Process for improving the surface yield in the fabrication of ta

Details Process for improving the surface yield in the fabrication of ta Process for improving the surface yield in the fabrication of ta

1997-04-02

1998-11-03

Diamond, Alan

Bleaching and dyeing; fluid treatment and chemical modification

Treatment of hides, skins, feathers and animal tissues

Tanning

69 21, C14B 126

Patent

active

058302387

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/ES96/00017 filed Jan. 1, 1996.
The present Invention refers to a process for increasing the area yield and adaption of the elasticity modulus in the manufacture of leather, applicable after the tanning, dyeing or fatliquoring process, and before the drying operation.
In the manufacture of leather, raw material, hides and skins, are mainly bougth by weight while the finished product is generally sold by area. Thus, any process which manages to increase the area yield in conventional manufacturing is of great economic interest.
Practically all the operations in the manufacture of leather can have a positive or negative effect on the area yield of the finished product. In the drying process, for example, by previously treating the skin in a vacuum dryer or stretching it on a plate, a better area yield will be achieved than by drying it in the open air, although, with this process some characteristics can be obtained which are otherwise difficult to obtain by other methods.
The treatments used, in the stretching system, aims, in addition to gaining area, to achieve certain organoleptic characteristics. The improvement in area is apparent, then gradually disappears during the later finishing processes, especially when the leather is re-dampened and dried again. Likewise, this improvement partially or completely disappears during storing of the finished product.
The procedure of the present invention consists of a thermal treatment on damp leather previously spread or stretched, with the special feature that during the said treatment no significant loss in the leather's water content is produced.
After tanning, dyeing or fatliquoring and before the drying process, the leather is spread and/or stretched by one of the known methods, for example on perforated frames with manual or automatic stretching on similar plates to those used in "pasting" drying, etc., or simply placed between boards or laminates which keep it extended.
Whatever the case, the tension to apply will mainly depend on the type of leather and its final use; for example, for grain leather, linear stretching will be between 5% and 25%, and for suedes, splits and leathers which require low elasticity, the enlargements may be greater.
The leathers prepared in this way undergo a thermal treatment in an open or closed container, with the possible addition of water or water vapour, in order to maintain the leather's water content and the temperature of the leather/water/air throughout the treatment.
The temperature applied for the thermal treatment will depend on the characteristics of the leather and its final use, but it will be between 40 and 100 degrees centigrade, preferably between 50 and 90 degrees centigrade, for a period of between 2 minutes and several hours, preferably between 10 and 30 minutes.
If after this treatment, object of the present invention, the leather proceeds to the drying process, this may be done by any of the conventional methods, even on the stretched leather, although it is preferable to reduce the tension applied before proceeding to a conventional drying method.
Being a specific procedure for increasing the area yield of the leather, the verification of its efficiency is relatively simple, it is enough to apply it to whatever conventional leather manufacturing system, without modifying the rest of the process at all, comparing the area yield results.
The improvement in the area yield obtained by this treatment, object of the present invention, is between 5 and 15% for conventional processes for leathers in which the grain elasticity must be controlled. The values mentioned may be greater in the case of suede leathers and splits, and in cases when leathers with reduced elasticity are required, to be used, for example, in clothing, upholstery and some types of footwear.
As a result of the thermal treatment applied, the fixation of the different products is also improved, as is the application of dyestuffs and fats substances used in the elaboration of leather, which can be seen as a general

REFERENCES:
Thorstensen, Practical Leather Technology, pp. 248-251, 1976.
The Oxford English Dictionary, Second Edition, vol. XX, pp. 170-176. (Month Unknown), 1989.
Thorstensen, "Practical Leather Technology." 1976, pp. 214-215.

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