EP0304677A1 - Tanning method with high chrome exhaustion - Google Patents

Abstract

The present invention relates to a process for the chrome tanning of pickled pelts with a reaction product of a basic chromium(III) sulphate and aliphatic dicarboxylic acids having 4 to 6 C atoms and/or salts thereof, the reaction product being prepared in aqueous solution from the basic chromium(III) sulphate and 0.2 to 0.8 mol of the aliphatic dicarboxylic acids per mol of chromium oxide of the basic chromium sulphate with subsequent adjustment of the theoretical basicity to 0 to 50% with the customary alkalis, and the reaction products being added to the pickling liquor as an aqueous solution having a chromium oxide content of at least 5% or in pulverulent form in an amount of 0.9 to 1.5% of chromium oxide (based on pelt weight), the liquor volume being less than 100% (based on pelt weight), the final pH being above 4.0 and the final temperature being above 40 DEG C.

Description

When it comes to improving the environmental situation of leather factories, reducing the chromium content in wastewater is an important concern today. In addition to the recovery of unused chrome from residual fleets of tanning and retanning, etc., high-performance chrome tanning processes have become established to achieve this goal (K. Faber, Bibliothek des Leders, Volume 3, page 158 ff., Umschau-Verlag, Frankfurt / Main, 1. Edition, 1985). Here, unlike in recycling processes, excess chrome is used in the tanning process, which is actually not required and must always be circulated. Rather, only as much chromium is offered in the tanning as is necessary to set the desired chromium content in the leather. The remaining liquors in tanning and retanning accordingly contain only small amounts of chromium.

To improve chromium exhaustion, it has been proposed, among other things, so-called crosslinking aliphatic dicarboxylic acids such as Use succinic acid, adipic acid and glutaric acid in pimples or chrome tanning (see e.g. Leder 23 (1972), 174 ff .; Das Leder 28 (1977), 155 ff .; Leder- und Häutemarkt 30 (1978), 132 ff.) .

The aliphatic dicarboxylic acids are added in the form of their disodium salts to the chrome tanning liquor following the chrome tanning agent. The chromium exhaustion is significantly improved compared to a conventional tanning process, but the leather quality can be impaired (cf. K. Faber, loc. Cit. P. 83). In particular with thick or uncleaved pelt material there is a deterioration in the chromium distribution and the dyeability. This has a negative effect that the penetration of the chrome tanning agent through the skin cross-section is hindered due to the presence of the dicarboxylic acids in the process described (Leder- und Häutemarkt 30 (1978) 140).

To improve, it is recommended to work at tanning temperatures below 4.0 and temperatures around 40 ° C. However, only degrees of exhaustion of up to 95% are possible here (Das Leder 28 (1977), 157).

It is also suggested to add the dicarboxylic acid salts in several proportions. This further complicates the tanning process.

According to a method described in DE-PS 2 424 301, the difficulties described are eliminated if tanning mixtures consisting of chromium (III) salts, acid-binding agents and aliphatic dicarboxylic acids with 4 to 6 carbon atoms or their salts are used in chrome tanning used in advance together with conventional chrome tanning agents. To achieve good exhaustion, you need at least 1.6 moles of dicarboxylic acid per mole of chromium oxide in the tanning mixture for tanning.

It is also known that solutions of chromium (III) salts and sodium adipinate can be used for the chrome tanning of calfskins (Journal of the International Society of Leather Trades Chemists 27 (1943), 83 ff.). However, the use of more than 1.5% chromium oxide (based on the weight of the pimples, corresponds to significantly more than 1.5% chromium oxide based on the weight of the skin) is necessary in order to obtain a sufficient tanning effect (cooking temperature). The chrome liquors used only have a chromium oxide content of max. 2.8% and are therefore not suitable for use in technology. The chromium exhaustion in the case of chromium oxide offers of more than 1.5% (based on the weight of the pimple) is well above 1.0 g chromium oxide / l.

In all previously known high-exhaustion chrome tanning processes in which aliphatic dicarboxylic acids are also used, the total amount of the chrome tanning agent and the dicarboxylic acids in unreacted form must always be added in at least 2 parts of the liquor.

It has now been found that chrome tanning with a high exhaustion and a good chrome distribution in the leather is possible with only one addition of the total amount of the chrome tanning agent and the dicarboxylic acids if the pickled pelts are reacted with a reaction product of a basic chromium sulfate and 0.2-0. 8 moles / per mole of chromium oxide of the basic chromium sulfate) of an aliphatic dicarboxylic acid with 4 to 6 carbon atoms or their mixtures chrome-tanned.

