Tanning method for raw leather, manufacturing method for tanned leather, and detanning method

Abstract

The present invention relates to a method for tanning raw hides using a tanning solution containing a silicon compound and no metals. The present invention also relates to a method for producing tanned leather including such a tanning method. The present invention also relates to tanned raw hides obtained by such a tanning method. Furthermore, the present invention also relates to a method for de-tanning the hides obtained by this tanning method.

Description

[Technical Field]

[0001] The present invention relates to a method for tanning raw hides using a silicon compound as a tanning agent, and to a means for carrying out such a method to produce tanned leather. The present invention also relates to a method for de-tanning the tanned raw hides and the tanned leather obtained thereby. [Background technology]

[0002] The production of tanned leather from animal hides requires many steps, all of which can be divided into three broad groups defined as follows: (i) the steps of processing the raw hides, (ii) the steps of the tanning operation, and (iii) the steps of polishing and finishing.

[0003] In the raw hide processing step, raw hides from animals are received. These raw hides are sorted based on quality, size, weight, etc. During this processing step, unwanted parts, such as legs, are cut off and removed. The raw hides are then washed. For this, they are immersed in a large amount of water, for example in a drum (a rotating barrel) or a paddle (a stationary container with moving blades). Preservatives may be added. After washing, the hair is removed from the raw hides, for example by chemical means. The raw hides are also subjected to a fleshing step, in which the subcutaneous tissue is removed. These steps are called the river step.

[0004] At the end of the processing steps, so-called "pickled" or so-called "demineralized" raw hides are obtained. "Pickled" raw hides have a high salinity and a low pH, generally below 3. "Demineralized" raw hides generally end the processing step with a pH between 7.5 and 9.0.

[0005] During the tanning process, hides treated as described above, such as "pickled" and "demineralized" hides, are degreased. If necessary, they are rehydrated. At this stage, the hides are perishable and ready for tanning. The tanning step itself consists of a chemical treatment that transforms the perishable hides into perishable, durable tanned leather. The resulting tanned leather is drained, rinsed, and optionally wrung out.

[0006] The polishing and finishing steps are those that make the tanned leather obtained at the end of the tanning operation usable for the manufacture of tanned leather products. These steps may include squeezing, adjusting thickness, stretching, re-tanning, dyeing and nourishing. Finishing steps include those that make the tanned leather soft, smooth, satin-finished and printed, which give it resistance to stains, abrasion, water and light, for example. These steps also give the tanned leather aesthetic properties, such as luster, color, velvet, satin and grain.

[0007] The key step in the tanning process is the tanning step itself, during which the prepared hides are tanned and transformed into rot-resistant tanned leather by the action of tanning agents. During the tanning process, the tanning agents bind to the collagen fibers of the hides, stabilizing them and transforming them into rot-resistant, strong tanned leather. Summary of the Invention [Problem to be solved by the invention]

[0008] Since the publication of the European REACH Regulation (Registration, Evaluation, Authorisation and Restriction of Chemical Substances (EC) No. 1907 / 2006), the sale of consumer goods has become increasingly regulated, especially with regard to chemical risks. Tanned leather products are no exception and must comply with the new restrictions. The most widely used tanning agent in the leather tanning industry is chromium (Cr) in the oxidation state 3.3+ ) In fact, Cr 3+ The chrome tanning method is easy to implement and efficient, and it can produce tanned leather with properties that meet market expectations. Under certain conditions, the Cr content of certain tanned leathers can be 3+ Some of these compounds can cause allergic reactions when they come into contact with the skin. 6+ For this reason, the European Union (EU) has imposed restrictions on the sale of tanned leather products with a Cr6+ content above 3 mg / kg (Regulation No. 301 / 2014 amending Annex XVII of Regulation 1907 / 2006). The EU is also considering lowering this limit in the coming years. Therefore, the leather tanning industry is looking for alternative solutions to chromium for tanning raw hides.

[0009] Glutaraldehyde can be used as a tanning agent. However, the compound is classified as a substance of very high concern by ECHA (European Chemical Agency) as part of the European REACH regulation. It is a respiratory and skin sensitizer.

[0010] Vegetable tannins can also be used to tan raw hides, but the large quantities required and the hardness of the resulting tanned leather limit their use to specific applications.

[0011] Other tanning agents containing metals such as aluminum, iron, titanium or zirconium, and synthetic organic compounds may also be used.

[0012] Furthermore, the production of tanned leather or tanned leather products generates tanned leather waste (shavings, floor waste, manufacturing offcuts) which are difficult to recycle if the raw hides were tanned in the presence of chromium.

[0013] Finally, the wastewater discharged from the chrome tanning process contains unreacted chromium and must be treated before being discharged into the environment.

[0014] Document US 3,116,965 describes a method for tanning raw hides with silatrioxane.

[0015] In view of the above constraints, alternative solutions for tanning raw hides are needed for the sustainability of the leather tanning industry.Therefore, there remains a need for a method for tanning raw hides that avoids the use of metals, in particular chromium, in order to obtain tanned leather that guarantees the safety of employees of companies in the leather tanning industry, consumer protection (safety), the recovery of tanned leather waste (production scrap or used products), and environmental protection.There remains a need for a method for tanning raw hides that allows for the obtaining of tanned raw hides that can be easily de-tanned.There is also a need for a method for de-tanning such leather, which allows for the recycling of tanned raw hides and tanned leather. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention relates to a method for tanning raw hides that are ready for tanning, comprising the following steps: (A) The prepared hides are immersed in an aqueous solution in a drum, and the pH of the hides and aqueous solution is adjusted to a value between 1.5 and 10.5 by adding an acid or base. (B) Treating the raw hides from step (A) with a tanning solution containing the following components by weight relative to the weight of the raw hides: 1 to 1200% water, Optionally, salt in an amount sufficient to prevent swelling of the raw hides, and 1 to 100% of a compound of formula (I):

[0017] [ka]

[0018] wherein Y1, Y2, Y3 and Y4 each independently represent a halogen atom, -[OSi m R 1 3-m ] n group, or -OR 2 two or more -[OSim R 1 3-m ] n group, or -OR 2 The groups may be covalently linked to each other; m is an integer from 0 to 3, n is an integer equal to or greater than 1, and R 1 is a hydrogen atom, C1-C 10 Alkyl groups, aryl groups, C2-C 10 Alkenyl groups, C2-C 10 R is selected from an alkynyl group, a polyalkylene oxide group, or a derivative thereof; 1 is optionally substituted with one or more amine, ammonium, amide, ketone, ester, aldehyde, thiol, or thioether groups; R 2 is a hydrogen atom, C1-C 10 Alkyl groups, aryl groups, C2-C 10 Alkenyl groups, C2-C 10 R is selected from an alkynyl group, a polyalkylene oxide group, or a derivative thereof; 2 is optionally substituted with one or more amine, ammonium, amide, ketone, ester, aldehyde, thiol, or thioether groups; The raw hides are treated with the tanning solution until the tanning solution penetrates the raw hides. (C) Optionally, the pH of the raw hides obtained at the end of step (B) is adjusted to a range of 2.1 to 10.5, preferably 4.0 to 8.0.

