GB2298562A - Insole - Google Patents

Description

Title - Footwear Components This invention relates to components for footwear, in particular to insoles for insertion in shoes, boots and the like.

According to the invention, there is provided an insole for insertion into a shoe, boot or similar item of footwear, the insole comprising granules of a material capable of emitting heat as a result of absorbing moisture dispersed in a polymeric binder matrix.

In the following, the material which emits heat upon absorption of moisture is referred to as "thermal material".

The insole according to the invention is advantageous primarily in that as the insoles absorb moisture emitted by the wearer's foot, they emit heat and thereby produce a warming effect, adding to the wearer's comfort. After use, the insoles or the items of footwear containing the insoles may be placed in a suitable environment, eg a warm and dry environment, for the moisture to be released. The insoles are then ready for use again. They may, for instance, be worn by a user all day and then dried in a warm place overnight ready for use the next day.

The granules of thermal material preferably have an average particle size of the order of 1 mm or less. Depending on the particle size, and also on the thermal properties of the material, an insole for insertion into a typical shoe preferably contains between 1 g and 50g of material. A preferred range would be 1 5g to 30g, eg about 25g. Typically, the granular thermal material might account for between 40% and 70% by weight of the insole.

One suitable thermal material having the desired thermal properties is aluminium oxide, which is commercially available in granular form. Without limiting the invention in any way, it is postulated that the warming effect is the result of a reversible, exothermic, hydration process.

The polymeric binder may be any suitable binder material having the requisite physical properties, eg adequate structural integrity and flexibility. An emulsion of the binder or of a binder precursor is preferably mixed with the granular thermal material and sandwiched between two layers of fabric to form a laminate, which is then dried and ultimately cut to shape. By "binder precursor" is meant a material which is capable of undergoing polymerisation to form a polymeric binder. The laminate, and hence the finished insole, preferably has a thickness of not greater than 5mm, more preferably 4mm or less, so as not to interfere with the fit of the shoe into which it is inserted.

One suitable binder material is the terpolymer emulsion known as Emultex VV530 sold by Harlow Chemicals Co Ltd of Templefields, Harlow, Essex CM20 2BH, United Kingdom. This material contains vinyl acetate and butyl acrylate, contains approximately 50% by weight of solids, and is of relatively low viscosity.

Another suitable binder is the water-based vinyl acetate/ethylene copolymer dispersion known as Vinamul 3252 and supplied by Vinamul Limited, Mill Lane, Carshalton, Surrey.

In order to improve the physical properties of the insole, one or more additives, such as a plasticizer to improve flexibility, may be incorporated. One suitable plasticizer is dibutylphthalate, eg at a level of 3-5% in the finished insole.

The insole is preferably provided with a wearing surface on the foot-facing side, in the form of a suitable fabric. One suitable such fabric is a needled non-woven fabric on a polypropylene scrim.

The insole may also be provided with a fabric backing on the sole-facing side. Suitable fabrics include hydro-entangled non-woven polyester or spun-bonded polyester.

Whatever fabrics are used on the foot-facing and sole-facing sides of the insole, they should preferably have a pore size which is less than the average particle size of the granular thermal material, in order to inhibit loss of thermal material from the insole.

The insole according to the invention is preferably prepared by mixing the granular thermal material with the polymeric binder or a binder precursor in emulsion form, and spreading the resulting mixture. The fabric wearing surface and backing are preferably simultaneously laminated, then dried and cut into suitably sized pieces. Insoles may then be cut from these pieces. In order to prevent loss of granular thermal material from the edges of the cut insoles, the edges may be treated, eg by spraying with a suitable sealant.

Preferred embodiments of the invention will now be described in greater detail, by way of illustration only, with reference to the following Examples.

Example Granular thermal material 40% wlw Emultex VV530 60% The Emultex VV530 (an emulsion containing 52.5% solids) is mixed with the thermal material to form a slurry. The slurry is spread onto a hydro-entangled non-woven polyester backing and a needled non-woven fabric forming an upper wearing surface, to form a sheet of approximate thickness 4mm. The sheet is dried in a drying chamber and then cut into suitably sized pieces.

Example 2 Granular thermal material 40% w/w Emultex VV530 57% Dibutylphthalate 3% Prepared as for Example 1, save that the dibutylphthalate is added as a plasticizer to the Emultex VV530 prior to mixing with the thermal material.

In both the above Examples, the thermal material may be granular aluminium oxide, preferably with an average particle size less than lmm.

Claims (11)

Claims

1. An insole for insertion into a shoe, boot or similar item of footwear, the insole comprising granules of a material capable of emitting heat as a result of absorbing moisture dispersed in a polymeric binder matrix.

2. An insole as claimed in claim 1, wherein the granules of thermal material have an average particle size of lmm or less.

3. An insole as claimed in claim 1 or claim 2, which contains between lg and 50g of thermal material.

4. An insole as claimed in claim 1 or claim 2, which contains between 1 5g and 30g of thermal material.

5. An insole as claimed in any preceding claim, wherein the thermal material accounts for between 40% and 70% by weight of the insole.

6. An insole as claimed in any preceding claim, wherein the thermal material is aluminium oxide.

7. An insole as claimed in any preceding claim, which further comprises, on the foot-facing side, a wearing surface in the form of a suitable fabric.

8. An insole as claimed in any preceding claim, which further comprises, on the sole-facing side, a fabric backing.

9. A process for the manufacture of an insole as claimed in claim 1, which method comprises forming a mixture of the granular thermal material and the polymeric binder or a binder precursor.

10. A process as claimed in claim 9, comprising the further step of laminating the mixture with a fabric wearing surface and a fabric backing.

11. An insole substantially as hereinbefore described.