Solving gravure

Paste version is also called dirty version, which is a problem often encountered in gravure printing. Simply put, ink is on a film that should not be printed. Its causes and solutions are as follows:

One, scraper

Because the blade is not sharp enough, it cannot clean the ink; due to the blade angle is too small or installed into a soft blade, blade pressure is too small can cause paste phenomenon. At this time, the blade angle or pressure should be adjusted and even the blade replaced.

Second, rough layout

This situation is generally only produced when the amount of printing is excessive, and the new version generally does not appear this phenomenon. At this point, the surface should be polished with metallographic sandpaper or the ink in the fast-drying solvent should be allowed to rotate for 1-2 hours. If this problem cannot be solved, the plate factory can only be chromed again.

Third, the ink has a strong affinity for chromium

This situation will also cause paste phenomenon. At this time, you can change the ink of different manufacturers to try, or add the amount of not more than 2% of the isopropyl alcohol (when the ambient air is relatively dry).

Fourth, slow dry solvent

When a slow-drying solvent is used and the doctor blade is close to the plate copper, the area where the printing plate comes into contact with air is very small, and the plate surface is still wet due to the use of a slow-drying solvent, and it is easy to form a paste phenomenon. At this time, the quick-drying solvent should be changed or the scraper should be kept as far as possible from the copper plate. If it still cannot be solved, the plate can be dried by the wind. When these measures are taken, attention is paid to the speed of the vehicle. If the speed is too slow, the ink may not be transferred to the film.

Fifth, the ink is mixed with impurities or ink viscosity is too high

When there are impurities in the ink, sometimes it sticks firmly to the edge of the blade, so that the blade can not scrape the ink cleanly in a sharp state, resulting in a paste-type phenomenon. At this time, the 80-120 mesh filter filters the ink. When the viscosity of the ink is too large, some solvents may be appropriately added to solve the problem of stencil.

In practice, the most difficult reason for stencil printing is that when a single solvent is used and the quality of the ink is not very good, printing is generally not a problem at the beginning, but it will take a long time to produce a stencil printing phenomenon. . At this time, it can be seen that the surface of the plate is covered with a layer of colored material and is hard to be wiped off with a solvent. This is because the resin in the ink is firmly adhered to the plate after deposition, and only the ester solvent can wipe it off. It is best to use a special cleaning agent. After cleaning the plate, use a mixed solvent such as ethyl ester:toluene (8:2), ethyl ester:toluene:butanone (7:2:1) to effectively solve the problem, but one issue to note here is: If With ethyl ester, toluene can solve, it is best not to butanone, because the residual odor of butanone is relatively strong, may have an impact on the quality of the print. In addition, when using this mixed solvent, it is necessary to pay attention to the speed of the vehicle. If the vehicle speed is too slow, it is easy to produce a dry plate phenomenon.

To solve the problem of stencil in practice, it is sometimes necessary to use the above methods in a comprehensive manner. For example, use a quick-drying solvent and a sharp blade to keep the scraper as far away as possible from the copper plate, and use a duct to blow the air toward the plate.
The above has made a comprehensive analysis of the cause of the paste and its solution. Here we will discuss in detail how to improve the ink transfer effect.

In Tuen Tun, the ink transfer is to stick the ink in the surface texture to the film. In general, the transfer rate (that is, the ratio of the ink adhered to the film to the ink in the texture) is unlikely to reach 100%, and the size of this transfer rate directly affects the quality of the printed matter. On the surface, the prints appear as snowflakes. In some shallowly textured editions, this problem is often encountered and is a more difficult problem. The following analysis of the cause of this problem and its solutions are provided for your reference.

1. Use chronic solvents. For example, toluene mixed with xylene or xylene alone, especially when the humidity is high, care must be taken not to use fast-drying solvents. If necessary, install a central air conditioner to control the humidity of the printing environment, or put some desiccant near the printing plate. .
2, adjust the scraper. Including the small blade pressure, the blade installed as a soft blade, the knife's angle is properly reduced, so as not to scrape the ink to scrape most of the film and can not be transferred. Or make the scraper as close to the printing plate as possible, so that the printer can adjust the ink plate, so that the area of ​​the printing plate is soaked in the ink to a large extent, so as to keep the plate surface moist. .
4, cleaning the printing plate. Carefully clean the texture with a copper wire brush and wash away the ink that is clogged inside. Use a special cleaning agent or decontamination powder when cleaning.
5, adjust the speed, so that the speed as fast as possible.
6, adjust the pressure of the imprint rubber roller, so that the pressure of the rubber roller is properly reduced.
7, adjust the ink viscosity, because too large or too small viscosity will affect the ink transfer effect.
From the aspect of plate making, we should deepen the texture system as much as possible. This is a key issue and we must ensure the quality. If not, how long it will take to print a lot of textures will reduce the amount of ink contained in the texture, and thus Affects the ink transfer effect.

From the ink point of view, it is critical to have good stickiness. If the characteristics of the ink is poor, it is difficult to achieve a good printing effect. On the other hand, new ink should be used as much as possible, because some old inks will cause the resin to separate out after repeated use for many times, so that it can hardly be adhered to the web, or it can be re-attached just after cleaning. This is easy to ignore for many people. Considerations.


(Liu Jiao)

Reprinted from: Printed in China