US3316610A - Method of rendering fabrics stretchable - Google Patents

Description

y 2, 1967 G. w. MANOCK 3,316,610

METHOD OF RENDERING FABRICS STRETCHABLE Filed Dec. 2, 1963 2 Sheets-Sheet 1 [NVf/V/Z/Z fia w M44016 42N006 y 2, 1967 G. w MANOCK 3,316,610

METHOD OF RENDERING FABRICS STRETGHABLE Filed Dec. 2, 1963 2 Sheets-Sheet 2 United States Patent 3,316,610 METHOD OF RENDERING FABRICS STRETCHABLE Geoffrey Windle Manock, Han-agate, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed Dec. 2, 1963, Ser. No. 327,215 Claims priority, application Great Britain, Nov. 30, 1962, 45,345/ 62 Claims. (Cl. 2$-72) This invention relates to Woven fabrics having stretch characteristics.

Woven fabrics having stretch characteristics in the warp and or weft are known. They may be produced by known methods comprising (i) Incorporating yarns containing fibres or filaments with elastic properties during weaving such as rubber or stretchable elastic synthetic polyurethane fibres or filaments.

(ii) Incorporating a yarn made from crimped filaments, examples are Ban-lon a stuffer box crimped filament yarn, Helanca a twist crimped filament yarn and Crimplene a stabilised false twist crimped filament yarn.

(iii) Subjecting a woven fabric to a treatment which results in yarn crimp and chemically setting this crimp.

We have found that with certain types of thermoplastic fibres, which may be blended with natural or other manmade fibres, a chemical treatment is not required if, instead, a major proportion of such suitable thermoplastic fibres are incorporated and this fabric is heated to fiX the stretch properties.

According to my invention I provide a woven fabric which has stretch characteristics and which may be elongated by at least under a load of 2 kg. on a 2 inch strip of the fabric in one direction i.e. either in the warp or in the weft, due to yarn crimp which has been imparted by crimp inter-change and fixed by a heat treatment between two sets of yarns, the yarns with the yarn crimp comprising a proportion of synthetic thermoplastic fibres having a glass-rubber transition temperature when wet, above 80 C.

The yarns of the first set having the yarn crimp, lie substantially parallel but with the crimps in neighbouring yarns out of phase with each other, the yarns of said first set intertwining the yarns of the second set according to the weave pattern, the yarns of said second set lie in sub stantially parallel straight lines all in substantially one plane, when the fabric is supported on a fiat planar surface.

The glass-rubber transition temperature of the synthetic thermoplastic fibres is determined by the dynamic extension method as described by P. R. Pinnock and I. M. Ward in Proc. Phys. Soc., vol. 81, part 2, No. 520, pages 260275, 1963. 1

Suitable synthetic thermoplastic fibres are polyester fibres derived from terephthalic acid, particularly polyethylene terephthalate and other fibres derived from fibreforming polymers having a plastic memory and a transition temperature when wet, above 80 C' The term fibres includes staple fibres and filaments where the context so allows.

We also provide a process for imparting stretch characteristics to a woven fabric, comprising a proportion of synthetic thermoplastic fibres having a glass rubber transition temperature when wet, above 80 C., which has substantially no long floats and is preferably of a plain weave construction and which may be dyed if desired, comprising stretching the fabric in the direction of one set of parallel yarns, suitably by at least 5 to and as much as possible without breaking the yarns, whilst allowing the yarns in the other direction of the fabric to relax, suitably by at least 10 to 30%, to bring about yarn 3,3 lfifi W Patented May 2, 1967 crimp inter-change between the yarns in the two directions of the woven fabric and heating the fabric for a time and at a temperature suitable for bringing about heat setting of the yarns which must comprise a proportion of the suitable synthetic thermoplastic fibres at least in the direction where no stretching has taken place and allowing the fabric to cool in that configuration before removing a substantial proportion of the stretching force and so to maintain said crimp interchange.

