Classifications

• • C—CHEMISTRY; METALLURGY
  • C14—SKINS; HIDES; PELTS; LEATHER
  • C14C—CHEMICAL TREATMENT OF HIDES, SKINS OR LEATHER, e.g. TANNING, IMPREGNATING, FINISHING; APPARATUS THEREFOR; COMPOSITIONS FOR TANNING
  • C14C3/00—Tanning; Compositions for tanning
  • C14C3/02—Chemical tanning
  • C14C3/08—Chemical tanning by organic agents

Definitions

• TITLE Skin tanning process, leather preparation method and detanning process
• the present invention relates to a process for tanning hides using a silicon compound as a tanning agent, a method for preparing leather using such a process.
• the present invention also relates to a process for detanning tanned skins and leathers thus obtained.
• Preparing leather from animal skins requires many steps. We can classify all of these stages into three large groups which can be defined as follows: i) the stages of skin preparation, ii) the stages of tanning operations, and iii) the stages of grinding and finishing. .
• the raw animal skins are received. These skins can be sorted according to their quality, their size, their weight, etc. During these preparation stages, the parts of the skins that we do not wish to keep, such as for example the legs, are cut out and eliminated. .
• the skins are then cleaned. To do this, the skins are soaked in a large volume of water, for example in a fuller (rotating barrel) or in a sewing machine (stationary tank with moving blades). An antiseptic can be added. Once cleaned, the skins are shaved to remove hair, for example by chemical means.
• the skins also undergo a fleshing stage which consists of removing the subcutaneous tissues. These stages are called river stages.
• skins which can be so-called “pickled” skins or so-called “delimed” skins.
• “Pickled” skins are skins with high salinity and a low pH, generally below 3.0.
• “Delimed” skins are skins coming out of river stages with a pH generally between 7.5 and 9.0.
• the skins prepared as indicated above for example “pickled” skins and “delimed” skins, are degreased. If necessary, these skins are rehydrated. At this stage, the hides are putrescible and ready to be tanned.
• the tanning stage itself consists of a chemical treatment to transform these putrescible skins into rot-proof and resistant leathers. The leathers obtained are then drained, rinsed and possibly dried.
• the grinding and finishing stages are the stages which make it possible to make the leathers obtained at the end of the tanning operations usable for the manufacture of leather objects. These steps may include steps of spinning, setting to thickness, stretching, retanning, dyeing, food.
• the finishing stages may include stages during which the leather is softened, smoothed, satined, printed, stages giving the leather, for example, properties of resistance to stains, abrasion, water or light. They can also give leathers aesthetic properties, such as shine, color, a velvety, satin or grained appearance, etc.
• the key step is the tanning step itself, during which the hides ready to be tanned are tanned in order to be transformed into rot-proof leathers thanks to the action of agents tanning.
• the skins are made up of collagen fibers.
• the tanning agents form bonds between the collagen fibers of the hides, helping to stabilize these hides and transforming them into strong, rot-proof leather.
• the European Union imposes a restriction on the marketing of articles whose Cr 6+ content in leather in contact with the skin is greater than 3 mg/kg (EU regulation n°301/2014 amending Annex XVII of Regulation 1907/2006).
• the European Union is even considering lowering this threshold in the years to come.
• the leather industry is therefore looking for alternative solutions to chrome for tanning hides.
• Glutaraldehyde can be used as a tanning agent: however, this compound has been classified as a Substance of Extreme Concern by ECHA (European Chemical Agency) as part of the European REACH regulation.
• the substance is a respiratory and skin sensitizer.
• Vegetable tannins can also be used for tanning hides.
• the large quantity of product required and the hardness of the resulting leathers limit the use of these tannins to specific applications.
• tanning agents may be used, including metals such as aluminum, iron, titanium or zirconium, as well as synthetic organic compounds. Furthermore, the manufacturing of leather or leather articles generates leather waste (scratches, splits, manufacturing scraps). When the hides have been tanned in the presence of chromium, this waste is difficult to recover.
• the effluent from the chrome tanning process includes unreacted chromium. Effluents must be treated before discharge into the natural environment.
