IE20110307U1 - Improvements in and relating to an energy dispersing liner for a helmet - Google Patents

Abstract

ABSTRACT A liner assembly for a helmet, the liner assembly including an energy dispersing liner comprising a sheet of thermoset polymer adapted to be received in a helmet outer shell. The liner assembly further comprises a layer of padding conneotable between the sheet of thermoset polymer and the helmet outer shell. The PU energy dispersing liner comprises deformable protrusions, preferably in the form of "pyramids" which act as a "suspension" system. These deformable pyramids are provided on the liner where an air gap will exist between the liner assembly and the shell of a helmet incorporating the liner assembly. The liner assembly may also include sweat absorbent and antibacterial material.

Description

The present invention relates to an improved energy dispersing liner for a helmet.

The energy associated with an impact on a sporting helmet, such as is used in the game of hurling, is absorbed by a combination of an outer protective shell and an inner energy dispersing liner. Comfort is achieved by adding a third, softer, layer of foam, which presses softly against the skull forming a cushion between it and the relatively firm energy dispersing liner.

Irish Short-Term Patent Publication No. 884713 (formerly application no. 8200710035) discloses a energy dispersing liner for a hurling helmet. The liner of S84713 is disclosed as being made of "a thermoelastic polymer”.

Throughout this specification, the terms, “thermop|astic" and “thermoset” will be used to describe polymer materials. These terms are well known in the field of polymer science and polymer technology. The following explanation is provided regarding these terms in the context of the present invention.

Explanation of the terms “Thermoplastic” and “Thermoset” Thermoplastics consist of linear or lightly branched chains that can slide past one another under the influence of temperature and pressure. These polymers flow at high temperatures, allowing them to be molded into useful products.

Thermosets consist of a network of interconnected chains whose positions are fixed relative to their neighbours. Such polymers do not flow when heated. Examples of thermosets include some polyurethanes and epoxy resins.

To understand the difference between thermoplastic and thermoset polymers, the molecular structure of such polymers must be understood. In thermoplastics, the individual polymer chains are chemically separate from one another while being physically entangled. The chains can slide over one another when heated and sheared, allowing the polymer to flow or become rubbery. This, in turn, allows the polymer to take on new V /5110307 shapes. The polymer chains in thermosets differ from thermoplastics because their chains are linked to one another through chemical crosslinks. The crosslinks create an extended network in which every chain is attached to every other chain. Therefore, the molecular weight of a full crosslinked thermoset article is equal to its weight in grams. prevent large scale Thermoset polymers cannot flow because the crosslinks reorganization of their polymer chains.

Thermoplastic polymers are thermally sensitive 3-phase materials. They exhibit a low temperature ‘glassy phase’ below their glass transition temperature (Tg). A thermoplastic below its Tg value tends to be hard and brittle in terms of its physical properties.

A thermoplastic heated to above its Tg value becomes progressively softer in nature and is said to have entered its ‘rubbery’ phase. The properties of a thermoplastic in its rubbery phase are ‘visco-elastic‘ in nature, exhibiting the properties of a viscous liquid and an elastic solid. The material will have elastic properties and a tendency to creep under load‘, which can result in a degree of permanent deformation.

Progressive heating of a thermoplastic in its rubbery phase will lead to melting of the polymer once the melting temperature (Tm) has been reached. The material then enters its liquid phase.

A soft thermoplastic elastomer (TPE) will typically exhibit a low Tg value, eg, - 60° C (typical example value) and a Tm of 180 to 200° C (typical example values). A helmet liner component manufactured from a TPE material will be approximately % into its rubbery phase at 20° C (room temperature), at this temperature it will exhibit elastomeric properties, however it will be susceptible to creep -induced deformation under loading conditions.

Thermoset polymers rely upon molecular covalent cross-links which link the chains together permanently upon polymerisation. A thermoset polymer still exhibits a glassy phase below its Tg value and a rubbery phase if heated above it. However, due to the cross-linked molecular structure these polymers are unable to melt and enter a liquid phase, they degrade if over— heated without melting. The covalent cross-links stop the molecules sliding past each other when loaded in the rubbery phase. In effect, the cross- lE11o3 3 links unravel and the bonds stretch when loaded imparting elastic properties without creep deformation. The structure returns to its original state once the load is removed.

