In addition to the choice of plate-making materials, the key to improving the quality of silk-screen products lies in the rationality of the screen-printing plate production process. At present, the technology of screen printing has been greatly improved, and the technology of computer-to-plate is becoming mature. The professional screen printing has been digitally made. And the general enterprises use manual plate making more. Here, on some issues of manual plate-making, talk about a little light-sensitive plate-making process.
We have used three types of plate-making materials: dichromate screen photosensitive film (film), diazo screen photosensitive adhesive and alcohol-soluble nylon screen photosensitive adhesive (F, D, N) Photographic plate-making process.
Photographic platemaking uses the photochemical changes of the photoresist, that is, the light-receiving part of the photoresist is cross-linked with the screen, and the non-photosensitive part is washed with water to form a graphic transparent part on the screen, which can penetrate the ink when printing.
Process flow:
Manuscript → Processing → Stretching the Net → Cleaning → Blow Drying → Coated with Photosensitive Adhesive → Blow Drying → Exposure → Development (Water) → Blow Drying → Check the Revised Plate → Double Exposure → Edge Banding → Printing.
1. The original manuscript requires that the greater the contrast, the better, that is, the darker the picture and text, the better the transparency.
1. Use a computer to type, copy manuscripts (copiers can zoom in and out), hand-painted hand-painted manuscripts, and use the plants (such as peanut oil, soybean oil, etc.) on the reverse side of the manuscript to make the manuscript transparent, and then wipe off the excess treatment agent.
2. If the original is multi-color, the original version is not too; it should be divided into several colors accordingly, and can be copied with a copier. Each copy is only left in one color (the scraper is scraped off). To ensure accurate overprinting, you can write in the manuscript before copying. Draw a double crosshair for alignment.
2. The choice of selecting the silk screen and stretching the screen mesh depends on the printed pattern and the requirements on the pattern. If the pattern is large and the lines are thick, but the requirements for the pattern are not so accurate, a mesh with a relatively low mesh number can be used. Conversely, if the pattern is small and the lines are thin and narrow, and the requirements for the pattern are accurate, a mesh with a relatively high mesh number should be used.
The screen mesh number directly affects the printing quality. Because the printing plate with relatively low mesh screen number has good penetrability of the printing paste, the mesh is not easy to be clogged. However, if the mesh number is too low, it is easy to cause too much penetration of the printing material, resulting in unclear edges of the pattern and distortion of the pattern.
The screen mesh has a high mesh number, which can meet the requirements of the edges of the pattern and the lines are very scratchy. However, the screen mesh number cannot be higher than the printing material mesh number, otherwise, it is easy to block the mesh. Therefore, a moderate mesh number should be selected, generally between 120 meshes and 300 meshes, and the bisection method in the single-factor advantage selection method can be used for selection experiments.
Third, the preparation of photosensitive adhesive 1. Our commonly used diazo photosensitive adhesive has the characteristics of slow dark reaction and long shelf life. It only needs a semi-dark room when preparing (the red or black safety driving curtain can be pulled up during the day), The screen version can be reused to reduce costs, the plate making is highly precise, and it is non-toxic and pollution-free.
The diazo photosensitive adhesive is divided into water-resistant and oil-resistant types. The water-resistant type is used for printing water-soluble printing materials, and the oil-resistant type is used for printing solvent-based printing materials.
2. Preparation of photosensitive adhesive Diazo photosensitive adhesive (100 parts), diazo photosensitizer (1 part), distilled water (30-50 parts) in a semi-dark room after dissolving the photosensitizer in distilled water, add diazo photosensitive adhesive Stir in the medium and let it sit for 20 minutes before use. The prepared photoresist can be kept away from light for about a month.
4. Coating photosensitive glue 1. Preparation (1) Coating equipment coating photosensitive glue can use brush, plastic ruler, preferably using sizing device, sizing device is made of stainless steel, the upper mouth width is lower and the bottom is narrow, the upper mouth is smooth.
(2) After coating the photoresist at the drying temperature, it should be dried at a low temperature. The temperature should be about 40 degrees, and should not exceed 45 degrees. You can use a hair dryer to dry at a low temperature.
(3) The studio requires that the plate-making room is a semi-dark room, so red brains can be used as the lighting source, so it is better to see the objects clearly. In actual work, it is sufficient to draw curtains in ordinary rooms.
(4) Manuscript inspection In order to make a plate, the manuscript must be further checked. The content includes: manuscript blackness, broken lines, graphic errors, etc.
