Common types of pigment dispersants for coatings and their functions
Dispersant is also called wetting and dispersing agent, which has the function of wetting, and one end of its active group can be adsorbed on the surface of pigment crushed into fine particles, and the other end can be solventized into the paint base to form an adsorption layer (the more adsorption groups, the longer the chain link, the thicker the adsorption layer), which can produce 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, avoiding flocculation again, thus ensuring This ensures the storage stability of the finished paint system. There are many kinds of dispersants, preliminary estimate, there are more than 1000 kinds of substances with dispersing effect in the world, according to their structure, can be divided into the following 7 types:
Anionic wetting and dispersing agent
Most of them are composed of non-polar negatively charged hydrocarbon chains and polar hydrophilic groups. 2 kinds of groups are at the two ends of the molecule, forming an asymmetric hydrophilic and oleophilic molecular structure. It has the following varieties: sodium oleate C17H33COONa, carboxylate, sulfate (R-O-SO3Na), sulfonate (R-SO3Na), etc. Anionic dispersants have good compatibility and are widely used in aqueous coatings and inks. Polycarboxylic acid polymers etc. can also be applied to solvent-based coatings and are widely used as controlled flocculation type dispersants.
Cationic wetting and dispersing agents
They are compounds with positive charge of non-polar group, mainly amine salts, quaternary amine salts, pyridinium salts, etc. Cationic surfactants have strong adsorption power and have better dispersing effect on carbon black, various iron oxides and organic pigments, but it should be noted that they react chemically with the carboxyl group in the base material and should not be used simultaneously with anionic dispersants.
Non-ionic wetting and dispersing agent
They do not ionize in water, do not carry charge, and are weakly adsorbed on the surface of pigments, and are mainly used in aqueous coatings. It is mainly divided into glycol and polyol type, which can reduce surface tension and improve wettability. Used with anionic dispersants as wetting agent or emulsifier, it is widely used in aqueous color paste, aqueous coatings and inks.
Amphoteric type wetting and dispersing agent
It is a compound composed of anion and cation. Typical applications are phosphate ester salt type polymers. These polymers have high acid values, which may affect interlayer adhesion.
Electrically neutral wetting and dispersing agents
The size of the anionic and cationic organic groups in the molecule is basically equal, and the whole molecule appears neutral, but is polar.
Polymer type hyperdispersants
Polymeric non-ionic dispersants are most commonly used and have the best stability. Polymeric dispersants are also divided into poly(caprolactone) polyol-poly(vinylimine) block copolymer dispersants, acrylate polymeric dispersants, polyurethane, polymeric polyether or polyester polymeric dispersants, etc. Since their anchoring groups are attached to the pigment particles at one end and entangled with the resin at the other end, the storage stability is better. In addition, polymer dispersants are not only the above types of structures, they can also graft and cooperate with each other to achieve the best performance. For example, the core chemical dispersant Disuper S19 is widely used in water-based, alcoholic water and other high polarity systems of industrial coatings, nano general color paste, ink, pigment inkjet, resin-free color paste system, good color spreading, excellent anti-sink performance, prevent floating color, stable performance!
Controlled free radical type hyperdispersant
The latest controlled free radical polymerization technology (CFPP) can make the structure of dispersant more regular. Commonly used methods are: GTP, ATRP (atomic transfer radical polymerization), RAFT (reversible addition breakage 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 dispersants can be more concentrated, and the anchoring groups are also more concentrated and more efficient. For example, the core chemical dispersant Disuper SN36D is widely compatible and has excellent color spreading ability especially for colored organic pigments, which is widely used in nano universal color paste and other industries.
The role of dispersant
1、Improve the gloss and increase the leveling effect Some tests show that the exact same formula, using different dispersants, the resulting paint film gloss will have a significant difference. For example, in the black coil coating system, different 3 dispersants produced by the coating film of 20 ° gloss were 69.7%, 81.5%, 77.1%. If the dispersant used is not appropriate, the color flocculation becomes coarse, its role on the luster is similar to the matting powder, which will naturally affect the luster.
2, to prevent floating color flowering to prevent floating color flowering, is one of the well-known role of dispersant. To prevent floating color blossoms, you should choose the right dispersant, whether it is floating color blossoms in the tank or floating color blossoms in the paint film, can be improved or eliminated. There are also some dispersants, which are controlled flocculation type dispersants, with some carboxyl groups in the molecular chain, which will form hydrogen bonds with each other while affinity with the pigment, thus making the pigment particles stable and achieving the effect of preventing floating color bloom.
3、Improve coloring powerThe pigment is better dispersed and stabilized, and its coloring power will be obviously strengthened.
4、Lower viscosity, increase the pigment loading using the appropriate dispersant, the viscosity of the resulting color paste will be significantly reduced. This can increase the loading amount of pigment and improve the production efficiency.
5、Reduce flocculation, increase constructability and usability Many people will do finger study tests when evaluating dispersants. If the dispersant is not properly matched, the area of finger study and the area of no finger study will produce obvious color difference, and the pigment coloring power will be reduced after flocculation, which will bring difficulties to color mixing and paint construction. Using flow plate test, can also observe the flocculation of the color paste or not.
6、Prevent coarse and increase storage stability, if you choose unsuitable dispersant, color paste coarse or color change due to flocculation is not what you want. In addition to the resin system, dispersant is an important factor affecting the storage stability of coatings. Poorly dispersed color paste will be coarse, sink and coloring power decline.
7、Increase color spreading and color saturation, this role of dispersant is most easily ignored. There are examples that show that the use of different dispersants to disperse the same pigment, the color phase and saturation will have a significant difference. Generally speaking, the better the dispersion, the higher the saturation will be (in the case of carbon black, the better the dispersion, the lower the L value, the higher the blackness).
8、Increase transparency or coverage For aluminum powder paint, you will hope that the higher the transparency of the color paste, the better. And for plain paint, the higher the covering power of the color paste, the better. In fact, this is related to the pigment particle size. Some information shows that, in addition to the refractive index, the pigment particle size distribution is another important factor of transparency. As the particle size increases, the ability of scattering light increases until the maximum value, and then starts to decrease. This ability to scatter light enhances the covering power of the pigment and reaches the maximum when the scattering ability is strongest, and the covering power decreases when the particle size continues to increase. When the pigment particle size is below a certain value, the transparency increases as the particle size decreases. Dispersing agent can not change the characteristics of the pigment itself, but can control the pigment particle size distribution to achieve a more ideal color effect.
9、Improve grinding efficiency and reduce production cost The wetting function of the wetting dispersant enables the air and water on the surface of the pigment to be replaced by the liquid of the grinding medium more quickly, while the separation of the primary particles of the pigment obtained in the dispersion stage is maintained and controlled. All these improve the grinding efficiency and reduce the energy and labor cost.
10、Prevent sinking Many people take it for granted that anti-sink must rely on anti-sinker, in fact, this is one-sided. Grinding good color paste if the flocculation, pigment particles become larger, the density increases, it will quickly sink. The selection of a suitable dispersant color paste can add less or even do not need to add anti-settling agent.
