US3837797A

US3837797A - Leather

Info

Publication number: US3837797A
Application number: US00171752A
Authority: US
Inventors: A Conklin
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-08-13
Filing date: 1971-08-13
Publication date: 1974-09-24
Anticipated expiration: 1991-09-24

Abstract

An improved iron tanned leather is produced by the use of a novel acidic aqueous solution containing ferric iron and citric acid as essential ingredients. Optionally, glycerine may be added. This solution is used substantially according to known tanning procedures. The novel leather obtained is characterized by a pleasing light-fast, tan color, a shrink temperature which compares favorably with that required of the more expensive chrome tanning and stability of aging. On ashing at 1,000*C. in air the leather leaves an 8 to 17 percent by weight residue which is at least 90 percent ferric oxide.

Description

United States Patent 11 1 Conklin 1 LEATHER [76] Inventor: Alfred R. Conklin, Rt. 4,

Harr odsburg, K y 403 [22] Filed: Aug. 13, 1971 21 Appl.No.: 171,752

OTHER PUBLICATIONS Chambard et al., I 3ulletin de lAssocia ti on Francaise des Chimistes desIndiistiEBiiCuir, i6 Annee, No. 2-3, Feb-Mar. 1954. Dawson; W. O. Journal of American Leather Chemists Assocn., July 1952, pages 457, 458, 468.

11 3,837,797 14 1 Sept. 24, 1974 Kanagy et al., Journal of the Society of Leather Trades Chemists, May 1944, page 121.

Chemical Abstracts, 1954, I3249d.

Primary ExaminerLeon D. Rosdol Assistant Examiner-H. Wolman Attorney, Agent, or FirmFrank W. Lane 57 ABSTRACT An improved iron tanned leather is produced by the use of a novel acidic aqueous solution containing ferric iron and citric acid as essential ingredients. Optionally, glycerine may be added. This solution is used substantially according to known tanning procedures. The novel leather obtained is characterized by a pleasing light-fast, tan color, a shrink temperature which compares favorably with that required of the more expensive chrome tanning and stability of aging. On ashing at 1,000C. in air the leather leaves an 8 to 17 percent by weight residue which is at least 90 percent ferric oxide.

6 Claims, N0 Drawings SUMMARY tric acid combination as well as the added improvement obtained by the use of glycerine. Tests under columns A, B and G illustrate the invention. In these columns in Table l the volumes of the solutions used along The Solutions 5 with the weights of reagents used are listed. The con- The solutions of this invention to be used for tanning Centrations of the reagents are calculated from these contain water, ferric iron supplied in the form of ferric values. The procedure involved placing fifteen grams of chloride, and citric acid as the primary essential ingrebate a d pickled Sheepskin in each of Seven 400 ml. clients. The amount of ferric chloride is in the range of beakers and covering each with one of the solutions as from 30 to 70 grams per liter of the solution and the citlisted in the table. The skin was stirred in the solution ric acid ranges from to grams per liter. Preferred and allowed to stand over night at room temperature. ranges are respectively from to 55 grams per liter Sodium carbonate solution was then added slowly to and 15 to 25 grams per liter. Glycerine up t 30 grams each until the pH was raised to about 4.5 and remained per liter may be added to obtain additional improve- *a t s al r 0 m t sh s a removed, ment. These various solutions are quite acid. The ex- 15 Washed by hand and squeezed dry, treated with glycercess acid may be partially neutralized to a pH under 2 inc and then with mineral oil and tacked to a drying with the usual alkaline agents prior to impregnating the After y g Samples A, B and G were found P skin to be tanned. This pre-neutralization is not essenable, and Of a medium tan 001013 Shrink tests were ri l b t it i f d made and the results shown in the table. Sample A was 20 kept 2 years and re-examined. It appeared generally the TANNING PROCESS same with respect to color, feel, and pliability, and had Tanning is accomplished by immersing the skin in the the same shrink temperature. Sample showed no evichosen solution at a temperature not over 100F. long dance fbeiI 1g tanned f p G "l to Show enough to impregnate. Th ki i prepared f hi that the preliminary partial neutrallzauon of the solustep the usual methods Following impregnation the 25 U011 18 not necessary for the SUCCESS Of the process.

