US2228133A - Treatment of hides and skins - Google Patents

Description

Patented Jan. 7, 1941 UNITED STATES 2,228,133 TREATMENT ornmns AND SKINS Arthur M. Breach, Frame, England, assignor to Hall Laboratories, Inc., Pittsburgh, Pa., a company of Pennsylvania No Drawing. Application October 13, 1939, Se-

rial No. 299,353. In Great Britain October 11,

2 Claims.

leather from skins, light hides and the like, and has for its object the provision of a method of treatment in which the somewhat crude and uncertain process of puering or bating asipracticed for many years is superseded by a neater and cleaner operation, and one that affords opportunity for accurate yet easy control.

As is known, the process of puering or bating follows the successive operations of de-wooling or unhairlng, liming, splitting, washing and deliming, and is usually followed by washing, scudding, washing, drenching and pickling.

As is well known, the object of puering or bat ing is to render the skins, and the resulting leather, soft and supple. Skins which have undergone the liming process must be thoroughly freed of lime before tanning, and for light and soft leathers must be reduced or brought down so that the elasticity or resilience of the skin fibers is got rid of, so that the skin, when tanned, can be stretched without springing back. These objects have hitherto been achieved by, passing the skins through an infusion of dung, or an enzyme bate. The operation of drenching, frequently carried out in the manufacture of light leathers, has similar objects, viz: the ultimate production of a soft and stretchy leather. It will be seen, therefore, that the effects achieved by the puering, bating and/or drenching processes are entirely different in every way from the process of tanning, which has for its object the conversion of skin tissue into an imputrescible and permanent material known as leather.

According to the present invention, the results ordinarily obtained by puering or bating is produced by the use of a water soluble metaphosphate in conjunction with a suitable acid of which sufficient is used to produce a final pH of about 2.6 of both liquor and goods, and without the aid of bacteria or hating enzymes, such as are essentials in the already known excremental puers or artificial bates. Furthermore, by my process the use of the drenching process may be avoided.

The term water-soluble metaphosphates includes alkali metal and ammonium hexametaphosphates, with or without trimeric metaphosphates and/or pyrophosphates and/or polyphosphates.

A satisfactory concentration of the salt in the solution for my purpose in accordance with the present invention is one per cent, and a satisfactory quantity of the solution to use is three times the weight of skins being treated.

This invention relates to the manufacture of 7 The bath used according to the present invention may start neutral and be brought to the pH value of about 2.6 gradually, for which purpose organic and/or inorganic acids may be used. If desired, salts such as sodium chloride may also be added for their buffering and antiseptic value.

The known process of puering, depending as it does upon the action of bacteria, enzymes, and the chemical constituents naturally present in dung, is an uncertain, and moreover disgusting,

process and, furthermore, one which may rightly be regarded as a nuisance by neighboring residents on account of its obnoxious smell.

Dung, as received from kennels, varies very considerably in composition; furthermore, the process, as commonly practiced, is influenced considerably by atmospheric and climatic changes, No proper standards exist to determine whether or not the skins are sufficiently puered, and consequently the operators discretion and experience have to be relied upon in order to ensure the goods getting accurate treatment. The only practical tests available, in order to determine whether or note skin is sufilciently puered or bated, is feel and to some extent, appearance. According to the kind of. silkiness and freedom from harshness or gristle, a decision has to be made as to whether the skin has had sufficient treatment.

By reason of the lack of concrete standards, and the fact that the operator's judgment may be frequently at fault, many errors arise in the excrementalpuering process. Furthermore, the skins comprising a parcel for treatment, numbering perhaps 240 skin's, react in different ways with the dung, some yielding very much quicker than others, some having to receive very pro longed treatment before they are in a fit condition. It is frequently found that skins which are sufficiently puered or bated on the sides are still hard on the backs, and such skins yield most irregular and unsatisfactory results in the finished leather. Cockly skins, especially, demand prolonged treatment, and are then frequently unsatisfactory when tanned.

Insufficient puering causes the production of a harsh and discolored leather, While over-puering leads to holes and weakness in the valuable grain surface. The process of puering, at best, is accompanied by considerable loss of skin substance. As much as 1.254 gms. skin substance per litre has been found in a puer liquor after normal use; this amount would be much greater with excessive puering, but even this quantity is equivalent to 1% on the dry ash free skin. The ordinary feel, by which is meant a Gil process of puering, if carried to only slight excess, destroys the hyaline or glassy layer of the grain surface; such skins when tanned possess a dull, hungry, and open etched appearance.

Much that has been said of excremental puers may be applied to artificial bates. In practice they are no less offensive, as it is customary, in order to obtain maximum bating eiiiciency, to use a stock liquor and to strengthen it for each successive pack. Although a fresh bating liquor is free from bacteria and is dependent entirely upon enzyme action, together with chemical delimlng, for its efficiency, the practice of using such a liquor repeatedly results in it becoming bacterially active. The action of a freshly made hate is much slower than that of a dung liquor, and in some cases, unless the action is strengthened by the use of old stock liquor, or by the addition of a quantity of dog dung, the degree of softness or flacciclity obtainable is insufficient.