The relevant national safety standard for hurling helmets is IS 355 and the main aim of the IS 355 standard is to achieve an energy dispersing helmet. The liner of S84713 aims to achieve this by creating a thermoplastic liner (specifically Tetrapolyethylene (TPE)) which creates an air gap between the helmet shell and the sheet of thermoplastic material comprising the liner. When a helmet incorporating the liner of 884713 is impacted, the liner stretches and absorbs the force of the impact. However, the chemical makeup (due to polymer chains) of thermoplastics polymers means that when impacted or stretched, the component can go into the materials‘ plastic region. In other words, the liner stretches to absorb the impact but after repeated impacts, the material has stretched to the extent that it is no longer in the “elastic region" but is instead in its "plastic region”. When this happens, the liner of 884713 does not return to its original shape. Therefore, with every impact, the liner of 884713 stretches further and in turn, reduces the size of the air gap.

When the liner has stretched excessively (after repeated impacts during testing), the applicant found that the air gap diminishes and then the liner of 884713 is no longer achieving its purpose of shock-absorption.

The present invention seeks to alleviate the disadvantages associated with the prior art.

Summary of Invention The present invention provides a liner assembly for a helmet including an energy dispersing liner comprising a sheet of thermoset polymer. Preferably, the sheet of thermoset polymer is adapted to be received in a helmet outer shell.

The energy dispersing liner is constructed from a polyurethane thermoset elastomer. The material molecular structure is cross-linked in nature. The covalent cross-links stop the molecular chains sliding past each other when the polymer is loaded during use. In effect, the coiled cross—links unravel and the bonds stretch when under load, imparting elastic properties without creep deformation.

The PU thermoset elastomer included in the helmet liner of the present invention will typically exhibit a rubbery use range from — 50° C up to approximately 150° C. At room IE1l03 4 temperature (20° C) a PU thermoset elastomer helmet liner will be tough and should exhibit a tensile elastic range up to_ approximately 600 to 700% without the risk of significant creep induced deformation.

In one embodiment of the present invention. the energy dispersing liner is formed from a PU thermoset elastomer which is non-cellular (i.e. non-foamed) and in an alternative, preferred embodiment, the energy dispersing liner is formed of a thermoset PU foam.

Advantageously, the liner assembly further comprises a layer of padding connectable between the sheet of thermoset polymer and the helmet outer shell, the layer of padding providing a comfort layer for the wearer of a helmet which includes the liner assembly.

The following are features of the liner assembly of the present invention: The liner preferably comprises a thermoset polymer which has p_ure elastomeric properties and achieves consistent performance.

The liner comprises of a thermoset elastomer, preferably, a non-cellular polyurethane thermoset elastomer (as distinct from a Thermo-Plastic Elastomer (TPE)).

In one embodiment, the polyurethane thermoset elastomer is in the form of an elastomer and in an alternative preferred, embodiment the PU thermoset is in the form of a cellular foam. In a further alternative, and most preferred embodiment, the PU thermoset elastomer is in the form of a self-skinning elastomer foam comprising a non-cellular “skin" layer and a cellular foam core layer.

Cross linked material reduces performance variability, most notably pure elastomeric properties with no plastic region in the material behavioral characteristics of the liner. in the embodiment in which the liner material is formed from the non—cellular (i.e. non- foamed) PU thermoset elastomer, the liner material has a hardness within the range of 50-100 Shore A hardness; more preferably in the range of 60-95 Shore A hardness; more preferably within the range 80-90 Shore A hardness; and most preferably having an optimum hardness of 85A Shore A hardness.

IE11 0330 In the alternative embodiment in which the liner material is formed from a PU foam, the density of the foam is preferably in the range of 650-850 kg/m3; and more preferably in the range 700-800 kg/m3. In the preferred embodiment, the foam energy liner component is made from a self skinning, crosslinked polyurethane (PU) micro-cellular elastomer which exhibits an average density range of 850 to 700 kg/m3. In this case the average density value is the result of combining an inner foam, of approximately density 600 kglm3, with an unfoamed skin, of approximate density 950 kg/m3.

Preferably, the liner is manufactured from polyurethane (PU) and most preferably from Methylene diphenyl diisocyanate (MDI) prepolymer but can also be formed from any one or more of the following in hot or cold processing; TDI based prepolymers and low-free isocyanate prepolymers based on MDI, TDI, PPDI and HDl. .

In the most preferred embodiment, the foam energy liner component is made from a self skinning, cross-linked polyurethane (PU) micro-cellular elastomer. The material is polymerized from the reaction of the following pre-polymer components: (i) A Polyol resin which exhibits a viscosity of 950 m Pa.s and a density of 1.03 ‘ g/cc at 20°C. (ii) A di-phenylmethane di—isocyanate (MDI) which exhibits a viscosity of 750 m Pa.s and a density of 1.21 g/cc at 20°C.