TABLE I A B C D E F G Total Volume, ml. 240 200 150 140 240 240 190 gms. FeCl l0 l0 l0 0 l0 l0 10 Cone. gm/l 41.6 50.0 56.7 0 41.6 41.6 52.6 Citric acid, girls. 5 5 0 5 0 0 5 Cone. gm/l 20.8 25.0 0 35.7 0 0 26.3 Glycerine, gms. 4 0 0 4 4 4 4 Cone. gm/l 16.7 0 0 28.5 l6.7 16.7 21.0 Tartaric acid, gms. 0 0 0 0 5 0 0 Cone. gm/l 20.8

Oxalic acid, gms. 0 0 0 0 0 0 Cone. gm/l 20.8 Na Co gms. 5 5 5 5 5 0 Cone. gm/l 20.8 25.0 33.3 35.7 20.8 20.8

pH of solu. 0.4 ash in leather 13.7 Shrink Temperature 212 200 170 170 170 200 solution in contact with the skin is neu trali zed witli so EXAMPLE II dlum carbonate to a pH 1n the 3 to 6 range. The result- This example shows the effect of using a by product mg leather washed and fimshed by known ferric chloride obtained from the chlorination if ilmenmeans' tie for the purpose of manufacturing titanium tetra- THE LEATHER chloride. Two tanning solutions were made up identically except that one solution contained laboratory The leather bl by the above P F h h grade ferric chloride and the other the by-product. The usual good qual1t1es of tanned leather. It is unlque in composition of the Solution was as follows: view of 1ts two mam charactenstics taken together. First, it has an ash content of from 8 to 17 percent by weight which is at least 90 percent iron calculated as Ferric chloride 41.6 gm/liter Fe O and second, it has a stable shrink temperature of El i i l2? 3- ycerlne O. at least 200 1 Sodium carbonate 20.8 do.

waaaw. a ...a-.. a. DETAILED DESCRIPTION A small amount of solid matter settled from theby- The following examples illustrate and demonstrate product solution and was removed. One 15 gm. piece specific instances of the utility of the invention, showof pickled sheepskin with wool removed was placed in ing in particular that the combination of ferric iron and. 240 ml. portions of each solution and allowed to recitric acid is essential to obtaining good tanning. main there over night at room temperature. Both solu- EXAMPLE I This example shows the essential nature ofthe ironcitions were then adjusted to a pH of 4 with 10 percent sodium carbonate solution. The samples were removed, washed and treated as in example 1. Both samples of leather appeared to be of high quality as to color and pliability. The sample treated with laboratory ferric chloride had a shrink temperature of 210 while the product that prepared with the by-product had one of than a haired hide tanned by a standard chrome tanning method.

Although in the foregoing examples the treatment temperature is ambient, elevated temperatures up to 230F. and their ash contents were respectively 1 l per- 100F. may be used with the same good results and the cent and 13 percent. Both samples of ash contained 90 time of treatment may be correspondingly shortened. percent of iron calculated as Fe O The discarding of tanning liquors has long raised a EXAMPLE polution problem. Fortunately the compositions of this This example shows that the addition of even sm ll invention are far less toxic than the known chromium amounts of glycerine to the solution will improve the containing liquors thus aleviating an important aspect shrink temperature with further improvement being of the problem. Ferric chloride is a relatively cheap obtained with concentrations just over gm./l. Again tanning agent. bated and pickled sheepskin was used and the proce- The product leather of this invention is believed to be dure was the same as that in Example I. 5 novel. While others have prepared iron tanned leather A B c D E F Volume, ml. 200 220 230 240 250 260 Fecl gms. 10 10 10 10 10 10 Cone. gmsJl. 50 45.5 43.5 41.6 40.0 38.5

Citric acid, grns. 5 5 5 5 S 5 Cone. gmS./l. 25.0 22.7 21.7 20.8 20.0 19.2

Glycerine, gins. 0 2 3 4 S 6 Cone. gmsJl. 0 9.1 13.0 16.7 20.0 23.0

Na co gms. 5 5 5 5 5 5 Cone. gmSJl. 22.7 21.7 20.8 20.0 19.2

P 0.4 Shrink Temperature 200 210 216 212 212 214F EXAMPLE v no record has been found of such a leather containing treated in the manner used in Example 111 but using the solutions listed in the following table.

iron and at the same time exhibiting the high shrink temperatures characteristic of the leather described herein in terms of the ash content. The ash content varies considerably as shown in the data given below in correspondence with shrink temperatures.

