In the printing process, plate printing is an important link between the past and the future. Some of the problems in the previous process can be made up in the plate printing process, and some special requirements of the subsequent printing process can also be adjusted and solved in the plate printing process. Therefore, the quality of the printing plate has a direct impact on the quality of the final printed matter.
1. The difference between the proofing version and the machine version
In fact, for proofing and printing, two different sets of plates should be printed. For proofing, from the structure of the proofing machine itself, it is generally a platform type, and the pressure of proofing is smaller than that of printing, and the speed is slower than that of printing. At the same time, because of the dot increase caused by proofing, when printing is required, the dots between 2% and 3% are reserved, and 98% of the dots cannot be posted. For printing, due to the high printing pressure and fast speed, the printing ink is softer (lower viscosity) than the proofing ink, which is easy to cause dots to increase, and can increase to 30% to 40% at most, so the same plate is used for proofing The effect is different from that of printing, and this contradiction has not been resolved for a long time. Therefore, when printing the printing plate, it is required to keep 4% to 5% of the dots, and 96% of the dots are not blurred, leaving room for the expansion of dots caused by printing, and the printed matter is easy to approach the proofs.
2. Lost ideas during printing
In case of dot loss, you should first check the degree of dot restoration of the film itself, such as whether 50% of the dots on the film are square, whether 4% to 5% of the dots are complete, etc. In short, check the quality of the phototypesetting film, and then judge according to it Whether the dots are lost in the printing process. Lost ideas often occur due to the problem of the plate printing operation, which is directly related to exposure time, development time, temperature, and concentration of the developer. Excessive exposure and excessive developer concentration will cause the dots that should be retained on the layout to be lost or the strokes of the text to be thinner. Strictly speaking, the printing staff should control the exposure and development through the printing test strip and grayscale, and test their own test data.
3. The layout is false
Investigating the reason for the blurring of the printing plate may be related to the printing film first. If the exposure is too much when the film is output, it will cause the dots on the printing film to be weak, and the printed version will naturally be weak.
From the point of view of the printing operation, it may be because there are foreign objects or dirt attached to the glass or film of the printing machine; the gasket of the printing machine is not suitable; or the vacuum is not solid so that the film and the plate are tightly bonded Insufficient; improper collage of printing film; too strong light before exposure (during punching) or after exposure to before development, etc. may cause the straight plate to become blurred; and the temperature of the developing solution is too high, the concentration is too high, and the developing time is too long, Excessive development caused by too much developer replenishment solution is also the reason why the layout cannot be ignored.
At this time, the glass or film should be cleaned with a cleaning agent; the liner should be adjusted to be flat; the tape should be pasted 3mm away from the image part, and it should be confirmed whether the film is close to the plate; under safe light, such as an anti-fading fluorescent lamp, yellow light, Fluorescent lamps equipped with safety lampshades, etc.; for the problem of inappropriate development, it should be carried out according to the standard.
4. Uneven development
Uneven development or poor development is often caused by the decrease in the activity of the developer, which is mainly reflected in several aspects: the developer is not replenished in time; the development time is too short; the temperature of the developer is too low; At this time, in addition to standardizing the development conditions, the developer should be replenished quantitatively and in time. the
In addition, dirty spots or foreign objects on the plate will also hinder the development, which requires the staff to regularly check the developing machine and plate printing machine, and clean the machine in time.
5. The layout is dirty
There are different situations and reasons for the dirt on the layout. If the layout is dirty, it may be due to underexposure. There are two possibilities. One is that the transparency of the film is not good or the film is expired and the fog is large; If you encounter the first situation, you can only remake the film; if there is a problem with the exposure light source, you need to use grayscale to adjust the exposure time appropriately, or directly replace the exposure light source. Of course, poor development may also cause the layout to be dirty. At this time, it is necessary to check out the specific reasons for the poor development and adjust to the standard conditions in time.
