Views:101 Author:Site Editor Publish Time: 2021-10-01 Origin:Site
In packaging offset printing, many products require post-press processing. Among the many processes of post-press surface treatment is the coating process. However, many quality problems will be encountered during processing, and many of them are related to packaging offset printing. We say that the effect of the film is not only related to the material of the film and the process method of the film, but there are many reasons related to printing. In order to ensure the quality of film processing, we must analyze those quality-related factors, find out the reasons, and solve quality problems. Today, I will take you to understand the impact of offset printing.
The factors related to packaging and printing generally include: the thickness of the ink layer of the printed matter, the area of the image and text, the nature of the ink printed, the nature of the printing paper, the printing process and so on. These factors affect the mechanical bonding force, physical and chemical bonding force. As a result, the adhesive performance of the film on the surface of the packaging printed matter changes, and quality problems occur.
Some packaging prints have a large graphic area, and some are printed on the spot, so that the ink layer is relatively thick. The thick ink layer is often difficult to bond with the plastic film, and it will delaminate and foam soon after bonding. This is because the thick ink layer changes the porous surface characteristics of the paper, seals the pores of the paper fibers, and prevents the penetration and expansion of the adhesive on the paper. In this way, the fastness of the film is greatly affected. In addition, changes in the thickness and area of the ink layer cause changes in surface tension, which in turn causes changes in bonding fastness. Therefore, when packaging and printing, we must strictly control the amount of ink printed. Control the field density value. Compared with other printing, the ink layer of packaging offset printing has the lowest ink layer thickness, which is beneficial to the film, generally controlled at 2-3μm.
For packaging and printing film-coated products, fast-setting bright offset printing inks should be used. Because of the fast-setting bright offset printing ink, its binder is composed of synthetic resin, dry vegetable oil, high boiling point kerosene, etc. The molecular groups in these synthetic resins and the molecular groups in the cross-adhesive will expand and penetrate each other, resulting in cross-linking, forming a physical and chemical bonding force, which is conducive to coating.
In the application of packaging offset printing inks, it should be noted that kerosene should not be excessive, otherwise it will cause the ink to dry too fast and crystallize the surface of the ink layer, which will affect the coating effect. When printing light colors, you need to add some thinner. Use high-quality diluent when applying. White oil is an emulsifier. Don't use it. Inferior white ink has obvious powdery particles that are not firmly combined with the binder. After printing, the binder will penetrate the paper, and the pigment will float on the paper surface and will hinder the adhesion.
Weili oil is a transparent slurry made of aluminum hydroxide and dry vegetable oil binder dispersed and rolled. Although it has better printability, aluminum hydroxide is light in weight and will float on the surface of the ink layer after printing, resulting in poor adhesion or foaming. Weili oil is slow to dry, and inhibiting the drying of ink is not good for coating. Therefore, virgin oil should be used with caution. The quick-drying gloss oil can make the prints rich in gloss, good drying properties and good printing performance. We say that it is best to use a quick-drying gloss oil as a thinner.