• the present invention relates to a process for tanning hides ready to be tanned comprising the following steps:
• the hides ready to be tanned are soaked in a drum in an aqueous solution and the pH of the hides and the aqueous solution is brought to a value ranging from 1.5 to 10.5 by adding an acid or from a base,
• step B) the skins from step A) are treated using a tanning solution consisting of, by mass relative to the mass of the skins: o 1 to 1200% water, o optionally, a sufficient quantity of salt to prevent swelling of the skin, and o 1 to 100% of a compound of formula (I):
• R 1 is chosen to be a hydrogen atom, a C1-C10 alkyl group, an aryl group, a C2 group -C10 alkenyl, a C2-C10 alkynyl group, a polyalkylene oxide group or its derivatives, R 1 being optionally substituted by one or more amine, ammonium, amides, ketones, esters, aldehydes, thiols or thioethers groups,
• R 2 is chosen as being a hydrogen atom, a C1-C10 alkyl group, an aryl group, a C2-C10 alkenyl group, a C2-C10 alkynyl group, a polyalkylene oxide group or its derivatives, R 2 being optionally substituted by one or more amine, ammonium, amides, ketones, esters, aldehydes, thiols or thioethers groups, said skins being treated using said tanning solution until penetration of the skins by said tanning solution,
• the pH of the skins obtained at the end of step B) is increased to a value ranging from 2.1 to 10.5, preferably ranging from 4.0 to 8.0.
• the process according to the invention makes it possible to obtain tanned skins free of metals.
• the tanned hides obtained with the tanning process according to the invention are free of chromium.
• the skins obtained with the tanning process according to the invention have a satisfactory shrinkage temperature for the manufacture of leather articles (shoes, leather goods, gloves, automobiles, furniture). These skins can thus be used to shape leather objects without risk to the health of future users of these objects, whatever the conditions of use of these objects.
• these skins can be detanned so as to revalue them.
• the present invention also relates to tanned hides capable of being obtained by the above tanning process.
• the present invention also relates to a method of preparing leather from raw hides comprising the following steps: i) a step of preparing raw hides in order to obtain hides ready to be tanned, ii) a step of tanning the hides ready to be tanned, said tanning step being carried out in accordance with the tanning process as described above, iii) a step of grinding and/or finishing the tanned hides obtained at the end of step ii) in order to obtain finished leathers.
• the present invention also relates to a process for detanning skins obtained by the tanning process as described above and/or finished leathers obtained according to the leather preparation method described above comprising at least one step during which said skins and/or leathers are soaked in a basifying solution in order to bring the pH of said skins and/or leathers to a value greater than or equal to 10.5, preferably to a value ranging from 11, 5 to 13.0.
• the skins concerned by the tanning and detanning processes according to the invention can be any skins containing collagen, whether these skins are synthetic or natural. These skins can for example come from animals whose skin contains collagen, such as cattle, sheep, goats, reptiles (snakes, lizards, crocodilians, alligatoridae), fish, birds, amphibians, pigs.
• skin ready to be tanned we mean skins resulting from skin preparation operations as described above, for example pickled or delimed skins, which have also been degreased.
• rehydration and degreasing operations are well known to those skilled in the art.
• the degreaser can in a known manner be chosen from surfactants, for example nonionic and anionic surfactants.
• the term “raw skins” means natural or synthetic skins containing collagen, but which have not yet undergone the skin preparation steps as described above, making these hides ready to be tanned.
• step A) of the tanning process according to the invention the skins ready to be tanned are soaked in a drum in an aqueous solution and the pH of the skins and of the aqueous solution is brought to a value ranging from 1.5 to 10.5 by addition of an acid or a base.
• the fuller is a rotating drum well known to those skilled in the art.
• the term fuller means any container configured to receive the skins to be tanner and equipped with a system allowing the mixing of the skins and the aqueous solution.
• a seamstress falls within the definition of a fuller according to the present application.
• the aqueous solution may include a salt.
• This salt has the function of preventing swelling of the skin in the aqueous solution.
• salt is understood to mean an ionic compound of cations and anions forming a neutral product without a net electric charge.
• the salt can for example be chosen from potassium chloride, sodium chloride and mixtures thereof.
• the aqueous solution will preferably include a salt.
• the preparation of such a salty solution is within the reach of those skilled in the art. Determining the quantity of salt, for example sodium chloride, necessary to prevent swelling of the skins is within the reach of those skilled in the art.
• the aqueous solution may comprise from 1 to 1200% water, by mass relative to the mass of the skins, and from 6 to 12% sodium chloride, by mass relative to the mass of the skins. water.
• the pH of the skins and the aqueous solution is increased to a value ranging from 1.5 to 10.5 by adding an acid or a base.
• the pH of the skins and of the aqueous solution is brought to a value ranging from 1.5 to 2.0, preferably ranging from 1.7 to 1.9, for example by adding one or several acids used alone or in a mixture, for example by adding an acid chosen from formic acid, sulfuric acid and mixtures thereof.
