DESCRIPTION

The invention relates to a tanning process for animal hides and a related tanning agent to be used in the aforementioned tanning process.

The tanning processes are long and complicated processes, consisting of a plurality of successive working phases of an essentially chemical nature, interspersed with substantially mechanical working phases, in which the treated leathers are made rot-proof and aesthetically interesting for the reference market.

The tanning process can be carried out in different ways according to the type of raw hide of origin and the type of product to be obtained.

The operations carried out during the tanning process are usually grouped into four macro-groups: riviera; tanning; retanning, dyeing and fattening and finally finishing.

More specifically, the riviera operations are the first chemical and mechanical operations to which the raw hide is subjected, and are necessary to prepare the latter for the next tanning.

The term tanning refers to the set of operations that make it possible to obtain a stable cross-linking of the collagen fibers of the dermis to obtain a rot-proof material: leather.

The group of retanning, dyeing and fattening operations substantially includes chemical treatments that make it possible to improve the aesthetic and product characteristics of the leather.

Finally, the finishing concerns those processes performed on dry leathers in order to protect their surface and improve the appearance thereof.

As regards the tanning processes, they are usually classified according to the type of tanning agent or the type of bond that these agents are able to establish with the collagen. The tanning agents can be of the inorganic or organic type.

Among the inorganic tanning agents, the use of chromium is widespread, followed by tanning with aluminum, iron, zirconium, titanium or silicon. Among the organic tanning agents there are instead molecules belonging to the chemical class of tannins (synthetic or vegetable), oils, aldehydes, chlorosulfonated paraffins, resins with synthetic polymers.

However, the most commonly used tanning agent is chromium which, thanks to the ability of trivalent chromium to form complexes with the carboxyl groups of collagen fibers, makes the tanning process a relatively simple, economical, rather rapid and versatile enough process for production of leathers intended for different uses.

Disadvantageously, this type of tanning process has a high environmental impact, mainly attributable to the production of waste water, sludge and other waste containing pollutants derived from such metal.

US4526581A and US4313800A describe tanning processes for animal hides using aqueous solutions of copolymers of ethyl acrylate (EA) or aqueous mixtures of metal salts such as zirconium sulfate and Cr ₂ O ₃ and a copolymer based on methacrylates.

The need to develop tanning processes and tanning agents that are free from metals, in particular from chromium, is therefore increasing, in order to reduce the environmental, but also economic, impact of the massive use of this heavy metal.

In order to have new tanning processes widely used in industry, alternative to those with chromium, it is necessary that the leather obtained from these alternative processes is of comparable or higher quality to that obtained with chrome tanning.

In fact, during the tanning operations, bonds are established between the collagen fibers of the treated leather and the tanning agent. In mineral tanning processes these bonds can be of the dative covalent type: relatively strong bonds that allow to obtain a treated leather with a good resistance to chemical agents.

Depending on the type of bonds that are established with the collagen then, the treated leathers have a different temperature stability, which is expressed by the so-called gelatinization or contraction temperature Tg. Tg is essentially the temperature above which collagen begins to be damaged by the action of water.

The higher the Tg, the greater the resistance of the tanned leather to water. It is known that chrome tanning makes it possible to obtain a leather with a particularly high Tg.

Therefore, the identification of tanning agents alternative to chromium represents a challenge for industry experts, precisely because of the excellent tanning qualities of chromium. In fact, chrome tanning allows to obtain a good tanned product from the point of view of tactile sensation and mechanical properties, up to resistance and allergometric compatibility.

In addition, the leather obtained with chrome tanning has a good firmness, that is the ability of the leather surface to keep the grain pattern of the leather intact even when the latter is manipulated and folded.

To date, tanning processes alternative to chromium, such as the vegetable tanning, despite having a lower environmental impact, still does not allow the production of a leather with the qualitative characteristics obtained from chrome tanning.

It is therefore the object of the present invention to propose a tanning process alternative to those known.

