US2155087A - Process of depilating hides and skins - Google Patents

Description

Patented Apr. 18, 1939 PATENT OFFICE rnocnss or DEPILATING HIDES AND sxms Wolfgang Grassmann, Dresden-Loschwitz, and Herbert Schelz, Dresden, Germany, assignors to the firm: Studiengesellschaft der Deutschen Lederindustrie G. m. b. H., Dresden, Germany, a company of Germany No Drawing. Application January 13, 1938, Se-

rial No. 1937 12 Claims.

The present invention relates to a process of unhairing hides and skins while saving the hair, said process being specially applicable to hea y skins also.

The strong lime liquors or the highly concentrated pure sodium sulfide vat liquors which are mostly used for heavy hides, i. e., hides to be worked into heavy leathers, particularly sole leathers, have the disadvantage that the hair which is an important raw material for the felt industry andfor the spinning of hair yarn, is to a considerable extent, or completely, destroyed.

According to the process of the present invention the sulihydrate or sulfide ions, respectively, are permitted to come into contact with the hydroxy ions of the alkali absorbed by the skin, only within the upper layers of the epidermis, and

su'lfhydrates' or sulfides whose concentrations there to break down the, epidermal tissue or the hair roots, respectively. The remainder of the epidermis, more particularly the hair, is not attacked because it is not acted upon by sulfhydrate or sulfide ions and hydroxy ions simultaneously.-

According to the present invention the hides are treated in an alkaline bath which, per se, does not act as a depilating agent, with a view to conveying the alkali to the hair roots. The hides are then rinsed in water for a short time so that the alkali present at the hair roots is not removed. Thereupon the hides are treated with and/or pH values are such that they will only Thus, the process according to the invention is carried out in two stages, the essential feature being the differential attack on the hair roots. According to this process heavy hides can be depilated within a short time and without damage to the leather skin, while at the same time the hair is obtained in a condition suitable for further working, particularly in the manufacture of felt.

Prior to being treated with alkali, the hides can be soaked in the usual manner, preferably while using, sharpening or wetting agents. The soaking liquor may contain, for example, .01 to 05% of caustic soda and/or .02 to .05% of the wetting agent, e. g., sulfonates of high molecular fatty alcohols.

The alkali treatment is carried out for a short time in a bath containing alkali or earth alkali and, in addition, buffer agents, if desired. Caustic soda solution of .5% or a solution containing .5% of sodium hydroxide and .25 to .5% of soas starch, bentonite, glue, or the like.

184,772. In Germany January 14,

dium carbonate, have been found suitable for this treatment; however, the composition and the pH value of the treating bath can be varied within wide limits. This treatment neither results in loosening the hair nor in damaging the hide substance and the hair. The hides havingbeen soaked at least as far as the hair roots and showing an alkaline reaction, which is usually the case after half an hour to twohours, they are removed from the bath. Then their surface is rinsed which removes the major part of the alkali from the hair.

The hides are now treated with a solution of a sulfhydrate or sulfite whose concentration and/or pH value is such that it does not, per se, act as a depilating or hair destroying agent, when acting for a short time on the hide not previously treated with alkali. Both the alkali treatment carried out in the first stage of the process, and the treatment with sulfhydrates or sulfides, respectively, may be carried out, if desired, while stirring, for example, in a drum or in a paddlevat.

The sulfhydrate solution is used in a concentration of 1 to 2% and the sulfide solution in a concentration of .5 to 1%.

Regarding the method to be followed, both in the first and in the second stage, it is pointed out that concentration and temperatures of the solutions employed, and duration of treatment are brought into proper correlation. High temperatures can be used when the period of treatment is correspondingly reduced. Solutions of lower concentration can be used when longer periods of treatment or higher temperatures are employed.

The sulfhydrates or sulfides, respectively, may also be applied, ifdesired, to the. grain side of the hides in the form of a paste that may contain, as thickening agents, suitable additions such Suitable for this purpose are concentrated solutions of sodium sulfhydrate, calcium sulfhydrate, or ammonium sulfide, which in addition may contain ,buffer agents, if desired. The use of thickening agents, such as starch and the like, in the paste has not only the advantage of facilitating the application of said paste, but it has the additional advantage that the alkali absorbed by the hide will less readily diffuse into the hair.

The sulfhydrate or sulfide ions, respectively, used in the second stage of the process, in the presence of the alkali left at the hair roots act as hair destroying agents, so that the hides slip quickly and can already be depilqg ed after to 2 hours without difiiculty. Even the short hairs .can be easily removed, the pelts being obtained in a normal, unswollen condition. The sulfhydrates or sulfides, respectively, are then removed from the hair by washing, the hair being obtained in a. very good condition.

It is advisable to carry out depilation and to work pelts and hair further, immediately the hair has become loosened, in order to avoid damaging hide and hair.

