How to choose a waterborne coating dispersant?

2022-06-02   Pageview:185

Coating dispersant refers to an additive that can improve and improve the dispersion performance of solid or liquid materials. When grinding solid coatings, adding dispersants can help the particles to be crushed and prevent the agglomeration of the crushed particles to keep the dispersion stable. Water-insoluble oily liquids can be dispersed into small droplets under high shear stirring. After stopping stirring, they are quickly layered under the action of interfacial tension. Emulsion. Its main function is to reduce the interfacial tension between liquid-liquid and solid-liquid.

Among the components of water-based coatings, there are film-forming substances, solvents (water), pigments and fillers, and additives. Among them, the additive is the smallest part of the coating, but it is also a very important part and cannot be ignored. Most of the pigments used in water-based coatings exist in the form of aggregates and aggregates. If these particles cannot be dispersed into smaller particles or primary particles and form a stable dispersion, defects such as coarsening, flocculation, precipitation, floating color, and reduced tinting strength will occur. Auxiliary for water-based coatings – dispersant, the main function is 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 mobility of the pigment particles. The dispersants used in water-based coatings must be water-soluble, and they are selectively adsorbed on the powder-water interface. There is a big difference between water-based industrial coatings and ordinary architectural coatings. The viscosity is generally low. The viscosity is measured by coating-4 cups, which is generally 60-120s. Therefore, the requirements of water-based industrial coatings for dispersants are not only good reduction Sticky, but also need to have good anti-settling properties.

The quality of the dispersion of the coating slurry is not only related to the formulation of the material formulation and the selection of raw materials, but also to the dispersant. Therefore, in the coating production process, pigment dispersion is a very important production link, which is directly related to the storage, construction, appearance and performance of the paint film, so the rational selection of dispersants is a very important production link. The types of dispersants are anionic, cationic, nonionic, amphoteric and polymer.

Most dispersants achieve the purpose of dispersing pigments and fillers through the processes of wetting, grinding and dispersing, coupling and encapsulation stabilization. In water-based coatings, more expensive dispersants cannot be used due to cost control reasons. Most of the wetting and dispersing additives currently on the market are anionic and nonionic. Their principle is that low surface tension quickly wets the pigment particles, and then through high shear forces, such as dispersing machines, grinding machines, etc., the pigment particles form a semi-flocculated, or controlled-flocculated dispersion. If the viscosity of the coating is relatively high at this time, there will be no pigment coarsening and serious flocculation, but if the viscosity is not well controlled, problems will occur over time; some use a coupling agent as a dispersant. Their hydrophilic and sulphur water groups couple together two dissimilar species. The advantages of doing so are: good overall performance, dispersibility, and less dosage, which can increase the adhesion of the coating. But the disadvantage is that it is not a deflocculation group, and it is not suitable for coatings with high color development and strong requirements. Through research and practice, it is recommended to use dispersants that can deflocculate in waterborne coatings. The advantages of this are: good color development, high brightness and good gloss for pigments and fillers.

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