US2767043A - Process for tanning skins - Google Patents

Description

Oct. 16, 1956 A. E. USHAKOFF 2,767,043

PROCESS FOR TANNING SKINS Filed Jan. 12, 1953 V INVENTOR. ALEXIS E. USHAKOFF gzmgw, 3 4m 11412:

ATTORNEYS United States Patent PROCESS FOR TANNING SKINS Alexis E. Ushakolf, Beverly, Mass, assignor to Secotan, Inc., Somerville, Mass., a corporation of Massachusetts Application January 12, 1953, Serial No. 330,632

14' Claims. (Cl. 8-15059' The present invention relates to the tanning of animal skins and the like and provides improvements to tanning processes during which a water-miscible organic solvent is forced through the skin to extract and replace the water. Such processes applied to the formafion of molded hollow leather articles are disclosed in my U. S. Patent No. 2,582,298 and my copending application Ser. No. 233,923 filed June 27, 1951, now Pat. No. 2,704,238; and applied to the production of flat leather in my copending application Ser. No. 233,924 filed June 27, 1951, now Pat. No. 2,702,229.

In these tanning processes a water-wet skin is supported on a porous surface of a filter material such as wool felt, plaster of Paris or other material of equivalent fine porosity. The surface may be flat to form flat leather, or concave to form hollow leather articles. A watermiscible organic solvent is then forced through the skin and the supporting surface until substantially all the Water in the skin has been extracted. Thereafter the skin is treated under substantially non-aqueous conditions until it is finally tanned, as by forcing tanning agents, and neutralizing agents through the skin and the supporting member. In this manner, the time required for complete tannage is reduced to a few minutes, and in addition, the skin may be dried rapidly without the precautions necessary to produce soft pliable leather from skins treated in aqueous tanning solutions, and without being fat liquored.

A difficulty sometimes encountered in such processes arises from the fact that the water-wet skin is not uniformly permeable. When the solvent is applied, it first permeates the more permeable regions, extracting the water from them and rendering them even more permeable. Thereafter, the solvent applied to the skin tends to channel through these regions leaving other regions substantially untreated. A further difliculty which results from the forcing of the tanning agents through the skin while it is supported on a porous surface of a filter material, such as wool felt, plaster of Paris or material of equivalent fine porosity, is the precipitation of tanning agent in the pores of the supporting surface which clogs them. Such finely porous materials are desirably used to support the skin during the solvent treatment since they may be formed with a smooth appearing surface. As pointed out in Patent No. 2,582,298 the configuration of the surface is imparted to the skin during the solvent extraction operation and this fact rules out the use of more coarsely porous materials. The present invention overcomes these difficulties and in addition reduces the number of steps performed in the apparatus in which the skin is supported, thus enhancing the productivity of the apparatus.

According to this invention the skin, prior to treatment with the organic solvent, is treated with an aqueous solution of an inorganic or mineral tanning agent, and if desired the tanning agent is neutralized in the skin. Alternatively, the tanning agent is left unneutralized in the skin to be subsequently neutralized after the water has been extracted. V

The effect of such a treatment is to improve the permeability of the skin and render is substantially uniform.- Thus, not only is selective extraction of the water in the more permeable regions avoided, but less solvent is required for the extraction. In addition, the Water Wet skin, although containing tanning agents, is still semiplastic like an untanned skin, and it may be molded to form hollow articles, such as shoe uppers, in the manner disclosed in my U. S. Patent No. 2,582,298. Apparently the skin does not become finally tanned until it has been dried.

It will further be seen, that, because the tanning agents are incorporated in the skin before it is further treated on the supporting porous surface, the tanning agents are not forced through the porous support and the danger of their precipitating in the pores is avoided.

An additional feature which may be used with the process of this invention is the incorporation of a fatty acid in the skin after the water has been extracted and before the skin has been dried. This is accomplished by dissolving a fatty acid in a suitable solvent and forcing the solution through the skin while it is supported on the porous surface, and results in a marked increase in the tensile strength of the skin without rendering it greasy. If on the other hand, the skin is dried without the addition of a fatty acid, the subsequent addition of fatty acid does not substantially enhance the tensile strength but renders the skin greasy in feel and appearance. Ordinary fat liquoring compounds, such as neetsfoot oil, may also be added to the skin, but Without imparting the beneficial effects of the fatty acid. The efiects of fat liquoring are thus realized in the process of this invention, While the critical control over pH necessary for fat liquoring by the conventional aqueous tanning operations, is avoided.

