Screen printing 1000 questions (31-37)

â–¼31. What are the commonly used solvents for screen printing?

Solvents are mainly used in screen printing to adjust the viscosity of inks, regulate the drying speed of inks, and to clean screen printing plates and printing squeegees after printing. Commonly used solvents include aliphatic hydrocarbons, aromatic hydrocarbons, ketene, esters, ethanol, and glycol ethers. The solvents in each major category can be divided into several categories.

â–¼32. There are several methods for coating the photosensitive liquid.

The coating method of the photosensitive liquid is divided according to the operation method and can be divided into two major categories of manual coating and mechanical coating. Each category can be further subdivided into several subcategories. Details are as follows:
Manual coating can be divided into the following methods depending on the tool used.
1 Brush with a lint-free brush.
2 Scrape with a thin plastic plate.
3 Scrape with a stainless steel blade.
4 cast coating method, also belongs to the hand-coated plate. The special feature is that instead of using the tool directly, the photosensitive adhesive is placed in a container, and the photosensitive adhesive is directly and continuously poured onto the vertically erected screen frame so that the photosensitive adhesive flows downwards automatically on the screen. Form a film. This plate making method is suitable for making special screen printing plates.
The above 1, 2, and 3 kinds of manual coating are more suitable for small-size screen printing plates, and the operation is simple.
Mechanical coating mainly refers to the application of a photosensitive liquid by mechanical action. Mechanical coating can be divided into semi-automatic and fully automatic coating (semi-automatic coating in addition to mechanical coating, but also need to manually assist the operation. Automatic coating is completed by the machine automatically). Mechanical coating is suitable for large area screen coating.

â–¼33. What is the significance of double exposure and how do you grasp the double exposure time?

In order to further improve the water resistance of the screen printing plates made after printing, the friction resistance, solvent resistance, and the strength and fastness of the screen printing plates are increased, and the printing resistance is improved. Usually, the double exposure method is used for yarns. The screen printing plate is hardened (in addition to the double exposure method, the screen printing plate is hardened by the drug). The second exposure time is usually determined according to the actual situation of the screen, including the selected screen, coating thickness and many other factors. The general secondary exposure time is one to three times the exposure time. `
Screen printing plates are hardened for high volume printing and disposable screen printing plates. Under what circumstances can the screen printing plate not be screen-hardened? First, the screen printing plate may not be hardened in a small batch printing. Secondly, in the case of preparing a release film after printing the screen printing plate and reusing the screen printing plate, the double-exposure hardening treatment cannot be performed, otherwise it would cause difficulty in film release.

â–¼34. What are the basic conditions for choosing a light source when making screen printing plates?

When making screen printing plates, the basic conditions for selecting a light source are the following:
1 The intensity of the light source used must have a certain intensity. For any type of original, it should be able to meet the need for exposure in a short time.
2 Stability requirements The intensity of the light source used must be stable during exposure and must not be strong or weak. `
3 Light Source Illumination Uniformity The intensity of light used on the original must be the same. That is, the center of the original and the surrounding position must be under the same light intensity.
4 The light source used for high efficiency should be exposed in a short time and reach the exposure effect.
5 Operation, maintenance Simple selection of light source equipment is easy to operate and easy to maintain.

â–¼35. How to calculate the finest width of screen reproduction of fine lines?

In screen printing, the precision of reproduction of a replica is closely related to the screen. The number of screen meshes has an important influence on the reproduction of the fine lines of a manuscript. Therefore, when selecting a screen, careful selection must be made. The number of screen meshes must be selected. Corresponds to printed fine lines. The selected screen size has the ability to reproduce the fine lines of the original so as to ensure the printing effect.
Screen printing fine lines generally refers to line widths between 0.1-0.2 mm.
The finest width of the silkscreen reproduction fine line is the width value of the screen that can be used to reproduce the thinst line in screen printing. This is usually directly related to the width of the mesh and the mesh. When selecting a network, the following formula can be used as a basis for selecting a screen calculation. The formula for calculating the thinnest line width:
K=2S ten R where: K represents the width of the thinnest line, S represents the value of the screen wire width, and R represents the width of the mesh.
Calculation Example: If a 200 mesh/inch nylon screen is used, what is the finest width of the reproduced line?
Check the NM200 inch wire mesh, the wire diameter (S) is 0.05mm, and the mesh width (R) is 0.077mm. Substitute the above formula to obtain K=2×5077=177=0.177mm then the NM200 mesh/inch mesh reproduction The thinnest line width is 0.177 mm.

â–¼36. How does the color of the screen affect plate making?

Wire mesh is white, yellow, amber, red and so on. The color of the screen has a great influence on the quality of the plate. Colored silk screens, such as yellow, red, and amber screens, can prevent light from diffusing when printed, while the use of white screen prints can cause noticeable diffusion. This is because the photosensitive material has a large absorption peak in the ultraviolet region, and since the white screen reflects white light when the light source is irradiated, it affects the photosensitive material. The irradiation light passes through the transparent part of the positive graphic film to reach the emulsion coating, and reflection, inflection-reflection, and diffuse reflection phenomenon occur when the irradiation light contacts the white screen, so that a floating phenomenon of the printing plate is vignetting. If colored screens are used, this phenomenon will be prevented because colored screens can absorb some of the irradiated light, thereby reducing the reflection intensity of the irradiated light, and colored screens reflect colored light. This colored light is inactive light, so it is sensitive to selection. Material does not affect, especially when the fine print is printed, the color of the screen is particularly important.

â–¼37. What is the relationship between the number of screen meshes and outlets?

The number of screen meshes and outlets only have a certain relationship when copying continuous originals. Use silk-screen printing technology to copy continuous color originals, if it is to directly use a continuous photographic film to print screen printing plates and printing is not the same as the manuscript of the same continuous tone reproduction. Because the screen printing plate presents only two states, namely, the mesh portion of the graphic and text is open, and the non-graphical portion of the mesh is closed and closed. And because a size of the screen mesh size and arrangement rules are uniform, the amount of ink passing through the screen mesh aperture during printing is basically the same, so that it cannot express the level change of the original image and text. In order to make the depth change of the original pattern fully reflected on the screen printing plate, a continuous tone original is made into a dot negative film. The changes in the depth of the manuscript will be expressed in terms of dots of different sizes and uniform density. The high density part of the screen printing plate has a large area of ​​dots, a small part of the dots with a low density, and the same part of the dots with the same density. The center distance between the dots and the dots is equal, and they are regularly arranged at a certain angle. Using this dot negative film to print a screen plate and print it, continuous reproductions can be obtained. Density of the network arrangement is usually expressed by the number of screen lines. The unit notation is line/inch or line/cm. Meaning means the number of dots arranged within the unit length.

---Qi Lu Graphic Arts