Dew-cycle exposure

Figure 7.13. Effect of acrylic resin content on the glosses of PVDF blue paints upon dew-cycle exposure. PVDF content ( ) 95% (0) 80% (o) 75% ( ) 70% ( ) 60% ( ) 50%.

Figure 7.14. The final gloss of PVDF blue paint after exposures as a function of PVDF content in resin composition ( ) 5000 h of QUV, ( ) 1000 h of dew cycle.

Practice for operating light- and water-exposure apparatus (unfiltered carbon-arc type) for testing paint, varnish, lacquer, and related products using the dew cycle. 

Under outdoor exposure conditions the aqueous layer is influenced by seasonal and daily changes in humidity and by precipitation (dew, fog, or snow), whereas indoors the aqueous layer is apt to be governed by relatively constant humidity conditions. In this situation, for all practical purposes, there will be an absence of wet-dry cycles, and therefore the effect of indoor humidity will not introduce a time-of-wetness factor. 

The aqueous layer formed under outdoor exposure conditions is strongly influenced by seasonal and diurnal variations in humidity and by precipitation, dew, snow, or fog. Indoors, on the other hand, the aqueous layer is often governed by relatively constant humidity conditions. This means that there are practically no wet-dry cycles indoors and that the influence of indoor humidity can hardly be described by introducing a time of wetness factor. 

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