CA1039936A - Bulked fabric and method to produce the same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The production of an improved mouldable fabric by relaxing in air at elevated temperature a precursor weft knitted fabric of a low-tensioned, loose, open construction composed of shrinkable, unstabilized bulked continuous filament yarns, the precursor fabric having an area stretch of at least 100%, and weight and light transmission (%) characteristics within are ABCD of Figure 1 of the accompanying drawings.

Description

1~)39936 The ~ese~t i~v~nt-~n r~lat~s to t~ r~u~tiGn of improved fabrics and to the fabrics so produced, which are par-ticularly, though not exclusively, suitable for moulding. ~-The preparation of three dimensional, shaped articles from fabrics using moulding techniques is increasing. For most moulding purposes, conventional knitted fabrics made from sta-bilised continuous filament thermoplastic yarns have been con-sidered to be the most desirable. In the case of conventional fabrics knitted from yarns composed of thermoplastic synthetic continuous filaments, such fabrics have exhibited area stretches up to about 400% (an area stretch of 100% represents a doubling ` `
oE the area o~ fabric when the fabric is stretched in two ~ `
directions at right angles) which is considered to be insu-ficient to achieve deep draw mouldability for some outlets. ', The degree of area stretch of a conventional knitted fabric may be inCreased by recourse to the use of yarns of undrawn ~ila- ~
ments, but consequential disadvantages such as brittleness and ` ``
lack of strength tend to arise.
The use of conventional knitted fabrics`composed of yarns made from stuffer box crimped, partially drawn, unset (i.e. unstabilised) polyester staple fibres, has been proposed for moulding outlets. Advantages of such a fabric are claimed ;'`~
to arise because (i) the total draw obtainable during moulding r!r .1 ~ . ~
is increased because of inter-fibre slippage and ~ii) the ~ ;

fabric is extremely stable, that is, it has an area stretch, ~-.. . . :
prior to being shrunk, which is at least several times lower than that of conventional knitted fabrics composed of sta- ~

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~3~3fi bilised continuous filament yarns, However, a disadvantage of this fabric stability is considered to be that the amount of the initial area stretch is limited thereby. ~ -According to the present invention, a method for the production of an improved fabric comprises making a weft knitted fabric having a low cover factor from shrinkable, un- ;
stabilised or partly stabilised bulked or potentially bulkable yarn of continuous, synthetic, thermoplastic homofilaments, ~`
and developing the bulk in the fabric by subjecting it to a tumble bulking treatment at elevated temperature.
The cover ~actor of the knitted "precursor" fabric de~ines the openness of the fabric, and a fabric exhibiting such a low cover factor as required by the invention would be considered to be commercially valueless in normal fabric out- ;~
lets. This non-conventional ~abric exhi,bits a low tensioned, loose, open construction. This desired construction is achieved ~;
by making the fabric under sufficiently low knitting tension and with sufficiently large stitch length such that the fabric has an area stretch of at least 100%, preferably in the range 20 100% to 200%. In addition to this requirement of area stretch, the precursor weft knitted fabric should lie within a certain weight range and a certain light transmission range. Light ~ `~
transmission through the fabric is a measure of its cover factor, the relationship being that the lower the cover factor the -~
greater the percentage of light transmitted. Thus, a pre- `, cursor fabric is considered to be suitable for the ~resent invention when its weight lies in the range 20 to 80 g~/sq, ' _ 3 _ ~ ~

