US3799737A - Curing and pretannage of hides - Google Patents

Abstract

HIDES MAY BE CURED AND PRETANNED BY: TREATING RAWHIDES WITH A SODIUM HYDROXIDE SOLUTION SO AS TO REACT THE LIPID MATERIAL IN ORDER TO CAUSE FORMATION OF SOAPS, LIMITED ATTACK ON PROTEIN MATERIAL PRESENT IN THE HIDES, AND SWELLING OF THE COLLAGEN IN THE HIDES; ADDING SODIUM CHLORIDE TO THE SODIUM HYDROXIDE SOLUTION IN ORDER TO ENABLE THIS SALT TO BE TAKEN UP FROM THE SOLUTION BY THE HIDES, CAUSING AN INCREASE IN THE STRENGTH OF THE SWOLLEN COLLAGEN; DEHAIRING THE HIDES; TREATING THE HIDES WITH SODIUM SULPHITE SOLUTION SO AS TO ADD STRENGTH TO THE SWOLLEN COLLAGEN; TREATING THE HIDES WITH A MIXTURE OF A QUATERNARY AMMONIUM SALT, AND A CALCIUM SALT IN ORDER TO PRECIPITATE ANY SOAPS PRESENT AND TO PLACE THE AMMONIUM SALT WITHIN THE REMAINING HIDE MATERIAL AND TO SEPARATE FASCIA TISSUE FROM THE REMAINING HIDE MATERIAL; AND PICKLLING THE HIDES WITH AN ACID SOLUTION SO AS TO EFFECT A SIZE REDUCTION AND STRENGTHENING OF THE SWOLLEN COLLAGEN. IF DESIRED, THE HIDES MAY BE BATED PRIOR TO BEING PICKLED. THE SO-CURED HIDES HAVE PROPERTIES WHICH ARE RELATED TO THE PROPERTIES OF AMMONIUM SALT. THE RESULTING HIDES CAN BE FURTHER TREATED IN ACCORDANCE WITH CONVENTIONAL TANNING PRACTICES.

D R A W I N G

Description

nited States Patent 3,799,737 CURING AND PRETANNAGE 0F HIDES Don S. Elvrum, 6233 Saylin Lane, Annandale, Los Angeles, Calif. 90042 Original application July 19, 1967, Ser. No. 654,432, now Patent No. 3,574,517, dated Apr. 13, 1971. Divided and this application July 2, 1970, Ser. No. 52,017

Int. Cl. C142 1/02, l/06, 1/08 US. Cl. 8-94.16 9 Claims ABSTRACT OF THE DISCLOSURE Hides may be cured and pretanned by: treating rawhides with a sodium hydroxide solution so as to react the lipid material in order to cause formation of soaps, limited attack on protein material present in the hides, and swelling of the collagen in the hides; adding sodium chloride to the sodium hydroxide solution in order to enable this salt to be taken up from the solution by the hides, causing an increase in the strength of the swollen collagen; dehairing the hides; treating the hides with sodium sulphite solution so as to add strength to the swollen collagen; treating the hides with a mixture of a quaternary ammonium salt, and a calcium salt in order to precipitate any soaps present and to place the ammonium salt within the remaining hide material and to separate fascia tissue from the remaining hide material; and pickling the hides with an acid solution so as to effect a size reduction and strengthening of the swollen collagen. If desired, the hides may be bated prior to being pickled. The so-cured hides have properties which are related to the properties of the ammonium salt. The resulting hides can be further treated in accordance with conventional tanning practices.

This is a division of Ser. No. 654,432, filed July 19, 1967, now US. Pat. NO. 3,574,517, dated Apr. 13, 1971.

BACKGROUND OF THE INVENTION One of the oldest arts or sciences known to civilization pertains to the curing and tanning of hides so as to convert them to a condition in which they are stable. As this field has been developed, it has been discovered that the curing and tanning of hides involves extremely complex physical and chemical factors which even today are not considered to be completely understood. To a degree, the curing and tanning of hides remains a field which tends to be more of an art than a science.

A hide on an animal such as a cow or steer is frequently considered to consist of three layers: an ectodermal or outer layer; a mesodermal or middle layer; and an endodermal or inside layer. The ectoderma is sometimes referred to as the epidermis of a hide. The endoderma carries an adherent fascia layer of a hide. This fascia layer is a thin tissue-like layer. The fatty tissues which are often found on the inside of a hide attached to the endoderma are normally referred to as adipose tissues. Although various other terms are at times applied to designate parts of a hide, these terms are used herein so as to avoid confusion.

Both the physical and chemical characteristics of the various layers indicated in the preceding are quite important in curing and tanning hides. To understand this invention, it is necessary to understand something of the interrelationship and nature of these characteristics. Upon examination of a rawhide, it is apparent that such a hide contains various hairs emplanted within the follicles which extend into the ectodermal layer of a hide and occasionally to a degree into the mesodermal layer. The endodermal layer in common hides is distinctly different from the ectodermal and mesodermal layers, and re- "ice sembles a white type ofparchment tissue. Both the fascia and adipose tissue on a normal rawhide are, of course, of the character of other body tissue, and have a different appearance from the hide material proper.

Generally speaking all parts of the hide consist of two different types of material. The first is protein material; the second is lipid material. Other types of materials such as serums may be present in a hide. The protein material is normally classified as collagen and keratin material. A third type of protein material is termed elastin and may also be present to a degree in a hide, particularly in adipose tissue. In general, the elastin is a fibrous type of material present in a hide as connective tissue. Generally it can be recognized by a yellowish cast.

