Talking about the exposure and development of the positive image PS plate
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Place the original version on the PS plate and measure the size of the bite or the middle crosshair. Stick it with tape, just prepare an intro part of the print. In the actual operation, a qualified PS plate shall be mechanically (ie, the standard operation and maintenance of the plate-printing machine), and the optical (the original plate with different density will have a great difference under the transmission of the ultraviolet lamp), and the chemical (developing powder) Correct proportions), accurate and correct operation of all links.
First, the definition of exposure
"The positive version of the PS version uses the original positive image of the positive image. The exposed ultraviolet light passes through the low-density and blank parts of the original plate to reach the photosensitive layer of the PS plate, which is absorbed by the sensitizer, and is photo-imaged. The principle is the positive image PS version. Under the action of ultraviolet light, decomposition and structural rearrangement reaction occur, so that the photosensitive part is insoluble from dilute alkali to dilute alkali, and as the photosensitive group disappears, the color of the photosensitive part changes from green to color in the photosensitive layer. s color--blue. ”
First of all, it must be ensured that no stains are left on the upper cover glass, and the upper cover glass can be wiped clean with anhydrous ethanol or glass cleaning liquid. Secondly, the suction rubber of the printing machine should also be carefully checked for foreign matter. When the confirmation is correct, the upper cover glass can be put down for pumping. When the original plate is in close contact with the PS plate, the exposure light source is activated, and the light is stable (iodine The home lamp generally takes about 10 minutes to perform the exposure reading. (At this time, the length of the exposure should be determined according to the type and density of the original)
In terms of the original version that I have contacted, there are roughly three types.
1. Full-film type: This type of original version, its exposure time is relatively longer (taking 1500W lamp as an example, around 9~10min), and in order to eliminate the edge marks of the film on the PS plate, it is also necessary to block. Technical processing (the occlusion paper can be used with the partition type paper from the PS version of the box, the time can be increased by about 1/2 of the total exposure time, which also reduces the use of the correction solution to eliminate the edge marks of the film, the dots There is no loss in terms of it).
2. Full sulfuric acid paper type: This type of persulfuric acid paper should also reduce the exposure time according to the density of the layout image. Even if the toner is used for a long time, it does not add new toner to the toner cartridge in time, resulting in several The line graph is faint. At this time, according to the actual size of the light part, cut a type of paper. When the exposure time is considered to be possible (at this time, it is necessary to rely on past work experience), the paper is blocked in the word map. Location (should master the location, fast forward and fast, to avoid UV light burns). Other parts continue to be exposed until the normal exposure.
3. Film and sulfuric acid papers of each type: The original version of this type should be carefully and carefully grasped during the exposure time, because some images of the film need to increase the exposure time by the image with sulfuric acid paper. Times, or even more, this type of original is not only prepared to have a type of paper to block a part of the exposure time, but also to prepare a scrap PS version slightly larger than the area of sulfuric acid paper. The sulfuric acid paper blocks the typed paper, and the PS plate is used to expose the side of the sulfuric acid paper, so as to extend the exposure time of the original half of the film, so that the text on both sides is shallow. Consistent. That is to say, the side of the sulfuric acid paper should be shielded twice to produce a qualified PS plate. If the sulfuric acid paper is only a small part of it, cut the blank sulfuric acid paper of the same size according to the position of the sulfuric acid paper, and stick it on the reverse side (to ensure that the original liquid film faces the PS plate), and the same density as the original film can be achieved. Use the same exposure time.
For the PS plate, different processing methods, changes in the composition of the photosensitive liquid, thick and thin coating of the photosensitive layer, there are also some tips for mastering the exposure time. The first is electrolytic sand, anodized plate, the photosensitive layer is about 1.5μm, and the resolution is 0.5%. The second is electrolytic sand, centrifugal coating, photosensitive layer thickness, resolution of 2%. The third is the ball sanding mesh, the photosensitive layer is thick, the surface is rough, and the resolution is 3%. Fourth, the ratio of photosensitive liquid is more or less. Therefore, the plates of different compositions should be clearly identified. If different plates are used for printing, the exposure time should be increased or decreased accordingly.
