WO2010026387A2

WO2010026387A2 - Protective fabrics

Info

Publication number: WO2010026387A2
Application number: PCT/GB2009/002131
Authority: WO
Inventors: Subhash Chander Anand; Aidan Tracey; Subbiyan Rajendran; Karthick Kanchi Govarthanam
Original assignee: Future Textiles Limited
Priority date: 2008-09-06
Filing date: 2009-09-07
Publication date: 2010-03-11
Also published as: GB0816321D0; WO2010026387A3; GB2478208A; GB201105248D0; GB2478208B

Abstract

A protective fabric has a two layer flat-knit structure with opposite facing layers. One facing layer is made from a first high performance yarn, such as aramid and the second facing layer comprises a second high performance yarn, such as ultra-high molecular weight polyethylene.

Description

PROTECTIVE FABRICS

This invention relates to protective fabrics for the manufacture of personal garments to provide cut and slash protection against knives and other sharp instruments. In England, where criminal use of hand guns is not prevalent, knifes are the most commonly used weapons in violent incidents. This poses a threat to officers working in the community, especially youth and community workers and officers in protective service occupations. Security and protective services are the occupations with the highest risk of violence while at work. Police are at most risk followed by social workers, probation officers, publicans, bar staff and security guards.

A review of real life wounding patterns reveals that the majority of wounds caused by knives are slash type and less than a quarter of the fatal wounds caused by stabs are in the chest region. The distribution of the wounds suggests that in real life attacks, most knife assaults are slash attacks at the arms, neck, shoulder and thigh regions.

Even though protective garments are available to protect against such slashes and stabs, they are typically made from materials that are very heavy and stiff, have limited breathability and comfort, causing heat stress and discomfort, especially if worn for long periods. These garments are also expensive for the general public to purchase for personal security and protection.

It is also known to make protective garments from textile fabrics which are woven or knitted from strong yarns, such as aramid fibres or ultra-high molecular weight polyethylene fibres. Aramid fibres, such as KEVLAR and NOMEX (registered trade marks), are heat-resistant, strong synthetic fibres which have aromatic polyamide chain molecules which are aligned along the fibre axis with bonds between adjacent chains. Ultra-high molecular weight polyethylene (UHMWPE) fibres, such as SPECTRA and DYNEEMA (registered trade marks), are also strong but have much longer molecules than aramid fibres, the physical properties being derived from chain length and integrity rather than chain-to-chain bonding. Garments made solely from one of these materials can be light flexible and breathable but may not give adequate protection in all circumstances. This may be due to deterioration or change in properties over time, or due to inherent deficiencies with regard to certain kinds of threats. It is also known to use composite yarns made from two or more materials. For example, WO 2007/640905 describes the use of a yarn made from ultra-high molecular weight polyethylene fibres combined with other fibres or filaments such as metal wire, glass filaments, or polyester or nylon. However such composite yarns can be difficult or expensive to manufacture and may not be wholly satisfactory in the end product protective garment, with regard to efficacy and comfort.

An object of the present invention is to provide a protective fabric which can be conveniently and inexpensively manufactured and which can be used to make a personal garment which has good, sustainable cut and slash resistance and which is comfortable to wear. According to the invention therefore there is provided a protective fabric having a two layer flat-knit structure with opposite facing layers thereto one high performance yarn being used for one facing layer, and a different high performance yarn being used for the other facing layer.

With this arrangement, the two high-performance yarns can give a combination of properties ensuring sustainable good cut and slash resistance while maintaining flexibility, comfort and breathability in a wide range of circumstances. In particular the respective yarn layers can have complementary properties whereby good properties can be reinforced and deficiencies compensated. In so far as the manufacture of the fabric involves conventional knitting techniques, the fabric can be made conveniently and inexpensively using conventional knitting apparatus. Preferably the two different yarns, while being complementary, preferably have generally similar properties particularly with regard to strength and/or surface comfort. The two yarns may consist of or largely comprise high molecular weight polyolefm particularly ultra high molecular weight polyethylene yarns, and aramid, respectively. Other yarns may also be used if desired. These may consist of or largely comprise polybenzoxazole, for example.

Generally speaking, aramid fibres would be used for one facing layer of the fabric. Aramid yarns, such as KEVLAR (registered trade mark) are generally available as either continuous filament yarn or as spun yarn. Spun yarns are preferred for cut and slash resistance and also for comfort. The yarns may comprise minor amounts of other materials, such as metal, glass and other polymeric materials so as to optimise performance, whilst simultaneously controlling the cost. Composite yarns may be used in which a core has layers of material around it. Composite yarns are less likely to be used for the aramid facing layer than the other facing layer. The other facing layer may comprise a core of say glass or metal, such as stainless steel, over which is wrapped one or more layers of ultra high molecular weight polyethylene or polybenzoxazole optionally in combination with wraps of other fibres. The other fibres may comprise any of the following either alone or in combination:- polyester, polyamide, or any other fibre including natural fibres, such as cotton and/or wool. Blends of fibres may be used. These additional fibres are mainly included to give comfort properties and to provide the ability to print or dye the fabric. The knit structure is preferably such as to define a two layer knitted fabric with the layers linked by cross-over or link stitches, such as tuck stitches, which may act to bind the layers together while leaving gaps or holes which facilitate breathability. The fabrics of the invention may be weft knitted structures in which one or both faces may exhibit straight wales (Jersey) or zig zag wales (racked). The fabric may be used to make complete garments or parts of garments, such as balaclavas, jumpers, scarves, vests, gloves, etc. By appropriate selection of materials and construction of the fabric it is possible to attain a soft, elastic fabric with good drapability which can incorporate appropriate barrier properties if required, and which can be breathable and comfortable even when worn for long periods at a time. Garments can be made for use by the police, armed forces, children and the general public to give effective cut and slash protection. Examples

Various composite yarns were tested and analysed, which consisted of a) a composite layered structure comprising Spectra (ultra-high molecular weight polyethylene fibres), glass and polyamides; b) Stainless steel core with wraps of Dyneema (ultra-high molecular weight polyethylene fibres) and polyester; and c) Kevlar (aramid fibre). The results of some properties of the yarns studied are given in Table 1. Table 1: Yarn Test Results

The two yams that were used to make a knitted fabric (described hereinafter) were Spectra WF 528 and Kevlar two ply yarn with zero twist.

