coatings from
penetrating into the paper fibres. Thus the silicone layer will be in contact to the thin filmic layer on top of
these papers.
Therefore, many PEKs are suitable for cationic siliconizing, too. The polyolefin used for the coating of the
kraft paper should be free of poisoning ingredients for the cationic curing silicones as described before.

However, keeping the following preconditions in mind, even the pot life of cationic curing silicones can be
extended to weeks or even months:
o Prevent exposure to UV light. Use containers that prevent light from getting through to the silicone.
o Store the material below 30°C. Above 30°C polymerization will start resulting in higher viscosities over
time.
o Do not store the silicone outside where it can be exposed to direct sunlight or high temperatures.
o Clearly identify the container to avoid confusion.
To make sure that the silicones are still good to be used, check the viscosity before use, e.g. by means of a Ford
cup flow time measurement.
It is also advisable to run a short trial with the material after longer storage time before starting bigger
production campaigns.
Cleaning Procedure
In contrast to silicone acrylates, epoxy silicones left on the coating equipment, holding tank and pipes must be
removed prior to a lengthy downtime (overnight or weekend breaks) in order to avoid silicone build up.
Therefore it is recommended to clean the whole equipment after every use.

To clean the coater head, drain the silicone from the coater head and piping into the holding tank.
Keep the silicones in the holding tank or put them into a properly identified container.
The silicone blend should be used in the shortest possible time or disposed immediately to avoid
gelation in the holding tank or container.
The rollers and the silicone pan or closed chamber system should be cleaned by means of disposable
towels and a suitable solvent such as isopropanol.
If you need a thorough cleaning, stronger solvents like white spirit may be used to clean the roller.
Please make sure that all regulations for the use of solvents are observed and that the solvent would not
tend to swell the rubber rollers.

Test Methods
QUALITY TESTS
Off machine tests are useful to gather first information on the silicone coating quality right after production.
These tests should be known to the operators and performed frequently,e. g. every jumbo roll:
SMEAR TEST
Rub the silicone surface with your finger. There should be no sign of liquid silicone (= smear).
The smear test is a good indication for the initial cure of cationic curing silicones.
Very slight smear/marks in the silicone layer from the finger might be acceptable and should disappear within
one day after production (post curing).
If smear is observed on free radical curing silicones, there is something wrong in the curing process. Check the
formulation (photo initiator), the UV bulbs and reflectors and the inerting setup.
RUB-OFF TEST
Rub the silicone surface a bit harder with your finger. There should be no rub-off of any dry particles of
silicone. Please note that if you rub hard enough, you may abrade the surface, especially at higher coat
weights. This is not a sign of poor cure or anchorage failure. It is the nature of solventless silicones to
have a more rubber-like behavior.

The anchorage of cationic curing silicones may improve within the first 24 hours after production due to
post curing of the silicone layer in contact with the substrate.
Loop Test
Apply an approximately 20 cm (8 inch) piece of TESA tape 4154 on the cured silicone coating, peel it off
and form a loop by putting the adhesive coated sides together. Opening the loop should require a certain
level of force. In case of a transfer of liquid (uncured) silicone, a considerable reduction of the release
force will be noticed.
Dye Stain Test
A test ink of 1% methylene blue in water is applied for one minute onto the silicone coated surface by
means of a Cobb tester. The blue ink will stain any uncoated areas of the paper.
A certain level of staining may be acceptable. A standard should be defined for each product. This method
works only on paper substrates, not with poly-coated papers or films.

Microscope
To evaluate the silicone coverage on filmic substrates, a coaxial illuminated microscope with a 50x
magnification can be very helpful. A small, portable and battery operated microscope,
can be used on the production line for quality control.

Release And Subsequent Adhesion Test
For a full quality control, release and proper cure tests need to be done. For the European label industry
FINAT test methods FTM 3, 4, 10 (release) and FTM 11 (subsequent adhesion) are often used. The
European tape industry also employs AFERA test methods. In the US and in Asia, there are various ASTM,
TLMI and/or PSTC methods used.
For most of the different test methods we have more detailed information at hand. Please consult with our
technical service teams for assistance.
The subsequent adhesion test (FTM 11) is a good indication if the test tape has been contaminated by liquid
silicone residues, i.e. the test can indicate insufficient curing. Due to the post curing of cationic curing
silicones, subsequent adhesion tests can improve to a great extent within the first day after production.
Therefore, this test is not meaningful in this period of time. After 24 hours, the post curing should finally
have taken place, therefore, the subsequent adhesion will normally show very high (good) numbers. Hence,
this test method is not suitable as quality control test for cationic curing silicones.

