Several problems needing attention in the process of adding ink to packaging offset printing
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The order of ink refilling should be from large to small, that is, the main color ink with a large proportion is added first. For the blending of light-colored inks, first put a thinner, then gradually add dark ink to the thinner. There are two ways to mix inks: a small amount of ink can be mixed by hand; a large number of inks should be mechanically mixed.
The hiding power of the ink refers to the ability of the ink to cover the ground color. The stronger the hiding power, the lower the transparency of the ink. The four-color printing requires the ink to have a high transparency, otherwise it will affect the color reproduction effect of the printed matter.
In the printing, the adhesion of the ink is adjusted according to the following factors:
1 The surface strength of the paper. The surface strength of the paper is large, and the adhesion of the ink can be adjusted to be larger: on the contrary, the adhesion should be smaller, otherwise the paper will be "dropped". “Lint” is very powerful, seriously affecting product quality and production efficiency, which is often the main motivation for adjusting ink adhesion.
2 printing speed. When the speed is fast, the adhesive deployment requirement is smaller, and vice versa. The faster the speed, the more likely the phenomenon of "slipping" and unevenness of ink transmission, and the need to reduce the adhesion to suit it.
3 layout graphics structure. When printing the image of the mesh, the most important thing is that the shape and area of the dot should be correctly copied, and the adhesiveness should be adjusted larger. When printing a solid image, it is desirable to obtain a uniform and solid field, and since there is no problem of dot gain, the adhesion is smaller.
4 workshop temperature. When the temperature rises, the cohesive force of the ink will decrease, and problems such as emulsification increase and dot gain increase rate are more likely to occur. When the ink is adjusted, the adhesion of the ink should be adjusted in advance. On the contrary, it adjusts the adhesion of the ink.
In the production of packaging offset printing, the ink drying is too slow. The most common drawback is that it is prone to "back scum". In addition, the drying speed of the ink is too slow, and the free permeation amount of the binder increases, which causes the ink color to be dim and lacks luster. The ink is dried too fast, and the surface layer of the ink is easily conjuncted during the printing process, which affects the progress of the production, and may also cause the ink to crystallize, which affects the printing of the subsequent ink color of the dry overprint.