1. What are the causes and solutions for the mesh clogging?
Mesh clogging, also known as mesh blocking, refers to the phenomenon that the through-hole part of the screen printing stencil cannot transfer ink to the substrate during printing. The occurrence of this phenomenon will affect the printing quality, and in severe cases, normal printing may not be possible.
The causes of the mesh clogging phenomenon during screen printing are complicated. The causes of plate smearing can be analyzed from the following aspects.
① The reasons for the substrate. Screen printing substrates are diverse, and the texture characteristics of the substrates are also a factor in the occurrence of mesh clogging. For example: paper and wood. Fabrics and other substrates have low surface smoothness and poor surface strength. They are more likely to produce powder and hair loss during the printing process, resulting in mesh clogging.
② The reasons for the workshop temperature, humidity and ink properties. The screen printing workshop requires a certain temperature and relative humidity. If the temperature is high and the relative humidity is low, the volatile solvent in the ink will evaporate quickly, and the viscosity of the ink will increase, thereby blocking the mesh. Another point to note is that if the downtime is too long, the stencil will be clogged, and the longer the time, the more serious the block. Secondly, if the ambient temperature is low and the ink has poor fluidity, it is easy to cause mesh clogging.
③The reason for the screen printing stencil. The prepared screen printing stencil should be rinsed with water and dried before use. If the stencil is left for too long and not printed in time after it is made, dust will adhere to it more or less during the storage process. If it is not cleaned during printing, it will cause mesh clogging.
④The reason for printing pressure. If the printing force is too large during the printing process, the scraper will bend. The scraper is not in line contact with the screen printing stencil and the substrate, but in surface contact. In this way, the ink cannot be scraped clean every time it is scraped, and residual ink is left. After a certain period of time, it will form a film and cause mesh clogging.
⑤The reason for the improper gap between the screen printing stencil and the substrate. The gap between the screen printing stencil and the substrate cannot be too small. If the gap is too small, the screen printing stencil cannot be separated from the substrate after scraping. When the screen printing plate is lifted, a certain amount of ink adheres to the bottom of the printing plate, which is also easy to cause mesh clogging.
⑥ Ink reasons. When the particles of pigments and other solid materials in screen printing ink are large, it is easy to block the mesh. In addition, the mesh size and through-hole area of the selected screen are smaller than the particle size of the ink, which makes it difficult for coarser particles of ink to pass through the mesh and cause the blocking phenomenon. For the paste caused by the large particles of ink, it can be solved from the time of making the ink. The main method is to strictly control the fineness of the ink.
The ink dries too quickly during the printing process, which is easy to cause paste failure. Especially when using volatile drying ink, this phenomenon is more prominent, so the appropriate solvent must be selected to control the drying speed during printing. When selecting ink, the influence of climate should be considered. Generally, quick-drying ink is used in winter, and retarder should be added to the ink in summer. If the retarder still causes paste, other types of ink must be used.
When using oxidative drying ink, the paste phenomenon does not occur very often, but if excessive use of desiccant is used in summer, the paste phenomenon will also occur. Generally, the use of desiccant should be controlled in summer.
When using two-liquid reactive ink, the plate is almost never mesh clogging because the ink itself dries slowly, but it occasionally does.
During the printing process, the viscosity of the ink increases and causes the plate to block. The main reason is that the solvent of the ink on the plate evaporates, causing the viscosity of the ink to increase, and the screen is blocked. If the area of the printed image is relatively large, the ink on the screen printing plate is consumed more, and the plate is less clogging. If the area of the image is small, the ink on the screen printing plate is consumed less, it is easy to cause the plate to blocking. The countermeasure is to frequently replace new ink. The poor fluidity of the ink will cause the ink to smear before passing through the screen. This situation can be solved by reducing the viscosity of the ink and increasing the fluidity of the ink.
After the plate smearing failure occurs, you can use an appropriate solvent to scrub it according to the nature of the ink on the plate. The key to scrubbing is to start from the printing surface and wipe gently from the middle to the periphery. Check the printing plate after wiping. If there is any defect, it should be repaired in time, and printing can be restarted after repair. It should be noted that each time the film is scrubbed, it becomes thinner. If the film is seriously damaged during wiping, a new one will have to be replaced for printing.