STAB AND BULLET PROTECTION MATERIAL

Abstract: The present invention relates to a flexible and lightweight protection material that is both bullet resistant and that meets the PSDB standard for knife protection. The protection material includes: a) a metallic based structure which is itself flexible and which may have interlocked rings or a combination of rings and plates; b) an impact energy absorbing material, a secondary layer of stab-resistant material, or a combination thereof; and, optionally, c) a ballistic pack.

Description: TITLE STAB AND BULLET PROTECTION MATERIAL BACKGROUND Field of the Invention This invention relates to the field of stab and bullet protection material. Description of the Related Art Bullet resistant vests, such as those made using DuPont Kevlar® para-aramid fiber, are well known. However, more restrictive laws on the possession of handguns in places like Europe have led to the situation where knives are an important threat, and in some countries even the most important one. The first test standards for stab- resistant body armor were established by national organizations in the United Kingdom, Switzerland and Germany in the early 1990s. The United Kingdom Police Scientific Development Branch (PSDB) standard, for example, adopted in 1993, allows that for a threat of PSDB blades No. 1 and No. 5, shot with air cannon (90°) at an energy of 20 to 65 Joules, there should be a maximum blade penetration behind the armor of 5 mm if the energy is less than or equal to 42 Joules, and there should be a maximum blade penetration behind the armor of (1.2 x energy in joules - 45) mm if the energy is greater than 42 Joules. Most of the soft and flexible textile systems available today, at an areal density suitable for daily wear, are not often adequate to stop stabbing forces of greater than 30 Joules with either a German knife as specified in German Specification (Technische Richtlinie, Schutzwesten, 1994) or the PSDB knifes. To stop stabbing forces of this magnitude, hybrid systems combining a metallic or ceramic stab-resistant pack mixed with a textile backing are normally used. A common problem with such hybrid systems is that the front stab-resistant pack tends to be bulky, heavy and inflexible, especially when small metallic or ceramic plates are employed. To improve the flexibility of such hybrid systems, a chainmail system has been employed as the stab-resistant pack. EP 0 670 466 Al, for example, describes a ballistic and stab-resistant system where the stab resistance is imparted by embedding a chainmail system in a polymeric resin. The system, however, offers less than maximum stab resistance as anyone skilled in the art of chainmail systems would be aware that restricting the relative movement of rings in a chainmail system adversely affects its stab resistance. Furthermore, the resin used for imbedding the chainmail undesirably increases the areal density of the overall protection system. What is needed, therefore, is a flexible and lightweight protective material that is both bullet resistant and that offers the knife protection at relatively high stabbing energy levels such as those specified by the UK PSDB and Germany. SUMMARY OF THE INVENTION The present invention relates to a flexible and lightweight material with an enhanced stab protection at high stabbing energy levels, that is, greater than 30 joules; the stab protection material may optionally be combined with a ballistic pack to form an integral stab and bullet protection material. The stab protection material includes (a) a metallic based structure which is itself flexible and which may have interlocked rings or a combination of rings and plates and (b) an impact energy absorbing material, a secondary layer of stab-resistant material, or a combination thereof. Optionally, the stab protection material includes (c) a ballistic pack. BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a side view in elevation of the stab test device used in the Examples to test the stab resistance of the inventive protective material. DETAILED DESCRIPTION The present invention relates to a flexible and lightweight material with an enhanced stab protection at high stabbing energy levels, that is, levels greater than 30 joules. The stab protection material may optionally be combined with a ballistic pack to form an integral stab and bullet protection material. The stab protection material includes two components that form an integral protective material: (a) a metallic based structure which is itself flexible and able to block and stop sharp objects, and which may have interlocked rings or a combination of rings and plates,; and (b) an impact energy-absorbing