According to the standard norm which has been established after repeated trials at industries in particular, the surface of a polymer film is well wetted with printing inks, paints, coatings, and adhesives when the surface energy of the films is higher by at least 10 mJ/m2 than that of the coating material. For this reason, the PVC film need to be corona treatment.
Corona discharge is extensively used in industry so as to improve the wetting and adhesion characteristics of the PVC sheet. It is based on electric discharge under a substantially high potential difference between two asymmetric electrodes producing plasma-a highly reactive gas that contains ions, radicals, and also reactive ozone (that decomposes into O2 and active nascent oxygen) which interacts with the surface and increases surface polarity.
The problem becomes most crucial for treated/treated surface combination. It is the oxidation of the surface due to treatment that raises the melting range. If the temperature is raised to that level or the sealing time is increased there is every possibility that the contents within the pack may undergo thermal degradation because of the enhanced heat flux in the sealing region.
After corona treatment, the surface energy of the substrates decreases with time. Ambient unprotected sheets show a greater decrease with time compared to protected sheets (protected from exposure to light, air, moisture and dust). Similarly, unprotected sheets showed a faster increase in the contact angle of ink on the unprotected sheets/surfaces than protected sheets. The spreading coefficient of the ink was influenced in the same manner.
Our transparent PVC film with corona treatment can be used for a long time, as long as it is stored in well-sealed bag at room temperature below 40℃.
