Analysis and Solution of Malfunctions in Offset Printing

Analysis and Solution of Malfunctions in Offset Printing

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In recent years, the number of color prints with negative characters has increased. Offset printing of the negative text has also occurred from time to time. If you encounter this fault, if you do not analyze it correctly, find out the cause of the fault as soon as possible, and eliminate it, you will definitely take more detours and increase consumption. I would like to make a few comments on this issue, for reference only.

1. After the phenomenon of negative text paste, first check the printing plate for any problems.

Yin text is mostly in the "real". The Yin characters or letters and patterns are large and small, and the lines and strokes are thick and thin. Paste phenomenon occurs mostly in small strokes and lines. Because of the contrast between the "field" and the blank words, if you do not observe carefully, you can't see the plate making problem and it is easy to be ignored.

In addition to the original factors, the reasons for the plate making cause the paste:

1PS version manufacturing quality:

First, the PS version of the sand is too shallow, too thin, and less water storage;

Second, some PS plates have insufficient sealing time, and there is no tiny hole in the plate to make the plate suction capacity too large;

The third is the regeneration of the PS version of the sand and the photosensitive layer is not uniform. Printing with the above-mentioned PS plate printing, because the Yin text is partially hydrophilic, the water storage capacity is poor, and it is easy to be polluted, so that the "in-situ" ink film spread can not be achieved, resulting in a paste.

2 printing version:

First, the exposure time is not enough or the developer concentration is low;

Secondly, due to the lack of attention to the indoor light during the printing process, the PS plate is fogged under natural light, which brings difficulties to the development, resulting in the fatness of the Yin text. The "field" and the graphic part are poorly lipophilic. Printing, the "solid part" ink absorption performance is weakened, in order to achieve the thickness of the ink film, it is necessary to increase the amount of ink in the ink fountain, which is more likely to cause a negative text paste.

Solution:

The first is to use the PS version of the high quality standardization printing plate;

Second, the exposure should be sufficient for the printing operation, and the development should be thorough;

Third, the indoor lighting of the printing process can not use the light source with strong light, the window should be covered with ink cloth, and the door should be double-passed with a ribbon.

2. In addition to the plate making factor, the ink film is too thick during printing is also the main reason. Due to the high surface smoothness of the color printing, the absorption is not strong, and the ink film is slightly thicker and spreads easily into the negative characters, resulting in a paste failure.

There are two cases where the ink film is too thick:

First，the ink film caused by "small water and large ink" is too thick. After the official printing, the ink film is too thick, and the amount of water is increased.

The second， is that "the water is big and big" and the film is too thick. This is because the amount of ink in the official printing ink fountain is excessively adjusted, and the water supply amount is erroneously increased after continuous printing, or the water is large at the start of printing, and the ink film is thinned, and the amount of ink is increased erroneously, resulting in "large water and large ink". , vicious circle, ink emulsification is serious, viscosity is reduced, and it is easy to paste.