Flexo is a flexible, high resolution, warped letterpress plate. In recent years, flexo printing has developed rapidly in the field of printing, and its development prospects are generally optimistic. Flexographic printing presses transfer the right amount of ink to the substrate through a unique mesh roller. The appropriate use of ink is directly related to the printing production operation and printing quality, the general flexographic printing ink used is very thin, belongs to the liquid ink, from the rheological point of view is a close to Newton fluid ink, with good fluidity, viscosity is only 0.1-1Pa/s. At present, three types of inks are mainly used in flexographic printing: organic solvent inks, water-based inks and ultraviolet curing inks. Among them, water-based ink has always been a large part of flexographic printing for its environmental protection, economy and other advantages. This paper mainly discusses the printability of water-based ink and its use in flexo printing.

1.Composition and characteristics of water-based ink

Like the general printing ink composition, water-based ink usually also has colorant, binder, auxiliary agent and other components. Colorant is the color substance of water-based ink, giving the ink a specific color. In order to make the printing color gorgeous, the colorant is generally selected with good chemical stability and high coloring power. The binder consists of water, resins, amines and other organic solvents.

Resin is the most important component of water-based ink, usually the use of water-soluble acrylic resin, binder composition directly affects the ink adhesion function, drying speed, anti-sticky performance, etc., but also affects the ink gloss and ink transfer, amine compounds mainly maintain the alkaline PH value of water-based ink, so that acrylic resin to provide better printing effect. Water or other organic solvents are mainly dissolved resins, adjust the viscosity of the ink and drying speed; Auxiliary agents mainly include: defoamer, blocker, stabilizer, diluent and so on. Since water-based ink is a soap composition, it is easy to produce bubbles during use, so silicone oil should be added as a defoamer to inhibit and eliminate bubbles, while improving the transfer performance of the ink. The blocking agent is used to inhibit the drying speed of the water-based ink, prevent the ink from drying on the roller and reduce the paste plate.

The stabilizer can adjust the PH value of the ink, and can also be used as a diluent to reduce the viscosity of the ink. Diluent is used to reduce the color of fresh water ink, and can also be used as a brightening agent to improve the brightness of water-based ink. In addition, some wax should be added to the water-based ink to increase its wear resistance.

2.The PH value of water-based ink

The PH value of water-based ink is directly related to the viscosity, dryness and other printability of water-based ink. The experiment shows that the viscosity of water-based ink increases linearly with the decrease of PH value, and its dryness decreases linearly with the gradual increase of PH value. The PH value of water-based ink is mainly maintained by amine compounds, and the volatilization of amine substances during the printing process reduces the PH value, which causes the viscosity of the ink to rise, the transfer is poor, the drying is accelerated, the gridding roller is blocked, and the paste plate is faulty. Therefore, to keep the PH value of water-based ink stable, on the one hand, try to avoid the leakage of amine substances, such as covering the top cover of the ink tank. On the other hand, the stabilizer should be added regularly and quantitatively. Usually the PH value of water-based ink should be maintained between 8.0-9.5, PH value is too high and too low affect the printing quality, PH value is too low, affect the printing performance of acrylic resin play; When the PH value is too high, the ink dries slowly, and the problems of sticky and dirty back of the printed product and poor water resistance are easy to occur.

3.The use of water-based ink problems

Water-based ink can be mixed with water before drying, and once the ink is dry and solid, it is no longer soluble in water and ink. Therefore, the water-based ink must be fully stirred before use to keep the ink composition uniform. When adding ink, the residual ink in the ink tank should be filtered out first if it contains impurities, and then used with new ink. When printing, do not let the ink dry on the roller, so as not to block the ink hole. Hindering the quantitative transmission of ink resulting in printing instability. In the printing process, the flexographic plate should always be kept wet by the ink to avoid blocking the text pattern on the printing plate after the ink is dried. In addition, it is found that when the viscosity of water-based ink is slightly larger, it is not appropriate to add water, so as not to affect the stability of the ink, and an appropriate amount of stabilizer can be added to adjust.

Sinograce Chemical production of a variety of water-based resins, and a variety of water-based ink resins, as well as used in a variety of film water-based paint, additives, welcome to consult.