Influence of light source on exposure time
During the exposure of the screen, the photo-curing reaction of the emulsion is similar to the curing reaction of the UV ink or other ink on the substrate. The screen emulsion is sensitive to the wavelength of the mixed spectrum of UV light and blue-violet light. Because the scraping knife repetitively scrapes back and forth on the screen during printing, the exposed emulsion completely covers the cable after curing. Specifically, there are two factors that affect exposure:
1. Exposure light source
The spectral characteristics and intensity of the light source are decisive factors in the exposure. Screen emulsions are sensitive to UV light in the 365-420 nm wavelength range. The emulsion must be completely cured and requires a certain amount of energy to cause a chemical reaction.
In general, incandescent lamps and floodlights emit light with a wavelength of 365 nm to 420 nm. Therefore, they are not the best choice for exposure light sources. Metal halide lamps, mercury lamps, and some fluorescent lamps produce photochemical light sources, but they emit different amounts of UV light and blue-violet light. Except for special circumstances, all screen emulsions can use the above three light sources as exposure light sources. Since they emit slightly different ratios of UV light and blue-violet light, the exposure time is slightly different, and the images on the finished screen are slightly different.
The intensity of the light source refers to the energy of the light source reaching the screen emulsion. It does not mean the brightness of the light source seen by the human eye, because the UV light is invisible light. The length of the exposure light source, the power of the exposure device, and the distance from the light source to the screen are the three most important factors affecting the intensity of the light source. In the work, the intensity of the light source should be checked regularly, because the lamp tube will be attenuated during use, resulting in a weakened light source.
2. Distance from the light source to the screen During the plate making process, once the distance from the light source to the screen is changed, the optimal exposure time must be recalculated. This is a squared proportional relationship. As an example, if the distance is increased by twice, the current exposure time is 4 times the original exposure time. Conversely, if the distance is reduced by half, the exposure time is reduced by 1/4.
Effects of Exposure on the Moisture of the Emulsion Coating Layer <br> Imaging speed and resolution of the emulsion are also factors that affect the exposure time. With the advent of new sensitizing emulsions, the exposure speed has been significantly accelerated, and several types of sensational emulsions are now used. Let's use an analogy. The relationship between the thickness of the screen emulsion and the exposure time is like the relationship between the ink layer thickness and the ink drying time.
If the emulsion coating is not yet dry, it is exposed, and it is almost impossible to achieve optimum exposure. So, after the emulsion layer is completely dry, it is exposed again. Otherwise, the residual humidity in the emulsion coating will greatly inhibit the thermal cross-linking reaction during exposure. Even if it does not help to prolong the exposure time, it will only end up facing the embarrassing situation of underexposure.
The effect of screen mesh number and color on the exposure time <br>The number of screen fibers and the thickness of the fiber determine the open area of ​​the screen and the thickness of the screen, which in turn affects the ability of the screen to reside. How much emulsion is on top. Obviously, if the area of ​​the opening is large and the mesh line is thick, then the resident dose of the emulsion is more and the exposure time required is longer. On the contrary, the exposure time is shorter! In general, white screens have a short exposure time, but white screens are more prone to light diffusion, thus affecting the resolution of the image, ie, reducing the resolution. Dyeing screen material effectively inhibits light diffusion. Therefore, a better resolution can be obtained. On the other hand, no matter which type of screen material is used, inevitably there will be a certain degree of light diffusion. This is a natural feature of screen printing.
The density of the positive film affects the exposure time <br>If the density Dmin (ie, the background density) of the non-image area of ​​the Zhengyang film used in the plate making is too high, or the density Dmax of the graphic area is too low, it will Exposure has a bad effect. In screen printing, the positive film needed for platemaking should have a clean, transparent background and a high-density (high density) graphic area. Let us suppose that if the background and the graphic area of ​​the positive film are translucent, there is no doubt that light must pass through the graphic area to reach the emulsion.
