Home > Knowledge > Content
How to control ink printing viscosity in high speed rotary gravure
- Aug 07, 2018 -

The ink is composed of an organic solvent, a binder, a pigment, an additive, a binder, and the like. When these raw materials have been determined, the degree of processing, the method, and the composition of each component have been determined, and the quality of the pigment transfer is mainly related to the printing viscosity of the ink. Practice has proved that the ink printing viscosity has a certain range (11 ~ 24S, using the Zahn viscosity cup No. 3), the greater the viscosity of the ink printing, the worse the effect of pigment transfer. Since the action of the solvent is to dissolve the resin or the additive and the auxiliary agent, the fluidity is imparted to make the pigment easy to disperse. When the viscosity of the ink printing is too large, the entire ink system is in an excessively saturated state, and the fluidity of the pigment and the like is poor, and it cannot be uniformly dispersed, but is formed into a cluster and is easily piled up, so that the pigment cannot smoothly enter and exit the mesh. When the ink printing viscosity is too large, the pigment can not even enter the mesh at all, and it is even more difficult to transfer. This is what is commonly referred to as blocking.

Therefore, we only need to make the colloidal system composed of resin, pigment and other organic solvents not in an excessively saturated state, but in a saturated state or a non-saturated state, so that pigments and the like can be well dispersed therein to form a uniform and fine colloidal system. So that the pigment enters and exits the mesh smoothly, and the problem can be solved. Some ink manufacturers recommend ink printing viscosity between 15 and 18 seconds (Zahn viscosity cup No. 3). However, in practice, especially in high-speed gravure printing machines (printing speed of 100 ~ 260m / min), in order to ensure a good transfer effect, but also for a long time printing, improve efficiency, ink printing viscosity is generally 11 ~ 15S ( Look for the ideal state point between the Zahn Viscosity Cup No. 3).

Dirty problems often occur in plastic gravure printing. The phenomenon is that the non-printing surface of the drum is also stained with a layer of resin (the pigment is entrained in the resin) and transferred to the substrate, so that the substrate is stained in a sheet form or appears as a linear stain. The root cause of the dirty plate phenomenon is mainly related to the printing viscosity of the ink, in addition to the hardness of the blade, the blade pressure, the contact angle of the blade, the quality of the plate, and the like. As described above, when the printing viscosity is too large, the resin pigment and the like have poor fluidity, are not uniformly dispersed, and are easily piled up together. Under the relatively high-speed movement of the blade and the plate, the blade and the plate are easily damaged, thereby being easy. Linear contamination occurred. At the same time, since the resin is also in a state of supersaturation, a large amount of resin is agglomerated together, and the affinity of the resin to the drum, under the pressure of the blade, the resin is tightly adhered to the drum (the pigment is entrained in the resin). This will result in flaky dirt. In general, the ink printing viscosity is small, and the dirty plate phenomenon is not easy to occur.

However, if the ink printing viscosity is too small, it means that the organic solvent content in the ink is large, and the components such as resin and pigment are relatively small, so that a smooth film layer cannot be formed when dried, and the printed product will be whitened and become dull. Light, lack of luster. Therefore, if the printed product needs to have a good gloss, it is generally considered to use a larger ink printing viscosity (13-19S, Zahn No. 3 cup), that is, the resin and pigment components are relatively more to meet the printed matter. need.

At the same time, when the ink is printed on the plastic and becomes an ink film, the coated pigment can be firmly adhered to the plastic surface, and the resin is the main material for firmly adhering to the plastic. Therefore, the degree of pigment adhesion is also related to the printing viscosity of the ink. This indicates that the ratio of the resin and the pigment in the ink should not be too large, nor should it be too small, but should be within the normal range, and the pigment bonding firmness is large. Under the normal ambient humidity, the ink printing viscosity is above 16S (Zahn No. 3 cup), and static electricity generally does not occur. The ink printing viscosity is below 16S (Zahn No. 3 cup). As the viscosity becomes smaller, electrostatic phenomena such as whisker, striated, edge repulsion, flying ink, poor transfer, and extremely irregular water stains will follow. Occurs and aggravates.

In view of the above reasons, the industry believes that the ideal state of ink printing viscosity is generally found between 11 and 17S (Zahn No. 3 cup). If static electricity occurs in this range, in principle, the method of improving the ink printing viscosity is generally not necessary to eliminate static electricity, but by maintaining normal environmental humidity, changing the composition of the diluent component, installing a static eliminating brush, and using static electricity. A method such as an anti-static agent eliminates static electricity. In this way, we can improve the efficiency and yield while ensuring the quality, and lay the necessary foundation for the printing enterprises to obtain profits.