WO2001016381A1

WO2001016381A1 - Treated leather

Info

Publication number: WO2001016381A1
Application number: PCT/GB2000/003248
Authority: WO
Inventors: Darryl Cassingham; Andrew Paul Hawkins
Original assignee: Pittards Plc
Priority date: 1999-09-02
Filing date: 2000-08-23
Publication date: 2001-03-08
Also published as: AU6853100A

Abstract

Leather is impregnating with a dry lubricant to provide improved physical properties such as water vapour permeability and absorption, abrasion resistance and improved grip characteristics. The dry lubricants disclosed are selected from the group comprising tungsten disulphide, molybdenum disulphide, boron nitride, talc, magnesium silicate, polytetrafluoroethylene (PTFE) and lubricant derivatives of the above. The treated leather may be used for clothing, gloves, footwear, and leather goods.

Description

Treated Leather This invention relates to treated leather and methods for treating leather and in particular, but not exclusively, to lubricated tanned leathers and methods for producing such leather.

There are many applications where a lubricated tanned leather is required, so that it can be used in products that require softness, stretchability and resilience. For many years the process of "fat-liquoring" has been used. This process involves adding oil, at a rate of between 1% to 30% of the tanned leather into the leather by agitation in a processing vessel or "drum". The fat-liquoring oil is usually sulphated or sulphited, to help it disperse within the leather fibre structure and to be more resistant to the effects of acids such as those found in sweat. Synthetic fat-liquors are sometimes used and these include synthetic esters, chlorinated hydrocarbons, and amphoteric derivatives .

Although fat-liquoring provides lubricity, it can also impart properties which are undesirable. For example too much fat-liquor can make the leather oily and give it a heavy feel. In addition, properties such as breathability, abrasion resistance and grip characteristics may also be limited. In many applications, such as for example the provision of gloves for golf or other sporting activity, breathability, abrasion resistance and grip characteristics are key properties.

Therefore there is a need for an improved treatment process and resultant leather which reduces or obviates the need for fat-liquoring, whilst providing enhanced properties such as, for example, softness, stretchability and resilience, and an improved feel compared to that provided by fat-liquors. In addition, we have found that by impregnating the leather with a "dry" lubricant enables a leather to be produced with improved physical properties, such as water vapour permeability and absorption, abrasion resistance and improved grip characteristics. These may be achieved without otherwise adversely affecting the performance or structure of the leather for the desired purpose.

Accordingly, in one aspect, this invention provides a treated leather, comprising leather impregnated with one or more dry lubricants selected from the group comprising: tungsten disulphide, molybdenum disulphide, boron nitride, talc, magnesium silicate, polytetrafluoroethylene (PTFE) and lubricant derivatives of the above.

In one preferred material, said dry lubricant comprises boron nitride alone. Preferably the leather is treated with an offer of between 1% - 10% by weight of dry lubricant, and more preferably between 2% to 6% by weight dry lubricant.

In another aspect, this invention provides a method of treating a tanned leather which comprises introducing into the structure of said leather one or more dry lubricants selected from the group comprising: - tungsten disulphide, molybdenum disulphide, boron nitride, talc, magnesium silicate, polytetrafluoroethylene (PTFE) and lubricant derivatives of the above.

The dry lubricant (or mixtures thereof) may be introduced into the leather by mixing with a re-tanning agent whereby particles of the dry lubricant are trapped in the internal fibre matrix of the leather, thereby internally lubricating the leather. The re-tanning agent is preferably a syntan. Examples of suitable syntans are formaldehyde condensates and resins based on acrylic, styrene, maleic anhydride, etc.

Preferably, the dry lubricant (or mixture thereof) is dispersed in the leather by means of a syntan or fat- liquor. In this case the syntan or fat-liquor is preferably offered to the leather in an amount equal to from 1% to 10% by weight of the dry leather, and more preferably between 2% to 6% thereof. Optionally, a further amount of fat-liquor may be added further to increase softness, in an amount between 10% and 30% of the dry weight of the leather.

The mixture of the dry lubricant and syntan or fat- liquor is preferably mixed with water and added substantially at the same time as the further amount of fat-liquor (if provided). The mixture of the dry lubricant and syntan or fat-liquor, together with the further fat- liquor (if provided) are preferably added to a drum or other processing vessel containing the leather and an amount of water. The amount of water may be typically 500% by weight.

