Screen printing is composed of five major elements,namely, screen printing plate, squeegee,ink, printing table and substrate. The basic principle of screen printing is to use the basic principle that the screen printing plate’s graphic part has a mesh through ink, and the non-graphic part is impervious to ink. When printing, pour ink on one end of the screen printing plate, and use a squeegee to apply a certain pressure on the ink position on the screen printing plate while moving toward the other end of the screen printing plate. The ink is squeezed from the mesh of the graphic part to the substrate by the scraper while it is moving.
Due to the viscosity of the ink, the imprint is fixed within a certain range. During the printing process, the squeegee is always in line contact with the screen printing plate and the substrate, and the contact line moves with the movement of the squeegee, due to the screen printing plate and the substrate a certain gap is maintained between them, so that the screen printing plate during printing produces a reaction force against the squeegee through its own tension. This reaction force is called resilience.
Due to the effect of resilience, the screen printing plate and the substrate are only in mobile line contact, while other parts of the screen printing plate and the substrate are in a separated state. The ink and the screen are broken to ensure the printing dimensional accuracy and avoid smearing the substrate. When the squeegee is lifted after scraping the entire layout, the screen printing plate is also lifted, and the ink is gently scraped back to the original position.
For companies that produce membrane switches, screen printing is a necessary process, and it is also a very critical process technology. Many people who have not touched the technology of printing may think that screen printing should be a very good job. It’s easy to do, but the fact is that I admire those who have done screen printing, because when you really go through the process of learning printing, you will find that this is indeed a technical job, so it is very important to understand the printing process of screen printing.
The choice of wire mesh
Screen printing plates generally include synthetic fiber screens, stainless steel screens, and natural fiber screens, but printing can be applied to many places, and you must choose according to your own products.
2.The choice of screen frame
The more regular and less deformed screen frame is an aluminum alloy screen frame, and its size should be larger than the pattern. The specific size should be that the distance between the outer edge of the pattern and the screen frame should be between 70~100mm. It is very important to choose the strength of the screen frame. The key is that the rigidity in the horizontal direction is sufficient.
3.Stretch the net
I chose the net silk and the net frame, and combined the two, this is the stretched net. You can use manual, motorized, and pneumatic methods to stretch the net. The more advanced one is the pneumatic stretcher that stretcher that stretches high-quality screens. The requirement of the stretched net is uniform tension, the warp and weft of the screen are kept vertical, and the glue of the net must be firm and not slack.
4.Choose photosensitive glue
Photosensitive adhesives on the market include dichromate, diazonium, and iron salts. The requirement of screen printing plate-making for photosensitive glue is to have good plate-making performance and easy coating. The photosensitive spectral range is 340~440nm, the development performance is good, the resolution is high, the stability is good, it is easy to store, and it is economical and hygienic, non-toxic and pollution-free. The requirement of printing on photosensitive materials is that the plate film formed by photosensitive materials can adapt to the performance requirements of different types of inks. It has considerable printing resistance and can withstand a considerable number of squeegees of the squeegee; it has a good bonding force with the screen, and no demolding failure occurs during printing; it is easy to peel, which is conducive to the recycling of the screen printing plate.
After selecting the above materials, apply photosensitive glue in a dark room; it is required to be uniform, and then dry, generally requiring two coatings. Exposure is required for exposure on a cold light source exposure machine, exposure time should be determined according to the pattern, generally between 12 and 30 minutes. After exposure and development, a screen printing screen is prepared.
Conductive ink is one of the most critical materials for the production of printed membrane switches. Its quality and price are directly related to the quality of membrane switch products and the cost of product production. Conductive ink is a kind of functional ink, which mainly contains carbon is printing. Conductive ink such as paste and silver paste. Conductive ink is needed to print the membrane switch circuit.
There are several types of printing machines: manual, semi-manual, and fully automatic. Manual printers are suitable for small batches and small specifications. Semi-automatic and full-automatic printing machines are suitable for large-volume, large-format, multi-color printing, and have the advantages of accuracy and speed.