EP1416058A1 - Condensation products for the retanning of iron-tanned leather - Google Patents

Abstract

Use is claimed in the post-tanning of iron-tanned leather of condensation products of (A) sulfonated aromatics; (B) aldehydes or ketones; and optionally also (C) non-sulfonated aromatics, urea or urea derivatives with the proviso that the content of naphthalenesulfonic acid-formaldehyde condensates and phenol-formaldehyde condensates is below 25 (especially below 5)% of the total weight of condensation products. Independent claims are also included for: (1) leather of iron content 1-7 wt.% containing a condensation product of (A)-(C) as above; and (2) production of leather especially of softness above 15 units (IUP/36) obtained by post-tanning iron-tanned leather with condensation products of (A)-(C) as above.

Description

The invention relates to the use of special condensation products for retanning of iron-tanned leather, a process for retanning iron-tanned leather Leather and leather containing corresponding condensation products.

Tanning with iron is already known cf. Stather, tanning chemistry and tanning technology, Akademie Verlag, Berlin, 1957, 474-480; Heidemann E. at al., Possibilities and limits of iron tanning, Das Leder, 1990, 8-14; Balasubramanian S. et al., Iron Complexes as Tanning Agents, JALCA, 1997, 218-224.

The leather tanned in Heidemann (see above), for example, was made with commercially available leather Naphthalenesulfonic acid-formaldehyde condensates (TANIGAN® BN) or Phenolic condensation products (BASYNTAN® DLX) retanned. The so obtained However, leather still leaves something to be desired in terms of its softness (see Example 7) and are not suitable for furniture leather or automotive cover leather

The object of the present invention was therefore to provide soft iron-tanned Leather.

A) sulfonierten Aromaten,

B) Aldehyden und/oder Ketonen und gegebenenfalls

C) einer oder mehreren Verbindungen, ausgewählt aus der Gruppe der nicht sulfonierten Aromaten, Harnstoff und Harnstoffderivaten,

zum Nachgerben von eisengegerbtem Leder, mit der Maßgabe, dass der Gehalt an Naphthalinsulfonsäure-Formaldehyd-Kondensat, und solchen auf Basis von Phenol und Formaldehyd bezogen auf die Gesamtmenge an Kondensationsprodukt kleiner als 25 Gew.-%, bevorzugt kleiner als 5 Gew.-% ist.The invention therefore relates to the use of condensation products based on

A) sulfonated aromatics,

B) aldehydes and / or ketones and optionally

C) one or more compounds selected from the group of unsulfonated aromatics, urea and urea derivatives,

for retanning iron-tanned leather, with the proviso that the content of naphthalenesulfonic acid-formaldehyde condensate and those based on phenol and formaldehyde, based on the total amount of condensation product, is less than 25% by weight, preferably less than 5% by weight is.

"Based on" means that the condensation product may consist of further Reactants in addition to A, B and optionally C was prepared. Preferably However, in the context of this application, the condensation products are only made up of A, B and possibly C.

"Phenol and formaldehyde based" means that the condensate is next to phenol and formaldehyde is produced from other reactants, for example phenolsulfonic acid and urea.

In the context of this application, "retanning" means post-treatment from iron-tanned leather to color, levelness, softness, fullness and behavior against water (hydrophobicity) and to fix tannins.

The iron-tanned leather is preferably also chrome-free.

Chromium-free in the sense of the present invention does not mean with chromium salts tanned. The maximum amount of chromium, e.g. caused by natural sources of Cr contents in animal skins or chromium-containing dyes in leather less than 2000 ppm.

For leather not dyed with chrome dye, the maximum proportion is Chromium in leather is preferably less than 100 ppm.

The leather used for retanning preferably has a shrinking temperature greater than 70 ° C, especially greater than 75 ° C.

The iron-tanned leather also preferably has an iron content of 1 to 7 Wt .-%. The iron content is determined as follows: A sample of the leather becomes Preservation of the reference weight at 70 ° C in a vacuum to constant weight. Then ashed at 800 ° C, the content of Fe (III) with a commercially available Method determined by wet chemistry and calculated back to the reference weight.