During the exposure of the screen, the photo-curing reaction of the emulsion is similar to the curing reaction of the UV ink or other ink on the substrate. The screen emulsion is sensitive to the wavelength of the mixed spectrum of UV light and blue-violet light. Because the scraping knife repetitively scrapes back and forth on the screen during printing, the exposed emulsion completely covers the cable after curing. Specifically, there are two factors that affect exposure:
1. Exposure light source
The spectral characteristics and intensity of the light source are decisive factors in the exposure. Screen emulsions are sensitive to UV light in the 365-420 nm wavelength range. The emulsion must be completely cured and requires a certain amount of energy to cause a chemical reaction.
In general, incandescent lamps and floodlights emit light with a wavelength of 365 nm to 420 nm. Therefore, they are not the best choice for exposure light sources. Metal halide lamps, mercury lamps, and some fluorescent lamps produce photochemical light sources, but they emit different amounts of UV light and blue-violet light. Except for special circumstances, all screen emulsions can use the above three light sources as exposure light sources. Since they emit slightly different ratios of UV light and blue-violet light, the exposure time is slightly different, and the images on the finished screen are slightly different.
The intensity of the light source refers to the energy of the light source reaching the screen emulsion. It does not mean the brightness of the light source seen by the human eye, because the UV light is invisible light. The length of the exposure light source, the power of the exposure device, and the distance from the light source to the screen are the three most important factors affecting the intensity of the light source. In the work, the intensity of the light source should be checked regularly, because the lamp tube will be attenuated during use, resulting in a weakened light source.
2. Distance from the light source to the screen During the plate making process, once the distance from the light source to the screen is changed, the optimal exposure time must be recalculated. This is a squared proportional relationship. As an example, if the distance is increased by twice, the current exposure time is 4 times the original exposure time. Conversely, if the distance is reduced by half, the exposure time is reduced by 1/4.
Effects of Exposure on the Moisture of the Emulsion Coating Layer <br> Imaging speed and resolution of the emulsion are also factors that affect the exposure time. With the advent of new sensitizing emulsions, the exposure speed has been significantly accelerated, and several types of sensational emulsions are now used. Let's use an analogy. The relationship between the thickness of the screen emulsion and the exposure time is like the relationship between the ink layer thickness and the ink drying time.
If the emulsion coating is not yet dry, it is exposed, and it is almost impossible to achieve optimum exposure. So, after the emulsion layer is completely dry, it is exposed again. Otherwise, the residual humidity in the emulsion coating will greatly inhibit the thermal cross-linking reaction during exposure. Even if it does not help to prolong the exposure time, it will only end up facing the embarrassing situation of underexposure.
The effect of screen mesh number and color on the exposure time <br>The number of screen fibers and the thickness of the fiber determine the open area of ​​the screen and the thickness of the screen, which in turn affects the ability of the screen to reside. How much emulsion is on top. Obviously, if the area of ​​the opening is large and the mesh line is thick, then the resident dose of the emulsion is more and the exposure time required is longer. On the contrary, the exposure time is shorter! In general, white screens have a short exposure time, but white screens are more prone to light diffusion, thus affecting the resolution of the image, ie, reducing the resolution. Dyeing screen material effectively inhibits light diffusion. Therefore, a better resolution can be obtained. On the other hand, no matter which type of screen material is used, inevitably there will be a certain degree of light diffusion. This is a natural feature of screen printing.
The density of the positive film affects the exposure time <br>If the density Dmin (ie, the background density) of the non-image area of ​​the Zhengyang film used in the plate making is too high, or the density Dmax of the graphic area is too low, it will Exposure has a bad effect. In screen printing, the positive film needed for platemaking should have a clean, transparent background and a high-density (high density) graphic area. Let us suppose that if the background and the graphic area of ​​the positive film are translucent, there is no doubt that light must pass through the graphic area to reach the emulsion.
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