Whereas a dung puer is three-fold in action, viz: bacterial, enz-ymical and chemical, a freshly made bate liquor is twofold, viz: enzymical and chemical. As this liquor becomes older, and thus bacterially active, or is assisted by the addition of dung, the action is speeded up. Under unfavorable conditions, or through lack of judgment on the part of the operator, such bating liquors will give rise to the same faults as are experienced in the puering operation proper, such as damaged grain, excessive loss of skin substance, and tenderness.

Indeed, it may be said that cockly sheepskins and goat skins, which are by nature harsh and in consequence require a very thorough softening, are-frequently inadequately depleted by a fresh bate liquor, or if so, only after very prolonged treatment. The increased and quicker action, brought about by the use of stock solutions, or by the addition of excrement, bring the relationship of the puer liquor and the bacterially active enzyme bate liquor very close, certainly as far as liability to errors is concerned, such as grain damage, loss of skin substance, and weakness.

Having given a brief description of the dung and enzyme bates, together with some account of their shortcomings and the difficulties in applying them in such a way as to ensure uniform results .in the finished leather, I will set out the advantages of the present invention, as follows:

(a) Complete freedom from obnoxious odors.

(b) Consequent easier disposal of waste liquors.

(c) A neater and more positive process than is offered by either dung or enzyme bates.

(d) A process easily controlled, and not requiring the services or experience 01' a skilled puerman.

(e) A process which affects all skins in the parcel under treatment equally, and which is productive of the necessary uniform results within a definite time, as opposed to the erratic results produced by the dung and enzyme bates, and to the uncertain period required for their proper performance.

(f) A process which cleanses the skins under treatment and which solubilizes any lime and magnesium soap present in the goods as a result of the previously performed processes, so much so that the operation of scudding, as ordinarily performed for this purpose, may be dispensed with.

(g) A process which affords the necessary depleting action, yet which at the same time conserves skin substance and strength, and preserves effectively the hyaline or glassy layer of the grain surface of the skin.

(h) A process which, applied to washed and delimed skins and light hides, functions as a bate, washing and/or cleansing agent, a drench and a pickle, and which produces in a few hours the results at present obtained by the lengthy sequence of operations of 'deliming, washing, puering or hating, washing, drenching, washing, and pickling; in fact, my process does in, say three hours, in one operation, the work ordinarily performed by means of the named older fashioned processes in about twelve to eighteen hours. Y

(i) A process which is neater, simpler, and cheaper, on account of the elimination of the skilled labor ordinarily employed in the deliming, washing, puering or bating, washing, drenching and pickling operations, and which saves by reason of the elimination of these processes, considerable handling.

(9) A process which reduces the cost of the results ordinarily obtained by puering or hating,

washing, drenching, washing and pickling by more than and which is capable of easy application without requiring the services of an experienced puerman or chemist.

(k) A process by which skins and light hides may be brought to the properly depleted, cleansed and pickled condition, and in which the goods may be kept until required for tanning.

Having set out the advantages of the present process, I will now give an example of how to carry it into practice. Limed sheep or lamb grains, limed sheep or lamb pelts, or such like limed skins are washed in running water until the wash liquor is clear of lime, and then carefully delimed by any suitable means to pH '7.

The operation or softening the hides and skins is carried out in a shelved drum, rotating 'preferably at about 18 R. P. M. I

A 1% solution of sodium metaphosphate is carefully prepared and fed into the drum in quantity equal to three times the weight of the delimed goods to be treated. The goods are then treated in the drum by rotating the latter for one hour, after which time the pH of the goods and liquor is gradually reduced to about pH 2.6 by the several cautious additions of diluted sulphuric or other suitable acids.

When equilibrium has been reached (i. e. the pH value 2.6 has been established substantially throughout the bath and the goods themselves) an addition of 10% sodium chloride is made, and drumming continued for a further period of half an hour. The goods are then ready for tanning, using salt in the tanning liquor in the usual way and as is customary when processing pickled stock.

When processing hard natured stock, such as goat skins, it is advantageous to commence the operation at a temperature of 80 F. and to prolong it before making the addition of salt. During the drumming process, however, it is necessary to avoid too high a temperature, and to this end the drum should be stopped occasionally and ventilated by removing the door.

The invention is not limited to the preferred example but may be otherwise embodied or practiced within the scope of the following claims.

I claim:

1. The process of softening limed hides and skins prior to tanning, which comprises delimthem to pH about 7, drumming them with a soiu-.

tion containing a. water soluble metaphosphate and having a pH of about 7, said drumming being continued for a period of about one hour,

thereafter reducing the pH of the solution to about 2.6 and continuing the drumming for a period oi about half an hour, the .combined' drumming treatments with metaphosphate solution before and after making it strongly acid rendering the hides and skins in a soft flaccideom dition so that when tanned they can be stretched without springing back.

ARTHUR M. BREACH.