What is a dispersant in paint? What is the role of paint dispersants

Hello, the mechanism of action of the dispersant.

The surface of inorganic pigments has high polarity, so low molecular weight pigment dispersants are easy to adsorb and can be adsorbed on the surface of pigments for a long time. However, the surface of organic pigments is basically non-polar, so it is difficult for low molecular weight pigment dispersants to adsorb for a long time, so it is necessary to use higher molecular weight dispersants or polymer dispersants with anchor groups. The adsorption of high molecular weight dispersants on the surface of pigments is achieved by adsorption on the surface of pigment particles by functional groups and polymer anchor chains. At the same time, the adsorption form is related to the characteristics, morphology, charge distribution of the pigment surface, the structure, composition and properties of polymer compounds, the types of solvents in the dispersion medium, and the solubility of polymers.

Polymer dispersant is a compound specially designed for the purpose of dispersion required by the properties of pigments.

Compared with small molecule dispersants with single anchor groups, polymer dispersants contain multiple anchoring points, which can be more effectively adsorbed on the surface of dispersed particles and have a large adsorption capacity. Generally speaking, homopolymers are not good dispersants, because they are good solvation chains or good anchor groups, and good repulsion stabilization requires both, and most of the copolymers that can meet this requirement are copolymers, such as polymers as pigment dispersants in aqueous systems are usually random copolymers, graft copolymers or block copolymers that have both.

Dispersants can promote the dispersion of pigments and make pigments and resins mix evenly, mainly used in paint production.

1. The principle of action of coating dispersant.

1. Mechanically, the purpose of dispersing the pigment in the medium is to disperse the lipophilic condensed particles caused by the drying of the pigment during the manufacturing process. When the fineness of the particles decreases, the exposed surface area increases, which improves the optical properties of the pigment, such as tinting properties, gloss, brightness, opacity or transparency.

2. In the general dispersant grinding system, such as inks and coatings, resin is one of the components in the formula, but resin and dispersant will compete with each other in pigments. The adsorption capacity of the dispersant on the pigment surface is also affected by the resin, and the resin and the dispersant compete with each other for adsorption on the pigment surface. But the difference between the dispersant and the resin is the fastness of the dispersant to adsorb the surface of the pigment, and the dispersant not only has a strong adsorption force for the pigment, but also has a good affinity for the solvent.

The resin on the surface of the pigment, in fact, only plays a wetting role, it does not stick to the surface of the pigment for a long time, after a long time, the resin will slowly leave the surface of the pigment and cause flocculation, although so, the presence of the resin still hinders the anchoring of the dispersant on the surface of the pigment.

Therefore, when choosing a resin, it is necessary to consider whether the resin content in the grinding base is sufficient to maintain the stability of the formulation.

3. The use of dispersant in grinding binders, compared with traditional grinding binders, the key to the adjustment of its formula is the concentration of resin solution. The traditional grinding medium has a higher resin concentration and a smaller amount of pigment filler. Although reducing the resin concentration can reduce the viscosity of the dispersion medium itself and increase the amount of pigment filling, such a dispersion system is not stable and cannot be used in actual production.

If a good dispersant is used, the dispersion system can be stabilized at a lower resin concentration, so that the pigment filling in the grinding base is greatly increased, and the spatial barrier generated by the solvation chain of the dispersant in the medium reduces the suction between the particles and greatly reduces the grinding viscosity, which is also one of the reasons why the pigment filling amount can be improved.

Under the action of dispersant, the increase in pigment filling varies with the dispersion system, but the grinding base should be kept with a moderate viscosity during the adjustment process.

4. Pigment stability is theoretically the stability of pigment dispersions, and there are basically two mechanisms: electrostatic stability and steric resistance stability, both of which must be molecular adsorption of the pigment surface.

Second, the use method and dosage of dispersant.

If the amount of dispersant is too small, the dispersant will not show its advantages, and too much will also affect the stability of the grinding. This is mainly due to the fact that the overcrowded dispersant does not fully extend the solvation chain of the dispersant on the pigment surface, and the large amount of free dispersant can have a negative impact on the coating film.

