Correlation between natural and accelerated weathering of coated wood（II） －Changes in L , a , b parameters and gloss

Sugi heartwood specimens finished with commercially available wood preservative semitransparent coatings(seven water-borne and two solvent-borne)were exposed to accelerated weathering by a xenon lamp(JIS K5600-7-7)and a fluorescent UV lamp(EN 927-6) and to natural weathering(45° inclination facing south in Tsukuba, Japan). Our previous report focused on the test periods of the two accelerated weathering conditions that corresponded to 2 years of natural weathering. However, the details of the changes in color of the naturally weathered specimens and the reproducibility of outdoor exposure by accelerated weathering were not well explained. Therefore, the parameters of color(L *, a *, b *) and gloss(Gs(60°))of the specimens used in the previous tests were compared and examined. Exposure to a fluorescent UV lamp was found to be more similar to natural weathering than exposure to a xenon lamp with respect to changes in a *, b *, and gloss. Furthermore, it was found that the correlation of performance ranking between natural and accelerated weathering was low for ΔL * and high for Δa *. The correlation coefficient of the ranking of Δb * between natural weathering and weathering by the fluorescent UV lamp was significantly higher than that between natural weathering and weathering by the xenon lamp.