The theoretical basicity of the reaction product is 0 - 50%. The reaction product can also contain monocarboxylic acids as masking agents. The amount used is 0.9-1.5%, calculated as chromium oxide, based on the weight of the bare skin.

In a preferred variant of the process, the reaction product used according to the invention, hereinafter referred to as chromium-dicarboxylate complex, is dried and optionally mixed with the customary acid-binding agents.

The process according to the invention is carried out in a liquor volume of less than 100%, preferably 10-50% (based on pelvis weight), at a final pH of more than 4.0, preferably 4.2-4.6, and a final Temperature of over 40 ° C, preferably 42-50 ° C, carried out.

If the chromium-dicarboxylate complex is not used together with acid-binding agents in chrome tanning, it is blunted in the usual way with alkalis to the desired pH.

The chromium oxide content of the residual tannins obtained by the process according to the invention is less than 1 g / l.

The chromium-dicarboxylate complex is prepared by reacting basic chromium (III) sulfates with the corresponding aliphatic dicarboxylic acids with 4-6 C atoms or their mixtures in aqueous solution at temperatures of 50-100 ° C. over a period of 30-80 minutes. The desired theoretical basicity of 0-50% is then set with an alkali solution, preferably with a soda solution. (For the calculation of the theoretical basicity, see DE-OS 3 519 287).

The chromium-dicarboxylate complex thus obtained can be used in the present solution for chrome tanning. In a preferred variant of the method, the solution is evaporated, preferably spray dried. The powder tanning agent obtained in this way can be used as such or mixed with acid-binding agents in chrome tanning.

The basic reaction products of hexavalent chromium compounds with reducing agents which are customary in chrome tanning are suitable as basic chromium (III) sulfates (see, for example, K. Faber, loc. Cit. P. 83). They can additionally contain monocarboxylic acids (eg formic or acetic acid) or their salts as masking agents.

The chromium oxide content of the solutions according to the invention should be at least 5%, preferably 10 to 15%.

Aliphatic dicarboxylic acids with 4 to 6 carbon atoms are e.g. Succinic, glutaric, adipic, maleic, fumaric, aspartic and glutamic acid or mixtures thereof. Glutaric acid and adipic acid or mixtures of these acids, optionally together with other dicarboxylic acids, are preferably used.

Suitable acid-binding agents (basifying agents) are, for example Dolomite, alkali carbonates and bicarbonates and magnesium oxides.

The mineral double salt CaCO₃.MgCO₃, which has a content of 20 to 40% CaO, preferably 25 to 35% CaO and a content of 10 to 25% MgO, preferably 16 to 24% MgO, is used as dolomite.

Mixtures which contain at least 40% of the total amount of acid-binding agents used in the form of dolomite and / or magnesium oxides with low reactivity are particularly suitable.

Magnesium oxides with low reactivity are, for example, commercial products such as ®TANBASE (manufacturer: Steetley Quarry Products Ltd.) or ®NEUTRIGAN MO (manufacturer: BASF).

The chrome dicarboxylate complexes according to the invention are also suitable for use in retanning chrome leather. Here, 0.3 to 1.5% chromium oxide (based on fold weight) is offered.

The value of the process according to the invention lies above all in the fact that the use of the chrome dicarboxylate complexes according to the invention enables high emaciations in the chrome tanning with a particularly simple procedure and a particularly low workload without impairing the quality of the leather. With only a single addition of chrome tanning agent and dicarboxylic acid, residual liquors with a chromium oxide content of less than 1 g / l are obtained. It was not foreseeable that the use of the chromium-dicarboxylate complexes according to the invention would improve the through-tanning to a high degree and that despite the low amount of dicarboxylic acid relative to the chromium supply, such high levels of emaciation could be achieved.

The process according to the invention is to be explained in more detail with the aid of the following examples (percentages mean, unless stated otherwise,% by weight).

example 1

722 kg of a chromium (III) sulfate solution with a basicity of 33.2% (according to Stiasny) and a chromium (III) oxide content of 16.8% are heated to 80 ° C. in a 1000 liter kettle. 42 kg of technical glutaric acid (40% glutaric acid, 30% succinic acid and 30% adipic acid) are added and the mixture is stirred for 30 minutes. After adding 100 ml of defoamer based on polysiloxane defoamer E 100 (manufacturer: BAYER AG), 347 kg of a 3n soda solution are pumped in over a period of about 120 minutes. The reaction solution is then stirred at 80 ° C. for 60 minutes and has a theoretical basicity of 40% with a chromium oxide content of 10.9%. The still hot solution is then dried using a spray dryer (inlet temperature: 185 ° C, outlet temperature: 120 ° C). 490 kg of chromium-dicarboxylate complex with a chromium oxide content of 24%, 0.4 mol of technical glutaric acid per mol of chromium oxide and a theoretical basicity of 40% are obtained.