By the term stretch characteristics we mean that the fabric can be elongated by at least 10% in at least one direction i.e. in the warp or weft direction and that this elongation under a load which must be below the elastic limit of the yarn crimp and not cause fibre rupture, is recoverable by at least i.e. when releasing the stretching force, the fabric will rapidly assume substantially its previous size and shape. A convenient minimum load is 2 kg. on a 2 inch strip of the fabric.

It should be noted that although most fabrics can be stretched and recovered from stretch the amount of stretch is only about 1 to 3% whereas our fabrics with the defined stretch characteristics can be elongated by at least 10%, preferably 15-30% after the treatment, but not before.

We have found that quite simple operations in finishing can increase yarn crimp and so give stretch characteristics. If warp stretch is required then warp crimp should be increased. This can be done by stretching the fabric in Width so that weft crimp is removed. This causes the warp crimp to increase, by virtue of the crimp interchange properties of woven fabrics, and the correct amount of overfeed, the fabric will be reduced in length, as the wanp crimp develops.

The heat setting can conveniently be carried out during stentering and should clearly be under conditions more severe than those likely to be met during subsequent making-up or laundering treatments and temperatures between and 220 C. preferably e.g. 180 C.200 C. for 30- 60 secs. are considered adequate for our defined fibres. Under Wet conditions and in steam lower temperatures are adequate and temperatures between the glass-rubber transition temperature and 30 C. below the melting point of the fibres may be used.

If weft stretch is needed, the fabric should be stretched in the warp direction and allowed to relax in the weft direction, again the new fabric configuration being fixed by heat.

It has been found that the stretch characteristics vary with fabric construction and, for example, the effect is far greater in a loosely woven skirting than in a tightly woven rainwear fabric. If desired fabric setts can be modified so that the required finished construction is obtained.

If e.g. a pretreated fabric has little or no weft crimp, then we cannot stretch it in the weft direction and therefore, we cannot crimp the yarns in the warp to give warp stretch or vice versa.

Very firm fabrics, e.g. rainwear fabrics are diflicult to distort and therefore difiicult to convert into our fabrics with stretch characteristics.

The yarns in the woven fabrics must be thermoplastic i.e. capable of being heat set after crimp inter-change has taken place and this deformation of the crimped yarns must be elastic so that when a load is applied of 2 kg. to a 2 inch strip of fabric, the fabric retracts again on removal of the load, due to the recovery from bending of the heat set yarns. It should be appreciated that the stretch properties of the fabric are due specifically to bending of the heat set yarns rather than elongation of the individual filaments either by uncoiling of crimp or actual elastic elongation-as happens in known stretch fabrics composed of elongatable fibres such as rubber or of crimped filament yarns.

It will be apparent that in order to obtain the greatest elastic recovery in bending, the yarns should be capable of being bent without separation of the individual fibre or filament components. In other words yarns of substantially circular cross-section are preferred. The yarns may be doubled or plied yarns but the individual yarns should have a circular cross-section; because of this, spun staple yarns are preferred. If filament yarns are used they should be made to retain their substantially circular cross-section e.g. by twisting or by a coating.

After my treatment an examination of the heat set thermoplastic yarns show a sinusoidal crimp in one plane with a high birefringence of the oriented drawn filaments in the yarn and a high degree of crystallinity whereas the yarns in the transverse direction are substantially straight particularly if they also consist of thermoplastic yarns.

Natural and non-thermoplastic fibres can also be used in the transverse direction, if inferior stretch properties can be tolerated.

The condition for the heat fixation of the yarns in the fabric when tensioned in one direction will depend on the polymer from which the thermoplastic yarns are made. The temperature conditions must be chosen depending on the heat resistance of any fibres which may be blended with the fibres responsible for the stretch characteristics and the weight of the fabric to allow suflicient heat penetration. The other consideration is that the treatment temperature should be in excess of that likely to be encountered in subsequent processing, use and wear.

