What is a dispersant?
The surfactant that can stably disperse the solid particles in the solid-liquid suspension in the medium is called a dispersant. As the name implies, it is to reasonably disperse various powders in the solvent, and through a certain charge repulsion principle or polymer steric hindrance effect, various solids are stably suspended in the solvent (or dispersion). A dispersant is a surfactant that has two opposite properties, lipophilicity and hydrophilicity, in the molecule. It can evenly disperse the solid and liquid particles of inorganic and organic pigments that are difficult to dissolve in liquids.
What are the principles and mechanisms of dispersants?
The functions of dispersants are twofold: one is to speed up the deagglomeration of “agglomerates” and shorten the dispersion time; the other is to delay the time for particles to reagglomerate and keep the particles in a dispersed state for a long time. The molecular weight of the dispersant is large, and a large molecular weight can provide a better steric hindrance effect, prevent pigment flocculation, and keep the dispersion system in a stable state.
- Adsorb on the surface of solid particles to make the surface of condensed solid particles easy to wet.
- The polymer dispersant forms an adsorption layer on the surface of solid particles; it increases the charge on the surface of solid particles and improves the reaction force between particles that form a three-dimensional barrier.
- It forms a double-layer structure on the surface of solid particles. The polar end of the outer dispersant has a strong affinity with water, which increases the degree of wetting of solid particles by water. The solid particles are kept away from each other due to electrostatic repulsion.
- It makes the system uniform, increases the suspension performance, does not precipitate, and makes the physical and chemical properties of the entire system the same.
What is the process of pigment dispersion using dispersants?
The working principle of dispersants – dispersion is the process of evenly distributing solid particles in a dispersion liquid, and the dispersion liquid has a certain stability. The pigment dispersion process consists of three steps: wetting, dispersion, and stabilization.
Dispersion process #1: wetting. During the wetting process, the dispersant penetrates into the space of the agglomerate, and the air and moisture on the surface of the pigment are replaced by the dispersant, and the solid/gas two-phase (pigment/air) is converted into a solid/liquid two-phase (pigment, dispersant solution).
Dispersion process #2: dispersion. During the dispersion process, the pigment agglomerates are broken by mechanical energy (impact and shear force), and the particle size is reduced accordingly.
Dispersion process #3: stabilization. In the stabilization process, the dispersant is used to maintain the stability of the pigment dispersion state, prevent uncontrolled flocculation, and promote the suspension to obtain different degrees of stability according to the type and molecular structure of the dispersant adsorbed on the pigment surface.
Why is the pigment dispersion process important?
In the coating production process, pigment dispersion is a major production link. The wetting and dispersion effect of pigments has an important influence on the performance of colored coatings. It is related to the storage, construction, appearance and performance of paint films.
Well-dispersed slurry has good fluidity and small pigment particle size. When grinding slurry, the pigment content can be increased and the grinding efficiency can be improved. When applied to colored paint, it can improve the gloss and coloring effect of the paint film, make transparent pigments more transparent, and opaque pigments have better covering power, thereby relatively reducing the amount of pigment in the colored paint, which can reduce the manufacturing cost of the coating as a whole.
Therefore, the reasonable selection of dispersants is a very important production link.