GB2311250A

GB2311250A - Leather or leather substitute laminates

Info

Publication number: GB2311250A
Application number: GB9705613A
Authority: GB
Inventors: Paul Michael Fielden; John Frederick Loxston
Original assignee: Pittards PLC
Current assignee: Pittards PLC
Priority date: 1996-03-18
Filing date: 1997-03-18
Publication date: 1997-09-24
Anticipated expiration: 2017-03-18
Also published as: GB2311250B; GB9705613D0

Abstract

A leather or leather substitute laminate is made by bonding together a first layer of leather or leather substitute material and a second layer of woven synthetic or part synthetic material, for example Lycra{ spun elastomeric fibre, with the layers having an anisotropic elasticity property and arranged such that the axis or axes of minimum modulus of elasticity in the first layer extend at an angle of 45{ or less to that or those in the second layer. The elastic modulus and the elastic power of the second layer may be selected so that is high enough for the second layer to reverse at least a major part of the non-elastic portion of the leather extension on relaxation thereof.

Description

Leather or Leather Substitute Laminates This invention relates to laminates made by combining leather or leather substitute materials with a layer of synthetic backing material, to methods of production thereof, and to articles made from said laminates.

It has previously been proposed to laminate leather to a backing material consisting of a mixture of synthetic fibres and natural cotton fibres. Although this laminate material may provide good comfort and feel characteristics, we have determined that it has undesirable mechanical properties which mitigate against its use in the manufacture of shoes, gloves and other footwear or clothing, where the laminate is repeatedly flexed and stressed in use.

We have found that, by a suitable selection of the specific materials making up the laminate, and in particular their relative rheological properties we can provide a laminate which has highly beneficial mechanical properties lending it to use for the manufacture of shoes, gloves etc.

We have found that a laminate made of leather with a backing of structural synthetic fibre including elastomeric fibres has several advantages, in terms of the enhanced mechanical and/or wear characteristics. By suitable selection of the respective elastic moduli of the layers we can provide a laminate in which, following extension and/or flexing, the elastomeric backing layer on recovery can return the leather layer to the required shape. This means that softer grades of leather can be used, with the synthetic backing providing added strength and enhancing elastic recovery, which tends to reduce the amount of permanent plastic deformation of the leather as the shoe or other article is worn in.

Of particular importance in attaining these benefits are the relative alignment of the axis or axes of minimum modulus of elasticity and elastic recovery of the two layers.

Similar considerations apply to leather substitute materials although the base anisotropy of these materials is more regular and more easily defined.

Accordingly, in one aspect of this invention, there is provided a laminate comprising a first layer of leather or leather substitute secured to a second layer of woven synthetic or part synthetic material containing elastomeric fibres, characterised in that each of said layers has an anisotropic elasticity property, and in that the layers are oriented with respect to each other so that the axis or axes of minimum modulus of elasticity in the first layer extends at an angle of 450 or less to that or those in the second layer.

It should be appreciated that, in a natural animal skin, there may well be small areas, amounting to about 5% of the total, where the angular orientation of the axes of the minimum modulus of elasticity may differ locally with regard to the remainder by as much as 900. However this does not detract from the benefit of the process applied to the remaining majority of the skin.

In any natural skin the orientation of the fibres is such that the modulus of elasticity varies in different regions relative to a fixed axis normally taken to be the line of the backbone, and accommodates body, curvature and movement of the animal. In the tanned state the fibre orientation of curvature can be modified by a variety of means well known to those practised in the art so that the topographical distribution of the orientation of the axis or axes of minimum modulus of elasticity can range from generally parallel to the backbone to generally perpendicular to the backbone. Even so, there will be localised distortions particularly in the shank or axillae regions where the vector can lie up to approximately 450 from the principal direction of high modulus.

The maximum elastic recovery of the skin will usually be along the line of minimum modulus of elasticity. Thus, in a natural leather laminate, the second or backing layer is preferably aligned with its minimum modulus of elasticity parallel to the minimum modulus of elasticity of the leather layer. Its lower modulus vector will then be harmonised with the lower modulus direction in the leather layer.

This arrangement retains the basic characteristics of the leather.

Another important factor is the elastic power of recovery of the second or backing layer. This is ideally selected so that it is high enough to reverse at least a major part of the non-elastic portion of the leather extension. The power required will be naturally dependent on the modulus of the leather and its thickness.

There is a further consideration in selecting the second or backing layer. A relatively high initial modulus of elasticity in the second or backing layer and a high degree of continuous adhesion to the leather would give a laminate which when either bent with the leather side innermost or compressed in its principal plane, beyond the original relaxed position, would have a high tendency to form wave patterns or wrinkles. This can be minimised or reduced by having a non-continuous adhesive film and fabric of a sufficiently low modulus of elasticity not to cause the formation of such wrinkles when the leather is bent.

