Do you know leveling agent?

Overview of leveling

After the paint is applied, there is a process of flow and drying film formation, and then a flat, smooth and uniform coating film is gradually formed. Whether the coating film can achieve the characteristic of flatness and smoothness is called leveling. In the actual construction process of the paint, common coating defects include orange peel, fish eyes, shrinkage, pinholes, shrinkage, Benard vortex, airflow sensitivity and poor leveling. Brush marks when brushing and roller marks when rolling are all called poor leveling. The occurrence of these phenomena reduces the decorative and protective functions of the paint.

There are many factors that affect the leveling of the paint, including the evaporation gradient and solubility of the solvent, the surface tension of the paint, the wet film thickness and surface tension gradient, the rheology of the paint, the construction process and the environment.

The most important factors are the surface tension of the paint, the surface tension gradient of the wet film during the film formation process, and the surface tension uniformity of the wet film surface. To improve the leveling of the paint, it is necessary to consider adjusting the formula and adding appropriate additives to make the paint have a suitable surface tension and the ability to reduce the surface tension gradient.

Factors affecting leveling speed

● The greater the viscosity, the slower the leveling

● The thicker the coating, the faster the leveling

● The greater the surface tension, the faster the leveling

How to judge the quality of the leveling agent

Generally speaking, we can use the following visual method to roughly judge the quality of the coating leveling agent.

● After the coating is applied and dried according to the specified brushing method, if there are no shrinkage holes, pinholes, orange peel, silk patterns, brush marks, fog and other defects on the coating surface, it can be determined that the leveling property of this coating leveling agent is good.

● However, the above method has no quantitative indicators and is easy to cause disagreements. Therefore, in the domestic and international coatings industry, people have formulated special standards to evaluate the leveling property of coating leveling agents. For example:

①GB/T l750-1979 Coating leveling determination method: This method is to determine the time required to achieve leveling by brushing/spraying the coating on a certain substrate in a certain method.

②GB-Sl07 horizontal flowability test method: This method is to measure the diameter of the epoxy powder coating specimen after melting at a certain temperature.

③ASTM D2801 leveling test method: This method uses the New York Paint Association (NYPC) leveling scraper to determine the leveling grade based on the ability of two pairs of paint strips to flow together.