The author believes that to solve the overprint problem must control the stability of paper deformation and paper rules. There is no doubt that the requirements for these two elements are much stricter than for ordinary four-color printing . In ordinary four-color printing, one side of the paper is printed only once, and once formed, even if the paper is slightly deformed and the rules are a little small, the four colors are always overprinted, and there is no serious quality problem. Multi-color printing is sloppy, as long as the first printing is completed, the paper changes, the rules are beating, it will be reflected on the overprinting of the second printing, resulting in inaccurate overprinting, whitening, seriously affecting product quality, and even The roads, rivers, and boundaries on the multi-color atlas are misplaced and mislead readers.
Control paper deformation
There are two main factors that cause paper deformation: the temperature and humidity of the workshop and the amount of dampening solution used in the printing process.
1. Strict control of workshop temperature and humidity
The author has encountered several versions of the work of too many color atlases. Because the temperature and humidity are not well controlled, the paper is severely deformed after the four-color printing is finished. When the secondary color is printed twice, the two sides "fighting" and relying on the top paper. The paper should be unloaded by the outside, and the captain had no choice. In the end, he had to print a special color version, burn half of the content, and half of the half printed. It was time-consuming and could not guarantee the printing quality (the paper was not deformed regularly). Therefore, when printing multi-color atlas, each team should observe the temperature and humidity meter before starting and during the production process. If it does not meet the standard, it can turn on the humidifier, air conditioner or sprinkle water on the ground to improve the temperature and humidity of the workshop. Generally, the ideal environment of the workshop is that the temperature is maintained at about 25 ° C and the relative humidity is maintained at about 60%.
2. Control the amount of dampening solution
The amount of water in printing should follow the principle that “the work piece is as small as possible without being dirty or dirtyâ€. The amount of water used is small, not only the color of the graphic is full and bright, but also the paper deformation is negligible, laying a good foundation for the second overprint. On the contrary, the use of water is large, and the four colors may be overprinted, and the spot color of the post-order is overprinted.
How to judge the size of the water volume? The simple and easy way is to observe the plate cylinder from the side, if the layout is dark gray, it means the water is just right; if the layout is bright and shiny, it means the water is big and it has to go down.
Keep the paper running rules consistent during the printing process
1. The adjustment parts are adjusted to the best condition, without sick operation
According to the author's many years of experience, when multi-color printing, the probability of the bottom rule is small, and more is the side of the situation. In daily production, we must do a good job of daily maintenance of the side rules. Before printing the fine multi-color atlas, check and test, observe whether the side gauge work is normal, have problems in time, and do not take sick work.
Of course, while paying attention to the side rules, you can't ignore the bottom rules. In order to stabilize the bottom gauge, the pressure of the paper feed roller on the paperboard, the tightness of the paper feeding belt, and the pressure of the brush wheel should be moderate and uniform, so as to prevent the paper from being skewed, under- and under.
2. Diligent paper during the printing process, check the rules
When the captain prints the multi-color atlas, he must diligently draw paper and diligently cut the paper, and open the printed sheet to check whether the ruled line is at the same horizontal line. Whether the edge line is constant riding, find abnormalities, deal with it in time, and ensure the stability of the rules. Consistent.
In addition, the assistant should assist the captain in closing the rules and working hard in the details. For example, each time you print, you must draw a “ten†rule line on the plate, and the “—†line is used to check the bottom rule. “
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