1、 Nonpolar characteristics of molecular structure
Among the main substrates of plastic film packaging and printing, polyethylene (PE) is a non-polar polymer organic compound with low critical surface tension, strong inertia and poor affinity with ink.
Each unit of polypropylene (PP) contains a methyl group, which is a weak polar group, and basically belongs to the non-polar polymer organic cutting, but its critical surface tension is greater than that of polyethylene (PE), so the printability of polypropylene (PP) is better than that of polyethylene (PE).
2、 Low surface energy
The surface energy of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET) and polyvinyl chloride (PVC) are all low.
The lower the surface energy of polymer is, the smaller its surface tension is, and the more difficult it is to be wetted by liquid. Polyolefin plastics have this property.
In order to make the ink and substrate get full infiltration, the surface tension of the substrate should be equal to or greater than that of the ink. The solution is to pretreat polyolefin plastics to improve their surface energy.
3、 Effect of additives
In the manufacturing process of PE, PP and other resins, in order to make the film easy to open, with anti-static, anti-aging, anti-ultraviolet radiation and other properties, it is necessary to add a certain amount of additives, such as opening agent, antistatic agent, stabilizer, etc., these additives in the resin, in the plastic molding process at high temperature, will slowly occur surface migration, forming oil, so that the film is not easy to be with other substances Bonding.
This phenomenon has continuity, so the plastic film and plastic products should be printed immediately after surface pretreatment. The longer the storage time, the worse the printing fastness.
4、 Strong chemical stability
PE and PP films are not only smooth in surface, but also resistant to most acid and alkali corrosion. They are insoluble in common solvents at room temperature, so that the adhesion of film surface to ink and coating is poor.
The above situation shows that the surface treatment must be carried out before the second processing such as bonding, coating, compounding, electroplating and bronzing. The polarity of plastic surface is given, the surface state and properties are improved, and the interfacial adhesion is increased.
To sum up, the plastic film and plastic products should be printed immediately after surface pretreatment. The longer the storage time, the worse the printing fastness.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service.
The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries.
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