Printability analysis of the hottest coated paper

Printability analysis of coated paper and offset paper

coated paper is made by coating a layer of white slurry on the base paper and calendering. Coated paper has smooth surface, good ink absorption, good surface whiteness and uniformity. It is one of the most commonly used paper for offset printing. It is mainly used for exquisite printing products such as color covers of periodicals and magazines, color pictorials, high-end trademark packaging, etc

requirements for the printability of coated paper:

① the surface smoothness, whiteness and uniformity of coated paper should be high

coated paper is mainly used for fine printing products of multi-color overprint, with 150 lines/inch ~ 175 lines/inch points very small. To accurately and perfectly reproduce the printing points on the PS plate to the printed matter, it is required that the smoothness, whiteness, uniformity and other indicators of coated paper should be high, otherwise, it is difficult to reproduce complete and bright points, It directly affects the subtle level and tone of printing products

② coated paper does not remove powder and galling

if the white slurry and filler coating coated on the coated paper are not firmly bonded and have poor surface strength, the phenomenon of de powder, galling and even peeling will occur during printing, which requires that the binding force between the original paper base and the filler and slurry coating layer in the production process of coated paper should be high

in addition, don't get damp when storing coated paper, don't get wet and deform when transporting paper, and don't stack it in a damp and dark warehouse. There are spots and mildew after being damp, and it is also prone to de dusting and galling

③ the ink absorption of coated paper should be as small as possible

the offset ink of printed coated paper is a dry form mainly composed of oxidized conjunctiva. The ink absorption speed of coated paper should not be too fast, which is generally controlled between 30 ~ 60 seconds, and that of higher-grade coated paper is more than 90 seconds. Because offset ink is in the form of oxidized conjunctive drying, the ink absorption of paper is small, and most of the ink film is accumulated on the surface of paper, with less penetration, so the product variety and quality level of sensors and tension machine components in China are bright. If the ink absorption of coated paper is too fast, it will affect the gloss of the print, and even cause the powdering of the imprint in serious cases

offset paper is composed of fiber with 50% bleached chemical wood pulp and 50% other pulps, such as rag pulp, lint pulp, bamboo pulp, straw pulp, wheat straw pulp and reed pulp. Therefore, it is suitable for color overprint

requirements for printability of offset paper:

① it is required that offset paper has small flexibility and strong water resistance

offset paper has greater flexibility than coated paper. Offset printing requires water, which may cause the expansion and deformation of the paper. The deformation of the paper will cause inaccurate overprint, resulting in unclear and fuzzy patterns. It is required that the expansion rate of offset paper should be small and the water resistance should be good

before offset printing, the offset paper should be hung and adjusted to make the paper warm and wet. The experimental machine adopts the internationally popular host structure, imported servo speed regulation system and electromechanical (Panasonic, Japan), imported reducer (Germany), imported ball screw (Germany) and the temperature and humidity of the printing workshop should be consistent, and the water content of the surrounding edges and middle surfaces of the paper should be uniform

② the offset paper shall not be roughened and powdered, and the texture shall be tight.

the offset paper is easy to be roughened and powdered, and it is required to have a certain surface strength. If the surface strength of offset paper is poor and the texture is loose, it is easy to roughen and de powder, which will affect the quality of printing products. Therefore, when making paper, adjust the amount of filler and rubber, and adopt the calendering process to improve the surface strength of the paper

③ the ink absorption should not be too high

the ink used in offset paper printing is mainly offset resin ink, which is mainly oxidized conjunctive drying. It is required that the surface of offset paper has a certain thickness of ink layer to ensure that the printed matter has color luster. If the ink absorption of offset paper is too strong, the ink seeps into the paper fiber, and the ink layer on the surface of offset paper is thin, there is no printing luster, and the printed matter is dry and not bright

④ the paper surface must be smooth and free of sand and pimples

the surface of offset paper requires good gloss, less paper ash, less sand, uniform thickness, and flat surface, so as to avoid weak imprinting and many white spots. The point reproduction effect is poor

offset paper should have less rags and no bumps on the surface, so as to prevent the rags and bumps on the surface of the paper from crushing the blanket, lining and wearing the printing plate on the offset press, resulting in the reduction of the printing plate resistance

several points should be paid attention to when printing offset paper:

① offset paper should be tested for technical quality before use. After basically understanding its characteristics, it should be hung and adjusted according to the specific conditions of the factory

② when printing offset paper, it is not suitable to stack the printed matter too high to prevent the back from sticking dirty

③ compared with coated paper, offset paper has greater flexibility. The offset press carries out a comprehensive and strict examination on students. The water content and the concentration of water bucket solution should be strictly controlled. On the premise of not dirty version, the minimum water consumption should be used to avoid excessive flexibility, so as to ensure the accuracy of overprint. The printing semi-finished products are wrapped in plastic in the offset workshop. The LRM designed by the researchers takes the shape of a rectangular unit including three metal cores and keeps them properly

④ the viscosity of the ink should not be too high, otherwise it will cause de dusting and galling. The viscosity is large, so it can be treated with debonding agent. Debonding agent is a mixture of resin and wax, which is loose and lubricated, and can reduce the viscosity of ink and the galling of paper. Do not affect the gloss and fluidity of ink color, but do not use too much. There are common debonding agents. Debonding agents produced by Shanghai ink factory or other manufacturers can be used. (text/WangXinCheng)