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Corona treatment on the surface of PET plastic film

2025/6/13 11:30:35     18
After plastic films are printed with patterns through gravure printing, they can beautify the packaging of goods and have a good promotional effect on the products. They have unique advantages that other printing materials cannot compare with. However, the most commonly used polyhydrocarbon film materials (such as PE, PP, modified polyolefins, etc.) are non-polar polymers, and their surface free energy is rather low, only 2.9 to 3.0×10-6J/cm ². Theoretically speaking, if the surface free energy of a certain object is lower than 3.3×10-6J/cm ², then it is almost impossible to hold any known adhesive at present. Therefore, to achieve a certain printing fastness of the ink on the polyolefin surface, it is necessary to increase its surface free energy. According to the current process requirements, it should reach 3.8 to 4.0×10-6J/cm ². So far, the most commonly adopted effective treatment method for plastic films both at home and abroad is the corona treatment method.
Since corona treatment is generally carried out in the air, under the impact conditions of high-voltage and high-frequency electric sparks, on the one hand, the air undergoes ionization, generating various polar groups; On the other hand, the double chains in the polyene molecular structure, especially those on its side chains, are more easily opened. In this way, at the moment of processing, various polar groups undergo grafting reactions with the surface of the polymer, thereby transforming the non-polar surface of the polyolefin into a polar one. It can be said that after halo discharge treatment, the surface of polyolefin, with a thickness of approximately several 10-10m, has transformed into a polar substance completely different from the original polyolefin structure, and the surface free energy has thus been greatly enhanced, reaching 3.8 to 4.0 × 10-6J/cm ² as measured. Meanwhile, high-voltage and high-frequency electric sparks roughen the surface of the film material through impact (when observed with a high-magnification electron microscope, small groove-like unevenness can be seen on the treated surface), thereby enhancing the wettability and contact area of the ink. Thus, the adhesion of the ink on its surface is enhanced through the effects of both chemical and physical aspects.