The weathering fastness properties of organic pigments in rizid P. V. C. are important because of the demands of usage for rigid P. V. C.. These properties have been the subject of considerable studies, but most of the work, reported in the literature, lacks unity in their evaluation methods.
Authors contemplated to examine the weathering fastness mainly about, so-called, high-grade organic pigments to compare the properties with inorganic pigments. The pigments tested include 29 organic and 11 inorganic pigments.
The test pieces, coloured with pigments, were exposed 30° facing south in Takarazuka City, under which condition the test pieces yielded maximum amount of radiation throughout a year.
Exposed test pieces, both opaque and transparent shade, were compared with unexposed control pieces, and extent of the colour change was estimated by reference to the grey-Scale for assessing colour change. The test pieces of opaque shade were measured on a Colour Master (V-type). From these data, the results were expressed in NBS unit.
This paper reports, the results of exposure test for six months. It is true that six months of out-door exposure is insufficient for the test of materials to be used out-door, but, in our experience, fair parts of colour change of a year occur during three months in summer. Then, authors believe that these data are useful for the selection of pigments used in P. V. C.
(1) Perylene reds, quinacridone reds, quinacridone violet, phthalocyanine blue, phthalocyanine green, phthalocyanine black, indanthrone, and carbazole dioxazine violet showed excellent fastness enough comparable to the high-grade inorganic pigments.
(2) Uuexpectedly, the fastness of some condensation azo pigments, flavanthrone, anthrayrimidine yellow, and brominated anthanthrone, were not so fast as they are in the paint systems.
(3) From the results it can be said that, with regard to the most of pigments were examined, the 500-700 hours' exposure of the 6 kW xenon weather-o-meter (SW-SV-S-S type Shimazu Seisakusho Ltd.) is generally equal to the three months' exposure of out-door test in summer time.
As the exception from above mentioned, some azo pigments such as nickel azo yellow are comparatively fast in weather-o-meter test, but they showed remarkable colour change in out-door exposure test.
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