Silicone Coat Weight Measurement
The silicone coat weight can be measured with a precision balance (4 decimal points) by washing off the
silicone by means of a solvent. This can only be made on smooth filmic substrates and without corona
treatment.
A more versatile method is the X-ray analysis that gives a signal proportional to the Si-atoms concentration
in the coating.
TEGO® RC Silicones are silicone acrylates or epoxy functional silicones. These organic groups must be
considered when determining the actual silicone coat weight.
Since calibration curves in X-ray units are generally based on 100% polydimethylsiloxanes, The readings
observed must be adjusted to calculate the actual silicone coat weight when using TEGO® RC Silicones.

For this, we have introduced the “RC-Number” which is a measure for the organic content of the silicone
(or silicone blend).
Extremely high Si blank values (as found with clay coated paper and pigmented films) can cause errors in
the coat weight determination.
Very porous papers can absorb silicones which results in lower readings. On thin filmic substrates, make
sure to measure on the silicone coated side. Thin substrates will give readings even on the uncoated side by
scanning through the substrate.
This effect will lead to erroneous readings on double side coated thin films, too.

The quality of a silicone coating is dependent on the conditions of curing. For a good silicone cure, a
sufficient amount of UV light and – for free radical curing - good inerting conditions are required. Using
too much UV light cannot harm the properties of UV silicone systems.
However, using too little UV light, e. g. by reduced transparency of the quartz plates or worn-out UV-
bulbs, can reduce the degree of cure.
This is an example of a maintenance plan for an inert UV unit. This maintenance schedule can be used as a
guideline for operators and the engineering department.
For non-inert UV units, just ignore the recommendations for the maintenance
of the nitrogen supply system.

Silicone release liners, problem solving in
release applications
Introduction
Elkem Silicones is one of the foremost fully integrated silicone manufacturer. Elkem Silicones offers a
comprehensive range of silicone products in the sectors of release coating, textile, engineering
elastomers, healthcare, specialty fluids.
The Silcolease® range is unique in its ability to cover all technologies used in silicone release coatings:
Solventless thermal, Solventless radiation, Emulsion and Solvent.
The problems that are commonly associated with end use of Silcolease® products for release
applications against pressure sensitive adhesives are relatively few in number, but each has many
contributing factors, and many problems are interlinked. This document tries to relate problems to
possible causes or what should be analyzed and gives advice on how to resolve certain problems.

Problems commonly encountered
1. Release Force
2. Bad curing/Migration
3. Change of subsequent adhesion
4. Printability
5. Rub-Off
6. Slip/Friction
7. Die-cutting
8. Bath life/gelling
9. Gloss Problems
11. Blocking
12. Telescoping
13. Laminate curl
14. Emulsion coating problems
10. Oven dust

Release Force
When you have a release force problem, a question to
ask yourself is “Have I got the right combination of raw
materials?”.
You should always keep in mind that
not all silicones and adhesives
give the same release and that the chemical
and
physical nature of your liner substrate can have a
significant impact on the release force.
Stock Face
Adhesive
• Chemical nature
• Coat weight
• Residuals (solvents & component migration)
Silicone
• Polymer type & stoichiometry
• Coat weight and uniformity
• Surface energy & release additives
Paper (or filmic substrate)
• Smoothness
• Porosity
• Stiffness
• pH & residual chemicals

Here is an example of how the release force can change with
silicone polymer type and the speed of peel for any given
adhesive system.
Polymer A giving similar release force at any
speed whilst
Polymer C rapidly increases
with speed of release.

