In order to ensure the quality of the offset printing plate, the operators and quality inspectors of the plate making process must carefully inspect the printing plate after the printing, so as to find out the plate-making quality problems before large-volume printing, and provide them in a timely manner so as to improve the printing products. Quality, good connection between platemaking and offset printing.

1. Inspection of plate tone

The inspection of the printing plate tone refers to the inspection of the printing plate layer, mainly to see whether the entire printing plate layout highlights, intermediate tone, and dark tone levels are rich, and whether it can meet the requirements for printing on the machine. Comparing and analyzing the sunburned printing plates and proofs to see if the areas of the highlights, midtones and shadows meet the requirements. The specific requirement is that 3% to 5% of small spots in the highlight area are not lost; 50% to 70% of the dots in the intermediate tone area do not spread; 90% to 98% of dark spots in the dark spot are not pasted.

By checking the depth of the tone level of the printing plate, we can observe whether there are any problems with the PS version printing plate, the tone level of the prepress production, and the fineness of the dot, and whether the film has fog or clarity.

When checking the printing plate, the observation and analysis of 5%, 50%, and 95% of the dots are generally performed with the aid of a 5-10x magnifying glass, and for the monochrome dots of the offset printing plate and the printing sample, and the corresponding colors of the overlapping color dots. Compare. If the dot size of the high-light part, the mid-tone part, and the dark part is basically consistent with the print proofs, it means that the depth of the print plate meets the printing requirements of the machine. If the outlets are enlarged, the tone is too deep; the outlets are smaller, indicating that the tone is too shallow.

2. Inspection of printing plate outlets and photosensitive films

After the offset printing plate is printed, quality “three inspections”, namely self-inspection, mutual inspection, and special inspection, must be performed before the printing is delivered. The quality of the outlets must be checked, and inspections are made with a 5-10x magnifying glass to observe the outlets on the PS version. If hairballs, hairlines, and white spots on the outlets indicate that the outlets are not strong, the fat and oil-binding properties of the outlets are not ideal. Problems arise from prepress production, development and fixing of films, and development of PS plates. The dots that meet the quality requirements should be round, smooth, full and solid.
3. Printing plate color check

After the development of the printing plate, it is necessary to check the printing color according to the proofing to see if it meets the printing requirements. For electric four-color overprint printing plates, there are certain difficulties in distinguishing the colors. This requires marking blocks and colors at the edges of printing plates during the imposition. When printing on the machine, the colors are distinguished according to the marks on the plate. Marking should be standardized and clear at a glance, avoiding confusion of color and color order.

4. Inspection of plate size and rule lines

1) The printing plate should carefully measure the size of text, lines, and patterns on the plate before printing on the machine to check whether the specification size meets the user's requirements; whether the layout size leaves room on the substrate; To achieve the machine requirements, if you use the renewable PS version, but also use the T-foot ruler to check the size of the PS version to see whether the machine, the printing plate drum is installed, clipped.

2) Check whether the printing plate is reversed (upside down) according to the position of the proofing text. The positive version of the positive PS version should be positive. Each color version of the mouth can not be reversed; graphics should be in the PS version of the center position, can not be skewed, otherwise it is not conducive to correction of plate rules.

3) Check the rules and regulations of the graphic set. After the plates are in good condition, be sure to check the rules, angle lines, and cutting lines to ensure that the lines are complete. Also pay attention to the location of the rules and corner lines to avoid cutting and attach them to printed materials.

5. Inspection of printing plate texts and blanks

Whether the printing plate graphic is complete or continuous; whether the text, graphics, and lines are smooth and complete. PS version of photosensitive film is strong, true, does not fall off. The blank part of the PS plate needs to be clean and tidy. Check the layout for any spots, scratches, etc. Dirty points with the PS version of the cleaning solution to remove dirt, impurities, dust and other dirt with water; washed clean, timely rub Arabic gum, to prevent the blank part of the printing plate oxidation.