老化方式对聚氨酯涂层钢板失效行为的影响

运用四种加速方法对聚氨酯有机涂层钢板进行老化，并通过涂层的表观性能和电化学特征对比研究了老化方式对涂层失效的影响.紫外老化对涂层光泽的影响最大，老化32 d失光度达85.7%.盐雾实验前期线性极化阻力Rp迅速下降，后期由于盐膜的生成使得Rp保持稳定；氙灯和盐雾混合老化的光泽度和Rp的变化规律都表现为实验前期与光老化相似，后期则与盐雾实验相类似.此外，拟合不同老化方式的电化学交流阻抗谱发现：混合老化前期主要受氙灯影响，与单一氙灯老化的等效电路一致，表现为两个时间常数；后期产生盐膜，出现三个时间常数.

Effect of aging approaches on the aging behavior of polyurethane coated steels

Four accelerated weathering tests were carried out on polyurethane coated steels. The apparent properties and electro-chemical characteristics of the coatings were studied to compare the effects of different accelerated weathering tests on the coating fail-ure behavior. It is found that UV exerts the greatest influence on the glossiness of the coatings and the gloss loss reaches up to 85. 7%after 32 d aging. The linear polarization resistance decreases rapidly in the early period of the salt spray test and stabilizes in the later period due to the formation of a salt film. In the mixed aging ( xenon light aging+salt spray) test, the variation tendency of both gloss loss and linear polarization resistance are similar to those presented in the early period of xenon light aging and similar to those presen-ted in the later period of salt spray test. Moreover, the equivalent circuit of the mixed aging test shows two time constants in the early period, which is consistent with the single xenon light aging test. In the later period, the failure process of the coatings can be mani-fested with three time constants, in which the formation of a salt film is the typical feature.