[0019] According to the means of the present invention, tanned raw leathers free from metals can be obtained. In particular, the tanned raw leathers obtained according to the tanning method of the present invention are chromium-free. The raw leathers obtained according to the tanning method of the present invention have a desirable shrinkage temperature for producing tanned leather products (shoes, tanned leather goods, gloves, automobiles, furniture). Therefore, these raw leathers can be used to form tanned leather goods that do not pose a risk to the health of future users, regardless of the conditions of use. In particular, the tanned raw leathers obtained according to the method of the present invention can be easily de-tanned to recover their value, since only silicon is used.

[0020] The present invention also relates to tanned raw hides obtained by the above-mentioned tanning method.

[0021] The present invention also relates to a method for producing tanned leather from rawhide, said method comprising the following steps: (i) processing the raw hide to obtain a raw hide ready for tanning; (ii) A step of tanning the raw hides prepared for tanning based on the above tanning method. (iii) polishing and / or finishing the tanned raw hides obtained at the end of step (ii) to obtain finished tanned leather.

[0022] The present invention also relates to a method for de-tanning raw leather obtained by the above-mentioned method and / or finished tanned leather obtained by the above-mentioned tanned leather manufacturing means, which comprises at least immersing the raw leather and / or tanned leather in a solution for basifying the raw leather and / or tanned leather to a pH in the range of 11.5 to 13.0, preferably 11.5 to 13.0.

[0023] The raw hides that can be subjected to the tanning and detanning methods according to the present invention are any collagen-containing raw hides, whether synthetic or natural, that originate from animals that contain collagen, such as cattle, sheep, goats, reptiles (snakes, lizards, crocodiles, alligators), fish, birds, amphibians, and pigs.

[0024] In the tanning method of the present invention, "raw hides prepared for tanning" refers to raw hides that have been treated as described above, such as pickled raw hides or demineralized raw hides, and which have also been degreased.

[0025] The rehydration and degreasing processes are well known to those skilled in the art. For example, to rehydrate and degrease pickled hides, the hides may be placed in a drum and water, salt, and a degreasing agent may be added. The degreasing agent may be selected from nonionic and anionic surfactants in a known manner. For example, the drum may be rotated without heating for a period of 15 minutes to 10 hours, the drum may be drained, and the hides may be washed with salt water at room temperature. In this manner, tanning-ready hides may be obtained.

[0026] In the process for producing tanned leather according to the present invention, "rawhide" means natural or artificial hides containing collagen, but which have not yet been subjected to the above-mentioned raw hide processing steps which prepare them for tanning.

[0027] According to the first step, step (A) of the tanning method of the present invention, the raw hides prepared for tanning are immersed in an aqueous solution in a drum, and the pH of the raw hides and the aqueous solution is adjusted to a value in the range of 1.5 to 10.5 by adding an acid or a base.

[0028] A drum is a rotating container known to those skilled in the art. In this specification, the term drum refers to any container that receives raw hides for tanning and has a mechanism for allowing the raw hides and the aqueous solution to mix. Therefore, for the purposes of this application, paddles are included in the definition of drum. Depending on the pH selected for soaking the raw hides, the aqueous solution may contain salt. This salt prevents the raw hides from swelling in the aqueous solution. For purposes of this application, the term salt refers to any compound in which an anion and a cation form a neutral product with no total charge. Salts may be selected from potassium chloride, sodium chloride, and mixtures thereof. For example, if the pH of the aqueous solution is less than 5.0, it is preferable for the aqueous solution to contain salt. Preparation of such an aqueous solution with a high salt concentration is within the skill of those skilled in the art. Determining the amount of salt, such as sodium chloride, required to prevent swelling of the raw hides is within the skill of those skilled in the art. For example, the aqueous solution may contain 1 to 1200% water by weight relative to the weight of the raw hides and 6 to 12% sodium chloride by weight relative to the weight of the water.

[0029] The pH of the raw skin and aqueous solution is adjusted to a value in the range of 1.5 to 10.5 by adding an acid or a base.

[0030] In one embodiment, the pH of the raw hides and aqueous solution is adjusted to a value in the range of 1.5 to 2.0, preferably 1.7 to 1.9, for example by adding one or more acids, alone or in combination, such as an acid selected from formic acid, sulfuric acid, and mixtures thereof. As will be seen below, adjusting the pH of the raw hides and aqueous solution to such an acidic pH allows the tanning solution to be added directly to the drum in the form of a solution of the compound Si(OH). This compound is prepared outside the drum in advance from a compound of formula (I) above, for example, Si(OCHCH). As will also be seen below, adjusting the pH of the raw hides and aqueous solution to such an acidic pH also allows the tanning solution to be prepared in situ, i.e., within the drum, by adding a solution of the compound Si(OCHCH).

[0031] In another embodiment, the pH of the raw hides and aqueous solution in step (A) is in the range of 2.1 to 10.5. As will be seen below, when the pH of the raw hides and aqueous solution in step (A) is in the range of 2.1 to 10.5, the tanning solution can be prepared in situ, i.e., in the drum, by adding a solution of the compound Si(OCH2CH3)4. Furthermore, the pH during treatment with the tanning solution can be maintained relatively high, for example, at about pH 7.0, eliminating the need for a subsequent basification step. Similarly, if the treatment step with the tanning solution is carried out at a pH of 5.0 or higher, the addition of salt to the tanning solution is unnecessary.

[0032] According to the second step, step (B), of the tanning method according to the present invention, the raw hides of step (A) are treated with a tanning solution. To do this, the aqueous solution of step (A) may or may not be drained from the drum. When the aqueous solution of step (A) is drained from the drum, it is preferred to empty it without rinsing the raw hides.

[0033] The tanning solution contains the following components in weight ratio relative to the weight of raw hides: 1 to 1200% water, Optionally, salt, preferably sodium chloride, in a sufficient amount to prevent swelling of the raw hides. 1 to 100% of a compound of formula 1

[0034] [ka]

[0035] wherein Y1, Y2, Y3 and Y4 each independently represent a halogen atom, -[OSi m R 1 3-m ] n group, or -OR 2 two or more -[OSi m R 1 3-m ] n group, or -OR 2The groups may be covalently linked to each other; m is an integer from 0 to 3, n is an integer equal to or greater than 1, and R 1 is a hydrogen atom, C1-C 10 Alkyl groups, aryl groups, C2-C 10 Alkenyl groups, C2-C 10 R is selected from an alkynyl group, a polyalkylene oxide group, or a derivative thereof; 1 is optionally substituted with one or more amine, ammonium, amide, ketone, ester, aldehyde, thiol, or thioether groups; R 2 is a hydrogen atom, C1-C 10 Alkyl groups, aryl groups, C2-C 10 Alkenyl groups, C2-C 10 R is selected from an alkynyl group, a polyalkylene oxide group, or a derivative thereof; 2 is optionally substituted with one or more amine, ammonium, amide, ketone, ester, aldehyde, thiol, or thioether groups.

