EP0814168A1 - Process for tanning of leather - Google Patents

Abstract

A tanning process comprises (1) treatment with a compound containing carbamoyl sulphonate groups and (2) treatment at a pH greater than 4 with a mineral tanning agent chosen from chromium (III), iron (II) or (III), aluminium (III), titanium (IV) or zirconium (IV) compounds, without the use of a pickling agent. The compound used in step (1) is a reaction product of the following components : (A) an organic polyisocyanate ; (B) 0.01-0.4 equivalents per isocyanate group in (A) of a polyether alcohol containing polyalkylene oxide groups, of which 40-100 mol.% are polyethylene oxide units with a sequence length of 5-70 (the equivalents are based on the hydroxyl groups in the alcohol) ; (C) optional further components which can react with isocyanate groups ; and (D) ammonium or alkali bi- or di-sulphites.

Description

The invention relates to a method for pretanning and tanning leather using blocked polyisocyanates containing ether groups and mineral tanning agents.

The tanning transforms animal skins into leather by cross-linking the collagen. One of the most important characteristics of leather is the increased shrinking temperature compared to untanned hides, i.e. the improved hot water resistance, and the white appearance (non-transparent, non-pigment-like) after drying.

The still dominant type of tanning is chrome tanning, in which covalent bonds with the carboxyl groups of the collagen are formed using chromium (III) compounds under the influence of OH ions. In contrast, the hydrogen bonds to the amide groups of collagen that can be obtained with polyfunctional vegetable tannins are much weaker, which also results in a moderately increased shrinking temperature. Aliphatic aldehydes, e.g. Glutaraldehyde, which leads to crosslinking via the primary amino groups of collagen, has been recommended as a tanning agent (US Pat. No. 2,941,859). However, the resulting aldimines can reversibly react back to aldehyde and amine in the presence of water.

The use of aliphatic diisocyanates such as hexamethylene diisocyanate (DE-PS 72 981) has not been able to gain acceptance for toxicological reasons.

Although the use of bisulfite-blocked aliphatic, cycloaliphatic or aromatic diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate and tolylene diisocyanate as tannins, as recommended in US Pat. Nos. 2,923,594 and 4,413,997, gives light, lightfast leather, the tanning liquors are not pH-stable.

The use of the bisulfite-blocked polyisocyanates containing polyethylene oxide groups and described in EP-A 690 135 has application-technical advantages because residual liquors of the tanning are obtained which are free of heavy metal ions. The shrinking temperatures of the leather that can be achieved with these products are included more than 80 ° C within the shrinking temperatures required for most types of leather. But if you want to produce shoes very efficiently, you have to use the so-called thermosetting process. Here, shoe uppers are pulled onto lasts and fixed by heat (> 100 ° C) and water vapor (> 80% relative humidity). This process makes it possible to significantly shorten the manufacturing time of the shoe and to make better use of the expensive lasts. If you want to use the thermosetting process, the materials used for this must withstand these processing conditions.

It has been shown that leather is required for these and similar purposes, the shrinking temperatures (Ts) of which are approximately 100 ° C. in the dry state. On the other hand, one does not want to give up the ecological advantages which are achieved with the process on which EP-A 690 135 is based. There was therefore a need for a process which supplies leather containing mineral tannins and which is associated with the lowest possible environmental impact.

The invention relates to a method for tanning using

• I. Carbamoyl sulfonate group-containing reaction products
  • A. organic polyisocyanate,
  • B. per isocyanate group of A. 0.01 to 0.4 equivalents of polyether alcohol with built-in polyalkylene oxide units (the equivalents relate to the hydroxyl groups of the polyether alcohol), the polyalkylene oxide units being 40 to 100, preferably 50 to 100 mol% of polyethylene oxide units of a sequence length from 5 to 70, preferably 6 to 60, in particular 7 to 40,
  • C. optionally other NCO-reactive components, and
  • D. ammonium or alkali bisulfites or disulfites,
  and below
• II. Mineral tanning agents from the series chromium (III), iron (II), iron (III), aluminum (III), titanium (IV) and zirconium (IV) without pimples at a pH value above 4, preferably above 5.

