THE LEVELING OF THERMOSETTING WATERBORNE COATINGS .1. OBSERVATION OF LEVELING PROCESS

A modified observation system for the leveling process of a coated flu id is proposed, and the observation results are presented and compared with previous results. For the thermosetting waterborne coatings, the theory of Orchard, et al., and ones based on it are not applicable an d fail to give even a qualitative description. The theory of Overdiep was found to be reasonable. However, it was tnsufficient to predict th e leveling performances of coatings without experimentation. Qualitati vely, the original theory suggests the possibility of the reappearance of surface ripples, in other words, the occurrence of the negative am plitude in the surface ripples during the course of leveling, although little data were presented regarding the phenomenon. It was found her e that added co-solvent plays an important role on the leveling rate a nd also the occurrence and the control of the negative amplitude of th e surface ripples. These are thought to relate closely to the volatili ty of the co-solvent and the composition of the solvent residue in the coated film during the leveling process.