GB2220126A - Method for manufacture of thermoplastic long counters - Google Patents

Abstract

A method for the manufacture of thermoplastic long counters, having areas of different stiffness, comprises utilising a stiffening material formed from sintered powder having hot melt adhesive properties, applied to those areas of a hot melt adhesive coated thermoplastic counter which are required to be of increased stiffness. The counters may be manufactured in sheet form or as individual counters.

Description

METHOD FOR MANUFACTURE OF THERMOPLASTIC LONG COUNTERS This invention relates to a method for the manufacture of a thermoplastic counter for stiffening a heel end portion of a shoe upper. 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 it is a common practice to attach a stiffener to the material, for example leather forming the outer part of the shoe upper to reinforce this outer part. Known stiffeners exhibit a combination 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 shoemakers, especially makers of ladies' fashion shoes, prefer their shoe uppers to be supported by the heel end shoe stiffener, right through to the joint region of the shoe. Such a shoe stiffener is known as a "long counter.

The use of long counters in the manufacture of shoes in particular ladies' fashion shoes, is known to give a number of advantages, in particular improved shoe appearance, improved shape retention in wear, and a better clip to the wearer's foot.

Known long counters include leatherboard counters, solvent activated counters made from suitably impregnated non-woven textile fabrics, and thermoplastic counters.

Where long counters are made from leatherboard, it is required from the point of view of shoe design and comfort, as well as for ease of shoe-making, that there should be a gradation in the stiffness of the counter from the heel bowl to the joint region of the shoe. In leatherboard long counters, this gradation is achieved by deep skiving of the wings of the counter, which is then coated with adhesive.

When using leatherboard counters, the choice of adhesive is limited, in practice to water-based dipping adhesives (latex-type). These adhesives do not always give satisfactory adhesion.

The known solvent activated long counters have the disadvantage that they are inconvenient to handle, in particular the necessity to observe the stringent safety and environmental requirements of solvent handling.

In UK Patent Application No. 2 081 067, long counters are described which can be partially softened. The counters described are a combination of thermoplastic and solvent activated, and are less inconvenient to handle, although still involve solvent hazards.

It is also known to manufacture thermoplastic long counters. These known thermoplastic long counters have the disadvantage that they have to be heated and preshaped before insertion into the shoes, backpart moulded on long moulds to give the required shape over most of their length to form the heel end counter, allowed to stiffen and then reheated later with a special infra-red heater to shape the front wing portions of the counter. For the different sizes of shoe, different backpart moulds have to be provided, and the shaping of the stiffener cannot be carried out on the machinery which is used for the shaping of short counters, that is a backpart moulding machine with a standard mould, which machinery is generally available in shoe-making factories.

It is an object of the present invention to provide a method for the manufacture of long counters in which the above disadvantages are reduced or substantially obviated.

The present invention provides a method for the manufacture of a thermoplastic long counter having areas of different stiffness, which comprises utilising a stiffening material formed from sintered powder having hot melt adhesive properties, applied to those areas of a hot melt adhesive coated thermoplastic counter which are required to be of increased stiffness.

The thermoplastic long counters manufactured by the method according to the present invention have a number of advantages over the known long counters. By using the method according to the invention it is possible to produce a counter with graded stiffness from the bowl to the wings, which stiffness can readily be adjusted by control of the added powder. It is thus possible to produce a wider variety of reinforcement options than is possible with either deep-skived pre-moulded board stiffeners or with solvent activated stiffeners. The softer flexible wings of the counters manufactured by the method according to the invention allow easy waist lasting without re-heating. Any tendency to elastic recovery is relaxed during heat setting, and the wings then take on the shape of the last.

In the method of manufacture according to the invention, the stiffening material is applied to the substrate by known powder printing methods, such as curtain coating, mask printing, screen printing, or using a combined screen and mould system such as used in a USM Printing and Reinforcing Machine.

The counters may be produced in sheet form, or as individual counters.

Where the counters are to be produced in sheet form, the stiffening material is applied to the substrate by curtain coating or by mask printing. By selection of an appropriate curtain coating slot, and by allowing the powder to fall a distance before hitting the counter material, it is possible to obtain satisfactory edge graduation of the powder patch, thus avoiding the formation of a step at the edge of the patch, which step would be visible from the outside of the shoe.

In a preferred method of manufacture according to the invention, in which the counters are produced in sheet form by curtain coating, the powder is preferably deposited in bands on the substrate, the spacing of the bands being selected for economy of cutting, depending on the counter length required.

After application of the powder to the substrate, the powder is sintered. A preferred method of sintering comprises pressing and heating the substrate on which the powder has been deposited in a special through-feed heating press, using reusable release paper on one side if the substrate is single coated with adhesive, and on both sides if it is double coated.

In an alternative preferred method according to the invention for the manufacture of counters in sheet form, the powder zones are sintered selectively using infra-red graduation, by using appropriate lamp arrays and/or by shielding the rest of the base material. The powder zones can then be consolidated, while hot, by passing under a chilled roller.

The method of manufacture according to the invention can also be used for the manufacture of individual counters.

In this preferred method, the reinforcing powder patch is applied to counters which have already been cut.

In one embodiment the band of reinforcing powder is curtain coated or screen printed directly onto the pre-cut substrate shape, sintered selectively with infra-red radiation, and then simultaneously consolidated and shaped in a freezer-chilled mould.

