In recent years, China's printing industry is striving to transform into a sustainable development industry, and green printing has become the main direction of China's printing industry. Especially in the cigarette package printing industry , as the tobacco industry in China has strict requirements on the limits of various harmful substances in cigarettes and their packaging, cigarette package printing enterprises have sought green and environmentally friendly printing materials. The gravure aqueous ink uses water as the main solvent, and no VOCs are emitted during the printing process, which can improve the safety of the working environment, ensure the health of the operator, reduce the residual organic solvent of the printed product, and reduce energy consumption, thus becoming the future development of the printing industry. The inevitable direction.
However, the gravure aqueous ink is due to the use of water as the main solvent, which also brings some problems to its application, such as low printing durability of the printing plate and uneven transfer of the solid plate. Below, the author based on his own practice for many years, the main reasons and solutions for these problems and the precautions for the storage and use of gravure aqueous ink are summarized as follows, I hope to inspire and help the industry colleagues.
Analysis of common problems
Shadow (fog version) phenomenon
The main reason: the friction coefficient of the gravure aqueous ink is higher than that of the solvent type ink, the blade is easy to wear, or the surface tension of water is large, and the affinity with the metal is high, which causes the blank part of the printing pattern to be scraped due to the corresponding position of the printing plate. Clean and accompanied by a touch of color, the phenomenon of shadow (fog).
Solution: 1 Use a blade with better wear resistance when printing, and increase the blade pressure appropriately during the printing process; 2 Add a blowing device between the blade and the platen roller; 3 Polish the plate; 4 Use ethanol to reduce the concave The viscosity of printing water-based inks.
2. The printing plate has low printing durability
Main reasons: 1 scraper and pressure are not used properly; 2 plate chrome layer hardness is not enough; 3 printing quality problems, resulting in excessive plate grinding; 4 water on the plate (metal) caused some corrosion.
Solution: 1 Standardize the operation method of the operator, improve its operation technology level and reduce the production quality problem; 2 It is recommended that the plate making factory improve the hardness of the plate chrome layer; 3 The replaced plate should be cleaned and stored in a ventilated environment. .
3. The field version is not smooth
Main reasons: 1 gravure aqueous ink with water as the main solvent, the surface tension of water is large, which makes it difficult for the gravure aqueous ink to wet and level on the surface of the substrate; 2 after the printing product enters the oven, the surface of the gravure aqueous ink is dried quickly. In the conjunctiva, the water in the membrane is temporarily closed, but when it continues to be heated, water vapor is formed to escape outward. When the energy is large enough, the ink film can be broken, thereby forming a white point similar to the crater on the surface of the ink film. ; 3 The pH value of the gravure aqueous ink changes during the printing process, resulting in uneven transfer.
Solution: 1Requires the ink supplier to reduce the surface tension of the gravure aqueous ink, so that the gravure aqueous ink can be fully wetted and leveled on the surface of the substrate, and the transfer is more flat; 2. Appropriately improve the gravure water quality during the printing process. Ink viscosity, at the same time reduce the oven temperature, increase the amount of blowing, reduce the printing speed, ensure that the gravure ink is dry thoroughly; 3 each time the ink must be filtered, while strictly controlling the viscosity of the ink; 4 printing process should be used in a small number of ways Add new ink to ensure the stability of the pH of the gravure aqueous ink.
4. Paste (block) version, the layout color is inconsistent
Main reasons: 1 ink tank, ink tank, scraper holder mixed with other ink impurities; 2 gravure aqueous ink added solvent-based ink or other solvent; 3 scraper angle adjustment is not appropriate; 4 scraper does not lift after shutdown, not let The printing plate is idling; 5 the pH of the ink is too small, resulting in an increase in viscosity; 6 plates are severely worn, and the cells are shallow; 7 plates are less immersed in the ink.
Solution: 1 The ink tank, ink tank and scraper frame must be thoroughly cleaned before printing with gravure water-based ink; 2 must be filtered when refilling
Ink; 3 scraper angle must be carefully adjusted, the angle should be appropriate, the pressure can not be too large; 4 after the shutdown, the scraper should be lifted to make the plate idling; 5 the plate must be cleaned before starting the plate, the plate must be removed when the paste is serious. After soaking with ethyl acetate or washing powder, rinse it clean; 6 new ink should be added in a small amount in the printing process, and the new ink viscosity must be adjusted to the printing viscosity when adding ink, and then slowly added.
5. Water pattern (bubble) phenomenon
The main reasons are: 1 the water content in the ink is too high; 2 the ink volume in the ink cylinder is small; 3 the ink tank stirring speed is too fast; 4 the ink viscosity is too low.
Solution: 1 Add antifoaming agent or ethanol to increase the viscosity of the ink; 2 Increase the amount of ink in the ink tank, raise the ink tank, so that the printing plate can be more immersed in the ink; 3 Reduce the stirring speed of the ink cylinder; 4 Add an ink transfer roller or add a stir bar in the ink tank.
6. Dot increase phenomenon
The gravure aqueous ink has a slow drying speed and is prone to dot gain, especially when printing small characters and lines, and the small text and lines tend to become thicker. In this regard, fine text and lines need to be thinned during plate making.
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