After the plastic film is printed with patterns by gravure printing, it can play the role of beautifying the packaging of the goods, has a good publicity effect on the goods, and has unique advantages that are incomparable to other printing materials. However, the most commonly used polyhydrocarbon film materials (PE, PP, modified polyolefin, etc.) are non-polar polymers, and their surface free energy is quite low, only 2.9 ～ 3.0 × 10-6J / cm2. In theory, if the surface free energy of a certain object is lower than 3.3 × 10-6J / cm2, it is almost impossible to pay any of the currently known adhesives. Therefore, in order to obtain a certain printing fastness of the ink on the surface of polyolefin, it is necessary to increase the surface free energy. According to the current process requirements, it should be 3.8 ～ 4.0 × 10-6J / cm2. So far, the most commonly used effective treatment method of plastic film at home and abroad is the corona treatment method.

Since corona treatment is generally carried out in air, under the impact of high-pressure and high-frequency sparks, on the one hand, the air is ionized and various polar groups are generated; on the other hand, the double chain in the molecular structure of polyene , Especially the double chains on its branches are easier to open. In this way, at the moment of treatment, various polar groups have undergone a graft reaction with the surface of the polymer, thereby changing the surface of the polyolefin from a non-polar to a polar surface. It can be said that the surface of the polyolefin after corona discharge treatment has a thickness of about 10-10m that has become a polar substance completely different from the original polyolefin structure. The surface free energy is greatly improved by this test. Up to 3.8 ～ 4.0 * 10-6J / cm2. At the same time, the high-voltage high-frequency sparks roughen the surface of the film material by impact (observation with a high-magnification electron microscope, small groove-like bumps can be seen on the treated surface), thereby improving the ink wettability and contact area. Thereby, the adhesion fastness of the ink on the surface is improved by the action of both chemical and physical aspects.