EP0158077A1 - Process for retanning mineral-tanned leather - Google Patents

Abstract

The present invention relates to retanning agents for mineral-tanned leather. They consist of aqueous solutions of carboxyl group-containing, chromium-doped organic polymer complex compounds. These agents are characterized by high chromium exhaustion and retanning effects.

Description

The main tanning with mineral tanning agents alone is not sufficient to give finished leather the required variety of properties. To emphasize special properties or to achieve them in the first place, a retanning is connected to the main tanning. In addition to the quality requirements of the processors, the leather producers still have to consider considerable environmental requirements. One of the main requirements relates to chromium in the wastewater, which is introduced into the wastewater through a main mineral tanning process with various chrome tanning agents. Many factories are therefore required to either have the main tanning section carried out by those companies that have the option of recovering chromium from the residual tanning liquor or to process the chrome-tanned wetbLue merchandise on the market. However, problems of this type have not yet been completely solved, since astonishingly much, too much chromium is still transferred from the leather into the waste water during further processing of this product.

The chromium concentration in Spüt- or NachgerbefLotten is largely ^g of the ability of the chromfixierenden After he ^b e-means dependent and occurs in the present state of the art at about 0.1 to 2 g Cr ₂ O ₃ / L residual liquor. Since the permissible amount of chromium in the wastewater only with 2 mg Cr / L (= 2.9 m ^g Cr ₂ 0 ₃ / l) is handled without criticism, there are considerable problems with the usual amount of chromium being flattened due to the concentration being exceeded. There has therefore been no attempt to generally reduce these problems by means of special processes and / or auxiliaries, but it was practically impossible - without impairing the quality of the leather - the chromium concentration of the remaining feet was noticeable below 0.1 g Cr ₂ O ₃ / L to lower.

DE-OS 27 55 087 describes pre-tanning of raw material, with concentrations of 0.13 g Cr ₂ O ₃ / L, 0.18 g Cr ₂ O ₃ / L or 0 at the end of the tanning by means of polymers made from monomers containing carboxyl groups , 3 g of Cr ₂ O ₃ / L remaining liquor can be reached. These polymers are also suitable for retanning. In DE-OS 31 41 496 A 1, CopoLymerisate of PoLyacryLamid and MethacryLamid with cationic groupings in retanning are recommended, whereby coloring effects are in the foreground, but which do not cause any abnormal chromium fixation.

The manufacturers of polymer tanning agents often recommend that the leather be rinsed before retanning, which, however, leads to pollution of the wastewater by chromium which has not been sufficiently fixed beforehand. Other types of polymer tanning agents are sensitive to acid and form precipitates, so that the chrome leather must also be neutralized before use, which, depending on the neutralizing agent used, causes particularly high concentrations of chromium in the waste water.

The outer aspect plays a major role in achieving leather properties. For example, leather with the brightest possible color is sought in order to be able to dye very pastel or clear shades in the first place. The same requirements apply to leather that has been dyed dry and then kept in stock and then in stock - opffärbung be colored by means of a so-called _K - depending on the requirement fashion. The versatility of such dry leathers in terms of color depends very much on a neutral, light base color.

The mode of action of polymer tanning agents can generally be described in terms of leather properties in such a way that the leather treated with them is soft and more or less full and full-grain. In the case of the polymer tanning agents designated as firm-graining, however, it must be established that the term "firm-grained" is relatively stretchy and does not come up to the usual level of with specially designed auxiliary agents, e.g. on leather treated with polyphosphates.

However, polyphosphates have a coloring disadvantage in the case of very clear colors, since the leather is given a greenish basic color and thus introduces parts of achromatic color in the complementary area. In addition, polyphosphates cannot achieve the very high levels of exhaustion required.

The present invention has therefore set itself the task of creating a retanning process for mineral-tanned, in particular chrome-tanned leather, which i.a. leads to a very high brightness of the leather as well as to a very low pollution of the waste water. This problem is solved with the features set out in the patent claims.

The chromium polymer polymer complexes doped with chromium that are used here are new; they can be produced in an inventive manner by the manner also characterized in the claims.

To the great surprise, auxiliaries were found in the complexes of polymer compounds with trivalent chromium claimed according to the invention, with which chromium exhaustions far beyond the prior art were achieved with simultaneous retanning, although chromium was additionally introduced into the retanning system. Since the leathers treated with the polymer complexes according to the invention are unusually pitted and at the same time maintain softness, an improvement over the prior art has also been achieved here. Another advantage that should not be underestimated is the characteristic, very bright basic color, which goes far beyond the usual level. The polymer complexes according to the invention are insensitive to acids and exchange undesired acid residues in the leather, so that the neutralization step in the conventional sense can also be dispensed with. Alkaline additives are still possible, they serve to set a desired pH range.

