US2162015A - Preservation of tanned leather - Google Patents

Description

Patented June 13, 1939 UNITED STATES 2,162,015 PRESERVATION F TANNED" LEATHER Alfred W. Hoppenste'dt, Buffalo, N. Y., assignor'to "J. A. Webb Belting 00., 1110., Buffalo, N. Y.

No Drawing. Application September 23, 1936, Serial ,No. 102,255

Claims.

This invention relates to the preservation of tanned leather, andit has particular reference to a method of, and means for, preventing the .de-

ter ioration of leather from those causes com- 5 monly termed rot.

The word-leather, as generally used and as employed in' this specificatiomconnotes the product resulting from the treatment of hides or skins with various media t'e'r'me'd tanning agents, which convert the hides into a more durable and less putrescible condition. Leather, as a product of tanning operations, finds many industrial uses, suchasin power transmission belting, coverings; and the like. Over a periodof time, however, leather loses its strength and resiliency, and becomes dry, powdery,- and actually disintegrates. Leather in such condition is said to be rotten, and the causes of the decaymay generally be termed rot. Rot in leather may be caused in various ways, as, for example, by contact-of the leather with harmful chemicals. It has been observed that vegetable tanned leather is notably susceptible to deterioration from this source, Rot may also be causedby physical means. For example, excess heat will causeleather to disintegrate. In leathers for mechanical purposes where stress and strain and friction of the fibers are present, excessive oil' or grease on the leather, or insufficient or low grade oil or grease may cause disintegration of the fibers and substance of the leather. Users of beltsclassify variousspecies of decay according to appearance and texture by such terms as oil rot, dry rotfland red rot while bookbinders and other leather workers employ the terms dry rot and red rot.

I have'disc'overed that rot, particularly insofar as it is induced by chemical action, may be counteracted and prevented if the tanned leather is 40 occasionally treated with a composition having the power to penetrate the pores of the leather and also having a basic reactive character. As a further specification of suitable means to prevent or counteract rot, I have discovered that its effects may be offset by neutralizing the ingredients producing rot with a suitable solution of one of the class of substances known as organic bases, the solvent being a medium which is comparatively inert chemically, but physically able to penetrate the pores of the leather.

I attribute the beneficial results obtained by such treatment to the fact that normal or healthy leather has an acid or pH value, as determined by the hydrogen-ion concentration method, of about 3 to 4. That is to say, if a number of samples of healthy leather, as prepared by various tanning methods, be extracted with water, and the extract tested in the usual ways-the pH values of the solutions will fall in this range,-thus showing that normal leather is pronouncedly acid. 5 However, if the pH value falls below say 2.95 to 3.0, and particularly as low as say 2.35, the leather shows all the effects symptomatic of rot. That is to say, while healthy leather is acid, rotten leather is more acid in nature,'and it may be said that the condition of rot in leather is caused by the absorption, as from the atmosphere, of acid carbonic or sulphur vapors.

Accordingly, the present invention contemplates the treatment of leather, Whose pH value has dropped into the danger zone, with a penetrating solution of an organic base, so that the absorbed acids may be neutralized, and the leather restored to its normal acidrange. It has been found that leather having a normal or slightly sub-normal acid value may be so treated to prevent any development of rot, While leather having a somewhat increased acid content may be treatedto oflfset the" effects of rot, thus curing the condition, provided, of course, it has not advanced too far.

The general chemical class called organic bases includes such substances as the primary, secondary, and tertiary amines, the amino-com pounds or aromatic amines, and the Vegetable bases or pyridine nucleus compounds. To name some of the species of these groups, it may be stated that the following have been found effica'cious: mono--, di-, and tri-amylamine, triethylene tetramine, anilin, toluidine, xylidine, pyridine, and quinoline. These compounds (whichever may be selected, or a kindred compound havinglike desirable properties) are dissolved in a suitable solvent which is chemically inert to the leather, such, for example, as carbon tetrachloride, benzol, butanol, naphtha, or turpentine. The various chlorinated organic solvents may also be used, but care should be taken in such event to select one which, upon any decomposition, will not develop a free acid. It is preferred to employ as a solvent a material which will not dissolve the cement (such as animal glue or nitrocellulose) which may be used in making a multi-ply leather product, such as a belt. The solvent should also penetrate the pores of the leather quickly, yet not react with the bonding media between the fibers. It may also have a relatively low boiling point and be non-flammable, so that, upon application of the dissolved compound, the solvent may safely vaporize and leave 2 behind the organic base to react with the absorbed acids.