material, a secondary layer of stab-resistant material, or a combination thereof, wherein the impact energy-absorbing material is placed normally but not exclusively next to component (a) and away from the striking face. Optionally, the stab protection material 4 includes (c) a ballistic pack, which is a ballistic resistant component, to form a stab and bullet protection material. The ballistic pack comprises multiple layers of woven or non-woven fabrics which are based on high-strength fibres such as para-aramid, ultra-high molecular weight polyethylene, ballistic nylon and the like. Component (a) is a metallic based structure which is itself flexible and which is itself able to block and stop sharp objects. Typically, this structure will have interlocked rings or a combination of rings and plates. The structure may be in the form of a steel or a titanium based chainmail. The chainmail should be light and flexible, yet stab-resistant. There are no other special requirements for the chainmail, but if the chainmail is made from metallic rings, it is preferred that the metallic rings have a diameter of from about 1.0 mm to about 20 mm. The diameter of wire used to fabricate the rings may range from 0.2 to 2.0 mm. Component (b) is an impact energy absorbing material, or a secondary layer of stab-resistant material, or a combination thereof. The impact energy-absorbing material may be a soft material that has a dimensional stability and in which the thickness thereof reduces dramatically on energy impact. Preferred materials include woven, knitted, or non-woven textiles such as needle- punched felt or non-textile materials such as rubber or elastomer sheets or foam. A combination of textile and non-textile materials may be used. Further, single or multiple layers of the material may be employed. The secondary layer of stab-resistant material may be a metallic based structure such as component (a) . If this material is chainmail there are no other special requirements for this layer. If the chainmail is made from welded rings, it is preferred that the welded rings have a diameter of about 1.0 mm to about 20 mm. The diameter of the wire used to fabricate the rings can range from 0.2 to 2.0 mm. Typically, to keep within the overall desired weight limits of the inventive protective material, the wire diameter and hence the overall areal density used in the second chainmail layer will be less than that of the first chainmail layer. The secondary layer of stab-resistant material may also be single or multiple layers of a flexible impregnated fabric based on high- strength fibres such as para-aramid, high strength polyethylene, nylon and the like. This is a preferred embodiment of the secondary layer of stab-resistant material. The flexible coated fabric layer comprises a plurality of fibres capable of resisting penetration and a support material, said fibres being at least partially embedded within the support material to restrict relative movement of the fibres therein. This flexible impregnated fabric may be further defined as a fabric which, when tested at an areal density of 9.1-9.2 kg/m 2 , stops a Metropolitan triangular knife at 25 joules of attacking energy, leaving no more than 16-20 mm of penetration of a Plastiline Roma backing material conditioned according to NIJ 010103 placed behind the fabric. Note that the areal density of the fabric that forms part of component (b) may vary, provided that the areal density of the stab protection material of the 6 invention is within the overall limits as set forth herein. Examples of such a flexible impregnated fabric include DuPont Kevlar® Comfort AS Style 288, which is a thermoplastic coated Kevlar® woven fabric. Component (b) may be a combination of the impact energy-absorbing material and one or both of the secondary stab-resistant materials. That is, component (b) may be a combination of the energy absorbing material and a metallic based structure; a combination of the energy absorbing material and single or multiple layers of a flexible impregnated fabric; or a combination of the energy absorbing material, a metallic based structure and single or multiple layers of a flexible impregnated fabric. The third component (c) , which is optional, is a ballistic pack. "Ballistic pack" is defined as one or more layers of a stab-resistant and bullet-resistant fabric comprising a network of high strength fibers. These fibers may be coated or uncoated. The fibers in such a fabric are typically of the type that have a high tensile strength and a high stretch resistance. The fibers may comprise high strength polyethylene fibers, aramid fibers, ballistic nylon or the like. In the preferred embodiment