Treatment of shrinkage in packaging printing

Shrinkage is one of the failures of packaging ink film due to poor leveling. After the ink is printed, the wet ink film retracts in the process of leveling and becomes a small circle, exposing the substrate material (bottom) or the upper ink layer. The main reason for shrinkage is that the surface tension of the upper and lower parts of the printed ink film is different. Some people think: a wet ink film can be regarded as a double liquid ink film. 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 occurs due to the wet material material relationship. Sometimes when the phenomenon is about to occur, the wet ink film loses its fluidity and happens to suppress the shrinkage phenomenon. For example, in some gravure or offset printing operations, the wet film may become fluid as the temperature increases, which may cause secondary shrinkage.

In theory: The remedial measures are 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 there is a tension difference at the interface between the upper wet ink film and the lower wet ink film, after the package is printed, the surface tension of the system is decreased, so that the printing ink will develop into a complete ink film from the development. The shrinkage failure caused by this, the specific approach is: 1 in the printing ink appropriate to add leveling agent; 2 the use of low surface tension solvents; 3 on the surface of the substrate wetting treatment (such as printing with solvent before printing The surface of the material is rubbed); 4 the environmental temperature and humidity of the printing operation are controlled; 5 the appropriate interpreter is selected; 6 the surface tension between the printing ink and the printing substrate is reduced, so that the ink and the carrier have good wettability so that it does not cause Forms a surface tension gradient between the material that causes the shrinkage cavity); 7 Adjusts the solvent evaporation rate, reduces the viscosity, improves the fluidity of the ink, and prolongs the leveling time; 8 forms an extremely thin monolayer on the ink film of the packaging printing ink. To provide stable and even surface tension.

In order to correctly select the anti-crater agent for printing ink, the following describes various types of anti-crater agents.

Solvents: Generally referred to as high-boiling mixed solvent, it is not only a good solvent, but also a good wetting agent for the pigment (caused by volatilization of the solvent, the solubility of the ink (film-forming) body becomes poor, resulting in shrinkage, or Bake marks, blisters and other defects occur in baked iron offset inks.

Resins: Acetylcellulose is generally used, especially polyacrylate-resistant shrink-resin resins with limited compatibility. The dosage is: 1% to 1.5% of acrylic resin, 0.5% to 1% of epoxy resin, and 1% of polyester resin.

Silicone resins have the function of anti-shrinkage, leveling, anti-floating, and defoaming. For example, domestic XH204 water-based silicone oil helps to promote the flow, leveling, and brightening of printing inks in water-soluble acrylic inks.

In addition to the above-mentioned anti-crater agents, there are silicone-free fluorine-based surfactants that are high molecular surfactants, which prevent shrinkage of the ink film, promote leveling, and improve the luster of the ink (printing). The degree is also very effective.

The prevention of the shrinkage of the ink film of the packaging printing ink is an important measure to improve the effect of the ink on the decoration of the packaging printing and decoration. The purpose of using different anti-shrinkage holes and leveling agents is to improve the printing quality and to extend the printing (surface ink film) grade.

Although their types are numerous, their uses are limited. Sometimes even improper use or improper use, not only difficult to achieve the desired effect, and sometimes will bring side effects.

Years of practice have proved that before use, different varieties and quantities should be screened and tested strictly to find the best variety and the most suitable amount. In addition, it is also necessary to select more scientific process flow through batch comparison tests, and even include adding application methods during the printing process. Only in this way can we continuously improve the product quality of packaging and printing products in China so as to accumulate more theoretical knowledge in practice.