A Brief Talk on Exposure and Development of Positive Image PS Plate
Put the original version on the PS version and measure the size of the bite or mid-seam cross line, and stick it with adhesive tape. It is just a prelude to the printing version. In the actual operation, a qualified PS printing plate must be mechanically (that is, the standard operation and maintenance of the plate-making machine), optical (the original plate with different density, a large difference will occur under the transmission of the ultraviolet lamp), chemical (developing powder Correct ratio), accurate operation of all links.
The process flow of the positive version PS version is:
According to the sequence of the above picture, I will briefly describe some actual situations and some experiences that I have been engaged in printing for many years.
1. Definition of Exposure
"The positive version of the positive version uses the positive version of the positive version of the positive version. The exposed ultraviolet light reaches the photosensitive layer of the PS version through the low density and blank parts of the original version, is absorbed by the sensitizer, and is formed into a picture after being photosensitive. Under the action of ultraviolet light, decomposition and rearrangement reactions take place, making the photosensitive parts change from insoluble in dilute alkali to soluble in dilute alkali. At the same time, as the photosensitive group disappears, the color of the photosensitive part changes from green to colorant in the photosensitive layer Color-blue. "
First of all, it is necessary to ensure that no dirty stains are left on the upper cover glass, and the upper cover glass can be wiped clean with absolute ethanol or glass cleaning liquid. Secondly, the suction rubber of the plate-making machine should also be carefully checked for foreign objects. After confirming that it is correct, the upper cover glass can be lowered for suction. After the original version and the PS version are in close contact, the exposure light source is activated and the light is stabilized (iodine The home lamp usually takes about 10 minutes) for exposure reading. (At this time, the length of the exposure time should be determined according to the type and density of the original version)
As far as the originals I have come into contact with, there are roughly three types.
1. Full film type: This type of original version has a relatively longer exposure time (take 1500W lamp as an example, about 9 ~ 10min), and in order to eliminate the edge marks of the film on the PS version, it must be blocked. Technical treatment (the masking paper can be used with the PS type packaging box of the interlayer typing paper, the time can be increased by about 1/2 of the entire exposure time, this also reduces the use of revision liquid to eliminate the edges of the film, the dot In terms of no loss).
2. Full sulfuric acid paper type: This type of full sulfuric acid paper should also reduce the exposure time according to the density of the graphic image. Even because the toner takes a long time, new toner is not added to the toner cartridge in time, resulting in several The line drawing is faint. At this time, according to the actual size of the light part, cut a piece of typing paper. When the exposure time thinks it is possible (at this time, it is necessary to rely on previous work experience) to block the paper in the light. Location (should find the location, fast-in and fast-out to avoid burns caused by ultraviolet rays). The other parts continue to be exposed until the normal exposure.
3. Film and sulfuric acid paper: half of this type: the original version of this type should be carefully mastered in terms of exposure time, because some pictures and text with film are two times longer than those with sulfuric acid paper. Times, even more, when this type of original version is exposed, not only must prepare a piece of typing paper to block part of the exposure time, but also prepare a waste PS version that is slightly larger than the area of ​​sulfuric acid paper. If the sulfuric acid paper covers the typing paper, and the film is still exposed on one side, this PS version will play the role of blocking all the sulfuric acid paper to extend the exposure time of the original half of the film and make the graphics on both sides shallow. Consistent. That is to say, the sulfuric acid paper needs to be masked 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 paste it on the reverse side (ensure that the original liquid film faces the PS version), which can also achieve the same density as the original film. Use the same exposure time.
For the PS version, different processing methods, changes in the composition of the photosensitive liquid, and the thickness and thickness of the photosensitive layer coating also have some skills to master the exposure time. The first is electrolytic sand mesh, anodized plate, the photosensitive layer is about 1.5μm, and the resolution is 0.5%. The second is electrolytic sand mesh, centrifugal coating, the photosensitive layer is thick, and the resolution is 2%. The third is the ball matte 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 with different compositions should be clearly distinguished. If different plates are used for printing, the exposure time should be increased or decreased accordingly.
