In order to ensure the quality of the offset printing plates, the operators and quality inspectors in the plate making process must carefully check the plates after printing, so as to find out the quality problems of plate making before mass printing and correct them in time, so as to improve the quality of printed products , Do a good job in the connection between plate making and offset printing.
1. Check the tone of printing plate
The inspection of the tone of the printing plate refers to the inspection of the printing plate level. It mainly depends on whether the entire printing plate is rich in highlights, middle tones and dark tones, and whether it can meet the requirements of printing on the machine. Make a comprehensive comparative analysis of the printed plate and proofing proofs to see if the range of the highlight area, the middle tone area and the dark tone area meets the requirements. The specific requirements are that 3% -5% of the small dots in the highlight area are not lost; 50% -70% of the dots in the mid-tone area are basically not diffused; and 90% -98% of the large dots in the dark-tone area are not pasted.
By checking the depth of the tone level of the printing plate, you can observe whether there is a problem with the tone level of the PS version, the tone level of the pre-press production, and the dot finish, and whether the film has gray haze and unclear phenomena.
When checking the printing plate, it is generally necessary to observe and analyze 5%, 50%, 95% of the dots with the help of a magnifying glass of 5-10 times, and perform the corresponding color dots of the monochromatic and overlapping color samples of the offset printing plate and the printed sample. Compare. If the dot size of the highlight part, middle part, and dark part basically matches with the printed sample, it means that the printing plate depth meets the requirements of machine printing. If the dots are enlarged, it means that the tone is too deep; if the dots become smaller, it means that the tone is too shallow.
2. Inspection of printing plate dots and photosensitive film
After the offset printing plate is printed, the quality "three inspections" are carried out before delivery to printing, that is, self-inspection, mutual inspection and special inspection. The quality of the dots must be checked, and the dots on the PS version are observed with the help of a 5-10x magnifying glass during the inspection. If the dots are fluffy, dull, or have white spots, it means that the dots are not strong, and the lipophilic and lipophilic performance of the dots is not ideal. Find problems from pre-press production or film development, fixing, and PS plate development. The outlets that meet the quality requirements should be round, smooth, full and strong.
3. Check the color of printing plate
After printing and developing, we must check the color of printing according to proofing to see if it meets the requirements of overprinting. For electro-printed four-color overprinted printing plates, there are certain difficulties in identifying colors. This requires that color blocks and color types be marked on the edge of the printing plate during imposition. When printing on the machine, distinguish the color according to the mark on the printing plate. Markings should be standardized and clear at a glance, to avoid confusion of color classification and color sequence.
4. Inspection of plate size and rule line
1) Before printing on the machine, the size of the text, lines, and patterns on the plate should be carefully measured to check whether the specification size meets the user's requirements; whether the plate size leaves room on the substrate; whether the gripper position can be To meet the requirements of the machine, if you use the regenerated PS version, you also need to use the T-shaped ruler to check the size of the PS version to see if it can be used on the machine, whether the plate cylinder can be installed and clamped.
2) Check whether the printing plate is reversed (upside down) according to the position of the proof image. The positive version of the PS version should be a positive image of the positive version. The positions of the grips of each color version cannot be reversed; the graphics and text should be in the center of the PS version and cannot be skewed, otherwise it is not conducive to the correction of the printing plate rules.
3) Check the rule lines of graphic overprinting. After the printing plate is dried, be sure to carefully check the rule line, corner line and cutting line to ensure that each line is complete. Also pay attention to the position of the rule line and corner line to avoid cutting and attaching to the printed matter.
5. Examination of printed images and blank parts
Whether the printed graphics are complete and continuous; whether the text, graphics, lines are smooth and complete. PS version of the photosensitive film is strong, not false, and does not fall off. The blank part of the PS plate should be clean and tidy. Check the layout for dirt and scratches. Dirty spots should be cleaned with PS plate revision liquid. Impurities, dust and other contaminants should be cleaned with water; wash in the middle and apply gum arabic in time to prevent oxidation of blank parts of the printing plate
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