In the halftone reproduction of printing industry, how to eliminate the moiré is an important issue because it has a great influence on the printing quality. In the color printing screen printing, it was interfered by the screen, which further complicated the appearance of the moiré. Improper handling in the screen printing process, prone to two types of moire: overprinted moiré and silk screen moiré.

In color reproduction, the predecessors informed that the angle between two strong colors must be greater than 22 degrees and a half, and less than 22 degrees and a half, the moire will appear.

First, the production of moire

In the case of multicolor halftone copying, two types of moiré appear due to improper technology handling: overprinting moiré and silk screen moiré.

Second, the elimination of moire:

1, the correct choice of manuscript screen number of lines and screen mesh match: the smaller the head / line ratio, the more serious mole pattern, the general requirements in the 3.5: l or more. At present, the head/line ratio is more than 4.5:1 times. Within this range is the appearance of moiré and slight moiré, which is within the scope of printing permission. Color silk screen printing generally used more than 5:1. This proportion is generally stretch net or positive print version does not appear moire.

Michele Kaytout of France: In the half-tone screen printing, many experiments were done on the generation and elimination of moire, and in the case of head/line mismatch, he used a diagonal stretching method. Eliminate the occurrence of moiré. He cited two examples:

The above method works well. The disadvantage is that it consumes net cloth.

2, the correct master template plate making technology:

In the stretch net, pay attention to the surface tension of the screen. If the stretch net is not good, the screen will be deformed, and the wavy shape or the internal sight will not be good, which will cause partial moire. Must stretch the net in accordance with the requirements of the specification, once a good two sets of screens (each set of four), must be consistent with the print size requirements.

The use of positive stretch net (zero degree stretch net) mesh wire diameter parallel to the frame, can save mesh cloth and can make minor positioning correction. Oblique stretch net, net cloth latitude and longitude wire and net frame edge into ± 4 degrees -8 degrees angled net, four screen mesh number, tension should be consistent. The disadvantage is the cost of net cloth, the advantage is to ensure that the screen lines are completely parallel and square. In order to save the net cloth, you can use a positive stretch net, oblique printing ± 4 degrees - 8 degrees, the exposure can be oblique on the fixed version of the film on the plate, or in the printing platen position must also be rotated an angle.

To master the correct exposure time, the current process uses the light cross-linked diazo photosensitive light source matched to ultraviolet light with a wavelength of 365 to 420 um. The exposure is equal to the illuminance times (H=Ext). The number of mesh cloths and colors affect the exposure time. The higher the mesh number, the thinner the film and the shorter the exposure time; the lower the film thickness is, the longer the exposure time is; the shorter the exposure time of the white screen, the longer the screen exposure time of the color screen.

3, choose the ink and substrate:

The ink should be selected from the substrate material and affinity of the binder ink. The pigment should have a small particle size. Generally, the pigment size of the ink should be one-third of the inner diameter of the mesh. Substrate to choose surface texture and ink affinity substrate. The texture must use double-sided coating template paper.

4, correct choice of screening angle:

The selection of the screening angle is very important. The purpose is to prevent the appearance of moiré, to identify the beautiful patterns of graphic sites, and to reproduce the powerful graphic colors. The conventionally set screen angles are 0, 15, 45, 75, and four angles. The other method is not enough eyeballs/numbers, and the angle of oblique stretch or oblique printing is used. It is guaranteed that there will be no silk moire between the film and the screen, and at the same time, no overprinting pattern will be generated after each color printing is overprinted. The single intersect angle of 45 degrees is generally set to the main color angle, 75 degrees and 15 degrees for the strong color angle, 0 degrees (90 degrees) for the weak yellow color.

5, the choice of network shape:

According to the middle tone of the manuscript, dark spots in the image layer are used to select different dots. Midtone-level rich images use diamond dots and circular dots. Shadow tone rich multi-square network. Dark circles can be used as circular dots, and diamond dots are generally used.

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