The printing network process is basically as follows
1, the choice of plate film
To get a rich layer of screen prints, first make a film like offset printing, use 100 ~ 133 lines / inch of dot output, too high line number is not conducive to the reproduction of the low-key level. If a circular dot is selected, since the screen printing mesh dot reproduction curve is reduced below 20%, 70% of the dot is enlarged, and the tone curve adjustment is performed on the image before the film is taken out. Generally, the screening angle of the film is: magenta plate 15°, cyan plate 75°, yellow plate 90°, black plate 45°, and practice has proved that there are very few overprinting moiré. In addition, in order to ensure accurate overprinting, even if it is a line draft, it is not necessary to use sulfuric acid paper negatives. If you don't have a prepress production department, don't ask the advertising banner production company to make the printing film, because they have a low number of film lines and the level is lost, which will affect the printing clarity.
2, the choice of screen printing mesh
High-mesh yellow plain woven polyester mesh is a necessary condition for high-precision screen printing. The yellow color is to reduce the diffuse reflection of the exposure light when printing, and the flat woven mesh can form a thin screen to facilitate high-level, low-key reproduction. The same mesh number of mesh has a variety of wire diameters to choose from, it should be easy to break the net. The ratio of the mesh number to the number of film screen lines is 3.5:1. If the number of screen lines is 120 lines/inch, the screen should be 420 mesh.
3, stretch net
Large-format mechanical stretcher can be used to obtain large tension, prevent tension slack during printing, and screen deformation; the tension of the same set of screens should be consistent; oblique stretch net, mesh warp and weft and frame are 22.5 ° clip The corner helps to reduce the defects of the dot, making the small text and lines perfect. When stretching the net, the initial tensile force should be large, and the net should be pulled once every 1 hour. After 12 hours, the tension of the screen should be measured with a tensiometer. The difference in tension between the parts is not more than 1 N/cm (the tension after the screen printing is 24 to 25 N). /cm). In addition, aluminum alloy or steel mesh frames should be used, and the wooden frame is easily deformed after being immersed in water.
4, screen production
Take the direct legal plate as an example. After the pretreatment of the screen, the high resolution sensitizer is used, the squeegee surface is coated twice, the printing surface is coated once, and the printing surface is laid down (should be in a dust-free environment); then, at a suitable temperature ( Drying is generally completed within 35~45°C), the measured tension is not less than 18 N/cm; the thickness of the photosensitive layer is controlled at 10~18μm, the thickness of the emulsion layer on the printing surface is about 10% of the thickness of the screen, and the Rz value is rough. Degree) is less than the thickness of the emulsion layer. During the coating process, it is very necessary to control the thickness of the screen. When the thickness is too thick, the dark layer cannot be separated, and the highlight is not printed. The rough screen is uneven, which will cause the dot to increase abnormally and the color tone to change. These data can be controlled by instrumental measurements.
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