EP0204213A1 - Method of retanning chrome-tanned leather - Google Patents

Abstract

The present invention relates to a method for retanning chrome leather with a mixture which consists essentially of Cr (III) salts, dicarboxylic acids, truncating agents and synthetic tanning agents.

Description

The present invention relates to a process for retanning (post-chrome plating) chrome leather, in which chrome (III) salts are used and a very high chromium consumption of the liquor is achieved.

In the case of customary post-chrome plating, the chrome leathers are washed, treated with a chromium (III) salt, possibly in the presence of a syntan, and then in a new or the same liquor with the known acid-binding agents such as sodium or ammonium bicarbonate, sodium formate and others pH values between 4 and 7, depending on the type of leather. In these processes, less than half of the chrome tanning agent offered is often fixed by the leather. In the course of the subsequent operations, a further part of the unbound chromium is removed from the leather (see S.C. O'Connor, The Leather Manufacturer 1984, 8, 20-29).

There has been no shortage of attempts to improve the chromium depletion during post-chromium plating.

For example, combinations of chromium (III) salts, sodium sulfite and an intermediate formaldehyde-releasing heterocyclic compound were used (see S.C. O'Connor loc. Cit.). Apart from the presence of formaldehyde, which is often not desirable for ecological reasons, a pH of, for example, 6.9 in the liquor must be set in this process in order to achieve high exhaustion. However, pH values of this magnitude are only common when neutralizing furniture or clothing leathers that have to be dyed through.

In the case of upper leather, however, they lead to an impairment of grain strength and fineness (see also US Pat. No. 3,888,625).

Furthermore, it was proposed to use strongly buffering synthetic mixed products in combination with magnesium oxide for the neutralization of post-chrome plating (cf. Wachsmann and Hilzinger, Leder- und Häutemarkt 32 (1980), 188-191).

Also in this method must be set to a pH of about 6 / in order to obtain a depletion of about 0.1 g Cr ₂ O _3. 1 However, the high pH and the cumbersome separate addition of the products have prevented the method from being widely used.

In addition, attempts have been made to reduce the chrome depletion of the retanning liquors by adding dicarboxylic acid salts improve. In order to avoid chromium precipitation due to the high alkalinity of these salts, large quantities of masking agents must also be offered, which, however, counteract good chromium exhaustion. High amounts of crosslinking dicarboxylic acids and higher final pH values than 4.0 lead to an impairment of the scar fineness and the levelness of the colors according to this method (Magerkurth and Miller, The Leather Manufacturer 1981, 8, 10 - 31).

• a) Chrom(III)-salzen,
• b) 1,0 - 2,5 Mol (pro Mol Cr₂0₃ des verwendeten Chrom-(III)-salzes), vorzugsweise 1,5 - 2,3 Mol aliphatischer Dicarbonsäuren mit 4 - 6 C-Atomen beziehungsweise aromatischer Dicarbonsäuren mit 8 - 12 C-Atomen und/oder deren Salzen,
• c) solchen Mengen an Calciumcarbonat und/oder Dolomit sowie eventuell anderen Abstumpfmitteln, daß sich unter Berücksichtigung der eingesetzten Dicarbonsäuren und Abstumpfmittel eine theoretische Basizität des verwendeten Chromsalzes von 80 - 120 % einstellt, wobei das Molverhältnis der übrigen Abstumpfungsmittel zu Calciumcarbonat und/oder Dolomit 0-3 : 1 beträgt sowie
• d) 150 - 250 g (pro Mol Cr₂0₃ des verwendeten Chromgerbstoffes) eines synthetischen organischen Gerbstoffes (Syntan) beziehungsweise einer Syntanmischung

nachgegerbt werden.It has now been found that the exhaustion of the retanning liquors can be improved considerably if the chrome leather is made with mixtures