Furthermore, it is an object of the invention that such a process overcomes the limitations of chrome tanning processes and improves the quality of the tanned products that can be obtained with the tanning processes alternative to chromium, of the known type.

In particular, the object of the present invention is to provide a tanning process and a related tanning agent free from metals and which allow to produce a leather of comparable or higher quality to that obtained with chrome tanning.

Furthermore, it is an object of the present invention that the aforesaid process allows to obtain a tanned product of a higher quality than that known with metal-free tannings, in particular in terms of whiteness, softness, biodegradability, Tg and firmness.

Furthermore, it is an object of the invention that this tanning process uses tanning agents with a lower environmental impact than known tanning processes, and therefore is more sustainable than these latter.

Furthermore, it is an object of the present invention that this tanning process and related tanning agent can be used for the tanning of any type of hide.

The objects mentioned above and others which will be better highlighted hereinafter are achieved by a tanning process and a tanning agent, as described in claims 1 and 19.

These objects are also achieved through the use of a tanning composition, as reported in claims 20 to 22.

Other characteristics of the tanning process, of the tanning agent and of the composition are specified in the dependent claims. Further features and advantages of the present invention will result from the following detailed and non-limiting description of a preferred embodiment of the invention.

In particular, the applicant has discovered that it is possible to carry out a metal-free tanning process which allows to obtain a leather qualitatively comparable to that obtained with chrome tanning, by using a tanning agent comprising a copolymer obtainable by polymerization of acrylic or methacrylic acid and a monomeric unit, or a salt of such monomeric unit, this monomeric unit having the general formula (I)

[CH ₂ =C(R ¹ )-CO-Z] _n -R ² (I) wherein R ¹ is H or CH ₃ ; Z is selected from 0, NH and N-R ³ ; R ² and R ³ , equal or different from each other, are selected independently of each other from H, CH ₃ , a linear or branched Ci-Ci ₈ alkyl group substituted with one or more alkoxy groups and/or with one or more hydroxyl groups and/or with one or more amino groups and/or with one or more epoxy groups and/or with one or more halogens, and wherein n is 1 or 2.

Preferably, said copolymer can be obtained by polymerization of the monomeric unit with acrylic acid.

Preferably Z is 0.

The term “C1-C18 alkyl group” refers to a linear or branched alkyl group having from 1 to 18 carbon atoms. Specific examples of Ci-Ci ₈ alkyl group include: methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, t-butyl, pentyl, ethyl-hexyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl.

The term “alkoxy group” refers to a linear or branched alkoxy group. Preferably, the alkoxy groups are selected from the groups having a linear or branched chain having from 1 to 5 carbon atoms. Specific examples of this alkoxy group include: methoxyl, ethoxyl, n-propoxyl, iso-propoxyl, n-butoxy, iso-butoxy, t-butoxy, pentoxyl.

The term “amino group” refers to a primary, secondary, tertiary amino group or a quaternary ammonium.

The term “epoxy group” refers to a cyclic ether preferably having from 3 to 5 terms. Specific examples of this epoxy group include: epoxyethane, epoxypropane, epoxybutane.

The preferred halogen is chlorine.

It is not excluded that, according to variant embodiments of the invention, said one or more halogens can comprise fluorine, iodine or bromine.

It is specified that, when the monomeric unit is in the form of salt, the halide salts are preferred, even more preferred are the chlorides.

Particularly preferred is the acrylic copolymer in which R ² is a linear or branched C1-C5 alkyl group substituted with one or more amino groups and/or with one or more alkoxy groups and/or with one or more hydroxyl groups and/or with one or more epoxy groups and/or with one or more halogens.