Preferably the axis or axes of minimum elastic modulus extend in substantially the same direction in each layer.

However, in certain circumstances it may be beneficial to provide a bias effect by orienting the layers at up to 450.

It will also be appreciated that, particularly where the first layer is leather, the orientation of the axis of minimum modulus of elasticity (or the vector of maximum elasticity) will vary at different positions on the hide or skin. For example, in leather produced for shoemaking, the axis may run along the backbone region in the centre of the hide or skin, whereas in the leg regions the axis may run at 300 or 400 to the backbone region. Thus, if a complete hide is laminated to a second layer in which the orientation of the axis of minimum modulus of elasticity is constant, the extent of alignment of the axes between the two layers will differ at different positions. In this instance, the relative orientation of the axes may be selected to optimise the mechanical/elasticity properties of the finished laminate taking into account its required use and the principal regions of interest in the finished laminate.

The laminate may be produced by laminating a whole or a substantial part of the hide, or selected parts only of the hide may be cut out and laminated. Thus the laminate may be produced in bulk and then shipped to the manufacturer of the end goods, or it may be produced on site by the manufacturer of the end goods, after cutting the leather or substitute into pieces.

The first layer may be selected from a wide range of materials. For example it may comprise natural leather which has been treated or formed to provide or maintain anisotropic elasticity properties. The processing and handling steps for producing such materials are well known to those skilled in the art.

Alternatively, the first layer may comprise a piece of synthetic leather material treated or formed to have anisotropic elasticity properties. By the term "synthetic leather material" is meant any material having leather or leather-like properties and capable of being used as a substitute therefor. A typical example is Microfibre, (TM) available from Du Pont, a synthetic suede material, and many more will be known to those skilled in the art, as will methods of producing anisotropic elasticity properties therein.

The first and second layers are preferably secured together by adhesive bonding. A wide variety of adhesives and methods of application may be used. Thus the adhesive may be applied by spraying, roller coating, knife coating, or applied to a release sheet and then attached to the layer, or applied by any other application method known to those skilled in the art. In one example, a liquid adhesive may be sprayed onto the back of the first layer and dried or allowed to dry to a low tack state so that a supply of said first layers may be stacked for storage, without bonding to each other. The adhesive-coated first layer and the second layer are then brought together in a press at an elevated temperature and pressure for a period sufficient to bond the two layers together.

A typical example of a suitable adhesive for bonding the layers together could comprise a mixture of acrylic copolymer dispersions and a polyurethane aqueous emulsion blended to provide a modulus compatible with the two layers of the laminate.

We have found that blends of: Acronyl 14D(BASF) 10-40 pts Acronyl 50D(BASF) 10-40 pts UW 99 (from Fenice, Valdagno, Italy) 5-30 pts Water to 100 pts are particularly suitable.

The pressing conditions should be selected with regard to the adhesive employed and the natures of the first and second layers. For example, where the first layer is leather of thickness 0.6/0.7mm, and the second layer is a 29%:71% Lycra/Nylon mix 0.4mm thick, and the adhesive used is of the class described above, the press temperature may lie in the range of from 900C to 1100C and ideally be around 1000C. The pressure may lie in the range of 50 kg/cm2 to 200 kg/cm2 and ideally be around 150 kg/cm2. The pressing period may lie in the range of from 2 sec. to 6 sec and ideally be around 4 sec.

The adhesive is preferably applied in an amount corresponding to between 30g/m2 and 50g/m2, and preferably around 40g/m2.

Preferably, in the finished laminate the adhesive layer is discontinuous, to allow water vapour to permeate through the laminate in use, and to reduce or minimise the possibility of wrinkling.

The second layer may take many forms. In one example it comprises a woven mixture of synthetic elastomeric fibres and polyester and/or polyamide fibres. We have found that the use of a wholly or substantially wholly synthetic second layer provides important mechanical and other advantages such as tactile satisfaction, hydrothermal comfort, wearer benefits and general longevity. An example of a suitable synthetic fibre is the synthetic spun elastomeric fibre sold under the Trade Mark LYCRA by Du Pont. However the invention also extends to laminates where the second layer consists of a mixture of synthetic elastomeric fibres and natural fibres such as cotton.

The mechanical properties of the two layers are preferably selected to be harmonious and consistent with the required properties of the laminate, and with those of the other layer.

We normally use a 2:1 or 3:1 leather & Lycra material thickness but these limits are not necessarily constrictive.

The invention also extends to a method of producing a laminate material as herein described, and to articles made from said laminate material. It will be appreciated that the laminate may include one or more additional layers either between the first and second layer, or to the other side of the second layer.

Whilst the invention has been described above, it extends to any inventive combinations of features set out above or in the following examples.

