US2371875A - Processing skins - Google Patents

Description

I Patented Mar. 20, 1945 rno'oessmo SKINS Edward F. Christopher, Chicago, 111., assignor .to Industrial Patents Corporation, Chicago, 111., a

corporation of Delaware No Drawing. Application May 22, 1942,

Serial No. 444,102

22 Claims. (01. 894.16)

This invention relates to a method of, treating hides and skins to prepare the hides and skins for the subsequent tanning process.

prlhenolder ,conventional-methed of treating hides and skins for the removal of hair Ell 001*? consists of soaking the hides or skins in a lime bath for from about five days to seven days. At the end of this soaking period the hides are removed and thoroughly washed. The hides are then subjected to a beaming operation in which the hides are scraped or beamed with a dull knife or blade to remove the hair and to squeeze out any wool or hair roots. This operation simul-' taneously removes foreign materials and dirt from the skin, but it is a costly operation because it is of necessity a hand operation. In this method for removing hair and wool, a considerable time is required and large spaces must be provided for the tanks in which the hides are treated with the lime liquor.

1 Numerous methods have been employed and v have been proposed to hasten the dewooling'and dehairing process or to provide a method of re-.

moving the hair or wool in a shorter period of time. Perhaps the most commonly used method of treating hidesand skins for the removal of hair or wool consists of what may be classed as a two stage method including dewooling and dehairing the pelts. wooled by painting or treating the flesh side of the hide or skin with a depilatory consisting of a paste containing lime, sodium sulfide and water. The paste is generally prepared by mixing slaked lime with powdered sodium'sulfide in a ratio of about 60 parts of lime to 40 parts of sulfide and adding suflicient water so that the paste may be painted on the skin or hide with a brush. The treated skins are then allowed to remain in a cool place over night or for from about 16 hours to 24 hours to permit a penetratioh of the depilatory from the flesh side through the skin to the roots of the hair or wool. "I'heskins are then subjected to mechanical action, as by rubbing, scraping or brushing, whereby the wool is removed. The pulling of the wool removes the major portion of the wool and hair, however, some fine hair, some hair or wool roots remain. The skins treated with the 'depilatory and'from which the wool has been-pulled are generally known as dewooled skins.

The dewooled skins are then "dehaired by soaking the skins in a bath containing sodium, sulfide, usually from about 1.3 per cent to 1.5 per cent for about 24 hoursto 72 hours. The stins are then subjected to a reeling operation whereby the hides are agitated in the bath for a sufiicient period of time to substantially. remove the remaining fine hair and wool and the re- ,maininghair or wool roots.- 'This method of treating hides and skins permits the removal of the hair and wool in from twodays to three days, however, the skins are affected to a much greater extent than in the older conventional method.

One of the principal objections to this method is that the skins become drawn. This condition produces a loose grained leather and one side of the hide appears to draw or shrink to a greater extent than the other surface. The other principal objection to skins processed in this manner is that they do not possess the same degree of stretch or elasticity a skins processed in accordance with the older conventional manner.

Numerous compositions have been proposed, including the use of various enzymes, various organic materials andvarious inorganic salts, for

m the treatment of dewooled hides and skins to aid maining hair roots.

in removing the remaining fine hair and re- However, these substances are in many instances too costly for commercial application, and many of the substances are so severe in their action that they injure the skin The skins or hides are dealthough a close control of the process is attempted. it

. The principal object of the present invention is to provide a method whereby the removal of hair and wool may be accomplished in a shorter period of time than the older lime method but which produces a type of skin which is substantially the same as. the .type of skin produced by this old method. Another of the objects of this invention is to provide a method for treating dewooled hides. and skins which is more efiicient in the removal of the fine hair and hair or wool roots so that hand beaming of hides and skins is unnecessary.

Another object of this invention is to provide a method of treating dewooled hides and skins for the removal of residual hair and hair or wool roots so as to yield a higher quality hide or skin for ,the subsequent preparation of leather.

The present invention contemplates the addition to an alkaline-sodium sulfide dehairing liquor of a small proportion of water oluble compounds and thiocyanates. .Examples of derivatives of these acids are normal and isocyanuric acid or tricyanic acid, cyanuromonoamid'e or ammelide, cyanurotriamide, and the like. The foregoing specific substances are not intended as limitations, but are set forth merely as illustrative- It is obvious that other compounds and derivatives are satisfactory. The term water soluble isused to designate a sufiicient solubility to form an aqueous solution of the required concentration for the purposes of this invention.