Spectra WF 528 showed the highest tenacity amongst all six yarns and also had the lowest linear density. The breaking extension of the Spectra WF 528 was also the lowest with a value of 3.02%. It also showed the second highest Initial Modulus. The maximum force required to break the yarn was only 5633 cN. The yarn that required the highest force was Spectra WF 408 at 15182.59 cN, but it also had the

10 highest linear density (268.77 Tex) which reduced its tenacity to 56 cNTex^"1.

The Kevlar yarns were tested with single yarn and as a 2 ply yarn with '0' Twist. The results between the single ply and two ply are fairly similar.

The Spectra WF528 and Kevlar two ply yarns were knitted to form a fabric with Spectra on one facing layer and Kevlar on the opposite facing layer as shown in

15 accompanying Figure 1.

Home Office Scientific Development Branch (HOSDB) Slash Resistance Standard for UK Police (2006), Publication No. 48/05 was used to characterise the fabrics produced as described above. The HOSDB Slash resistant standard requires the fabric to be tested in 3 directions, Walewise (0°), Coursewise (90°) and 30° to the vertical axis and to withstand a failure force of 60 N in each direction and an average of 80 N for all 3 directions. The results are shown in Table 2.

Table 2. HOSDB Slash Resistant test results for Kevlar / Spectra WF 528

The results of the slash tests shown in Table 2 reveal that minimum failure force of 71.64 N and the average failure force of 158.38 N were achieved. The average force of 158.38 N was almost twice the minimum average required to pass the test. A second set of walewise and coursewise slash tests were performed in order to substantiate the results obtained. Table 3. HOSDB Slash Resistant Test Results With WF 528 as Face

The above fabric also passed the slash resistance standard with the WF 528 as the test face. It passed with a force of 65.81 N in walewise direction, 122.17 N in coursewise direction and 61.61 N in diagonal direction. The high resistance of 122.17 N to slash in the coursewise direction enabled the fabric to obtain the required average of 8O N.

The following data for the fabric establishes its comfort properties. Table 4. Thermo physiological (comfort) properties

* Typical range for protective clothing

The fabric has good breathability. Furthermore one of the faces of the fabric is flame retardant, as is below.

Ignition Test Results

Test Standard: BS EN 5438:1989

The test is- carried out by applying a small igniting flame with a horizontal flame length of 21mm to the face of the fabric for a minimum of 10 seconds. 30 seconds is generally used for protective fabrics and therefore the same has been used here. Table 5: Ignition Test Results.

The Kevlar side of the fabric can be used as a flame retardant (FR) layer. The face with the WF528 yarn can be used for other purposes. The face with WF 528 yarn can also be treated with Fire retardant chemicals thereby enabling the WF528 face to be used as the flame retardant (FR) layer. The treatment can either be carried out on the yarn or on polyamide/poly ester fibre used as an outer cover of the yarn.

The above fabric, which was made using the described yarns, has an advantageous two layer structure achieved with standard flat knitting equipment.

Different yarn types were used on the two layers of the two layer structure, although both materials exhibited similar performance.

The resulting fabric was able successfully to pass the most stringent test method stipulated for such products and applications, and is relatively light, soft, elastic and above all, when worn as a garment, can be comfortable to the wearer for long periods of use.

The fabric structure is a two layer material which is comfortable to the user and shows similar performance when tested on both layers as the body-facing face in spite of the fact that two different yarn types were used on the two layers. The results in Table 2 and 3 were obtained for a straight Jersey structure. Results obtained for a racked structure are set out below.

Table 6. HOSDB Slash Resistant Test Results for Racked Structure with Kevlar Face

Table 7. HOSDB Slash Resistant Test Results for Racked Structure with WF528 Face

Again the resulting fabric successfully passes the most stringent test and yet is relatively light, soft and comfortable for the wearer. It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiments which are described by way of example only.

Claims

1. A protective fabric having a two layer flat-knit structure with opposite facing layers thereto, one high performance yarn being used for one facing layer, and a different high performance yarn being used for the other facing layer.

2. A protective fabric as claimed in claim 1, wherein at least one of the yarns is a composite yarn.

3. A protective fabric as claimed in claim 1 or claim 2, wherein at least one of the high performance yarns comprises a glass or metal core.

4. A protective fabric as claimed in claim 1 or claim 2, wherein one of the facing layers comprises ultra high molecular weight polyethylene.

5. A protective fabric as claimed in claim 1 or claim 2, wherein one of the facing layers comprises polybenzoxazole.

6. A protective fabric as claimed in any of claims 1 to 5, wherein one of the facing layers comprises aramid.

7. A protective fabric as claimed in claim 6, wherein one of the facing layers consists of aramid.

8. A protective fabric as claimed in any preceding claim, wherein at least one of the faces of the fabric is flame retardant.

9. A protective fabric as claimed in any of claims 1 to 8, wherein the facing layers are linked by cross-over or link stitches.

10. A garment made from the protective fabric of any of claims 1 to 9.

11. A part of a garment made from the protective fabric of any of claims 1 to 9.