• bringing the pH of the hides and the aqueous solution to such an acidic pH makes it possible to add the tanning solution directly to the drum in the form of a solution of the compound Si(OH)4 , the latter having been previously prepared outside the drum from a compound of formula (I) above, for example from Si(OCH2CH3)4.
• the pH of the skins and of the aqueous solution of step A) is increased to a value ranging from 2.1 to 10.5.
• bringing the pH of the hides and of the aqueous solution of step A) to a value ranging from 2.1 to 10.5 makes it possible to prepare the tanning solution in-situ, in other words in the drum, by adding a solution of the compound Si(OCH2CH3)4, while maintaining a relatively high pH during the treatment step with the tanning solution, for example a pH of approximately 7.0, and free from a subsequent basification stage.
• step B) the skins of step A) are treated with a tanning solution.
• the aqueous solution from step A) can be evacuated from the drum or not. In the case where the aqueous solution from step A) is evacuated from the drum, this emptying is preferably done without rinsing the skins.
• the tanning solution consists of, by mass relative to the mass of the skins: o 1 to 1200% water, o optionally, a sufficient quantity of salt, preferably sodium chloride, to prevent swelling of the skins, and o 1 to 100% of a compound of formula (I): in which Y1, Y2, Y3 and Y4 are chosen independently of each other as being a halogen atom, a -[OSiO m R 1 3-m]n group or an -OR 2 group, two or more - groups [OSiO m R 1 3-m]n and -OR 2 which can be connected together by a covalent bond, in which:
• R 1 is chosen to be a hydrogen atom, a C1-C10 alkyl group, an aryl group, a C2 group -C10 alkenyl, a C2-C10 alkynyl group, a polyalkylene oxide group or its derivatives, R 1 being optionally substituted by one or more amine, ammonium, amides, ketones, esters, aldehydes, thiols or thioethers groups,
• R 2 is chosen as being a hydrogen atom, a C1-C10 alkyl group, an aryl group, a C2-C10 alkenyl group, a C2-C10 alkynyl group, a polyalkylene oxide group or its derivatives, R 2 being optionally substituted by one or more amine, ammonium, amides, ketones, esters, aldehydes, thiols or thioethers groups.
• C1-C10 alkyl a saturated hydrocarbon chain, linear or branched, comprising from 1 to 10 carbon atoms, such as for example a methyl, ethyl, isopropyl, tert-butyl, pentyl, etc. group.
• aryl group an aromatic group, preferably comprising from 5 to 10 carbon atoms, comprising one or more rings and optionally comprising a heteroatom, in particular an oxygen, a nitrogen or a sulfur, such as for example a phenyl group, furan, indole, pyridine, naphthalene, etc.
• C2-C10 alkenyl a hydrocarbon chain, linear or branched, comprising at least one unsaturation and comprising from 2 to 10 carbon atoms, such as for example an ethenyl (vinyl), propenyl, 2,4-hexafienyl group, etc...
• C2-C10 alkynyl group a hydrocarbon chain, linear or branched, comprising at least one double unsaturation and comprising from 2 to 10 carbon atoms, such as for example an acetylene, propyne, butyne group, etc.
• polyalkylene oxide polymers of ethylene oxide units, the number of ethylene oxide units is an integer greater than or equal to 1,
• derivatives of polyalkylene oxides is meant one or more synthetic polymers chosen from copolymers of carboxylic acids and carboxylic esters of poly(alkylene glycol), copolymers of carboxylic acids and poly(alkylene amide glycol), copolymers of carboxylic acids and poly(alkylene glycol) imide, copolymers of carboxylic acids and poly(alkylene glycol) vinyl ethers, neutralized or non-neutralized, and mixtures thereof.
• the tanning solution is thus free of any metal other than silicon.
• the tanning solution is free of chromium.
• Y1, Y2, Y3 and Y4 are chosen independently of each other to be a chlorine atom, an -OH group or an -OCH2CH3 group.
• the compound of formula (I) is Si(OH)4.
• the pH of the skins and of the aqueous solution of step A) will have previously been increased to a value ranging from 1.5 to 2.0, preferably ranging from 1.7 to 1.9.
• the tanning solution can then consist of, in mass relative to the mass of the hides: o 1 to 1200% water, o A sufficient quantity of salt, preferably sodium chloride, to prevent swelling of the skin, and o 5 to 60%, preferably 5 to 30%, more preferably 10 to 20%, of Si(OH) 4 .
