Viscose Barre- Causes, Precautions, Analysis

Barre- Causes, Precautions, Analysis

Rushikesh Raghav, Dr. Ravinder Tuteja

Textile Research and Application Development Centre

Introduction

Softness & Skin friendliness of the viscose fiber empowering the growth of viscose in knit wears specially women wears. Use of spandex in knit fabric gives unique feature of stretch to fit in knit garments. Viscose is regenerated fiber produced at controlled plant with average 80 ton per Day at single spinning Line. It means almost 80 ton yarn will not have any dyeability variation problem, if produce at one spinner and at same time & in controlled condition. Whereas cotton is natural fiber & its growth depends on type of field, weather & Climatic conditions, which are beyond Human control.

The properties of the cotton fiber vary between lots and within lots. The properties like maturity, micronaire, whiteness index influence dyeability of the fiber. High variation in these parameters leads to dyeability variation in the fabric. To eliminate or minimise the dyeability variation we must ensure uniform distribution of fiber properties throughout the yarn manufacturing process.

In knit fabric production one of the most common quality control challenges is Barre. Barre is the result of defects in the fiber, yarn, fabric structure or material handling. Most serious issue with the Barre identification is, most of the times it gets detected after the processing at the end of the fabric production. Therefore purchase and sale of the Fiber suppliers, spinners & Knitters take place on the guarantee provided by the supplier that, no barre will occur in the end knit fabric. Fabric barre are unintentional stripes or bars mostly in the knit fabric in the course direction. It appears as light and dark bars running throughout the width of the fabric.

The factors contributing to the barre are varied and diverse, so when the barre is detected it needs skill to identify and eliminate the reason of the barre. Barre can be caused by differences in the yarn fiber or fabric structure or any combination of these differences. Barre is visual phenomenon based on subtle differences in the reflectance of the adjacent yarns in the knit structure. Mechanism responsible for the reflectance of the yarn was responsible for Barre.

Consistency in all phases of the textile can prevent the occurrence of the barre. Material should be properly labelled to avoid mix up. Fugitive tinting o t he cones can help to segregate the material. FIFO must be followed for inventory control. Equipment must be periodically checked for maintenance. In spinning and knitting before going for full scale production, sample dyeing can be done it will be helpful to check the Barre appearance. Training of the knitter will also help if he can identify the barre occurrence at the knitting stage. [4]

Literature review

Barre is the problem that results from the inconsistencies and poor management of the fiber, yarn and/or related knitting processes. The spinner, knitter and processor must communicate and work together as a team to overcome the Barre [8].

Barré problem arises in fabric due to fluctuation of number of fibres in yarn cross section. And the Micronaire value of cotton determines the no. of fibre in yarn cross section. By performing the author suggested method for any cotton lot, it is possible to maintain the average Micronaire value with a limited CV% and also possible to distribute the color grades uniformly against it’s Micronaire value. Author defined procedure of bale selection for each lay down can confirm the uniform distribution of fibre in yarn cross section which will lead to minimizing Barré problem [2].

The fabric analysis in the case of fabric made from different yarn counts (16s, 20s and 30s) show that yarn counts do not create the fabric barre, however if there is a mixing of yarn of different counts then knitted fabric may produce fabric barre or streaks. [6]

The results obtained in case of different twist multipliers show that if T.M. is higher from a certain limit, the fabric barre are visually shown in the knitted fabric samples.[6]

In the case of yarn count deviation, fabric barre are produced if there is an excessive yarn count fluctuation. Those yarns which fluctuate ±1 from nominal value of the yarn count, cause the fabric barre or streaks in knitted fabric.[6]

Of the fibre parameters, the degree of yellowness of cotton seems to have a relatively more significant effect on the Barre intensity in fabrics than the micronaire. Difference more than 1.5 of +b value leads to barre appearance. However even deviation of micronaire value to the extent of +0.15 results in a visible barre defect. Deviations in yarn count also shows up significantly as Barre defects [7].

Definition

The noun “barré” 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 knit fabric. In a warp knit fabric, barré normally runs in the length direction, following the direction of yarn flow. Barré can be caused by physical or optical or dye differences in the yarn, geometric difference in the fabric structure or by any combination of these difference.

