Now is an era of rapid development. This new era has driven the development of new technologies. Screen printing technology has moved from the ancient civilization thousands of years ago to the 20th century. Today, it is also facing the challenges of the times and experiencing such Pain period. The development of screen printing in recent years has entered a bottleneck period, and screen printing is a main printing method in stencil printing. The printing plate is in the form of a mesh, and the ink on the printing plate is leaked from the through-hole part of the layout to the substrate under the extrusion of the squeegee during printing. Maybe you don’t know much about screen printing technology. Let’s introduce the screen printing operation steps, basic process principles, and the determinants of the amount of ink.
Screen printing operation steps:
photosensitive platemaking
The printing plate used for silk screen printing plate requires high precision, and generally adopts the advanced indirect, direct and direct photosensitive plate-making methods.
1. Prepare the screen frame and photosensitive film: Wash the stretched screen frame (220-260 mesh nylon wire) with 10% sodium phosphate aqueous solution to remove oil stains. The wire mesh photosensitive film is a kind of photosensitive adhesive with polyvinyl alcohol as the main body. The film is coated with gelatin as the main photosensitive agent on a transparent plastic base of 0.12-0.06 mm. mm, wipe off the powder dirt on the membrane with a cloth.
2. Exposure: Press the film and the bottom plate in the printing machine, and expose with a carbon lamp or a xenon lamp. The distance between the screen frame and the light source is 50-60 cm, and the exposure time is 2-6 minutes.
3. Development: After exposure, put the phenanthrene film on a flat plate, soak the omentum with warm water for 1-2 minutes, spray it with a water nozzle, and dissolve the non-photosensitive part (graphic part) with water to remove the printed and developed phenanthrene film, until until the graphics are clear.
4. Film: paste the exposed film surface on the silk screen, use a rubber plate or other straight plate on the back of the film in the sign making, gently scrape the film to make the film and the net contact firmly, immediately put it in the oven, at the temperature Bake for 8-12 minutes under the condition of 55±2 degrees, after drying, fix the screen frame on the printing plate table for trial printing.
5. Removal method: In the process of exposure and development, when the plate is found to be unqualified, immediately use warm water to brush off the film and make it again. If the plate has been dried or the film is removed after production for a period of time, one part of industrial sodium hypochlorite and one part of water can be used and soaked for 10-20 minutes. Or a 5% sodium hydroxide aqueous solution can be used to heat the screen to remove the film.
The basic process principle of screen printing
Printing is carried out using the basic principle that the mesh of the screen printing plate is transparent to the ink, and the mesh of the non-graphic part is impermeable to the ink. When printing, pour ink on one end of the screen printing plate, apply a certain pressure to the ink part of the screen printing plate with a scraper, and move to the other end of the screen printing plate at the same time. The ink is squeezed onto the substrate by the scraper from the mesh of the graphic part during the movement. 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. A certain gap is maintained between them, so that the screen printing plate during printing can generate a reaction force on the squeegee through its own tension, so that the ink and the screen can break and move, ensuring the printing dimensional accuracy and avoiding smudging the substrate. When the squeegee scrapes the entire layout and lifts, the screen printing plate is also lifted, and the ink is gently scraped back to the original position.
What factors determine the amount of ink in screen printing?
1. Screen polyester mesh:
A. Screens of different meshes, the lower the mesh, the more ink is placed, and the higher the mesh, the less ink is placed.
B. For the same mesh with different wire thickness, the thicker the wire thickness, the greater the amount of ink. On the contrary, the thinner the wire thickness, the less ink.
C. Screens with the same mesh number and the same thickness have more ink under the inclined screen and less ink under the straight screen.
D. Under the same other conditions, the greater the tension of the screen, the greater the amount of ink.
2. Ink:
A. Inkability of ink.
B. The ink is thin and the ink is too much. If the ink is relatively dry, it will form a drying phenomenon on the screen, and the ink will be reduced accordingly.
3. Film thickness of photosensitive paste: The thicker the thickness of photosensitive paste during plate making, the more ink will be loaded. This method is commonly used in the process of increasing ink thickness.
4. Factors in the process of squeegee printing: the speed of squeegee printing is slow, and the ink film layer is also behind. If the squeegee printing speed is fast, the ink layer will be thin.
5. Squeegee: This is also crucial.
A. The more inclined the scraper is placed, the larger the amount of ink will be placed, and the less ink will be placed if it is too vertical.
B. The softer the squeegee, the larger the ink will be, on the contrary, the harder the squeegee, the less ink will be deposited.
C. The more round and blunt the blade of the scraper is, the more ink it will put down, and the sharper it will be, the less ink it will put down.