PS plate is the main plate material for lithographic printing, and it is the source link of printing quality. How its production quality directly affects printing efficiency and printing quality. Therefore, it is of great significance to carry out a series of serious inspections on the printing plate in the pre-press process to effectively prevent production errors and printing quality accidents, improve printing production efficiency and product printing quality.
According to the author's experience of quality management, the PS version should mainly carry out the following quality checks:
1. Check the specifications of the PS version.
Because the diameters of the cylinders of various offset presses are not the same, the specifications of the printing plates are also different. In addition, for the same type of offset printing equipment, due to different product specifications and layout size, the printing plate is also different. Therefore, we must carefully check the position of the printing plate and text according to product specifications, and check whether it meets the requirements of printing positioning, binding process and trimming size, so as to avoid blindly finding the problem after printing, which causes unnecessary waste of time and labor. .
2. Check the cleanliness and flatness of the printing plate.
The inspection of the cleanliness and flatness of the printing plate is mainly to check the appearance of the front and back of the printing plate. See if there are any unclean dirty spots, hardened film and other residual impurities on the front printing plate. The back of the printing plate should also be carefully checked for foreign objects. If there are hard foreign objects, they should be cleaned in time to avoid rolling the blanket. In addition, the uniformity of the thickness of the printing plate should also be tested, that is, the thickness error of the four corners of the printing plate should not exceed ± 0.05mm, otherwise the pressure unevenness will inevitably occur, and the defect of uneven pressure should be compensated for by this. If during inspection, it is found that there are obvious scratches, creases, cracks and embossed defects on the surface of the printing plate, this plate cannot be printed on the machine, and the plate should be remade to ensure the printing quality of the product.
3. Check the color code, color type, gauge line and test strip of the printing plate.
In order to easily identify whether the ink color of each color printing product is consistent with the sample, there is a printing color block at the appropriate position of each color printing plate, and each color color label is arranged in order and placed under the body of the printing plate or above the outer edge, so that it can be compared Accurately check out the "white pages", double sheets, reverse printing, and scraps that are not allowed by the pull rule. Checking the color of the printing plate can prevent errors in the pre-press process, and cause quality problems and troubles to the printing. I once encountered such a platemaking quality problem during the inspection: the blue version of the film and the yellow version are mutually colored Confused, it was found that the color was not right (the mesh layout was not the same) after the plate was printed, so it was very troublesome to change the plate and reinstall the plate. Therefore, in order to be cautious, it is very necessary to check carefully whether the color of the printing plate matches the graphic before the printing process. The method is as follows: recognition based on the graphic features and tone depth of the layout, because the image structure and tone level of different pictures are different. You can compare and identify the parts with large contrast of colors. For example, taking a landscape picture as an example, the forest leaf layer is deeper and the sky has a darker layer. The cyan version is the darker leaf layer and the lighter sky is the yellow version. The inspection of the printing plate gauge line is mainly to see whether the position of the cross line and corner line on the plate is placed accurately, so as not to affect the post-processing and the appearance quality of the finished product. The ruled line is the basis for overprinting and cutting of finished products, and the appropriateness of the position cannot be ignored. If there is a test strip on the layout, you should check whether its position is accurate.
4. Check the screen dots and tone levels.
During the inspection, the dots observed with a high magnification magnifier should be smooth and clean, and the circle can be clearly distinguished, and there are no burrs and defects on the edges of the dots. The dot shape of the dots cannot be elliptical or flat. The color of the dots should be clear in black and white, and the snacks should not be gray or have white spots. Otherwise, the fat-sensing performance of the dots is poor. When printing, the ideas appear unrealistic. For the inspection of the tonal gradation of the printing plate, three different levels of high-key, middle-tone and low-key can be selected and compared with the monochrome sample of the sample. When the dots on the printing plate are slightly smaller than the dots in the relative area of ​​the sample, after printing Under the influence of various objective factors, it is normal for the dots to increase. If you find that small ideas are missing, it means that the printing plate is too light. If the small white dots on the low-key layout are confused, and 50% of the square dots have too many angles, it means that the printing plate is too deep. The above conditions will affect the printing quality, so the negative film, printing operation and plate quality should be carefully checked. The unqualified printing plate cannot be printed on the machine, and the plate should be re-made.
5. Check the layout text and lines.
Due to the inadequate film trimming or improper printing operation, the printed plates are prone to quality defects, so it is necessary to check the layout text and lines, which can better avoid printing quality failures and improve printing production efficiency. The text check mainly depends on the absence of broken strokes, missing words or punctuation marks, etc., and if problems are found, they can be corrected in time or remedial measures (such as reprinting) can be taken to ensure the printing quality. The inspection of the lines depends on whether the lines on the layout are broken, broken, multi-pointed, and whether the line thickness is consistent with the sample. If the printing plate of fine products is printed, such as maps, etc., it is better to copy the polyester sheet of the opposite color for overlapping inspection. If the printed text is a blue line, the standard map with the same pattern and red line should be used. The polyester sheet is aligned with it, and when the lines on the map appear almost black, it indicates that the lines of the graphic are accurate and intact. If a part appears red, it indicates that there is a missing line on the layout; if there are blue lines or small dots, it indicates multiple points and multiple lines.
In summary, careful quality inspection of printing plates can not only discover and deal with hidden quality problems in a timely manner, avoid printing quality problems in printing, ensure the printing quality of products, but also effectively improve production efficiency.
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