GB2300795A - Insole - Google Patents

Abstract

An insole construction comprising a base layer 1 of a polypropylene core sandwiched between two impregnated non-woven fabrics 3, 4 adhered to fusion bonded non-woven backer fabric 5 made from synthetic fibres and impregnated with filled styrene copolymer and coated on at least one side with heat activated adhesive. The backer layer 5 is adhered to the base layer through pressure and heat. Alternatively the backer layer maybe an extruded thermo-plastic film sandwiched between fusion bonded non-woven fabric and having an impregnation of styrene copolymer. This insole construction allows formation of exceptionally stiff insoles in the necessary ankle section of the insole without creating thermal distortion problems or lamination difficulties.

Description

RIGID INSOLE CONSTRUCTION The present invention relates to rigid insole construction and more particularly to a rigid insole construction of exceptional strength for use in military or safety boots.

A fundamental component of most shoe constructions is an insole which provides the base upon which the shoe or boot is manufactured. Typically, insole board is made of cellulose material or a non-woven fabric impregnated to provide rigidity. More recently, insole board constructions have been made comprising sandwiches of non woven or cellulose board material with a rigid polymeric central layer.

An example of a recent extremely stiff insole material is manufactured by USM Texon Ltd under there designation at stated T70 and is especially suited for military boots. This insole material comprises a polypropylene core sandwiched between two impregnated non-woven fabrics. The polypropylene core provides the principal rigidity for the insole whilst the non-woven fabric provides a suitable surface to enable attachment of an injection moulded sole and to enable boot uppers to be lasted to the insole It will be appreciated that this insole material is relatively thick and thus can be difficult to manufacture through usual laminating equipment. Thus, where exceptionally rigid insoles are required it is not merely a question of increasing the thickness of the insole material to provide the greater rigidity.

Normally in order to enhance insole rigidity a metal shank would be added however within some safety boots this would present additional dangers and within anti-mine military boots would present the additional problem with regard to magnetic explosive mines i.e.

triggering them.

Solutions attempted to overcome this practical limitation to insole rigidity have included laminating the insole board to conventional shank board i.e. the material from which non metallic shanks are made. However, such shank board is not thermoplastic and consequently with a polypropylene core insole board presents problems with polyurethane injection moulded soles due to gaps between the insole and board.

It is an objective of the present invention to provide an insole construction of exceptional rigidity suitable for explosive mine boot protection.

In accordance with the present invention there is provided an insole construction comprising an insole base consisting of a polypropylene core sandwiched between two non-woven fabrics treated to provide an adhesive barrier, and a backer comprising a non woven fabric suitably fusion bonded or impregnated and coated on at least one side with a heat activated adhesive in order to secure the backer layer to the base layer and so provide an exceptionally rigid insole in an ankle section.

Preferably, the backer comprises a sandwich having a thermoplastic layer sandwiched between layers of non-woven fusion bonded fabric.

Further in accordance with the present invention there is provided a method of forming an exceptionally rigid insole comprising these steps of: 1. Cutting an insole prerequisite from a sheet of insole material consisting a polypropylene core sandwiched between two impregnated non-woven fabrics, 2. Cutting a backer layer of fusion bonded non-woven material of similar configuration to the insole cut in step 1. in the ankle section of the insole, 3. Abutting the insole prerequisites and said backer layer, 4. Adhering said backer layer to said insole layer by appropriate means.

Preferably, the backer layer is adhered to the base insole layer using infra-red heating.

An embodiment of the present invention will now describe by example by reference to the accompanying drawing in which Fig.l is a schematic cross section of an insole construction and Fig. 2 is a schematic plan view of the insole construction.

Considering the drawings. A base layer 1 comprises a polypropylene core 2 of appropriate thickness and sandwiched between impregnated non-woven fabrics 3,4. This layer 1 provides the base for the insole construction and thus any boot formed with the insole construction in accordance with the present invention. The base layer 1 is produced by conventional laminating techniques such that the 3 layers 2,3,4 are amalgamated to form the sandwich as illustrated.

A backer layer 5 is formed from a thermally fused non-woven material made from a blend of synthetic fibres and impregnated with a styrene copolymer. Typically the backer layer 5 will be coated with a thermally activated adhesive on both sides. In addition, the back layer my include a thermoplastic core to provide additional strength.

An insole construction in accordance with the present invention is provided by cutting the base layer 1 to form a typical shoe sole configuration as shown in 2 and also cutting the backer layer 5 to coincide with the base layer configuration about a heel section 6.

These base layer 1 and backer layer 5 are brought into the abutment. Thus, under pressure and suitable heating the thermally activated adhesive surface of the backer layer 5 adheres the backer to the base layer 1. Typically heating is provided by infra-red radiation to avoid heat elements scorching the insole. Once the base layer 1 and backer layer 5 are adhered together they are in effect one integral component.

It will be appreciated that as both the base layer 1 and backer layer 5 are formed from thermoplastic materials there are no inherent relative thermal expansion problems when a polyurethane sole is injection moulded onto this insole construction.

The present invention allows formation of exceptionally rigid insoles without the necessity of a laminating step.

It will be understood that the present invention allows localised stiffening in the ankle section 6 of the insole construction.

By using a fused non-woven material as the backer layer you will be understood that any thermoforming problems are eliminated.

Claims (4)

Claims:

1. An insole construction comprising a base layer consisting of a polypropylene core sandwiched between two non-woven materials treated to provide an adhesive barrier and a backer layer comprising a suitably fusion bonded or impregnated non-woven material having a heat activated adhesive layer adhering it to the base layer, the base layer and the backer layer having substantially the same configuration in a ankle zone of the insole construction and adhered together by heat activation of the heat activated adhesive under pressure.

2. An insole construction as claimed in claim 1 wherein the non-woven material in either the base layer or the backer layer is substantially formed of polyester fibres of appropriate size.

3. An insole construction as claimed in Claim 1 or Claim 2 wherein the backer layer fusion bonded woven fabric is impregnated with a styrene copolymer.

4. Trimming as necessary the edge between the base and backer layers.

4. An insole construction as claimed in claim 1, 2 or 3 wherein the heat activated adhesive is of an EVA type.

5. An insole construction as claimed in any proceeding claim wherein the back layer includes a thermoplastic core between layers of non-woven material.

6. A method of forming an insole comprising steps of:

1. Cutting a base layer from a sheet of material consisting a polypropylene core sandwiched between two impregnated non-woven fabrics,

2. Cutting a backer layer of fused non-woven material having at least one side covered with hot melt adhesive, the shape of the backer layer being substantially the same as that of the base layer in the heel zone,

3. Attaching the base layer to the backer layer using heat and pressure such that the two layers become integral,