Water-based inks are  composed of colorants, linking materials and ink additives. When choosing pigments for water-based inks, attention should be paid to the alkali resistance of the pigments, relative density and the matching of pigments. Sometimes the pigment will be made into paste, and then mixed with the linking material and additives to make  into water-based ink.

    The note on the selection of pigment in water-based ink:

    (a) The alkali resistance of pigment

    pigment is to make ink colorful to meet the printing requirements of the  material. As most of the water-based ink link resin is alkali-soluble, the viscosity and pH value of the ink needs to be precisely controlled, the pH value is generally controlled between 8.0 ~ 9.5. When the pH value is higher than 9.5, the alkali is too strong, the viscosity of the ink will be reduced, so that the drying speed becomes slower, water resistance  becomes worse; and when the pH value is lower than 8.0, the alkali is too weak, the viscosity of the ink will rise, the ink is easy to dry, will cause dirty plate, paste plate and blistering and other defects. Therefore, the choice of pigments must use good alkali-resistant pigments.

    (B) The relative density of pigment

    The pigment relative density in water-based ink  is very different from each other. If the relative density of pigment is small,it is easy to float on the ink. for example, dark green water-based ink often mix carbon black, phthalocyanine blue lead chromium yellow pigment, it is easy to produce floating, flowering, precipitation and other phenomena; If the pigment relative density is too large, it is easy to precipitate clumps and destroy the stability of water-based ink.

    (C) The combination of pigments

    Different physical and chemical properties of pigment fillers, such as relative density, acidity and alkalinity, polarity and crystallization are not the same. Therefore, in the process of manufacturing ink,The difference of pigments, fillers in their physical and chemical properties. It is easy to appear pigment precipitation, floating color and other phenomena if storage time is long. Therefore, the pigments and fillers used in the production of ink should be as little as possible. 

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