Knife-stab-resistant ballistic article

Details Knife-stab-resistant ballistic article Knife-stab-resistant ballistic article

2000-06-13

2002-11-05

Cole, Elizabeth M. (Department: 1771)

Fabric (woven, knitted, or nonwoven textile or cloth, etc.)

Woven fabric

Woven fabric is characterized by a particular or...

C442S239000, C442S246000, C442S247000, C442S301000, C442S381000, C442S392000, C442S414000, C428S902000, C428S911000, C002S002500

Reexamination Certificate

active

06475936

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
It is well known that flexible garments made for protection from ballistic threats are not necessarily effective against stabbing by knives. The converse is also true—knife stab resistant articles are not necessarily effective against ballistic threats. This invention relates to articles that are flexible and provide protection from both knife stab threats and ballistic threats.
2. Discussion of the Prior Art
U.S. Pat. No. 5,622,771, issued Apr. 22, 1997, on the application of Chiou et al. discloses a penetration-resistant article made from tightly woven aramid yarns having particularly low linear density.
International Publication No. WO 93/00564, published Jan. 7, 1993, discloses ballistic structures using layers of fabric woven from high tenacity para-aramid yarn.
European Patent Application No. 670,466, published Sep. 6, 1995, describes a ballistic and stab-resistant system wherein the knife stab resistance is imparted by embedding chain mail in a polymer resin.
U.S. patent application Ser. No. 08/963,094, filed Nov. 3, 1997 (KB-4180-A), discloses an ice-pick-penetration-resistant composite with an outer face of tightly-woven yarn and an inner face of ballistic resistant material wherein the outer face must be the threat strike face.
SUMMARY OF THE INVENTION
This invention relates to a knife stab resistant ballistic article comprising an outer face that comprises a plurality of loosely woven knife stab resistant fabric layers and an inner face that comprises a plurality of ballistic layers.
DETAILED DESCRIPTION
The protective article of this invention was specifically developed to provide dual protection from penetration by knives and knife blades such as stilettos, kitchen knives, butterfly knives, boning knives, and the like, as well as protection from ballistic threats. It is becoming ever more important that police and security personnel have simultaneous protection from both knife stab threats and ballistic threats in the same protective garment. Such garments must be as flexible as possible to ensure sufficient comfort so that the garments will be readily worn. The inventor herein has investigated knife stab resistant articles and ballistic articles and has made startling discoveries relating to the combination of those articles.
Considerable effort has been expended in the past on improvement of protection from penetration by stabbing threats; and the assumption has been that improved stab resistance will be obtained from use of fabrics that are more tightly woven.
The inventor herein has found that assumption to be incorrect insofar as knife stabs are concerned. He has discovered that a woven fabric composite with a loose weave, quite surprisingly, exhibits improved resistance to penetration by knife stabs.
The inventor herein has discovered that the knife stab penetration resistance of a fabric composite is dramatically improved when yarns used to make the fabric of the article are woven to a tightness factor of less than 0.65. It is believed that a tightness factor as low as 0.20 will provide improved knife stab resistance. Up to the present invention, penetration resistant fabrics were tightly woven or impregnated by a matrix resin or both. In efforts completely opposite to the current technical understanding, the inventor herein, discovered that matrix-resin-free fabrics with a low fabric tightness factor exhibit improved knife stab penetration resistance. While any fabrics with any reduced tightness factor are expected to exhibit some improvement, the most improvement is found at a tightness factor of less than 0.65 and greater than 0.20. As the tightness factor is further reduced below 0.20, the fabric weave becomes so loose that an unacceptably high a real density would be required for effective protection.
Ballistic garments are generally made using several layers of protective fabric and the several layers are nearly always fastened together in a way to hold faces of the adjacent layers in fixed position relative to each other. It has been found that knife stab penetration resistance is improved if adjacent layers in a protective composite are not held together; but are free to move relative to each other. When adjacent layers are stitched closely together, knife stab penetration resistance is decreased.
The invention herein is constructed entirely of flexible woven fabric without rigid plates or platelets and without matrix resins impregnating the fabric materials. The articles of this invention are more flexible, lighter in weight, softer to the touch, more comfortable to be worn, and more pliable than penetration resistant constructions of the prior art offering comparable knife-stab protection.
Fabrics of the present invention are made, in whole or in part, from yarns having a tenacity of at least 10 grams per dtex and a tensile modulus of at least 150 grams per dtex. Such yarns can be made from aramids, polyolefins, polybenzoxazole, polybenzothiazole, and the like.
By “aramid” is meant a polyamide wherein at least 85% of the amide (—CO—NH—) linkages are attached directly to two aromatic rings. Suitable aramid fibers are described in Man-Made Fibers—Science and Technology, Volume 2, Section titled Fiber-Forming Aromatic Polyamides, page 297, W. Black et al., Interscience Publishers, 1968. Aramid fibers are, also, disclosed in U.S. Pat. Nos. 4,172,938; 3,869,429; 3,819,587; 3,673,143; 3,354,127; and 3,094,511.
Additives can be used with the aramid and it has been found that up to as much as 10 percent, by weight, of other polymeric material can be blended with the aramid or that copolymers can be used having as much as 10 percent of other diamine substituted for the diamine of the aramid or as much as 10 percent of other diacid chloride substituted for the diacid chloride of the aramid.
Para-aramids are the primary polymers in aramid yarn fibers of this invention and poly(p-phenylene terephthalamide) (PPD-T) is the preferred para-aramid. By PPD-T is meant the homopolymer resulting from mole-for-mole polymerization of p-phenylene diamine and terephthaloyl chloride and, also, copolymers resulting from incorporation of small amounts of other diamines with the p-phenylene diamine and of small amounts of other diacid chlorides with the terephthaloyl chloride. As a general rule, other diamines and other diacid chlorides can be used in amounts up to as much as about 10 mole percent of the p-phenylene diamine or the terephthaloyl chloride, or perhaps slightly higher, provided only that the other diamines and diacid chlorides have no reactive groups which interfere with the polymerization reaction. PPD-T, also, means copolymers resulting from incorporation of other aromatic diamines and other aromatic diacid chlorides such as, for example, 2,6-naphthaloyl chloride or chloro- or dichloroterephthaloyl chloride or 3,4′-diaminodiphenylether. Preparation of PPD-T is described in U.S. Pat. Nos. 3,869,429; 4,308,374; and 4,698,414.
By “polyolefin” is meant polyethylene or polypropylene. By polyethylene is meant a predominantly linear polyethylene material of preferably more than one million molecular weight that may contain minor amounts of chain branching or comonomers not exceeding 5 modifying units per 100 main chain carbon atoms, and that may also contain admixed therewith not more than about 50 weight percent of one or more polymeric additives such as alkene-1-polymers, in particular low density polyethylene, propylene, and the like, or low molecular weight additives such as anti-oxidants, lubricants, ultra-violet screening agents, colorants and the like which are commonly incorporated. Such is commonly known as extended chain polyethylene (ECPE). Similarly, polypropylene is a predominantly linear polypropylene material of preferably more than one million molecular weight. High molecular weight linear polyolefin fibers are commercially available. Preparation of polyolefin fibers is discussed in U.S. Pat. No. 4,457,985.
Polybenzoxazole and polybenzothiazole are preferably made up of mers of the following

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