What performance requirements should printing paper meet?

Paper Printing Requirements

The color tone of the paper should be as pure as possible to achieve the same texture, the degree of dust on the paper should not exceed the allowable range, have the smallest light transmittance, and have the mechanical strength to ensure normal printing. The thickness, tightness, structural properties, etc. of the paper should be consistent within the same printing run. The edges of the paper should be at right angles, and the slope error should not exceed 3mm.

Paper Flatness Requirements

The flatness of paper directly determines the printing quality of printed matter. When printing, paper with high smoothness can better contact with the layout, so that the ink layer on the printing plate can be evenly transferred to the surface of the paper. During printing, paper with low flatness will cause uneven contact between the layout and the paper surface, and will cause uneven transfer of the ink layer to the paper surface. If you encounter paper with low flatness, you can increase the pressure appropriately during printing to make up for the phenomenon of printing errors caused by uneven surface.

Requirements for paper ink absorption

The absorption of ink by paper mainly depends on the compactness of paper fibers (the size of voids). When the gap between the paper fibers is small, the effect of the fiber capillary is affected due to too few suspended fibers, resulting in a decrease in the ink absorption of the paper. If the gap is too large, the ink and pigment will be absorbed together due to too much absorption of the connecting material, resulting in printing penetration.

Requirements for paper elasticity and plasticity

During storage, printing, etc., paper changes due to the surrounding environment. For example, under the action of external force, it will change its shape and size instantly, and when the external force stops, the paper will return to its original shape and size. This deformation process is called sensitive elastic deformation; when the paper is subjected to an external force, it will change shape and size within a certain period of time. When the external force is stopped, it will slowly return to its original shape and size. This deformation process is called elastic deformation; when the external force is canceled, the paper is still in the state of shape and size deformation caused by external force, which is called plastic deformation. Sensitive elastic deformation and inelastic deformation are reversible deformations, while plastic deformations are irreversible deformations.

Paper Surface Strength Requirements

The surface strength of paper determines its surface abrasion resistance, anti-dusting, anti-fluffing and other decisive functions during printing. In order to obtain clearer dots during printing, some inks with higher viscosity will be used. If the surface strength of the paper is not strong enough, it is easy to lose powder and lint, and adhere to the surface of the printing plate; if ink with low viscosity is used, the ink will emulsify with the fountain solution during lithographic printing, resulting in dirty blank areas of the printing plate.

Paper Moisture Content Requirements

The moisture content of paper directly affects the quality of printed matter. If the moisture content is too high, the strength of the paper will be reduced. Under the action of external force, the water fiber of the paper will be pulled out, which will strengthen the periodic deformation and affect the drying speed of the printed matter; if the water content is too low, the paper will become brittle, easily damaged and generate static electricity. Since the moisture content of the paper has a great correlation with the surrounding environment, the humidity and temperature of the brush room should be properly arranged to maintain the balance of the moisture content of the paper.