3.Relationship between molecular weight and dispersion performance and compatibility
The molecular weight of the polymer-type wetting and dispersing agent must be within a reasonable range. If the molecular weight is too low, the additive is similar to a surfactant and has poor stability in pigment dispersion. However, if the molecular weight is too high, problems such as excessive viscosity and intertwined long chains may occur, which is not conducive to pigment dispersion.

It is well known that dispersants have two basic components, namely pigment affinity groups and system compatible segments. Therefore, generally speaking, an increase in molecular weight corresponds to a longer segment of the pigment affinity portion and / or a system compatible segment. The former usually means more pigment affinity groups, and therefore the adsorption of pigment particles is more Is strong and durable; after the latter is fully extended in a compatible system, a polymer protective layer can be formed on the surface of the pigment particles, and the thickness of this protective layer is similar to that of the compatible segments in the dispersant length. Therefore, it is not difficult to understand that within a reasonable molecular weight range, a common phenomenon is that the dispersion stability of dispersants for organic pigments and carbon black increases with the increase of molecular weight, but the problem it may bring is dispersion. The compatibility of the agent with the dispersion system will decrease as the molecular weight increases. Scott's equation based on the theory of the Flory-Huggins lattice model can quantify this phenomenon.

4.New varieties of high molecular weight wetting and dispersing agents-CPT polymers
Common high-molecular-weight wetting and dispersing agents for dispersing organic pigments and carbon blacks are classified by chemical structure, mainly including polyurethane, acrylate, and highly branched polyamines. Among them, acrylate-based dispersants have different synthetic technologies at different periods. They can be roughly divided into two categories, namely random radical polymerization technology and controlled polymerization technology (CPT, Controlled Polymerization Technologies).

Controllable polymerization technology is also called living polymerization technology. It first started with anionic polymerization technology discovered in the 1950s, but it was not until the discovery of the group transfer polymerization method of one of the controllable polymerization technologies in the 1980s. The door to industrial applications. In the 1990s, the emergence of various forms of living radical polymerization technology brought the development of controllable polymerization technology to a new level. Controllable polymerization has become easier and easier to implement, manufacturing costs have been drastically reduced, and its applications are becoming more and more popular. Therefore, the controllable polymerization technology includes different types of polymerization technologies found in different periods, and this technology can only be applied to the polymerization of acrylic monomers.

When random radical polymerization is used for polymer polymerization, the reactions of the individual polymer chains cannot be guaranteed to proceed simultaneously and remain synchronized, so the reactions of each polymer chain come first, and some polymer chains have lost their activity during the reaction. At the same time, other polymer chains are still active. The resulting polymer product is a random copolymer, and the positions of various monomers in the polymer are randomly distributed. Therefore, this method cannot locate special functional groups or polarities in the polymer chain, nor can it obtain structured polymers, such as block copolymers or gradient copolymers. The molecular weight of each molecule varies widely, and the molecular weight distribution is wide. Generally, the polydispersity coefficient is greater than 2.

More importantly, many CPT wetting and dispersing additives have high dispersing properties, such as being particularly suitable for dispersing organic pigments and carbon black and other difficult-to-disperse pigments. The following figure is the comparison result of the blackness of different types of dispersants dispersing FW200 in the solvent-based 2KPU system.

Controllable polymerization technology is limited to acrylic polymers. It is a supplement to traditional polymerization technology. This new type of synthesis technology can use the same raw materials to obtain higher performance wetting and dispersing agent products, which meets the production of coatings. Manufacturers address the formulation requirements for more and more different use cases.

In addition, there is a special class of pigment derivatives that can be used as synergists for the various wetting and dispersing agents mentioned above to help improve the dispersion properties of organic pigments and carbon black. The role of such additives is usually to reduce the viscosity of abrasives And to improve the appearance of the paint film, such as transparency, gloss, haze, etc.

in conclusion
The dispersion of organic pigments and carbon black pigments is more challenging than inorganic pigments. High molecular weight types of wetting and dispersing agents must be used. At the same time, good compatibility between the dispersing agent and the binder system must be ensured. The latest high molecular weight wetting and dispersing agent synthesis technology is a controllable polymerization technology applied to the polymerization of acrylate monomers. This technology can use the same monomer raw materials to synthesize new dispersant products with better performance, and then improve the coatings Performance to meet the various needs of the market.