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Photolithography is the use of photosensitive chemical changes. That is, the light-receiving part of the photosensitive adhesive produces cross-linking, which is firmly combined with the screen, and the unexposed part is washed with water, and a graphic transparent part is formed on the screen, which can pass ink during printing.
Process flow:
Manuscript Making -> Choosing -> Stretching -> Cleaning -> Drying -> Formulating Sensitive Adhesives -> Coating Sensitive Adhesives -> Blow Drying -> Development -> Absorbent Drying -> Checking Revised -> Second Exposure -> Edge Printing
First, the production of manuscripts
The greater the contrast of the original manuscript, the better, that is, the darker the better the graphic part, and there is no part of the graphic, the more transparent the better. The original is divided into rubber, sulfuric acid and paper. Film is the best manuscript in the manuscript, followed by sulphuric acid, both of which are directly plateable. The manuscript is coated with vegetable oil (peanut oil, soybean oil, etc.) on the opposite side of the manuscript to make the manuscript transparent, and then wipe off excess vegetable oil to make plates.
1, using computer typing, copying (copiers can zoom in and out), hand-written draft can be.
2. If the original is multi-colored (color blocks), the original version is also divided into several colors.
In order to ensure the accuracy of overprinting, a crosshair can be set on each draft.
Second, the choice of screen
Wire mesh is one of the main materials for making silk screens. It is the carrier of the photosensitive film image, which forms a screen printing plate together with the photosensitive film and the silk frame. The most commonly used screen types are nylon (also known as nylon) and polyester (also known as polyester) as two types of screen-making material. From the preparation method is divided into plain weave, semi-woven, full interweave, flat weave woven screen is the thinnest, interweave thickest. Generally we use plain weave silk screen. When the ink layer is required to be extremely thick, full twist may be used.
Nylon (cotton-nylon) wire mesh: It has good elasticity and ink passing properties; It can resist a certain degree of alkali solution; Wear resistance and resistance to pull are good. It is not acid-resistant and has a large extension. It is not suitable for large-area screen printing; exposure to sunlight for a long time will become brittle and affect the strength.
Polyester mesh: less extensibility than nylon mesh, excellent dimensional stability, color printing plate should be made; chemical resistance, abrasion resistance, pull resistance are very good. Its combination with photosensitive materials is not as rough as nylon mesh. The through hole rate is slightly smaller than nylon mesh. Long-term exposure to sunlight decreased slightly.
The wire mesh specification is used to describe the unit mesh area. At present, domestic wire mesh product specifications are expressed in terms of the number of holes per unit length (cm). Imported products are also expressed in English units of measurement. The number indicates the density of the screen. The higher the number of meshes, the denser the screen and the smaller the mesh.
In screen printing, there are a wide variety of substrates and the materials have their own characteristics. The choice of the screen can usually be selected based on the material to be printed and the precision of the printing. Such as: posters, hard fiber prints, rough panels, coarse grain foil, optional 200 mesh screen. Printed fine graphics, can use more than 300 mesh screen, monochrome screen printing, trademarks, dials and other optional 350 mesh screen. Printed special graphics, use more than 420 mesh screen. In general, the higher the number of screen meshes of the same type, the more suitable it is for making fine screens. On the textiles; printing cotton cloth used 150 mesh ~ 200 mesh screen, indeed choose 250 mesh ~ 300 mesh screen. Silk uses 300-350 mesh screen. Foam printing is generally 80 mesh to 150 mesh screen. Here, the printing paint mesh is selected to be about 120 mesh.
Third, screen mesh and stretch net
1. The frame is the carrier of the screen used for screen printing. Requirements of the screen frame on the screen: The frame must have the strength required to resist the tension of the screen plate. After the screen is stretched, it must be firm, durable, stable in performance, and durable without deformation. There are also materials that are resistant to water, solvents, acids, and other chemical materials. It should also be light and inexpensive. Commonly used wire mesh frame materials are: wood, aluminum frame.
(1) Wooden frame - It has the characteristics of simple production, light weight, low price, convenient operation and use, simple and reliable fixed network. Suitable for small-scale factory manual operators. However, because of its poor water resistance, the frame surface is easily deformed and the stability is difficult to be sustained. To prevent deformation, attach L-shaped hardware accessories around the frame. (If the quality of the printed matter is higher, aluminum frame is preferred.)
(2) Aluminum frame - good strength, stable performance, easy operation, and not easily deformed. Does not rust. Although the investment is large at one time, it can be used repeatedly for a long time. Therefore, the printing accuracy may be higher or the aluminum frame may be used to overprint the product. The area is a little larger than the actual printing area, and it is usually necessary to ensure that the left and right 4cm to 6cm, the upper and lower 6cm ~ 8cm of free space. NMT-1 type stretcher can be used to stretch the net more quickly and conveniently.
2. Stretching is the process of tightening the screen and combining it with the frame. (1) Manually stretch the net (wooden frame): First tear the screen to the desired size. Wash with detergent, rinse the water, and then stretch the wire mesh on the frame. First use the slats (made with plywood, the same length as the inner frame of the frame). Scroll one side of the screen, nail it on one side of the frame, and then use a wooden strip to wrap the opposite side. Tighten it tightly and nail it. . The other two sides are pinned in turn. The water is washed away and the hair dryer is blown dry for use. The screen is generally stretched ahead of time, and it strives to be flat and tight. (2) Tensioning machine stretcher (wooden frame, aluminum frame): Place the frame on the adjustment plate fixed on the stretcher, and then place the mesh on the stretcher stand, place the edge fixed Fix the net. Adjust the four handles and adjust them with gentle force. Slowly stretch the screen, flatten it, and tighten until it is tight. Then adjust the tensioner below to make the mesh frame and the mesh tightly, and then apply the adhesive mesh. After the adhesive is dry, cut it along the outer edge of the frame with a blade.
Fourth, coated with photosensitive adhesive
1. The NMT-1 microcomputer multi-function platemaking machine is suitable for all kinds of photosensitive adhesives. Our commonly used diazo photosensitive adhesives have the characteristics of slow dark reaction and long shelf life. In the preparation, only a semi-dark room is required. During the day, red or black can be used. The curtains can be pulled up. Reusable screens reduce costs. High precision plate making, non-toxic and pollution-free.
Diazo photosensitive adhesives are classified into water-resistant and oil-resistant types, and water-resistant photosensitive adhesives are used for the printing of water-soluble printing materials; oil-resistant photosensitive adhesives are used for the printing of solvent-based printing materials.
In a semi-dark room, the photosensitizer is completely dissolved with 50 ml of distilled water or purified water, and 950 g of glue is added and stirred for 4 hours. After standing for 4 hours, the air bubbles disappear and can be used. Do not use metal products to stir, so as not to affect the stability. With a good glue storage temperature between 5-20 °C best placed in the refrigerator fresh-keeping layer. Shelf life is 1-2 months.
Screen printing belongs to orifice printing. In the modern printing industry, letterpress printing, gravure printing, lithography, and screen printing became the four major printing methods. The graphic part of the printing can be printed on the paper or other printed matter through the ink. Screen printing is the most widely used one in the printing industry. Widely used in plastic, paper, metal, rubber, glass, knitted fabrics and other materials on the decoration printing and printing, electronic equipment, printed circuits, advertising and other industries. According to experts, screen printing can be printed on all materials except air and water. With a universal print. With the continuous emergence of new technologies, new materials, and new technologies, screen printing products tend to be high-grade. Screen printing is a very promising industry both at home and abroad.