Knit

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RELAXED KNIT FABRIC FINISHING AND COMPACTING (TUBULAR AND OPEN WIDTH)

R. Michael Tyndall Director, Technical Services Dyeing & Finishing Cotton Incorporated

COTTECH CONFERENCE 1993 Cotton Incorporated Raleigh Marriott Crabtree Valley November I 1-1 2, 1993

Commercially available extractors and dryers are equipped with spreading and overfeeding

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devices to regain width and return the stretched loops to a more normal state. Spreading must be accompanied with overfeed in order to be effective

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Relaxation drying allows those

excessive tensions to be released since the fabric is dried under little or no restraints. Most relaxation dryers are based on the belt principle, where the fabric is placed between two belts and then passed through the drying zone. The bottom belt supports the fabric but allows for shrinkage, while the top belt prevents any stretching. In some cases, the bottom belt can be vibrated for additional mechanical action. Air flow is normally directed down and up through the fabric to give a ripple/wave effect. Once the drying is completed under relaxed condtions, those excessive tensions which have occurred during prior processing, have been released. If the fabric has been spread with overfeed prior to relax drying, width shrinkage occurs first. This may prevent the length from shrinking initially, but as the drying progresses, both width and length shrinkage occurs. At the exit of the relaxation dryer, the fabric width will be inconsistent and may not be completely wrinkle-free.

Thus, calendering or compacting is

necessary to provide a uniform, finished roll for cut and sew3.

Fabrication If there is any one statement which should provide a quideline for optimum shrinkage control, it is that prouer construction is essential. Without a doubt, too often many fabrics are not

constructed properly to meet end-use specifications. In most cases, a particular fabric is made using a certain gauge machine with a specific yarn which should have 5x5 shrinkage at a certain weight and width. Once finished, the customer may find that at 5x5 shrinkage, the

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RELAXED KNIT FABRIC FINISHING AND COMPACTING TUBULAR AND OPEN-WIDTH R. Michael Tyndall

Introduction Knit fabrics are popular for today's active lifestyle and will remain strong at retail. Many of these garments are constructed of 100% cotton which makes shrinkage reduction all the more difficult. Finishing of tubular and open-width knitted fabrics present a constant challenge to the finisher.

This challenge is to consistentlv produce a finished fabric which possesses

acceptable shrinkage. Because knitted fabrics are elastic, processing by normal methods often stretches the fabric lengthwise, thus increasing shrinkage in that direction. What must happen next, is to "normalize" or regain that bulk which in turn will reduce shrinkage. Because of research such as STARFISH' which emphasizes proper construction and processing techniques like relaxation drying and compacting, low shrinkage values are more within reason than ever before.

Many of these techniques are now in commercial practice and offer the finisher

opportunities to minimize shrinkage.

Relax Processinq Of course. any processing sequence involves the movement of the fabric through some equipment or from one station to the next. Normally, this involves length tension which will increase the length shrinkage and decrease the width. Depending upon the type of equipment and the condition of the fabric (wet vs. dry), these lengthwise tensions can vary significantly.

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Taking these four fabrics and determining their relaxed dimensions by washing and tumble drving five times according to AATCC Test Method 135-78 IIB, the following results were obtained.

SHRINKAGE LXW

WIDTH, INS

WEIGHT

ozm2

THREAD COUNT cxw

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4.0 5.3 (5.3)

38 x 34 56 x 41 (56 x 40)

240 Inches Initi ai 5 HLTD

13.0 x 17.0

66.8 63.0

265 Inches Initial 5 HLTD

-21.0 x 5.0

67.0 64.8

3.7 4.9 (4.9)

42 x 34 49 x 38 (50 x 38)

260 Inches Initial 5 HLTD

-16.5 x 13.5

65.8 63.0

5.2 7.3 (7.8)

40 x 34 49 x 39 (49 x 40)

285 Inches Initial 5 HLTD

20.0 x 10.0

66.3 63.5

5.1 6.9 (7.3)

36 x 34 43 x 39 (45 x 39)

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The values in parentheses are STARFISH predictions. predictions are very close to actual values.

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As shown by this table, those

weight is too heavy

Then you have a situation where changes need to be made in the

construction which might involve increasing the stitch length (makes a lighter fabric, but increases shrinkage), substituting a finer yarn (may be too costly), changing machines (not the best solution) or revising the specifications (not likely). Stitch length is often increased or lowered to help meet these targets and is one parameter used in the STARFISH program for prediction of shrinkage and reference state. Fabrics knit tight, or with low stitch lengths, tend to be heavier in weight, have lower shrinkage and are more consistent in shrinkage values. Fabrics knit loose, or with a higher stitch length, tend to be lighter in weight, have higher shrinkage and are inconsistent in shrinkage. Stitch length is calculated by dividing the coarse length (inches of yarn per revolution) by the total number of needles.

