GB2496638A

GB2496638A - Impact resistant material

Info

Publication number: GB2496638A
Application number: GB1119835.5A
Authority: GB
Inventors: Richard Walker
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-11-17
Filing date: 2011-11-17
Publication date: 2013-05-22
Anticipated expiration: 2031-11-17
Also published as: GB201119835D0; GB2496638B

Abstract

An impact resistant material 10 comprises a composite material comprising granular beads 12 dispersed in a cured plastics gel matrix. The matrix is supported by a deformable substrate 14.

Description

AN IMPACT RESISTANT MATERIAL

Background

The present invention relates to an impact resistant material.

Prior Art

Protective clothing is known for example for protecting a motor cyclist from injury in the event of an accident. Kevlar® material has been used to resist such associated impacts but typically Keviar clothing or other protective arrangements comprising Kevlar are bulky and cumbersome.

The present invention seeks to provide an alternative to such known impact resistant materials.

Summary of the Invention

The present invention provides an impact resistant material comprising a composite material comprising granular beads dispersed in a cured plastics gel matrix and supported by a deformable substrate.

The invention also provides a method of forming an impact resistant material comprising dispersing granular beads in a plastics gel, curing the dispersion and supporting it by a deformable substrate.

The material may be incorporated into apparel worn by a person or affixed to an object to which impacts are to be resisted.

Other preferred and/or optional features of the invention are defined in the accompanying claims.

In order that the present invention may be well understood, an embodiment thereof, which is given by way of example only, will now be described with reference to the accompanying drawings, in which:

Brief Description of the Drawing

Figure 1 is a section taken through an impact resistant material.

Detailed Description of Preferred Embodiments

Referring to Figure 1, an impact resistant material 10 is shown which comprises a composite material comprising a layer 12 of granular beads dispersed in a cured plastics gel matrix and supported by a deformable substrate 14. The granular beads are generally resistant to deformation whereas the gel matrix is absorbent of deformation. Consequently, the material is impact resistant because the beads absorb the momentum of the impact and gel matrix dissipates the energy.

As described in more detail below with reference to the Example, the beads are preferably made of a ceramic material. Ceramic material is generally impact resistant but relatively non-compressive whereas the gel matrix is compliant and can absorb and disperse in two and preferably three dimensions the impact forces created within the layer. The granular beads may alternatively be made fiom other hard materials such as a metal or a metal alloy, for example steel ball bearings.

The granular beads may be shaped as required and need not be of regular configuration and at least in the Example detailed below may be produced by grinding material to a powder or by other techniques.

It is preferred that at least 95% of the granular beads have a particle size of less than 500 microns. Preferably substantially all of the particles have a size less than 500 micron, Still more preferably, the particle size of the granular beads is in the range of 90 to 150 microns. It is found that particle size in this range is particularly suitable for absorbing impact forces.

The beads, whether ceramic or made from another hard material, are dispersed in the plastics gel in a ratio of at least 2 per cubic centimetre. In the example provided below of A1203 having a density of approximately 4 g/cm3, the beads are dispersed by weight of about 2 to 3 g/cm3 and preferably around 2.16 g/cni3.

A ceramic material is suitable for the present arrangement because ceramics have a hardness of at least 1000 kg/mm2 and in the case of Al203 it has a hardness of 1175 kg/mm2.

The plastics gel matrix comprises polyurethane gel. Polyurethane gel material is used in many applications for cushioning, vibration damping, and other effects. Polyurethane elastomer gels are made by mixing the two components; prepolymer and curative. The prepolymer is also called part-A in short. The curative is called part-B. Typically, polyurethane gel formulations are made in such way that the user or the parts manufacturer can control the softness of the gel product by changing the mixing ratio of part-A and pad-B components. Generally, increasing part-A ratio will give softer products.

The hardness of the plastics gel matrix is preferably in the range of 45 to 65 to Shore A scale which has been found to be suitable for maintaining stability of the matrix under impacts.

