US3013858A - Process of and composition for neutralizing chrome-tanned leather - Google Patents

Process of and composition for neutralizing chrome-tanned leather Download PDF

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US3013858A
US3013858A US836385A US83638559A US3013858A US 3013858 A US3013858 A US 3013858A US 836385 A US836385 A US 836385A US 83638559 A US83638559 A US 83638559A US 3013858 A US3013858 A US 3013858A
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leather
neutralizing
fat
chrome
liquoring
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Pruetz Adalbert
Quendt Erwin
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Schill and Seilacher AG
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    • C—CHEMISTRY; METALLURGY
    • C14—SKINS; HIDES; PELTS; LEATHER
    • C14C—CHEMICAL TREATMENT OF HIDES, SKINS OR LEATHER, e.g. TANNING, IMPREGNATING, FINISHING; APPARATUS THEREFOR; COMPOSITIONS FOR TANNING
    • C14C9/00—Impregnating leather for preserving, waterproofing, making resistant to heat or similar purposes

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  • the present invention relates to a process of neutralizing and, if desired, simultaneously fat-liquoring chrometanned leather and to a composition adapted for neutralization and fat-liquoring of such leather.
  • Chrome-tanned leather must be neutralized after ten ning in order to remove the acid which is present in the leather and is released on storage of the leather by hydrolysis of the chromium complex compounds bound by the skin fibers. Neutralization is necessary in order to assure uniform fixation of the dye to and fat-honoring of the leather by means of suitable dyestuffs and fat-liquoring agents, and in order to prevent hardening of the leather on drying which may occur even if the leather is sufilciently fat-liquored.
  • buffering salts such as sodium bicarbonate, sodium acetate, calcium formate, and sodium sulfite are used for neutralization.
  • Sodium phosphate, sodium thiosulfate, sodium nitrite, and borax have also been employed for this purpose, likewise salts of aromatic hydroXy carboxylic acids and polycarboxylic acids, such as phthalic acid and sulfo phthalic acid, salts of hydroxy dicarboxylic acids, and, furthermore, ammonium salts of sulfonic acids of synthetic tanning agents.
  • Such ammonium salts have simultaneously a supplementary tanning action.
  • the neutralizing agents used heretofore convert the sulfuric acid which is mainly present in the leather, into sodium sulfate. Ordinarily they also cause formation of basic chromium complex compounds in the leather. It is another advantage of many neutralizing agents'that their anions enter the molecule of the chromium compounds. As a result thereof improvement of the grain, the fullness, and the grain strength of the leather is frequently achieved.
  • chrome-tanned leather has been neutralized by a treatment with a neutralizing solution, usually at a temperature of about 30 C. for a prolonged period of time.
  • Said neutralizing solution contains a suitable neutralization agent in amounts depending on the kind of leather used.
  • the neutralized leather is washed with water whereby the salts formed on neutralization are removed from the leather.
  • washing of the leather with water is continued at gradually increasing temperature until a temperature of about 60 C. is reached as it is required for dyeing and fat-liquoring.
  • dyeing and fat-liquoring of the leather is efiected in fresh solutions at about 60 C.
  • the leather is to be dried according to the pasting process, processing of the chrome-tanned leather is even more complicated. After washing, the leather is first dyed and subjected to a preliminary fat-liquoring treatment. Thereafter, it is re-tanned in a fresh, cold solution of vegetable and synthetic tanning agents in order to im part to its sufficient fullness. Usually it is finally again fat-liquored in a fresh fat-liquoring solution at an increased temperature.
  • the neutralizing agents used heretofore, however, and especially sodium bicarbonate, are poorly compatible with rat-liquoring agents. As strong electrolytes they have a precipitating effect on the fat emulsion. They also prevent proper absorption of the oil by the leather fiber. This disadvantage is especially encountered when using sodium bicarbonate because it causes over-neutralization of the surface of the leather fiber. llt'is also known that many of the conventionally used neutralizing agents, especially sodium bicarbonate, permeate leather only very slowly. In order to achieve complete neutralization with sodium bicarbonate it is, for instance, necessary to expose the leather. to the neutralizing solution for at least one day and even the leather.
  • Another object of the present invention is to provide a novel and improved neutralizing solution for neutralizing chrome-tanned leather, said solution containing the new neutralizing agent, said neutralizing solution having a mild effect, being capable of rapidly and uniformly permeating chrome-tanned leather, advantageously affecting the tanning chromium complex compounds in the leather and improving its tanning effect, and being well compatibl with the fat-liquoring agents.
  • Still another object of the present invention is to provide a simple and effective process of simultaneously neutralizing and fat-liquoring chrome-tanned leather.
  • chrome-tanned leather is neutralized by means of alkali metal, ammoniurn, or alkaline earth metal salts of sulfomethylated ot-arnino acids of the following formula:
  • Such sulfomethylated a-amino carboxylic acids are oblonger, depending on the thickness of tained from amino acids as they are present in natural proteins. They can be used in the pure state or in the form of mixtures produced by sulfomethylation of the pure u-arnino acids or of the a-amino acid mixtures obtained on hydrolysis of proteins and especially of glue and waste materials from animal skins.
  • the required salts of such sulfomethylated a-amino acids are obtained, for instance, by hydrolyzing glue, other waste materials from animal skin, or other proteinaceous material with a sodium hydroxide solution at 110120 C.
  • the amount of the sodium hydroxide exceeds preferably by the amount required for converting the resulting amino acids into their sodium salts.
  • the pH-value of the resulting strongly alkaline solution of the salts of ot-amino acids is then adjusted to a pH of 8.5, for instance, by the addition of acetic acid.
  • the sodium salt or another alkali metal salt, the ammonium salt, or the magnesium salt of hydroxy methyl sulfonic acid i.e., the reaction product of formaldehyde and sodium hydrogen sulfite is added to said amino acid solution in an amount equimolecular to each free amino group of the amino acid.
  • the reaction mixture is heated to 80-90" C. for about one hour and is then adjusted to a pH of 9.5. In this form the reaction solution can directly be used for neutralization.
  • the neutralizing action of the neutralizing solution according to the present invention is characterized by a gradual decrease of the pH-value and a uniform penetration of the leather. Thus continuous deacidification is achieved and no substantial differences in pH-value within the leather layers are observed.
  • a sodium bicarbonate solution as used heretofore, first causes diffusion of a considerable amount of acid from the leather fibers, before, the pH-value is considerably decreased. As a result thereof great differences in pH- value occur within the leather. Such differences have the disadvantage that a certain de-tanning effect takes place within the skin, due to over-neutralization of the chromium complex compound, and that permeation of the leather by the neutralizing agent is retarded.