It is well-known that the ordinary conventional alkaline solutions or suspensions of sodium sulfide are relatively slow in their dehairing action and various reagents have been added in an attempt to increase the rate of dehairing. However, these substances are generally injurious to the hides and skins. The reagents employed in the practice of the present invention are not injurious to the hides and skins, and, in general, permit the use of smaller quantities of lime and sodium sulfide. In the practice of the present invention the reagent is added to the dehairing liquor, preferably during treatment of the hides with the liquor.

The liquor isfirst prepared by dissolving from about 0.1 per cent to 1.3 per cent, preferably from about 0.3 per cent to 0.5 per cent, sodium sulfide in water. The dewooled hides or skins are then soaked in this solution, about 3 parts to 4 parts by weight of solution being employed for about each part by weight of hides'or skins. The hides are reeled in this liquor or solution for about one hour. Lime is then added in the proportion of from about 1 per cent to 5,per cent, based upon the weight of the solution, and the hides are again reeled for about one-half hour. then added to and dissolved in the solution and the skins or hides again reeled for about one hour. The hides are then allowed to remain in the liquor for from 16 hours to 24 hours after which they are again reeled to remove the swollen or pulped wool and hair. The hides are then separated from the liquor, thoroughly rinsed and are ready for the subsequent hating and pickling operations. I

It is obvious to those skilled in the art that the proportions which are set forth arenot critical and may be varied. The reagents employed in the practice of the present invention are preferably employed in quantities between 0.1 per cent and 0.5'per cent. For certain special pur- The reagent is' of hair and wool remaining after dewooling had been removed or dissolved. However, to remove the remaining pulped wool and hair, the skins were reeled for about one hour after which the liquor was drained from the skins and the skins thoroughly washed with water.

Skins treated in accordance with the method described are, free from all hair and hair roots and appear to remain unafiected in all other respects. The skins are not drawn and they possess about the same stretch or elasticity as skins processed by the straight lime method.

The precise nature of the action of the particular reagents is 'not understood. However, the reagents greatly accelerate the dissolving or pulping 01' the hair and hair roots remaining after dewooling. At the same time the action is not so severe that it injures in any way the skins or hides. The improvements in the dehaired skins may be due to the lower alkalinity of the dehairing bath or solution as compared to the conventional dehairing solutions.

The term dewooled skins is employed herein and in the claims-jo designate, hide d skins which have been subjected to the first stage in the method "of removing hair and wool. This stage comprises treating the hide or skin with a depilatory and subjecting the treated hide or skin to mechanicalaction whereby the major portion of the hair and wool is removed. The term dewooling is used to designate this first stage in the removal of hair and wool from hides and skins.

poses it may be desirable to employ as much as 10 on the flesh side of the skins and the skins held in a cool place over night. The following morning the skins were dewooled. About 80 pounds of the dewooled skins'were soaked in about 280 pounds of sodium sulfide solution containing between 0.3

.per cent and 0.35 per cent sodium sulfide. The

skins were reeled in this solution for about one hour and about 1 per cent lime based upon the weight of the solution was added directly to the liquor. Reeling was continued for about onehalf hour. About 0.1 per cent ammonium cyanate, sodium cyanate or thiocyanate was then added and reeling continued for a further period of about one hour. Theskins were then allowed to soak in this liquor over night. The following morning it was found that the greater proportion The smaller The term dehaired skins is used herein and in the claims to designate dewooled skins which have been subjected to a treatment which removes the hair and wool remaining after the dewooling stage- The term dehairing is used to designate the secondstage in the removal of hair and wool from hides and skins.

It is to be understood that the foregoing specific examples are not intended as limitations, but have been set forth as being merely illustrative of the invention. Various modifications will suggest themselves to those skilled in the art and may be made without departing from the spirit and scope of this invention. For example, it is obvious to those skilled in the art that sulfides' other than sodium sulfide, such as potassium or ammonium sulfides, might be used in the dehairing bath.

I claim:

1. In a method of removing hair and wool from hides and skins, the step which comprises subjecting the hides and skins to the action of an aque ous, alkaline medium containing lime, an alkali sulfide and a substance selected from the group consisting of salts of cyanic and thiocyanic acids, cyanuric and isocyanuric acids and amides oi cyanuric acid.