A B C D E F Volume, ml. 200 220 230 240 250 260 FeCl gms. 10 10 10 l0 10 10 Cone. gins/l. 50.0 45.5 43.5 41.6 40.0 38.5

Citric Acid, gms. O 3 4 5 6 7 Cone. gmsJl. 0 13.7 17.4 20.8 24.0 27.0

Glycerine, grns. 4 4 4 4 4 4 Cone. gmS./l. 20.0 18.2 17.4 16.7 16.0 15.4

Na CO gms. 5 5 5 5 5 5 Cone. gins-li- 25.0 22.7 21.7 20.8 20.0 19.2

Shrink Temp. F. 208 206 212 :97 202 no substantial evidence of tanning EXAMPLE V Shrink Temp. Ash.

Tanning a pelt An unsheared white sheepskin which had been pick- 200 4'2 led but not bated was treated by the tanning solution 35 1;? and method as described in example 1, Sample A. The 2x6 1 resulting haired leather was brown, pliable, and softer 220 13.6

-Continued Shrink Temp.

' ashing to 1000C in air Representative samples of ash were analyzed and found to contain at least 90 percent by weight of iron calculated as Fe O The remainder of the ash is probably residual sodium chloride and/or sodium carbonate. The amount probably depending on the degree of washing. Since the ash content of the starting skin is essentially zero it is believed that with thorough washing and the use of pure ferric chloride, that the ash from the leather would be substantially 100 percent ferric oxide.

According to this invention, as illustrated in part by the above examples, a solution of somewhat variable composition is prepared for impregnating the skin or hide to be tanned. This solution contains, as primary essential ingredients, from 30 to 70 gms./liter of ferric chloride and from to 35 gms./liter of citric acid. Preferred ranges are from 40 to 55 gm./l. of ferric chloride and from 15 to 25 gm./l. of citric acid. The piece to be tanned is immersed in this solution until impregnated. The temperature of the solution during impregnation should not be above 100F. The solution is, of course, very acid and it is preferred to reduce its acidity by adding an alkalizing agent such as ammonia, sodium carbonate or sodium hydroxide. Only partial neutralization is desired prior to full impregnation of the leather; the extent of neutralization is limited so that the pH value of the solution is less than about 2.0 and preferably not more than 1. The neutralization in the range below 2 pH is preferably done before immersion because of potential local heating and high alkalinity which might damage the product. Neutralizing agents used at this stage can be in any form such as solid, gas or solution according to the nature of each. It is therefore to be understood that the partially neutralized solutions are included within the scope of this invention.

Inasmuch as the ferric chloride and citric acid probably will not be present in the solution entirely as such, especially after alkalizing agents have been added, the appended claims should be interpreted as including all species resulting from the mixing and interaction of the added essential ingredients. Thus the iron chloride may be converted to ferric citrate or various citrate complexes, basic ferric chloride, or citrates, etc. Similarly the chloride may be present as hydrochloric acid or sodium or ammonium chloride. Therefore, in defining the concentration of the components of the solutions of this invention in terms of ferric chloride, citric acid etc., the definition indicates the chemically equivalent amount of these ingredients present no matter what form they may take as a result of mixing them together in preparing the solution. It should be understood also that the alkalizing agents added also react and that specified quantities or concentrations of them in the solution should be interpreted as including the equivalent reaction products such as sodium chloride, sodium citrate and the like. In this sense the claimed solution may be said to be composed or consist essentially of the specified added substances.

The impregnation of the skin etc. may require various times depending on the temperature used, the 7 thickness of the piece and its porosity and the nature of any agitation used. Preferably the raw leather is immersed in a minimum of the solution for the sake of economy and agitated in a manner that flexes such as tumbling or periodic squeezing. These techniques are common in the leather industry, the mechanics of the procedure being analogous to those used in chrome tanning.

