Printing Performance of Paper

        The general requirements for the quality of printing paper are as follows: the color of the paper shall be as white as possible, and each paper in the same batch of paper shall have the same texture, and the dust degree of the paper shall not exceed the allowable range; Printing Performance of Paper

        Minimum light transmittance and the same gloss; It has the mechanical strength to ensure normal printing, and the thickness, tightness, structure and other properties of the paper should be the same in the same batch, if there is a great difference. Printing Performance of Paper

       It will increase the difficulties in the printing process and reduce the quality of printed matter. The water content is between 6-8%. The edge of flat paper shall be at right angles, and the slope error shall not exceed ± 3mm.Printing Performance of Paper

The printing performance of paper mainly includes:

(1) Smoothness

        Smoothness is the most important printing performance of paper. No matter what kind of printing, the outline of handwriting and image printed by paper with smooth surface is relatively clear, because 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; Some Operating Specifications for Improving Printing Quality

        For the paper with low smoothness, due to the uneven surface during printing, the contact between the paper surface and the printing plate must be uneven during embossing, and the transfer of the ink layer will be affected, so the transfer of the ink layer to the paper surface is uneven.Some Operating Specifications for Improving Printing Quality

          In lithography, due to the use of elastic blanket as an indirect transfer ink layer, the requirement for smoothness is not very high. However, when printing advanced products, in order to ensure that the reproduction of layers is not lost, paper with high smoothness should also be selected for printing.Some Operating Specifications for Improving Printing Quality

       For the paper with low smoothness, properly increasing the printing pressure during printing can appropriately make up for the phenomenon of false imprinting due to its unevenness.Some Operating Specifications for Improving Printing Quality

       The gloss of the paper also depends on the smoothness of the paper surface. The paper with very smooth surface is shiny, while the paper with rough surface is dim.Some Operating Specifications for Improving Printing Quality

(2) Ink absorption of paper

       The ink absorption of paper is the degree of ink absorption of paper. The more ink absorbed by the paper, the stronger the ink absorption of the paper. On the contrary, it is poor. The strength of ink absorption is mainly reflected by the penetration of connecting materials in the ink.Some Operating Specifications for Improving Printing Quality

        The paper’s absorption of ink mainly depends on the size of the gap between the paper fibers, that is, the tightness of the paper.Some Operating Specifications for Improving Printing Quality

      When the gap between the paper fibers is small and there are few broomed fibers, the fiber capillary effect is affected, and the ink absorption of this paper is poor. If the gap is too large, it will not only absorb more connecting materials, but also absorb the pigments together, resulting in through printing.Some Operating Specifications for Improving Printing Quality

       The ink absorption of paper is related to the structure of paper itself. It is also related to the viscosity of ink, printing pressure and embossing time.Some Operating Specifications for Improving Printing Quality

(3) Elasticity and plasticity of paper

       In the printing process, the paper will be deformed. For example, during relief printing, due to the bulge of the printing part of the layout, the printing plate presses the paper tightly, so that the paper is deformed and uneven.Some Operating Specifications for Improving Printing Quality

        Under the action of machinery, paper will produce sensitive elastic deformation, anelastic deformation and plastic deformation due to different pressure. Under the action of external force, the paper will instantly change its shape and size. Some Operating Specifications for Improving Printing Quality

       When the external force stops, the paper will immediately return to its original shape and size, which is called sensitive elastic deformation; The paper changes its shape and size in a certain time interval under the action of external force. Some Operating Specifications for Improving Printing Quality

       When the external force stops, the paper gradually and completely returns to its original shape and size, which is called anelastic deformation; Some Operating Specifications for Improving Printing Quality

       When the external force is cancelled, the paper still maintains the deformation caused by the external force, which is called plastic deformation. Sensitive elastic deformation and anelastic deformation are reversible deformation, while plastic deformation is irreversible deformation.Some Operating Specifications for Improving Printing Quality

         The deformation of paper depends on the humidity, calendering and compaction of the paper itself. The fiber has elasticity, and the sensitive elasticity of the fiber is beneficial to the printing process.Some Operating Specifications for Improving Printing Quality

(4) Surface strength of paper

       The surface strength of the paper is particularly important for the wear resistance, powder and hair loss of the surface during printing. In order to obtain a clear dot, it is necessary to use ink with high viscosity.Some Operating Specifications for Improving Printing Quality

       If the paper strength is not enough, it is easy to produce powder and hair loss and adhere to the plate surface. If the ink viscosity is low, in lithography, the ink and fountain solution are emulsified, The blank part of the printing plate will get dirty.Some Operating Specifications for Improving Printing Quality

(5) Moisture content of paper

       The percentage of the weight of water contained in the paper to the weight of the paper is called the water content of the paper.Some Operating Specifications for Improving Printing Quality

       The water content of the paper affects the printing quality. If the water content of the paper is too much, the strength of the paper will be reduced. Under the action of external force, the fiber will be pulled out, the plasticity will be enhanced, and the imprinting drying speed will be affected; If the water content of the paper is too small, the paper will be brittle, easy to cause damage and static electricity.Some Operating Specifications for Improving Printing Quality

       The fiber of the paper is hygroscopic. The temperature and humidity of the surrounding environment determine the water content of the paper. The water content of the paper is balanced with the ambient temperature and humidity, and the humidity changes with the temperature. Some Operating Specifications for Improving Printing Quality

         The relative humidity in the air changes by 10% and the water content in the paper changes by 1%. Therefore, to control the water content in the paper, it is necessary to control the temperature and humidity of the workshop.Some Operating Specifications for Improving Printing Quality

        Generally, the temperature is controlled at 18 ° – 24 ℃ and the relative humidity is controlled at 60-65% to maintain the balance of water content.Some Operating Specifications for Improving Printing Quality