GB1588309A

GB1588309A - Shoe stiffeners

Info

Publication number: GB1588309A
Application number: GB5024376A
Authority: GB
Original assignee: British United Shoe Machinery Ltd
Current assignee: Noxet UK Ltd
Priority date: 1977-12-01
Filing date: 1977-12-01
Publication date: 1981-04-23

Description

(54) IMPROVEMENTS IN OR RELATING TO SHOE STIFFENERS (71) We, The BRITISH UNITED SHOE MACHINERY COMPANY LIMITED, a British Company of Union Works, Belgrave Road in the City of Leicester, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is concerned with improvements in or relating to shoe stiffeners, especially stiffeners which are intended to be incorporated in the toe or heel end portion of the shoe upper in the manufacture of shoes. The term "shoe" where used herein generically is intended to denote outer footwear generally whether ready for wear or in the course of manufacture.

In the manufacture of shoes, stiffeners are attached to the material, for example leather, forming the outer part of the shoe upper, to reinforce this outer part. Known shoe stiffeners exhibit a blend of properties, the intention being to provide a stiffener which will maintain the outer part of the shoe upper in shape during prolonged wear. Some stiffeners are made rigid, in an attempt to achieve this aim, so that they can only be deformed from the desired shape by application of a large force; however, when such stiffeners have been deformed they, usually, do not recover their original shape and the shoe upper remains, to some extent, in the deformed condition. Other stiffeners yield relatively readily under a deforming force but are elastic so that when the deforming force is removed, the stiffener springs back to its original shape, restoring the upper to the desired shape.

In the manufacture of shoes the upper is conformed to a last to impart the desired shape thereto. Toe end stiffeners (commonly referred to as "toe puffs") are commonly attached to a toe end portion of the outer part of the upper before the outer part of the upper is conformed about the last, this practice being simple and convenient. However, if a toe puff is to be attached to a shoe upper while the upper is flat, it is essential that the toe puff is flaccid, or can be readily rendered flaccid for the lasting operation, so that the toe end of the shoe upper can readily be conformed to the last, and further, that the toe puff should thereafter be set to the shape imparted to the toe end of the upper by the lasting operation whereby to retain the toe end of the upper in the desired shape.It is also important that the toe puffs have sufficient tensile strength. even when in the flaccid condition, to withstand the strains imposed on them during the lasting operation without tearing, while yet yielding sufficiently to conform to the desired shape.

Known toe puffs which have been used with a reasonable amount of success in the manufacture of shoes include textile fabrics impregnated with plastics material, the plastics material being softened by application of a solvent or by heat to render the toe puff flaccid so that it can be shaped during the lasting operation and the plastic, after removal of the softening agent. being stiff, to retain the shape of the toe portion.However, toe puffs softened by solvent are not very desirable to many shoe manufacturers because the solvent must evaporate (thus allowing the plastics material to reach its stiff condition) before the shoe can be removed from the last and evaporation of the solvent takes some time during which no useful operation can be carried out on the shoe; toe puffs comprising plastics material softened by heat harden when the toe puffs cool and this does not take very long but plastics materials softenable by heat at temperatures not harmful to the remainder of the shoe tend to be too soft and not sufficiently stiff at room temperature.

Plastics materials suitable for use in manufacture of toe puffs by impregnation of a suitable fabric also tend to be rather brittle (in order to give sufficient rigidity in combination with the textile material) and puffs including such plastics material tend to collapse when subjected to substantial pressures and not recover their desired shape; if less brittle plastics are used the puffs tend tohave insufficient rigidity to adequately support the outer part of the upper.

It is also known, see for example Patent Specifications Nos. 1063876 and 1083849, to make toe puffs out of sheets of plastics material without any textile reinforcement; however, plastics materials heretofore proposed, while being sufficiently shape retaining and resilient at room temperature, have not proved to be readily softenable (at temperatures which the remainder of the shoe could withstand) or where the plastics material could be readily softened for lasting it proved to be not ideally resilient and/or shape retaining or had less than ideal tensile strength for lasting, when in a flaccid condition. Problems were also encountered in sticking toe puffs of sheet plastics material to certain shoe upper materials.

The present invention provides a shoe stiffener comprising a mixture of acrylonitrile butadiene styrene polymer, polyvinyl chloride, nitrile rubber, and plasticiser for the polyvinyl chloride.

