Shrinkage is one of the failures of packaging printing ink film due to poor leveling. After the ink is printed, the wet ink film shrinks during the leveling process and becomes a small circle, exposing the substrate material (bottom) or the upper ink layer. The main cause of shrinkage is the difference in surface tension between the upper and lower parts of the printed ink film. Some people think that: a wet ink film can be regarded as a liquid ink film of upper and lower 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 cavitation occurs, which is due to the wetting of the substrate material. Sometimes when this phenomenon is about to happen, the wet ink film loses fluidity and happens to suppress the occurrence of shrinkage. For example, in some gravure or iron 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 must not only be low, but also the wettability of the substrate material. Because of the difference in tension between the upper wet ink film and the lower wet ink film, after packaging and printing, the surface tension of the system drops, causing the printing ink to develop into a complete ink film. For the shrinkage hole failure, the specific methods are: ① add a leveling agent to the printing ink; ② use a solvent with low surface tension; ③ wetting the surface of the substrate (such as printing with solvent before printing) Wipe the surface of the material); ④ control the ambient temperature and humidity of the printing operation; ⑤ choose an appropriate interpreter; ⑥ reduce the surface tension between the printing ink and the printing carrier, so that the ink and the carrier have good wetting so that it will not cause Form a surface tension gradient between the material causing shrinkage); ⑦ Adjust the solvent evaporation rate, reduce the viscosity, improve the fluidity of the ink, and extend the leveling time; ⑧ form a very thin monomolecular layer on the surface of the packaging printing ink film To provide stable and uniform surface tension.

In order to choose the anti-cratering agent of printing ink correctly, the following introduces the selection of various anti-cratering agents.

Solvents: generally refers to a mixed solvent with a high boiling point, which is both a good solvent and a good pigment wetting agent (due to the volatilization of the solvent, the solubility of the ink (film-forming) body becomes poor and shrinkage occurs, or in Baking marks, blisters and other disadvantages in baked iron offset printing ink).

Resins: There are generally acetocellulose, especially polyacrylate anti-crater resins with limited compatibility. Its dosage is: acrylic resin 1% ~ 1.5%, epoxy resin 0.5% ~ 1%, polyester resin about 1%.

In addition to anti-cratering, the functions of silicone resins are also leveling, anti-floating hair, and defoaming. For example, domestic XH204 water-based silicone oil helps to promote the flow, leveling and gloss enhancement of printing ink in water-soluble acrylic ink.

In addition to the above-mentioned anti-cratering agents, there are silicon-free fluorine-based surfactants which are polymer surfactants, which are used to prevent shrinkage of the ink film, improve leveling and improve the gloss of the printing (graphic) ink film Degree is also very effective.

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

Although there are many types of them, their uses are also limited. Sometimes even the wrong dosage or improper use is not only difficult to achieve the desired effect, but sometimes also 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 varieties and the most suitable dosage. In addition, a more scientific process should be selected through batch comparison tests, even including the application method to be added during the printing process. Only in this way can we continuously improve the product quality of our country's packaging and printing products and accumulate more theoretical knowledge in practice.

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