GB2306392A

GB2306392A - Waterproof insole material

Info

Publication number: GB2306392A
Application number: GB9522225A
Authority: GB
Inventors: Robert Owen Symcox; Clinton Bailey
Original assignee: British United Shoe Machinery Ltd
Current assignee: Noxet UK Ltd
Priority date: 1995-10-31
Filing date: 1995-10-31
Publication date: 1997-05-07
Anticipated expiration: 2015-10-31
Also published as: GB9522225D0; GB2306392B

Abstract

A waterproof insole comprises a polymeric core (1) which presents a waterproof barrier and this core is laminated with a fabric layer (2,3) which contains an impregnant for enhanced bonding within any footwear manufactured with the insole material. The polymeric core is preferably in excess of 0.5mm in thickness and the impregnant comprises styrene butadiene latex, inorganic filler such as clay, water, resin and traces of ammonia, silicone and fluorocarbon.

Description

WATERPROOF INSOLE MATERIAL The present invention relates to a waterproof insole material and more particularly but not exclusively to a waterproof insole material for use with cement-lasted footwear.

There is a requirement particularly in outdoor footwear used in vigorous or extreme conditions e.g. hiking boots or golf shoes to ensure that the footwear used is both waterproof and resilient. However, as with most consumer products the price of the components in footwear is highly significant and should be as low as possible. This cost requirement constrains considerably the range of materials that can be used in footwear.

Cement-lasted footwear is manufactured about a shoe last by the process of placing assembled upper components upon the last with an appropriately cut insole board and where necessary also a shank upon the bottom of the last. This arrangement of the upper assembly and insole/shank about the shoe last is cemented in place by a lasting machine by folding the overhanging upper component over the insole board and securing the arrangement in place with cement adhesive and/or tacks. In waterproof shoes tacks are rarely used for the obvious reason that they break the waterproof barrier and so may allow water to ingress into the shoe. Once the arrangement of shoe upper and insole board/shank are cemented in place and conditioned it is usual to apply either a premoulded outer sole or injection mould a sole about the arrangement.

It will be appreciated from the above that the outer sole presents the main barrier to water ingression. However, this outer sole may be breached by wear or puncture and there is always the possibility of seal failure about the edge seam of the shoe which will allow water to become incident upon the insole.

With footwear it is important that when not in use any sweat build-up within the footwear created by the wearer is released. The shoe must breathe otherwise, irrespective of whether water penetrates from the exterior of the shoe, the inside of the shoe will become moist and unhygienic.

Traditionally, to allow this breathing or moisture release when footwear is not in use materials such as cellulose board or impregnated non-woven fabrics have been used to provide insoles. These materials allow the sweat of a user to evaporate when the shoe is not in use. Furthermore, cellulose materials are sufficiently flexible, resilient and normally strong enough for shoe manufacture. However, once wet cellulose materials can become susceptible to fragmentation and disintegration particularly when flexed as often as within the footwear. Thus, even if a waterproof insock is provided for the footwear in order to protect the wearer a cellulose insole may still fail in an unacceptably short period of time.

The normal approach to overcome the problems of waterproofing an insole material is to simply apply a waterproof layer to that material either prior to or subsequent to cutting of an insole. Unfortunately, such waterproof layers can diminish the strength of the lasted bond between the upper component and the insole. Furthermore, these waterproof layers may not be able to withstand the expected degree of flexing over a sustained period of time which is inherent in footwear use. Consequently, it has been typical where waterproofing is highly important to ensure even though the insole has been waterproofed that a waterproof insock is provided for the footwear to almost guarantee a waterproof nature for the footwear. It will be appreciated that such a waterproof insock can also provide additional waterproofing to protect against failure of assembled upper component seams etc.

It is an objective of the present invention to provide a waterproof insole material suitable for footwear manufacture.

In accordance with the present invention there is provided a waterproof insole material for footwear, the material comprising a waterproof polymeric core laminated with at least one fabric layer and at least one of the fabric layers having an impregnant to facilitate bond strength in use between the material and other footwear components though an adhesive, the impregnant comprising the following constituents as wet weight percentages: styrenebutadiene latex 28-32%, inorganic filler such as clay 45-55%, water 12-18%, resin 1-2% and traces of ammonia, silicone and fluorocarbon.

Preferably, the fabric layer is a non-woven felt.

Furthermore, this non-woven felt may comprise of polyester fibres in an appropriate blend such as 70% 1.5 decitex fibre with 30% 3.3 decitex fibre, the felt being needle entangled and 2 mm thick.

Preferably, the waterproof insole material has a weight in the range 1500-1750 gms/m2 and a thickness of 1.5-3 mm.

Preferably, the core comprises ethylene vinyl acetate copolymer with polypropylene to achieve a thickness of at least 0.5 mm.

Preferably, the waterproof insole material is laminated with a fabric layer on either side of the polymeric core.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawing in which a schematic cross-section of the material is shown.