The iron content preferably results from tanning with iron salts.

Preferred iron salts are those of iron in the +3 oxidation state, for example Iron chloride, iron sulfate, basic iron sulfate and those of iron in the Oxidation level +2 like iron sulfate. Based on the nakedness used, the is Amount of Fe (III) or Fe (II) preferably from 0.3 to 5% by weight, in particular 1 to 3% by weight.

The use according to the invention preferably leads to leathers with a softness of greater than 15 units, preferably greater than 20, in particular greater than 30, measured according to IUP / 36, with a measuring device ST 300 from Heights Design Production Ltd., Halifax, UK or an equivalent device.

The leather obtained can improve the surface properties and physical fastness with commercially available products and machines with a polymeric film layer can be prepared, such as. B. described by W. Wenzel in Aqueos Finishing of Leather, JALCA, 1991, 442-455.

In the context of this application, sulfomethylated aromatics are also used as sulfonated aromatics Aromatics and biarylsulfones understood. Preferred sulfonated aromatics are: Naphthalenesulfonic acids, phenolsulfonic acid, sulfonated ditolyl ethers, 4,4'-dihydroxydiphenyl sulfone, sulfonated diphenylmethane, sulfonated diphenyl, sulfonated Terphenyl or benzenesulfonic acids.

Aldehydes and / or ketones include, in particular, aliphatic, cycloaliphatic as well as aromatic in question. Aliphatic aldehydes are preferred, particularly preferably formaldehyde and other aliphatic aldehydes with 2 to 5 carbon atoms in Question come.

Examples of unsulfonated aromatics are phenol, cresol or dihydroxydiphenylmethane in question.

As urea derivatives, for example, dimethylol urea, melamine or Guanidine can be called.

Phenol and phenol derivatives, such as phenolsulfonic acid, are common also by simultaneous exposure to formaldehyde and urea or by Dimethylolurea linked (DE-A 1 113 457). Sulfonation products more aromatic Connections are (according to Ullmann's Encyklopadie der Technische Chemie Volume 16 (4th edition) Weinheim 1979, p. 138) usually without the unreacted starting compounds separate, alone or together with other starting compounds condensed with formaldehyde. A solubilizing group can Phenols also by sulfomethylation under the simultaneous action of Alkali hydrogen sulfite and formaldehyde are introduced along with the condensation become. This sulfomethylation is e.g. described in DE-A 848 823.

Further preferred condensation products are condensates of ditolyl ether sulfonic acid with 4,4'-dioxydiphenyl sulfone, phenol sulfonic acid with phenol and urea.

Particularly preferred condensation products are those by condensation of sulfonated and optionally non-sulfonated aromatics with aliphatic Aldehydes, preferably formaldehyde, are obtained, with sulfonated Aromatics in particular no sulfomethylated aromatics are understood.

Such condensation products are preferably by condensation of obtained sulfonated phenol and / or 4,4'-dihydroxydiphenyl sulfone with formaldehyde.

The condensation product preferably obtained in the condensation has preferably a degree of condensation from 2 to 150, preferably from 2 to 20 and preferably a preferred number average molecular weight from 500 to 35,000 g / mol. Particularly preferred condensation products have a molecular weight of less than 3,000 g / mol.

A) sulfonierten Aromaten,

B) Formaldehyd und gegebenenfalls

C) nicht sulfonierten Aromaten

hergestellt worden sind.The method according to the invention is particularly preferred when the condensation products are out

A) sulfonated aromatics,

B) formaldehyde and optionally

C) unsulfonated aromatics

have been produced.

The condensation generally takes place at pH values from -1 to 9. In a particularly preferred embodiment, the condensation of sulfonated and optionally non-sulfonated aromatics, where the aromatics have no hydroxyl groups, is carried out with aldehydes and / or ketones, in particular an aldehyde, preferably formaldehyde and optionally urea or urea derivatives, in the acidic pH range. The condensation of sulfonated aromatics which carry hydroxyl groups with an aldehyde, in particular with formaldehyde, is preferably carried out at pH 6-8. The condensation products are preferably in the form of alkali metal, alkaline earth metal or ammonium salts or a mixture thereof. Particularly preferred salt forms are the Na, K, Li, NH ₄ , Ca, Mg or NR ₁ R ₂ R ₃ R ₄ salts, where

R ₁ to R _{4 are} identical or different C ₁ -C ₈ alkyl or C ₆ -C ₁₀ aryl radicals or H.

