The present invention relates to energy absorbent material. In particular, the invention relates to relatively thin and lightweight energy absorbent material comprising two or more cones formed from an elastomeric material in which the cones have the property that, under impact, they collapse inwardly and thereby optimize the absorption of impact energy.

There are numerous situations in which at least some degree of impact protection for the human or animal body may be advantageous. These range from work situations, in which uncontrolled falling or fast moving objects may be encountered; various sporting situations, in which falls and/or contact with various forms of equipment or other participant may occur, and also include combat situations. Similarly, many situations exist in which vibration in mechanical parts can lead to damage of surrounding components and/or unacceptable noise levels.

Various materials have been developed for use in impact protection systems, and many conventional systems use, as the energy absorbent material, elastomeric foams or similar relatively soft, resiliently compressible materials. However, only limited protection is achieved thereby. Similarly, materials having particular three dimensional shapes have also been developed for use as impact protection systems, for example materials comprising combinations of regularly or irregularly spaced columns of energy absorbent material. In some systems, energy absorbent and/or elastic materials are employed in combination with one or more rigid members, the purpose of which is to spread the impact force over a greater area and therefore reduce its effect. However, such systems tend to be inflexible and uncomfortable if in contact with a human or animal body. More recently, impact protection materials based on the combination of foamed or unfoamed polymers and dilatant materials have been developed, see for example WO 03/055339 and WO 2005/000966.

The present invention is based on the finding that three dimensional structures formed from elastomeric materials having the property of collapsing inwardly upon impact are particularly useful as energy absorbent materials. In particular, cones formed from an elastomeric material and having particular combinations of inner angle, wall thickness and height have particularly effective energy absorbent properties. In addition, the selection of suitable inner angles, wall thicknesses and cone heights allows the production of energy absorbing materials having optimum geometry, i.e. being relatively thin and lightweight, whilst providing sufficient impact protection, in accordance with various national and international standards.

According to the present invention, there is provided an energy absorbent material comprising two or more frustoconical cones formed from an elastomeric material, the two or more cones having an inner angle of from 62° to 85°, a wall thickness of from 0.8 mm to 1.8 mm and a height of from 10 to 20 mm.

The cones of the energy absorbent materials of the present invention are hollow in order to facilitate the property of collapsing inwardly upon impact, i.e. when the cones receive an impact of sufficient force the walls of the cones fold inwards and, under sufficient impact, the cones may be substantially flattened. This is in contrast to solid shaped materials or hollow materials that do not have the property of collapsing inwardly, which are displaced sideways and/or unevenly collapsed under impact. The property of collapsing inwardly leads to particularly efficient absorption of impact energy, meaning that the materials of the present invention are particularly useful for absorbing impact energy, such as vibrational, mechanical, kinetic, heat and acoustic energy. Also, because the cones are formed from an elastomeric material they will return to essentially their original shape subsequent to collapse following impact. The "inner angle" of the cones of the energy absorbent materials of the present invention means the angle formed between the inner side of the wall of the cone and the horizontal plane of the cone (or the plane of the base of the cone when the cone is formed with a surrounding base material). A particularly suitable range of inner angles is from 65° to 80°, preferably from 65° to 75°, such as 70°.

The optimum inner wall angle for a given wall thickness (or vice versa) for any particular viscoelastic material may be determined by comparing the crushing resistance properties for various combinations of wall thicknesses and inner angles. The walls of the cones of the energy absorbent materials of the present invention may be of uniform thickness, or the thickness of the walls may vary. When the thickness of the walls varies, the "wall thickness" refers to the average thickness. A particular suitable range of wall thicknesses is from 0.80 mm to 1.5 mm, such as 1.0 mm to 1.2 mm.

The "height" of the cones of the energy absorbent materials of the present invention means the vertical height from the tip of the cone to the lowest point thereof, i.e. the lower surface of base on which the cone is formed. A particularly suitable range of heights is from 12 to 18 mm, such as 15 mm.

The cones of the energy absorbent materials of the present invention each have a circular base, and are generally symmetrical, in order to assist even inward collapse. The base diameter is measured from the inner edges of the walls of the cones, and a particularly suitable range of base diameters is from 12 to 20 mm, such as 14 to 18 mm.

The diameter of the upper surface of the cones of the energy absorbent materials of the present invention is measured between the inner surfaces of the walls at the peak of the cones, and a particularly suitable range of diameters is from 2 mm to 10 mm, such as from 4 mm to 8 mm, for example 6 mm.

