GB2325846A - Treatment method for producing a low shrink elastic material. - Google Patents

Abstract

An elastic material 8, suitable for use in a waistband or similar, is passed between elastic belts 26 which grip it and compress it along its length, in direction T. The compressive force results from rollers 20 rotating at a higher rate, B, than that of rollers 22, C. The elastic material 8 is of the type with elastic filaments (10, Figure 1) enclosed in a fibrous component (12, 14), with the fibrous component having been applied while the filaments were in tension. Treating such an elastic material by compression before it is included in a garment alleviates the problems of shrinkage of the material when in the garment, e.g. due to washing of the garment.

Description

PRE-SHRUNK ELASTIC MATERIAL AND METHOD OF MAKING SAME This invention is concerned with a pre-shrunk elastic material and a method of making same and is especially concerned with elastic suitable for use in garments, for example in waist bands of garments.

In the manufacture of garments it is common to include elasticated regions, for example a garment waist band. The elastic material which is commonly used consists of strips or filaments of an elastomeric material, for example rubber or synthetic elastomeric material such as Lycra (RTM), enclosed by a fibrous/component, for example by knitting, crochet, braiding or weaving. Such enclosed elastic material is manufactured with the elastic strip or filament material under a tension force, the enclosed elastic material being allowed to relax by release of the tension after manufacture. When such enclosed elastic material is to be incorporated in a garment, for example a waist band, the enclosed elastic material is tensioned during its inclusion in the garment eg by stitching in known manner and again allowed to relax after insertion to provide an elasticated region of the garment. Sometimes when the enclosed elastic material is inserted in the garment it is inserted with regions of the material under tension, these tensioned regions being spaced by regions where the elastic material is inserted under no tension: this is referred to as intermittent elastication.

It has been noted that after the elastic material has been enclosed by the fibrous component, when it is allowed to relax the fibrous component interferes with the relaxation of the elastic material and prevents full recovery of the elastic material to its unextended length.

When such a material is included in a garment which is subject to washing, the washing action tends to soften the fibrous component and this allows the elastic material to relax further: when such a wetted enclosed elastic material dries, the unextended length of the enclosed elastic material is found to be less than prior to washing.

This effect is particularly significant where the enclosed elastic material is to be used for intermittent elastication of a garment. It is often important that the parts of the enclosed elastic material which are inserted into the garment in a relaxed condition are not ruched but remain smooth and flat, for aesthetic reasons. Where such enclosed elastic material is washed, there is a tendency (as mentioned above) for the material to relax further and this has been noted because it causes ruching in the part of the enclosed elastic material which is intended to be smooth.

Various methods of reducing the tendency of the elastic material to shrink on washing have been proposed but none has been entirely satisfactory. Amongst the proposed treatments has been "wet finishing" of the manufactured enclosed elastic material: by wet finishing the material the tendency of the material to relax further when washed is reduced by wetting the enclosed elastic material to allow it to relax before it is incorporated in a garment. Wet finishing, however, requires the finished product to be dried and this is relatively costly and time consuming. It has also been proposed to heat-treat the enclosed elastic material by passing it between heated rollers or pressing the enclosed elastic material against a heated plate: both have been found to reduce the tendency to shrink; treatment by rollers followed by pressing against the heated plate is generally found to be somewhat more effective than a single treatment by roller or hot plates alone. None of these proposed methods of treatment to reduce the tendency of the elastic to shrink on washing has been effective to eliminate the shrinkage completely, although it has been possible to reduce the amount of subsequent shrinkage to about 246, that is a reduction in length of the enclosed elastic after washing of about 2 % compared with the relaxed length of the elastic before washing.

In addition should excess heat be applied for any reason, there is a risk that the elastic material may be degraded to some extent, and its performance change. Furthermore, for a variety of reasons, eg temperature fluctuations, heat treatment may also give inconsistent results.

