With the improvement of living standards, people have put forward higher requirements for food packaging. Ink as a printing material, when it is applied to food packaging, must adhere to the principle of no transfer. Food packaging should not use conventional inks. The printer must ensure that all the solvents in the ink after printing are volatilized. The inks require thorough curing and meet the corresponding standards in the application industry.
Alkali resistance of pigments: Pigments are materials that impart color characteristics to the ink and meet the color requirements of printing. Since the resin of the aqueous ink is mostly alkali-soluble, the viscosity and pH of the ink are precisely controlled, and the pH is generally controlled between 8.0 and 9.5. When the pH is higher than 9.5, the alkalinity is too strong, the viscosity of the ink will decrease, the monotonic speed will be slow, and the water resistance will be deteriorated; when the pH is lower than 8.0, the alkalinity will be too weak, and the viscosity of the ink will rise. The ink is easy to monotonous and will form defects such as dirty plate, paste and blistering. Therefore, pigments with excellent alkali resistance must be used when selecting pigments.
Relative density of pigments: When the relative densities of pigments for aqueous inks are very different from each other, pigments with relatively low density are simply floating on them. For example, ink-green inks are often co-colored with pigments such as carbon black and phthalocyanine blue lead chrome. The phenomenon of floating color, hair flowering, sedimentation, etc.; when the relative density of the pigment is too large, the stability of the aqueous ink is damaged due to its simple deposition and agglomeration, such as iron red, chrome yellow, etc., often because the agglomeration cannot be stirred.
Through the above analysis, it is a key link in offset printing to show that the balance of ink and water is mastered. In addition to experience, the operator is more important to master the correct use and adjustment of the offset machine water delivery mechanism.
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