• the tanning solution is preferably prepared outside the drum by hydrolysis of the compound Si(OCH2CH3)4 into Si(OH)4, the tanning solution then being added to the skins in the drum.
• the tanning solution can be prepared by mixing an aqueous solution with a pH ranging from 1.5 to 2.0 and Si(OCH2CH3)4 in a volume ratio (v/v) ranging from 1/1 to 25 /1, preferably ranging from 1/1 to 10/1.
• the Si(OH)4 thus obtained is added to the drum, in a content, by mass relative to the mass of the skins, ranging from 5 to 60%, preferably from 5 to 30%, more preferably 10 to 20%. .
• This content can be adjusted depending on the type of hides to be tanned and the thickness of these hides.
• salt such as for example sodium chloride, can also be added to the drum, for example in a content, by mass relative to the mass of Si(OH)4 added, ranging from 6 to 12%.
• water can be present in a mass content relative to the mass of the skins, ranging from 1 to 1200%.
• the fuller is preferably left to rotate for a period of time allowing the silicic acid to penetrate the skins.
• This duration can thus vary depending on the thickness of the hides and the nature of the hides: for example, the penetration of the hide to be tanned with silicic acid may require a longer duration for a bovine hide than for a hide. of sheep.
• the duration of this step can be easily determined by those skilled in the art depending on the skin to be tanned.
• the rotation of the drum is preferably carried out at room temperature, in other words a temperature less than or equal to 30°C, preferably a temperature ranging from 20 to 25°C.
• the skins can be taken directly out of the fuller and left to dry.
• the skins are taken out of the drum and left to dry at the end of step B).
• we obtain dried leathers which can be directly stored.
• the pH of the latter is increased to a value ranging from 2.1 to 10.5, preferably ranging from 4.0 to 8.0 .
• This optional step C will be described below.
• the compound of formula (I) is Si(OCH2CH3) 4 .
• the tanning solution can then consist of, by mass relative to the mass of the skins: o 1 to 1200% water, o A sufficient quantity of salt, preferably sodium chloride, to prevent swelling of the skins, and o 5 to 100%, preferably 10 to 60%, more preferably 25 to 45%, of Si(OCH 2 CH 3 ) 4 .
• salt preferably sodium chloride
• the tanning solution can be produced directly in situ by adding Si(OCH2CH3) 4 to the drum in a content, by mass relative to the mass of the hides, ranging from 5 to 100%, preferably ranging from 10 to 60%, more preferably ranging from 25 to 45%.
• water can be present in a mass content relative to the mass of the skins, ranging from 1 to 1200%.
• Si(OCH2CH3) 4 the hydrolysis of Si(OCH2CH3) 4 to Si(OH) 4 will thus take place within the drum.
• Si(OCH2CH3) 4 is added to the drum, two insoluble phases are present in the drum, water on the one hand, and Si(OCH2CH3) 4 on the other hand.
• the fuller is preferably left to rotate for the time necessary for the complete hydrolysis of the Si(OCH2CH3) 4 into Si(OH) 4 , in order to obtain a single soluble phase of silicic acid solution and to allow the acid silicic acid to penetrate the skin.
• this duration can range from 1 hour to a week.
• the duration necessary for silicic acid to penetrate the skins may depend on the nature of the skins. This duration is easily determinable by those skilled in the art.
• the rotation of the drum is preferably carried out at room temperature, in other words a temperature less than or equal to 30°C, preferably a temperature ranging from 20 to 25°C.
• duration of the complete hydrolysis of Si(OCH2CH3) 4 to Si(OH) 4 can also depend on the pH of the tanning solution.
• the compound of formula (I) is Si(OCH2CH3) 4 and the pH of the skins and of the aqueous solution of step A) will have previously been brought to a value ranging from 1.5 to 2.0, preferably ranging from 1.7 to 1.9.
• the skins can be taken directly out of the fuller and allowed to dry, as described above. Alternatively, they can be subjected to a basifying treatment as will be described below.
• the compound of formula (I) is Si(OCH2CH3)4 and the pH of the skins and of the aqueous solution of step A) will have previously been increased to a value ranging from 2.1 to 10 ,5.
• the pH of the aqueous solution and the skins is adjusted to a pH ranging from 2.1 to 10.5, preferably from 4.0 to 8.0, more preferably from 4.0 to 5, 0 before adding the Si(OCH2CH3)4 to the drum as described above.
• the tanning solution thus has a pH ranging from 2.1 to 10.5, preferably from 4.0 to 8.0, more preferably from 4.0 to 5.0.