The deformable substrate 14 comprises a first fibrous layer 16 and a second fibrous layer 18 bonded by a cured plastics gel matrix. The fibrous layers are preferably non-woven because in non-woven fabric the fibres are randomly distributed and therefore provide better tensile strength in the plane of the substrate than a woven fabric Ideally randomly dispersed threads are bonded, for example with a thermoplastic material, and so they do not rely on a woven material for strength.

In the Example below, the first fibrous layer comprises a non-woven polyester fabric, such as Tyvek® by Dupont and the second fibrous layer comprises polyester and cotton mix fabric, such as a fabric spunlaced by the Sontara® process by Dupont. The plastics gel matrix bonds the first and second fibrous layers comprises a polyurethane gel. The hardness of the plastics gel matrix is in the range Df 45 to 65 to Shore A scale and preferably comprises a polyurethane gel elastorner. In addition to supporting the granular bead and gel matrix layer the deformable substrate provides Fabric layers are effective at resisting high velocity projectiles and therefore additional layers of woven material assist in retarding the impact of projectiles by absorbing a large proportion of the kinetic energy of the projectile.

Depending on specific requirements, more than one deformable substrate may be required to resist impacts. For example, a composite material may be employed as body armour, or with an impact resistive structure -for example in land based vehicles -so as to provide blast resistance.

The granular bead and plastics gel matrix is bonded to the deformable substrate by a cured plastics gel matrix 20 which preferably comprises a polyurethane gel elastomer. The plastics gel matrix when cured preferably has a hardness of 45 to 55 to Shore 00 scale.

The layer of material is elastically deformable and so absorbs a high proportion of energy The Shore hardness which gives the material its elasticity possesses another useful property -namely an adhesive surface that allows the material to adhere to another layer of (the same or a different) material, thereby enabling a multi-layered composite to be formed.

The impact resistant material may be of any suitable thickness dependent on requirements but one of the advantages of some embodiments of the invention is that it may relatively thin. In one example, the granular bead and cured plastics gel matrix layer 12 has a thickness of less than 50 mm and preferably less than 20 mm. The relatively thin composite material means that it is less bulky than known arrangements and can be worn without unduly restricting movement. The deformable substrate 14 may have a thickness of less than 10 mm and preferably less than 5 mm. The cured plastics gel 20 bonding the granular bead and cured plastics gel matrix to the deformable substrate may have thickness of less than 10 mm and preferably less than 5 mm.

The impact resistant material may be shaped to be worn by a person for protecting the person from impacts. The material may be arranged to protect for example a person's chest, shoulders, legs, or head. It may be incorporated in or as at least part of a jacket, vest, trousers, helmet or other such apparel to be worn by a person. It may also be located on a vehicle for example a motorbike for protecting impacts against the vehicle from objects travelling at relatively high speeds in relation to and impact upon the vehicle.

In its simplest form the impact resistant material may be manufactured as a sheet or a planar composite material. In this case, the sheet may be cut or fashioned to allow it to be worn by person for protection. In order to be worn it would then comprise selective cuts to allow the material to be fitted to at least a portion of a person for protection. In an alternative, the impact resistant material is moulded to form a shape which is suitable to be fitted to at least a portion of a person for protection.

In some circumstances or applications, it may be desirable to provide an arrangement which combines with the impact resistant material a further protective layer or layers which may be attached or fixed relative to the material by any suitable or known manner. Such an additional layer may include for example a layer of woven fibrous material comprising aramid fibres, such as Kevlar® by DuPont.

Example

One Example of the invention comprises three layers. The first layer is an outer surface of located distal from the person or thing which is to be protected from impacts. The first layer is a composite fabric material, bound with Polyurethane gel. The second layer is a middle layer comprising a softer Polyurethane gel material which absorbs energy. The third layer is the innermost layer, comprising the hardest material, aluminium oxide bound with a Polyurethane gel material. The Polyurethane gel materials used are susceptible to moisture, therefore all materials and components used must be thoroughly pre-dried before exposure to the PU gels.