  • FIG. 1 illustrates the neutralizing curve obtained by titrating 100 cc. of a solution containing 7.5% of the sodium salt of sulfomethylated amino acid obtained as described hereinabove by alkaline hydrolysis of glue and reaction with formaldehyde-sodium hydrogen sulfite, with N/ 2 sulfuric acid
  • FIG. 2 illustrates the neutralization curve obtained by titrating 100 cc. of a 3.5% sodium bicarbonate solution with N/2 sulfuric acid.
  • the curve descends gradual- 1y, uniformly, and continuously with progressing neutralization, whereas with sodium bicarbonate (FIG. 2) the curve first proceeds horizontally at a pH-value between 8.0 and 7.0 for a considerable period of time, and thereafter drops rapidly and abruptly to the acid pH-value of 4.0 and lower.
  • the curves also illustrate very clearly the action of the mild neutralizing agent according to the present invention.
  • the neutralizing agent according to the present invention makes such a procedure possible. If the treating solution contains neutralizing agents according to the present invention and fat-liquoring agents and is employed at 20-60 C., neutralization and fat-liquoring can be carried out in the same vat.
  • the new neutralizing agents exhibit good compatibility with chromium and a remarkable complex forming activity. During neutralization and fatliquoring they enter the chromium complex and contribute substantially to the improvement and strengthening of the grain.
  • Another advantage of the process according to the present invention is the fact that a composition containing neutralizing and fat-liquoring agents is remarkably stable against high electrolyte and acid concentrations so that, even without preliminary washing, simultaneous neutralization and fat-liquoring can be carried out immediately after tanning.
  • Still another advantageous feature of the process according to the present invention is the possibility of dyeing, neutralizing, fat-liquoring, and re-tanning at a temperature between about 20 C. and about 30 C. As a result thereof a substantial saving in time, energy, and labor is achieved. When using the known neutralizing agents, operation at such a low temperature was not possible.
  • Fat-liquoring agents as they are useful in the process according to the present invention, are stable emulsions of mixtures of various oils, are not deemulsified at the rather low pH-value of 3.6-4.0 as it is encountered in the beginning of the neutralization step.
  • Such fat-liquoring agents are, for instance, sulfonated train-oils or vegetable and animal oils in mixture with unsulfonated oils and, if desired, with emulsifiers of the ethylene oxide type.
  • Example 1 Pared chrome-tanned calf-leather is rinsed with water of 20 C. for five minutes and is then immersed into twice its weight of the neutralizing solution containing 1.5% of the sodium salt of sulfomethylated amino acids obtained as described hereinabove from glue, at 20 C. for 30 minutes.
  • the leather is rinsed with water of 60 C. for 10 minutes and dyed with a dye bath containing 1% of the brown acid dyestutf sold under the trademark Coranilbrown HEG by the Farbwerke Hoechst A.G., Franlc furt am Main-Hoechst, Germany, at 60 C. for 30 minutes.
  • the amounts of neutralizing agent, fat-liquoring agent, and other additives are given in percent of the leather to be treated.
  • the amount of tanning agent added is calculated as actual tanning agent in the tanning composition in percent of the leather to be treated.
  • Example 2 Shaved chrome-tanned kid-leather is rinsed with water of 20 C. for 5 minutes and is then treated with twice its amount by weight of a neutralizing solution containing 1% of the potassium salts of the above mentioned sulfomethylated amino acids.
  • a neutralizing solution containing 1% of the potassium salts of the above mentioned sulfomethylated amino acids.
  • a pre-emulsified mixture of fatliquoring agents consisting of 2.5% of train-oil sulfonate, sold under the trademark Lipsol BN7 by Schill & Seilacher of Stuttgart, Germany, and 0.8% of unsulfonated train-oil or sperm oil is added.
  • the leather is completely and uniformly neutralized and shows a bluish-green color throughout its cross-section when dyed with bromo cresol green.
  • the fat is uniformly absorbed by the leather.
  • Re-tanning is carried out in the same drum using 3% pure tanning agent consisting of equal parts of vegetable and synthetic tanning agents, such as a mixture of mimosa extract and chestnut wood extract (1:1) or of mimosa extract, chestnut wood extract, and quebracho wood extract (1:1:1).
  • the leather treated in this manner has a fine, firm grain and full, firmly grained flank parts. After finishing, an especially soft leather is obtained.
  • Example 3 Chrome-tar1ned, shaved calf leather is rinsed with water of 30 C. for 5 minutes. it is then dyed at 30 C. in twice its amount by weight of a dye solution containing 0.5 of an'acid black dye sold under the trademark Suede Leather Black ET Cone. by Badische Anilin- & Sodafabrik A.G. of Ludwigshafen, Germany, for 30 minutes. Thereafter, 0.4% of a basic dye which has been mixed with 0.2% of formic acid to form a paste are added to the dye bath. After minutes a mixture of 3% of the neuralizing agent according to the present invention, 1% of soap, 1% of unsulfonated neats foot oil, and 1% of egg yolk are added. The leather is completely and uniformly neutralized after one hour and the fat is completely absorbed by the leather. After drying, the leather has a fine grain, said firm grain and fullness extending into the flank parts of the leather.
  • Example 4 Chrome-tanned, shaved calf leather to be dried by pasting to a glass plate or metal sheet, is rinsed with water for 3 minutes and is then dyed at C. in twice its amount by weight of a dye bath containing 1% of an acid black dye sold under the trademark Leather Black MB by Baclische Anilin- & Sodafabrik A6. of Ludwigshafen, Germany, for 30 minutes.
  • the leather is then re-tanned in the same bath with 3% of a tanning agent consisting of a mixture of vegetable and synthetic tanning agents, such as quebracho wood extractand the synthetic tanning agent sold under the trademark Tannigan Q by Wegriken Bayer A.G. of Leverkusen, Germany.
  • the resulting re-tanned leather is then pasted to a glass plate or metal sheet and dried.
  • the distribution of the fat in the leather is uniform.
  • a thin film of fat remains on the surface and prevents any deep penetration of the adhesive required for pasting.
  • the adhesive is composed of a cellulose methyl ether sold under the trademark Tylose by Kalle & Co. AG. of Wiesbaden-Biebrich, Germany.
  • the dried leather is distinguished from leath r neutralized with the conven- I tional neutralizing agents by its increased fullness and its better grain.