The following examples illustrate the present invention and are not intended to limit the scope of the invention in any way.

ExamPle 1 - Laminate of Water Repellent Aniline Hairsheep Shoe Leather with Sleeknit Fabric.

A first layer of water repellent aniline hairsheep shoe leather (0.7mm thick) with the maximum elasticity, (i.e. axis of minimum modulus of elasticity) running generally parallel to the backbone was laminated to Sleeknit fabric (0.4mm thick) available from Penn Nyla, Nottingham, UK, and comprising a 1%:29% polyamide elastane mix. The following adhesive mix was used: 300 pts Acronyl 300 pts Acronyl SOD 200 pts UW 99 200 pts Water The adhesive was sprayed onto the flesh side of the leather at a coverage rate of 35g/m2, and then allowed to dry. The Sleeknit fabric was placed onto the flesh side of the leather with the maximum elasticity (i.e. axis of minimum modulus of elasticity in the fabric running parallel to the backbone, and the layers pressed at 150 kg/cm2 for 4 seconds at 1050C.

This laminate would be suitable for a ladies fashion shoe with a simple construction (whole or 3/4 cut), for indoor and outdoor use.

Example 2 - Pigmented Hairshees Shoe Leather with Coolmax (TM) Fabric.

A layer of pigmented Hairsheep shoe leather (0.7mm thick), with the maximum elasticity (i.e. axis of minimum modulus of elasticity) running generally parallel to the backbone, was laminated with a 0.3mm thick layer of Coolmax 9TMO, available from Penn Nyla, Nottingham, and comprising an 84%:16% polyester elastane mix. The following adhesive mix was used: 250 pts Acronyl 14D 350 pts Acronyl SOD 200 pts UW 99 200 pts Water The adhesive was sprayed onto the flesh side of the leather at a coverage rate of 40g/m2, and then allowed to dry. The Coolmax fabric was placed onto the flesh side of the leather, with the maximum elasticity (i.e. axis of minimum modulus of elasticity) running parallel to the backbone and the layers pressed at 150 kg/cm2 for 6 seconds at 1000C.

This laminate would be suitable for a ladies comfort shoe, predominantly for outdoor use.

Example 3 - Aniline Hairsheet stortsqlove leather with Coolmax (TM) fabric.

A layer of aniline hairsheep sportsglove leather (0.4mm thick), with the maximum elasticity (i.e. axis of minimum modulus of elasticity) running generally perpendicular to the backbone, was laminated with Coolmax fabric (0.3mm thick), using the following adhesive mix: 350 pts Acronyl 14D 250 pts Acronyl 50D 200 pts UW 99 200 pts Water The adhesive was sprayed onto the flesh side of the leather at 30g/m2, and then allowed to dry. The Coolmax fabric was placed onto the leather with the maximum elasticity (i.e. axis of minimum modulus of elasticity) running perpendicular to the backbone and pressed at 100 kg/cm2 for 4 seconds at 950C.

This laminate would be suitable for manufacturing sports gloves.

Example 4 - Various Bovine Leather/Lvcra Laminates.

In this example, samples of Bovine leather (Bovine (Sirena) Grain Split, in various finishes, colours and shades, and Bovine Nubuck in various colours and shades) were laminated to a Lycra-containing material comprising 82% polyamide and 18% Elastane (Lycra) in a Powernet weave.

In each case a layer of the leather material (between 0.8 and 1.0 mm thick), with the maximum elasticity (i.e.

axis of minimum modulus of elasticity) running generally perpendicular to the backbone, was laminated to the synthetic layer (0.45 mm thick) using Mybond 3143, a single component polyurethane emulsion adhesive. The adhesive was sprayed at a coverage rate of 12-15 g/m2 onto both bonding surfaces and then allowed to dry. The Powernet material was placed onto the leather with the Lycra fibres (i.e. axis of minimum modulus of elasticity) oriented perpendicular to the backbone of the leather and then ironed, with steam, at 80 to 100C at a pressure of up to 2kPa.

This laminate would be suitable for ladies formal footwear and men's lightweight footwear.

Example 5 - Various Bovine (Sirena) Leather Lycra Laminates In this example, thicker layers of Bovine Sirena Leather were laminated to the Lycra-containing material of the same type as in Example 4.

In each case a layer of leather material (1.4 to 1.6 mm thick) with the maximum elasticity (i.e. axis of minimum modulus of elasticity) running generally perpendicular to the backbone) was laminated to the synthetic layer using Mybond 4143 adhesive. The adhesive was sprayed at a coverage rate of from 15 to 20 g/m2 onto both bonding surfaces, and then allowed to dry. The Powernet material was placed onto the leather with the Lycra fibres (i.e. axis of minimum modulus of elasticity) perpendicular to the backbone of the leather and the layers introduced into a plate press and pressed at 850C at a low pressure typically of less than 100 kg/cm2, for a dwell time of 2 seconds, with the pressing step repeated a total of three times.