Example 2

735 kg of a chromium (III) sulfate solution with a basicity of 33.2% (according to Stiasny) and a chromium oxide content of 15.6% are heated to approx. 80 ° C in a 1 m³ agitator tank and reacted with 64 kg of technical glutaric acid . After stirring for 30 minutes at 80 ° C, the chrome tanning solution (13% basicity and 15.2% chromium oxide content) is dried over a spray dryer (Inlet temperature: 185 ° C, outlet temperature: 115 ° C). 485 kg of chromium-dicarboxylate complex tanning agent are obtained with a theoretical basicity of 13% and a chromium oxide content of 23.5%; the molar ratio of chromium oxide / glutaric acid is 1: 0.6.

Example 3

In a 1 m³ agitator container 700 kg of a solution of chromium sulfate with a basicity of 33.2% (according to Stiasny) and a Cr₂O₃ content of 18% are brought to a temperature of 80 ° C. 43.8 kg of a mixture consisting of 32% succinic acid, 39% glutaric acid and 29% adipic acid are then dissolved therein and the mixture is stirred for 30 minutes. The liquid mixture thus obtained has a theoretical basicity of about 20% and a Cr₂O₃ content of 16.9%; the molar ratio of chromium oxide to dicarboxylic acid is 1: 0.4. The amounts used for the production of further chromium dicarboxylate complex tanning agents which can be used in liquid form are listed in the table below as examples 3a to 3d (preparation instructions as in example 3). E.g. Molar ratio Cr₂O₃: glutaric acid Parts by weight of chromium sulfate * Gwe.-Tl. Glutars. Basicity % Cr₂O₃ 3a 1: 0.2 700 21.9 26.5% 17.5 3b 1: 0.3 700 32.8 23.2% 17.2 3c 1: 0.6 700 65.6 13.2% 16.5 3d 1: 0.8 700 87.5 6.5% 16.0 * Composition as in example 3

Example 4

750 kg of a 33.2% basic chromium (III) sulfate solution with a chromium oxide content of 16.2% are placed in a 1000 l kettle and heated to approx. 90 ° C. Then 70 kg of adipic acid are added and stirring is continued for 30 minutes in the heat. After adding a commercially available defoaming agent (E 100, BAYER AG), 343 kg of a 20% sodium carbonate solution are pumped in over a period of 180 minutes. The reaction solution is then stirred under heat for 60 minutes; the theoretical basicity is approx. 40%, the chromium oxide content is 10.4%. The still hot, liquid tannin mixture is then spray dried (inlet temperature: 180 ° C, outlet temperature: 118 ° C).

A chromium-dicarboxylate complex tanning agent with a chromium oxide content of 22.8%, 0.6 mol of adipic acid per mol of chromium oxide and a theoretical basicity of approx. 40% is obtained.

Example 5

For the production of upper leather, ashed 1000 kg of beef pelts (unsplit) in a tanning drum (diameter 2 m, width 2.25 m, speed of rotation 12 rpm) are first washed with 150% (based on pel weight), water of 38 ° C 10 Minutes washed. The liquor is drained and then without liquor with 2.5% ammonium sulfate, 0.3% sodium bisulfate and Decalcified for 60 minutes with 0.4% formic acid, 50% water at 35 ° C. added and pickled with 0.5% of a commercial pickling agent (1500 trypt. units) for 50 minutes (pH of the liquor 7.5). The cross-section of the nakedness no longer gives a red color with phenolphthalene. Then it is washed twice with 150% water at 20 ° C. and the liquor is drained apart from a remaining liquor of approx. 50%. 5 minutes after the addition of 6% sodium chloride, 1.6% sulfuric acid (diluted 1:10) are added and the mixture is pounded for 120 minutes (pH 1.8).

6.7% of the tannin mixture described below is added to the pickling liquor and further tumbled for 20 hours. The final pH is 4.5 and the final temperature is 50 ° C.

The remaining liquor contains 0.6 g chromium oxide / l. The chrome leathers show excellent tanning when assessed after splitting. After the usual completion, upper leather with a soft, full grip, a fine grain and a very level coloring are obtained.

The tannin mixture used consists of:

800 parts of the powdery chromium dicarboxylate complex prepared according to Example 1 and

174 parts of dolomite.

The chromium oxide content is 19.7%.

