There are many kinds of dispersants, and it is estimated that there are more than 1000 substances in the world. According to its structure, it can be divided into the following seven types:
1, anionic wetting dispersant
Most of them are composed of nonpolar lipophilic hydrocarbon chains with negative charges and polar hydrophilic groups. These two groups are located at both ends of the molecule, forming an asymmetric hydrophilic and lipophilic molecular structure.
2. Cationic wetting dispersant
Nonpolar baseband positive charge compounds, mainly amine salts, quaternary ammonium salts, pyridine salts, etc. Cationic surfactant has strong adsorption and good dispersion effect on carbon black, various iron oxides and organic pigments, but it should be noted that it reacts chemically with carboxyl groups in the binder and should not be used at the same time with anionic dispersant.
3. Controllable free radical hyperdispersant
The latest controlled radical polymerization technology (CFPP) can make the structure of dispersant more regular. Commonly used methods include GTP, ATRP (atom transfer radical polymerization), RAFT (reversible addition-fragmentation chain transfer controlled radical polymerization, including C-RAFT and S-RAFT), NMP, SFRP (stable radical polymerization), TEMPO, etc.
4, nonionic wetting dispersant
It does not ionize in water, has no charge, and has weak adsorption on the surface of pigment. Mainly used for water-based coatings. Mainly divided into glycol type and polyol type to reduce surface tension and improve wettability.
5. Amphoteric wetting dispersant
It is a compound composed of anions and cations. Typical applications are phosphate polymers. This polymer has a high acid value, which may affect the adhesion between layers.
6. Electrically neutral wetting dispersant
The size of anionic and cationic organic groups in the molecule is basically the same, and the whole molecule is neutral but polar.
7. Macromolecular Hyperdispersant
Polymer nonionic dispersant is the most commonly used and has the best stability. Polymer dispersants can also be divided into polycaprolactone polyol-polyethyleneimine block polymer dispersant, acrylate polymer dispersant, polyurethane, polymer polyether or polyester polymer dispersant, etc. Because one end of their anchoring group is attached to pigment particles and the other end is entangled with resin for adsorption, their storage stability is better.
Second, what is the function of pigment dispersant?
Dispersants usually contain anchoring groups and solvated chains. The anchoring group interacts with the pigment and is adsorbed on the surface of the pigment. The solvation chain provides stability to the pigment. Generally, the stabilizing function of solvation chain is to generate charge repulsion or steric hindrance, thus preventing harmful flocculation of pigment and keeping the dispersion system in a stable state.