Analyze the application and factors of leveling agents in coatings:
For a determined formula system, the appropriate type of leveling agent should be selected based on the properties of the formula and the desired performance of the leveling agent. The following lists the applications of leveling agents in different systems:
1. Solvent based coating system
Acrylic leveling agents are commonly used in primer and intermediate coat formulations. If degassing and substrate wetting are required, it is advisable to choose medium or high molecular weight acrylic leveling agents. In primer, if stronger substrate wettability is required, it is recommended to use organic silicon leveling agents and modified acrylic leveling agents that can significantly reduce surface tension (such as fluorine modified acrylic leveling agents and phosphate modified acrylic leveling agents). If organic silicon leveling agents and fluorine modified acrylic leveling agents have side effects such as foam stabilization and affecting interlayer adhesion, phosphate modified acrylic leveling agents should be used.
In the formulation of topcoat and transparent paint, the requirements for the appearance of the paint film are relatively high. Generally, low molecular weight acrylic leveling agents can be used to achieve good leveling performance and avoid fogging in the paint film. In cross-linked curing systems, the use of acrylic leveling agents containing reactive functional groups often results in better leveling performance and improves the physical and chemical properties of the paint film. If better fluidity or smoothness and scratch resistance are required for the paint film, organic silicon leveling agent is necessary. In this case, organic silicon leveling agent and acrylic leveling agent are used in combination.
2. Water based coating systems are divided into water-soluble systems and latex systems.
In water-soluble systems, it is necessary to strongly reduce the surface tension of the system, commonly using organic silicon leveling agents and fluorocarbon compounds.
Class leveling agents have the same effect as their application in solvent based coating systems. Of course, if a truly smooth surface is required, acrylic leveling agents for water-based systems are necessary.
For latex systems, the film-forming mechanism is completely different, and viscosity does not change with the evaporation of solvents. The use of leveling agents in the formula may improve the substrate wettability of the coating, while acrylic leveling agents can improve the smoothness of the paint film. However, the main flowability of the coating is mainly controlled and adjusted by adding rheological control agents. 3. Factors affecting the flow and leveling of coatings
3.1 The influence of coating fluid properties on flow and leveling
Both flow and leveling are forms of motion of coatings, which are affected by the viscosity of the coating. The properties of coating fluids are different, and the relationship between viscosity and shear rate varies, so the degree of influence on flow and leveling is also different. How to utilize the property of coatings to achieve flow and leveling while overcoming certain drawbacks of coatings is the goal pursued by our technicians. There are approximately five fluid types for coatings: Newtonian fluid, plastic fluid, pseudoplastic fluid, swelling fluid, and thixotropic fluid. Pseudo plastic fluid and thixotropic fluid are two commonly used fluid structures in coatings. They are quite beneficial for anti sinking, anti floating, anti sagging, and preventing ripples during facade painting. But it will have a certain impact on leveling and gloss. As long as attention is paid to the selection of thixotropic agents and the appropriate adjustment of the flow hanging limit film thickness, it is still possible to achieve the ideal coating leveling effect.
3.2 The influence of coating surface morphology on leveling
There are two reasons for the irregular shape of the coating film. One is the traces generated by the painting tool, such as brush marks, which depend on the type of bristle brush and have varying depths. The rolling marks depend on the roller coating machine and the winding rod, and the unevenness generated by rolling or scraping coating varies. The greater the irregularity of the coating, the more difficult it is to level. The second reason is due to the shape of the substrate. The surface of the substrate is rough, making it difficult to obtain a smooth and even coating. The method of leveling is to scrape and apply thick primer. The solution to the surface leveling problem caused by the above situation is to maintain high surface tension of the coating, enhance the wetting and spreading ability of the substrate, maintain the maximum thickness of the coating, dilute the resin with a good solvent, and control its volatilization rate and balance.
3.3 The Effect of Coating Drying Time on Flow Leveling
The flow and leveling of coatings are affected by viscosity, which is influenced by solvents. Controlling the solvent evaporation rate to keep the coating in a low viscosity liquid state for a longer period of time is more beneficial for the leveling of the coating film. In other words, by controlling the solvent evaporation rate, suitable leveling properties can be obtained. For coatings, the solubility of solvents varies depending on their solubility parameters. Strong solubility, high solid content, low viscosity, good leveling, and high film fullness of the coating. The dissolution parameters of the mixed solvent must match the resin. Mixed solvents are mostly composed of real solvents, diluents, and co solvents. When the solvent evaporates, it is necessary to control the evaporation equilibrium. After the solvent evaporates, the real solvent should account for a relatively large proportion. This can ensure that the viscosity of the coating does not undergo sudden changes during the drying process, and is in a state of balanced growth. It has a certain control effect on the flow and leveling of the coating.