One of the difficulties in causing the enclosed elastic material to relax as far as possible arises because as the elastic material approaches its relaxed, unextended length, the force exerted tending to urge it towards its relaxed condition becomes progressively smaller; at the same time, the tendency of the fibrous component to prevent relaxation becomes greater because the fibres of the fibrous component become more densely packed and therefore tend to prevent further relaxation.

It is one of the various objects of the present invention to provide an improved method of treating strip or filamentary elastic material which has been enclosed by a fibrous component, to reduce the tendency of the enclosed elastic material to relax further in use, for example when a garment incorporating the enclosed elastic material is washed.

It is another object of the present invention to provide an improved enclosed elastic material having little or no tendency to shrink when washed.

In one aspect the invention may be considered to provide a method of treating strip or filamentary elastic material which has been enclosed by a fibrous component whilst a tensioning force is applied to the elastic material in a first direction to extend the elastic material in said first direction, the method comprising feeding the enclosed elastic material between gripping means by which the enclosed elastic material is gripped, the gripping means applying a force to the enclosed elastic material in a direction opposite to said tensioning force whereby to urge the enclosed elastic towards a relaxed condition.

Preferably the enclosed elastic material is allowed to relax from its extended condition to an intermediate relaxed condition before it is fed to the gripping means.

In a preferred method in accordance with the invention the gripping means comprises two pairs of rollers, each pair of rollers consisting of an entrance roller and an exit roller around which a resiliently extendable continuous belt is stretched in an extended condition, wherein the entrance and exit rollers of each pair are spaced apart and positioned with first runs of the belts extending in close proximity, the method comprising applying pressure to urge the first runs of the belts towards one another, rotating the entrance rollers at the same first surface speed and rotating the exit rollers at a second surface speed lower than the first surface speed, the directions of rotation being such as to cause the first runs of the belts to travel from the entrance rollers towards the exit rollers, and feeding the enclosed elastic material between the first runs of the belts from the entrance towards the exit with the enclosed elastic material gripped between the first runs of the belts.

Preferably, in carrying out a method in accordance with the invention, when the elastic material is in the relaxed condition, the elastic material has a potential lengthwise shrinkage, of less than 0.25%, more preferably 0%.

Conveniently, the potential shrinkage is measured by a standard wash shrinkage test which is generally as follows.

Having first allowed an enclosed elastic material to be tested to relax, samples of material of a first standard length eg 500mm are prepared and, on each sample, indelible marks are placed a first standard distance apart. The standard distance is less than the standard length and the standard distance is marked in a central region of the sample spaced from its ends; a convenient standard distance may be 300mm or 350mm.

Several samples are prepared and each in a flat condition is stitched at each end of the sample to a flat pre-shrunk fabric.

The fabric carrying the samples is then washed in a typical load in a washing machine of closely controlled performance and tolerances eg a Wascator FOM 71S machine. A detergent (or other washing aid) is included in substantial quantities. The washing is carried out with the water at a controlled temperature for example 60"C.

The samples are subjected to severe washing conditions, more severe than are likely to be met when washing garments in typical domestic washing machines.

The fabric carrying the samples is then spin dried, if necessary, and subsequently dried in a typical domestic tumble dryer at a "hot" setting and with a typical load in the dryer, for a considerable period of time, sufficient to completely dry the load to usual levels of dryness.

The fabric carrying the samples is then laid on a flat surface for several hours to allow complete relaxation of the samples.

The distance between the indelible marks on each sample is then measured and the percentage shrinkage calculated by comparison with the standard length.

In another aspect, the invention may be considered to provide an enclosed elastic material comprising a strip filamentary elastic material enclosed by a fibrous component, in a relaxed condition in which the enclosed elastic material has a potential lengthwise shrinkage of less than 0.25% eg when measured by said standard wash shrinkage test method.

Preferably, the potential lengthwise shrinkage is zero.

Suitably, the elastic material in accordance with the invention is made by a method in accordance with the invention.

Preferably, an enclosed elastic material in accordance with the invention comprises an elastic band in which the elastic material comprises filaments of elastomeric material and the fibrous component comprises textile fibres knitted, woven, crocheted or braided to enclose the filaments of elastomeric material and provide a fibrous cover around the filaments.