Second, the development definition
The development of the positive PS plate is carried out by utilizing the characteristic that the photosensitive layer causes exposure change after exposure. After the PS version was exposed, although the original text, image and other information were recorded, the photolysis product remained on the plate surface, and the blank portion did not have hydrophilic printing performance, and then the development process was used. "Removing the photosensitive coating of the blank part, revealing the hydrophilic metal oxide layer, forming a blank basis of the printing plate. The principle is that the bismuth acidic compound produced by the exposure and decomposition of the sensitizer generates soluble salts and loses under the action of the alkaline substance. The protective function of the film-forming material is dissolved together during development."
The development process has two methods of hand display and machine display. Since I am manually operated, I can only talk about the experience of manual development.
1. "Generally speaking, the temperature of development should be around 25 °C, the weather is cold, the developing water is easy to crystallize, and the weather is hot, the oxidation (ie, volatility) of the syrup is fast, which will have a certain impact on the development of the PS plate. The former is easy to be dirty, and the printing durability is lowered, while the photosensitive film of the latter PS plate is easy to fall off, bubbling, and the number of plates of the display plate is not normal. Therefore, the development is slow in winter, the developing solution is crystallized, and the room temperature and liquid temperature are lower than normal. At this time, the room temperature should be raised, and the liquid water should be heated to solve the problem. On the contrary, the room temperature and the liquid temperature are lowered, and the ice cube is slightly added to the liquid water to cool down.
2. Strong alkaline developer, sodium hydroxide, cannot be used alone. Because the strong base is easy to make the dot loss, the film is degummed and so on.
3. When it is determined that the original version is faint, and the exposure is not blocked, the development should be carried out by placing the dense side in the sink and developing it. After the film is nearly half, the whole PS plate can be placed in the slot. Normal development is carried out in the liquid water inside.
4. During the development process, as the number of developing blocks and time elapses, the developing solution is continuously oxidized by the photodecomposed sensitizer and air, and the fatigue of the developer is easily broken. In this case, a new developer solution may be used, or slightly A method of adding a concentrated developing powder or agent. Since the old developer is already a good corrosion inhibitor, even a little sodium hydroxide can be added.
5. The development speed, the fatigue degree of the developer and the control of the development end point can be checked by the sun and the gray scale ruler. Generally, the dot size of 3% is not lost, and 95% of the dots are not dead.
Third, the development of the order
After the development is completed, the developing water component remaining on the plate is rinsed with water, but the developer water is not completely left in the plate. In this case, the PS plate should be placed in a sink equipped with 3% phosphoric acid and the plate residue. .
After the above process is completed, it is necessary to carefully check whether there are edge marks or dirty spots on the sides of the text and graphics of the entire printing plate to ensure that the blank portion of the printing plate is clean.
1. The conditioning fluid has the ability to dissolve marks and dirty spots, and to ensure that the dissolved glue marks will not re-contaminate the plate.
2. Light liquid is not acceptable, it must be accompanied by a repairing paste. Because the liquid is moisture, it will be free to open. If it is close to the picture and the text, it will seep into the figure and the text, and repair the required picture and text. It does not fall, so it must be thickened to keep the dressing liquid within a certain range.
3. Wash the edges with dirty spots (the time is about tens of seconds) and wash them with water.
4. After use, tighten the cover to avoid volatilization, so that it will not function properly when it is used again.
After the PS version is rinsed again with water to remove the correction solution, the plate can be used for cleaning. Because the gum arabic has good hydrophilicity, small surface tension, can produce directional adsorption, has certain emulsifying ability, and becomes a high-quality hydrophilic colloid that other colloids cannot compare. Therefore, the PS plate is exposed, developed, fixed, trimmed, and dirty. After each step of the treatment, it is necessary to apply glue to make the printing plate reach the function of blank oleophobic and hydrophilic.
When drying the plate, hand it to the next printing process, it should be vertical or flat, and avoid placing heavy objects on it. Plates that are not on the machine should be placed away from strong light to avoid re-exposure and become a waste plate.