In the process of coating construction, the shrinkage problem of the paint film may lead to the quality and appearance of the coating, so it is necessary to deeply understand the causes of shrinkage holes and solutions. This paper will discuss the causes of paint shrinkage and how to effectively deal with this challenge.

1. Causes of shrinkage holes
Shrinkage holes are usually caused by small particles or droplets with low surface tension. These low surface tension substances can be present on the substrate surface, in the paint, or fall from the air just after the wet film has been applied. The following are the main causes of shrinkage:

A. Surface tension gradient: When there is a low surface tension substance in the paint or substrate surface, the surface tension gradient will be generated. The low surface tension part of the paint will try to flow to cover the surrounding high surface tension part, but the volatilization of the solvent will cause the viscosity to increase, and eventually hinder the flow, forming a shrinkage hole.

Causes and solutions of paint shrinkage holes

b. Thick edge phenomenon: When spraying the plate, the paint film is usually thicker at the edge and thinner slightly away from the edge. This is because the air flow is strongest at the edge, and the solvent volatilizes the fastest, resulting in an increase in the resin concentration at the edge and an increase in the surface tension, so that the paint at the edge flows to the center.

c. Airborne effects: airborne particles may fall on the wet paint film during the spraying process. If the surface tension of the flying material is low, shrinkage holes will be created. Conversely, if the surface tension of the flying object is high, it will lead to the orange peel effect.

2. Solutions for shrinkage holes
In order to avoid or reduce the shrinkage problem of the paint film, the following measures can be taken:

a. Increase the thickness of wet paint film: Increase the thickness of wet paint film can reduce the formation of shrinkage holes. Thicker wet paint films are less susceptible to impurity particles, so shrinkage is less likely.

Causes and solutions of paint shrinkage holes

b. Increase the viscosity of wet paint film: by adding thixotropic agents, etc., you can increase the viscosity of wet paint film, thereby preventing paint flow, even if there is the possibility of shrinkage can also reduce its occurrence.

c. Reasonable choice of paint: The choice of paint has an important impact on the shrinkage problem. Solubility between the different components in the paint should be considered to avoid indissolution or precipitation during the drying process.

d. Control coating formulation: The formulation of the coating should be reasonably designed to reduce factors that may cause shrinkage. In particular, attention should be paid to controlling the formation of impurity particles and droplets in the coating.

Causes and solutions of paint shrinkage holes

e. Use leveling agents: For coatings prone to shrinkage, leveling agents can be added to reduce surface tension while promoting the leveling of the paint. Levelling agents can also be used to prevent the orange peel effect.

f. Curtain coating: Curtain coating is an effective coating method that can reduce shrinkage problems. Under this method, the paint screen needs to remain intact, ensuring that no particles or droplets of low surface tension fall on the paint screen.

Shrinkage hole is a common problem that may occur in coating construction, but through reasonable control and prevention measures, this problem can be effectively reduced or avoided. For applications that require high-quality coating, special attention needs to be paid to the shrinkage problem to ensure that the quality and appearance of the final coating meets the requirements.