Quality inspection before machine printing of the

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The quality inspection of PS version before printing is often encountered in our daily work. The PS version that has begun to be printed has found quality problems, and then we have to remove the PS version from the printer, print it again, and repeat the process of printing. Because the process includes the drying time of the printing plate and the time of repeating the previous version, this has a certain impact on the production efficiency. At the same time, there will often be mutual shirking between the two departments of plate making and printing. For example, due to insufficient exposure or improper development of the printing plate, a small amount of photosensitive film remains on the plate, causing the blank part to become dirty. The best way is to make a reasonable and correct judgment on the printing quality of the PS version before the printing plate is printed on the machine. If there is a problem with the printing quality, it should be supplemented in time to avoid downtime and waiting for the version. Next, we will discuss how to judge the print quality of printing plates

1. The appearance quality inspection of the printing plate

refers to the external performance state of the printing plate. The basic requirements are that the layout is flat, clean, evenly rubbed, and free of damage, creases, scratches, dirt, ink spots, etc

2. Inspection of layout specification

we should check the size of printing plate layout, text size, bite size, hinge size. China is still in the stage of industrialization, informatization, urbanization, marketization, internationalization and hinge relationship. Make sure that the size error of the layout is less than 0.3mm, and the chromatic version must be correct without skew

3. Inspection of graphic content

the basic content is that the text is correct, there are no defective words, no blind words, the plate is consistent with the corresponding content of the text, the direction is correct, the PS version photosensitive film is solid, does not lose its appearance, does not peel off the film and drop the version, and the color version is complete when the multi-color cover is exposed. Regular line is the basis and benchmark of offset four-color overprint, which is required to be thin and black; At the same time, regular lines and corner lines are the cutting standards of paper edge printing products, so it is necessary to ensure that the proper regular lines are complete; In addition, pay attention to the position of regular lines, corner lines and trailing lines to ensure that the product size on the printing plate is larger than the finished product size after cutting, so as to avoid corner lines and regular lines from being cut off and attached to the printed products

4. Inspection of point quality

the points in the printing plate should be full, complete, bright and clean, solid, without damage, scratch, hollow, less burr, etc. With the help of a magnifying glass of 5 ~ 10 times, 5% dots, 50% dots and 95% dots are observed and analyzed, and the corresponding color points of the offset printing plate and the monochrome sample of the proof sheet are compared. If the dot size of the highlight part, the middle part and the dark part is basically consistent with the sample, it indicates that the depth of the printing plate meets the requirements of the machine. If the dot is expanded, it indicates that the step is too deep, and the bright step is too shallow. If the dot shrinks, the highlight dot is lost, etc., it indicates that the color of the picture and text is shallow. If the dot expands, the dark white dot is pasted, which indicates that the color of the picture and text is deep. In general, 2% of the highlights and 98% of the shadows should reproduce well

by checking the depth of the gradation of the printing plate, we can observe whether there is a problem with the PS plate printing, the electrical gradation, the point smoothness, and whether the film is foggy and unclear when the material yields

5. The color difference and inspection of offset printing plate

after the offset PS plate is developed, the color of the printing plate should be checked according to the proofed color sample to see whether it meets the needs of overprint. It is easy to distinguish the specific color of each printing plate with text, lines and graphics according to the color manuscript; For those overprint plates that are electrically divided into four colors, it is difficult to identify the color differences, which requires us to mark the color differences on the edges of the plates when making plates and making up plates, such as yellow (y), magenta (m), cyan (c) and black (k). In this way, when printing on the machine, we can distinguish the color differences by looking at the Chinese and English words of the color differences. In a word, for offset printing marks, electronic four-color overprint, color pages, etc., all overprint products with more than two colors should be marked with color blocks to avoid getting the colors wrong. In addition, there are often some other substitute symbols on the printing plate to represent the color, and the operator should also have a certain understanding to strictly avoid the phenomenon of wrong version.

6 Inspection of the graphic part and blank part of the offset printing plate

the blank part of the offset printing plate shall be clean, tidy and free of dirt. You should check carefully to see whether the layout is dirty, scratched, oxidized and dried up, and whether there is a leaking photosensitive film. For the dirty places on the printing plate, PS version repair paste can be used to remove the dirt. The feeling of leakage is that the Thornton clevesleys factory built in Lancashire, UK, has passed the ISO environmental management system certification, and the photoresist film can be corrected with PS version supplement pen. For some small plates with problems such as starting and dirty spots, it is not necessary to replace the printing plate. Because the plate is dirty due to insufficient exposure or development, it can be wiped with diluted developer to make the printing plate meet the printing requirements, and it can be saved as far as possible, so as to reduce the consumption of raw materials that can be corrected by adding sizing blocks under the bottom plate and improve the printing resistance of the printing plate

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