A shoe stiffener in accordance with the invention may include known additives for plastics materials of the type mentioned in amounts commonly employed, including fillers, for example inorganic fillers, e.g. whiting, carbon black, or fibres, e.g. short lengths of textile fibres, if desired.

Shoe stiffeners in accordance with the invention preferably do not exceed forty thousandths of an inch in thickness, more preferably thirty thousandths of an inch in thickness.

Each of the constituents of shoe stiffeners in accordance with the invention imparts certain properties. The polyvinyl chloride imparts stiffness. The acrylonitrile butadiene styrene copolymer also imparts some stiffness but is present primarily to give resilience. The plasticiser for the polyvinyl chloride is present to soften the polyvinyl chloride (also, usually, having a lesser plasticising capability in respect of acrylonitrile butadiene styrene) sufficiently for the stiffener material to be rendered sufficiently soft for lasting i.e. it improves the lastability of the material. The nitrile rubber imparts improved flexibility without affecting the stiffness of the material unduly and improves the resistance to cracking of the material (as compared with similar material not containing nitrile rubber); the nitrile rubber acts as a plasticiser for the mixture to some extent.Preferably, the amount of acrylonitrile butadiene styrene polymer incorporated in the mixture does not exceed 50% by weight of the mixtures, mixtures including over 50% by weight tending to be too brittle. In stiffeners in accordance with the invention the proportions of acrylonitrile, butadiene and styrene in the polymer are selected in accordance with the properties required in the final material, in accordance with the properties of the three components: for example styrene polymers are very hard and rather brittle, butadiene polymers are rubbery and tend to be sticky while acrylontrile polymers are rather hard, horny substances more tough than polystyrene.Acrylonitrile butadiene styrene polymers used in making materials in accordance with the invention are preferably quite hard, have good flexural strength (an important factor in toe puffs) and have reasonable resistance to impact.

One grade of acrylonitrile butadiene styrene copolymer which has proved satisfactory in making fairlv rigid toe puffs has a notched impact strength (measured by the test DIN 53453) of 11 KJ/m at 23"C, a tensile strength (DIN 53455) of 45 MPa, a flexural yield strength (DIN 53452-E) of 65 MPa, a ball indentation hardness (DIN 53456) of 82 MPa, and a Vicat softening temperature (DIN 53460/A) of 92"C; such an acrylonitrile butadiene styrene copolymer is available from Bayer U.K. Limited. Richmond, Surrey under the designation "Novodur" PH/AT ("Novodur" is a Registered Trade Mark). Toe puffs in accordance with the invention including such an acrylontrile butadiene styrene copolymer are rigid but have a slight tendency to crack after extended wear.Novodur PH/AT is a graft copolymer of general purpose type which is suitable, inter alia, for injection moulding. The tendency of toe puffs to crack may be reduced. along with a reduction in rigidity of the toe puff (assuming the other constituent remains the same), by using a high impact grade of acrylonitrile butadiene styrene copolymer, that is one having a higher butadiene content, instead of a general grade such as Novodur PH/AT.A high impact acrylonitrile butadiene styrene copolymer which has been found suitable for use has a notched impact strength (DIN 53453) of 16.7 KJ/m2, a tensile strength (DIN 53455) of 34 MN/m2, flexural yield strength (DIN 53452) of 55 MN/m2, a ball indentation hardness (DIN 53456) of 69 MN/m and a a Vicat softening temperature (DIN 53460) of 93"C; such an acrylonitrile butadiene styrene copolymer is available from Borg-Warner Chemicals U.K. Limited, York House, Clarendon Avenue, Royal Leamington Spa. Warwickshire, England, under the designation "Cycolac" LA ("Cycolac" is a Registered Trade Mark).

The polyvinyl chloride used in a stiffener in accordance with the invention is preferably a suspension polymer in the medium to high molecular weight range which is hard but is resistant to cracking at low temperatures. Materials having too high a percentage by weight of acrylontrile butadiene styrene polymer plus polyvinyl chloride are likely to be too stiff and rigid and insufficiently resilient for use as shoe stiffeners; it is therefore preferred that the weight of acrylonitrile butadiene styrene polymer plus the weight of polyvinyl chloride amounts to less than 76% by weight of the mixture.

