The feature of gravure printing is that the graphic part of the printing plate is concave, while the blank part is convex. When printing, the ink is filled in the graphic part under the depression, and then the ink attached to the outside of the graphic is scraped off with a scraper, and then The role of embossing force makes the graphic ink transfer to the surface of the substrate. According to this feature, we can know that the three elements of printing are: ink, printing plate, paper
The printability of the gravure printing ink is not only directly affected by the normal transfer and transfer of the ink during the printing process, but also affects the quality of the printed matter. The following discusses some problems that we encounter.
Because the gravure printing speed is faster and the ink layer is thicker, the dry conjunctiva of the ink is used to volatilize, and the purpose of quick drying is achieved by selecting the volatile solvent and adjusting the volatilization conditions. Because most of the cigarette labels printed by our company are full plates, there is a strict requirement on the drying properties of inks. I remember that in the "fine cloud smoke" "new Hongshan tea" test machine, there have been ink stuck by the transfer roller, when the analysis was considered poor ink flow, caused by rapid drying. In actual fact, the slow drying and drying of ink are the causes of this printing failure. First we must understand what is the drying of the ink. The printer defines it as the ink is transferred from the printing plate to the substrate. The ink layer is gradually increased in viscosity and hardness by physical or chemical means, or a combination of both, and finally formed on the surface of the substrate (paper). The film layer. Intaglio printing inks are composed of low-boiling organic solvents and high-molecular polymers, and their drying must be done in a volatile manner. In other words, the solvent in the ink dissolves the resin and sucks the pigment particles, absorbs energy during printing, and evaporates the remaining components of the ink to form a film on the paper. Thus, the key to volatile drying is the solvent of the ink vehicle. In general, the ambient temperature is high, the more volatile the solvent is, the lower the relative temperature is, and the faster the solvent volatilizes. Therefore, the printing plant often adjusts the dryness of the ink to suit the printing according to changes in the season humidity and temperature. In addition, gravure and flexo inks are not formulated with the same solvent, but are formulated with several solvents. The purpose is to adjust the drying speed of the ink. For example, ethanol and acetic acid ethyl acetate are commonly used in gravure printing. They have the same boiling point. However, the latent heat of evaporation is different, so the rate of evaporation of ethyl acetate is almost twice that of ethanol.
One of the difficulties with gravure is the printing of the gradation. Because the level transition of the pattern needs to be represented by the depth, the size of the printing plate dot, or the thickness of the ink layer. For volatilized and dried inks, the dry part of the ink in the shallow mesh part often appears and the pattern cannot be completely reproduced. In order to improve the effect of reducing the number of printed products, we have adopted a method to increase the viscosity of the ink on the machine, increase the adhesion of the ink between the dots, and use the corresponding slow-drying solvent to improve the transition point. solve. Of course, we can't simply deal with the issue of lithography, because sometimes you will observe the same printing ink, plate, and two different papers, and there will be obvious differences in the reproduction of the layers, even before and after the same roll. The time effect is not the same. In the printing process of "fine cloud cigarettes" and "new Hongshan tea", similar problems are often encountered.
In order to make the ink have good printability and better printing effect, the best one is to reflect the original, and the ink must be properly adjusted so as to have the fluidity, adhesiveness, and drying property suitable for printing.
Author/Li Ye Source: Print World