Paper and board smoothness

Smoothness refers to the time in seconds required for a given volume of air to pass through a gap between the surface of a specimen subjected to a certain pressure and the glass surface under a certain degree of vacuum. The smoothness is determined by the surface condition of the paper. If the paper is uneven, the smoothness of the paper is poor. Paper reports have wrinkles, embossments, cardboard blocks, creases, curtains, spots, dust and copper nets and blankets, or there are powder, hair loss, fiber gaps, etc. will reduce the leveling of the paper surface, This reduces the smoothness of the paper. Therefore, the general smoothness is related to the appearance of the paper. A rough sheet of paper cannot attract people's interest. There are too many stencils on the surface of the paper, blanket prints, or wrinkles, fluffs, and very bad embossing phenomena. Most of them cannot meet the requirements. Smoothness is an important property of writing paper, because writing paper is used on both sides, and no matter which side is required to be impermeable to ink while writing, it affects the other side. The writing tip is not hooked on the paper and is fluent in writing. For printed paper, the greater the smoothness of the system, the more uniform the surface, the better the printing process. This is especially important for printing pictures. Different printing methods have different requirements on the smoothness and surface uniformity of the paper. Gravure printing requires total smoothness and surface uniformity, followed by offset printing. The smoothness of letterpress printed paper can be slightly lower. For papers with different uses, consider smoothness:

(1) Smoothness and softness must cooperate with each other. To maintain a certain degree of smoothness and softness, it is possible to produce good-quality paper. This is because relatively soft paper can make the surface of the paper sufficiently fully in contact with the surface of the printing plate, which is particularly important for the printing of the convex plate. Sometimes in order to ensure the softness of the paper, the degree of calendering of the paper has to be reduced so as to reduce the smoothness of the paper. It is often found that the smoothness is relatively low, and the softer paper has better printing performance than the harder paper with higher smoothness. Therefore, in the manufacture of printing paper, it is required to produce as much as possible a relatively smooth and relatively soft paper.

(2) The relationship between smoothness and ink absorption. Paper with high smoothness tends to have a large degree of tightness (especially in the case where paper machine calendering is used to increase the smoothness), so that the ink absorbency of the paper is reduced, so that high ink-absorbing paper is required (for example, for high-speed rotation The newsprint of the press should not be too smooth.

(3) The problem of poor smoothness on both sides of the paper. The smoothness of both sides of the paper is inconsistent. In general, the smoothness of the front surface is greater than the smoothness of the back surface. As the general paper is printed on both sides, the quality of the print has a great influence. According to the requirements of printing, the difference between the smoothness of the front and the back of the gravure printing paper is not more than 20%, that of the No.1 offset printing paper is no more than 20%, that of the No.2 offset printing paper is no more than 30%, and that of the relief printing paper is no more than 25 to 35%. .