The resultant polymerized micro-cellular foam structure typically features an inner foam density range from 450 Kgm3 to an outer skin density of 950 Kgm3.

The PU energy dispersing liner ideally includes at least one and preferably, a plurality of deformable projections (most preferably in the form of ‘pyramids’) which act as a suspension system. Advantageously, these deformable projections are iocated where the air gap is present i.e. between the liner assembly and the helmet outer shell.

In the first embodiment, in which the liner is formed of PU Thermoset Elastomer elastomer which is cross linked and non-cellular (i.e. non-foamed) in nature, is unable to absorb energy in compression, since it is virtually incompressible in nature being a solid elastic material containing very little free volume. in this embodiment, the energy dispersing “"0307 liner relies on tension of the liner material to disperse the energy resulting from an impact to a helmet in which the liner assembly is inserted.

Thermoset polyurethane elastomer (non-cellular) embodiment. A true elastomeric material. When extended under load the coiled molecular chain cross-links unravel and its covalent bonds stretch. The chains are unable to slip past each other, once the applied load is removed the polymer returns to its original shape/form.

In the second embodiment in which the liner is formed of a thermoset PU flexible foam, the liner is able to absorb a degree of energy in compression. This is achieved by deformation/collapse of the rubbery cell walls under load. The amount of energy absorbed will depend upon the foam density and the mechanical properties of the material. On impact force to the helmet, the energy from the impact is absorbed by stretching and deforming the liner projections into the air gaps between the liner assembly and the helmet outer shell. in an embodiment of the liner in which the liner may not include the projections, the liner will absorb energy by tensioning I stretching against its anchor points to the outer helmet shell. In such an embodiment in which the liner does not include the projections,, the air gap between the liner and shell would allow space for this tensioning movement to occur.

In a third embodiment, the energy dispersing liner is in the form of a self-skinning elastomer foam comprising a non-cellular “skin” layer and a cellular foam core layer.

Thermoset polyurethane self-skinning elastomeric foam embodiment. The material comprises a non-cellular skin over a cellular foam inner core. With regard to a helmet liner energy absorbing use application, the material skin is capable of tensile force dissipation when stretched under load. Its cetlular foam core is capable of compressive force absorption when crushed. Being cross-linked, the material exhibits good elastomeric recovery properties without creep induced deformation within its elastic range.

Another advantage of the projections is that they also aid the assembly worker to locate the liner assembly within the helmet shell so as to achieve a consistent air gap during manufacture of a helmet including the liner assembly of the present invention. ideally, both the energy dispersing liner and the comfort layer include a sweat absorbent and antibacterial material.

E1io3o7 In one embodiment of the manufacturing process, the energy dispersing liner and comfort layer are not combined in the same moulding process. The energy dispersing liner footprint is smaller than the comfort liner footprint. The energy dispersing liner could be stitched to the comfort liner to define it in the correct location within the larger comfort liner footprint. However, inythe preferred embodiment the connection between the energy dispersing liner and the comfort liner is made using a removeable connection means such as Velcro TM. Thus, in the preferred-embodiment, the energy dispersing liner is fastened to the helmet outer shell; ideally using an appropriate adhesive at predetermined specific locations on the helmet outer shell.

In one embodiment, the entire liner assembly is washable and removable from the heimet.

The liner assembly comprises a means of mechanical fastening such as a hook and loop system of which VELCRO TM is typical. In one embodiment, the hook or loop component can be stitched to the liner at a location corresponding to the location of the other of the hook or loop component which is adhered to the inside of the helmet shell. The helmet shell includes location markers so as to help assembly workers locate the hook or loop component in the correct location on the helmet shell. .

However, in the preferred embodiment, it is only the comfort layer which is removeable for washing purposes; the comfort layer being removeably connectable to the outer shell using Velcro TM and the energy dispersing liner being fixedly connected to the outer shell using adhesive; at a different location of connection to the outer shell from the comfort foam connection locations. Marker indications on the inner wall of the outer shell indicate to assembly operators, the correct locations to apply adhesive to ensure the appropriate air gap is achieved.

