EP3249058A1 - Method for preparing leather from raw hide - Google Patents

Abstract

The present invention relates to a method for preparing a leather from a raw hide, the process being free of chromium, permanganate and sulphide. This process comprises the following steps: - obtaining a raw hide; - toughening of the raw skin; - depilage-peeling skin soaked by enzymatic treatment in the absence of sulfide; - fleshing of the skin resulting from the depilage-pelanage; - picklage of the skin; obtaining a leather by tanning the skin resulting from pickling in the absence of chromium; the skin being a skin of an animal selected from the group consisting of crocodilians, snakes and lizards. The present invention also relates to the leather crust obtainable by this method and its use in the field of leather goods or watchmaking.

Description

FIELD OF THE INVENTION

The present invention relates to a process for preparing a leather whose tanning step does not use a compound based on chromium.

The field of use of the present invention relates to the leather industry, especially leather goods.

PRIOR STATE OF THE TECHNIQUE

The processes for preparing a leather for use in the leather goods industry require a multitude of specific steps.

• conservation de la peau en présence de sel et/ou à basse température ;
• trempe de la peau pendant 3 à 5 jours dans une solution bactéricide ;
• écaillage/épilage-pelanage entre 1 et 2 jours dans une solution contenant de la chaux et du sulfure de sodium ;
• écharnage ;
• déchaulage pendant une durée allant jusqu'à 24 heures en présence de sulfate d'ammonium ou d'acide faible ;
• confitage pendant une durée allant jusqu'à 24 heures en présence d'une enzyme de confitage ;
• dégraissage pendant plusieurs heures en utilisant un savon éthoxylé issu du pétrole ;
• picklage pendant 10 à 20 heures avec de l'acide formique, de l'acide sulfurique et du sel ;
• tannage ;
• basification pendant 3 jours en présence de sulfate de chrome et de fongicide, puis de formiate de sodium et/ou de bicarbonate de sodium ;
• murissement de la peau tannée entre 5 et 20 jours ;
• dérayage (opération mécanique) pendant quelques minutes ;
• blanchiment pendant quelques heures en présence de permanganate de potassium ou manganèse ou de métabisulfite de sodium ;
• crusting pendant un jour en présence de tanin synthétique blanc, d'huile blanche et d'acide formique ;
• dégraissage à sec de quelques minutes à 2 heures en présence de perchloroéthylène, composé jugé nuisible pour la santé.

By way of example, a conventional method of preparing a leather comprises the following steps, generally carried out in 27 to 29 days:

• preservation of the skin in the presence of salt and / or at low temperature;
• hardening of the skin for 3 to 5 days in a bactericidal solution;
• chipping / dehairing-pelaning between 1 and 2 days in a solution containing lime and sodium sulphide;
• fleshing;
• dehulling for up to 24 hours in the presence of ammonium sulfate or weak acid;
• confection for up to 24 hours in the presence of a conferring enzyme;
• degreasing for several hours using an ethoxylated soap derived from petroleum;
• pickling for 10 to 20 hours with formic acid, sulfuric acid and salt;
• tanning;
• basification for 3 days in the presence of chromium sulphate and fungicide, then sodium formate and / or sodium bicarbonate;
• ripening of tanned skin between 5 and 20 days;
• clutch (mechanical operation) for a few minutes;
• bleaching for a few hours in the presence of potassium permanganate or manganese or sodium metabisulfite;
• crusting for one day in the presence of white synthetic tannin, white oil and formic acid;
• dry degreasing for a few minutes to 2 hours in the presence of perchlorethylene, a compound considered harmful to health.

Some of these steps may be optional depending on the nature of the skin. Indeed, flaking-flaking is not usually essential for ostrich skin.

Be that as it may, conventional processes have the disadvantage of using chemical compounds, especially sulphides during the peeling-flaking step, chromium during tanning, or potassium permanganate during bleaching.

They therefore generate effluents that can be highly polluting, particularly in the case of tanning of the skin, which is one of the most problematic steps because of the presence of chromium compounds.

