Silkscreen Platemaking Process (4)

2. The production of monochrome mesh bottom version.

Continuously-tuned manuscripts are manuscripts with varying shades of intensity, that is, changes in the brightness and darkness of the manuscript are represented by different density changes. The density range of any continuous adjustment manuscript can be divided into three parts: high, medium and low. The high density part is called the dark part of the manuscript, the low density part is called the high profile part of the manuscript, and the density is between two. The part between them is called the middle of the manuscript. The difference between the darkest point and the density of the brightest point in the hierarchy on the original is called the contrast of the original. The density change between these two points is called the adjustment of the original.

1 Monochrome mesh bottom edition production process. Monochrome Continually tune the color of the original is a continuous gradient, such as black and white photos, ink paintings and so on. Copying a monochrome continuous original requires a halftone (halftone) plate.

Monochrome halftone screen printing is the use of dots to express a continuous dark layer, so the monochrome mesh bottom version must be made using the mesh photographing method (see Figure 2-72), and the images are reproduced through dots of different sizes. The tone level is much more complicated than the line and text photography. The process of mesh photography is roughly as follows:

Detecting the density of originals → Performing a standard exposure test strip → Calculating the zoom ratio → Setting the light → Calculating the exposure time → Adjusting the aperture → Placing the photosensitive web and screens → Exposure → Developing → Fixing → Washing → Checking → Copying the positive image

The density of the originals can be measured by using a reflection densitometer or a gray scale for comparison.

The standard exposure test piece must be produced under the same film, screen, exposure conditions, and development conditions in order to obtain correct exposure control. The purpose of standard exposure test strips is to obtain the correct exposure time.

Before placing the screen, check the color, line, tone, latitude, size, and angle of the screen. After selecting the screen, cover it on the sucked photosensitive sheet. When covering, be careful that the film surface of the screen must be in contact with the photosensitive sheet.

The exposure sequence is generally no screen exposure, main exposure, flash exposure. Normally only two exposures are used or only the main exposure, depending on the situation. The flash exposure can be either before or after the main exposure. After the exposure is completed, the screen and the photosensitive sheet can be removed to perform the flushing operation.

After the negative film is washed and dried, you should check the photographic quality. The main contents of the inspection are: whether the size is correct, whether it meets the layout requirements, whether the adjustment of the tone is correct, whether the layout is clean, and whether the layout is blisters.

2 outlets. Dots are the elements of the halftone print image. Simulating the density of the original with large and small dots of any shape is an excellent way to reproduce the continuous color of the manuscript or the density of ink (monochrome).

a. The role of outlets. Dots are the use of screen splitting effect of light, decomposition of the original tune to obtain the original, that is, when shooting in front of the photosensitive screen plus an Internet screen, so that the photosensitive film on the shade of image from the size of the network to represent. Net adjustment of the sunrays on the screen The screen is printed on the screen. The shading level on the original can be correctly flipped to the screen plate: the dark part of the original, the dot area is large; the bright part of the original, the dot area is small . According to the stencil printing plate, there is a difference between the hardening and non-hardening of the photosensitive layer and the photosensitive layer. If a certain dot area of ​​a screen printing plate is small, the amount of ink to be transmitted is small, and the printed color is light; a certain dot area is large, the amount of ink passing through is large, and the printed color is thick, thereby reproducing The continuous tone of the original. This kind of printed matter that uses dot size to express shades is called halftone print, also known as screen print and halftone print.

In addition to the above-mentioned functions, outlets also play a role in organizing color, gradation, and image contours in screen printing in color halftone screens.

b. The size of the outlet. There are three ways to identify the dot size: one is to use a dot density meter to measure the dot area percentage directly, that is, dot coverage; the second is to use a continuous density meter to measure the dot integral density, and then converted into percent dot coverage. The third is to use a magnifying glass to visually measure the ratio of the dot area to the blank area to estimate the size of the dot. It is customary to use the word “Cheng”. This is a relatively easy method and is widely used in plate making.

The number of outlets in a network determines the area occupied by a network of cells in a unit area. Such as 20% of outlets, the area occupied by the unit area is 2/10; 50% of outlets, and the area occupied by the unit area is 5/10.

When the number of outlets is determined, the following method can be used: 3 grids of the same size can be placed between 2 nets, which is called 1 point; 2 grids of the same size can be placed, 2 is called; and 11 can be placed. 2 meshes of the same size are called 3 points; 11/4 meshes of the same size can be placed, called 40%; half and half, 50%, as shown in Figure 2-73. 50% into the Internet, can be similar, that can put down a 40% net, called 60%; can put down a 3% net, called 70% and so on.