TISSUE SOFTNESS EVALUATION BY MECHANICAL STYLUS SCANNING

A mechanical stylus surface analyzer (MSSA) system and the corresponding software were used to conduct standard surface analysis procedures. The MSSA instrumentation measures surface characteristics of soft bathroom tissue products. This paper describes the applicability of MSSA and how human tactile response may be modeled through characterization of surfaces. The concepts of passive and active touch as related to human perceived softness are reviewed. In particular, parameters pertinent to these kinds of tactile exploration are mentioned, as well as how they can be used to build a better model of human tactile response. A novel frequency analysis parameter called the frequency index for tactile sensitivity (FITS) is based on tissue paper surface analysis results from MSSA and provides the basis for the human response model. Included is a review of subjective human softness evaluation data for select tissues gathered to represent actual human responses. The MSSA and optical image analysis (OIA) data were collected on the same tissues, and the FITS parameter was found using MSSA. Also, MSSA data were used to reproduce an old standard parameter for evaluating tissue softness called the human tactile response (HTR) index. Since it is not possible to exactly reproduce HTR, the reproduced parameter calculated in this study is called HTR equivalent (HTR}EQ). Finally, standard deviation of luminance (SDL) and loosely bonded surface fibers (LBSF) parameters are determined for select tissues using OIA. Correlation results of the human data with FITS, HTR}EQ, SDL, and LBSF are discussed; FITS correlates best with the human response data and, together MSSA and FITS, has the ability to model human response to the softness of tissue paper products.