Mould description

The current moulds used are wood frames, cut to size and laid onto laminated chipboard. Alternatively moulds can be aluminium, or other materials, but due to the low viscosity of the liquid gel, moulds require suitable sealing. An HDPE cling film may be used to line the moulds. The film seals the mould and allows easy handling of the finished material. A vacuum arrangement may be used to tension the cling film against the mould.

Deformable Substrate A single substrate is formed as described below. Further substrates may be manufactures by similar technique.

The substrate comprises two fabric materials. The first fibrous material is Tyvek fabric by Dupont, which is a non-woven Polyester material. The second material is a non-woven mix of cotton and Polyester fibres made by the Sontara process, also by Dupont. The first and second fabric layers are bonded with liquid Polyurethane gel. The Polyurethane gel is supplied as a two part chemical, part A and Part B, supplied by Alchemie Ltd of Kinerton Warwickshire, PU3664 and type PU7163 have been found to be suitable, although other gels may be acceptable.

The following tables are supplied by Alechemic Ltd. Pro duct Data Property Units PU 36$4A PU 3664B Mix Material -Polyol Isocyariate PolyUrethane Appearance -Clear liquid Clear liquid Clear liquid / _________________ ____________ _______________ _______________ cured material Viscosity mPa.s 150-250 20-40 30 -100 (25°C) ___________ ______________ ______________ ______________ Density gicriY 1.00-1.05 1.04-1.09 1.03-1.08 (25°C) ____________ _______________ _______________ _______________ Pot life Minutes --»= 120 {200g,_25°C) ___________ ______________ ______________ ______________ Gel Time Minutes --50-SO (200g,_45°C) ___________ ______________ ______________ ______________ Full Cure Hours --18-24 (200g,_25°C) ___________ ______________ ______________ ______________ Minimum mlii --3 Recommended Casting Thickness ___________ ______________ ______________ ______________ Cured Properties Properties Standard Units Result (Full Cure) Hardness BS 2782: Part 3: Shore A 45-55 Method 3658 Product Data Property Units PU 7163A PU 7163B Mix Material -Polyol Isocyanate Polyurethane Appearance -Clear liquid Clear liquid Clear liquid / ________________ ___________ ______________ ______________ cured material Viscosity rnPa.s 230-250 25-40 80-100 (_25°C) _________ ___________ ___________ ___________ Density g/cnY 1.01 -1.06 1.04-1.09 1.03 -1.08 (25°C) _____________ ________________ ________________ ________________ Pot Lite Minutes --25-30 (200g,_25°C) ___________ ______________ ______________ ______________ Gel Time Minutes --30-40 (200g,_25°C) _____________ ________________ ________________ ________________ Handling Time Hours --5 (200g,_25°C) ___________ ______________ ______________ ______________ Full Cure Hours --18-24 (200g. 25°C) ___________ ______________ ______________ ______________ Minimum mm --.3 Recommended Casting Thickness ___________ ______________ ______________ ______________ Cured Properties Properties Standard Units Result (Full Cure) Hardness SS 2782: Part 3: Shore A 55-65 Method 365B Gels are mixed in the ratio 1 part B to 1 part A, by weight. Part B is added first to a mixing bowl, then part A is added next. The two parts are then mixed thoroughly for 3 minutes until a clear non-streaky liquid is obtained. The mixed gel has a consistency similar to water, having a SO of around 0.98. The cured hardness of the materials is 45 -65 to Shore A scale. Liquid gel is poured into the mould, then a piece of Sontara sheet is placed in the mould and coated with liquid gel, a sheet of Tyvek material is placed on top of the Sontara and coated with liquid gel. The Tyvek layer will therefore be the outermost surface. The resulting composite is around 2.5mm thick. This layer or layers can then be cured in a curing cabinet at 50 -60 degrees C and can be handled within 5 hours. The material will cure also at room temperature, but will take 36 hours or so for sufficient cure to be easily handled.

Aluminium Oxide Layer The granular bead and plastics gel matrix layer is formed from aluminium oxide in the form of brown aluminium oxide powder, particle size 90 -150 micron, -40 mesh. The Polyurethane gel is the same material as described for the substrate and may be either PU3664 or PU7163. In this example the layer has been formed by one of two methods although other methods will be apparent to the skilled person.

