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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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