EP0624203B1 - Dilutable aluminium triformate tanning agent in storage-stable highly concentrated, water-dissolved form, and its use - Google Patents

Abstract

Described is the use of at least substantially storage-stable supersaturated and acidified aqueous solutions of mixtures of aluminium triformate and alkali-metal and/or alkaline-earth formates as a means of supplying a water-dissolved mineral tanning agent based on aluminium formate for the tanning of leather and/or hides using little or no chromium. The invention thus concerns, in particular, storage-stabilized supersaturated and acidified aqueous solutions of this kind which also contain small quantities of stabilizers, preferred stabilizers being 1,2,3,4-butanetetracarboxylic acid and/or xanthane gum. The invention also concerns the use of such stabilized supersaturated aqueous forms of aluminium triformate solutions for use as tanning auxiliaries with a fixing and/or tanning action in the tanning or finishing of leather and hides.

Description

The invention relates to and describes a new, highly concentrated form of aluminum triformate in supersaturated, yet storage-stable, aqueous solution which is particularly suitable for use in the field of chrome-free or low-chrome mineral tanning of leather and / or furs. Compared to the commercial forms of mineral tanning agents based on aluminum that are commercially available today, the aqueous high concentrates according to the invention are not only distinguished by the fact that the active ingredient component aluminum triformate is already predefined in the state of the aqueous solution, it has also been shown that a plurality of mineral tanning agents in this form of supply Improvements and simplifications for the field of tanning, finishing and finishing of leather and fur are given.

The use of mineral tanning agents or auxiliaries such as aluminum-based fixing aids is becoming increasingly important in the manufacture and finishing of leather and furs. This is due to the not inconsiderable concerns from an ecological point of view of the chrome-based work equipment or auxiliary materials used to this day. In practice, two offer forms, both of which are in solid form, are used in practice as aluminum-based mineral tannins: on the one hand solid basic aluminum chloride and, on the other hand, fine-crystalline solid aluminum triformate is offered and used as a feedstock in the leather and fur industry. For the adjustable work results, the advantages are known which result from the simultaneous use of aluminum and lower carboxylic acids, for example in the form of the aluminum triformate. A disadvantage in this connection is the comparatively low solubility of the pure crystalline aluminum triformate in aqueous solutions, which is below 5% by weight at usual tanning temperatures. This is probably the key to the fact that, up to the present day, watery forms of aluminum triformiate as feedstock for the leather and fur industry have not gained any practical importance.

The invention is based on the object of providing aqueous concentrates which contain the aluminum triformate in active compound concentrations well above its solubility in water, are nevertheless sufficiently stable in storage and are simple to dilute in the leather-producing operation into the concentration ranges of the aluminum material required in each case can be brought. The solution to the problem according to the invention is based on the finding that under certain conditions, which are described in detail below, aqueous active substance concentrates based on aluminum triformate can be prepared which contain this valuable substance in a supersaturated but nevertheless storage-stable form. It has also been shown that the use of such forms of preparation of the mineral tanning agents or auxiliary substances can have further advantages which are noticeable, for example, in an unprecedented degree of liquor depletion.

The teaching according to the invention

A first embodiment of the invention accordingly relates to the use of aqueous solutions of mixtures of aluminum triformate with alkali metal and / or alkaline earth metal formate - hereinafter also referred to as "formate salts" - which are at least largely storage-stable and acidified, as a concentrated form of an aqueous dissolved mineral tanning agent based on aluminum triformate for chrome-free or low-chrome leather and / or fur tanning.

In an important embodiment of the invention, these supersaturated aqueous solutions of formate salts contain small amounts of selected acid-stable stabilizers. Of particular importance in this context is the addition of butanetetracarboxylic acid as a stabilizer of the supersaturated active ingredient solutions, but selected organic polymer compounds are also suitable for the virtually unlimited storage stabilization of these supersaturated formate salt solutions.

Accordingly, in a further embodiment, the invention relates to supersaturated and acidic aqueous solutions of aluminum triformate in a mixture with sodium formate with solids contents of the formate salt mixtures of at least 35% by weight, preferably at least 40% by weight, which are stable in storage and which contain small amounts contain butane tetracarboxylic acid and / or xanthan gum as stabilizers.

