US3006177A - Leather - Google Patents

Description

United States Patent 3,006,177 LEATHER Norman Limon Holmes, Beverley, and Peter Bryan Curtis, Harrow-Weald, England, assignors to Richard Hodgson & Sons Limited, London, England, and The General Electric Company Limited, London, England, both British companies No Drawing. Filed Oct. 21, 1958, Ser. No. 768,536 Claims priority, application Great Britain Oct. 22, 1957 14 Claims. (Cl. 69-21) This invention relates to the preparation of leather for moulding or other manipulative operation.

In the preparation of leather for moulding or other manipulative operation, the conventional practice is to soak the leather in water in order to render it sufficiently pliant. After, for example, moulding, the leather must then be dried in order to set it permanently in the shape to which it has been moulded. Again, for example, sole leather which has been softened prior to stitching must be dried thereafter in order to restore its original more elastic form. Soaking and drying stages consume a considerable amount of time, and may even affect permanently and adversely the physical properties of the leather.

An object of the present invention is to reduce the total time necessary for the preparation of leather for moulding or other manipulative operation, which is reflected in a saving of labour.

A further object of the present invention is to provide a method of preparing leather for moulding or other manipulative operation which is designed to ensure that the original physical properties of the leather are retained as far as possible after working.

According to the present invention a method of moulding or otherwise manipulating leather comprises heating the leather under conditions effective to ensure that at least part of the combined or bound water present therein is temporarily freed whilst avoiding any appreciable evaporation from the leather, whereby the leather is rendered pliant, moulding or otherwise manipulating the resultant heated leather as required, and thereafterallowing the freed water present in the leather to re-enter into its combined or bound form.

The heating should be rapid and of short duration. It should be suflicient to ensure that the combined or bound water is freed for the purpose indicated whilst avoiding making the leather too hot to handle conveniently. Under ordinary atmospheric conditions, a temperature of the order of 60-90 C., dependent upon the type and condition of the leather, is envisaged.

- It may be advantageous to supplement the atmospheric cooling normally envisaged by means of applied cooling means.

The precise manner in which the combined or bound 3,006,177 Patented Oct. 31, 1961 Leather Trades Chemists, 1942, 26, pages 237 to 255, it has been stated that the combined or bound water present in leather is estimated as slightly over 50% of the hide substance.

The invention is applicable to both non-impregnated and impregnated leathers, the conventional impregnants comprising fats and waxes. In the latter instance it is of course necessary that the leather is heated to an extent suflicient to soften the thermoplastic impregnant used as dressing. No amount of bound or combined water liber-' ated will enable leather to be moulded or otherwise manipulated if any rigid impregnant associated therewith is not rendered plastic. 0n the other hand, it has been established that in the presence of an impregnant the amount of bound or combined water which is required to be liberated by the heat treatment in order that the leather shall be capable of being moulded or otherwise manipulated can be reduced. To this extent the liberated bound or combined water and the impregnant are complementary to one another but it is a basic feature of the present invention that the liberation of some bound or combined water is essential to its successful operation.

In a preferred form of the invention, dielectric heating is employed, ensuring a substantially uniform temperature throughout the leather being treated. Thus, the

leather may be heated by placing it for a period of, say, from 20 seconds to 1. minute in an electric field applied at frequencies of up to 100 megacycles. A frequency in the range of 10 to 50 megacycles is preferred. A gen- I erator providing a power density ranging between 10 leather.

The electric field may conveniently be applied between two parallel plates, on one of which the leather rests. Since the heating frees the combined or bound water in the leather, it may on occasions be undesirable for the leather to contact both plates because of the relatively high electric conductivity of the freed water, and therefore an air space may be left between the leather and the upper plate. Since, however, the presence of such an air space may assist the evaporation of freed water 3 from the leather, particularly if it is thin, which evaporanipulative operation of the leather has not been definitely I established. The water may well act as an interstitial lubricant. porarily dissolve or dilute any tanning material which cross links fibres and this removal of material then allows greater freedom of movement. t

The present invention thus involves the novel concept of temporarily releasing at least part of the combined or bound water present in leather, so that it may serve to liberate and lubricate the fibres whilst the leather is subjected to moulding or the like manipulative operation, and thereafter allowing the water to re-enter into its combined or bound state. In an article-entitled The Influence of Bound Water on the Equilibrium in Leather- Water Systems, by A. Cheshire and N. L. Holmes, published in the Journal of the International Society of Alternatively, or in addition, it may teme tion is to be discouraged, it may be found expedient to fill the air space with a layer of an electrically insulating material, such as mica, particularly when employing a Warm air blast to keep the plates free from atmospheric condensation. Further, the leather itself may be coated with a resin or other similar material to prevent loss of moisture.

If the leather is allowed to cool in air after moulding, several minutes may elapse before the leather has set in the shape to which it has been moulded. It may therefore be advantageous to carry out the moulding step using a water cooled mould.

