Questions about screen printing and four-color printing

Q: With daylight exposure, the final result is often to see the image clearly, but the mesh that composes the image is sealed by the film. What causes this?

A: First of all, it is certain that sunlight can be used as an exposure light source in areas with poor working conditions. However, due to the alternation of winter and summer natural and sunny weather, there is a big difference between morning and evening and noon. If it is not a long-term practice operator, it is difficult to accurately grasp the exposure time. Second, without seeing actual operations, it is difficult to make a correct judgment of the cause of the failure. Therefore, this is only discussed based on operational common sense. The following reasons are listed as the reference for analyzing failures:
1. Due to exposure in the sun, during the movement from the dark room to the outside (or window), if there is a slight looseness between the film and the screen, it will cause some light leakage and the mesh will be easily unsafe. Light irradiation and residual hardened adhesive film form a blocking net;
2. Photoresist surpasses the storage period, and it is difficult to develop. Finally, the mesh of the image part is blocked and the platemaking fails;
3. Bright daylight is much more powerful than indoor lighting. Operators are prone to overexposure in the absence of practical experience, and may also cause network blocking problems.
4. The density of the original film is too low (gray and yellowish to the naked eye). After the screen plate is exposed and developed, the residual hardened film is not easy to remove, and this is the reason why the mesh is blocked.
In addition to the above reasons, there may be other reasons for blocking the network. Therefore, during the plate making process, the quality of each process must be inspected at any time, and the real cause of the plate making failure must be found in time to facilitate troubleshooting and to make a high quality printing plate.

Q: I just participated in screen printing. Due to insufficient funds, it is impossible to purchase application equipment. Is there no pressure gun development, is there any other alternative?

Answer: Yes. The simplest way is to use a soft rubber tube that is attached to the tap of the tap water and is fixed and strong, and the other end is trimmed with scissors. When using, open the tap, pay attention to the moderate pressure of the water, should not be too large, and then squeeze the rubber nozzle by hand, leaving only a gap to let the water pass through, this water becomes a certain pressure of the water flow, and pressure Water spray approximation. With a few more uses, you can apply it freely.
If it is done in a country without running water, it is really difficult to work under such conditions, so we have to adopt the “water tray immersion method”, that is, soak the exposed screen plate in water to make the unexposed film fully. Dissolve until the mesh in the image part is completely transparent. Finally, rinse with water to prevent residual film from adhering to the transparent mesh.

Question: After the completion of the plate-making work, it was found that the individual line segments were not transparent and certainly not printed. A “broken line” would appear on the printed matter. In order to repair it, the method of using a needle was good?

A: Not good. Because the result of the needle penetration does not completely penetrate the sealed mesh, only the film is pierced and the film is not removed. These parts of the film that are pierced do not reach the “clean and smooth printing lines”. "The effect of screen printing quality. There is also a shortcoming: In the part that is needled, the mesh is easily broken and forms a tiny break. If there is a recycling task, it will affect the quality of the next plate making. Therefore, under the premise of ensuring the quality of plate making, a plate should be rebuilt, and the repair method of the needle should not be used. Needless to say, the needle can not be repaired.

Q: I used a nylon mesh to make a silkscreen version of water-resistant glue. After it was completed, everything was normal. After drying, the hardener is brushed once and then dried in a drying oven. When it is removed, it is found that one side of the frame is cracked, resulting in a waste plate. What is the reason?

Answer: According to the situation of plate making, all things are normal before the hardener (for screen printing of water-resistant textiles, which acts as a solid film), indicating that the photosensitive adhesive is good, operates normally, and no problems are found. However, after the curing agent is applied, problems occur in the drying process. The reason is that the hardening agent is not properly painted, for example, excessive accumulation occurs, and the local composition of the screen plate is too thick, because the hardening agent is acidic, and the nylon mesh Silk is not very acid-resistant. It is easy to accumulate acid when it is not applied to the edge area of ​​the emulsion. The nylon mesh may be broken due to acid resistance. Another reason is that the hardener may be too acid. Diluted with clear water. Before dilution, multiple tests should be done to avoid the effect of solid film.

Q: What does "four-color printing" often refer to in print books?

A: In the process of printing color images, there are processes for producing color separations in offset printing (gravure printing), gravure printing, or screen printing. The traditional method is to use screening (or hanging net) technology. The color manuscripts are color-coded and plate-making. The principle of additive coloration and subtractive coloring is applied. Three primary colors are used in printing to make copies to reproduce originals, including color and image layers. If the three primary color printing materials, printing materials, color separation plate making, printing machinery and so on all reach the ideal degree, then as long as the three primary color printing materials are used for printing, the original image can be reproduced on the substrate. However, in reality it is not ideal, so it is also necessary to make up for it with black ink so that the hue of the image completely or substantially matches the original. Therefore, printing such products, all use four-color printing materials (yellow, magenta, blue three primary colors plus black ink), often referred to as "four-color printing", meaning the use of color separation plate, as long as the three primary colors printing materials Adding a black print, you can copy the color image. In actual operation, it is not always to use four colors. According to the original document and the design requirements of the finished product, five colors or six colors (for example, printing shading, borders, characteristic marks, etc.) may also be printed.