Preferably, R ² is selected from (CH ₂ ) _m -X, CH(CH ₃ )-X, CH((CH ₂ )m-CH ₃ )-X, (CH ₂ ) _m -CH(CH ₃ )-X, CH(X)-(CH ₂ ) _m -X, (CH ₂ ) _m -N(CH ₃ ) _p , (CH ₂ ) _m -CH(X)-CH ₂ -X, (CH ₂ ) _m -CH(O)CH ₂ with X being OH or a halogen, 1 < m < 18 and 1 < p < 3. More preferably 1 < m < 5.

The preferred X halogen is chlorine.

According to an embodiment of the invention, R ² is a linear or branched C1-C5 alkyl group substituted with one or more amino groups. Preferably according to such an embodiment, in the monomeric unit R ¹ is H or CH ₃ and R ² is (CH ₂ ) _m -N(CH ₃ ) _p with 1 < m < 5 and 1 < p < 3.

Preferred, according to such an embodiment of the invention, are the copolymers in which the monomeric unit, or the salt thereof, is CH ₂ =C(R ¹ )-CO- O-(CH ₂ ) _m -N(CH ₃ ) _p with R ¹ being H or CH ₃ , preferably CH ₃ , and with 1 < m < 5 and 1 < p < 3.

Still preferred are the copolymers in which the monomeric unit, or the salt thereof, has the formula CH ₂ =C(R ¹ )-CO-NH-(CH ₂ ) _m -N(CH ₃ )p with R ¹ being H or CH ₃ , preferably CH ₃ , and with 1 < m < 5 and 1 < p < 3.

According to a preferred embodiment of the invention, R ² is a linear or branched C1-C5 alkyl group substituted with one or more epoxy groups and/or with one or more halogens and/or with one or more hydroxyl groups.

Preferably, R ² is a linear or branched C1-C5 alkyl group substituted with one or more epoxy groups or with one or more halogens or with one or more halogens and one or more hydroxyl groups.

According to an embodiment of the invention, R ² is a linear or branched C1-C5 alkyl group substituted with one or more halogens or with one or more halogens and one or more hydroxyl groups.

Preferably, R ² is selected from (CH ₂ ) _m -X, CH(CH ₃ )-X, CH((CH ₂ ) _m -CH ₃ )-X, (CH ₂ ) _m -CH(CH ₃ )-X, CH(OH)-(CH ₂ ) _m -X, (CH ₂ ) _m -CH(OH)-CH ₂ -X with X being a halogen, and wherein 1 < m < 18. Preferably 1 < m < 5. Particularly, according to such preferred embodiment of the invention, R ² is a linear or branched C1-C5 alkyl group substituted with one or more halogens and one or more hydroxyl groups.

Particularly preferred is the monomeric unit wherein R ² is (CH ₂ ) _m -CH(OH)-CH ₂ - X with X being a halogen, and wherein 1 < m < 18. Preferably 1 < m < 5.

Even more preferred is the monomeric unit of the formula CH ₂ =C(R ¹ )-CO-O- CH ₂ -CH(OH)-CH ₂ -CI with R ¹ being H or CH ₃ , preferably CH ₃ .

According to another embodiment of the invention, the copolymer has the monomeric unit wherein R ² is a linear or branched C1-C5 alkyl group substituted with one or more epoxy groups.

Particularly preferred is the monomeric unit wherein R ² is (CH ₂ ) _m -CH(O)CH ₂ with 1 < m < 18, preferably 1 < m < 5.

Even more preferred is the monomeric unit of the formula CH ₂ =C(R ¹ )-CO-O- CH ₂ -CH(O)CH ₂ with R ¹ being H or CH ₃ , preferably CH ₃ . Some examples not to be considered limitative of the monomeric unit of the invention are reported in the following table A, in which the terms R ¹ , Z, R ² and n are highlighted, grouped by rows, of variants of the monomeric unit having the general formula (I).

Table A

Advantageously, the copolymer of the present invention is provided with a plurality of functional groups, particularly of hydroxyl and halogenated groups sterically suitable to react with the free amino groups of the collagen and the functional groups containing reactive hydrogens of the proteins that make up the collagen of the hide.