• Such a pH of the tanning solution makes it possible to have simultaneously in the drum, on the one hand a hydrolysis reaction of Si(OCH2CH3)4 to Si(OH)4, and on the other hand a polymerization reaction of Si(OH) )4.
• the skins obtained at the end of step B) can be directly used for subsequent working steps or be dried to complete the polymerization and stored.
• the pH of the tanning solution ranges from 2.1 to 10.5, preferably from 4.0 to 8.0, more preferably from 4.0 at 5.0, it is possible to carry out a step of treating the skins with a basifying solution as described below.
• the tanning process according to the invention may comprise an additional step, step C).
• step C) the pH of the skins obtained at the end of step B) is increased to a value ranging from 2.1 to 10.5, preferably ranging from 4.0 to 8.0.
• step C) is preferably implemented when the tanning solution is too acidic to trigger the polymerization of Si(OH)4, for example when the pH of the tanning solution is less than or equal to 2.0 .
• the skins can for example be treated using a basifying solution.
• the basification of the bath containing the skins will allow and/or accelerate the polymerization of Si(OH)4 within the skins. Bonds between the silicon and the collagen of the skin fibers will be able to form and a three-dimensional Si-O-Si network linked to the collagen of the skin will be able to be created, thus stabilizing the skins.
• a basifying agent for example chosen from sodium formate. , sodium bicarbonate, sodium acetate, calcium formate, sodium carbonate and their mixtures, in a content, by mass relative to the mass of the skins, ranging from 0.5 to 20%.
• the treatment using a basifying solution can be carried out outside the drum.
• processing may include the following steps:
• the skins are installed in a tray, placed flat, one on top of the other,
• the tank is filled with said basifying solution so as to completely immerse all of the skins, said basifying solution comprising a basifying agent chosen from sodium formate, sodium bicarbonate, sodium acetate, calcium formate , sodium carbonate and their mixtures,
• the skins are left in the basifying solution in the tank, to rest, for example for at least 1 hour.
• the basifying agent content is calculated according to the desired final pH.
• the skins can be removed from the drum with or without prior rinsing.
• the skins can be dried in order to carry out the polymerization of Si(OH)4 by evaporation.
• the skins obtained by the process according to the invention are tanned and rot-proof. These skins generally have a white color. They have an appearance which makes them appear round and fuller than in their initial state before tanning. These skins have a shrinkage temperature ranging from 65 to 90°C. Such a shrinkage temperature allows these skins to be able to undergo treatments during which they can be subjected to relatively high temperatures, for example of the order of 50°C to 75°C, such as putting thickness, hot dyeing for better fixation of dyes, etc. while maintaining their flexibility and the quality of their appearance.
• the present invention also relates to a method of preparing leather from raw hides comprising the following steps: i) a step of preparing the raw hides in order to obtain hides ready to be tanned, ii) a step of tanning the hides ready to be tanned, said tanning step being carried out in accordance with the tanning process described above, iii) a step of grinding and/or finishing the tanned skins obtained at the end of step ii) in order to obtain finished leathers.
• the present invention also relates to a process for detanning tanned skins obtained by the process described above and/or leathers obtained from the preparation method described above, comprising at least one step during which said skins and/or leathers are soaked in a basifying solution in order to bring the pH of said skins and/or leathers to a value greater than or equal to 10.5, preferably to a value ranging from 11.5 to 13 ,0.
• the tanned skins can for example be in a “dry white” state.
• dry white means a tanned skin, dried but not wrought.
• Tanned hides can alternatively be in the state of wet white, stain, crust, finished or semi-finished leather, scratches, splits, terms well known to those skilled in the art.
• Leather scraps and leather dust from wet white, dry white, stain, crust or finished leather can also be detanned by the detanning process according to the invention.
• tanned skins and/or finished leathers can be soaked in an aqueous solution, for example in a fuller.
• an aqueous solution for example in a fuller.
• the aqueous solution may include a degreaser.
• the aqueous solution may comprise, by mass relative to the mass of the skins: from 50 to 2000% water, from 0.1 to 2% of a degreaser.
• the degreaser can be chosen from surfactants, for example from nonionic and anionic surfactants.
• the purpose of such a step is to degrease and rehydrate the skins and/or leather.
• the drum is rotated for a period of time allowing this degreasing and this rehydration, for example for a period ranging from 15 min to overnight, for example from 45 min to 1 hour 30 mins, at a temperature ranging from 10 to 80° C, for example from 30 to 45°C.
• the fuller can then be drained and the hides and/or hides can be rinsed in the fuller at room temperature.