In general, this invention consists first in treating a skin, which may be pickled, bated, or fresh, with an aqueous tanning bath of an inorganic or mineral tanning agent such as chrome, iron, titanium, zirconium, or the like compounds, to introduce the tanning agent into the skin. Preferably, to accelerate the treatment, the temperature of the bath is increased and maintained at a point about 20 F. below the shrinkage temperature of the skin. The aqueous treatment may terminate with the neutralization of the tanning agent in the skin, as by the addition of a base to the tanning bath, or if desired neutralization may be delayed until after the skin has been dehydrated with the organic solvent.

After the tanning agent has been incorporated in the skin and While the skin is still wet, it is placed on and in contact with a supporting porous surface and the organic solvent is forced through it to extract the water.

The skin is then treated with an organic solvent solution of a fatty acid, and dried. If the tanning agent has not been neutralized prior to dehydration, a base may be added to the organic solvent used for dehydration, or if desired, dehydration may be followed by a separate treatment of the skin with an organic solvent solution of a base, or the base may be included in the fatty acid solution.

It will be apparent from the foregoing general description that this invention lends itself to a multitude of variations. In the following examples, representative and preferred embodiments of this invention as applied to the production of molded shoe uppers are described in detail.

In the drawings:

Fig. 1 shows in cross-sectional elevation a suitable mold for forming shoe uppers, and

Fig. 2 is a perspective view of a typical shoe upper produced by the process of this invention.

7 Example 1 A wet bated skin was pickled, then treated in an aqueous tanning bath and neutralized to insolubilize the tanning agents and washed in Water. While still freshly wet,

a blank'of the skin was molded, dehydrated while in the V material, sold by Diamond Alkali Corp., Cleveland, Ohio,

and having the following analysis:

removed from the mold and dried in the air to render it completely and permanently tanned.

' ExampIe'Z A wet bated skin was pickled, treated in an aqueous tanning bath, then molded and dehydrated in the mold.

The tanning agent in the molded blank was then'neutralized in the mold, and the skin was finally fat liquored and dried. a e

The skin was treated as described in: Example 1, supra, to the point just after; the tanning agent was added to the drum and allowed to penetrate through the skin. Without neutralizing the tanning agents, the skin was re- V moved from the drum and cut intov appropriate blanks Percent CI'zOs i 23.5 Hydrolyzable SOs 20.8 A1203 1.6 NazSOa 51.8 Basicity 42-44 was dissolved in hot water to a concentration of about 20% by weight and added to the drum, and the skin was tumbled until thetanning solution had fully penetratedthe skin during which time the tannning bath was heated to about 140 F. as the shrinkage temperature of the skin rose to about 160 F. Sodium bicarbonate was thenadded slowly to the drum until the pH of the solution reached 3.8-4.0 during which time the tanning bath was heated to about 160 F. The skin was then removed from the drum, washed infresh water to remove excess dissolved salts, and cut into blanks of appropriate shape and size to fit the mold.

A blank of the skin was then placed in the apparatus shown in Fig. 1 to be molded. The apparatus consisted of a box-shaped casing 10 containing the mold 12 and provided with a cooperating cover 14 having a fluid inlet tap 15. The casing 10 engaged the cover 14 along 'a peripheral flange 16, and supported the mold at its marginal edge on a recessed peripheral shoulder 17. The

' mold was constructed of a. porous material, such. as

plaster of Paris or other suitable ceramicmaterial, and was provided with a concave molding surface accurately conforming to the shape of a shoe last. Inthe construction shown the mold was supported on the shoulder 17 of the casing10 on a soft gasket '18, while the body of the mold rested on sand 19 with which the casing 10 was filled. A discharge connection 20 covered witha screen 22 connected into the bottom of the casing '10-atany convenient location. I 7 r The cover 14 engaged the casing along its marginal surface 21 which cooperates with the flange 16 of .the

casing.

