Different dispersants have different dispersing effects on different pigments, and the dispersion efficiency of dispersants on various pigments should be determined through a large number of experiments. How much dispersant is needed to produce the initial dispersing effect and maintain good dispersion varies widely with different pigments. Since other components are sometimes added to the final formulation (these components may destroy the dispersion state), more dispersants need to be added to keep the pigment in a dispersed state, and the amount added varies for each pigment. Taking these adverse effects into consideration, the amount of dispersant required to keep the pigment in a dispersed state is called the dispersant requirement of the pigment.
The method for determining the dispersant requirement of a pigment is the concentration-aggregation method.
The specific operation is: mix 50 g of the specific test pigment with enough water to make a wet hard paste. Add 10% dispersant in water in small batches and stir until the compound reaches a fluid state, at which point the surface wrinkles disappear with slight shaking. At this point, pour about 1 ml of the fluid mixture onto the watch glass and add 2-3 drops of 6% ionic thickener solution. If the dispersant is insufficient, flocculation, or even gelation, occurs.
Because the ionic thickener increases the ion concentration, and the long thickener molecule causes the connection between the pigment particles to form a bridging effect. If this phenomenon of flocculation occurs. This test method was repeated, increasing the amount of dispersant until no flocculation was seen on the surface. When the required amount of dispersant of the pigment is reached, all or most of the adsorption points on the pigment particles should be occupied by the dispersant molecules, and the thickener molecules have little chance to be adsorbed on the pigment particles, so as to achieve an ideal dispersion state.
The amount of dispersant in pigment should not be too much. In the case of determining P/B, there is an optimum amount of dispersant. By this point, the viscosity of the dispersant will drop significantly. When the amount of dispersant is too much, the viscosity of the coating will change greatly, and there will also be disadvantages such as loss of gloss, gel formation, decreased adhesion and decreased water resistance.
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