Second, the definition of development
The development of the positive PS version is carried out by utilizing the characteristic of the solubility change caused by the exposure of the photosensitive layer. After the PS plate was exposed, although the original text, images and other information were recorded, the photolysis products still remained on the plate surface, and the blank part did not have hydrophilic printing performance. Next, it should be processed by the development process. "Remove the photosensitive coating of the blank part, expose the hydrophilic metal oxide layer, and form the blank foundation of the printing plate. The principle is that the indenic acid compound produced by the exposure and decomposition of the photosensitizer will produce soluble salts under the action of alkaline substances and lose In order to protect the film-forming material, it will be dissolved together during development. "
There are two methods for the development process: hand display and machine display. Since I am a manual operator, I can only talk about the experience of manual development.
1. "Generally speaking, the development temperature should be around 25 ° C. The weather is cold, the development water is easy to crystallize, and the weather is hot, the oxidation (ie volatility) of the potion is fast, which will have a certain impact on the development of the PS version. The former is easy to be dirty and the printing resistance is reduced, while the latter PS version of the photosensitive film is easy to fall off, bubbling, and the number of blocks is not normal. Therefore, the development is slow in winter, the developer liquid crystallizes, and the room temperature and liquid temperature are lower than normal At this time, the room temperature should be raised and the liquid water heated to solve it. On the contrary, the room temperature and liquid temperature should be lowered? Add ice cubes to the liquid water to cool down.
2. Strong alkaline developer, sodium hydroxide, cannot be used alone. Because strong alkali is easy to lose the dots, the photosensitive film is degummed and so on.
3. After confirming that the original version is dull and the exposure is not blocked, the developer should put the dense side into the water tank for development first. After the film is almost half, then the entire PS version can be put into the tank. Normal development is carried out in the liquid water inside.
4. During the development process, as the number of development blocks and time elapses, as the developing solution is continuously oxidized by the photosensitizing agent and air, it is easy for the developing solution to fatigue and eventually fail. At this time, a new developing solution can be used. , Or a slightly concentrated method of developing powder and 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 developing solution and the control of the development end point can be inspected with the sun or gray ladder. Generally, it is required that 3% of the dots are not lost, and 95% of the dots are not dead.
3. Development sequence
After the development is completed, rinse the developing water components left on the plate surface with water, but it does not completely prevent the plate surface from developing water. At this time, the PS plate should be placed in a water tank equipped with 3% phosphoric acid and the plate residual liquid .
After the above process is completed, it is necessary to carefully check whether there are any edge marks and dirty spots on the edges of the entire printing plate text and graphics to ensure that the blank part of the printing plate is clean.
1. The dressing solution has the ability to dissolve the marks and dirty spots, and can ensure that the dissolved glue stains will not re-contaminate the printing plate.
2. It is not possible to use liquid alone, and it must be equipped with a revision paste, because the liquid is water, it will spread freely. If it is close to the pictures and texts, it will penetrate into the pictures and texts. It has not been repaired, so it must be thickened to control the dressing fluid within a certain range.
3. Wait for the emulsification of the dirty spots (the time is about tens of seconds), then wash with water.
4. After use, the cover should be tightened to avoid volatilization, so that the next time it is used, it will not play its due role.
After the PS version is rinsed with water to remove the revision liquid, the version can be erased and ready for use. Because gum arabic has good hydrophilicity, small surface tension, can produce directional adsorption, and has a certain emulsifying ability, it becomes a high-quality hydrophilic colloid that cannot be compared with other colloids. Therefore, the PS plate has been exposed and developed, fixed, trimmed, and dirty After the treatment of each link, the glue must be applied to make the printing plate achieve the function of oleophobicity and hydrophilicity of the blank base.
After printing the plate and handing it to the next printing process, it should be placed vertically or horizontally, and no heavy objects should be placed on it. Plates that are not on the machine should be placed so as to avoid strong light exposure, so as not to be exposed again and become a waste version.
The above are some experiences I have accumulated in the years of printing, I hope all experts and masters will advise.
Note:
1.3 Excerpt from the article of teacher Li Yongqiang of Shaanxi Printing Technology School.
2.4.5 Excerpt from Shanghai Printing School "Principle of Lithography"
(Author: Jiangxi Shangrao Jiangbei Northeast Printing Factory)
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