As already stated spun yarns are preferred to filament yarns for imparting the stretch properties to the fabric. For maximum stretch properties the greatest possible amount of crimp interchange is required and this occurs with yarns which, as previously stated, maintain their circular cross-section under transverse pressure against adjacent yarns. When filament yarns are used which have low twist, flattening occurs with resulting filament separation at the bends and as a result such fabrics when subsequently stretched do not generate high yarn crimp by crimp interchange because of filament interference.

For practical purposes the tensions required can be determined sufficiently accurately by measuring the extension under loads which of course must be less than those which would ruin the fabric by breaking individual yarns. Extensions of -20% in one direction and allowing the fabric to relax in the transverse direction in which the thermoplastic heat settable yarns are by about 40%, are suitable for our fabrics.

Such fabrics after the treatment should have stretch characteristics of at least 10% and may have 15-30% stretch in the warp or weft when tested under a 2 kg. load for a 2 inch strip of fabric.

In order to obtain the required stretch in a fabric by our crimp interchange method as a result of which the high sinusoidal yarn crimp is imparted by the transversely crossing threads, the plain weave constructions are preferred with approximately equal thread spacing both in the warp and weft.

Fabrics having a cover factor of 13 have been found eminently suitable when woven from 67/33 Terylene/ Cotton blends.

The cover factor D denotes the number and denier or count of yarns in the warp and weft of the fabric thus:

ends or picks per inch cotton count Lubrication of the yarns in the fabric is of importance. The tension required to produce a crimp interchange is lower if inter-fibre and inter-yarn friction is low. Textile lubricants containing silicones are preferred.

The yarn crimp in the fabric increases with fabric sett and is at its highest in a plain weave construction which therefore is preferred. For example a Terylene Cotton/Poplin rainwear fabric of a firm construction which gives only 5% stretch after treatment i.e. stretching in one direction and heat setting whilst relaxing in the other direction transversely thereto, is unsuitable.

When crimp interchange takes place the slightly ondulating parallel yarns in one direction of the fabric are pulled substantially straight, and at the same time the parallel yarns in the other direction are thereby pulled closer together and the ondulating path over and under the substantially straight yarns in the other direction is very much enhanced. It will be appreciated that for this crimp interchange to be possible the following requirements in fabric construction will have to be met:

(a) The spacing between the yarns in both directions should be such that the yarns lie in an ondulating path due to inter-twining at substantially right angles to each other.

(b) The spacing between the yarns should be such as to allow movement of the yarns in the transverse diree= tion when the other set of yarns is pulled into straight lines under high tension.

(c) The spacing should not be too large between the yarns but appreciable ondulation should be present to cause a substantial movement of the yarns in the other direction when one set of yarns is pulled into straights.

(d) To assist movement between the yarns a lubricant should be provided on the surface of the yarns. I

(e) During the heat treatment in the tensioned condition the ondulated yarns should contain a major proportion of fibres or filaments which can be heat set in that position under conditions such that this setting becomes practically irreversible during any subsequent processing or during wear.

Regarding (e) we have found that synthetic fibres hav; ing a glass rubber transition tempearture below C. do not show any particular merit when used in the fabrics of our invention because the imparted setting is not permanent and is removed by subsequent heat treatments at temperatures even below the setting temperature when wet. Such synthetic filaments and fibres comprise the polyamides and isotactic polypropylene. On the other hand polyester fibres derived from terephthalic acid par ticularly polyethylene terephthalate fibres or copolyester fibres containing up to 10% of a second component, as well as polyacrylonitrile fibres and fibres containing at least 80% polyacrylonitrile are suitable since the stretch characteristics imparted during our process are not sub: stantially affected by subsequent heat treatment at least at tempeartures up to 80 C. i.e. below the glass-rubber transition temperature. No substantial distortion of the fabric during any subsequent heat treatment at tempera t-ures above the treatment temperature should be allowed to take place.