Tight Release
The most fundamental property of the release coating is the requirement of giving suitable
release of the adhesive material that it is protecting. The most common of problems is that
release is not easy enough and this fact can be caused by any number of the conditions that
follow. When we talk about tight release this can be at:
– High speed only
– Low speed only
– All speeds
The following factors have been found to affect the release, and some understanding of these factors will be
essential for each case
to be investigated:

• Silicone Release Layer
– Polymer type
– Uniformity of coating weight
– Surface energy
– Polymer properties
– Smoothness of coating
– Extent of cure
– Crosslink density
– Level of release additive
– Modulus
– Film continuity
– Coating weight
– Cure mechanism
• Adhesive
– Chemical nature
– Coating weight
– Residual solvent level
– Modulus
– Uniformity of coating
weight
– Component migration
– Surface energy
– Cure (crosslinking)
• Substrate
– Type of paper or film
– Calliper consistency
– Surface absorbency
– Porosity
– Surface energy
– Residual chemicals from
manufacturing
– Smoothness
– pH
– Stiffness / Flexibility
– Internal bond strength

• Laminate
– Type of substrate and
face sheet
– Mode of adhesive
application
– Elongation
– Moisture content
balance
• Converting
– Stripping speed
– Stripping angle
– Mode
– Physical
dimension
• Key Paper Properties
– Porosity
– Surface bond strength
– pH
– Internal bond strength
– Smoothness
– Surface absorbency
– Caliper consistency
• Paper Chemicals
– Nature of clay
coating
– Binder chemistry
– Sizing chemistry
– Inhibitors of
platinum
However, many of these factors will be well known when any problem is reported. From the silicone side of
the problem it is essential to establish for any complaint of tight release that the following factors are known:
– Coat weight
– Coverage (pinholes etc....)
– Cure
– Silicone formulation / composition
– Release specificity to particular adhesives
By establishing these basics, it should then be possible to decide on which area to concentrate to explain the
occurrence of tight release.
Only from an understanding of these factors can a solution be proposed with any confidence.

Release instability/Variation in release values
Release values are measured usually after a certain set period of time for either silicone coated papers or
for laminates.
The variation in the release test results (typically FINAT TM 3, 4 & 10) can vary by at least 10% simply
due to experimental error/ variation and the vast number of factors affecting a single measurement.
Obviously each construction will have different parameters with varying degrees of effect, and so there
will be cases of perfect reproducibility and others of huge variation. These variations are unavoidable, in
practice, when measuring a liner release against the most relevant adhesive.
The release values vary to differing degrees, but on certain occasions an increase or reduction of release
values over time (for either the liner alone or the laminate) can cause problems for end applications.

In summary, the main effects are as follows:
• Lock-up - Release values increase with age of laminate
Because of an interaction between “acrylic” adhesives and residual silicone reactive groups, by poor coverage
of silicone, poor silicone cure, poor adhesive drying, silicone or adhesive formulation (migration of tackifier or
resins in adhesive or silicone).
• Drop-off - Release values decrease with age of laminate or paper
– Poor cure of silicone (migration)
– Hydrolysis of excess crosslinker (SiH) groups
– Migration from face or backing substrate (particularly PVC)
– General adhesive degradation
• Reel to reel - Where inconsistent values are seen from one run to another

Too Low Release
o Silicone formulation (e.g. not enough tight RCA for solventless silicone)
o Coat weight too high
o Under-cure (migration)
Zippy Release
– Adhesive problem (drying, formulation, de-wetting…)
Two other common release phenomena can occur, namely Zippy release, otherwise known as a Slip-Stick type
of release, and Peak release, an initial high release force.
Zippy Release
This problem manifests itself mainly in low speed release. The average release can be good but
the release curve is very spiky with a large variation between minimum and maximum values for
a peel test.
The reasons for the zippy release are most commonly very similar to those causing peak release problems but
when compared to a smooth release profile sample, a slow speed zippy release will also show more “zippy”
nature at high speed.

