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Steel barrel wire printing and plate making (III)

(III) the production method of silk screen plate usually adopts photoresist coating method. Photosensitive glue coating plate making is to directly coat photosensitive glue on silk, and then make a plate film through drying, plate printing, development and other processes. The specific production process is shown in Figure 4. 1. Positive negatives are required when making screen printing plates. There are two methods to make positive negative, one is manual drawing, the other is photography. (1) Manual drawing method uses a brush, pen, etc. to draw pictures and texts on a transparent film or drawing paper. This is a positive negative for printing. In order to prevent the ink on the negative from cracking after drying, a small amount of granulated sugar can be added to the ink, and a small amount of beer can be added to defoaming. Manual drawing method is mainly used to make positive negative films with low requirements and simple graphics and texts. If it is necessary to make a layered positive negative, the photographic method should be used. (2) Photographic method uses photographic equipment to take the original into a negative picture, and then turn the negative picture into a positive negative. If it is an original with changes in intensity and shade levels, it needs to be made into a negative picture first, and then turned into a positive picture. If it is a color original, it needs to be made into a color separation picture first, and then turned into a component color positive negative. 2. Pretreatment of silk pretreatment of silk mainly includes degreasing treatment and dyeing treatment. (1) Degreased silk first has grease and dirt, which will reduce the combination fastness of plate film and silk and affect the quality of plate making. Therefore, degreasing treatment is required. There are three commonly used degreasing treatments: ① degreasing with decontamination powder: first wet the silk, then place it on the plane, dip it with a brush, brush it on the silk, rinse it with clean water, and dry it naturally or at low temperature. ② Solvent degreasing: dip cotton cloth with acetone, alcohol, banana water and other solvents, scrub on the silk, and dry it for use. ③ Degrease with dilute alkaline solution, brush with 10% sodium hydroxide solution, then rinse with clean water, and dry naturally or at low temperature. This method is not suitable for metal frames. (2) Dyeing treatment the purpose of dyeing treatment is to absorb the light shining on the silk, so as to eliminate the diffuse reflection of the light line when printing, so as to improve the clarity of plate making pictures and texts. The method of dyeing treatment is to evenly coat the dyeing solution on the silk with a brush, and then apply photosensitive glue after drying. The dyeing solution is made by adding cresol or red alcohol soluble dye to the ethanol solution. If there are colored filaments, there is no need for dyeing. 3. Preparation and coating of photosensitive adhesive (1) preparation of photosensitive adhesive photosensitive adhesive can generally be divided into solvent resistant and water-resistant. Solvent resistant photosensitive adhesive, suitable for water-based ink printing. The former version can be stripped and recycled; The latter generally cannot be removed from the film for recycling. Special water-resistant photosensitive adhesives include nylon photosensitive adhesives and diazo photosensitive adhesives. The user must select and use the appropriate photosensitive adhesive according to the specific situation of the steel drum and the relevant instructions. This paper introduces the formula of several photosensitive adhesives: ① Formula 1 of polyvinyl alcohol photosensitive adhesive: 100g s sericin, 25g 8% ammonium dichromate solution. S sericin is produced by Kanto chemical company in Japan. The preparation method is as follows: 10g ammonium dichromate is dissolved in 100g water, then mixed with s sericin in proportion, and stirred evenly. The newly adjusted photosensitive adhesive cannot be used immediately, and it generally needs to be placed in a cold and dark place for 8h. This is because many of the newly adjusted photosensitive adhesives only ensure the flexibility and accuracy of the pendulum and other motion mechanisms. Bubbles will produce pinholes when coated on the silk, and the photosensitive performance of the newly prepared photosensitive adhesive is still poor. Formula 2: Meinong 100 × sericin or 200 × sericin 100g, 4% ammonium dichromate 20g. Meinong 100# and 200# sericin are produced by Fuji pharmaceutical company in Japan. 