The energy dispersing thermoset liner included in the liner assembly of the present invention has the advantage that it provides consistent safety performance. A PU Thermoset Elastomer does have a plastic region within the confines ofthe cross-links, the bonds are stretched and the chains / cross-links do unravel under load then return to their original position once the load is removed. Thus, in the energy dispersing liner of the present invention, the cross—links in the PU thermoset elastomer prevent the chains slipping past each other, unlike a thermoplastic elastomer in which creep induced deformation can occur as chains slip. Therefore, the thermoset polymers of which the energy dispersing liner is comprised, will always return to its original shape after impact. lE11o3 8 In other words, the air gap is always maintained between the helmet shell and liner assembly of the present invention. To note, failure will occur if the load is beyond the materials yield point. However, in testing, it was found that the load is nowhere close to this level of impact as to be even near to the yield point of the material. The thermoset liner of the present invention produces a helmet with consistently high safety performance.

The testing procedures set out in IS 355 have been carried out on the liner of the present invention and the liner has passed all the tests.

Preferably, there is a layer of padding connectable between the inner surface of the thermoset polymer liner and the helmet outer shell using suitable connecting means. This layer of padding provides a comfort layer for the user wearing the helmet.

The connecting means for connecting the layer of padding to the inner surface of the thermoset polymer liner may comprise any suitable means such as by adhering.

Alternatively, connection may be made by way of pins, studs or any such like as meet the appropriate safety standards.

In a third aspect of the present invention, the energy dispersing liner is formed of a thermoset polyurethane (PU) self-skinning elastomeric foam. This material comprises a non"-cellular “skin” layer over a cellular foam core layer. With regard to a helmet liner energy absorbing use application, the material skin is capable of tensile force dissipation of energy when stretched under load. its cellular inner foam core is capable of compressive force absorption when crushed. Being cross—linked, the material exhibits good elastomeric recovery properties without creep induced deformation within its elastic range.

With regard to the helmet liner energy absorbing mechanics, the use of a micro—cellular self skinning thermoset PU elastomeric foam puts this materiat in between a conventional flexible foam (with no skin and a much lower density) and a solid thermoset PU eiastomer.

Such a material will be able to absorb a degree of impact energy through compression as well as through tensioning. lts foam density will be lower at its wall section centre (eg, approx 65OKG/M3) and higher below its skin (eg, approx 800KG/M3), its skin could be soiid polymer with a density range up to that of a solid PU elastomer — approximately in IE110307 the region of 850 - QOOKG/M3. The densities obtained will also be subject to the mix ratio's used and processing conditions (e.g. degree of humidity).

The material is a micro-celiular self-skinning thermoset PU elastomeric foam, applying accurate density values to this material will be difficult. An average density value be applied to this material, a skin surface hardness value and tensile/elastic rangevalues.

These values should be obtained from the actual component — not from the material data sheets in this instance. The skin on this material will have an influence on mechanical properties in particular. Some design features of the liner will include areas of increased skin density compared to others which may exhibit lower foam densities.

A further embodiment of the liner formed of a micro-cellular self skinning thermoset PU elastomeric foam if the liner wall section is increased, thus, a softer micro cellular foam structure results in the thicker wall section. By tapering the wall down to the edges, the foam does not form in the thinner sections and the polymer is much stronger in tension.

Thus, the soft, energy absorbing thick wall features can be incorporated along side thinner (un-foamed) tension load bearing sections attached to the helmet outer shell - in the same component — and there is then no need for a separate comfort liner. Being self skinning, the structure does not absorb moisture and does not small.

The concept is with no liner but with a shell that acts in tension as it currently does but in cross section, the shell has air pockets or alternative. The skin of the shett would act in tension and the foamed inside would compress under load.

The present invention will now be described with reference to the following Examples.

Example 1 Energy dispensing liner comprising PU thermoset elastomer Material chemistry: One suitable material is the Vibrathane TM 8000Nibracure 8155 PU The polyol backbone comprises a polyester and the M system available from Chemtura. hardness of the resulting material is 55A-95A. The preferred system is Vibrathane T 8000/ Vibracure 7559 which is also based on a polyol backbone comprising polyester and also has hardness of 55A-95A.

IE11-03 4,4 Methylene di-isocyanate + Polyester Polyol + 1,4 Butane Diol Prepolymer Section + Chain Extender Section + Cross Link Section of the PU system.

The ratios of polyester polyol: 1,4 will influence the final hardness of the liner sheet material. The iiner is preferably at 85 Shore ‘A’ hardness.

