Whether the paper can be used for printing smoothly and high quality depends on the printability of the paper. The requirements for printing paper are: the color tone of the paper shall reach the color purity of the same texture as far as possible, the dust degree of the paper shall not exceed the allowable range, have the minimum light transmittance, and ensure the mechanical strength during normal printing, and the thickness, tightness and structural characteristics of the paper shall be the same in the same printing batch, The paper edge shall be right angle and the slope error shall not exceed ± 3mm.
Smoothness of paper: the smoothness of paper directly determines the printing quality of printed matter. The paper with high smoothness can better contact with the layout during embossing, so that the ink layer on the printing plate can be evenly transferred to the paper surface. The paper with low smoothness will cause uneven contact between the layout and the surface of the paper during embossing due to the uneven surface during printing, so that the transfer of the ink layer to the paper surface is uneven, such as touching the paper with low smoothness, The pressure during printing can be appropriately increased, and the phenomenon of false imprinting due to uneven surface can be appropriately compensated.
Ink absorption of paper: the absorption of ink by paper mainly depends on the tightness between the fibers of the paper (the size of the gap). When the gap between paper fibers is small, there are too few broomed fibers, which affects the function of fiber capillary and reduces the absorption of paper to ink; If the gap between the paper fibers is too large, the ink and pigment will be absorbed together due to excessive absorption of connecting materials, resulting in the phenomenon of through printing of the printed matter.
Elasticity and plasticity of paper: paper will change due to different surrounding environment in various processes such as storage and printing. For example, under the action of external force, it will change its shape and size instantaneously, 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 external force, it changes its shape and size within a certain interval. When the external force stops, it slowly returns to its original shape and size. This deformation process is called anelastic deformation; When the external force is cancelled and the paper remains in the state of shape and size deformation caused by external force, it is called plastic deformation. Sensitive elastic deformation and anelastic deformation are reversible deformation, while plastic deformation is irreversible deformation.
Surface strength of paper: the surface strength of paper determines the wear resistance, powder dropping resistance and fuzzing resistance of the surface of paper during printing. In order to obtain a clearer dot during printing, some inks with high viscosity will be used. If the surface strength of the paper is not enough, it will be easy to lose powder and hair, and adhere to the surface of the plate; If the ink with lower viscosity is used, the blank of the printing plate will be dirty due to the emulsification of the ink and the fountain solution in lithography.
Water content of paper: the water content of paper directly affects the quality of printed matter. If the water content is too much, the strength of paper will be reduced. Under the action of external force, the paper fiber will be pulled out to enhance the plastic deformation and affect the drying speed of imprinting; If the water content is too low, the paper will be brittle, easy to cause damage and generate static electricity. Due to the great correlation between the water content of the paper and the surrounding environment, the humidity and temperature of the printing room should be properly arranged to maintain the balance of the water content of the paper.
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