• the skins and/or leathers are soaked in an aqueous solution comprising a basifying agent in order to bring the pH of the skins and/or leathers to a value greater than or equal to 10.5, preferably to a value ranging from 11.5 at 13.0.
• the basifying agent can for example be chosen from sodium bicarbonate, sodium carbonate, ammonia, sodium hydroxide and their mixtures.
• the basifying agent can for example be added to the aqueous solution in several stages, with the use of different basifying agents or not for each stage, and at a working temperature which can vary from one stage to another.
• a first addition of basifying agent can bring the pH of skins and/or leathers to a value ranging from 7.0 to 10.0.
• basifying agent in order to bring the pH of the skins and/or leathers to a value ranging from 11.5 to 13.0.
• wet whites, “dry whites”, stains, crusts, finished leathers, scratches, splits, dust and scraps of leather thus detanned can either remain in the form of non-crosslinked protein or be revalued, for example by being tanned again or by being used for the manufacture of gelatin, the manufacture of protein for animal feed or the manufacture of fertilizers for the fields, etc.
• the pH of this mixture is adjusted to a value ranging from 1.5 to 2.0 using a strong acid, such as hydrochloric acid or sulfuric acid, this list not being exhaustive.
• the hydrolysis reaction of Si(OCH2CH3)4 to Si(OH)4 is exothermic.
• the mixture is maintained at the desired temperature, for example around 30°C by means of a cooling bath.
• the mixture is stirred vigorously for 15 min to 120 min.
• the duration of the hydrolysis reaction can range from 20 min to 2 hours.
• 10% by mass of sodium chloride is added, relative to the total mass of the silicic acid solution previously prepared.
• Sheep skins are tanned according to the tanning process according to the invention as follows:
• the hides ready to be tanned are pickled hides from a storage pickle or delimed hides previously degreased and rehydrated according to the know-how of those skilled in the trade.
• the skins are weighed.
• the skins are placed in a drum in a salt solution.
• the pH of the skins and the salt solution is brought to a value ranging from 1.5 to 2.0, for example by adding sulfuric acid alone or mixed with formic acid.
• the drum is rotated for 4 hours at room temperature, i.e. 25°C.
• 5% of sodium formate by mass relative to the mass of the skins is added to the drum at a temperature of 25°C.
• the drum is rotated for 1 hour.
• the pH measured on the skins ranges from 3.8 to 4.0.
• the drum is emptied and the skins are rinsed.
• the skins are white, round and have a beautiful appearance.
• Bovine hides are tanned according to the tanning process according to the invention as follows:
• the hides ready to be tanned are pickled hides from a storage pickle or delimed hides previously degreased and rehydrated according to the know-how of those skilled in the trade.
• the skins are weighed.
• the skins are placed in a drum in a salt solution.
• the pH of the skins and the salt solution is brought to a value ranging from 1.5 to 2.0, for example by adding sulfuric acid alone or mixed with formic acid.
• the drum is rotated overnight at room temperature, i.e. 25°C.
• 5% of sodium formate by mass relative to the mass of the skins is added to the drum at a temperature of 25°C.
• the drum is rotated for 1 hour.
• the pH measured on the skins ranges from 3.8 to 4.0.
• the drum is emptied and the skins are rinsed.
• the skins are white, round and have a beautiful appearance.
• Sheep skins are tanned according to the tanning process according to the invention as follows:
• the hides ready to be tanned are pickled hides from a storage pickle or delimed hides previously degreased and rehydrated according to the know-how of those skilled in the trade.
• the skins are weighed.
• the skins are placed in a drum in a salt solution.
• the pH of the skins and the salt solution is brought to a value ranging from 1.5 to 2.0, for example by adding sulfuric acid alone or mixed with formic acid.
• the drum is rotated for 4 hours at room temperature, i.e. 25°C.
• 5% of sodium formate by mass relative to the mass of the skins is added to the drum at a temperature of 25°C.
• the drum is rotated for one minute and then stopped for 1 hour.
• the pH measured on the skins ranges from 3.8 to 4.0.
• the skins are white, round and have a beautiful appearance.
• Bovine hides are tanned according to the tanning process according to the invention as follows:
• the hides ready to be tanned are pickled hides from a storage pickle or delimed hides previously degreased and rehydrated according to the know-how of those skilled in the trade.
• the skins are weighed.
• the skins are placed in a drum in a salt solution.
• the pH of the skins and the salt solution is brought to a value ranging from 1.5 to 2.0, for example by adding sulfuric acid alone or mixed with formic acid.
