Paper performance: ink absorption
Paper ink absorption is one of the important technical indicators for evaluating printing paper. In the printing process, the ink absorption of the paper is related to the tightness of the paper, the surface properties of the paper-making fibers, fillers and sizing materials. At the same time, it is also related to the nature of printing ink, printing method, printing speed, printing pressure and other factors.
The ink absorption performance of the paper itself mainly depends on two factors. One is the chemical properties of the paper surface, that is, the force of polar chemical bonds on the ink. There are fibers, fillers, and pulp on the surface of the paper, and increasing the polarity of various molecules on the surface of the paper can improve the ink absorption of the paper. Some materials are not chemically polar enough, and the ink absorption performance is obviously improved after being treated with a corona treater.
The second factor is the physical properties of the paper surface, that is, the number of hooks on the surface and the size of the surface area. There are pores on the surface of the paper, and the ink binder penetrates into the pores, and the ink is caught by the non-smooth pores on the inner wall, thereby increasing the pulling force on the ink, so that the paper has a strong ability to absorb ink. In addition, if the surface roughness of the paper is high, the effective surface area for ink absorption of the paper will be large, which will also increase the ink absorption.
The influence of paper ink absorption on printing is that the paper has strong ink absorption, and too much binder in the ink is sucked into the paper, so less binder is deposited in the ink on the surface of the paper, and more pigment particles are floating on the surface of the paper. On the surface of the paper, the ink film lacks luster after drying, and in severe cases, the imprint will fall off as soon as it is wiped, which is the so-called ink pulverization phenomenon. Printing will occur when the ink absorption ability of the paper is too strong, the viscosity of the ink is low, and the printing pressure is high. If the paper is too loose and the capillary pores are too large, when the binder of the ink and the pigment penetrate into the surface of the paper together, the ink layer on the surface of the paper will be thin, which will affect the color saturation of the printed product. If the ink absorbency of the paper is too small, and the penetration of the ink binder is too small, the drying speed of the ink will be slow, and the phenomenon of sticking on the back will easily occur.