The first method comprises measuring dry aluminium oxide powder by weight to give a depth or thickness, of 5mm. The material weighs 2.14 grams per cubic centimetre and so can be measured by weight to give 5mm depth.

Dependent on the requirements of the material and the impact forces anticipated the thickness of this layer may be selected as appropriate If high energy impacts are anticipated a thickness of 20mm may be required.

The dry powder is placed in a mould, and can be lightly compacted by vibration or pressing a plate onto the top surface. The liquid gel is then added to soak into the dry powder. The amount of liquid gel is calculated to ensure total saturation of the dry powder. The aluminium oxide material is only slightly porous, but the small particle size gives a high surface area, which must be thoroughly coated. When the pouring is complete, any surplus liquid can be drained or removed from the top surface.

In a second method, the dry aluminium oxide powder and the liquid gel are mixed together in a mixing bowl, and the resulting composite material is laid in a mould and smoothed over. Any surplus gel can be drained or removed from the surface.

During curing of the aluminium oxide layer, the mould is placed in a curing cabinet at 50 -60 degrees C and can be handled within 5 hours. The material cures at room temperature, but will take 36 hours or so for sufficient cure to be easily handled.

Intermediate Layer This layer comprises a softer Polyurethane gel relative to the hardness of the of the inner and outer layers. This material absorbs the energy imparted to the outer layer fibrous layer. The cured consistency of the middle layer is sticky, or readily adherent, and therefore suitable for bonding together the inner and outer layers.

In a first method, a mould is configured for a depth of 2 -3mm depth, although this depth can be varied according to requirements. Optionally the same mould as is used to form the aluminium oxide layer, so that the softer gel is poured over the cured aluminium oxide layer. When this layer has cured, one or more outer layer(s) of fabric are then laid over the cured composite sheet. In an alternative method of construction the three layers may be formed separately then bonded together as layers using a softer gel as a bonding agent or adhesive.

The gel is then cured and used to join the inner and outer layers.

In a further alternative method liquid gel of the bonding layer is added to the aluminium oxide layer, after the aluminium oxide layer is cured. The deformable substrate layer is then placed on the combined bonding layer and aluminium oxide layer.

The Polyurethane gel of the intermediate layer is supplied as a two part chemical, part A and Part B, by Alchemie of Kinerton Warwickshire. The material description is PU7161 and preferably has a cured hardness of 45 -55 to Shore 00 scale.

Product Data Property Units PU TiBiA PU 7161B Mix Material -Pol'ol Isocyanate Polyurethane Appearance -Clear liquid Clear liquid Clear liquid! ________________ ___________ ______________ ______________ cured material Viscosity(25°C) mpa.s 800-1000 100-110 400-600 Density (25°C) -g/cm 0.98-1.00 0.96-0.98 0.97 -0.99 Pot Life Hours --4 -6 (200g,_25°C) ___________ _____________ ______________ ______________ Gel Time Minutes --60 -90 (200g,_40°C) _________ _____________ ______________ ______________ Handling Time Hours! --18/25 °C (200g) Temperature _____________ ______________ 4 /40 °C Full Cure Days --7 (200g,_25°C) ___________ _____________ ______________ ______________ Minimum mm --2 Recommended Casting Thickness ___________ ______________ Cured Properties Properties Standard Units Result _____________________ _________________ _________________ (Full Cure) Hardness OS 2782: Part 3: Snore 00 50-70 4depends upon mixing Method 3658 ratio) ____________________ Temperature -°C -20 to +123 Tolerance _______________ The gel is mixed in the ratio 4 Parts B to 5 Parts A by weight. Part B material is added first to a mixing bowl, and then part A is added and mixed for three minutes. The resulting liquid is close to water viscosity, SC around 096.

The liquid gel can be cured in a curing cabinet at 50 -60 degrees C for 5 hours.

The material may be cured at room temperature, but will take around 36 hours to be easily handled.

