Common types of pigment dispersants used in coatings and their function description
Dispersant is also called wetting dispersant. In addition to its wetting effect, one end of its active group can be adsorbed on the surface of the pigment crushed into fine particles, and the other end can be solvated into the paint base to form an adsorption layer (the more adsorption groups, the more chain links) (longer, the thicker the adsorption layer), generating charge repulsion (water-based paint) or entropy repulsion (solvent-based paint), so that the pigment particles can be dispersed and suspended in the paint base for a long time to avoid re-flocculation, thus ensuring the storage stability of the made paint system. . There are many kinds of dispersants. According to preliminary estimates, there are more than 1,000 substances with dispersing effects in the world. They can be divided into the following 7 types according to their structures:
Anionic wetting and dispersing agent
Most of them are composed of non-polar negatively charged lipophilic hydrocarbon chain parts and polar hydrophilic groups. The two groups are located at both ends of the molecule, forming an asymmetric hydrophilic and lipophilic molecular structure. Its varieties include: sodium oleate C17H33COONa, carboxylate, sulfate ester salt (R—O—SO3Na), sulfonate (R—SO3Na), etc. Anionic dispersants have good compatibility and are widely used in water-based coatings and inks. Polycarboxylic acid polymers can also be used in solvent-based coatings and are widely used as controlled flocculation dispersants.
Cationic wetting and dispersing agent
It is a compound with a non-polar base and a positive charge, mainly including amine salts, quaternary ammonium salts, pyridinium salts, etc. Cationic surfactants have strong adsorption power and have good dispersion effects on carbon black, various iron oxides, and organic pigments. However, attention should be paid to its chemical reaction with the carboxyl groups in the base material, and care should be taken not to use it at the same time with anionic dispersants.
Nonionic wetting and dispersing agents
It is non-ionized and uncharged in water, and has weak adsorption on the surface of pigments. It is mainly used in water-based paints. Mainly divided into glycol type and polyol type, which reduce surface tension and improve wettability. Used in conjunction with anionic dispersants as wetting agents or emulsifiers, it is widely used in water-based color pastes, water-based coatings and inks.
Amphoteric wetting and dispersing agent
It is a compound composed of anions and cations. Typical applications are phosphate ester salt type polymers. This type of polymer has a higher acid value, which may affect interlayer adhesion.
Electrically neutral wetting and dispersing agent
The sizes of the anionic and cationic organic groups in the molecule are basically equal, and the entire molecule is neutral but polar.
Polymer hyperdispersant
Polymer nonionic dispersants are the most commonly used and have the best stability. Polymer dispersants are also divided into polycaprolactone polyester polyol-polyethyleneimine block copolymer dispersants, acrylate polymer dispersants, polyurethane, polymer polyether or polyester polymer dispersants. etc., because one end of their anchoring group is attached to the pigment particles, and the other end is entangled and adsorbed with the resin, so the storage stability is relatively good. In addition, polymer dispersants are not just simple structures of the above types, they can also be grafted and coordinated with each other to maximize their performance. For example, the core chemical dispersant Disuper S19 is widely used in industrial coatings, nano universal color pastes, inks, pigment inkjet, and resin-free color paste systems with high polarity systems such as water-based and alcohol-water systems. It has good color development and excellent anti-settling properties. Prevent color floating and have stable performance!
Controlled free radical hyperdispersant
Using the latest controlled free radical polymerization technology (CFPP), the structure of the dispersant can be made 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, etc.), NMP, SFRP (stable radical polymerization) , TEMPO, etc.��By using controlled radical polymerization technology, the relative molecular mass distribution of the dispersant can be more concentrated, the anchoring groups can also be more concentrated, and the efficiency is higher. For example, the core chemical dispersant Disuper SN36D has wide compatibility, especially excellent color development ability for colored organic pigments, and is widely used in industries such as nano universal colorants.
The role of dispersant
1. Improve the gloss and increase the leveling effect. Tests have shown that the gloss of the paint film produced by using the same formula with different dispersants will be significantly different. For example, in a black coil coating system, the 20° gloss of coating films prepared with three different dispersants are 69.7%, 81.5%, and 77.1% respectively. If the dispersant used is inappropriate and the color becomes coarse after flocculation, its effect on gloss will be similar to that of matting powder, which will naturally affect gloss.
2. Prevent color floating and blooming. Preventing color floating and blooming is one of the well-known functions of dispersants. To prevent blooming, appropriate dispersants should be used. Whether it is blooming in the tank or blooming on the paint film, it can be improved or eliminated. There are also some dispersants, which are controlled flocculation dispersants. The molecular chain contains some carboxyl groups. While being compatible with the pigment, it will also form hydrogen bonds with each other, thereby stabilizing the pigment particles and preventing floating and blooming. Effect.
3. Improve the tinting power. The pigments are better dispersed and stable, and the tinting power will be significantly enhanced.
4. Reduce the viscosity, increase the pigment loading and use appropriate dispersants. The viscosity of the resulting color paste will be significantly reduced. This can increase the amount of pigment loaded and improve production efficiency.
5. Reduce flocculation and increase workability and usability. Many people will do finger grinding tests when evaluating dispersants. If the dispersant is not properly matched, there will be a significant color difference between the finger-pulled area and the non-finger-pulled area, and the tinting strength of the flocculated pigment will decrease, which will cause difficulties in color mixing and paint construction. The flow plate test can also be used to observe whether the color paste is flocculated or not.
6. When preventing coarsening and increasing storage stability, if an inappropriate dispersant is used, the color paste will coarsen or change color due to flocculation, which is not what everyone wants. In addition to the resin system, dispersants are an important factor affecting the storage stability of coatings. Poorly dispersed color pastes will coarsen, settle, and have reduced tinting strength.
7. The role of dispersants in increasing color development and color saturation is most easily overlooked. There are examples that show that when the same pigment is dispersed using different dispersants, the hue and saturation will be significantly different. Generally speaking, the better the dispersion, the higher the saturation (if it is carbon black, the better the dispersion, the lower the L value, the higher the blackness).
8. Increase transparency or hiding power. For aluminum paint, you would hope that the transparency of the color paste should be as high as possible. For plain paint, it is hoped that the hiding power of the color paste will be as high as possible. In fact, this is related to the pigment particle size. Data shows that in addition to the refractive index, the pigment particle size distribution is another important factor in transparency. As the particle size increases, the ability to scatter light increases until it reaches a maximum value, and then begins to decrease. This ability to scatter light enhances the hiding power of the pigment, which reaches its maximum when the scattering ability is strongest. As the particle size continues to increase, the hiding power will decrease. When the pigment particle size is below a certain value, the transparency increases as the particle size decreases. Dispersants cannot change the characteristics of the pigment itself, but can control the particle size distribution of the pigment to achieve a more ideal color effect.
9. Improve grinding efficiency and reduce production costs. The wetting function of the wetting and dispersing agent enables the air and water on the surface of the pigment to be replaced more quickly by the liquid of the grinding medium, while maintaining the separation of primary pigment particles obtained in the dispersion stage. and control. These improve grinding efficiency and reduce energy consumption and labor costs.
10. To prevent subsidence, many people take it for granted that anti-settlement must rely on anti-settlement agents. In fact, this is one-sided. If the ground color paste flocculates, the pigment particles become larger and the density increases, they will settle quickly. Color pastes that use a suitable dispersant can add less or even no anti-settling agent.
