SHOE INSOLE AND SHEET MATERIAL SUITABLE FOR USE IN
MAKING A SHOE INSOLE
Technical Field
This invention is concerned with a shoe insole suitable for use in the manufacture of footwear and to a sheet material from which such a shoe insole may be made. The term "shoe" where used herein is to be understood as denoting outer footwear generally, whether ready for wear or in the course of manufacture.
Background Art
One known method of shaping shoe uppers, in the course of manufacture of shoes, is by a technique which is known as bag-lasting. In preparing a shoe upper for bag-lasting a margin of the upper is stitched to the peripheral margin of a shoe insole by so-called Strobel stitching and the upper is lasted by drawing it tightly around a shoe last. The insole stitched to the upper is subjected to a considerable tensile load in carrying out this bag-lasting process. An insole suitable for use in the manufacture of shoes by bag-lasting must, therefore have sufficient overall tensile strength to resist the lasting forces as well as sufficient strength to resist tearing of the Strobel stitching by the forces exerted during lasting. Bag- lasted footwear is commonly completed by adhering a mid-sole to the insole, an outsole being attached to the mid-sole.
Training and leisure shoes are commonly made by bag-lasting techniques. Frequently, the mid-sole includes means for improving the shock absorption of the shoe or may carry decorative patterns and it has become desirable to be able to see, at least in part, material within the mid-sole.
One of the various objects of the present invention is to provide an improved shoe insole suitable for use in the manufacture of bag-lasted footwear.
Disclosure of Invention
The invention may be considered to provide, in one aspect, a shoe insole suitable for use in the manufacture of bag-lasted footwear comprising a transparent layer of fibre sheet material and a layer of a transparent polymeric material adhered thereto, the insole also being transparent.
The invention may also be considered to provide, in another aspect, a transparent sheet material suitable for use in the manufacture of shoe insoles for use in the manufacture of shoes by bag-lasting, the material comprising a transparent layer of fibre material and a layer of a transparent polymeric material adhered thereto.
In a preferred sheet material in accordance with the invention, the fibre sheet material is preferably a glass fibre veil and the polymeric material is preferably polyurethane.
A sheet material in accordance with the invention may be made in any convenient manner. For example the layer of fibre material may be fed into the nip of a calendar roll stack and the polymeric material extruded as a sheet into the nip to be hot-melt laminated with the fibre sheet material. In another method, the fibre sheet material may be hot-melt coated with a layer of polymeric material. The polymeric material may, if desired, be applied to the fibre sheet material by coating it with a solution or dispersion of an appropriate polymeric material, the polymeric material being deposited on the fibre sheet material when the solution or dispersion is dried. In another method of making a sheet material in accordance with the invention, a sheet of the transparent polymeric material may first be procured and the polymeric material sheet laid against the fibre layer and laminated therewith by subjecting the assembled materials to heat and pressure to soften the polymeric material sufficiently to cause it to bond to the fibre layer. Other methods of manufacturing the sheet material in accordance with the invention may also be devised.
A layer of polymeric material may be applied to one or both sides of a single layer of fibre material, dependent on the properties required of the end product. In some circumstances it may be desirable to provide a sheet material in accordance with the invention comprising more than one fibre sheet material layer and in that event, material in accordance with the invention comprises alternating layers of polymeric material and of fibre sheet material.
Whereas in the preferred insole material in accordance with the invention the layer of fibre material is glass fibre veil, other fibre materials with sufficient strength, transparency and a suitable weight may be used.
Whereas the preferred polymeric material used in an insole material in accordance with the invention is polyurethane, other transparent polymeric materials with suitable characteristics may be used.
In order to be suitable for use in the manufacture of shoe insoles for making bag-lasted footwear the sheet material must have suitable strength and stiffness, as well as being transparent. As discussed above, in bag- lasted footwear the stitch tear strength of the sheet material is important and it is preferred that the stitch tear strength of the sheet material is at least 140 N/cm. The stitch tear strength is measured by SATRA physical test method PM.33/STD.176M entitled "Strength at Right Angles to Stitch Perforations in Upper Materials", modified to use 4 needles over a 1cm length (the centres of the extreme needles being 1cm apart), instead of 17 needles over a 1 inch length as specified in the standard SATRA test. Details of the SATRA physical test method PM.33/STD.176M are available from SATRA, SATRA House, Rockingham Road, Kettering, Northants, United Kingdom. In carrying out this test a piece of material to be tested is positioned in a jig. The 4 needles mounted in the jig are pushed through a central region of the test sample. The sample is clamped in the jig which is clamped in the moving jaw of a tensile testing machine and a free end portion of the sample (through which the needles pass at a specified distance from the edge of the free end portion appropriate to the sample eg. inch (about 0.32cm) in the other jaw so that the needles are perpendicular to the direction of pull. The tester is operated at a rate of 3 inches/minute (about 7.62 cm/minute) and the tensile load at which a failure in the material occurs is measured. Likewise the tensile strength of the insole sheet material is relevant and preferably the sheet material has a tensile strength of at least 137 N/cm. Furthermore, a preferred insole material has a strain at 35 N/cm of less than 2 % and a strain at break of at least 8 % . The tensile strength and strain measurements are made using a standard tensile testing machine, well known to those skilled in the art.
Preferably a sheet material in accordance with the invention weighs up to 2000 gsm (grams per square metre), more preferably between 500 and 1600 gsm. Preferably in a sheet material in accordance with the invention the ratio of weight of polymeric material to weight of fibre material lies between 10:1 and 40:1, more preferably between 12:1 and 25:1.
A sheet material in accordance with the invention is used in the manufacture of shoe insoles in accordance with the invention, the insole conveniently being cut from the sheet material in a manner well known to those skilled in the art.
Modes for Carrying Out the Invention
There now follows a detailed description of a transparent sheet material suitable for use in the manufacture of shoe insoles for making shoes using the bag-lasting method and of a shoe insole made from the illustrative material. It will be realised that this sheet material and the insole made therefrom have been selected for description to illustrate the invention by way of example.
The illustrative transparent sheet material has a weight of 1350 gsm (grams per square metre) and has a gauge of about 1.0 mm. The illustrative material consists of a glass fibre veil, weight 70 gsm and available from Owens Corning, this being a commercially available product. Sheets of a polyurethane material are positioned on either side of the glass fibre veil and laminated therewith by subjecting the assembly to heat and pressure to produce the illustrative sheet material. The polyurethane used in making the illustrative sheet material is Estane 58277. The illustrative sheet material has a stitch tear strength of 155 N/cm. The tensile strength of the illustrative sheet material is 192 N/cm. The illustrative sheet material has a strain at break of greater than 100% and has a strain at 35 N/cm of 1.2 % .
Insoles which are themselves illustrative of the invention are cut from the illustrative sheet material using a cutting press in a manner well known to those skilled in the art.
The illustrative insole is found to perform satisfactorily in the manufacture of footwear by the bag-lasting method and is sufficiently transparent that the structure of the mid-sole is readily visible through the illustrative insole when it is incorporated in a complete shoe.
The mid-sole may be secured to the insole by any appropriate means, for example by using a thin, transparent, film of an appropriate adhesive or by using thermal bonding techniques which are known to those skilled in the art.