Before or after the condensation has taken place, the acid which may have originated from the preceding sulfonation of the aromatic and / or the acid used in the condensation reaction can preferably be completely or partially neutralized. After condensation, a pH of 3 to 8 is preferably set. The pH is preferably adjusted so that a 1% solution has the specified pH. In particular, an inorganic base such as NaOH, Na ₂ CO ₃ , KOH, LiOH, NH ₄ OH is used for this purpose.

The sulfonation of the aromatics to produce the sulfonated above Aromatics are generally carried out using generally known methods, such as those used are described for example in DE-A 29 34 980. As a suitable sulfonating agent can, for example, chlorosulfonic acid, amidosulfonic acid, oleum and sulfuric acid be used.

The reaction mixture obtained is preferably used for the subsequent one Condensation used without intermediate isolation of the sulfonated aromatic he follows. The reaction mixture is preferably used without the sulfonated aromatics are separated.

A) Phenolsulfonsäure und gegebenenfalls andere sulfonierte Aromaten, insbesondere Arylsulfone,

B) Formaldehyd und gegebenenfalls

C) einer oder mehreren Verbindungen, ausgewählt aus der Gruppe der nicht sulfonierten Aromaten, Harnstoff und Harnstoffderivaten.

Particularly preferred condensation products are those based on

A) phenol sulfonic acid and optionally other sulfonated aromatics, especially aryl sulfones,

B) formaldehyde and optionally

C) one or more compounds selected from the group of unsulfonated aromatics, urea and urea derivatives.

Such condensation products based on the Components A) and B) above.

A) Phenolsulfonsäure und Bishydroxyphenylsulfon,

B) Formaldehyd und gegebenenfalls

C) Harnstoff.

It is also particularly preferred as a component

A) phenolsulfonic acid and bishydroxyphenylsulfone,

B) formaldehyde and optionally

C) urea.

The molar ratio of phenolsulfonic acid to bishydroxyphenylsulfone (diphenolsulfone) is preferably 80:20 to 10:90, in particular 50:50 to 20:80.

The mixture of phenol sulfonic acid and bishydroxyphenyl sulfone is preferred with 0.2 to 2.0 mol equivalents of formaldehyde per aromatic monomer, in particular 0.3 to 1.0 mol equivalents implemented.

The amount of the condensation product used for retanning is preferably 1 to 20 wt .-%, in particular 2 to 10 wt .-%, based on the iron-tanned Leather.

A) sulfonierten Aromaten,

B) Aldehyden und/oder Ketonen und gegebenenfalls

C) einer oder mehreren Verbindungen, ausgewählt aus der Gruppe der nicht sulfonierten Aromaten, Harnstoff und Harnstoffderivaten,

nachgerbt, mit der Maßgabe, dass der Gehalt an Naphthalinsulfonsäure-Formaldehyd-Kondensat und Kondensaten auf Basis von Phenol und Formaldehyd, bezogen auf die Gesamtmenge an Kondensationsprodukt, kleiner als 25 Gew.-%, bevorzugt kleiner als 5 Gew.-% ist.The invention also relates to a process for producing leather, in particular leather with a softness of greater than 15 units according to IUP / 36 with preferably greater than 20 units, characterized in that an iron-tanned leather with a condensation product based on

A) sulfonated aromatics,

B) aldehydes and / or ketones and optionally

C) one or more compounds selected from the group of unsulfonated aromatics, urea and urea derivatives,

retanned, with the proviso that the content of naphthalenesulfonic acid-formaldehyde condensate and condensates based on phenol and formaldehyde, based on the total amount of condensation product, is less than 25% by weight, preferably less than 5% by weight.

