The most important part in the exposure process is to closely attach the screen to the base plate to prevent the printed image from being false or even scrapped.
Before the exposure, the negative should be checked once to see if the edge of the negative is smooth, whether the handwriting is clear, and whether there are scratches, dew points, etc., and then use the exposure machine for exposure.
During exposure, the interval between the lamps should be based on the diagonal of the actual figure of the plate (for reference), and the time is determined by the fineness of the exposed master.
First of all, you should choose the screen to match with the phase plate, clean it with high efficiency, wash it repeatedly with water, and dry it for use.
If there are holes or openings that should not be on the plate, the sealing glue can be used for proper repair (the drying time should not be too long, otherwise it will cause the problem of stripping when the screen is reused). With the printing machine (single lamp 2000W), generally 80 seconds to 100 seconds is appropriate. It uses the chemical changes of the photosensitive paste, that is, the photosensitive paste is cross-linked and hardened in the light department and is firmly combined with the screen to form a plate film. The unsensitized section is washed and developed with water or other developer to form a through hole to make the screen The printing plate. If the time is too long, the wet expansion of the film layer is severe, which affects the clarity of the image, and it is easy to be lost, and the plate film is perishable. No matter what kind of screen version, the unexposed department must be completely washed. The residual glue is a very thin film of photosensitive glue. It is easy to show high transparency in the details of the image, which is difficult to distinguish. It is often mistaken for transparency, and the ink cannot pass through during printing.
There are many plate-making methods of screen printing, and they also have their own advantages and disadvantages. Our current plate-making method mainly uses the indirect method of photosensitive plate-making method.
The control principle of the development degree is: under the conditions of transparency and development, the shorter the time, the better. Then, paint the prepared photosensitive paste on the silk screen evenly, place the screen in an oven at 60-65 ℃, bake for 10-13 minutes, then brush the photosensitive paste evenly again, and dry it in the oven. Take it out for exposure. If the drying time is too long or too high, it will be difficult to develop and take off the net. On the contrary, the plate film is not strong and the exposure is not transparent. Long exposure time and development problems, short time, the film is not strong, easy to fall off during development and easy to form jagged edges. In order to achieve a good plate-making edge effect, the angle is generally preferably 30 degrees to the mesh. The straight stretched net should be completely perpendicular to the frame, and it is necessary to avoid the holes and bubbles on the screen.
Development: Immerse the exposed screen in water for a minute or two (30 ℃ -40 ℃ warm water is better, can shorten the development time). After shaking the screen and other unexposed parts to fully absorb water and swell, It can be rinsed with strong water, and the developed images should be completed within a short period of time when the pictures and texts appear. When placing photographic plates, they should generally be placed in the center of the web or according to their own actual printing requirements. The see-through glass should be carefully cleaned.
After developing, take out the screen plate and absorb the running water of the screen plate with absorbent paper or newspaper, dry it in an oven at 60-65 ℃ and take it out.
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