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Why do we use wetting dispersant in waterborne coatings?

In order to get better effect of wetting and dispersing agent in the production process of waterborne coatings, the following aspects must be paid attention to.

1. Compatibility between wetting dispersant and resin

The resin should have good compatibility with dispersant. In particular, if the compatibility of polymer dispersant is not good, the stretching chain segment of polymer dispersant can not be well extended in the dispersion medium, curled around the pigment particles, the thickness of adsorption layer is reduced, the steric hindrance effect is reduced, and the stability is not good, which will affect the properties of gloss, coloring power, brightness, development, adhesion and other properties. Therefore, it is necessary to test the compatibility before using, so as to avoid problems.

2. Properties of resin

The properties of the resin also have a great influence on the application of dispersant. For example, alkyd resin with medium and long oil content contains more active groups and has strong wetting and adsorption capacity. If used properly, it can be used without wetting dispersant or less. But for some resins, such as thermoplastic acrylic resin and vinyl resin, which do not contain or contain little active groups, their wetting and adsorption capacities are very poor, so wetting and dispersing agents must be added when dispersing pigments. Therefore, the wetting and dispersing agent should be selected according to the different properties of the resin.

3. Surface properties of pigments

When dispersing pigments, the first thing to pay attention to is the type of pigments, organic or inorganic. We should also pay attention to the characteristics of the pigment surface, especially the inorganic pigment. We should know whether the surface has acidic center, alkaline center, or both. The ionic type of low molecular weight surfactant was selected according to its acidity and basicity. Most organic pigments use high molecular weight wetting and dispersing agents. It is necessary to pay attention to the affinity between the anchoring groups of dispersants and pigments, so that they can form a strong adsorption layer on the surface of pigments.

4. The addition of wetting and dispersing agent

When providing auxiliary samples, there will be a recommended amount, but this amount is only rough, and the accuracy is poor. When using it, we should carry out comprehensive, systematic and accurate tests to determine the amount of additives according to the situation described above and the requirements of formula design. The specific surface area and dispersion fineness of pigment should be a reference condition for the amount of dispersant added. The larger the specific surface area and the smaller the dispersion fineness, the more dispersant should be added. There are many methods to determine the amount of additives. No matter which method is used, the stability of pigment dispersion and the effect of dispersant addition should be measured by thermal storage or room temperature storage.

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