PROPOSAL ON WEATHERABILITY EVALUATION OF COATING MATERIALS BASED ON LITERATURE SURVEYS

Abstract

From the viewpoint of the durability of coating materials for buildings, the estimation of their weatherability is critical. JIS A 6909 has regulated the weatherability types for coating materials based on the accelerated weatherability tests. However, the relationship between the deterioration progress in coating materials under the accelerated weatherability test and that under the outdoor exposure test is not clear yet. An outdoor exposure test on coating materials for 13 years in Sapporo, a literature survey on the results of the outdoor exposure tests and accelerated weatherability tests (using the sunshine and Xenon lamp weather meters) were carried out to elucidate the relationship. In a previous study, the authors proposed an equation for estimating the gloss retention decrease, which is an indicator of deterioration in coating materials. In this study, the applicability of the proposed equation to the experimental results of the outdoor exposure test and literature survey was investigated. The results showed a high correlation between the estimated results and the measured results for gloss retention though there are some exceptions. To investigate the estimation method of the gloss retention after the long term exposure at the initial material age, we also compared the ten years gloss retention measured values to estimated values using two years values. The estimation of the long-term outdoor exposure results from the short-term results was difficult. The outdoor exposure test results from multiple regions showed that the weatherability was mainly affected by the coating material type. A method for the estimation of the gloss retention decrease during the outdoor exposure test using the accelerated weatherability test results was proposed. The average gloss retention was determined using the gloss retention obtained from the accelerated weatherability test. The dispersion for the average gloss retention showed the regional differences. The gloss retention was estimated by a probabilistic model using the average gloss retention and standard deviation obtained from the experimental results. Consequently, the obtained experimental results were almost within the significance level of 5%. Finally, the standard deterioration of the gloss retention for each resin type of the coating materials was also analyzed. The standard degradation progress of gloss retention and this definition enabled to calculate the service life of each resin type. The results showed that the weatherability types 1, 2, and three regulated in JIS A 6909 were equivalent to the service lives of fluorine, urethane, and acrylic resins respectively. The estimation results correlated with the empirical service life of the coating materials.