In yet another aspect the invention may be considered to provide apparatus suitable for use in treating strip or filamentary elastic material which has been enclosed by a fibrous component comprising two pairs of rollers, each pair of rollers consisting of an entrance roller and an exit roller around which a resiliently extendable continuous belt is stretched in an extended condition, wherein the entrance and exit rollers of each pair are spaced apart and positioned with first runs of the belts extending in close proximity, means for applying pressure to urge the first runs of the belts towards one another, means for rotating the entrance rollers at the same first surface speed and means for rotating the exit rollers at the same second surface speed lower than the first surface speed, said means for rotating being such as to cause the first runs of the belts to travel from the entrance rollers towards the exit rollers.

Suitably the belts comprise an elastomeric material, for example rubber.

In yet another aspect the invention may be considered to provide a garment incorporating an enclosed elastic material in accordance with the invention.

There now follows a detailed description, to be read with reference to the accompanying drawings of a method of treating strip or filamentary elastic material which has been enclosed by a fibrous component and an enclosed elastic material made by the method. It will be realised that the method and material has been selected for description to illustrate the invention by way of example.

In the accompanying drawings: Figure 1 is a diagrammatic view showing enclosed elastic material with parts broken away; Figure 2 is a diagrammatic view of apparatus embodying the invention; and Figure 3 is a diagrammatic view of a garment including a waist band incorporating enclosed elastic material.

The enclosed elastic material 8 shown in Figure 1 comprises a plurality of filaments 10 of elastic material, namely rubber; only two of the filaments are shown for ease of illustration but it is to be understood that more filaments will normally be present in the enclosed elastics materials. The rubber filaments 10 are enclosed by fibrous components 12 and 14. In Figure 1 the fibrous component comprises textile fibre threads 14 which are knitted around the filaments 10 with a textile fibre weft thread 12. This enclosed elastic material is well known and is available commercially from various manufacturers of garment elastic, including the applicants who supply such elastic under the trade name Tricoflex (registered trademark).

During the manufacture of enclosed elastic material of the type shown in Figure 1, a tensioning force P is applied to the rubber filaments 10 whilst the threads 12, 14 are knitted to enclose the filaments 10, the tensioning force being applied in a first direction to extend the filaments 10 of elastic material in said first direction. After manufacture, the enclosed elastic material is normally allowed to relax to a relaxed condition which is referred to herein as an "intermediate relaxed condition".

As discussed previously, this intermediate relaxed condition is such that further relaxation of the enclosed elastic material is possible, for example when the enclosed elastic material is subjected to washing when incorporated into a garment and this can cause problems as outlined previously.

In Figure 2 is shown, diagrammatically, apparatus embodying the invention. The apparatus shown in Figure 2 comprises gripping means provided by a pair of roller and belt assemblies 18, 19. Each of the assemblies 18, 19 comprises a pair of rollers 20, 22, each pair of rollers consisting of an entrance roller 20 and an exit roller 22. Around each pair of rollers 20, 22, a resiliently extendable continuous belt 24 is stretched in an extended condition so that each of the belts 24 is tensioned. The belts 24 are conveniently made of a suitable extensible rubber material but may be made of any convenient resiliently extendible material. As can be seen viewing figure 2, the entrance and exit rollers 20, 22 of each pair are spaced apart and positioned with first runs 26 of the belts 24 extending in close proximity to one another. The first runs of the belts 24 are in contact with pressure applying means, namely plates 28, by which the first runs 26 may be urged towards one another as indicated by the arrows X in Figure 2. The pressure applying means may be provided by any convenient apparatus. In addition, the entrance rollers 20 of the assemblies 18, 19 and exit rollers 22 of the assemblies 18, 19 are disposed opposite one another and urged towards one another as indicated by the arrows A in Figure 2. The pressure applying means may be provided by any convenient apparatus, for example a series of rollers or a single convexly curved pressure plate urged into engagement with one of the belts to tension belts firmly: in this latter case the first runs of the belts will each be curved as they run over the pressure plate. The pressure applying means 28 and the entrance rollers 20 and exit rollers 22 may be urged towards one another by any convenient means, for example by a spring loading system, or, preferably, by a pneumatic ram assembly so that the pressure applied can be adjusted if necessary.

