Pinholes are the most troublesome problem for silicone ink screen printing workers. If it is an opaque printing such as billboards and thick paper, this kind of small hole that is not easy to observe is generally not a problem. However, when precision printing is performed on aluminum plates, glass plates, and acrylic plates, pinholes are not allowed to occur when post-processing and etching are required. In addition, there are many reasons for pinholes, many of which cannot be explained at present, and some are still quality management issues. Pinholes are one of the most important inspection items in the inspection of printed products.
① Dust and foreign matter attached to the plate. When making plates, some sol will be mixed in during water washing and development. In addition, when emulsion is coated, dust is also mixed in, and pinholes will be generated when attached to the screen. These can be found and repaired in time if they are carefully checked during the test. If dust and foreign matter are attached to the screen, blocking the screen opening will also cause pinholes. Before formal printing, if you use paper with strong ink absorption, you can remove these dust from the plate after printing several sheets.
② Cleaning of the surface of the substrate. Aluminum plates, glass plates, acrylic plates, etc. should be pre-treated before printing and should be printed immediately. In multi-color printing, the method of rubbing with alcohol before printing is generally adopted. In addition, semi-automatic and fully automatic ultrasonic cleaning machines can also be used. After pre-treatment, dirt such as grease can be removed, and at the same time, dust attached to the surface can also be removed.
The detergent of the cleaning machine is often mixed with broken fibers. This detergent is dissolved in alcohol. When cleaning the surface of the substrate, a thin surfactant film is often formed, and pinholes will occur when printing ink on the film. Therefore, special attention should be paid when using detergents and alcohol. When the substrate is carried by hand, the fingerprints of the hand will also adhere to the printing surface, forming pinholes during printing.
