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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.