1. After the phenomenon of overprinting of negative characters occurs, first check whether there is a problem with the printing plate.
In addition to the original factors, the reasons for the plate-making are:
â‘ PS version manufacturing quality:
One is that the PS version is too shallow, too thin, and has little water storage;
The second is that some PS plates have insufficient sealing time, and they have not sealed the very tiny holes in the layout, which makes the layout too powerful to absorb;
The third is the unevenness of the regenerated PS version of the sand mesh and the sense layer. With the above-mentioned Ps Plate printing, because the negative part of the text is hydrophilic, the water storage capacity is poor, it is easy to contaminate, and it cannot resist the spreading of the "field" ink film, resulting in paste.
â‘¡Reproduction:
First, the exposure time is insufficient or the developer concentration is low;
Second, due to the lack of attention to the indoor light during the printing process, the PS version produces gray fog under natural light irradiation, which causes difficulties in development, causing the negative text part to be fat-sensitive, and the "field" and graphic parts are poor in lipophilicity. In 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 under the ink fountain, which is more likely to cause negative text to paste.
Solution:
One is to use PS version with high quality standardization to produce printing plate;
The second is that exposure should be sufficient when printing, and development should be thorough;
The third is that the indoor lighting of the printing process cannot use a light source with strong light, the windows should be covered with ink cloth, and the doors should be double doors separated by ribbons.
2. In addition to plate-making factors, excessive ink film thickness during printing is also the main reason
Due to the high smoothness of the surface for color printing, the absorption is not strong, and the ink film is slightly thicker, it is easy to spread into the negative characters, resulting in paste failure.
There are two situations when the ink film is too thick:
First, the ink film is too thick due to "small water and large ink". After the official printing, the ink film is found to be too thick, increase the amount of water, and then adjust the amount of ink under a small amount to eliminate it;
The second is "big water and big ink," which may cause the ink film to be too thick. This is because the ink volume under the ink fountain is adjusted excessively before the official printing, the water supply volume is incorrectly increased after continuous printing, or the water is large when the printing starts, and the ink film is thinned, and the ink volume is incorrectly increased, resulting in "large water and large ink. ", A vicious cycle, serious ink emulsification, reduced viscosity, very easy to paste.
Solution:
â‘ In daily operation, you should always sum up experience to improve the technical level. Before the official printing, the ink amount should be calculated correctly at the ink tank. It is better to use a small amount of ink, rather than an excessive amount of ink. Debugging to achieve the ink film thickness is suitable not to paste.
â‘¡Because the water supply of the "field" layout cannot be small, in order to avoid the "large water and large ink" causing the ink film to be too thick, you can take the PH value of the potion (increasing the acid value), or add an appropriate amount of surfactant to reduce the water supply. If there is large water, large ink, and ink emulsification, you should clean the emulsified ink on the ink roller in time, then reduce the amount of ink, and re-ink printing;
â‘¢When adjusting ink, the color of double-color and light-color inks should be a little darker than the original. The color of the three primary colors should also be selected with strong coloring power. Take the "dark ink thin printing" measure to avoid too thick ink film.
3. In addition to the above two main reasons, the following factors will also cause negative text to be printed during printing:
â‘ The printing pressure is too high, mainly because the pressure of printing one rubber is too large;
â‘¡ The fluidity of the ink is too large;
â‘¢The water resistance of the ink particle group or pigment is poor;
â‘£ Too much oil is added when adjusting the ink;
⑤ Ink roller aging;
â‘¥ The inking roller is too soft and bent, and it slides relative to the plate cylinder during operation;
⑦The pressure between the inking roller and the printing plate is too high;
⑧ The water content of the plate is too small or the water roller is too dirty, the pressure of the water roller and the printing plate is too light or too heavy;
⑨The blanket is not stretched tightly;
â‘©Roller lining is not suitable;
⑾The PH value of the paper is greater than 7 (alkaline), easy to dilute the concentration of the liquid medicine;
â‘¿Paper dedusting is serious;
â’€Summer room temperature, due to the moisture of the PS plate is drying quickly, the plate is not coated with protective glue when it is stopped, and reprinting will cause paste.
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