  • Example 5 Chrome-tanned and shaved neats leather is rinsed for 5 minutes and dyed in twice its amount by weight of a dye bath containing 0.5 of an acid dye sold under the trademark Baygenal Brown CRG by Konverkusen, Germany, for 20 minutes.
  • a mixture of 2% of the sodium salt of sulfomethylated amino acids used in the preceding examples, 2.5% of sulfonated sperm oil, and 0.75% of sperm oil is added to the same bath, and the leather is agitated therein for one hour. The fat is then completely absorbed by the leather.
  • the leather is dried as usually and, after drying, shows an extremely fine grain and a high grain strength even in the flank parts thereof. It is also much softer than leather treated in the usual manner with the same amount of fat.
  • Example 6 Chorome-tanned and shaved neats'leather to be dried according to the pasting process is rinsed with water of 20 C. for 5 minutes and is then treated in twice its amount of neutralizing solution containing 2% of the ammonium salt of sulfomethylated amino acids obtained in a similar manner as described hereinabove for the sodium salt.
  • liquoring emulsion consisting of 2.8% of sulfated trainoil sold under the trademark Lipsol A by Schill & Seilacher of Stuttgart, Germany, and 1.5% of a mixture consisting of animal and vegetable oils and an emulsifier on the basisof ethylene oxide, said mixture being sold under the trademark Ossipol KLM by Schill &Seilacher of Stuttgart, Germany, is added thereto.
  • Said liquoring emulsion is prepared by pouring the sulfated train-oil and the oil mixture Lipsol A into 10 times their amount of water heated to 60 C. while stirring vigorously and The fat is completely The leather is thereby emulsifying the oils. absorbed by the leather after one hour.
  • tanning 7 agent consisting of a mixture of the synthetic tanning agent sold under the trademark Tannigan Extra B by Kontigriken Bayer A.G. of Leverkusen, Germany, and
  • Example 7 Normally chrome-tanned and shaved leather to be dried by pasting is rinsed with water of 40 C. for 5 minutes and is treated with the same amount by weight of a neutralizing, fat-liquoring, and retanning preparation consisting of 3% of the neutralizingagent according to the present invention as used in Example 1, 3.5% of sulfated sperm oil, 1.2% of an emulsifiable oil consisting of a saponifiable oil, mineral oil, and an emulsifier on the basis of ethylene oxide, and 4% of a commercial resinous tanning agent.
  • a neutralizing, fat-liquoring, and retanning preparation consisting of 3% of the neutralizingagent according to the present invention as used in Example 1, 3.5% of sulfated sperm oil, 1.2% of an emulsifiable oil consisting of a saponifiable oil, mineral oil, and an emulsifier on the basis of ethylene oxide, and 4% of a
  • the sulfated sperm oil used in this preparation is sold under the trademark Lipsol DN 3.
  • the mixture of emulsifiable oil consisting of saponifiable oil, mineral oil, and emulsifier based on ethylene oxide is sold under the trademark Ossipol KLM.
  • Th'e resinous tanning agent is either an agent sold under the trademark Chemtan R6 by Chemtan Company, Morris, NH, or under the trademark Retingan R6 by Weg, Germany.
  • the leather After a treatment of one hour the'mixture has completely been forced into the leather.
  • the leather shows a film on its surface as it is required for the paste-drying process.
  • the dried and finished leather exhibits excellent grain strength and fineness of the grain and also a good fullness even of the flank parts of the leather.
  • Example 8 Normally chrome-tanned and shaved garment leather is rinsed with water for 5 minutes and is dyed at 30- C. in twice itsamount by weight'of a dye bath containing 1.5% of an acid dyestuff, sold under the trademark Baygenal Dark Brown CGV by Konriken Bayer A.G. of Leverkusen, Germany, for one hour.
  • a mixture of 4% of the magnesium salts of sulfomethylated a-amino acids obtained in a similar manner as described hereinabove for the sodium salts and of 4% of a sulfitated trainoil sold under the trademark Lipsol GT by Schill & Seilacher of Stuttgart, Germany, is added to the dye bath and the leather is treated therein for 1 /2 hours.
  • the fat has been completely absorbed by the leather which is uniformly neutralized.
  • the leather can be retanned in the same bath by adding thereto a suitable amount of a tanning agent mixture consisting of vegetable tanning agents or a mixture of a vegetable and a synthetic tanning agent such as a mixture of chestnut wood extract and the synthetic tanning agent sold under the trademark Tannigan Extra Q" by Konverkusen, Germany.
  • the resulting leather is distinguished by an extraordinary softness, grain strength, and grain fineness.
  • Example 9 Suede leather which has been pretanned and retanned with chromium salts is rinsed with water of 30 C. for minutes in order to remove the crystallized salt and adhering shavings. It is then treated with twice its amount of a neutralizing and fat liquoring preparation containing 2% of the neutralizing agent used in Example 1 which was mixed, before use, with 3% of an oil emulsified by a cationic emulsifier, such as a neats-foot oil emulsion emulsified by the cationic emulsifier sold under the trademark Vinkolamin K by Schill & Seilacher of Stuttgart, Germany.
  • a neutralizing and fat liquoring preparation containing 2% of the neutralizing agent used in Example 1 which was mixed, before use, with 3% of an oil emulsified by a cationic emulsifier, such as a neats-foot oil emulsion emulsified by the cationic emulsifier sold under the trademark Vinkolamin K
  • the fat After a treatment of one hour with such a preparation, the fat has been completely and uniformly absorbed by the leather which is thoroughly neutralized. Subsequent fat-liquoring of the leather after dyeing is not necessary.
  • the resulting suede leather is distinguished by a close and smooth surface and has no tendency of becoming smeary and greasy.
  • neutralizing agents other sodium, potassium, ammonium, magnesium, and other alkali metal and alkaline earth metal salts of N-sulfornethylated a-amino acids, such as, for instance, the sodium salts of N-sulfomethylated glycine, alanine, leucine (obtained, for instance, by acid hydrolysis of horn waste), glutamic acid (obtained from molasses or gluten or synthetically), histidine (obtained from blood corpuscles), cysteine (obtained from hair and other keratinous matter by hydrolysis with hydrochloric acid), phenyl alanine, proline, hydroxy proline, serine, threonine, tryptophan, aspartic acid, lysine, and others.