• a) chromium (III) salts,
• b) 1.0-2.5 moles (per mole of Cr ₂ 0 _{3 of} the chromium (III) salt used), preferably 1.5-2.3 moles of aliphatic dicarboxylic acids having 4 to 6 carbon atoms or aromatic dicarboxylic acids 8 - 12 carbon atoms and / or their salts,
• c) such quantities of calcium carbonate and / or dolomite and possibly other truncating agents that, taking into account the dicarboxylic acids and truncating agents used, the theoretical basicity of the chromium salt used is 80-120%, the molar ratio of the other truncating agents to calcium carbonate and / or dolomite being 0 Is -3: 1 as well
• d) 150-250 g (per mole of Cr ₂ 0 _{3 of} the chrome tanning agent used) of a synthetic organic tanning agent (Syntan) or a Syntan mixture

be retanned.

• a) Chrom(III)-Salzen,
• b) 1,0 - 2,5 Mol (pro Mol Cr₂0₃ des verwendeten Chrom-(III)salzes) aliphatischer Dicarbonsäuren mit 4-6 C-Atomen bzw. aromatischer Dicarbonsäuren mit 8-12 C-Atomen und/oder deren Salzen
• c) solchen Mengen an Abstumpfmitteln, um eine theoretische Basizität des verwendeten Chrom(III)-salzes von ca. 80-120 % einzustellen und
• d) 150-250 g (pro Mol Cr₂0₃ des verwendeten Chrom(III)-salzes) eines oder mehrerer synthetischer Gerbstoffe (Syntan)

durchgeführt wird.The present invention thus relates to a process for retanning chrome leather, which is characterized in that the retanning is composed of a mixture of

• a) chromium (III) salts,
• b) 1.0 - 2.5 moles (per mole of Cr ₂ 0 _{3 of} the chromium (III) salt used) aliphatic dicarboxylic acids with 4-6 C atoms or aromatic dicarboxylic acids with 8-12 C atoms and / or their Salt
• c) such amounts of truncating agents to set a theoretical basicity of the chromium (III) salt used of approx. 80-120% and
• d) 150-250 g (per mole of Cr ₂ 0 _{3 of} the chromium (III) salt used) of one or more synthetic tanning agents (Syntan)

is carried out.

The retanning is expediently carried out in the case of liquor lengths of over 100% (based on the fold weight) and liquor temperatures of 35-55 ° C. over a period of 1.5 to 4 Hours at final pH values above 4.0. The Cr ₂ 0 _{3 range} is 0.3-1.0% (based on shaved weight), preferably 0.4 - 0.6% (based on shaved weight).

Suitable chromium (III) salts for retanning are the usual chromium (III) salts which can be used for chromium tanning, in particular chromium (III) sulfates, basic chromium (III) sulfates, furthermore with organic acids, for example formic acid or Acetic acid, masked chromium (III) salts, chromium tanning agents which, in addition to chromium (III) salts, also contain inorganic salts, such as sodium sulfate, or reaction products of hexavalent chromium compounds with reducing agents.

Aliphatic dicarboxylic acids with 4 to 6 carbon atoms are, for example, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, aspartic acid, glutamic acid or mixtures thereof. Glutaric acid and adipic acid or mixtures of these acids, if appropriate with other dicarboxylic acids, are preferably used.

Aliphatic dicarboxylic acids with 4 to 6 carbon atoms, which contain a hydroxy group alpha to the carboxyl group and / or the sulfonic acid groups, should only be used up to about 1/3 of the total amount of dicarboxylic acid used.

Aromatic dicarboxylic acids with 8 to 12 carbon atoms are those of the benzene and naphthalene series which, in addition to the carboxyl groups, also contain hydroxyl, amino or nitro groups and / or may contain halogen atoms. Phthalic acid and isophthalic acid are preferably used.

The carboxylic acids can be used both in the form of free acids, in the form of mixtures of the free acids and the salts of such carboxylic acids, and alone in the form of the salts, advantageously the alkali metal salts.