The reaction products to be used according to the invention can be obtained from the intermediates obtainable from A, B and optionally C with NCO contents of 3 to 50, preferably 5 to 45, in particular 20 to 45% by weight (based on the intermediate) by subsequently blocking the free ones Obtained isocyanate groups. The products according to the invention then - calculated as sodium salt and based on solids - contain 9.7 to 78, preferably 14 to 74, in particular 46.5 to 74% by weight of carbamoyl sulfonate groups.

Suitable organic polyisocyanates A) are aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic polyisocyanates as described, for example, by W. Siefken in Liebigs Annalen der Chemie 562 , pages 75 to 136.

Preferred polyisocyanates A) are compounds of the formula Q (NCO) _n with an average molecular weight below 800, where n is a number of at least 2, preferably from 2 to 4, Q is an aliphatic C ₄ -C ₁₂ -hydrocarbon radical, a cycloaliphatic C ₆ - C ₁₅ hydrocarbon radical, an araliphatic C ₇ -C ₁₅ hydrocarbon radical or a heterocyclic C ₂ -C ₁₂ radical with 1 to 3 heteroatoms from the series oxygen, sulfur, nitrogen, for example (i) diisocyanates such as ethylene diisocyanate, 1.4 -Tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate and any mixtures of these isomers, 1-isocyanato-2-isocyanatomethyl- cyclopentane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane, 2,4- and 2,6-hexahydrotoluenediisocyanate and any mixtures of these isomers, hexahydro-1,3- and / or -1,4- phenylene diisocyanate, perhydro-2,4'- and / or -4,4'-diphenylmet hyl diisocyanate, 1,3- and 1,4-phenylene diisocyanate, 2,4- and 2,6-tolylene diisocyanate and any mixtures of these isomers, diphenylmethane-2,4'- and / or -4,4'-diisocyanate , Naphthalene-1,5-diisocyanate, uretdione group-containing polyisocyanates such as bis- (6-isocyanatohexyl) uretdione or the uretdione structure-containing dimer of 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane and any Mixtures of the aforementioned polyisocyanates; (ii) trifunctional and higher functional polyisocyanates such as the isomers of Triisocyanatotriphenylmethane series (such as triphenylmethane 4,4 ', 4''triisocyanate) and their mixtures; (iii) Compounds prepared by allophanatization, trimerization or biuretization from the polyisocyanates (i) and / or (ii) which have at least 3 isocyanate groups per molecule. Examples of polyisocyanates produced by trimerization are the trimerizate of 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane obtainable by isocyanurate formation and the isocyanurate groups containing isocyanurate groups obtainable by trimerization of hexamethylene diisocyanate, optionally in a mixture with 2,4-diisocyanatotoluene Polyisocyanates. Examples of polyisocyanates produced by biuretization are tris (isocyanatohexyl) biuret and its mixtures with its higher homologs, as are accessible, for example, according to DE-OS 23 08 015.

können verwendet werden.Particularly preferred polyisocyanates A are those with a molecular weight of 140 to 400 with NCO groups bound to aliphatics or cycloaliphatics, such as 1,4-diisocyanatobutane, 1,6-diisocyanatohexane, 1,5-diisocyanato-2,2-dimethylpentane, 2 , 2,4- or 2,4,4-trimethyl-1,6-diisocyanatohexane, 1,3- and 1,4-diisocyanatohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane, 1-isocyanato-1-methyl-4-isocyanatomethyl-cyclohexane and 4,4'-diisocyanatodicyclohexyl-methane, and any mixtures of such diisocyanates. Also araliphatic polyisocyanates such as the xylylene diisocyanates of the formulas

can be used.

The above diisocyanates are preferably used. However, it is also possible to use monofunctional aliphatic isocyanates such as, for example, butyl isocyanate, hexyl isocyanate, cyclohexyl isocyanate, stearyl isocyanate or dodecyl isocyanate and / or polyisocyanates with an average functionality of 2.2 to 4.2.