From the foregoing it will be noted that the denier of the yarns will have an effect on the amount of stretch which can be obtained in any particular fabric and that for the treatment to be effective our fabrics will have a characteristic appearance when examining the threads in the fabric preferably using a low degree of optical magnification. The yarns or threads in one direction will be substantially straight and show a crimp elongation or ondulation of less than 3% under a load of 0.5 g.p.d. whereas the yarns which are causing the stretch characteristics in the fabric will show a crimp elongation of at least 15% and up to 50% under the same load. The ondulations which are illustrated in the drawing, take a substantially sinusoidal path, the angle of straight lines between the apices of the ondulations or crimps are preferably less than of angle.

If our process is carried out on a continuous and commercial scale on a pin stenter and it is desired to impart e.g. warp stretch characteristics to the fabric, the stenter is adjusted to give a high weft tension and overfeed is increased until waviness along the selvedge of the suitable fabric is noticed. The overfeed is then reduced until the waviness just disappears. In a suitable fabric, crimp interchange will take place, provided the weft tension is sufiicient i.e. that the weft yarns come to lie in a single plane in substantially parallel straight lines, whereas before this weft tensioning, the weft yarns lay in ondulating substantially parallel path.

It is also possible, instead, to impart weft stretch to the fabric by applying warp tension and weft relaxation. If a pin or clip stenter is used the fabric should be stretched to the full desired extent before it is pinned or clipped. If this is not done the pins or clips will prevent warp extension. It is desirable to increase the grip of the delivery rollers.

When the desired tension has been applied to bring about the crimp interchange, the fabric is heat set in that condition and cooled, before allowing any relaxation.

Instead of a stenter, cylinder setting machines can be used in which the fabric is held on cylinders rotating at progressively faster speeds, while it is pressed e.g. by pressure belts against the cylinders. Such machines are commercially available. One type is known as the Bates Cylinder Machine; it requires some modifications, by including the provision of tensioning bars at the feed end. In this case setting. occurs on the cylinders which are heated to an appropriate temperature in order to bring about heating of the fabric to a temperature throughout of up to 200 C., preferably 180 C., depending on a given speed and heat transfer properties of the fabric.

In the case of fibres which have a rubber transition temperature when wet above 80 C., such as polyethylene terephthalate fibres I have surprisingly found that fabrics containing a major proportion of such fibres can be heat set e.g. to a first temperature as high as up to 30 C. below the melting point of the fibre, followed by my treatment at a lower second temperature, i.e. above the glass rubber transition temperature and at least 60 C. below the melting point, cooled to room temperature and then if desired heated a third time at a temperature lower than the second temperature but without applying any overall tensions in the stretch direction of the fabric, treated according to our invention.

This is of considerable practical importance since such a woven fabric can be heat set and stabilised against creasing at say 180 C., then treated according to our invention including heating for a second time at say 180 C. for 30 secs, to impart stretch properties to the fabric and cooling to below the glass rubber transition temperature, and when made up in garment form e.g. trousers, a pleat may be inserted e.g. on a Hoffman press at say 135 C. for 1 minute without overall distortion of the fabric, thus resulting in a garment with a durable pleat, stretch characteristics in one direction and stabilised against shrinkage.

I, therefore, also provide a process for imparting stretch characteristics in one direction to a woven fabric made from polyester fibres at least in the direction in which it is desired to impart stretch characteristics comprising heat setting the fabric at a temperature 30 C. above the glass rubber transition temperature and at least 30 C. below the melting temperature of the polyester, stretching the fabric in one direction and allowing the fabric to relax in the other direction and which must contain a major proportion of polyester fibres or filaments to bring about crimp interchange and so that the yarns in the direction of tensioning come to lie substantially in a single plane along substantially straight parallel lines, heating the fabric in that condition at a temperature above the glass rubber temperature and 30 C. below the melt temperature, cooling the fabric in that condition and if desired subjecting the fabric to a subsequent third heating at a temperature above the rubber transition temperature and if desired below the said second temperature without, however, applying any overall distortion to the fabric for the purpose of, for example, ironing or pleating but excluding stretching in the direction in which stretch characteristics have been imparted to the fabric.

