Streaks and Bars in Textile Fabrics Due to Yarn Differences and Technological Reasons

Abstract

Differences in the yarn count, yarn twist and plytwist create different yarn volumes. They are generally referred to as yarn differences and are noticeable as streaks or bars parallel to the threads in woven fabrics and knitwear. They must be attributed to purely optical effects. During examination in reflected light they are caused by the fact that adjacent, more voluminous yarns reflect light to a greater extent. The observer thus gains the impression that there are lighter streaks in these areas than in those with larger gaps between the threads. Here, light is reflected to a lesser extent, thus giving the impression of a darker dyeing or a darker color streak. In transmitted light, conditions are exactly the opposite. This is schematically illustrated in Fig. 173 and 174. However, luster differences between more or less intensively twisted yarns can lead to differences in lightness [44]. There are several possibilities for macroscopic and/or microscopic detection of yarn differences:

• Examination of the streaky textile fabric in transmitted light under the stereo microscope [5,43,45],

• Microscopic examination of the isolated yarns [46],

• Preparation of imprints of the textile fabrics or the isolated yarns [6, 7, 8, 10,47].