ABOUT PRINTING INKS

Transfer of ink
When the ink is transferred and distributed (from Mo Dou, after complicated transfer and distribution, until it is successfully transferred to the surface of the printing sheet to form a mark), the flowing phenomenon is called ink transfer, which is the main body of ink operation adaptability. The transfer of ink can be understood from two aspects: on the one hand, the transfer of ink between ink transfer, ink uniformity and ink roller; On the other hand, it is the transfer of ink between printing plate and blanket, blanket and printing sheet. The former is mainly influenced by inking and transferability, while the latter is also influenced by printing conditions (such as printing model, printing speed, printing pressure, etc.) and blanket and paper. That is, the transfer of ink is shown in the whole process of ink transfer, distribution and ink layer separation (or split), which is of great significance to offset printing. The transferability of ink mainly depends on the drawability and viscosity of ink, and it is also related to its wettability, viscosity, yield value, thixotropy and surface tension.

Transferability of ink
After the ink is output by the ink roller, the flowing phenomenon is called ink transitivity. In the printing process, the thickness and uniformity of the ink layer on the surface of the printing plate are realized by a series of ink rollers, so the quality of ink transmission is directly related to the distribution and distribution of ink quantity and its smooth transfer in the whole process. Generally speaking, the process from Mo Dou inking to printing plate inking mainly depends on the viscosity, wiredrawing and thixotropy of the ink itself. Under normal circumstances, when the drawability and viscosity are appropriate, the ink presents better transferability and ink quantity distribution; When the drawability and viscosity are too large, the transferability becomes worse and the ink distribution becomes worse. When the ink is too long, it is easy to cause ink flying.

What is the permeability of ink
Ink permeability refers to the permeability of the ink layer transferred to the surface of the printing sheet, which represents the infiltration phenomenon and properties of the ink in the early stage of drying process. In the process of offset printing, the infiltration process of ink (binder) includes two processes, namely, the instant rapid infiltration process at the moment of printing pressure and the slow free infiltration process after printing pressure disappears. In the process of offset printing, the permeability of printing ink mainly depends on the properties of the binder itself, and it is also related to printing pressure, printing speed, the type of paper used, and surface properties (such as ink absorption, smoothness, etc.). Generally, the penetration of ink layer on paper shows different penetration properties and seepage velocity due to different ink types and viscosities. Generally, the penetration of oxidized polymer conjunctival ink is smaller than that of permeable gel conjunctival ink.

How to determine the color of ink
According to the specific situation and conditions, there are three methods to determine the color of ink: ① Scraping method. After mixing a small amount of standard sample ink and sample ink, place them on the top of standard sample paper (offset printing paper or offset printing coating paper) and juxtapose them left and right. Scrape them from top to bottom with a scraper to form a thin strip ink film layer of 3 ~ 5 mm, and the thick ink film layer will be harvested after passing through the black belt. Then, visually inspect the differences of background color, complexion and ink color between the standard sample and the sample ink layer above the black belt, and compare the color differences between them to make an evaluation. ② Densitometer method. The field density samples of three primary colors ink are placed under the red, green and blue-violet filters of color reflection densitometer, and their high, medium and low optical densities are measured successively, and then their hue error, gray level and actual efficiency are obtained according to the prescribed calculation formula. ③ The color of ink can also be determined by roller coating method, printability tester and colorimetric spectrophotometer.