The wet skin 23 was placed over the mold with its marginal edges overlying the peripheral flange 16,- and the cover was clamped in position by conventional means V slowly, but as the water was extracted by the acetone the flow increased considerably. The. flow of acetone was continued until the skin was substantially dehydrated as was indicated by a specific gravity no more than 0.792 at 70 F. for the acetone. was next fat liquore'dby forcing an acetone solution containing 7% by weight of oleic acid through the skin while itwas; supported in the. mold. The blank then in the molded form of;a.1shoe upper, as shown in Fig. 2, was;

The dehydrated molded blank' which were molded and dehydrated in the manner described in Example 1. The molded and dehydrated skin was then simultaneously neutralized and fat liquored by forcing through it 500 cc. of an acetonesolution containing 7% by weight. of oleic acid. and 10 cc. of triethanolamine. The skin was then removed from "theimold and dried to render. itcompletely and permanently tanned. i

Example 3 A pickled calfskin was treated in an acidic aqueous tanning bath then, before'the tanning agent was neutralized, removed from the bath, and cut into shoe upper blanks. A blank, while Wet with water, was then molded to shoe upper form, dehydrated, neutralized, fat liquoredf and dried.

A pickled calfskin was drummed in twice its weight of 7 an aqueous solutioncontaining 4 percent by Weight of salt and having a pH of-1 .8'imparted; by adding sulfuric acid. When equilibrium was reached, 10 percent, based A blank cut from the skinand wet with water was A V molded .under the pressure of acetone, and-dehydrated as described in Example 1. a Following the dehydration, the

tanning agent in the skin was. neutralized by forcing through the skin'whilestill in the mold, a solution consisting of: a

V 'Cc. Ammonia (concentrated commercial) 75 Acetone 500 The molded blank was finally fatliquored with oleic'acid as described inExample 2,"removed from the mold and dried. i

'The' foregoing examples describe 'indetail a representative few of the methods by which this invention may be practiced, and show the latitude in which the various stepsmay -be varied. For instance, neutralization of the skin maybe .carried'out before, after or While 'the skin is molded. It will also be. understood that inorganic or mineral tanningagents, other than chromium salts maybe used in invention, and that water-miscible organic solvents other than acetone may be used for the dehydration andv subsequent treatment, including lower aliphatic alcohols, and water-miscible polyalcohols, ethers,

andesters, examples of which are given in my-copending application:Ser. No. 233,923 filed June 27, 1951. Similarly, fatty acids other than oleic may also be used for the; improved fat liquoringstep, including stearic acid, lauric acid; palmitic acid and the like.

It willalso be appreciated that for the purposes of this invention, the skin after dehydration need not beabsolutely anhydrous, nor must the organic solvent solutions subsequently applied to the skin, so longas substantially 7 all the. Water-is out of theskin. In this connection a skin- 7 containing-less than about- 20%"by weightof water may be considered to'be dryfor purposes of this invention.

Although this invention has beendescribed in detail with reference to the formation of shoe uppers, other leather articles, both molded and flat, may obviously be produced without departing from the scope of the invention.

This application is a continuation in part of my copending applications Ser. Nos. 233,923 and 233,924 both filed June 27, 1951.

Having thus disclosed my invention and described in detail representative examples of the best manner known for practicing the invention, I claim and desire to secure by Letters Patent:

1. In the method of tanning animal skins and the like wherein a water-wet skin is extracted of Water by forcing an inert water-miscible organic solvent through the skin in an amount sufiicient to extract and replace substan tially all the water with the solvent, a mineral tanning agent is incorporated in the skin and the skin is finally dried of solvent with the mineral tanning agent neutralized therein: the improvement comprising contacting the skin with an aqueous solution of a mineral tanning agent to distribute the tanning agent throughout the skin before the water in the skin is extracted and replaced with the organic solvent, thereafter supporting the skin upon and in conformity with a porous surface of a filter material having a porosity at least as fine as wool felt, and then forcing the organic solvent under a fluid pressure differential through the skin in the direction such that the solvent flows from the skin to the surface.

2. In the method of tanning animal skins and the like wherein a Water-wet skin is extracted of water by forcing an inert water-miscible organic solvent through the skin in an amount suflicient to extract and replace substantially all the water with the solvent, a mineral tanning agent is incorporated in the skin and the skin is finally dried of solvent with the mineral tanning agent neutralized therein: the improvement comprising contacting the skin with an aqueous solution of a mineral tanning agent to distribute the tanning agent throughout the skin before the water in the skin is extracted and replaced with the organic solvent and heating the solution to an elevated temperature lower than the shrinkage temperature of the skin, and thereafter supporting the skin upon and in conformity with a porous surface of a filter material having a porosity at least as fine as wool felt, and forcing the organic solvent under a fluid pressure differential through the skin in the direction such that the solvent flows from the skin to the surface.