The higher-functionality polyisocyanates are preferably essentially composed of trimeric 1,6-diisocyanatohexane or 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane and optionally dimeric 1,6-diisocyanatohexane or 1-isocyanato-3 , 3,5-trimethyl-5-isocyanatomethyl-cyclohexane and the correspondingly higher homologues of isocyanurate groups and optionally uretdione groups containing polyisocyanate mixtures with an NCO content of 19 to 24 wt .-%, as obtained by known catalytic trimerization and under isocyanurate Formation of 1,6-diisocyanatohexane or 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane can be obtained and which preferably have an (average) NCO functionality of 3.2 to 4.2.

Further suitable polyisocyanates A are polyisocyanates prepared by modifying aliphatic or cycloaliphatic diisocyanates with uretdione and / or isocyanurate, urethane and / or allophanate, biuret or oxadiazine structure, as described, for example, in DE-OS 1 670 666, 3 700 209 and 3 900 053 and are described by way of example in EP 336 205 and 339 396. Suitable polyisocyanates are e.g. also the ester group-containing polyisocyanates, e.g. the tetrakis or triisocyanates accessible by reacting pentaerythritol or trimethylolpropane silyl ethers with isocyanatocaproic acid chloride (cf. DE-OS 3 743 782). It is also possible to use triisocyanates such as e.g. Tris-isocyanatodicyclohexylmethane to use.

In both cases, the use of monofunctional and more than difunctional isocyanates is preferably limited to amounts of at most 10 mol%, based on all polyisocyanates A.

However, the abovementioned aliphatic, cycloaliphatic and araliphatic diisocyanates are very particularly preferred.

The polyether alcohols B are accessible in a manner known per se by alkoxylation of suitable starter molecules. Any mono- or polyhydric alcohols with a molecular weight of 32 to 250 can be used as starter molecules to produce the polyether alcohols. Monofunctional aliphatic C ₁ -C ₁₈ , preferably C ₁ -C ₄ alcohols are preferably used as starter molecules. The use of methanol, butanol, ethylene glycol monomethyl ether or ethylene glycol monobutyl ether as starter is particularly preferred.

Alkylene oxides suitable for the alkoxylation reaction are, in particular, ethylene oxide and propylene oxide, which can be used in the alkoxylation reaction in any order. Any other epoxides such as butylene oxide, dodecene oxide or styrene oxide can also be used. Pure polyethylene oxide alcohols are particularly preferred.

Polyalkylene oxide alcohols containing ester groups can also be used. Suitable polyalkylene oxide alcohols containing ester groups are OH-terminated polyester ethers which, by reacting aliphatic C ₂ -C ₈ -dicarboxylic acids or their esters or acid chlorides with polyethers from the group consisting of polyethylene oxides, polypropylene oxides, their mixtures or mixed polyethers, with 0 per OH equivalent of the polyether, 8 to 0.99 equivalents of carboxyl groups or their derivatives are used, are available and have an average molecular weight below 10,000, preferably below 3,000.

The optionally used NCO-reactive components C include conventional mono- to tetrafunctional building blocks used in polyurethane chemistry, such as alcohols, amines, amino alcohols and mercaptans with molecular weights below 6,000, preferably below 2,000, such as e.g. Polyesters, polyether esters, aminopolyethers and polycarbonates, unless they fall under definition B.

Preferred components C are long-chain, optionally branched, so-called fatty alcohols or fatty amines with 12 to 30 carbon atoms which have a "fatty" or "re-fatty" effect, and esters of natural fatty acids, such as stearic acid, oleic acid, palmitic acid, linoleic acid, linolenic acid, etc., which contain OH groups.

Very particularly preferred components C are natural fats and oils carrying OH groups, such as castor oil.

The reaction products from components A to D to be used according to the invention can contain up to 20% by weight of component C.

Preferred blocking agents D are the sodium salts of sulphurous or disulphurous acid, ie sodium bisulphite (NaHSO ₃ ) or sodium disulphite (Na ₂ S ₂ O ₅ ).

The other alkali and ammonium salts of these acids, namely potassium bisulfite, potassium disulfite, lithium bisulfite, lithium disulfite, ammonium bisulfite, ammonium disulfite, and simple tetraalkylammonium salts of these acids, such as, for example, tetramethylammonium bisulfite, tetraethylammonium bisulfite, etc., can also be used advantageously Solutions with solids contents of 5 to 40% by weight are used.

