Process technology and detailed operation of the h

2022-07-31
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Process technology and detailed operation of printing plate (III)

III. photosensitive plate printing plate making by photosensitive plate printing method there are direct method, indirect diaphragm method and direct diaphragm method. The direct method is to expose and print directly after coating photosensitive glue on the plate surface; The indirect diaphragm method first pastes the pictures and texts on the photosensitive diaphragm, and then pastes them on the plate; Direct diaphragm method is to paste the diaphragm on the plate surface before exposure and development

direct plate making is to replace manual plate making with chemical methods. The direct method plate cannot be separated from a photosensitive colloid, namely photosensitive colloid. Photosensitive adhesive is basically based on gelatin, polyvinyl alcohol, nylon, etc. Most photosensitive agents are dichromate, and diazonium salts are also used

1. formula and production of direct printing plate

① formula and production of gelatin chromate photosensitive adhesive

formula

super grade gelatin 180g

potassium jarosite 30g

clean water 1000ml

ammonium dichromate 10g

citric acid 10g

barium sulfate 10g

alcohol 25ml

ammonia 55ml

operation

heat, dissolve and filter, and apply the glue solution to the silk in the dark room with an automatic glue applicator or manual glue scraping, Standby after drying

② formula and preparation of polyvinyl alcohol chromate photosensitive solution

formula

a solution

polyvinyl alcohol 40g

sodium dodecyl cumene sulfonate 0.5g

glacial acetic acid 4ml

water 250ml

B solution

ammonium dichromate 5g

water 30ml

eosin a small amount

polyvinyl acetate (or dibutyl 4ml) 40ml

operation

1788 polyvinyl alcohol is selected, and 88% degree of polymerization and saponification is preferred

a solution is prepared by mixing polyvinyl alcohol, sodium sulfonate and water, melting them in a water bath, and then filtering them with 100 mesh silk. The second solution is filtered with filter paper after dissolution

mix liquid a and liquid B in the dark room. After fully stirring, you can use an automatic coater or manual squeegee to apply the glue to the silk. It will be used to implement this experimental project when it is dry

note: glacial acetic acid can accelerate the dissolution of polyvinyl alcohol, facilitate the development, and improve the resolution of photosensitive adhesive. Eosin dye makes the colloid bright red after photosensitive curing. The non photosensitive part is washed away by water to expose the silk for easy observation. Polyvinyl acetate makes the photosensitive adhesive firmly combined with the silk to improve the resolution

③ formulation and production of polyvinyl alcohol diazonium salt photosensitive solution

formulation

polyvinyl alcohol (degree of polymerization 1400, degree of saponification 88%) 40g

polyvinyl acetate (containing 50% solid components) 160g

water 240ml

diazo resin 6g

eosin a small amount

operation

at room temperature, stir and dissolve the above components in a dark room, apply the glue solution to the silk with an automatic coater or a manual scraping method, and dry it spare

2. coating of photosensitive adhesive layer. There are two ways of coating: automatic coating machine coating and manual scraping coating. Generally, small and medium-sized printing manufacturers use manual scraping and coating of photosensitive adhesive layer. The manual scraping method is the secondary scraping. The first scraping is from the oblique position, which requires the manufacturer to provide a more compact and sensitive scraping surface of the "fine" version of the experimental machine. The scraping is performed from bottom to top, and then the version is reversed from bottom to top to make the thickness of the adhesive layer of the whole panel uniform. Then, it is put into the constant temperature oven, and the scraping surface is downward to make the printing film surface flat and dry for about 15min. Take it out of the oven, Perform the second glue scraping. For the second time, scrape twice on the scraped surface, and then on the printing surface and perpendicular to the plane of the leaf spring seat: scrape twice on the axis line of the 2 steering knuckle with the fulcrum, wipe off the excess glue on the plate edge, and then dry it in the oven for about 10min

the coated adhesive layer shall be flat and uniform in thickness. In particular, four plates shall be made for color competing plate making, and the thickness of the four plates shall be basically the same. As for the number of times of scraping, it depends on the requirements of the customer for the increase in carbon fiber consumption of Boeing b777x and the next generation aircraft body. The dot and dot adjustment printing plate is generally scraped twice on the printing surface and then dried twice on the ink scraping surface and the printing surface. After drying, it can meet the requirements of plate printing

it is not allowed to scrape the photosensitive adhesive on both sides at the same time. The wire is through-hole. During the glue scraping process, the excess photosensitive glue will be squeezed to the back, and then when scraping the other side, the excess glue on the back will be squeezed to the front. Some glue will be squeezed to the front, and some glue will flow to the sizing device. On the contrary, the glue film will not be thickened due to the number of times of scraping. The correct glue scraping is to scrape one side, and then scrape the second side after the glue liquid is dry and seals the hole. In this way, the dry photosensitive adhesive layer will expand when it meets the water-based adhesive during the second glue scraping, adsorb the glue liquid, and increase the thickness of the film layer

