Leveling is a measure of the ability of a coating to flow when applied. The purpose of the flow is to remove any surface defects such as brush marks, orange peel, pitting or craters, which are caused by the mechanical process of coating application. Leveling additives can reduce the surface tension of the coating film and improve the flow mode to obtain a good appearance of the coating film. Some special additives can also provide the effects of smoothness, hardening, scratch resistance and anti-blocking. The main varieties are: silicone series leveling agent, acrylate leveling agent, other types of leveling agent (fluorine modified leveling agent, high boiling point solvent) and so on.

Factors Affecting Flow and Leveling

1. Surface morphology
The depth and type of irregularities on the surface of the liquid coating can affect leveling. The more serious the irregularity is, the higher the leveling requirements of the coating are. Surface roughness is affected by the coating method. For example, brushing can produce thicker or shallower brush marks, depending on the type of bristles used for brushing and the shape of the brush, which requires the film to be leveled. While some coating methods can directly obtain a smooth surface, such as reverse roller coating, spray coating, flow coating or blade coating, these coating methods usually do not produce surface irregularities like the above, but they require the surface of the coating film to be smooth. Stability to ensure that the smooth surface of the coating film is maintained during curing. The roughness of the substrate is also very important, and its own surface state is clearly reflected on the surface of the coating film, which depends on the thickness of the rough surface. The shrinkage of the film during drying is the cause of this phenomenon. This phenomenon can be eliminated by applying a suitable primer to the substrate, but the increased surface roughness of the substrate usually results in improved wetting and adhesion.

2. Thickness of wet film
The second criterion for judging the leveling is the wet film thickness. Generally speaking, the thicker the coating film, the flatter the surface of the formed coating film, but the thickness is usually limited, such as construction on a vertical surface. May cause sagging.

3. Viscosity
Viscosity in coatings mainly affects the rheological properties after coating. Too low viscosity will cause sagging, and too high viscosity will lead to reduced leveling.

4. Drying time
Flow also depends on the drying time of the coating, which is how long the coating film needs to remain liquid. The drying time depends on the volatilization speed of the solvent used in the coating and the change in the composition of the coating during the volatilization process. Appropriate leveling can be obtained by controlling the volatilization speed of the solvent. Similarly, the control of the volatilization speed of the solvent can determine the drying process of the coating film. The increase in the viscosity of the intermediate coating film.

5. Surface tension
The most important point for forming a good coating film is the maintenance of the surface tension of the coating and the proper balance of surface tension. Surface tension is a force that keeps the liquid together and can make the liquid occupy the smallest possible volume. On a glass plate, the liquid can cover more or less area, depending on the surface tension of the liquid and the surface tension of the substrate being coated. When the surface tension of the substrate is equal to or greater than the surface tension of the liquid itself, the liquid is said to "wet" the substrate. The spread of a liquid coating on a substrate has nothing to do with the surface quality of the liquid coating, but only indicates the relative extent to which a particular feature wets the substrate. A liquid film with high surface tension is more helpful to obtain a smooth surface than a liquid film with low surface tension, but only when it reaches a sufficient thickness, a smooth coating film can be formed. The surface of some coatings with a tendency to shrink and shrink is particularly smooth and glossy. Generally, the thickness of the coating film used is between 25-200μm. In order to cover the surface of the substrate well, its surface tension must be low.

6. Construction technology and environment
During the construction and film-forming process of the coating, if there are external pollutants, it may also cause leveling defects such as shrinkage cavities and fish eyes. These pollutants are usually oil, dust and paint mist from the air, construction tools and substrates. , water vapor, etc. In addition, the properties of the coating itself, such as application viscosity, drying time, etc., will also have a significant impact on the final leveling of the paint film. Excessive application viscosities and short drying times often result in poorly leveled surfaces.