Deterioration of Coating Films by Weathering

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  • 塗膜の耐候劣化
  • 塗膜の耐候劣化(2)色の経時変化
  • トマク ノ タイコウ レッカ 2 イロ ノ ケイジ ヘンカ
  • II. 色の経時変化
  • Part 2 : Color change (of Coating Films) with Time

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Abstract

The purposes of this paper are as follows : 1) trial to systematization of the degradation of coating films with passage of time in natural weathering and accelerated weathering tests;2) expression with mathematical model for easy quantitative consideration. The air-drying alkyd resin enamels (8 samples prepared from same vehicle with different tint) were treated by sunshine and xenone accelerated weathering machine up to 1000h. <BR>The color difference between the original and the tested panels was calculated by CIE94 color difference equation. For the relation between the color difference and test period, following two equations showed good fitting and high determination coefficient. _??_E=p√t+q, _??_E=_??_Ef (1-e-kt)<BR>where _??_Ef is a presumed upper limit of color difference. The former equation that fitted well at the initial stage of deterioration was interesting because it suggested the participation of the diffusion control mechanism in the discoloration mechanism, but it did not converge to maximum color difference at long exposure. The latter equation was better to be understood than the former one because it was derived easier by the assumption of the 1 st-order reaction mechanism. The coefficients of regression formula, showed that the induction period in xenone aqccerelated weathering machine was shorter than that of sunshine accerelated weathering machine. Also it was shown that the ratio between sunshine and xenone accelarations, namely the ratio between periods that required to show a same color difference was not constant, but vary with the level of the color difference.

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