The effect of viscosity on gravure printing ink

Abstract: In this paper, the actual printing, due to the problems caused by the viscosity of the gravure ink for a brief exploration, and its reasons for how to adjust the instructions to be described.

Keywords: Viscosity, Pattern fog, Ink flying, Printing speed, Gloss, Surface tension value

The ink used in gravure printing is an extremely volatile solvent ink that is dried by the evaporation of gravure paper and solvents of high quality ink absorption. Because gravure inks require high fluidity and low viscosity for their own viscosity, the requirements for drying are adapted to the speed of the printing machine, the length of the travel path, the quality of the printing materials, the corrosion of the layout, and the indoor temperature and humidity for real-time adjustment. Once the operator is negligent or improperly controlled, various problems can easily arise.

Viscosity plays a very important role in this. In this paper, we will make a brief exploration of the problems caused by the viscosity of gravure ink in actual printing, and explain why the reasons for this change are as follows.

First, version fog problem

In plastic intaglio printing, the non-printing surface of the printing platen roller is often stuck with a layer of ink. When transferred to the printing substrate, it often appears as a sheet or line-like stain. This is the dirty plate. , Also known as the fog version. Ingravure printing, the cause of the dirty version of the ink is due to the squeegee ink, in particular, is not scraping the ink during the scraping process of non-graphic part of the ink, the blank part of the ink scraping is not clean due to the main mechanical and ink components problem.

Mechanical factors: The first reason is that the squeegee wears badly. During the normal use of the squeegee, it eventually wears out. To solve this problem, it is possible to check the direction of the squeegee along the gravure roll to ensure that the squeegee is evenly pressed against the gravure roll. At the same time, make sure that the squeegee itself is free of wear and dirt, which can affect the squeegee's squeegee effect. If these unresolvable problems occur, it is best to replace the squeegee again; the second reason is that if the surface of the copper plated and chrome plated layers of the gravure platen is rough, then the squeegee blade will not be clean. , Sometimes changing the angle of the squeegee can solve this problem. If the adjustment of the squeegee cannot overcome the roughness on the gravure roll, then the plate roll needs to be polished.

Ink component factor: If the squeegee is frequently replaced during the production process, it is likely that the colorant in the ink has a strong abrasive property. It should be considered whether to replace another ink. In addition, improper use of solvents or excessive use of solvents in the ink can result in flocculation of the colorant in the ink. The flocculation causes the color material to remain under the squeegee, causing a dirty plate or abrasion of the squeegee. In addition, the lubricating properties of the ink is also a cause of the dirty version. The lubricity of the ink is related to the resin in the ink composition. Some gravure ink manufacturers will add a small amount of dark asphalt to the ink components to improve the ink squeegee performance.

In a word, the main reason for the fog problem is that a large amount of resin precipitates and coalesces, or the selected resin has affinity for the printing plate cylinder. Under the pressure of the blade, the resin will stick tightly to the roller.

The cause of the smudge problem has a great relationship with the printing viscosity of the ink in addition to the ink formulation itself, the pressure and the contact angle of the doctor blade, and the quality of the printing plate. If the ink printing viscosity is too high, the viscosity of the ink becomes larger. In the high-speed movement of the printing plate, the ink will have a great impact impact on the squeegee, so that the squeegee is difficult to smoothly scrape off the ink of the non-graphic part, and thus the printing plate is also generated. If the pigment in the ink is unevenly distributed in the ink system, or the resin in the ink fails to wrap the pigment particles well, the pigment particles will re-aggregate. Formation of pigment groups, which is often referred to as the phenomenon of back-coarseness, can easily result in the formation of linear or stripe-shaped cutting lines in printing. In general, the lower the printing viscosity of the ink, the less likely it is to cause smearing problems. Therefore, in the actual printing process, special attention must be paid to changes in the viscosity of the printing ink, and the printing viscosity should be adjusted in time to improve the quality of the printed matter.

Second, high speed printing ink problem

When the gravure printing speed exceeds 20m/min or more, if the gravure printing ink uses a chlorinated polypropylene resin with a wide molecular weight distribution, the viscosity of the printing ink is too low, which may cause the problem of “flying ink”.

The reason for this is that the viscosity of the printing ink is too low. The cohesion of the ink is greatly reduced, and when the ink is transferred to the printing film, the low molecular weight resin is easily separated, and a small “ink spot” can be seen in the blank part of the print. To solve the problem of "flying ink", we can generally start from the following two aspects: - using a chlorinated polypropylene resin with a narrow molecular weight distribution; second, according to the printing situation, properly increase the printing viscosity of the ink.

Source: China Yinguang