Evaluation of Surface Softness of Tissue Paper Products Using Mechanical Stylus Scanning, Optical Image Analysis and Fuzzy Sets, 1994 Nonwovens Conference Proceedings

J.P. Rust, I. Shalev, T.L. Keadle, R. L. Barker

A previous paper outlined development of mechanical stylus surface analysis (MSSA) instrumentation used to measure surface characteristics of soft tissue paper products. This paper details how this novel system can be used to characterize surface features of tissue paper in order to model human tactile response. The concepts of passive and active touch are discussed. Variables pertinent to these types of tactile exploration are reviewed and used in modeling human tactile response. This model is a novel frequency analysis parameter called the Frequency Index for Tactile Sensitivity (FITS). FITS is calculated from raw surface feature data obtained from the MSSA. The MSSA data were also used to reproduce a standard parameter of tissue softness called Human Tactile Response-Index (HTR). Since it is not possible to exactly reproduce HTR, a similar parameter was created called HTR Equivalent (HTR_EQ). Optical image analysis (OIA) was also performed on these same tissues. The OIA data collected were Standard Deviation of Luminance (SDL) and loosely bonded surface fibers (LBSF). Subjective human softness evaluation data (PROBIT) for select tissues were gathered and these procedures and results are presented. Results of correlations of FITS, HTR_EQ, SDL and LBSF with the human data are discussed. FITS is shown to be superior to the other parameters as a predictor of human tactile response. The FITS parameter gained from MSSA data provided the best single means of modeling human response to softness of lofty, tissue paper products. Fuzzy sets were also used to develop a parameter which combine MSSA and OIA data, in order to reproduce the uncertainty associated with human tactile response. This fuzzy parameter correlated better with the human data than any single or multiple regression of FITS, HTR_EQ, SDL and LBSF data.