Keratin, on the other hand, is generally considered as the protein of epithelial or outer tissue. Thus, the term keratin is generally applied to the protein found in hair, horns, feathers, nails and the like. Such keratin protein on a hide proper frequently is of a scale-like appearance. The collagen protein in a hide normally has a sort of coil-like physical structure appearing much like a bundle, and is the predominant protein tissue in a hide, which is important in an ultimate leather product. The lipid material may be classified as fatty material; it is found to various extents throughout the entire protein structure of a hide.

The curing of a hide in a conventional process essentially involves the removal of at least some of the lipid material, keratin material, and removal of adipose and fascia material from the ectodermal and mesodermal layers of the hide. In other than the most conventional curing processes, it may be desirable to retain on the hide keratin material such as hair, and the endodermal or fascia layer on the hide proper. The present invention is not primarily directed to such specialized curing processes. The curing of a hide normally involves the treatment of a hide so that the collagen within such a hide is placed in a form which can be rendered stable and is usable. To a degree, such stability and usability normally result from subsequent tanning and related leather treatment processes.

Conventional curing processes employed with hides normally include the steps of (l) soaking in water or dilute alkaline solutions; (2) mechanically defleshing so as to remove adipose tissue; (3) soaking in a lime solution so as to attack and loosen keratin; (4) removing keratin material such as hair; (5) washing so as to delime; (6) bating so as to alter the chemical character of the collagen; and, an optional step (7) soaking in an acid so as to pickle the hide. A hide cured in this manner is normally treated by a conventional tanning process such as vegetable, mineral, oil or solvent processes so as to be tanned into leather.

These steps are all related to, or are an outgrowth of the physical and chemical character of hides. As such hides are obtained for processing they are covered with all sorts of extraneous matter such as dried blood, dirt and the like. The initial soaking softens this type of material. It also may result in the hide unevenly taking up some water. The defleshing operation serves to remove:

much adipose tissue and some of the contaminants on the hide surface that have not been removed in the soaking operation. The soaking in a lime solution which follows in conventional curing process is designed to aid in the removal of unwanted keratin.

Such removal is based upon the fact that different types of protein can be chemically attacked in different manners, so as to break down the peptide linkage. In the lime soaking process the peptide linkages in the keratin are attacked. It is noted that this step does not normally completely remove the keratin from hides. It only loosens 3 and attacks the keratin so as to facilitate removal of such keratin structures as hair during a subsequent operation.

An important facet of the present invention is related to a degree to the so-called liming of hides in conventional curing process. The lipids which permeate all parts of a hide, although present to greater degrees in some parts of the hide than others, are not salvageable in the form of their by-products by soaking hides in a lime solution. This is because, to the extent that such lipids are attacked by lime so as to produce fatty acid radicals, such radicals are precipitated in place in the hide by the lime in the form of calcium soaps. It is considered that any attack on lipids occurring during the liming is comparatively limited.

The necessity of removing keratin material during a conventional curing process is easily understood. Normally, hairy leather is not desired. Such removal may be accomplished mechanically once the hair on a hide has been loosened by the liming step. It is also known to accomplish it chemically through the use of known reagents which preferentially attack keratin. The washing which follows dehairing in a conventional curing process prevents any carryover on the hides proper to the subsequent treatment. Sometimes it is carried out using an acidic solution so as to decrease the alkalinity of the hide material.

The bating operation referred to in the preceding is essentially an operation in which proteins remaining in the hide are to a degree chemically attacked so as to alter or vary the properties in the protein in a final leather. The bating process in conventional hide curing may be carried out in a number of ways using acids or various salts such as ammonium chloride or ammonium sulphate and one or more enzymes. Such enzymes are considered to tend to remove various degradation products resulting from the earlier operations on the ectodermal and endodermal layer of hides, to modify and attack to a degree all proteins including the collagen and the elastin.

The final pickling operation frequently used in curing hides, to modify the protein structure of the hide so as to give the remaining hide material which has been cured as indicated in the preceding a certain degree of physical strength, is accomplished by regulating the pH of the hide protein so as to cause a variation in the swollen character of this type of material.

All of these steps in conventional hide curing processes require relatively prolonged periods. It is well established that it takes a significant time interval to cure a hide. Such a period is disadvantageous economically, inasmuch as it requires that an appropriate hide treating plant be relatively large in order to process a given volume of hides. Conventional curing processes as indicated in the preceding do not make any provision for the economic recovery of fatty acids from lipids. Since such acids have a significant value it is readily seen that this is disadvantageous. Further, conventional curing processes require mechanical operations such as defleshing and removing keratin material. Such mechanical operations are not considered to be desirable from an economic standpoint. Such mechanical operations may result in disadvantageous hide damage if not carefully carried out.

SUMMARY OF THE INVENTION A broad objective of the present invention is to provide a new and improved method of curing hides which eliminates various disadvantages and limitations of prior methods such as are briefly indicated in the preceding discussion. A more specific object of this invention is to provide a method of curing hides which enables a hide to be cured in a comparatively limited time period. This is considered to be very advantageous economically.

Another object of the present invention is to provide a method for curing hides which permits the recovery of lipid by-products such as fatty acid radicals. This is also considered to be of significant economic importance.

Another object of this invention is to provide a method for curing hides in which defieshing is essentially accomplished chemically. This is considered important from an economic standpoint because it eliminates the disadvantages and limitations of mechanical defleshing.

The present invention is not only directed to interrelated process steps having advantages as indicated in the preceding. These advantages are to a degree related to, and are to a degree secondary to the production of good cured hides. An object of the present invention is also to provide satisfactory cured hides capable of being further processed into leather by conventional methods. The invention, however, goes further than this. An object of the present invention is to provide hides containing a bacteriostatic and fungicidal agent which serves to protect the leather resulting from such hides from attack by bacteria and fungi. This is quite important in connection with mildew and the like attack upon leather.

