WO2023118736A1

WO2023118736A1 - Tanning method and tanning composition enabling implementation thereof

Info

Publication number: WO2023118736A1
Application number: PCT/FR2022/052447
Authority: WO
Inventors: Jacques BOBILLON
Original assignee: Alfabore
Priority date: 2021-12-22
Filing date: 2022-12-20
Publication date: 2023-06-29

Abstract

The invention concerns a method for tanning a skin, comprising a prior pickling operation, notable in that it comprises using, for tanning purposes, zeolite and vegetable tannin obtained from a plant of the subfamily Mimosoideae, with a minimal amount relative to the mass of pickled, drained skin of 12% of tanning extract or equivalent thereof in original material, for obtaining a leather having a shrinkage temperature of at least 100 degrees Celsius. The invention also relates to a tanning composition for implementing said method.

Description

Title of the invention: TANNING PROCESS AND TANNING COMPOSITION ALLOWING IT

IMPLEMENT ,

[0001] FIELD OF APPLICATION OF THE INVENTION

The invention relates to the technical field of tanning and adaptations for tanning in the best conditions without using chromium salts.

[0003] DESCRIPTION OF PRIOR ART

[0004] Tanning is a technical process known since the earliest ages for the ability of certain compounds to preserve the skin from decomposition and to transform it into a substance that can be used in industry, such as leather.

[0005] The techniques used have evolved over time. The oldest are based on the use of powdered tree bark, fruit or wood (tan) or mineral products such as aluminum alum or realgar (arsenic ore). The most used products were tannins from crushed plants such as oak bark, mimosa bark, acorn cupules and holm oak galls (hilly), sumac leaves, divi -divi, tara, cachou, mirobolam nuts.

[0006] At the end of the nineteenth century, liquid extracts appeared, the most widely used of which were and remain extracts of quebracho, mimosa, chestnut, hilly myrobalan and gambier. Tara is still used in the form of crushed pods.

[0007] At the beginning of the twentieth century, tanning with chromium salts appeared, the technique of use of which was perfected during the first decades to find its full development after the Second World War. Tanning with chromium salts has the advantage of obtaining a leather shrinkage temperature (and therefore denaturation of its properties) greater than 100°C and therefore of allowing certain assembly operations for leather objects involving heating phases. steamed. [0008] The shrinkage temperature of a leather can be measured according to several methods. Among these methods, one of them consists in placing a tongue of tanned leather between two movable jaws holding the ends of the tongue, in placing this assembly in a humid medium (water according to a preferred embodiment but not limiting) whose temperature is gradually increased and measured. The retraction temperature then corresponds to that measured when the jaws move due to the change in length of the tongue.

[0009] Furthermore, whereas vegetable-tanned leather is brown and therefore difficult to dye if it is desired to obtain bright and pure colors, chrome-tanned leather is blue and therefore much more suitable for dyeing.

[0010] Finally, chrome tanning makes it possible to produce an intermediate material in the manufacture of articles, which makes it possible to sort the skins easily to direct them towards one manufacture rather than another according to their quality and also to constitute a buffer stock. This leather, baptized wet-blue, is also marketed as it is as a raw material for certain tanneries.

[0011] Tanning with chromium salts has been the subject of theoretical studies, in particular as regards the mechanism of action of chromium molecules. The most advanced theory describes the tanning process as the result of a mechanism called "Link and lock". In such a process, chromium molecules react in two steps.

[0012] Initially, the molecules of relatively small size bind to the collagen chain of the skin to be tanned in an acid medium (pH 3.2), but the tanning remains low because if they bind to the reactive sites, they do not create bonds between the chains or between two sites making it possible to avoid the collapse of the spatial structure of the proteins.

Secondly, after increasing the pH to 3.8 during the so-called basification operation, the chromium molecules polymerize to a certain degree by the phenomenon of oxolation and cause the establishment of bonds of the complexation or covalent which, by creating bridges between the various reactive sites of the fiber, bring about a modification of its structure and prevent its collapse under the action of heat. However, chromium is the only (practically usable) metal with this oxolation property. Aluminum salts which are chemically very close to chromium do not have this property and do not make it possible to establish bonds that are stable enough to obtain sufficient resistance to temperature.

[0014] Over the past two decades, concerns for the environment, public health and that of workers have led to questioning the use of chromium salts for the manufacture of shoes and other leather objects. In particular, the possible formation of chromium VI during the aging of the leather has led to the tightening of safety standards and brought some discredit to this tanning method.