In view of their potential harmfulness to the environment, it is important to control the use of these chemical compounds.

On the other hand, residues of these compounds, especially chromium, may remain in the leather, which can also cause allergic reactions in contact with the skin.

For these reasons, the leather industry is constantly looking for alternatives to prepare a leather, while minimizing the ecological impact of the process and the risks of allergy.

Alternatives of the prior art include in particular vegetable tanning or the use of polysaccharide derivatives as described in the document EP2607500 . The document CN 105441600 describes a method for simultaneously tanning and coloring a skin.

Even though these alternatives may prove satisfactory, they do not necessarily make it possible to overcome the presence of sulphides and / or permanganate.

The Applicant has developed a method for preparing a leather from a raw hide, according to which the steps of dehairing / peeling, tanning and bleaching can be carried out respectively in the absence of sulphides, chromium and permanganate.

SUMMARY OF THE INVENTION

The present invention makes it possible to transform an animal skin into leather by using natural products free from chromium, sulphides and potassium permanganate.

• obtention d'une peau brute ;
• trempe de la peau brute ;
• épilage-pelanage de la peau par traitement enzymatique en l'absence de sulfure ;
• écharnage de la peau ;
• optionnellement déchaulage ;
• optionnellement confitage ;
• optionnellement blanchiment en l'absence de permanganate ;
• optionnellement dégraissage ;
• picklage ;
• obtention d'un cuir par tannage de la peau en l'absence de chrome ;
• optionnellement crusting ;
• optionnellement séchage ;
• optionnellement une seconde étape de dégraissage.

More specifically, the present invention relates to a method for preparing a leather, from a raw hide, comprising the following steps:

• obtaining a raw hide;
• quenching of the raw skin;
• epilage-skin peeling by enzymatic treatment in the absence of sulphide;
• fleshing of the skin;
• optionally deliming;
• optionally conferring;
• optionally bleaching in the absence of permanganate;
• optionally degreasing;
• picklage;
• obtaining a leather by tanning the skin in the absence of chromium;
• optionally crusting;
• optionally drying;
• optionally a second degreasing step.

As already indicated, this process is free of chromium, permanganate and sulfide.

• obtention d'une peau brute ;
• trempe de la peau brute ;
• épilage-pelanage de la peau reverdie, autrement dit trempée, par traitement enzymatique en l'absence de sulfure ;
• écharnage de la peau résultant de l'épilage-pelanage ;
• optionnellement confitage de la peau ;
• optionnellement dégraissage de la peau;
• picklage de la peau ;
• obtention d'un cuir par tannage de la peau issue du picklage en l'absence de chrome.

Thus, according to a preferred embodiment, the method according to the invention comprises the following steps:

• obtaining a raw hide;
• quenching of the raw skin;
• depilatory-peeling skin reverdie, in other words quenched, by enzymatic treatment in the absence of sulfide;
• fleshing of the skin resulting from the depilage-pelanage;
• optionally conferring of the skin;
• optionally degreasing the skin;
• picklage of the skin;
• obtaining a leather by tanning the skin resulting from pickling in the absence of chromium.

The different steps of this process are described one after the other below. They are made using conventionally used devices, for example rotating drums, called fullers, which the skilled person can adjust the speed.

Unless otherwise indicated, the amounts indicated in the following description are given in percentage relative to the mass of the skin, with the exception of the pickling step. For the steps preceding the fleshing, these percentages are given with respect to the mass of the raw skin, for the steps following the fleshing, they are given with respect to the mass of the skin at the end of the step d fleshing. Although in practice these masses are relatively close, it is necessary to bring this precision.

Unless otherwise stated, the various steps are generally carried out under standard conditions, particularly in terms of temperature, pH, and treatment time.

Obtaining a noisy skin :

The skin used in this process is a raw skin, that is to say a freshly recovered skin or skin that has been preserved, for example by freezing. It can be a skin directly from the slaughter. It can have residues of flesh and fat.

