In last article, we introduced the emergence of dispersants, some mechanisms and functions of dispersants. In this passage, we will explore the types of dispersants in different periods with the development history of dispersants.

Traditional low molecular weight wetting and dispersing agent
The earliest dispersant was triethanolamine salt of fatty acid, which was launched on the market about 100 years ago. This dispersant is very efficient and economical in general industrial paint applications. It is not impossible to use it, and its initial performance in medium oil alkyd system is not bad.

In the 1940s to 1970s, the pigments used in the coatings industry were inorganic pigments and some organic pigments that were easier to disperse. Dispersants during this period were substances similar to surfactants, with a pigment anchoring group at one end and a resin compatible segment at the other end. Most molecules had only one pigment anchoring point.

From a structural point of view, they can be divided into three categories:

(1) fatty acid derivatives, including fatty acid amides, fatty acid amide salts, and fatty acid polyethers. For example, the modified fatty acids with blocks developed by BYK in 1920-1930, which were salted with long-chain amines to obtain Anti-Terra U. There is also BYK’s P104/104S with high functional end groups based on D-A addition reaction. BESM® 9116 from Shierli is a deflocculating dispersant and a standard dispersant in the putty industry. It has good wettability, anti-settling properties and storage stability. It can also improve anti-corrosion properties and is widely used in anti-corrosion primers. BESM® 9104/9104S is also a typical controlled flocculation dispersant with multiple anchoring groups. It can form a network structure when dispersed, which is very helpful in controlling pigment sedimentation and floating color. Since fatty acid derivative dispersant raw materials are no longer dependent on petrochemical raw materials, they are renewable.

(2) Organic phosphoric acid ester polymers. This type of dispersant has a universal anchoring ability for inorganic pigments. For example, BYK 110/180/111 and BESM® 9110/9108/9101 from Shierli are excellent dispersants for dispersing titanium dioxide and inorganic pigments, with outstanding viscosity reduction, color development and storage performance. In addition, BYK 103 and BESM® 9103 from Shierli both show excellent viscosity reduction advantages and storage stability when dispersing matte slurries.

(3) Non-ionic aliphatic polyethers and alkylphenol polyoxyethylene ethers. The molecular weight of this type of dispersant is generally less than 2000 g/mol, and it focuses more on the dispersion of inorganic pigments and fillers. They can help wet the pigments during grinding, effectively adsorb on the surface of inorganic pigments and prevent the stratification and precipitation of pigments, and can control flocculation and prevent floating colors. However, due to the small molecular weight, they cannot provide effective steric hindrance, nor can they improve the gloss and distinctness of the paint film. Ionic anchoring groups cannot be adsorbed on the surface of organic pigments.

High molecular weight dispersants
In 1970, organic pigments began to be used in large quantities. ICI’s phthalocyanine pigments, DuPont’s quinacridone pigments, CIBA’s azo condensation pigments, Clariant’s benzimidazolone pigments, etc. were all industrialized and entered the market in the 1970s. The original low molecular weight wetting and dispersing agents could no longer stabilize these pigments, and new high molecular weight dispersants began to be developed.

This type of dispersant has a molecular weight of 5000-25000 g/mol, with a large number of pigment anchoring groups on the molecule. The polymer main chain provides wide compatibility, and the solvated side chain provides steric hindrance, so that the pigment particles are completely in a deflocculated and stable state. High molecular weight dispersants can stabilize various pigments and completely solve problems such as floating color and floating, especially for organic pigments and carbon black with small particle size and easy flocculation. High molecular weight dispersants are all deflocculating dispersants with multiple pigment anchoring groups on the molecular chain, which can strongly reduce the viscosity of the color paste, improve the pigment tinting strength, paint gloss and vividness, and improve the transparency of transparent pigments. In water-based systems, high molecular weight dispersants have excellent water resistance and saponification resistance. Of course, high molecular weight dispersants may also have some side effects, which mainly come from the amine value of the dispersant. High amine value will lead to increased viscosity of epoxy systems during storage; reduced activation period of two-component polyurethanes (using aromatic isocyanates); reduced reactivity of acid-curing systems; and weakened catalytic effect of cobalt catalysts in air-drying alkyds.

From the perspective of chemical structure, this type of dispersant is mainly divided into three categories:

(1) High molecular weight polyurethane dispersants, which are typical polyurethane dispersants. For example, BYK 160/161/163/164, BESM® 9160/9161/9163/9164, EFKA 4060/4061/4063, and the latest generation of polyurethane dispersants BYK 2155 and BESM® 9248. This type of dispersant appeared relatively early and has a wide audience. It has good viscosity reduction and color development properties for organic pigments and carbon black, and once became the standard dispersant for organic pigments. The latest generation of polyurethane dispersants has significantly improved both viscosity reduction and color development properties. BYK 170 and BESM® 9107 are more suitable for acid-catalyzed systems. The dispersant has no amine value, which reduces the risk of agglomeration during paint storage and does not affect the drying of the paint.

(2) Polyacrylate dispersants. These dispersants, such as BYK 190 and BESM® 9003, have become universal standard dispersants for water-based coatings.

(3) Hyperbranched polymer dispersants. The most widely used hyperbranched dispersants are Lubrizol 24000 and BESM® 9240, which are amides + imides based on long-chain polyesters. These two products are patented products that mainly rely on the polyester backbone to stabilize pigments. Their ability to handle carbon black is still excellent. However, polyester will crystallize at low temperatures and will also precipitate in the finished paint. This problem means that 24000 can only be used in inks. After all, it can show very good color development and stability when used to disperse carbon black in the ink industry. In order to improve the crystallization performance, Lubrizol 32500 and BESM® 9245 appeared one after another. Compared with the first two categories, hyperbranched polymer dispersants have a spherical molecular structure and highly concentrated pigment affinity groups, usually with outstanding color development and stronger viscosity reduction performance. The compatibility of polyurethane dispersants can be adjusted over a wide range, mainly covering all alkyd resins from long oil to short oil, all saturated polyester resins, and hydroxyl acrylic resins, and can stabilize most carbon blacks and organic pigments of various structures. Since there are still a large number of different grades between 6000-15000 molecular weights, customers need to screen for compatibility and addition amount.

Controllable free radical polymerization dispersants
After 1990, the market demand for pigment dispersion was further improved and there were breakthroughs in polymer synthesis technology, and the latest generation of controlled free radical polymerization dispersants was developed.

Controllable free radical polymerization (CFRP) has a precisely designed structure, with an anchoring group at one end of the polymer and a solvated segment at the other end. CFRP uses the same monomers as conventional polymerization, but because the monomers are arranged more regularly on the molecular segments and the molecular weight distribution is more uniform, the performance of the synthesized polymer dispersant has a qualitative leap. This efficient anchoring group greatly improves the anti-flocculation ability of the dispersant and the color development of the pigment. The precise solvated segment gives the dispersant a lower color paste grinding viscosity and a high pigment addition, and the dispersant has a wide compatibility with various resin base materials.

The development of modern coating dispersants has a history of less than 100 years. There are many types of dispersants for various pigments and systems on the market. The main source of dispersant raw materials is still petrochemical raw materials. Increasing the proportion of renewable raw materials in dispersants is a very promising development direction. From the development process of dispersants, dispersants are becoming more and more efficient. Whether it is viscosity reduction ability or color development and other abilities are improving simultaneously, this process will continue in the future.

Nanjing Reborn New Materials provides wetting dispersant agent for paints and coating, including some that match Disperbyk.