Download - Non silicone release coating
No : PCP 005 Date : 30 JAN 2014
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Non Silicone Release Coating
A coating applied to the backing , on the
side opposite to the adhesive coated that
provides ease of unwind and prevents
delaminating or tearing. Without a
release coating, the tape would adhere to
its own back and would not unwind.
This coating is also , termed as
Abhesive. The coated abhesive , creates
a surface that discourages adhesion.
Hence the release values ( or the
adhesion to self ) , is suitably controlled.
The applications for abhesives are nearly
as numerous and as commercially
important as they are for adhesives.
A variety of materials and processes
have been developed to provide surfaces
that function as abhesives.
However, the main purpose of this
review will be to explain the material
and surface science fundamentals
required for an abhesive to function.
In order to understand how abhesives
work,
Let us understand the mechanism of
adhesion and the factors that affect it.
Adhesion occurs through a:
mechanical interlocking,
interdiffusion,
adsorption (surface reaction),
and electrostatic attraction.
adhesion depends on
the surface topology,
surface tension and energy,
wetting, and
thermodynamic work of adhesion.
Therefore, surface treatment is
required to enhance adhesion.
This is done by
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removing weak boundary
layers,
changing surface
topography,
changing the chemical
nature of the surfaces, and
modifying the physical
structure of the surface.
Abhesion or Release Coating
requires just the opposite. For
maximum abhesion, or resistance to
adhesion, the surface should exhibit the
following characteristics.
1. A barrier to mechanical interlocking
2. Prevention of inter diffusion
3. Poor adsorption and surface reaction
4. Low surface tension and
thermodynamic work of separation
5. Limited or no electrostatic attraction
6. Incorporation of a weak boundary
layer.
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.
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.
Thus, there are several ways in which
abhesives 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.
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Flour, grease, or oil used for non-stick
baking are examples of sacrificial
abherends.
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).
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.
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.
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.
Theory 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
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minimal, and the surface has the
properties of a good abherend.
Wetting can be determined by contact
angle measurements
Types of Abherend materials There are many materials that can be
used as abhesives. 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. Many commercial abhesives
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.
All abhesive materials are characterized
by providing a low energy surface, and
any liquid placed on such a surface will
exhibit a contact angle, which will be
larger as - increases. When is large
enough, such poor adhesion will occur
that the application of a modest external
stress will cause the bond to separate.
Table 2 gives values of for common
abhesive materials.
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
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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.
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.
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.
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
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unwanted wrinkle formation and
wastage.
Types of Non Silicone Release Coatings
There are many materials that can be
used as abhesives. 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. Many commercial abhesives
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.
Applications of Non Silicone Release
Coating.
Surface protection tapes, based on PE
Film , paper
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Self wound Film tapes based on PET ,
PP, PVC Tapes , Fabric tapes, Foil tapes
Liner less Labels
Heat Transfer Labels.
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Just to sum up
The Non Silicone Release coating
should be
1. Quick drying.
2. Non curing type , no chemical
reaction or Cross linking is involved.
3. very low coat weight
4. Should not interfere with the PS
Adhesive , or lower the peel adhesion
, due to unwanted pick up of the
release coating by adhesive
5. cost effective
6. Able to coat in line , along with
adhesive.