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metre and its percentage light transmission lies in the range 50 to 90 and these properties lie within the area ABCD of Figure 1 of the accompanying drawings.
Thus, the present invention also provides a method for the production of an improved fabric, suitable for moulding, ;~`
having an area stretch of at least 450% which comprises tumble bulking at an elevated temperature a weft knitted fabric com- --posed of shrinkable, unstabilised or partly stabilised, bulked ;-or potentially bulkable yarn of continuous, synthetic, thermo- ; :
plastic homofilaments, and having an area stretch greater than 100%, and having weight and percentage light transmission characteristics such as to lie within the area ABCD of Figure 1 of the accompanying drawings.
The unstabilised or partly stabilised yarns of the precursor fabric are yarns which have not: undergone treatment to permanently set the bulk in the yarn. It i5 preferred that the bulk in the yarn has not been fully developed. Bulked yarns of this type made by false-twisting and knit-de-knit pro-cesses are typical of those suitable. The yarns preferably 20 comprise nylon or polyester, although polyolefine or any com- -, .:
bination of these may be used.
For a given knitting construction in the precursor ~ .
fabric and for a given bulking potential of the yarns therein, a lower yarn decitex generally results in a higher area stretch -in the fabric after the tumble bulking treatment. This is con- `
sidered to arise because the yarn with a low decitex is better `~
able to develop bulk within the confines of the knitted structure. '~
Therefore, the yarn decitex desirably should lie within the ;
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range 30 -to 200, the range 50 to 170 being preferred. Also, individual filament decitex in a yarn advantageously should be relatively high, e.g. a 78 decitex 20 filament nylon yarn is considered superior to a 7~ decitex 34 filament nylon yarn. It is preferred that filament decitex should be from

3 to 10, inclusive. ~
The relaxation treatment at elevated temperature, -which allows for fabric shrinkage as a result of filament linear shrinkage and further bulk development, involves exposing the precursor fabric to hot air in a tumble dryer which largely ensures that free relaxation occurs equally in all clirections.
~s a result of such tumble bulking treatment the maximum area stretch potential of the knitted fabric may be realised, and the eventual area stretch is found to have increased beyond that dictated by the loose, open construction of the fabric alone, and i5 in excess of 450%. Preferably, the area stretch of the tumbled fabric, which is measured at room temperature, is in the range 500 to 900%.
Therefore, the invention provides an improved weft knitted fabric composed of bulked yaxn of contlnuous, synthetic, thermoplastic homo-filaments which exhibits an area stretch of at least 450%~ ` `
The time and temperature of the tumble bulking treat-ment will depend upon the nature of the yarn used and upon the tumble drier itself, but are readily arrived at by simple experimentation. In order to obtain crease-free fabric, it is desirable to continue tumbling after switching off the heat, until the fabric is cooled. Desirably, the fabric is fed into . .

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a eocl ~umble ~ryer, th~ temperat~r~ is raise~ h~ req~ired i`
level for the required time, and then allowing to cool again before removing the fabric. It is also preferable to feed ~
the fabric into the tumble drier in such a manner that the -`
length direction of the fabric coincides with the motion of -the machine.
The precursor fabrics of the invention may be made on flat bed or circular weft knitting machines which are capable of making single jersey constructions. The cam settings of the machine are set as high as possible to give maximum loop length on the stiches in the fabric. To ensure minimum yarn tension, the yarn may be positively fed by feed rolls to the machine.
To counteract any torque i.e. "twist-liveliness", in the un- ;~
stabilised or partly stabilised yarns of the false-twist in the abric, it is preferable to use combinations of g- and S-twist yarns.
Optionally, the fabric may be stentered so that a) the fabric width may be controlled, `
b) The stretch properties of the fabric longitudinally and transversely may be controlled, e.g. they may be :
equalised if desired.
If the fabric is tùbular, it may be slit and an ad-hesive selvedge applied.
The knitted fabric of the invention is highly suitable for moulding and may be made to conform to the shape of a male `
mould, or may be shaped in a cavity mould by Vacuum forming.
In the latter case it may be necessary to place an impermeable ''., ,". ~

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1()3~936 m~mbrane over the fabric ~o permit t~e n~ces~a~y pr~ssu~e ~irc2 within the cavity. The achievement of the desired shape may be assisted by heat application and/or the use of a compatible plasticiser, e.g. water for fabrics knitted from nylon yarns.
The knitted fabric may be coated with a thermoplas~ic plastics material, for example poly vinyl chloride, before moulding to produce a coated moulded fabric suitable for up-holstery, for example. Resinous and plastisol finishes may be applied to the underside o~ the fabric, i.e. the side placed adjacent the mould surface, prior to moulding to achieve some desired performance characteristic. For example, polyethylene and acrylic resins may be used, if desired, to aid shape reten-tion of the moulded ~abric.
The fabric of the invention may be used as stretch and pressure bandages. Preferably these are knitted on a flat bed machlne with suitable selvedges knitted in.
I elevated temperatures have been utilised during the moulding process, then the moulded ~abric is allowed to cool in the mould. Forced cooling conditions may be used by circu-lating a cooling medium through the mould.
Convenient moulding temperatures used for mouldingfabrics made according to the invention lie in the range 125C
to 150C.
The invention will be further described and illustrated by the following Examples:-. ~