[0036] For the purposes of this invention, "C1-C 10 An "alkyl" group means a saturated straight or branched chain hydrocarbon containing from 1 to 10 carbon atoms, such as methyl, ethyl, isopropyl, tert-butyl, pentyl, and the like groups.

[0037] An aryl group is an aromatic group, preferably containing 5 to 10 carbon atoms, containing one or more rings, and optionally containing heteroatoms, especially oxygen, nitrogen, or sulfur, such as phenyl, furan, indole, pyridine, naphthalene, and the like groups.

[0038] "C2-C 10 An "alkenyl" group refers to a straight or branched chain hydrocarbon containing at least one unsaturation and containing from 2 to 10 carbon atoms, such as ethenyl (vinyl), propenyl, 2,4-hexadienyl, and the like groups.

[0039] "C2-C10 An "alkynyl" group refers to a straight or branched chain hydrocarbon containing at least one double unsaturation and containing from 2 to 10 carbon atoms, such as acetylene, propyne, butyne, and the like groups.

[0040] A "polyalkylene oxide" group refers to a polymer of ethylene oxide units, the number of ethylene oxide units being one or greater.

[0041] Derivatives of polyalkylene oxides refer to one or more synthetic polymers selected from the following: copolymers of carboxylic acids and carboxylic acid esters of poly(alkylene glycols), copolymers of carboxylic acids and carboxylic acid esters of poly(alkyleneamide glycols), copolymers of carboxylic acids and poly(alkylene glycol)imides, copolymers of carboxylic acids and poly(alkylene glycol)vinyl ethers, and mixtures thereof, which may or may not be neutralized.

[0042] The tanning solution therefore contains no metals other than silicon, in particular the tanning solution does not contain chromium.

[0043] In one embodiment, Y1, Y2, Y3 and Y4 are each independently selected from a chlorine atom, an -OH group or an -OCH2CH3 group.

[0044] In one embodiment of the method according to the invention, the compound of formula (I) is Si(OH)4. In this case, the pH of the raw hides and aqueous solution in step (A) is previously adjusted to a value ranging from 1.5 to 2.0, preferably from 1.7 to 1.9. The tanning solution contains the following components, by weight relative to the weight of the raw hides: 1 to 1200% water, A sufficient amount of salt, preferably sodium chloride, to prevent swelling of the raw hides. · 5 to 60%, preferably 5 to 30%, more preferably 10 to 20% Si(OH)4.

[0045] In this form of practice, the tanning solution is prepared, preferably outside the drum, by hydrolyzing the compound Si(OCH2CH3)4 to Si(OH)4, and then added to the raw hides in the drum. For example, the tanning solution may be prepared by mixing an aqueous solution having a pH in the range of 1.5 to 2.0 with Si(OCH2CH3)4 in a volume ratio (v / v) of 1 / 1 to 25 / 1, preferably 1 / 1 to 10 / 1.

[0046] The Si(OH)4 thus obtained is then added to the drum in an amount of 5 to 60%, preferably 5 to 30%, and more preferably 10 to 20%, by weight relative to the weight of the raw hides. This amount may be adjusted depending on the type of raw hides to be tanned and their thickness. Furthermore, to prevent swelling of the raw hides, a salt such as sodium chloride may be added to the drum in an amount of, for example, 6 to 12% by weight relative to the weight of the added Si(OH)4.

[0047] An acidic brine may also be added to the drum. Finally, the drum may contain 1 to 1200% water by weight relative to the weight of raw hides.

[0048] The drum is preferably rotated for a period of time sufficient to allow the silicic acid to penetrate the hides. This period depends on the thickness and properties of the hides. For example, it may take longer for the silicic acid to penetrate the hides being tanned from cattle hides than from sheep hides. The period of this step can be easily determined by those skilled in the art based on the hides being tanned. The rotation of the drum is preferably carried out at room temperature, i.e., below 30°C, preferably in the range of 20 to 25°C.

[0049] After the silicic acid has penetrated the hides, they can be directly removed from the drum and dried. In such cases, the hides are removed from the drum at the end of step (B) and dried. During this drying step, the water content evaporates. This evaporation leads to the polymerization of Si(OH)4, forming a three-dimensional network of Si-O-Si bonded to the collagen of the hide, stabilizing the hide. At the end of this drying step, a dry tanned leather is obtained, which can be stored as is.

[0050] In another embodiment, after the silicic acid has impregnated the raw hides, the pH of the raw hides is brought to a value in the range of 2.1 to 10.5, preferably in the range of 4.0 to 8.0. This optional step (C) is as follows:

[0051] In another embodiment of the process according to the invention, the compound of formula (I) is Si(OCH2CH3)4.

[0052] The tanning solution may then contain, by weight relative to the weight of the hides, the following components: 1 to 1200% water, Optionally, salt, preferably sodium chloride, in a sufficient amount to prevent swelling of the raw hides. 5 to 100%, preferably 10 to 60%, more preferably 25 to 45% of Si(OCH2CH3)4.

[0053] In this form of implementation, the tanning liquor may be generated directly in situ by adding Si(OCH2CH3)4 to the drum in an amount of 5 to 100%, preferably 10 to 60%, more preferably 25 to 45%, by weight relative to the weight of the raw hides.

[0054] If necessary, an acidic brine can be added to the drum. Finally, the drum may contain 1 to 1200% water by weight relative to the weight of the raw hides.

[0055] In this embodiment, hydrolysis of Si(OCHCH) to Si(OH) occurs within the drum. When Si(OCHCH) is added to the drum, two insoluble phases form within the drum, one is water and the other is Si(OCHCH).

[0056] The drum is preferably rotated for a period of time necessary to complete the hydrolysis of Si(OCH2CH3)4 to Si(OH)4, obtain a single soluble phase of silicic acid solution, and allow the silicic acid to penetrate the raw hides. For example, this period can range from one hour to one week. As noted above, the period of time necessary for the silicic acid to penetrate the raw hides depends on the nature of the raw hides. This period can be easily determined by one skilled in the art. The rotation of the drum is preferably carried out at room temperature, i.e., below 30°C, preferably in the range of 20 to 25°C.

[0057] Furthermore, the time period for the hydrolysis of Si(OCH2CH3)4 to Si(OH)4 to be complete may also depend on the pH of the tanning solution.

[0058] Thus, in one embodiment, the compound of formula (I) is Si(OCH2CH3)4, and the pH of the raw hides and aqueous solution in step (A) is pre-set to a value in the range of 1.5 to 10.5, preferably 1.7 to 1.9. In this embodiment, after the silicic acid has impregnated the raw hides, as described above, the raw hides can be directly removed from the drum and dried. Alternatively, the raw hides can be subjected to a basification treatment, as described below.

