US967215A - Process for detanning. - Google Patents

Description

scams.

" NITE STATES PATENT OFFICE.

ALBEBTG. mus, OE OCONOMOWOC, WISCONSIN, ASSIGNOB 'lO ALBERT O. TBOSIEL,

' OF .MILWAUKEE, WISCONSI N.

raocnss For. nnrnmme.

1T0 Drawing.

1o aliy to' a process for detanning chrome tanned leather or leather waste, etc. I

The salient objectof the invention is to provide a process whereby chrome tanned eathcr or leather waste may be thoroughly detanned without impairing, or substantia-lly impairing, its strength or structure, so that upon the completion of this detanning process it will be restored practically to its original untanned con'dition and the product may thereafter be utilized for any of the numerous uses to which untanned hides or scrapsfof hides might be converted.

Other objects of the invention are to provide. a process which is sim le, economlcal,

and by means of which the c emical used in tanning the leather may be recovered-as abyproduct; to provide a rocess which is admirabliy. suited for p acing the material treate rovi e a process which is especially appllcable for treating finely comminuted 'wasteleather without loss or waste of the material; to provide a process which may be carried through in a comparatively short time, and

in general to provide an improved process 7 of thecharacter referred V In the manufacture and working up of chrome tanned leather there is a compara- 4.o .tively large percentage of so-called waste,

whichhas heretofore been of little or no value because of. the lack of any suitable process for utilizing such waste. Such waste includes so-called' skivings, splits,

'45 trimmings, skiflings, shavings, their pieces torn off in shaving for other working-of skins, and inferior and rejected. pieces of lathen Moreover, in making chrome 'tanned leather for grain finish there usually results a certain proportion of hides 'which turn out to be 'unsat1sfactory for this kind of leathery-the defective character of y the hides being onl determinable by tanningthem, and these 'des. can be advantageously detanned by my process and then retanned Specification of Letters Patent.

inlcondition for making either ood 30 gelatin orhigh grade glue; to -p Patented Au 16, 1910.

Application filed April 5, 1909. Serial No. @8305.

by some other rocess, as for example to produce a flesh hed leather. Where the waste is in the form of scraps or F shavings, unsuitable for use as leather, the detanned product secured by my process may be converted into gelatin, lueor even into animal food, since the, product is, as above stated, returned substantially to its original animal condition. p

, The preferred way of carrying out my process is as follows: I first subject leather or leather waste to a bath or treatment of hot water, which rapidly softens the material and puts it in condition for the subsequent chemical treatment to affect it rapidly and uniformly. The hot water treatment is continued until the material is all thoroughly penetrated and softened. I

alkaline solution, which has the effect of next treat the material in a bath of a weak loosening the'chrome so that it will readily and thoroughly dissolve in the subsequent acid treatment. For this chemical bath I prefer to use lime water,-not milk of lime, because the use of'the latter results in mix ing the mineral lime into the finelycom- Imnuted and powdered waste to such an extent that a substantial percentage of it is inevitably lost in the subsequent washing out of the lime, besides makin it more di'flicult toseparate the alkali and hue from the material being treated. Ordinarily the lime water treatment will cover a period of from six totwelve hours. I next remove. the lime water and preferably also wash the material with'the water so as to minimize v the amount ofalkali remaining in the material to be neutralized. I next subject the material to an acid treatment, which dissolves the' chrome and extracts it from the animal fiber. .For this purpose I use a weak so1ution,say a'one to two per cent. solution, of sulfuric or sulfurous acids. Pref: erabl-y, wherea light colored product is de-' sired, I use sulfurous acid solution, or a mixtureof sulfurous and sulfuric acids, be-

.cause this, tosome extent, bleaches at the 1 same time that it dissolves out the chrome. After the acid has thoroughly dissolved the chrome, this bath is drained 011:, and inas- 'much as it will contain practically all of the chrome, the latter may be recovered from the drawn .ofl" liquid by any suitable I process known tochemists. The material is now agam washed to remove excess of acid,

' course, be omitted, since the leather w and then the remaining acid neutralized by a second treatment with weak alkaline solution, preferably lime water, after which the material is washed and the detanning process thus completed. To make lue or gelatill, the dtanned material will e afterward boiled in the usual manner, while if it is to be retanned it may be retanned by an ordinary tanning process. s

The detanning process above described results in completely (or at least to all practical intents) freeing the leather from the tanning chemicals, and this without, so far. as I have been able to determine, in any Wise impairing the tissue structure, strength or origlnal character of the hide materlal. Pieces of leather detanned by the above process, and then retann'ed, appear to take the second tanning as perfectly and in precisely the same manner as though being tanned forthe first time.

In the case of detanning freshly tanned h des, for the purpose of retanning by a different process, for example, the preparatory step of soaking up the leather ma of I not be in dry and hard condition.

While I have hereinbefore indicated the preferred chemicals; and indicated these in the proportions which I find best suited to secure t e desired results, nevertheless different equivalent chemicals can be substituted, and the proportions varied within reasonable limits, Without departing from the spirit of the invention.

An important characteristic of the present invention is that throughout the entire serles of steps the leather is at no time treated drastically with chemical, nor is any step of the treatment continued so long as to result 1n impairing the tissue structure ofthe ma-' terial.

I claim as my invention:

1.- The improved process of detanning and restoring mineral tanned leather to its original untanned condition, which consists in subjecting the leather material to treatment in a weak alkaline solution substantiall 1 'free from undissolved mineral matters until the leather is thoroughly impregnated there: with throlfighout, next substantially separat ing the a aline' solution from the leather and subjecting the latter to a treatment with an acid having an effective strength, over and above that necessary to neutralize the alkali remaining in the batch, of not much less than 1% and so weak as to be incapable substantially attacking the animal matter during the period that it requires to completely dissolve the mineral tanning material, and continuing this step of the treatment until thetanning chemical has been thoroughly dissolved, then, before the animal matter has been appreciably attacked by the chemical, substantially removing the last mentioned solution.

2. The improved process of detanning and restoring mineral tanned leather to its original untanned condition, which consists in subjecting the leather material to treatment in a weak. alkaline solution substantially free from undissolved mineral matters until the leather is thoroughly impregnated there with throughout, next substantially separating the alkaline solution from the leather and subjecting the latter to a treatment with an acid having an effective strength, over and above that necessary to neutralize the alkali remaining in the batch, of not much less than 1% and so weak asjto be incapable of substantially attackingithe animal matter during the period that it requires to completely dissolve the mineral tanning material, continuing this step of the treatment until the tanning chemical has been thoroughly dissolved, then, before the animal matter has been appreciably attacked by the chemical, substantially removing the last mentioned solution,;and subjecting the material to a neutralizing treatment with a second weak alkaline solution untilit remains alkaline, and finally washing out the free chemicals.

'3. The process of detanning chrome or analogous mineral tanned leather or leather Waste, which consists in first subjecting the material to a hydrous bath until thoroughly soaked throughout, next subjecting the material to a treatment in a bath of lime water substantially free from suspended lime, next separating the material from the lime water and subjecting it to a treatment in an acid solution of a strength not greater than 10% and not less than1%, next removing the free acid solution and subjecting the material to treatment with a' neutralizing weak alkaline solution and thereby rendering the batch alkaline, and finally washing out the free.

chemicals.

T ALBERTGJMANNS.

Witnesses: a ALBERT H. Gmvas,

EMILm Rosa.