The copolymer of the present invention also has high reactivity towards the free carboxyl groups of collagen, thus showing a high tanning capacity and improving the quality of the obtainable tanned leather. Advantageously, the use of the copolymer in the tanning process allows to reduce and possibly eliminate harmful chemical substances such as sulphates and chromates from the waste water since they are not necessary in the tanning process to obtain a high quality leather.

Advantageously, the tanning process according to the preferred embodiment of the invention provides for the use of the tanning agent in one or more of the phases that follow the hide hair removal process, known in jargon as “liming”. More specifically, the tanning agent can be used in deliming, maceration, pickel, pre-tanning, tanning, retanning, dyeing and fattening operations and/or in the intermediate phases among these operations.

To facilitate the diffusion of the copolymer inside the hide to be tanned, the pH of the aqueous bath is acidic, more preferably pH<5.

Preferably, in the aqueous bath the copolymer is used in a quantity comprised between 0.1 % and 20% by weight, preferably between 0.1 % and 10% by weight, more preferably between 0.1 % and 5% by weight, even more preferably between 1 % and 4% by weight, with respect to the pelt weight of the hide to be tanned.

Advantageously, the tanning process according to the invention allows to obtain a very white tanned leather, with the possibility of modifying its softness. Still advantageously, the tanning process of the present invention allows to obtain a leather with a Tg comprised between 65°C and 80°C.

The aforementioned copolymer can be applied to the hide alone or in combination with other tanning agents known per se, such as, by way of example not to be considered as limiting, metal salts, preferably chromium, titanium, zirconium, aluminum, iron, or with derivatives of silicon, glutaraldehyde, acetaldehyde, modified aldehydes, oxazolidines, phosphonium salts, phenol condensates and their derivatives, vegetable or synthetic tannins. According to the preferred embodiment of the process of the invention, before treating the hide with the tanning agent, the hide is treated with a polysiloxane of the general formula (II)

R ⁴ -[Si(R ⁵ )(R ⁷ )-O] _q -R ⁶ (II) wherein R ⁴ , R ⁵ , R ⁶ and R ⁷ , equal or different from each other, are selected independently of each other from H, OH, CH ₃ , a linear or branched Ci-Cis alkyl group, a linear or branched Ci -Ci s alkoxyl group, an optionally substituted aryl group, an ether group, a polyether group, Si(R ⁵ )(R ⁷ )(R ⁶ ), Si(R ⁴ )(R ⁵ )(R ⁶ )-O and wherein 1 < q < 500.

Preferably, the above alkyl group is a linear or branched C2-C18 alkyl group.

Still preferably, 2 < q < 500.

The term “aryl group” refers to an aromatic carbocyclic group. This aromatic carbocyclic group can optionally be substituted with one or more groups, equal or different from each other, selected from halogen atoms, hydroxyl groups, C1-C18 alkyl groups, C1-C18 alkoxyl groups, cyano groups, amino groups, nitro groups. Specific examples of aryl group are: phenyl, methylphenyl, trimethylphenyl, methoxyphenyl, hydroxyphenyl, phenyloxyphenyl, fluorophenyl, pentafluorophenyl, chlorophenyl, nitrophenyl, dimethylaminophenyl.

The term “ether group” refers to a functional group in which two alkyl groups are connected by the same atom of oxygen. Specific examples of such ether groups not to be considered as limiting include dimethyl ether, diethyl ether, ethyl methyl ether, or even cyclic ethers such as epoxyethane, epoxypropane, epoxybutane.

The term “polyether group” refers to a linear or branched Ci-Cis alkyl group in which two or more ether groups are present.

Preferably, at least one of R ⁵ and R ⁷ is an ether group so as to form a polyether-modified polysiloxane.

Advantageously, the polysiloxane chain reduces the surface tension of the solution, favoring the diffusion and distribution of the copolymer of the tanning agent of the invention.