Barre defined by AATCC Monograph M10 barre, n.—an unintentional, usually repetitive, pattern of continuous bars or stripes, parallel to the courses of circular knit fabric, or, the filling of woven fabric. NOTE: The term “barré” is sometimes used as a synonym for “filling bands” in woven fabrics.

Terminology AATCC Monograph M10

There are different terminologies used worldwide for dealing with Barre, Below mentioned are terminologies given in the AATCC.

Darker appearing — A barré that appears darker than the normal portion of the fabric. This barré can appear as darker in dyed shade when the fabric is viewed with reflected light, or darker in appearance when the fabric is viewed with transmitted light.

Lighter appearing —A barré that appears lighter than the normal portion of the fabric. This barré can appear as lighter in dyed shade when the fabric is viewed with reflected light, or lighter in appearance when the fabric is viewed with transmitted light.

Multiple End type —A regularly repeating barré wherein more than one course from the knitting machine creel repeat exhibits a barré appearance, unlike the band type barré. However, a multiple

End type barré appearance does not involve consecutive ends (from the knitting machine creel).

Random — A barré that does not repeat periodically along the length of the fabric. (Syn: short term.)

Regularly repeating — A barré that repeats periodically along the length of the fabric.

Single end type— A regularly repeating barré wherein only one course from the knitting machine creel repeat exhibits a barré appearance.

Figure 01 Light appearing & Multiple end type     Figure 02 Regularly repeating

Figure 03 Darker Appearing & Random Barre

Identification of Barre

The First Step in Barre analysis is identification of the Barre.  As per ASTM & AATCC Bars or bands must come in the repetitive fashion to declare it a Barre, It must follow a pattern. Dyeing or processing related problem can create repetitive pattern but it’s very difficult to produce sharp boundary line of the Barre which follows single course. Many articles are saying that fabric must analysed on the inclined inspection Table for Barre identification, But not all type of Barre are visible on inclined Table. Barre are very tricky sometimes we can see on horizontal table, sometimes on inclined, sometimes inclined but in course direction. It is better to hold the both side edges with hands and try all possible position by changing the hand positions. Few barre can be visible only in particular position and in peculiar angle.

Dos and Don’ts of Barre

It is better to prevent rather cure & barre are difficult to rectify. Some guidelines to prevent the Barre appearance.

Fibre Stage:

1. Fiber of different whiteness level should not be mixed up.
2. Fiber of different Moisture content level should be conditioned for adequate time after mixing.
3. Fiber of different production plants should not be mixed up.
4. Fiber of different production lots should not be mixed up.
5. Fiber of different storage conditions should be conditioned for adequate time after mixing.

At spinning stage:

1. Fibers having Different dyeabily should not mix together.
2. Hardness of yarn cones must be maintained same throughout the lot.
3. Steamed yarns of different Lots must be labeled separately & correctly.
4. The Spinning oil used should be the same thorough out the spinning of complete lot.
5. Yarns treated and untreated with paraffin should not be mixed.
6. Normally yarns should not be rewinded.
7. Rewinded yarn should not be mix with Normal yarn.
8. Count CV must be at lowest Level.
9. Yarn must be labeled properly with yarn count & Lot No.
10. Yarn count variation more than two must not mix up.

At knitting Stage:

1. Yarn from the different spinning Unit or different lot from the same spinning unit should not be mixed up.
2. Housekeeping must be maintained throughout the department to avoid material mix up.
3. Waxed & Normal yarn should not be mixed up.
4. Normal & rewinded yarn should not be mixed up.
5. Material must be conditioned for sufficient time prior to knitting.
6. Constant tension must be maintained at all yarn feeders.
7. All feeding cones must be of same size to maintain uniform tension distribution throughout the feeders.
8. Run the Knitting machine at optimum and constant speed.
9. Machine area must be clean & regular machine cleaning need to be done to avoid saturation of Fly & Fluff on the machine parts.
10. All machine parts of yarn path must be check regularly for smoothness.

For Elastanes:

1. Low pretension in elastane feeding ensures Heat setting at Lower temperature. (e.g. 170° C instead of 190°C).
2. Elastane cones should be of same size and diameter. Remnant cones can be used for white fabrics and should be creeled up in an alternate manner of new and old, small and big etc.
3. Path of spandex from creel to knitting needle should be absolutely clean and abrasion free.

