US3726637A - Zirconium tanning - Google Patents

Abstract

TANNING OF ANIMAL HIDES AND SKINS BY SILICATE SODIUM ZIRCONIUM SULFATE AT A PH BETWEEN 1.0 AND 2.5 IS ACCELERATED WHEN THERE ARE PRESENT IN THE TANNING BATH AT LEAST FOUR SULFATE IONS PER ATOM OF ZIRCONIUM IN ADDITION TO THE SULFATE REQUIRED TO REACT WITH CATIONS PRESENT IN THE HIDES OR BATH WHICH FORM SPARINGLY SOLUBLE SULFATES.

Description

United States Patent O 3,726,637 ZIRCONIUM TANNING Warren B. Blumenthal, North Tonawauda, N.Y., assignor to NL Industries, Inc., New York, N.Y. No Drawing. Filed Oct. 26, 1971, Ser. No. 192,636 Int. Cl. C14c 3/02, 3/04 US. Cl. 8--94.25 4 Claims ABSTRACT OF THE DISCLOSURE Tanning of animal hides and skins by silicated sodium zirconium sulfate at a pH between 1.0 and 2.5 is accelerated when there are present in the tanning bath at least four sulfate ions per atom of zirconium in addition to the sulfate required to react with cations present in the hides or bath which form sparingly soluble sulfates.

BACKGROUND OF THE INVENTION The present invention relates to tanning with soluble zirconium salts and is particularly concerned with the acceleration of tanning processes in which silicated sodium zirconium sulfate is employed as the tanning agent.

It has been known for many years that solutions of zirconium salts can be employed for tanning animal hides and skins. The resultant leather is desirable because of its very light, substantially white, color which is of value as such and which also permits it to be dyed in clean pastel shades. In addition, leather tanned with zirconium salts does not continue to glow when, after ignition the flame is extinguished. In this respect it is different from and superior to chrome-tanned leather. Although various salts of zirconium have been suggested and used for tanning, silicated sodium zirconium sulfate, because of its relatively low cost as compared to other zirconium tanning agents, is extensively employed. The preparation of a silicated sodium zirconium sulfate is described in Horrigan US. Pat. No. 3,096,143, granted July 2, 1963.

In the use of silicated sodium zirconium sulfate, however, it has been found that the tanning process often requires an inordinate length of time to reach completion, particularly with thick hides and with hides from older animals. This has been accepted as necessary by tanners but the prolonged tanning time required has resulted in restriction of the use of zirconium tanning because of the additional expense involved. Observation and study of zirconium tanning operations have revealed that penetration of the hide by the zirconium when silicated sodium zirconium sulfate is used takes place at a moderate rate initially but gradually slows down so that after about three or four hours further penetration is extremely slow, with the result that several days may be required to completely tan a thick hide. Evidence has been found to support the belief that the slowing down of the tanning process results from extensive olation and condensation of zirconium species in the zirconium tanning bath with resulting large molecules that do not penetrate the hide.

SUMMARY OF TI-H5 INVENTION It has been discovered that the time required for thorough tanning when using silicated sodium zirconium sulfate as the tanning agent can be greatly decreased, particularly when tanning thick hides, if a tanning bath is used which contains, per atom of zirconium, at least four available sulfate ions, i.e. ions selected from the group of ions consisting of 80 and HSO4 As is well known, H80 further ionizes to H+ and SO; The sulfate ions (this term hereinafter being intended to include both S0 and HSO4 can be provided from a number of sources but, since the pH of the tanning bath is preferably maintained in the range from about 1.0 to about 2.5, it is p CC usually most convenient to provide the sulfate ions by adding sodium bisulfate (NaHSOQ to the bath. This addition is preferably made substantially simultaneously with the addition of the silicated sodium zirconium sulfate. Alternatively, the bath can be formed by adding silicated sodium zirconium sulfate to a bisulfate solution. In any event, however, the addition of bisulfate to the bath should not be delayed once the solution of silicated sodium zirconium sulfate has been prepared. By the term available sulfate ions as used above is meant sulfate ions in addition to the sulfate required to react with cations present in the hides or the bath which form sparingly soluble sulfates.

The preliminady hide treatment procedures, for example soaking, dehairing, lining, bating and pickling, may be conventional. On the other hand, zirconium tannage is quite tolerant as respects prior hide treatment and in many cases modified preliminary treatment can be used if desired. Subsequent to tanning and neutralization of the wet leather to a pH of from about 3.0 to about 6.2, preferably about 3.5 to about 6.0, the leather may be fat liquored and dried in accordance with well known procedures.

EMBODIMENTS The following examples illustrate the benefits of the present invention in tanning with silicated sodium zirconium sulfate.

Example 1 Using an experimental tanning drum, a piece of cattle hide having a limed weight of 4.77 kg. was, after washing and bating, tanned. To approximately 1200 ml. of water in the drum there was added 477 g. of sodium bisulfate and 851 g. of silicated sodium zirconium sulfate and the drum was run for five hours during which time the pH in the wheel rose from 1.1 to 1.7. Neutralization was then acomplished by slowly adding to the drum 1750 ml. of a 5% solution of sodium hydroxide over a period of two hours. The tanned hide was left in the float overnight and the next day, after addition of another 250 ml. of the sodium hydroxide solution, the drum was run for an additional hour. The final pH of the tanned hide was found to be 5.8 and it had a shrinkage temperature of over C. It was then drained, wrung, and split, the wet weight after trimming being 3.4 kg.