It is believed that the polysiloxane, in particular the polyether-modified polysiloxane, improves the mobility of the copolymer by increasing the probability of the amino groups of the amino acids of the collagen meeting with the halogenated and/or oxygenated functional groups of the copolymer, thus favoring the cross-linking action on the proteins of the hide.

Furthermore, with the same cross-linking capacity, the combined action of the polysiloxane advantageously allows to reduce the quantity of copolymer to be used during the process.

According to the preferred embodiment of the process of the invention, the polysiloxane is used in the aqueous bath in a quantity comprised between 0.05% and 1 % by weight, with respect to the pelt weight of the hide to be tanned.

Preferably, the polysiloxane is used in a quantity comprised between 0.15% and 0.25% by weight, with respect to the pelt weight of the hide.

It is not excluded that, according to variant embodiments of the process of the invention, the hide is treated with the aforementioned polysiloxane in quantities different from what is indicated, or that the hide is not treated with the aforementioned polysiloxane.

According to the preferred embodiment of the process of the invention, before the treatment of the hide with the polysiloxane of formula (II), in the aqueous bath the hide is treated with a tannin or a mixture of tannins.

This tannin, or mixture of tannins, is added to the aqueous bath in a quantity comprised between 5% and 25% by weight, preferably between 10% and 20% by weight, more preferably between 10% and 15%, with respect to the pelt weight of the hide to be tanned.

Tannins known per se in the tanning sector, such as vegetable tannins and synthetic tannins, are suitable for use in the process of the invention.

Examples of vegetable tannins include condensed polyflavonoid tannins, for example tannins extracted from the bark or wood of mimosa, quebracho, pine, fir, pecan, acacia, tara, vallonea, chestnut, myrobalan and others.

Examples of synthetic tannins include products and their sodium and/or amine salts obtainable from the condensation reaction of formaldehyde with phenols, sulphonated phenols, with naphthalenesulfonic acids, nitrogenous resins and others.

Preferred in the process according to the invention is the use of synthetic or vegetable tannins based on dihydroxydiphenylsulfone.

Even more preferred is the use of a mixture of condensed synthetic tannins starting from S/formaldehyde bisphenol, S/formaldehyde/urea bisphenol and/or naphthalen sulfonate/formaldehyde, preferably together with an aliquot of vegetable tannins.

It is not excluded that, according to a variant of the process of the invention, the hide is treated with such one or more tannins after the treatment with the polysiloxane and before the treatment with the copolymer of the invention, as reported in example 3.

According to the preferred embodiment of the process of the invention, tannin, polysiloxane and copolymer are added to the aqueous bath containing the hide to be tanned.

The applicants found that, in the tanning process in which tannin, polysiloxane and copolymer are added in this order to the aqueous bath with the hide to be tanned, the leather takes on characteristics of optimal softness, firmness and workability, and a particularly advantageous dimensional yield and equalization of the tanned, as shown in examples 1 , 2, 5 and 7 reported below.

The applicants have also identified that, by varying the order of addition of these components to the aqueous bath, it is possible to vary the characteristics of softness, firmness, workability of the tanned leather, particularly conditioning the retanning, dyeing and fattening phases of the aforementioned leather.

According to the characteristics of the tanned leather to be obtained, it is in fact possible to add to the aqueous bath the components and the copolymer described above according to the following order: polysiloxane, tannin, copolymer, as shown in example 3, or according to the order polysiloxane, copolymer, tannin, as reported in examples 4 and 6.

It is also not excluded that, according to variants embodiments of the process of the invention, the order of addition of these components to the aqueous bath is copolymer, polysiloxane, tannin or copolymer, tannin, polysiloxane, or even tannin, copolymer, polysiloxane.

According to the preferred embodiment of the process of the invention, the copolymer is used on leathers previously prepared for tanning according to the usual operations of soaking, hair removal and calcination, fleshing, splitting, deliming, maceration and, optionally, pickel.

