This paper gives an overview of the potential of the photometric stereo principle to determine the surface topography of tissue, paper, and board. For paper and board grades, these modern analyzers do not just estimate PPS or other traditional measures, they provide quite another dimension for topography characterization that no air leak-based-method can offer. Up until now, the objective determination of tissue softness has only been possible with few test devices in the laboratory. In tissue grades, topography analysis of final tissue product after creping makes it possible to determine a number of useful quality parameters including tissue softness.
Photometric stereo techniques are already able to measure, on-line, detailed features of the web surface moving at typical paper and tissue production speeds, that the human eye cannot resolve. Photometric stereo-based techniques have enabled on-line topography analysis of paper or board in astonishingly high resolution. The photoclinometric method with oblique surface illumination is suitable for the prediction of surface softness and water-absorption capacity of tissue paper products.
On the other hand, the surface softness increased with decreasing of the optical surface variability of tissue paper products. Water-absorption capacity and optical surface variability were the highest for kitchen towels and decreased in following order: toilet papers, napkins, handkerchiefs and cosmetic towels. Lower correlation coefficient values are related to differences in production technologies of tissue paper products such as pulp selection and refining method, application of wet strength agents, type and dose of debonder. The correlation coefficient of the relationship between optical surface variability and water-absorption capacity was 0.75 and surface softness was 0.78. The analysis showed that the water-absorption capacity and surface softness depend to some extent on the optical surface variability. Simple analysis of the image obtained by the photoclinometric method with oblique surface illumination was used to determine the optical surface variability of tissue paper products.
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