US2041732A - Leather manufacturing - Google Patents

Description

Patented May 26, 1936 g UNITED STATES PATENT OFFICE 2,041,732 LEATHER MANUFACTURING No Drawing. Application July 7, 1934,

Serial No. 734,193

5 Claims.

The present invention relates to improvements in leather manufacture and it particularly relates to an improvement in the dehairing and unhairing of skins and hides.

5 Considerable dimculty has been encountered in satisfactorily employing enzymes, particularly of proteolytic-nature, in commercial processes for dehairing and/or bating skins and hides. In the .various processes involved in the manufacture of 10 leather, and particularly in the dehairing and bating processes, the various steps and processes are closely inter-related and it is necessary at all times to carefully adjust each step and operation in relation to each other step and operation,

15 as otherwise the skin or hide will not be satisfactorily. treated nor will it be converted into a most desirable grade of leather.

In dehairing with enzyme preparations it has been found desirable to treat the skin or hide with 20 a relatively strong alkali, as caustic soda, sodium sulphide and other strong alkalies, to cause proper swellingthereof. It was usually customary, subsequent to the alkali swelling process, to neutralize skin or hide, as for example, with sodium bi- 25 carbonate until a relatively low pH, slightly above the neutral point was obtained, as for example, at a pH of about 7 to 8. At this relatively low pH the hide or skin was treated with the enzyme preparation which preferably would not be disiO advantageously affected if the leather were maintained at relatively low pH values just on the alkaline side of neutrality.

To give one example of the prior art practices it was customary to reduce the alkalinity of the i5 hides or skins after the alkali swelling process from a pH of above 12 down to a pH of from 7 to about 8, as for example with such neutralizing agents as sodium bicarbonate and boric acid.

This neutralizing operation was quite disad- 10 vantageous in many respects. It tended to shrink the extended fibres quite rapidly and apparently tended to shorten them irreversibly, with the result that after tanning a fiat piece of leather was formed. 5 Moreover, the neutralizing reaction tended to break up the soaps and emulsions or colloidal solutions of fats or greases, with the result that these fats or greases or free fatty acids formed by hydrolysis were precipitated upon and/or ab- 9 sorbed by the surface of the hide or skin. This inclusion of a relatively impervious layer of fatty, greasy, and/r waxy materials over the surface of the skins or hides often interfered with the uniform action of the enzyme preparation during the unhairing process, but in addition made it impossible to remove readily the fats, greases, and waxes contained in the skins or hides.

In order to obtain a good and uniform piece of leather, particularly of a uniform color without mottling or spotting, and/or with a uniform ap- 5 plication of finish,'it was necessary subsequently to degrease the skins or hides, as for example with acetone and benzene, as otherwise the subsequent processes would tend to take place irregularly. In addition the skin or hide would 10 tend to spew, resulting in the grease or fat gradually working itself to the surface and spoiling the appearance thereof.

An object of the present invention is to provide an enzymatic dehairing process for skins or hides, in which it will not be necessary to cause substantial neutralization of the skin or hide after preliminary alkalization treatments, and in which assurance will be had that the greases, oils and fats and relatively insoluble soap combinations will not be precipitated upon the skin or hide previous to the unhairing, bating, tanning, and other treating processes.

Another object is to provide an enzymatic treatment for hides or skins in the preparation of leather in which the preliminary alkalization treatment may be substantially directly followed .by the enzymatic dehairing treatment without a substantial neutralization operation or with only relatively slight neutralization of the skin or hide after alkalization, such neutralization being insufficient to cause deposition of greasy, waxy and/or fatty materials upon the surface of the leather.

Other objects will appear during the course of the following specification.

It has been found according to the present mvention that it is possible to eliminate the customary neutralization process, which reduces the pH of the hide or skin after alkalization from about above 12 to about 7 to 8. According to the present invention, on the other hand, the alkalized skin or hide is subjected without substantial neutralization to an enzymatic dehairing process after it has been only slightly modified by reducing the pH to between 11 and 9 or preferably from about 12 to about 9.6.

