Dispersants are surface additives used to stabilize solid particles in media such as adhesives, paints, plastics and plastic blends.

In the past, coatings basically did not need dispersants. Systems such as alkyd and nitro paint did not need dispersants. Dispersants did not appear until acrylic resin paint and polyester resin paint. This is also closely related to the development of pigments, because the application of high-end pigments cannot be separated from the help of dispersants.
Dispersants are surface additives used to stabilize solid particles in media such as adhesives, paints, plastics and plastic blends. One end of it is a solvation chain that can be dissolved in various dispersion media, and the other end is a pigment anchoring group that can be adsorbed on the surface of various pigments and used to transform into a solid/liquid interface (pigment/resin solution).

The resin solution must penetrate the spaces between the pigment agglomerates. All pigments exist as pigment agglomerates, which are “collections” of pigment particles, with air and moisture contained in the internal spaces between the individual pigment particles. The particles are in contact with each other at the edges and corners, and the interactions between the particles are relatively small, so these forces can be overcome by ordinary dispersion equipment. On the other hand, the aggregates are more compact, and there is face-to-face contact between the individual pigment particles, so it is much more difficult to disperse them into primary particles. During the pigment dispersion grinding process, the pigment agglomerates gradually become smaller; the ideal situation is to obtain primary particles.

The pigment grinding process can be divided into the following three steps: the first step is wetting. Under stirring, all the air and moisture on the surface of the pigment are expelled and replaced by the resin solution. The dispersant improves the wettability of the pigment, turning the solid/gas interface into a solid/liquid interface and improving the grinding efficiency; the second step is the actual pigment dispersion grinding process. Through mechanical energy impact and shear force, the pigment agglomerates are broken and the particle size is reduced to primary particles. When the pigment is opened by mechanical force, the dispersant will promptly adsorb and wrap the small particle size particles; in the final third step, the pigment dispersion must be stable enough to prevent the formation of uncontrolled flocculation.

The use of a suitable dispersant can keep the pigment particles at a suitable distance from each other without restoring contact. In most applications, a stable deflocculated state is desired. In some applications, the pigment dispersion can remain stable under controlled coflocculation conditions. Wetting aids can reduce the surface tension difference between the pigment and the resin solution, accelerating the wetting of the pigment agglomerates by the resin; dispersing aids enhance the stability of the pigment dispersion. Therefore, the same product often has the functions of both wetting and dispersing aids.

Pigment dispersion is a process from aggregate to dispersed state. As the particle size decreases and the surface area increases, the surface energy of the system also increases.
Since the surface energy of the system is a spontaneously decreasing process, the more obvious the increase in surface area, the more energy is required to be applied from the outside during the grinding process, and the stronger the stabilizing effect of the dispersant is required to maintain the dispersion stability of the system. Generally, inorganic pigments have larger particle sizes, lower specific surface areas, and higher surface polarity, so they are easier to disperse and stabilize; while various organic pigments and carbon black have smaller particle sizes, larger specific surface areas, and lower surface polarity, so it is more difficult to disperse and stabilize them.

Therefore, dispersants mainly provide three aspects of performance: (1) improving pigment wetting and improving grinding efficiency; (2) reducing viscosity and improving compatibility with the base material, improving gloss, fullness and distinctness of image, and improving storage stability; (3) increasing pigment tinting strength and pigment concentration and improving color tinting stability.

Nanjing Reborn New Materials provides wetting dispersant agent for paints and coatings, including some that match Disperbyk.

In next article, we will explore the types of dispersants in different periods with the development history of dispersants.