Classification and principle of action of shrinkage leveling agents, commonly used anti shrinkage agents
1. Modified polydimethylsiloxane type. This type of anti shrinkage leveling agent is a polydimethylsiloxane modified with polyether, polyester, long-chain alkyl, or arylalkyl groups. Its application varies depending on the structure, quantity, and molecular weight of the modified groups, but most of them can strongly reduce the surface tension of the coating, improve the wettability of the coating to the substrate, and prevent shrinkage; It can reduce the surface tension difference caused by solvent evaporation on the wet film surface, improve the surface flow state, shorten the coating leveling time, and avoid problems such as orange peel, brush marks, roller marks, and floating colors; This type of leveling agent can also form a very thin and smooth film on the surface of the coating, thereby improving the smoothness and gloss of the coating.
When the dosage is within a certain range, modified polydimethylsiloxane generally does not affect the adhesion and recoating properties of the coating film. When using this type of anti shrinkage and leveling agent, the appropriate dosage and addition method should be determined through experiments to avoid side effects such as affecting the adhesion between coating layers or causing shrinkage. Although unmodified polydimethylsiloxane has properties such as reducing surface tension and improving leveling, its compatibility with coatings is poor, which can easily lead to shrinkage of the coating film. Therefore, it is basically not used in modern coatings. Polyether modified polydimethylsiloxane is the most commonly used and diverse anti shrinkage and leveling agent, which can reduce the surface tension of coatings and improve the flow and leveling of wet films. Polyester and arylalkyl modified polydimethylsiloxane have excellent high temperature resistance and can be used under temperature conditions of 200-250 ℃. The use of arylalkyl modified polydimethylsiloxane has a relatively small effect on reducing the surface tension of coatings and increasing the gloss of coatings, but it has significant leveling and smoothing effects, and can also help the directional arrangement of matting powder and flake metal pigments in coatings.
2. Long chain resin leveling agents with limited compatibility. Commonly used are acrylic homopolymers or copolymers, which can reduce the surface tension of coatings to a certain extent and improve the wetting and anti shrinkage ability of substrates. Due to their limited compatibility with coatings, they can quickly migrate to the surface of the coating to form a monolayer, making the surface tension uniform, suppressing solvent evaporation rate, improving surface fluidity, eliminating defects such as orange peel and brush marks, and making the coating smooth and flat.
This type of leveling agent has a relatively small impact on the recoating ability between coatings and is not affected by the curing temperature. It can be used in primer, varnish, color paint, and baking paint systems. Fluorine modified acrylic polymers have strong advantages in reducing surface tension, preventing coating shrinkage, improving flow and leveling properties due to their low surface tension. They also have little impact on recoating properties and are excellent non silicone resin anti shrinkage and leveling agents with comprehensive performance.
3. A leveling agent mainly composed of high boiling point solvents. By using a mixed solvent composed of high boiling point aromatic hydrocarbons, esters, ketones, ethers, and ether esters, the evaporation rate of the solvent and its solubility in the resin can be adjusted, so that the coating film has a relatively balanced evaporation rate and solubility during the drying process. This prevents the flow of the coating film from being hindered due to rapid solvent evaporation and high viscosity, resulting in poor leveling, and can also prevent shrinkage caused by poor solubility of the base material and precipitation due to rapid solvent evaporation.
