As an indispensable coating additive, the main function of dispersants is to reduce the interfacial tension between liquid-liquid and solid-liquid, and improve the dispersibility of solid or liquid materials. In the latex paint system, each pigment and filler requires a certain amount of dispersant to disperse, and for a given dispersant, there will be an effective concentration range for a stable system. The lowest point in this range is called the "flow point", which represents the concentration of dispersant required to achieve the flow state of the pigment or filler wetted with water, that is, the minimum amount of dispersant required to suspend the pigment or filler.
So how should the amount of dispersant added to the coating be determined? Suitable for solvent based coatings, not very suitable for latex paints. Gradually drip the dispersant solvent into a certain amount of pigment mixture using a dropper, and carefully grind it evenly with a small scraper until the ground pigment slurry can flow down from the scraper as the endpoint. Calculate the ratio of pigment dispersant to pigment. To a thick water slurry made from a certain amount of pigment mixture, gradually add a concentrated pigment dispersant solution while stirring, and measure the viscosity with each addition. The viscosity curve for the amount of pigment dispersant, with the lowest point being the optimal amount of dispersant. This method is suitable for the water slurry itself, and there is often a shortage of dispersants in latex paint. In practical applications, it is necessary to add more (up to double). Make a thick water slurry with a certain amount of pigment mixture, gradually add pigment dispersant solution, and mix evenly until it can completely flow out from the scraper. Drip an ionic thickener onto a glass plate with a black background, and then add a drop of dispersed pigment slurry. Then gently mix well. If flocculation occurs, add pigment dispersant to the pigment slurry until no flocculation occurs. Calculate the amount of pigment dispersant used at this point based on the pigment, which is called the concentration flocculation value.
In the process of coating preparation, water-insoluble oily liquids will disperse into small droplets under high shear force stirring. After stopping stirring, they will quickly layer under the action of interfacial tension. However, by adding dispersants and stirring, a stable emulsion can be formed. The dosage of dispersant is too small, which cannot achieve the ideal dispersion effect. The particle diameter will increase, making it easy to settle and the system stable; Excessive usage can lead to increased costs and poor dissolution of dispersants.
