GB2322638A - Knife-resistant sheet - Google Patents

Abstract

A knife-resistant sheet, eg for a protective garment, comprises a cut-resistant self-supporting structure formed from one or more lengths of knitted wire, the wire having a diameter of at least 0.25mm. The sheet also comprises a deformation-resisting self-supporting structure formed from one or more lengths of knitted textile yarn, said structures both extending substantially throughout the sheet. The sheet may be formed by co-knitting two continuous lengths of wire and a continuous yarn on a circular knitting machine.

Description

KNIFE-RESISTANT SHEET This invention is concerned with a knife-resistant sheet. For example, a sheet according to the invention may be utilised as a knife-resistant layer in a garment, such as a protective vest, which may also comprise antiballistic protection. A sheet according to the invention may also be utilised as a layer of upholstered seating, eg in public transport, to resist knife attacks by vandals.

It is well known that one or more lengths of wire can be formed into a sheet, for example by knitting or weaving, and such sheets can be used in, for example seating, to provide a cut-resistant structure making slashing difficult. However, such a cut-resistant structure is found not to be very effective at resisting penetration of the sheet by stabbing. This is because, a knife can often penetrate by deforming the wire structure by pushing the lengths of wire apart, rather than by break the wires. Use of thicker or stiffer wire to reduce such deformation is not practical, in many cases, because of the difficulties of knitting or weaving such a wire and also because the sheet would have greatly reduced flexibility.

Penetration by a knife into seating, while undesirable, is not so serious as penetration of a protective garment where stabbing rather than slashing is the prime concern. Although penetration resistance can be increased by providing multiple layers, this decreases the flexibility of the garment, increases its weight, and increases its cost. Accordingly, many knife-resistant protective garments rely on metal platelets arranged in overlapping layers or in an interlocking structure, such garments being heavy, expensive to make, and often vulnerable to oblique stabbing threats.

It is an object of the present invention to provide a knife-resistant sheet in which the penetration-resistance of a cut-resistant wire structure is improved.

The invention provides a knife-resistant sheet comprising a cut-resistant self-supporting structure formed from one or more lengths of knitted wire, the wire having a diameter of at least 0.25mm, wherein the sheet also comprises a deformation-resisting self-supporting structure formed from one or more lengths of knitted textile yarn, said structures both extending substantially throughout the sheet.

It is known to reinforce fabric sheets by incorporating wires in the structure. The wire either cooperates with other materials in forming a single structure or the wire or the other material forms a structure in which the other material is supported. Thus, the wire and other material do not individually form selfsupporting structures.

In a sheet according to the invention, the deformation-resisting structure interferes with relative wire movement and hence reduces the degree to which a knife can push apart the lengths of wire in the cut-resistant structure, thereby enabling adequate penetration resistance to be achieved from a reduced number of sheets. This improvement is achieved even when the non-metallic material does not in itself constitute a significant obstacle to a knife. The interference to wire movement may be due to tying the wires together or due to reducing the available space for the wire to move into. Both components forming a self-supporting structure, ie both would form a sheet-in the absence of the other, enables stresses to be distributed over a large area. A sheet according to the invention is light, flexible, achieves good protection, and allows the passage of air which is important in a garment.

Said cut-resistant structure is, preferably, formed by knitted wire, eg circular knitting can be employed. For example, in order to provide increased cut-resistance without significantly increasing the difficulties of knitting, said cut-resistant structure may be formed by two or more lengths of wire which are co-knitted. Co-knitting involves carrying out a knitting operation on two pieces of elongated material simultaneously, ie the pieces are drawn together into the knitting machine and the pieces pass side-by-side around each loop within the knitted sheet.

The feed can be from separate bobbins in a parallel feed.

The knitting machine may be a circular knitting machine producing a tube which can be slit and opened out to provide a single layer or, alternatively, the tube may be squashed flat to provide a double layer. It is also possible for the knitting machine to be arranged to knit to shape, eg the shape of a section of a garment.

The wire may be made of any suitable metal, eg high carbon steel, but stainless steel is preferred because of its anti-corrosion properties. The wire may be a multistrand wire. It is preferred that the wire has a Vickers hardness of at least 450 Hv02 (determined on a microhardness tester) and a thickness not more than 0.32mm.