The leather is preferably subjected to drumming or agitation at a solution temperature of around 50°C and preferably at a pH range of between 6.3 and 6.7 for a period of typically 45 minutes.

At the end of this period, formic acid or another suitable pH reducing fixative is added and the leather subjected to further drumming or agitation to complete the process. The fixative lowers the pH of the solution and causes fixation of the fat to the leather fibres. In another aspect, this invention provides a method of producing a dry lubricant leather which includes the following steps:- introducing the leather into a treatment vessel such as a rotatable drum, introducing water to the treatment vessel, introducing into said vessel a dry lubricant selected from the group comprising one or more of tungsten disulphide, molybdenum disulphide, boron nitride, talc, magnesium silicate, polytetrafluoroethylene (PTFE) or lubricant derivatives of the above, together with a syntan or fat-liquor and water, optionally adding a further amount of fat-liquor; subjecting the treatment vessel to a period of agitation for a period of time sufficient to cause an amount of the dry lubricant to be impregnated into the internal fibre structure of the leather, introducing into said vessel a pH reducing fixative agent such as formic acid, draining the drum of liquid contents, and rinsing said leather.

Where the dry lubricant is PTFE in any of the above aspects, it is preferably in the form of a loose agglomerate of finely divided PTFE powder, e.g. at micron or sub-micron size. A typical such material may have an average particle size of 12μm. The loose agglomerate may break down into smaller particles as it is impregnated into the leather and this can provide a beneficial fine distribution throughout the leather fibre matrix. A preferred material is Zonyl® MP 1000 marketed by DuPont.

The invention also extends to articles made wholly or partially of leather treated in accordance with this invention. Thus the leather so treated may be used in gloves, footwear, clothing, leathergoods such as suitcases, wallets, straps, etc, upholstery, saddlery, machinery, and in any other applications where lubricated leather is required.

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

A non-limiting embodiment of the invention will now be described by way of example only. Example 1

A batch of previously tanned skins (using a conventional tanning process such as chrome tanning) is introduced into a treatment drum, together with an amount of treatment water. Boron nitride in the form of a dry powder is offered to the leather at an amount of between 1% to 10% of the weight of the dry leather. The boron nitride is pre-mixed with an amount of an syntan or a fat-liquor, for dispersing the dry lubricant through the leather matrix, at an amount equal to between 1% to 10% of the weight of the dry leather. If required, an amount of fat- liquor is added to further increase softness at a rate of between 10% and 30% of the dry weight of the leather. The dry lubricant and syntan/fat-liquor mixture, and the further fat-liquor (where used) are mixed with water at a ratio of 4:1 (water : fat-liquor) at 60°C, and added at the same time as the dry lubricant suspension which is added with water at 60°C, in the ratio 4:1 (water: suspension). The mixture is then added to the drum which contains 500% (by weight) of water at 50°C and typically at a pH range of between 6.3 and 6.7. The leather and mixtures are drummed for typically 45 minutes, after which 2.5% (by weight) of formic acid is added and the drumming is continued for another period. At this point the dry lubricant has been distributed and trapped between the internal leather fibres, producing a resultant product that is soft and supple due to the distributed dry lubricant. Where added, the further fat-liquor component contributes additional softness and suppleness to the product.

The product so obtained exhibited softness, stretchability, increased abrasion resistance, increased breathability, increased grip and further can be dyed into a shade as the boron nitride does not significantly discolour the leather or inhibit absorption of dye.

Due to the dry lubricant particles being distributed throughout the leather fibres, the leather is more resilient as can be determined by increased abrasion resistance. Also, because of the reduction in oily fat- liquors, and the presence of the dry lubricant, the water vapour permeability and water vapour absorption characteristics are improved. Due to the distribution of the dry lubricant particles throughout the leather fibre structure, the ability of the leather to "grip" in wet conditions is much improved, and this is especially useful in a glove product such as for golf.

The leather so produced may be used for a wide range of applications although it is particularly well adapted for sports gloves.