3. plate drying

when drying the plate, place the scraped adhesive layer flat in a constant temperature oven for drying. The plate cannot be placed vertically, otherwise the glue will flow downward. After drying, the adhesive layer is thin at the top and thick at the bottom, which will affect the image quality of the printing plate when printing. The oven temperature is generally controlled at 39-45 ℃, and the best is 39-40 ℃. The drying time of the first squeegee in the oven is 15 minutes, and the drying time of the second squeegee in the oven is 10 minutes. The drying time is too short, the temperature is too low, and the photosensitive adhesive layer is not completely dried, which will cause the developing plate to drop or the printing plate to have low printing resistance; If the drying time is too long and the temperature is too high, the photosensitive adhesive layer will produce self crosslinking, resulting in difficulties in development. Plate drying is the key to ensure the quality of the plate. The temperature and time of plate drying must be strictly controlled

it is worth noting that the constant temperature oven for coating photosensitive adhesive should be dedicated. It is not allowed to bake the photosensitive adhesive while drying the water washed version. The evaporation of water vapor from the water washed version will affect the complete drying of the photosensitive film and the sensitivity of the photosensitive adhesive

4. exposure

exposure is also called plate printing. Put the photographic image and text positive or the four-color common magenta, cyan and black eye adjustment positive after color separation into the plate printing machine, and vacuum seal the exposure and plate printing. When printing, the negative film cannot be reversed, otherwise the light passing through the film surface needs to pass through the film base and then be exposed on the plate, which is easy to lose the image hierarchy, make the graphics and text weak, and make the color lighter

regular positioning shall be carried out before printing the multi-color plate. Put the four color separation positive plates of yellow, magenta, cyan and black respectively at the same position of the four photosensitive plates, set the regular lines, and fix them with transparent tape

The function of

exposure is to make the photoreceptor layer at the non graphic part cross-linked under the action of light, lose the hydrophilic group, form a like structure and insoluble in water, and remain on the surface after development. Because the image and text parts are not affected by light, they do not react. After water development and washing, the glue solution takes off the silk to form a through hole. During printing, the printing material passes through the hole and presents the required image and text prints on the substrate

UV light is often used as the light source for printing and printing machines, and fluorescent tubes can also be used as the light source for self-made exposure boxes. The exposure time of dichromate or diazonium salt photoresist is 3-4min under the UV light source, 7-8min under the fluorescent lamp source, and the lamp distance is 50-60cm. The accurate exposure time shall be flexibly adjusted according to the color temperature of light source, light source distance, film thickness, photosensitive material characteristics and development temperature

5. development

after the photosensitive plate is exposed, remove the closed photographic positive, place the printing surface of the photosensitive plate upward in the plate containing the developer, and develop for 2-3min. The developing temperature is controlled at about 20 ℃. Make the adhesive layer at the non photosensitive part expand with water, spray it with water under pressure, wash the dissolved adhesive liquid, and make the pictures and pictures transparent

it is better to develop the printing plate with eye tone by basin rather than by high-pressure spray gun. In this way, the produced version has rich levels of graphics and text, bright and clean lines, fine points are not lost, large points are not deformed, and the edges of the handwriting are bright and clean. High pressure water spray gun development will make the local density of the version thinner, the layers are damaged to varying degrees, the lines are hairy, the dots are broken, the fine dots are lost, the price adjustment layer is lost, and the color restoration is difficult

6. revision and sealing

revision refers to the repair of defects such as thin film and sand holes formed on the plate due to defects of photographic positive film and printing dust. The sand holes in the image part of the eye tone printing plate generally do not need to be repaired, because the sand holes are not obvious after four-color overprint;; If it is not repaired properly, there will be obvious ink spots after overprint

sealing is to use sealing glue or photosensitive glue to seal the parts of the layout that should not be perforated to prevent the printing material from leaking and sticking the printed matter

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