• une peau préalablement salée, c'est-à-dire une peau ayant été traitée avec du chlorure de sodium puis nettoyée ;
• une peau fraîche n'ayant pas subi de traitement préalable comme le salage ;
• une peau congelée n'ayant pas subi de traitement préalable comme le salage ;
• une peau conservée par électricité, notamment en la soumettant à des courants alternatifs et/ou continus pouvant atteindre quelques ampères au travers d'un bain dans lequel elles sont trempées ;
• une peau ayant subi un tannage réversible, par exemple au cinnamaldéhyde.

In general, the skin used can be:

• previously salted skin, that is to say a skin that has been treated with sodium chloride and then cleaned;
• fresh skin that has not been previously treated, such as salting;
• frozen skin that has not been previously treated, such as salting;
• a skin preserved by electricity, in particular by subjecting it to alternating and / or continuous currents of up to a few amperes through a bath in which they are soaked;
• reversibly tanned skin, for example cinnamaldehyde.

Raw skin, especially salty or fresh, can be stored in the cold, at a temperature advantageously between -5 ° C and 20 ° C, more preferably between 5 ° C and 15 ° C.

Advantageously, the skin used is saline skin and stored at a temperature between 5 ° C and 15 ° C.

The skin is a skin of an animal selected from the group consisting of crocodilians, snakes and lizards.

• de reptile, par exemple de crocodilien (crocodile, alligator, caïman) ou de serpent (python, vipère...) ou de lézard (dont iguane) ;
• d'oiseau, par exemple d'autruche ou d'émeu ;
• de bovin, par exemple de veau ;
• d'ovin, par exemple d'agneau ;
• de poisson ou de poisson cartilagineux, par exemple de saumon, perche, tilapia, raie, requins, galuchat ;
• de marsupial, par exemple de kangourou.

However, the method can also be used for a skin:

• reptile, for example crocodilian (crocodile, alligator, caiman) or snake (python, viper ...) or lizard (including iguana);
• bird, for example ostrich or emu;
• cattle, for example veal;
• sheep, for example lamb;
• fish or cartilaginous fish, for example salmon, perch, tilapia, skate, sharks, stingray;
• marsupial, for example kangaroo.

Once the skin is obtained, it is soaked, ie "reverd" (quenching = re-greening).

Tempering skin:

This step involves moistening the skin. In particular, it makes it possible to eliminate any impurities, dirt, salt, if any, and soluble proteins from the skin.

Advantageously, the quenching is performed by immersing the skin in an aqueous solution comprising at least one type of essential oil or a natural and biodegradable quenching agent with similar functions and at least one additive such as a surfactant or a detergent.

The essential oils used have bactericidal properties. They may be selected from the group consisting of thyme, clove, cardamom, caraway and lemongrass.

The quantity of essential oil is advantageously between 0.25% and 3%, more advantageously between 0.5 and 1.5% by weight relative to the mass of the skin.

The surfactant may in particular be based on glucose or be a natural surfactant.

The detergent may especially be a plant saponin (plant) or animal.

The amount of additive (surfactant or detergent) is advantageously limited to 5% (less than or equal to 5%), more preferably between 0.5 and 3% by weight relative to the mass of the skin.

After quenching, the skin undergoes a depilage-pelanage step.

Skin-peeling :

The dehairing allows to chemically remove the hairs for the skin with hairs (calf ...) or the scales for the skins with scales (crocodile ...). The depilage therefore also refers to the peeling of a skin.

Pelanage makes it possible to prepare the skin, in particular by removing the eventual epidermis. Pelanage has an action of swelling of the skin.

These two steps are generally performed simultaneously.

This epilage-pelanage step is optional for bird or snake skins.

Similar to conventional processes, this step is performed prior to the tanning step.

On the other hand, unlike conventional processes, this step is carried out in the absence of sulfides, thus reducing its environmental impact. Thus, the present invention makes it possible to avoid the pitfalls of the prior art, in particular the possible degradation of the skin resulting from an excess of treatment with sulphides.

The epilage-pelanage step of the process according to the invention is carried out by enzymatic treatment.

The enzyme used is advantageously a keratinase, which has an action on keratin.