3. The method of tanning skins comprising contacting an untanned skin with an aqueous solution of a mineral tanning agent until the tanning agent is distributed throughout the skin, thereafter supporting the skin upon and in conformity with a porous surface of a filter material having a porosity at least as fine as wool felt, forcing an inert water-miscible organic solvent under a fluid pressure diiferential through the skin in the direction such that the solvent flows from the skin to the surface and in an amount to extract and replace substantially all the water in the skin with solvent, neutralizing the tanning agent by contacting the skin with a non-aqueous solution of a base, and finally drying the skin of solvent.

4. The method defined by claim 3 wherein the mineral tanning agent in the skin is neutralized by forcing an organic solvent solution of a base through the skin while the skin is supported on the porous surface.

5. In the method of producing hollow leather articles wherein a water-wet skin is conformed by fluid pressure to the surfaces of a suitable concave mold having a depth substantially in excess of the thickness of the skin and the skin is then extracted of water by forcing an inert Water-miscible organic solvent through the skin in an amount suflicient to extract and replace substantially all the water with the solvent, a mineral tanning agent is incorporated in the skin and the skin is finally dried with the mineral tanning agent neutralized therein: the improvement comprising contacting the skin with an aque- 6 ous solution of a mineral tanning agent to distribute tarining agent throughout the skin before the skin is conformed to the mold surface, then forcing the skin by fluid pressure into conformity with the surface of a porous concave mold of a filter material having a porosity at least as fine as wool felt, said mold having a depth substantially in excess of the thickness of the skin, and forcing an inert water-miscible organic solvent through the skin, while the skin is supported on the porous mold surface, under a fluid pressure diiferential in the direction such that the solvent flows from the skin to the surface.

6. In the method of producing hollow leather articles wherein a water-wet skin is conformed by fluid pressure to the surfaces of a suitable concave mold having a depth substantially in excess of the thickness of the skin and the skin is then extracted of water by forcing an inert watermiscible organic solvent through the skin in an amount sufiicient to extract and replace substantially all the water with the solvent, a mineral tanning agent is incorporated in the skin and the skin is finally dried with the mineral tanning agent neutralized therein: the improvement comprising contacting the skin with an aqueous solution of a mineral tanning agent and heating the solution to an elevated temperature lower than the shrinkage temperature of the skin to distribute tanning agent throughout the skin before the skin is conformed to the mold surface, then forcing the skin by fluid pressure into conformity with the surface of a porous concave mold of a filter material having a porosity at least as fine as wool felt, said mold having a depth substantially in excess of the thickness of the skin, and forcing an inert water-miscible organic solvent through the skin, while the skin is supported on the porous mold surface, under a fluid pressure dilferential in the direction such that the solvent flows from the skin to the surface.

7. The method of forming hollow leather articles comprising contacting an untanned skin with an aqueous solution of a mineral tanning agent until the tanning agent is distributed throughout the skin and neutralizing the tanning agent to fix it in the skin, thereafter forcing the skin by fluid pressure into conformity with the surface of a concave porous mold of a filter material having a porosity at least as fine as wool felt, said mold having a depth substantially in excess of the thickness of the skin, and forcing an inert water-miscible organic solvent through the skin, while the skin is supported on the porous mold surface, under a fluid pressure differential in the direction such that the solvent flows from the skin to the surface and in an amount to extract and replace substantially all the Water in the skin with solvent, and finally drying the skin of solvent.

8. The method defined by claim 7 wherein the mineral tanning agent is neutralized in an aqueous solution before the skin is extracted of water with the solvent.

9. The method of forming hollow leather articles comprising contacting an untanned skin with an aqueous solution of a mineral tanning agent until the tanning agent is distributed throughout the skin, thereafter forcing the skin by fluid pressure into conformity with the surface of a concave porous mold of a filter material having a porosity at least as fine as wool felt, said mold having a depth substantially in excess of the thickness of the skin and forcing an inert water-miscible organic solvent through the skin, while the skin is supported on the porous mold surface, under a fluid pressure differential in the direction such that the solvent flows from the skin to the surface and in an amount to extract and replace substantially all the water in the skin with solvent, neutralizing the tanning agent by contacting the skin with a non-aqueous solution of a base, and finally drying the skin of solvent.

