Exclude dirty problems on photosensitive CTP plates
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The application of a new technology is not completely smooth. CTP computer direct plate-making technology will also have some problems, including the printing plate's printing durability is not ideal. After the printing, the layout is easy to remove dirt and the printing is not accurate.
CTP plates can be considered in three aspects in the printing process: the quality of the plate, the correct operation of the plate making process, and printing problems.
First, the quality of the plate
The transportation and storage conditions of CTP plates are strict and have a certain shelf life. For example, it is required to be placed in a sealed package before exposure. The environment should be dry and cool, and only when it is exposed to yellow light, the package can be opened for exposure and development. Its shelf life is generally one. About a year. Due to the relatively low stability of the CTP plate photosensitive layer, it is 1000 times lower than the PS plate. Therefore, a slight inadvertent effect will affect the chemical properties of the surface coating layer of the CTP plate, so that the hydrophilic property of the blank portion of the plate after exposure and development is affected, causing the surface of the plate after printing to be dirty.
In the early purchase of the CTP plate, the plate produced by the machine was printed on a large area, and it was difficult to remove it, so it was necessary to replace the new plate. The plate printed on the plate made under the same conditions with the plate material that was just purchased is very clean, and there is no dirty surface. Repeated comparison tests have shown that there is a problem with the quality of the old plates. It is possible that the quality of the plate material will not be off the factory. It is also possible that the quality of the plate material deteriorates during the transportation and storage process. The solution is to require the manufacturer to ensure that the product quality, transportation and storage processes are strictly in accordance with the specifications.
Second, the plate-making process is reasonable operation:
Insufficient exposure time of the CTP plate and insufficient developer concentration or development time will also make the hydrophilic properties of the blank portion of the CTP plate unsatisfactory; this will also make the CTP plate easy to get dirty after printing on the machine.
Here is a small experience: If we know that there is a problem with the quality of a batch of plates, or the developer concentration on the CTP platesetter has dropped to a certain extent, and this situation will cause the CTP plate to be printed on the plate after the machine is dirty, you can Before printing the machine, a thin layer of 100% dampening solution is applied to the surface of the plate to achieve a satisfactory result. This is based on the pre-emptive performance of the offset printing plate on oily or water-based materials. That is, if the printing plate first contacts which properties, the printing plate will have certain preferential affinity for that material, and the fountain solution itself is water-based. Substance, which promotes the hydrophilic and oil-repellent properties of the blank portion of the printing plate. This will prevent the blank portion of the layout from affecting the ink to a certain extent to achieve the dirty surface of the layout. Of course, this is only a remedy. The fundamental solution to the problem is that the CTP version exposure time, developer concentration, and development time should be appropriate. The factors affecting the quality of the CTP plate during transportation and storage should be eliminated.
Third, printing problems
Printing is also directly related to the dirty problem on CTPE plates. Improper adjustment of the pressure of the ink roller of the printing press will immediately produce a paste, which may also cause dirty plates. If the CTP plate quality is qualified, the dampening solution concentration is appropriate, as long as the water roller roller and related pressure are adjusted, satisfactory results will be obtained.
Please note: Since the PS version of the cleaning paste is highly corrosive to the CTP plate image, it is not possible to wipe the CTP plate directly with this cleaning paste to make the plate dirty. Wiping the plate with the dampening solution can achieve a certain effect. In addition, if the hardness of the plate roller is too high or the thickness of the rubber is too thin, the CTP plate may be dirty. This is because the adhesive layer of the ink roller is not sufficiently elastic, and its surface friction against the printing plate is very large, thereby causing a dirty plate.
Once a 72mm diameter ink roller was processed, no matter which printing color group the ink roller was used for, the printing plate of that color was dirty on the whole plate, and the other normal ink roller did not have this problem. After inspection, the thickness of the encapsulation roller is too thin, so that its softness and hardness are suitable, but the elasticity of the entire rubber layer is not enough, and the sliding friction force on the printing plate is too large, causing the dirty plate to be natural. thing.