In the actual operation process, the approximate dosage of dispersant can be calculated according to the theoretical rules, and then this is used as the midpoint to float up and down, and the viscosity, gloss and tinting strength of the dispersion system and other performance indicators with the amount of dispersant can be observed.

When grinding solid coatings, a dispersant is added to help the particles crush and prevent the crushed particles from agglomerating to keep the dispersion stable.

The oily liquid insoluble in water can be dispersed into very small liquid beads under high shear stirring, and after stopping stirring, it can quickly stratify under the action of interfacial tension, and stirring after adding dispersant can form a stable emulsion.

Its main function is to reduce the interfacial tension between liquid-liquid and solid-liquid.

1. The main function of the dispersant is to disperse the particles that need to be dispersed in the water-based coating on the surface to make it more stable.

2. The dispersant can improve the gloss of the water-based coating, improve the flatness of the surface of the water-based coating, and maintain a certain stability, so that when the sunlight shines on the wall, the water-based paint will exude a good gloss.

3. It can prevent the color of the surface of the water-based coating from changing, and if the dispersant is not used well, the color will appear.

4. The dispersant can also reduce the viscosity of the coating, so that more pigments can be put in.

5. The dispersant can also increase the stability of the water-based coating, if the strength of the dispersant is not good, the stability of the water-based coating will be destroyed, which is not easy to see from the surface.

6. The dispersant can also increase the color transparency and saturation of water-based coatings, and strengthen the covering ability of water-based coatings.

The function of the dispersant is to use the wetting and dispersing agent to reduce the time and energy required to complete the dispersion process, stabilize the dispersed pigment dispersion, modify the surface properties of the pigment particles, and adjust the kinematics of the pigment particles [2]. It is embodied in the following aspects:

1. Enhance the gloss and increase the leveling effect, the gloss actually depends on the scattering of light on the surface of the coating (that is, a certain flatness. Of course, it is necessary to test the instrument to decide whether it is flat enough, not only considering the number and shape of the primary particles, but also considering their way of bonding), when the particle size is less than the incident light 1 2 (this value is uncertain), it is manifested as refracted light, and the gloss will not be improved, and the hiding power that relies on scattering to provide the main hiding power will not increase (except for carbon black, which mainly relies on light absorption, and organic pigments are forgotten). Note:

The incident light refers to the range of visible light, and the leveling is not good; However, it should be noted that the reduction of the original number of particles is to reduce the viscosity of its structure, but the increase of the specific surface will reduce the number of free resins.

2. Prevent floating color.

3. Improve the tinting strength, pay attention to the tinting strength in the automatic tinting system, the higher the better.

4. Reduce viscosity and increase pigment loading.

5. Reducing flocculation is like this, but the finer the particles, the higher the surface energy, the higher the adsorption strength of the dispersant, but the dispersant with too high adsorption strength may cause disadvantage to the performance of the coating film.

6. The reason for increasing storage stability is similar to the above, once the stability strength of the dispersant is not enough, the storage stability becomes worse (of course, it is no problem from your ** point of view).

7. Increase color spread, increase color saturation, increase transparency (organic pigments) or hiding power (inorganic pigments).

TEGO Dispersing dispersants help to wet and stabilize pigments, prevent fluffing and pigment settling, maintain consistent pigment hiding and color strength during storage, and ensure maximum color yield with minimal grinding steps. Since these additives reduce viscosity and increase to the highest pigment concentrations when dispersed, coating and pigment concentrates can be produced more cost-effectively. Tegodispers 757 W is recommended for the production of aqueous pigment concentrates.

It is also the product of choice for corrosion-resistant water-based coatings. Like TegoDispers 750W and TegoDispers 755 W, the highest optical and rheological performance requirements are met. For general-purpose colorants suitable for both solvent-based and water-based formulations, the Tegodispers 65X series is the existing market standard for ethoxyalkylphenol-free.

