State Analysis and Observation under Different Lighting Conditions of Center Marks Occurring in Spandex Plated Fabric Produced by Circular Knitting Machines

Center marks are vertical line defects which are invariably visible in spandex plated fabrics knitted by a circular knitting machine. Center marks result in unnecessary efforts and waste fabric. Therefore, solutions to eliminate the occurrence of these defects are necessary. It is not clear whether center marks are a product of knitting or the dyeing process. The marks are usually inspected visually by the operator at the production line using front and back lighting. In this study, we examined the shapes and color distributions of the loops in dyed and finished fabrics and we assessed the state of these visual inspection methods using different lighting conditions. Consequently, the exact shape of the center marks was found to be caused by the bulging of successive vertical loops and the center marks are not caused by dyeing. More exactly, the bulging shape consisted of narrowed loops and two neighboring loops. Furthermore, it became clear that center marks were visually recognized (1) by the shadow casted by the bulging due to the side light, or (2) by the reduction of light transmission by the reduced loop space when using back light. Finally, we concluded that the prevention of the formation of the bulging shape and prevention of the reduction of loop space are the two counter-measures necessary to eliminate center marks in the future.