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Printing color processing

2016-07-11 15:09:56

In offset lithography process, often encounter the phenomenon of false color seal, main show is on the print print field part spotted or weak, graphic or lines incomplete is not complete, the image of the gradual levels of reproducibility difference or points lost. Appeared in the process of printing ink is not true for many reasons, it involves many factors, including the performance of the paper, ink performance, the quality of the plate, printing rubber cloth, printing pressure, printing machine performance and the quality of the printing process, etc.

If in the process of printing, paper, ink, the performance is stable, quality meet the requirement of printing plate production, printing machine working performance is relatively stable, or the ink printing false phenomenon, its main reason is the problem of printing pressure. In offset printing, the printing pressure directly determines the size of the printing ink in the process of transfer, if uneven local appeared in the process of printing pressure, will directly result in the printing ink.

In offset printing, rubber blanket compression deformation is the fundamental guarantee of printing pressure, printing ink transfer are the result of the rubber blanket compression deformation. As a result, the size of the printing pressure and uniform degree of offset printing has a direct relationship with the rubber cloth.

Coated in the roller rubber cloth, at the same time, by the action of the tension and the printing pressure, with the increasing the number of roller, rubber cloth compression deformation stress accumulation, rubber cloth will become stiff and lost the original softness and high elasticity, even in the rubber blanket surface will appear bright or signs of cracking, which leads to uneven local printing process of printing pressure.

Another aspect, because the rubber roller installed between the plate cylinder and embossing roller, rubber cloth on each small unit a week per rotation, are respectively and two roller contact each one. Therefore, the force is a cyclical change, it is because of rubber cloth periodical change of force, can lead to internal friction rubber cloth, lead to the ageing of the rubber cloth, affect the uniformity of printing pressure, could eventually lead to the scrap rubber cloth. Especially in modern high-speed offset press, rubber cloth stress cycle frequency is higher, more internal friction of rubber cloth, rubber cloth life will be more short, the impact on the printing pressure will lead to greater.

Except for offset printing pressure rubber cloth, rubber cloth under the action of the stamping force, should also have good plate picture and text part of the ability of printing ink to the surface of substrates, i.e. the ability to ink and ink, but the aging of rubber cloth will change the ink transfer ability, can also lead to inky false phenomenon.

So, the printing ink is one of the main causes of false printing rubber cloth performance degradation, reduce the processing of the offset printing process printing ink false way also should from the rubber cloth. When choosing a rubber cloth should consider the following technical indicators:

1, suitable hardness, suitable hardness points clear, printed ink evenly, and generally choose 70-70 degrees (xiao) rubber cloth;

2, small compression deformation, in order to prevent the printing process to reduce the thickness of the rubber cloth, elastic reduction, hardness increases, so should choose small compression deformation of rubber cloth is preferred;

3, excellent transmission performance: rubber cloth as by the middle of the network transfer media, must have good ink absorption ability, ink transfer ability and strong hydrophobicity, otherwise can't enough amount of ink transfer printing, can't reach the effect of print color required. At the same time, the surface of rubber cloth glue line should have a certain roughness, surface fine clean without impurities;

4, good oil resistance, solvent resistance, surface rubber cloth does not happen because of the chemicals in the process of contact printing, and violation of its application performance.

5, uniform thickness to: rubber cloth the flatness error should be less than 0.04 mm, otherwise the printing pressure is uneven, product ink will obviously uneven, seriously affecting the quality of printed matter;

6, elongation is appropriate: rubber blanket elongation as small as possible, so that in the printing process to guarantee the accuracy of the overprint, network complete, by clear.

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