Alternatived polyurethane (PU) thermoset polymers which can be used to form the thermoset liner of the present invention include: o Toluene dl-isocyanate prepolymers having a polyester or polyether polyol content reacted with amine curatives, - 4,4 Methylene dl-isocyanate prepolymers having a polyester or polyether polyol content reacted with amine curatives or diol curatives Thus, the liner assembly of the present invention comprises thermoset -PU sheet materials based upon prepolymer chemistries such as 4,4 Methylene di-isocyanate chain extended via polyester or poiyether polyols and cured/cross-linked with diols curatives or via the use of prepolymer chemistries such as Toluene dl-isocyanate ( based upon ratios of the 2,4 & 2,6 isomers of TDI ) having a polyether or polyester polyol content and subsequently cured I cross—linked with amine system or diol systems.

Example 2 gnerqv dispersing liner comprising PU thermoset foam As an alternative to the PU elastomer set out in Example 1, the energy dispersing liner prefereably is comprised of a PU form, most preferably this can be Flexocel MC 300w microcellular water blown foam system supplied by Baxenden Chemicals Ltd. Typical moulded densities of this material are 450-900 kgm‘3. Flexocel MC 330W is the resin component of a two part, MDI based system for producing microcellular polyurethane foam mouldings. This material is designed for use on both high and low-pressure dispensing equipment.

The resin component is a fully formulated liquid mixture.

The isocyanate component is a liquid diphenylmethane dl-isocyanate (MD!) composition of low polymeric content.

|E110307., Typical Properties Resin Component Viscosity @ 20°C 950 mPa s Typicai Specific Gravity @ 20°C 1.03 Isocyanate Component (Type 130) Viscosity @ 20°c 750 mPa s Typicai Specific Gravity @ 20°c 1.21 Mix Ratio 63% Resin I 37% lsocyanate by weight Typical reaction and density (at above ratio) Cream time 30 sec Laboratory cup mix Rise time 125 sec (electric drill stirrer) Free rise cup density 325 kgm'3 The liner assembly of the present invention will now be described, more particularly, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a top plan view of the assembly of the energy dispersing liner and comfort layer; Figure 2 is an isometric view of the energy dispersing liner and the comfort layer; Figure 3 is atop pian view of the comfort later shown without the energy dispersing liner; Figure 4 is an isometric view of the comfort layer shown in Figure 3; Figure 5 is a plan view of the energy dispersing iiner without the comfort layer; Figure 6 is an isometric View of the energy dispersing liner of Figure 5; and |E1103 12 Figure 7 is a side view of a helmet including the energy dispersing liner and the comfort layer; and Figure 8 is a graph in which the liner of thermoset material of the present invention is indicated with the wording “new material" and prior art Sample 1 TPE and prior art Sample TPE are also identified in the graph.

The liner assembly of the present invention will now be discussed more particularly with reference to the drawings.

Referring initially to Figs. 1 and 2 of the drawings, the liner assembly of the present invention is indicated generally by reference numeral 1 and includes a liner 2 comprising a sheet of thermoset material and a layer of padding 3 which provides a comfort layer for a user wearing a helmet incorporating the liner assembly 1. In use, when the liner assembly 1 is inserted in a helmet outer shell (not shown in the drawings), the comfort layer of padding 3 is located adjacent the wearer's head and the liner sheet 2 of thermoset material is sandwiched between the comfort layer 3 and the helmet outer shell.

The energy dispersing liner 2 and comfort layer of padding 3 will now be described in turn.

The Energy Dispersing Liner The liner comprises a thermoset polymer which has pure elastomeric properties and achieves consistent performance. The non-foamed cross-linked PU thermoset elastomer liner material is unable to absorb impact energy in compression, it is virtually incompressible in nature being a high density cross-linked elastomeric material containing very little free volume within its molecular structure. ‘Free volume’ can be described as the amount of space within a polymers molecular entanglements, amorphous thermoplastics (including some TPEs) can contain larger amounts of free volume than semi—crystalline or thermoset polymers and are therefore more susceptible to creep induced molecular slippage under loading conditions as a result. The PU foam liner polymers used in the present invention are all cross-linked thermosets (foam, solid or self skinning). The polymers are essentially the same material, they just use different foam cell formats. The free volume applies to the polymer molecular structure — not the air in the foam cells. $1103 In the case of the cross-linked PU thermoset elastomer liner the impact energy is absorbed by stretching the material, internally the covalent cross-links unravel and the bonds stretch under load. The structure returns to its original ‘memory state’ once the load is removed. in one embodiment, the polyurethane thermoset is in the form of a non-cellular (i.e. non- foamed) elastomer and in an alternative preferred embodiment, the PU thermoset is in the form of a foam.