The activity of the enzyme makes it possible to remove / detach the hairs, scales and / or epidermis from the skin.

Thus, the hair, scales and / or epidermis of the skin are not destroyed, they are removed / detached from the skin without altering it. On the contrary, in the processes of the prior art, the sulphides make it possible to dissolve the hairs, scales and / or epidermis of the skin.

• 250 à 3000% d'eau, avantageusement 250 à 1500% ;
• 1 à 5% d'enzyme, avantageusement 2.5 à 3.5%.

The depilage-pelanage is advantageously carried out by treatment of the skin with a solution comprising, in mass relative to the mass of the skin:

• 250 to 3000% water, advantageously 250 to 1500%;
• 1 to 5% of enzyme, advantageously 2.5 to 3.5%.

This solution may also comprise 1 to 5% lime (calcium oxide CaO), advantageously 2.5 to 3.5%.

The duration of the depilage-pelanage stage is advantageously between 4 and 48 hours, more advantageously between 6 and 24 hours.

The pH of the solution used in this step is advantageously between 10 and 14, more advantageously between 11.5 and 13, especially when lime is used.

Once the epilage-pelanage step is complete, the skin is broken.

Skin flaking :

Fleshing consists of mechanically removing any residues of flesh or subcutaneous fat.

Those skilled in the art will know how to implement this step in accordance with the usual practice.

Decoupling :

This step is optional. It makes it possible to remove the possible presence of lime, which may result from the dehairing-pelanage step.

It is advantageously carried out immediately after the fleshing step.

Dehulling is generally carried out when the dehairing-peeling solution comprises lime.

• 200 à 3000% d'eau, avantageusement 250 à 1500% ;
• 1.5 à 4% d'acide, avantageusement 2.5 à 4%.

Advantageously, this step is performed by treating the skin with a solution comprising, in mass relative to the mass of the skin:

• 200 to 3000% water, preferably 250 to 1500%;
• 1.5 to 4% acid, preferably 2.5 to 4%.

The acid is advantageously selected from the group comprising citric acid and lactic acid.

The duration of the deliming step is advantageously between 1 and 16 hours, more preferably between 2 hours and 10 hours.

At the end of this step, the pH of the solution is advantageously between 3.5 and 7.5, more advantageously between 4 and 6.

bating:

This step destroys the elastic fibers of the skin and cleans the flower. It is optional and carried out after the fleshing step or, if necessary, after deliming, and is not necessary for the skins of certain species such as crocodilians.

In general, this step is performed between fleshing and picklage of the skin.

Advantageously, this step corresponds to an enzymatic treatment.

In this case, it uses an aqueous solution of 300 to 3000% water, preferably 300 to 1500%, by weight relative to the mass of the skin, this aqueous solution containing up to 4% of enzyme.

The confitating enzyme is advantageously chosen from the group comprising elastases.

The duration of the conferring step may advantageously be up to 24 hours.

The pH of the solution used in this step is advantageously between 6 and 9, more advantageously between 6.5 and 8.

Once the confection stage is complete, the skin is bleached or degreased.

Whitening:

This step is optional. It is free from chemical compounds of the permanganate type.

The bleaching makes it possible to eliminate any stains present on the skin so as to improve and homogenize the color of the skin.

Unlike the processes of the prior art, this step is performed prior to tanning. It is performed between fleshing and pickling of the skin, if necessary after the confection.

The bleaching can be carried out in the presence of an enzyme or in the presence of peroxides.

• 300 à 1000% d'eau, avantageusement 500 à 1000% ;
• 8 à 30% de peroxyde ou d'un précurseur de peroxyde, avantageusement 12 à 20%.

Thus, according to a particular embodiment, the bleaching may be carried out by treatment with a solution comprising, in mass relative to the mass of the skin:

• 300 to 1000% water, preferably 500 to 1000%;
• 8 to 30% peroxide or a peroxide precursor, advantageously 12 to 20%.

Thus, the solution used may comprise hydrogen peroxide or sodium percarbonate.

