1, Water is used as the dispersion medium, and the system is weakly alkaline, so the coloring agent should have good stability in water.
2, Most of the film-forming macromolecules of water-based coatings contain -COOH group, which can be dissolved by the action with organic amine. If the colorant is acidic or alkaline, it will affect the dispersion stability of the system, and coalescence or saponification will occur; especially, it is not suitable to use certain inorganic pigments (acid-prepared titanium dioxide, zinc oxide, lead white, etc).
3, When choosing two or more colorants for coloring, the relative density should be close to each other to prevent floating color or precipitation phenomenon.
4, In order to improve the dispersion stability of water-based paint, the surface modification treatment of pigment for coloring should be implemented, such as compounding with anionic and non-ionic surfactants to improve the pro-media characteristics of pigment.
5, The pigments for emulsion paint coloring should be treated by surface treatment to increase their hydrophilicity, including inorganic pigments with high polarity, such as titanium dioxide, paraffin based emulsion, which can improve the stability of dispersion, organic pigments such as phthalocyanines and azo species can also be treated by anionic and nonionic surfactants compounded with methyl cellulose, or the ammonium salt of polymer type compounds, such as styrene-maleic anhydride copolymer, can be used as a treatment agent.
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