[0015] It has been attempted to find an alternative to chromium by using other metals or organic products, but which have so far only resulted in imperfect solutions, the final product not having typically a shrink temperature of up to 100°C. Certain organic compounds such as oxazolidines have made it possible to obtain this performance, but the cost of the products is prohibitive with regard to current techniques and in most cases, they exhibit proven or suspected toxicity which makes them unusable in practice.

The best results in this area have been obtained by using a combination of two tannings: a first tanning with vegetable tannins then a retanning with aluminum salts.

[0017] N. Slabbed in particular obtained a leather having a shrinkage temperature of 100° C. with the mimosa extract. Unfortunately, the mechanical properties of the leather thus obtained are degraded, in particular the resistance to bursting of the grain. The leather made brittle by this treatment cannot be marketed, which led to the abandonment of this process. As for the other vegetable tannins, none has proved capable of producing a shrinkage temperature close to 100° C. on a regular basis or of presenting sufficient flower bursting resistance performance. Moreover, if we disregard the thermal performance of the leather, the mimosa/aluminium tanning process requires first vegetable tanning, which gives the finished leather characteristics specific to this type of material and which cannot be removed by adding aluminum salts or other produced during retanning operations. This means that this method of tanning does not make it possible to produce a leather that can serve as an intermediate support for manufacturing the whole range of articles permitted by tanning with chromium salts.

An alternative to the use of aluminum was developed in the 1990s using aluminum silicates in the form of kaolin or zeolites. The leathers obtained by this technique have not made it possible to obtain, associated with vegetable tanning, a sufficient shrinkage temperature: it is generally between 75 and 85°C as described in document WO2013114414 which specifies that the techniques described lead always at a shrink temperature below 100°C.

[0019] The shrinkage temperature of skins using other vegetable tannins, which is generally between 70 and 75° C., can be markedly improved by aluminum salts and is increased to around 90° C. for most skins. 'between them. However, despite this performance, the leather obtained does not have good mechanical qualities due to its low resistance to bursting.

[0020] To date, therefore, there is no alternative solution to tanning based on chromium salts that is technically and economically viable.

[0021] The document FR2397459 describes a tanning process which comprises a step of degreasing-pretanning skins in tripe pickled with a composition which contains an alkaline aluminosilicate in very fine particles and tanning with chromium, compositions containing synthetic tannins and powdered mimosa and quebracho tannins, to obtain good quality leather but not a leather shrink temperature of at least 100 degrees Celsius.

[0022] The document GB2057497 describes a tanning process which comprises a first step of tanning the pickled skins using an extract of mimosa in powder and a second tanning stage using an aluminum salt making it possible to obtain leathers which, while excluding chromium salts, have in certain examples a shrinkage temperature greater than or equal to 100° Celcius.

[0023] The document FR889837 describes a deliming agent for hides and skins based on the seed of the finely ground acacia "Arabica", known as Gonakié.

[0024] DESCRIPTION OF THE INVENTION

[0025] Finding this, the plaintiff has carried out research aimed at finding an alternative to tanning based on chromium salts that is technically and economically viable. For this, the applicant started from the principle that it is appropriate, in order to obtain a tanning resistant to 100° C., to implement a mechanism similar to that of chromium salts with materials which can act in such a way as to fix themselves on the chains of the fibers and then react between them in order to create bridges making it possible to connect the reactive sites which can then be either the chemical groups of the protein chains which have remained free, or those of the first component linked to the chain after having reacted with the latter.

[0026] However, this first condition is not sufficient, because if many chemical components react with each other and/or with the collagen fiber of the skin, they only lead to the linking stage (known as "link"). and do not make it possible to reach a suitable retraction temperature due to the fact that the blocking step (called "lock") is missing.

[0027] Furthermore, of all the materials studied which have the property of reacting with reactive sites, vegetable tannins are known, in particular mimosa tannin which can react with aluminum, but under conditions which stiffen the fiber at such a point that it becomes brittle as described above. One would think that by using a polymerized form of aluminum such as aluminum polychloride instead of a simple salt, it would be possible to reproduce the blocking mechanism as oxolated chromium does. This is not the case and the leather obtained is no different from that produced using simple salts. This leads to estimate that the molecules participating in the blocking must be able to react during their formation by reaching a suitable size allowing them to bind appropriately with the different sites. We therefore deduce that, in order to reproduce the mechanism specific to chromium salts, it must rather be necessary to use an aluminum compound having the capacity to be reactive with vegetable tannin on the one hand, with the groups fiber on the other hand and finally to polymerize.