The nitrile rubber used in stiffeners in accordance with the invention is conveniently a medium nitrile content nitrile rubber, for example containing between 30 and 35%by weight acrylonitrile, the balance being butadiene. Both the acrylonitrile butadiene styrene polymer and the nitrile rubber impart resilience to the stiffener in accordance with the invention; preferably the weight of acrylonitrile butadiene styrene polymer plus the weight of the nitrile rubber represent at least 64 % by weight of the mixture.

The nitrile rubber, as mentioned above, also imparts resistance to cracking of shoe stiffeners in accordance with the invention, during wear. It also aids in plasticising the material to give sufficient softness for good lastability. However, the efficiency of nitrile rubber in acting as a plasticiser for the material is not as great as some other plasticisers.

Plasticisers suitable for use in stiffeners in accordance with the invention are those used to plasticise polyvinyl chloride, for example phthalate plasticisers, e.g. dioctyl phthalate, or adipate plasticisers may be used. The amount of nitrile rubber plus plasticiser used conveniently lies between 20 and 30% by weight of the mixture; because of the need to provide a material which is readily softened to a lastable condition it is important to ensure that the mixture is sufficiently plasticised and a certain amount of the plasticser is required for this purpose - it is equally important, however, to obtain sufficient resistance to cracking which is imparted by the nitrile rubber and it is therefore necessary to strike a compromise between the inclusion of nitrile rubber and other plasticisers giving the best overall result.

A shoe stiffener in accordance with the invention may be stuck to the outer part of a shoe upper using a suitable adhesive. To obtain adequate adhesion to the surface of the stiffener it may be necessary to give the surface of the stiffener, or of sheet material from which the stiffener is made, a suitable pre-treatment to facilitate adhesion, before applying the adhesive layer, for example the surface of the stiffener may be wiped with a suitable solvent e.g. white spirit. Shoe stiffeners in accordance with the invention may conveniently comprise a film consisting principally of a mixture of acrylonitrile butadiene styrene polymer, polyvinyl chloride, nitrile rubber, and plasticiser for the polyvinyl chloride laminated with a lightweight textile material e.g. a scrim, for example of cotton.

Shoe stiffeners in accordance with the invention are preferably softened, for lasting, by the application of heat and for this purpose it is important to ensure that the mixture employed softens sufficiently for lasting at temperatures commonly employed in shoemaking, that is temperatures not harmful to the remainder of the shoe; it is also important to ensure that the softening point of the mixture is sufficiently high that the shoe stiffeners will not soften when exposed to conditions likely to be met after manufacture, for example prolonged exposure of the shoe to the sun in a shop window or exposure to a normal amount of heat from a domestic heating system.

Sheet materials from which shoe stiffeners in accordance with the invention may be made, may be made by known means for making plastics materials, for example the constituents may be mixed in solid form and supplied to a suitable extruder for extruding through a suitably shaped die or the materials in solid form may be supplied to the rolls of a calender and the sheet material by a calendering operation.

Shoe stiffeners in accordance with the invention may be used in shoes of many different types and it is important to select a blend of constituents giving a stiffener material having the properties desired in the shoe, for example, some shoes require a toe puff of a rigid nature which is difficult to deform by pressure whereas, on the other hand, other shoes require toe puffs which are readily deformable by pressure but which are resilient and return to their undeformed shape after the deforming pressure is released.

The invention further provides a shoe stiffener comprising a mixture of acrylonitrile butadient styrene polymer, polyvinyl chloride, nitrile rubber and plasticiser for the polyvinyl chloride, the acrylonitrile butadiene styrene polymer not exceeding 50% by weight of the mixture, the acrylonitrile butadiene styrene polymer plus the polyvinyl chloride amounting to less than 76%by weight of the mixture, the acrylonitrile butadiene styrene polymer plus the nitrile rubber amounting to at least 64%by weight of the mixture and the nitrile rubber plus plasticiser being between 20 and 30%by weight of the mixture.

There now follow detailed descriptions, set out hereinafter as Examples I to VII, ofshoe stiffeners, viz, toe puffs, and sheet materials from which the stiffeners may be cut. It will be realised that these materials and toe puffs have been selected for description to illustrate the invention by way of example and not by way of limitation of the invention.

