Film retraction is a common but troublesome problem during Coating construction. It can lead to uneven Coating during painting, ultimately affecting the mass and Appearance of the film. In this article, we will explore the reasons for film retraction and how to effectively address this challenge.
Coating leveling is usually affected by surface tension. Surface tension is a manifestation of the force on the surface of liquid molecules. Liquids with high surface tension tend to form spherical shapes and are not easy to wet the surface of the substrate. When Coating cannot fully wet the surface of the substrate, the wet paint film will naturally retract into a spherical shape, forming a phenomenon of uneven paint film thickness, which we call retraction.
The surface tension of oils and some organic molecules is usually low, which in some cases can cause the paint film to retract. For example, if organic dirt (such as rust-proof oil) on the metal surface is not removed before painting, these oil stains may push the coating away, causing the film to have an uneven surface. This phenomenon is often referred to as through printing.
Materials such as plastics tend to have lower surface tension and are therefore more prone to retraction when coating their surfaces. To overcome this problem, polar groups such as hydroxyl or carboxyl groups need to be introduced on the plastic surface to increase its surface tension.
To solve the problem of paint film retraction, it is usually necessary to pretreat the substrate to improve the wettability of the coating to the substrate. For metal surfaces, it is common practice to remove organic contaminants and perform chemical treatments (such as phosphating) to homogenize surface properties. For low surface tension materials such as plastics, polar functional groups are often introduced to increase surface tension.
Coatings with high solids content have certain challenges in terms of surface tension. In order to achieve high solids content, Coatings usually need to reduce the molecular weight of Resin and increase the number of polar functional groups (such as hydroxyl or carboxyl groups), which will lead to Coatings with high surface tension. In addition, in order to reduce viscosity, high solids Coatings usually use hydrogen bond receptor-type solvents instead of hydrocarbon solvents. These hydrogen bond receptor-type solvents include high polar compounds such as alcohols, ethers, esters, and ketones, which also increase surface tension. Therefore, high solids Coatings are more prone to retraction due to their high surface tension. It is usually necessary to add surfactants to reduce surface tension to improve leveling.
In conclusion, film retraction is a challenge in the painting process, but it can be effectively solved by pretreating the substrate, selecting the appropriate Coating and adding surfactants. By comprehensively considering various factors in the coating process, a uniform, high-mass film can be obtained to meet the requirements of various industrial applications.