Leveling American Coatings Association（水准,美国涂料协会）.pdf

Coatings CliniC By Clifford K. Schoff, Schoff Associates Leveling I recently realized that, in 10 years of writing “Coatings raising surface tension may affect wetting of the substrate Clinics,” I had never written one on leveling. So, here it is. and a thicker film may not be desirable, so reducing viscos- When paint is applied, it rarely is smooth. It usually ity often is the only practical choice among the three. has a non-uniform thickness with irregularities such as However, if the film can be kept open longer, then it brushmarks, orange peel, roughness, or patterns. The term is likely that both the rates of increase of viscosity and de- leveling refers to the flowout of these often ugly surface crease in film thickness will be lower. The time over which characteristics. It is a process that receives little notice leveling occurs can be stretched through the use of slower when it works well, but the effect is very apparent when solvents, less or a weaker thickener, and with baked coat- it does not. The driving force for leveling is surface ten- ings, the use of less crosslinker or a weaker catalyst. sion, which acts to reduce the surface area to a minimum, It is possible to predict the leveling tendencies of a thereby promoting a smooth, even surface. Viscosity, vis- formulation by characterizing its viscosity behavior using a coelasticity, and yield behavior act to resist this flow, and step-shear m