Airbag and method of producing an airbag

Abstract

The invention relates to a two-ply airbag consisting of a textile surface structure, said plies lying opposite one another and enclosing at least one chamber that can be filled with gas. The piles have surfaces that face outwards. The airbag is characterized in that coatings, which are suitable for sealing and reinforcing the airbag, are applied to said surfaces.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT Application No. PCT/EP03/05697 filed on May 30, 2003, which claims priority to German Application No. DE 102 24 771.4-42, filed on Jun. 4, 2002; both of which are incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to an air bag comprising two plies of a textile sheet fabric, the plies facing each other and enclosing at least one chamber that can be filled with gas, the plies having surfaces facing outwards, the invention also relating to a method of producing such an air bag.

Air bag fabrics are in use whose technical properties are dictated by the dense structure of the fabric. To attain the needed strength and airtightness the fabric must be fabricated suitably high set which because of the high material consumption results in fabrication being expensive. Fully fabricated or one-piece woven (OPW) air bags need to satisfy the crash withstanding performance, in other words it is vital that the pressure in the air bag is maintained for the critical duration, i.e. the air bags must not leak. For this purpose such air bags are woven extremely dense, major efforts being made to change the weave in the transition of two-ply portions into single-ply portions in attaining, for example, a high fabric tear strength or comb withdrawal force.

Since in many cases the air bag fabric made in this way still fails to exhibit an adequate leakage resistance, additional thin films are added in an expensive process with the sole objective of sealing the fine pores of the fabric to achieve the necessary leakage resistance. Air bags fabricated as such are, on the one hand, because of the weaving method very expensive. On the other, the expense of the air bags is further increased by the complicated coating process. Because of its high density, finishing such a fabric is a slow and thus cost-intensive process.

Known air bag fabrics have the further drawback that because of the dense set and involving the slower weaving process the load on the yarn is correspondingly higher. Thus, during the transition in weaving the threads from the upper into the lower position and vice-versa the threads rub against each other all the more often and intensified because of the dense set, to the detriment of the quality in weaving (capillary damage, fluffing, conglomerations, thread breakage and the like) resulting in a high degree of spoilage. Moreover, thread damage in weaving results in many cases in downtime of the weaving machine, also due to machine speeds needing to be increasingly higher causing a serious loss of efficiency which in turn further adds to the already high costs of production. Another drawback of the air bags as discussed is that due to the high set and because of the correspondingly high fabric thickness of the air bag fabric a certain packing volume of the finished air bag needs to be assured in the folded condition. Because of the high set the fabric or air bag becomes stiffer, further adversely influencing working the fabric.

The present invention is based on the objective of producing a low-cost air bag in avoiding or at least greatly diminishing the drawbacks of prior art, as well as proposing a method for producing such an air bag. This objective is firstly achieved by an air bag as it reads from claim 1. This air bag in accordance with the invention can now be fabricated significantly cheaper than air bags as known from prior art. By arranging the coatings on the surfaces of the fabric plies of the air bag facing outwards as suitable for forming the leakage resistance and strengthening of the air bag, the textile sheet fabric of the air bag can now be woven relatively loosely. Strengthening the air bag in this sense is meant as coating the air bag to achieve particularly high strength, leakage resistance and keying to the fabric. The fabric itself is responsible so-to-speak for forming the outer and inner structure of the air bag and its at least one chamber, i.e. it not primarily contributing towards leakage resistance and strength of the fabric as handled namely by the coating e.g. also in the form of a film. Now, because of this, the set of the fabric can be strongly redimensioned. Thus, for instance, the single-ply portions in a one-piece woven (OPW) can now be executed solid and tight in a (simpler) plain weave instead of a panama weave as hitherto. This greatly reduces the load on the fabric by shear forces at critical transitions from single-ply to two-ply portions with the same weave as achieved by the plain weave as proposed in this case, resulting in a drastic reduction in the risk of the coating becoming detached or damaged as arranged on the fabric, i.e. risk of leakage. By satisfying the required airtightness the air bag in accordance with the invention thus ensures the vital pressure withstanding duration.

Another advantage materializes from the smoother surface of the plain weave permitting better adhesion of the coating in further reducing the risk of leakage. Because of the lower set and the resulting higher output of the weaving machine, the air bag fabric and one-piece wovens (OPW) in the shop and finishing can now be produced and worked to advantage substantially cheaper. Due to the fewer shed changes as well as due to the lesser attrition of the threads against each other the load on the yarn material is significantly reduced, resulting in a drastic reduction in impairments (capillary damage, fluffing, conglomerations, thread breakage and the like) in thus immensely enhancing product quality. Since this involves the weaving machine being down far less because of yarn impairment, efficiency is boosted substantially.

Yet another advantage of the air bag in accordance with the invention materializes from the reduced packing volume in the folded condition. The reduction in set as made possible by the invention now makes it possible to reduce the cover factor and result in a fabric with a softer feel with added flexibility. As a result of this, the fabric coming from the weaving machine can now be worked much better in the subsequent steps in the process. Further features and advantages of the invention read from the sub-claims.

The objective is further achieved by a method as it reads from claim 8. For this purpose, particular mention is made to the advantages of hot rolling thermoplastic films to the surfaces, resulting in the keying points in the fabric being flattened by the pressure in thus providing a more expansive receiving surface for the roll-applied films. In other words, this relatively simple trick now makes it possible to achieve a smoother surface for better keying between coating and fabric. As a rule the surfaces of e.g. of woven, knitted or netted textile sheet fabrics as representing the aforementioned surfaces, for example, are not smooth in structure but “bumpy”, resulting in no continuous flat contact surface being available for a coating, e.g. in the form of a film. The threads of the textile sheet fabric merely “ripple” from the surface thereof in a bumpy structure, whereby in a knit, for example, the peaks of the loops protrude from the surface whilst the valleys of the loops are located deeper in the knit.

