GB2072485A - Wedge shaped heel - Google Patents

Abstract

A wedge-shaped member which can be used to form or underlie the heel end of the ground- engaging surface of footwear, for example, a running shoe, is formed of a closed-cell, foamed, cross- linked polyolefin, and preferably of a plurality of layers whose bulk density increases from the bottom to the top, in use. <IMAGE>

Description

SPECIFICATION Wedge This invention relates to wedge-shaped members which can be used in the heels of, for example, running shoes. It is conventional to mould the sole of a sports shoes in order to provide the wearer's foot with the sufficiently high degree of support. However, the heels of running shoes have to combine hard wear with low weight, and this has been difficult to achieve.

According to the present invention, a wedge-shaped member is formed of a closedcell, foamed, cross-linked polyolefin. Such a member can be used in the heel portion of an article of foot wear, e.g. a sports of running shoe.

The preferred polyolefin is polyethylene.

The foam is preferably soft. The degree of cross linking is preferably from 40 to 70%.

Soft foams with the given degree of crosslinking, and having a closed pore structure exhibit high mechanical strength, especially at a bulk density of 150 to 210 kg/m3. Further, such foams have a limited plastic flowability under a steady load so that they can form well to the foot of the wearer. During running the repeated impacts are well damped, thereby decreasing fatigue in a runner having a shoe including a wedge-shaped member of the invention as part of its heel.

It is preferred that the wedge-shaped member of the invention should comprise a plurality of superposed layers. These may be individually wedge-shaped. Preferably, the various layers have different bulk densities. It is therefore possible to provide a wedge-shaped member of the invention exhibiting uniform mechanical behaviour over its entire length, the elastic properties and the damping properties being different, depending on the thickness of the layers. At the relatively thin edge of the wedge, the foam structure may be consolidated to a degree in which pores are substantially or wholly eliminated. Consolidation can provide an even transition from the normal foam structure at the thick end of the wedge, towards the thin end.

The bulk density of the superposed layers preferably decreases from one face of the wedge to the other, so that the lowermost layer, in use has the lowest bulk density.

It is particularly preferred that the lowermost layer should have a bulk density of from 1 5p to 1 80 kg/m3, and that the uppermost layer should have a bulk density of from 1 70 to 210 kg/m3. Values outside those given can lead to unsatisfactoy appearance or provide insufficient damping. The most preferred bulk densities for the lowermost and uppermost layers are, respectively, 1 60 and 1 75 kg/m3.

It will often be desirable to form the upper face of a wedge-shaped member of the invention as a foot support, i.e. so that it conforms moreorless to the foot of a potential wearer.

The underface may be provided, if desired, with additional traction aids such as spikes.

A wedge-shaped member of the invention can be fixed directly beneath a wear sole of a solid plastics material, without the wearer noticing any transition in rigidity in the region of the wear sole. A less than rigid bond between the front part of a wear sole and a wedgeshaped member of the invention can provide sufficient flexibility to contribute positively to the wear characteristics of the sole as a whole.

The invention will now be described by way of example with reference to the accompanying drawing which is a plan view of a member embodying the present invention. The drawing shows a wedge-shaped member comprising an upper layer 1 or a closed-cell, foamed, cross-linked polyolefin. The upper face of this layer is formed as a foot support. A lower foam material layer 2 is formed on its lower face as a carrier for a wear sole. The layers are bonded by flame-lamination. Both layers are wedge-shaped, their thickness decreasing towards front edge 3 where the material has been consolidated and is substantially free from pores.

1. A wedge-shaped member formed of a closed-cell, foamed, cross-linked polyolefin.

2. A member according to claim 1 in which the polyolefin is polyethylene.

3. A member according to claim 1 or claim 2 which comprises a plurality of superposed layers having different bulk densities.

4. A member according to claim 3 in which the bulk density of the layers decreases from one face of the member to the other.

5. A member according to claim 3 in which the lowest bulk density is from 1 50 to 180 kg/m3.

6. A member according to claim 4 or claim 5 in which the highest bulk density is from 170 to 210 kg/m3.

7. A member according to any preceding claim in which one face (which is the face of the layer having the highest bulk density in a member according to any of claims 3 to 6) is formed as a heel or foot support.