In the case of leather tanned with aluminum tanning agents, the polymer complexes according to the invention improve the scar strength, particularly in the loose skin regions. The yellow tint characteristic of leather tanned with aluminum can be compensated very well.

The polymer compounds can be prepared in a manner known per se (see, for example, E. Müller, Houben-Weyt, Methods of Organic Chemistry, Volume XIV-I 1961, p.1010-1080 and Volume XIV-II, 1963, p. 631- 633 and 705-713). The K values according to Fikentscher are between 5 and 120, preferably between 10 and 50. In the further description, the polymer compound as an aqueous solution is from 1 to 80% based on active ingredient (see above), preferably between 5 and 60X and particularly preferably between 10 and 40% before.

By setting the doping ratio, i.e. the ratio of polymer component to chromium content, can surprisingly be chosen between the brightness of the leather and the chromium content of the waste water.

However, even with a low chromium content, there is a lower wastewater load than in the prior art.

The production of the polymer complexes themselves is extremely simple, as can be seen from the exemplary embodiments. It is sufficient to add carboxyl group-containing polymers, preferably acidic polymers and / or copolymers in aqueous solution, with a soluble chromium III compound (e.g. chromium sulfate) and to heat the solution until a complex reaction occurs. Here, as well as in the further descriptions, chromium compounds are generally understood to mean the soluble chromium-III compounds capable of complexation, even if chromium-VI compounds were applied, which were reduced to chromium-III compounds for the purpose of complexation in the mixture with polymers.

Preferred substances for the polymerisation or polycondensation for the production of the polymers and / or copolymers claimed according to the invention are so-called monomer substances, such as e.g. Acrylic acid and / or methacrylic acid and / or maleic acid and / or their hydroxy compounds, which can also be present in the form of fully or partially neutralized salts.

The preferred doping ratio of chromium to carboxyl groups of the polymers is between 1: 500 and 1: 1, preferably between 1: 100 and 1: 3 and in particular between 1:50 and 1: 5, the polymeric K values according to Fikentscher between 5 and 120, preferably between 10 and 50.

The retanning process itself is not critical in itself. The leather piece is added, with the necessary amount of water, and previous rinsing can be dispensed with, and the complex solution is added and the drum is tumbled.

Particularly good results in the chrome fixation are achieved if the folded wetblue leather without rinsing in a fleet of 100 to 300% water, based on the shaved weight of the wetblue leather, at a temperature of 35 to 60 ° C with 4 to 6X treated with a complex solution that contains 20 to 50% polymers, depending on the composition. The pH values necessary for the Fotge processes can be taken into account here, the alkali metals necessary for a higher desired pH value of the liquor and / or leather from pH 4 to 7, such as e.g. Sodium bicarbonate and / or sodium formate and / or the like can also be introduced in solid or dissolved form in the process of chromium fixation. This compact way of working does not in any way affect the results of chromium depletion, whereby it can also be used to simplify the technology, because the neutralization or the leaking of the leather unfold as separate operations.

Lickers and alkaties can, however, also be added separately in a manner known per se.

In the examples described below, the temperature of the surface of the undyed leather was measured using an electric reflectance photometer (ELREPHO) using a Y filter to determine the frequency (= E value). The resulting relative number states that a surface the higher the number of the E-value, the more helper it is. White BaSO ₄ powder, for example, has a value of 100. Pieces of leather that reach or even exceed 60 can be described as exceptionally bright.

Furthermore, the improvements in leather and wastewater quality should be clarified in the following examples. ALL EXAMPLES were based on the same wetblue material, whereby the best possible reproducibility of the leather up to the wetblue stage was ensured by the same raw material, chemicals, process technology and all mechanical work. The fold thickness of this starting material was 1.8 / 1.9 mm. Percentages refer to the fold weight of the wetbLue pieces.

Example 1

A wet blue piece was introduced without rinsing into a float of 300% water at 45 ° C. together with 4% of a commercially available, 33 percent aqueous sodium polyacrylate solution and drummed in a tanning drum for 1 hour. This neutralization fleet was drained and the chromium content was determined. The leather piece was rinsed, treated with a standardized amount of 7X of a mixture of commercially available licker for this series and finished. The result was a very soft, not very firm-grained, moderately filled, but little brightened leather. Chromium content of the remaining liquor: 100 mg Cr ₂ O ₃ / L E value of the finished leather: 53.5.