  • sodium salts of N-sulfomethylated glycine, alanine, leucine obtained, for instance, by acid hydrolysis of horn waste
  • glutamic acid obtained from molasses or gluten or
  • alkali metal, ammonium, and alkaline earth metal salts of the sulfomethylation products of other protein hydrolysates i.e., of mixtures of amino acids, such as the acid, alkaline. or enzymatic hydrolysates of casein, blood plasma, fibrin, and the like.
  • amino acids may, of course, also be produced synthetically.
  • the least expensive starting materials for sulfomethylation are the hydrolysates obtained from proteinaceous byproducts and waste products of the leather industry such as collagen, i.e., the protein of connective tissue present in animal hides and skin and the organic substance of the bones, and keratin, i.e., the protein of epithelial tissue, such as hair, wool, horn, feathers, nails.
  • collagen i.e., the protein of connective tissue present in animal hides and skin and the organic substance of the bones
  • keratin i.e., the protein of epithelial tissue, such as hair, wool, horn, feathers, nails.
  • Sulfomethylation of these protein hydrolysates or u-amino acids is carried out in the same manner as described hereinabove, i.e., by heating a solution of equimolecular proportions of sodium hydroxy methyl sulfonate or formaldehyde-sodium bisulfite and the sodium salts of the amino acids or sodium sulfite, formaldehyde and amino acid mixtures at 80-90 C. for one hour and adjusting the pH-value to a pH of 9.5.
  • the resulting solution can be added to the chrome-tanned leather as such without isolation of the 8 salts of the N-sulfonated amino acids and without their purification. It is, of course, also possible to isolate and purify said salts and to use them in the dry state for leather neutralization.
  • the amounts of neutralizing agent added to neutralize chrome-tanned leather according to the present invention are between about 0.5% and about 4% calculated for the weight of the leather to be treated depending upon the acid content of the leather.
  • the temperature during neutralization is preferably room temperature. However, when combining neutralization with dyeing and/or fat-liquoring and/or retanning, the treatment may be carried out at higher temperatures. Temperatures of about 70 C. are preferably not exceeded.
  • the duration of the neutralizing treatment depends on the type of leather treated and its acid content. The required time is readily determined by preliminary tests.
  • Emulsifiers as they are preferably used in preparing the fat-liquoring emulsions are emulsifiers based on ethylene oxide.
  • Such emulsifiers are, for instance, the polyoxy ethylene fatty alcohol ethers, the polyoxy ethylene fatty acid esters, the fatty acid esters of polyvalent alcohols and polyoxy ethylene, and the like compounds as they are well known to the art. It is, of course, understood that other emulsifiers may also be used provided they produce acid-stable aqueous emulsions of the fat-liquoring agents.
  • compositions of the neutralizing agent and the amounts employed, in the mode of application, and the temperature and duration of the treatment, in the fat-liquoring agents, dyestuffs, and retanning agents used, in the manner of working up and of finishing the chrome-tanned leather neutralized according to the present invention, and the like may be made by those skilled in the art in accordance with the principles set forth herein and in the claims annexed hereto.
  • the new tralizing agent is the alkali metal salt of a mixture of N-sulfomethylated u-amino acids obtained by hydrolysis of a proteinaceous material selected from the group consisting of collagen and keratin.
  • the neutralizing agent is the alkali metal salt of a mixture of N- sulfomethylated a-amino acids obtained by alkaline hydrolysis of glue.
  • a composition for simultaneously neutralizing and fat-liquoring chrome-tanned leather comprising water, the Water soluble salt of an N-sulfomethylated ot-amino acid present in natural proteins, said salt being dissolved in said water and serving as neutralizing agent, and a fat-liquoring agent stable at an acid pH-value, said fat-liquoring agent being emulsified in said Water.
  • the fatliquor emulsion is an aqueous emulsion of a mixture of sulfated oils selected from the group consisting of vegetable oils, animal oils, and train-oils, with such unsulfated oils and emulsifiers based on ethylene oxide.
  • a composition according to claim 10, wherein the neutralizing agent is the alkali metal salt of a mixture of N-sulfornethylated a-amino acids obtained by hydrolysis of a proteinaceous material selected from the group consisting of collagen and keratin.
  • a composition according to claim 10, wherein the neutralizing agent is the alkali metal salt of a mixture of N-sulfomethylated a-amino acids obtained by alkaline hydrolysis of glue.

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Description

Dec. 19, 1961 PRUETZ ETAL 3,013,858
PROCESS OF AND COMPOSITION FOR NEUTRALIZING CHROME-TANNEDI LEATHER Filed Aug. 27, 1959 I so so /00 CC. "/1 H1504 IO 10 3O 4O 5O 6O 70 W I00 [/0 IN V EN TORS ADA LBEQT Peusrz BY gfk/lly Que/vor- MMKW Patented Dec. 19, 1961 3,013,853 PROCESS 6F AND CQMKQSHTEGN FQR NEUTRAL- IZING CHROME-TANNED LEATHER Adalhert Pruetz, hopfingen, Wurttemberg, and Erwin Quendt, Kemnat, Germany, assignors to Schill & Seilaehcr, 'Chernische Fahrilr, Stuttgart, Germany, a company of Germany Filed Aug. 27, 1959, Ser. No. 836,335 Claims priority, application Germany Sept. 3, 1958 16 Claims. (Cl. 8-34.23
The present invention relates to a process of neutralizing and, if desired, simultaneously fat-liquoring chrometanned leather and to a composition adapted for neutralization and fat-liquoring of such leather.
Chrome-tanned leather must be neutralized after ten ning in order to remove the acid which is present in the leather and is released on storage of the leather by hydrolysis of the chromium complex compounds bound by the skin fibers. Neutralization is necessary in order to assure uniform fixation of the dye to and fat-honoring of the leather by means of suitable dyestuffs and fat-liquoring agents, and in order to prevent hardening of the leather on drying which may occur even if the leather is sufilciently fat-liquored.
lt is knownthat buffering salts, such as sodium bicarbonate, sodium acetate, calcium formate, and sodium sulfite are used for neutralization. Sodium phosphate, sodium thiosulfate, sodium nitrite, and borax have also been employed for this purpose, likewise salts of aromatic hydroXy carboxylic acids and polycarboxylic acids, such as phthalic acid and sulfo phthalic acid, salts of hydroxy dicarboxylic acids, and, furthermore, ammonium salts of sulfonic acids of synthetic tanning agents. Such ammonium salts have simultaneously a supplementary tanning action.
