When the paper fiber swells with water, the size of the fiber cross-sectional direction changes greatly, while the length direction hardly changes. Therefore, in the printing process, the stretch rate of the paper thread in the lateral direction is larger than that in the longitudinal direction. During paper storage, the edges are in contact with the air and the middle part is less. When the environmental humidity is lower than the paper humidity, the paper absorbs moisture and produces a "lotus edge" phenomenon; when the environmental humidity is lower than the paper humidity, the paper is wet and produces " "Tight edge" phenomenon. If the paper has a "lotus edge" or "tight edge" phenomenon before printing, the paper undergoes different compression deformations when it is subjected to pressure during printing, which will cause the problem of inaccurate printing of printed images and text. In serious cases, the paper is prone to wrinkles.
Changes in water content can also cause paper curl problems. One-sided coated paper is coated on one side and highly absorbent fibers on the other. The coating basically does not stretch, and the degree of fiber expansion and contraction is relatively large, so the curling problem of single-sided coated paper is more prominent than double-sided coated paper. In the environment with relatively high humidity, the single copper paper easily curls to the coated surface; in the environment with relatively low humidity, the single copper paper easily curls to the fiber surface. At the same time, during the printing process of single-coated paper, if the moisture content changes (excessive drying or excessive wetting), the moisture balance of the fiber and the coating is destroyed, and the loss of moisture will curl to the uncoated surface, and the absorption of moisture will The coated surface is curled. If the paper has a curl problem before printing, it will affect the smoothness and printing efficiency of the printing; if the paper has a curl problem during or after printing, it will have a serious impact on subsequent processing, packaging and other operations.
The change of paper moisture content will not only cause the deformation of the paper, but also cause the change of other properties of the paper, which directly affects the printing suitability of the paper. If the moisture content of the paper is too large, the tensile strength and surface strength of the paper will be reduced, the plasticity will be enhanced, and the drying speed of the blot will be affected, which will easily make the back of the paper dirty; if the moisture content of the paper is too small, the paper will be brittle and hard during the printing process A large amount of static electricity will be generated due to friction, resulting in poor paper feeding or uneven paper collection, which wastes paper and affects printing efficiency.
Since paper is greatly affected by the environment, it is recommended that the outer packaging of the paper should not be removed prematurely.
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