Tegodispers 656, 670 and 685 are particularly suitable for modern solvent-based formulations. In UV systems, TegoDispers 685 is suitable for all pigments and Tegodispers 688 is suitable for matting agents. All tegodispers products are free of ethoxyalkylphenols.

A dispersant is a kind of surfactant that has two opposite properties, lipophilic and hydrophilic in the molecule.

It can uniformly disperse solid and liquid particles of inorganic and organic pigments that are difficult to dissolve in liquids, and can also prevent the sedimentation and agglomeration of particles, forming amphiphilic reagents required to stabilize suspensions.

Dispersant is a kind of surfactant that has two opposite properties, lipophilic and hydrophilic, in the molecule. It can uniformly disperse back the solid and liquid particles of inorganic and organic pigments that are difficult to dissolve in the liquid body, and can also prevent the sedimentation and agglomeration of the particles, forming the amphiphilic reagents required to stabilize the suspension. Dispersants are amphiphilic chemicals that increase the compatibility of oily and aqueous components in the same system.

The dispersant has S19 S28 in water and S27 in oil

A mixed system formed by the dispersion of one or several substances (called dispersions) into another substance (called dispersants) is called a dispersion system. A dispersant is a substance that accommodates a dispersion.

One or several substances are dispersed into another substance, such a system is called a dispersion system, in which the dispersed substance is called dispersed substance, and the substance that bears the dispersed substance is called dispersant.

For example, sodium chloride is soluble in water, which is the solvent and is also a dispersant.

Anionic wetting and dispersing agent.

Most of them are composed of non-polar, negatively charged, lipophilic hydrocarbon chain moieties and polar hydrophilic groups. The two groups are located at both ends of the molecule, forming an asymmetrical hydrophilic and lipophilic molecular structure. Its varieties are:

Sodium oleate C17H33Coona, carboxylate, sulfate (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 flocculating dispersants.

Cationic wetting and dispersing agent.

It is a non-polar base positively charged compound, mainly including amine salts, quaternary amine salts, pyridinium salts, etc. The cationic surfactant has strong adsorption and good dispersion effect on carbon black, various iron oxides and organic pigments, but it should be noted that it reacts chemically with the carboxyl group in the base material, and it should also be noted that it should not be used at the same time as anionic dispersant.

Non-ionic wetting and dispersing agent.

It is not ionized in water, does not have an electric charge, and has weak adsorption on the surface of pigments, so it is mainly used in aqueous coatings. It is mainly divided into ethylene glycol and polyol type, which reduces surface tension and improves wettability. It is used in combination with anionic dispersant as a wetting agent or emulsifier, and 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-based polymers. These polymers have a high acid number, which may affect interlayer adhesion.

Electrically neutral wetting and dispersing additives.

The anions and cationic organic groups in the molecule are basically equal in size, and the whole molecule is neutral but polar. For example, oil amino oleate C18H35NH3OOCC17H33 and so on belong to this type and are widely used in coatings.

Polymer hyperdispersant.

Polymer dispersants are the most commonly used and have the best stability. Polymer dispersants are also divided into polycaprolactoeride polyol-polyethylene imide block copolymer dispersants, acrylate polymer dispersants, polyurethane or polyester polymer dispersants, etc., because their anchor groups are wound and adsorbed with resin at one end, and encapsulated with pigment particles at the other end, so the storage stability is relatively good.

Controlled radical hyperdispersants.

The use of the latest controlled radical polymerization technology (CFPP) can make the structure of the dispersant more regular. Commonly used methods are: GTP, ATRP (atom transfer radical polymerization), RAFT (reversible addition break chain transfer controllable radical polymerization, including C-Raft and S-Raft, etc.), NMP, SFRP (stable radical polymerization), TEMPO, etc.

By employing controlled radical polymerization technology, the relative molecular mass distribution of the dispersant can be more concentrated, and the anchor groups can be more concentrated, resulting in higher efficiency.