2. .In a method or removing hair and wool from hides and skins, the step which comprises subjecting the hides and skinsto the action of an aqueous alkaline solution containing lime, an alkali sulfide and a small proportion of a substance selected from the grou consisting of water soluble salts of cyanic and thiocyanic acids, cy-

anuric and isocyanuric acids and amides of cyof cyanuric acid.

cyanuric and isocyanuric acids and amides of fide' and up to 10 per cent of a substance se-- lected from the group consisting of salts of cyanic and thiocyanic acids, cyanuric and isocyanuri acids and amides of cyanuric acid.

5. In a method of removing hair and wool from hides and skins, the step which comprises soaking dewooled hides and skins in an aqueous solution containing about 1 per cent to 5 per cent lime,

about 0.1 per cent to about 1.3 per cent sodiumsulfide and about 0.1 per cent to about 0.5 per cent of a substance selected from the group consisting of water soluble salts of cyanic and thiocyanic acids, cyanuric and isocyanuric acids and amides of cyanuric acid.

6. In a method of removing hair and wool from hides and skins, the steps of soaking dewooled hides and skins in an aqueous solution.

of sodium sulfide, adding lime to the aqueous solution and reeling the hides and skins in the resulting liquor, adding a small proportion of a substance selected from the group consisting of water soluble salts of cyanic and thiocyanic acids, cyanuricand isocyanuric acids and amides 7. The method of accelerating the dehairing of dewooled hides and skins by the use of alkaline dehairing liquors containing lime and sodium sulflde, which comprises adding to the dehairing liquor an amount of a substance selected from the group consisting of salts of cyanic and thiocyanic acids, cyanuric and isocyanuric acids and amides of cyanuric acid. r

8. In thdmethod oi dehairing dewooled hides and s by the action of an alkaline medium contai g lime and sodium sulfide, the improveoyanic acids, cyanuric and isocyanuric acids and amides of cyanuric acid.

9. A dehairing liquor comprising lime, an alkali sulfide and a substance selected from the group consisting of salts of cyanic and thiocyanic acids,

,11. In a method of removing hair and time! 'ment which comprises adding to the alkaline ,medium an amount of a substance selected from the group consisting of salts of cyanic and thi sodium sulfide and about 0.1 per centto about 0.5 per cent sodium cyanate.

13. In a method of removing hair and wool from hides and skins, the step which comprises subjecting dewooled hides and skins to the action of an aqueous alkaline medium containing lime, an alkali sulfide and sodium thiocyanate.

14. In a method of removing hair and wool. from hides and skins, the step which comprises soaking dewooled hides and skins in an aqueous solution containing about 1 per cent to about 5 per cent lime, about 0.3 per cent to about 0.5 per cent sodium sulfide and about 0.1 per cent to about 0.5 ,per cent sodium thiocyanate.

15. In a method of removing hair and wool from hides and skins, the step which comprises subjecting dewooled hides and skins to the action of an aqueous alkaline medium containing an alkali sulfide and ammonium thiocyanate.

16. In a method of removing hair and woolsolution containing about 1' per cent to about 5 per cent lime, about 0.3 per cent to about 0.5 per cent sodium sulfide and about 0.1 per cent to about 0.5 per cent ammonium thiocyanate.

1'7. The method of accelerating the dehairing of dewooled hides and skins by the use of alkaline lime-sodium sulfide dehairing liquors, which comprises adding to the dehairing liquor a small proportion of sodium cyanate.

18. The method of accelerating the dehairing of dewooled hides and skins by the use of alkaline lime-sodium sulfide dehairing liquors, which comprises adding to the dehairing liquor a small proportion of sodium thiocyanate,

19. The method of accelerating the dehairing I of dewooled hides and skins by the use of alkaline lime-sodium sulfide dehairing liquors, which comprises adding to the dehairing liquor a small proportion of ammonium thiocyanate.

20. A dehairing liquor comprising lime, sodium sulfide and sodium cyanate. 21. A dehairing liquor comprising lime, so

' diumsulfide and sodium thiocyanate. 1

22, A dehairing liquor comprising lime, sodi sulfide and ammonium thiocyanate.

' EDWARD F. CHRISTOPHER.