Since the amount of free acid required to change the pH value of leather from say 3.0'to

2.9 is very small, it will be apparent that fairly dilute solutions of the organic base may be employed, the exact concentration of base in solution and the amount of solution used depending upon the activity of the compound selected, and the probable amount'of acid absorption over a given period of time. it will be found that effective preservation may be obtained by brushing or swabbing the surface of the leather with the solution, say every si months.

In order to indicate the relative strengths of s 1 b f i o ution e ore a ter Solvent solute strength treattreatment ment 7 Percent Benzol Monoa1nylarnine 6 2. 75 3.15

D0 Diamylamine 20 2.37 3.06 Gasoline 'Triamylamine 30 2.45 3.17 Toluol Triethylene-tetra- 4 2. 70 3.30

mine.

D0 do l2 2. l0 3. l0 Turpentine Anilin 10 2. 65 3.00 Naphtha Xylidin l4 2. 65 2. 95 Toluol-butanoL- Pyridine 6 2.80 3.17 Xylol l. Quinoline 10 2.85 3.20

- It will be observed that in each case, a leather having an acid value synonymous with a condition of rot was restored to a normal or healthy condition; thus preventing the, development of further rot, and it will also be noted from the compounds used that the function of preventing such rot is common to widely selected members of the class of organic bases. It will also be noted that the solvents employed are not harmful to the leather, and that they do not include water,

since water has a deleterious eifect on leather if allowed to penetrate the pores.

In this connection it may be noted that some forms of belt dressings are miscible with the basic solutions of the present invention, which suggests making a suitable mixture so that the belt dressing andrpreservative are applied concurrently. However, since it is a simple matter to swab the belt with the preservative and rot For ordinary commercial use,

inhibitor, and a mixed solution might have so high a viscosity as to prevent complete penetration, this suggestion, while feasible, is not to be recommended too strongly. t

I am, of course, aware of the fact that heretofore it has been proposed to load leather during the tanning process with inert ingredients to protect the finished product against rot, and that proposals have been advanced to employ organic bases as ingredients of tanning baths. However, the present invention contemplates leather as it exists in commerce, and further contemplates the treatment of diseased leather with a reactive organic base, rather than with the reaction product of such a compound which, at the time of application, has lost its corrective virtues.

It will therefore ,be understood that I do not claim merely the contacting of raw or partially prepared hides with organic bases or their reaction products, but what I do claim is:

1. The method of correcting and inhibiting a condition of rot in tanned leather, which comprises applying to the surface of such leather a penetrating solution of an organic nitrogenous base in an inert organic solvent.

2. The method of correcting and inhibiting a condition of rot in tanned leather, which comprises impregnating such leather with an organic nitrogenous base in a quantity sufficient to raise the pH value of the leather to between 3.0 and 4.0.

3. The method of correcting and inhibiting a 4 condition of rot in tanned leather which coml f prises treating a piece of tanned leather whose pH value is less than 2.95 with a penetrating none aqueous solution of an organic nitrogenous base in an amount sufficient to raise the pH value to more than 2.95 but less than 4.0.

4. In the preservation of leather, the process which comprises selecting a piece of leather which has been subjected to an acid atmosphere to an extent sufiicient to reduce its pH value to less than 3.0, and impregnating such leather with a solution of a reactive organic nitrogenous base in ,a

volatile organic solvent chemically inert with respect to the leather in an amount sufiicient to restore the pH value to between 3.0 and 4.0.

5. The method of correcting and inhibiting a condition of rot in tanned leather which comprises treating such leather with anorganic nitrogenous base typified by the class of compounds including amylamine, ethylene-tetramine, anilin,

xylidin, pyridine, and quinoline and dissolved in a non-aqueous organic solvent, said treatment being with a quantity suflicient to increase the pH value of such leather to more than 2.95 but less than 4.0.

ALFRED W. HOPPENSTEDT.