The reaction products to be used according to the invention can be prepared, for example, as follows:

In a first step, the polyisocyanate is reacted with the polyether alcohol B until all OH groups have been urethanized. The NCO-terminated prepolymer thus obtained is then blocked in a second step with alkali metal or ammonium bisulfite or disulfite until all NCO groups have been reacted.

The entire process is particularly preferably carried out solvent-free as a one-pot process. The reaction (1st step) is carried out in the temperature range up to 130 ° C., preferably in the range between 50 ° C. and 120 ° C., particularly preferably between 80 ° C. and 110 ° C. The reaction can be followed by titration of the NCO content or by measuring the IR spectra and evaluating the carbonyl band at approx. 2 100 cm ^-1 and is complete when the isocyanate content is not more than 0.1% by weight above the value which is to be achieved with complete sales. As a rule, response times of less than 4 hours are sufficient.

The reaction can be accelerated by using catalysts such as dibutyltin dilaurate, tin (II) octoate or 1,4-diazabicyclo [2.2.2] octane in amounts of 10 to 1000 ppm, based on the reaction components. The NCO prepolymers thus obtained with NCO contents of 5 to 45% by weight are then in a second step at 0 to 60 ° C, preferably at 10 to 40 ° C, with aqueous solutions of alkali or ammonium sulfites and Water reacted until all NCO groups have reacted. This generally requires reaction times of 1 to 12, preferably 3 to 8 hours. The end products are optically clear aqueous solutions, in a few individual cases stable, fine-particle emulsions with average particle diameters below 8000 nanometers. It may be advantageous to initially add 20 to 50% by weight of the NCO prepolymers implement aqueous solutions of the alkali metal or ammonium bisulfites or disulfites and add the remaining water after 5 to 45 minutes, so that the solids content of the aqueous preparations is 10 to 50% by weight, preferably 25 to 40% by weight .

In the first stage of such a combined tanning, as described in EP-A 690 135, optionally with the aid of a base agent, 0.1-30, preferably 0.5-10, very particularly preferably 1-7,% by weight of carbamoyl sulfonate pre-tanned at pH 5-14, preferably 7.5-9.5. All known tamping agents commonly used in tannery are suitable for basification:
Sodium carbonate and bicarbonate, magnesium oxide, dolomite, tertiary amines, etc. The controlled addition of sodium or potassium hydroxide is generally possible (but not common). Magnesium oxide is particularly preferred.

When tanning with the reaction products to be used according to the invention, a low pH is not required, as is customary in mineral tanning. This can save you the addition of salt (pimples). Nakedness is e.g. decalcified to a pH of 5 to 8, preferably by 7, the reaction product to be used according to the invention is added and the basification is started after one hour's running time. (In the case of annealed magnesium oxide, the addition can be started immediately). Depending on the mechanical flexing effect and thickness as well as the digestion (e.g. enzymatically) of the bare, the pre-tanning and preferably the simultaneous basification can be completed in 4 to 6 hours. In general, however - as is customary in chrome tanning - after running for 1 hour and after adding the base agent, the mixture is left to run overnight in a further 2 steps (each after 1 hour running time), rinsing the next morning and continuing as usual.

Of the reaction products to be used according to the invention, amounts of 1 to 20% by weight, preferably 3 to 15% by weight, of the reaction product are generally used, based on the weight of the raw material. The leather tanned with the reaction product with shrinking temperatures of above 70 ° C., preferably above 75 ° C., serves as a preliminary stage (analogue wet blue) for tanning.

Then, at a pH value above 4, preferably above 5, you can tan free of pimples and salt-free with a minimal amount of mineral tanning agent. Suitable mineral tannins are salts of aluminum, chromium, iron, titanium and zircon. The aluminum (Ts = 70 - 80 ° C), iron (Ts = 70 - 80 ° C), titanium (Ts = 75 - 85 ° C) or zirconium (Ts = 70 - 80 ° C) according to J. Kochta et al., Das Leder, Aug. 1990, maximum achievable shrinkage temperatures are partially increased by this combined tanning. In the process according to the invention, 100 ° C. is reached and - depending on the amount used and the process control (pH, temperature etc.) - clearly exceeded.