Most common causes are:
– Adhesive modulus, tackifier level and type, etc.
– Pinholes / poor coverage of silicone
Release Force Trend Line
– Chemical or physical interactions
– Backing and face substrates stiffness and strength
– Silicone modulus
Figure 3. Zippy Release Peak Release
Release Force trendline
Usually appears as a very tight release peak at low to medium peeling speed.
Most common causes are :
– Adhesive modulus
– Chemical or physical interactions
– Silicone modulus
– Pinholes/poor coverage of
– Backing and face substrates
– Die-cutting problems silicone stiffness and strength

Bad Curing/Migration
Cure is difficult to define as an absolute factor as the only true effect is whether the laminate
performs adequately under the end use. Some laminate constructions are capable of accepting
a degree of under-cure that in other more sensitive areas would cause total rejection of the
laminate.
• Bad cure (under-cure/smear/migration/extractables) can be most commonly attributed to:
– Machine speed too fast
– Temperature too low (oven air velocities, etc.)
– Coat weight
– Silicone formulation (SiH/SiVi, catalyst level, etc.)
– Substrate - catalyst poisoning
– Age of bath
– Other potential inhibitors of reaction (from machine, raw materials, etc)
– Solvent type & grade - volatility, inhibition (Sulphur free grades)

• Silicone extractables as a measure of cure
A commonly used industry standard but it is important to understand the relevance of this test!
o Non-chemically linked materials are extracted from the cured network by an organic solvent and
measured analytically
o Some silicone materials can be non-chemically linked but form a stable and reliable release
performance
o Extractable species are not necessarily the same thing as migrating species
o Many applications can be unaffected by, or even benefit, from a small amount of migrating silicone:
o Bitumen
o High adhesive coat weight applications
o Zippy release

Change of subsequent adhesion
Sometimes the tack and adhesive performance can be changed after contact with the silicone coated
substrate. The single most important factor is likely to be silicone migration caused by poor curing, but this
is not the only effect.
The most important factors are:
• Low subsequent adhesion
o Under cure of silicone leading to migration
o Other migratory material from backing or top face or from within adhesive itself
o Very rough silicone surface can reduce the smoothness of the adhesive
o Adhesive deterioration with age, atmospheric exposure, moisture content of paper etc...

• Higher subsequent adhesion
o Very smooth silicone surface can improve the smoothness of the adhesive
o There can be adhesive changes due to contact with silicone such as tackifier migration etc...
o Printability Problems
o These can be either on the back of the silicone paper, or on the top face of the laminate.
o Off-line: Silicone under-cure causing migration to the back of the paper (and then potentially on to top
face).
o In-line: Silicone volatiles or misting.
o Substrate problems: penetration of silicone through paper.
o Silicone or other sprays used around printing machines.
o General contamination from a dirty machine, or another source.

Rub-Off
This can be seen immediately or on ageing of the silicone coated substrate:
• Silicone formulation (can be anchorage or adhesive failure, or cohesive failure of the cured silicone):
o Too low crosslinker level
o Wrong crosslinker type
o Poor cure
o Crosslink density of the silicone (more relevant for solventless silicone grades)
• Substrate (will lead to anchorage or adhesive failure):
✓ Too smooth or too low in porosity
✓ Surface energy (films)
✓ Surface inhibition
✓ Lack of adequate corona or other surface treatment
Type of solvent used for dilution
• Aged rub-off can be due to:
o Post curing
o Re-orientation of silicone matrix
o Migration to substrate surface of disruptive materials
o Surface energy changes

Slip/Friction
The lack of friction or slipperiness of the silicone surface can cause production problems further
down the converting line.
These can be controlled to some extent by:
✓ Silicone type: solvent Vs solventless, hardness, etc.
✓ Silicone cure: migrating silicone
✓ Coat weight
✓ Additives
Figure 6. Slip/F

Die Cutting
Not usually a silicone problem but matrix removal may highlight release problems. Soft silicones
can be more easily damaged by die-cutting process and could lead to subsequent problems.
Bath Life/Gelling
Bath life problems can lead to bad release, bad cure, rub-off or general runnability problems caused
by viscosity changes and gelling. The main reasons for bath life problems are:
Silicone formulation (too reactive - high catalyst, high crosslinker or low inhibitor levels)
✓ Solvent type and grade (volatility, inhibiting nature)
✓ Ambient temperature
✓ Inhibitor evaporation or reaction with other material
✓ In emulsions - droplet coalescence leading to micro-gelling
✓ Temperature on the machine generated by coating head or bath handling apparatus
✓ Bath size and storage

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