Anionic aromatic syntans (see Ullmanns Encyklopadie der Technische Chemie, Verlag Chemie, Weinheim, 4th edition, volume 16 (1978), pp. 138-139), aromatic syntans from lignin sulfonates (see Ullmann, loc. cit., p. 139), resin tanning agents (cf. Ullmann, loc. cit. pp. 142-143) polymer tanning agents (Ullmann, loc. cit. p. 144) or mixtures thereof.

Suitable syntans are, for example, naphthalenesulfonic acid-formaldehyde, diaryl ether sulfonic acid-formaldehyde, polyphenylsulfonic acid-formaldehyde, phenolsulfonic acid-formaldehyde, naphthalenesulfonic acid-4,4'-dihydroxydiphenylsulfone-formaldehyde condensates, polyphenylsulfonic acids and their lignin sulfonic acids.

Protein hydrolyzates are also suitable as synthetic organic tanning agents (see K. Faber, Library of Leather, Volume 3, Umschau-Verlag, Franktfurt am Main, p. 236).

Dicyandiamide-formaldehyde condensates and mixtures thereof with anionic dispersants are preferred based on lignin sulfonate or naphthalene sulfonic acid.

In addition to calcium carbonate and / or dolomite, alkali or ammonium carbonates and magnesium oxide are suitable as deadening agents.

Magnesium oxide or sodium bicarbonate or mixtures thereof are preferably used.

The mineral double salt CaC0 ₃ . MgC0 ₃ , which has a content of 20-40 X CaO, preferably 25-35 X Ca0 and an MgO content of 10-25%, preferably 16-24% MgO, understood.

The addition of calcium carbonate and / or dolomite and the other dulling agents depend on the basicity of the chromium salts used and the degree of neutralization of the dicarboxylic acids used. They are to be dimensioned such that, taking into account the dicarboxylic acids or their salts, the calcium carbonate and / or dolomite and the other deadening agents, the resulting theoretical basicity of the chromium salt is 80-120%.

The calculation of the total basicity is explained using the following example:

In the process according to the invention, the wet blues which have been chrome-tanned, withered and folded in the usual manner are preferably retanned in the manner described without prior washing. After retanning, the leather can be dulled if necessary by adding deacidifying agents in the same or in a new liquor. They are then dyed in the usual way, possibly retanned with vegetable tannins and / or syntans, greased etc.

All conventional types of chrome leather from large cattle hides or small animal skins, including the corresponding split leather, are suitable for the process according to the invention.

The use of mixtures of chromium (III) salts, acid-binding agents and aliphatic or aromatic dicarboxylic acids has already been described (see De-AS 24 24 300 and DE-AS 24 24 301). However, the mixtures were not used for retanning wet blues, but for chrome tanning of bare. However, the conditions of the tanning (Cr ₂ 0 ₃ supply: at least 1.2 X, liquor length: max. 100%, based on the pelt weight) differ fundamentally from those of the retanning according to the invention.

The value of the process consists in the fact that, with a very simple method of working, it leads to leather of all colors, full, soft, fine-grain and grain-resistant, and at the same time high chrome depletion of the retanning brisk. The residual liquors have, depending on the liquor length, duration and temperature of chromium oxide of less than 0.5 g Cr ₂ 0. _3/1

It was not foreseeable that the consumption of the substances according to the invention would be improved so much without the use of at least 1.5 moles of dicarboxylic acids per mole of Cr ₂ 0 _{3 of} the chromium salt used and the final pH of the remaining liquor from above 4.0, the grain fineness and grain strength of the leather as well as the levelness of the coloring are impaired.

The process according to the invention is to be explained in more detail with reference to the following examples (X figures are% by weight):

example 1

Retanning of chrome-tanned, folded beef or calf leather (final pH of the chrome tanning: 3.6)

Drain the fleet

Leather is obtained which is distinguished by a level, deep color, a soft, full grip and an excellent grain strength and smoothness.

* The chrome-syntan mixed tanning agent used has the following composition.

Example 2

Procedure as described in Example 1. Instead of water at 50 ° C, retanning is carried out with water at a temperature of 60 ° C.

The Cr ₂ 0 ₃ content of the retanning liquor is 0.1 g / l.