[0059] In another embodiment, the compound of formula (I) is Si(OCHCH), and the pH of the raw hides and aqueous solution in step (A) is preliminarily adjusted to a range of 2.1 to 10.5. In this case, the pH of the aqueous solution and raw hides is adjusted to a range of 2.1 to 10.5, preferably 4.0 to 8.0, and more preferably 4.0 to 5.0, before adding Si(OCHCH) to the drum as described above. Thus, the pH of the tanning solution is in the range of 2.1 to 10.5, preferably 4.0 to 8.0, and more preferably 4.0 to 5.0. This pH of the tanning solution allows for simultaneous hydrolysis of Si(OCHCH) to Si(OH) and polymerization of Si(OH) within the drum. The polymerization of Si(OH) leads to the formation of a three-dimensional Si-O-Si network and the establishment of bonds to the collagen fibers of the raw hides. This three-dimensional network transforms the initially perishable raw hides into perishable, tanned raw hides, and thus into stable and durable tanned leather. Thus, in embodiments of the method according to the present invention in which the pH of the tanning solution is in the range of 2.1 to 10.5, preferably 4.0 to 8.0, and more preferably 4.0 to 5.0, it is not necessary to carry out an additional step, such as a step of basifying the raw hides so that they can be tanned. In such embodiments, the raw hides obtained at the end of step (B) can be used directly in a subsequent polishing step or dried to complete polymerization and stored. However, in other embodiments of the method according to the present invention in which the pH of the tanning solution is in the range of 2.1 to 10.5, preferably 4.0 to 8.0, and more preferably 4.0 to 5.0, a step of treating the raw hides with a basifying solution can also be carried out, as described below.

[0060] That is, in an embodiment, the tanning method according to the present invention may comprise an additional step, step (C), in which the pH of the raw hides obtained at the end of step (B) is adjusted to a value ranging from 2.1 to 10.5, preferably from 4.0 to 8.0.

[0061] That is, step (C) is preferably carried out when the tanning solution is too acidic to initiate polymerization of Si(OH)4, for example when the pH of the tanning solution is below 2.0.

[0062] During step (C), the raw hides may be treated with, for example, a basifying solution. By basifying the bath containing the raw hides, the polymerization of Si(OH)4 in the raw hides is initiated and / or accelerated. Bonds can be formed between silicon and collagen in the fibers of the raw hides, allowing the formation of a three-dimensional network of Si-O-Si connected to the collagen of the raw hides, resulting in the stabilization of the raw hides. Tanned raw hides are obtained.

[0063] In one form of implementation of the method according to the invention, the treatment with the basifying solution is carried out by adding a basifying agent to the drum, selected from sodium formate, sodium bicarbonate, sodium acetate, calcium formate, sodium carbonate and mixtures thereof, in an amount ranging from 0.5 to 20% by weight relative to the weight of the raw hides.

[0064] In other embodiments, the treatment with the basifying solution can be carried out outside the drum. For example, this treatment can include the following steps: (C1) At the end of step (B), the raw skin is removed from the drum. (C2) Place the raw hides flatly on top of each other in the container. (C3) Fill the container with the basifying solution and completely immerse the raw hides. The basifying solution contains a basifying agent selected from sodium formate, sodium bicarbonate, sodium acetate, calcium formate, sodium carbonate, and mixtures thereof. (C4) The raw hides are allowed to stand in the basifying solution in the container for, for example, at least one hour.

[0065] The amount of basifying agent is calculated depending on the desired final pH. During step (C), the raw hides can be removed from the drum either after or without prior rinsing.

[0066] At any time during step (C), the raw hides may be dried to effect polymerization of Si(OH)4 by evaporation.

[0067] The raw hides obtained by the method of the present invention are tanned and resistant to decay. These hides are generally white in color. They have a fuller, fuller appearance than their original state before tanning. These hides have a shrink temperature of 65 to 90°C. This shrink temperature allows these hides to maintain their flexibility and excellent appearance even when subjected to treatments that involve exposure to relatively high temperatures, for example, in the range of 50 to 75°C, such as thickening and high-temperature dyeing for better dye fixation.

[0068] The present invention also relates to a method for producing tanned leather from rawhide, comprising the steps of: (i) processing raw hides to obtain raw hides ready for tanning; (ii) tanning the raw hides prepared for tanning according to the above tanning method; (iii) Polishing and / or finishing the tanned raw hides obtained at the end of step (ii) to obtain finished tanned leather.

[0069] The present invention also relates to a method for detanning tanned raw hides obtained by the above method and / or tanned leather produced by the above means, said method comprising at least one step of immersing said raw hides and / or tanned leather in a basifying solution to bring the pH of said raw hides and / or tanned leather to a value of 10.5 or higher, preferably 11.5 or higher, and desirably in the range of 11.5 to 13.0.

[0070] In the detanning method according to the present invention, the tanned raw hide may be, for example, in the "dry white" state. For the purposes of the present invention, the term "dry white" means raw hide that has been tanned and dried but not polished. Alternatively, the tanned raw hide may be in the form of wet white, dyed, crusted, finished or semi-finished tanned leather, or in the form of shaved or split, terms that are well known to those skilled in the art. Tanned leather waste or powder derived from wet white, "dry white", dyed, crusted or finished tanned leather can also be detanned by the detanning method according to the present invention.

[0071] For example, to perform the detanning, the tanned raw hides and / or the finished tanned leather may be immersed in an aqueous solution, for example in a drum. Alternatively, the tanned raw hides, in the form of tanned leather scraps and tanned leather powder, may be placed in a container equipped with a stirring blade or a mixing system. The aqueous solution may also contain a degreasing agent. For example, the aqueous solution may contain, in weight ratio to the weight of the raw hides: 50 to 2000% water, · 0.1 to 2% degreaser.

[0072] The degreasing agent may be selected from surfactants, such as nonionic and anionic surfactants.

[0073] The purpose of such a step is to degrease and rehydrate the raw hides and / or tanned leather, and the drum is preferably rotated for a period sufficient to allow this, for example from 15 minutes to overnight, for example from 45 minutes to 1 hour 30 minutes, at a temperature in the range of 10 to 80°C, for example from 30 to 45°C.

[0074] The drum can then be emptied and / or the tanned leather can be rinsed at room temperature.

[0075] The raw hides and / or tanned leather are immersed in an aqueous solution containing a basifying agent to adjust the pH of the raw hides and / or tanned leather to 10.5 or higher, preferably in the range of 11.5 to 14.

[0076] The basifying agent may be selected, for example, from sodium bicarbonate, sodium carbonate, ammonia, sodium hydroxide, and mixtures thereof.

[0077] The basifying agent may, for example, be added to the aqueous solution in multiple steps, each step may or may not use the same basifying agent, and the operating temperature may be different in each step.

[0078] For example, the pH of the raw hides and / or tanned leather may be brought to a value in the range of 7.0 to 10.0 by first adding a basifying agent, for example sodium bicarbonate and / or sodium carbonate and / or ammonia, and maintaining the temperature of the aqueous solution in the range of 10 to 80°C, for example 30 to 45°C.

