Abstract
The texture of powder cosmetics, such as “smoothness” and “moist feeling”, is one of the most important properties for a usability assessment. In general, we rely upon a sensory evaluation to assess the usability of cosmetics. However, such subjective evaluation tends to be vague, not only due to the lack of evaluators'skill but also due to the reproducibility error of environmental factors. Therefore, a highly reliable and efficient evaluation method using physical properties has been in demand. In the fields where powder products are handled, such as the pharmaceutical and food industries, the direct shear testing of the powder bed (DST) has been applied for evaluating the powder's flowability, as an important physical property in the filling process. In this study, the correlation between sense of use and physical properties was investigated by DST for powder ingredients and powdery foundations. As a result, it was found that the internal friction coefficient μi was correlated with “smoothness”, while the shearing cohesion τc was related to “moist feeling”. This evaluation method can be applied to powder ingredients as well as to molded powders. Furthermore, this method can precisely detect the differences in texture between powdery foundations obtained from different molding processes (i.e. dry and wet molding processes).
