Comparison of Hair Heat-Treatment Effects between Monolithic Alumina Ceramic and Ceramic-Coated Heating Plates for Hair Irons

This study compared hair heat-treatment responses between ceramic-coated and monolithic alumina ceramic heating plates using the same hair iron model at set temperatures of 100℃, 130℃, and 160℃. Hair-tress compactness was evaluated using image-based mean tress width, color change was assessed by CIE L*a*b* colorimetry, and cuticle surface microtopography was examined by atomic force microscopy (AFM). Virgin hair was used for image and AFM analyses, and bleached and blue-dyed tresses for colorimetric analysis. Color difference (ΔE*ab) was measured after 10, 20, and 30 cumulative passes using three independent tresses per condition, whereas mean tress width and AFM roughness were interpreted descriptively. At all three set temperatures, the alumina ceramic groups showed lower mean tress width and lower mean ΔE*ab than the ceramic-coated groups, and the main effect of heating plate type on ΔE*ab was statistically significant. Descriptive AFM roughness values were also lower in the alumina groups. The 130℃ alumina condition showed a comparatively balanced pattern in tress compactness, color change, and surface roughness, whereas raising the set temperature to 160℃ yielded little additional reduction in mean tress width while color change and roughness increased. These findings indicate that hair responses may differ according to heating-plate configuration even at the same set temperature. Because the actual surface temperature, heat distribution, clamping pressure, and friction were not measured in this study, the specific thermal and mechanical mechanisms underlying these differences remain to be clarified.