Pigment wetting and dispersing agent: also known as wetting and dispersing agent, it has a wetting effect. One end of its active group can adsorb on the surface of the pigment crushed into small particles, and the other end solvates into the paint base to form an adsorption layer (the more adsorption groups, the longer the chain links, and the thicker the adsorption layer), generating charge repulsion (water-based coatings) or entropy repulsion (solvent based coatings), dispersing and suspending pigment particles in the paint base for a long time, avoiding re coagulation, thus ensuring the storage stability of the produced paint system.
There are many types of dispersants, and preliminary estimates suggest that there are over 1000 substances in the world that have dispersing properties. According to its structure, it can be divided into the following 7 types.
Anionic wetting and dispersing agent
Most of them are composed of non-polar negatively charged lipophilic hydrocarbon chain segments and polar hydrophilic functional groups. Two types of functional groups are located at both ends of the molecule, forming an asymmetric hydrophilic and oleophilic molecular structure. Its varieties include sodium oleate C17H33COONa, carboxylate salts, and sulfate salts (R—O—SO3Na)、 Sulfonate salt (R&SO3Na, etc. Anionic dispersants have good compatibility and are widely used in water-based coatings and inks. Polycarboxylate polymers can also be applied to solvent based coatings and widely used as controlled flocculent dispersants.
Cationic wetting and dispersing agent
It is a compound with a non-polar base positive charge, mainly including amine salts, quaternary amine salts, pyridinium salts, etc. Cationic surfactants have strong adsorption capacity and good dispersion effect on carbon black, various iron oxides, and organic pigments. However, attention should be paid to their chemical reaction with carboxyl groups in the base material, and they should not be used together with anionic dispersants.
Non ionic wetting and dispersing agent
Non ionizing and uncharged in water, with weak adsorption on pigment surfaces, mainly used in water-based coatings. It is mainly divided into ethylene glycol and polyol types, which reduce surface tension and improve wettability. Used in combination with anionic dispersants as wetting agents or emulsifiers, it is widely used in water-based colorants, water-based coatings, and inks.
Amphoteric wetting and dispersing agent
It is a compound composed of anions and cations. The typical application is high molecular weight polymers of phosphate ester salt type. This type of polymer has a high acid value, which may affect interlayer adhesion.
Electric neutral wetting and dispersing agent
The size of anionic and cationic organic groups in the molecule is basically equal, and the entire molecule appears neutral, but it has polarity. Oil amino oleate esters such as C18H35NH3OOCC17H33 belong to this type and are widely used in coatings.
Polymer based hyperdispersant
Polymer dispersants are the most commonly used and have the best stability. Polymer dispersants are also divided into poly (ε - caprolactam) - poly (ethylene imine) block copolymer dispersants, acrylic polymer dispersants, polyurethane or polyester polymer dispersants, etc. Due to their anchoring groups being entangled and adsorbed on one end of the resin and encapsulated on the other end with pigment particles, their storage stability is relatively good.
Controlled radical type hyperdispersant
By adopting the latest controlled radical polymerization technology (CFPP), the structure of dispersants can be made more regular. Common methods include GTP, ATRP (atom transfer radical polymerization), RAFT (reversible addition cleavage chain transfer controlled radical polymerization, including C-RAFT and S-RAFT), NMP, SFRP (stable radical polymerization), TEMPO, etc. By using controlled radical polymerization technology, the relative molecular weight distribution of dispersants can be more concentrated, and the anchoring groups can also be more concentrated, resulting in higher efficiency.