Cross linked material reduces performance variability, most notably pure elastomeric properties with no plastic region in the material behavioral characteristics of the liner.

In thelembodiment in which the liner material is formed from a PU thermoset elastomer, the liner material has a hardness within the range of 50-100 Shore A hardness; more preferably in the range of 60-95 Shore A hardness; more preferably within the range 80- 90 Shore A hardness; and most preferably having an optimum hardness of 85A Shore A hardness.

In the alternative embodiment in which the liner material is formed from a PU thermoset foam, the density of the foam is preferably in the range of 650-850 kg/ms; and more preferably in the range 700~800 kg/m3. A density of 650-850 kglms applies to the inner core foam and the density is up to and over 900 kg/m3 (preferably approximately 950 kg/m3) for the solid non-foamed skin.

Air gaps which allow for tensile stretching of the liner under load are created by two methods: (i) Anchorage of the liner ends to the helmet shell lift the liner away from the helmet walls when suspended over the skull. An impact load to the shell is transmitted in tension to the liner ends, thus absorbing energy as the non-cellular thermoset PU elastomer elastomeric liner component is tensioned over the skull and against the anchorage points. (ii) In areas where the liner is in direct contact with the helmet shell projections are located on the liner to generate an air gap. Over such features, an impact load is absorbed by E1103o7 deflection of the projection material into the surrounding air gap and by tensile transmission into the connecting liner component material wall. in the embodiment shown in the drawings, the PU energy dispersing liner 2 includes deformable protrusions. In this -embodiment, the protrusions 20 are in the form of pyramids 20 which act as a ‘suspension’ system. These deformable pyramids 20 are located along the liner where the air gap will be when the liner assembly 1 is iocated in a helmet. These protrusions 20 aid energy absorption (shock absorptionlfollowing an impact to the helmet and also aid the assembly worker locate the part within the helmet shell to achieve a consistent air gap during manufacture of a helmet including the liner assembly of the present invention. Both the energy dispersing (shock absorbing) liner and the comfort layer are clad within a sweat absorbent and antibacterial material.

During the manufacturing process, in one embodiment, the energy dispersing liner and comfort layer are not combined in the same moulding process. The energy dispersing liner footprint is smaller than the comfort liner footprint. The energy dispersing liner could be stitched to the comfort liner to define it in the correct location within the larger comfort liner footprint. However, in the preferred embodiment the connection between the energy dispersing liner and the comfort liner is made using removeable connection means such as Velcro TM. Thus, in the preferred embodiment, the energy dispersing liner is fastened to the helmet outer shell; ideally using an appropriate adhesive at predetermined specific locations on the helmet outer shell.

In one embodiment, the entire liner assembly 1 removable from the helmet and is washable. The liner assembly comprises a means of mechanical fastening such as in one embodiment VELCRO TM stitched to the liner 2. This corresponds to Velcro adhered to the inside of the helmet sheil. The helmet shell includes location markers to help assembly workers locate the Velcro in the correct place.

However, in the preferred embodiment, it is only the comfort layer which is removeable for washing purposes; the comfort layer being removeably connectable to the outer sheli using Velcro TM and the energy dispersing liner being fixedly connected to the outer shetl using adhesive; at a different location of connection to the outer shell from the comfort foam connection locations. Marker indications on the inner wall of the outer shell indicate E11o3o7 to assembly operators, the correct locations to apply adhesive to ensure the appropriate air gap is achieved.

The inclusion of a plurality of pyramidal—shaped protrusions 20 in the energy dispersing liner 2 has the main advantage of providing a suspension system since the protrusions 20 deform on impact and aid in shock—absorption on impact to the helmet. This is achieved in the following way: when the hard shell of the helmet is impacted, the shell flexes and this puts the protrusions 20 under compressive forces and puts the energy dispersing liner 2 under tension, resulting in stretching of the liner 2. Because the liner 2 and the integrally formed protrusions 20 has pure elastomeric properties, the liner material 2 recovers fully from the impact.

Comfort Layer of Padding (3) The comfort layer 3»is manufactured of polyurethane foam which is preferably a low density polyethylene foam. The foam may be Plastoazote TM LD 24 which is a closed cell, cross linked polyethylene foam manufactured by Zotefoam.

The PU foam included in the comfort layer of the present invention comprises silver material incorporated therein so as to provide anti-micobial and sweat absorption properties. in a most preferred embodiment, the comfort liner 3 includes silver in the form of Aerosilver TM which is available from Hyosung.

The Aerosilver TM material channels perspiration away from the wearer of the helmet incorporating the liner assembly 1.

