What is the Role of Wetting Agent in Coatings

Jul 26, 2021

Paint wetting agents are divided into two types: substrate wetting agent and wetting dispersing agent. The substrate wetting agent is used to improve the surface tension and permeability of the coating, so that it can better wet the substrate, thereby improving Coating adhesion, especially for improving the adhesion of primers to substrates, is widely used, generally some fluorocarbon or fluorocarbon modified ionic or non-ionic substances or other substances that can improve the wetting of the substrate Material, domestic manufacturers of products in this area have done a good job; 

In addition to this function, the wetting and dispersing agent for coatings has one of the most important functions to assist in the dispersion of fillers and pigments and assist in the anti-settling effect, which can assist in the dispersion and dispersion of pigments, fillers and other powders in the coating. Assist the subsequent anti-settling of the coating anti-settling agent. In the anti-settling after the coating is diluted, the anti-settling effect of the wetting and dispersing agent is far more important than that of the anti-settling agent. So wetting and dispersing agent is a very important additive in coatings.

Wetting and wetting agent
Wetting is usually a phenomenon in which liquid substances have affinity for solids and infiltrate, spread and penetrate on the solid surface. The wettability 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, and the better the wettability of the liquid to the solid. The liquid can form a large surface on the solid surface. Exhibition area. Many procedures in the industrial production process are inseparable from wetting, such as color paste manufacturing, pigment dispersion in base materials, paint coating, fabric finishing, ink printing, emulsification, adsorption, penetration, cleaning, etc.

Surfactant is the key to wetting. You can add such additives to reduce the surface tension of the liquid and promote the liquid to better wet the solid material. This surfactant is the wetting agent. According to the objects 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 for spreading wetting, and the function of the latter is Promote the wetting and dispersing of pigments and fillers in the base material, which is immersion wetting.

Substrate wetting agent
When coating on low surface energy substrates, the coating needs to add a substrate wetting agent, which can not only improve the wetting and spreadability of the coating on the substrate, enhance the smoothness and flatness of the coating film surface, but also prevent the substrate The shrinkage and edge shrinkage caused by low surface tension can improve the adhesion of the coating film. The types of substrate wetting agents include: anionic surfactants, nonionic surfactants, polyether modified polysiloxane compounds, acetylene glycol compounds, 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.

However, everyone has always had a misunderstanding about this, thinking that as long as the surface tension of the coating is reduced, the coating will have good wetting and spreading properties on the substrate. The wetting efficiency cannot be determined only by its effect of reducing surface tension. In fact, the spreading ability of the coating on the substrate is more important. For example, alkyl nonylphenol ethoxy ether surfactants can reduce the surface tension of water to 35mN/m; a non-ionic organic fluorosurfactant can reduce the surface tension of water to 17mN/m. Two aqueous solutions of the same amount were dropped on the polyester film. The aqueous solution of alkyl nonylphenol ethoxy ether produced spreading and wetting, but the aqueous solution of fluorine-based additives became spherical and the contact angle was very small. Polyether organosilicon compounds are based on siloxane as the middle segment, and the end groups are modified with hydrophilic and lipophilic polyethers respectively, so that the molecule has a strong surface tension reduction characteristic and an amphiphilic structure. It is easily oriented at the interface, has excellent spreading ability, and the price is much lower than fluorocarbon compounds, so it is widely used as an ideal wetting agent for difficult-to-wet substrates such as metals, woods and plastics.