Improving the durability of printing plates is a key link to reduce the consumption of bag-making raw materials, reduce product production costs, shorten production cycles, and improve economic benefits. Apply the following methods in actual work to improve the durability of the printing plate.
1. Strictly control the storage of printing raw materials. In particular, we must ensure the purchase of high-quality paper and high-quality PS plates. For example, 52g/m2~60g/m2 book paper for printed books and periodicals, if purchasers are greedy to buy low-quality paper from informal paper manufacturers, the whiteness, uniformity, smoothness, smoothness, surface tension, sizing degree, etc. None of the technical indicators can meet the requirements of printing. The rough surface of the paper, large paper ash, and many fine sand particles will easily wear the photosensitive resin film of the PS plate and reduce the printing resistance of the printing plate. Therefore, to improve the durability of offset printing plates, we must first start from the material purchase channels. Unqualified raw and auxiliary materials will not enter the factory or warehouse. At present, there are many brands in the printing material market, and it is difficult to distinguish between good and bad. Printing companies should shop around when purchasing materials to ensure quality and purchase high-quality printing materials.
2. To master the correct exposure time of the PS version. Pay special attention to the amount of exposure, do not overexpose, so as not to affect the printing durability of the printing plate. Under normal circumstances, the four-color separation film requires that 3% of the small dots are not lost due to drying, and 98% of the large dots are not smeared; the patterns, lines, and text are clear, the small pictures and texts do not fall off, and the text pen is full and bright. Break strokes, etc.
3. The concentration of PS plate developer should be strictly controlled. When preparing the developer, it must be prepared strictly in accordance with the manufacturer’s instruction manual. The developer or developer powder, sodium hydroxide, and water must be accurately measured through a measuring instrument. Do not use experience or feel to prepare or dilute the developer. If the exposure is too much during the printing process, the high concentration of the alkaline solution of the PS plate developer or the high water temperature will directly reduce the printing durability of the PS plate.
4. Improve the printing durability of the printing plate by baking the PS plate. At present, many printing companies adopt baking methods to improve the printing durability for the printing of long-run, large-volume books, newspapers and other products. That is, after the PS plate is exposed, it is cleaned, wiped the baking liquid, and used to open the electricity. Bake the plate in the oven. ①Before baking, you must pay attention to clean up the dirt and dirty spots on the blank part of the PS plate with revision paste, otherwise it will be difficult to remove the dirty spots after baking. ②The towel used to wipe the baking plate liquid is not clean, or the fiber on the towel falls off and it is easy to get dirty on the PS plate. ③The baking temperature is 200～220℃, and the baking time is generally about 10-15 minutes. It should not be too long. At the same time, the baking time should be determined according to the temperature resistance of the photosensitive resin film of the PS plate. . If the photosensitive film of the PS plate is light brown, brown, or plum ripe, it means that the plate is properly baked; if the baking time is too long and the temperature is too high, the photosensitive resin film of the PS plate will be baked. Paste, or soften the plate base.
5. Before printing, check whether the density of the film is appropriate. The blackness of the text, lines, and patterns on the sulfuric acid paper should be full without missing strokes. The large characters and wider lines should be output again if the blackness is not enough. Bake it on an electric stove to increase the darkness. When baking, it is necessary to prevent the sulfuric acid paper from wrinkling, which will affect the air absorption of the printing plate. Whether printing large-volume books, trademarks, and packaging and decorating products, whether it is to produce film or sulfuric acid paper, the strokes and lines of the text should be as thick as possible, and the printing will be more resistant accordingly. Density and blackness are not up to the requirements, can not be accommodated, rework and rework, in order to guarantee the printing durability of the PS plate.
6. The pressure of the water roller on the printing plate should not be too great. When debugging the pressure of the two water rollers and the printing plate, it is best not to use a good printing plate that is formally printed, but a waste PS plate can be used for debugging to avoid damage to the printing plate. At the same time, the thickness of the liner paper in the plate cylinder should be appropriate. If the pressure of the water rubber roller on the printing plate is too high, the graphic abrasion of the printing plate will increase, and the printing durability will decrease.
7. When loading the plate, check whether the liner paper on the back of the printing plate has wrinkles, discounts, paper scraps, and small pieces of paper. If there are such conditions, the printing plate should be removed and the liner paper should be smoothed.
8. When repairing the plate after printing and on the machine, the residual repair paste was accidentally applied to the photosensitive resin film of the graphic part of the PS plate, which played a role in thinning the film and also affected the printing resistance of the PS plate. rate. In addition, the plate surface is dirty after the plate is loaded, and it is often used to wipe the plate with a cloth moistened with powder. However, do not use too much force when wiping the plate with the wetting powder, and the wiping time should not be too long, otherwise the photosensitive resin film of the printing plate will not resist printing after being wiped thin.
9. Use less pressure when printing. After the printing plate is installed on the printing plate cylinder, the pressure between the printing plate cylinder and the blanket cylinder should not be too large. The thickness of the PS plate plus lining paper should not exceed 0.65mm, and the thickness of the blanket plus lining should not exceed 3.25～3.40mm (Measured with a micrometer). When installing the plate, it must be compacted to prevent relative slippage during the operation of the offset press. In addition, the pressure between the ink application roller, the water application roller and the printing plate cylinder of the offset printing press can be accurately adjusted and controlled to avoid direct wear of the plate surface.
10. Strictly control the water and ink balance during the printing process. Pay attention to control the thickness of the ink layer to avoid spreading the ink to the blank part of the printing plate. If the ink is too thick, the small particles of the pigment, binder, and rubber in the ink will increase the friction of the printing plate, which will also accelerate the wear of the printing plate. Maintain the normal water supply, and use the minimum amount of water to moisten the page under the premise that the blank part of the printing plate does not stick to the ink, so as to reduce paper deformation, ink emulsification, inaccurate overprinting, and ink dilution. If there is too much moisture on the plate surface, it will also have a corrosive effect on the printing plate when combined with the weak acid water tank fluid (used to clean oil stains). Maintain the balance of ink and wash, and at the same time can avoid the phenomenon of dirty plate, patterned plate and plate falling caused by improper ink and wash.
11. Prevent oxidation of the surface of the printing plate. The gum arabic must be rubbed when the offset printing machine is stopped in the middle of the machine or during lunch and rest, so as to prevent the printing plate from being exposed to the air for a long time, which will cause the printing plate to oxidize and reduce the printing durability of the printing plate.
12. Prevent wear and tear of debris and layout. Also pay attention not to allow double sheets, multiple sheets and other debris to crush the printing plate during the paper conveying process.