Example 6

100 parts of beef peat pretreated as in Example 5 are mixed with 7 parts of the tannin mixture described below and drummed for 20 hours. The final pH is 4.6, the final temperature is 48 ° C; in the remaining liquor there are 0.6 g Cr₂O₃ / l.

The tannin mixture used, which has a Cr₂O₃ content of 18.6%, is composed as follows:

100 parts of the chrome-dicarboxylate complex tanning agent prepared according to Example 2

5 parts tanbase (manufacturer Steetley, Great Britain)

21 parts of dolomite.

Example 7

100 parts of beef peat pretreated as in Example 5 are mixed with 7.9 parts of a chromium-dicarboxylate complex solution prepared according to the instructions in Example 2. After 1 hour, 1.8% soda (1:15 dissolved), blunted within 1 hour and further tumbling for 15 hours. Towards the end of the tanning process, the temperature and pH are 46 ° C and 4.3, respectively. The remaining liquor contains 0.5 g Cr₂O₃ / l.

Example 8

Corresponding beef halves pretreated up to and including the pimple are chrome-tanned by comparison.

100 parts of the nakedness of one half A are drummed with 7.6 parts of the tannin mixture described below over a period of 20 hours.

Composition of the tannin mixture containing 17.4% chromium oxide (molar ratio Cr₂O₃: glutaric acid = 1: 0.4) for A:

500 parts of a powdery 33% basic chromium (III) sulfate with 26% chromium oxide content

45 parts techn. Glutaric acid

86 parts of sodium bicarbonate

118 parts of dolomite.

The final temperature of the tanning is 42 ° C, the final pH is 4.3. The remaining liquor contains 0.6 g Cr₂O₃ / l.

100 parts of the corresponding piece B are treated with 6.7 parts of the mixture described below for 20 hours.

Composition of the mixture for B containing 19.7% of Cr₂O₃:

80 parts of the chromium dicarboxylate complex prepared according to the instructions in Example 1 and

18 parts of dolomite.

The temperature reached at the end of the tanning is 42 ° C, the final pH is 4.3 and the chromium oxide content of the remaining liquor is 0.8 g / l.

Compared to B, the leather of the corresponding pieces A has a significantly poorer tanning after splitting.

The subsequent dyeings carried out in the usual way are also significantly more uneven at A.

Example 9

The production of upper leather is in the usual way washed 3000 kg beef pelts (split approx. 3.5 mm) in the tanning drum (diameter 3 m, width 3 m, speed of rotation 5 and 10 rev / min) first with 150% (based on paw weight) of water washed at 38 ° C for 10 minutes. The liquor is drained and then decalcified with 30% water at 35 ° C with 2% ammonium sulfate, 0.2% sodium bisulfate and 0.2% formic acid for 30 minutes and with 0.5% of a commercial pickling agent (1500 tryptic units) pickled for 30 minutes (pH of the liquor 8.3).

The cross-section of the nakedness no longer gives a red color with phenolphthalein. Then it is washed twice with 150% water at 20 ° C. and the liquor is drained apart from a remaining liquor of approx. 20%. 5 minutes after the addition of 4% sodium chloride, 0.5% formic acid (diluted 1: 5) and after 10 minutes 0.8% sulfuric acid (diluted 1:10) are added and the mixture is wound for 60 minutes (pH 2.7). 8.1% of the chromium-dicarboxylate complex solution prepared according to the instructions in Example 3d are pumped into the pickle liquor.

After one hour, blunted with 2.2% soda (1:15 dissolved in water) in six installments within one hour and further tumbling for 18 hours.

Towards the end of the tanning the temperature is 40 ° C, the pH is 4.0: the chromium (III) oxide concentration of the remaining liquor was determined to be 0.4 g / l.

After the usual completion, full, soft leather is obtained, which is characterized by an excellent color uniformity.

Example 10

100 parts as present in example 9, on about 3.5 mm split beef pelts, with 6.7 parts of the after the tanning mixture described above is added to the pickling liquor.

The tanning mixture with a Cr₂O₃ content of 21.0% is composed as follows:

100 parts of the chromium-diocarboxylate complex tanning agent and produced according to the instructions in Example 4

8.5 parts tanbase.

The final pH is 4.3 at a temperature of 45 ° C. The remaining liquor contains 0.5 g / l Cr₂O₃.