10. The method defined by claim 9 wherein the mineral tanning agent in the skin is neutralized by forcing an organic solvent solution of a base through the skin while the skin is supported on the porous mold surface.

are wherein a water-wet skin is extracted of water by forcing afi inert water-miscible organic solvent through j the skin an amountsufiiciht to extract and replace substantially all the water with the solvent, a ,chrome tanning'agent is incorporated in the skin and the skin is finally dried, of solvent with the creme tanning agent neutralized therein: the improvement comprising 'contacting the skin with an aqueous solution of a chrome 'tanning' agent to distribute the tanning agent throughout the skin before the water in the skin is extracted and re placed with the organic solyent, thereafter supporting'the skin upon and in conformity with' a poroussurface of a filter material having" a porosity at least as fine'as wool felt, and then forcing the, organic solvent under a fluid that the solvent flows from the skin to'the surface."

7 12. In the method of tanning animal skins and the like wherein a water-wet skin is extracted of water by forcing acetone through the skin in an amount sufficient' to extract and replace substantially all the water with the V acetone,; a' chrome tanning agent is incorporated 'in the skin and the skin is finally dried of acetone with the chrome tanning agent neutralizedtherein: the improvement comprising contacting the skinrwith an aqueous solution of a chrome tanning agent to distribute the tanning throughout the skin before the water inithe skin is extracted and replaced with the acetone, thereafter supporting the skin upon and in conformity with a porous surface, of a filter material having a porosity at'least as fine as wool felt, and then forcing the acetone under a fluid pressure differential through the skin in the direction such that the acetone flows from the skin to the surface. p r

13. The method of tanning skins comprising contacting an untanned skin with an aqueoussolution of a chrome tanning agent until the tanning agent is distributed throughout the skin, thereafter supporting the'skin upon and in conformity with a porous surface of a filter material having a porosity at least as fine as wool felt, forc- 7 pressure differential through the skin in the direction such ventthrough the skin, while the skin is supported on the an inert water-miscible organicfsolvent 'under a fluid pressure differentialthrough the skin in the direction such that the solvent flows from the skin to the surface and in an amount to extract and replace substantially all the water 'inttheiskin with solvent, neutralizing-the tanning] agent by contacting the skin with a non-aqueous solution 7 of a base, and finally drying the skin of solvent.- 7

14. The method of forming hollow leather articles comprising contacting an untanned skin with an aqueous solution of chrome tanning agent until the tanning agent is distributed throughout the skin, thereafter forcing the skin by fluid pressure intoconformitywith the surface of a concave porous mold of a filtermaterial haw-1- ing a porosity at least as fineaswool felt, said Irnold having a depth substantially in excess of the thickness of the skin and forcing an inert'water-misc'ible organic solporous mold surface, under a fluid pressure diiferential in the direction such that the solvent flows from the skin to the surface and inan amount to extract and replace substantially all the water in the skin with solvent,rneutralizing the tanning agent by contacting the skin with a non-aqueous solution of a'base, and finally drying the skin of solvent. 7

References Cited in the file of this patent UNITED STATES PATENTS Great Britain of 1902'

Claims (1)

1. IN THE METHOD OF TANNING ANIMAL SKINS AND THE LIKE WHEREIN A WATER-SKIN IS EXTRACTED OF WATER BY FORCING AN INERT WATER-MISCIBLE ORGANIC SOLVENT THROUGH THE SKIN IN AN AMOUNT SUFFICIENT TO EXTRACT AND REPLACE SUBSTANTIALLY ALL THE WATER WITH THE SOLVENT, A MINERAL TANNING AGENT IS INCORPORATED INT HE SKIN AND THE SKIN IS FINALLY DRIED OF SOLVENT WITH THE MINERAL TANNING AGENT NEUTRALIZED THEREIN: THE IMPROVEMENT COMPRISING CONTACTING THE SKIN WITH AN AQUEOUS SOLUTION OF A MINERAL TANNING AGENT TO DISTRIBUTE THE TANNING AGENT THROUGHOUT THE SKIN BEFORE THE WATER IN THE SKIN IS EXTRACTED AND REPLACED WITH THE ORGANIC SOLVENT, THEREAFTER SUPPORTING THE SKIN UPON AND IN CONFORMITY WITH A POROUS SURFACE OF A FILTER MATERIAL HAVING A POROSITY AT LEAST AS FINE AS WOOL FELT, AND THEN FORCING THE ORGANIC SOLVENT UNDER A FLUID PRESSURE DIFFERENTIAL THROUGH THE SKIN IN THE DIRECTION SUCH THAT THE SOLVENT FLOWS FROM THE SKIN TO THE SURFACE.

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