Water-based inks, like other printing inks, are composed of colorants, binders, and ink additives. When using pigments for water-based inks, attention should be paid to the alkali resistance, relative density and pigmentation of the pigments. Sometimes, the pigment is first formed into a pigment particle aqueous dispersion, that is, a pigment color paste, and then mixed with a binder and an auxiliary agent to prepare an aqueous ink.
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.
Viscosity is the primary control indicator in ink applications because it directly affects the transfer properties of the ink and the quality of the flexographic print. The viscosity is related to the viscosity and density of the resin in the binder, and also to the type and particle size of the pigment.
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