The action of the above impregnating solutions may be further enhanced by the addition of up to 30 gm./liter, of glycerine and preferably from 10 to 25 gms./l.

Ordinary commercial grades of chemicals may be used. In fact it was found that ferric chloride obtained as a by-product from the preparation of titanium tetrachloride from ilmenite by chlorination gave exceptionally good results.

When the desired impregnation of the skin is attained, the solution is neutralized by the addition of sodium carbonate until the pH is in the range of from 3 to 6, preferably near 4.5. This neutralization is done by ading sodium carbonate, preferably as a 10 percent aqueous solution, to the impregnating solution in the presence of the leather. The use of sodium carbonate rather than stronger caustic minimizes the heat and local alkalinity generated, and is thus substantially harmless to the product. The addition of the sodium carbonate is made during agitation and checking the pH until it has become stable at the desired level. This pH adjustment in the 3 to 6 range appears to insolubilize the agent and set the tan. The resulting leather is then washed to remove residual salts, etc. and finished in known manner.

While the foregoing data is based only on tests with sheepskin, it should be understood that the novel tanning solution is also applicable to other skins. The testing of tanning methods has customarily been based on sheepskin and found to carry over to other materials of similar collagen content. To test this briefly, samples of rabbit skin and calf skin were treated by the herein described method and found, on the basis of appearance and feel, to have been satisfactorily tanned.

In previous attempts to use iron as a tanning agent in the form of its sulfate salt it was found difficult to remove residual salts which later hydrolyzed, liberating acid to the detriment of the leather. The method of this invention is free of this weakness yielding leather having, for example, a stable shrink temperature. This advantage may be related to the use of ferric chloride along with citric acid which appears to be uniquely well suited to this process.

The shrink temperature is an important measure of the quality of tanning obtained. Briefly the test involves suspending a weighted strip of the leather sample in a glycerine bath, gradually raising the temperature of the bath and noting at what temperature the sample undergoes a pronounced shrinking. The procedure is more fully described in Volume 2, page 32 of The Chemistry and Technology of Leather, Fred OFlaherty, Reinhold Publishing Co, 1958 Edition.

I claim 1. An acidic tanning solution consisting essentially of water, from 30 to gms./liter of ferric chloride, and

from to 30 gmsjliter of citric acid.

2. The tanning solution of claim 1 in which the acid has been partially neutralized by the addition of an alkalizing agent selected from the group consisting of sodium carbonate, ammonia, and sodium hydroxide but is still in the acid range below pH 2.

3. The acidic tanning solution of claim one which also contains from 9.1 to 30 grams per liter of glycerme.

4. The tanning solution of claim 3 in which the acid has been partially neutralized by the addition of an alkalizing agent selected from the group consisting of sodium carbonate, ammonia, and sodium hydroxide but 6. The tanning solution of claim 3 in which the acid has been partially neutralized by the addition of an alkalizing agent selected from the group consisting of sodium carbonate, ammonia, and sodium hydroxide so that the pH value of said solution is not more than 1.

Claims

2. The tanning solution of claim 1 in which the acid has been partially neutralized by the addition of an alkalizing agent selected from the group consisting of sodium carbonate, ammonia, and sodium hydroxide but is still in the acid range below pH 2.
3. The acidic tanning solution of claim one which also contains from 9.1 to 30 grams per liter of glycerine.
4. The tanning solution of claim 3 in which the acid has been partially neutralized by the addition of an alkalizing agent selected from the group consisting of sodium carbonate, ammonia, and sodium hydroxide but is still in the acid range below pH 2.
5. The tanning solution of claim 1 in which the acid has been partially neutralized by the addition of an alkalizing agent selected from the group consisting of sodium carbonate, ammonia, and sodium hydroxide so that the pH value of said solution is not more than 1.
6. The tanning solution of claim 3 in which the acid has been partially neutralized by the addition of an alkalizing agent selected from the group consisting of sodium carbonate, ammonia, and sodium hydroxide so that the pH value of said solution is not more than 1.