Silk screen printing platemaking process (7)

b. direct screening method. The direct screening method is to add the negative picture directly from the manuscript, and then to make the positive picture dot base version from the negative point of the network.

1 Yin Tu screen shot. When taking negative pictures, the screen used is usually gray or magenta negative contact screen. The screen latitude should be compatible with the original contrast. If the original contrast is too large, you can use the mask method to correct, when shooting The screen is placed between the mask and the photosensitive sheet, and the vacuum suction method is used so that the three are sealed and exposed. The exposure method is the same as the indirect method and requires multiple exposures.

Main exposure: capture the original through the screen, so that the main level of the original is fixed, and the exposure is based on the appropriateness of the middle tone.

Flash exposure: only through the screen, without the original white light exposure for a short time, the amount of exposure in the middle of the appropriate tone as the standard.

Flash exposure: only through the screen, without a white light exposure of the original, the purpose is to enhance the dark tone level, while increasing the darkness of the small point of reality. The exposure method is to install the light source in the dark room, open the suction plate for exposure, and the light source position should be on the open vertical line of the inspiratory analysis. You can also use a camera light source to expose white paper or expose it directly through the lens. No net exposure (also known as high light exposure): Remove the screen, only a small amount of no net exposure of the original, the main role is to improve the level of high light areas.

Although the above three kinds of exposures can separately make certain adjustments to the high, medium and low-key levels of the Yin pictures, they are very limited, and the three are not independent, and the three exposures are closely related, especially the main The determination of the exposure will play a decisive role in the tone of the Yin picture. Under normal circumstances, to determine the main exposure time in addition to ensuring the network density above the middle tone, but also to the auxiliary exposure to leave some room for adjustment. Therefore, the test shot should be taken before the official shooting to determine the main exposure time, and then determine the auxiliary exposure time according to the test shooting and plate making requirements, the original situation. Films that make negative images can use either positive or special full-color rigid films. The developer uses hard developer. The gradation range of Yin picture should be determined according to the silk screen printing and the tone reproduction performance of printing. At the same time, the gradation change of the overtone pattern must be taken into consideration. Generally speaking, the tone of the overturning picture is easy to change, especially It's time to use a camera to turn positives.

2 production of positive plates. It is relatively simple to make the positive edition by the direct screening method. The conditions and methods for exposure and development are basically the same as those for the lines and texts. It is only necessary to strictly control the exposure time and avoid or reduce the steps. Loss adjustment.

There are two ways to make positive plates. One is the camera overturning the sun, and the other is copying over the sun. The advantage of the former method is that the number of screen lines can be changed according to the plate-making requirements. Because the number of screen lines used for screening is fixed and the specifications are limited, this method can be used to obtain any line number by changing the zoom ratio. Plus net positive version. Such as: request to add 50 lines / inch of the net, and only 150 lines / inch of the net, when Yang Yang map, and then shrink the Yin picture three times, plus 150 lines / inch net, when Yang Yang map, and then A three-fold enlargement of the vaginal image yields a 50-line/inch plus positive image. The disadvantage of the camera overturning is that the tone is easy to change, so to use the camera to turn the map, the tone of the overtones will be flat. The advantages of the copy-overflow diagram are: simple operation, low loss of tone, and easy reproduction of the tone level of negative editions. However, the number of screens cannot be changed. The above two methods can be flexibly applied according to specific conditions.

In the above, two kinds of direct and indirect screening methods are simply introduced. By comparison, the direct screening method is easier to grasp than the indirect screening method, the level of copying accuracy is high, the resolution is good, and the plate making speed is fast. Direct screening process. However, sometimes due to special circumstances, it is necessary to use an indirect screening process.

5 check and correction of the monochrome master. The monochrome version is divided into two kinds: one is a monochrome text and a line bottom board, and the second is a monochrome mesh bottom version. The inspection and correction of the monochrome version are as follows:

a. Inspection and correction of monochrome text and lines. The monochromatic manuscript is used to describe only lines, patterns, and text of a hue. The monochrome manuscript is divided into lines (tables, comics, maps, patterns) and text (writing words, artistic words, phototype words, phototype words, type words, etc.). It is characterized by clear colors and no continuous tone.

The requirements of the platemaking manuscripts for the monochrome manuscripts are: the line text should be clear and the ink should be black and even. There should be no pen breaks and the manuscripts should be clean. If the above requirements are not met, corrections must be made on the original. If there is a single manuscript, the manuscript should be changed.

After making a negative film, the revision personnel should check the layout:

(a) The size is correct.

(b) Whether the thickness of the lines and text strokes is the same as the manuscript. In particular, the fine brush strokes cannot be broken, and the thick strokes cannot be obliterated.

(c) Whether the trachoma and fog are too heavy and can be corrected.

(d) After zooming in and out, whether the scale of the line and text is still consistent with the original.

The correction is to use ink to fill in the unwanted white sand eyes, especially when correcting it next to the text. Do not correct the word.

The modified negative film is copied or reproduced into a positive image. Be careful when you copy or remake. The positive version of the image is always reversed. Check the text carefully.