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1. The process of transforming ordinary polyester into high
shrinkage PET film is called copolymerization. Ordinary
polyester is modified from its crystalline form,
polyethylene terephthalate, to high shrinkage polyester so
it can be used to make a wider range of products. A 70%
shrinkage rate is possible once it has been modified from
its crystalline form to high shrinkage PET film..

2. In the copolymerization process Isophthalic Acid (IPA) is
the most commonly used of the dicarboxylic acids. IPA
transforms the symmetry of the polyester's tight structure,
breaks up the order of the macromolecular chains and
minimizes the force between molecules. This makes
polyester's molecular structure more supple. By adding a
maximum of 20% IPA to the mixture of crystalline and
amorphous polymers the resulting product can be used to
make high shrinkage film.

3. Depending on the product one is trying to manufacture a
diol, usually Cyclohexanedimethanol (CHDM), is the third
element added. When Cyclohexanedimethanol (CHDM) is
added to the copolymerization process the crystallization
rate changes and the melting point of the PETG
copolyester decreases. By increasing the transitional
temperature the copolymers structure becomes
amorphous. High shrinkage polyester, heat sealing film,
high transparent membrane and an array of other
products can be created when the glycol modified PETG
film is mixed with 30% to 40% CHDM.

4. In order to eliminate the 'memory effect' of the PET
molecular chains during the BOPET film production
process, the PET copolymer resin is dried, the extrusions
are melted in an extruder and it is then passed through a
die or cooling drum and the film is cast. Next the cast film
will be stretched horizontally to 3.5 to 4 times its original
size after having been heated. A one-way or two-way
stretch is performed by applying force to the PET
molecular chains. The molecular chains are stretched
along the direction of orientation and quickly cooled. This
quick cooling changes the shape of the molecular
structure of the PET. This makes them “freeze” in their
new orientation. By using this high-elastic deformation
process the film will not be able to return to its original
shape. The possibility of contraction is eliminated by this

5. The amorphous polymer is the main ingredient of the PET
film. Thus modified amorphous PET (APET or PETG) is
preferred over the crystalline version because it allows for
far more shrinkage. Increasing the amorphous portion of
the PET film increases the amount of shrinkage that is
possible. With the amorphous polymer shrinkage of up to
70% is possible while the shrinkage rate of crystalline
polyester film is only 30%.

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