2021 Volume 70 Issue 2 Pages 83-88
In infrared thermographic tests, background reflection from the sun or neighboring structures is one of the serious problems that lead to false detection of flaws. Generally, the background reflection appears as a hot spot on the thermal image, and can lead to faults during inspection. To avoid this, the background reflection must be removed from the thermal image. Metals, owing to their high reflectivity, are especially susceptible to background reflection during conventional infrared thermographic tests. In this study, the authors have developed a blackbody film made of polyvinyl alcohol that has a high emissivity in the infrared range and a high transmissivity in the visible range. At first, the authors measured the spectral emissivity of the film by using a Fourier transform infrared spectrometer. A measuring equation was proposed for the film that has high emissivity and low transmissivity. Further, the measurements revealed that: a higher degree of saponification leads to higher emissivity; it has a sufficiently high emissivity; and a long infrared range. Next, the authors carried out infrared thermographic tests on a stainless steel plate having background reflection. The results show that the film is effective as a material with low emissivity.
