Abstract
The degradation of acryl-melamine resin films in hot water was investigated in the temperature range between 70 and 100°C by means of stress relaxation. The films were prepared by electrocoating in water and non-electrocoating in an organic solvent. (1) The stress relaxation curves for the swollen films may be represented as the sum of two or three exponential terms of stress decay. The final term is shown to be due to the breakage of crosslinks, i. e., a chemical stress relaxation. (2) The maximum relaxation time (τ2) and the degree of crosslinking (n0) of the electrocoated films increased proportionally with the rise of curing temperature. The values of τ2 for electrocoated films are smaller than those for non-electrocoated films cured at the same curing temperature. (3) When curing reaction was accelerated, p-toluene sulfonic acid was mixed as catalyst into the acryl-melamine resin, but the τ2 and n0 no longer increased proportionally with the rise of curing temperature. These results can be ascribed to the presence of microgel structures in acryl-melamine co-networks.