[0079] The pH of the raw hides and / or tanned leather may then be brought to a value in the range of 11.5 to 13.0 by a second addition of a basifying agent, for example sodium hydroxide, and the temperature of the aqueous solution is maintained in the range of 10 to 30°C, for example 20 to 25°C.

[0080] The pH of raw hides and / or tanned leather is 10.5 or higher, preferably At pH values ​​between 11.5 and 13.0, the three-dimensional network of Si-O-Si bonds in the collagen of the hides is decomposed. At such pH values, the hides and / or leathers, such as wet white, "dry white", dyed, crusted, finished hides, tanned leather powder and waste, lose their resistance to shrinkage temperatures. This loss of resistance indicates the de-tanning of the hides and / or leathers.

[0081] The wet white, "dry white", dyed, crusted, finished tanned leather, shavings or floor waste, tanned leather powder and waste thus detanned can be left in the non-crosslinked protein state or can be re-evaluated, for example by re-tanning or by using it for the production of gelatin, protein for animal feed, fertilizer for fields, etc.

[0082] (Experimental Department) --Example 1-- Preparation of Si(OH)4 from Si(OCH2CH3)4 Mix 1 L of Si(OCH2CH3)4 with 1 L of water.

[0083] The pH of this liquid is adjusted to a range of 1.5 to 2.0 using a strong acid, such as, but not limited to, hydrochloric acid or sulfuric acid.

[0084] The hydrolysis reaction of Si(OCH2CH3)4 to Si(OH)4 is exothermic. Therefore, it is preferable to maintain the mixture at a desired temperature, for example, around 30°C, using a cooling bath. The mixture is preferably vigorously stirred for 15 to 120 minutes. The hydrolysis reaction lasts for 20 minutes to 2 hours. When the reaction is complete, a clear solution of silicic acid with the chemical formula Si(OH)4 is obtained. 10% by mass of sodium chloride was added to the total mass of the silicic acid solution prepared earlier.

[0085] --Example 2-- The raw sheep hide was tanned according to the tanning method of the present invention as follows.

[0086] (Step A) The tanning-ready raw hides are pickled raw hides removed from the pickling storehouse or demineralised raw hides which have previously been degreased and rehydrated by methods known to those skilled in the art. The raw hides are weighed.

[0087] The hides are placed in a drum in a salt solution, and the pH of the hides and aqueous solution is adjusted to a value between 1.5 and 2.0, for example, by adding sulfuric acid, either alone or in combination with formic acid.

[0088] (Step B) In terms of mass relative to the mass of raw hide, Cold water (25°C), 50% Sodium chloride, 5% Si(OH)4, 13%, hydrolyzed from Si(OCH2CH3)4 as described in Example 1, is added to the drum.

[0089] The drum is rotated for 4 hours at room temperature, ie, 25°C.

[0090] (Step C) First, 5% by weight of sodium formate based on the weight of the raw hides is added to the drum at 25°C. The drum is rotated for 1 hour. The pH measured for the raw hides ranges from 3.8 to 4.0.

[0091] Second, 5% by weight of sodium formate based on the weight of the raw hides is added to the drum at 25°C. The drum is rotated overnight. The final pH of the raw hides is measured to be in the range of 4.0 to 4.2.

[0092] The drum is emptied and the raw hides are rinsed.

[0093] Tanned raw hides are obtained which are free from metals, in particular chromium.

[0094] The raw hide is white, plump, and has a beautiful appearance.

[0095] --Example 3-- The raw cowhide hide was tanned according to the tanning method of the present invention as follows.

[0096] (Step A) The tanning-ready raw hides are pickled raw hides removed from the pickling storehouse or demineralised raw hides which have previously been degreased and rehydrated by methods known to those skilled in the art. The raw hides are weighed.

[0097] The hides are placed in a drum in a salt solution, and the pH of the hides and aqueous solution is adjusted to a value between 1.5 and 2.0, for example, by adding sulfuric acid, either alone or in combination with formic acid.

[0098] (Step B) In terms of mass relative to the mass of raw hide, Cold water (25°C), 50% Sodium chloride, 5% 20% of Si(OH)4, hydrolyzed from Si(OCH2CH3)4 as described in Example 1, is added to the drum.

[0099] The drum is allowed to roll overnight at room temperature, ie, 25°C.

[0100] (Step C) First, 5% by weight of sodium formate based on the weight of the raw hides is added to the drum at 25°C. The drum is rotated for 1 hour. The pH measured for the raw hides is in the range of 3.8 to 4.0.

[0101] Second, 5% by weight of sodium formate based on the weight of the raw hides is added to the drum at 25° C. The drum is rotated overnight. The final pH of the raw hides is measured to be in the range of 4.0 to 4.2.

[0102] The drum is emptied and the raw hides are rinsed.

[0103] Tanned raw hides are obtained which are free from metals, in particular chromium.

[0104] The raw hide is white, plump, and has a beautiful appearance.

[0105] --Example 4-- The raw sheep hide was tanned according to the tanning method of the present invention as follows.

[0106] (Step A) The tanning-ready raw hides are pickled raw hides removed from the pickling storehouse or demineralised raw hides which have previously been degreased and rehydrated by methods known to those skilled in the art. The raw hides are weighed.

[0107] The hides are placed in a drum in a salt solution, and the pH of the hides and aqueous solution is adjusted to a value between 1.5 and 2.0, for example, by adding sulfuric acid, either alone or in combination with formic acid.

[0108] (Step B) In terms of mass relative to the mass of raw hide, Cold water (25°C), 50% Sodium chloride, 5% Si(OH)4, 13%, hydrolyzed from Si(OCH2CH3)4 as described in Example 1, is added to the drum.

[0109] The drum is rotated for 4 hours at room temperature, ie, 25°C.

[0110] (Step C) First, 5% by weight of sodium formate based on the weight of the raw hides is added to the drum at 25°C. The drum is rotated for 1 minute and then allowed to rest overnight. The pH measured for the raw hides is in the range of 3.8 to 4.0.

[0111] Second, 5% by weight of sodium formate based on the weight of the raw hides is added to the drum at 25°C. The drum is rotated for 1 minute and then allowed to stand for 1 hour. The final pH of the raw hides is measured to be in the range of 4.0 to 4.2.

[0112] Tanned raw hides are obtained which are free from metals, in particular chromium.

[0113] The raw hide is white, plump, and has a beautiful appearance.

[0114] Example 5 The raw cowhide hide was tanned according to the tanning method of the present invention as follows.

[0115] (Step A) The tanning-ready raw hides are pickled raw hides removed from the pickling storehouse or demineralised raw hides which have previously been degreased and rehydrated by methods known to those skilled in the art. The raw hides are weighed.

[0116] The hides are placed in a drum in a salt solution, and the pH of the hides and aqueous solution is adjusted to a value between 1.5 and 2.0, for example, by adding sulfuric acid, either alone or in combination with formic acid.

