How to Control Printing ink Printing Viscosity

In plastic printing, the control of ink printing viscosity is the key, especially in high-speed rotogravure printing, whether the ink printing viscosity control is appropriate or not, directly with the transfer of pigments, dirty plates, printing gloss, pigment adhesion firmness, static electricity, etc. Most quality problems affect the yield and work efficiency of printed products. How to control the viscosity of ink printing can take all aspects into consideration and ensure the quality of printed products; this requires us to understand the relationship between ink printing viscosity and these quality problems.

Ink is composed of organic solvents, linking materials, pigments, additives, auxiliary materials, etc. When these raw materials have been determined, the processing method and the composition of each component have also been determined. The quality of pigment transfer is mainly related to the printing viscosity of the ink. Practice has proved that within a certain range (11-245, using Zahn Viscosity Cup No. 3), the greater the ink printing viscosity, the worse the effect of pigment transfer. Because the role of the solvent is to dissolve the resin or additives and additives to give fluidity and make the pigment easy to disperse. When the ink printing viscosity is too high, the entire ink system is in a supersaturated state, and the fluidity of pigments and other substances is poor, and they cannot be evenly dispersed, but form agglomerates and easily accumulate together. In this way, the pigment cannot enter and exit the mesh smoothly. When the printing viscosity of the ink is too high, the pigment cannot even enter the mesh at all, let alone transfer, which is the so-called plate blocking phenomenon. Therefore, as long as the colloidal system composed of resins, pigments, etc. in organic solvents is not in a supersaturated state but in a saturated or unsaturated state, pigments and other substances can be well dispersed in it to form a uniform and fine colloidal system, so that the pigments enter and exit the mesh. If it goes well, the problem can be solved. Some ink manufacturers suggest that the ink printing viscosity should be between 15 and 185 (Zahn Viscosity Cup No. 3). But in practice, especially in high-speed gravure printing machines (printing speed of 100-260m/min), in order to ensure good forwarding effect and long-term printing, the effective ink printing viscosity is generally 11-155 (Zarn viscosity Cup No. 3) to find its satisfactory state point.

Dirty printing often occurs in plastic gravure printing. The phenomenon is that the non-printing surface of the cylinder will also be stained with a thin layer of resin (pigment is entrained in the resin), and transferred to the substrate to make the substrate dirty in flakes or in lines. The source of the dirty plate phenomenon is not only related to the hardness of the scraper, the pressure of the scraper, the contact angle of the scraper, the quality of the plate cylinder, etc., but also mainly related to the printing viscosity of the ink. As mentioned above, when the printing viscosity is too high, resins, pigments and other substances have poor fluidity. They cannot be uniformly dispersed, and they are easy to accumulate together. Under the relatively high-speed movement of the scraper and the cylinder, the scraper and the cylinder are easily damaged, which is prone to line dirty. 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 roller, the resin will stick tightly to the roller under the pressure of the scraper (pigment is entrained in the resin), so flakes will appear. dirty. Generally speaking, the smaller the printing viscosity of the ink, the less likely the dirty plate phenomenon will occur.

If the printing viscosity of the ink is too small, it means that the organic solvent content in the ink is too much, and the components such as resin and pigment are relatively small, so that it cannot form a smooth film when drying, so it is white and lacks luster. Therefore, if the printed matter needs to have better gloss, it is generally considered to use a larger ink printing viscosity (13-195, Zahn No. 3 cup), that is, the resin and pigment components are relatively more to meet the needs of the printed matter. .

When the ink is printed on the plastic and becomes an ink film after drying, it should be able to firmly attach the wrapped pigment to the surface of the plastic. Resin is the main material for the firm adhesion of the plastic. Therefore, the adhesion of the pigment is also related to the printing viscosity of the ink. This shows that the ratio of the resin and the pigment in the ink should not be too large or too small, but should be within the normal range, so that the adhesion of the pigment can meet the requirements.

The ink printing viscosity is 16 under normal ambient humidity conditions. (Zaen No. 3 Cup) The above electrostatic phenomena generally do not occur. The ink printing viscosity is 16. (Zaen No. 3 Cup) Below "As the viscosity becomes smaller, electrostatic phenomena such as whiskers, streaks, edge repulsion, flying ink, poor transfer, and extremely irregular water stains of pigments will occur and aggravate.

Therefore, based on the above reasons, the satisfactory state point of ink printing viscosity is generally found between 11 and 175 (Zaen No. 3 cup). If static electricity occurs within this range, it is generally not necessary to increase the ink printing viscosity to eliminate static electricity, but to eliminate static electricity by maintaining normal ambient humidity, changing the composition structure of the diluent, installing an antistatic brush, and using an antistatic agent. Only in this way can the efficiency and yield be improved while ensuring the quality, so that the company can obtain higher profits.