紙層構造パラメータによるパルプシート光学的性質の評価 厚壁繊維シートの光学的性質

Abstract

Interrelationships between optical properties and layered structure of the sheets from beaten thick-walled (TK) elements and from mixture of thin-walled short (TNS) elements and lightly beaten TK elements were discussed quantitatively by applying the layered model theory developed by Scallan and Borch.The “apparent” layer thickness, t', determined from the experimental values of reflectance and basis weight by using Eq. [3A] was a good structural parameter which relates optical properties to layered structure of the sheets especially from highly bleached pulp elements. Since the layered structure of real sheet is different from the parallel layered model illustrated by Scallan and Borch, it is pointed out that the “apparent” layer thickness, t', is practically affected by two geometrical parameters of the sheet, the layer thickness in z-direction, tf, and anisotropy parameter, s, and expressed as t'=tf/ε. The tf estimated by analyzing the cross sections of the sheets and t' from optical data for the thick-walled element sheets are tabulated in Table 3.Peculiar characteristics in optical properties of the sample sheets were found. The opacity and specific scattering coefficient of the sheets from beaten TK elements increase with the progress in beating and those of the sheets from the mixture of TNS elements and TK elements also increase with the increase in the content of the TNS elements (Table 2 and Fig. 4). The increase in specific scattering coefficient indicates that optically effective surface area of the sheet increases. It was reflecteted on the increase in the number of optically effective layers. n0, and on the decrease in “apparent” layer thickness, t', of the sheets (Table 3).These structural changes in the thick-walled element sheets estimated from the optical data could be supported by the layered structure observed on the cross sections of the sheets (Fig. 3). In the case of beaten TK element sheets, thin filmy layers were found among the element-to-element spaces due to the separation of TK elements during beating process. In the sheets from mixture of TNS elements and TK elements, the TNS elements were located in the sheets like a bridge between TK elements.