In carrying out theprocess according to the invention, it has been found highly advantageous to add wetting agents. They may be used during soaking, with the alkali bath, and with the baths or pastes which consist of sulfhydrates or sulfides, respectively. As wetting agents may be used aliphatic and aromatic sulfonic acids, more particularly those of the Nekal type, sulfuric acid esters of high molecular fatty alcohols, amines such as triethanol amine, ethylene diamine, hexamethylene tetramine, pyridine, quaternary ammonium bases, etc. These wetting agents, in the treatment with alkali and sulfhydrate, are employed in a concentration of about 1 to 2%.

The process according to the invention can also be used to advantage for skins and light hides, particularly in those cases in which particular saving of the hide substance is to be effected.

The invention is illustrated by the following examples, but it is not intended to limit the scope of the invention to the concentrations, pc-

riods of treatment, etc., given in the examples.

Example 1 The hides which have been soaked in the usual manner, while using sharpening or wetting agents, if desired, are treated for two hours in a solution containing .5% of caustic soda, 25% of sodium carbonate, and 1% of fatty alcohol sulionate, for example, the solution sold under the trade name of Seprol A. After the grain side of the hides has been sprayed with water for a short time, a 1% solution of sodium sulfhydrate'having a pH value of about 10.0 to 11.0 measured with indicators, is applied to it. After about 2 hours the hides slip well.

Example 2 Cow-hide soaked as usual is immersed for two hours in a solution containing grams of sodium hydroxide and 5 grams of calcined soda per litre. The surface of the hide pretreated in this manner is well rinsed so that the alkali is removed from the hair; then the grain side of the hide is coated with a paste which consists of 3% of starch, about 1% of sodium sulfhydrate, and 96% .of water. After said paste has acted for a period of V4 to hour, the hair (even the short hairs) can be removed without difficulty. The pelts, depending on the kind of leather to be produced, may be subjected to further treatment with'fresh lime. In order to remove the adhering paste, the hair is washed; it is obtained in very good condition. Sometimes, the hair'is so well preserved that it must be subjected to further treatment with lime or suitable alkalis in order to secure suflicient felting and tumbling ability.

Example 4 The bath for the preliminary treatment consists of a solution containing 5 grams of NaOH and 20 cc. of pyridine per litre. The paste employed consists of 2% of calcium sulfhydrate, 7% of bentonite, and 91% of water. The treatment is carried out in the same manner as described in Example 3.

We desire to emphasize the fact that in our invention the treatment with alkali precedes the treatment with sulfhydrate or sulfide. This order in the carrying out of said two steps is important in that it enables the entire treatment to be carried out in a much shorter time (from about one to four hours) than in prior art methods and particularly those prior art processes in which steps somewhat similar to those described by us were used in the reverse order. The considerable shortening of the treatment not only effects a great economy in time and consequently reduces the cost of the treatment and the space required for its performance, but the skins or hides and the hairs, being subjected to the action of the chemicals only for a relatively short time, are attacked much less and are therefore obtained in a much better condition.

What we claim is:

1. A process of. depilating hides and skins which comprises soaking them, treating them in an alkaline bath which, per se, does not ac as a depilating or hair destroying agent, rinsing them with water, and subsequently treating them with sulhydrates or sulfides of a concentration and/or a pH value which, per se, will not destroy the hair.

2. A process according to claim 1 which comprises using wetting agents while soaking the hides.

3. A process according to claim 1 which comprises using wetting agents while treating the hides with alkalis..

4. A process according to claim 1 which comprises using wetting agents while treating the hides with sulfhydrates or sulfides.

5. A process of depilating hides and skins which comprises soaking them, treating them in an alkaline bath which, per se, does not act as a depilating or hair destroying agent, rinsing them with water, and subsequently treating them with sulfhydrates or sulfides of a concentration and/or pH value which, per se, will not destroy the hair,

while using wetting agents that have been selected from the group of aliphatic or aromatic sulfonic acids, sulfuric acid esters of high molecuor sulfides being effected while adding 1 to 2% of wetting agents.

7. A process of depilating hides and skins which comprises soaking them, treating them in an alkaline bath which. per se, does not act as a depilating or hair destroying agent, rinsing them with water, and subsequently treating them with sulihydrates or sulfides of a concentration and/or pH value which, per se, will not destroy the hair, the sulihydrates or sulfides being caused to act on the grain side of the hides as a paste.

8. A process according to claim 'I which comprises causing the suli'hydrates or sulfides to act on the grain side 01 the hides as a paste to which inert thickening agents and wetting agents have been added.

9. A process of depilating hides and skins which includes the steps of treating the hides or skins with an alkaline agent and subsequently with a. sulfhydrate agent or a sulfide agent.

10. A process of depiiating hides and skins which includes the steps of treating the hides or skins with an alkaline agent which by itself does I which includes the steps of treating the hides or skins with an alkaline agent, then rinsing the hides or skins to remove said alkaline agent from the hairs, and subsequently treating the hides or skins with a sulihydrate agent or a sulfide agent.

12. A process of depilating hides and skins which includes the steps of treating the hides or skins with an alkaline agent and subsequently applying to the grain side of such hides or skins a paste containing a sulfhydrate agent or a sulilde agent of a concentration and/or a pH value which by itself will not destroy the hair.

WOL'HEANG GRASSHANN. HERBERT SCHELZ.

depilating hides and skins