the fibers comprise aramid fibers, particularly fibers of poly (p-phenylene terephthalamide) . An example of aramid fibers that may be used are Kevlar® fibers available from E. I. du Pont de Nemours and Company. The order in which components (a) and (b) or (a) , (b) and (c) are arranged is not critical. Further, component (b) may be placed on both sides of component (a) , and component (c) may be placed on both sides of component (a) . The stab protection material, which includes components (a) and (b) , has an areal density of not greater than 10 kg/m 2 , preferably not greater than 6.5 kg/m 2 , and most preferably not greater than 4.6 kg/m 2 . The stab and bullet protection material, which includes components (a) , (b) and (c) , has an areal density of not greater than 14 kg/m 2 , preferably not greater than 12 kg/m 2 , and most preferably not greater than 10.5 kg/m 2 . These ranges are preferred in order to meet the PSDBHG1/KR42 (Hand Gun 1/Knife-Resistance -42 joules) standard. The current invention has the following characteristics: (i) The presence of component (b) , an energy- absorbing layer, behind the chainmail layer significantly increases the stab resistance of the stab protection material. It is well known in the art of stab-protection that the stab resistance of a chainmail system depends on the ability of the system to absorb energy. (ii) When high stabbing energy, that is, stabbing energy greater than 35 Joules, is applied to the stab protection material, a secondary layer of stab-resistant material such as a chainmail layer or a multiple layers of a coated Kevlar® fabric prevents the occurrence of "catastrophic failure", a term used to describe the residual energy of a knife that penetrates a protection systems completely. (iii) When coated Kevlar® fabrics are used as the secondary layer of stab-resistant material, as those fabrics are bullet-resistant themselves, the areal density of the stab protection material is reduced because the ballistic pack σ (c) is either not necessary since the stab- resistant material alone gives adequate protection against bullets, or the ballistic pack may be of a lower areal density than would otherwise be required. EXAMPLES Unless otherwise noted, the stab-tests in the following examples were conducted on a "Drop- weight" test device shown in Figure 1. Such machine is based on the vertical free fall of a sabot and dead weight 10 which holds a blade 11. The weight (m) of the projectile (sabot + blade + dead weight) and the height from which the projectile drops (drop height 12) defines the stab energy: E (Joule) = 9.8 (m/s 2 ) x m (kg) x h (m) Test pack 13 of protective materials were horizontally mounted on a plastiline block 14. The type of the plastiline was Plastilina Roma No.l conditioned so that the drop-test according to NIJ 0101.03 gave 25 +/- 3 mm indentation. After each drop, test pack 13 was removed from plastiline block 14 and the penetration depth of blade 11 was measured. This penetration depth was determined as being the length of blade 11 protruding from the rear surface of test pack 13. Examples 1-2 and Comparative Examples 3-4 In Examples 1 and 2, a flexible stab and bullet protection material was constructed of (a) chainmail of 3.2 kg/m 2 ; and (b) a secondary stab- resistant pack made of 26 layers of Kevlar® Comfort AS Style 288 of 6.3 kg/m 2 . The units "kg/m 2" or "g/m refer to the areal density of a material. The total areal density of the protective material in Examples 1 and 2 was 9.5 kg/m 2 . In Comparative Examples 3 and 4, a protection material was constructed of (a) as above; and (b) 32 layers of a uncoated Kevlar® HT fabric of 200 g/m 2 each for a total of 6.4 kg/m 2 . Both materials were tested with PSDB No .1 knife at 42 joules and gave depths of penetration as follows : Example Number Depth of Penetration (mm) 1 0 2 0 C*3 7 C4 9 ^denotes Comparative Example Example 5-6 and Comparative Example 7-8 In Examples 5 and 6, a flexible stab and bullet protection material was constructed of: (a) chainmail pack of 2.4 kg/m 2 under slight tension in both vertical and horizontal directions; (b) 3 layers of Kevlar® needle-punched felt of 185 g/m 2 each for a total of 0.555 kg/m 2 ; and (c) a ballistic pack made of 48 layers of uncoated Kevlar® fabric of 120 g/m 2 each, for a total of 5.76 kg/m 2 , designed for NIJ Level IIIA protection. The total areal density of this system was 8.715 kg/m 2 . In Comparative Examples 7 and 8, a protection material was constructed of (a) and (c) only. 10 A drop-test of 35 joules with PSDB No.l blade gave depths of penetration as follows: Example Number Depth of Penetration (mm) 5 5 6 0 C7 18 C8 15 Examples 9-13 A flexible stab