[0117] (Step B) In terms of mass relative to the mass of raw hide, Cold water (25°C), 50% Sodium chloride, 5% 20% of Si(OH)4, hydrolyzed from Si(OCH2CH3)4 as described in Example 1, is added to the drum.

[0118] The drum is allowed to roll overnight at room temperature, ie, 25°C.

[0119] (Step C) First, 5% by weight of sodium formate based on the weight of the raw hides is added to the drum at 25°C. The drum is rotated for 1 minute and then allowed to stand for 1 hour. The pH measured for the raw hides is in the range of 3.8 to 4.0.

[0120] Second, 5% by weight of sodium formate based on the weight of the raw hides is added to the drum at 25°C. The drum is rotated for 1 minute and then allowed to rest overnight. The final pH of the raw hides is measured to be in the range of 4.0 to 4.2.

[0121] Tanned raw hides are obtained which are free from metals, in particular chromium.

[0122] The raw hide is white, plump, and has a beautiful appearance.

[0123] Example 6 The raw sheep hide was tanned according to the tanning method of the present invention as follows.

[0124] (Step A) The tanning-ready raw hides are pickled raw hides removed from the pickling storehouse or demineralised raw hides which have previously been degreased and rehydrated by methods known to those skilled in the art. The raw hides are weighed.

[0125] The hides are placed in a drum in a salt solution, and the pH of the hides and aqueous solution is adjusted to a value between 1.5 and 2.0, for example, by adding sulfuric acid, either alone or in combination with formic acid.

[0126] (Step B) · Add 28% by mass of Si(OCH2CH3)4 to the mass of raw hides into the drum.

[0127] This amount of Si(OCH2CH3)4 represents an amount equivalent to 13% Si(OH)4 by mass relative to the mass of raw hides.

[0128] The drum is rotated for 4 hours at room temperature, ie, 25°C.

[0129] after that, In terms of mass relative to the mass of raw hide, 25°C water, 150% Sodium chloride, 15% Add to the drum.

[0130] The drum is rotated for 20 minutes at 25°C.

[0131] (Step C) First, 5% by weight of sodium formate based on the weight of the raw hides is added to the drum at 25°C. The drum is rotated for 1 hour. The pH measured for the raw hides ranges from 3.8 to 4.0.

[0132] Second, 5% by weight of sodium formate based on the weight of the raw hides is added to the drum at 25° C. The drum is rotated overnight. The final pH of the raw hides is measured to be in the range of 4.0 to 4.2.

[0133] The drum is emptied and the raw hides are rinsed.

[0134] Tanned raw hides are obtained which are free from metals, in particular chromium.

[0135] The raw hide is white, plump, and has a beautiful appearance.

[0136] Example 7 The raw sheep hide was tanned according to the tanning method of the present invention as follows.

[0137] (Step A) The tanning-ready raw hides are pickled raw hides removed from the pickling storehouse or demineralised raw hides which have previously been degreased and rehydrated by methods known to those skilled in the art. The raw hides are weighed.

[0138] The hides are placed in a drum in a salt solution, and the pH of the hides and aqueous solution is adjusted to a value between 1.5 and 2.0, for example, by adding sulfuric acid, either alone or in combination with formic acid.

[0139] (Step B) · Add 28% by mass of Si(OCH2CH3)4 to the mass of raw hides into the drum.

[0140] This amount of Si(OCH2CH3)4 represents an amount equivalent to 13% Si(OH)4 by mass relative to the mass of raw hides.

[0141] The drum is rotated for 4 hours at room temperature, ie, 25°C.

[0142] after that, In terms of mass relative to the mass of raw hide, 25°C water, 150% Sodium chloride, 15% Add to the drum.

[0143] The drum is rotated for 20 minutes at 25°C.

[0144] (Step C) First, 5% by weight of sodium formate based on the weight of the raw hides is added to the drum at 25°C. The drum is rotated for 1 minute and then allowed to stand for 1 hour. The pH measured for the raw hides is in the range of 3.8 to 4.0.

[0145] Second, 5% by weight of sodium formate based on the weight of the raw hides is added to the drum at 25°C. The drum is rotated for 1 minute and then allowed to rest overnight. The final pH of the raw hides is measured to be in the range of 4.0 to 4.2.

[0146] The drum is emptied and the raw hides are rinsed.

[0147] Tanned raw hides are obtained which are free from metals, in particular chromium.

[0148] The raw hide is white, plump, and has a beautiful appearance.

[0149] --Example 8-- The raw cowhide hide was tanned according to the tanning method of the present invention as follows.

[0150] (Step A) The tanning-ready raw hides are pickled raw hides removed from the pickling storehouse or demineralised raw hides which have previously been degreased and rehydrated by methods known to those skilled in the art. The raw hides are weighed.

[0151] The hides are placed in a drum in a salt solution, and the pH of the hides and aqueous solution is adjusted to a value between 1.5 and 2.0, for example, by adding sulfuric acid, either alone or in combination with formic acid.

[0152] (Step B) Si(OH)4, hydrolyzed from Si(OCH2CH3)4 as described in Example 1, is added in steps according to the following procedure, where percentages are given as relative mass to the mass of raw hides. · After adding 0.6% Si(OH)4, rotate the drum for 4 hours at 25°C. · After adding 0.6% Si(OH)4, rotate the drum for 4 hours at 25°C. · After adding 3.8% Si(OH)4, rotate the drum overnight at 25°C. After adding 5% Si(OH)4, the drum is rotated for 10 hours at 25°C. · After adding 5% Si(OH)4, rotate the drum overnight at 25°C. After adding 7.5% Si(OH)4, the drum is rotated for 24 hours at 25°C. After adding 7.5% Si(OH)4, the drum is rotated for 24 hours at 25°C.

[0153] After this, 25°C water, 100% Sodium chloride 10% at 25°C In both cases, a mass relative to the mass of raw hides is added to the drum.

[0154] The drum is rotated for 20 minutes.

[0155] (Step C) Sodium formate, 1.5% by weight based on the weight of the raw hides, is added to the drum at 25° C. The drum is rotated for 1 minute every 30 minutes for 12 hours. The pH of the raw hides is measured to be 3.88.

[0156] Sodium formate, 1.5% by weight based on the weight of the raw hides, is then added to the drum at 25° C. The drum is rotated for 1 minute every 30 minutes for 12 hours. The pH of the raw hides is measured to be 4.40.

[0157] Sodium formate, 4.0% by weight based on the weight of the raw hides, is then added to the drum at 25° C. The drum is rotated for 1 minute every 30 minutes for 6 hours. The pH of the raw hides is measured to be 4.50.

[0158] The drum is emptied and the raw hides are rinsed.

[0159] Tanned raw hides are obtained which are free from metals, in particular chromium.

[0160] The raw hide is white, plump, and has a beautiful appearance.

[0161] --Example 9-- The raw sheep hide was tanned according to the tanning method of the present invention as follows.

