In our daily work, we can often encounter that the quality problems of the PS plate that has been printed on the machine have been found, and then the PS plate has to be removed from the printing press, re-printed, and the process of repeating the plate. Due to The process includes the printing time of the plate and the repeated printing time, which has a certain impact on production efficiency. At the same time, there is often a phenomenon of shirking responsibility between the plate making and printing departments. For example: the blank part due to insufficient exposure or improper development of the plate, there are trace sensitive film on the page, causing the blank part to be dirty. The best way is to make a reasonable and correct judgment on the quality of the PS plate before the printing plate is printed on the machine. If there is a quality problem of the printing plate, it should be repaired in time to avoid the shutdown of the plate. Below we will do some discussion on how to judge the quality of printing plates.

1. Print plate appearance quality check

2. Check the format specifications

Should be printed plate layout size, graphic size, bite size, folding size, folding relationship and so on to check. So that the layout size error is less than 0.3mm, the color plate must be correct, not skewed.

3. Check the graphic content

The basic content is that the text is correct, no defective words, no blind words, the plate and the corresponding content of the text are consistent, the direction is correct, the photosensitive film of the PS plate is strong, no deficiency, no film off the plate, and the color plate is complete when the multi-color set is basked. The standard line is the basis and benchmark of offset four-color overprinting, which requires fine and black; At the same time, the rule line and the corner line are the standards for cutting paper edge printing products, so it is necessary to ensure that the rule line is complete and complete; In addition, pay attention to the position of the rule line, corner line and drag tip line to ensure that the product size on the printing plate is greater than the finished product size after cutting, to avoid the corner line and the rule line can not be cut off, and it is not elegant to attach to the printed product.

4. Check the quality of outlets

The dot in the printing plate should be full, complete, smooth, real, no damage, no scratch, no hollow, less burr, etc. With a magnifying glass of 5 ~ l0 times, 5% of the small dots, 50% of the dots and 95% of the dots were observed and analyzed, and the corresponding color dots of the offset printing plate and the monochrome sample of the sample were compared. If the dot size of the highlight part, the middle part and the dark part is basically consistent with the proof, it indicates that the depth of the printing plate meets the requirements of the machine, if the dot is enlarged, it indicates that the level is too deep, and the dot is too small, it indicates that the level is too shallow. If the dot shrinks, the loss of small highlight dot and other phenomena, indicating that the color of the text is light, if the dot expands, the dark white dot paste dead phenomenon, indicating that the color of the text is dark. In general, 2% of the highlights and 98% of the darkening should reproduce well.

5. Offset printing plate color difference and check

After the development of the offset PS plate, the color of the printing plate should be checked according to the color sample of the proofing to see whether it meets the needs of overprinting. Printing plates with text, lines, graphics are easier to distinguish the specific color of each plate according to the color manuscript; For those electric four-color overprinting plates, there are certain difficulties in identifying colors, which requires us to mark the color at the edge of the plate, such as: yellow (Y), magenta (M), green (C), black (K), so that when printing on the machine, just look at the color of the Chinese and English words can be separated by color. In short, offset printing signs, electrical four-color overprinting, color pages and other overprinting products with more than two colors should be marked with color blocks, so as not to make the color wrong. In addition, there are often some other substitute symbols on the plate to represent the color, and the operator should also have a certain understanding to strictly avoid the phenomenon of the wrong version.

6. Check the graphic part and blank part of offset printing plate