Silkscreen Platemaking Process (5)

The network size is divided into ten levels, and the field is 100%. As shown in Figure 2-74, the next is ten common levels except for the field; the upper level is a semi-point level between ten levels.

Visually measuring the number of dots, the difference is negative or positive. The dot of the negative version is the white dot (ie, the transparent portion). The larger the white dot area, the darker the graphic plate. Conversely, it is shallow. The number of dots is as many as the white dot. Increase and increase.

The shades of the positive map are black dots. The depth of the layout is determined by the size of the black dot. The larger the black dot, the darker the plate. Conversely, it is shallower. The number of dots in the dot increases with the increase of the black dot.

3 screens. Screens are commonly referred to as mesh editions, screen editions, and anilox editions. They are the tools for shooting websites when making photographs. According to their different materials, they can be divided into glass screens and contact screens.

a. Glass screen. The glass screen is made of two special plane optical glasses. The thickness of one glass is 3mm, and the thickness of the other glass is 4mm. Each machine uses a precision machine to sculpt 45° concave slashes on the glass surface, and in the concave lines. The opaque black glue is filled in, and then the grooved side of the two pieces of glass is intersected with the groove at an angle of 90[deg.] and adhered firmly to form a glass screen with a fine and uniform grid of black and transparent phases. .

b. Touch screen. The commonly used contact screens are a gray contact screen and a magenta contact screen. In addition, there are various forms of artistic contact screens.

Gray contact screen, named after its appearance color, is mainly used for direct screen color separation, and can also be used to copy positive pictures. The magenta touch screen is generally used to copy positive images.

Photographic plate-screening screens have different dot shapes due to different patterns. Its main shapes are round, oval, square, sand-shaped, brick wall, concentric circles, horizontal waves and so on.

When the coverage of the elliptical dot is higher than 50%, the connection of the dots is in the shape of a bead chain, and the dots and the screen are bonded more firmly. Therefore, it is an ideal dot shape for the screen filament printing.

The sand-mesh-shaped dot is an irregular-structured dot, but it does not have moire (moiré). Therefore, the accuracy of the printing layer is required to be poor in monochrome screen printing and large-scale advertisement screen printing. The printing is used more widely.

c. The point of view of outlets. The point of view of the network is the angle of the network arrangement (network line). The commonly used cable angles are generally 90° (0°); 15° (105°); 45° (135°); 75° (165°), as shown in Figure 2-75.

When shooting monochrome screening negatives, the commonly used dot angle is 45°; when indirect screening is used, the general screening angle is: yellow 90°, cyan 15°, device red 75°, black 45°; Indirect Screening The negative screen angle is the same as that of indirect screen shots. Direct Screening usually sets the most prominent color version to 45°. The other two color versions differ from each by 30°. The angle can be inserted 15 degrees between these angles, for example: black version 45 degrees, magenta version 15 degrees, cyan version 75 degrees, yellow version 30 degrees (or 90 degrees), you can also use the black version of 15 degrees, Magenta 75°, cyan 45°, and yellow 30° (or 90°).

Correct screening angle can get clear and beautiful images. When the screen angle is inaccurate or the weaker colors become stronger, the moiré pattern that damages the beauty of the image will appear after printing, which is commonly known as "rhizard pattern".

In screen printing, the angle of the screen is closely related to the angle of the screen. When the screen is not properly handled, the angle of the screen and the angle of the screen will interfere with each other, and a moire will also be produced. The choice of stretch angle can refer to the relevant chapters of this book.

d. The number of screen lines. The number of screen lines refers to the number of unidirectional parallel lines within each inch of the screen. The commonly used screen lines are 80, 100, 120, 133, 150, 175, 200 and so on. The more lines, the finer the network cable, the richer the performance level; the fewer lines, the thicker the network cable, and the lower the performance level. Our country gradually replaces the inch screen lines with metric screen lines. The unit of metric screen lines is lines/cm.

In the production of halftone screen printing plates, due to the overlapping of the number of screen lines and the number of screen meshes when photographing the screening screen, it is easy to cause moire on the printed matter. Therefore, the number of screen lines must be taken into consideration when making the screen bottom plate. The matching relationship with the number of screen meshes. Screen plate, due to the limitations of the plate material conditions, should not use the high number of screens, the general selection of 30 ~ 100 lines / inch screen can be.

4 screening. In the case of duplication of manuscripts with high and low tone, the original version should be screened, that is, the shades of the manuscript should be represented by the size of the dots.

There are two kinds of screening methods: glass screens and contact screens. At present, the contact screen method is mainly used. This method involves affixing the film surface of the photosensitive film to the film surface of the contact screen through the contact screen. Expose.

The contact screen method forms dots with different sizes depending on the intensity of reflected light from the original. There are two kinds of contact screens: gray screen and magenta screen. The square screen screen is used for monochrome screens, and the circular screen screen is used for multicolor screens. The number of lines is 30 to 200 lines per inch. Screen printing mainly uses 55 lines/inch (available under 55 lines/inch of available magnification), 60 lines/inch, and 80 lines/inch. If 150 lines are used to contact the screen, the negative film can be magnified by 2x to 3x to produce a 75- or 50-line mesh.

When the monochrome screen is used for photography, the screen is 45°. When the two colors are used, the angle should be slightly staggered so as to avoid moire after development. In the four-color printing, the dots of the red, blue, and black printing plates are staggered by 30°, and the insignificant yellow color is in between. Framed screens and mesh negatives also produce moire, so the number of holes in the screen should be higher than four times that of the image screen in order not to suffer from this drawback.

When the photosensitive film is in close contact with the touch screen, the screen must be larger than the film so that the four sides are adsorbed on the vacuum plate. To prevent poor adhesion, place a piece of paper on the screen, and use a rubber roller to roll the film one or two times so that the film and the screen are completely closed.

The screening exposure is divided into three stages: exposure, flash exposure, and high light exposure. If you want to make the tone softer, you can omit the highlight exposure. To make a hard tone, you can omit the flash exposure.