The entrance and exit rollers 20, 22 are of the same diameter in the illustrative apparatus. The entrance rollers 20 are drivingly coupled to one another, for example by gearing or any other suitable means so that they rotate in a direction indicated by the arrows B, at the same first surface speed. The exit rollers 22 are likewise drivingly coupled to one another, for example by gearing, so that the exit rollers 22 also rotate at the same second surface speed. Direction of rotation of the rollers 20, 22 is such as to cause the first runs 26 of the belts 24 to travel from the entrance rollers 20 towards the exit rollers 22.

The illustrative apparatus shown in Figure 2 further comprises tL jl drive means (not shown) for rotating the entrance rollers 20 and second drive means (not shown) for rotating the exit rollers 22. The drive means may be any suitable drive unit for example an electric motor and associated gear box unit. The drive means are arranged to rotate the rollers 20, 22 as indicated by the arrows B, C in Figure 2.

In carrying out the illustrative method of treating enclosed elastic material, the enclosed elastic material 8 is fed into the nip between the entrance rollers 20 with the drive means rotating the entrance rollers 20 and exit rollers 22 as indicated by the arrows B, C. At the same time pressure is applied to the rollers 20, 22 as indicated by the arrows A, to urge them towards one another under a known pressure and the pressure plates 28 are likewise urged together under a known load as indicated by the arrows X. Thus, the enclosed elastic material 8 which is fed into the illustrative apparatus is gripped between the rollers 20 and the belt 24, in particular the first runs 26 of the belts 24.

In carrying out the illustrative method the drive means are caused to operate so that the first surface speed of the entrance rollers 20 is greater than the second surface speed at which the exit rollers 22 rotate.

The affect of this is that the first runs 26 of the belts 24 tend to be compressed as indicated by the arrow T. Because the first runs 26 are constrained by the pressure plates 28, the first runs of the belts tend to apply a force to the enclosed elastic material 8 gripped between them in a direction opposite to the tensioning force P applied to the filaments 10 during manufacture of the enclosed elastic material 8 thus to urge the enclosed elastic 8 towards a relaxed condition.

In the second, return runs 30 of the belts 24, it will be appreciated that, because the exit rollers 22 are rotating at a speed slower than the rollers 20, the belts 24 will return to their uncompressed condition, while still remaining in tension.

It can also prove useful to heat the belts and rollers somewhat (but to a much lower temperature than would be commonly used in known methods of controlling potential shrinkage).

The elastic material 8 leaving the illustrative apparatus between the exit rollers 22 is found to have a relaxed condition in which the elastic material has a potential lengthwise shrinkage when measured by the aforementioned standard test which is governed by the relative rates of rotation of the entrance and exit rollers 20, 22, and is generally less than 0.25% but may be zero or indeed it has been found that the enclosed elastic material can be compressed to a length less than that to which it would normally shrink in the test. By control of the relative speed of the entrance rollers 20 and the exit rollers 22 it is possible to vary the degree of treatment over a range such as to achieve a desired degree of relaxation of the enclosed elastic material.

The treated enclosed elastic material thus produced is therefore illustrative of the invention in one of its aspects. When such illustrative elastic material is incorporated into the waist band 32 of a garment 34 by an intermittent elastication process, the elastic material 8 inserted in the garment in a tensioned condition at regions 38 is separated by regions 40 where the elastic material 8 is in a relaxed condition. The regions 38 of the waist band 32 corresponding with the tensioned elastic portions are ruched whereas in the regions 40 where the elastic is in a relaxed condition, the waist band is flat and smooth. When such a garment is subjected to washing it is found that the regions 40 remain smooth and flat. By comparison, where an otherwise similar elastic material has not been treated by the method embodying the invention, the region 40 tends to become ruched after the garment has been washed and this is found to be unattractive and unsatisfactory to the user, commonly generating complaints of the appearance of the waist band.

