Screen printing board
1. Paint film engraving method:
It is a kind of manual plate making method, which is relatively simple. It can print monochromatic patterns and texts that are generally not too delicate.
(1) Spraying engraved paint film paper: paste the tracing paper on the flat wood plate, use a pen to adjust 1 part of rubber water (volume ratio), 1 part of gasoline, and apply it evenly on the paper. , After drying, spray the soft varnish 3-5 times. After each spraying, dry it in an oven at 40-50 degrees. The thickness of the paint film should be sprayed to 5-6 mm. The paint film should be bright, uniform and free of bubbles. , No stains.
(2) Engraving graphics: Paste the paint film paper on the graphics, use a carving knife, compass knife, and ruler to engrave the graphics, and gently remove the paint film
(3) Reposting: After engraving the graphics, it can be reposted on the screen frame made in advance in the past. The method is to put the carved paint film under the screen frame and press it tightly, and gently rub it with cotton dampened with a little thinner until the paint film and the screen are firmly adhered. After drying for a few minutes, remove the tracing paper. If the paper is not all off, wipe it with cotton dampened with water. The blank part is coated with a layer of nitrocellulose paint to block the mesh of the screen. It can be printed after drying.
2. Carbon paper printing method:
It is also a simpler manual plate making method.
(1) Cut photosensitive paper: photosensitive paper is a kind of carbon paper made by thickly coating the mixture with oxygen and barium base paper, and cut it according to the size of the figure for use.
(2) Sensitization: soak in a solution of 500 milliliters and 20 grams of ammonium dichromate for 3-5 minutes, take out the carbon paper, and drain the water.
(3) Exposure: Stick the carbon paper flat on the clean glass, with the glue film facing upwards, cover the positive polyester film base plate on the top, and use the exposure machine for exposure. The exposure time is 8-12 minutes.
(4) Development: After exposure, soak in 40~50 degrees warm water for several minutes to make the film and positive plate and the zinc oxide base paper separate naturally, and carefully develop with warm water until the force-shaped characters are clear.
(5) Repost: Place the prepared plate under the frame of the pre-stretched screen, cover several layers of newspaper on the screen, press on the glass plate, and press it with a weight of 1-2 kg/cm². When the adhesive film is firmly attached to the screen, remove the heavy objects and newspapers, use the electric oven to dry the adhesive film, and then remove the base paper, the film graphics will be transferred to the screen. Check the graphics carefully for defects. After passing the test, coat the screen around the graphics with a layer of nitro enamel for protection, and install the screen printing plate on the printing plate table for printing. The scope of application of this plate-making method is the same as that of the paint film engraving method.
3. Sensitive plate-making method
The printing plate used for silk-screening signs requires high precision, and generally adopts three advanced photosensitive plate-making methods: direct, indirect, and direct.
A. Direct plate making method:
(1) The post frame uses an aluminum frame, and does not need to stretch the net. The air pressure is 5-6 kg/cm², and the acetal adhesive net is used. The tension is measured by tension, and the tension is 5-7 kg, sinking The size should be less than 2 mm.
(2) Cleaning the screen: Use washing powder, detergent, ethanol, etc. as a cleaning agent to clean both sides of the screen, rinse with water, and dry it with hot air for later use. The purpose is to make the net better bond with the photosensitive glue.
(3) Scraper (coating hopper, coater): The squeegee for coating photosensitive glue can be made of stainless steel, or it can be made of organic glass plate. Its length is generally slightly smaller than the inner diameter of the screen frame (a set of scrapers with different lengths are matched as a set) B. The edge of the scraper must be thin and not edged, smooth and straight, and no defects such as bumps, burrs, scars, etc., are allowed to affect the quality of plate making. When coating the silk screen photosensitive glue, it should be dried every three times, and it needs to be done continuously 3-4 times until the glue film reaches the required thickness, and then the exposure is carried out.
(4) The temperature of the drying oven is preferably an adjustable temperature drying oven. The drying temperature of the photosensitive adhesive is generally controlled at about 40 degrees. If the baking time is too long or the temperature is too high, the quality of the photosensitive layer will be affected.
(5) Safety light: The lighting source of the studio generally uses orange, yellow or red light as the safety light, but from the visual point of view, the orange-yellow light source is more comfortable. Its brightness is suitable to be able to see all objects clearly.
(6) Inspection of the master plate: the master plate must be carefully checked before printing, including dust on the plate surface, blackness of the master plate, line breaks, sand hole defects, etc. and whether the front and back of the image and text meet the requirements.
B. Indirect manufacturing method:
(1) Prepare the screen frame and photosensitive film: Wash the stretched screen frame (220-260 mesh nylon wire) with a 10% sodium phosphate aqueous solution to remove oil stains.
(2) Exposure: Press the film and the base plate tightly in the exposure machine, and use carbon lamp or xenon lamp for exposure. 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, place 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 exposed and developed phenanthrene film. Until the graphics are clear.
(4) Paste the film film: stick the exposed film surface on the screen, use a rubber plate or other straight board on the back of the human film, and gently scrape it to make the film and the net contact firmly, and immediately put it in the oven at the temperature Bake for 8-12 minutes at 55±2 degrees. After drying, fix the screen frame on the printing plate for trial printing.
(5) Wire mesh photosensitive film is a kind of photosensitive glue with polyenol glue as the main body. The film film is coated with gelatin as the main photosensitive agent on a transparent plastic base of 0.12-0.06 mm. Before use, it is connected to the size of the pattern, and each side is wide. Use a cloth to wipe off the powder and dirt on the film.
(6) Film removal method: In the process of exposure and development, if 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 a period of production, one part each of industrial sodium hypochlorite and water can be used and soaked for 10-20 minutes. Or the screen plate can be heated with 5% sodium hydroxide aqueous solution to remove the film.