Eliminate the dirty problem on the photosensitive CTP plate
The application of a new technology is not completely smooth, and CTP computer direct plate-making technology will also have some problems, including the printing plate is not ideal for printing resistance, the layout is easy to get dirty after printing on the machine, and the overprint is not accurate.
The problem of dirty plates on the CTP printing plate during printing can be considered from three aspects: the quality of the plate material, whether the plate making process is operated reasonably, and the printing problem.
1. Plate quality
The transportation and storage conditions of CTP plates are strict and have a certain shelf life. For example, it requires that it should be placed in a sealed packaging box before exposure. The environment should be dry and cool, and only when the yellow light is selected, the packaging box can be opened for exposure and development. Its shelf life is generally one Year or so. Because the stability of the photosensitive layer of the CTP plate is relatively low, it is 1000 times lower than that of the PS plate. Therefore, a little carelessness will affect the chemical properties of the coating layer on the surface of the CTP plate, so that the hydrophilic performance of the blank part of the plate after exposure and development will be affected, causing the plate to be dirty after printing on the machine.
The CTP plates purchased in the early days, the printed plates produced by them were dirty on a large area as soon as they were printed on the machine, and it was difficult to remove them, so they had to replace them with new plates. However, the printing on the printing plate produced under the same conditions with the plate material just purchased is very clean, and there is no dirt on the plate. After repeated comparison tests, it is shown that there are problems with the quality of the batch of old plates. The quality of the plate may not be close to the factory when it leaves the factory, or there may be operations in the plate that are not in accordance with the specifications during the transportation and storage process, causing the plate quality to deteriorate. The solution is to require the manufacturer to ensure that the product quality, transportation, and storage procedures are strictly in accordance with the specifications.
2. Whether the plate making process is operated reasonably:
Insufficient exposure time of the CTP plate and insufficient developer concentration or development time will also make the hydrophilic properties of the chemical substances in the blank part of the CTP plate not meet the requirements; this will also make the CTP plate easy to get dirty after machine printing.
Here is a small experience: If we know that there is a batch of plate quality problems, or the concentration of the developer on the CTP plate-making machine has dropped to a certain level, and this situation will cause the CTP plate to be dirty after printing on the machine, it can be on the Before machine printing, wipe a thin layer of 100% fountain solution on the surface of the printing plate to achieve satisfactory results. This is because offset plates have pre-emptive properties for oily or water-based substances, that is, if the printing plate is first exposed to which kind of performance substance, the printing plate will have a certain priority affinity for that substance, and the fountain solution itself is water-based Substance, it can promote the hydrophilic part of the blank part of the printing plate. This prevents the blank portion of the layout from having an affinity for the ink to a certain extent, so as to achieve the purpose of removing the dirty layout. Of course, this is only a remedy. The fundamental solution to the problem is that the exposure time, developer concentration, and development time of the CTP plate should be appropriate. Factors that affect the quality of the CTP plate during transportation and storage should be eliminated.
3. Printing problems
The printing aspect is also directly related to the dirty problem on the CTPE plate. Improper adjustment of the ink roller pressure of the printing press will immediately produce a paste version, and it is also easy to cause a dirty version. If the quality of CTP printing plate is qualified and the concentration of fountain solution is appropriate, as long as the water roller ink roller and related pressure are adjusted, satisfactory results will be obtained.
Please note: PS version of the cleaning paste is very corrosive to the graphic part of the CTP printing plate, so you should not use this cleaning paste to directly wipe the CTP printing plate to get the plate dirty. Wiping the printing plate with the fountain solution stock solution can achieve a certain effect. In addition, if the hardness of the plate ink roller is too high or the thickness of the encapsulation is too thin, the dirty phenomenon of the CTP printing plate will also appear. This is because the rubber layer of this type of ink roller is not elastic enough, and its friction force on the surface of the printing plate is very large, thereby causing dirty plates.
I once processed a plate-based ink roller with a diameter of 72mm. No matter which printing color set this ink roller is used in, the printing plate of that color is dirty on the whole plate, and it is not a problem to replace it with other normal ink rollers. After inspection, the thickness of the rubber coating on the plate ink roller is too thin, so that although its softness and hardness are appropriate, the elasticity of the entire adhesive layer is still not enough, and its sliding friction against the printing plate is too large, causing the dirty version to be natural. thing.
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