100# belongs to thick film type and 200# belongs to solvent resistant type. The preparation method is the same as that of Formula 1. Formula 3: 32 × EZ sericin 100g, 10% ammonium dichromate solution 20g. 32 #ez sericin is produced by nazdar company in the United States. The preparation method is the same as that of Formula 1. ② Gelatin photosensitive adhesive formula: 180g gelatin, 10g citric acid, 20ml alcohol, 1000ml water, 30g potassium alum, 10g ammonium dichromate, 10g barium sulfate, 55ml ammonia. The preparation method is as follows: after the above substances are heated, dissolved and filtered, the glue is easy to freeze, so it is kept at a high temperature (such as 70 ℃), and coated on the back of the silk in a dark room. ③ Formula 1 of nylon photosensitive adhesive: 200g ternary nylon, 50g methylene bisacrylamide, 2G benzoin ether, 0.4ml diethanolamine, 5g benzophenone, 1000ml ethanol, 2G reactive k-blue dye, 0.8ml phthalic anhydride. The preparation method is as follows: dissolve ternary nylon with 750ml ethanol; Dissolve other additives with 250ml ethanol, heat with water bath and stir constantly when dissolving; After the above two solutions are fully dissolved, mix them, dissolve the reactive k-blue dye with a small amount of hot water, add the mixed solution, stir it fully, and filter it for use. Formula 2: 100g ternary nylon, 30~40g methylene dipropylammonium, 6~7g benzophenone, 1g reactive k-blue dye, 400~500ml ethanol. Formula 3: 100g ternary nylon, 20~40g ammonium dichromate, 400~500ml ethanol. Dissolve the ternary nylon in ethanol; Dissolve ammonium dichromate with a small amount of hot water, mix the above two solutions, stir them fully, and filter them for use. The easiest way is to buy photosensitive adhesive from the market. For example, the high-strength nylon photosensitive adhesive made by Shanghai Zhonghua printing factory is made of polybasic nylon as film-forming agent, coupled with cross-linking agent, photosensitive agent and other auxiliary materials. It has the following characteristics: A. It is resistant to water, acid and alkali, organic solvents, toluene, xylene, cyclohexanone, acetophenone, ethyl acetate, banana water, gasoline, kerosene and other solvents. b. Large sensitivity tolerance, high resolution, minimum line width up to 0.025mm, and can make line version. c. Thick film silk plate can be made, and the coating film can reach more than 0.20mm. d. It is easy to operate. The nylon photosensitive adhesive is a single liquid type, which can be operated in the open room (you can operate under the fluorescent lamp, but do not operate under the sunlight); The light source for plate printing is ultraviolet (which can be printed in the sun), and the development is made of industrial ethanol, which can be cleaned with a brush. e. The printing resistance rate is high, and the printing number can reach more than 100000 times. f. You can make prefabricated plates. After gluing, store the plates and print them when you use them. g. The glue solution has a long storage period and can be stored at room temperature away from light. The validity period can reach more than 2 years. h. Suitable for all kinds of silk printing plate making. Its disadvantage is that it can't be removed and the version can't be used repeatedly. If the version can be used repeatedly, you can buy A38 (oily) photosensitive adhesive made in Italy or AUTOSAL plus II photosensitive adhesive made in the Netherlands. If the pattern is not ideal, it can be removed with film stripping powder and remade until it is satisfactory. Its coating is thin and easy to master, and its sensitivity tolerance is large; The resolution, printability and graphics definition are better than those made in China. (2) Coating of photosensitive adhesive there are many coating methods of photosensitive adhesive, including stainless steel tank coating method, brush coating method, tape casting coating method, plastic film coating method and machine coating method, among which stainless steel tank coating method is more commonly used. When coating, the film surface must be free of spots, uniform in thickness, and shiny after drying. The coating thickness is generally 10~30 M. If the coating layer is too thin, the edges of printed graphics and texts are easy to produce rough serrations; If the coating layer is too thick, it will affect the transmission of ink. The coating process of stainless steel tank is as follows: A. pour photosensitive glue into the stainless steel tank to half of the tank capacity. b. Tilt the silk plate 70. c. The stainless steel groove is in contact with the lower end of the wire. While tilting the groove to flow out the photosensitive glue, slowly lift the groove up and apply it along the wire surface. It should be noted that the coating should be slow, otherwise bubbles will be generated. d. Turn the wire frame upside down and apply it again according to the above steps. e. Blow with hot air at 32~36 ℃ to fully dry the film surface. f. Apply another 2-4 times according to the above steps until the film surface produces gloss. 