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A weft knitted fabric of plain single jersey con-struction was produced on a 28 gauge, 30" (76.2 cm.) diameter, Wilde ~ellor Bromley single jersey machine, which was set to give maximum loop length and minimum yarn tension. The fabric `~
was knitted from 33 decitex 10 filament, shrinkable, partly stabilised, false twist bulked yarn of continuous nylon 6.6 ~ilaments. The ~abric coming off the machine had the following properties: `
Weight (gms/sq.m) 21 `
Light Transmission (%) 73 ~
Area Stretch ~%) > 100 ` -The knitted ~abric wa~ then relaxed as ~ollows:-The fabric was reverse tumbled in hot air, starting at 55C, raising the temperature to 90C' ~or 25 minutes, and ;
then lowering again to 55C over a period o~ 10 minutes, the fabric being tumbled throughout the whole cycle. The ~abric had an area stretch of 820%. - -The relaxed ~abric was loaded, under various con- `
ditions, to produce its ~ullest area stretch, allowed to relax, and the permanent increase in length measured.
Conditions Permanent Area Increase .. , .. ~ ~ .. :
;) Loaded at room temperaturè 22%
ii) Loaded while subjected to dry heating at 140C. 153%
iii) Loaded while subjected to wet heating at 140C. 300%

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Cond tions Permanent Area Increase iv) Loaded while subjected to wet heating at 140~C and treated with an acrylic resin finish --at 90 gm/sq.m. application. 430%

A weft knitted fabric was produced from 78 decitex 20 filament, shrinXable, partly stabilised, falst twist bulked nylon 6.6 continuous filament yarn on an 18 gauge, 26" (66 cm.) diameter, Camber machine, in a plain single jersey construction.
The machine was set to give maximum loop length and minimum yarn tension. The fabric coming o~f the machine had the follow-ing properties:-Weight (gm/sq.metre) 35 Light Transmission (%) 65 Area Stretch ~%) 150 The fabric was scoured in a winch dye bath with BDX
(a biodegradable detergent of Imperial Chemical Industries Limited) at 40-45C for 20 minutes and spun dry. It was then 20 relax bulked in air at 88C in a reverse tumble dryer for 5 ;
minutes. The relaxed fabric then had the following properties:-Weight (gms/sq. metre3 96 ~ -Area Stretch (%) 600 After slitting, the fabric was stentered to a width of 36 inches (91.4 cm) at a temperature of 210~C for a dwell time of 30 seconds. The properties of the finished fabric were:- j~, '', ,': :
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Weight (gms/sq. metre) 85 -` `
Area Stretch (%) 550 ~ -~

A weft knitted fabric was produced from 78 decitex 20 filament, shrinkable, unstabilised, false twist bulked nylon -6.6 continuous filament yarn on a 70 gauge, 3.5" (7.7 cm) -diameter Chell machine. The machine was set to make the slack- ~ `
est fabric quality possible for this particular decitex yarn.
The fabric coming off the m~chine had the following properties~
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Weight (gm/sq. metre) 60 ~;
Light Transmission (%) 51 Area Stretch ~%) 200 The fabric was relax bulked in air at 88C in a reverse tumble dryer for 5 minutes. The relaxed fabric was then steam pressed by hand. It had the following properties:-Weight ( ~ sq. metre) 117 Area Stretch (%) 750 This fabric was useful as a tubular, shape conformingbandage.

