Filter Fabric With Core Sheating Thread, and a Bag Produced Therefrom

The present invention is directed to a woven filter fabric having a core/sheath thread with a reversible fabric elongation of 20% to 50% for the manufacture of inflatable airbags for vehicles.

Airbags as impact protection devices for passengers of a motor vehicle are known (U.S. Pat. No. 4,840,397). In the known airbags, a portion of the walls is constructed as a woven filter fabric. The filter fabric is made up of a mixture of aramid fibers and polyamide fibers. Aramid/polyamide fabrics woven from staple fibers were chosen in view of their coarseness and dimensional stability. The coarseness ensures a better filtering effect on particles in the air. Pore density is also more uniform when staple fibers or spinning fibers are used.

However, woven fabrics produced from spun yarns have the disadvantage that they are more expensive to produce than filament yarns. When used as a raw material for fibers, aramid has the disadvantage that the fabric elongation or springiness is too limited so that the passage of air is delayed. The tear propagation resistance is also inadequate. Aramid is very expensive to produce.

The object of the present invention is to provide a heat-resistant air-permeable woven fabric which is suitable for uncoated filter fabrics, in particular for airbags, and can be manufactured economically, and airbag produced therefrom.

This object is met according to the invention by a core thread produced from a heat-stabilized thermoplastic filament yarn. Preferred heat-stabilized polyamide yarns have heat resistance properties based on Cu/I in yarn, as described, e.g., in WO 93/15138.

The advantage of a thermoplastic filament yarn used as core thread or foundation thread compared to aramid consists in the improvement in processing to form a woven fabric. Polyamide or polyester are substantially simpler and accordingly more economical to manufacture than the known aramid materials. Preferred polyamide materials are Polyamide 66, Polyamide 6 or Polyamide 46; polyethylene terephthalate is preferred as polyester.

The air-permeability is 30 to 100 l per dm.sup.2 /min, in particular 30 to 80 l pro dm.sup.2 /min, preferably 25 to 80 l pro dm.sup.2 /min, and a pressure of 500 pa. The polyamide core thread has the advantage that it permits any desired elongation, depending on its manufacture, between 20% and 50%, in particularly 25%-30%, preferably 30%, with respect to the length of the filament when not stretched.

In a preferred embodiment form, a sheathing of yarn or twisted yarn is provided around the core thread using the core twisting process. Any heat-stable yarn or twisted yarn may be used for this purpose.

In a variant, the core thread is provided with a sheathing or outer layer in the core spinning process, as it is called. The sheathing can be achieved using heat-stabilized or particularly heat-resistant fibers or yarn, e.g., made of aramid or imid.

In another variant, the core thread is coated with a particularly heat-resistant or heat-conducting compound such as PVC. The coating is applied only to the thread and not to the woven fabric.

In a further variant, the core thread is coated by vapor deposition, preferably with copper.

The sheathing thread is preferably made from heat-stabilized fiber material. The fiber material can be aramid, for example. The yarn can be used both as thread and as slubbing. The slubbing can be made of heat-stabilized staple or spinning fibers. The spinning fibers, in turn, have the advantage of an additional filtering effect during pyrolysis when the airbag is used so that occurring particles are retained.

The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

FIG. 1a shows a core thread with a single-ply covering for airbags in accordance with the present invention;

FIG. 1b shows a core thread with a two-ply covering for airbags in accordance with the present invention;

FIG. 2 shows a core thread with a spun covering for airbags in accordance with the present invention;

FIG. 3 shows a coated core thread for airbags in accordance with the present invention;

FIG. 4 shows a core thread coated by vapor deposition for airbags in accordance with the present invention.

FIG. 5 shows a fabric for a filler; and

FIG. 6 shows an airbag.

In FIG. 1a, a core thread 1 made of a Polyamide 66 filament yarn is covered by a single wrapping of yarn or twisted yarn 2.

In FIG. 1b, the core thread 1 is covered with a yarn or twisted yarn 2 and a yarn or twisted yarn 2'. The yarns or twisted yarns 2 and 2' can be produced from identical or different fiber mixtures or twisted yarns.

In FIG. 2, spinning fibers 3 are spun around the core thread 1. The spinning fibers 3 can be enclosed additionally by an accompanying thread, not shown, for reinforcement.

In FIG. 3, the core thread 1 is coated with a plastic 4.

In FIG. 4, a metal coat 5 is deposited on the core thread 1 as a heat shield.

The invention is described more fully with the aid of examples whose results are shown in the following table:

The woven filter fabric according to the invention is especially suitable for the manufacture of safety airbags in vehicles, particularly in automobiles, busses and aircraft. However, it may also be used wherever a rapid compensation of air pressure must be effected accompanied by a simultaneous filtering action.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a filter fabric for airbags and airbag produced therefrom, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way form the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.