The leather treated with the copolymer of the invention is therefore preferably a full grain or split hide.

An example of a tanning process according to the preferred embodiment of the invention preferably comprises the following phases:

- introduction of the leather coming from the maceration phase or the pickel phase into a container for tanning, the so-called drum;

- introduction of one or more of the aforesaid tannins in the form of powder or of an aqueous solution of such tannin(s) in the aforementioned drum to form an aqueous bath in which the quantity of tannins is comprised between 5% and 25% by weight with respect to the pelt weight of the hide to be tanned; it is not excluded that these tannins are introduced into the drum at the same time as the hide to be tanned or prior to the introduction of the hide;

- introduction of a concentrated or dilute solution of a polysiloxane into the aforementioned aqueous bath so that in the aqueous bath the quantity of polysiloxane is comprised between 0.15% and 0.25% by weight, with respect to the pelt weight of the hide to be tanned;

- introduction into the aqueous bath containing the solution of tannins and polysiloxane of an aqueous solution of the copolymer of the invention so that in the aqueous bath the quantity of copolymer is comprised between 0.1 % and 20% by weight with respect to the pelt weight of the hide to be tanned;

- activation of the rotation of the drum for a predefined time sufficient to allow the absorption of the various tanning agents into the hide to be tanned.

This predefined time can be identified by an expert in the sector on the basis of the technical knowledge typical of the tanning sector. It may depend, for example, on the number of hides present in the drum, on the type of leather treated and its thickness, or even on the use to which the tanned leather will be destined, eg. automotive, leather goods, clothing, furniture etc.

It is not excluded that, according to alternative embodiments of the invention, the order of addition of the various components, including the hide, in the aqueous bath is different from what has been indicated above.

Following numerous experiments, the applicants have identified that, for the treatment of grain hides with a thickness comprised between 2 and 5 mm, this predefined time of drum rotation is comprised between 2 and 24 hours, preferably between 7 and 14 hours.

Optionally, tannin and/or polysiloxane and/or copolymer are added to the drum in small doses, up to the quantities indicated above, favoring the mixing of each component with the hide and/or with the other components already present in the aqueous bath.

According to the preferred embodiment of the process of the invention, after the rotation of the drum, the process involves introducing a medium strength base into the aqueous bath.

Said base is added to the aqueous bath preferably in a quantity comprised between 0.1 % and 2% by weight with respect to the pelt weight of the hide to be tanned.

This addition advantageously promotes a greater cross-linking of the collagen. Preferred is the use of an inorganic base, such as for example sodium bicarbonate.

Further, the addition of the aforementioned base to the aqueous bath ends when the pH of the aqueous bath is higher than 4, more preferably comprised between 4.5 and 5.

Preferably, the aforesaid base is added at predefined doses and gradually to the aqueous bath, so as to prevent the pH of the aqueous bath from undergoing sudden variations.

At the end of the addition of the aforementioned base, the hide is left cross- linked in the aqueous bath in the drum for a time preferably less than 20 hours, more preferably comprised between 8 and 15 hours.

Once the hide cross-linking phase is over, the hide can be discharged from the drum to be subjected to pressing, drying and any subsequent processes known per se in the tanning processes.

The tanning process according to the present invention is suitable to be used for the tanning of any type of skin such as for example bovine, swine, sheep, goat skin, exotic skin or other types of skin.

Also, part of the invention is a composition for carrying out a tanning process as described for the preferred embodiment of the invention, including the variants.

In particular, the composition includes a combination of:

- tanning agent comprising the copolymer as defined above;

- polysiloxane of general formula (II).

Preferably, such composition includes also a tannin or a mixture of tannins as previously defined.

According to a variant of the composition of the invention, it includes a combination of:

- tanning agent comprising the copolymer of the invention;

- a tannin or a mixture of tannins as previously defined.

The composition of the invention includes the aforementioned components, independently of each other, in liquid or solid form, such as for example in powder form.

