Silk-screen printing plate making process (6)

Because some of the originals have too dark tones, the dots on the photosensitive sheet are not easy to form in black. To make the parts form finely detailed, flash exposure is required, as shown in Figure 2-76.

Figure 2-76 is to adsorb the film and the contact screen on a vacuum plate. At the turn-off of the cassette, the screening film is at right angles to the cassette, and flash exposure is performed with the yellow filter-added light. The flash exposure time is selected according to the standard density hierarchy.

At the end of the flash exposure, the cassette is closed and the aperture is adjusted to 16 to 22F. The main exposure is performed at a selected time. In general, this will show all levels. If the highlights of the manuscript do not perform well, highlights can be performed. Exposure, the aperture is about 12F, remove the contact screen for a very short exposure.

This screening exposure must be performed in two to three segments. Although it is more troublesome, it is possible to freely control the color tone of the original.

The development of mesh negatives is slightly different from that of line fragments. The development of the line piece should be constantly shaking the developing plate, but if the mesh negative piece is constantly developing, the plate will become a hard tone if it is constantly shaken, and if it is only placed in the developing plate for strong shaking or static development, it will become a soft tone. Therefore, adjusting the shaking and resting time can control the tone of the mesh negative. The development time must be controlled according to the provisions of the film manufacturer, in accordance with the situation of the manuscript or half of the half moving, or a quarter of a quarter of three static, you can achieve the purpose of control tone. Or, in the development process, it is determined whether it is shaking or still, depending on whether or not the negative version is checked at the time.

The time for stopping, fixing, and flushing is the same as the time for the line piece.

For good mesh negatives, use a magnifying glass to carefully inspect the shape and overall tone of the dot, and sometimes black spots on the periphery can be found to be uneven, which is a defect with the film itself, poor contact with the screen, and overexposure. Excessive development and so on, light can be treated with red blood soda solution.

The quality of mesh negatives has a close relationship with the final printing effect, so check the tone should always put the printing effect in the brain.

After mesh negatives are completed, they must be made in order to make a positive print. The method is the same as that of line plate making. However, the screens used for screen printing, such as 30 lines and 40 lines, are not available on the market. Therefore, 130-line or 150-line screens can be used to create fine-tuned mesh screen negatives, which can be enlarged three to five times. , made into a positive mesh.

After making the mesh, you should check whether the tone is appropriate again. Screen prints tend to be harder than the original. The high profile part of the network should be maintained at about 20%; the dark part of the network should be controlled at about 60 to 70%. However, these should be based on the printing conditions and cannot be generalized.

The idea can be made smaller after the thinning correction. If it is corrected with a positive film, it will be bright. If it is corrected with a negative film, it will be darkened. If you use a mixture of red blood salt and soda, the dots will only become smaller and cannot be restored. Therefore, the simplest method is to apply a thin layer of liquid with a brush while rinsing it with running water to make it act a little bit and repeat it in order to achieve the desired brightness.

The following briefly describes the process of indirect screening and direct screening:

a. Indirect screening method. The indirect screening method is to take a continuous tone picture first, and after a certain trimming, the positive picture dot negatives are made through the screen.

a.Continuously tone picture production. When taking continuous tone pictures, one should consider the contrast of the manuscript on the one hand, and on the other hand, consider the latitude of the screen used when the positive picture is screened. It is necessary to reproduce the original tone level on the photosensitive sheet, and to ensure that the density of the negative picture is within the screen latitude. The former is mainly solved by a mask method, and the latter is solved by controlling the exposure time and development on the basis of the mask. The density range of the Yin picture is generally controlled between 0.3 and 1.6. After shooting, you can make impositions and trim properly according to the platemaking requirements. If the contrast of the negative edition still needs to be adjusted, a mask after photographing can be adopted, ie, a short-cut low-contrast mask can be copied through the negative image, and then the negative-tone version can be overlaid with the negative-tone version to create a screen-connected version.

b. Production of screen plus positive plate. The screen used in the indirect screening method is mainly a magenta screen with a tolerance of about 1.6. The dots on the positive screen of the screen plus mesh must have sufficient density to meet the requirements of silk screen printing. The contrast of the positive tone must conform to the original and screen printing requirements. In actual operation, it is often difficult to achieve the above requirements with only one exposure, in particular, the density of small dots is insufficient, and the increase in the amount of exposure is subject to loss. Therefore, screening exposure often uses multiple exposures. The specific method is as follows:

Main Exposure: Exposure is performed with proper mid-tone adjustment, so that the main body of the pattern is fixed.

Flash exposure: remove the negative version, only through the screen on the photosensitive film for a comprehensive, uniform, short-term exposure, so that high-profile small ideas to meet the requirements. It should be noted that the position of the screen and the photosensitive film can not be displaced. This is generally ensured by the hanging nail method.

Networkless exposure: If the above two exposures have already reached the requirements, no network exposure can be performed. However, sometimes dark levels are not enough and further adjustments are needed. This exposure can be used. The specific method is to remove the screen and only briefly expose it through the negative picture. The relative position of the Yin picture and the photosensitive sheet should be the same as the main exposure.

Networkless exposure and flash exposure are also called auxiliary exposures. In operation, the negative images, masks, screens, and photosensitive films all need to be punched and positioned without relative displacement. Auxiliary exposure should be strictly controlled. Under normal circumstances, the flash exposure range should be about 3% of the main exposure, and the net-free exposure range should be 1 to 2% of the main exposure.

In addition, if the red picture is applied to the screen, the color of the exposure light source may be changed to adjust the tone of the positive drawing plate. The principle is that the magenta screen has different absorption effects for light of different wavelengths, and the used photosensitive film is a positive-color photosensitive film, has a certain color sensing range, has different sensitivity to different wavelengths of light, and the screen is connected to the Internet. The absorption of light is also different from that of the blank. Therefore, the gradation change of a positive image produced with different colors is different. For example, using a yellow-green light can make the positive plate flat, and blue light can make the positive plate more obtrusive. In operation, the color temperature of the light source is generally changed by a color filter, and the darker the color filter, the greater the degree of change.