Process for incorporating Aerosilver 7'“ Material into the Comfort Liner (3) Aerosilver TM is sweat absorbent, odour free and anti bacteria! whilst having the ability to channel perspiration away from the wearer. The main technology on the fabric is the Aero Silver i.e. construction and blending of the yarn fibres. With regard to the fabric construction, this is a standard towelling knit.

‘E11030? The application of the Aerosilver TM material to the PU comfort foam liner is achieved using lamination. The glue comprises EVA and is applied using the following optimum PFOCSSS parameters: Time 10-15 seconds 0 Pressure 2-4 Bar 0 Temperature Press temperature 125-130° Centigrade Method of Assembling the Energy Dispersing Liner with the Comfort Layer There are alternative methods of assembling the energy dispensing liner with the comfort layer and these methods are set out in the following Examples 3 and 4.

ExamQle3 1. Foam sheets of 1x1.5m in size are provided to form the comfort layer are laminated with Aerosilver material; 2. The footprint of the comfort layer is cut out from a sheet of PU foam using a laser machine; 3. In this example, the comfort layer and energy dispersing liner are fastened together; for example they are stitched together; 4. The sewable hook & loop system (Velcro TM) is stitched onto the energy dispersing liner 2, e.g. the hook is stitched onto the liner which corresponds to the loop in the helmet shell; Note: The location of stitching takes into account the folding of the liner assembly into the shape and curvature of the helmet shell . The loop side of the ‘hoop and loop’ system is glued into the helmet using a elastomer based gel tape; 6. The liner assembly is inserted and attached into the helmet with the hook and loop system correspondingly located so that the hooks and loops engage to securely hold the liner assembly in position in the helmet. important considerations are: o Ensuring that the hook and loop system are matched up properly. This ensures that the correct size of air gap is achieved. The location of the air gap is shown in Figure 7. This is aided with the conical features which not only absorb energy with their |E1‘lO3 compression/collapsing but also spaces the liner assembly out from the outer plastic shell of the helmet ensuring an adequate and constant air gap is achieved.

Many fastening methods can be used. In a preferred embodiment, the fastening means is Velcro, allowing the liner assembly to be removed and washed/replaced etc.

Example 4 Preferred method of manufacture The energy dispersing liner is moulded in a vented tool. To aid the moulding process by minimising complex geometry, a flat, square sheet is formed which features the pyramid protrusions. Using a laser machine, the desired footprint is cut from the flat sheet taking into account that the pyramid features must be located correctly. T To aid adhesion, the surface of the foam energy liner which tends to have a shiny surface created by the material meeting the smooth surface of the Al mould is removed by sand blasting or alternative.

To achieve various sizes of helmets using the same plastic mouldings, the shell is riveted together using common holes apart from_ the rear base of the helmet at each side. Included on each side are 6 holes which create a range of tighter or looser openings at the entry to the helmet. In addition to this, sizing is achieved by various thicknesses of foam comfort liners. In a small helmet, the thickness of internal comfort padding is much greater compared to an adult helmet which has a much thinner comfort liner.

The foam is supplied as sheets and the sheets are laminated with Aerosilver as the first process. From this, the large sheet is located in the laser machine and the desired footprint cut out.

VELCRO TM is sewn to the interior of the foam comfort liner which will correlate with adhered VELCRO “which is located within the shell In order to aid adhesion for both the energy liner and VELCRO “within the hetmet shell, again sand blasting is used to create a rougher surface.

With the shell and face guard assembled whilst featuring the correct rivet location for sizing, the energy liner is firstly adhered to the inside of the helmet whilst maintaining an air gap. The adhesive used is a hot met which has a very fast cure time. $1103 ‘I8 8. The adhesive VELCRO “is adhered to the inside of the helmet and the foam comfort liner is inserted. The adhered and sewn VELCRO T"‘wil| correlate and fasten the foam comfort liner is place. important considerations are: e Ensuring that the adhesive points on the helmet outer shell are matched up properly with the points on the energy dispersing liner at which the liner is to be adhered to the helmet outer shell. This ensures that the correct size of air gap is achieved. The location of the air gap is shown in Figure 7. This is aided with the conical features which not only absorb energy with their compression/collapsing but also spaces the liner assembly out from the outer plastic shell of the helmet ensuring an adequate and constant air gap is achieved.

Many fastening methods can be used. In a preferred embodiment, the fastening means is VELCRO W, allowing the liner assembly to be removed and washed/replaced etc.

