What factors determine the ink absorption of paper

Press imprinting moment, relying on the role of Printing pressure to transfer to the surface of the paper sector press into the larger pores of the paper, that is, the entire ink (including the pigment in the ink) into the paper pores, this process is generally known as pressure infiltration Out of phase. At this stage, the absorption of ink by paper depends mainly on the size of the printing pressure, the structure of the paper, and the viscosity of the ink. If the printing pressure is large or the structure of the paper is loose, the ink absorption ability of the paper will also be stronger. In general, printed paper with loose structure, such as newsprint, letterpress, and other non-coated papers, should have lower printing pressure and lower ink viscosity. For papers with tightly printed structures, such as coated paper, the printing pressure can be appropriately increased and the ink viscosity can be slightly higher.

The paper leaves the embossing area until the ink is completely dry. This stage mainly relies on the capillary action of the paper to absorb the ink, which is called the free-penetration exudation stage. At this stage, the binder is separated from the entire ink and passes through the rough surface of the small pores and the fibers of the paper, entering the interior of the paper at a commensurately slow speed. Therefore, this process is actually a process in which the binder migrates from the ink to the pores of the paper. Since the binder is separated from the entire ink, the conjunctiva property of the ink film remaining on the paper surface will be changed, and the fixation and drying of the ink will also be in the process. carry out. At this stage, the rate of absorption of ink by the paper determines the glossiness of the printed matter, and whether or not overprinting, chalking, etc. will occur. When the ink is transferred to the paper, along with the prolongation of time, the low molecular weight binder (solvent) will begin to infiltrate into the paper layer, so that the solvent content in the ink layer on the paper will decrease and the viscosity of the ink will increase. The ink layer produces condensation.

Ink absorption characteristics and determinants of paper

The absorbency of paper depends on the number of paper capillaries and the size of the capillary diameter. Paper is a kind of porous material. There are many unequal gaps between the fiber and fiber inside the paper, between the fiber and the filler, and between the pigment particles. These gaps are equivalent to many capillary tubes. Under the action of these capillaries, the binder in the ink can be absorbed, and the thicker the diameter of the capillary, the faster the ink can be absorbed. Therefore, the pore structure of the paper determines its ink absorption.

The looser the paper, the bigger the porosity and the stronger the ink absorption. For example, newsprint is relatively loose and has strong ink absorption. Therefore, the transfer of ink on newsprint is fast and is conducive to the improvement of printing speed. Coated paper is not as loose as offset paper, and its aperture is not as large as that of offset paper. However, the fixation of ink during printing is not necessarily slower than that of offset paper. There are two main reasons. First, the amount of ink supplied for coated paper is small; The second is that there are innumerable small capillaries between the pigment particles attached to the coated paper surface. The absorption capacity of many small capillary tubes is much larger than that of a few coarse capillary tubes. In addition, the absorption selectivity of the coated paper to the binder is strong, and the low-molecular-weight components in the binder are allowed to penetrate into the paper, and the polymer components in the binder still remain in the ink layer, so the ink layer can be improved. Firmness and gloss.