[0028] This research led to the design and implementation of a process for tanning a skin using zeolite which, being a silicoaluminate, contains aluminum atoms capable of reacting with a vegetable tannin, then, just like the oxolated chromium molecules, can polymerize and react either with the molecules already fixed or, incidentally, with the free reactive sites of the fibre.

According to the invention, the process for tanning a hide comprising a prior pickling operation is remarkable in that it consists in using, for tanning purposes, zeolite and vegetable tannin from a plant of the mimosaideae subfamily, with a minimum quantity, in relation to the mass of wrung-out pickled skin, of 12% of tanning extract or its equivalent in source material, to obtain leather with a temperature of shrinkage of at least 100 degrees Celsius.

[0030] By equivalent in source material, we mean the percentage of material (wood, bark, pod or other) in relation to the mass of spin-dried pickled skin from which the same quantity of tanning extract can be drawn.

[0031] Pickling is a known operation of the state of the art consisting in treating the skin with acid and salt to a pH value generally between 2.5 and 3.5, with a view to its conservation or to make it suitable for the tanning operation. The acidity of this pickled skin is particularly important for the rest of the process because it lowers the pH to a level ensuring the dissolution of the zeolite.

[0032] It thus appears that an important aspect of the invention which ensures for the first time the obtaining of a temperature of 100° of retraction for a usable leather with a vegetable tannin resulting from a plant of the sub- family of mimosaideae lies in the greater proportion of the latter compared to what is usually used in this technical field.

[0033] The applicant discovered during her research that the skin tanned with zeolite could be retanned or co-tanned or pre-tanned using vegetable tannin from a plant of the mimosaideae subfamily and which , if present at a certain concentration, makes it possible to obtain that the shrinkage temperature of the leather is 100°C.

[0034] These are new technical effects of known tanning products which have appeared during their use in combination during the applicant's experiments.

[0035] In addition, the leather obtained resists boiling for several minutes, just like leather tanned with chromium salts. Thus, all the processes described below make it possible to obtain leather with a shrinkage temperature of 100°Celcius.

According to a particularly advantageous characteristic of the invention, said vegetable tannin is gonaki tannin. Gonakia tannin can be in the form of tanning extract or powder. In this last situation, its mass is then equivalent in percentage of the mass of drained pickled hide to twice that of the tanning extract, i.e. 24%.

The gonakié is a tree of the species Acacia Nilotica and/or Arabica and also known under the local names of Gaoudi, Amour, Diabbé, Bagana, Boïna, Nep Nep (sometimes spelled Neb Neb).

[0038] Another advantage of gonaki tannin is that it is stable to light.

According to a particularly advantageous characteristic of the invention, said vegetable tannin is mimosa tannin. It comes mainly from Acacia negra and Acacia mearnsii species.

[0040] Mimosa tannin is conventionally used as a natural or bisulphite atomized tanning extract according to various processes so as to obtain a lighter leather.

[0041] According to a first implementation of the invention, the method is remarkable in that it comprises the following operations: [0042] -Tanning by said vegetable tannin,

[0043] - Retanning with zeolite.

The leather obtained has a shrinkage temperature of 100° Celsius with the characteristics of vegetable leather and therefore without the possibility of having an intermediate product as defined below.

[0045] The leather thus obtained with the gonakié is beige-white and has acceptable mechanical characteristics, in particular as regards the resistance to bursting of the flower.

[0046] The leather thus obtained with mimosa is pinkish and has, as explained above, acceptable mechanical characteristics, in particular as regards the resistance to bursting of the flower with the characteristics of vegetable leather but without the possibility of having of an intermediate product as defined above.

For explanation, in this process, the zeolite is partially dissolved under the action of the acid pH of the leather after tanning with the plant extract and can therefore penetrate the leather; it can then recrystallize by autobasification (zeolite is an alkaline product) causing the formation of a polymer-type structure which is the counterpart of the oxolation phenomenon during chrome tanning. As a result, a "Link" (vegetable tanning) and "lock" (zeolite tanning) system is reproduced, leading to the formation of stable bonds in the fiber and, therefore, to an increase in the shrinkage temperature. up to 100 degrees.

