Surface pretreatment must be performed before printing and compounding of plastic film
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1. Non-polar characteristics of molecular structure: Among the main substrates of plastic film packaging and printing, PE is a non-polar polymer organic compound with a small critical surface tension, strong inertia and poor affinity with ink.
Each unit of PP contains a methyl group, which is a weakly polar group, which is basically a non-polar polymer organic table, but its critical surface tension is greater than PE, so the printing suitability of PP It is better than PE.
2. The surface energy is low. Plastic films such as PE, PP, PET, and pvc have low surface energies. The lower the surface energy of the polymer, the smaller the surface tension, and the less likely it is to be infiltrated by the liquid. Polyolefin plastics have this property. In order to fully infiltrate the ink and the substrate, the surface tension of the substrate should be equal to or greater than the surface tension of the ink. The solution is to pretreat the polyolefin plastic to improve its surface energy.
3, the impact of additives: PE, PP and other resins in the manufacturing process, in order to make the film easy to open, anti-static, anti-aging, anti-ultraviolet radiation and other properties, it is necessary to add a certain amount of additives, such as opening agent, anti- Electrostatic agents, stabilizers, etc., these additives in the resin, in the high-temperature molding process of plastics, the surface migration slowly occurs, forming oil stains, making the film difficult to adhere to other substances. This phenomenon is continuous, so after the surface of the plastic film and the plastic product is pretreated, it is printed immediately, and the longer the standing time, the worse the printing fastness.
4. Strong chemical stability. The PE and PP films not only have a smooth surface, but also are resistant to most of the acid and alkali corrosion, and are insoluble in common solvents at normal temperature, so that the adhesion of the film surface to inks, paints, and the like is poor.
The above situation indicates that the polyolefin plastic film printing must be surface treated before the second processing such as bonding, painting, compounding, electroplating, and bronzing. Gives plastic surface polarity, improves surface condition and performance, and increases interface bonding.