Silk-screen engraving handmade (bottom)

4. Degreasing

Degreasing is to ensure the adhesion of the screen and the photosensitive adhesive, also known as screen pre-treatment. Screens may become oily or otherwise contaminated during manufacture and use. If they are not removed, the effect of plate making will be affected. There are many types of degreasing detergents, all of which are alkaline solutions. The simple method is to use washing powder by flushing the screen with water first, spreading it evenly after lying flat, and then rubbing it evenly with a clean cotton cloth. The particles of the detergent powder have a roughening effect on the surface of the screen during the rubbing process, which is beneficial to the adhesion of the photosensitive adhesive, but it is necessary to pay attention to flushing with strong water. It is easy to accumulate detergent residue at the corner of the net, especially for washing. After the screen is cleaned and dried naturally, it can be stenciled.

There are many screen printing methods, but the direct printing of the photosensitive plate is the most commonly used plate making method. At present, the main use of photosensitive adhesive is diazo photosensitive adhesive, which is divided into solvent-resistant (oily) and water-resistant (water-based) photosensitive adhesives. Respectively for oily inks and aqueous pigments. The photosensitive adhesives sold on the market are divided into two packages. The large bottles are colloids, and the black ones are photosensitive powders. It is necessary to thoroughly mix the photosensitive powder and colloid in the darkroom for 10 minutes and place it for 2 hours until the bubbles completely disappear. use. Stir using sticks or glass sticks, the metal rods are prone to chemical reactions and cannot be used. The unblended gel was blue and the colloidal mixture was light green. Tuned emulsion can not take out the dark room to avoid exposure. Sensitive glue is best used immediately, and it should not be stored in the refrigerator, because the heat will make the modified emulsion unusable after a few days.

Membrane is coated directly on the screen. Squeegee strives for uniform thickness, smooth surface and certain thickness. There are two ways to manually apply the glue. The first is to prepare a stainless steel scraper with a thickness of 1.5 mm, a width of 4 cm (but less than the inner diameter of the net frame) and a height of about 10 cm. One side of the scraper should be sharpened, but not too sharp to avoid inadvertently injuring the limbs and mesh. Then, the cleaned and dried screen plate is laid flat on one side, and then the photosensitive adhesive is put into strips on one side of the screen plate, and the photosensitive adhesive is evenly scraped by the stainless steel scraper across the corresponding side of the screen plate. When scraping the sensitized adhesive, be sure to lightly press the squeegee to the surface of the net and hold the squeegee on the top of the squeegee in a straight line. Do not stop in the middle. The amount of photoresist depends on the size of the screen. Normal screen can be scraped twice, fine prints just have to scrape it. Squeegee is best done once. Where the photoresist is missing, a small scraper is used to make up the scraping, but this too much affects the quality of the plate. The second is to use a scraper to scrape rubber. This is a commonly used manual scraping tool and is available on the market. The length of the scraper is preferably 4 cm larger than the side of the print (but less than the inner diameter of the frame). Put enough photosensitive adhesive into the scraper before scraping, and set the screen upright when scraping. Slightly forward, hold both ends of the scraper with both hands, affixed to the bottom of the screen, and let the glue flow to the surface of the screen, then keep the scraper and the screen at a certain angle, and smoothly and uniformly squeezing from the bottom up. When the scraper moves to the top, the scraper is tilted downward and continues to be scraped upwards. The glue on the screen plate will return to the scraper by himself. At this time, the scraper is removed to complete the coating. The number of squeegees depends on the need, and the fine prints require that the squeegee be thin. When the squeegee is running, the squeegee pressure should be moderate, too light to move and shave, and the coating uneven; too heavy can damage the screen. Squeegee speed should be even and moderate. If the coating is too thin, it will easily generate bubbles. If it is too slow, it will cause excessive flow and affect the uniformity of the coating. Squeegee should be as full as possible, and excessive use of adhesive tape will affect the printing of the next step.

