The cause of the trouble caused by the printing plate in the screen printing process

Faults related to printing plates can be divided into failures in plate making and failures in printing. The main right here is still the failure of printing plates. 1. The layout is blocked. After the printing plate is blocked, the ink cannot pass through. The reason is that the printing plate is badly degraded, so the plate should be exchanged. If you use a needle to open the blocked way to scrub the blocked area with alcohol will not get good results. Some of the reasons for the blockage of the printing plate are caused by the ink drying too fast, the printing speed being too fast or the blade being too hard. At this time, the solvent is used to thoroughly wipe the ink in the plate, and the newly formulated ink is used, and other reasons must be checked at the same time. Improve it together. It is important to note that the lifetime of the plate will be reduced once for each use of solvents. When rubbing the plate, use a fine cotton wool that is assessed to be soft with a solvent. After printing, the same method is used to wipe the plate from the inside of the plate. 2. Printing plate leaks ink. If dust is mixed on the substrate or in the ink, the dust will scratch the plate under the pressure of the squeegee during printing; the solvent in the ink will also make the plate produce pinholes, which will cause the printing plate to leak ink. the reason. If there is ink leakage, emergency measures can be taken to replenish it with tape or paper tape from the back of the plate. This kind of operation should be carried out quickly. Otherwise, once the ink on the plate is dry, it should not be thoroughly wiped with solvent. Rubbing can also cause peeling of the plate. Should pay attention as much as possible. The ink leakage of printing plates is most likely to occur in the place where ink is stored, so it is necessary to pay attention to strengthening these places when making plates. When the substrate is a metal plate or a rigid plastic plate, its sharp corner sometimes punctures the plate during the feeding process. This should be particularly noted. Printing should be checked or repaired before printing begins: the text's mistakes should be corrected, the pinholes of the film should be repaired, the printing plates must be fully reinforced, and printing should begin. In the printing, it should be avoided as much as possible due to the failure of the printing plate, ink, squeegee, etc. 3. Inking unevenly. The ink thickness in the graphic part is uneven because of various aspects. The reason for the ink is poor ink formulation, or the normally formulated ink is mixed with hard particles. During the printing, the ink expands and softens due to the effect of the solvent, blocking the mesh that should be penetrated by the ink, and acting as a printing plate to make the ink. Failed to pass. In order to prevent such failures, the formulated ink (especially the old ink) should be filtered with a very fine mesh before use. When you reuse a used plate, you must completely remove the old ink that has adhered to the plate. When the plates are stored after printing, they must be fully washed (including plates). If this is done as described above, accidents with ink unevenness will not happen. The problem of the squeegee is described below. If the tip of the squeegee is damaged, a trace will appear along the direction of movement of the squeegee, especially when the transparent material is printed, the ink will show a distinct inconsistency. Therefore, it is necessary to protect the front end of the squeegee so as not to cause damage. If it is damaged, it must be grinded with a grinder. The unevenness of the printing table also affects the uniform ink. The convex ink layer is thin, and the recessed ink layer is thick. This phenomenon is also called ink inhomogeneity. In addition, if the dust is stuck on the back surface of the substrate or on the printing table, the above trouble will occur (about the dust prevention of the printed material, which is described in detail). 4. The life of the printing plate, under the scraping of the blade for a long time, the normal strength of the printing plate will decrease until it is damaged, which is called the life of the printing plate. According to the plate-making method, the life of the printing plate has a long or short life. Generally, the direct-photosensitive plate-making has a longer life than the indirect-photosensitive plate-making. The direct method printing plate can withstand 2 to 30,000 printings under normal conditions, and the indirect carbon paper method can only print about 3 thousand printings. The stripping film printing plate has a longer life than the carbon paper plate. The indirect method of printing plate breakage is not a time when the film is detached from the screen, but the partially destroyed plate is peeled off first. Contrary to this, the printing plate of the direct method has a thicker picture line, and sometimes the inside of the plate is broken due to the effect of the ink solvent, so that the printing cannot be performed. This phenomenon is most likely to occur during the wet season in the rainy season. 5. Insufficient pressure caused by printing. The printing pressure applied to the printing plate by the squeegee during printing can enable the linear contact between the printing plate and the printed object, and it should not exceed. The necessary pressure is determined by the tension of the plate, the length of the squeegee, and the size of the gap between the plate and the substrate. If the press pressure exceeds the required pressure, the amount of ink that is pressed out will not increase. On the contrary, the excessive pressure will cause the blade tip to bend too much, so that the blade will not be able to fully scrape the ink. If the printing plate comes into contact with the surface of the printing material, it will cause the color of the printing material not to be bright, and it will also easily cause the loss of the squeegee and the peeling of the printing plate. At the same time, the screen will also easily expand and contract, resulting in deformation of the printing image and a decrease in printing quality. In short, over-pressing can be said to be useless. Screen printing is the smallest type of printing in various printing methods. If we forget this, we cannot print good prints. 6. Drying failure. The screen printed ink layer is very thick, so it often fails to dry. If the ink is bad, the layout is blocked, the flowability is poor, the ink is moistened, the ink is smeared, the adhesiveness is bad, the sticking, the printing, the poor drying and some other reasons. Printed materials should be dried by proper methods. Whether it is manual prints or mechanical prints, different drying methods should be adopted according to different printing conditions. Drying methods include natural drying and forced drying using hot air, ultraviolet rays, and other thermal energy. When the printing material is paper, it is best to use a natural drying method. In particular, when multi-color printing is performed, the paper will be stretched due to heating, which will cause errors in the dimensions, resulting in inaccurate rules during printing. However, in order to improve the printing efficiency, a forced drying method is generally used to dry a metal having a relatively stable size or a harder plastic plate that does not affect the heating. The heating temperature range depends on the inert conditions of the substrate and ink. The most commonly used screen printing is a dry-type ink. This type of ink uses a solvent with a different boiling point for drying. The boiling point is generally between 120 to 190 °C. Each type of ink, such as a volatile drying type, an oxidative polymerization type, and a two-liquid reaction type, has an appropriate heat-drying method to increase the bonding strength and accelerate the drying speed. G (Author: Anshan Printing Plant, Liaoning Province) Editor-in-Chief Li Danmei