The deformation-resisting structure is, preferably, formed simultaneously with the cut-resistant structure, eg by co-knitting the wire and the yarn.

Suitable textile yarns, for use in the invention, may be selected from a wide range of natural and synthetic yarns. It is preferred, however, that non-abrasive material is used because this considerably reduces the abrasiveness of the sheet, making it more acceptable for contact with skin or clothing fabric. The "feel" of the sheet can be further improved if the yarn is texturised, ie has its fibres brushed to make them stand out. If the textile yarn is made of tough material, such as para-aramid fibre, the yarn can make a direct contribution to kniferesistance, since it resists breakage.

A sheet according to the invention may have an areal density of 1.4 to 1.9 kg/m2.

There now follows a detailed description of an example of a sheet which is illustrative of the invention.

The illustrative example is a knife-resistant sheet which comprises a cut-resistant self-supporting structure formed from two lengths of wire by knitting. The wire is 0.7% stainless steel 304, 0.32mm in diameter, hard drawn and with a strength of 139-142 tons per sq. in ( 45-46 MN/m2) tensile. The sheet also comprises a deformationresisting self-supporting structure formed from a length of textile yarn made from para-aramid fibre (sold under the tradename "Kevlar") of 1640 denier.

The sheet of the illustrative example was formed by co-knitting on a circular knitting machine. The machine was fed simultaneously with two continuous wires and one continuous strand of the yarn. The machine was set to produce knitting with loops spaced by approximately 4mm.

This produced a tube formed from the wire and the yarn, with each length of the wire in the sheet having a length of the yarn running beside it. Specifically, each loop of the knitted tube had three approximately parallel components two of wire and one of yarn. Thus, the cutresistant structure formed by the wire and the deformationresistant structure formed by the yarn were co-extensive in the sheet with the yarn extending in the spaces between said lengths of wire.

The knitted tube was flattened to form a component of a protective vest, the component consisting of two sheets overlying one another. Each layer of the component had an areal density of 1.772 kg/sq. m. The component was cut to the required shape, ie the shape of the front of the vest.

The cut edges were then covered with fabric to avoid the cut ends of the wire from being a hazard and the component was assembled into a vest. The vest also comprised facing layers of fabric and a conventional "ballistic pack" consisting of 21 layers of woven para-aramid fibre.

The completed vest was subjected to a standard stabbing test in which a standard knife was dropped on to the vest from 1.5 metres with a loading of 3 kg. The knife penetrated the vest by less than 5mm which is within acceptable prescribed limits.

For comparison purposes, a vest similar to the illustrative example was prepared exactly as described above except that the yarn was omitted from the knitted sheet. In this case, each layer of the component had an areal density of 1.433 kg/sq. m. The above-mentioned tests were repeated with the result the knife penetrated the vest by llmm (well above the test limit of 5mm recommended for a safe vest). This difference in performance cannot be explained as being the result of the additional strength provided by the yarn.

Claims (9)

1 A knife-resistant sheet comprising a cut-resistant self-supporting structure formed from one or more lengths of knitted wire, the wire having a diameter of at least 0.25mm, wherein the sheet also comprises a deformation-resisting self-supporting structure formed from one or more lengths of knitted textile yarn, said structures both extending substantially throughout the sheet.

2 A sheet according to claim 1, wherein said cut resistant structure is formed by two or more lengths of wire which are co-knitted.

3 A sheet according to either of claims 1 and 2, wherein the wire has a Vickers hardness of at least 450 Hv02.

4 A sheet according to any one of claims 1 to 3, wherein the wire is made of stainless steel.

5 A sheet according to any one of claims 1 to 4, wherein the sheet is formed from co-knitted wire and textile yarn.

6 A sheet according to any one of claims 1 to 5, wherein the yarn is texturised.

7 A sheet according to any one of claims 1 to 6, wherein the yarn is made from para-aramid fibre.

8 A sheet according to any one of claims 1 to 7, wherein the sheet has an areal density of 1.4 to 1.9 kg/m2.

9 A knife-resistant sheet substantially as hereinbefore described with reference to the illustrative example.