Causes and remedial measures of shrinkage holes in printing ink film
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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 retracts into a small circle during the leveling process, exposing the substrate material (bottom) or the previous ink layer. The main reason for the occurrence of shrinkage cavities is that the surface tension of the upper and lower portions of the printed ink film is different. Some people think that a wet ink film can be regarded as a liquid film of upper and lower double layers. In the film formation process, when the surface tension of the upper wet ink film is lower than the surface tension of the lower wet ink film, shrinkage cavities occur due to the relationship of the wet 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 the wettability of the substrate material. Because of the poor tension at the interface between the upper wet ink film and the underlying wet ink film, the surface tension of the system is reduced after the package printing, so that the printing ink is self-developed into a complete ink film. For the shrinkage failure caused by this, the specific method is: 1 to properly add a leveling agent in the printing ink; 2 to use a solvent with a low surface tension; 3 to wet the surface of the substrate (such as printing with a solvent before printing) The surface of the material is wiped; 4) control the ambient temperature and humidity of the printing operation; 5 select a suitable interpreting agent; 6 reduce the surface tension between the printing ink and the carrier, so that the ink and the carrier have good wettability, so as not to cause Forming a surface tension gradient between the substance causing the shrinkage cavity); 7 adjusting the solvent evaporation rate, lowering the viscosity, improving the fluidity of the ink, and prolonging the leveling time; 8 forming a very thin monolayer on the surface of the packaging printing ink film To provide a stable and uniform surface tension.
In order to properly select the anti-cratering agent for printing inks, the following describes the selection of various anti-cratering agents.
Solvents: generally refers to a high-boiling mixed solvent, which is both a good solvent and a good humectant for pigments (the solubility of the ink (film-forming) body is deteriorated due to solvent volatilization, resulting in shrinkage cavities, or Boiled iron offset printing inks produce boiling marks, blistering and other drawbacks).
Resin type: Generally, there is acetaminophen cellulose, especially a polycondensation-preventing resin of a compatibility-limited polyacrylate type. The amount is: 1% to 1.5% of acrylic resin, 0.5% to 1% of epoxy resin, and about 1% of polyester resin.
In addition to anti-cratering holes, silicone resins also have the functions of leveling, anti-floating, and defoaming. For example, domestic XH204 water-based silicone oil helps to promote the flow, leveling and brightness enhancement of printing inks in water-soluble acrylic inks.
In addition to the above-mentioned anti-cratering agent, there is also a silicon-free fluorine-based surfactant which is a polymer surfactant, which prevents the shrinkage of the ink film, enhances the leveling and improves the gloss of the printing (graphic) ink film. Degree is also very effective.
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 and decoration. The purpose of using different anti-cratering and leveling agents is to improve the printing quality and to extend the printing (surface ink film) grade.
Although they have many types of varieties, their 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 before use, different varieties and dosages should be strictly screened and tested to find the best variety and optimum dosage. In addition, more scientific processes should be selected through batch comparison tests, including even adding application methods in the process to be printed. Only in this way can we continuously improve the product quality of China's packaging and printing products, in order to accumulate more theoretical knowledge in practice.