At the end of this process in the tests carried out by the applicant, the leather has a structure and a physical behavior similar to that of chrome leather, confirming the validity of the method implemented. The latter is also validated by the fact that it is possible to reverse the sequence of operations: the zeolite can play the role of "link" which establishes structures without obtaining a very high retraction temperature but potentially sufficiently polymerized by crystallization creating inter-chain bonds. The role of "lock" is played by the vegetable tannin which, being able to react simultaneously with the zeolite and the fibre, causes the formation of bonds capable of stabilizing the latter and thus reaching the desired shrinkage temperature of 100°.

Thus, according to a second implementation of the invention, the method is remarkable in that it comprises the following operations:

[0050] - Tanning with zeolite,

[0051] - Retanning with said vegetable tannin.

[0052] While in the methods used to obtain a shrinkage temperature of 100° C. by metal-vegetable tannin systems, it is first necessary to carry out vegetable tanning and then to react the mineral compounds, in general aluminum salts , the plaintiff has proceeded here in the opposite direction.

[0053] It also allows the creation of an intermediate product tanned with zeolite awaiting its retanning with vegetable tannin.

The leather thus obtained with mimosa is beige and has, as explained above, acceptable mechanical characteristics, in particular as regards the resistance to bursting of the flower. It also has fairly good light stability.

According to a third implementation of the invention, the method is remarkable in that it comprises the following operation:

- Simultaneous tanning by said vegetable tannin and by zeolite.

[0057] The shrinkage temperature of the leather depends on the amount of vegetable tannin involved in the retanning and increases with it.

The minimum percentage of mimosa extract for this latter implementation is then 16%.

According to another characteristic of the invention, the minimum quantity of zeolite with respect to the mass of the dewatered pickled skin is 6%. The mass taken as reference is conventionally the mass of dewatered pickled skin. [0060] According to a preferred but non-limiting embodiment, the optimal minimum quantity of zeolite with respect to the mass of the dewatered pickled skin is 8%.

[0061] Conventionally, we count that the weight of the dewatered pickled skin corresponds approximately to the weight of the tripe skin divided by a factor of 2.6 to 2.2.

According to another particularly advantageous characteristic of the invention, the zeolite is a zeolite whose silica/aluminum ratio is between 1.0 and 5.0.

To be more precise, according to another particularly advantageous characteristic of the invention, the zeolite is selected from the following list:

[0064] Zeolite A,

[0065] Zeolite X.

According to another particularly advantageous characteristic of the invention, the gonakia tannin comes from the grinding of the pods of the gonakia fruit. More precisely, the 12% tanning extract of gonakia comes from 24% of powder obtained by grinding gonakia pods.

The tanning can be carried out according to all the preceding methods using either ground pod or an extract in solid or liquid form of said pod in proportions equivalent to the latter in terms of pure tannin.

According to a preferred but non-limiting embodiment, the optimum quantity of ground gonaki pods relative to the weight of dewatered pickled skin is 30%.

[0069] Most of the leathers produced with other extracts have a dark beige to brown color. According to another characteristic of the invention, the process is remarkable in that the tanning extract or its equivalent in the original material is combined with bisulphite. It is advantageous to use a bisulphite gonakia extract or a mixture of crushed pods and bisulphite to obtain perfectly white leather at the end of the tanning or retanning operation according to the method used.

Thus, according to another characteristic of the invention, the process comprises an operation of adding bisulphite which ensures the obtaining of a white leather (with the tannin of gonakié) or light beige (with the tannin of mimosa ) more easily exploitable for the operations to follow. It is possible to dispense with the addition of bisulphite by using a commercial sulphite extract instead of the ordinary extract.

According to another characteristic of the invention, acid is regularly added simultaneously with the addition of zeolite to counter the basification caused by the latter. Indeed, the tanning operation begins on skins in the pickled state. In this phase of the process, the pH must be maintained at a value of between 2.2 and 3.8 so as to partially dissolve the zeolite and allow it to penetrate inside the skin. This solubilization occurs at a pH below 4.0. Since zeolite is an alkaline product, the pH tends to rise to a value of 4.0-4.2 as a result of the so-called "self-basification" reaction between it and the acid present in the pickling bath. In order not to exceed the pH value of 4.0, the zeolite is added in two, three or more times, and, at each addition, a quantity of acid sufficient to bring the pH back to a value below 3, 2. Any acid can be used to implement this solubilization function.

