The direct screen-printing method of the screen is the photochemical reaction of the photo-resist, the photo-sensitive part of the photo-resist is cross-linked and hardened, and it is firmly combined with the screen to form a printing film. The unexposed part is treated with water or other developer; it is washed out to form a through hole. And form a screen printing plate.
Photographic platemaking method is of high quality, economical and practical, with good results. It is the most important method of plate making in modern screen printing. Photographic plate making method can be divided into direct method, indirect method and straight line method according to different operation methods.
The direct photoengraving method is one of the earliest proposed plate making techniques. It is also the most widely used method. It is to apply a photosensitive adhesive on a stretched screen plate. After the film is dried, the positive picture film is affixed to the photosensitive film. The surface of the screen is exposed so that the transparent portion of the positive image film is photo-cured, the graphic portion is not light-transmissive, the photosensitive material does not harden, the developing mesh is formed after processing, and the printing plate is formed.
Pre-coating treatment: Whether it is a newly-purchased screen printing plate or a regenerated plate, the screen must be processed before applying the photo-sensitive film. The main purpose is to prevent the shrinkage of the photo-sensitive film layer caused by dirt, dust, grease, etc. Blisters, image breakage, detachment, etc. occur. The common processing steps are degreasing agent cleaning, flushing, dehydration, and drying. There are many kinds of mold release agents commonly used in the market, and their performance is good or bad. The main component is a 20% aqueous caustic soda solution with good results. Of course, there is another, that is, the use of neutral or weak alkaline washing powder as a release agent. In the condition of the allowable parts, the best use of film remover degreasing effect is good, can improve the lubricity of the photosensitive liquid on the screen, improve the combination of photosensitive adhesive and screen.
Screen coating: Common direct photosensitive plate coating methods include scraping and rotating methods. Here is due to some limitations of the rotation method itself, resulting in the most used is the scraping method. The factors affecting the coating quality of the scraper method mainly include the flatness of the edge of the scraper groove, the coating angle, the coating strength, the coating speed, and the coating frequency. If the edge of the scraping groove is not smooth or has a wound, the striations or uneven thickness will occur in the film layer, resulting in burrs or uneven thickness of the ink layer, color cast, etc. in the printed matter. The coating angle refers to the tilt angle of the screen when it is applied, and is generally 80 to 90 degrees. An angle too large or too small causes the thickness of the release layer of the screen before and after the screen to be unequal. The screen has a certain amount of elastic tension. The strength of the coating can also cause the thickness of the coating layer to be different. The left and right hands use the same force, and the coating is applied at a smooth speed. If the speed is too fast, bubbles are likely to form and pinholes are formed. If the speed is too slow, lines will appear on the coating layer. Therefore, there is a certain amount of experience in coating. According to the specific conditions of the prints, the number of coating applications was decided to achieve the desired results. The coating can be applied back and forth 1 to 2 times on the concave surface of the screen, which can reduce the abrasion of the doctor blade to the screen and improve the printing plate resistance to printing.
Screen Exposure: The film of the film is attached to a suitable place on a dry, dust-free screen coated with a photosensitive film and exposed on a printing machine. Exposure is the most critical step in the process of plate making and directly affects the quality of plate making.
The principle of exposure is the principle of photolithography. In general, it is the non-graphic part that is hardened to form a film, and no light is seen in the graphic part, and the developing is washed out through the ink.
Exposure conditions directly affect the quality of the screen, exposure conditions should be in accordance with the type of emulsion, the type of coating thickness of the light source, the distance of the light source film surface, exposure time, etc., in fact, in the exposure process, can control Only the exposure time, so in the professional printing company, should test in advance in advance, find the appropriate data, and then control the other conditions based on the actual work of the data. Anyway, over or underexposure will cause roughening of the edge of the photoresist, affecting the size and clarity of the print.
Development: In the graphic part, the photosensitive film absorbs water and swells, and it is developed by rinsing with water. The time is too long, the film is wet, and the expansion seriously affects the image sharpness. Therefore, the shorter the soaking time is, the better it is.
In short, in the whole process of plate-making, pay attention to the following requirements: Apply sufficient degreasing prior to coating, experience stable coating, dry and dry film, exposure time is appropriate, soaking water as short as possible, revision corrected inspection.