By carrying out the illustrative method it is possible to allow the filaments to relax to remove the tendency of the enclosed elastic material to shrink: without treatment by the illustrative method, the elastic material commonly remains in a slightly tensioned condition so that when an intermittently elasticated garment waist band containing said elastic is washed it shrinks slightly, causing unsightly wrinkles in the unelasticated portions of the covering fabric.

Although a method in accordance with the invention is specially useful in the manufacture of garment elastic, for subsequent incorporation in garments, it may also be applied in the manufacture of garments themselves. In this latter event, the strip elastic material may be garment elastic and the fibrous component may be provided by a hem tunnel of a garment in which the garment elastic is enclosed by sewing, to provide an elasticated region of the garment eg a waist band. The elasticated region of the garment may then be treated by a method in accordance with the invention.

Claims (12)

1. A method of treating strip or filamentary elastic material which has been enclosed by a fibrous component whilst a tensioning force is applied to the elastic material in a first direction to extend the elastic material in said first direction, the method comprising, feeding the enclosed elastic material between gripping means by which the enclosed elastic material is gripped, the gripping means applying a force to the enclosed elastic material in a direction opposite to said tensioning force whereby to urge the enclosed elastic towards a relaxed condition.

2. A method according to claim 1 wherein the enclosed elastic material is allowed to relax from its extended condition to an intermediate relaxed condition before it is fed to the gripping means.

3. A method according to either one of claims 1 and 2 wherein the gripping means comprises two pairs of rollers, each pair of rollers consisting of an entrance roller and an exit roller around which a resiliently extendable continuous belt is stretched in an extended condition, wherein the entrance and exit rollers of each pair are spaced apart and positioned with first rims of the belts extending in close proximity, the method comprising applying pressure to urge the first runs of the belts towards one another, rotating the entrance rollers at the same first surface speed and rotating the exit rollers at a second surface speed lower than the first surface speed, the directions of rotation being such as to cause the first runs of the belts to travel from the entrance rollers towards the exit rollers, and feeding the enclosed elastic material between the first runs of the belts from the entrance towards the exit with the enclosed elastic material gripped between the first runs of the belts.

4. A method according to any one of the preceding claims wherein in the relaxed condition of the elastic material the elastic material has a potential lengthwise shrinkage of less than 0.25%.

5. A method of treating elastic material which has been enclosed in a fibrous cover substantially as hereinbefore described with reference to the accompanying drawings.

6. An enclosed elastic material comprising a strip or filamentary elastic material enclosed by a fibrous component, in a relaxed condition in which the enclosed elastic material has a potential lengthwise shrinkage of less than 0.25%.

7. An enclosed elastic material according to claim 6 wherein the potential lengthwise shrinkage is zero.

8. An enclosed elastic material according to either one of claims 6 and 7 comprising an elastic band in which the elastic material comprises filaments of elastomeric material and the fibrous component comprises textile fibres knitted, woven, crocheted or braided to enclose the filaments of elastomeric material.

9. An elastic material made by a method according to any one of claims 1 to 5.

10. Apparatus suitable for use in treating strip or filamentary elastic material which has been enclosed by a fibrous component comprising two pairs of rollers, each pair of rollers consisting of an entrance roller and an exit roller around which a resiliently extendable continuous belt is stretched in an extended condition, wherein the entrance and exit rollers of each pair are spaced apart and positioned with first runs of the belts extending in close proximity, means for applying pressure to urge the first runs of the belts towards one another, means for rotating the entrance rollers at the same first surface speed and means for rotating the exit rollers at the same second surface speed lower than the first surface speed, said means for rotating being such as to cause the first runs of the belts to travel from the entrance rollers towards the exit rollers.

11. Apparatus according to claim 10 wherein the belts comprise elastomeric material.

12. A garment incorporating an enclosed elastic material according to any one of claims 6 to 8.