Industry information

　　Wetting is actually a surface replacement process. The wetting agent molecules displace the air on the surface of pigments and fillers, so as to reduce the interfacial tension between liquid and solid, and enhance the hydrophilicity of pigments and fillers, so as to improve the dispersion efficiency and dispersion stability. There are two key indicators for the selection of wetting agent: cloud point of wetting agent and ability of wetting agent to reduce surface tension. At present, anionic and nonionic wetting agents are widely used.

　　In fact, the wetting, dispersion and stabilization of pigments and fillers are three inseparable processes

　　The main purpose of wetting is to reduce the interfacial tension of materials. If the surface tension of many pigments and fillers is not wetted, their dispersion time will be long or even poor;

　　Dispersion is the process of separation of powder pigments and fillers under the action of external force, while stability is the process of no flocculation (coarsening) after dispersion.

　　The mechanical dispersion of pigments and fillers can be realized by high-speed disperser, sanding machine and three roller grinder: the tightly adhered particles will be crushed to obtain fine pigments and fillers, and the decisive step is to stabilize the dispersed particles by adding dispersant.

　　In order to disperse the pigments and fillers in the system and form a stable system, three basic conditions should be met: firstly, the pigments and fillers can be well wetted by the medium; secondly, the polymers produced by the adhesion of the primary pigments and fillers are dispersed; thirdly, the good dispersion system obtained is stable, that is, the secondary agglomeration is inhibited. The prerequisite for the pigment dispersion to reach a stable state is that the wetting dispersant is firmly adsorbed on the surface of the pigment particles to form charge effect or steric hindrance effect, so that the dispersion is in a stable state.

　　It has good dispersing performance for pigments and fillers, prevents particles from gathering together, has proper compatibility with resin and pigments and fillers, and does not affect the performance of the main body.

　　Considering its compatibility with main resin and other additives is very important to select wetting and dispersing agent. Poor compatibility will affect the transparency, and some properties will be destroyed if the light one is serious. In particular, if the polymer dispersant is not compatible with the resin base material, its long-chain stretching group in the dispersant is rolled into a linear cluster and cannot be extended. Even if the adsorption base is adsorbed on the surface of the pigment, it will not form a steric hindrance effect, and even lead to high viscosity of the coating, poor color development, coarsening and thickening, and decreased gloss of the film.

　　Modern auxiliaries, especially polymer dispersants, have both wetting and dispersing effects. Therefore, they are often called wetting and dispersing agents.

　　The addition of wetting dispersant not only plays its due role, but also has some side effects on the system. For example, polyether modified polydimethylsiloxane has the ability to control the surface state of the film, reduce the interfacial tension, improve the wettability of the substrate, and enhance the adhesion and distribution. However, it also has a stable bubble, which is not conducive to the flow and affects the adhesion between layers. It is easy to decompose into long chain siloxane and cause surface defects. Traditional low molecular weight dispersant is helpful for wetting and dispersing pigment, but it has foaming effect.