US2150919A - Treating hides - Google Patents

Description

Patented Mar. 21, 1939 UNITED STATES $3 tiiigi't iiiiii'tt PATENT OFFICE TREATING HIDES Erich Hansen, Hohokus, N. J., assignor to Buffalo Electro-Chemioal Company, Inc., Tonawanda, N. Y.

No Drawing.

3 Claims.

This invention relates to a method for improving the usefulproperties of tanned animal skins and hides, and more particularly to a process of improving the color and resilience of leather without adversely affecting the tensile strength thereof.

In the process of preparing leather as practiced heretofore, including all operations as are conventionally used to convert the raw animal hide into a finished product suitable for use where the product 'must possess a light color and withstand wear and tear, the tanner ordinarily has difliculty' in producing finished leathers of constant uniformity of color, and matching is therefore difficult. Due to the varied origin of each hide, the tanner is always confronted with the problem ofworking with hides, the history and composition of which he knows very little, to produce a salable article possessing a substantially uniform grade or finish with the possibility of matching hides with respect to color, feel, level, and tensile strength, among other characteristics.

Heretofore substantially all efforts to obtain uniformity of color in tanned skins or hides have consisted in exposing the tanned skins to sunlight to obtain a sunbleach, the so-called natural bleach. Thlsproceeding is a purely arbitrary or rule of thumb method and it is possible during such exposures to injure the tanned hides or skins since tanned hides and skins are prone to dry out, with a resultant loss of valuable properties in the finished leather. Further, with adverse weather conditions, the task of producing a leather of light and even color is rendered extremely diflicult. In order to prevent the drying out of the skins it has been necessary heretofore to impregnate the tanned skins with mixtures of fat liquors and even oils to prevent drying out and protect the tensile strength of the leather. While the skin is exposed to sunlight in the open the fat liquor or oil and dirt, soot, dust or other extraneous impurities depositing upon the skin, prevent uniform color elimination by the sunlight. All of these foreign matters must finally be removed from the leather before it is suitable for ultimate use.

Due to this sunlight method of treatment, efficient operations in tanneries are seasonal, intermittent, and at best limited to a few good weather months of the year. Since the average time of bleaching by sunlight is on the order of two weeks or more, although under'ideal weather conditions, a bleaching can be effected within p wwv s Application April 17, 1935, 5 Serial No. 16,930 x95 1.

(01. 8-411) fi J capacity must be available for" the 'rposure and storage of the skins during this operation, this method of procedure increases the investment necessary as well as the risk, a large capacity being necessary to insure continuous production. In any case, no matter how long the skin might have been exposed to sunlight a uniform bleach throughout the skin can never be obtained by sunlight bleaching. Upon splitting the tanned and sun treated skin, the back side (the inner part of the skin before splitting) will have the original yellowish color, a color impossible of elimination by this procedure and, therefore, leathers produced by sunlight treatment are useful on one side only, at least insofar as desirability of color, and possibility of matching color is concerned.

In accordance with the procedures of the present invention, the hide is shaken to remove the salt, naphthalene or the like, then brushed or cleansed to remove foreign matter in the usual way, the type of treatment being selected in accordance with the particular hide and in ac-v cordance with the type of leather to be produced. The hide thereafter is dehaired, and is therefore subjected to any suitable depilatory, the selection of the type of depilatory or the method of treatment for hair removal being governed by practical operating considerations.

Subsequent to depilation the hide is tanned in conformity with usual and standard tanning operations, as, for instance, bymeans of an alum or a formaldehyde tannage. Where skins are tanned they are at times dried and always contain more or less oil or fat liquor. The dry tanned skins or those skins containing no excess of oil or fat liquor are thereafter immersed and soaked with an aqueous solution containingv active oxygen or oxygen evolving material. Where the skins contain an abundance of oil or fat liquor they are washed, as, for instance, in a suitable drum in order to flush out the excess fat liquor, and in general warm water is employed for this operation, that is, water having a temperature in the neighborhood of from about 90 to 115 degrees F. although water having a higher temperature may be employed providing no adverse eifect is produced in the leather, and thereafter treated with the oxidizing solution.

The oxygen evolving solution preferably used is a fairly concentrated solution of hydrogen peroxide. Generally the peroxide is poured upon the wet skins which absorb the peroxide so that a solution expressed from the skin would show a concentration of hydrogen peroxide of about 0.1 to 20 volumes or higher depending upon the type of skin treated, although the usual concentration will be from about 2 to 5 volumes. The absorption of the peroxide solution into the skin is generally complete in about a half hour whereupon the skins, still impregnated with the peroxide solution, are stacked upon trucks or at the convenience of the tanner placed upon racks, and air dried for a period of from about 12 to 20 hours depending upon the type of skin, the humidity, and other factors.

The bleaching of the skins is preferably carried out in acid or nearly neutral solutions, i. e., solutions preferably of a pH of about 5 to '7. In general where soft, glovey leathers are desired, the pH of the solution is maintained near '7 and the leather is most desirable as glove leather and possesses an enhanced resilience. In fact, in addition to the leveling of color, the resilient quality imparted to the leather is the characteristic most desired in tanned skins used for gloves. Where it is desired to impart firmness to the leather, for instance, shoe leather, the peroxide is introduced into the leather under a lower pH, for instance, in the neighborhood of 4 to 5.5.

