Abstract

The surface of tissue paper is relatively complex compared to other paper grades and consists of several overlapping structures like protruding fibres, crepe and fabric-based patterns at different spatial frequencies. The knowledge of tissue surface characteristics is crucial when it comes to improvement with respect to surface softness and the perceptual handfeel of tissue products. In this work we used the optical based, non-contact measurement principle of focus variation for surface characterization of dry-creped, textured and through air dried (TAD) tissue. Based on the three tissue grades, a procedure which includes the characterization of the whole tissue surface throughout different scales within one setup, was developed. Surprisingly, focus variation was rarely used in tissue-related research, as it provides robust and reliable 3D surface information which can be used for further areal surface analysis. Special attention was given to the preparation and discussion of the raw data up to the final analysis including several spatial filtering steps. Enhanced surface parameters like the developed interfacial area ratio (Sdr) and the power spectral density (PSD) were used to describe the surface adequately. The surface roughness of the three tissue grades was compared, with the textured tissue showing the highest roughness in Sdr and PSD analysis. Although both methods are based on different principles, a high correlation in terms of evaluated roughness is evident. Regular structures like crepe and patterns are obtainable as peaks at the respective frequency with a certain intensity in the PSD evaluation. Apart from topography in terms of structures and roughness, the wide field of view of the focus variation measurement also allows assessment of effects related to flocculation and sheet formation. The developed procedure could also be appropriate for other fibre based materials and/or fabrics, which are similar to tissue with respect to optical properties such as for example nonwovens.

Graphic abstract

中文翻译：

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聚焦变异技术作为组织表面表征的工具

摘要

与其他纸张等级相比，薄纸的表面相对复杂，由几种重叠结构组成，如不同空间频率下的突出纤维、绉纹和基于织物的图案。在改善纸巾产品的表面柔软度和感知手感时，了解纸巾表面特性至关重要。在这项工作中，我们使用基于光学的非接触式焦点变化测量原理来表征干绉、纹理和空气干燥 (TAD) 组织的表面特征。基于三个组织等级，开发了一种程序，该程序包括在一个设置内的不同尺度上表征整个组织表面。令人惊讶的是，焦点变化很少用于组织相关研究，因为它提供了强大而可靠的 3D 表面信息，可用于进一步的区域表面分析。特别注意原始数据的准备和讨论，直到最终分析，包括几个空间过滤步骤。增强的表面参数如发达的界面面积比 (Sdr) 和功率谱密度 (PSD) 被用来充分描述表面。比较了三种组织等级的表面粗糙度，纹理组织在 Sdr 和 PSD 分析中显示出最高的粗糙度。尽管这两种方法基于不同的原理，但在评估粗糙度方面的高度相关性是显而易见的。像绉纹和图案这样的规则结构可以在 PSD 评估中作为具有特定强度的相应频率的峰值获得。除了结构和粗糙度方面的地形外，焦距变化测量的宽视野还允许评估与絮凝和片材形成相关的影响。所开发的程序也可能适用于其他基于纤维的材料和/或织物，就光学性能而言，它们类似于薄纸，例如非织造布。

图形摘要