The possibility of providing a generator adapted to serve also as a press is envisaged. Thus, the upper electrode may have a formed, insulating face and the two electrodes may be used to mould the leather to shape after heating.

Some guide to the interrelationship of the moisture content of the leather, the time of heating and the power density will be apparent from the succeeding table in the derivation of which specimens of non-impregnated dress- 3 ing hide, each measuring approximately 7" by 2 /2" and 4 mm. thick, and taken from hides which had been lightly oiled and thereafter subjected to atmospheric drying, were subjected to different times and varying intensities of heating. A constant RF voltage of 5.5 kv. at 20 megacycles was applied to the electrodes.

VISUAL APPEARANCE Weight of Water in Leather (Le. X gms. water/IOO- X Air 'H'Pafi'nn' gms. dry matter) Gap, Time, Ins. Secs.

20 gJlOO g. wet 25 g./l g. wet 30 gJlOO g. wet leather leather leather 30 Normal Normal Normal. 60 do do Do. syn.-. 120 do Slight internal D0.

gluclng. Normal Glueing at the centre. .....de Normal. do Do.

Slight sln-lnk- Drawn grain. ing; extract glueing at one en 180 do Shrunk; warped Exploded. and charred at one end. 30 d0 Slight shrink- Drawn and ing at one curled up at en one end. 60 .d0 Blown up at D0.

one end. 134'. 120 do Blown up and grain shrunk at both ends. 180 Very slight ex- Blown up and tract glueing charred at on flesh side. one end. 30 Normal 60 -.--.do d 120 Slight extract do glueing on flesh. 180 do d0 20 gms./ 100 gms. wet leather represents approximately the full combined or bound water content of the leather under examination and it will be apparent that the presence of free water in cold untreated leather may leadto damage to the leather on heating for more than quite short periods. Thus, generally speaking the upper limit of water present in the leather must not greatly exceed the extent of the bound water inherent in the leather. This will vary with the type of tannage but is normally 50% by weight of the hide substance. Any significant increase in the amount of free water present can very readily lead to rapid deterioration of the leather.

It is equally important to ensure that the leather is not too dry before being subjected to the heat treatment. Though dependent to some extent on the impregnaut content, leather which is too dry may crack.

Generally speaking, leather can be moulded effectively in accordance with the present invention if it is in equilibrium With an atmosphere having a relative humidity of between not less than 30% and not more than 85%. The following data exemplify typical operating conditions which may be encountered in the successful heat treatment of two different types of leather.

(1) Using a 20 megacycle generator supplying 5.5 kv. to electrodes presenting an air gap of 1", then the insertion of a 4 /2" diameter disc of impregnated leather of A" thickness (stearic acid as impregnant; 25 parts per 100 parts leather) resulted in a temperature rise in the leather of approximately 65 C. above ambient in a time of 30 seconds.

(2) A sample of non-impregnated dressing hide measuring 7 /2 by 2 /2 and being A" thick when placed between electrodes presenting an air gap of 1 /2" and fed with a voltage of 5.5 kv. at 20 megacycles resulted in a temperature rise of 52 C. in 30 seconds.

It must again be emphasised that these data are included by way of exemplification only. The optimum conditions for treating any particular type of leather must be determined by experiment.

The invention is capable of widespread application in the leather industry. Thus, the production of saddles for bicycles and horses, from heavy leathers is envisaged. Again, the invention is likely to find a ready application in the treatment of leather intended for soles for footwear and in the production of moulded uppers for footwear. The possibility is envisaged wherein a veldtschoen upper may be. moulded from a softened blank of leather using, for example, a pneumatic bag moulding technique wherein an inflated rubber diaphragm is employed to blow the leather blank into a wooden negative mould shape.

Again, the invention has obvious application in the production of cup washers of all descriptions and this particular aspect of the invention is exemplified in the following two examples.

Example 1.-Meth0d of producing 3" oak tanned cup leather Size of finished cup-33" outside diameter, 1'' deep, thick. Size of circle to be cut from leather-5. Thickness- 7 Time for dielectric treatment-35 seconds. Time left in mould--2 /z to 4 minutes dependent on type of leather.

Example 2.2" chrome ram leather Finished size3" outside diameter, 2" inside diameter deep, A thick. Size of circle to be cut from leather-6". Thickness- A Time for dielectric treatment 35 seconds. Time left in mould 2 /2 to 4 minutes dependent on type of leather.

We claim:

1. A method of manipulating leather which comprises heating the leather under conditions elfective to ensure that at least part of the bound water present therein is temporarily freed whilst avoiding any appreciable evaporation from the leather, whereby the leather is rendered pliant, manipulating the resultant heated leather as required, and thereafter allowing the freed water present in the leather to re-cuter into its bound form.

2. A method of manipulating leather which comprises first adjusting the moisture content of the leather such that it is in equilibrium with an atmosphere of which the relative humidity lies between 30% and heating the leather under conditions efiective to ensure that at least part of the combined water present therein is temporarily freed whilst avoiding any appreciable evaporation from the leather, whereby the leather is rendered pliant, manipulating the resultant heated leather as required, and thereafter allowing the freed water present in the leather to re-enter into its combined form.