• the drum is rotated overnight at room temperature, i.e. 25°C.
• 5% of sodium formate by mass relative to the mass of the skins is added to the drum at a temperature of 25°C.
• the drum is rotated for one minute and then stopped for 1 hour.
• the pH measured on the skins ranges from 3.8 to 4.0.
• Sheep skins are tanned according to the tanning process according to the invention as follows:
• the hides ready to be tanned are pickled hides from a storage pickle or delimed hides previously degreased and rehydrated according to the know-how of those skilled in the trade.
• the skins are weighed.
• the skins are placed in a drum in a salt solution.
• the pH of the skins and the salt solution is brought to a value ranging from 1.5 to 2.0, for example by adding sulfuric acid alone or mixed with formic acid.
• This quantity of Si(OCH2CH 3 )4 represents the equivalent of 13% of Si(OH)4 by mass relative to the mass of the skins.
• the drum is rotated for 4 hours at room temperature, i.e. 25°C.
• the drum is rotated for 20 minutes at 25°C.
• 5% of sodium formate by mass relative to the weight of the skins is added to the drum at a temperature of 25°C.
• the drum is rotated for 1 hour.
• the pH measured on the skins ranges from 3.8 to 4.0.
• 5% of sodium formate by mass relative to the weight of the skins is added to the drum at a temperature of 25°C.
• the drum is rotated for 1 night.
• the final pH measured on the skins ranges from 4.0 to 4.2.
• the drum is emptied and the skins are rinsed.
• the skins are white, round and have a beautiful appearance.
• Sheep skins are tanned according to the tanning process according to the invention as follows:
• the hides ready to be tanned are pickled hides from a storage pickle or delimed hides previously degreased and rehydrated according to the know-how of those skilled in the trade.
• the skins are weighed.
• the skins are placed in a drum in a salt solution.
• the pH of the skins and the salt solution is brought to a value ranging from 1.5 to 2.0, for example by adding sulfuric acid alone or mixed with formic acid.
• This quantity of Si(OCH2CH 3 )4 represents the equivalent of 13% of Si(OH)4 by mass relative to the mass of the skins.
• the drum is rotated for 4 hours at room temperature, i.e. 25°C.
• the drum is rotated for 20 minutes at 25°C.
• Step C) Firstly, 5% of sodium formate by mass relative to the weight of the skins is added to the drum at a temperature of 25°C. The drum is rotated for one minute and then stopped for 1 hour. The pH measured on the skins ranges from 3.8 to 4.0.
• the drum is emptied and the skins are rinsed.
• the skins are white, round and have a beautiful appearance.
• Bovine hides are tanned according to the tanning process according to the invention as follows:
• the hides ready to be tanned are pickled hides from a storage pickle or delimed hides previously degreased and rehydrated according to the know-how of those skilled in the trade.
• the skins are weighed.
• the skins are placed in a drum in a salt solution.
• the pH of the skins and the salt solution is brought to a value ranging from 1.5 to 2.0, for example by adding sulfuric acid alone or mixed with formic acid.
• Si(OH)4 hydrolyzed from Si(OCH2CH3)4 as described in Example 1 is added in several steps according to the following procedure. The percentages are given in mass in relation to the mass of the skins:
• the drum is rotated for 20 minutes.
• the drum is emptied and the skins are rinsed.
• the skins are white, round and have a beautiful appearance.
• Sheep skins are tanned according to the tanning process according to the invention as follows:
• the skins ready to be tanned are pickled skins from a storage pickle or delimed skins previously degreased and rehydrated according to the know-how of those skilled in the art.
• the skins are weighed.
• the skins are placed in a drum in a salt solution.
• the pH of the skins and the salt solution is brought to a value ranging from 1.5 to 2.0, for example by adding sulfuric acid alone or mixed with formic acid.
• the drum is rotated for 4 hours at room temperature, i.e. 25°C.
• the drum is emptied and the skins are rinsed.
• the skins are taken out of the drum and placed on a rack to drain for the time necessary for the surface water to drain.
• the skins are then framed damp and left to rest in the open air while they dry, generally overnight or a little longer depending on the thickness of the skin and the daily weather.
• Bovine hides are tanned according to the tanning process according to the invention as follows:
• the skins ready to be tanned are pickled skins from a storage pickle or delimed skins previously degreased and rehydrated according to the know-how of those skilled in the art.
• the skins are weighed.
• the skins are placed in a drum in a salt solution.