The neutralizing agents used heretofore convert the sulfuric acid which is mainly present in the leather, into sodium sulfate. Ordinarily they also cause formation of basic chromium complex compounds in the leather. It is another advantage of many neutralizing agents'that their anions enter the molecule of the chromium compounds. As a result thereof improvement of the grain, the fullness, and the grain strength of the leather is frequently achieved.
Heretofore, chrome-tanned leather has been neutralized by a treatment with a neutralizing solution, usually at a temperature of about 30 C. for a prolonged period of time. Said neutralizing solution contains a suitable neutralization agent in amounts depending on the kind of leather used. Thereafter, the neutralized leather is washed with water whereby the salts formed on neutralization are removed from the leather. Thereafter, washing of the leather with water is continued at gradually increasing temperature until a temperature of about 60 C. is reached as it is required for dyeing and fat-liquoring. Finally, dyeing and fat-liquoring of the leather is efiected in fresh solutions at about 60 C.
If the leather is to be dried according to the pasting process, processing of the chrome-tanned leather is even more complicated. After washing, the leather is first dyed and subjected to a preliminary fat-liquoring treatment. Thereafter, it is re-tanned in a fresh, cold solution of vegetable and synthetic tanning agents in order to im part to its sufficient fullness. Usually it is finally again fat-liquored in a fresh fat-liquoring solution at an increased temperature.
These procedures and the known neutralizing agents as they have been used heretofore are, however, highly unsatisfactory. The procedures are rather complicated and bothersome and require considerable time and labor. The neutralizing agents have a number of disadvantages especially inasmuch as they do not meet all the requirements of present day operation. For instance, a satisfactory neutralizing agent-must have a rather mild and uniform neutralizingetfect throughout the entire cross-section of the leather. It must not disadvantageously affect'the tanning chromiumcomplex compounds acting upon and within the leather, but must actually improve their tanning effect due to the combination of its anion with the chromium complex compound. Furthermore, it should be compatible with the fat-liquoring agent.
The neutralizing agents used heretofore, however, and especially sodium bicarbonate, are poorly compatible with rat-liquoring agents. As strong electrolytes they have a precipitating effect on the fat emulsion. They also prevent proper absorption of the oil by the leather fiber. This disadvantage is especially encountered when using sodium bicarbonate because it causes over-neutralization of the surface of the leather fiber. llt'is also known that many of the conventionally used neutralizing agents, especially sodium bicarbonate, permeate leather only very slowly. In order to achieve complete neutralization with sodium bicarbonate it is, for instance, necessary to expose the leather. to the neutralizing solution for at least one day and even the leather.
is one objsct'of the present invention to provide a new neutralizing agent which avoids all the disadvantages of the known neutralizing agents and permits to very considerably reduce the time required for neutralization.
Another object of the present invention is to provide a novel and improved neutralizing solution for neutralizing chrome-tanned leather, said solution containing the new neutralizing agent, said neutralizing solution having a mild effect, being capable of rapidly and uniformly permeating chrome-tanned leather, advantageously affecting the tanning chromium complex compounds in the leather and improving its tanning effect, and being well compatibl with the fat-liquoring agents.
Still another object of the present invention is to provide a simple and effective process of simultaneously neutralizing and fat-liquoring chrome-tanned leather.
Other objects of the present invention and advantageous features thereof will become apparent as the description proceeds.
According to the present invention chrome-tanned leather is neutralized by means of alkali metal, ammoniurn, or alkaline earth metal salts of sulfomethylated ot-arnino acids of the following formula:
X-OSO2CH2l$'( 3- COOY wherein X and Y are alkali metals, ammonium, or the equivalent Such sulfomethylated a-amino carboxylic acids are oblonger, depending on the thickness of tained from amino acids as they are present in natural proteins. They can be used in the pure state or in the form of mixtures produced by sulfomethylation of the pure u-arnino acids or of the a-amino acid mixtures obtained on hydrolysis of proteins and especially of glue and waste materials from animal skins. The required salts of such sulfomethylated a-amino acids are obtained, for instance, by hydrolyzing glue, other waste materials from animal skin, or other proteinaceous material with a sodium hydroxide solution at 110120 C. The amount of the sodium hydroxide exceeds preferably by the amount required for converting the resulting amino acids into their sodium salts. The pH-value of the resulting strongly alkaline solution of the salts of ot-amino acids is then adjusted to a pH of 8.5, for instance, by the addition of acetic acid. The sodium salt or another alkali metal salt, the ammonium salt, or the magnesium salt of hydroxy methyl sulfonic acid, i.e., the reaction product of formaldehyde and sodium hydrogen sulfite is added to said amino acid solution in an amount equimolecular to each free amino group of the amino acid. The reaction mixture is heated to 80-90" C. for about one hour and is then adjusted to a pH of 9.5. In this form the reaction solution can directly be used for neutralization.
The resulting salts of sulfornethylated a-amino acids have proved to be especially useful neutralizing agents of mild and uniform neutralizing action.
The neutralizing action of the neutralizing solution according to the present invention is characterized by a gradual decrease of the pH-value and a uniform penetration of the leather. Thus continuous deacidification is achieved and no substantial differences in pH-value within the leather layers are observed. In contrast to the neutralizing agents according to the present invention a sodium bicarbonate solution, as used heretofore, first causes diffusion of a considerable amount of acid from the leather fibers, before, the pH-value is considerably decreased. As a result thereof great differences in pH- value occur within the leather. Such differences have the disadvantage that a certain de-tanning effect takes place within the skin, due to over-neutralization of the chromium complex compound, and that permeation of the leather by the neutralizing agent is retarded.
The different chemical behavior of the neutralizing agents according to the present invention compared, for instance, with that of sodium bicarbonate, may best be demonstrated by the attached neutralization curves.
The attached drawings illustrate the neutralizing effect of the neutralizing agent according to the present invention and of sodium bicarbonate. In said drawings:
FIG. 1 illustrates the neutralizing curve obtained by titrating 100 cc. of a solution containing 7.5% of the sodium salt of sulfomethylated amino acid obtained as described hereinabove by alkaline hydrolysis of glue and reaction with formaldehyde-sodium hydrogen sulfite, with N/ 2 sulfuric acid, while FIG. 2 illustrates the neutralization curve obtained by titrating 100 cc. of a 3.5% sodium bicarbonate solution with N/2 sulfuric acid.
When using the neutralizing agent according to the present invention (FIG. 1), the curve descends gradual- 1y, uniformly, and continuously with progressing neutralization, whereas with sodium bicarbonate (FIG. 2) the curve first proceeds horizontally at a pH-value between 8.0 and 7.0 for a considerable period of time, and thereafter drops rapidly and abruptly to the acid pH-value of 4.0 and lower. The curves also illustrate very clearly the action of the mild neutralizing agent according to the present invention.