[0073] It is understood that tanning can be carried out according to all the preceding methods using, instead of an extract, bark or crushed pod in equivalent proportions in terms of pure tannin. The resulting leather also has a shrink temperature of 100°C.

The applicant has also found that it is possible to produce black leather by bringing the pH of the leather treated with zeolite and gonakia tannin to a value greater than 6 by simple addition of sodium bicarbonate. The leather thus obtained has a natural black color without the addition of synthetic dyes. Subsequent operations are carried out as for normal chrome leather. Thus, according to another particularly advantageous characteristic of the invention, the process is remarkable in that it comprises an operation of alkalizing the skin tanned with zeolite and gonaki, making it possible to bring its pH to a higher value. to 6 ensuring the obtaining of a black colored leather.

The retanning of the wet-white (tanned skin with zeolite) can be carried out in a bath at any pH around 4 which is the end point of basification (precipitation) of the alumina silicate (zeolite) .

According to another characteristic of the invention, the pH of the bath containing the zeolite-tanned skin is brought to an interval of between 3.5 and 5 before retanning with vegetable tannin.

According to a preferred embodiment, the optimum pH of said bath is between 3.9 and 4.2.

[0079] Depending on the implementation chosen, the leather can be produced by various methods:

In the context of the second implementation, one can first proceed with the tanning operation using zeolite. An intermediate product called wet-white is then produced, which has a shrinkage temperature of around 65°C to 75°C and which makes it possible to sort the skins according to the destination articles and to strip the skins to the appropriate thickness to pass retanning operations.

[0081 ] The wet-white leather may or may not have undergone a prior shaving operation. Shaving is a known state-of-the-art operation consisting of equalizing the thickness of the leather by eliminating fine shavings from the flesh side. The leather obtained after retanning with vegetable tannin then acquired a shrinkage temperature of 100°C. The sequence of operations is similar to that of tanning leather with chrome.

As explained above, it is also possible to operate in one go, that is to say to carry out the two operations in the same drum. In this case, one proceeds successively to tanning with zeolite as in the previous case, then in the same drum, one proceeds to vegetable tanning without stage intermediate. Here again, the shrinkage temperature obtained is 100°C. The leather obtained is then worked as in the previous cases.

In the context of the first implementation, one can proceed first to vegetable tanning according to the usual techniques of the art starting from the pickling step at a pH between 2.6 and 3.5 . The skin is then retanned with zeolite as in the previous case.

In the context of the third implementation, tanning can be carried out by simultaneously adding the zeolite-based product and the vegetable tannin to the drum, after pickling the skin so as to obtain a pH of 2.6 at 3.5 and preferably 2.6 to 2.9. The procedure is as for the zeolite tanning process. The resulting leather also has a shrink temperature of 100°C.

In the context of the third implementation, one can also carry out the tanning by adding to the drum a prepared mixture comprising the product based on zeolite, the vegetable tannin and the bisulphite, by operating on a pickled skin at pH between 2.6 and 2.9. The procedure is as for the zeolite tanning process. The resulting leather also has a shrink temperature of 100°C.

Still in the context of this third implementation, one can also carry out the tanning by mixing the product based on zeolite and vegetable tannin as described in the previous paragraph with the acid necessary to maintain a pH between 2.2 and 3.8 during the penetration phase of the products to avoid a pH higher than 3.9 caused by the self-basification of the zeolite.

A composition is thus obtained which makes it possible to carry out the tanning operation by adding a single product to the pickled leather. The shrinkage temperature of the leather thus obtained is 100°C.

The mixture formulated above can be added in several batches, preferably in three batches, in order to obtain a shrinkage temperature of 100° C. after four to six hours. It is possible to add the mixture in two stages in order to reach a shrinkage temperature of 100°C after 16 hours. A mono-product formulation simplifies the process by making it similar in practice to that of chrome tanning.

[0090] Thus, another object of the invention consists of a new tanning composition making it possible to implement said process.

According to one characteristic of the invention, said composition comprises a mixture of zeolite and vegetable tannin from a plant of the mimosaideae subfamily. The gonakié and the mimosa are part of this subfamily.

According to another characteristic of the invention, the composition further comprises an acid which compensates for self-basification during tanning.

The acid used to maintain the pH in the appropriate interval is of the carboxylic acid type such as formic acid, acetic acid, propionic acid, glycolic acid, lactic acid, as well as mixtures of these various acids.