• the pH of the skins and the salt solution is brought to a value ranging from 1.5 to 2.0, for example by adding sulfuric acid alone or mixed with formic acid.
• the drum is rotated overnight at room temperature, i.e. 25°C.
• the drum is emptied and the skins are rinsed.
• the skins are taken out of the drum and placed on a rack to drain for the time necessary for the surface water to drain.
• the skins are then framed damp and left to rest in the open air while they dry, generally overnight or a little longer depending on the thickness of the skin and the daily weather.
• Sheep skins are tanned according to the tanning process according to the invention as follows:
• the skins ready to be tanned are pickled skins from a storage pickle or delimed skins previously degreased and rehydrated according to the know-how of those skilled in the art.
• the skins are weighed.
• the skins are placed in a drum in a salt solution.
• the pH of the skins and the salt solution is brought to a value ranging from 2.1 to 10.5 for example by adding sulfuric acid alone or mixed with formic acid or by adding basifying agents.
• the pH of the skins and the salt solution is adjusted to a value ranging from 4.0 to 5.0, for example to 4.2.
• This quantity of Si(OCH2CH 3 )4 represents the equivalent of 13% of Si(OH)4 by mass relative to the mass of the skins.
• the drum is rotated for a period of 7 days at room temperature, i.e. at 25°C
• the drum is then emptied and the skins are rinsed.
• the shrinkage temperature for the tanned skins obtained in Examples 2 to 9 and 11 was measured according to the following protocol:
• thermometer is placed in the same beaker, fixed on the retractometer. The base of the thermometer is placed in front of the tanned skin sample,
• the assembly (beaker filled with water + retractometer containing the sample + thermometer) is placed on a heating plate,
• shrinkage temperatures of hides tanned with the tanning process according to the invention are particularly satisfactory. Such shrinkage temperatures allow these skins to be suitable for undergoing treatments during which they can be subjected to relatively high temperatures, for example of the order of 50 to 75°C, such as thicknessing. , hot dyeing for better fixation of dyes, etc. while maintaining their flexibility and the quality of their appearance.
• Example 13 The skins obtained in Examples 2 to 11 above can be easily detanned, according to the detanning process according to the invention described below.
• the tanned hides are introduced into a drum.
• the skins are weighed.
• the mass will serve as a reference.
• the drum is rotated for a period ranging from 15 minutes to overnight, ideally between 45 minutes and 1 hour 30 minutes, at a temperature ranging from 10 to 80°C, ideally from 30 to 45°C.
• the drum is emptied and the skins are rinsed at room temperature, i.e. 25°C.
• a basifying agent chosen from sodium bicarbonate, sodium carbonate, ammonia and their mixtures is added to the drum in order to bring the pH of the skins to a value ranging from 7.0 to 10.0, preferably to a value ranging from 8.0 to 9.0.
• the basifying agent is added at a content, by mass relative to the mass of the skins, ranging from 0.1 to 15%, preferably ranging from 1 to 5%.
• the drum is rotated for a period ranging from 15 to 120 minutes, for example ranging from 45 to 90 minutes.
• the temperature ranges from 10 to 80°C, for example from 30 to 45°C.
• Sodium hydroxide is then added to the drum in order to bring the pH of the skins to a value greater than or equal to 10.5, preferably to a value ranging from 11.5 to 13.0.
• the drum is rotated for a period ranging from 30 minutes to 24 hours, for example overnight.
• the temperature ranges from 10 to 30°C, for example from 20 to 25°C.
• the three-dimensional Si-O-Si network linked to the skin's collagen is unraveled and the skins are detanned.
• the skins thus detanned can either remain in the form of non-crosslinked protein or be revalorized. Detanned skins are free of metals, particularly chromium.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Treatment And Processing Of Natural Fur Or Leather (AREA)

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• 2022
  • 2022-09-23 FR FR2209659A patent/FR3140094A1/fr active Pending
• 2023
  • 2023-09-18 KR KR1020257013433A patent/KR20250079170A/ko active Pending
  • 2023-09-18 JP JP2025517577A patent/JP2025532165A/ja active Pending
  • 2023-09-18 US US19/114,198 patent/US20260098311A1/en active Pending
  • 2023-09-18 CN CN202380081225.1A patent/CN120265793A/zh active Pending
  • 2023-09-18 WO PCT/FR2023/051416 patent/WO2024062184A1/fr not_active Ceased
  • 2023-09-18 AU AU2023345810A patent/AU2023345810A1/en active Pending
  • 2023-09-18 EP EP23790716.7A patent/EP4590864A1/de active Pending
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