Some time ago, the entire layout of the newspapers we printed made people feel dirty, but this was different from the problem of floating dirty in individual ink areas, because at least there would be a contrast between light and dark in the newspaper. But the entire layout of our printed newspapers is gray, and if not carefully observed, it is the color of the newsprint itself. If we compare the printed newspaper with the unprinted newsprint, we will find that there is a problem in the printing process. So which part of the problem is wrong? How to solve it?
Go straight to the offset shop to find the answer
Since the newsprint has become gray after printing, it must be that the paper is dirty during the printing process. The first reaction of everyone is to go to the offset printing shop to find the answer. Is the water in the offset fountain water too dirty? Or is it too much water? With these questions, everyone started a series of work.
We found a newspaper product that had quality problems with the offset press starting to track. First, clean the water supply system of the offset press, including pipes, water buckets, bucket rollers, and so on. Then, replace the dampening solution and measure the pH and conductance of the dampening solution to ensure it is within the normal range. When everything is ready, start printing the newspaper that night. Before printing, we deliberately reduced the amount of water supplied to each layout, starting with the smallest amount of water, and trying to print qualified prints with the smallest amount of water.
But the result is that the printed newspapers are basically the same as the ones printed before the presses were cleaned. It seems that this problem has nothing to do with the offset process.
Is the plate making process yours?
So we changed our minds and started from the pre-press link. Our factory currently uses two kinds of CTP plates, photosensitive and thermal. Although the imaging principle is different, because this survey is dirty on the layout, that is, the blank part of the layout has a problem. In the process of plate making, the chemical film of the blank part of the two plates does not need to be chemically changed, and only needs to be rinsed off by the syrup during the development process. That is to say, from the viewpoint of plate making, as long as the chemical film which does not undergo chemical change on the surface of the plate material is completely washed out during the development process, the blank portion exposes the hydrophilic alumina surface layer. And as long as the blank portion of the alumina surface has no film, under normal offset conditions, the ink will not be adsorbed, and of course the plate surface is prevented from being dirty, so that the blank portion of the plate is kept clean.
Following this line of thinking, we first cleaned the developing part of the CTP platesetter and replaced the new developer. After publication, the blank part of the CTP plate was observed with a magnifying glass, and no residual film was found. Printing on the offset press, the problem remains unchanged. Is there no solution to the problem?
A flash of light, a smooth solution
Just when everyone was desperate, we inadvertently thought of the revision pen. For the photosensitive plate, we used a matching correction pen to lightly apply a few times on the blank part of the layout, and found that the place where the revision pen was painted was obviously lighter than the blank part without the painting. For the thermal version, a cotton ball that has been smeared with alcohol is applied to the blank portion of the thermal plate, and the same phenomenon as the photosensitive plate is found. This shows that there is still a small amount of residual film in the blank portion of the plate we use, and this film will reduce the hydrophilicity of the blank portion and increase the lipophilicity.
We are surprised by this result, but solving the problem is the most important. We increased the temperature of the developer by 1 ° C while reducing the development speed and published it again. The blank portion of the CTP plate was examined using the method mentioned above. As a result, it was found that there was almost no difference in the color of the plate and the place where it was not painted after the place where the pen or the alcohol was painted. This is a small victory, which shows that there is almost no film residue in the blank part of the CTP version. But what about the printing effect? ​​After the start-up test, it was found that the printing effect was very good. The blank part of the printed newspaper was exactly the same as the unprinted newsprint!
The problem is solved smoothly, our mood can be described by the use of the cloud! So why did you change the development temperature and speed? The person in charge of the prepress workshop told us that the speed of development is because there was a time when the plate making amount was too large. As soon as possible, the plate is printed out, and the method of publishing the newspaper is not delayed. The temperature of the developer is lowered to extend the life of the developer. It has been found that after the temperature of the developer is lowered, the same developer can be used. In some editions, this is done for cost reduction considerations.
From the solution of this problem, we can find that no matter how complicated the surface looks, as long as the key points are grasped, the problem can be solved.
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