On the basis of maintaining the same printing quality as solvent-based inks, a good water-based gravure printing ink must achieve zero VOC emissions; it must have good printability; be able to print on the surface of various substrate materials; at the same time It is hoped that the cost of this printing ink is relatively low.
The use of water-based gravure printing ink will cause problems such as changing the engraving of the gravure printing roller, changing the operation of the printing press, maintenance of the printing press, and replacement of the dryer. Similarly, the substrate material will also strongly affect the printing effect of ink, especially for the printing of low surface tension substrates such as plastic film materials and coated paper surfaces. For non-coated paper, water ink may even cause deformation and curling of the paper. These problems do not exist for solvent-based gravure printing inks.
The importance of PH value of water-based gravure printing ink:
Comparing water-based and solvent-based gravure printing inks, in the process of scraping the excess ink from the printing ink holes of the gravure, the gravure printing process using solvent-based ink printing should minimize the volatilization of the solvent. After the process is completed, the ink is transferred to the substrate material, and then the ink film is slowly formed. In this process, the solvent in the ink must complete the volatilization process before the ink film is adhered to quickly reach the drying of the ink film. In water-based inks, organic solvents are replaced with a certain percentage of water, co-solvents, and volatile amines, which are necessary to neutralize acidic resins. Due to the slow water volatility, there is no problem of water volatile drying in the ink hole of the printing plate, but there is a problem of drying after printing. Therefore, the selection of amines in water ink, the adjustment of PH value and the control of ink viscosity As important. Because the premature release of the amine solvent before the completion of the imprinting process will cause the pH value to drop, causing the resin to dry in the ink hole of the gravure printing cylinder. In addition, water and co-solvent systems cannot re-dissolve the resin, which is different from solvent-based inks. Therefore any re-dissolution is possible if the pH value drops. In gravure printing, the PH value should be controlled very carefully, because the drop of the ink PH value causes the ink hole to be slowly blocked until it is completely blocked. This is a very serious problem and will cause the printing operation to continue.
The importance of surface tension of water-based gravure printing ink:
At the same time, the surface tension of the ink is also an unavoidable factor, which is completely different from the solvent ink. Compared with solvent-based inks, the surface tension of water ink is much higher; and too high surface tension will cause the water ink to not wet the surface of the substrate material well and the ink hole of the gravure printing roller, which will cause the printing ink film to fail. Uniform; due to the high surface tension of the ink, the ink film will shrink on the surface of the substrate, causing the ink film to show a clear mesh, and it will also cause the ink to not be uniformly transferred from the ink hole to the surface of the substrate.
However, the surface tension can be reduced, which requires careful selection of the appropriate surfactant or a small amount of alcohol. Although it takes a lot of work to develop printing ink for printing plate, while maintaining the printing quality of printing ink (as the printing quality of solvent-based ink), it is still a difficult challenge to completely reduce the VOC emission of ink in gravure printing.
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