3. A method of manipulating an impregnated leather which comprises heating the leather under conditions effective to ensure that at least part of the bound water present therein is temporarily freed whilst avoiding any appreciable evaporation from the leather and that the impregnant is softened, whereby the leather is rendered pliant, manipulating the resultant heated leather as required and thereafter allowing the freed water present in the: leather to re-enter into its bound form and allowing the impregnant to harden.

4. A method of moulding leather which comprises subjecting the leather to dielectric heating in order to libcrate temporarily at least part of the bound water present in said leather whilst avoiding any appreciable evaporation, whereby the leather is rendered pliant, moulding the resultant heated leather as required, and thereafter allowing the freed water present in the leather to re-enter into its bound form.

5. A method of moulding an impregnated leather which comprises subjecting the leather to dielectric heating efiective to liberate temporarily at least part of the bound water present in said leather whilst avoiding any appreciable evaporation and to soften the impregnant, whereby the leather is rendered pliant, moulding the resultant heated leather as required, and thereafter allowing the freed water present in the leather to re-enter into its bound form and allowing the impregnant to harden.

6. A method of moulding leather which comprises first ad usting the moisture content of the leather such that it is in equilibrium with an atmosphere of which the relative humidity lies between 30% and 85%, subjecting the leather to dielectric heating in ,order to liberate temporarily at least part of the bound water present in said leather whilst avoiding any appreciable evaporation, whereby the leather is rendered pliant, moulding the resultant heated leather as required, and thereafter allowing the freed water present in the leather to re-enter into its bound form.

7. A method of moulding leather which comprises supporting the leather between the electrodes of a dielectric heating apparatus, applying an electric field between the electrodes at a power density ranging between and 100 watts per cubic inch of leather and a frequency lying within the range 10 to 100 megacycles for a period of time of from 20 seconds to 1 /2 minutes in order to heat the leather and thereby render it pliant, moulding the resultant heated leather, and thereafter allowing the worked leather to cool and permanently set in its moulded shape.

8. A method as claimed in claim 7 in which the frequency is 20 megacycles.

9. A method of moulding leather which comprises supporting the leather on the lower of a pair of parallel plate electrodes forming part of a dielectric heating apparatus, interposing an electrically insulating material between the leather and the upper electrode, applying an electric field between the electrodes at a power density ranging between 10 and 100 watts per cubic inch of leather and at a frequency lying in the range 10 to 100 megacycles for a period of time of from 20 seconds to 1 /2 minutes in order to heat the leather and thereby render it pliant, moulding the resultant heated leather and thereafter allowing the worked leather to cool and permanently set in its moulded shape.

10. A method of moulding leather which comprises supporting the leather between the electrodes of a dielectric heating apparatus, applying an electric field between the electrodes at a power density ranging between 10 and 100 watts per cubic inch of leather and at a frequency in the range 10 to 100 megacycles for a period of time of from 20 seconds to 1 /2 minutes in order to heat the leather and thereby render it pliant, moulding the resultant leather by pressing it between the electrodes and thereafter allowing the pressed leather to cool and permanently set in its moulded shape.

11. A method of manipulating leather which comprises temporarily releasing at least part of the combined water present in the leather so that it may serve to liberate and lubricate the fibres by subjecting the leather to dielectric heating, whereby the leather is rendered pliant, manipulating the resultant heated leather as required, and thereafter allowing the worked leather to regain its original physical state.

12. A method of moulding leather which comprises placing said leather in an electric field applied at a frequency lying within the range 10 to megacycles until the leather becomes hot and pliant, manipulating the pliant leather to a predetermined shape and thereafter allowing the leather to cool in order to retain said shape.

13. A method of making leather cup washers which comprises placing a disc of leather in an electric field applied at a frequency lying within the range 10 to 100 megacycles until the leather becomes hot and pliant, manipulating the pliant leather disc into cup shape and thereafter allowing the leather to cool in order to retain said shape.

14. A method of moulding leather which comprises coating one surface of the leather with a resin to prevent loss of moisture from that surface, supporting the leather on the lower electrode of a dielectric heating apparatus with the coated surface uppermost, applying an electric field between the electrodes at a power density ranging between 10 and 100 watts per cubic inch of leather and a frequency lying within the range 10 to 100 megacycles for a period of time of from 20 seconds to IV: minutes in order to heat the leather and thereby render it pliant, moulding the resultant heated leather, and thereafter allowing the worked leather to cool.

References Cited in the file of this patent UNITED STATES PATENTS 2,321,131 Crandell June 8, 194

2,619,661 Hart Dec. 2, 1952 2,644,966 Juhola July 14, 1953 FOREIGN PATENTS 113,232 Australia May 30, 1941 608,537 Great Britain Sept. 16, 1948