In a preferred embodiment of the energy absorbent materials of the present invention, the ratio of the base diameter to the diameter of the upper surface of each of the cones is from 2.5 to 3.5, preferably from 2.7 to 3.3.

Energy absorbent materials according to the present invention may comprise any suitable number of cones, depending upon the dimensions of the individual cones and the use to which the energy absorbent material is to be put. In some cases, the energy absorbent materials may be produced in relatively large sheets and cut to the appropriate size and shape, depending upon the intended use.

The cones of the energy absorbent materials according to the present invention may be arranged in any suitable manner, for example in a single, one-dimensional line, but are preferably arranged in a two-dimensional array. The two-dimensional array of cones may be irregular, i.e. the distances between the individual cones may vary in an irregular manner or the cones may be arranged in a regular two-dimensional array. Any suitable regular two-dimensional array may be used, but in a preferred embodiment the energy absorbent materials of the present invention comprise parallel rows of cones, preferably at least four rows of cones, each row comprising at least four cones. In a particular arrangement of this embodiment the spaces between the rows of cones may be different to the spaces between the cones in each row, but preferably the spaces between the rows are the same as the spaces between the individual cones in each row. The rows of cones may be arranged out of register, for example the cones in a first and second row of a regular array may be arranged so that the cones of the second row are in line with the gaps between the cones in the first row; or, alternatively, individual rows of cones may be arranged in register so that the rows and columns of cones in the array are perpendicular.

The individual cones forming the energy absorbent materials according to the present invention cones may be arranged with any suitable spacing, for example depending upon the intended use of the energy absorbent material. However, preferably the cones are arranged so that the shortest distance between the centres of adjacent cones is from 14 mm to 30 mm, more preferably from 18 mm to 23 mm.

In energy absorbent materials according to the present invention, the cones may vary in size and shape, but preferably each of the cones have substantially the same inner angle, wall thickness and height. Similarly, preferably each of the cones has substantially the same base diameter.

In preferred embodiments of energy absorbent materials according to the present invention, the diameter of the upper surface of each cone is substantially the same. In preferred embodiments of energy absorbent materials according to the present invention, each of the cones are substantially identical.

In energy absorbent materials according to the present invention, the cones may be formed separately and combined together to form the energy absorbent material, but preferably the two or more cones are formed from a common base, preferably wherein the common base is flexible. In a particularly preferred embodiment, the common base and the two or more cones are formed from the same material.

The cones of the energy absorbent materials of the present invention may be formed from any elastomeric material, i.e. a polymer with viscoelasticity (i.e. having viscosity and/or elasticity), generally having low Young's modulus, such as 16 to 20 MPa, and high failure strain, such as greater than 300%, compared with other materials.

The elastomeric material may comprise a natural elastomer, such as latex rubber. Alternatively or additionally, the elastomeric material may comprise a synthetic elastomer. Particularly suitable synthetic elastomers include silicone rubber, polyurethanes or ethylene-propylene (EP) rubbers, such as EPDM, and thermoplastic elastomers, particularly thermoplastic elastomers comprising polyurethane or polyester.

A suitable elastomeric material comprises a composite material which comprises i) a first polymer-based material and ii) a second polymer-based material, different from i) , which exhibits dilatency in the absence of i), wherein the second polymer-based material ii) is entrapped in a matrix of the first polymer-based material i).

Preferably the composite material is unfoamed and is preparable by incorporating the second polymer-based material ii) with the first polymer-based material i) prior to formation of the matrix. Preferably, the matrix of the first polymer-based material i) is a solid matrix, i.e. a matrix material which retains its own boundaries without need of a container.

Preferably, the first polymer-based material i) and second polymer-based material ii) are an intimate admixture; for example, as attainable by blending i) and ii) together. By blending is meant herein the mixing together of polymer-based material i) and polymer- based material ii) in the semi-molten or molten state to form a composite material wherein the first polymer-based material i) and the second polymer-based material ii) are in intimate admixture. Thus, the second polymer-based material ii) is distributed within the body of a matrix formed from the first polymer-based material i) in the finished composite material.

The first polymer-based material i) may be one wherein the polymer comprising the first polymer-based material i) comprises ethylene-vinyl acetate (EVA), or an olefin polymer, for example polypropylene, or an ethylene polymer, such as high pressure polyethylene (LDPE), (LLDPE) or (HDPE).