In order to achieve mild neutralization it has previously been proposed to neutralize the leather first with a relatively acid neutralizing agent, such as calcium formate, and then to complete neutralization with sodium bicarbonate. This process, however, has the disadvantage that it does not permit simultaneous fat-liquoring.
By using the heretofore known neutralizing agents, it is also not possible to dye, neutralize, fat-liquor, and, if desired, re-tan the leather in the same vat without rins ing it with water between each treatment and without changing the treating solutions. The neutralizing agent according to the present invention makes such a procedure possible. If the treating solution contains neutralizing agents according to the present invention and fat-liquoring agents and is employed at 20-60 C., neutralization and fat-liquoring can be carried out in the same vat. The new neutralizing agents exhibit good compatibility with chromium and a remarkable complex forming activity. During neutralization and fatliquoring they enter the chromium complex and contribute substantially to the improvement and strengthening of the grain.
Another advantage of the process according to the present invention is the fact that a composition containing neutralizing and fat-liquoring agents is remarkably stable against high electrolyte and acid concentrations so that, even without preliminary washing, simultaneous neutralization and fat-liquoring can be carried out immediately after tanning.
Still another advantageous feature of the process according to the present invention is the possibility of dyeing, neutralizing, fat-liquoring, and re-tanning at a temperature between about 20 C. and about 30 C. As a result thereof a substantial saving in time, energy, and labor is achieved. When using the known neutralizing agents, operation at such a low temperature was not possible.
Fat-liquoring agents, as they are useful in the process according to the present invention, are stable emulsions of mixtures of various oils, are not deemulsified at the rather low pH-value of 3.6-4.0 as it is encountered in the beginning of the neutralization step. Such fat-liquoring agents are, for instance, sulfonated train-oils or vegetable and animal oils in mixture with unsulfonated oils and, if desired, with emulsifiers of the ethylene oxide type.
The following examples serve to illustrate the process according to the present invention without, however, limiting the same thereto.
Example 1 Pared chrome-tanned calf-leather is rinsed with water of 20 C. for five minutes and is then immersed into twice its weight of the neutralizing solution containing 1.5% of the sodium salt of sulfomethylated amino acids obtained as described hereinabove from glue, at 20 C. for 30 minutes. The leather is rinsed with water of 60 C. for 10 minutes and dyed with a dye bath containing 1% of the brown acid dyestutf sold under the trademark Coranilbrown HEG by the Farbwerke Hoechst A.G., Franlc furt am Main-Hoechst, Germany, at 60 C. for 30 minutes. Thereafter 1.5% of sulfonated neats-foot oil sold under the trademark Ossipol SRA by Schill & Seilacher of Stuttgart, Germany, and 0.5% of unsulfonated neatsfoot oil are added to the dye bath and the leather is drummed for another 45 minutes. The resulting leather is placed on a rack and further processed in the manner customary for this kind of leather.
In this and the following examples the amounts of neutralizing agent, fat-liquoring agent, and other additives are given in percent of the leather to be treated. Likewise, the amount of tanning agent added is calculated as actual tanning agent in the tanning composition in percent of the leather to be treated.
Example 2 Shaved chrome-tanned kid-leather is rinsed with water of 20 C. for 5 minutes and is then treated with twice its amount by weight of a neutralizing solution containing 1% of the potassium salts of the above mentioned sulfomethylated amino acids. Immediately after the addition of the neutralizing agent, a pre-emulsified mixture of fatliquoring agents consisting of 2.5% of train-oil sulfonate, sold under the trademark Lipsol BN7 by Schill & Seilacher of Stuttgart, Germany, and 0.8% of unsulfonated train-oil or sperm oil is added. After one hour the leather is completely and uniformly neutralized and shows a bluish-green color throughout its cross-section when dyed with bromo cresol green. The fat is uniformly absorbed by the leather. Re-tanning is carried out in the same drum using 3% pure tanning agent consisting of equal parts of vegetable and synthetic tanning agents, such as a mixture of mimosa extract and chestnut wood extract (1:1) or of mimosa extract, chestnut wood extract, and quebracho wood extract (1:1:1). The leather treated in this manner has a fine, firm grain and full, firmly grained flank parts. After finishing, an especially soft leather is obtained.
Example 3 Chrome-tar1ned, shaved calf leather is rinsed with water of 30 C. for 5 minutes. it is then dyed at 30 C. in twice its amount by weight of a dye solution containing 0.5 of an'acid black dye sold under the trademark Suede Leather Black ET Cone. by Badische Anilin- & Sodafabrik A.G. of Ludwigshafen, Germany, for 30 minutes. Thereafter, 0.4% of a basic dye which has been mixed with 0.2% of formic acid to form a paste are added to the dye bath. After minutes a mixture of 3% of the neuralizing agent according to the present invention, 1% of soap, 1% of unsulfonated neats foot oil, and 1% of egg yolk are added. The leather is completely and uniformly neutralized after one hour and the fat is completely absorbed by the leather. After drying, the leather has a fine grain, said firm grain and fullness extending into the flank parts of the leather.
Example 4 Chrome-tanned, shaved calf leather to be dried by pasting to a glass plate or metal sheet, is rinsed with water for 3 minutes and is then dyed at C. in twice its amount by weight of a dye bath containing 1% of an acid black dye sold under the trademark Leather Black MB by Baclische Anilin- & Sodafabrik A6. of Ludwigshafen, Germany, for 30 minutes. Thereafter, there is added to the same bath a mixture of 0.5% of the neutralizing agent according to the present invention, 2.5% of a sulfated sperm oil sold under the trademark Lipsol BN3 by Schill & Seilacher of Stuttgart, Germany, and 1% of an unsulfated sperm oil which oils have been emulsified by an emulsifier of the ethylene'oxide type. After one hour the fat is completely absorbed by the leather which is also uniformly and thoroughly neutralized. The leather is then re-tanned in the same bath with 3% of a tanning agent consisting of a mixture of vegetable and synthetic tanning agents, such as quebracho wood extractand the synthetic tanning agent sold under the trademark Tannigan Q by Farbenfabriken Bayer A.G. of Leverkusen, Germany. The resulting re-tanned leather is then pasted to a glass plate or metal sheet and dried. The distribution of the fat in the leather is uniform. A thin film of fat remains on the surface and prevents any deep penetration of the adhesive required for pasting. The adhesive is composed of a cellulose methyl ether sold under the trademark Tylose by Kalle & Co. AG. of Wiesbaden-Biebrich, Germany. The dried leather is distinguished from leath r neutralized with the conven- I tional neutralizing agents by its increased fullness and its better grain.