[0162] (Step A) The tanning-ready raw hides are pickled raw hides removed from the pickling storehouse or demineralised raw hides which have previously been degreased and rehydrated by methods known to those skilled in the art. The raw hides are weighed.

[0163] The hides are placed in a drum in a salt solution, and the pH of the hides and aqueous solution is adjusted to a value between 1.5 and 2.0, for example, by adding sulfuric acid, either alone or in combination with formic acid.

[0164] (Step B) In terms of mass relative to the mass of raw hide, Cold water (25°C), 50% Sodium chloride, 5% Si(OH)4, 13%, hydrolyzed from Si(OCH2CH3)4 as described in Example 1, is added to the drum.

[0165] The drum is rotated for 4 hours at room temperature, ie, 25°C.

[0166] The drum is emptied and the raw hides are rinsed.

[0167] (Step C) The mass of hides is removed from the drum and placed on a draining rack for the time required for the surface water to evaporate. The hides are then stretched wet on a frame and placed outside to dry, usually overnight or somewhat longer depending on the thickness of the hides and the weather that day.

[0168] The next day, after the water in the raw hides has evaporated, the hides are dry, white, and tanned.

[0169] Example 10 The raw cowhide hide was tanned according to the tanning method of the present invention as follows.

[0170] (Step A) The tanning-ready raw hides are pickled raw hides removed from the pickling storehouse or demineralised raw hides which have previously been degreased and rehydrated by methods known to those skilled in the art. The raw hides are weighed.

[0171] The hides are placed in a drum in a salt solution, and the pH of the hides and aqueous solution is adjusted to a value between 1.5 and 2.0, for example, by adding sulfuric acid, either alone or in combination with formic acid.

[0172] (Step B) Cold water (25°C), 50% Sodium chloride, 5% Add 20% of Si(OH)4, hydrolyzed from Si(OCH2CH3)4 as described in Example 1, to the drum, in proportion to the mass of the raw hides.

[0173] The drum is allowed to roll overnight at room temperature, ie, 25°C.

[0174] The drum is emptied and the raw hides are rinsed.

[0175] (Step C) The mass of hides is removed from the drum and placed on a draining rack for the time required for the surface water to evaporate. The hides are then stretched wet on a frame and placed outside to dry, usually overnight or somewhat longer depending on the thickness of the hides and the weather that day.

[0176] The next day, after the water in the raw hides has evaporated, the hides are dry, white, and tanned.

[0177] Example 11 The raw sheep hide was tanned according to the tanning method of the present invention as follows.

[0178] (Step A) The tanning-ready raw hides are pickled raw hides removed from the pickling storehouse or demineralised raw hides which have previously been degreased and rehydrated by methods known to those skilled in the art. The raw hides are weighed.

[0179] The hides are placed in a drum in a salt solution, and the pH of the hides and aqueous solution is adjusted to a value between 2.1 and 10.5, for example, by adding sulfuric acid, either alone or in combination with formic acid, or by adding a basifying agent.

[0180] (Step B) The pH of the raw hide and salt solution is adjusted to a value in the range of 4.0 to 5.0, for example 4.2.

[0181] 28% by mass of Si(OCH2CH3)4 relative to the mass of raw hides is added to the drum.

[0182] This amount of Si(OCH2CH3)4 represents an amount equivalent to 13% Si(OH)4 by mass relative to the mass of raw hides.

[0183] The drum is rotated at room temperature, ie, 25° C., for seven days.

[0184] The drum is then emptied and the raw hides are rinsed.

[0185] Tanned raw hides are obtained.

[0186] Example 12 Shrinkage temperature measurement The shrinkage temperatures of the tanned raw hides obtained in Examples 2 to 9 and 11 were measured according to the following procedure. -Cut a small piece of tanned raw hide approximately 2cm x 1cm from the neck area. Place one end of the prepared sample in the fixed area of ​​the shrinkage temperature measuring device. The opposite end of the same sample is placed in the movable hook of the shrinkage temperature measuring device, which is counterbalanced by a weight. The shrink temperature measuring device containing the sample is placed in a beaker filled with cold water (temperature strictly below 25°C). The raw hide sample must be completely submerged in water. A thermometer is placed in the same beaker and fixed to the shrinkage temperature measuring device. The base of the thermometer is placed in front of the sample of tanned raw hide. - Place the contraction pointer at 0 Place the assembly (beaker filled with water + shrinkage temperature measuring device containing the sample + thermometer) on the heating plate Turn on the heating plate When the pointer starts to move from zero at first, record the temperature. This temperature indicates the moment when the hide begins to shrink.

[0187] The results obtained for the raw hides obtained from Examples 2 to 9 and 11 above are summarized in Table 1 below.

[0188] [Table 1]

[0189] Table 1: Shrinkage Temperature The shrinkage temperature of the hides obtained by the tanning method according to the invention is particularly satisfactory, as it allows these hides to maintain their flexibility and good appearance even when subjected to treatments at relatively high temperatures, for example from 50°C to 75°C, such as thickening, high-temperature dyeing for better dye fixation, etc.

[0190] Example 13 The raw hides obtained in Examples 1 to 12 above can be easily detanned by the detanning method of the present invention described below.

[0191] The tanned hides are introduced into the drum. They are weighed and their mass serves as a reference point. Water, 50 to 2000% Degreaser, 0.1 to 2% In both cases, a mass relative to the mass of raw hides is added to the drum.

[0192] The drum is rotated for a period of 15 minutes to overnight, ideally between 45 minutes and 1 hour 30 minutes, at a temperature of 10 to 80°C, ideally 30 to 45°C.

[0193] The drum is emptied and the raw hides are rinsed at room temperature, ie 25°C.

[0194] A basifying agent selected from sodium bicarbonate, sodium carbonate, ammonia and mixtures thereof is added to the drum to bring the pH of the raw hides to a value in the range of 7.0 to 10.0, preferably 8.0 to 9.0. The basifying agent is added in an amount in the range of 0.1 to 15%, preferably 1 to 5%, by weight relative to the weight of the raw hides.

[0195] The drum is rotated for a period ranging from 15 to 120 minutes, for example from 45 to 90 minutes, and the temperature is in the range of from 10 to 80°C, preferably from 30 to 45°C.

[0196] Sodium hydroxide is then added to the drum to bring the pH of the raw hides to, for example, a value above 10.5, preferably in the range of 11.5 to 13.0.

[0197] The drum is rotated for a period of 30 minutes to 24 hours, for example overnight, at a temperature in the range of 10 to 30°C, for example 20 to 25°C.

[0198] In this step, the three-dimensional network of Si-O-Si connected to the collagen of the raw hide is broken down, and the raw hide is de-tanned. The de-tanned raw hide is left in the form of uncrosslinked proteins or recycled. The de-tanned raw hide is free of metals, especially chromium.

Claims

1. 1. A method for tanning raw hides prepared for tanning, comprising the steps of: (A) The raw hides prepared for tanning are immersed in an aqueous solution in a drum, and an acid or base is added to adjust the pH of the raw hides and the aqueous solution to a value in the range of 1.5 to 10.