In an alternative embodiment, individual counters are assembled by first making a reinforcing patch and then transfer laminating it in position on a pre-cut substrate shape. This method can suitably be carried out using a USM Printing and Reinforcing Machine in which a powder patch is screen printed onto a heated non-stick belt. It then passes under infra-red heaters and is sintered, before being precisely attached to the base shape, in a transfer moulding station, while it is still hot and sticky. The formation of a step at the edge of the patch is suitably avoided by having a shaped mould below the transfer belt and conforming the belt to this shape, by clamping against the powder screen, during the powder dispensing period. The USM Printing and Reinforcing Machine is described in UK Patent Application No. 2 136 324.

The stiffening material which is deposited in powder form in the method of manufacture according to the invention preferably has hot melt adhesive properties and must be thermoplastically shapeable and make an adhesive bond at a temperature of between 65 and 100C, preferably in the range 65 - 850C. It may comprise a single component which exhibits both stiffening and hot melt adhesive properties, or may comprise a blend of two or more components which blend exhibits both properties.

The powder may be of any suitable particle size, typically up to 1000; more preferably up to 600ss. Where the powder comprises a blend of two or more components, the different components are preferably of a comparable particle size.

Particularly preferred powder stiffening materials with hot melt adhesive properties include polycaprolactone, optionally in admixture with a filler, such as described in our co-pending UK Patent Application of even date No. (Folio 14720) and blends of Surlyn and ethylene vinyl acetate, which may also contain a filler. By a suitable choice of polymer and filler, polymer to filler ratio, and the coating weight applied the stiffness and properties of the finished counter may be varied, depending on the practical requirements.

The powder blend may further comprise other additives such as flow improvement additives, processing aids or pigments.

Suitable substrate materials include thermoplastic materials which are known for the manufacture of toe puffs and counters for shoes, for example the Tut flex T range of Toe Puff materials manufactured and sold by Emhart Materials UK Limited, of Leicester, England. These substrate materials are coated on one or both sides, depending on whether they are for use in unlined or lined shoes, with a hot melt adhesive.

The method of manufacture according to the invention will now be described with reference to the following examples.

Example 1 7 kg (70% by weight) of Ionomer Resin powder and 3 kg 130% by weight) of powdered EVA adhesive were tumbled together to produce a uniform mixture. The Ionomer Resin was Dupont Surlyn 8940, and the EVA powder was Dermil DR 336 with a melting point of 65 - 75"C. Both powders had a particle size in the range 0 - 600ss.

This powder blend was then curtain coated in a number of 10 cm wide bands onto 1.5 metre wide pre-coated Emhart Tuf flex N 245 H, by passing it on a conveyor below a powder sprinkler-coater of the type supplied by Web Processing of Whaley Bridge, Cheshire.

The coated powder was then sintered under infra-red lamps, arranged to heat the powder zones selectively to 100 - 1200C during the materials passage below them. The hot powder was then consolidated to the base material by passing through chilled nip rolls.

Example 2 5 kg (50% by weight) of polycaprolactone powder with a particle size of 0 - 500cur and 5 kg (50% by weight) of silver sand of similar particle size range were tumbled together to produce a uniform mixture. Patches of this powder mixture were then sprinkled onto the centre-back zone of pre-cut counter shapes of Tut flex N 245 H, by means of a special sprinkle coater, arranged to be switched on and off intermittently as the base counters passed below. The powder coated counters then passed into an automatic pre-moulding machine in which the powder patch and centre zone of the base material were sintered and heated with infra-red before passing into a freezer chilled mould system.

Example 3 8.4 kg (70% by weight) of polycaprolactone powder with a particle size of 0 to 500tri and a molecular weight of 50,000, and 4,8 kg (30% by weight) of pulverised fuel ash (PFA) with a particle size distribution of 5 to 350cm were tumbled together to produce a uniform mixture.

The powder blend was then curtain coated in bands on to a substrate, as described in Example 1,' and then sintered and consolidated as described in that Example.

Example 4 The powder blend prepared according to Example 3 was sprinkled onto individual pre-cut counter shapes as described in Example 2. The counter shapes were then further processed as described in Example 2.

The counters manufactured by the methods of Examples 1 to 4 have been incorporated in finished ladies shoes, and have produced excellent results.

In the finished shoe, the counters produce a very desirable graduation of stiffness from bowl to waist without any sign of print-through of the reinforced patch, and with the bowl region of the shoe back generally stiffer than would normally be achieved with an impregnated non-woven stiffener of the same gauge.

Claims (13)

CLAIMS:

1. A method for the manufacture of a thermoplastic long counter having areas of different stiffness, which comprises utilising a stiffening material formed from sintered powder having hot melt adhesive properties, applied to those areas of a hot melt adhesive coated thermoplastic counter which are required to be of increased stiffness.

2. A method according to claim 1 in which the counters are produced in sheet form.

3. A method according to claim 2 in which the stiffening material is applied by curtain coating or mask printing.

4. A method according to claim 3 in which the stiffening material is deposited by curtain coating in bands on a substrate.

5. A method according to claim 1 in which the counters are produced as individual counters.

6. A method according to claim 5 in which the reinforcing powder is curtain coated or screen printed directly onto a pre-cut substrate shape.

7. A method according to claim 5 in which a reinforcing patch is deposited in powder form on a temporary substrate and then transferred to a pre-cut substrate shape.

8. A method according to any of claims 1 to 7 in which the stiffening material comprises a blend of an Ionomer resin and ethylene vinyl acetate.

9. A method according to any of claims 1 to 7 in which the stiffening material comprises a blend of polycaprolactone and a filler.

10. A method according to claim 9 in which the filler comprises pulverised fuel ash or silver sand.

11. A method according to any one of claims 1 to 10 in which the powder has a particle size of up to 600it.

12. A method for the manufacture of a thermoplastic long counter substantially as herein described with reference to the Examples.

13. A method for the manufacture of a thermoplastic long counter substantially as herein described.