The aforegoing objects of this invention are achieved by a process which preferably involves the following steps: treating raw hides with an alkali metal hydroxide so as to saponify lipid materials under conditions so that the hydroxide attacks the protein materials in the hides to only a limited extent and tends to cause swelling of this protein material, particularly the collagen; treating the hides with a salt solution so as to cause an increase in strength of the collagen material; chemically dehairing the hides using agents which are known to be efiective for this purpose; contacting the hides with a salt solution tending to give strength to the protein material, especially the collagen; treating the hides with a quaternary ammonium salt which serves to physically separate remaining fascia and adipose tissue fragments from the hides proper while simultaneously penetrating the swollen hide material in such a manner as to remain to a degree within this material; and pickling the hides with an acid brine so as to reduce the size of the swollen material, particularly swollen collagen, and to strengthen this material so that the hides can be handled safely in further operations.

The hides resulting from this series of process steps can further be treated in accordance with conventional curing processes. In the practice of the invention advantageous results can be achieved by employing only certain of the process steps indicated in the preceding without other of these process steps, although the entire sequence of steps indicated is designed and intended to be used together because of the manner in which the protein material in hides resulting from any one of these steps is conditioned for the next following step to be most effective. Thus, it is possible to obtain the advantageous result of the recovery of products from lipids by merely using the first step of the entire process indicated in the preceding. The hides resulting from this can be treated further or cured in other manners, as, for example, by being mechanically defleshed in accordance with conventional practice after being treated so as to lower their pH, although this is not considered advantageous. Similarly, a quarternary ammonium salt may be used in the removal of fascia or adipose tissue without employing all the process steps indicated. Such a quaternary ammonium salt may also be placed in a hide cured by other processes, as for example, by soaking an otherwise cured hide in a solution of this material so as to produce a hide having advantageous characteristics as indicated.

Because of the complex character of the invention and the field to which it pertains, the invention is best more fully described by reference to a specific method of treating hides. Various other objects and advantages of this invention will be apparent from a detailed study of the remainder of this specification and the appended claims.

DESCRIPTION OF THE DRAWlNG FIG. is a cross-sectional view of a conventional steer hide which is intended to illustrate the parts of the hide referred to in the following detailed description so that this description may be understood readily;

FIG. 2 is a side elevational view, partially in section, of a preferred apparatus for carrying out the process of this invention;

FIG. 3 is a crss-sectional view taken at line 33 of FIG. 2; and

FIG. 4 is a diagrammatic flow sheet indicating the preferred series of process steps described in the following detailed description.

DETAILED DESCRIPTION OF THE INVENTION As indicated in the preceding brief summary, the first step in the preferred manner of carrying out this invention involves saponifying the lipid material with an alkali metal hydroxide under such conditions that the protein material present within a hide is only attacked to a limited extent, and under such conditions that the collagen protein material present within the hide is preserved and is caused to swell so as to increase significantly in physical dimension. These results require relatively careful and accurate control of process conditions. It is desired in this step to degrade substantially all Of the lipid material so that the reaction products can be recovered without affecting the basic protein structure of the hide in such a manner as to affect detrimentally the ultimate properties of leather created from the hide.

The significance of this first step is best considered with reference to FIG. 1 of the drawing. Here the ectodermal, mesodermal and endodermal layers of a hide are indicated in a generalized manner. It will be noted that hairs extend from hair follicles in the ectodermal layer and the adipose tissue is attached to the endodermal layer in an irregular manner. Although FIG. 1 does not indicate it, various amount of flesh may be attached to the hide along with this adipose tissue. In an actual hide, the layers indicated are not sharply defined, but tend to blend into one another in an irregular manner which depends upon many factors.

The hairs on the ectodermal layers are primarily keratin protein. This protein is present in a somewhat scaly form. Some keratin may also be present on the surface of the ectoderma in a form of scaly type deposits. In all of the dermal layers collagen protein is present, primarily in a physical structure which in some respects tends to resemble a tightly wound series of overlapped, crossed coil springs. Such springs tend to appear as ropes which are laid upon one another like the fibers in a nonwoven fabric. This is particularly the case in the mesodermal layer. In all of these dermal layers some elastin tissue, appearing in a yellow form, serves to interlock other materials together,

All of this structure is permeated to a degree with lipids. In effect, these lipids can be considered as a secondary material associated with the protein compounds present in a hide. Because of this, in order to recover products from the lipids it is also necessary to permeate the entire protein structure of a hide. It is well known that lipids can be saponified by alkali metal hydroxides so that soaps andglycerins can be recovered. Such recovery is a matter of prime importance as to the economics of this invention. This is because such by-products have significant economic value.

Although the first step of the present invention is directed to the recovery of such by-products it is also di-' rected to hide treatment so as to make the hide take on a physical character which facilitates subsequent steps of the process. This is best explained by referring again to the nature of the collagen within a hide. As previously indicated such collagen has a coil-like physical structure somewhat resembling a coil spring. These individual collagen springs or bundles are extremely complex from a chemical standpoint, and include a series of different protein compounds joined together in what is best de scribed as a polymer type of structure, such a structure being interlocked with related structures. The various protein compounds contain a large number of different acidic and basic groups. These groups influence, if not determine, various reactions of the collagen material.

