In the process of coating construction, paint film retraction is a common but troublesome problem. It will cause the coating to be uneven during the coating process, ultimately affecting the quality and appearance of the coating film. In this article, we will explore the causes of paint film retraction and how to effectively address this challenge.

The flatness of coatings is usually affected by surface tension. Surface tension is a manifestation of the force exerted on the surface of the liquid molecule. High surface tension of the liquid tends to form a ball, and it is not easy to wet the surface of the substrate. When the paint can not fully wet the surface of the substrate, the wet paint film will naturally shrink back into a ball, forming a phenomenon of uneven film thickness, which is called shrinkage.

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 anti-rust oil) is not removed from the metal surface before painting, these oil stains may push away the paint, resulting in an uneven surface of the film. This phenomenon is often referred to as through printing.

Reasons and countermeasures of paint film retraction

Materials such as plastics tend to have lower surface tension, so retraction is more likely to occur when coating their surfaces. In order to overcome this problem, groups with polarity (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 on the substrate. For metal surfaces, it is common practice to remove organic dirt and apply chemical treatments (such as phosphating) to homogenize surface properties. For materials with low surface tension, such as plastics, it is usually necessary to introduce polar functional groups to improve the surface tension.

Reasons and countermeasures of paint film retraction

The surface tension of high solid coating is a challenge. To achieve a high solid content, coatings usually need to reduce the molecular weight of the resin and increase the number of polar functional groups, such as hydroxyl or carboxylic groups, which results in a higher surface tension of the coating. In addition, in order to reduce viscosity, high solid separation coatings usually use hydrogen bond receptor solvents rather than hydrocarbon solvents. These hydrogen bond receptor solvents include highly polar compounds such as alcohols, ethers, esters, ketones, etc., which also increase surface tension. Therefore, high-solid coatings are more prone to shrinkage due to their high surface tension, and it is usually necessary to add surfactants to reduce the surface tension in order to improve leveling.

In short, film retraction is a challenge in the coating process, but it can be effectively solved by pretreating the substrate, selecting the right paint and adding surfactants. By comprehensively considering various factors in the coating process, a uniform and high-quality coating film can be obtained to meet the requirements of various industrial applications.