Wetting agents are surfactants, which are composed of hydrophilic and lipophilic groups. They can make solid materials more easily wetted by water. Wetting agents reduce the surface tension or interfacial tension of water so that water can spread on the surface of solid materials or penetrate into their surfaces, thereby moistening solid materials. When in contact with a solid surface, the lipophilic group adheres to the solid surface, and the hydrophilic group extends outward into the liquid, causing the liquid to form a continuous phase on the solid surface. This is the basic principle of wetting.
Wetting agent is a very important additive in coating formulations. Wetting agents for coatings are divided into substrate wetting agents andwetting and dispersing agents. AgentsTwo kinds. Substrate wetting agents are used to improve the surface tension and permeability of the coating so that it can better wet the substrate, thereby improving the adhesion of the coating. It is especially used to improve the adhesion of the primer to the substrate. Very extensive. When coating on low surface energy substrates, a substrate wetting agent needs to be added to the coating. This can not only improve the wetting and spreading properties of the coating on the substrate, enhance the smoothness and flatness of the coating surface, but also prevent the coating from being damaged by the substrate. It improves the adhesion of the coating film by preventing undesirable phenomena such as shrinkage cavities and edge shrinkage caused by low surface tension. Common types of substrate wetting agents include anionic surfactants, nonionic surfactants, polyether modified polysiloxane compounds, acetylene glycol surfactants, etc. Common substrate wetting agents include ethylene oxide adducts, polyether silicones and non-ionic fluorocarbon polymer compounds, among which fluorocarbon polymer compounds have the most obvious effect of reducing surface tension.
In order to obtain good dispersion effects of wetting and dispersing agents in coating formulations, you need to pay attention to the following points.
1. Compatibility of wetting and dispersing agent with resin.
Resin and dispersant must have good compatibility, especially polymer dispersants. If the compatibility is not good, , the extended chain segment of the polymer dispersant cannot stretch well in the dispersion medium and curls around the pigment particles. The thickness of the adsorption layer is reduced, the steric hindrance effect is reduced, and the stability is poor. In severe cases, gloss, tinting strength, brightness, developability, and adhesion will be affected.
2. Properties of resin.
The properties of the resin also have a great relationship with the application of dispersants. The use of wetting and dispersing agents should vary according to the properties of the resin.
3. Surface properties of pigments.
Most organic pigments use high molecular weight wetting and dispersing agents. It should be noted that the affinity of the anchoring group of the dispersing agent with the pigment enables it to form a strong bond on the surface of the pigment. adsorption layer.
4. The amount of wetting and dispersing agent added.
The specific surface area of the pigment and the fineness of dispersion requirements 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.