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To demonstrate this theory, two constructions were selected for this study. One a 100% cotton single jersey constructed from 30/1 CP ring spun and the other an interlock made with 40/1

CP ring spun cotton yarns. Both fabrics were knit at two different stitch lengths to illustrate the influence stitch length has on process and residual shrinkage. Table I summarizes both fabrics.

YARN

GAUGE

DIAMETER

NEEDLES

STITCH LENGTH

COARSE LENGTH

TIGHTNESS LENGTH

A 30/1 CPRS B 30/1 CPRS

28 28

26 26

2256 2256

0 106 0 117

240 0 265 0

16 4 14 9

A 40/1 CPRS B 40/1 CPRS

21 24

30 30

2232 2232

0 116 0 128

260 0 285 0

13 0 11 8

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Resu I ts After the first drying stage and after compaction. each fabric was checked for residual (actual fabric shrinkage after SHLTD) shrinkage

The following graphs summarize those values

SHRINKAGE DATA

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SINGLE JERSEY TUBULAR % Length Shrinkage

25 240 Inches

21.0

. I2 6 5

20

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inches

15 11.0

10

9.0

5 0

Greige

Dry No Spread

Dry Spread Table

I

Compact No Spread

Compact Spread

Processinq

Each fabric was then processed by the following routes and checked after drying. before finishing to determine process and residual shrinkage

PROCESSING ROUTE Tubular No

Jet Prep Wet-on-Wet Soften And Dye -b Extract -b

f

Spread

I

I

Relax

f

-+ Compact

Dry

Spread w/OF

PROCESSING ROUTE Open Width

-onJet Prep -b Extract -b Slit -b Wet And Dye ’Often

Compact

\

Tenter Dry

/”

Tubular processing includes relax drying with and without spreading. Open-width evaluates +

relax drying in comparison with tenter drying.

SHRINKAGE DATA

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SINGLE JERSEY OPEN WIDTH % Length Shrinkage

25 2 4 0 inches

2 1.0

20

265 inches

15 12.5 11.0

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10

8.0

5

0

Greige

Dry Tenter

Dry Relax Table I11

Compact Tenter

Compact Relax

SHRINKAGE DATA INTERLOCK = TUBULAR % Length Shrinkage

25 20.0

260 Inches

2 1.0

285 inches

20

18.0 15.0

15

,13.0

L

10

5 0

Greige

'Growth in Width

No Spread

Dry Spread Table I1

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* Compact No Spread

Compact Spread

Conclusions Taking each graph and summarizing those results. certain statements can be made

Graph I

- Single Jersey,

Tubular

1 . Length shrinkage was reduced bv = 50% by relaxation drying 2. Spreading prior to drying gave even lower shrinkage. 3. It is more difficult to obtain lower shrinkage after compacting when spreading is not used. 4. Spreading with compacting gave best results. 5 . Knitting tighter gave best shrinkage.

Graph I1 - Interlock, Tubular 1. 2. 3. 4.

Shrinkage reduced substantially more by spreading with overfeed prior to drying. Without spreading, shrinkage that occurred during relax drying was difficult to stabilize. Width growth was measured when no spread was used. Knitting tighter gave best shrinkage values.

Graph HI

- Single Jersey,

Open Width

1. Tenter drying did not reduce shrinkage as much as relax drying. 2 . Compacting after relax drying (with spread and overfeed) gave lower shrinkage than tenter. 3. Again, the fabric knit tighter gave best results.

Graph IV

- Interlock,

Open Width

1. Drying relaxed was not much better than tenter. 2 . Due to the stitch instability, compacting to a low shrinkage was difficult 3. Fabric knit at 285 inches was very unstable and difficult to process.

References Burkitt, F. H., "The STARFISH Project, An Integrated Approach to Shrinkage Control in Cotton Knits", International Institute for Cotton Publication, 1986.

' Gordon,

B. W., et.al., "Shrinkage Control of Cotton Knits bv Mechanical Techniques", AATCC Journal, November 1984., p. 25

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Tyndall, R. M., et.al., AATCC Journal, March 1990, p. 19 10

SHRINKAGE DATA -

INTERLOCK = OPEN WIDTH % Length Shrinkage

25 1 2 6 0 Inches

20.0

20

2 8 5 Inches

15

13.0

12.5 10.5

11.0

10 5 0 Greige L

Dry Tenter

Dry Relax

Compact Tenter

Compact Relax

Table I V

All of these values were determined after five home launderings and tumble dryings. Other data was collected such as thread count, width and weight in order to establish finish width Before compaction. the tarset width was to be two to three inches above the desired finish width in order to accommodate expected width shrinkage during compaction. For tubular processing. spreadins with overfeed was incorporated prior to compacting. Relaxation drving before compacting gave low shrinkage values. but in most cases at a width less than that specified .-