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Modification and application of the suitable cleaning process for the surface plasma treatment of plastic printing products

Keywords:

the,surface,of,and,plastic,is,to,treatment,printing

Published on:

26 May,2021

        Plasma surface treatment of plastic printing products, suitable cleaning process modification application:
        Printing is an important way of information transmission and an effective means of beautifying products. The popularization and application of plastic products has promoted the development of plastic printing, and the development of plastic printing has made the application of plastic products more abundant and full. However, not all plastics have good natural printability. Some plastics are affected by ink adhesion due to non-polar molecular structure, low surface tension, or too smooth and stable chemical properties. Collectively referred to as difficult-to-print plastics, which require plasma treatment to be modified by an adaptive cleaning process to improve adhesion.

Plasma treatment

Plasma treatment on the surface of plastic printing products
        Introducing polar groups into the plastic surface, or increasing the surface tension, or increasing the surface roughness and using plasma treatment, this process provides a new way for the printing of difficult-to-print plastics. When considering ink wetting and adhesion, the contact angle is an important parameter. The contact angle is the tangent to the droplet surface from the three-phase boundary point where the liquid contacts the solid and the gas. The angle between the tangent and the solid surface is called the contact angle (the angle on the liquid side).
The adhesion of printing ink is also related to the surface roughness of plastic products. Only when the surface roughness is appropriate can a great adhesion be obtained. The effective bonding area between the roughness of the ink and the plastic increases, and the ink can directly enter the micropores. When the solvent evaporates, the ink resin is mechanically embedded in the pores, forming many tiny mechanical connection points. Firmly "rivet" the ink on the plastic product.
        However, too rough surface is also detrimental to ink adhesion, because too rough surface will make the wettability of the ink worse, fail to fill the micropores, cause adhesion defects, and decrease the adhesion. The critical surface tension means that when the surface of the plastic is completely wetted by the liquid (that is, the contact angle is exactly equal to zero), the surface tension of the liquid is defined as the critical surface tension of the plastic. The surface tension of various measuring liquids is known. If a certain measuring liquid can just completely wet the plastic, its surface tension is the critical surface tension of the plastic.
        After the plasma treatment of the surface of the plastic printing product, the surface roughness, surface wettability and adhesion of the surface molecular structure of the plasma cleaning activation modification have obvious changes. Plasma treatment produces a large number of plasma particles, which directly or indirectly interact with the surface molecules of the plastic to produce polar groups such as carbonyl groups and nitrogen-containing groups on the surface molecular chains. At the same time, the surface molecular chains can be cross-linked and polarized charges can be generated.
        After the plasma treatment of the surface of the plastic printing product, the surface roughness changes and becomes larger with the increase of temperature and processing time. This can be explained as the result of the oxidative degradation of the surface of the polymer and the interaction of the surface dielectric. The oxidative degradation products of molecules physically accumulate in the surface charge center, forming surface protrusions. Extending the treatment time and increasing the treatment temperature will reduce the charge center of the surface dielectric, but increase the strength, so that large and small protrusions are formed on the surface, and the surface roughness changes greatly. The increase in surface tension is mainly the result of the contribution of polar components, which is due to the increase of surface polar molecules due to the oxidation reaction of the plastic surface.

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