Example 2 Pieces of a salt cured green cowhide were soaked in water for rehydration. After conventional treatment including liming and dehairing, the pieces were washed and delimed and bated, using a commercial bate, in an experimental drum. The tanning was then carried out, without removal of the bate solution, by adding to the drum sutlicient silicated sodium zirconium sulfate to provide 2% soluble ZrO and six mols of sodium bisulfate. Drumming was continued for about six hours and was followed by neutralization with sodium bicarbonate to a pH of 3.23. A sample of leather taken after neutralization was found to have a shrinkage temperature of 91 C.

Example 3 Twenty-three pounds of green calfskin which had been put through conventional beamhouse procedures was placed in an experimental drum with a float containing suflicient silicated sodium zirconium sulfate to provide 6% soluble ZrO and 12% of sodium bisulfate. After operation of the drum for three hours, the pH of the hide was raised to 3.1 with sodium carbonate. The thus neutralized leather was found to have a shrinkage temperature of 91.5 C. and inspection showed no untanned streaks or layers.

3 Example 4 Eight sides of brine-cured, fleshed cattle hide were given conventional washing, soaking and liming beamhouse processing. The washed sides were then placed, in a large drum, in a 25% float containing 1% ammonium persulfate and a commercial enzymatic bate containing the equivalent of 2% enzyme. After running the drum for 30 minutes, silicated sodium zirconium sulfate in an amount calculated to provide 5% soluble zirconium, and sodium bisulfate were added and drumming was continued for five hours. The pH of the leather was subsequently adjusted to 3.5 with sodium bicarbonate. Tannage was observed to be complete and the leather was white with a shrinkage temperature of 93 C.

The following example illustrates the deleterious effect of aging on the tanning efiectiveness of a silicated sodium zirconium sulfate bath.

Example 5 (a) Using an experimental drum, a beamhouse-processed hide was drummed for six hours in a tanning bath containing an amount of silicated sodium zirconium sulfate calculated to provide 6% soluble ZrO and 12% sodium bisulfate. The bath had been aged for a number of hours after preparation and before introduction of the hide. After neutralization, the hide was found to be well tanned.

(b) Using the same drum, a closely similar hide was drummed for six hours in a bath containing the same amount of silicated sodium zirconium sulfate as in (a) above, the bath after preparation having been aged for the same time as in (a) above. No sodium bisulfate or other source of additional sulfate ions was, however, present. After the six hour drumming period and neutralization, it was found that when soaked in water long enough to remove the salt content thereof, the hide was not tanned as evidenced by its having the same shrinkage temperature as the untanned hide.

Tanning can in some cases be carried out with an amount of silicated sodium zirconium sulfate as low as about 2% (calculated as soluble Z102). Ordinarily, however, high quality tannage requires about 5% to 6% of soluble ZrO Additional tanning agent may, of course, be employed since the tanning process may thereby be accelerated and the leather obtained may be tougher and more opaque because of zirconium dioxide deposited therein.

Since silicated sodium zirconium sulfates furnish sulfate ions, only the additional sulfate ions required for the process of the invention need be provided from another source. The most convenient source is believed to be sodium bisulfate although other materials such, for example, as sulfuric acid, ammonium bisulfate, or normal sodium sulfate may be used. In general, such other sources are not as desirable as sodium bisulfate since they will usually require a pH adjustment of the tanning bath to obtain the desired pH range for tanning. It is of great impor tance, however, for optimum results, that there be enough sulfate ions present in the bath to provide at least four such ions for each zirconium atom present, after allowing sulfate ions sufncient to react with cations present in the hide and/or the bath which form sparingly soluble sulfates. Sulfate ions in excess of those necessary for cations that form sparingly soluble sulfates and the four for each atom of zirconium may be present in the bath if care is taken to maintain the pH of the bath in the desired range. On the other hand, when there are fewer than the ideal number of sulfate ions present, the overall accelerating effect on the tanning process is diminished, but some efiect is still observable if sulfate ions are present in substantial amounts. The situation is then tantamount, for operational purposes, to providing four available sulfate ions for only some of the zirconium atoms present.

Obviously, many modifications of and variations from the procedure described in the foregoing examples are possible. The tolerance of zirconium tannage for other materials has been mentioned above. Such tolerance, for example, permits the addition of the tanning agent to the hate without intermediate washing as illustrated in Examples 2 and 3, and thus savings of time and water can be obtained.

It will be understood that the present novel tanning process can be employed not only with calfskins and cattle hides, but also with other animal hides and skins such, for example, as horse hides and sheep skins. Consequently, the term hides herein is intended to include both hides and skins and the term leather includes both tanned hides and tanned skins.

Percentages set forth herein are percentages by weight and the percentages of materials comprised in the tanning bath are based on the white weight of the hide or hides being tanned.

What is claimed is:

1. A processfor tanning an animal hide which comprises treating such hide with an aqueous tanning bath comprising silicated sodium zirconium sulfate, while maintaining the pH of said bath between 1.0 and 2.5, said bath containing sufiicient silicated sodium zirconium sulfate to provide at least 2% soluble ZrO therein and containing sufficient soluble sulfate to provide, in solution, at least four sulfate ions per atom of zirconium in said bath in addition to sulfate ions required for formation of sparingly soluble sulfates of other cationic elements present in said hide and/ or bath, and neutralizing said hide to a pH of from about 3.0 to about 6.2.

2. A process as set forth in claim 1 in which said bath contains about 5% to 6% soluble ZrO;,.

3. A process as set forth in claim 1 in which at least a portion of said soluble sulfate is provided by sodium bisulfate.

4. A process as set forth in claim 2 in which at least a portion of said soluble sulfate is provided by sodium bisulfate.

References Cited UNITED STATES PATENTS 3,096,143 7/1963 Horrigan 894.25

GEORGE F. LESMES, Primary Examiner W. R. DIXON, Assistant Examiner U.S. Cl. X.R. 252-857