The reasons for the thickening and expansion of the storage stability of PU color paste are mainly due to the poor matching or compatibility between the polarity of the particle surface of the pigment and the polarity of the dispersion medium
If the pigment is treated with lipophilic rosin resin, especially when the dosage is high, the polarity of the particle surface is reduced, and it is easier to separate from the dispersion medium and show expansion when used for PU color paste coloring. That is, the pigment particles aggregate with each other, and the colorant is precipitated and precipitated from the dispersion medium.
2. Adjust the molecular weight of the dispersant
Additives are added during the preparation of PU color paste to improve the stability of the dispersion, and the selection of additives should pay attention to the molecular weight of the additives, additives with higher molecular weight, especially additives with long fat chains and branched chains according to their spatial barrier principle help prevent the accumulation of pigment particles, thereby improving the phenomenon of thickening or expansion.
3. Surface treatment of PU pigment
Improved dispersion stability in aqueous media, or coating pigments with hydrophilic acrylic monomers, greatly reduces thickening and expansion.
In addition, when the water quality or pigment pH value is acidic, bacteria are easy to grow, which also causes agglomeration, thickening and precipitation, and agglomeration and expansion in severe cases.
