US2019568A - Process of tanning - Google Patents

Description

Patented Nov. 5, 1935 ATN OFFICE PROCESS OF TANNING No Drawing. Application March 18, 1933, Serial No. 661,587

17 Claims.

The present invention relates to a tanning process and product, and more particularly to a process of tanning adapted to secure a white leather.

Heretofore, the attempt to obtain a white leather from cow and steer hides, calf, sheep, goat and the like have been unsatisfactory in their results for a number of reasons, among which are the following: Where an alum or an alum formaldehyde tannage has been employed the skin has not been completely or permanently tanned, the tanning material being easily washed out if such leather is exposed to water, and the skin or hide returning in greater or less degree to its original untanned condition.

Where a chrome tannage is employed, and this is the common present method of producing a white leather, it is necessary to subject the tanned leather to a further step or treatment, namely, the application of pigments to cover or overcome a distinct blue or green color resulting from the tanning process. The pigment or pigments so applied do not become a permanent part of the leather, being more or less in the nature of a coating, and when such pigmented leather has its surface removed, or is cut or skived to present a raw edge or face, this will show a very undesirable dirty bluish shade.

Oil tannage avoids the objection of lack of permanency or completeness of the tannage found with the alum formaldehyde tanning, and the objectionable colors and the necessity of pigmentation present in the chrome tanning, but such oil tannage is a very long and slow process, requiring weeks for its completion.

I have found that a tungsten compound may be used as a tanning agent, in combination with other suitable reagents and under certain conditions, to quickly, completely, and permanently tan cowhides, calfskins, sheepskins and the like to a leather which not only possesses the characteristics necessary to adapt it for such uses as shoes, garments, gloves, etc., but which, when desired, may be of a permanent white color both on its surface and throughout its body.

The present invention consists in the process of tanning wherein a compound of tungsten is employed as a tanning agent and a completely and permanently tanned leather is produced. This invention further consists in the leather tanned by such process.

In practising the present invention, the preferred method is as follows: The skin or stock, such as cowhide, as it comes from the pickle, w ch may m e 2 of sulphuric acid and 6% of salt, will be given three washings in the wheel with salt solution. This removes most of the uncombined sulphuric acid from the skins. The wheel is then drained and a solution of a tungsten compound is added. A satisfactory 5" at the end of which time an alum bath is added 7 slowly and at intervals for one hour. A suitable alum bath consists of ten pounds of aluminum sulphate per one hundred pounds of stock or skins, dissolved in fifteen gallons of 5% sodium chloride solution. After the alum solution has been added the wheel is run for two hours longer, making three hours in all from the time the first portion of the alum bath was added.

The mixed solution is then drawn off and the skins thoroughly washed in the running water. They are now ready to be fat-liquored and. subjected to the other usual steps or process to finish and prepare them for consumption.

Instead of leaving the tungsten solution in the wheel and adding to it the alum solutions, it may be desirable or convenient first to withdraw the tungsten solution before addingthe alum.

While preferably the skins are first subjected to the tungstate liquor for a substantial period of time, after which the alum bath is added, the process is not necessarily limited to this particular procedure or order but may be practised otherwise within the scope of the appended claims.

In practising the above described process it is 4 essential that the hydrogen ion concentration (pH) be carefully controlled within fairly narrow limits if a true tanning is to be effected. It has been found that with a pH value of from 3 to 4 and again slightly below 8 the best results are secured, giving a leather with a tungsten content in the form of oxides of from 14 to 18% by weight, although a satisfactory leather may be obtained in which the tungsten content as calculated on the basis of the tungstic oxide is only a portion of these amounts.

The process which is the subject of the present invention produces a leather which is permanently tanned by a tungsten compound; that is, tungsten in some form is combined with the 55 portion of the tungsten will be lost upon washing. Where the tungsten compound, such as sodium tungstate, is used in combination with aluminum sulphate, as above described, the leather will have not only a surface of pleasing whiteness, but the same shade or color will be present throughout the body of the leather so that all cut and skived edges have the same shade or color as the adjacent surfaces.

