Method (1) for metal-free tanning of a quantity of hide having initial weight (w), said quantity of hide being contained in a drum, wherein said method (1) comprises at least one tanning treatment (B) of said hide including at least the following operating steps: B.1 feeding aliphatic aldehyde into said drum, in a percentage ranging between about 1% and 3% by weight with respect to the initial weight (w) of said hide, optionally equal to about 2% by weight, and B.2 moving said drum for a time period of at least about 10 min, optionally approximately 20 min at an operating speed between 1 and 8 revolutions/minute, preferably comprised between 4 and 5 revolutions/minute; B.3 feeding citric acid into said drum, in a percentage ranging between about 0.1% and 0.3% by weight with respect to the initial weight (w) of said hide, optionally equal to about 0.2% by weight, and B.4 moving said drum for a time period of at least about other 10 min, optionally approximately 20 min at said operating speed; B.5 feeding aliphatic aldehyde into said drum, in a percentage ranging between about 1% and about 3% by weight with respect to the initial weight (w) of said hide, optionally equal to about 2% by weight, and B.6 moving said drum for a time period of at least about 150 min, optionally approximately 180 min at said operating speed; B.7 feeding sodium formate into said drum, in a percentage ranging between about 0.3% and about 0.7% by weight with respect to the initial weight (w) of said hide, optionally equal to about 0.5% by weight, and B.8 moving said drum for a time period of at least about 20 min, optionally approximately 30 min at said operating speed; B.9 feeding magnesium oxide into said drum, in a percentage ranging between about 0.3% and about 0.7% by weight with respect to the initial weight (w) of said hide, optionally equal to about 0.5% by weight, and B.10 moving said drum for a time period of at least about 60 min, optionally approximately 90 min at said operating speed; B.11 feeding water into said drum, at a temperature ranging between about 30 C. and about 60 C., optionally equal to about 50 C., in a percentage ranging between about 30% and 50% by weight with respect to the initial weight (w) of said hide, optionally equal to about 40% by weight, and B.12 moving said drum for a time period of at least about 100 min, optionally approximately 120 min at said operating speed; B.13 feeding aliphatic aldehyde into said drum, in a percentage ranging between about 1% and 5% by weight with respect to the initial weight (w) of said hide, optionally equal to about 3% by weight, and B.14 moving said drum for a time period of at least about 100 min, optionally appro

Method (1) for metal-free tanning of a quantity of hide having initial weight (w), said quantity of hide being contained in a drum, wherein said method (1) comprises at least one tanning treatment (B) of said hide including at least the following operating steps: B.1 feeding aliphatic aldehyde into said drum, in a percentage ranging between about 1% and 3% by weight with respect to the initial weight (w) of said hide, optionally equal to about 2% by weight, and B.2 moving said drum for a time period of at least about 10 min, optionally approximately 20 min at an operating speed between 1 and 8 revolutions/minute, preferably comprised between 4 and 5 revolutions/minute; B.3 feeding citric acid into said drum, in a percentage ranging between about 0.1% and 0.3% by weight with respect to the initial weight (w) of said hide, optionally equal to about 0.2% by weight, and B.4 moving said drum for a time period of at least about other 10 min, optionally approximately 20 min at said operating speed; B.5 feeding aliphatic aldehyde into said drum, in a percentage ranging between about 1% and about 3% by weight with respect to the initial weight (w) of said hide, optionally equal to about 2% by weight, and B.6 moving said drum for a time period of at least about 150 min, optionally approximately 180 min at said operating speed; B.7 feeding sodium formate into said drum, in a percentage ranging between about 0.3% and about 0.7% by weight with respect to the initial weight (w) of said hide, optionally equal to about 0.5% by weight, and B.8 moving said drum for a time period of at least about 20 min, optionally approximately 30 min at said operating speed; B.9 feeding magnesium oxide into said drum, in a percentage ranging between about 0.3% and about 0.7% by weight with respect to the initial weight (w) of said hide, optionally equal to about 0.5% by weight, and B.10 moving said drum for a time period of at least about 60 min, optionally approximately 90 min at said operating speed; B.11 feeding water into said drum, at a temperature ranging between about 30 C. and about 60 C., optionally equal to about 50 C., in a percentage ranging between about 30% and 50% by weight with respect to the initial weight (w) of said hide, optionally equal to about 40% by weight, and B.12 moving said drum for a time period of at least about 100 min, optionally approximately 120 min at said operating speed; B.13 feeding aliphatic aldehyde into said drum, in a percentage ranging between about 1% and 5% by weight with respect to the initial weight (w) of said hide, optionally equal to about 3% by weight, and B.14 moving said drum for a time period of at least about 100 min, optionally appro

A method for forming chrome-free retanned leather including: (a) contacting wet white (chrome-free tanned hide) with a retanning mixture comprising from 2% to 15%, by solids weight, based on the wet weight of the wet white, of an amphoteric polymer composition comprising amine functional units and acid functional units; and (b) applying a polymeric overcoat containing an acrylic copolymer with one or more metal transition elements, with a thickness of no greater than 100 microns, to the retanned wet white, is provided. The present invention also provides a chrome-free retanned leather formed by the method.