Example I The following mixture was extruded to form a sheet about 0.025 inch thick: Constituent Parts by weight NovodurPH/AT 50 Polyvinyl chloride 22.5 Phthalate plasticiser 15.5 Nitrile rubber 12 100 The nitrile rubber used was Breon 1442, ("Breon" is a Registered Trade Mark) a medium nitrile rubber available from BP Chemicals (U.K.) Ltd.,Plastics Division.

The extruded sheet material (the first sheet material) was coated with a hot moIten polyester adhesive which was applied in molten condition to the surface and allowed to cool.

A toe puff was cut from the adhesive-coated sheet, the toe puff being illustrative of the invention. A rear edge portion of this first illustrative toe puff was skived, on the face opposite the adhesive coated face, to provide a tapering feather edge to the rear portion of the toe puff.

The toe puff was then positioned at a toe end portion of the shoe upper with the adhesive coated face against the material of the outer part of the shoe upper and the assembly was subjected to heat and pressure in a toe puff fusing press as commercially available from the Applicant Company.

The upper was lasted under normal lasting conditions using known lasting machinery for example as available from the Applicant Company and commonly used in the shoe manufacturing industry; before lasting the toe end portion of the upper (carrying the toe puff), the toe end portion was heated by steam in a toe puff lasting heater of a type commonly used in the shoe manufacturing industry, to soften the toe puff sufficiently for lasting. The toe puff was rendered sufficiently soft for lasting by exposure to the steam in the heater for a length of time generally similar to that used to soften the known plastics-impregnated textile fabric toe puffs.The illustrative toe puff softened sufficiently for lasting at about 70"C. On cooling the toe puff set in the shape of the toe end portion of the last to which it had been conformed and retained the toe end portion of the shoe in the desired shape. However, this illustrative toe puff was rather soft and, although being of acceptable resistance to cracking during wear, was barely of sufficient resilience to provide an acceptable toe puff. In the Satra flex test (in which a one inch wide sample of the material laminated to a polyvinyl chloride coated fabric upper material is flexed in a machine until the sample fails) the sample of the material made according to Example I failed after 25,000 flexes. The first sheet material, made according to Example I, had a hardness on the Shore D scale of 58.

Example II The following mixture was extruded to form a sheet about 0.025 inch thick : Constituent Parts by weight Novodur PH/AT 48.5 Polyvinyl chloride 28.2 Phthalate plasticiser 8.7 Nitrile rubber 14.6 100 The nitrile rubber used was Breon 1442 which is a medium nitrile rubber.

The extruded second sheet material was treated and coated with adhesive in the same way as the material made according to Example I and a toe puff cut therefrom incorporated in a shoe also in the manner hereinbefore described with reference to Example I.

The second sheet material had a hardness on the Shore D scale of 67 and failed after 18,000 flexes on the Satra flex test. In wear, the material gave a rigid toe but cracked after a relatively short period of wear. However, although the material cracked in wear, the toe of the shoe still retained its shape adequately when cracked.

Example 111 The following mixture was extruded to form a sheet about 0.025 inch thick : Constituent Parts by Weight Cycolac LA 45 Polyvinyl chloride 29.8 Phthalate plasticiser 5.4 Nitrile rubber 19.8 100 The nitrile ruber was Breon 1442.

The third sheet material, having the above noted composition, was treated and coated with adhesive as described above in relation to Example I and a third illustrative toe puff was cut from this third sheet material and incorporated in a shoe as described above in relation to Example I. The third illustrative toe puff incorporated in the shoe wore well and showed little or no tendency to crack during wear; it gave a firm toe, even on bulbous toe shapes, but nevertheless had a degree of resilience so that when deformed somewhat by applied pressure, it recovered its shape well when the deforming pressure was released.

This third sheet material made according to Example III had a hardness on the Shore D scale of 56 and excellent resistance to cracking when subjected to the Satra flex test, the sample cracking after 108,000 cycles. The third sheet material is considered to be superior, for use as a shoe stiffener, in most respects; to either the first or second sheet materials (made according to Examples land II).

Example IV The following mixture was extruded to form a sheet about 0.025 inch thick : Constituent Parts by Weight NovodurPH/AT 45 Polyvinyl chloride 26.6 Phthalate plasticiser 8.6 Nitrile rubber 19.8 100 The nitrile rubber was Breon 1442.