5. (B) treating the raw hides after step (A) with a tanning solution containing the following components in relative weight to the weight of the raw hides: 1 to 1200% water, Optionally, salt in an amount sufficient to prevent swelling of the raw hides; and 1 to 100% of a compound of formula (I): 【Chemistry 3】 wherein Y1, Y2, Y3 and Y4 each independently represent a halogen atom, —[OSi ｍ R １ ３－ｍ ] ｎ group, or -OR ２ group, and two or more —[OSi ｍ R １ ３－ｍ ] ｎ group, or -OR ２ The groups may be covalently linked to each other; m is an integer from 0 to 3, n is an integer of 1 or more, and R １ is a hydrogen atom, C １ -C １０ Alkyl group, aryl group, C ２ -C １０ Alkenyl group, C ２ -C １０ R is selected from an alkynyl group, a polyalkylene oxide group, or a derivative thereof; １ is optionally substituted with one or more amine, ammonium, amide, ketone, ester, aldehyde, thiol, or thioether groups; R ２ is a hydrogen atom, C １ -C １０ Alkyl group, aryl group, C ２ -C １０ Alkenyl group, C ２ -C １０ R is selected from an alkynyl group, a polyalkylene oxide group, or a derivative thereof; ２ is optionally substituted with one or more amine, ammonium, amide, ketone, ester, aldehyde, thiol, or thioether groups; The raw hides are treated with the tanning solution until the tanning solution penetrates the raw hides; (C) Optionally, the pH of the raw hide obtained at the end of step (B) is adjusted to a range of 2.1 to 10.5, preferably 4.0 to 8.

0. A method comprising:

2. 10. The method of claim 1, Y1, Y2, Y3 and Y4 each independently represent a chlorine atom, an —OH group or an —OCH ２ CH ３ The method is characterized in that the compound is selected from the group consisting of:

3. In the method of claim 1 or 2, A method characterized in that the pH of the raw hides and the aqueous solution in step (A) is adjusted to a value in the range of 1.5 to 2.0, preferably 1.7 to 1.9, by adding, for example, formic acid, sulfuric acid, or mixtures thereof.

4. The method of claim 3, The compound of formula (I) is Si(OH) ４ The method according to claim 1, wherein

5. 5. The method of claim 4, The tanning solution contains, by weight relative to the weight of the raw hides: 1 to 1200% water, a sufficient amount of salt, preferably sodium chloride, to prevent swelling of the raw hides; 5 to 60%, preferably 5 to 30%, more preferably 10 to 20% Si(OH) ４ A method comprising:

6. In the method of claim 4 or 5, When carrying out step (B), the tanning liquor is passed outside the drum to remove Si(OCH ２ CH ３ ) ４ is hydrolyzed to give Si(OH) ４ and thereafter said tanning liquor is added to said raw hides in said drum.

7. 7. The method of claim 6, The tanning solution is a mixture of an aqueous solution having a pH in the range of 1.5 to 2.0 and Si(OCH ２ CH ３ ) ４ and in a volume ratio (v / v) of 1 / 1 to 25 / 1, preferably 1 / 1 to 10 / 1.

8. In the method of claim 1 or 2, The compound of formula (I) is Si(OCH ２ CH ３ ) ４ The method according to claim 1, wherein

9. 9. The method of claim 8, The tanning solution contains, by weight relative to the weight of the raw hides: 1 to 1200% water, a sufficient amount of salt, preferably sodium chloride, to prevent swelling of the raw hides; 5 to 100%, preferably 10 to 60%, more preferably 25 to 45% Si(OCH ２ CH ３ ) ４ A method comprising:

10. 10. The method of claim 8 or 9, When carrying out step (B), the tanning solution is prepared by adding Si(OCH) in an amount of 5 to 100%, preferably 10 to 60%, more preferably 25 to 45% by weight relative to the weight of the raw hides. ２ CH ３ ) ４ to said drum.

11. The method of any one of claims 8 to 10, A method characterized in that the pH of the raw skins and the aqueous solution in step (A) is adjusted to a value in the range of 1.5 to 10.5, preferably in the range of 1.7 to 1.9, by adding an acid selected from, for example, formic acid, sulfuric acid, and mixtures thereof.

12. The method of any one of claims 8 to 10, A method characterized in that the pH of the raw skins and the aqueous solution in step (A) is set to a value in the range of 2.1 to 10.

5.

13. 13. The method of claim 12, Si(OCH ２ CH ３ ) ４ before adding the raw skins and the aqueous solution in step (A) to a pH value in the range of 2.1 to 10.5, preferably in the range of 4.0 to 8.0, more preferably in the range of 4.0 to 5.

0.

14. The method of any one of claims 1 to 13, At the end of step (B), the raw hides are removed from the drum and dried.

15. The method of any one of claims 1 to 13, A method comprising the step (C).

16. 16. The method of claim 15, A method characterized in that during step (C), the raw hides are treated with a basifying solution.

17. 17. The method of claim 16, The method characterized in that step (C) is carried out in the drum by adding a basifying agent selected from sodium formate, sodium bicarbonate, sodium acetate, calcium formate, sodium carbonate and mixtures thereof in an amount ranging from 0.5 to 20% by mass relative to the mass of the raw hides.

18. 17. The method of claim 16, Step (C) is performed outside the drum and includes the following steps: (C1) At the end of step (B), the raw hides are removed from the drum. (C2) Place the raw hides flatly on top of each other in a container. (C3) Filling the container with the basifying solution to completely immerse the raw hides. The basifying solution comprises a basifying agent selected from sodium formate, sodium bicarbonate, sodium acetate, calcium formate, sodium carbonate, and mixtures thereof. (C4) The raw hides are allowed to stand in the basifying solution in the container for, for example, at least 1 hour. A method comprising:

19. 20. The method of claim 18, The method is characterized in that the basifying agent is selected from sodium bicarbonate, sodium acetate and mixtures thereof, and the amount of the basifying solution is in the range of 0.1 to 10% by mass relative to the mass of the raw hides.

20. Tanned raw hide obtained by the method of any one of claims 1 to 19.

21. 1. A method for preparing tanned leather from rawhide, comprising the steps of: (i) processing said rawhide to obtain raw hides ready for tanning; (ii) Tanning the tanning-ready raw hides according to any one of the methods of claims 1 to 19. (iii) Polishing and / or finishing the tanned raw hides obtained at the end of step (ii) to obtain finished tanned leather. A method comprising:

22. A method for detanning the raw leather according to claim 20 and / or the raw leather obtained by the method of any one of claims 1 to 19 and / or the finished tanned leather obtained according to claim 21, A method comprising at least one step of immersing the raw hides and / or the tanned leather in a basifying solution to bring the pH of the raw hides and / or the tanned leather to a value of 10.5 or higher, preferably 11.5 or higher, and desirably in the range of 11.5 to 13.0.

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