The preferred embodiments above apply to the condensation products also for the method according to the invention.

Iron tanning is generally carried out in such a way that the pickled nakedness is removed with a Treated with iron salt. Possible iron salts are those listed above Question.

The tanning is preferably done in water at a temperature of 0 - 60 ° C, preferably 20-37 ° C.

After adding the iron salts for tanning, the tanning liquor should have a pH of 1.0 to 3.2, preferably from 1.4 to 2.5. After a reasonable time to penetrate from 30 min. up to 24 h, preferably 1 h to 6 h, the pH of the tanning liquor becomes Fixation of the iron salts raised. For this purpose, a basic compound, e.g. B. Sodium hydroxide, carbonate, bicarbonate, formate, calcium carbonate or magnesium oxide used. A pH range from 3.0 to 6.0, preferably 3.1 to 4.0 should preferably be achieved.

The iron-tanned leather thus obtained has a shrinking temperature of greater than 70 ° C, preferably greater than 75 ° C. It also has a uniform yellow color. For example, it can be mechanically aftertreated by wilting, folding, etc. on conventional tanneries.

The method is preferably carried out by removing the bare to be tanned from the Iron tanning acid-treated, especially with an organic polycarboxylic acid.

The preferably used pickled pelts for iron tanning are preferred acid pretreated, especially at pH 2-5, especially preferred at 3-4. This acid pretreatment is preferably decalcified and pickled nakedness used.

Compounds such as carboxy acids are particularly used for pimples such as formic acid, acetic acid or oxalic acid or inorganic acids such as sulfuric acid or acidic salts of sulfuric acid or mixtures thereof.

It has been found that the addition of di- or polyfunctional carboxylic acids for example polymeric or non-polymeric compounds in the acidic Pretreatment has a particularly positive effect on the properties of the leather.

Particularly preferred non-polymeric acids are difunctional carboxylic acids such as Succinic acid, maleic acid, glutaric acid and / or adipic acid; trifunctional carboxylic acids such as citric acid or polymeric carboxylic acids such as (co) polymerized Products using (meth) acrylic acid, maleic acid or itaconic acid or their derivatives.

These acids are preferably obtained in an amount of 0.5 to 10% by weight used on the nakedness used, in particular 1-4 wt .-%.

The acidic pretreatment preferably proceeds in such a way that pimples are added to the nakedness used be given in an amount so that the pH of the pickled bare on a value of 2-5, in particular reduced to 3-4. The pimple connections are preferably added to the nakedness in a tanning drum in aqueous solution. This is generally done at a temperature of 0 to 60 ° C, especially at 20 to 37 ° C. It is preferably 10 min. up to 24 h, especially 30 min. up to 2 h pretreated.

A fatty agent is particularly preferably added to the acidic pretreatment.

Preferred lubricants for this use are as an emulsion or solution in water stable against low pH values and high electrolyte concentrations. she exist z. B. from sulfonated, sulfated or sulfited fats, that are z. B. long chain alkanes, alcohols, carboxylic acids or esters natural or synthetic Origin, e.g. B. fish oils, claw oils, vegetable oils or synthetic oils. A A more detailed description of such fatty agents can be found in R. P. Daniels in Fatliquoring and Softening Agents, World Leather, 2001, 68-70.

In preparation for the retanning process, the water content of the iron-tanned Leather preferably reduced by withering, and then the thickness of the leather corrected by folding if necessary.

The retanning process is preferably carried out in a tanning drum in an aqueous liquor Temperature from 0 to 70 ° C, especially from 20 to 50 ° C instead and includes optional in addition to the condensation products according to the invention, further aids such as e.g. Polymers, fatliquors, colorants, acids and bases.

Preferred lubricants for this use are e.g. B. sulfonated, sulfated or sulfited fats, e.g. B. long-chain alkanes, alcohols, carboxylic acids or esters natural or synthetic origin, e.g. B. fish oils, claw oils, vegetable oils or synthetic oils.

The dyes are generally to make water-soluble solutions common in leather applications Dyes, e.g. B. those from the groups of acid dyes, direct dyes, Metal complex dyes or substantive dyes.