and bullet protection material was constructed of (a) chainmail of 3.2 kg/m 2 ; (b) two layers of Kevlar® felt at 185 g/m 2 each for a total of 0.37 kg/m 2 , and chainmail at 3.2 kg/m 2 ; and (c) ballistic and trauma pack for HGl PSDB Protection level which comprised Kevlar® HT fabric style 363 and backface control material, said pack having an areal density of 5.4 kg/m 2 . The total areal density of the protection material was 12.2 kg/m 2 . The material was tested 5 times at varying energy levels with a PSBD No.l Knife mounted in an air cannon stab-resistant test device as specified in the PSDB standard. The results were as follows: Example No. Stabbing Depth of energy knife (joules) penetration (mm) 9 41 0 10 47 0 11 45 5 12 52 0 13 63 9 11 Examples 14-23 A flexible stab and bullet protection material was constructed (a) one layer of chainmail of 4.0 kg/m 2 ; (b) three layers of Kevlar® felt at 185 g/m 2 each for a total of 0.56 kg/m 2 , and (c) ballistic and trauma pack for HGl PSDB Protection level having an areal density of 5.9 kg/m 2 which comprised 20 layers of Kevlar® HT fabric (style 363) and a backface control material that included 4 layers of a laminated Kevlar® HT fabric (style 363) . The total areal density of the protection material was 10.5 kg/m 2 . The material was tested with a PSBD No.l Knife and a PSBD No. 5 knife as in the previous examples. The results were as follows: Example Knife Stabbing Depth of No. type energy knife (joules) penetrat ion (mm) 14 1 44 0 15 1 42 0 16 1 46 0 17 1 52 0 18 1 66 13 19 5 44 0 20 5 41 0 21 5 45 0 22 5 53 0 23 5 64 0 The examples show that the protection material of the invention shows an unexpected improvement to knife penetration compared to conventional protection materials. 12 EXAMPLES 24-35 The protection material of the previous Examples 14-23 was tested for PSDB Handgun 1 levels using 9mm and 0.357 magnum ammunition, The results were as follows: Example Ammunitio velocity Held/ trauma No. n type m/sec "1 penetrate mm d 24 9mm 370 held 23 25 9mm 363 held 16 26 9mm 370 held 17 27 9mm 354 held 12 28 9mm 356 held 14 29 9mm 356 held 13 30 0.357 392 held 19 31 0.357 395 held 12 32 0.357 390 held 15 33 0.357 387 held 16 34 0.357 393 held 11 35 0.357 392 held 15 These results show that the inventive protection material of the invention which included a ballistic pack stopped bullets from the PDSB Handgun 1 levels.

Claims: 13 CLAIMS 1. A flexible protection material comprising (a) a flexible metallic based structure and (b) an impact energy absorbing material, a secondary layer of stab-resistant material, or a combination thereof. 2. The flexible protection material of claim 1, further comprising (c) a ballistic pack having one or more layers of a stab-resistant and bullet resistant fabric which includes high strength fibers . 3. The flexible protection material of claim 1, wherein the flexible metallic based structure comprises interlocked metal rings or a combination of metal rings and plates 4. The flexible protection material of claim 1, wherein the stab-resistant material comprises a flexible metallic based structure which has interlocked metal rings or a combination of metal rings and plates. 5. The flexible protection material of claim 1, wherein the stab-resistant material comprises at least one flexible layer having a plurality of fibers capable of resisting penetration by a bullet or a knife, and a support material, at least part of said fibers being embedded with the support material to restrict relative movement of the fibers. 6. The protection material of claim 1, wherein the stab-resistant material comprises a combination of a flexible metallic based structure which has interlocked metal rings or a combination of metal rings and plates and at least one flexible layer comprising a plurality of fibers capable of resisting penetration by a bullet or a knife, and a support material, at least part of 14 said fibers being embedded with the support material to restrict relative movement of the fibers . 7. The protection material of claims 2, 5 or 6 , wherein the fibers comprise high strength polyethylene fibers, glass fibers, carbon fibers or aramid fibers . 8. The protection material of claim 2, 5 or 6, wherein the fibers comprise fibers of poly(p- phenylene terephthalamide) . 9. The protection material of claim 1, wherein the areal density of said material does not exceed 10 kg/m 2 . 10. A garment made at least partially from the protection material of claim 1 or 2.

Inventors: REN JIANRONG, VAN ZIJL NICOLAS A, REN, JIANRONG, VAN ZIJL, NICOLAS, A.
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1999
Main classification: F41H5
IPC codes: A41D13, A41D31, F41H1, F41H5