A particularly preferred working method is the use of tanning chromium compounds that are stable at high pH values. Such pH-resistant chromium compounds are described, for example, in EP-A 304 677; there one uses an aqueous solution of basic chromium (III) sulfate and, per mole of chromium oxide of the basic chromium (III) sulfate, 0.2 to 0.8 mol of aliphatic C ₄ -C ₆ dicarboxylic acid and subsequent adjustment of the theoretical Basicity to 0 to 50% prepared reaction product, the addition of the reaction product to the pickling liquor as an aqueous solution with a chromium oxide content of at least 5% by weight or in powdered form in an amount of 0.9 to 1.5% by weight chromium oxide (based on pelt weight), the liquor volume is less than 100% by weight (based on pelt weight), the final pH is above 4.0 and the final temperature is above 40 ° C. Whether a chromium (III) compound is tanned or not is determined by its basicity (see F. Stather, Gerbereichemie und Gerfertechnologie, Leipzig, 1967, p. 409, 458-459).

Example 1 of EP-A 304 677 describes a product which has 0.2 mol of glutaric acid with a basicity of 30 per mol of Cr ₂ O ₃ . This product can be added free of salt and pimples in a short liquor of up to pH 9, preferably 5-8, to the material to be tanned without spontaneous precipitation. The tanning proceeds without having to be basified. Shrinking temperatures of approximately 100 ° C. are achieved with quantities of 1.25% by weight of Cr ₂ O ₃ (based on shaved weight). A particular advantage of such a combined procedure is the high exhaustion of chromium III salt from the residual liquor of the tanning: With a liquor length of, for example, 50% by weight at 40 ° C, after 1 to 3 hours, the seam is folded to approx. 1 mm Leather tanned through (with a Cr ₂ O ₃ content in the leather of approx. 3% by weight) and in the remaining liquor of this tanning a Cr ₂ O ₃ content of 0.4 g per liter at a final pH (the pH -Value drops due to the added tanning agent) of 4.1 found.

In purely arithmetic terms, the following picture emerges, for example, compared to Example 12 of EP-A 304 677, which is a process optimized with regard to consumption: Comparison: material balance conventional against carbamoyl sulfonate highly exhausting tanning according to EP-A 304 677 Carbamoyl sulfonate according to EP-A 690 135 Salt weight 430 kg 430 kg Gap weight (nakedness) 142 kg Fold weight 67 kg fleet 72 kg 34 kg NaCl 7.2 kg 0 sulfuric acid 1.5 kg 0 Cr ₂ O ₃ / l remaining liquor 0.3 g 0.4 g Cr in total fleet 14.4 g 9.2 g Comparison / according to the invention Rawhide Example 12 of EP-A 304 677 Example carbamoylsulfonate / chromium Salted insert 1000 kg 430 kg 430 kg Total wastewater 18000 kg 7740 kg 7740 kg Cr-containing shavings 145 kg 65 kg 0 Cr-free shavings 0 0 23 kg Cr in total wastewater 0 2 ppm 1.2 ppm

In EP-A 690 135, example A 66 describes a tanning process in which formic acid and then a commercially available, self-dulling chrome tanning agent were added after pretanning with carbamoyl sulfonate. This type of tanning already provides leather with a high shrinking temperature and residual liquors with sufficiently good chromium exhaustion. However, if a formate- or dicarboxylate-stabilized chromium tanning agent according to EP-A 304 677 is used, there is a further reduction in the chromium 3+ ion content of the remaining liquor.

If you use a stabilized, self-dulling chrome tanning agent, you can tan after pretanning, if necessary after folding, without lowering the pH value and without pimples at a pH of at least 4 and then retanning in the usual way.

As usual, retanning can be carried out with synthetic organic polymers (incl. Resin tanning agents) or with vegetable tanning agents.

The average molecular weights mentioned in this application are number average molecular weights.

The percentages in the following examples relate to the weight and to the bare / leather.