Such material is frequently referred to as having an isoelectric point, and such an iso-electric point is frequently defined by pH. Strictly speaking, this is improper since pH refers to the log of the reciprocal of hydrogen ion concentration in a solution. Obviously a hide is a solid, not a solution in the usual sense of the term. Hence, pH is a somewhat misleading Way of expressing the iso-electric point of collagen. It is better to consider the iso-electric point of collagens as that condition of the collagen where structure are balanced in such a manner that the structure itself can be said to be as dense as it can become. That is,

collagen is at its iso-electric point when it occupies the minimum physical dimension that it can occupy without breakdown of the material itself,

From this it will be apparent that the physical dimension of collagen bundles can be altered. When hide material is placed within an acidic or a basic solution acidic or basic radicals are taken up in one manner or another from the solution so as to be held by the basic protein structure of the collagen. As this occurs the collagen bundles will tend to expand, much in the manner in which a coil spring expands when its ends are pulled. In general the higher the concentration of the acidic or basic radicals placed in contact with hide collagen, the greater such expansion.

Such expansion is visibly noticeable in hide collagen. It is apparent as an increase in the thickness of the hide. Such increase in thickness resulting from expansion of hide collagen is accompanied by a deterioration in the physical strength of the entire hide material, presumably because the collagen bundles are stretched or elongated in such a manner that the physical interlocking between them is disturbed. This is in many ways analogous to the loss in physical strength of common newspaper type inexpensive paper when the fibers within such paper swell as a result of contact with water.

The first step in the process is intended to bring about collagen swelling so as to make the interior of hide material more open so that the saponification carried out during this first step may go substantially to completion, removing substantially all of hide lipid material, including such lipid material which is locked in place within the various dermal layers by the physical structure of the hide collagen. Once a hide is opened up in this manner, various subsequent treatment solutions gain access to the interior of these dermal layers so as to accomplish various objectives as hereinafter indicated. Such opening up or swelling of the collagen materials in a hide also makes it easier to remove the products of the saponification from the hide structure.

The first step of the process can fortunately be carried out so that the same reagent can be used both to cause saponrfication and so as to cause: collagen swelling. This reagent is, as previously indicated, an alkali metal hydroxrde such as sodium hydroxide. This reagent also accompl shes during this first step other effects which are beneficial to the entire treatment process. It is well known that protein material can be digested with such a hydrox- 1de so as to be degraded to various different degrees. The first step of the process is controlled so that such degradation is apparently limited to attack all hair keratin without significant attack on other protein present such as ectodermal keratin which is quite important to the grain of leather. If such attack is limited to hair keratin by proper control of this first step, the hair on a hide can be subsequently removed from it by a subsequent step in the process with a minimum of difiiculty.

It will be apparent from the preceding that it is possible to completely digest a hide during the first step of the process. This result, or any result reasonably approaching it is avoided by careful control of reaction temperature, concentration and time during this first step. Such control also involves careful control of the amount of agitation of the treatment solution during the first step. It further involves a buffering type action achieved essentially as a bonus as a result of using unclean hides containing adipose tissue, dirt, straw, dried blood and the like. All of these factors to a degree are considered to be interrelated to what is believed to be a synergistic type action achieved as a result of this saponification.

During the first step, it is considered that the temperature of the hide in the treatment solution should be maintained at from about 85 F. to about 100 F. and preferably at from 90 F. to 95 F. At lower temperatures than this, the desired saponification reactions tend to be too slow for practical purposes. At temperatures above about 100 F., the degradation reactions affecting hide proteins including keratin and collagen tend to become sufficiently pronounced so that hide material is apt to be damaged. All of the various reactions considered are however influenced by the other factors indicated in the preceding paragraph.

The time required to accomplish this first step will vary depending upon the nature of specific hides being treated. It is presently considered that this first step should be carried out for a period of from to 90 minutes. In general the time should be sufficient so that the first step is carried out for a time just under the time necessary for hide collagen to tend to break up and go into solution. While this is a limiting factor it is preferred to relate the time required in this first step not only to the hide collagen tending to go into solution, but also to the point where ectodermal keratin will tend to do the same thing. The maximum time for any specific type of hide required with the process can within these limits be deterrnined by routine experimentation.

The amount of time will of course depend upon the concentration of the treatment solution during this first step. For the saponification reactions to go on satisfactorily, it is considered that the alkali metal concentration in the treatment solution must be at least that necessary for this solution to have a pH of at least 12. On the other hand it is apparent that at hydroxyl ion concentrations of at least 12, attack on protein material such as hide keratin and collagen becomes quite pronounced. Such attack must be limited so that the hide is not physically destroyed, and preferably so that the ectodermal keratin other than hair is not measurably destroyed. In general, however, the greater the hydroxyl concentration during this step, the more rapid the saponification.

Because of these factors, it is considered that the limiting factor during this first step must be the degree in which control of the hydroxyl ions attack on hide protein material can be achieved through the use of a buffering type of action. When various contaminants of an organic nature are present, during this first step, such contaminants tend to be preferentially attacked by a high hydroxyl ion concentration in preference to hide protein.

In general, therefore, the more contaminants present the greater the alkali concentration permissible during this initial treatment step. There is, however, a limiting value. When the alkali metal hydroxide concentration reaches a point at which the various contaminants present do not serve to control or to buffer the high hydroxyl content so that attack on hide proteins such as collagen and ectodermal keratin other than hair is minimized the hydroxyl concentration is too high for use in the process. Such attack on hide proteins must be minimized so as to avoid ultimate detrimental affects to leather produced from the hide. The maximum hydroxyl concentration which can be used is best determined by routine experimentation since this concentration will vary depending upon a number of factors such as the specific type of hide being treated, the amount and nature of the contaminants present and the temperature at which the first step is carried out.

