Screen printing direct photosensitive plate making method and precautions
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The direct photolithography method of the screen is to use the photochemical reaction of the photosensitive adhesive, the photoreceptor is cross-linked and hardened by the light-receiving part, and is firmly combined with the screen to form a plate film, and the non-photosensitive portion is washed away by water or other developing solution to form a through hole. Screen printing plate.
The photosensitive plate making method is of high quality, economical and practical, and has good effects. It is the most important plate making method in modern screen printing. Photosensitive plate making method can be divided into direct method, indirect method and straight method according to different operation modes.
The direct photosensitive plate making 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. After drying, the positive film is attached to the photosensitive adhesive. Exposure is performed on the screen surface, so that the transparent portion of the positive film is photohardened, the image portion is opaque, the photosensitive adhesive is not hardened, and the mesh is formed after washing and development to form a printing plate.
Pre-coating treatment: Whether it is a new screen or recycled version, the screen should be treated before the coating of the photoresist. The main purpose is to prevent the shrinkage of the photosensitive film layer caused by dirt, dust, grease, etc. Blisters, image breakage, photoreceptor peeling, etc. occur. Common processing steps are degreasing agent cleaning - flushing cleaning - dehydration - drying, etc. There are many kinds of release agents commonly used in the market, and the performance is good or bad. The main component is 20% caustic soda aqueous solution, and the effect is good. Of course, there is also a use of neutral or weakly alkaline detergent as a release agent. In the case of conditional parts, it is better to use the release agent to remove the grease, improve the lubricity of the photo-sensitive liquid to the screen, and improve the bonding degree between the photosensitive glue and the screen.
Screen coating. Common direct photosensitive plate coating methods include the scraping method and the rotating method. What is proposed here is that due to some shortcomings of the rotation method itself, the most used one is the bucket method. The factors affecting the coating quality of the bucket method mainly include the flatness of the edge of the bucket groove, the coating angle, the coating strength, and the coating. Cloth speed, number of coatings, etc. If the edge of the scraping groove is uneven or there is a wound, the film layer may have streaks or uneven thickness, resulting in burrs or uneven thickness of the ink layer, color cast, and the like. The coating angle refers to the inclination angle of the screen placement when coating, generally 80 to 90°. If the angle is too large or too small, the thickness of the front and back screen release layers is not equal. The screen has a certain elastic tension, and the strength used during coating also causes the thickness of the coating layer to be different. The left and right hands use the same strength and the speed is applied flat. The speed is too fast, it is easy to generate bubbles, which form pinholes; too slow will cause lines in the coating layer, so it requires some experience in coating. According to the specific conditions of the print, the number of coatings is determined to achieve the desired effect. It can be applied to the concave surface of the screen for one or two times, which can reduce the abrasion of the screen by the scraper and improve the printing durability of the printing plate.
After screen exposure, the film surface of the film is attached to a dry, dust-free screen coated with a photosensitive film, and exposed on a plate printer. Exposure is the most critical step in the plate making process and directly affects the quality of the plate making.
The principle of exposure is the principle of photosensitive plate making. Generally speaking, the non-image part is hardened to form a plate film, and the image part has no light, and the development process washes away the ink.
The exposure conditions directly affect the quality of the screen. The exposure conditions should be determined according to the type of emulsion, the type of photosensitive light source coated, the distance of the film surface of the light source, the exposure time, etc. In fact, during the exposure process, it can be controlled. Only the exposure time, so in a professional printing company, you should pre-test the sun, find the appropriate data, and then control other conditions based on the actual work. In any case, overexposure or underexposure can cause the edge of the photoresist to coarsen, affecting the size and clarity of the print.
Development: The photosensitive film absorbs moisture and expands in the image. It is washed and developed with water. The film is wet for a long time, and the expansion seriously affects the image clarity. Therefore, under the premise of being able to be transparent, the soaking time is as short as possible.
In short, the following procedures should be paid attention to during the whole process of plate making: sufficient degreasing before application, stable application of coating, dust-free drying of the film layer, proper exposure time, and the shorter the soaking water, the better the revision.