The acids used in the mixture can be of the solid carboxylic acid type such as oxalic acid, adipic acid, sulfamic acid, citric acid.

According to a preferred but non-limiting embodiment, the composition comprises:

[0096] - 12% equivalent of gonaki tannin extract,

[0097] - 6% zeolite,

[0098] - 3.5% sulfamic acid.

The percentages are always given with respect to the weight of the dewatered pickled skin. This composition, which is added in several stages, therefore represents 21.5% by weight of the pickled skin dewatered to be tanned.

[0100] According to another characteristic of the invention, the composition also comprises sodium metabisulphite to whiten the leather obtained.

According to another characteristic of the invention, the composition is remarkable in that it comprises a mixture of zeolite and tanning extract of mimosa, with the tanning extract of mimosa dosed according to an optimal concentration of 16% of the weight of the dewatered pickled skin. [0102] The fundamental concepts of the invention having just been explained above in their most elementary form, other details and characteristics will emerge more clearly on reading the non-limiting examples of tanning methods in accordance with the invention. .

[0103] DESCRIPTION OF TESTS AND PREFERRED EMBODIMENTS

[0104] The applicant has carried out several tests enabling it to confirm the technical effects described above.

[0105] Each leather obtained was subjected to a shrinkage test. The invention is thus illustrated by non-limiting examples 2, 3, 4, 5 and 7 of formulations described below using gonaki tannin. Examples 1 and 6 illustrate inconclusive tests with:

[0106] - a different vegetable tannin for Example 1,

[0107] - a test with an insufficient percentage of gonakia for Example 6,

[0108] which do not make it possible to obtain the desired shrinkage temperature of 100 degrees.

[0109] Example 1

[01 10] The first example describes a conventional tanning as it is known in the prior art and in particular the tanning carried out on a mass of 1.2 kilograms of sheepskin of the wetwhite type (skin having been the subject of pre-tanned with zeolite) with chestnut tannin.

[01 11 ] [Table 1 ]

As described above and as noted, the shrinkage temperature of the leather obtained is around 85 degrees Celsius and does not reach the desired 100 degrees.

[0114] Example 2

Example 2 is the first example of an embodiment of the invention. The tanning carried out on a mass of 0.8 kilograms wetwhite sheepskin (skin having already been tanned with zeolite)

[0116] [Table 2]

[0118] Example 3

[0119] The tanning is carried out here on a mass of 3 kilograms of pickled sheepskin in two stages (tanning with zeolite then tanning with gonaki tannin)

[0120] [Table 3]

[0122] IGCALD7 is a nourishing/nourishing oil.

[0123] Example 4

[0124] The tanning is carried out here on a mass of 1.1 kilograms of sheepskin in the form of wetwhite by gonakia extract

[0125] [Table 4]

[0127] Example 5

This tanning is carried out on a mass of 1 kilogram of depickled and degreased sheepskin with a monoproduct consisting of a mixture of gonaki tannin, zeolite and sodium metabisulphite.

[0129] [Table 5]

[0131] Example 6

Example 6 shows a tanning carried out on a mass of 1 kilogram of depickled and degreased sheepskin but with an insufficient percentage of gonaki tannin.

[0133] [Table 6]

It can be seen that the retraction temperature reaches 75 degrees Celsius and not the desired 100 degrees.

[0136] Example 7

Example 7 shows a tanning carried out on a mass of 1.03 kilograms of pickled sheepskin with a sufficient percentage of gonaki tannin then with zeolite.

[0138] [Table 7]

[0139] Example 8

Example 8 is the first example of an embodiment of the invention using mimosa tannin. Tanning carried out on a mass of 4.1 kilograms of pickled wet-white sheepskin (skin having already been tanned with zeolite)

[0141] [Table 8]

[0142]

[0143] Example 9

[0144] The tanning is carried out here on a mass of 3.887 kilograms of wrung pickled wet-white type sheepskin

[0145] [Table 9] [0146]

The term OP denotes a powdered product.

[0148] Example 10

The tanning is carried out here on a mass of 4.870 kilograms of sheepskin pickled first with mimosa and then with zeolite.

[0150] [Table 10] [0151]

[0152] Example 11

This tanning is carried out on a mass of 4,870 kilograms of sheepskin pickled first with mimosa and then with zeolite.