The extruded sheet material (the fourth sheet material) was treated and coated with adhesive as described previously in relation to Example land a fourth illustrative toe puff was cut from the fourth sheet material and incorporated in a shoe as hereinbefore described in relation to Example I. In wear the toe puff behaved satisfactorily giving a fairly rigid toe which retained its shape well under pressure and which, after deformation under moderate pressures, was sufficiently resilient to recover its shape. The fourth illustrative toe puff showed little or no tendency to crack in wear. In general the performance of the fourth illustrative toe puff was similar in wear to the third illustrative toe puff (made according to Example III).

The fourth sheet material had a hardness on the Shore D scale of 56 and completed 44,000 flexes before failure in the Satra flex test. In this test the performance of the fourth sheet material was not as good as that of the third sheet material but there appeared to be little difference in wear.

Example V The following mixture was extruded to form a sheet about 0.025 inch thick: Constituent Parts by weight Cycolac LA 45 Polyvinyl chloride 26.5 Phthalate plasticiser 8.5 Nitrile rubber 20.0 100 The nitrile rubber used was Breon 1442.

The extruded sheet material (the fifth sheet material) was treated and coated with adhesive in the same manner as the first sheet material. A fifth illustrative toe puff was cut from the fifth sheet material and incorporated in a shoe as hereinbefore described in Example I.

The fifth illustrative toe puff had excellent flex performance and showed no tendency to crack during wear over a protracted period. However, the fifth illustrative toe puff was too soft and lacking in resilience for use in most shoes and was only suitable for use in shoes having soft toes. The fifth sheet material had a hardness on the Shore D scale of 52. In the Satra flex test the fifth sheet material exceeded 200,000 cycles without failure.

Example VI The following mixture was extruded to form a sheet about 0.025 inch thick Constituent Parts by weight NovodurPH/AT 40 Polyvinyl chloride 34 Phthalate plasticiser 11 Nitrile rubber 15 100 The nitrile rubber used was Breon 1442.

The sheet material formed (the sixth sheet material) was treated and coated with adhesive in the manner hereinbefore described with reference to the first sheet material in Example I.

A toe puff (the sixth illustrative toe puff) was cut from the sixth sheet material and incorporated in a shoe in the same manner as described in Example I with reference to the first sheet material.

The sixth sheet material was similar in stiffness and resilience to the fourth sheet material; however, in wear the sixth sheet material showed a greater tendency to crack than did the fourth sheet material.

The sixth sheet material had a hardness on the Shore D scale of 60 and in the Satra flex test failed after 64,000 cycles.

Example VII The following mixture was extruded to form a sheet about 0.025 inch thick : Constituent Parts by weight Novodur PH/AT 44 Polyvinyl chloride 31 Phthalate plasticiser 10 Nitrile rubber 15 100 The nitrile rubber was Breon 1442.

The extruded sheet material (seventh sheet material) was treated and coated with adhesive in the manner described previously in relation to the first sheet material. A toe puff was cut from the seventh sheet material and incorporated in a shoe in the same manner as hereinbefore described in Example I with reference to the first sheet material.

The seventh illustrative toe puff was stiffer than the third and fourth illustrative toe puffs, though not as stiff as the second illustrative puff; however it had a greater tendency to crack in wear than did the third and fourth illustrative puffs, though not as great a tendency to crack as the second illustrative toe puff. Accordingly, where a very rigid toe is required, it may be preferred to the third and fourth illustrative toe puffs.

The seventh sheet material had a hardness on the Shore D scale of 60 and, in the Satra flex test, the seventh sheet material failed after 38,000 flexes.

WHAT WE CLAIM IS: 1. A shoe stiffener comprising a mixture of acrylonitrile butadiene styrene polymer, polyvinyl chloride, nitrile rubber, and plasticiser for the polyvinyl chloride.

2. A shoe stiffener comprising a mixture of acrylonitrile butadiene styrene polymer, polyvinyl chloride, nitrile rubber, and plasticiser for the polyvinyl chloride, the acrylonitrile butadiene styrene polymer not exceeding 50% by weight of the mixture, the acrylonitrile butadiene styrene polymer plus the polyvinyl chloride amounting to less than 76%by weight of the mixture, the acrylonitrile butadiene styrene polymer plus the nitrile rubber amounting to at least 64 % by weight of the mixture and the nitrile rubber plus plasticiser being between 20 and 30% by weight of the mixture.