A weft knitted fabric was produced according to the conditions described in Example 2, except that an 85 decitex 15 filament shrinkable/unstabilised, false twist bulked poly-~.. ..
ester continuous filament yarn was used. The fabric coming off the machine had the following properties:- -- 10 ~

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Weight (g~/sq. metre) 41 Light Transmission (%) 70 Area Stretch (%) 100 The fabric was relax bulked in air at 90C in a reverse tumble dryer for 5 minutes. It had the following properties:-Weight (g~/sq. metre) 119 Area Stretch (%) 450EXAMPLE 5 A weft knitted fabric was produced according to the conditions described in Example 2, except that a 78 decitex 17 filament, shrinkable, unstabilised, false twist bulked nylon 6.6 continuous filament yarn was used. The fabric coming off the machine had the following properties:-Weight ~gm/sq. metre) 36 Light Transmission (%) 70 Area Stretch (%) 200 After relax bulking in hot air at 88C in a reverse tumble dryer to develop the maximum bulk, the fabric had the properties:-Weight (~m/sq. metre) 140 Area Stretch (%) 870 ~ ~
After slitting, the fabric was stentered to a ; `
width of 36 inches (91.4 cm) at 210C for 30 seconds, where-after it had the following properties:-Weight (gm/sq. metre) 120 Area stretch (%) 630 ~
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Example 2 was repeated using shrinkable, unstabilised, ~ `

false twist bulked nylon 6.6 continuous filament yarns of - ;

(a) 78 decitex 13 filament ``

(b) 78 decitex 10 f~lament -The fabrics coming off the machine had the properties:
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(a)(b) Weight (gm/s~. metre) 41 37 Light Transmission (%) 65 75 Area Stretch (%) ~ 100 >100 After relax bulking the fabric properties were:- -(a) -~b) Weight (gm/sq. metre) 161 176 Area Stretch (%) 970 1200 After slitting and stentering l:o 36 inches (91.4 cm) the fabric properties were:
(a) ~b) Weight (gm/sq. metre)132 123 Area Stretch (%) 680 700 ~ ~ -EXAMPLE A (Comparative) Example 4 was repeated, except that an 85 decitex 15 filament, stabilised, false twist bulked polyester continuous filament yarn was used. The fabric coming off the machine had the following properties:- -'' .', ' :
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Weight (gms/sq. metre) 39 Light Transmission (%) 70 Area Stretch (%) 90 After relax bulking in the manner of Example 4, the -properties of the fabric were:-Weight (gm/sq. metre) 39 Area Stretch (%) 90 This example shows that although a fabric, in terms of its weight/light transmission characteristics, may be initially within the area ABCD of Figure 1, if it is not capable of developing bulk and does not have a suficient inikial area stretch, then the final fabric is not within ~he invention.
EXAMPLE B (Comparative) : .
A weft knitted ~abric was prodluced according to the .
condition5 described in Example 2, except that the yarn used was a 2-fold 78 decitex 20 filament, shrinkable, partly stabil-ised, false twist bulked nylon 6.6 continuous filament yarn. . .
The fabric coming o~f the machine had the following properties~
Weight (gm/sq. metre) 58 ~ . -Light Transmission (%) 60 .-Area Stretch (%) 65 After tumble drying in hot air at 88C in a reverse : : .:
tumble dryer to develop maximum bulk, the properties of the : :. :
fabric were:- ~.
Weight (gm/sq. metre) 154 ~ :
Area Stretch (%) 240 ~` ~
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, ., :;',, .' ' 1~39~3Çi This example shows that a fabric made from bulk-able yarn and initially having weight/light transmission characteristics within the area ABCD of Figure 1, does not produce a final fabric within the invention because the ini-tial area stretch is less than 100%.
Area Stretch Determination This is determined by marking a sample of fabric `.
with a circle; this is area Xl. This sample is then drawn over a male mould under hand pressure until stretching ceases, and the final area of the circle determined; this is area X2.
The percentage area stretch is given by -X2-Xl X 100 Xi ` , Determination of Light transmission measurements are made on fabric samples taken from the roll of fabric immediatel~ it is removed from the knitting machine, because of the possibility of the fabric spontaneously bulking up when left standing at room temperature. .
The apparatus for use in determining the light trans-mission of a fabric is illustrated in Figures 2 and 3 of the accompanying drawings, and consists of a stabilised power source ~1), which energises a projector bulb (2) and powers a 'bridge' circuit A (see Figure 3), and a rectangular box :
divided into three compartments (3_, 3b, 3c).
The compaxtment (3b) contains a light sensitive cell

(4), the compartment (3b) houses the 'bridge' circuit of Figure 3 and has a microammeter (5) connected exteriorly thereof. .