Examples Resources used

®BAYCHROM A

self-dulling chrome tanning agent from Bayer AG with 21% chromium oxide

®BAYKANOL TF-2N

Dyeing aids based on aromatic sulfonic acid from Bayer AG

®BAYGENAL Braun CGG

Acid Brown 83 from Bayer AG

®BAYMOL FD fl.

80% aqueous solution of a nonionic emulsifier from Bayer AG

®BLANCOROL ZB 33

0% basic zirconium sulfate with 33% zirconium oxide from Bayer AG

®BLANCOROL ZBE

50% basic zirconium sulfate with 31% zirconium oxide from Bayer AG

®TANIGAN BN

Organic synthetic exchange tanning agent from Bayer AG based on dioxydiphenyl sulfone and naphthalenesulfonic acid; Acid number 85

®TANIGAN LF

Synthetic exchange and white tanning agents from Bayer AG

®TANIGAN PAK-N

Neutralization tanning agent based on aromatic, sulfonic acid from Bayer AG

®TANIGAN OS

Analogue TANIGAN BN replacement tanning agent from Bayer AG with acid number 32

®RETINGAN R7

anionic resin tanning agent from Bayer AG with selective filling effect based on dicyandiamide

Quebracho, Mimosa, Chestnut:

commercially available vegetable tanning agents

®CUTAPOL TIS-MF

sulfited fish oil, 65% WS by Dr.Th.Böhme

®CORIPOL MK

Mixture of sulfited, natural oils and synthetic sulfoesters from Stockhausen & Cie.

®LUTAN BN

basic aluminum chloride from BASF AG

®TETRAPOL SAF

softening stabilizer based on fatty alcohols from Stockhausen & Cie.

®POLYZIM 202

proteolytic mordant based on pancreas from Diamalt

Magnesium oxide

Magnesia 322 from Magnesia GmbH, Lüneburg

example 1

Normally ashed nakedness is split to 2 mm. Then the pelts are placed in a conventional tanning drum and washed once with 200% (percentages refer here and hereinafter to the gap weight) of water at 35 ° C. for 15 minutes. Then let the fleet down. In the subsequent descaling, 30% water at 35 ° C, 2% ammonium sulfate and 0.2% sodium meta-bisulfite is added and agitation is carried out for 10 minutes. Then add 0.2% formic acid (diluted 1:10) and 0.2% BAYMOL FD liquid and let it run for 20 minutes. Stain with 0.5% Polyzim 202 in the same liquor for 30 minutes. The result is a pH of 7.9 (cut the nakedness with colorless phenolphthalein). Then let the fleet down.

It is washed twice with 150% water (from room temperature) and the liquor is drained off.

30% of water at 30 ° C. and 0.35% of magnesium oxide (Magnesia 322) are introduced into the tanning now beginning, and after 60 minutes 7.5% (based on active substance) of a product which is described in Example 1 of EP-A 690 135 manufactured had been admitted. After a running time of 6 hours, a pH of 7.1 is established; another 0.35% magnesium oxide (Magnesia 322) is added and the mixture is left to run overnight (final pH 6.8).
The next morning the resulting leather has a shrinking temperature of 78 ° C.

The liquor is drained, the leathers are rinsed for 10 minutes at room temperature, then they are wilted and folded to a thickness of 1 mm.
The folded leather is placed in a barrel and washed for 10 minutes with 200% (based on the fold weight) of water (from room temperature). The fleet is released.

The subsequent mineral tanning is initiated by 50% water at 35 ° C. (the pH value has reached 6.8) and 5% of a product which has been prepared according to Example 1 of EP-A 304677. After 150 minutes of movement, the pH value becomes 4.1.