The proportion of synthetic thermoplastic fibres required will depend on a number of disconnected factors such as fabric and yarn construction and the end-use for which the fabric is required; a proportion of 35% in blends with wool may be used but higher proportions i.e. a major proportion and including of the synthetic fibres have given excellent results.

The attached drawings illustrate a preferred embodiment of our invention in which FIGURE 1 is a diagrammatic isometric view of an untreated fabric on a greatly enlarged scale.

FIGURE 2 is an isometric diagrammatic view of the fabric of FIGURE 1 as it appears during or after the heat treatment.

FIGURE 3 is a sectional end view of the fabric of FIG URE 1.

FIGURE 4 is a sectional end view of the fabric of FIGURE 2.

FIGURE 5 is a diagrammatic side view of a cylinder setting machine, on a much reduced scale.

Referring to FIGURE 1 it will be seen that the yarns 1, 2 and 3 are interwoven with yarns 5, 6, 7 and 8. It will be seen that the yarns 1, 2 and 3 are slightly displaced through interaction with the yarn 5 (in the warp) and as can be seen by reference to FIGURE 3, where an additional yarn 4 is shown. When such a fabric is overfed onto a stenter in the warp direction and then stretched in the weft direction the weft yarns are straightened along virtually straight lines as can be seen by reference to FIG- URE 2, whereas the yarns in the warp direction are dis placed by crimp interchange, the ondulations having been taken out from the weft yarns and increased in the Warp direction in the yarns 5, 6, 7, 8 and 9. FIGURE 4 which is a section through the fabric of FIGURE 2 along yarn 5 illustrates more clearly the greater crimp imparted to the yarn 5 and also that the yarns 1, 2, 3 and 4 in the warp direction now lie virtually in one plane.

Referring to FIGURE 5 a suitably woven fabric is unwound from a cloth beam 10 and taken over an adjustable tensioning device comprising quadrangular beams 11, 12, 13, 14 and 15, in which the two beams 12 and 13 can be pivoted around axis 16 by a hand wheel 17. From beam 15 the cloth is taken up by feed rolls 18 and 19 followed by expander roll 20 for spreading the cloth before it is taken up by the heated cylinders 21 and 22, against which the cloth is pressed under higher pressure from driven transport rolls 23 and 24. Additional rolls 25, 26, 27 and 28 are covered with two sets of aprons 29 and 30 which help to press the cloth against the cylinders 21 and 22. Delivery roll 31 feeds the cloth into a cooling zone 33 where the fabric may be suitably cooled with a blower using air at ambient temperature, before it is taken up by winding roll 32 to be wound up as cloth roll 34 The following examples illustrate but do not limit our invention.

Example 1 A 100% Terylene 1 plain weave fabric, made from 2/30s (cotton count) yarn was stretched 10% in the weft direction and allowed to relax 15% in the warp direction, the fabric being heat fixed at 200 C. for 30 secs.

The treatment gave over 12% warp stretch which was Registered trademark, a polyethylene terephthalate fibre 711515 a )g1ass-rubber transition temperature when wet of durable to washing and which had good recovery properties.

Example 2 A 67/33 Terylene cotton fabric woven plain from 1/12s (cc.) was stentered at 180 C. for 30 secs. with 20% overfeed and 15% Weft stretch. The treatment gave 15% warp stretch again with good recovery and durability to washing.

Settl Percent Yarn Crimp Initial 56 x 40 warp x 7% welt. After treatment 48 x 50 18% warp x 2% \veit. Stretch at 2 kg./2 inch st Recovery from stretch... 97%.