Claims

<claim-text>Claims 1. An impact resistant material comprising a composite material comprising granular beads dispersed in a cured plastics gel matrix and supported by a deformable substrate.</claim-text> <claim-text>2. An impact resistant material as claimed in claim 1, wherein the beads are made of a ceramic material.</claim-text> <claim-text>3. An impact resistant material as claimed in claim 1 or 2, wherein at least 95% of the beads have a particle size of less than 500 microns.</claim-text> <claim-text>4. An impact resistant material as claimed in any of the preceding claims, wherein the ceramic beads are dispersed in the plastics gel in a ratio of at least
2.OOg/cm3, preferably at least 2.lOg/cm3, and most preferably at least 2.2OgIcm3.</claim-text> <claim-text>5. An impact resistant material as claimed in any preceding claim, wherein the beads are made of ceramic having a hardness of at least 1000 kg/mm2.</claim-text> <claim-text>6. An impact resistant material as claimed in any preceding claim, wherein the ceramic is aluminium oxide.</claim-text> <claim-text>7. An impact resistant material as claimed in any preceding claim, wherein the plastics gel matrix comprises polyurethane gel.</claim-text> <claim-text>8. An impact resistant material as claimed in any preceding claim, wherein the hardness of the plastics gel matrix is in the range of 45 to 65 to Shore A scale.</claim-text> <claim-text>9. An impact resistant material as claimed in any preceding claim, wherein the deformable substrate comprises first and second fibrous layers bonded by a cured plastics gel matrix.</claim-text> <claim-text>10. An impact resistant material as claimed in claim 9, wherein the first and second fibrous layers are non-woven, 11. An impact resistant material as claimed in claim 10, wherein the first fibrous layer comprises polyester fabric, such as Tyvek®.12. An impact resistant material as claimed in claim 10 or 11, wherein the second fibrous layer comprises polyester and cotton mix fabric, such as a fabric spuntaced by the Sontara® process.13. An impact resistant material as claimed in any of claims 9 to 12, wherein the plastics gel matrix which bonds the first and second fibrous layers comprises a polyurethane gel.14. An impact resistant material as claimed in claim 13, wherein the hardness of the plastics gel matrix is in the range of 45 to 65 to Shore A scale.15. An impact resistant material as claimed in any preceding claim, wherein the granular bead and plastics gel matrix is bonded to the deformable substrate by a cured plastics gel matrix.16. An impact resistant material as claimed in claim 15, wherein the cured plastics gel matrix comprises polyurethane gel.17. An impact resistant material as claimed in claim 15 or 16, wherein the plastics gel matrix when cured has a hardness 0145 to 55 to Shore 00 scale.18. An impact resistant material as claimed in any of the preceding claims, wherein the granular bead and cured plastics gel matrix has a thickness of less than 20 mm.19. An impact resistant material as claimed in any of the preceding claims, wherein the deformable substrate has a thickness of less than 5 mm.20. An impact resistant material as claimed in any of claims 15 to 19, wherein the cured plastics gel matrix bonding the granular bead and cured plastics gel matrix to the deformable substrate has a thickness of less than 5 mm.21. An impact resistant material as claimed in any preceding claim, which is shaped to be worn by a person for protecting the person from impacts.22. An impact resistant material as claimed in claim 21, which is generally flat and comprises selective cuts to allow the material to be fitted to at least a portion of a person for protection.23. An impact resistant material as claimed in claim 21, which is moulded to form a shape which is suitable to be fitted to at least a portion of an item, such as a vehicle, for protection.24. An impact resistant arrangement comprising an impact resistant material as claimed in any of the preceding claims to which a further layer of protective material is attached, such as a layer of woven fibrous material comprising aramid fibres.25. A method of forming an impact resistant material comprising dispersing granular beads in a plastics gel, curing the dispersion and supporting it by a deformable substrate.26. An impact resistant material as claimed in any of the preceding claims, which is adapted to be shaped on by a mould tool on a former and to take up the shape of the mould tool or former.</claim-text>