Effect of screen mesh and color on exposure

At present, there are many kinds of screens, and the products are uneven. However, it must be clear that the mesh number and wire diameter of the screen determine the aperture ratio and the thickness of the screen, and at the same time, it affects the online presence of the emulsion. Retention, apparently, the aperture ratio is large, silk thick silk screen can be coated emulsion is thick, so the exposure time should be increased accordingly, otherwise the exposure time is shortened.

In general, white screens are prone to light scattering, reflecting ultraviolet rays to the edges of the images that should not be exposed, causing the edges of the images to be unclear and jagged. Although the exposure time is short, the screen resolution and lines are affected. Sharpness. The yellow screen can absorb ultraviolet rays at a wavelength of 350 to 420 nm, effectively reducing the damage of the scattered light to the screen. Experiments have shown that with the warm yellow screen plate, ultraviolet rays shine on the yellow screen, and the reflected light does not contain harmful wavelengths of 350 to 420 nm. Since the elimination of ultraviolet light scattering can provide clear graphics with sharp edges, when making a fine screen, yellow screen printing should be selected as much as possible, and the screen printing resistance should be improved by selecting the best exposure time. Help screen recovery.

Influence of temperature and humidity on exposure

Temperature changes have a greater influence on the emulsion layer. Under normal circumstances, the temperature is below 4°C, the sensitivity of the film is very slow; and when the temperature rises by 1.8°C, the sensitivity of the photosensitive layer increases by 3 times. The photocuring speed of the adhesive layer is also increased accordingly, and the exposure time is reduced. However, when the temperature is too high (above 40°C), the unexposed photosensitizer is prone to dark reaction, resulting in self-crosslinking of the photosensitive resin. As a result, the dots of the high-light part are lost and the screen resolution is significantly reduced. Therefore, the operating environment should be controlled. About 25 °C.

Humidity changes will also affect the screen exposure quality. When the screen is not completely dry or the environment is exposed to humidity, the screen printing resistance will be reduced, and the relative humidity of the operating environment will be controlled at 50% to 70%. The best exposure.

Correct choice of exposure time

There are several ways to determine the best exposure time for a screen, depending on the emulsion used. In general, the manufacturer of the emulsion will provide the basic parameters for the exposure of your product. You can select the appropriate one for your own reference. The best exposure time, or take the following method to determine the exposure time.
1. Grading exposure test

The grading exposure test method is a commonly used exposure time test method, which uses the calculated approximate exposure time as the medium exposure time, and then carries out different degrees of exposure on the same screen part to obtain the best exposure time. . The specific steps are: first, expose the screen to 50% of the approximate exposure time, then cover 1/5 of the screen, and then press 25% of the approximate exposure time, that is, cover 1/5 more times and press Exposing 50% of the previous exposure time, you can get 5 areas with different exposure levels. After the screen is washed and dried, you can find the best exposure time after proofing.

2. Exposure test strip (sheet) test method

The exposure test strip is a necessary tool for screen printing. It can accurately test the correct exposure time of different photosensitive materials and different film thicknesses for different light sources, and plays an important auxiliary role in improving the screen quality. Commonly used EC test strips and wedge test strips, the latter control effect is better, you can increase or decrease the exposure time as you like.

Since there are many factors affecting the quality of screen exposure, the correct choice of exposure time with exposure control tools is the most effective means of ensuring screen quality.

Source: "Printing Technology"

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