Example 5 Chrome-tanned and shaved neats leather is rinsed for 5 minutes and dyed in twice its amount by weight of a dye bath containing 0.5 of an acid dye sold under the trademark Baygenal Brown CRG by Farbenfabriken Bayer AG. of Leverkusen, Germany, for 20 minutes. A mixture of 2% of the sodium salt of sulfomethylated amino acids used in the preceding examples, 2.5% of sulfonated sperm oil, and 0.75% of sperm oil is added to the same bath, and the leather is agitated therein for one hour. The fat is then completely absorbed by the leather. The leather is dried as usually and, after drying, shows an extremely fine grain and a high grain strength even in the flank parts thereof. It is also much softer than leather treated in the usual manner with the same amount of fat. I
Example 6 "Chrome-tanned and shaved neats'leather to be dried according to the pasting process is rinsed with water of 20 C. for 5 minutes and is then treated in twice its amount of neutralizing solution containing 2% of the ammonium salt of sulfomethylated amino acids obtained in a similar manner as described hereinabove for the sodium salt. Immediately thereafter a previously prepared liquoring emulsion consisting of 2.8% of sulfated trainoil sold under the trademark Lipsol A by Schill & Seilacher of Stuttgart, Germany, and 1.5% of a mixture consisting of animal and vegetable oils and an emulsifier on the basisof ethylene oxide, said mixture being sold under the trademark Ossipol KLM by Schill &Seilacher of Stuttgart, Germany, is added thereto. Said liquoring emulsion is prepared by pouring the sulfated train-oil and the oil mixture Lipsol A into 10 times their amount of water heated to 60 C. while stirring vigorously and The fat is completely The leather is thereby emulsifying the oils. absorbed by the leather after one hour.
then re--tanned in the same bath with 5% of a tanning 7 agent consisting of a mixture of the synthetic tanning agent sold under the trademark Tannigan Extra B by Farbenfabriken Bayer A.G. of Leverkusen, Germany, and
Example 7 Normally chrome-tanned and shaved leather to be dried by pasting is rinsed with water of 40 C. for 5 minutes and is treated with the same amount by weight of a neutralizing, fat-liquoring, and retanning preparation consisting of 3% of the neutralizingagent according to the present invention as used in Example 1, 3.5% of sulfated sperm oil, 1.2% of an emulsifiable oil consisting of a saponifiable oil, mineral oil, and an emulsifier on the basis of ethylene oxide, and 4% of a commercial resinous tanning agent.
The sulfated sperm oil used in this preparation is sold under the trademark Lipsol DN 3. The mixture of emulsifiable oil consisting of saponifiable oil, mineral oil, and emulsifier based on ethylene oxide is sold under the trademark Ossipol KLM. Th'e resinous tanning agent is either an agent sold under the trademark Chemtan R6 by Chemtan Company, Exeter, NH, or under the trademark Retingan R6 by Farbenfabriken Bayer AG. of Leverkusen, Germany.
After a treatment of one hour the'mixture has completely been forced into the leather. The leather shows a film on its surface as it is required for the paste-drying process. The dried and finished leather exhibits excellent grain strength and fineness of the grain and also a good fullness even of the flank parts of the leather.
Example 8 Normally chrome-tanned and shaved garment leather is rinsed with water for 5 minutes and is dyed at 30- C. in twice itsamount by weight'of a dye bath containing 1.5% of an acid dyestuff, sold under the trademark Baygenal Dark Brown CGV by Farbenfabriken Bayer A.G. of Leverkusen, Germany, for one hour. A mixture of 4% of the magnesium salts of sulfomethylated a-amino acids obtained in a similar manner as described hereinabove for the sodium salts and of 4% of a sulfitated trainoil sold under the trademark Lipsol GT by Schill & Seilacher of Stuttgart, Germany, is added to the dye bath and the leather is treated therein for 1 /2 hours. Thereafter, the fat has been completely absorbed by the leather which is uniformly neutralized. If desired, the leather can be retanned in the same bath by adding thereto a suitable amount of a tanning agent mixture consisting of vegetable tanning agents or a mixture of a vegetable and a synthetic tanning agent such as a mixture of chestnut wood extract and the synthetic tanning agent sold under the trademark Tannigan Extra Q" by Farbenfabriken Bayer A6. of Leverkusen, Germany. The resulting leather is distinguished by an extraordinary softness, grain strength, and grain fineness.
Example 9 Suede leather which has been pretanned and retanned with chromium salts is rinsed with water of 30 C. for minutes in order to remove the crystallized salt and adhering shavings. It is then treated with twice its amount of a neutralizing and fat liquoring preparation containing 2% of the neutralizing agent used in Example 1 which was mixed, before use, with 3% of an oil emulsified by a cationic emulsifier, such as a neats-foot oil emulsion emulsified by the cationic emulsifier sold under the trademark Vinkolamin K by Schill & Seilacher of Stuttgart, Germany. After a treatment of one hour with such a preparation, the fat has been completely and uniformly absorbed by the leather which is thoroughly neutralized. Subsequent fat-liquoring of the leather after dyeing is not necessary. The resulting suede leather is distinguished by a close and smooth surface and has no tendency of becoming smeary and greasy.
Of course, in place of the neutralizing agents used in the preceding examples which are the preferred agents due to their ready availability, there may be used as neutralizing agents other sodium, potassium, ammonium, magnesium, and other alkali metal and alkaline earth metal salts of N-sulfornethylated a-amino acids, such as, for instance, the sodium salts of N-sulfomethylated glycine, alanine, leucine (obtained, for instance, by acid hydrolysis of horn waste), glutamic acid (obtained from molasses or gluten or synthetically), histidine (obtained from blood corpuscles), cysteine (obtained from hair and other keratinous matter by hydrolysis with hydrochloric acid), phenyl alanine, proline, hydroxy proline, serine, threonine, tryptophan, aspartic acid, lysine, and others. It is also possible to use the alkali metal, ammonium, and alkaline earth metal salts of the sulfomethylation products of other protein hydrolysates, i.e., of mixtures of amino acids, such as the acid, alkaline. or enzymatic hydrolysates of casein, blood plasma, fibrin, and the like. The amino acids may, of course, also be produced synthetically. It is, however, understood that the least expensive starting materials for sulfomethylation are the hydrolysates obtained from proteinaceous byproducts and waste products of the leather industry such as collagen, i.e., the protein of connective tissue present in animal hides and skin and the organic substance of the bones, and keratin, i.e., the protein of epithelial tissue, such as hair, wool, horn, feathers, nails. Sulfomethylation of these protein hydrolysates or u-amino acids is carried out in the same manner as described hereinabove, i.e., by heating a solution of equimolecular proportions of sodium hydroxy methyl sulfonate or formaldehyde-sodium bisulfite and the sodium salts of the amino acids or sodium sulfite, formaldehyde and amino acid mixtures at 80-90 C. for one hour and adjusting the pH-value to a pH of 9.5. The resulting solution can be added to the chrome-tanned leather as such without isolation of the 8 salts of the N-sulfonated amino acids and without their purification. It is, of course, also possible to isolate and purify said salts and to use them in the dry state for leather neutralization.