4. Drying in the coating process, although the photosensitive film has been dried, it needs to be further dried before printing. Hot air drying is generally adopted. The drying temperature should be about 35 ℃, and it is not allowed to exceed 40 ℃, which has good chemical stability for organic solvents and oils. When drying, do not let dust fall on the film surface, otherwise pinholes will be generated. After drying, you should print as soon as possible to ensure the quality of plate making. 5. For printing, first brush the silk photosensitive film, printing glass and positive negative with a soft brush, then put the positive negative and the frame stretched with silk into the printing box, look at the position of the positive negative in the silk frame through the printing glass, place it accurately, and finally expose it. In order to make the positive negative film close to the photosensitive film of silk, it is best to use a plate printing box with a vacuum pumping device. The plate can be printed with the light of arc lamp, fluorescent lamp, high-pressure mercury lamp, xenon lamp, incandescent lamp and sunlight. The exposure time varies greatly due to the type of photosensitive adhesive, the thickness of photosensitive film, the type of light source, the distance between the light source and the wire, etc. the specific exposure time is best determined by the test method. The specific operations are as follows: cover the light barrier at the position that needs to be mapped, expose it under 1000w/220v high-pressure mercury lamp for 5min, and then cover the positive photographic film on the wire, expose it for 10~20min. In the process of exposure, the frame is about 30cm away from the high-pressure mercury lamp and is cooled by a fan (if a cold light source is used, it can be cooled without a fan). 6. Developing put the sun dried printing plate in water for 1~2min, and then rinse it with clean water after the non photosensitive part absorbs water and expands. The photosensitive film with good solvent resistance should be developed with warm water (35 ℃) for 1~2min, and then washed with warm water at about 42 ℃. Nylon photosensitive film needs to be soaked in ethanol or brushed for development. The development time of the printing plate should be as short as possible. 7. Then dry the printing plate first, "he pointed out, then use a sponge to absorb the water at the corner of the film, and finally dry it with hot air or natural drying. If hot air drying is adopted, the temperature of hot air shall not exceed 40 ℃, otherwise the printed text and text will be out of shape, otherwise the version will be loose. 8. Plate repair and film removal (1) after the plate is dry, it usually needs to be slightly repaired, such as the blockage of pinholes in the plate film. Blocking the pinhole can be coated with photosensitive glue for plate making, and then photosensitive for 5min. It can also be filled with sealing paste. (2) Remove the plate film on the silk when there is an error in plate making or the pictures and texts need to be replaced due to the old printing plate. The silk after removing the film can still be used. The method of removing the film: first remove the residual ink on the silk screen printing plate, and then use the film remover or film remover to wipe both sides of the silk screen printing plate or soak it in the film remover. After 5~10min, the film turns white. At this time, wash it with water (or sponge). After the film is removed, dry the silk. The film removers include hydrogen peroxide, hypochlorite solution, sodium hydroxide solution, ammonia, lactic acid, etc. The photosensitive glue coating method has high quality, good effect, economy and practicality, so this plate making method is the most important plate making method in modern silk printing. Other plate making methods include manual engraving plate making method, non photosensitive glue coating method, carbon paper plate making method, photosensitive film plate making method, infrared plate making method and electronic plate making method

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