A method for forming chrome-free retanned leather including: (a) contacting wet white (chrome-free tanned hide) with a retanning mixture comprising from 2% to 15%, by solids weight, based on the wet weight of the wet white, of an amphoteric polymer composition comprising amine functional units and acid functional units; and (b) applying a polymeric overcoat containing an acrylic copolymer with one or more metal transition elements, with a thickness of no greater than 100 microns, to the retanned wet white, is provided. The present invention also provides a chrome-free retanned leather formed by the method.

A composition including an acetal of an aldehydic tanning agent for tanning hides and/or pelts, as well as a method for tanning hides and/or pelts in order to produce leather, wherein an acetal of an aldehydic tanning agent is used. By reducing the pH, the aldehydic tanning agent can be released, whereby a tanning step is initiated. The composition according to the invention and the method according to the invention are characterized by lower toxicity compared to conventional compositions and tanning methods based on aldehydic tanning agents. Furthermore, improved penetration of the tanning agents into deeper layers of the hide and/or the pelt is possible, so that particularly homogeneous tanning is achieved.

A composition including an acetal of an aldehydic tanning agent for tanning hides and/or pelts, as well as a method for tanning hides and/or pelts in order to produce leather, wherein an acetal of an aldehydic tanning agent is used. By reducing the pH, the aldehydic tanning agent can be released, whereby a tanning step is initiated. The composition according to the invention and the method according to the invention are characterized by lower toxicity compared to conventional compositions and tanning methods based on aldehydic tanning agents. Furthermore, improved penetration of the tanning agents into deeper layers of the hide and/or the pelt is possible, so that particularly homogeneous tanning is achieved.

A method for tanning an animal skin may include: (a) putting the animal skin in contact with a first tanning bath including at least one dialdehyde of general formula OCH(CH).sub.nHCO, wherein n is 0 or an integer number greater than or equal to 1 and less than or equal to 8, and wherein the first tanning bath has a pH greater than or equal to 1 and less than or equal to 5; (b) bringing the pH of the first tanning bath to a pH greater than 5 and less than 8; and/or (c) repeating one or more times the steps (a) and (b) on the animal skin coming from the step (b) using a second or further tanning bath. The first, second, and further tanning baths may be substantially free of surfactants.

A method for tanning an animal skin may include: (a) putting the animal skin in contact with a first tanning bath including at least one dialdehyde of general formula OCH(CH).sub.nHCO, wherein n is 0 or an integer number greater than or equal to 1 and less than or equal to 8, and wherein the first tanning bath has a pH greater than or equal to 1 and less than or equal to 5; (b) bringing the pH of the first tanning bath to a pH greater than 5 and less than 8; and/or (c) repeating one or more times the steps (a) and (b) on the animal skin coming from the step (b) using a second or further tanning bath. The first, second, and further tanning baths may be substantially free of surfactants.

A composition including an acetal of an aldehydic tanning agent for tanning hides and/or pelts, as well as a method for tanning hides and/or pelts in order to produce leather, wherein an acetal of an aldehydic tanning agent is used. By reducing the pH, the aldehydic tanning agent can be released, whereby a tanning step is initiated. The composition and the method are characterized by lower toxicity compared to conventional compositions and tanning methods based on aldehydic tanning agents. Furthermore, improved penetration of the tanning agents into deeper layers of the hide and/or the pelt is possible, so that particularly homogeneous tanning is achieved.

A composition including an acetal of an aldehydic tanning agent for tanning hides and/or pelts, as well as a method for tanning hides and/or pelts in order to produce leather, wherein an acetal of an aldehydic tanning agent is used. By reducing the pH, the aldehydic tanning agent can be released, whereby a tanning step is initiated. The composition and the method are characterized by lower toxicity compared to conventional compositions and tanning methods based on aldehydic tanning agents. Furthermore, improved penetration of the tanning agents into deeper layers of the hide and/or the pelt is possible, so that particularly homogeneous tanning is achieved.