7. dry

After coating the photosensitive emulsion, the screen can be exposed and developed. Drying at high temperatures during the summer can be achieved by drying naturally for 2 h. However, the cold weather, especially winter screen drying, is a problem because most screen-printing enthusiasts do not have professional screen-printing ovens. Drying tools are mostly hair dryers. The use of hair dryer baking is a matter of patience, because the screen dryness sensitivity decreased, the film plate resistance is poor, easy degumming when developing; drying temperature is too high, the hair dryer close to the screen, the photosensitive adhesive will heat hardening It is difficult to develop. Therefore, hand-held hair dryer baking plate, to maintain the distance between the outlet and the screen 5 cm, and to shake the plate uniformly, and the "Z" shape from top to bottom full-page transition, leaving no room. Whether the screen is dry or not is clearly discernible under the faint light of the dark room. The dried photosensitive adhesive is slightly lighter and has no moisture; the undried emulsion is slightly darker and has a moisturizing effect. In addition, it is also possible to dry the screen plate by using a domestic blade type or plate type heater. The method is to put the stencil surface parallel to the heater and maintain a certain distance. After drying for a certain time, the screen can be exposed and developed.

8. Printing

Also known as screen exposure, the key is to control the exposure time. Insufficient exposure time, film hardening is not enough, its resolution, resistance will all deteriorate; exposure time, the image is easy to lose the subtle level or incomplete. Since screen-printing enthusiasts mostly use fluorescent light exposure, the normal exposure time is 4 minutes when the lamps are separated by 5 cm and the light source is 15 cm away from the glass. Fine screen prints can be set at 3 minutes. The temperature of the exposure environment also has an effect on the exposure time, which is half a minute compared to the sky heat. Large screen exposure must pay attention to the exposure of the center and the surrounding exposure is not the same, so the exposure of the screen should be less than 3 CIN exposure lamp array to ensure exposure uniformity. The specific operation of the exposure is to expose the screen to the glass of the exposure table, and put it in close contact with the drafting film. Put the felt or sponge flat on the screen, lay the thick glass, and then apply the heavy material to suppress. Use the sandbag. It is reminded here that the sizing screen before the development, including the squeegee, and the exposure are all performed in the dark room. If there is no special dark room, be sure to turn off the lights, pull on the blinds, and use a small wattage red light to illuminate the dark room.

9. development

It is to completely dissolve the unsensitized portion of the screen printing plate after exposure, while leaving the photosensitive portion intact. There are two methods: (1) Development of multi-purpose pot immersion method, ie, immersing the exposed screen plate in a warm water bath for 2 minutes, then displaying the image and then rinsing it with tap water; (2) Developing the available water jet method, During operation, wet the front and back sides of the screen first, so that the film is softened and then developed by water. The control of the degree of development is under the premise of being transparent, and the shorter the time, the better. If the time is too long, the film will have serious wet expansion and will affect the sharpness of the plate. When the time is too short, the development will be incomplete, and the phenomenon of “light film” will appear. The light film is a thin film of photosensitive adhesive residue, which is easy to appear at the fine level of the image. It is highly transparent, difficult to distinguish with the water film, and is often mistaken for clearness. The simple method of detection is to use the mouth to align with the local tight mesh surface. If you can blow the water film, it means that it has been transparent. It is also possible to test the light, and it is not necessary to continue the shower until it is transparent. After the development is completed, white straw paper can be used to suck off the floating water on both sides of the screen. Sometimes the screen floating water contains a trace amount of sensitized adhesive. After flowing into the open area, the screen will form a light film after drying, so the floating water should be removed as much as possible. The developed screen can be dried naturally. If urgently used, a hair dryer or electric heater can be used to help bake.

10. Revision

After the screen is developed and dried, jamming of the image mesh or unwanted trachoma or blank may occur. Dealing with this work is called revision. The revised version is usually in the bright light of the environment, the screen to the bright spot to observe, and then on the side of the screen printing with a brush dipped in the photosensitive adhesive coating the image of unwanted trachoma and blank space, and dried with a hair dryer. The pores of the image mesh can be pierced with fine needles. Mesh openings around the screen, closed with wide adhesive tape. Finally, the film was exposed for 10 minutes. Screen printing was completed.

Source: Network