WO1996035343A1

WO1996035343A1 - Rigid insole construction

Info

Publication number: WO1996035343A1
Application number: PCT/GB1996/001088
Authority: WO
Inventors: Robert Owen Symcox
Original assignee: British United Shoe Machinery Ltd.; Usm Espana, S.L.
Priority date: 1995-05-13
Filing date: 1996-05-08
Publication date: 1996-11-14
Also published as: GB2300795A; GB9509737D0

Abstract

An insole construction is provided comprising a base layer (1) secured to a backer layer (5), the base layer (1) comprising a polypropylene core sandwiched between two impregnated non-woven fabrics. The backer layer (5) may have a similar construction and has a shape similar to the base layer (1) in a heel region of the insole. The backer layer (5) is adhered to the base layer (1) through pressure and heat. The backer layer (5) may be an extruded thermoplastic film sandwiched between layers of fusion-bonded non-woven fabric and having an impregnation of styrene copolymer. This insole construction allows formation of exceptionally stiff insoles in the necessary heel section of the insole without creating thermal distortion problems or lamination difficulties when a moulded outsole is attached.

Description

RIGID INSOLE CONSTRUCTION

The present invention relates to rigid insole construction, and more particularly to a rigid insole con- struction 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.

A recent example of an extremely stiff insole material is manufactured by British United Shoe Machinery Ltd. under their designation 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 is difficult to manufacture through laminating equipment, i.e. there is a limit to the thickness achievable. Thus, where exceptionally rigid insoles are required, it is not merely a question of increasing the thickness of the insole material to provide greater rigidity. Furthermore, it will be appreciated that there should be a balance between rigidity in the heel/ankle region with some flexibility in the forepart/ball region.

Normally, in order to enhance insole rigidity a metal shank would be added to the heel region of the insole. However, within some safety boots this would present additional dangers, and with military boots designed to be resistant to magnetically-activated explosive mines would present the additional problem of 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 so, in combination with a polypropylene-core insole board, presents problems with polyurethane injection- moulded soles due to gaps created by differential thermal expansion between the insole and the shank board.

It is an objective of the present invention to provide an insole construction of exceptional rigidity, suitable for safety boots and shoes.

In accordance with the present invention there is provided an insole construction comprising an insole base layer consisting of a polypropylene core sandwiched between two non-woven fabrics treated to provide an adhesive barrier, and a backer layer 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 a heel section.

Preferably, the backer layer comprises a sandwich having a thermoplastic layer sandwiched between layers of non-woven fusion bonded fabric. Furthermore, the backer layer may be substantially the same gauge and construction as the base layer.

Further in accordance with the present invention, there is provided a method of forming an exceptionally rigid insole comprising the steps of:

1. Cutting an insole prerequisite from a sheet of insole material consisting of 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. with regard to a heel section of that insole,

3. Abutting the insole prerequisite and said backer layer,

4. Adhering said backer layer to said insole prerequisite by appropriate means.

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

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawing in which Fig. 1 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 three 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 backer layer 5 may include a thermoplastic core to provide additional strength. The backer layer 5 reinforces the rigidity of the insole in the heel region.

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 Fig. 2 and also cutting the backer layer 5 to coincide with the base layer 1 configuration about a heel or ankle section 6. The 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 layer 5 to the base layer 1. Typically, heating is provided by infra-red radiation to avoid heat elements scorching the insole. It will be understood that the layers 1, 5 are thick and may require significant heat energy input, which may be difficult to present through a surface without damage to it.

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 or about 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 heel section 6 of the insole construction.

By using a fused non-woven material as the backer layer 5 it will be understood that any thermoforming problems are eliminated.

Generally, the base layer 1 and backer layer 5 will be the same material board. An example of such board is T70 I manufactured by British United Shoe Machinery Ltd. of Leicester, England. This is an exceptionally stiff non-woven insole material. Furthermore, it consists of a polypropylene extruded core sandwiched between two impregnated non-woven

5 felts. T70 is available in 2.5 mm, 3.0 mm and 4.0 mm gauges.

The non-woven felt may comprise, by weight, 33.3% 1.4/1.7 decitex polyester fibre (2nd grade), 33.4% 3.3 decitex polyester fibre and 33.3% 5.0 decitex polyester fibre. This

10 fibre blend is formed into a non-woven felt by needle entanglement to give a weight of about 420 g/m² and a gauge of about 3.25 mm for a 4.0 mm layer, 340 g/m² and 2.7 mm for a 3.0 mm layer and about 260 g/m² for a 2.5 mm layer. Typically, after impregnation the non-woven felt will have a

15 weight of 2250 g/m² (2.5 mm), 2750 g/m² (3.0 mm) and 3250 g/ra² (4.0 mm). To summarise, a 2.5 mm gauge non-woven felt would have a weight of about 2250 g/m² and a density of about 0.9 g/ cπ.3 to give a rigidity of 0.65 mm in the direction of manufacture and of 1.2 mm across that direction; a 3.0 mm 0 gauge material would weight 2750 g/m² and 0.85 g/cm³ with a rigidity of 0.5 mm and 0.7 mm respectively; whilst a 4.0 mm gauge material would weigh 3250 g/m² and have a density of 0.77 g/cm³ with a rigidity of 0.4 mm and 0.5 mm respectively. Rigidity is determined by cutting a 3" x 1" sample in the 5 orientation required, placing that sample centrally in a holder such that a 5.0 cm length is unsupported, placing a two-point 3.0 cm apart deflector centrally upon the sample, applying a 5 kg weight to the deflector and then measuring the deflection of the sample in mm. These felts are split as 0 required for incorporation into the board.

The layers 1, 5 which are used to form the insole include polypropylene extruded cores with a non-woven felt as described above to each side. Typically, this core will have 5 _a gauge of 0.8 mm and a weight of about 720 g/m².

The core is extruded between feeds of non-woven material as described above, and compressed into a unified layer in a mangle-type apparatus.

In order to provide an insole, layers 1, 5 of different gauges may be used as required to achieve insole performance.

The non-woven felt along with the core provide an adhesive barrier which also prevents strike-through of any polyurethane or other material moulded about the insole in order to provide an outsole.

Claims

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 heel region 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. 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:

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

b. 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 region of the insole,

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

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