Bulletproof woven fabric

Description

[0001] Bulletproof woven fabrics composed of filaments and yarns which are made of polymers of ultrahigh molecular weights and which have high strengths and moduli are known.

[0002] For instance, US Patent 4,181,768 describes bulletproof woven fabrics whose warp and weft filaments consist of polyaramid filaments or yarns. The disad­vantage of these fabrics is that they are relatively heavy, owing to the high specific weight of the poly­aramids, and that in addition the antiballistic proper­ties are substantially reduced by the action of moisture.

[0003] EP 89,537 discloses bulletproof woven fabrics where the warp and weft filaments consist of polyolefin fibers having ultrahigh molecular weights of more than 500,000 g/mol. These fabrics have the disadvantage that, owing to the very smooth surface of the polyolefin fila­ments, these filaments are easily moved aside in the fabric on penetration of a bullet, so that more layers are required to arrest impacting bullets.

[0004] It is an object of the present invention to remove the prior art disadvantages by providing bullet­proof woven fabrics of the above-described generic cate­gory which, on the one hand, are lightweight and whose filaments or yarns, on the other hand, are only dif­ficultly movable by impacting projectiles, so that said fabrics can be produced in lower layer thicknesses than the structures disclosed in EP 89,537.

[0005] This object is achieved by means of the bullet­proof woven fabrics according to the invention, which are composed of filaments or yarns having high strengths and high moduli and consisting of polymers of ultrahigh molecular weights, wherein the warp filaments or yarns consist of other polymers than the weft filaments or yarns.

[0006] The invention is based on the surprising finding that, if the warp filaments or yarns of bulletproof woven fabrics are made of other polymers than the weft filaments or yarns, the mutual gliding action of the filaments or yarns is substantially reduced, so that an impacting projectile is no longer capable, as in the case of existing woven fabrics whose warp and weft filaments or yarns consist of the same polymers, of moving apart these filaments or yarns. Accordingly, the woven fabrics according to the invention can be produced in lower thicknesses than those disclosed in EP 89,537.

[0007] Preferably, the weft filaments or yarns of the woven fabrics according to the invention consist of poly­ethylenes, in particular linear polyethylenes, of ultra­high molecular weight of in particular more than 600,000 g/mol (weight average of the molecular weight). These polyethylenes may contain minor amounts, prefer­ably not more than 5 mol %, of one or more other alkenes copolymerizable therewith, such as propylenes, butyl­enes, pentene, hexene, 4-methylpentene, octene etc. In addition they can preferably contain 1 to 10, in par­ticular 2 to 6, methyl or ethyl groups per 1,000 carbon atoms. However, it is also possible to use other polyole­fins, for example, polypropylene homopolymers and copoly­mers, which polyolefins may also contain minor amounts of one or more other polymers, in particular alkene-1, polymers.

[0008] However, the weft filaments can consist of still other polymers, for example polyvinyl alcohols having such high molecular weights that the filaments or yarns produced therefrom have high strengths and moduli as conventionally required for producing bulletproof fabrics. Also suitable are, for example, copolymers of polyvinyl alcohol and ethylene which have a low ethylene content.

[0009] The ultrahigh molecular weight filaments used in each case are preferably produced by the gel process, which comprises essentially dissolving the particular polymer in a solvent, then molding the solution into a filament at a temperature above the dissolving tempera­ture of the polymer, cooling the filament, to effect gelling, down to a temperature below the dissolving temperature and then drawing the gel filament with sol­vent removal, preferably to high draw ratios of more than 20, in particular more than 30. Such a process is described for example in GB-A-2,042,414 and -2,051,667 and also in DE Offenlegungsschrift 3,724,434.

[0010] The weft filaments preferably have a low linear density, in particular less than 700 d, particularly preferably less than 500 d.

[0011] It has also proved highly advantageous to use in the production of the bulletproof woven fabrics accord­ing to the invention weft yarns which are produced from very thin highly oriented monofilaments and preferably have deniers of less than 4, in particular less than 2, made preferably of polyethylenes having ultrahigh mole­cular weights of more than 600,000 g/mol (weight average of the molecular weight).

[0012] Preferably, the bulletproof woven fabrics according to the invention consist of warp filaments and/or yarns having lower moduli and higher elongations than the weft filaments and/or yarns. This embodiment is particularly advantageous insofar as it is easier to produce a woven fabric which has elastic warp filaments. Furthermore, it is advantageous for ballistic purposes if the stiffness of bulletproof fabrics is the same not only in the warp but also in the weft direction. Norm­ally, however, the stiffness in the warp direction is higher. By using warp filaments and/or yarns which have a lower modulus and a higher elongation than the weft fila­ments and/or yarns it is possible to keep the stiffness substantially the same both in the warp and in the weft direction.

[0013] The warp and weft filaments or yarns of which the bulletproof fabrics according to the invention are made can be subjected for improved antigliding prop­erties to a gentle surface treatment which does not affect the strength and modulus values, for example to a plasma treatment as described in European patent application filed with the European Patent Office under file reference 5410 on the same date as the present application. Other possib­ilities for this pretreatment include corona treatment or any of the existing mechanical and/or chemical methods for improving the antigliding properties, pro­vided the strength and modulus values are not reduced thereby. Even coating the filaments with known anti­gliding agents is possible. Furthermore, the antigliding properties of the warp and weft filaments or yarns can be improved by core spinning these filaments and yarns with filaments and/or yarns having high coefficients of friction and hence a rough surface.

Claims

1. A bulletproof woven fabric composed of filaments or yarns having high strengths and high moduli and con­sisting of polymers having ultrahigh molecular weights, wherein the warp filaments or yarns consist of other polymers than the weft filaments or yarns.

2. A bulletproof woven fabric as claimed in claim 1, wherein the weft filaments or yarns consist of poly­ethylene, in particular linear polyethylene.

3. A bulletproof woven fabric as claimed in either of claims 1 and 2, wherein the weft filaments have a low linear density, in particular less than 700 d.

4. A bulletproof woven fabric as claimed in any of claims 1 to 3, wherein the warp filaments or yarns con­sist of polyamides, in particular aramids.

5. A bulletproof woven fabric as claimed in either of claims 1 and 4, wherein the warp filaments or yarns have lower moduli and higher elongations than the weft filaments and yarns.

6. A bulletproof woven fabric as claimed in any of claims 1 to 5, which has weft yarns which are pro­duced from very thin, highly oriented monofilaments and have in particular deniers of less than 4 and have been produced in particular from polyethylenes of ultrahigh molecular weights of more than 600,000 g/mol (weight average of molecular weight).