Preferably, the polymer comprising the first polymer-based material i) comprises an elastomer. Suitable elastomers include any of the natural or synthetic elastomers discussed above.

Any polymer-based material, different from i), which exhibits dilatency and can be incorporated into the chosen elastic constituent(s) of first polymer-based material i) may be used as second polymer-based material ii). By a polymer-based material which exhibits dilatency is meant a material in which the dilatency is provided by one or more polymers alone, or by a combination of one or more polymers together with one or more other components, e.g. finally divided particulate material, viscus fluid, plasticizer, extender or mixtures thereof, and wherein the polymer is the principle component. In one preferred embodiment, the polymer comprising the second polymer-based material ii) is selected from silicone polymers exhibiting dilatant properties. The silicone-based polymer is preferably selected from borated siloxane polymers. For example, the dilatant may be selected from filled or unfilled polyborodimethylsiloxanes (PBDMSs) or any number of polymers where PBDMS is a constituent. The dilatency may be enhanced by the inclusion of other components, such as particulate fillers.

The dilatant may be combined with any other components in addition to the components providing the dilatency, e.g. fillers, plasticizers, colourants, lubricants and thinners. The fillers may be particulate (including microspheres or microballoons), or fibrous, or a mixture of particulate and fibrous. One class of particularly preferred dilatants based on PBDMS comprises the borated silicone-based materials that are marketed under the generic name of silicone bouncing putties and are produced by various manufacturers. These include those by Dow Corning under product catalogue number 3179 and Wacker GmbH under product numbers M48 and M29. Other companies such as Rhodia, GE Plastics, and ICI have also produced these materials, and other polymer-based dilatant materials having similar dilatency characteristics, e.g. a similar modulus at low rates of strain and a similar plot of modulus with respect to the applied strain rate.

The composite material for use in forming the two or more cones of the energy absorbent materials according to the present invention may be comminuted for ease of handling or for moulding purposes.

Particularly suitable elastomeric materials for forming the two or more cones of an energy absorbent material of the present invention are disclosed in WO 03/055339 and WO 2005/000966. Energy absorbent materials comprising two or more cones formed from an elastomeric material according to the present invention may be formed in any suitable manner, for example by moulding or by extrusion of suitable elastomeric materials.

The present invention also provides an impact protection system or vibration prevention system comprising an energy absorbent material according to the present invention.

The impact protection systems and vibration prevention systems according to the present invention are preferably impact energy protection systems or vibration energy absorption systems and are particularly useful for absorbing impact energy, such as vibrational, mechanical, kinetic, heat and acoustic energy.

The impact protection systems or vibration prevention systems according to the present invention may consist of an energy absorbent material according to the present invention shaped and/or adapted to provide protection again impact or to prevent the transmission of vibration between adjacent articles. Alternatively, the impact protection systems or vibration prevention system according to the present invention may comprise an energy absorbent material according to the present invention, together with additional materials which may also assist in impact protection or vibration prevention and/or assist in the utility of the impact protection system or vibration prevention system in other ways. For example, impact protection systems or vibration prevention systems according to the present invention may comprise additional impact protection or vibration prevention materials and/or materials to assist in locating and maintaining the impact protection system or vibration prevention system in a suitable position for use, for example attached to a particular body part or in contact with a vibrating mechanical component.

An impact protection system or vibration prevention system according to the present invention may be any suitable form, for example a helmet liner, a back support, an arm guard, a knee guard, a chest guard, a shoe, an impact plate or an engine support.

Preferably, impact protection systems or vibration prevention systems according to the present invention are configured so that each of the two or more cones are orientated substantially in the expected direction of impact, to provide maximum impact protection or vibration prevention.

In a particular embodiment, an impact protection system according to the present invention comprises an energy absorbent material according to the present invention encapsulated within an upper layer and a lower layer. Any number of cones may be enclosed within a single capsule, depending on the intended use of the impact protection system, but preferably at least four cones are enclosed within each capsule. In this embodiment, any suitable upper and lower layer may be used, but preferably the lower layer is substantially flat and the upper layer is shaped to encapsulate the two or more cones. Preferably, the energy absorbent material according to the present invention is disposed upon the substantially flat lower layer, and the upper layer is arranged in any suitable shape to encapsulate the two or morecones, for example the upper layer may be shaped as a hemisphere or may be further shaped to more closely follow the arrangement of the cones. In a particularly preferred embodiment, the lower layer comprises a padded material and/or the upper layer comprises a thermoplastic material. ln a preferred embodiment of an impact protection system comprising an energy absorbent material according to the present invention encapsulated within an upper layer and a lower layer, air is present in the capsule formed within the upper and lower layers to provide additional impact protection.

