Photographic platemaking method is of high quality, economical and practical, with good results. It is the most important plate making method in modern screen printing. Photographic platemaking 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, and 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 attached 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, and the developing mesh is formed after processing to form a printing plate.
Pre-coating treatment: Regardless of whether it is a newly-purchased screen printing plate or a regenerated plate, the screen must be processed before applying the photosensitive adhesive. The main purpose is to prevent the shrinkage of the photosensitive film layer caused by dirt, dust, grease, etc. Blisters, image breakage, detachment, etc. occur. The common processing steps are degreasing agent cleaning - flushing - dehydration - drying. There are many kinds of mold release agents commonly used in the market, and the performance is good and bad. The main component is a 20% aqueous solution of caustic soda with good effect. 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 rotary method itself, resulting in the most used is the scraping method. The factors affecting the coating quality of the scraper method are mainly the flatness of the edge of the scraper groove, the coating angle, the coating strength, and the coating. Cloth speed, coating times, etc. 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 that is too large or too small can cause unequal thicknesses of the front and back screen release layers. 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.
The screen was exposed, and the film of the film was 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 platemaking.
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 light source film surface distance, 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: Photographic film absorbs water and swells. It is developed by rinsing with water. The time is too long, the film is wet, and the expansion significantly affects image clarity. Therefore, the shorter the soaking time is, the better it is.
In short, the whole process of plate-making pays attention to the following clarifications: sufficient degreasing prior to coating, stable coating with experience, dust-free drying of the membrane layer, proper exposure time, shorter water soaking, the better, revision correction check.