Overprint Errors in Prints (1)

The yellow, magenta, cyan, black and other monochrome printing plates are installed on a monochrome printing machine or a multicolor printing machine. Each block printing plate must have a relatively precise registration position in order to obtain the printed matter with correct specifications and clear images. If the position of the plate is shifted,

The tone and color of prints have to change, and the clarity of the images will also decline.

Now, the design and manufacturing level of the printing press is relatively high, and the accuracy of overprinting can be controlled within 0.01mm. Therefore, as long as the printing press is debugged, the accuracy of the registration of the machinery can be guaranteed. However, the printed matter is the use of printing plates and printing materials.

Materials, inks, and printing machines cooperate with each other to produce large-volume products. Overprint errors in printed matter are accumulated during the printing process. Therefore, to understand the overprinting precision requirements of printed products, analyze the changing rules of overprinting errors, and adopt

Corresponding measures can minimize overprinting errors in printed matters.

First, the accuracy of print overprint requirements


Theory and practice have proved that the human eye can observe the normal distance, and the ability to recognize subtle lines can reach 0.1mm. The tonality of printed image is generally reproduced by dots. The diameter of each dot is actually less than 0.1mm. The human eye alone cannot

Recognition was made, and therefore, 0.1mm was taken as the reference for overprinting accuracy.

However, the human eye is extremely sensitive to changes in color. Even if the colors are less than 0.1 mm in the print, the human eye can recognize it. Therefore, in the printing process, from the point of color change, the requirement for overprint accuracy is more stringent.

When printing with a single-color offset press, the ink is superposed in a wet-laid manner, that is, the second color is printed when the first color ink is dried quickly. If the print image appears to be misaligned due to misregistration and overprinting errors, as long as it does not exceed 0.1 mm, the edge of the dot is slightly obscure when viewed with a magnifying glass, but the overall tone value does not change much and is not easily affected by the human eye. aware.

When printing with a multi-color offset printing press, the ink is superposed in a wet and wet manner, that is, when the first color is completely wet, the second color is printed. Changes in tone and color are caused by overprint errors in the printing process. When printing, the ink of the previous color is always printed on the difference of the rubber market of the next printing unit, and is transferred from this portion to the next printed sheet.

In this case, not only is there a subtle change in gradation, but also an increase in the number of dots. The increase of such dots involves the problem of ink transfer, which occurs through indirect re-inking. Even if the dot enlargement value is small, it will cause great changes in tone and color. According to experiments, if the overprint error exceeds 0.02-0.03 mm, the human eye will find the color change, so in the wet printing, the allowable overprint error must be equal to or less than 0.03 mm.


Figure 8-1 Misaligned Fishbone Diagram

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