Example 11

For the manufacture of furniture leather, 3000 kg of beef pestle (split approx. 2 mm) in the tanning drum (diameter 3 m, width 3 m, speed of rotation 5 and 10 rpm) are washed in the usual way, initially with 150% (based on the weight of the pelvis) of 38 water ° C washed for 10 minutes. The liquor is drained and then decalcified with 50% water at 35 ° C. with 2.5% ammonium chloride, 0.3% sodium bisulfite and 0.2% formic acid for 40 minutes and with 0.7% of a commercial pickling agent (1500 tryptic units) Stained for 45 minutes (pH of the liquor 8.5).

The cross-section of the nakedness no longer gives a red color with phenolphthalein. Then it is washed twice with 150% water at 20 ° C. and the liquor is drained apart from a remaining liquor of approx. 50%. 5 minutes after the addition of 6% sodium chloride, 1.1% sulfuric acid (diluted 1:10) are added and the mixture is wound for 120 minutes (pH 2.7).

6.3% of the tannin solution described in Example 3 are added to the pickling liquor and after 1 hour the solution is blunted with 1.4% soda (1:15 dissolved) within 1 hour and further tumbled for 15 hours. The final pH is 4.2 and the final temperature is 45 ° C.

The remaining liquor contains 0.2 g / l chromium oxide. After the usual completion, furniture leather with a soft feel and very level colors are obtained.

Example 12

100 parts as ashed, decalcified, pickled and pickled beef (split approx. 2 mm) as in Example 11 are mixed with 5.5 parts of the tanning mixture described below in the pickling liquor and further tumbled for 18 hours. The final pH is 4.5, the final temperature is 45 ° C. The chromium oxide content of the remaining liquor is 0.3 g / l.

Composition of the powdered tanning mixture containing 19% Cr₂O₃

750 parts of a chrome-dicarboxylate complex tanning agent prepared according to the instructions in Example 4

151 parts of dolomite.

Example 13

500 kg wet blue with a rebate thickness of 1.5 mm are placed in a tanning drum (diameter 2.5 m, width 2 m, speed of rotation 12 rpm) with 200% water at 55 ° C and 2.5% (based on the rebate weight ) drummed the tannin mixture described in Example 5 with a chromium oxide content of 19.7% for 90 minutes and moved overnight for 5 minutes on the automatic switch. The post-chrome liquor has a pH of 4.6 and contains 0.1 g Cr₂O₃ / l. The leathers are finished according to a standard practice for upper leather. The result is very different colored and grain-resistant upper leather.

Example 14

100 parts as pretreated in Example 9, split to 3.5 mm of beef patties are tanned in the pickling liquor with 6.75 parts of the mixture listed below.

Mix composition:

500 parts of the chromium dicarboxylate complex tanning agent prepared according to Example 1 and

101 parts of dolomite.

Cr₂O₃ content: 20%.

After a milling time of 12 hours, a final temperature of 42 ° C was reached at a pH of 4.1. The liquor contains 0.9 g Cr₂O₃ / l.

Claims (7)

1. A process for tanning chrome of pickled pelts with a reaction product of a basic chromium (III) sulfate and aliphatic dicarboxylic acids with 4 to 6 carbon atoms and / or their salts, characterized in that the reaction product in aqueous solution from the basic chromium ( III) sulfate and 0.2 to 0.8 mole of the aliphatic dicarboxylic acids per mole of chromium oxide of the basic chromium sulfate and subsequent adjustment of the theoretical basicity to 0 to 50% with the usual alkalis, the addition of the reaction product to the pickling liquor as an aqueous solution with a chromium oxide content of at least 5% or in pulverized form in an amount of 0.9 to 1.5% chromium oxide (based on pel weight), the liquor volume is less than 100% (based on pel weight), the final pH Value is over 4.0 and the final temperature is over 40 ° C. 2. The method according to claim 1, characterized in that the reaction product is added as a spray-dried powder. 3. The method according to claim 1, characterized in that the reaction product is used in spray-dried form mixed with acid-binding agents in the tanning. 4. The method according to any one of claims 1 to 3, characterized in that the reaction product in aqueous solution by heating the basic chromium (III) sulfate and the aliphatic dicarboxylic acids to 50 to 100 ° C over a period of 30 to 180 min and then Setting the theoretical basicity to 0 to 50% is made with an alkali solution. 5. The method according to any one of claims 1 to 4, characterized in that a technical mixture of glutaric, succinic and adipic acid is used as aliphatic dicarboxylic acids having 4 to 6 carbon atoms. 6. The method according to any one of claims 1 to 5, characterized in that dolomite, optionally in a mixture with other acid-binding agents, is used as the acid-binding agent. 7. The method according to any one of claims 1 to 5, characterized in that magnesium oxide with low reactivity, optionally in a mixture with other acid-binding agents, is used as the acid-binding agent.