The present invention further provides an impact protection system comprising a plurality of capsules as defined herein. Each of the plurality of capsules may be the same, or the shapes of the capsules and/or the number of cones contained in the capsules may vary, depending on the intended use of the plurality of capsules, for example to vary the flexibility of the impact protection system or to allow the impact protection system to conform to the shape of the body to be protected, such as a helmet shell. In a particularly preferred embodiment, the plurality of capsules is formed from a continuous layer of energy absorbent material according to the present invention, a continuous upper layer and a continuous lower layer, and each capsule is preferably sealed from every other capsule.

The present invention further provides the use of an energy absorbent material according to the present invention as an impact protection system or as a vibration prevention system.

The present invention further provides the use of an energy absorbent material according to the present invention to reduce the effect of an impact on a body part. The present invention will now be described by way of example and with reference to the accompanying Figures, in which:

Figure 1 of the accompanying drawings is a schematic diagram depicting a side view of an energy absorbent material according to a first embodiment of the present invention;

Figure 2 of the accompanying drawings is a schematic diagram showing a plan view of an energy absorbent material according to the first embodiment of the present invention;

Figure 3 of the accompanying drawings is a schematic diagram showing an impact protection system according to an embodiment of the invention;

Figure 4 of the accompanying drawings is a schematic diagram showing the component parts of the impact protection system according to an embodiment of the invention shown in Figure 3; Figure 5 of the accompanying drawings is a graph comparing FEA data and test data;

Figure 6 of the accompanying drawings is an example graph of FEM data, showing the principle relevant features;

Figure 7 of the accompanying drawings is a visual representation of the collapse of cones under simulated impact;

Figure 8 of the accompanying drawings shows the collapse of cones during a physical test; and

Figures 9 to 21 of the accompanying drawings are acceleration versus time graphs for the materials of Examples 3 to 15 respectively. Example 1

An energy absorbent material according to a first embodiment of the invention is illustrated in Figure 1. The energy absorbent material 1 comprises a plurality of cones 3 formed from a common base 5. Each of the cones 3 have the same size and dimensions.

Each cone 3 comprises a side wall 7 having an outer surface 9 and an inner surface 1 1. In this embodiment, the thickness t1 of the side walls 7 is uniform and is 1.1 mm. Each of the cones 3 is hollow and has a base diameter d1 measured between the edges of the inner surface 1 1 of the side wall 7 of 17 mm, and the distance d3 measured between the centres 14 of adjacent cones 3 is 421 mm. Each cone 3 has a height h measured between the lower surface of the common base 5 and the upper surface 13 of the cone 3 of 15 mm. Each cone has an inner angle a measured between the inner surface 1 1 of the side wall 7 and the plane of the common base 5 of 70°.

Each cone is a frustoconical cone having a flat upper surface 13 with a diameter d2 of 6 mm. The upper surface 13 of each cone 3 has a thickness t1 corresponding to the thickness t1 of the side wall 7.

A plan view of the energy absorbent material 1 according to a first embodiment of the invention as shown in Figure 1 is shown in Figure 2. As will be seen by reference to Figure 2, the energy absorbent material 1 comprises four parallel rows of cones 3, each row comprising four cones 3, the rows of cones 3 being in register, and the spacing between the cones d3 being the same in each row and each column.

The cones 3 and common base 5 of the energy absorbent material 1 according to the first embodiment of the invention shown in Figures 1 and 2 are formed from the same material, in this case Elastollan (RTM) B90A (available from BASF), an elastomeric material suitable for injection moulding and profile extrusion. Alternative possible materials include Elastolan (RTM) 1190, Elastolan (RTM) 119 and Elastolan (RTM) B955 (all available from Bayer) or various proprietary elastomeric materials.

Example 2

An impact protection system according to an embodiment of the present invention is illustrated in Figure 3.

The impact protection system 15 comprises four capsules 17 and a surrounding base 19. Each capsule 17 provides impact protection.