EXAMPLE 2

Under the same conditions as in Example 1, a wetbLue piece was treated with 5X of a 25 percent solution of a commercially available polymer product based on PoLyacryLamide instead of the sodium polyacrylate solution and finished. The result was a less soft, moderately filled, dark leather with moderate firm grain. Chromium content of the remaining liquor: 199.6 m ^g Cr ₂ O ₃ / L E value of the finished leather: 51.3.

EXAMPLE 3

500 g of a polyacrylic acid prepared by a process known per se with a content of 33% and a K value according to Fikentscher of approx. 23, which corresponds to the sodium polyacrylate mentioned in Example 1, were mixed with 16.7 g of a 33% basic chromium sulfate and stirred until completely dissolved. Instead of Cr (OH) (SO ₄ ), other chromium compounds which can be used can also be used, the preference arises, as in the following examples, for economic reasons. The solution is heated to 80 ° C, whereupon the complex reaction occurs. After cooling to room temperature, the result is a water-soluble complex with good flowability for practical handling. The doping ratio is approx. 40 carboxy groups per chromatom.

A wet blue leather cloth was treated with 300% water at 45 ° C. and 5% above complex solution without rinsing and drummed in a tanning drum for 1 hour. After the addition of 1% solid sodium bicarbonate and a milling time of 15 minutes, 7% licker mixture, Chandel's customary, water-emulsified fatliquor for leather) and another 1% sodium bicarbonate were added and the fabric was drummed for a further 45 minutes. The finished leather was soft, firm-grained than in example 1 and of a very light color. Chromium content of the compact remaining liquor: 10.1 mg Cr ₂ O ₃ / L E value of the finished leather: 60.3

Example 4

500 g of a 40 percent polyacrylic acid with a K value according to Fikentscher 18 produced according to a known method were mixed with 20.3 g of a 33% basic chromium sulfate with stirring and dissolved. With stirring, the mixture is then heated to 80 ° C. and then again cooled down. The result is a pourable, water-soluble complex with a doping ratio of approximately 40 carboxyl groups per chromate.

A piece of wetbLue leather was mixed without prior rinsing with 300% water at 45 ° C. and 5% of the above complex solution and drummed for one hour in a tanning drum. Thereafter, 0.9X sodium bicarbonate was added, the process was continued for 15 minutes and another 0.6% of sodium bicarbonate was added together with 7% of a licker mixture and the process was continued for 45 minutes. The result was a soft, light, filled and well-grained leather. Chromium content of the remaining liquor: 35.5 mg Cr ₂ O ₃ / L E value of the finished leather: 61.4.

EXAMPLE 5

3000 g of a 40 percent polyacrylic acid with a K-value according to Fikentscher of approx. 18 produced according to a known method were mixed with 121.8 g of a 33% basic chromium sulfate and stirred until completely dissolved. After heating to 80 ° C and cooling, a viscous but water-soluble paste with a doping ratio of approx. 40 carboxyl groups per chromate results.

A 5% paste and 300% water at 45 ° C. were added to a wet blue piece without rinsing beforehand, and drummed in a tanning drum for 1 hour. Then 0.8% sodium bicarbonate was added, drummed for 15 minutes, 7% of a licker mixture and 1% sodium bicarbonate was added. After 45 minutes of flexing, the leather piece was finished as before. The result was a firmer, but still soft, light leather with very good firm grain. Chromium content of the remaining liquor: 8.9 mg Cr ₂ O ₃ / L E value of the finished leather: 59.6.

Example 6

250 g of a 40% -polyacrylic acid with a K-value according to Fikentscher produced by a process known per se and having a K value of approx. 18 was diluted with 12.5 ml of distilled water and mixed with 10.2 g of 33% basic chromium sulfate. The mixture was heated to 80 ° C. with stirring and cooled again. The result was a well-liquid, water-soluble complex with a doping ratio of approx. 40 carboxyl groups per chromate.

A wet blue piece was treated exactly as in Example 5 with a 5 percent complex solution. The result was a slightly softer, light leather with still good firm grain. Chromium content of the remaining liquor: 11.4 mg Cr ₂ O ₃ / L E value of the finished leather: 60.4.

Example 7

250 g of a 40 percent polyacrylic acid prepared according to a known method with a K value according to Fikentscher of approx. 18 were diluted with 250 ml of distilled water, 40.6 g of 33% basic chromium sulfate were added, the mixture was heated to 75 ° C. and cooled again . The result was a very tough, but water-soluble paste with a doping ratio of 10 carboxyl groups per chromate.

