Shrinking edge, also known as fat edge or thick edge, frame, etc. After the coating film is formed, the area of contact between the edge of the paint film and the air is larger than the other middle parts. At the edge, it contacts all three sides, with only one side in the middle. So the evaporation rate of its solvent will be faster at the edges, and the viscosity of the paint in the area will increase more, resulting in a slightly higher surface elasticity than other parts. The difference in surface tension gradient can cause the flow of paint. The flow of liquid is from areas with low surface tension to areas with high surface tension. From the area with low surface tension in the middle, it flows towards the area with high surface tension at the edges, causing the phenomenon of fat edges. How to solve the problem of constipation? Firstly, we need to address the issue of uneven surface tension.
Adding organic silicon leveling agent, because organic silicon leveling agent has low surface energy, it will migrate to the surface and form a monolayer. Eliminating the overall surface tension difference means that the surface is entirely composed of a layer of monolayer organic silicon. In the later stage of solvent evaporation, the overall surface tension of the gas film will increase again.
In the later stage, it is necessary to use some non silicon leveling agents to balance the uniformity of surface tension. So, by using a combination of organic silicon leveling agents and non silicon leveling agents, the phenomenon of edge shrinkage can be improved. Secondly, by adding thickening agents with strong thixotropy and low alkali shear, the system’s thixotropy or pseudoplasticity can be increased, resulting in a decrease in the flowability of the paint film in a static state.
Even if there is an imbalance in surface tension, it cannot flow. Finally, it is important to pay attention to the solubility, parameters, volatilization gradient, and amount of diluent added. If all solvents or co solvents are used in the system, insufficient solubility is definitely not good.
Is it better to use real solvents or strong solvents? In fact, this is not good either. The solubility between strong solvents and resins is too strong, and the release of solvents is not good. If the paint film is in this wet state for a long time, various problems are more likely to occur. In addition, the evaporation gradient of the solvent should also be reasonable. The solvent should not run too fast or too slowly, and there should be a reasonable evaporation gradient to ensure uniform changes in the surface tension of the paint film, without large fluctuations.
The dilution ratio of the solvent is also important. For some friends who do painting, the more solvent they add, the better. 1:1 is not enough, and it is best to add 1:2 or 1:3. The final film-forming part of the paint film still relies on solid components, and all solvents added will eventually evaporate. Excessive addition of diluent system can cause significant changes in surface tension during film formation, leading to phenomena such as edge shrinkage and fat edges.
Post time: Sep-24-2026