The Reasons and Solution of the Offsets of Offset Yinyin

Editor's note: In recent years, color prints with negative text have increased. Offsets of offset printing stencils also occur from time to time. If you encounter this failure, if you do not analyze it correctly, you will find out the cause of the failure and eliminate it as soon as possible. This will inevitably lead the way and increase consumption. Several points are now discussed on this issue and are for reference only.

1. After the phenomenon of yin paste has appeared, first check whether there is any problem with the printing plate.

There are many types of Yin-characters in the large “field” of Yin-characters or letters and patterns. There are thick lines and strokes. The stencil phenomenon often occurs in small strokes and lines. Because there is a large contrast between “field” and blank, if you do not observe it carefully, you will not see the issue of plate making and it will be easily overlooked.

In addition to the original factors, the plate-making aspect causes the paste version cause:

1PS version of manufacturing quality:

First, the PS version is too shallow, too thin, and has little water storage;
The second is that some PS plates have not been sealed for a long time, and they have not closed the tiny holes on the layout, which makes the layout sucking capacity too large;
The third is the non-uniformity of the regenerated PS plateaus and the fluvial layer. With the above PS version printing, because the Yin text part of the hydrophilic, poor water storage capacity, easy to contaminate, arrived in the "field" ink film spread, resulting in paste version.

2 print version:

First, the exposure time is not enough or the developer concentration is low;
Second, due to the lack of attention to the indoor light during the printing process, the PS plate produces fog under natural light irradiation, which brings difficulties to the development and causes the negative part of the Yin language to have a fat-sensitive property. The “field” and the graphic part are poor in lipophilicity. Printing, "solid part" of ink absorption performance weakened, in order to reach the ink film thickness, ink must be added to the amount of ink, easier to cause Yin Yin paste.

Solution:
One is to use a high-quality standardized PS plate for printing;
The second is that the exposure of the printing operation should be sufficient and the development should be thorough;
The third is the printing process indoor lighting can not use strong light source, the window should be covered with ink cloth, the door should be double-channel door interval.

2. In addition to the plate making factors, the ink film is also the main reason for printing. Due to the high surface smoothness of the color prints and the weak absorption, the ink film is slightly thicker and spreads easily to the inside of the Yinyin, resulting in stencil failure.

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

First, the ink film caused by the "water ink" was too thick. After the official printing, the ink film was found to be too thick and the amount of water was increased. Then, the amount of ink under a slight adjustment could be eliminated.

The second is the "great water and ink" and caused the ink film to be too thick. This is because the amount of ink under the ink fountain is excessively adjusted before the official printing, the amount of water supply is erroneously increased after continuous printing, or the water is large at the start of printing, the ink film is thinned, and the amount of ink is increased by mistake, resulting in “water and ink” ” Vicious circle, serious ink emulsification, viscosity reduction, easy to paste version.

Solution:

1 In daily operations, we must often sum up experience and raise the technical level. We should calculate the amount of ink under ink before the official printing. We would prefer to lower the amount of ink under the ink. We cannot print too much ink. Inexperience can be used to absorb ink. Debugging to achieve the ink film thickness is not suitable paste version.

2 Because the water supply volume in the “field” layout cannot be small, in order to avoid the ink film being too thick due to the “water and ink”, the PH value of the medicine (increasing the acid value) may be reduced, or an appropriate amount of surfactant may be added to reduce the amount of water supply. If there is water and large ink, the phenomenon of ink emulsification, it should be cleaned in time on the ink roller emulsified ink, and then reduce the amount of ink, re-inking printing;

3 In the case of complex-colored and light-colored inks, the color should be slightly darker than the original. The three primary colors should also select inks with strong coloring power. Measure of “deep ink thin printing” can also avoid over-thickness of the ink film.

3, in addition to the above two main reasons, the following many factors will also result in Yinyin paste version :

1 The printing pressure is too large, mainly because the pressure of the ink is too large.
2 ink flow is too large;
3 ink particle group or pigment poor water resistance;
4 Drying oil plus excessive volume when adjusting ink;
5 ink roller aging;
6 The ink roller is too soft and bent, and relative slip occurs with the plate cylinder during operation;
7 ink roller and plate pressure is too large;
8 plate surface water is too small or dirty water roller, water roller and plate pressure is too light or too heavy;
9 The blanket is not tight;
10 roller lining is not suitable;
(11) Paper PH value is greater than 7 (alkaline), easy to dilute the concentration of medicine;
(12) Severe powder stripping;
(13) In the summer room temperature, due to the moisture of the PS plate layout, the surface of the plate was not coated with protective glue when it was shut down, and reprinting would cause a paste plate.


Excerpt from: HC