GB2376959A

GB2376959A - Tumescent filaments and yarns

Info

Publication number: GB2376959A
Application number: GB0115911A
Authority: GB
Inventors: Jack Johansson; Mats Johansson
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 2001-06-28
Filing date: 2001-06-28
Publication date: 2002-12-31
Also published as: GB0115911D0

Abstract

A filament 1 or yarn suitable for sewing or weaving, e.g. to manufacture an air-bag, comprises thermally activatable tumescent material 3, e.g. in the form of microspheres in a matrix, which can be expanded when subjected to a temperature above a predetermined threshold. This may be done either as a manufacturing step or in use, e.g. by the hot gases released on deployment of an air-bag. The expansion of the filament serves to seal stitch holes when used for sewing or to seal a relatively open fabric when used in weaving. The filament shown has a coating 3 of the tumescent material on a core 2 held in an outer sleeve 4 which may itself expand or be shed, e.g. by melting, when the material 3 expands. Alternatively a yarn may comprise both non-tumescent and tumescent fibres.

Description

DESCRIPTION OF INVENTION "IMPROVEMENTS IN OR RELATING TO A FILAMENT" THE PRESENT INVENTION relates to a filament, and more particularly relates to a filament in the form of a mono-filament, yam or thread for use as a sewing filament or a weaving filament.

The filament of the present invention may find particular applications in the field of air-bags, as used in vehicle safety devices, but the filament of the invention may find other applications.

It has been proposed previously to manufacture an air-bag by sewing together two or more pieces of fabric using a filament in the form of a sewing thread. The sewing thread is passed through the fabric that is to form the airbag using an appropriate needle. As the needle passes through the fabric of the air-bag, a hole is created, and typically the hole has a diameter which is greater than the diameter of the thread. When the air-bag is inflated gas can escape from the air-bag through the holes. The holes may enlarge during inflation of the air-bag as the fabric forming the air-bag and the seam formed by the stitched sewing thread are placed under tension and become stretched.

Another problem with sewing threads that are used currently in the manufacture of air-bags is that the threads may be sensitive to heat. The hot gasses in the air-bag may bum or melt the threads.

There is a requirement to reduce the overall weight of an air-bag unit, since vehicle manufacturers are interested in reducing the overall weight of each vehicle, since this helps in minimising fuel consumption. There is also a requirement for airbags that are relatively easy to fold, as the folding process contributes significantly to the total cost of an airbag. Also there is a requirement for air bag units that occupy a minimum of space.

The present invention seeks to provide an improved filament.

According to one aspect of this invention there is provided an elongate filament for use in sewing or weaving, the filament incorporating a thermally actuated tumescent material adapted to expand when subjected to a temperature in excess of a predetermined threshold.

The filament may comprise a core, the core being coated with the tumescent material. The coated core may be provided with an outer protected sleeve.

Alternatively the filament comprises a plurality of spun fibres, at least one of the fibres being formed of said tumescent material.

Preferably the tumescent material comprises a plurality of microspheres which encapsulate a liquid blowing agent, the microspheres being held in a matrix.

Conveniently the matrix comprises a thermo-setting plastics material.

This invention also relates to an air-bag, said air-bag incorporating fabric which is sewn with a filament, the filament being a filament as described above.

This invention also relates to a woven fabric, the woven fabric incorporating a plurality of filaments as described above.

The woven fabric may form part of an air-bag.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: FIGURE 1 is a perspective view of an end part of a filament in accordance with the invention, FIGURE 2 is a cross-sectional view of the filament of Figure 1 after the filament has been exposed to heat, FIGURE 3 is a perspective view of an end part of an alternative filament in accordance with the invention, FIGURE 4 is a diagrammatic view illustrating the filament in accordance with the invention forming part of an air-bag, and

FIGURE 5 is a diagrammatic view illustrating threads in accordance with the invention used in weaving a fabric.

Referring initially to Figure 1 of the accompanying drawings, a filament 1 in accordance with the invention comprises a central core 2. The core may be a mono-filament, or may be a spun yam or thread. The core is provided with a coating 3. The coating 3 uniformly surrounds the core 2. The coating 3 is formed of a thermally responsive tumescent material, that is to say a material which expands when subjected to a temperature in excess of a predetermined temperature. The preferred tumescent material, as utilised in the described embodiment of the invention, comprises a plurality of hollow microspheres which encapsulate a liquid blowing agent which are retained in a suitable matrix, such as a thermo-setting plastics material which has resilient properties, or which is capable of plastic deformation.

It has been proposed previously (see US-A-3, 615,972) to provide thermo-plastic microspheres which encapsulate a liquid blowing agent such that heating of the microspheres causes expansion of the microspheres.

The filament I is provided with an outer sheath or sleeve 4, which may be extruded on to the filament, and which may comprise a thermo-plastic material. The outer sleeve 4 will provide a degree of protection for the microspheres present in the coating 3. Thus the sleeve may facilitate the passing of the filament through, for example, the feed mechanism of a weaving or sewing apparatus, and thus may act as a lubricant.

The thermo-plastics material forming the sleeve 4 is selected so that the thenno-plastics material will melt, or at least will lose substantially all of its

strength, at a temperature at or below the temperature at which the microspheres will expand.

