Deterioration of Coating Films by Weathering

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  • 塗膜の耐候劣化
  • 塗膜の耐候劣化(1)光沢の経時変化
  • トマク ノ タイコウ レッカ 1 コウタク ノ ケイジ ヘンカ
  • I. 光沢の経時変化
  • Part 1 : Change of Gloss with Time

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Abstract

The changes of specular gloss of coatings by exposure tests obey well to a logistic equation.<BR>When a function of gloss (y), expressed as (y) as f (y) =ln {(A-y) / (y-B)}, <BR>was plotted against exposure time, a straight line was obtained, where A and B are higher and lower limits of gloss, respectively.<BR>The coefficient of determination for the regression of this plot was as high as over 0.9. The calculated gloss using the coefficients in the regression equation matched very well to those observed. The sample data used in this investigation were the gloss of air dried urethane resin enamels exposed at Choshi and Miyakojima. Fairly satisfactory gloss was estimated when A and B were assumed to be 100 and 0, respectively, except for a few samples that had high residual gloss after the exposure.<BR>The ratio of exposure periods to reach a same gloss at different exposure sites or conditions of exposures differed depending on the levels of gloss. We should pay attention that the ratio of the velocities of deterioration differs depending on the varieties of coatings, the compatibility or affinity of the components, properties associated with deterioration, and the levels of deterioration.<BR>Because the logistic equation has a symmetrical shape, detailed observation of the first half enables quite correct estimation of the latter half.

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