The drying property of printing ink refers to the speed and degree of the change of the liquid or paste into solid after the ink is adhered to the printed matter. The ink is transferred to the paper after printing. At this time, the solvent in the ink layer is instantly escaping, so that the ink on the paper is dried, and the printing process can be carried out normally. The drying of ink, that is, the speed of ink drying, has a great influence on the quality of printed matter. Some dry too fast, the ink will be in the printing plate or grinding roll paste, skin, so that the printing ink spots; if the ink drying too slow, printed matter may occur on the back of dirt and other phenomena.
It is not difficult to see that the drying of ink is an important indicator of ink. So how does ink dry? The drying of ink is accomplished by changing the binder in the ink into a solid. In the ink used in the connection and its formula proportion is not the same, so the drying process of ink is also different.
There are three kinds of ink drying methods, namely osmotic drying, volatile drying and oxidation of conjunctival drying.
The osmotic drying of ink refers to the drying of some parts of the ink when the ink is dried, and the other part is connected with the pigment to fix on the surface of the paper. This drying mainly depends on the absorption of paper and the penetration of ink. Paper is a porous material interwoven with fibers with small pore size. When the ink is transferred to the paper, the paper begins to absorb the binder in the ink because of the gap of the paper fiber. In the process of absorption, the composition and rheological properties of the ink change gradually, the liquid composition gradually decreases, the three-dimensional cohesion of the pigment gradually increases, and the ink gradually loses the fluid property and solidified. Rotary letterpress ink mainly relies on infiltration drying.
Volatile drying refers to the evaporation of the solvent in the binder when the ink layer is dried, and the remaining resin and pigment form a solid film layer, which is fixed on the surface of the paper. Gravure ink and flexographic printing ink are typical volatile drying inks. The rate of volatile drying mainly depends on the latent heat of evaporation, the proportion of pigments, the radius of particles, and the types of resins.
The greater the proportion of pigment in the ink, the slower the drying rate; the smaller the pigment particles, the greater the surface area, the slower the drying rate. Gravure printing ink uses volatile solvent as the connecting material, so it is mainly based on volatile drying.
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