[0154] [Table 11] [0155]

It is understood that the tanning process and the tanning composition which have just been described above were for the purpose of disclosure rather than limitation. Of course, various adjustments, modifications and improvements may be made to the above examples, without departing from the scope of the invention. Thus, for example, in the field considered, the percentages and proportions accept a certain tolerance evaluated at +/- 10%.

[0157] Moreover, even if the weight of the dewatered pickled skin is given in most cases as a reference, the person skilled in the art knows how to make the correspondence with the other states of the skin. An approximation of this correspondence is given below where the dewatered pickled weight is taken as reference and the factor indicated gives the weight corresponding to the state considered by multiplication.

[0158] Dermal material weight: 0.30

[0159] Dry leather weight: 0.38

[0160] Tripe weight: 2.40

[0161 ] Drained pickle weight: 1.00

[0162] Weight tanned with 8% zeolite drained 6 p.m.: 1.65

[0163] Wrung 8% zeolite tanned weight: 1.22

[0164] 8% dry zeolite tanned weight: 0.43.

Claims

[Claim 1] Process for tanning a skin comprising a prior pickling operation, CHARACTERIZED IN THAT it consists in using, for tanning purposes, zeolite and vegetable tannin from a plant of the subfamily mimosaideae, with a minimum quantity in relation to the wrung pickled skin mass of 12% of tanning extract or its equivalent in source material, to obtain leather with a shrinkage temperature of at least 100 degrees Celsius.

[Claim 2] Process according to claim 1, CHARACTERIZED IN THAT said vegetable tannin is gonakia tannin.

[Claim 3] Process according to claim 1, CHARACTERIZED IN THAT said vegetable tannin is mimosa tannin.

[Claim 4] Process according to any one of Claims 1 to 3, CHARACTERIZED IN THAT it comprises the following operations:

- Tanning with zeolite,

- Retanning with said vegetable tannin.

[Claim 5] Process according to any one of Claims 1 to 3, CHARACTERIZED IN THAT it comprises the following operations:

- Tanning with said vegetable tannin,

- Retanning with zeolite.

[Claim 6] Process according to claim according to any one of claims 1 to 3, CHARACTERIZED IN THAT it comprises the following operation:

- Simultaneous tanning by said vegetable tannin and by zeolite.

[Claim 7] Tanning process according to any one of Claims 1 to 6, CHARACTERIZED IN THAT the minimum quantity of zeolite relative to the mass of the dewatered pickled skin is 6%.

[Claim 8] Tanning process according to any one of Claims 1 to 7, CHARACTERIZED IN THAT the zeolite is a zeolite whose silica/aluminum ratio is between 1.0 and 5.0.

28

[Claim 9] Tanning process according to claim 8, CHARACTERIZED IN THAT the zeolite is selected from the following list:

- Zeolite A,

- Zeolite X.

[Claim 10] Tanning process according to claim 2, CHARACTERIZED IN THAT the 12% tanning extract of gonakia comes from 24% of powder obtained by grinding gonakia pods.

[Claim 11] Tanning process according to any one of claims 1 to 10, CHARACTERIZED IN THAT acid is added simultaneously with the addition of zeolite to counter the basification caused by the latter.

[Claim 12] Tanning process according to claim 4, CHARACTERIZED IN THAT the pH of the bath containing the skin tanned with zeolite is brought to an interval of between 3.5 and 5 before retanning with the vegetable tannin.

[Claim 13] Tanning process according to any one of Claims 2 and 4 to 12, CHARACTERIZED IN THAT it comprises an operation of alkalizing the tanned skin with zeolite and gonakia, making it possible to bring its pH to a value greater than 6 ensuring the production of black colored leather.

[Claim 14] Tanning process according to any one of the preceding claims, CHARACTERIZED IN THAT the tanning extract or its equivalent in source material is associated with bisulphite.

[Claim 15] Tanning composition for carrying out the process according to claim 6, CHARACTERIZED BY THE FACT THAT it comprises a mixture of zeolite and vegetable tannin from a plant of the mimosaideae subfamily.

[Claim 16] Tanning composition according to claim 14, CHARACTERIZED BY THE FACT THAT it comprises an acid.

[Claim 17] Tanning composition according to claim 14 or 15, CHARACTERIZED IN THAT it comprises sodium metabisulphite. [Claim 18] Tanning composition according to Claim 14, CHARACTERIZED BY THE FACT THAT it comprises a mixture of zeolite and tanning extract of mimosa, with the tanning extract of mimosa dosed at a concentration of 16% of the weight of the drained pickled skin.