Capillary Photosensitive Film Making Process II

3. Film drying

1) Strict control of drying temperature

Drying temperature should be controlled 35 ~ 40 °C, can not be higher than 40 °C, this temperature is the actual temperature on the screen, rather than the indicated temperature on the device. When the actual temperature on the screen is greater than 40°C, the dark reaction of the photosensitive layer will be accelerated. The longer the drying time is, the darker the degree of dark reaction will be, resulting in difficulty in development after exposure, or even showing no pattern, even causing Difficult to recycle screens, etc.

2) Complete removal of water

If the photosensitive film is not fully dried, it will be exposed even if the exposure time is just right, but due to residual moisture in the photosensitive layer, it will also affect the penetration of ultraviolet light, making the photosensitive film underexposure, affecting the screen printing resistance, causing A burr occurs on the edge of the pattern, and the photosensitive layer is thinned. In severe cases, the film can even be washed out during development. Therefore, it is essential that the dryness completely controls the thickness of the photosensitive layer to ensure the quality of the screen and the resistance to printing.

It is worth noting that after drying the photosensitive film to remove the protective film (PET sheet), it must be dried again at the same temperature, so that the moisture in the film between the transparent PET film and the photosensitive film can be further removed before exposure. . For screens that have been pre-patched and stored without peeling off the PET film, they must be dried before exposure so that the moisture absorbed by the photosensitive layer on the screen can be removed together with the air. quality.

3) How to determine if the drying is complete?

1 After the capillary membrane is dried, it is very easy to peel off the transparent film base (PET sheet), and there is no harsh sound. At the same time, the surface of the photosensitive film is bright, which means that the photosensitive film is completely dry, and vice versa.

2 After exposure, from the vacuum state of the printing machine for a while, the printing plate can be separated from the photosensitive film on the screen or separated automatically. This indicates that the photosensitive film has dried out, otherwise it has not dried.

4 exposure control

When the exposure is insufficient, if the film is not completely hardened, the pattern on the screen may be easily deformed during development, the image clarity is poor, the dots are lost, the resistance force is reduced, and pinholes and blisters are easily generated on the screen; after the screen is recovered There are shadows of the original text on the screen. When the exposure is excessive, the screen is difficult to develop, the resolution of the image is degraded, or no image can be produced at all. Therefore, the screen exposure must be just right, to ensure that the original as much as possible to achieve 100% reduction. Therefore, the exposure time should be determined according to the operating conditions such as ambient temperature, humidity, working voltage, performance of the UV lamp of the exposure machine, quality of the emitted UV light wavelength and its use time, quality of the capillary photosensitive film and batch, etc. In addition, the exposure ruler is used to detect the exposure before exposure, and the correct exposure time can be easily determined.

5. The choice of capillary photosensitive film

The proper combination of the thickness of the capillary photosensitive film and the screen mesh number is also a key technology to ensure the screen quality. The thickness of the capillary photosensitive film and the mesh mesh number can be determined with reference to Table 1. Photographic film on the screen is too thin, easy to produce dot distortion, surface roughness is too large, it is recommended that the minimum thickness of the photosensitive film should be controlled at about 8μm; when using light-curing ink, the thickness of the photosensitive film should be reduced accordingly, 4μm can.

The above points are the key technology for making screens with capillary photosensitive films. In addition, after screen exposure, punching and drying, if it is left for a certain period of time, that is, after exposure and development, it will stay for 24 hours before being used again. Improve the quality of the screen during use.

Sanhe International Printing Equipment Co., Ltd.
Source: "Printing Technology - Equipment and Special Printing"