• 300 à 1000% d'eau, avantageusement 500 à 1000% ;
• jusqu'à 10% d'enzyme, avantageusement entre 1 et 6%.

According to another particular embodiment, the bleaching may be carried out by treatment with a solution comprising, in mass relative to the mass of the solution:

• 300 to 1000% water, preferably 500 to 1000%;
• up to 10% of enzyme, advantageously between 1 and 6%.

The bleaching enzyme may especially be chosen from the group comprising melaninases.

The bleaching stage (peroxide or enzymatically) is advantageously carried out at a temperature of between 10 and 25 ° C., more advantageously between 10 and 18 ° C.

The duration of the bleaching stage (peroxide or enzymatically) is advantageously between 6 and 24 hours, more preferably between 12 and 24 hours.

degreasing:

After fleshing or, where appropriate, deliming and / or bleaching, the method according to the invention may comprise a degreasing step. This step is optional for some skins, such as cattle. It is performed between the fleshing and pickling stages, preferably just before pickling.

• blanchiment, le cas échéant après une étape de confitage ;
• dégraissage ;

le blanchiment, exempt de permanganate, étant réalisé en présence d'une enzyme ou de peroxydes.Thus, according to a particular embodiment, the method according to the invention may comprise at least one of the following successive steps between the fleshing and pickling steps:

• bleaching, if necessary after a conferring step;
• degreasing;

the bleaching, free of permanganate, being carried out in the presence of an enzyme or peroxides.

Degreasing removes any residual fat from the skin.

• 50 à 1500% d'eau, avantageusement 500 à 1500% ;
• 0.5 à 5% de tensio-actif, avantageusement 3 à 5%.

According to a particular embodiment, this step can be carried out with a solution containing, in mass relative to the mass of the skin:

• 50 to 1500% water, preferably 500 to 1500%;
• 0.5 to 5% of surfactant, advantageously 3 to 5%.

The surfactant used may in particular be based on glucose. It may be a degreaser like the one sold under the name Stahl Prodegrease.

• 50 à 1500% d'eau ;
• 1 à 5% d'enzyme.

According to another particular embodiment, this step can be carried out with a solution containing, in mass relative to the mass of the solution:

• 50 to 1500% water;
• 1 to 5% enzyme.

The solution of the enzymatic route may also comprise a detergent, advantageously 0.5 to 5% of detergent, advantageously 0.5 to 3% by weight relative to the mass of the skin.

The enzyme is advantageously a degreasing enzyme chosen from the group comprising lipases and pancreatins.

The detergent may in particular be a saponin of plant origin (plant, for example rita nut) or animal.

The degreasing step (surfactant or enzymatic) is advantageously carried out at a temperature between 10 and 25 ° C, more preferably between 10 and 18 ° C.

The duration of the degreasing step (surfactant or enzymatic) is advantageously between 1 and 12 hours, more preferably between 2 and 4 hours.

The pH of the solution used in this step (surfactant or enzymatic) is advantageously between 7 and 12, more advantageously between 8 and 11.

Picklage:

The picklage is performed after the degreasing of the skin. This step involves preparing the skin for tanning. This is a conventional step according to the state of the art.

This step uses an acidified salt solution.

For this step, the salt concentration (NaCl) is expressed in degrees Baumé (unit of measurement of a concentration). The salt is dosed according to the amount of water. The salt is advantageously between 3 and 15 Baumé, more preferably between 4 and 8.

This treatment is advantageously carried out by means of an acidic solution, for example a solution containing 0.5 to 5% by weight of acid, more advantageously 2.5 to 4% of acid relative to the mass of the skin.

The acid is advantageously selected from the group comprising citric acid and lactic acid.

The duration of the pickling stage is advantageously between 3 and 48 hours, more advantageously between 12 and 24 hours.

The pH of the solution used in this step is advantageously between 1.5 and 3.5, more advantageously between 2.8 and 3.0.

Once the pickling treatment is done, the skin is tanned.

Tanning:

As already indicated, the tanning step is carried out in the absence of chromium.