The hides or skins after depilation are tanned by an oil or formaldehyde, alum or vegetable tan and are generally alkaline in nature and to obtain the desired pH a suitable acid, such as sulfuric acid or other acid is added to the hides and skins in such quantity that upon agitation the desired degree of acidity is obtained through out the hides. To the properly acidified hides the hydrogen peroxide solution is then added. Where it has been determined what quantity of acid is required for a given quantity of hides, the acid may be added with the peroxide.

As another advantage of the process it may be mentioned that it is possible to eliminate the coloring matter generally adhering to the root holes of pigskin from which the bristles have been removed at the slaughter house or in the early stages of the tanning process. The normal color of the tanned pigskin at this stage of treatment is yellowish but the root holes are generally darker in color and somewhat unsightly thus detracting from the value of the skin. To eliminate this defect, the pigskin is immersed in a volume solution of hydrogen peroxide for a few minutes or until there is a surface penetration of the peroxide into the skin, the penetration being substantially immediate where the leather is of prime grade and not overloaded with oil or fat liquor. The skin is then removed from the solution and dried for one to two days at which time the darker spots caused by the higher pigmentation around the root holes have been leveled off and an even color appearance imparted to the pigskin. By regulating the time of immersion and the quantity of peroxide taken up by the skin, white leathers of very high resilience and tensile strength are produced, something impossible of achievement heretofore.

Example I About ten dozen tanned sheep skins containing substantially no excess of oil or fat liquor, are soaked in about 130 gallons of water and the pH of the solution adjusted to a pH of about 6.5 to 7.0 until the skin has assumed about the same pH as the solution itself. To this solution about 3 gallons of 100 volume hydrogen peroxide is added and the skins permitted to soak for a period of a half hour or more or until the peroxide has penetrated the skins, the skins removed and hung up for dyeing or stacked on trucks for about two days and subsequently dried. The finished skins are of excellent light color, all level as to color and capable of being matched and of a high resilience and glovey feel.

Ewample II About 200 pounds of wet kidskins, freed of excess fat or oil and containing sufiicient water to just drip, that is, about 200 to 300% water, are placed in a drum and about 8 gallons of 100 volume hydrogen peroxide, acidified with the quantity of acid, such as sulfuric acid, sufiicient to produce a pH of about 6.0 to 6.5, added and the drum rotated to induce good contact and absorption of the peroxide in the skins at which time the skins are removed from the drum and air dried. These skins possess an even and level color and greatly enhanced resilience.

Example III 250 pounds of buckskin, substantially free of excess fat or oil are immersed and soaked in water and the pH maintainedjat about 5.8 until the skins are well plumped. The plumping is usually performed in a drum andthen about 3 gallons of 100 volume hydrogen peroxide are added and the drum rotated. After about one hour the skins are dried, for instance, upon racks, and are white and well adapted for uses where good strength and ability to withstand deformation are required, as, for instance, in uppers of shoes and the like. .1,

From the foregoing, it will be seen that this invention provides a method of treating tanned skins to produce skins of high tensile strength and of good level color. It will be understood that certain of the metallic peroxides as well as the per salts, evoking hydrogen peroxide in acid solutions, may be used for the same purposes as hydrogen peroxide, due correction being made so that chemical equivalent quantities are employed.

It is claimed:

1. The method of treating animal hides or skins which comprises dehairing the hide or skin, immersing the hide or skin in an aqueous bath containing sulfuric acid in an amount suflicient to produce pH value of between about. 4 to 7 whereby the hide or skin is plumped and absorbs sufficient acid from the bath to render the skin acid and thereafter immersing the plumped hide or skin in a solution containing hydrogen peroxide until the hide or skin is impregnated with the same, removing the hide or skin so impregnated and permitting the same to dry until a substantial proportion of the water has been eliminated and the hide or skin has been bleached to the desired extent.

2. The method of treating animal hides or skins which comprises dehairing the hide or skin, immersing the hide or skin in an aqueous solution containing sufficient acid to produce a pH value of about 4 to 7 whereby the hide or skin absorbs sufiicient of the solution to render the same acid in reaction and thereafter adding to the bath an amount of hydrogen peroxide suflicient to produce the proper color and level in the skin when the same is dried, the pH value of the solution being maintained at less than about 7.

3. The method of leveling off the color of hides or skins which have been freed of hair which comprises treating the hide or skin with an acid WEOGIFI .a n e e W t e b m H p a g n w a h h M b S u w u G a the same and then drying the hide or skin until 4 to 7 until the hide or skin is plumped and aba substantial proportion of the water has been sorbs suflicient acid from the bath to render the eliminated and the hide or skin bleached to the skin acid, treating the plumped hide or skin with desired extent. 5 an aqueous solution containing hydrogen perox- ERICH HANSEN.

ide whereby the hide or skin is impregnated with