Eliminating Dirty Problems on Photosensitive CTP Plates

The application of a new technology is not entirely straightforward. There are also some problems with the CTP computer-to-platemaking technology, including the imperfections of the printing plate's resistance to printing forces. After the printing on the machine, the layout is easy to remove on the dirty surface and the overlay is not accurate.

There are three aspects that can be considered when printing a CTP plate in the printing area: the quality of the plate, the reasonable operation of the plate making process, and the printing problem.

First, the quality of the plate

CTP plate transport storage conditions are more stringent, and have a certain shelf life. For example, it is required to be placed in a sealed box before exposure. The environment should be dry and cool, and only under the illumination of yellow light can the package be opened and exposed for development. Its shelf life is generally one. Year or so. Due to the relatively low stability of the photosensitive layer of the CTP plate, it is 1000 times lower than the PS plate. Therefore, a slight carelessness will affect the chemical properties of the surface coating layer of the CTP plate, so that the hydrophilicity of the blank portion of the plate surface after exposure and development will be affected, causing the plate surface to be dirty after the printing on the machine.

The CTP plates purchased in the early days had a large area of ​​the printing plates printed on the machine that was dirty and difficult to remove, and had to be replaced with new printing plates. The printing plate produced under the same conditions using a plate that has just been purchased is printed on the machine with a clean surface without any dirt on the plate. Repeated comparison tests show that there are problems with the quality of the old plates. It may be that the quality of the plate is not enough when it is shipped from the factory. It is also possible that the plate does not follow the requirements of the specifications during the transportation and storage process, resulting in deterioration of the quality of the plate. The solution is to require the factory to ensure that the product quality, transportation, and storage processes are strictly in accordance with the specifications.

Second, whether the reasonable operation of the plate making process:

The insufficient exposure time of the CTP plate and insufficient developer concentration or development time will also make the hydrophilic properties of the blank part of the CTP plate not meet the requirements; this will also make the CTP plate easily dirty after being printed on the machine.

Here is a small experience: If we know there is a problem with the quality of a batch of plates, or the density of the developer on the CTP platesetter has dropped to a certain extent, and this situation will cause the CTP plates to be dirty after printing on the plates, and can be on Before machine printing, wipe a thin layer of 100% fountain solution on the surface of the printing plate to achieve satisfactory results. This is based on the preconceived performance of the offset printing plate for oily or waterborne substances. That is, if a printing plate is contacted with which of the properties of the printing plate, the printing plate will have a certain preferential affinity for that substance, and the fountain solution itself is waterborne. Substance, which can promote the hydrophilic and oil-repellent properties of the blank part of the printing plate. This will, to a certain extent, prevent the blank part of the layout from having an affinity for the ink, so as to achieve the goal of stencil removal. Of course, this is only a remedial measure. The fundamental solution to the problem is that the exposure time, developer concentration, and development time of the CTP plate should be appropriate. The factors affecting the quality of the CTP plate during transportation and storage should be eliminated.

Third, the printing problem

Printing is also directly related to the CTPE plate scum problem. Improper adjustment of the ink roller pressure of the printing press will immediately produce a stencil, and it will also easily cause a dirty plate. If the quality of the CTP plate is acceptable, the concentration of the fountain solution is appropriate, as long as the water rollers, rollers, and associated pressure are properly adjusted, satisfactory results will be obtained.

Please note: Since the PS plate cleaning paste has severe corrosiveness to the graphic part of the CTP plate, it is not possible to wipe the CTP plate directly with this cleaning paste in order to get the plate dirty. Wipe the plate with fountain solution to achieve a certain effect. In addition, if the hardness of the printing roller is too high or the thickness of the rubber coating is too thin, the CTP plate will appear dirty. This is because this type of ink roller is not sufficiently elastic, and its surface friction against the printing plate is very large, causing a dirty plate.

Once a roller with a diameter of 72mm was processed, regardless of which printing group the ink roller was placed on, the one-color printing plate was dirty on the whole plate, and replacing it with other normal ink rollers did not have this problem. After inspection, the thickness of the rubber coating on the printing roller is too thin, so that although its softness is appropriate, the entire rubber layer is not elastic enough, and its sliding friction force on the printing plate is too large, causing the dirty plate to be natural. thing.

Source: Bison