It is known to coat textile sheet fabrics with fluids, films, film-like materials or laminates and the like, serving e.g. to enhance the resistance to ageing and/or leakage and/or to reduce permeability and/or friction, etc. When such textile sheet fabrics are overtaxed mechanically, hydraulically or pneumatically the key between the textile sheet fabric and the coating is disrupted which may even result in a total malfunction of the textile sheet fabric.

In another advantageous aspect of the method in accordance with the invention as it reads from claim 9, a low-cost method of coating textile sheet fabrics, especially where wovens, air bag wovens and air bags are involved in achieving a better adhesion between the textile sheet fabrics and their coatings. A substantial improvement in the adhesion of the textile sheet fabric is achieved both by corona treatment and by plasma treatment as well as by fluorination. In the corona and plasma processes as described and discussed e.g. in German utility model DE 298 05 999 U1 electrostatic forces of attraction are activated to greatly enhance the adhesion of the substances applied to the textile sheet fabric. In fluorination of a textile sheet fabric, a reproducible, dry chemical reaction takes place at the surface in which hydrogen atoms are substituted by fluorine, creating a longer-active surface permitting mechanical and chemical bonding.

In still another advantageous aspect of the method in accordance with the invention the textile sheet fabric is coated with a film of silicone whose surface facing away from the textile sheet fabric is treated with fluorine gas. This fluorination produces a near totally smooth surface practically cancelling any silicone/silicone adhesion. This advantage is put to use particularly for air bags to be folded, since it does away with the need for a parting agent as required hitherto.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be briefly explained in the following by way of an example embodiment with reference to the drawing in which:

FIG. 1 is a diagrammatic cross-section through a fabric ply of an air bag in accordance with the invention.

FIG. 2 is a diagrammatic illustration of how thermoplastic films are rolled on to a fabric ply for producing a textile sheet fabric for the air bag in accordance with the invention.

DETAILED DESCRIPTION

Referring now to FIG. 1 there is illustrated a fabric including weft threads 6 and (not shown true to scale) warp threads 7. Indicated are so-called keying points 2 to which a film 1 optimized as to adhesion, resistance to leakage and strength is applied to a fabric 3 formed by weft and warp threads 6 and 7 respectively. Due to the fabric 3 being compressed by a pair of nip rollers 4 as shown in FIG. 2 the warp threads 7 are squeezed together so that they become elliptical cross-sectionally. Likewise evident from the arrangement as shown in FIG. 1 simply diagrammatical is how the keying “points” 2 become flattened between film/coating and fabric.

Referring now to FIG. 2 there is illustrated a pair of nip rollers 4 between which the film 1 as cited above and the backing fabric 3 thinned in the thread densities is guided and keyed. The resulting key of film/coating and fabric is achievable, chemically, thermally or mechanically, resulting in so-to-speak a textile-strengthened plastics surface 5 which can be additionally compounded by making use of bicomponent yarns. In a loose fabric setting the ondulation of the fabric is less. The keying points 2 of the textile-strengthened plastics surface 5 are flattened by the pressure in rolling and offer a larger contact surface for the film 1.

The air bag may also be configured as it reads from claim 3, whereby the advantages as discussed with reference to claim 1 are likewise provided. By thermally treating the air bag after weaving the necessary leakage resistance and strength are attainable due to cross-linking of the components of the plastics sheathing the threads of the fabric plies.

Claims

1. An air bag comprising two non-gastight plies of a textile sheet fabric, the plies facing each other and enclosing at least one chamber that can be filled with gas, the plies having surfaces facing outwards, comprising a fabric dictating the outer and inner structure of the air bag and on each surface facing outwards one coating is disposed for strengthening and rendering the air bag resistant to leakage.

2. The air bag as set forth in claim 1, wherein said coatings comprise films keyed to the surfaces chemically, thermally or mechanically.

3. The air bag as set forth in claim 1, wherein the coatings comprise plastics-sheathed threads of the fabric plies.

4. The air bag as set forth in claim 1, wherein said textile sheet fabric is a woven.

5. The air bag as set forth in claim 1, wherein said textile sheet fabric is a knit or a non-woven fleece.

6. The air bag as set forth in claim 4, wherein said textile sheet fabric comprises bicomponent yarns.

7. The air bag as set forth in claim 1, wherein said textile sheet fabric is a thinned fabric, whose surface is laminated with a coating or film.

8. A method of producing an air bag comprising two woven plies facing each other and enclosing at least one chamber that can be filled with gas, the plies having surfaces facing outwards, on which coatings, laminates, films or covering layers are deposited suitable for strengthening and/or rendering the air bag resistant to leakage, comprising the steps:

weaving the air bag on a weaving machine controlled particularly by a Jacquard device,

hot rolling thermoplastics films on the surfaces, the keying points in the fabric being flattened by pressure in thus forming a larger contact surface for the films.

9. The method as set forth in claim 8, wherein said surfaces and/or coatings, laminates, films or covering layers are prepared at least in part by a corona treatment or by a plasma treatment or by fluorination before roll application of the films.

10. The method as set forth in claim 8, wherein films of polyamide, polyester, silicone, neoprene or polyurethane are laminated to said surfaces.

11. The method as set forth in claim 8, wherein said surfaces are provided with a film of silicone which is in turn treated with fluorine gas.