The preferred polymers for use are high molecular weight water soluble or water dispersible products e.g. B. from the (Co) polymerization reaction of unsaturated acids and their derivatives with z. B. more filling or greasy effect on leather.

Acids and bases are used to change the pH of the aqueous liquor to influence the penetration properties of the compounds used or to fix them.

The condensates used according to the invention are preferably in 20 to 1000, preferably 50 to 200% aqueous liquor based on the weight of the used Leather used in a pH range from 3.0 to 8.0, preferably 3.5 to 6.5. The Addition of 1 - 20%, preferably 2 - 10% of the products can be in one or also take several steps. Other tools can also be used added in one or more steps, together with or separately of the products according to the invention.

The retanning process is carried out in 1 - 48 h, preferably in 1.5 - 24 h, especially in 2 - 8 h.

The course of a retanning process is to be illustrated by Examples 7-9, is by no means limited to these.

A) sulfonierten Aromaten,

B) Aldehyden und/oder Ketonen und gegebenenfalls

C) einer oder mehreren Verbindungen, ausgewählt aus der Gruppe der nicht sulfonierten Aromaten, Harnstoff und Harnstoffderivaten,

enthält, mit der Maßgabe, dass der Gehalt an Naphthalinsulfonsäure-Formaldehyd-Kondensat und solche Kondensate auf Basis von Phenol und Formaldehyd, bezogen auf die Gesamtmenge an Kondensationsprodukt kleiner als 25 Gew.-%, bevorzugt kleiner als 5 Gew.-% ist.The invention further relates to leather with an iron content of 1 to 7% by weight, characterized in that it contains at least one condensation product based on

A) sulfonated aromatics,

B) aldehydes and / or ketones and optionally

C) one or more compounds selected from the group of unsulfonated aromatics, urea and urea derivatives,

contains, with the proviso that the content of naphthalenesulfonic acid-formaldehyde condensate and such condensates based on phenol and formaldehyde, based on the total amount of condensation product, is less than 25% by weight, preferably less than 5% by weight.

The leather according to the invention preferably has a softness of greater than 15 Units measured according to IUP / 36, preferably greater than 20, in particular greater than 30 units.

Examples

1. Condensation product A
Phenolsulfonic acid and bishydroxyphenylsulfone are condensed in a molar ratio of 1: 3 in aqueous solution at pH 6-9 with 2 mol formaldehyde at 100 - 120 ° C, adjusted to pH 3.5 with sulfuric acid and to acid number (SZ) 120 with phthalic acid and dried.

2. Condensation product B
Phenolsulfonic acid (65% solution) sodium salt is mixed in a 2.5: 1 molar ratio with bishydroxyphenylsulfone (55% suspension). 2.5 equiv are added to the hot mixture. Formaldehyde (30% solution) and condenses for 3 h at 112 - 115 ° C. The raw condensate is adjusted to 100 with adipic acid and dried.

3. Condensation product C (comparative example analogous to Tanigan® BN)
Naphthalene is sulfonated with 1.4 equivalents of H ₂ SO ₄ at 145 ° C for 2 h. A mixture of 1000 g of the naphthalenesulfonic acids thus obtained, 800 g of bishydroxyphenylsulfone and 250 ml of 37% formaldehyde solution is condensed at 100-120 ° C. for 3 h. The product obtained is adjusted to pH 3.5 and SZ 80 with sodium hydroxide solution and phthalic acid and spray-dried. (DE-A-10 002 048, example 1).

4. Condensation product D (comparative example)
Naphthalene is sulfonated with 1.4 mol of H ₂ SO ₄ at 145 ° C. for 3 h, condensed with 0.66 mol of formaldehyde for 3 h, cooled, adjusted to pH 3.5 and SZ 50 with sodium hydroxide solution and glutaric acid and spray-dried. (DE-A-10 002 048, Example 3).