8. A member according to claim 1 substantially as herein described with reference to the accompanying drawing.

9. An article of footwear including a member according to any preceding claim.

10. A running shoe according to claim 9.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Wedge This invention relates to wedge-shaped members which can be used in the heels of, for example, running shoes. It is conventional to mould the sole of a sports shoes in order to provide the wearer's foot with the sufficiently high degree of support. However, the heels of running shoes have to combine hard wear with low weight, and this has been difficult to achieve. According to the present invention, a wedge-shaped member is formed of a closedcell, foamed, cross-linked polyolefin. Such a member can be used in the heel portion of an article of foot wear, e.g. a sports of running shoe. The preferred polyolefin is polyethylene. The foam is preferably soft. The degree of cross linking is preferably from 40 to 70%. Soft foams with the given degree of crosslinking, and having a closed pore structure exhibit high mechanical strength, especially at a bulk density of 150 to 210 kg/m3. Further, such foams have a limited plastic flowability under a steady load so that they can form well to the foot of the wearer. During running the repeated impacts are well damped, thereby decreasing fatigue in a runner having a shoe including a wedge-shaped member of the invention as part of its heel. It is preferred that the wedge-shaped member of the invention should comprise a plurality of superposed layers. These may be individually wedge-shaped. Preferably, the various layers have different bulk densities. It is therefore possible to provide a wedge-shaped member of the invention exhibiting uniform mechanical behaviour over its entire length, the elastic properties and the damping properties being different, depending on the thickness of the layers. At the relatively thin edge of the wedge, the foam structure may be consolidated to a degree in which pores are substantially or wholly eliminated. Consolidation can provide an even transition from the normal foam structure at the thick end of the wedge, towards the thin end. The bulk density of the superposed layers preferably decreases from one face of the wedge to the other, so that the lowermost layer, in use has the lowest bulk density. It is particularly preferred that the lowermost layer should have a bulk density of from 1 5p to 1 80 kg/m3, and that the uppermost layer should have a bulk density of from 1 70 to 210 kg/m3. Values outside those given can lead to unsatisfactoy appearance or provide insufficient damping. The most preferred bulk densities for the lowermost and uppermost layers are, respectively, 1 60 and 1 75 kg/m3. It will often be desirable to form the upper face of a wedge-shaped member of the invention as a foot support, i.e. so that it conforms moreorless to the foot of a potential wearer. The underface may be provided, if desired, with additional traction aids such as spikes. A wedge-shaped member of the invention can be fixed directly beneath a wear sole of a solid plastics material, without the wearer noticing any transition in rigidity in the region of the wear sole. A less than rigid bond between the front part of a wear sole and a wedgeshaped member of the invention can provide sufficient flexibility to contribute positively to the wear characteristics of the sole as a whole. The invention will now be described by way of example with reference to the accompanying drawing which is a plan view of a member embodying the present invention. The drawing shows a wedge-shaped member comprising an upper layer 1 or a closed-cell, foamed, cross-linked polyolefin. The upper face of this layer is formed as a foot support. A lower foam material layer 2 is formed on its lower face as a carrier for a wear sole. The layers are bonded by flame-lamination. Both layers are wedge-shaped, their thickness decreasing towards front edge 3 where the material has been consolidated and is substantially free from pores. CLAIMS

1. A wedge-shaped member formed of a closed-cell, foamed, cross-linked polyolefin.

2. A member according to claim 1 in which the polyolefin is polyethylene.

3. A member according to claim 1 or claim 2 which comprises a plurality of superposed layers having different bulk densities.

4. A member according to claim 3 in which the bulk density of the layers decreases from one face of the member to the other.

5. A member according to claim 3 in which the lowest bulk density is from 1 50 to 180 kg/m3.

6. A member according to claim 4 or claim 5 in which the highest bulk density is from 170 to 210 kg/m3.

7. A member according to any preceding claim in which one face (which is the face of the layer having the highest bulk density in a member according to any of claims 3 to 6) is formed as a heel or foot support.

8. A member according to claim 1 substantially as herein described with reference to the accompanying drawing.

9. An article of footwear including a member according to any preceding claim.

10. A running shoe according to claim 9.