Such control of hydroxyl attack on hide protein thus depends upon a number of factors which are interrelated to other factors in carrying out this first process step. As steer hides are normally obtained from slaughtering operations these fresh flayed hides carry various different materials such as are indicated in the preceding in an amount sufiicient so that an amount of sodium hydroxide of up to about 25 percent by weight of the flayed hide is the maximum amount which should satisfactorily be used. This percentage by weight is, of course, related to the degree of dilution during the first process step. It is based upon dilution with an amount of water equal to the weight of the hide being treated. It will be recognized that this concentration corresponds to a solution having a pH which is well above 12.

A surprising facet of the first step of the process is the role of the soluble soaps formed as a result of the saponification reactions which occur with the lipids present. These soaps appear to cause a synergistic type of effect which aid in penetration of hide collagen by the hydroxyl ions present. Such penetration is thus facilitated by the reaction products of alkali metal hydroxide and lipids as the saponification progresses. This is considered to make it possible for substantially all of the lipid material trapped within the collagen bundles to be saponified within a minimum period before any undesired unnecessary degradation of either collagen or ectodermal keratin occurs. This is considered to be quite important as far as the total results achieved of the process are concerned. It is of course related to the rate at which the collagen fibers or bundles swell during the initial treatment step.

Such swelling as indicated in the preceding tends to detrimentally affect the strength of the hide being treated. For this reason it is preferred to add a quantity of sodium chloride to the solution being used as the process step is being carried out. Such sodium chloride tends to act to a degree to depress the amount to which the collagen bundles Will swell during this first process step. This is and of itself is considered to aid in the maintenance of sufiicient hide strength so that there is no reasonable danger of hides being torn apart by handling, motion or the like. It is considered that the sodium chloride in some manner enters the intricacies of the collagen fibers or bundles so as to serve to link the various parts of these fibers or bundles in such a manner as to add physical strength as a result of an action which is other than the action of depressing collagen swelling.

The amount of the sodium chloride which should be added as indicated in the preceding paragraph is best determined on a purely empirical basis. The amount should be sufficiently great so as to serve to preserve and increase hide strength as much as possible, without any excess of the sodium chloride being used. It is presently preferred to use an amount of sodium chloride which is equal to about 10 percent by weight of the flayed hides being treated. It is considered that lower quantities can be used with various types of hides, particularly when the process conditions are carefully controlled so as to minimize physical damage to the hides. The results achieved through the use of this sodium chloride are essentially matters of degree, and a minor variation in the amount of sodium chloride applied is not considered to be overly important.

This first step of the process is preferably carried out with the hide or hides being treated being subject to mild agitation. Such agitation tends to remove reaction products such as soluble soaps and glycerine from the hide material so as to present unreacted hydroxyl ions to hides so that the desired saponification will occur. The agitation used during this step should preferably be a mild agitation since the swollen hides created during this first step are comparatively tender, and harsh or vigorous agitation will tend to disrupt the hide material once it has been swollen. In a sense this can be compared again with wet newspaper type paper. A dry newspaper type paper poses greater strength than a wet newspaper. If physical stresses and strain such as could be tolerated by such a sheet of dry paper are applied to such a sheet of paper when wet the paper will tend to be broken up and disrupted. The general type of consideration is present during the treatment of a swollen hide of this first process step, and during the subsequent steps of the process.

Although such agitation can be accomplished in a number of different ways, it is presently preferred to accomplish it using a rotatable drum apparatus as indicated in FIGS. 2 and 3 of the drawing. This apparatus 10 has a smooth interior wall drum 12 enclosed by smooth end walls 14. It is supported upon shafts 16 and 18 which in turn are supported by trunnions 20. One of the shafts 18 is hollow and is connected by a suitable conventional rotating joint 22 to a pipe 24 used to supply treatment solution to the drum 12. Belts 26 contact the drum for the purpose of rotating it in order to create agitation within it. Such agitation is increased by the use of relatively small lifters 28 located equidistant from each other around the interior of the drum 12. Each of these lifters is preferably provided with a rounded end in order to minimize the chances of hide damage. The drum 12 is provided with a drum opening adapted to be closed by a door 30. This opening is used in charging the drum 12 and in removing material from it.

The dimensions of the interior of the drum 12 in the apparatus 10 can, of course, be varied considerably depending upon various circumstances. With drums of different dimensions different quantities of hides can be treated and different quantities of reactants will be used. Also the most advantageous speed of rotation of the drum will vary depending upon the size. In experimental work on the process of this invention an apparatus such as the apparatus 10 was constructed in which the distance between the end walls 14 was six feet ten inches, in which the internal diameter of the drum was seven feet four inches and in which each of the lifters shown extended from the drum interior six inches and was two inches thick, and was provided with half inch radii rounded ends. These dimensions are considered to be important in reproducing the results achieved in one presently preferred manner of carrying out the process of this invention as hereinafter described.

In this presently preferred manner the first step of this invention was carried out using an apparatus 10 constructed as previously described. The drum 12 was charged with sixteen fresh flayed steer hides, the exteriors of which were coated with the usual quantities of dung, dried blood, straw, dirt and other material usually on such hides as they come from a flay operation. No effort was made to specifically analyze the precise types and quantities of such contaminants. The drum 12 was then charged through the pipe 24 with an amount of water equal to the weight of the hides containing 10 percent by weight of the hides of sodium hydroxide and 10 percent by weight of the hides of sodium chloride. The solution charged to the drum was at a temperature of about 95 F. although the solution could have been at other temperatures indicated. The drum was then rotated for twenty minutes at four revolutions per minute and then further rotated for ten minutes at seven revolutions per minute. At the end of this period the solution was drained from the drum 12 and the liquid obtained was segregated for separate recovery of the materials within it in accordance with known processes. At this point the drum was flooded with a hundred gallons of tap water and rotated for about one minute at 25 revolutions per minute,

drained, flooded again with a hundred gallons of tap water and rotated for about one minute at 25 revolutions per minute and then drained. Although products could have 10 been recovered from these rinse solutions they were discarded.