5. Condensation product E (comparative example analogous to Basyntan® DLX)
The condensation product from the strongly acidic reaction of 1 mol phenol with 0.5 mol sulfuric acid, 1 mol urea and 0.9 mol formaldehyde at 100-110 ° C is buffered with 0.2 mol sodium hydroxide solution. The intermediate product thus obtained is condensed with a further 0.8 mol of phenol and 1.2 mol of formaldehyde, cooled, adjusted to pH 3.5 and SZ 80 with sodium hydroxide solution, formic acid and phthalic acid and spray-dried.

6. Tanning process A, tanning with iron salts using a fatliquor. Raw split cowhide, 3.0 mm. All quantities refer to the weight of the sheer. % product ° C Time min comment do the washing up water 35 deliming, 100 water 35 2.0 ammonium sulfate 0.3 sodium bisulfite 10 0.2 Emulsifier (ethoxylated fatty acid) stain 1.1 Protease 90 pH: 9.1 Fleet off do the washing up water 20 pretreatment, 20 water 20 pimple 6.0 sodium chloride 5 ° Bé:> 6 0.3 Preservative (active ingredient CMK) 4.0 Fatliquor (based on sulfated synthetic oils) 3.0 Methacrylic acid copolymer 1.0 adipic acid 480 pH: 4.6 1.0 Formic acid 85% 1:10 15 0.5 sulfuric acid 60 pH: 3.4 tanning 13.5 Basic iron (III) sulfate 45% 120 pH: 1.7; penetration dull 100 water 2.0 sodium 30 pH: 2.3 0.7 magnesia 30 pH: 3.0 0.7 magnesia 30 pH: 4.2 do the washing up water

7. Tanning process B tanning with iron salts without the use of a fatliquor; Raw split cowhide, 2.5 mm. All quantities refer to the weight of the sheer. % product ° C Time min comment do the washing up water 35 deliming, 100 water 35 2.0 ammonium sulfate 0.3 sodium bisulfite 10 0.2 Emulsifier (ethoxylated fatty acid) stain 1.1 Protease 90 pH: 9.1 Fleet off do the washing up water 20 pretreatment, 20 water 20 pimple 6.0 sodium chloride 5 ° Bé:> 6 0.3 Preservative (active ingredient CMK) 2.5 glutaric 60 pH: 4.4 1.0 Formic acid 85% 1:10 15 0.5 sulfuric acid 60 pH: 3.4 tanning 6 Iron (III) sulfate 120 pH: 1.7; penetration dull 100 water 1.1 Soda 1:10 30 pH: 2.0 1.1 Soda 1:10 30 pH: 2.7 1.1 Soda 1:10 30 pH: 3.3 do the washing up water

8. Tanning process C, retanning, comparison of different retanning agents in a model recipe. Base product folded, iron-tanned leather, thickness 1.4 mm. All quantities refer to fold weight.

Comparison of leather from tanning process C, thickness 1.3 - 1.5 mm: inventively Comparative Examples sample A B C D e Softness, subjective very soft soft hard hard hard Softness IUD / 36 21 16 9 10 8th wealth full full less crowded empty empty colour light beige beige, reddish beige brown beige, yellowish Objective softness test in accordance with IUP / 36 of the BLC Leather Technology Center with measuring device ST 300 from Heights Design Produktion Ltd., Halifax, UK Evaluation: the leathers produced according to the invention are not only significantly softer than the comparative examples, but also have fullness and coloring (as bright as possible) benefits.

9. Tanning process D: retanning based on folded leather from tanning process B (cattle, thickness 1.1 mm) using the product according to the invention from Example 1 for the production of an automotive leather. All quantities refer to fold weight. % product ° C Time min comment To wash 200 water 40 15 Fleet off Neutralization 100 water 20 1.0 sodium bicarbonate 2.0 Retanning agent (example 1) 30 4.0 Synthetic fatliquor 60 pH 5.2 Fleet off retanning 100 water 20 greasing 5.0 Synthetic fatliquor coloring 4.0 resin tanning 30 1.0 chestnut 5.0 Retanning agent (example 1) 2.0 Black dye 60 100 water 50 5 2.0 Synthetic fatliquor: 4 2.0 Sulfated fish oil 1: 4 30 1.0 Retanning agent (example 1) 60 pH 5.2 fixation 1.0 Formic acid 1:10 15 1.5 Formic acid 1:10 30 pH 3.7 Fleet off do the washing up water 20 5 Fleet off The resulting deep black leather is tension-dried, air-conditioned, stolled and milled.
IUP / 36 softness: 40 units

