Paper superficial waviness: Conception and implementation of an industrial statistical measurement system

Abstract

The development of proper measurement methodologies for product evaluation is a critical issue to papermakers since their customers are increasingly demanding in regard to new product development and product quality. This paper addresses the conception of a measurement system to assess objectively and systematically paper superficial waviness in industrial practice. Such a system is based on mechanical stylus profilometry. The measurement system conception process is presented in this article, considering all of its stages: (i) gage selection and auxiliary components creation, (ii) drawing of a measurement procedure, (iii) assessment of the system capacities (through a repeatability and reproducibility (R&R) study), (iv) design of an appropriate categorical scale for paper waviness classification, and (v) validation of the classification model. The definition of the categorical scale encompassed the sensorial and instrumental characterization of several sheets of paper. The corresponding classification model strongly relies on the quality of judgments made by a panel of experts, and therefore the definition of a golden standard was carefully conducted. Two distinctive methodologies were used to assess the perceptiveness of the judges regarding paper superficial waviness, and linear discriminant analysis with stepwise variable selection for dimensional reduction was then applied to build a final classification model. The system conceived can be very helpful in the field of product design and process development, besides its obvious application to the monitoring of paper superficial quality. In fact, it can play an important role as an instrument used to define process–structure and structure–properties relationships, which may help in achieving faster product design time cycles.