Multi-color Printing Overprinting Reasons and Exclusion

After reading the article entitled “Analysis and exclusion of multi-color printing overprinting failures” written by Comrade Gu Dongying in the 6th edition of “Printing Technology” in 1996, I feel that in addition to some of the reasons for its discussion, there is little to look at. However, there are several other reasons that have an impact on the accuracy of overprinting that need to be explored for reference by peers.

First, the effect of printing plate deformation on overprint

1. Printed version of the tensile deformation of metal plates have a certain degree of extension, under the effect of tension will produce tensile deformation, and the zinc plate deformation is more pronounced. Under normal circumstances, we found that overprinting was inaccurate when printing. Most of them were adjusted by printing plates. When the panel is stretched by an external force, the printing plate is closely attached to the surface of the cylinder shell, and at the same time, tensile deformation is inevitable. The greater the tensile force, the greater the tensile deformation of the layout, and the uneven distribution of the tensile deformation, the greatest force is exerted on the crotch edge and the drag edge of the plate, the tensile deformation is also large, the internal force is small, and the tensile deformation is also small. small. Therefore, it is not always possible to solve the problem of overprinting through the pull-up version.

2. Reducing the way to set up printing errors caused by plate loading When the plate is loaded, the force is too large to be used. When the printing plate is displaced, the corresponding force should be relaxed first, ie, the plate screws are loosened so that the friction between the back of the printing plate and the surface of the roller is minimized. At this time, the printing plate will be displaced under the action of the pulling force, and The tensile deformation of the printing plate is controlled to a minimum value. Second, the timeline on the printing plate should be aligned. In the multicolor printing process, before the first color is printed, the position of the register line is marked on the plate cylinder, and when the printing plate after the second color is installed, the rules of the first color are aligned. line. This will not only increase the speed of the upper version, but also reduce the number of pull-outs and avoid abnormal stretching. Because the rule is found to be inaccurate after trapping, you need to pull the plate. The more times you pull, the greater the possibility of tensile deformation. Therefore, try to use as little as possible to solve the overprint problem.

3. Plate thickness and pattern size variation The pattern of the lithography is reproduced on the surface of the metal plate. When the printing plate is tightened on the cylinder, the plate is bent, the inside of the plate is partially compressed, and the outer part is stretched, causing the graphic to stretch. Therefore, the thicker the metal plate, the greater the dimensional elongation of the figure. In plate printing, the same manufacturer, the same model, or the same boxed printing plate should be used as much as possible.

Second, the increase or decrease of roller liner impact on the overprint

In the printing process, due to the expansion and contraction of the paper, overprinting can be inaccurate, and the method of increasing or decreasing the thickness of the drum liner can be used to solve the problem of misalignment between the radial paths. However, the increase or decrease in the thickness of the liner should not be too large, and a large increase or decrease in the thickness of the liner will have other disadvantages.

1. The increase and decrease of the printing plate liner by the printing plate liner affects the tensile deformation of the printing plate. The thicker the plate pad, the greater the dimensional elongation of the pattern.

2. Increase or decrease of the blanket cylinder liner When reducing the printing plate liner and increasing the blanket cylinder liner, the radial deformation of the pattern increases due to the increased deformation of the blanket. Another is to reduce the thickness of the blanket cylinder, while increasing the thickness of the printing plate liner, the deformation of the blanket extrusion deformation is reduced, the latter commonly used.

Third, the effect of rubber blanket elongation on the pattern overlay

The blanket is stretchable and the tighter the blanket is stretched on the drum, the smaller the elongation is, and the pattern change is small.

1. Use a blanket with a small elongation. When installing, the longitudinal and transverse directions of the blanket should be observed, and the longitudinal direction should be perpendicular to the axis of the drum to reduce the elongation.

2. In the process of overprinting, try to keep the rubber market tight.

3. If there is a trace of misalignment of the width, the elasticity of the blanket should be properly adjusted.

4. The cutting, punching of the blanket, the tightening of individual screws, the tearing of the rubber layout, the unevenness of the gasket, etc., can cause partial tightness and looseness, resulting in partial overprinting. In short, overprinting is not allowed except mechanical, adjustment, paper and other issues, it should also pay attention to these minor changes brought about by overprinting is not allowed. Improper overprinting usually occurs instantaneously at the time of high-speed printing. It is formed by the accumulation of trace changes and it is difficult to observe directly. Therefore, as long as we pay full attention to the printing, the analysis of the original position to take the most appropriate measures, so that it can avoid or reduce the occurrence of fitting errors.





Source: China Packaging Online