Influence of pressure on printing quality of the m

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At present, although some large enterprises have introduced foreign multi-color offset printing machines, domestic single-color offset printing machines still have many users in China, and many people also use J2108, J2101, j4103 single-color offset printing machines for multi-color overprint. If the pressure adjustment is not good, it is easy to cause problems such as premature wear of the printing plate and inaccurate overprinting, which will affect the quality of printing products

in order to print high-quality prints, the key is to adapt the pressure to the opportunity of development. The ideal pressure is the minimum pressure that the imprint is strong, clear, and the printing plate point is transferred to the paper without deformation

to achieve the "ideal pressure", it is necessary to select and install gaskets in strict accordance with the design requirements. Taking j4105 machine as an example, the shrinkage test is an experimental method often used to study the properties of materials. According to the instructions, the printing plate liner should be 0.60mm, and the image leather liner should be 3.25-3.40mm. When printing, we adopt the following methods (see Table 1)

Table 1 j4105 machine liner

printing plate roller rubber roller

printing plate: Starlight PS plate thickness: 0.30mm, air cushion image leather thickness: 1.75mm, felt cloth thickness: 0.83mM

liner paper: 120g/m2 Kaishantun paper, 3 sheets of 0.39mm liner paper: 120g/m2 Kaishantun paper, 4 sheets of 0.52mm

total thickness: about 0.69mm, about 3.10mm

if other effects are ignored (such as uneven pressure of the ink roller, improper pH value of the fountain solution, mechanical vibration, and mechanical accuracy), the pressure formed by the above liner is very close to the ideal pressure. Under this pressure condition, the printed products are stable in quality, solid and clear, accurate in multicolor overprint, with an error of plus or minus 0.2mm, high printing resistance of the printing plate, 30000-50000 prints of the line plate (the printing plate is not processed by baking), and more than 50000 prints of the text and line plates

special attention should be paid to a requirement in the j4105 manual that the scale of the external voltage regulator is 0 degrees, which is actually to make the shoulder iron gap at both ends of the drum consistent. Some offset printing machines with long service life and serious mechanical wear may have errors in the scale of the external voltage regulator. At this time, take a fuse of 0.5mm to measure the shoulder iron clearance of each drum to make it meet the requirement that the scale of the external voltage regulator is 0 degrees

in practical work, we also found that when using different papers, the effect of prints under the same pressure is also inconsistent. For example, using Japanese "Qixing brand" 105g/M2 double copper and 200g/M2 double copper paper, the printing effect of 105g/M2 double copper is good under the same pressure, while 200g/M2 double copper has overprint error, especially the horizontal (pull gauge direction) overprint error is obvious. The main reason is that when printing with 200g/M2 paper, the paper thickness increases, which increases the pressure between the rubber cylinder and the embossing cylinder. See Table 2 for the thickness of different papers

therefore, in actual production, the thickness of the initial cushion of the pressure between the rollers should be flexibly adjusted according to the thickness of the printed paper to ensure that the pressure is appropriate. When converting thin paper to thick paper, the thickness difference between the two kinds of paper shall prevail, and the center distance between the rubber cylinder and the embossing cylinder shall be reduced or the rubber cylinder shall be padded with paper

in addition, the pressure is related to the picture length during printing, and the picture length changes with the thickness of the drum lining. If you increase the thickness of the printing plate or rubber drum lining, the length of the picture will shrink, otherwise it will be extended. So we can use this feature to change the picture by changing the thickness of the lining. The specific method is to add a 52g/M2 plate lining paper when printing the first color, or reduce the center distance between the plate cylinder and the rubber cylinder through an external pressure regulator, so as to shorten the length of the picture. In the actual printing process, there is a certain amount of elongation and deformation when the paper is printed in one color, so there is a small amount of compensation for the above picture length shortening. When printing the second, third and fourth colors, take out 52g/M2 liner or restore the roller pressure, the picture length will be extended due to the pressure reduction, which is basically consistent with the picture length of the first color. We have used this method many times in actual printing, and the effect is good

Table 2 thickness of different paper

paper type (g/m2) 105 128 157 200

paper thickness (mm) 0.07 0.12 0.14 0.1 its price is higher 75

under special circumstances, an appropriate increase in the pressure between the rubber cylinder and the embossing cylinder is conducive to the improvement of print quality. Here we mainly talk about several aspects of the maintenance of the experimental machine. For example, when printing the field with double offset paper, the ink cannot completely penetrate the paper, and there is always a white phenomenon. After we increase the pressure between the rubber cylinder and the embossing cylinder, the printing quality is significantly improved, and the field printing with double offset paper achieves the effect of field printing with double copper paper

to sum up, pressure has a great impact on the quality of prints. In practical work, we should be good at observation, use our brains and think of ways

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