In plastic printing, the control of ink printing viscosity is very critical. Especially in high-speed rotogravure printing, whether the printing viscosity of ink is properly controlled is greatly related to the majority of quality problems such as pigment transfer, dirty plate, gloss of printed matter, firmness of ink layer, and static electricity, which affects the quality of printed matter. Yield and production efficiency. How to control the printing viscosity of ink can be taken into account in many aspects to ensure the quality of printing. This requires us to understand the relationship between the printing viscosity of ink and these common quality problems.
(1) Ink printing viscosity and pigment transfer effect We know that plastic film printing inks are composed of organic solvents, binders, pigments, additives, additives, etc. In the printing process, the quality of the pigment transfer effect is mainly related to the printing viscosity of the ink. Practice has proved that the ink printing viscosity has a certain range (11 ~ 24s, 3 # Zahn Cup), within this range, the greater the ink printing viscosity, the worse the pigment transfer effect. When the printing viscosity of the ink is too large, the entire ink system is in a supersaturated state, and the fluidity of the pigment and other substances is poor, and they cannot be evenly dispersed, but appear in clusters, which are easy to pile up together, so that the pigment cannot smoothly enter the printing plate Net caves can't even enter the net cave, let alone transfer, this is the so-called blocking phenomenon. Therefore, as long as the colloid system composed of resin, pigment and organic solvent is not in supersaturated state, but in saturated or unsaturated state, the pigment and other substances can be well dispersed in it to form a uniform and delicate colloid system In this way, the pigment can smoothly enter and exit the net hole, and the problem can be solved.
Some ink manufacturers suggest to control the printing viscosity of the ink to 15 ~ 18s (3 # Zahn Cup), but in practice, especially in high-speed gravure printing machines (printing speed is 100 ~ 260m / min), in order to ensure good The transfer effect can also be printed for a long time and improve production efficiency. Generally, the ideal state point of ink printing viscosity is found between 11-15s (3 # Chaen Cup).
(2) Ink printing viscosity and dirty plate faults In plastic film gravure, dirty plate problems often occur. The phenomenon is that the non-printed pattern part of the plate cylinder will also be stained with a hazy layer of resin (the resin is entrained with pigment), and transferred to the plastic film, which appears as a sheet or line on the printed product. . The root cause of the dirty plate phenomenon is not only related to the hardness of the blade, the pressure of the blade, the contact angle of the blade, and the quality of the plate cylinder, but also related to the printing viscosity of the ink. When the printing viscosity of the ink is too high, the fluidity of the pigments and other substances is poor, they cannot be dispersed evenly, and they are easy to accumulate together. Under the relatively high-speed movement of the blade and the plate cylinder, the blade and the plate cylinder are easy to be damaged, which is prone to linear contamination. Sewage.
At the same time, because the resin is also in a supersaturated state, a large amount of resin coalesces together, and the affinity of the resin to the plate cylinder, under the pressure of the blade, the resin will stick tightly to the plate cylinder (resin With paint), so that there will be flakes of dirt. Generally speaking, the lower the ink printing viscosity, the less likely the dirty version will occur.
(3) Ink printing viscosity, gloss and fastness of ink layer If the printing viscosity of ink is too small, it means that the content of organic solvent in the ink is large, and the components such as resin and pigment are relatively small, so that it cannot form a smooth The film layer makes the final print pattern white and lacks gloss. Therefore, if the printed product requires a good gloss, it is generally considered to use a larger ink printing viscosity (13 ~ 19s, 3 # Zahn Cup), that is, the resin and pigment components are relatively more to meet the requirements of the printed product. need.
When the ink is transferred to the plastic film and dried to form the ink film, the pigment can firmly adhere to the surface of the plastic film, and the resin is the main material that makes the pigment firmly adhere to the plastic film. Therefore, the fastness of pigment adhesion is also related to the viscosity of ink printing. The ratio of the resin and the pigment in the ink component cannot be too large or too small, but should be within the normal range to ensure that the pigment adheres firmly.
(4) Ink printing viscosity and static phenomenon When maintaining the normal environmental humidity, when the ink printing viscosity is above 16s (3 # Chaen Cup), generally no static phenomenon occurs; the ink printing viscosity is 16s (3 # Chaen Cup) ) In the following, as the viscosity decreases, electrostatic phenomena such as whiskers, stripes, edge repulsion, flying ink, poor transfer, and extremely irregular water stains will occur and increase.
Therefore, we generally establish the ideal state point of ink printing viscosity between 11 to 17s (3 # Chaen Cup). If static electricity occurs within this range, we will generally eliminate the static electricity by increasing the viscosity of the ink printing, but by maintaining the normal environmental humidity, changing the structure of the thinner composition, and installing the static electricity elimination brush. Use antistatic agents to eliminate static electricity. Only in this way can we improve efficiency and yield while ensuring quality.
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