The phenomenon of lengthening or shortening of imprints is more common in the printing process. Most of these failures are related to factors such as paper, printing pressure, the nature and material of the liner, and gripping teeth. However, the author has encountered a special case.
Fault phenomenon
The operation of a four-color offset printing machine has been good, but when switching printing operations, the set of printing plates that were just installed showed a marked shortening of the second-color printing plate (cyan version).
Failure analysis and elimination
After repeatedly checking the pressure, gripping teeth, and lining, no problems were found. The blue plate was reprinted and printed after installation. The failure remained the same, so it was suspected that the machine had serious problems.
Carefully listened to the introduction of the relevant operators in the workshop, and carefully checked the printed sheets. It was found that the axial and radial directions of the blue print were significantly shortened, and the other three-color overprints were very accurate. After that, the machine was briefly checked again, and basically no problems were found.
According to the condition of the printed sheet and the machine, it is not certain that it is a malfunction of the machine, or it may be caused by other reasons, so to avoid unnecessary trouble, we did not adjust the machine blindly.
When studying the specific operation details with the relevant operators in the printing and printing workshops, the operators' operating procedures and processes have no problems, and the film is completely accurate.
So what is the problem?
It turned out that this set of printing plates was produced a week ago and has not been used due to production scheduling. The plate-printing staff found that the green plate could not be used due to scratches, so he made another photo. In the work, I often encounter the damage of the printing plate and make up the sun, and there is no problem. However, it was a rainy day a week ago, and the air was very humid for a few days, so it may be that the original film was stretched due to moisture, resulting in the lengthening of the four printing plates. After the weather improved, coupled with the temperature of the printing workshop, the humidity control measures were not very effective. When re-printing the green version, the film was shortened due to the dry and shrinking weather.
In order to confirm this judgment, we found the scratched plate and the newly-printed plate to compare with the film, and found that the scratched plate was longer than the film and the newly-printed plate. Then the black, magenta, and yellow printing plates on the machine were all removed and compared with the printed sheets. The results confirmed everyone's judgment.
After reprinting and trial printing, the fault is eliminated.
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