Viscosity is an important index of ink rheology.In printing, a certain viscosity is the main condition to ensure the normal transfer and uniform transfer of ink.It is related to whether the printing process can proceed smoothly, and directly affects the uniformity, clarity and gloss of the imprinting ink, and also relates to the viscosity, fluidity, yield value, thixotropy, drawing and other properties of the ink, which is one of the important printability of the ink.

There are many types of printing forms and prints, and their requirements for ink viscosity are different:

Lithography requires high viscosity of ink, dynamic viscosity of 10 ~ 80 Pa·s; Intaglio and flexographic printing requires low ink viscosity, the viscosity of plastic gravure ink is 0.02 ~ 0.2 Pa·s, the viscosity of publication gravure ink is 0.01 ~ 0.1 Pa·s, the viscosity of solvent-based flexible ink is 0.09 ~ 0.15 Pa·s, and the viscosity of water flexible ink is 0.15 ~ 0.3 Pa·s. Because of the low viscosity of gravure and flexographic inks, a Chon cup is often used to measure viscosity in printing.

The faster the printing speed, the lower the viscosity of the ink is required, so as to meet the needs of high-speed printing. For example, the viscosity of 6 000 printing/hour offset printing ink is appropriate to 20 ~ 50 Pa·s. The viscosity of 20 000 printing/hour rotary ink is appropriate to 10 ~ 30 Pa·s, and even sometimes should be lower than 10 Pa·s.

When the structure of paper is loose and the surface strength is low, the viscosity of ink is required to be low. The structure of the paper is tight, the surface strength is high, and the viscosity of the ink can be slightly higher. If the ink used in newsprint printing, its viscosity should be lower than the ink used in offset printing.

The printing of network cable plate and character line plate requires the viscosity of the ink to be higher, and the viscosity of the ink to be lower for field printing.

In wet press dry stack printing, the viscosity of the overprint color ink is required to be higher than the viscosity of the base color ink, so as to ensure the clarity of the printing and the combination of the overprint color ink and the base color ink is more firm.

In the four-color machine wet continuous printing, in order to ensure that the base color ink can be stably attached to the surface of the substrate and does not fall off during overprinting, the viscosity of the overprinting color ink should be lower than the viscosity of the base color ink. Generally speaking, the viscosity of various colors of inks should be reduced from the first color in the color order, so as to ensure the normal overprinting between each color ink layer.

Ink viscosity does not meet the printing requirements will cause a lot of failures.

When the viscosity of the ink is too large, the drawing property is strong. During the ink transfer process, when splitting between ink rollers, the end of the filament is easy to cause free ink droplets to fly into the air, forming a flying ink phenomenon in printing. The phenomenon of flying ink is more obvious in high-speed printing. The viscosity of the ink is too large, it is easy to cause the depowder of the paper, hair drawing or delamination stripping phenomenon. This is caused by the adhesive force of the ink exceeding the surface strength of the paper under certain printing conditions.

When the ink is transferred and transferred between the ink rollers, the viscosity is too large to make the ink transfer difficult, because the ink transfer rate is inversely proportional to the viscosity. Therefore, the ink viscosity is too large will lead to the uneven distribution of ink, the amount of ink transferred to the plate and printed matter is insufficient, the ink color is uneven, and the phenomenon of the bare basis of printed matter.

The viscosity of the ink is too large on the printing process will have some other effects. If the amount of ink in the printing process increases, the ink layer of the print is too thick, the drying speed is slow, and the back of the print is easy to stick or stick. In lithographic printing, it is also easy to produce the phenomenon that the paper is involved in the ink roller.

The viscosity of the ink is too small, the fluidity is increased, and the appearance is shown as the dilution of the ink. Lithographic offset printing is easy to produce ink emulsification, resulting in dirty printed matter.

The ink with too small viscosity is easy to spread out on the paper, resulting in the expansion of the imprinting area and the reduction of clarity. Moreover, it reduces the firmness of adhesion between the imprinting conjunctiva and the substrate surface and the gloss of imprinting.

In order to ensure that the viscosity of the ink is suitable for the printing operation, the viscosity of the ink should be selected and adjusted appropriately. When adjusting ink viscosity, it should be comprehensively considered according to the requirements of the printing process, the speed of the printing machinery, the nature of the paper, the temperature of the working environment and other factors. No. 6 ink mixing oil can be used to increase the flow of ink, improve the transfer of ink, reduce the concentration of ink, viscosity, dryness. If the ink color is found to be too deep to be reduced in printing, you can add an appropriate amount of diluent (diluent). Diluent has little effect on ink viscosity.