Susumu Shimizu

Hue Change in Interference-Colored Fibers with an Alternating Multilayer Structure

The change in hue of interference-colored fibers, which are consisting of alternating multilayer structure of poly(ethylene terephthalate) (PET) and polyamide 6 (Ny-6) covered with PET clad, was investigated in comparison with that of ordinary dyed PET fibers. The results indicated that, when an incident light was applied to the dyed PET fibers either parallel to or vertical to the fiber axis, although the chromaticness index (a*, b*) plotted on a*- b* coordinates changed in distance from the origin as the receiving angle β was increased from -30° to 70°, no change was observed in its track direction. On the other hand, the track of the chromaticness index for the interference-colored fibers changed substantially between incident lights parallel to and vertical to the fiber axis. In the former case, the chromaticness index plots were virtually all near the origin even though β was varied and tended to move substantially away from the origin in the range of specular reflection angles between 44° and 46°. In the latter case, however, the track of the chromaticness index moved counterclockwise in an arc shape from the second quadrant to the third and fourth quadrants with increasing β, clearly indicating a substantial change in hue. The interference-colored fibers were regarded as an alternating multilayer structure, and their reflection spectra were simulated taking into account the refractive index anisotropy (birefringence) of PET and Ny-6. The chromaticness index was found from the data thus obtained and plotted as coordinates in the same way as described above. As a result, the index was evaluated on the basis of an analysis of the simulation results and its track was plotted on the a*- b* coordinates. It was observed that the tendency of the chromaticness index track relative to the change in β was nearly the same as that seen when an incident light was vertical to the fiber axis. It is thought that the change in hue of the interference-colored fibers due to β is mainly attributable to the variation in the length of the optical path in their alternating multilayer structure.