2. Coating photosensitive adhesive (1) Squeegee coating: we generally use a sizing device to apply the photosensitive adhesive, pour the prepared photosensitive adhesive into the sizing device, hold the screen frame with one hand, and sizing with the other hand The front height of the device is pushed onto the screen, and the sizing device forms an angle of 60-70 degrees with the screen. After all the glue at the contact of the sizing device blade and the wire mesh is applied, apply light pressure and pull it evenly from the bottom to the top. Do not stop during the movement so that the photosensitive glue is evenly coated on the wire mesh. Generally, the front and back sides of the general screen plate are scraped and coated 7-8 times, and then scraped on both sides (the glue is not in contact with the screen) 1-2 times, and dried at low temperature. Then glue on the side that contacts the substrate, blow dry, and then apply it as many times as needed, but the glue film should not be too thick, otherwise it is not easy to develop, and the adhesion fastness of the glue and the screen will also be reduced. After scraping, wipe off the excess glue on the edge of the screen. In order to save the photosensitive glue, the sealing glue can be applied to the parts of the screen frame other than the graphics.
(2) Brushing: used when there is no sizing device. Put the wire mesh on the off-duty or polyester sheet, pour the photosensitive glue on the silk mesh, and gently brush it back and forth with a row of pens until the surface is smooth and even, then blow dry to peel off the polyester sheet or remove it from work. This method is not easy for the Chinese who are not easy to paint.
Whether it is scraping or brushing, we must pay attention to cleaning.
V. Plate printing 1. Plate printing is the use of chemical changes of the photoresist, that is, the part of the photoresist that is irradiated with light of a certain spectral wavelength produces a crosslinking reaction and solidifies, while the other parts do not produce crosslinking and curing. Wash your ears and listen to the development. After forming the transparent part of the picture and text, you can pass the ink to form a screen for screen printing. This process is the key process to make a leap from quantitative to qualitative changes. The manuscript should be further checked before printing. The more opaque the graphic part, the better the transparency, and the higher the transparency of the part without graphic.
Before printing, put the manuscript on the off-duty work of the microcomputer universal color plate-making machine (in order to make the manuscript and the screen plate compact, you can put a glass on the equipment glass smaller than the inner frame of the screen plate before placing the manuscript (The manuscript is on top), then put the screen on the manuscript, cover the screen with a black velvet cloth, then put a piece of glass smaller than the inner frame of the screen, and compact it with a heavy object to make the manuscript tight to the screen paste.
The reference time for printing can be checked by yourself. Different light sources have different printing time. Water-resistant photosensitive adhesive under general black light: 3-5 minutes in summer, 8-13 minutes in winter, 5-10 minutes in spring and autumn. Oil-resistant photoresist: 5-10 minutes in summer, 10-20 minutes in winter, 8-15 minutes in spring and autumn, the above time is 300 mesh net, DS series photoresist as an example, for reference only. The correctness of the printing time directly affects the quality of the printing plate. Its determination depends on the experience of the operator, and it can also be tested with some tools or a combination of the two.
2. Development
The development is to dissolve the unexposed photosensitive adhesive film in the developing solution, so that the mesh on the screen is transparent.
Generally use cold or warm water for development. Place clean water in the developing tank, soak the screen in water for 1-2 minutes, lift the screen frame up and down in the water by hand, and use the force of water to display the pattern. After the text is displayed, rinse it with slightly pressured water (water-resistant photoresist is best washed with high-pressure water). After showing the fine parts of the picture and text, immediately rinse it with water once and drop the water drops (preferably use The old newspaper absorbs the water drops) and can be dried. It can be connected to the tap water with a rubber tube, and the rubber tube should be squeezed tightly to make the water flow have a certain pressure to rinse the screen, but it should not be used too violently, so as not to damage the film.
3. Post-processing and inspection After development, the screen should be dried with a hair dryer. The water on the surface of the screen should be dropped in advance (it is best to use old newspapers to absorb the water drops), so as to prevent the water from flowing down on the surface of the screen when it is dried and producing residual glue, which affects the clarity of the line edges. After the screen is dried, you can check whether there are bubbles and trachoma under the light source, and you can use photoresist to repair it. In order to enhance the durability of the plate film, the trimmed plate can be placed on a general black light lamp and then printed for 10-20 minutes. Screen inspection is the final process in the entire plate-making work. Small defects exposed after development can be corrected by plate revision. If important defects occur, the plate-making needs to be re-made.
Application of screen sealant: When printing with solvent-based ink, it can close the leaking parts other than the screen graphics to prevent the printing material from leaking. It can also be used to seal the temporarily unprinted part. If you want to print the part again, you can clean the printing material on the screen and wash it away with water.
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