Surface tension-induced coating defects and prevention methods (2)

Continuing from the introduction of coating disadvantages caused by surface tension and prevention methods (1), this article will introduce the disadvantages of surface tension on solvent-based coatings in detail. The coating ills caused by surface tension are especially common in solvent-based coatings. In water-based coatings, due to the use of surfactants, the surface tension of the coating is relatively constant, and the cause of the disadvantages is relatively less related to the surface tension. When the solvent volatilizes on the surface of the wet coating, two effects will occur: that is, due to the heat absorption of the solvent during volatilization, the temperature near the volatilization center will decrease; in addition, the concentration of pigments and film-forming substances near the volatilization center will increase. Both of these effects increase the surface tension near the volatilization center (the surface tension of the liquid in 2.1 decreases as the temperature increases). In this way, the paint around the volatilization center has a higher surface tension than the center, forming a pulling force from the center to the outside (see Figure 3). At the same time, due to the increase of the solid content near the volatilization center, its relative density will be greater than that at the bottom of the coating film, so a convective vortex in the up and down direction will be generated (see Figure 3). This eddy current due to surface tension gradients and density gradients continues until the surface tension is equalized everywhere and/or the viscosity of the paint becomes very high.