The leathers obtained are identical to those produced according to Example 1.

Example 3

Procedure as described in Example 1. The syntan part of the mixed tanning agent consists of 140 parts by weight. of a commercial auxiliary tanning agent based on ditolyl ether sulfonic acid.

Cr ₂ 0 ₃ content of the retanning liquor: approx. 0.25 g, pH value: 4.6.

The leathers have a somewhat lighter color than those produced according to Example 1. Otherwise, they are comparable in all properties.

Example 4

Process as in Example 1. Instead of the chromium-syntan tanning agent given there, based on Cr ₂ O ₃ , 0.5% of products I-III are used.

Composition (in parts by weight):

Example 5;

Procedure as described in Example 1. Instead of the chromium-syntan tanning agent used there, 0.5% (based on Cr ₂ 0 ₃ ) of the products IV-VI are used.

Composition (in parts by weight)

Example 6:

Retanning as described in Example 1. Instead of 0.5% (based on the chromium oxide content of the mixed product), 0.4% (based on chromium oxide content of the mixed product) is used.

Example 7:

Retanning as in Example 1. Instead of 0.5% (based on the chromium oxide content of the mixed product), 0.6% (based on chromium oxide content of the mixed product) are offered.

Example 8:

Retanning as in Example 1. Instead of the syntan component used there, the same amounts of a commercially available synthetic organic tanning agent based on a mixture of diphenyl and terphenyl sulfonic acid are offered.

The leather has a deeper color than that obtained in Example 1.

The exhaustion of the fleet remains unchanged.

Example 9

Retanning a furniture leather wet blue (final pH maintenance of chrome tanning: 4.1; fold thickness 1.0 - 1.1 mm)

Anschließend wird nach einer für Möbelleder üblichen Rezeptur nachgegerbt, gefärbt und gefettet.

It is then retanned, dyed and greased according to a recipe common for furniture leather.

Leather on jack, stretch out, wet stretch, air-conditioning, tunnel, mill, stretch.

Furniture leather is obtained which is characterized by a soft, full handle, a level, deep color and a fine mill grain.

Example 10

Retanning as in Example 1, except that 4.5 X (based on the shaved weight) of the following mixture are used instead of the chrome syntan tanning agent used there:

The final pH of the retanning liquor is 4.9 and the Cr ₂ 0 ₃ content is 0.2 gll.

Claims (5)

1. A method for retanning chrome leather, characterized in that the retanning with a mixture consisting of a) chromium (III) salts, b) 1.0 - 2.5 moles (per mole of Cr ₂ 0 _{3 of} the chromium (III) salt used) aliphatic dicarboxylic acids with 4-6 C atoms or aromatic dicarboxylic acids with 8-12 C atoms and / or their Salt c) such amounts of truncating agents to set a theoretical basicity of the chromium (III) salt used of approx. 80-120% and d) 150-250 g (per mole of Cr ₂ O _{3 of} the chromium (III) salt used) of one or more synthetic tanning agents (Syntane),
is carried out. 2. The method according to claim 1, characterized in that the syntan dicyandiamide-formaldehyde condensates and mixtures thereof with dispersants based on lignosulfonate or naphthalenesulfonic acid are used. 3. The method according to any one of claims 1 or 2, characterized in that calcium carbonate is used as the blunting agent. 4. The method according to any one of claims 1 or 2, characterized in that dolomite is used as the blunting agent. 5. Retanning mixture consisting essentially of a) chromium (III) salts, b) 1.0-2.5 moles (per mole of Cr ₂ 0 _{3 of} the chromium (III) salt used) aliphatic dicarboxylic acid with 4-6 C atoms or aromatic dicarboxylic acids with 8-12 C atoms and / or their Salt c) such amounts of truncating agents to set a theoretical basicity of the chromium (III) salt used of approx. 80-120% and d) 150-250 g (per mole of Cr ₂ 0 _{3 of} the chromium (III) salt used) of one or more synthetic tanning agents (Syntan).