In actual production, controlling the drying speed of ink is the most important means to prevent the back of the stain, the main factors affecting the drying of imprinting are paper, ink and ink layer thickness, wetting liquid and emulsification degree, environmental temperature and humidity and production technology.
a. Paper. The paper with rough surface, loose structure and small sizing has good absorbability and fast drying of imprinting; After the smooth paper is piled into paper stacks, the air is not easy to introduce into the lower part of the paper pile, which affects the drying speed of oxidation polymerization, and the low pH value and high water content of the paper will delay the drying of the ink.
b. The effects of adjuvants. The ink itself contains drying agents, printing in order to speed up the drying speed sometimes need to fill the ink with drying agents, but excessive drying agents will make the ink emulsification serious, but not conducive to drying. When the paper appears hair phenomenon, usually add a certain amount of adhesives to reduce the viscosity of the ink, but the adhesives are non-dry excipients, will reduce the drying speed of the imprinted ink layer.
c. Wetting fluid and degree of emulsification. The more acidic the wetting solution, the slower the ink will dry. The more serious the ink emulsification, the slower the drying, large format printing machine printing small format paper field background color, the back rub is most likely to appear on both sides of the paper axis, the solution as far as possible to use the water blower device or in the water roller paste paper method, reduce the water supply at both ends of the plate, reduce the ink emulsion value, in order to imprinting ink in time to dry.
d. Printing pressure, printing speed. Increasing the printing pressure can promote the pressure penetration of ink; Reduce the printing speed, you can increase the printing time, can play a role in preventing the back rub.
e. Ambient temperature and humidity. The ambient temperature is high, the chemical reaction speed is fast, and the blot drying is fast, in summer, the general light fast drying ink can be dried quickly without drying oil, and in winter, it is necessary to add some drying agents, therefore, the control of the workshop temperature and humidity is very important for mastering the blot drying speed.
f. Sheet stacking and powder spraying. After the printed finished product is stacked, the air is difficult to penetrate the lower middle of the paper stack, because of the lack of oxygen, this part of the printing sheet is difficult to dry. Therefore, in order to prevent slow drying and dirt on the back, it is very important to strengthen the management of semi-finished products after printing. Printing products that are not easy to dry, on the one hand, stacking should not be too high; On the other hand, after the ink layer is fixed, at a certain interval, the printing sheet should be gently shaken to make it breathable and increase the contact between the ink and the air to accelerate the drying of the ink. In sheet offset printing generally used powder to prevent the back of the dirt, powder is the use of powder support, increase the distance between the printing sheet, conducive to air circulation, speed up drying.