The structure of the impact protection system 15 according to an embodiment of the invention as shown in Figure 3 is illustrated in Figure 4, which shows an exploded view of the impact protection system 15, including the component parts thereof. As shown in Figure 4, the impact protection system 15 comprises an energy absorbent material 1 according to a first embodiment of the invention as shown in Figures 1 and 2. In addition, the impact protection system 15 comprises an upper layer 21 of thermoplastic elastomer comprising four shaped regions 23 each being adapted to cover four cones 3 of the energy absorbing material 1 to form the capsules 17 of the impact protection system 15.

The impact protection system 15 also comprises an intermediate padding layer of cushioning foam 25 adapted to cover the base of the energy absorbent material 1 except at the periphery thereof, and a lower fabric layer 27 adapted to cover the intermediate padding layer 25 and the periphery of the lower layer of the energy absorbent material 1.

Additionally, the impact protection system 15 comprises four shaped cushioning pads 29 adapted to fit on the outer surface of each capsule 17.

When constructed, the upper layer 21 is sealed to the upper surface of the energy absorbent material 1 , and the lower layer 27 is sealed to the periphery of the lower layer of the energy absorbent material 1 , holding the intermediate padding layer 25 in place so that four capsules, each comprising four cones 3 of the energy absorbent material 1 , and also comprising air, are formed, each capsule 17 being sealed from every other capsule 17. In addition, each of the four shaped cushioning pads 29 are fixed to the upper surfaces of the capsules 17, to provide further padding thereto. The various layers may be sealed together by any conventional methods, for example by RF Welding.

As will be appreciated by those skilled in the art, the arrangement of the various components of the impact protection system 15 illustrated in Figures 3 and 4 may be varied in any suitable manner. For example, the capsules 17 may enclose different numbers of cones and/or may be differently shaped, and the energy absorbent material may comprise different numbers of cones, for example a single capsule 17 may be formed from an energy absorbent material 1 comprising only four cones 3, or an impact protection system 15 comprising a 3x2 arrangement of capsules 17 each comprising four cones 3 may be produced using an energy absorbent material 1 comprising four rows of cones 3, each row comprising six cones 3. Various additional layers may also be incorporated. For example, a layer of thermopolymeric urethane adhesive may be incorporated between the energy absorbing material 1 and the cushioning layer 25 to prevent the cushioning layer being squeezed into the cones 3 of the energy absorbent material 1 , during the sealing of the impact protection system 15.

Example 3 to 15

The following Examples were conducted via FEM (finite element method) modelling using ANSYS (RTM) software to simulate the impact performance of different materials and cone structures. Comparison with physical test data showed that the simulation provides a reliable model for the investigated impact testing (see Figure 5). The simulation involves a flat impact surface applying an impact force to a material comprising a 4x4 array of evenly spaced cones, on a flat base. The energy absorbing material comprising the cones corresponds generally to the material according to the first embodiment of the invention shown in Figures 1 and 2, but with variations in the wall thickness and inner angle of the walls of the cones. The cones all have a height of 15 mm and a base diameter of 17 mm, and all of the energy absorbent materials are formed from elastomeric thermoplastic polyurethane Elastollan (RTM) B90A (obtainable from BASF). The impact duration was around 10 ms, the impact velocity was set at 4.27 ms ^"1 , and the impact energy was 50 J. The wall thickness of the material was varied between tests, along with the inner angle of the cones, as shown in Table 1 below.

The acceleration in the rigid body (striker) of the impact surface in the z axis direction of the impact was measured with respect to time (in ms), and the results were plotted graphically. An example graph is shown in Figure 6 with relevant features labelled (x axis ms (milliseconds) and y axis g x 100).

A visual representation of the collapse of the cones under simulated impact is shown in Figure 7, and the collapse of the cones during the testing of the material of Example 1 1 is shown in Figure 8.

Table 1 Example No. Wall Cone angle/ ⁰ Acceleration

thickness/mm vs time plot

3 0.85 63.0 Figure 9

4 0.85 65.0 Figure 10

5 0.85 67.5 Figure 1 1

6 0.85 70.0 Figure 12

7 0.85 75.0 Figure 13

8 0.85 80.0 Figure 14

9 1.10 62.0 Figure 15

10 1.10 65.0 Figure 16

1 1 1.10 70.0 Figure 17

12 1.10 72.5 Figure 18

13 1.10 75.0 Figure 19

14 1.10 80.0 Figure 20

15 1.10 85.0 Figure 21

As shown by reference to Figures 9 to 21 , the optimal impact performance is given by the material of Example 1 1 , which has a wall thickness of 1.1 mm and an inner angle of 70°.