At this point the so-treated hides resulting from this first treatment step were ready for further treatment in accordance with this process. However, these hides can be treated in accordance with this process. However, these hides can be treated in other different manners than hereinafter explained so as to produce cured hides or leather from these hides. As an example of this, the hides after this first step may be contacted with a buffering solution such as calcium chloride solution so as to cause a shrinkage of the collagen bundles or fibers, reducing the hide thickness to essentially a thickness suitable for sole leather tannage. This treatment will of course add physical strength to the hide material since it causes a collapse of the collagen bundles or fibers, increasing the physical strength. The so-processed hide may then be directly treated with conventional practice as, for example, by known processes of vegetable tanning so as to produce sole leather. Similarly, it would be possible to directly treat these hides in one or more other manners involving steps conventional to the leather curing industry.

In the preferred manner of practicing the invention, the second step of the process involves removing hair keratin since such hair is not normally desired on most leathers. If cured hides containing hair are desired, this step can be omitted. Such removal is preferably accomplished chemically in the process because of the fact that the hides resulting from the first step are swollen and are relatively tender, and cannot withstand the physical handling for mechanical dehairing without danger of damage to their physical structure. This second step is preferably carried out utilizing conventional dehairing reagents for chemical dehairing under conventional conditions. A large number of such dehairing reagents are well known in the leather industry. Hence, no effort is made herein to specify such reagents.

In the preferred manner of practicing the invention hides described in the preceding are left in the drum indicated and the drum is charged with a solution at about 70 F. containing an amount of water equal to percent of the initial hide weight and an amount of sodium sulfide equal to 2 percent of the initial hide weight. The drum is then rotated at seven revolutions per minute for a period of twenty minutes. During this period the hair keratin is attacked and is removed from the hides.

Inasmuch as the pH of the solution used to accomplish such chemical dehairing is significantly different from the pH of the solution used in the first treatment step as the result of the second treatment step there will be a tendency for the degree of swelling of the hides to change during the second step. In the method of practicing the step indicated the hides will tend to shrink in thickness so as to decrease roughly five to ten percent under their thickness as acquired during the first step. Such shrinkage tends to improve the strength of the collagen and grain keratin in the hides, but it also tends to compact the collagen material within the hides so as to make the collagen fibers or bundles less permeable to the entry of reagents of the subsequent steps of this process.

For this reason it is preferred to add to the solution used for chemical dehairing further alkali metal hydroxide in order to contol hide thickness so that the collagen bundles or fibers are expanded to the maximum extent reasonably possible with hide strength. Also it is preferred to contact the hides at this stage with additional sodium chloride in order to maintain hide strength as much as reasonably possible. Although such sodium hydroxide and sodium chloride may be added along with the solution of a chemical dehairing agent it is preferred to add the sodium hydroxide and sodium chloride as separate reagents after a certain degree of chemical attack on the hair keratin material has transpired. It is also preferred to contact the hides immediately following the chemical dehairing with sodium sulphite so as to accomplish a fixative type of action serving to strengthen the external surfaces of the hide without appreciably changing the hide thickness.

The amounts of sodium hydroxide, sodium chloride and sodium sulphite which can be used in order to accomplish these objectives can be varied within comparatively wide limits. In general, sufficient sodium hydroxide should either be added to the chemical dehairing solution or placed in contact with the hide as a separate solution so as to get the hide thickness back to the thickness at the end of the first operational step in accordance with the process of this invention. This amount of sodium hydroxide may be easily determined empirically. In such determination it should also be taken into consideration that the sodium hydroxide may tend to react with certain chemical dehairing solutions. The amount of sodium chloride used at this stage of the process of the invention is also best determined empirically. The increase in hide strength and the maintenance of hide strength through the use of sodium chloride either at this or other process steps of this invention essentially involve what may be referred to as a continuous variable situation up to the point where the further addition of sodium chloride serves no beneficial result.

The amount of sodium sulphite also involves what may be regarded as a continuous variable situation. The sodium sulphite in some manner not completely understood serves to make the external surfaces of a hide a comparatively tough, firm type of structure. Thus, when the sodium sulphite is used a hide becomes much like a laminate in which two rigid layers incase a comparatively soft core. The sodium sulphite is used in such a manner that the ectodermal keratin and the exposed surface collagen bundles are fixed or made more firm so as to make the hide more susceptible to satisfactory treatment in the subsequent step of the process. If hides are left for too long a period or at too elevated a temperature in contact with the sulphite ion, it is considered that this fixative action will tend to be manifested within a hide interior, and it is considered that this is a disadvantage. In general, any temperature from room temperature up to about 90 F. can be satisfactorily employed at this stage. It is considered that in general the contact of the sodium sulphite should be from about ten to about thirty minutes, and that the solution placed in contact with the hide should contain from about .1 to about percent by weight sodium sulphite.

In the preferred manner of practicing the invention at the end of the twenty minute period specified in the preceding, an amount of sodium hydroxide equal to 2 percent of the hide weight and an amount of sodium chloride equal to 2 percent of the initial hide weight and an amount of water equal to the initial hide weight is added to the drum. The drum is then rotated at seven revolutions per minute for additional period of fifteen minutes. This time period can be varied considerably depending upon the nature of the hair on the hides, and is best regulated emperically. Then as the drum is still rotated an amount of sodium sulphite equal to 0.2 percent by weight of the initial hide weight is added. Rotation of the drum is continued at the same speed for a period of fifteen minutes. The solution is then drained from the drum, the drain is flooded with fifty gallons of tap water, rotated for about a minute at seven revolutions per minute and then drained. The so-rinsed hides are then ready for what is referred to as the third process step of the invention.

