Dispersant is also known as wetting dispersant, in addition to the wetting effect, the active group of a section can be adsorbed on the surface of the pigment crushed into fine particles, the other end of the solvation into the lacquer base to form an adsorption layer (adsorption base more, the longer the chain, the thicker the adsorption layer), charge repulsion (water-based paint) or entropy repulsion (solvent-based paint), the pigment particles dispersed suspended in lacquer base for a long time, Avoid flocculation again, thus ensuring the storage stability of the color paint system.

There are many kinds of dispersant, preliminary estimate at least 1000 kinds of substances have dispersion effect. According to its structure, it can be divided into:

★ anionic type

Most are composed of non-polar, negatively charged, oil-loving parts of the hydrocarbon chain and polar, hydrophilic groups. The two groups are located at the two ends of the molecule, forming an asymmetric hydrophilic and oilophilic substructure. Its varieties are: sodium oleate, sodium carboxylate, sulfate salt, sulfonate and so on. Anionic dispersants have good compatibility and are widely used.

★ cationic

Non-polar compounds with positive charge can be used as cationic dispersants, varieties of octadecenamine acetate, alkyl quaternary ammonium salt, aminopropylamine dioleate and so on. Cationic surfactants have strong adsorption capacity and have good dispersion effect on carbon black, various iron oxides and organic pigments. However, it should be noted that they may become ineffective due to chemical reaction with carboxyl group in the base material. At the same time, they should not be used together with anionic dispersants.

★ Non-ionic type

Can not ionize, no charge, on the surface of the pigment adsorption is weak, mainly used in water-based coatings. Varieties have fatty acid ethylene oxide admixture and so on. Their role is to reduce surface tension and improve wettability. If you add some organosiloxane you can prevent flaking, color flaking and improve leveling.

★ amphoteric

A compound consisting of anions and cations. The typical product is a phosphate ester type polymer. This kind of polymer has a high acid value, which will affect the adhesion between layers and must be paid attention to.

Electric neutral type

The size of anionic and cationic groups in the molecular structure is basically equal, and the whole molecule is neutral but has polarity. The varieties are: oil amino oleate.

★ polymer type superdispersant

Polymer dispersants are the most commonly used and have the best stability. Polymer dispersants are divided into the following categories:

① Polycaprolactone polyol - polyvinyl imide block copolymer: polycaprolactone and trivinyl tetramine reactants.

(2) Acrylate polymer: with group transfer polymerization, first add methacrylate, and then add methacrylate anhydrous glyceryl ester made of acrylate polymer.

(3) Polyurethane or polyester polymer dispersant: polyhydroxystearic acid made of low molecular weight polyester, the introduction of anchoring group made of various polyurethane and polyacrylate, because of their anchoring group a segment and resin winding adsorption, the other end and pigment particles adsorption, so the storage stability is very good. Of course, we should also pay attention not to use too strong solvent, because solvent is too strong in the case of high shear force, will dissolve these polymer super-dispersant anchoring chain, and cause pigment back coarse flocculation.

★ Controlled free radical type superdispersant

Using the latest controlled free radical polymerization (CFRP) technology, the structure of dispersant can be made more regular. The commonly used methods include GTP, ATRP(atom transfer radical polymerization), RAFT(reversible addition fracture chain transfer controllable radical polymerization, including C-RAFT and S-RAFT, etc.), NMP, SFRP (stable radical polymerization), TEMPO, etc. By using controlled free radical polymerization, the molecular weight distribution of dispersants can be more concentrated, and the anchoring group can be more concentrated and efficient.