Essentially the present invention as can be seen in the drawing comprises a polymeric core 1 upon which fabric layers 2,3 are laminated. The laminating process is well-known and as such will not be described in detail herewith. However, it will be appreciated that the core 1 is most conveniently presented in the laminating process as a pre-formed layer in a roll such that the fabric layers 2,3 can be laid upon it and pressed into its surface when heat activated in order to laminate the three components i.e. core 1 and layers 2,3 together under compression.

The essential feature of the polymeric core 1 is that it is sufficiently thick to present an adequate water barrier and so make the insole material having it as its core waterproof.

Unfortunately polymeric materials are relatively expensive and do not readily achieve the necessary bond strength with typical adhesive used for shoe manufacture. Although a range of polymeric materials can be used it has been found that a core comprising ethylene vinyl acetate co-polymer with polypropylene is suitable. Most advantageously a composition of 70% by weight of ethylene vinyl acetate co-polymer with 30% by weight polypropylene has been found acceptable and furthermore, a thickness in excess of 0.5 mm and a weight of 400 gms/m2 has been found adequate to achieve a waterproof barrier.

In accordance with the present invention it is important that there is at least one fabric layer 2,3 in order to provide a matrix for an impregnant which facilitates good bond strength with adhesive to other shoe components. It is preferred to use non-woven felts for the fabric layers 2,3 in order to achieve cost containment. However, it will also be understood that woven fabrics could be used if necessary. It is preferred to have the core 1 laminated on both sides with a fabric layer 2,3 in order to achieve best results. In this way the waterproof insole material in accordance with the present invention can be bi-directional i.e. it is irrelevant which way up the material is in the shoe construction.

However, it will also be appreciated that by appropriate difference in impregnant the bottom surface of the insole material could be arranged to enhance bond strength with other shoe components through adhesive whilst the upper layer could be arranged to provide other facilities such as deodorising, comfort cushioning or enhanced sweat evaporation when the eventual footwear is not being worn. These features can be achieved through appropriate impregnants in the non-woven layer 2,3.

) It is in accordance with the present invention to provide the lower fabric layer i.e. in the drawing layer 3 with an impregnant which enhances bonding between the sole material and other shoe components through adhesive. The impregnant used comprises the following constituents by weight percentages: sytrenebutadiene latex 28-32%, inorganic filler such as clay 45-55%, water 12-18%, resin 1-3% and traces of ammonia, silicone and fluorocarbon. It is in this wet condition that the fabric layer is impregnated. However, in a dry state the water component of the impregnant is tsubstantially removed and thus the following dry weight percentages for each constituent are: styrenebutadiene latex in excess of 30%, inorganic filler in excess of 60%, resin in excess of 2i% and approximately doubling in trace constituents other than ammonia.These percentages are dependent upon the degree of drying. It will also be appreciated that pigments could be incorporated into the impregnant to provide desired colour to the insole material. Typically, the impregnant weight within the insole material will be in excess of 700 gms/m2.

In order to inhibit water transfer across the material an anti-wicking agent such as a fluorocarbon is included in the impregnant. This anti-wicking agent prevents migration of water which has penetrated the outer sole to the edge of an insole where it may circumvent the water barrier of the material.

It will be understood that the actual gauge or thickness of the waterproof insole material will depend upon the type of footwear in which the insole is to be located. For example, ladies' outdoor walking shoes would require a significantly thinner insole than heavy duty hiking boots to be worn by polar explorers. It has been found that a gauge of between 1.5 and 3 mm is appropriate, however the distribution of thickness between the polymeric core 1 and the fabric layers 2,3 may be varied. For example if necessary the polymeric core 1 as a proportion of the thickness may be increased in order to eliminate the necessity of providing a shank or shank board which is used to reinforce and strengthen the insole in respect of the heel end of the footwear i.e. the polymeric core 1 provides this strengthening function itself in addition to the waterproof barrier. This would obviously also reduce insole/shanks costs in footwear construction. Finally, it will also be appreciated that elimination of shanks which are secured to the insole by rivets which break the water barrier is an additional advantage of the present invention.

Claims

Claims:

1. A waterproof insole material for footwear, the material comprising a waterproof polymeric core laminated with at least one fabric layer and at least one of the fabric layers having an impregnant to facilitate good bond strength in use between the material and other footwear components through an adhesive, the impregnant comprising the following constituents as wet weight percentages: stryenebutadiene latex 28-32%, inorganic filler such as clay 45-55%, water 1218%, resin 1-2% and traces of ammonia, silicon and fluorocarbon.

2. A material as claimed in Claim 1 wherein the fabric layer is a non-woven felt.

3. A material as claimed in Claim 2 wherein the nonwoven felt is formed from needle entangled polyester fibre in a blend of 70% 1.5 decitex and 30% 3.3 decitex fibre.

4. A material as claimed in any preceding Claim wherein the material has a weight of 1500-1750 gms/m2 and in the range of 1.5-3mm gauge or thickness.

5. A material as claimed in any preceding Claim wherein the core is formed from ethylene vinyl acetate co-polymer with polypropylene and has a thickness in excess of 0.5mm.

6. A material as claimed in any preceding Claim wherein the polymeric core is laminated on both sides by a fabric layer.

7. A waterproof insole material substantially as hereinbefore described with reference to the accompanying drawing.