Normally, we used a 21-step gray scale (density difference 0.15) to test the exposure of the PS plate. According to different printing platemaking requirements, the gray ladder rule is generally controlled at about level 3 (also known as “no ink, blank or whiteningâ€), and the so-called “clean†is the photosensitive layer corresponding to the three steps of the plate and the gray step. See all light decomposition. However, in practice, test strips often cannot be placed in the printing area of ​​the PS plate, that is, the graphic part; they can only be placed on the edge of the plate material. At this time, if you press the gray ladder ruler level 3 to control the exposure As a result, the graphic image part in the center of the plate-making machine may be exposed to sunlight, resulting in the loss of the dot and the decline in the printing rate. The positive plate version of the PS plate is a photosensitive layer corresponding to the transparent part of the original plate (ie, the blank part), and is completely removed from the plate after development; and the photosensitive layer corresponding to the original blackened part (image part) is left after development. On the plate. The principle of this process is that the photosensitive layer of the PS plate is decomposed into substances that are soluble in an alkaline solution after being irradiated with light of a certain energy. The standard exposure after exposure to radiation is decomposed into substances dissolved in alkali solution. The standard exposure amount during the printing is the exposure amount that is regulated by the percentage of the specified dot and the yin and yang lines. That is, the standard exposure time is the exposure time of the screen reproduction and the width of the yin and yang lines. Which underexposure, the printing plate part of the screen line thicker, expanded dot area, the blank part may be dirty; if overexposed, the plate image part of the line becomes thinner, the screen area is reduced and directly affect the image of the tone. PS version printing is done with a printing machine. There are two types of structures that are commonly used in the printing machine, one is a light source upper setting plate printing machine, and the other is a light source lower setting box type rotary printing plate printing machine. Whether it is the upper light source upper and lower plate-making machine, the light source is a point light source. The illuminance on the layout when printing is determined by the intensity of the light source and the distance and angle between the light source and the illuminated surface. According to the law of inverse square of optics, the illuminance is proportional to the intensity of the light source and is inversely proportional to the distance from the light source to the illuminated surface. Illuminance: E=(F(luminous flux))/S=dF/dS=1/r2COSa According to the illuminance cosine law, the angle of the light source perpendicular to the illuminated surface is 0, and the illuminance is the maximum; when the illumined surface and the light source parallel rays are at an angle of 90°, the illuminance is 0; the illuminance of the illuminated surface changes with the incident angle of the light source. The size of the illumination is affected by the distance and angle. To reduce this effect, the light source of the plate printing machine is generally added with a convergent lampshade, so that the illumination of the illumination range is as uniform as possible, but there are still differences. The standard of the printing machine stipulates that the illuminance uniformity greater than 88% is a superior product. Therefore, the illuminance at each position of the stencil machine being illuminated will not be consistent. For this purpose, we test three kinds of printing machines: Table 1 Incidence angle (° degrees) 0 10 20 30 45 60 70 80 90 Illuminance (relative value) 1 0.89 0.94 0.87 0.71 0.50 0.34 0.17 0 First, Dainippon mesh printing machine Structure: Light source under-mounted rotary printing machine Model: P422-G Light source power 3300W layout size 1140×940mm lamp distance 900mm maximum incident angle 32° Test 1: The middle level of the layout of the three clean prevail, the layout of the left, right, front, rear, plus the test strips each exposed a PS version (the same exposure) data as shown in Table 2: Table 2 Location Left Front, Center Back, Right Exposure (S) 20 Step Scale (Pole) 1.0 1.5 3 1.5 1.0 Network reproduction (%) 2 to 97 2 to 97 2 to 98 2 to 97 2 to 97 Network cable (μ) 12 to 6 12 to 6 20 to 6 12 to 6 12 to 6 2. According to the cleanliness of the front edge of the layout, the left, right, front, back, and middle plus test strips of the layout will each expose a PS plate. The data is shown in Table 3: table 3 Position Left Front Center Right Rear Exposure (S) 40 The ruler (pole) 3.0 3.0 5 3 3.5 Network reproduction (%) 2 to 98 2 to 98 2 to 98 2 to 97 2 to 98 Network cable (μ) 12 to 6 12 to 6 20 to 6 12 to 6 12 to 6