Referring now the Figure 8 of the drawings; Figure 8 (load stress —vs- strain) compares the properties of a PU thermoset elastomer helmet liner material against an existing PU thermoplastic elastomer (TPE) liner material, the diagram graphically illustrates the difference in the mechanical behaviour of the two materials under tensile load. The TPE exhibits induced creep behaviour under load, resulting in permanent deformation once the load is removed, due to molecular chain slippage. Whereas, the cross-linked thermoset PU material exhibits high elastic strength without significant creep induced molecular deformation under normal helmet use conditions.

Figure 8 further iliustrates the effects of processing fiow orientation in the TPE liner (being injection moulded). The TPE liner suffers from ‘anisotropic’ orientation, graphically this is depicted in Diagram 1, it is evident that the TPE material is stronger in the direction of processing flow orientation and weaker across the flow direction. Whereas, the un- orientated cast cross-linked thermoset PU liner material exhibits even ‘isotropic’ properties when tested in different loading directions, Referring to the graph in Figure 8, the thermoset material of the present invention is indicated. The flat gradient indicates pure elastomeric properties until the point of yield |E1’l03 where the graph falls away. However, the liner of the present invention in the helmet will not reach this yield point in testing. in contrast, the prior art TPE samples, in accordance with prior art Patent No. 884713 have exponential curves illustrating that the prior art TPE liner is in the materials’ plastic region. Therefore, the prior art liner will not return to its original shape. The degree of stretch is determined by the level of polymer chain alignment in the sample. TPE sample 1 and TPE sample 2 were cut from two different parts of the prior art liner which explains the 2 different sets of results.

It will, of course, be understood that the invention is not limited to the specific details described herein which are given by way of example only and that various modifications and alterations are possible without departing from the scope of the invention.

MACLACHLAN & DONALDSON Applicants’ Agents Merrion Square Dublin 2

Claims (5)

CLAIMS:

1. A liner assembly for a helmet, the liner assembly including an energy dispersing liner comprising a sheet of thermoset polymer adapted to be received in a helmet outer shell; optionally wherein the liner assembly further comprises a layer of padding connectable between the sheet of thermoset polymer and the helmet outer shell; optionally wherein the energy dispersing liner has properties which resist creep induced deformation; optionally wherein the energy dispersing liner is formed of thermoset elastomer; optionally wherein the liner is manufactured from any one of the group comprising Methylene diphenyl diisocyanate (MDI) prepolymer, TDI based prepolymers and low-free isocyanate prepolymers based on MDI, TDI, PPDI and HDI; and optionally wherein the energy dispersing liner comprises material having a hardness within the range 60-95 Shore A hardness.

2. A liner assembly as claimed in claim '1 wherein the energy dispersing liner is made from a self skinning, cross-linked polyurethane (PU) micro-cellular elastomer; optionally wherein the foam energy liner is formed by polymerization from the‘ reaction of the following pre-polymer components: (i) A Poiyol resin which exhibits a viscosity of 950 m Pa.s and a density of 1.03 g/cc at 20°C. ‘ (ii) A di-phenylmethane di—isocyanate (MDi) which exhibits a viscosity of 750 m Pa.s and a density of 1.21 g/cc at 20°C; and optionally wherein the resultant polymerized micro-cellular foam structure typically features an inner foam density range from 450 Kgma to an outer skin density of 950 Kgm3.

3. A liner assembly as claimed in claim 1 or claim 2 wherein the energy dispersing liner comprises at least one deformable protrusion located on the energy dispersing liner along the location of an air gap between the liner and the helmet outer shell; optionally wherein the at ieast one protrusion comprises a plurality of protrusions provided along a centred portion of the liner; optionally wherein the protrusions are conical in configuration and preferably are pyramidal in configuration; optionally wherein at least one of the liner and comfort layer comprise a sweat absorbent and antibacterial material; optionally wherein the liner assembly is removably securable in the helmet; optionally wherein the liner assembly ‘10 |E1103 comprises a detachable means of mechanical fastening such as VELCRO TM; and preferably comprising an air gap between the outer shell and the liner.

4. A process for manufacturing a liner assembly of Claim 1 wherein the liner assembly is built up in layers and stitched appropriately around the assembly footprint and the smaller energy liner footprint is also stitched to define it in the correct location within the larger comfort liner footprint.

5. An energy dispersing liner substantially as herein described with reference to and as shown in the accompanying drawings; and a hurling helmet comprising an outer shell and an energy dispersing liner substantially as herein described with reference to and as shown in the accompanying drawings.