This laminate is suitable for men's formal or semiformal footwear.

Example 6 - Lamination of Pre-Cut Leather Pieces In this example a stock of leather or leather substitute is cut into pieces of the required size and shape and is then laminated to a layer of woven synthetic or part synthetic material. A layer of woven synthetic or part synthetic material is pre-coated with an adhesive, for example a hot-melt adhesive generally in accordance with the conditions and composition of the previous examples. The shoe manufacturer is supplied with the hot-melt adhesive coated synthetic or part synthetic material in bulk, for example on a roll, and the laminate may then be formed without requiring prior application of adhesive to the cut leather pieces.

In this way, the synthetic or part synthetic layer may be selectively applied only to those pieces of the shoe requiring lamination, and parts of the shoe not normally subjected to flexing or not normally visible or which otherwise do not require lamination can be left unlaminated.

Laminating the leather after cutting also means that the axis of maximum stretch of the synthetic or part synthetic layer can be more exactly aligned to the local axis of maximum stretch of the leather or leather substitute material, whereas if the whole hide is laminated, any local variations in orientation of the axes of maximum stretch in the hide mean that alignment of the axes in the leather/ leather substitute layer and the synthetic layer is inevitably a compromise. Furthermore, when cutting a hide, there will inevitably be some wastage or material at the edges and, if the hide as a whole has been laminated, then there will be a corresponding wastage of the synthetic or part synthetic material as well as of the leather or leather substitute itself, and this wastage can be avoided by laminating only the required cut pieces of leather or leather substitute.

Claims

1. A laminate comprising a first layer of leather or leather substitute secured to a second layer of synthetic or part-synthetic material containing elastomeric fibres, characterised in that each of said layers has an anisotropic elasticity property, and in that the layers are oriented with respect to each other so that the axis or axes of minimum modulus of elasticity in the first layer extends at an angle of 450 or less to that or those in the second layer.

2. A laminate as claimed in Claim 1, wherein the second or backing layer is aligned with its minimum modulus of elasticity generally parallel to the minimum modulus of elasticity of the first layer.

3. A laminate according to Claim 1, wherein the second or backing layer is aligned with its minimum modulus of elasticity aligned at about 450 to the minimum modulus of elasticity of the first layer.

4. A laminate according to any preceding Claim wherein the elastic power of recovery of the second or backing layer is selected so that it is high enough to reverse at least a major part of the non-elastic portion of the extension of the first layer, on relaxation thereof.

5. A laminate according to any preceding Claim, wherein the second or backing layer has a relatively low modulus of elasticity compared to said first layer.

6. A laminate according to any preceding Claim, wherein the first and second layers are bonded together by a non-continuous adhesive layer.

7. A laminate according to any preceding Claim, wherein the first layer comprises the whole or a substantial part of an animal hide.

8. A laminate according to any of Claims 1 to 6, wherein the first layer comprises a pre-cut portion of an animal hide.

9. A laminate according to any preceding Claims, wherein said second layer comprises a woven mixture of synthetic elastomeric fibres and polyester and/or polyamide fibres.

10. A laminate according to any preceding Claims, wherein the ratio of the thicknesses of the first and second layers is in the range of from 2:1 to 3:1.

11. An article of footwear including a laminate according to any of Claims 1 to 10.

12. A method of producing a laminate which comprises bonding a first layer of leather or leather substitute to a second layer of synthetic or part-synthetic material containing elastomeric fibres, wherein each of said layers has an anisotropic elasticity property, and the layers are oriented with respect to each other so that the axis or axes of minimum modulus of elasticity in the first layer extend at an angle of 450 or less to that or those in the second layer

13. A method according to Claim 12, wherein said bonding comprises applying a liquid adhesive composition onto the back of at least one of the first and second layers and allowing it to at least partially dry, and thereafter bringing together said first layer and said second layer at elevated temperature and pressure to cause said layers to be bonded to each other.

14. A method according to Claim 13, wherein said adhesive is applied by one or more spraying, roller coating, knife coating, or by applying to one side of a release sheet which is then applied to said layer.

15. A method according to Claim 14, wherein said layers are pressed together at a temperature in the range of from 900C to 1100C and at a pressure in the range of from 50kg/cm2 to 200kg/cm2, for a period of between 2 and 6 seconds.

16. A method according to any of Claims 12 to 15, wherein the adhesive is applied at a rate of between 30g/m2 and 50g/m2.

17. A method according to any of Claims 12 to 16 wherein said first layer is of leather material.

18. A method according to Claim 17, wherein said first layer is a pre-cut piece of leather material.