Barre in viscose knitted fabric

Barre is a problem that results from inconsistencies, say Dayal Mahara and Ganesh Jadhav, who advocate proper communication between spinner and knitter, who should work as a team to reduce the potential for barre to occur and provide a defect-free fabric.

In knitting production, one of the most common and perplexing quality issues is "barre". The factors that can cause or contribute to barre are varied and diverse. The noun "barre" is defined by ASTM as an unintentional, repetitive visual pattern of continuous bars and stripes usually parallel to the filling of woven fabric or to the courses of circular knitted fabric. In a warp knit, barre normally runs in the length direction, following the direction of yarn flow. Barre is basically a visual phenomenon and any property of yarn, which makes it look different from the adjacent yarn in a fabric would result in this defect.

Barre is a consequence of subtle difference in yarn reflectance between individual threads in knit structure. Barre is a continuous visual barred pattern or stripiness parallel to yarn direction that is caused by physical, optical, or dyeing differences in the yarns or geometric differences in the fabric structure acting either singly or in combination to produce the barred pattern.

Barre is a most frequent problem in knitting production (in both Cotton as well as in viscose). Nowadays viscose demand is increasing and people who are running viscose first time are facing the same problem. Various aspects of barre are important for flawless fabric. First discuss on identification of barre, second cause of barre and last prevention from barre.

A. Identification of barre

i) Flat Table or Inspection Tables Examination

Visual barre analysis can be done by laying full-width fabric sample on flat inspection table and observing it from both sides through various angles. Inspection table will be equipped with a proper light source at the back of fabric, which will show the physical presence of barre.

ii) Ultraviolet Light Observation

Ultraviolet light is also known as black light, examination may provide further useful information. Observations that should be made while viewing under lights are:

• Barre frequency and width.
• Barre prominence (dark or light).
• The total length of pattern repeat.

Ultraviolet light allows the presence of mineral oils to be more easily detected, due to their radiant energy (glow). A change in composition or content of oil/wax by the spinner or knitter without appropriate adjustments in scouring can create this problem.

iii) Fabric Dissection

A fabric sample, which contains several barre repetitions is required for performing the accurate dissection analysis. First, the barre streak boundaries are marked by the placement of straight pins and/or felt markers. Individual yarns are removed from light and dark streak sections, and twist levels, twist direction, and cut length weight determinations are made and recorded. For reliable mean values to be established, data should be collected from at least two light/dark repeats. After compilation of yarn information, the numbers can be compared individually to adjacent yarns as well as by groupings of light and dark shades.

iv) Microscopic

Yarns from different spinning systems can have different light reflectance and dye absorption properties. Ring spinning produces yarn that is smooth. Open-end spinning produces yarn with wrapper fibres at irregular intervals. Air-jet spinning produces yarn with more wrapper fibres than open end and inner fibres are more parallel. Microscopy can also reveal a s