The fleet is drained, the leathers have a Ts of 100 ° C. After washing with 300% water at 40 ° C (10 minutes), the liquor is drained off. In the neutralization which now begins, 200% water (40 ° C), 3% TANIGAN PAK-N are left to act for 1 hour (pH 4.7), then 4% CUTAPOL TIS-MF (diluted 1: 4) for 30 minutes. Then it is drained and washed with 200% water (35 ° C.) for 10 minutes. The retanning is started with 150% water (40 ° C): 3% TANIGAN BN and 2% TANIGAN LF for 20 minutes, then a solution of 3% BAYGENAL Braun CGG and 2% BAYKANOL TF-2N (1:20 at 60 ° C warm water) added. After 60 minutes, 100% water (70 ° C.) is added, after another 10 minutes 2% formic acid (diluted 1: 5) is added and the mixture is left to run for 30 minutes (pH 3.4). After draining the liquor, grease for 90 minutes in 200% water (50 ° C) with a mixture of 8% CORIPOL MK, 6% CUTAPOL TIS-MF and 1% TETRAPOL SAF (diluted 1: 4 with 60 ° C water). Then 1.5% formic acid (diluted 1: 5) is added for 45 minutes (pH 3.1); the fleet becomes clear. After draining the liquor, it is washed twice with 200% water at room temperature for 10 minutes each. The leathers are put on jack, are wet-tensioned, air-conditioned, stolled, grilled, tensioned and assessed.

Example 2

Based on Example A 1 of EP-A 690 135, 12 pieces of 100 g of bare bark in 40% liquor with 0.35% magnesium oxide were allowed to run for 1 hour in a test kettle from Dose (pH 7.4), then 7 , 5% (active substance) of a product according to Example 1 of EP-A 690 135 added, after 3 hours a further 0.35% magnesium oxide (pH 6.6) and then run overnight. The resulting leather had a Ts of 77 ° C. 5 of these leathers were treated in 100% liquor with 0.05% formic acid and 0.08% sulfuric acid to a pH of 3, a further 3 with 0.08% sulfuric acid to a pH of 4, and one each with 0. 03% formic acid to pH 5, one at 6.6 (left as is) and one with 0.04% 42% aqueous sodium hydroxide solution at 8.2.
All of these leathers have now been retanned minerally. leather Initially pH Tanned with % End pH Additives % Ts ° C 1 6.6 - - 6.6 - - 77 2nd 5 Chrome of example 1 5 3.7 - - 100 3rd 6.5 " 5 3.9 - - 100 4th 8.2 " 6 3.7 - - 100 5 3rd LUTAN BN 6 3rd - - 80 6 4th " 6 4.1 - - 79 7 3rd BLANCOROL ZB 33 4th 3rd - - 74 8th 4th " 4th 4th - - 75 9 3rd BLANCOROL ZBE 4th 3rd - - 74 10th 3rd Ammonium titanyl sulfate (22% TiO ₂ ) 6 4.2 citric acid 1 82

Examples 3 to 6

The example listed in EP-A 690 135 under A 66 was reworked (Examples 3 to 5) and compared with the process according to the invention (Example 6). The leather obtained was examined for the shrinkage temperature and the chromium contents of the leather and the remaining liquors were determined.

To get leather with a high shrinking temperature using the tanning method of EP-A 690 135, you should pick - to prevent failures. However, if you want to do without pimples, tanning agents analogous to those of EP-A 304 677 are recommended if, at the same time, you value high consumption from the remaining liquors of the tanning process.

Claims (5)

Method of using tanning I. Carbamoylsulfonate group-containing reaction products A. organic polyisocyanate, B. per isocyanate group of A. 0.01 to 0.4 equivalents of polyether alcohol with built-in polyalkylene oxide units (the equivalents relate to the hydroxyl groups of the polyether alcohol), the polyalkylene oxide units consisting of 40 to 100 mol% of polyethylene oxide units with a sequence length of 5 to 70 , C. optionally other NCO-reactive components, and D. ammonium or alkali bisulfites or disulfites, and below II. Mineral tanning agents from the series chromium (III), iron (II), iron (III), aluminum (III), titanium (IV) and zirconium (IV) without pimples at a pH value above 4. A method according to claim 1, wherein a C ₄ -C ₆ dicarboxylate complex of chromium is used as the mineral tanning agent. A method according to claim 1, wherein an ammonium titanyl sulfate and / or a citrate-complexed titanyl sulfate is used as the mineral tanning agent. The method of claim 1, wherein a basic, tanning active aluminum salt is used. The method of claim 1, wherein a tanning zirconium compound is used.