Magnetic Printing Technology and Mechanical Discussion--Screen Printing(1)

(a) The principle of screen printing

Screen printing originally used silk as a mesh material, so it was earlier known in the world as screen printing for silk screen printing. Since the net material was replaced by a large amount of synthetic silk wind, screen printing was used instead. The basic principle of screen printing is: part of the mesh of the screen printing plate can penetrate the ink and leak onto the substrate; the rest of the screen on the printing plate is blocked and can not pass through the ink, forming blank on the substrate . The traditional plate making method is manual, and the more modern one is the photochemical plate making method. The newly developed screen color desktop system is the development direction of the screen printing method in the future. Photochemical plate making method is to tighten the screen on the frame, and then apply the sensitized film on the screen to form a photosensitive film. Then the photographic plate of the positive image is sealed on the plate. After exposure and development, no printing plate is required. The part of the overprinted photoresist will form a cured film, which will seal the mesh and will not penetrate the ink during printing; the part of the printing plate that needs over ink will not be closed, and the ink will be transmitted through the printing to form ink on the substrate. Figure 2-46 shows.

When printing, pour ink on the screen printing plate, the ink will not leak on the printing line through the mesh hole under the action of no external force. When the ink is used to squeegee the ink with a certain inclination angle and pressure, the ink is used. Transferred to the substrate under the screen through the screen to achieve image replication.

The screen printing method is roughly divided into planar printing and curved printing. Plane printing includes paper printing, long printing, and frustum printing. Flat printing is mainly targeted at leaflets such as advertisements, cards, metal and plastic signs. Long stage printing is continuous printing on substrates such as webs and soft polyvinyl chloride films. Curved printing is a method of printing on cylindrical and conical outer surfaces of metals, plastics, pottery, glass, and the like.

(B) the characteristics of screen printing

Screen printing generally has the following features.

1. Not subject to the size and shape of the substrate

Unlike general printing methods, screen printing can not only print on the plane but also can print on special shaped objects, spherical surfaces and concave and convex surfaces, as well as various super large advertisements, curtains, and curtains. At present, general offset printing, gravure printing, etc. are limited by mechanical equipment, and the printing format is limited to 3m×4m or even larger in full sheets.

2. Layout soft and small

The screen printing plate is soft and flexible, and the printing pressure is small. Therefore, printing can be performed not only on soft substrates such as paper and textiles, but also on various glass and ceramic vessels that are easily damaged by pressurization.

3. Thick ink layer and strong coverage

The thickness of the ink layer in the relief printing is 1.0 μm, the thickness of the lithographic ink layer is 0.7 to 1.2 μm, the thickness of the ink layer in the gravure printing is 8 to 15 μm, and the thickness of the ink layer in the flexographic printing is 3.0 to 5.0 μm. The thickness of the screen printing ink can reach 30 to 100 μm. Therefore, the screen printing graphic has a strong three-dimensional effect and strong hiding power, and can be printed on pure black paper. Braille printed with foamed ink, foam thickness up to 300μm.

The screen printing ink layer is not only thick but also has a wide range of adjustment. Under normal conditions, the screen printing ink layer thickness is about 20 μm, special thick film printing is up to 1000 μm, and the extremely thin ink layer is 6 μm.

4. Suitable for all types of ink

Screen printing has the characteristic of being able to use any kind of coating for printing, such as oily, water-based, synthetic resin type, powder and other inks can be used. Screen inks are actually pastes, pastes, paints, adhesives, inks, and various kinds of coatings that can pass through the screen mesh. Therefore, screen printing inks are sometimes referred to as "printing materials."

5. High light resistance

Since screen printing can print thick ink layers, various adhesives and various colors can be used. Therefore, light fast pigments and fluorescent pigments can be added to the ink by an easy method, so that the graphic image of the print can be permanently maintained. Gloss is not affected by temperature and sunlight.

6. Flexible printing methods

Screen printing, like other printings such as plain printing, can be carried out on an industrial scale. Plate making is convenient, the price is cheap, printing methods are diverse and flexible, and technology is easy to master.