3. A stiffener according to claim 1 wherein the amount of acrylonitrile butadiene styrene polymei does not exceed 50% by weight of the mixture.

4. A stiffener according to either one of claims 1 and 3 wherein the weight of acrylonitrile butadiene styrene polymer plus the weight of polyvinyl chloride amounts to less than 76 % by weight of the mixture.

5. A stiffener according to any one of claims 1,3 and 4 wherein the weight of acrylonitrile butadiene styrene polymer plus the weight of nitrile rubber amounts to at least 64 % by weight of the mixturc.

6. A stiffener according to any one of claims 1. and 3 to 5 wherein the amount of nitrile rubber plus plasticiser is between 20 and 30 % by weight of the mixture.

7. A stiffener according to any one of claims 1 and 3 to 6 wherein the nitrile rubber is between 30 and 35% acrylonitrile, the balance being butadiene.

8. A stiffener according to any one of the preceding claims wherein the plasticiser comprises a phthalate plasticiser.

9. A stiffener according to any one of the preceding claims wherein the plasticiser comprises an adipate plasticiser.

10. A stiffener according to any one of the preceding claims comprising a filler.

11. A stiffener according to claim 10 wherein the filler comprises an inorganic filler.

12. A stiffener according to claim 10 wherein the filler comprises fibres.

13. A stiffener according to any one of the preceding claims not exceeding forty thousandths of an inch in thickness.

14. X stiffener according to any one of the preceding claims of sheet material which has had a surface pretreatment, to facilitate adhesion, before application of an adhesive to the pre-trea ted surface.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. in the manner hereinbefore described with reference to the first sheet material in Example I. A toe puff (the sixth illustrative toe puff) was cut from the sixth sheet material and incorporated in a shoe in the same manner as described in Example I with reference to the first sheet material. The sixth sheet material was similar in stiffness and resilience to the fourth sheet material; however, in wear the sixth sheet material showed a greater tendency to crack than did the fourth sheet material. The sixth sheet material had a hardness on the Shore D scale of 60 and in the Satra flex test failed after 64,000 cycles. Example VII The following mixture was extruded to form a sheet about 0.025 inch thick : Constituent Parts by weight Novodur PH/AT 44 Polyvinyl chloride 31 Phthalate plasticiser 10 Nitrile rubber 15 100 The nitrile rubber was Breon 1442. The extruded sheet material (seventh sheet material) was treated and coated with adhesive in the manner described previously in relation to the first sheet material. A toe puff was cut from the seventh sheet material and incorporated in a shoe in the same manner as hereinbefore described in Example I with reference to the first sheet material. The seventh illustrative toe puff was stiffer than the third and fourth illustrative toe puffs, though not as stiff as the second illustrative puff; however it had a greater tendency to crack in wear than did the third and fourth illustrative puffs, though not as great a tendency to crack as the second illustrative toe puff. Accordingly, where a very rigid toe is required, it may be preferred to the third and fourth illustrative toe puffs. The seventh sheet material had a hardness on the Shore D scale of 60 and, in the Satra flex test, the seventh sheet material failed after 38,000 flexes. WHAT WE CLAIM IS:

1. A shoe stiffener comprising a mixture of acrylonitrile butadiene styrene polymer, polyvinyl chloride, nitrile rubber, and plasticiser for the polyvinyl chloride.

12. A stiffener according to claim 10 wherein the filler comprises fibres.

15. A stiffener according to any one of the preceding claims comprising a film consisting

principally of a mixture of acrylonitrile butadiene styrene polymer, polyvinyl chloride, nitrile rubber, and plasticiser for the polyvinyl chloride.

16. A stiffener according to claim 15 comprising a textile material with which the film is laminated.

17. A stiffener according to any one of the preceding claims comprising sheet material made by a process comprising extrusion of a mixture of the acrylonitrile butadiene styrene polymer, polyvinyl chloride, nitrile rubber, and plasticiser for the polyvinyl chloride.

18. A stiffener according to any one of claims 1 to 16 comprising sheet material made by a process comprising calendering a mixture of acrylonitrile butadiene styrene polymer, polyvinyl chloride, nitrile rubber, and plasticiser for the polyvinyl chloride.

19. A shoe stiffener comprising sheet material substantially as hereinbefore described with reference to one of the Examples.

20. A shoe stiffener substantially as hereinbefore described with reference to one of the Examples.