10. Tanning process D: retanning based on folded leather from tanning process A (cattle, thickness 1.6 mm) using the products according to the invention from Examples 1 and 2 for producing a very soft furniture nappa. All quantities refer to fold weight. % product ° C Time min comment To wash 200 water 40 15 Fleet off Neutralization 100 water 40 2.0 sodium bicarbonate 2.0 Retanning agent (example 2) 30 3.0 Sulphated fish oil 60 pH 6.2 Fleet off retanning 100 water 30 greasing 3.0 Sulphated fish oil coloring 3.0 Synthetic fatliquor 4.0 resin tanning 60 5.0 Retanning agent (example 1) 2.0 Blue dye 60 100 water 50 5 2.0 Synthetic fat center: 4 2.0 Sulfated fish oil 1: 4 30 2.0 Retanning agent (example 2) 60 pH 5.5 fixation 1.2 Formic acid 1:10 15 1.5 Formic acid 1:10 30 pH 3.6 Fleet off do the washing up water 20 5 Fleet off

The brilliant blue leather thus obtained is hanging dried, air-conditioned, placed and milled.
IUP / 36 softness: 55 units

Claims (9)

Use of condensation products based on A) sulfonated aromatics, B) aldehydes and / or ketones and optionally C) one or more compounds selected from the group of unsulfonated aromatics, urea and urea derivatives, for retanning iron-tanned leather, with the proviso that the content of naphthalenesulfonic acid-formaldehyde condensate and condensate based on phenol and formaldehyde based on the total amount of condensation product is in each case less than 25% by weight, preferably less than 5% by weight % is. Use according to claim 1, characterized in that a leather with a softness of greater than 15 units, measured according to IUP / 36, is obtained. Use according to claim 1, characterized in that a condensation product based on A) phenol sulfonic acids and optionally other sulfonated aromatics, especially aryl sulfone, B) formaldehyde and optionally C) one or more compounds selected from the group of unsulfonated aromatics, urea and urea derivatives. Use according to claim 1, characterized in that a condensation product based on A) phenolsulfonic acid and bisphydroxyphenylsulfone and B) formaldehyde and optionally C) urea is used, the ratio of phenolsulfonic acid to bishydroxyphenolsulfon preferably 80:20 to 10:90, preferably 50:50 to 20:80. Use according to claim 1, characterized in that the condensation product is used in an amount of 1 to 20% by weight, in particular 2 to 10% by weight, based on the iron-tanned leather. Process for the production of leather, in particular leather with a softness of greater than 15 units according to IUP / 36, characterized in that an iron-tanned leather with a condensation product based on A) sulfonated aromatics, B) aldehydes and / or ketones and optionally C) one or more compounds selected from the group of unsulfonated aromatics, urea and urea derivatives, retanned, with the proviso that the content of naphthalenesulfonic acid-formaldehyde condensate and condensate based on phenol and formaldehyde, based on the total amount of condensation product, is less than 25% by weight, preferably less than 5% by weight. Process for the production of leather according to claim 6, characterized in that the bare to be tanned is acid-treated before iron tanning, in particular with an organic polycarboxylic acid. Leather with an iron content of 1-7 wt .-% characterized in that it is at least one condensation product based on A) sulfonated aromatics, B) aldehydes and / or ketones and optionally C) one or more compounds selected from the group of unsulfonated aromatics, urea and urea derivatives, contains, with the proviso that the content of naphthalenesulfonic acid-formaldehyde condensate, and condensate based on phenol and formaldehyde based on the total amount of condensation product is less than 25 wt .-%, preferably less than 5 wt .-%. Leather according to claim 8, characterized in that it has a softness greater than 15 units, measured according to IUP / 36.