It is therefore to be understood that if the filament 1 of Figure 1 is exposed to a temperature in excess of a predetermined temperature, the outer sleeve 4 will melt or lose its inherent strength, and the microspheres will expand, thus causing the coating 3 to expand so that the diameter thereof is substantially increased. Figure 2 illustrates the filament I after exposure to heat. The core 2 remains unchanged, but the diameter of the coating 3 has increased substantially, and individual microspheres 5, now in their expanded state, are readily discernible. The outer sleeve 4 has been shed, but in another embodiment the sleeve may just expand.

It is to be appreciated, therefore, that the tumescent material 3 forming the coating, will act to substantially increase the diameter of the filament, when the filament is exposed to a temperature in excess of a predetermined temperature. The expanded microspheres will provide a good thermal insulation property, and thus the expanded coating, as seen in Figure 2, will protect the inner core 2 from any high temperature environment which exists on the exterior of the filament 1.

Whilst Figure 1 and 2 illustrate an embodiment in which the filament comprises the core having a coating of tumescent material, Figure 3 illustrates an alternative embodiment of the invention in which a filament 10 is formed as a spun thread or yam formed from three fibres 11,12, 13. In this embodiment of the invention, two of the fibres are formed of an appropriately selected material, such as a natural fibre, or a polyester fibre, and the third fibre 13 is actually an elongate"fibre"formed of a thermally responsive tumescent material. The tumescent material may again comprise a matrix incorporating

microcapsules, or may comprise any other appropriate tumescent material adapted to expand when subjected to a temperature in excess of a predetermined temperature. It will be appreciated that when the filament 10 of Figure 3 is exposed to a temperature in excess of a predetermined temperature, the fibre 13 of tumescent material, which extends along the whole length of the filament 10, will expand, thus serving to increase the overall diameter of the filament 10. In modified versions of this embodiment there may be fewer or more fibres. More than one fibre may be of tumescent material.

Figure 4 illustrates a filament 20, which may be a filament 1 as shown in Figure 1, or a filament 10 as shown in Figure 3, passing through an aperture 21 formed in a layer of fabric 23 which, in this example, is a layer of fabric forming part of an air-bag. The filament 20 is used to secure another layer of fabric (not shown) to the layer 23.

The filament 20 is passed through the layer of fabric 23 using a needle which creates the aperture 21, the aperture 21 having a diameter much greater than the diameter of the filament 20.

On deployment of the air-bag, hot gas from the interior of the air-bag may begin to flow, as shown by the arrows 24, from the interior of the air-bag, through the aperture 21. Alternatively the airbag may be exposed to heat to expand the tumescent material during manufacture.

The hot gas will elevate the temperature of the part of the filament within the aperture 21, and the tumescent material will expand, thus causing the diameter of the filament 20 to increase, as shown by the arrow 25. The diameter will increase to such an extent that the aperture 21 will be substantially sealed.

Figure 5 illustrates part of a cloth or fabric woven from filaments 30 and 31. Some or all of the filaments of the fabric may be filaments 1 or filaments 10 as described above. When the fabric is subjected to a temperature in excess of a predetermined temperature, the filaments provided with tumescent material will expand, thus making the fabric much"tighter". Consequently, the filaments in the fabric of Figure 5 may be spaced relatively far apart, thus making the fabric light, but still, when the fabric is subjected to a temperature in excess of a predetermined temperature, the filaments provided with the tumescent material will expand, thus making the fabric a substantially gas-tight fabric. Consequently by using filaments incorporating tumescent material, as described, in a fabric, a very light fabric may be used which, when subjected to a temperature in excess of a predetermined threshold, is substantially gas-tight. The light fabric may be easy to fold, as it will not have the bulk and stiffness of a typical fabric, and also an airbag made with this fabric may be packaged within a very small housing.

In the present Specification"comprises"means"includes or consists of and"comprising"means"including or consisting of.

The features disclosed in the foregoing description, or the following Claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS: 1. An elongate filament for use in sewing or weaving, the filament incorporating a thermally actuated tumescent material adapted to expand when subjected to a temperature in excess of a predetermined threshold.
2. A filament according to Claim 1 comprising a core, the core being coated with the tumescent material.
3. A filament according to Claim 2 wherein the coated core is provided with an outer protected sleeve.
4. A filament according to Claim 1 wherein the filament comprises a plurality of spun fibres, at least one of the fibres being formed of said tumescent material.
5. A filament according to any one of the preceding Claims wherein the tumescent material comprises a plurality of microspheres which encapsulate a liquid blowing agent, the microspheres being held in a matrix.
6. A filament according to Claim 5 wherein the matrix comprises a thermosetting plastics material.
7. An air-bag, said air-bag incorporating fabric which is sewn with a filament, the filament being a filament according to any one of the preceding Claims.

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8. A woven fabric, the woven fabric incorporating a plurality of filaments according to any one of Claims 1 to 6.
9. A woven fabric according to Claim 8 forming part of an air-bag.
10. A filament substantially as herein described with reference to and as shown in Figures 1 and 2 of the accompanying drawings.
11. A filament substantially as herein described with reference to and as shown in Figure 3 of the accompanying drawings.
12. An air-bag substantially as herein described with reference to and as shown in Figure 4 of the accompanying drawings.
13. A fabric substantially as herein described with reference to and as shown in Figure 5 of the accompanying drawings.
14. Any novel feature or combination of features disclosed herein.