Inspection principles for various indicators of th

Inspection principles for various indicators of offset printing plate quality

in order to ensure the quality of offset printing plate, the operators and quality inspectors of plate making process must carefully check the printing plate after printing, so as to find out the plate making quality problems before mass printing and correct them in time, so as to improve the quality of printing products and do a good job in the connection between plate making and offset printing

1. Inspection of printing plate gradation

the inspection of printing plate gradation refers to the inspection of printing plate gradation, which mainly depends on whether the whole printing plate is rich in highlights, intermediate tones and dark tones, and whether it can meet the requirements of machine printing. Comprehensively compare and analyze the dried printing plate with the proofing sample to see whether the range of high light area, middle tone area and dark tone area meets the requirements. The specific requirement is that 3% to 5% of the dots in the highlight area are not lost; 50% to 70% of the points in the intermediate adjustment area are basically non-proliferation; 90% to 98% of the darkened areas are not pasted

by checking the depth of the tone level of the printing plate, we can observe whether there are problems in the tone level and point finish of the PS plate printing and prepress production, and whether the film has haze, unclear and other phenomena

when checking the printing plate, it is generally necessary to observe and analyze 5%, 50% and 95% of the points with the help of a 510 times magnifying glass. For offset printing plate and printing, it is expected that most of the manufacturing processes can be compared at room temperature with the corresponding color points of monochrome samples and laminated samples of samples. If the point size of the high light tone part, the middle tone part and the dark tone part produced by other companies adopts leverage loading and print samples, but the economic quality and the degree of benefiting the people (Social Security) have not reached the modernization level, which basically coincides with the print, indicating that the depth of the printing plate meets the requirements of machine printing. If the point is enlarged, the step is too deep; The point becomes smaller, indicating that the step is too shallow

2. Inspection of printing plate points and photosensitive film

after the offset printing plate is printed, three quality inspections, namely self inspection, mutual inspection and special inspection, must be carried out before delivery for printing. The spot quality must be checked. During the inspection, observe the spot condition on the PS plate with the help of a 510 times magnifying glass. If there are hairy spots, weak hair and white spots, it means that the spots are not strong and the lipophilic property of spots is not ideal. Find problems from the process of prepress production or film development, fixing in many medical plastic exhibits, PS version development and so on. The points that meet the quality requirements should be round, smooth, full and solid

3. Check the color of printing plate

after printing and developing, check the color of printing according to proofing to see whether it meets the overprint requirements. For the electric four-color overprint plate, it is difficult to identify the color difference, which requires that the color block and color difference should be marked on the edge of the plate when making up. When printing on the machine, the colors are distinguished according to the marks on the printing plate. The marking should be standardized and clear at a glance to avoid color difference and color sequence confusion

4. Check the size and regular line of the printing plate

1) before the printing plate is printed on the machine, carefully measure the size of the text, lines and patterns on the plate, and check whether the specification and size meet the requirements of the user; Whether the layout size leaves room on the substrate; Whether the mouth position can meet the requirements of the machine. If a regenerated PS version is used, check the size of the PS version with a t-ruler to see whether it can be used and whether the plate cylinder can be installed and clamped

2) check whether the printing plate is sunken (upside down) according to the position of proofing text. The positive PS version should be positive when printed. The mouth position of each color plate cannot be reversed; The graphics and text should be in the middle of the PS version and should not be skewed, otherwise it is not conducive to the correction of the printing plate rules

3) check the regular line of graphic overprint. After the printing plate is dried, be sure to check the regular lines, corner lines and cutting lines to ensure that all lines are complete. Also pay attention to the position of regular lines and corner lines to avoid being cut and attached to the printed matter

5. Inspection of printing plate text and blank parts

whether the printing plate text is complete and continuous; Whether the text, graphics and lines are smooth and complete. The photosensitive film of PS version is solid, not empty and not falling off. The blank part of PS plate shall be clean and tidy. Check the layout for dirt, scratches, etc. The dirty spots shall be cleaned with PS version revision solution, and the impurities, dust and other dirt shall be cleaned with water; Wash it in the middle, and apply Arabic gum in time to prevent oxidation of the blank part of the printing plate