Introduction of four types of hyperdispersants and analysis of its mechanism

What is a hyperdispersant?

Hyperdispersant, also known as super dispersant, a special surfactant, has a molecular structure containing two groups that are opposite in solubility and polarity, one of which is a shorter polar group called a hydrophilic group. Its molecular structure makes it easy to orient it on the surface of the material or the interface of the two phases, reducing the interfacial tension and having a good dispersion effect on the aqueous dispersion.

Conventional dispersants have some limitations in their molecular structure: hydrophilic groups are not firmly bonded on the surface of polar or non-polar particles, which are easily desorbed and cause re-flocculation of ions after dispersion; the lipophilic group does not have enough The carbon chain length (generally no more than 18 carbon atoms) does not produce sufficient steric hindrance effect in the non-aqueous dispersion system to stabilize. In order to overcome the limitations of traditional dispersants in non-aqueous dispersion systems, a new class of hyperdispersants has been developed, which has a unique dispersion effect on non-aqueous systems. Its main features are: fast and sufficient wetting of particles, shortening to reach Grinding time of qualified particle fineness; can greatly improve the solid particle content in the grinding base material, save processing equipment and processing energy consumption; uniform dispersion and good stability, so that the final use performance of the dispersion system is significantly improved.

characteristic

Hyperdispersants overcome the limitations of traditional dispersants in non-aqueous dispersion systems. Compared with traditional dispersants, it has the following characteristics:

(1) forming multiple anchors on the surface of the particles, improving the adsorption fastness and not easily desorbing;

(2) The solvation chain is longer than the traditional dispersant lipophilic group, and can effectively stabilize the space;

(3) Forming a very weak capsule, easy to move, can quickly move to the surface of the particle, and play a role of wetting protection;

(4) The lipophilic film will not be introduced on the surface of the particles, so as not to affect the application properties of the final product.

Mechanism of action

Anchoring mechanism

(1) For inorganic particles having a highly polar surface, such as titanium white, iron oxide or lead chromate, the superdispersant requires only a single anchoring group, which can be bonded to a strong polar group on the surface of the particle. The forms of ion pairs combine to form a "single point anchor."

(2) For organic particles of weakly polar surfaces, such as organic pigments and some inorganic pigments, generally a hyperdispersant with multiple anchoring groups, these anchoring groups can form "multi-point anchoring" on the surface of the particles by dipole force. .

(3) For completely non-polar or low-polarity organic pigments and some carbon blacks, since there is no active group for anchoring the hyperdispersant, the dispersion effect is not obvious regardless of the type of hyperdispersant used. At this time, a surface synergist, which is a pigment derivative with a polar group, has a molecular structure and a physicochemical property very similar to that of a dispersed pigment, and can be closely adsorbed to the organic substance by intermolecular van der Waals force. The surface of the pigment, while providing a chemical site for the adsorption of the anchoring group of the hyperdispersant through the polar group of its molecular structure, through this "synergy", the hyperdispersant can effectively wet and stabilize the organic pigment. effect.

2. Solvation mechanism

Another part of the superdispersant is a solvated polymeric chain, and the length of the polymeric chain is an important factor affecting the dispersion properties of the hyperdispersant. When the length of the polymer chain is too short, the stereoscopic effect is not obvious, and sufficient steric hindrance cannot be generated; if it is too long, the affinity for the medium is too high, which not only causes the superdispersant to desorb from the particle surface, but also causes the surface of the particle. The excessively long chain undergoes an anti-folding phenomenon, thereby compressing the steric hindrance of the steric hindrance or causing entanglement with adjacent molecules, eventually causing re-aggregation or flocculation of the particles.

Main classification

According to the unit structure of the solvation chain, the hyperdispersant can be roughly classified into the following four types:

Polyester type hyperdispersant

The solvation chain is generally prepared by polycondensation of a hydroxy acid or a ring opening reaction of a lactone compound, and the terminal group type and molecular weight can be controlled by the addition of a unit carboxylic acid or a unit alcohol. Hydroxy acids and lactone compounds which are relatively easy to obtain in the industry and which are suitable for the above polymerization reaction are very rare, and only 12-hydroxystearic acid and ε-caprolactone are practical. In the polymerization of a hydroxy acid and a lactone compound, a terminal carboxyl group polyester can be obtained by using a fatty acid or a resin as a blocking agent. The polyester may be used directly as a hyperdispersant in some cases (for example, for dispersion of a metal oxide powder in an aromatic hydrocarbon solvent), or may be attached to an anchor group by a certain chemical reaction. For example, the terminal carboxyl group polyester can be reacted with a polyamine and an alcohol amine to form a hyperdispersant having a C-NH- or C---- bridge group and an amine as an anchor group. The hyperdispersant can also react with mineral acids, organic carboxylic acids, and pigment sulfonated derivatives to convert anchoring groups to amine salts. The anchoring group can also be converted to a quaternary ammonium salt by reaction with an alkylating agent such as dimethyl sulfate or diethyl sulfate. Examples of suitable polyamines or alcohol amines are polyethene polyamines, N,N-dimethylaminopropylamine, stearylaminoamine, diethylethanolamine and the like.

The hydroxyl terminated polyester can be obtained by reacting a terminal carboxyl group with an epoxide, or by using a unit alcohol as a telogen, by a hydroxy acid polycondensation or a ring opening reaction of a lactone compound. The linkage between the hydroxyl terminated polyester and the anchoring group is generally based on a polyisocyanate. If the number of functional groups of the polyisocyanate is m, it will form (m-1) an NCO group at the end of the solvation chain after reaction with an equivalent amount of the terminal hydroxyl polyester. An NCO itself can be used as an anchor group. It is also possible to react with nitrogen, dicyandiamide and 2-thio-1,4-dicarboxylic acid to convert the anchor group into a urea group, a cyano group and a carboxyl group, respectively.

2. Polyether type hyperdispersant

The solvation chain is mainly a homopolymer and a copolymer of a substance such as ethylene oxide, propylene oxide, tetrahydrofuran, etc., and mainly includes a copolymer of ethylene oxide and propylene oxide. The synthesis of such a hyperdispersant can be carried out by using a anchoring group as a starting agent, in the presence of heat, pressure and a catalyst, by ring-opening reaction of a cyclic ether material. For example, when diethylethanolamine is used as the initiator, the obtained superdispersant of the following structure has a very good effect on the dispersion of the inorganic pigment in a highly polar medium such as an alcohol or an ether.

3. Polyacrylate type hyperdispersant

The range of choice of acrylate monomers is very wide, and the polarity and solubility parameters of the solvation chain can be conveniently adjusted by changing the feed ratio of the comonomer, so the scope of application is wide. In order to obtain a monofunctionalized solvated chain, a substance such as mercapto acid or mercapto alcohol is generally used as a chain transfer agent. The relative molecular mass of the solvate chain can be controlled by varying the amount of initiator and chain transfer agent. The resulting terminal carboxyl or terminal hydroxy polyacrylate has the same subsequent reaction process as the polyester solvate chain.

Polyolefin superdispersant

End group polyisobutylene is its most important representative. Such a type of hyperdispersant has an excellent dispersing effect in a hydrocarbon medium, and sometimes the volume fraction of solid particles in the dispersion system is more than 65%, and the dispersion still maintains a moderate operating viscosity.