Reasons and remedial measures for printing ink film shrinkage
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The shrinkage hole is one of the failures of the printed printing ink film due to poor leveling. After the ink is printed, the wet ink film is retracted during the leveling process and becomes a small circular exposed substrate material (bottom) or a layer of ink. The main reason for the shrinkage hole is to print the upper and lower portions of the wet ink film. The surface tension is different. Some people think that a wet ink film can be regarded as a double-layer liquid ink film. During the film forming process, when the surface tension of the upper wet ink film is lower than the surface tension of the lower wet ink film, shrinkage occurs. Holes, which are due to the relationship between the wetted substrate material. Sometimes when this phenomenon is about to occur, the wet ink film loses fluidity and happens to suppress the occurrence of shrinkage. For example, in some gravure or offset printing operations, the wet ink film has fluidity as the temperature rises, which may cause secondary shrinkage.
In theory: the remedy is to improve the flow and leveling of the wet ink film. The surface tension of the ink is not only low, but also has a low surface tension and good wettability to the substrate material. Because of the difference in interfacial tension between the upper wet ink film and the underlying wet ink film, once the package is printed, the surface tension of the system is lowered, so that the printing ink is self-developed into a complete ink film. For the shrinkage failure caused by this, our specific method is: 1 appropriate addition of leveling agent in the printing ink; 2 using a solvent with low surface tension; 3 wetting the surface of the substrate (such as solvent before printing) The surface of the substrate material is wetted and wiped; 4) control the ambient temperature and humidity of the printing operation; 5 select a suitable diluent; 6 reduce the surface tension between the printing ink and the carrier, so that the ink and the carrier have good wettability So that it does not form a surface tension gradient with the substance causing the shrinkage cavity; 7 adjust the evaporation rate of the solvent, reduce the viscosity, improve the fluidity of the ink, and prolong the leveling time; 8 form a very thin surface on the surface of the packaging printing ink film A monolayer to provide a stable and uniform surface tension.
In order to properly select the anti-cratering agent for printing ink, the following various materials are introduced for the operator to choose.
Solvents: generally refers to a high-boiling mixed solvent, which is both a good solvent and a good wetting agent for pigments. (The film is formed by the evaporation of the solvent, the solubility of the system is deteriorated to cause shrinkage, or baking. Boiled iron offset printing inks produce boiling marks, blistering and other defects).
Resin type: Generally, there is a butyl cellulose acetate, especially a polyacetal-resistant anti-crater resin of a compatible type. The amount is: 1% to 1.5% of acrylic resin, 0.5% to 1% of epoxy resin, and about 1% of polyester resin.
There are also silicone resins, which function in addition to anti-cratering holes, as well as leveling, anti-floating, and defoaming. For example, domestic XH204 water-based silicone oil can help promote the flow, leveling and brightness enhancement of printing inks in water-soluble acrylic inks.
In addition to the anti-cratering agents exemplified above, there are also silicon-free fluorine-based surfactants which are polymeric surfactants. It is also effective for preventing shrinkage of the ink film, improving leveling, and improving the gloss of the printed ink film.
Preventing the shrinkage of the ink film of the packaging printing ink is an important measure to improve the effect of the ink on the packaging, decoration and decoration. The purpose of using different anti-cratering and leveling agents is to improve the printing quality and extend the printing (surface ink film) grade. Although it has many types of varieties, its use is limited. Sometimes even improper use or improper use is not only difficult to achieve the desired effect, but sometimes brings side effects.
Years of practice have proved that different varieties and dosages should be rigorously screened and tested before use to determine the best variety and optimum dosage. In addition, batch-scale comparison tests should be carried out on the added process, and more scientific processes should be selected, including even adding application methods in the post-printing process. Only in this way can we continuously improve the quality of our products in packaging and printing products. Only in this way can we accumulate more theoretical knowledge in practice.