Study On Evaluation Methods Of Weathering Resistance Of Metal Based Decorative Coatings

Metal based decorative coatings have both decorative and protective properties.It is gradually affected by environmental factors in the process of natural exposure and leads to changes in appearance and properties.Therefore,it is necessary to carry out a series of environmental experiments to evaluate the durability of metal decorative coatings under different climatic conditions.At present,the experiments of coating durability mainly includes natural exposure and artificial accelerated experiments.The data of natural exposure is intuitive and reliable,but the experimental cycle is too long.Moreover,the durability evaluation methods of all kinds of metal decorative coating products are mostly single light weathering or salt spray corrosion experiments,which can not simulate the influence of the actual environment on the coating.Therefore,it is necessary to find an appropriate accelerated weathering experiment method to simulate the natural environment conditions,and to provide a reasonable basis for the durability evaluation of coatings.3 polyester coatings and 3 fluorocarbon coatings are choosed as the experimental objects since polyester and fluorocarbon coatings have a better durability in common coatings.The outdoor exposure tests of three places,mainly in Qionghai,Turpan and Shenyang,were carried out.This paper analyzes the main influence factors of coating weathering environment,combined with the meteorological data,thus design a comprehensive accelerated weathering experiment scheme of 3 "radiation + salt spray" experiments,and 3 kinds of single accelerated weathering experiments which include xenon lamp,UV aging test and salt spray test for comparison,a total of 6 kinds of artificial accelerated weathering corrosion experiments.Three aspects of appearance,color and glossiness are considered to evaluate 6 coatings’ indoor accelerated experiment and Qionghai natural exposure weathering law.Using Spearman rank correlation coefficient method,the correlation between indoor and outdoor experiments was analyzed,and the artificial accelerated weathering experiment method,which is the best correlation with the natural exposure,was selected.Finally,Raman spectroscopy was used to analyze whether the weathering mechanism of the coating after the artificial accelerated test was consistent with the weathering mechanism after the natural exposure.The result shows:The main morphological features of coating weathering are discoloration and loss of light.High temperature and high humidity exposure,corrosive ions and other environmental factors influence each other,synergistic effect,accelerating the coating weathering,while the single environmental factors had little effect on coating aging.Xenon lamp weathering test has the best acceleration and poor simulation.Salt spray corrosion experiment has little influence on the coating color aberration and glossiness,the acceleration of salt spray corrosion is the worst,the coating appearance of the salt spray corrosion has great difference with that of the natural exposure test,and the correlation is poor.The correlation between the comprehensive accelerated weathering experiments and the natural exposure are better.In the 6 coatings’ weathering process of the accelerated comprehensive experiment cycle 1 "7 d xenon +3 d salt spray" and natural exposure,the variation trend of color aberration and glossiness is the same;the acceleration of cycle 1 is good;the color aberration correlation coefficient value of cycle 1 and natural exposure in Qionghai is 0.83,a quite good correlation;the polyester coating laser Raman spectrum of the mid infrared section shows that pigments and fillers in the coating has a high degree of degradation,and the aging mechanism of the two is basically the same.It shows that the "7 d xenon +3 d salt spray" comprehensive accelerated weathering experiment can be used as an artificial accelerated weathering experiment method to evaluate the durability of metal based decorative coatings.