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The bcx h~s ~ s~c~ ~n o~ ~1 cm s~u~r~ an~ LS ~oun~
on a base board up against the circular aperture (6) which is cut centrally in the front of compartment (3a). The filament o~ the bulb (2) is 5.5 cm above the baseboard and on the common horizontal axis of the centres of circular apertures (6 & 7).
Compartment (3a) i9 18.5 cm long and is separated from compart-ment (3b) by a sample slot (8). The light sensitive cell (~
is mounted 4 cm from aperture (7) of compartment (3b) centrally on the common horizontal axis of the apertures (6 & 7) and is shielded by a tube (9) of internal diameter equal to that of the aperture (7).
~ pin frame used to mount the fabric samples consists of a piece of card with a 10 cm square cut out of it such that one side of the square is open. Around the three other sides ~i~
pins are fixed at 1 cm intervals at a distance of 1 cm from the, edge of the s~uare.
A 10 cm s~uare is marked on t~e fabric sample. The sample to be tested is cut out leaving about 5 cm waste around ~ ` `
the marked area. The sample is supported on the pin ~rame such `
20 that the sides of the square marked on the sample coincide with ;
the cut out shape o the pin frame. This is mounted in the ~ ;
sample slot (8) in the apparatus ensuring that the sample re~
mains flat as it is located in the fabric slot.
The light is switched on and the meter reading noted.
The test is repeated for a further two samples of the same fabric.
The meter reading is then taken with the bulb light `
and no fabric mounted, and this is taken as corresponding to 100% light transmission. The amount of light reaching the ~',.. "

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light sensitive cell (4) was reduced using neutral density ~ilters (Kodak*, Wratten* ND ~ilters) o~ known light trans-mission, and the meter reading corresponding to each ~ilter ~ -was recorded. From these results a calibration graph of meter readings against percentage light transmission is drawn, ~rom which the percentage light transmission corresponding to the meter reading for the fabric may be found.
Details o~ the various parts of the apparatus desig-nated in the drawings of~jFigure 1 and 2 are as follows:- -1. Stabilised Power Source; Model 7/10 RL, Input 240 v., 50 hz; Output 7v.DC.(Farnell Industries~ Wetherby, Yorkshire, England).
2. Atlas* Al/202 8v, 50w 3. Box (11 cm. x 11 cm x 38.5 cm) . Ericsson* K~2 UB

5. Ernest Ta~lor* Model 702, 0-100 yA

6. Diameter 2.0 cm. ;

7. Diameter 3.5 cm. -~

8. Sample slot 0.4 cm. wide

9. Tube; internal diameter 3.5 cm. `

10. Zener diodes, Z3B36CF. -. .

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Claims (4)

The embodiments of the invention in which an exclusive property and privilege is claimed are defined as follows:

1. A method for the production of an improved fabric suitable for moulding which has an area stretch of at least 450%, comprising making a precursor weft knitted fabric with a low cover factor in a low tensioned, loose, open construction from shrinkable, unstabilised or partly stabilised bulked or potentially bulkable yarn of continuous polyester or polyamide homofilaments such that it has an area stretch of at least 100%, and developing the bulk in the precursor fabric by subjecting it to a tumble bulking treatment in air at elevated temperature.

2. A method for the production of an improved bulked fabric, suitable for moulding, which has an area stretch of at least 450%, comprising making a precursor weft knitted fabric in a low tensioned, loose open construction from shrinkable, unstabilised or partly stabilised bulked or potentially bulkable yarn of continuous polyester or polyamide homofilaments such as to have an area stretch of at least 100% and weight and light transmission characteristics lying in the ranges of from 20 to 80 gms per square metre and from 50 to 90%
respectively, and subjecting the precursor fabric to a tumble bulking treatment at elevated temperature whereby it relaxes to its fullest potential.

3, An improved fabric suitable for moulding comprising a weft knitted fabric composed of bulked yarn of continuous, polyester or polyamide homofilaments and having an area stretch in the range 450% to 1200%.

4. A fabric according to Claim 3, having an area stretch in the range 500% to 900%.