According to an embodiment of the composition of the invention, this composition includes the tanning agent in liquid form, the polysiloxane in liquid form and the tannin or the mixture of tannins in powder form.

According to another embodiment of the composition of the invention, the composition includes the tanning agent in liquid form, the polysiloxane in liquid form and the tannin or the mixture of tannins in liquid form.

According to a further embodiment of the composition of the invention, the composition comprises the tanning agent in liquid form, the polysiloxane in liquid form and a mixture of tannins in which at least one of the aforementioned tannins is in liquid form and at least one of the aforementioned tannins is in powder form.

Advantageously, the composition of the present invention makes it possible to carry out a metal-free type tanning process, however obtaining a tanned leather qualitatively comparable to that obtained with a chrome salt tanning.

The tanning agent for animal hides comprising a copolymer that can be obtained by polymerization of acrylic or methacrylic acid and a monomeric unit, or a salt thereof, is also part of the present invention, as described above for the preferred embodiment of the invention, including the variants.

The invention will now be described with some examples of the tanning process with the tanning agent of the invention which are given by way of nonlimiting example.

Description of some preferred examples of embodiment of the tanning process The following examples refer to the application of the tanning agent of the invention in which the copolymer has been obtained from the polymerization of acrylic acid and a monomeric unit according to molar ratios from 1 to 0.01 , in which the monomeric unit is CH ₂ =C(CH3)-CO-O-CH2-CH(OH)-CH ₂ -CI.

The application of the copolymer is performed on full grain or split bovine hide, with a thickness ranging from 2 mm to 5 mm, and, for some examples, after the pickel operations.

It is specified that the application percentages of the following examples are referred to the pelt weight of the hides (weight of the hides after liming, split or not).

Example 1

The hides with pelt weight defined as 100%, the same weight of water (100%) and, as fattening, the product called VANOIL LLC by GSC Group Spa were loaded into the drum. A mixture of dihydroxydiphenyl sulphonic tannins called TAN 501 OP, TAN FA5 and TAN 212 by GSC Group Spa was then added with automatic slow rotation for the night.

The following morning, the polyether-modified polysiloxane was added to the aqueous bath with relative rotation of the drum.

The copolymer of the invention was then added, followed by the rotation of the drum for 2 hours.

Then, three aliquots of sodium bicarbonate were added to the aqueous bath with relative slow rotation.

Finally, the aqueous bath was discharged and the hides were sent to the subsequent processing phases.

The tanned leathers had a Tg of 70°C, and were well shaved and dry. Table 1 . Summary of example 1 .

Example 2

Some bovine hides with a thickness of about 2.4 mm with pelt weight defined as 100%, the same weight of water (100%) and, as fattening, the product called VANOIL LLC by GSC Group Spa were loaded into the drum. A mixture of tannins called TAN 501 OP, TAN FA5 and TAN 212 by GSC Group Spa was then added with automatic slow rotation for the night.

The following morning, the polyether-modified polysiloxane was added to the aqueous bath with relative rotation of the drum.

The copolymer of the invention was then added, followed by the rotation of the drum for 2 hours.

Then, three aliquots of sodium bicarbonate were added to the aqueous bath with relative slow rotation.

Finally, the aqueous bath was discharged and the hides were sent to the subsequent processing phases.

The tanned leathers had a Tg of 74°C, and were well shaved and dry. Table 2. Summary of example 2.

Example 3

The crusts of four cattle from pickel operations with the pelt weight defined as 100%, the same weight of water (100%) and, as fattening, the product called VANOIL LLC of GSC Group Spa, were loaded into the drum.

The polyether-modified polysiloxane was then added to the aqueous bath with relative rotation of the drum.

Subsequently, a mixture of tannins called TAN 501 OP, TAN FA5 and TAN 212 by GSC Group Spa was added with automatic rotation for the night.

The following morning, 4% of tannin called TAN 501 OP was added to the aqueous bath.