The present invention contemplates the dehairing of hides or skins under pH conditions much higher than heretofore contemplated in which connection certain enzymes may be most effectively employed. Among the proteolytic enzyme preparations which may be most satisfactorily employed are those which are derived by the growth of certain bacteria under specified conditions, said enzyme preparations being most desirably employed in a mixture containing carbohydrate and protein decomposition products which mixture tralized to a pH of between 7.5 to 9.5 and preferably about 8.5 and it is then sterilized, as for example; with steam under pressure and 140 C. for 35 minutes. 1

After the liquor has been sterilized and its pH has been reduced to about 6.2, it is inoculated with a pure culture of the bacillus of the mesentericus or subtilis families. The culture is allowed to develop at or about room temperature or slightly thereabove, and in one instance a temperature of 30 to 40 degrees C. was found most satisfactory.

' the subsequent enzymatic processes. 76

While "the culture is developed it is preferably kept in relatively. thin layers not exceeding onehalf of one inch thickness and is continuously supplied with sterile air which has free access thereto.

- After the culture has suitably developed and suflicient of the enzymatic product and metabolic carbohydrate and protein decomposition products have been formed ,in the liquor, a suitable disinfectant should be added to stop further bacterial growth and to devoid the liquor of living microorganisms.

The antiseptic must be most carefully regulated so as not to disadvantageously affect the relatively delicate enzymatic products formed and at the same time must be controlled so that it will assure that there will be no living bacteria present nor any living micro-organisms, as otherwise the subsequent dehairing process would be unsatisfactory. Among the preferred antiseptics which may be employed preferably in combination are phenol, cresylic acid, betanaphthol, and otherphenol derivatives and preferably consisting of the hydroxylated compounds-of monoalkylated or polyalkylated benzenesor of naphthalenes, which may also be halogenated or chlorinated.

Preferably these disinfectants are utilized in combination, as, for example, in combination of pine oil and naphthol or naphthol and cresylic acid, or cresylic acid and pine oil, or all three, since the compounds in combination appear to be more satisfactory than any of these antiseptics when utilized alone. Preferably the antiseptic is added to the mixture in amount of-much less than 2%, and preferably in amounts less than 1% with a preferred range of between 0.5v to 0.75%.

The enzymatic medium then which is preferably filtered from insoluble materials contains the proteolytic enzymatic composition and usually desirably also amylolytic and lypolytic enzymes, and in addition metabolic decomposition products of the proteins and carbohydrates, particularly various hexoses, polysaccharides, dextrines, amino acids, peptones, albuminoids, and so forth.

These protein decomposition products and particularly the amino acids appear to have a most advantageous action on the dehairing process in This enzyme composition may be most satisfactorily utilized with hides or skins which have been prepared as previously stated by alkaliz'awill be subsequently above 9 and say between 10 I and '11.-

The process of present application is particularly adapted to lightweight skins, such as kidskins, goatskins, sheepskins, calfskins and so forth.

In preparing these hides or skins for treatment with the enzyme, it has been found most satisfactory to treat them with caustic alkali solutions ranging from 0.01 to 1.0 normal concentration with a preferred concentration at about 0.10 or between 0.05 to 0.3 normal. The preferred temperature range is from 20 to 40 degrees and it may approximate about 30 degrees.

In one procedure about 100 parts by weight of skins or hides were placed in a bath containing 800 parts by weight of water and 4% to 6 parts of caustic soda, a sodium hydroxide between N/8 and N/10 being most preferably employed. The temperature of the bath at the commencement of the reaction was maintained at about 86 F. and it was gradually allowed to fall to about 70 F.

The treatment with alkali preferably takes place with agitation or stirring and may be conveniently performed for a period ranging from 12 hours to 96 hours with a preferred range from 1 to 3 days. After this treatment the hides will have a pH of 11 to 12 or above and in one preferred procedure it is desirable to reduce their pH to between about 10 to 11 or to between about 9.6 and 11.

In reducing the alkalinity of the skins or hides it has been found most suitable to cause a gradual reduction, as for example, bywashing with water, preferably without the utilization of sodium bicarbonate or boric acid in such quantities. It is not preferred that a reduction to between 7 to 9 in the pH value should be caused with the many disadvantageous effects above described.

According to one procedure, in accordance with the present application, 100 pounds of dried goat skins are soaked two days and are then preferably broken and fleshed. These goat skins are then subjected to a dilute caustic soda solution in a paddling apparatus. This paddling apparatus may be of 950 gallons capacity and contain in solution 41 A; pounds of caustic soda. It has been vfound desirable in this caustic soda treatment to also have present a neutral salt, as for example, 41% pounds of some neutral alkali metal salt, as sodium chloride or sodium sulphate.