This third process step is considered to be quite important and to mark a significant advance in the art of curing and pretanning hides. In it fascia or adipose tissue on the ectodermal layer of the hides is removed without the usual mechanical operations. Further, a hide is impreg nated with a quaternary ammonium compound which not only serves to make possible the stripping of the fascia tissue, but which also enters a hide being treated so as to affect the ultimate, final properties of these hides. This treatment step is preferably carried out with relatively mild agitation of the hides being treated so that such agitation aids in stripping the fascia tissue as it is loosened due to the reaction of the reagents used. During this step an empirically determined amount of sodium chloride is preferably present so as to aid in maintenance of hide strength in order to prevent any tendency for the hides to physically be damaged to as great an extent as possible.

The solution used in this third step preferably contains a soluble calcium salt such as calcium chloride for the purpose of forming insoluble soaps with any residual sodium soap remaining at or on the surface of hide as a result of the initial process step. It will be recalled that this initial process step yields a swollen hide structure in which the swollen bundles of collagen are interlocked and are relatively tender. Because of the chemical nature of such collagen and the physical condition of it, it is substantially impossible to remove from hides in the first process step, even by the rinsing operations specified and by such rinsing as occurs during the dehairing operation, all vestiges of the sodium soaps produced. These vestiges of sodium are considered quite important in this third process step. During this step the relative heavy metallic ions necessary to form insoluble soaps, and specifically the calcium ion, tend to provide what may be considered as heavy soap molecules which tend to make the physical hide structure amenable to splitting off of the fascia tissue.

Such splitting is however only accomplished in the presence of a quaternary ammonium salt having unique surface active properties. It is possible to utilize in the process of this invention such salts as n-alkyldimethylbenzylammoniumdichloroisocyanate in which the alkyl may be an alkyl radical from C to C or a mixture thereof, the dichloro-isocyanurate salt of this compound, n-alkyldimethylbenzylammoniumdichloro-isocyanate, or the dichloroisocyanurate salt of the preceding compound. From this it will be seen that all of the satisfactory quaternary ammonium salts used at this step of the process are isocyanates or isocyanurates. All of these compounds are considered to not only possess desirable surface active characteristics, but in addition are considered to be good bacteriostatic and fungicidal agents.

During this third process step, as insoluble calcium salts are formed in some incompletely understood manner, a quaternary ammonium compound as specified appears to act essentially as a wedge or knife, separating fascia or adipose tissue from the collagen material in the hide. In other words the two types of reagents used together cooperate in some incompletely understood manner to separate the collagen bundles or fibers from the remaining tissue structure. It is considered that as this occurs the calcium soaps somehow or other tend to weigh down the remaining tissue structures and the exposed surface of the collagen bundles in such a manner as to alter the normal physical bonds in a hide connecting the tissue structure to the collagen, enabling the suface active type of the quaternary salt to split these two types of animal matter.

Such splitting is best aided or facilitated by comparatively minor agitation. This agitation is considered to aid in the separation of the fascia tissues by gradually pulling away such tissue away from hide collagen, continuously exposing new areas of contact between the fascia tissue and the hide collagen for further splitting" action of the reagents employed.

This splitting action is also considered to be facilitated by another aspect of this third treatment step. Obviously a calcium chloride solution is much less basic than the sodium hydroxide solution used in this first treatment step. Because of this it will tend to cause the collagen fibers or bundles in the hides to decrease in physical dimension. Such a decrease in physical dimension obviously changes the physical properties of the hides themselves, making them somewhat less tender. As such shrinkage occurs on the surfaces of the hides it is accompanied by a physical change in the character of the collagen fibers or bundles which is considered to aid in separating fascia or adipose tissue, making the action of the quaternary salt or salts used more pronounced and eifective. No such corresponding change is noted on the tissue, and this is considered to be beneficial in facilitating tissue removal.

This third treatment step can conveniently be carried out at any temperature from about room temperature to about 90 F., and with careful control to about 100 F. At higher temperatures chemical damage to the hide collagen is apt to occur; at lower temperatures the splitting is apt to be too slow for practical purposes. The times required during this third treatment step can similarly be varied. It is preferred that the time be carefully regulated so that the only calcium soaps formed are at or adjacent to the hide surfaces so as to preserve the character of the hide material. Since penetration of solution within the interior of the hide is a function of time, this can be con trolled by keeping the duration of this third treatment step relatively short, preferably within the range of from ten to thirty mintues.

The formation of calcium soaps is also to a degree dependent upon the concentration. Sufiicient calcium ions should be present to accomplish the desired objectives, without any excess being used. Generally speaking the solution contacting the hides at this step should contain from about to 12.5 percent by weight of calcium chloride. If it is more dilute than within this range calcium soaps are not formed sufiiciently rapidly for the splitting to occur in a desired manner, and at higher concentration than are specified there is a tendency to undesirably load the hide material with calcium ions.

The quantity of the quaternary ammonium salt used during this step can also be varied within a comparatively wide limit. This salt, in its action, apparently involves continuous variable situations. The treatment solution used in this third step can contain as little as one-thousandth of a percent by weight of the quaternary ammonium salts, while amounts up to about 5 percent can be used. Inasmuch as no significant advantage is apparent from the use of such larger quantities, it is generally preferred to use as little of this salt as possible.