In production, sometimes spot-like dirt is encountered. Analyzing it, there are quite a few "culprits". like
① There are dirty spots on the glass of the printing machine, and there are dust or dirty spots on the film;
② When collaging the printing film, after the tape on the film is printing, the tape marks will be left on the printing plate;
③During development, the development is poor due to the adhesion of water bubbles (foaming due to clogging of the developer nozzle hole);
④ Due to unclean hands during the printing operation, fingerprints are left on the board;
⑤ The protective glue is thin;
⑥The protective glue is stacked and stored before it is dry, so that the plates stick together, causing the protective glue layer to peel off when taking it;
⑦ After plate making, the printing plate is stored under high temperature and high humidity conditions.
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"Prescribe the right medicine" for different reasons. Among them, the dirt caused by tape adhesive and tape marks is the most common. First of all, it should be prevented. When imposing, use thin and clean transparent tape as much as possible. If the tape adhesive touches the printing plate, it should be gently Wiped off and go to develop. When printing the plate, the air should be fully pumped to minimize the air layer around the imposition tape and the original film, so as to minimize the possibility of light interference. If after exposure, there are still tape marks on the plate, it needs to be desmeared manually with a desmear agent, or a second exposure is required to desmear.
For other aspects of desmearing, you can use a desmear, a masking knife, a pumice stick, or use a diffuser film for exposure or a desmearing cover.
6. Poor printing plate ink
If it is not caused by the low photosensitive agent content of the photosensitive glue of the plate, the reason should be found in the relationship between the ink-holding power of the printing plate, the exposure time, and the concentration of the developer. If the exposure time is too long or the developer concentration is too high, it is easy to have poor ink-holding power of the printing plate. Because the exposed photosensitive layer of the PS plate is not absolutely soluble or absolutely insoluble, but between the two. The rate is increased, and the ink is poor. In addition, if ① the protective glue does not meet the requirements, the glue is too thick, and the glue is applied unevenly by hand;
②The drying temperature of the printing plate is too high or too low, resulting in poor ink absorption or poor film-forming performance;
③The printing plate is exposed to strong light after gluing;
④ After plate making, if the printing plate is stored in a high temperature and high humidity environment, it will cause a drop in ink retention.
At this time, the protective glue specified by the plate material should be used, the glue should be diluted appropriately, and the drying temperature should be reasonably determined, generally at 60. About C; after gluing, prevent light, and store the plate-making plate in a qualified environment. If it is found that the printing plate is poorly inked during the printing process, it should be checked whether there is too much glue in the fountain solution, or whether it has not been washed with water after using the cleaning agent.
7. The printing plate endurance is reduced
The main reason for the decline in printing plate durability lies in two aspects of printing operation and printing. In terms of printing: ① run out before exposure or development;
②The density of the film is not high enough;
③ Due to the high temperature and concentration of the developer, the development time is long or excessive replenishment causes excessive development;
④ There are strong acids, strong alkalis, organic solvents, cleaning fluids, and other agents attached to the printing plate;
⑤ Too many times wiping with a plate cleaning agent, etc., will affect the printing durability of the printing plate.
In terms of printing, if the printing pressure is too high or there is too much paper powder, as well as the use of strong plate cleaning agents and cylinder cleaning agents in UV printing, it will inevitably cause a decline in printing resistance.
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In particular, it should be pointed out here that in order to prevent light from running out, the ordinary PS version should be illuminated with a yellow safety light to fully block harmful light.
8. There is a blue bottom on the printed plate after drying
During production, if a plate is published, no matter if it is because of the pre-production problems of the plate material, or the matching conditions of the exposure and development time of the printing plate itself are not suitable, the printed plate will have a blue background. The "secret" of the bottom blue is:
① When the plate is made, the sand mesh is too coarse, and the electrolytic oxidation current does not match;
②Insufficient exposure or insufficient concentration of developer during printing, or the two conditions are not matched properly.
The background blue phenomenon has caused headaches for many operators. If this problem occurs, more or less development will not work. If there is too much development, the dots that need to be kept will be reduced or lost; if there is less development, the entire layout will be affected. Under the condition of moderate exposure and development, if there is a background blue after developing the image, it needs to be repaired, but once it is repaired, there will be a watermark on the page. If you want to smear, if you use the smear liquid to repair this circle of smudges, another circle of smudges will swim out. If it is stained on pictures, text, or network cables, the printing plate will not be usable at all. To solve this problem, it is necessary to apply a thin layer of glue before cleaning, and high-quality prints cannot use this version.
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