A wetblue piece was treated exactly as in Examples 5 and 6 with 5% paste above. The result was a soft, full, not very firm grain, very light leather. Chromium content of the remaining liquor: 11.4 m ^g Cr ₂ O ₃ / L E-value of the finished tetrahedron: 61.1.

Example 8

Using a process known per se, a 32 percent polymethacrylic acid with a K value according to Fikentscher of approx. 20 was produced from a monomer fraction of 90X acrylic acid and 10X methacrylic acid and neutralized to pH 7.5 with sodium hydroxide solution. 2000 g of this neutralized polymethacrylic acid were mixed with a solution of 63.7 g of 33% basic chromium sulfate and heated to 80 ° C. The result was a complex solution with good fluidity.

A wetblue piece was mixed without prior rinsing with 300% water at 45 ° C. and 5% solution above and drummed in a tanning drum for 1 hour. The fleet was then drained and checked for chromium. The leather piece was washed in 200% water at 60 ° C for 10 minutes of flexing. In a new fleet of 200% water at 60 ° C, 7% licker mixture was added, drummed for 20 minutes and the fat substances of the licker fixed with 0.5% formic acid for 45 minutes.

The finished leather was soft, FULL, astonishingly pitted and exceptionally bright. Chromium content of the remaining liquor: 60.8 m ^g Cr ₂ O ₃ / L E value of the finished leather: 63.6.

Summary of data on chrome depletion in the liquors and brightness of the leather surfaces:

Claims (14)

1. A process for retanning mineral-tanned leather, in particular chrome leather, in an aqueous liquor, preferably at elevated temperatures, characterized in that the leather is treated with an aqueous solution of a carboxyl-containing organic polymer complex compound doped with chromium. 2. The method according to claim 1, characterized in that the organic component is acidic polymers and / or copolymers of acrylic acid and / or methacrylic acid, maleic acid and / or their hydroxy compounds, wherein the polymers can also be present in the form of fully or partially neutralized salts. 3. The method according to claim 2, characterized in that the polymer compounds have a K value according to Fikentscher from 5 to 120, preferably from 10 to 50. 4. The method according to claim 1 and 2, characterized in that the polymer compound is present before chromium doping in an aqueous solution between 1 to 80 wt .-% polymer compound, preferably between 5 and 60%, particularly preferably between 10 and 40%. 5. The method according to claim 1 and 2, characterized in that the polymer compounds are doped with water-soluble chromium salts and / or optionally based chromium salts, in particular based chromium sulfates. 6. The method according to claim 1 to 5, characterized in that the doping ratio of chromium to carboxyl groups of the polymer compounds 1: 500 to 1: 1, preferably 1: 100 to 1: 3 and in particular 1:50 to 1: 5. 7. The method according to claim 1 to 6, characterized in that the aqueous organic polymer component with the optionally dissolved chromium salt at temperatures of 40 to 100 ° C, preferably from 60 to 80 ° C is reacted. 8. The method according to claim 1 to 7, characterized in that the tanning liquor contains 0.1% to 20% chromium-doped polymer compound. 9. Retanned for retanning mineral-tanned leather based on carboxyl-containing polymeric compounds, characterized in that they contain chromium in a complex-bound form. 10. retanning agent according to claim 8, characterized in that the carboxyl group-containing polymeric compound contains acidic polymers and / or copolymers of acrylic acid and / or methacrylic acid, maleic acid and / or their hydroxy compounds, the polymers prepared by processes known per se also in the form of full - Or partially neutralized salts can be present. 11. retanning agent according to claim 8 and 9, characterized in that the polymer compounds have a Fikentscher K value of 5 to 120, preferably from 10 to 50. 12. NachgerbemitteL according to claim 8, characterized in that the polymeric compound contains chromium in the ratio of chromium to polymeric compound, such as 1: 500, preferably 1: 100 to 1: 3 and in particular 1:50 to 1: 5. 13. A process for the preparation of chromium-containing polymeric compounds containing carboxyl groups in complex form, characterized in that the desired amounts of chromium are preferably dissolved in water, the polymeric compounds are added and the mixture is heated to temperatures of up to about 80 ° C. 14. Chromium-bonded carboxyl groups containing homo- or copolymers of acrylic acid, methacrylic acid or maleic acid or their hydroxy compounds in free or in fully or partially neutralized form.