It is preferred to have present within the solution for this third treatment step a quantity of sodium chloride which will serve to aid the maintenance of hide strength. Such sodium chloride is not necessary. When it is used it should be used in an amount sufficient to maintain the maximum halide strength that can be obtained through its use. In general, a sodium chloride concentration of from to 25 percent in the treatment solution can be satisfactorily employed, although concentrations within this range involve the use of more sodium chloride than is normally considered necessary.

In the preferred manner of practicing the invention hides are left in the treatment drum following the chemical dehairing. An aqueous solution was used containing five percent by weight calcium chloride, 10 percent by weight sodium chloride and .001 percent by weight n-alkyldimethylbenzylammonium dichloro isocyanurate in which the alkyl radicals were a mixture of alkyl radicals from C to C The drum was then rotated at seven revolutions per minute for fifteen minutes. At the end of this period the drum was drained, rinsed with fifty gallons of tap water and then again drained.

The hides resulting from this treatment operation are susceptible of being directly further used in the manufacture of leather. It is preferred however to reduce the thickness of the collagen bundles or fibers within these hides to a reasonable extent so as to increase their strength and make them suitable for tannage without significant danger of damage occurring to them by handling. This may be conveniently done by contacting the hides with an acid solution so as to pickle the hides. If desired, such a solution may contain sodium chloride to help maintain,

at this step, hide strength. The acid concentration and times of contact with the hides in this final step are not considered critical so long as the acid used does not chemically attack the hide collagen and so long as the desired results are accomplished within a reasonable period. It is considered that any conventionally used acid may be used in this pickling step.

In the preferred manner of practicing the invention the hides remaining in the drum from the defieshing step are contacted in the drum with a solution containing five percent by weight sulfuric acid and 15 percent by weight sodium chloride while the drum is rotated at seven revolutions per minute for a period of thirty minutes. At the end of this time the hide collagen :is reduced significantly in thickness. The hides were then ready for removal and tannage in accordance with conventional practice.

An interesting and surprising facet of the invention is the fact that leather made from hide cured or pretanned as herein described possesses properties which are related to the properties of the quaternary ammonium salt used. Because the salts specified are fungicides and bactericides, this leather is remarkably resistant to various types of attack by ambient influences. This is considered to be particularly significant in the manufacture of leather for use in moist, humid tropical climates.

Those skilled in the art of the curing and pretanning of hides will realize that the invention herein set forth has a number of very distinct advantages, and that it is capable of being used in various manners. For this type of reason, this invention is to be considered as being limited solely by the appended claims forming a part of this disclosure.

What is claimed is:

1. In a process of treating a flayed hide, the following steps:

applying to the flayed hide a first solution at a temperature between approximately F. and 100 F. for a period between approximately 15 minutes and minutes, the first solution containing the following ingredients:

an alkali metal hydroxide to saponify lipids in the hide, the alkali metal hydroxide having a concentration to provide a pH of at least 12 and having up to approximately twenty-five percent (25%) by weight of the flayed hide,

a sodium salt to limit swelling of the collagen within the hide, the sodium salt having up to approximately ten percent (10%) by weight of the flayed hide;

applying to the flayed hide a second solution contain ing a calcium salt to cause shrinkage of the collagen within the hide; and

applying to the flayed hide at a temperature of approximately 70 F. for a period of approximately twenty (20) minutes a third solution containing the following ingredients:

an alkali metal hydroxide to control hide thickness, the alkali metal hydroxide having approximately two percent (2%) by weight of the flayed hide,

a sodium salt to maintain hide strength, the sodium salt having approximately two percent (2%) by weight of the flayed hide, and

sodium sulfide for removing hair keratin, the sodium sulfide having approximately two percent (2%) by weight of the fiayed hide.

2. In the process set forth in claim 1, the alkali metal hydroxide in the first solution constituting sodium hydroxide and the sodium salt in the first solution constituting sodium chloride.

3. The process set forth in claim 1, the alkali metal hydroxide in the third solution constituting sodium hydroxide and the sodium salt in the third solution con stituting sodium chloride.

4. In the process set forth in claim 1, the salt in the second solution constituting calcium chloride and the 15 alkali metal hydroxide in the third solution constituting sodium hydroxide and the salt in the third solution constituting sodium chloride.

5. The process set forth in claim 1 wherein the amount of sodium hydroxide in the third solution is suflicient to return the thickness of the hide to the thickness of the hide after the application of the first solution.

6. The process set forth in claim 1 wherein a solution of sodium sulfite is applied to the hide, after the application of the third solution to the hide, to strengthen the external surface of the hide.

7. The process set forth in claim 6 wherein the solution of sodium sulfite contains between approximately 0.1% and by weight of sodium sulfite and is applied to the hide for a time period between 10 and 30 minutes at a temperature up to 90 F.

8. The process set forth in claim 5 wherein a solution of sodium sulfite is applied to the hide, after the application of the third solution to the hide, to strengthen the external surface of the hide.

16 9. The process set forth in claim 8 wherein the solution of sodium sulfite contains between approximately 0.1% and 5% by weight of the flayed hide and is applied to the hide for a time period between 10 and minutes at a temperature up to F.

References Cited UNITED STATES PATENTS 3,421,832 1/1969 -Minklei 894.l6 3,415,610 12/1968 Dexter et al. 894.l6 1,859,417 5/1932 Wavra 894.l6 2,937,068 5/ 1960 Panepinto 894.l6 3,574,517 4/1971 Elvrum 894.l6

MAYER WEINBLATT, Primary Examiner H. WOLMAN, Assistant Examiner US. Cl. X.R.

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