This step makes the skin rot-proof. It makes it possible to transform the skin into leather.

The tanning step may be carried out by the mineral route, in particular in the presence of silica, or by the organic route, especially in the presence of aldehyde, advantageously a natural aldehyde.

By "natural aldehyde" is meant an aldehyde of natural origin, for example cinnamaldehyde or a non-toxic aldehyde.

• 100 à 1000% d'eau, avantageusement 200 à 500% ;
• 4 à 20% de silice, avantageusement 10 à 15% ;
• jusqu'à 1% de bicarbonate de sodium, avantageusement jusqu'à 0.5% (0 à 0.5%).

Thus, according to one particular embodiment, the tanning can be carried out in the presence of silica, with a solution containing, in mass relative to the mass of the skin:

• 100 to 1000% water, preferably 200 to 500%;
• 4 to 20% silica, preferably 10 to 15%;
• up to 1% sodium bicarbonate, preferably up to 0.5% (0 to 0.5%).

The silica may be in the form of simple silica (SiO ₂ ) or derived (sodium silicate).

The pH of the mineral treatment solution is advantageously between 4.2 and 4.5 at the end of the tanning.

• 100 à 1000% d'eau, avantageusement 200 à 500% ;
• 6 à 20% de cinnamaldéhyde, avantageusement 8 à 15%.

Thus, according to another particular embodiment, the tanning can be carried out in the presence of aldehyde, with a solution containing, in mass relative to the mass of the skin :

• 100 to 1000% water, preferably 200 to 500%;
• 6 to 20% of cinnamaldehyde, advantageously 8 to 15%.

The pH of the organic treatment solution is advantageously between 4.2 and 4.5 at the end of the tanning.

The tanning step (mineral and / or organic) is advantageously carried out at a temperature between 10 and 25 ° C, more preferably between 10 and 18 ° C.

The duration of the tanning step (inorganic or organic) is advantageously between 8 and 48 hours, more preferably between 12 and 24 hours.

Once the tanning step is complete, a leather is obtained. This leather can then be optionally subjected to "crusting" and / or drying and / or second degreasing steps.

Crusting:

Advantageously, the method may also include a so-called "crusting" step which makes it possible to reduce the thickness of the leather, to re-tan it and to nourish it.

Thus, the present invention also relates to the method for manufacturing a leather crust in the absence of chromium-based compounds.

Unlike the processes of the prior art, the crusting step is not performed directly after the bleaching. Indeed, it is performed after tanning, preferably directly after tanning.

The crusting is advantageously carried out from an aqueous solution containing sodium bicarbonate, a polymeric softener, an acid such as citric acid and one or more tannins.

• eau ;
• bicarbonate de sodium ;
• tanin (base minérale, organique, végétale ou synthétique) ;
• assouplissant polymérique ;
• acide citrique.

This is a conventional step forming part of the knowledge of the skilled person. It can be made from a solution based on:

• water;
• sodium bicarbonate ;
• tannin (mineral, organic, vegetable or synthetic base);
• polymeric softener;
• citric acid.

• un tanin synthétique de type syntan blanc ;
• de l'huile blanche ;
• de la noix de galle ;
• de la silice ;
• du cinnamaldéhyde ;
• de l'amidon, par exemple l'amidon de maïs ;
• de la gomme naturelle, par exemple le xanthane ou guar.

The tannin may be composed of one or more of the following additives:

• a synthetic tannin of the white syntan type;
• white oil;
• gall-nut;
• silica;
• cinnamaldehyde;
• starch, for example corn starch;
• natural gum, for example xanthan or guar.

Drying:

According to a particular embodiment, the method according to the invention may also comprise a drying step.

This is a conventional step forming part of the knowledge of the skilled person.

The drying can in particular be carried out by blowing air, the hot air and the cold air both making it possible to obtain the desired result.

Second degreasing steps:

According to a particular embodiment, the method according to the invention may comprise a second degreasing step. The latter is carried out after tanning, advantageously after possible crusting and / or drying.