Example 3 A 67/33 Terylene/viscose, 1/l6s cotton count plain weave fabric having a cover factor of 13.2 was treated on a stenter at 180 C. for 30 seconds giving it a warp extension of 8% and allowing weft contraction of 28%, as indicated in the following table which also includes the properties of the fabric before and after the treatment.

Treatment Before After Sett (threads per inch) 56 x 50 72 x 46 Percent yarn crimp 8 x 7 1 x 30 Percent stretch at 2 kg./2 in. strip. 26 Percent recovery from stretch 98 Warp extension 8%; Weft contraction 28%.

Example 4 Example 5 A 55/45 Terylene wool worsted plain weave 11 Registered trademark, e. polyethylene terephthalate fibre \vigh ac glass-rubber transition temperature when wet of t 0 8 oz./58" width suiting fabric, with x 60 threads per inch was treated as in Example 4. After the treatment the fabric had 14% stretch; x 58 threads per inch. On repeated stretching and release from a 2 kg. load on a 2 inch strip of fabric, 98% of the 14% stretch remained in the weft of the fabric.

What I claim is:

1. A process for imparting stretch characteristics to a fabric woven from two sets of parallel yarns, one of said sets including yarns comprising a proportion of synthetic thermoplastic fibres having a glass-rubber transition temperature when wet, above C., said process comprising: stretching the fabric in the direction of the other set of yarns to remove ondulations therefrom, as much as possible without breaking the yarns, while allowing the yarns in said one set to relax thereby to increase the yarn crimp therein and thereby establishing crimp interchange between the two sets of yarns; heat-setting the increased crimp in the yarns in said one set; and cooling the fabric to below the rubber transition temperature of the fibres in said one set before removing a substantial proportion of the stretching force so as to maintain said crimp interchange.

2. A process according to claim 1 comprising stretching the fabric in the direction of said other set of parallel yarns by at least 5 to 15%.

3. A process according to claim 1 comprising allowing the yarns in said one set to relax by at least 10 to 30% to bring about yarn crimp interchange.

4. A process according to claim 1 in which setting is carried out during stentering at temperatures between and 220 C.

5. A process according to claim 1 in which setting is carried out on a cylinder setting machine provided with tensioning bars at the feed end.

References Cited by the Examiner UNITED STATES PATENTS l/l934 Cluett 26--l8.6 2/1958 Skeer 2872

Claims (1)

1. A PROCESS FOR IMPARTING STRETCH CHARACTERISTICS TO A FABRIC WOVEN FROM TWO SETS OF PARALLEL YARNS, ONE OF SAID SETS INCLUDING YARNS COMPRISING A PROPORTION OF SYNTHETIC THERMOPLASTIC FIBRES HAVING A GLASS-RUBBER TRANSITION TEMPERATURE WHEN WET, ABOVE 80* C., SAID PROCESS COMPRISING: STRETCHING THE FABRIC IN THE DIRECTION OF THE OTHER SET OF YARNS TO REMOVE ONDULATIONS THEREFROM, AS MUCH AS POSSIBLE WITHOUT BREAKING THE YARNS, WHILE ALLOWING THE YARNS IN SAID ONE SET TO TELAX THEREBY TO INCREASE THE YARN CRIMP THERIN AND THERBY ESTABLISHING CRIMP INTERCHANGE BETWEEN THE TWO SETS OF YARNS; HEAT-SETTING THE INCREASED CRIMP IN THE YARNS IN SAID ONE SET; AND COOLING THE FABRIC TO BELOW THE RUBBER TRANSITION TEMPERATURE OF THE FIBRES IN SAID ONE SET BEFORE REMOVING A SUBSTANTIAL PROPORTION OF THE STRETCHING FORCE SO AS TO MAINTAIN SAID CRIMP INTERCHANGE.

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