In order to impregnate the leather with other dry lubricants the process and parameters outline above in relation to boron nitride may be adopted with some modification as desired to modify the qualities or feel of the leather. In one system the leather may be impregnated with a fluoro additive of PTFE powder offered in the same rate as the boron nitride, i.e. from 1% to 10% rate and the same process used to incorporate the PTFE powder with the leather matrix. A particularly suitable PTFE powder is that marketed by DuPont under the Trade Mark Zonyl© MP 1000.

Claims

1. A leather treated with one or more dry lubricants selected from the group comprising: tungsten disulphide, molybdenum disulphide, boron nitride, talc, magnesium silicate, polytetrafluoroethylene (PTFE) and lubricant derivatives of the above.

2. A leather according to Claim 1, wherein said dry lubricant comprises boron nitride.

3. A leather according to Claim 1 or Claim 2, wherein the leather is treated with an offer of between 1% to 10% by weight dry lubricant.

4. A leather according to Claim 3, wherein the leather is treated with an offer of between 2% and 6% by weight dry lubricant .

5. A method of treating a tanned leather which comprises introducing into the structure of said leather one or more dry lubricants selected from the group comprising: tungsten disulphide, molybdenum disulphide, boron nitride, talc, magnesium silicate, polytetrafluoroethylene (PTFE) and lubricant derivatives of the above.

6. A method according to Claim 5, wherein said one or more dry lubricants are introduced into the leather by mixing with a re-tanning agent whereby particles of the dry lubricant are trapped in the internal fibre matrix of the leather, thereby internally lubricating the leather.

7. A method according to Claim 6, wherein the re-tanning agent is a syntan.

8. A method according to Claim 7, wherein said syntan is selected from formaldehyde condensates and resins based on acrylic, styrene, maleic anhydride.

9. A method according to any of Claims 5 to 8, wherein said one or more dry lubricants are dispersed in the leather by means of a syntan or fat-liquor.

10. A method according to Claim 9, wherein the syntan or fat-liquor is offered to the leather in an amount equal to from 1% to 10% by weight of the dry leather.

11. A method according to Claim 10, wherein the syntan or fat-liquor is offered to the leather in an amount of between 2% and 6% by the weight of the dry leather.

12. A method according to any of Claims 6 to 11, wherein an amount of fat-liquor is applied further to increase softness .

13. A method according to Claim 12, wherein said fat- liquor is offered in an amount between 10% and 30% of the dry weight of the leather.

14. A method according to Claim 12 or Claim 13, wherein the mixture of the dry lubricant and syntan or fat-liquor is mixed with water and added at substantially the same time as the further amount of fat-liquor.

15. A method according to any of Claims 5 to 14, wherein the leather is preferably subjected to drumming or agitation at a solution temperature of about 50°C.

16. A method according to any claims 5 to 15, wherein the solution is maintained at a pH range of between 6.3 and 6.7.

17. A method according to Claim 16, wherein following said drumming and agitation a pH reducing fixative is added and the leather subjected to further drumming or agitation.

18. A method of producing a dry lubricant leather which includes the following stages: introducing the leather into a treatment vessel such as a rotatable drum, introducing water to the treatment vessel, introducing into said vessel a dry lubricant selected from the group comprising one or more of tungsten disulphide, molybdenum disulphide, boron nitride, talc, magnesium silicate, polytetrafluoroethylene (PTFE) or lubricant derivatives of the above, together with a syntan or fat-liquor and water, optionally adding a further amount of fat-liquor; subjecting the treatment vessel to a period of agitation for a period of time sufficient to cause an amount of the dry lubricant to be impregnated into the internal fibre structure of the leather, introducing into said vessel a pH reducing fixative agent such as formic acid, draining the drum of liquid contents, and rinsing said leather.

19. A leather treated in accordance with any of Claims 5 to 18.

20. A glove made wholly or partially of a leather according any of Claims 1 to 19.

21. An article of footwear made wholly or partially of a leather according any of Claims 1 to 19.

22. An article of clothing made wholly or partially of a leather according any of Claims 1 to 19.

23. An article of furniture upholstered wholly or partially of with leather according any of Claims 1 to 19.

24. Leathergoods made wholly or partially of a leather according to any of Claims 1 to 19.