Other Points:

1. Proper housekeeping & discipline in material handling must be follow.
2. FIFO (First in First out) must be followed for material flow to avoid lot mix ups

Causes of the Barre

Barre can be originate by one of following category – Raw Material (Fiber), Yarn production, Knitting.

Fibre:

1. Fibre Denier variation – Two or more fiber mixed up having different Denier.
2. High Fiber Denier CV%
3. Fibre colour variation – Improper Mixed up of the fibers having Whiteness variation.
4. Fibers of different production plant – Improper mixing of viscose Fiber from different production Plants.
5. Two different Lots – Improper mixing of Viscose Fibers of different Lots.
6. Different moisture content – Improper mixing of the material having different moisture content.
7. Different Storage conditions – Improper mixing of the fiber stored in different storage conditions.
8. For blended yarn, non-uniform mixing of the fiber.

Yarn properties:

1. High variation in yarn count.
2. Yarn Twist variation within Lot & Mixed up of Lots having different Twist Variation.
3. Yarn hairiness variation within Lot & Mixed up of Lots having different Hairiness level.
4. Yarn lot mix up
5. Packing coefficient variation of the cones of same lot or two different Lots.
6. Mixed up of the yarn having quality variation within or between yarn Lots e.g. U% & Total Imperfections.
7. Worn out cots used for yarn production can give variation within the lot.
8. Spindle belt slippage can create problem for particular ring spindles which will give yarn quality variation within the yarn lot.
9. Mixed up of paraffin treated yarn & Normal yarn. Uneven application of the paraffin on the yarn.
10. For blended yarn, if blend ration is not maintained at Draw Frame.
11. Mixed up of the material steamed differently.

Knitting:

1. Mixed up of the yarn having different fiber nature.
2. Mixed up of the yarn having different blend ration.
3. Non-Uniform conditioning of the material.

Variation in the feeder tension can create tight loops or Slack loop: Tight Loop may take the form of a shadow (several courses involved) or a discreet line (one course involved). It will normally show up as a dark or dense line or shadow. Slack loop similar to tight loop shows up as a sheer or light line. There are few other mechanical variations which can lead to Barre are as follows.

1. Improper setting for the stitch length.
2. Worn needles, which generally produce length direction streaks.
3. Uneven cylinder height needles (wavy barre).
4. Mixed up of Old & New Set of Spandex.
5. Tension variation at Spandex Feeding.
6. Use of self life expired spandex.
7. Poor Spandex Quality.
8. Tension variation due to different size of the spandex package.

Analysis of Barre

Flat Table or Inspection Tables Examination

It is necessary to analyse the fabric on Flat Table or inspection Table, to see the defect or any uneven surface appearance of the fabric. Barre can be easily visualised if fabric is in full width & more than 1 mtr length. We need to view the fabric by all possible angles and all possible sides. Sometimes fabric must be positioned by holding the fabric in hands at both sides of the fabric to view in all possible positions. Some Barre are visible only in top light.

Light Source Observation

Normal Light: After completing the Flat Table Examination, light source observation may provide useful information. Fabric must hold toward the light and observe the fabric, if still barre are visible there are more chances to get variation in physical parameters (e.g. Construction, Lycra) rather fiber parameter.

UV Light: If we have Greige fabric of Barre appearing fabric, It must be examine under UV light. Contamination of Cotton Fiber or Polyester Fiber in the Viscose Fiber can be easily identified under UV Light, It will glow differently. UV light also allows the mineral oils to be identified easily due to their radiant energy (glow). Mineral oils create Barre if affected fabric processed without appropriate adjustment in the scouring, a change in composition or content of oil/wax.

Atlas Streak Analyzer

The Atlas Streak analyser helps us to isolate the barre caused by physical differences. Streak analyser produces impression of the fabric on the plastic sheet under the specific conditions of pressure and heat. Streak analyser claims that the absence of the colour on the plastic sheet ensures that only physical affect will be seen. The plastic sheet was observed to see if streaks present on the sheet were matching the streaks appearing on the fabric.  Impressions are difficult to read if yarn has high variations in the yarn structure, too rapid cooling after making an impression can produce moir effect.