Preferably the improved process will be practised in such a manner and with such other ingredients or materials that a pleasing and uniform white color will be produced not only upon the surface of the leather but also extending throughout the body of the same. It is to be understood, however, that the invention is not necessarily so limited for .it comprehends in its broader aspects the use of a tungsten compound with materials and ingredients and a method of treatment to permanently and quickly tan the skin, irrespective of the color or shade produced.

Nor is the present invention limited to the use of a tungsten compound as the sole and exclusive tanning reagent, but contemplates the use of other tanning agents or materials simultaneously with, or proceeding, or following the use of the tungsten compound. Thus the skins may be given a preliminary or partial tanning by means of chrome tanning materials, the tanning being completed by the action of the tungsten compound.

While the tungsten compound specifically referred to in the foregoing specification has been sodium tungstate, it is to be understood that the present invention is not necessarily limited to this particular and specific compound, as other compounds and forms of tunsten may 'be employed as, for example, sodium paratungstate. Nor is the invention limited to the other specific ingredients or the particular proportions except where so specifically set forth in the claims.

Having thus described the invention, what is claimed is:

1. The process of tanning skins which includes the step of subjecting the skin to the action of a tungsten compound in acid solution, to effect tanning of the skin.

2. The process of tanning skins to produce white leather which includes the step of subjecting the skin to the action of a tungsten compound in combination with a salt and a weak acid, to effect tanning of the skin.

3. The process of tanning to produce white leather which consists of subjecting the skin to the action of a tungsten compound in acid solution and an aluminum compound, to tan the skin.

4. The process of tanning to produce white leather which consists. of subjecting the skin to the action of sodium tungstate with acetic acid and thereafter to aluminum sulphate, to tan the skin.

5. The process of tanning to produce white leather which consists of subjecting the skin for a substantial period of time to the action of a tungsten compound in acid solution, adding to said solution over a second substantial period of time a second solution containing an aluminum 4 fibres of the skin in such manner that no major compound and subjecting the skin to the action of both solutions through said second period of time, to tan the skin.

6. The process of tanning to produce white leather which includes the step of subjecting the skin to the action of sodium tungstate, together with sodium chloride, acetic acid, and aluminum sulphate, to tan the skin.

7. The process of tanning to produce white leather which consists in subjecting the skin to the action of sodium tungstate, sodium chloride, acetic acid, and aluminum sulphate, while controlling the hydrogen ion concentration, to tan the skin.

8. As an article of manufacture, tanned leather having a compound of tungsten fixedly combined with the fibres thereof.

9. As an article of manufacture, leather having a compound of tungsten fixedly combined with a portion thereof in amount, calculated on the basis of tungstic oxide, 14 to 18% of the weight of such portion.

10. As an article of manufacture, leather of white color on its surface and throughout its body and having a tungsten compound fixedly combined with its fibres as a tanning agent.

11. As an article of manufacture, leather containing a compound of tungsten combined in such a manner with the hide fibre that no major portion of the tungsten compound will be lost upon washing.

12. The process of tanning skins which includes the step of subjecting the skin to the action of a tungsten compound and effecting the fixation of the tungsten by controlling the pH at a point approximately from 3 to 4.

13. The process of tanning skins which includes the step of subjecting the skin to the action of a solution of a compound of tungsten with an alkali and effecting the fixation of the tungsten by controlling the 3 to 4.

14. The process of tanning skins which includes the step of subjecting the skin to the action of an alkali tungstate, and effecting the fixation of the tungsten by controlling the pH at a point approximately 3 to 4.

15. The process of tanning to produce white leather which consists in subjecting the skin to the action of a tungsten compound in solution and alum and eifecting the fixation of the tungsten by controlling the pH at a point approximately 3 to 4.

16. The process of tanning to produce white leather which consists in subjecting the skin to the action of a tanning agent to partially tan the skin and thereafter subjecting the partially tanned skin to the action of a tungsten compound and effecting the fixation of the tungsten by controlling the pH at a point approximately 3 to 4.

17. .The process of tanning to produce white leather which consists in subjecting the skin to the action of a plurality of tanning agents, each having a tanning action on the skin, one of such tanning agents being a compound of tungsten, and effecting the fixation of the tungsten by controlling the pH at a point approximately 3 to 4.

pH at a point approximately HERMAN A. HERZOG.