In one instance about 2 parts of sodium sulphate were utilized for about every one part of .soda to prepare a suitablealkalizing bath.

The goat skins were treated in this paddle with alternate agitation and rest periods, with the "rest periods increasing and the agitation periods After this washing to slightly reduce the sir of the skins or hides to between 9.6 and 11, these pending upon the amount of time which intervenes before the enzymatic treatment the washing period may be varied. For example, if the skins or hides are ready for treatment with the v enzymatic liquor prepared as stated above. .De-

skins are to be'subjected to enzymatic treatment but if they are to be subjected the next day they need be washed only for 40 to 45 minutes. On the other handif they are to be subjected to the enzymatic treatment two days later, they are washed for only twenty minutes. After the washing process the skins are preferably treated with an alkali material of substantially less alkalinity than caustic, as for example borax.

In the present instance it has been found satisfactory to add from 4 to 8 pounds of borax to 500-900 pounds of the skins in the paddle and then to alternately paddle and permit the skins to rest while maintaining a pH of the solution between 10 and 11. After this borax treatment the skins or hides may be directly subjected to the enzymatic treatment, the enzymatic liquor being added to the paddle. For example, the thirty pounds of the enzymatic liquor may be added to the paddle together with ammonium chloride, sodium bisulphite and a small amount of boric acid. In one instance from six to ten pounds of boric acid, from two to ten pounds of ammonium chloride, and from 1 to thirty pounds of the bacterial enzymatic liquor were utilized. The pH of the skin or hide at this time was substantially above 8 and preferably above 9.

To this enzymatic liquor during the unhairing process may be conveniently added some of the disinfectant solution, as mentioned above. After the unhairing treatment has been completed, the enzymatic liquor is removed, the skins are washed and some disinfectant is added to the paddle as above described. After unhairing the skin and hides are thenpreferably washed, most desirably with a wash water having a pH of above 9 and preferably between 10 and 11. This alkaline washing has the effect of cleansing the skins and hides.

1 The skins and hides may then be bated with a high degree of satisfaction. This hating process, of course, may be followed by the other leather manufacturing process including tanning.

By maintaining a relatively high pH during the unhairing process, as above described, and also by utilizing specially prepared enzymes, which are most satisfactorily employed undersuch conditions, a most satisfactory unhairing process is obtained with a production of a more desirable grade of leather of higher quality.

In addition to or in lieu of the bacterial enzymes preferred employed, may also be utilized proteolytic enzyme preparations containing pancreatin, papain, trypsin, bromelin, and enzyme mixtures or compositions derived from Aspergillus oryzae, niger and/or Penicillium, Mucor delemar, amylomycesrouxii, Tryotria: tennis and so forth.

What is claimed is: I

1. A process of dehairing skins and hides which comprises subjecting them to successive treatments with a caustic alkali solution and with an aqueous solution of a bacterial proteolytic enzyme at a pH substantially above 8.0, said successive treatments being carried out without intervention of an intermediate treatment with a solution of sodium bicarbonate.

2. A process of dehairing skins and hides which comprises subjecting them to successive treatments with a' caustic alkali solution and with an aqueous solution of a proteolytic enzyme derived from bacterial growth, said last treatment being carried out under sterile and highly alkaline conditions, said successive treatments being carried out without intervention of an intermediate treatment with a solution of sodium bicarbonate.

3. A process of dehairing skins and hides'which comprises subjecting them to successive treatments with a caustic alkali solution and with an aqueous solution of a bacterial proteolytic enzyme at a pH between 8 and 11, said successive treatments being carried out without intervention of an intermediate treatment with a solution of sodium bicarbonate.

4. A process of dehairing skins and hides which comprises subjecting them to successive treatments with a caustic alkali solution and with an aqueous solution of a bacterial proteolytic enzyme in presence of metabolic amino derivatives at a pH of above 9, said successive treatments being carried out without intervention of an intermediate treatment with a solution of sodium bicarbonate.

5. A process of dehairing skins and hides which comprises subjecting them to successive treatments with a caustic alkali solution and with an aqueous solution of a sterile bacterial liquor de-