On analysing the impression sheet if entire barre pattern were aligned to fabric barre then barre were due to physical problem such as tension variation, stitch length, yarn count, twist. If partially matching then issue can be physical as well as dyeing. If no pattern visible then barre is due to chemical cause or fiber.

Spandex Dissolution

To check the roll of Spandex in the Barre appearance we must dissolve the Spandex portion with the help of boiling DMF. If Fabric without spandex is not showing any Barre then improper use of spandex or spandex is the reason for creating Barre. On heat setting fabric gets stabilised & fabric deformation which was appearing like Barre will be permanent effect. Even after Spandex dissolution Barre will be visible because of permanent stabilisation of the fabric structure. Barre caused by structural parameter other than spandex will also get permanently set on heat setting.

Fabric Dissolution

If spandex was feed at each feeder then only spandex structure can be analysed on dissolving the other component. It is possible only with Viscose Spandex, Modal Spandex & Lyocell Spandex combinations using low concentration H₂SO₄. On analysing the spandex net, derived from the non heat set fabric & Barre are still visible then we can conclude that Spandex is the culprit other way Spandex is not responsible for the Barre. On heat setting Barre will be permanent which may have occurred due to Spandex or fabric structure.

Fabric Dissection

While observing on the inspection table mark the Barre portion by means of Pins, Pen Marks. Unravel the yarn from the dark & light portion. Check the Count, Twist Direction, TPI, RKM & Breaking Elongation of both the yarns. Compare the yarn test results. If there is variation of more than two counts, it will result in Barre. By checking the yarn parameters like RKM & Elongation, we can say that yarn was from the same lot or two different lots. After unravelling yarn from dark & light portion check for yarn technology, mixed up of the two yarns of different technology can produce the barre. Yarn Technologies can be identified by untwisting the yarn.

Ring Yarn – Untwist easily, fiber will become parallel to each other.

OE Yarn – Yarn will not untwist, At the same time surface will get twisted & untwisted. It will look like high twisted yarn. Localised opening is possible.

MVS Yarn – No localised opening, Yarn will start untwisting. It will untwist only surface fiber, core fibre will be intact. We can see fibers like hair near the yarn core.

Mixed up of the two different yarn having different quality can produce Barre. We can check the yarn quality by Loop method. On Uster Unevenness tester we can check the U%, Hairiness & Total imperfection of the yarn. Imperfections counted due to knots must be deducted from the calculation. Separate yarn lots were always shows difference in yarn quality parameters.

Fabric structural parameters

Check the fabric construction parameters for comparison it will help to find if any problem in the fabric structure. Construction parameters e.g. Loop Length, CPI, WPI and GSM any variation in any parameters will produce the Barre. Tension variation at the feeder will affect the stitch length. Quality of the Spandex used will also affect on the constructional parameters.

Stripping & Redyeing

Fabric with barre defect can stripped & redye to see the barre were due to dyeing or improper pre-treatment. With my three year experience in barre handling I haven’t seen the 100% stripping of the fabric so Barre was always visible after redyeing. It will be really helpful in the Cotton/Modal or Cotton/Viscose Blends. It needs proper pre-treatment to gate solid shade, which can be done after stripping.

References

1. Barré́: Methods to Prevent Barré in Knitted Fabric Source: New Cloth Market By: Donald L. Bailey
2. Impact of consistent fibre properties on optimization of fabric barre, daffodil international university journal of science and technology, volume 4, issue 2, July 2009.
3. Barré: Visual Assessment Descriptive Terms and Terminology, AATCC Monograph M10.
4. Using HVI data to contol barré, fiber management research report 2004, cotton incorporated, 6399 Weston Parkway, Cary, North Carolina 27513.
5. Barre in viscose knitted fabric, The Indian Textile journal May 2014.
6. Enhancing the quality of single jersey knitted fabric by preventing barre caused by yarn parameters, Pak. J. Agri. Sci., Vol. 44(4), 2007.
7. Preventions of Barre, www.cottonyarnmarket.net
8. Methods to Prevent Barre In Knitted Fabric Commerce Essay, www.ukessays.com/essays/commerce/ methods-to-prevent-barre-in-knitted-fabric-commerce-essay.php