This optional step is particularly suitable for so-called "fat" skins, especially the skins of reptiles, ostriches or fish.

It is preferentially a dry degreasing. It can in particular be carried out with a degreaser such as Prodegrease marketed in the range Proviera Stahl.

Advantageously, the duration of completion of all the steps of the process according to the invention may be between 6 and 21 days, advantageously between 6 and 10 days, less than that of the processes of the prior art (27- 29 days).

Leather resulting from the process according to the invention:

The present invention also relates to the leather crust obtainable by carrying out the method described above. This crust is devoid of chromium, permanganate and sulphide.

While the crusts of the prior art generally comprise chrome residues from tanning, this leather crust is free of chromium. It thus makes it possible to avoid any allergic reaction.

However, the crust may optionally comprise traces of chromium and / or permanganate and / or sulphide insofar as these traces are not derived from the voluntary use of such compounds in the process according to the invention. The term "traces" corresponds to a content that is difficult to detect or significantly lower than conventional levels.

The present invention further relates to the use of this leather crust in the field of leather goods or watchmaking.

This crust can be used in particular for the manufacture of watch bracelets and leather goods accessories.

The invention and the advantages thereof are not limited to those embodiments which are given to illustrate the invention and not in a limiting manner.

Claims (14)

A process for preparing a leather from a raw hide, the process being free of chromium, permanganate and sulfide, the process comprising the steps of: - obtaining a raw hide; - toughening of the raw skin; - depilage-peeling skin soaked by enzymatic treatment in the absence of sulfide; - fleshing of the skin resulting from the depilage-pelanage; - picklage of the skin; obtaining a leather by tanning the skin resulting from pickling in the absence of chromium; the skin being a skin of an animal selected from the group consisting of crocodilians, snakes and lizards. Process according to claim 1, characterized in that the enzyme used in the depilage-pelanage step is a keratinase. Process according to claim 1 or 2, characterized in that the depilage-pelanage step is carried out by treatment of the skin with a solution comprising, in mass relative to the mass of the skin: - 250 to 3000% water; - 1 to 5% enzyme. Method according to one of claims 1 to 3, characterized in that the epilage-pelanage step is performed by treating the skin with a solution comprising, in mass relative to the mass of the skin: - 250 to 1500% water; - 2.5 to 3.5% enzyme. Method according to one of claims 1 to 4, characterized in that it further comprises a step of conferring between the fleshing and pickling steps. Method according to one of claims 1 to 5, characterized in that it further comprises at least one of the following and successive steps between the fleshing and pickling steps: - bleaching, if necessary after a conferring step; - degreasing; the bleaching, free of permanganate, being carried out in the presence of an enzyme or peroxides. Process according to one of Claims 1 to 6, characterized in that the tanning step is carried out in the presence of silica, with a solution containing, in mass relative to the mass of the skin: - 100 to 1000% water; 4 to 20% of silica; - up to 1% sodium bicarbonate. Process according to one of Claims 1 to 7, characterized in that the tanning step is carried out in the presence of silica, with a solution containing, in mass relative to the mass of the skin: - 200 to 500% water; 10 to 15% of silica; - up to 0.5% sodium bicarbonate. Method according to one of claims 1 to 6, characterized in that the tanning step is carried out in the presence of aldehyde, with a solution containing, in mass relative to the mass of the skin: - 100 to 1000% water; - 6 to 20% of cinnamaldehyde. Method according to one of claims 1 to 6, characterized in that the tanning step is carried out in the presence of aldehyde, with a solution containing, in mass relative to the mass of the skin: - 200 to 500% water; - 8 to 15% of cinnamaldehyde. Method according to one of claims 1 to 10, characterized in that it further comprises the following and successive steps between the fleshing and pickling steps: - confection; - bleaching in the absence of permanganate; - degreasing. Method according to one of claims 1 to 11, characterized in that it further comprises a crusting step after the tanning step. Leather crust devoid of chromium, permanganate and sulphide obtainable by the process according to claim 12. Use of the leather crust according to claim 13 in the field of leather goods or watchmaking.