Wetting and wetting agents

Wetting is usually a phenomenon in which a liquid substance has an affinity for a solid and wets, spreads, and penetrates the surface of the solid. The wetting performance is related to the surface tension of solids and liquids. The smaller the surface tension of the liquid, the greater the surface tension of the solid, the better the wetting performance of the liquid on the solid, and the liquid can form a large amount on the solid surface. Exhibition area. In the industrial production process, many procedures are inseparable from wetting, such as color paste manufacturing, pigment dispersion in the base material, paint coating, fabric finishing, ink printing, emulsification, adsorption, penetration, cleaning and so on.

Surfactants are the key to wetting. The surface tension of a liquid can be reduced by adding such additives to promote better wetting of solid materials by liquids. Such surfactants are wetting agents. According to the object of wetting, wetting agents are mainly divided into substrate wetting agents and pigment wetting and dispersing agents. The former focuses on the wetting of the substrate and the coated surface, and the purpose of the wetting is to spread the wetting. It promotes the wetting and dispersion of pigments and fillers in the base material, which is the soaking and wetting.

Substrate wetting agent

When coating on a low surface energy substrate, a substrate wetting agent needs to be added to the coating, which can not only improve the wet spreadability of the coating on the substrate, enhance the smoothness and smoothness of the coating film surface, but also prevent Defects such as shrinkage and shrinkage caused by low surface tension improve the adhesion of the coating film. The types of substrate wetting agents include: anionic surfactants, non-ionic surfactants, polyether-modified polysiloxane compounds, acetylene glycol compounds, and the like. Common substrate wetting agents include ethylene oxide adducts, polyether silicones, and non-ionic fluorocarbon polymer compounds. Among them, the effect of fluorocarbon polymer compounds on reducing surface tension is most obvious.

However, there has always been a misunderstanding about this, as long as the surface tension of the coating is reduced, the coating will have good wetting and spreading properties to the substrate. Wetting performance cannot be determined solely by its effect of reducing surface tension. In fact, the ability of a coating to spread on a substrate is more important. For example, an alkyl nonylphenol ethoxy ether surfactant can reduce the surface tension of water to 35 mN / m; a non-ionic organic fluorine surfactant can reduce the surface tension of water to 17 mN / m. Take two kinds of the same amount of aqueous solution and drop them onto the polyester membrane. The aqueous solution of alkyl nonylphenol ethoxy ether produced spreading wetting, but the aqueous solution of fluorine-based auxiliary agent became spheroids and the contact angle was small and not spread. Polyether organosilicon compounds use siloxane as the middle segment, and the end groups are modified with hydrophilic and lipophilic polyethers, so that the molecule has a strong surface tension reduction property and an amphiphilic structure. It is easy to align at the interface, has excellent spreading ability, and the price is far lower than fluorocarbons, so it is widely used as an ideal wetting agent for difficult-to-wet substrates such as metal, wood and plastic.