SURFACE
TREATMENT
The following surface modification techniques are used:
Corona Treatment
This is generally done online through an electric discharge
between an electrode and a metal di-electric. The high voltage
discharge ionizes the air in the gap and modifies the surface
characteristic of the PET film.
Corona – treatment enhances the surface energy from
42 dynes/cm to 54-56 dynes/cm. It oxidizes the film surface
(creating hydroxyl, aldehyde and ester groups) and also modifies
by creating micro-surface roughness. These surface modifications
increase wetting and improves adhesion to inks and adhesives.
However corona treatment has a tendency to decay with time.
It is advisable to use these films within one year of production.
Chemical Treatment
A thin layer of coating normally in Angstroms (Ao) is applied
during the manufacturing process of PET films, between
the longitudinal and transverse direction orientation
process. These coatings are normally applied through
a reverse gravure process.
Chemically Treated PET films have no ageing issues and
provide a significant enhancement of adhesion properties
of films. Various water based co-polymers of Acrylics,
Polyesters, Polyurethanes, Polyvinyl acetates and Polyvinylidene
chlorides are possible for surface treatments.
Polyplex currently produces three different types of chemically
treated polyesters. ( S42, S56 and S60) required for different
inks / adhesives / applications.
S42 exhibits excellent adhesion to solvent base inks and
adhesives.
S56 film provides excellent bonding to both solvent and
water base systems as well as provides enhanced adhesion
to metal.
S60 is used in printing and lamination, where the demand
for laminates is for boiling water resistance, exposure
to oven conditions, microwave and retort conditions.
The comparative chart with respect to plain and corona
treated films is given below:
The information given above is to the best of our knowledge and experience.
Some of the properties can be changed as a result of suppliers’ efforts
to improve upon the quality or production efficiency of the subject. The
information is believed to be true and accurate and is not intended to
violate any statutory condition or right of a third party. Polyplex makes
no warranty, express or implied, as to the fitness of the product for any
specific use or purpose. The above data is purely for reader’s consideration,
investigation and verification and should be read in conjunction with the
conditions for sale or contract.
The above results demonstrate the improved
performance of chemically treated PET films over the Plain
or Corona versions. However, we recommend the user to first
ascertain the suitability of these films with respect to
their application / inks and adhesive systems used, as
different ink resins and solvents demonstrate different
affinity to chemical treatment.
Various “off-line” treatment
of Polyvinylidene chloride ( PVDC), EVOH , PVOH coatings
are also possible to modify the surface characteristics
of PET film and improve barrier properties to water vapor
and oxygen permeability.
Co-extruded films
This is typically a 3-layer structure.
The 2 outer layers are modified to significantly improve
the clarity and gloss of the film, without sacrificing
the surface properties / friction properties of the PET
film. Co-extrusion provides a glossier film thus improving
laminate / pack clarity and appearance.
A thin layer of chemical treatment (applied
similarly as explained earlier) over the outer layer forms
a strong diffusion bond with the substrate film and later
with the ink and adhesive applied during the customer’s
converting process.
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