The amounts of neutralizing agent added to neutralize chrome-tanned leather according to the present invention are between about 0.5% and about 4% calculated for the weight of the leather to be treated depending upon the acid content of the leather.
The temperature during neutralization is preferably room temperature. However, when combining neutralization with dyeing and/or fat-liquoring and/or retanning, the treatment may be carried out at higher temperatures. Temperatures of about 70 C. are preferably not exceeded.
The duration of the neutralizing treatment depends on the type of leather treated and its acid content. The required time is readily determined by preliminary tests.
Emulsifiers as they are preferably used in preparing the fat-liquoring emulsions are emulsifiers based on ethylene oxide. Such emulsifiers are, for instance, the polyoxy ethylene fatty alcohol ethers, the polyoxy ethylene fatty acid esters, the fatty acid esters of polyvalent alcohols and polyoxy ethylene, and the like compounds as they are well known to the art. It is, of course, understood that other emulsifiers may also be used provided they produce acid-stable aqueous emulsions of the fat-liquoring agents.
Of course, many changes and variations in the compositions of the neutralizing agent and the amounts employed, in the mode of application, and the temperature and duration of the treatment, in the fat-liquoring agents, dyestuffs, and retanning agents used, in the manner of working up and of finishing the chrome-tanned leather neutralized according to the present invention, and the like may be made by those skilled in the art in accordance with the principles set forth herein and in the claims annexed hereto.
We claim:
1. The process of neutralizing chrome-tanned leather, which process consists in working the leather with a solution of a water soluble salt of an N-sulfomethylated aamino acid present in natural proteins, until the leather is thoroughly and uniformly neutralized.
2. The process according to claim 1, wherein the salt of the N-sulfomethylated a-amino acid is the sodium salt.
3. The process according to claim 1, wherein the salt of the N-sulfomethylated oc-amino acid is the ammonium salt.
4. The process according to claim 1, wherein the salt of the N-sulfomethylated a-amino acid is the magnesium salt.
5. The process according to claim 1, wherein the neutralizing agent is added in an amount by weight between about 0.5% and about 4.0% calculated for the amount by weight of the leather to be treated.
6. The process according to claim 1, wherein the temperature during neutralization is maintained at a temperature not exceeding about 70 C.
7. The process according to claim 1, wherein the new tralizing agent is the alkali metal salt of a mixture of N-sulfomethylated u-amino acids obtained by hydrolysis of a proteinaceous material selected from the group consisting of collagen and keratin.
8. The process according to claim 1, wherein the neutralizing agent is the alkali metal salt of a mixture of N- sulfomethylated a-amino acids obtained by alkaline hydrolysis of glue.
9. The process of simultaneously neutralizing and fatliquoring chrome-tanned leather, which process consists in working the leather with a mixture of a water soluble salt of an N-sulfomethylated ot-amino acid present in natural proteins and an aqueous fat-liquor emulsion stable at an acid pH-value, until the leather is uniformly and thoroughly neutralized and fat-liquored.
10. A composition for simultaneously neutralizing and fat-liquoring chrome-tanned leather, said composition comprising water, the Water soluble salt of an N-sulfomethylated ot-amino acid present in natural proteins, said salt being dissolved in said water and serving as neutralizing agent, and a fat-liquoring agent stable at an acid pH-value, said fat-liquoring agent being emulsified in said Water.
11. The process according to claim 9, wherein neutralization and fat-liquoring are effected at a temperature between room temperature and a temperature of about 70 C.
12. The process according to claim 9, wherein the fatliquor emulsion is an aqueous emulsion of a mixture of sulfated oils selected from the group consisting of vegetable oils, animal oils, and train-oils, with such unsulfated oils and emulsifiers based on ethylene oxide.
13. The process according to claim 9, wherein the neutralizing agent is added in an amount by weight between about 0.5% and about 4.0% and the fat-liquoring agent is present in an amount by weight between about 0.5% 20 2,496,640
10 and about 5.0% calculated for the amount by Weight of the leather to be treated.
14. The process according to claim 9, wherein neutralization and fat-liquoring are effected at a temperature between about C. and about C.
15. A composition according to claim 10, wherein the neutralizing agent is the alkali metal salt of a mixture of N-sulfornethylated a-amino acids obtained by hydrolysis of a proteinaceous material selected from the group consisting of collagen and keratin.
16. A composition according to claim 10, wherein the neutralizing agent is the alkali metal salt of a mixture of N-sulfomethylated a-amino acids obtained by alkaline hydrolysis of glue.
References Cited in the file of this patent UNITED STATES PATENTS Jaeger Apr.26, 1938 Schiller et a1 Feb. 7, 1950

Claims (1)

1. THE PROCESS OF NEUTRALIZING CHROME-TANNED LEATHER, WHICH PROCESS CONSISTS IN WORKING THE LEATHER WITH A SOLUTION OF A WATER SOLUBLE SALT OF AN N-SULFOMETHYLATED AAMINO ACID PRESENT IN NATURAL PROTEINS, UNTIL THE LEATHER IS THOROUGHLY AND UNIFORMLY NEUTRALIZED.
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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2115509A (en) * 1936-08-08 1938-04-26 American Cyanamid & Chem Corp Lubricating of leather
US2496640A (en) * 1944-05-18 1950-02-07 Nopco Chem Co Fat liquoring and alum tanning

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2115509A (en) * 1936-08-08 1938-04-26 American Cyanamid & Chem Corp Lubricating of leather
US2496640A (en) * 1944-05-18 1950-02-07 Nopco Chem Co Fat liquoring and alum tanning

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