Coating surface temperature during artifical weathering

 
The surface temperature of a sample irradiated with natural solar radiation or artificial xenon arc radiation is not only influenced by the environment but also by its specific material properties such as its color. So far it has been impractical in weathering tests to measure the sample surface temperature directly. Experimenters mainly estimated sample surface temperatures based on measurements made with reference thermometers, such as insulated (black standard thermometers) or uninsulated black panels (black panel thermometers), which may, but not always, represent the hottest temperature a surface can achieve in a specific environment under irradiation. An inaccuracy in estimating the true sample temperature can significantly influence the evaluation of a weathering test regarding the aging behavior of the sample. Knowing the actual sample surface temperature more precisely facilitates the comparison of different weathering conditions (e.g. natural and artificial weathering, or between different colored samples). It is also possible to adjust the test parameters of artificial weathering cycles based on the specific sample characteristics, such as the glass transition temperature. In this paper, we present how non-contact temperature measurement can be implemented in artificial weathering to obtain more detailed information about the actual surface temperature during weathering. This method could be used, for example, to determine activation energies of photochemical degradation processes that can lead to yellowing or fading or other property changes of samples. This information can help to better understand artificial weathering. By knowing and considering the specific sample temperature, better estimations of service life can be made.