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CONCEPT OF CORONA TREATMENT

Plastics are non polar have chemically nonporous surfaces with low surface tension
i.e. most plastics are hydrophobic and are not wet table. With plastic films or webs
finding more and more applications in packaging industry the most common problem
encountered by the industry is that of plastic adhesion.
Corona Treatment is a process of high speed oxidation which creates polar
molecules on the film surface. The energy of the corona will break the bonds of the
atomic structure of the substrate. The oxygen rich ozone developed by the corona
discharge will readily fill the open valancies which create a charge surface thus
improving the surface characteristics and twistability.
Over or under corona treating can transfer too much energy to a plastic substrate
which is where a lot of problems could occur when printing or converting of plastic
material.
Under treated material can result in the use of excessive amounts of ink in an effort to
try to make up for the low treatment levels. Over treatment can result in damage to
the material itself as well as problems with the plastic film or plastic tubing blocking
together.
Corona Treatment is used for Blown Films, Cast Films, Sheet Extrusion, Metallic
Substrates, Polyester, Lamination, Aseptic Packaging Materials, Bottles and
moulded plastic surface, Printing and UV Applications.
PRINTING : The pre-treatment on the surface of plastic films to improve adhesion of
inks to various plastic films like HDPE, LDPE, PP, BOPP, Polystyrene, Polyester etc.
LAMINATION: Normally pre-treated films are used for lamination.
COATING: Pre-treatment by Corona Discharge significantly improves adhesion
between the substrate and the film and will ensure that a better bond will result from
subsequent coating operation. In many cases need for primer can be dispended. In
the case of dispersion coating of polyester film for photographic purposes, it is
essential that the pre-treatment takes place immediately before coating, limiting the
need for an adhesive layer

Mould Release Agents : All Plastic tends to shrink and gets adhered on to punch
or in corners and undercut design in the mould. A good mould release agent (MRA)
will allow the material to be removed quickly and effectively. Mould releases can
reduce cycle times, defects and browning of finished product. There different mould
release types available are:
Sacrificial coatings: the coating of MRA has to be applied each time because most
of the MRA comes off on the moulded part when it releases from the tool. Silicones
are typical MRA compounds in this category.
Semi-permanent coatings: the coating, if applied correctly, will last for a number of
releases before requiring to be re-applied or touched up. This type of coating is most
prevalent in today's Plastic industry.
Permanent coatings: Mostly PTFE coating in one of its form is applied to the mould.
Permanent coatings avoid the need for operator application, but may become
damaged by misuse.

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