The copolymer of the invention was then added, followed by the rotation of the drum.

Then, five aliquots of sodium bicarbonate were added to the aqueous bath with relative rotation.

Finally, the aqueous bath was discharged and the hides were sent to the subsequent processing phases.

The tanned leathers had a Tg of 74°C, and were well shaved and dry. Table 3. Summary of example 3.

Example 4

The hides with pelt weight defined as 100% and the same weight of water (100%) were loaded into the drum.

The polyether-modified polysiloxane was then added to the aqueous bath with relative rotation of the drum.

Subsequently, the copolymer of the invention was added, followed by the rotation of the drum. Subsequently, a mixture of tannins called TAN 501 OP and TAN 5090 by GSC Group Spa was added.

Finally, four aliquots of sodium bicarbonate were added to the aqueous bath with automatic slow rotation for the night.

The following morning, the aqueous bath was discharged and the hides were sent to the subsequent processing phases.

The tanned leathers had a Tg of 71 °C, and were well shaved and dry. Table 4. Summary of example 4.

Example 5

The hides with pelt weight defined as 100%, the same weight of water (100%) and, as fattening, the product called VANOIL LLC by GSC Group Spa were loaded into the drum.

A mixture of tannins called TAN 501 OP and TAN 5090 by GSC Group Spa was then added to the aqueous bath.

Subsequently, the polyether-modified polysiloxane was added with relative rotation of the drum.

Subsequently, the copolymer was added into the drum and again water by weight corresponding to the pelt weight of the hide for the night, without rotating the drum.

The following morning, seven aliquots of sodium bicarbonate were added to the aqueous bath with relative rotation.

Finally, the aqueous bath was discharged and the hides were sent to the subsequent processing phases.

The tanned leathers had a Tg of 72°C, and were well shaved and dry. Table 5. Summary of example 5.

Example 6

The hides with pelt weight defined as 100% and the same weight of water (100%) were loaded into the drum.

The polyether-modified polysiloxane was then added to the aqueous bath with relative rotation of the drum.

Subsequently, the copolymer of the invention was added, followed by the rotation of the drum. Subsequently, a mixture of tannins called TAN 501 OP and TAN 5090 by GSC Group Spa was added and again water by weight corresponding to the pelt weight of the hide for the night.

The following morning, seven aliquots of sodium bicarbonate were added to the aqueous bath with automatic rotation. The hides were then drained and directed to the subsequent processing phases.

The tanned leathers had a Tg of 72°C, and were well shaved and dry. Table 6. Summary of example 6.

Example 7

The hides with pelt weight defined as 100%, the same weight of water (100%) and, as fattening, the product called VANOIL LLC by GSC Group Spa were loaded into the drum.

Then a tannin called SUSTAN 2020 (which comprises the mixture of tannins used in the examples previously described of GSC Group Spa) has been added to the aqueous bath.

Subsequently, the polyether-modified polysiloxane was added with relative rotation of the drum.

Subsequently, the copolymer was added into the drum and again water by weight corresponding to the pelt weight of the hide for the night, without rotating the drum.

The following morning, seven aliquots of sodium bicarbonate were added to the aqueous bath with relative rotation.

Finally, the aqueous bath was discharged and the hides were sent to the subsequent processing phases.

The tanned leathers had a Tg of 74°C, and were well shaved and dry. Table 7. Summary of example 7.

According to the above description, the tanning process, the tanning agent and the composition for carrying out a tanning process of the invention thus achieve all the intended purposes.

In particular, the tanning process with the related tanning agent are metal-free and allow the production of a leather of comparable quality to that obtained with chrome tanning, with evident benefits for the environment.

Furthermore, the aforesaid process allows to obtain a tanned product of a higher quality in terms of whiteness, softness, biodegradability, Tg and firmness compared to that obtained with the known metal-free tanning processes.

Furthermore, the tanning process of the invention is suitable to be implemented for the tanning of any type of hide.