Finally, the teaching according to the invention comprises, in a further embodiment, the use of these stabilized supersaturated aqueous formate salt solutions as water-dilutable, but already aqueous-dissolved aluminum triformate preparation for use as a tanning aid with fixing and / or tanning effect when tanning and / or dressing leather and fur skins.

Details of the teaching according to the invention

The teaching of the invention is based on the knowledge and details of the older but not prepublished German patent application P 40 10 930.5 (DE 40 10 930), the details of which are hereby expressly made the subject of the present disclosure of the invention.

This earlier application describes a process for the preparation of an alkali and / or alkaline earth-containing aluminum triformate solution from an aluminate solution with formic acid, the process being characterized in that an aqueous alkali and / or alkaline earth metal containing alkali solution with a formic acid present neutralized and the precipitated solid transferred into an aluminum triformate solution while increasing the temperature. Aqueous sodium aluminate lyes are preferably used in the reaction. Weight ratios of sodium oxide / aluminum oxide can be used in a wide range of, for example, 5: 1 to 1: 5 in these aluminate solutions. Ranges from 2: 1 to 1: 2 are preferred here.

The following reaction parameters can be important for the preparation of a supersaturated aluminum triformate solution on this basis: It is usually necessary to add the formic acid and to add the aluminate solution dropwise. The reaction proceeds in two steps. During the addition of lye, a gelatinous, easily movable precipitate increasingly forms in an exothermic reaction. In a second step, this can be brought back into solution by heating - after cooling, there is little or no re-precipitation. With the implementations Formic acid and aluminate used in the formation of sodium formate and aluminum triformate in stoichiometric ratios.

In particular in the production of corresponding supersaturated solutions with high contents of formate salts, which are preferably above 40% by weight and particularly preferably above 50% by weight, it has proven to be important to remove the heat of reaction which occurs during the neutralization. Internal temperatures of the reaction mixture of about 25 to 30 ° C. should be avoided here in the neutralization stage if possible. After the addition of aluminate has ended, the crude product solution must be heated in a second step to dissolve the precipitate formed as an intermediate until a clear solution is obtained, for example to temperatures between about 60 ° C. and 80 ° C. After the subsequent cooling to room temperature, the product solution initially remains clear. With longer standing times - a few weeks or months - a slight cloudiness can recede, but the state of the supersaturated solution remains.

The teaching of the earlier application cited here provides for the use of the aluminum triformate solutions containing alkali and / or alkaline earth metal for different purposes. These include the impregnation of textiles, the use in disinfectants and cleaning agents or as a coagulant for paints. Finally, their use as fixing aids in leather processing is also mentioned. However, the use of such supersaturated aqueous aluminum triformate solutions directly as a mineral tanning agent for the production of chromium-free or at least low-chromium leather is not disclosed in the earlier application.

The meaning and chemical nature of tanning agents on the one hand and fixing aids on the other hand in leather extraction or leather finishing are not congruent terms. Is It is known that selected tanning agents can also be used as fixing aids in leather finishing, but the term fixing auxiliary for leather finishing does not normally cover the field of tanning agents for leather production from suitably prepared natural skins. In this respect alone, the teaching according to the invention goes beyond the teaching of the earlier application mentioned with the application concerned here for the highly concentrated supersaturated aqueous formate salt solutions based on aluminum triformate.

In the preferred embodiment of the invention, as stated, small amounts of selected acid-resistant stabilizing agents are used, the butane tetracarboxylic acid - in particular 1,2,3,4-butane tetracarboxylic acid - being of particular importance. Even extremely high concentrations of the formate salts in the supersaturated aqueous solution, which are particularly preferably in the range above 50% by weight and in particular in the range from approximately 55 to 60% by weight, are stabilized by adding small amounts of this stabilizer, that a month-long storage of the supersaturated concentrates is also possible using temperature fluctuations that are common in practice. Not only is there a decisive advance in the field of mineral tanning agents based on aluminum triformate, but also the area of fixing aids for leather dressing already mentioned in the earlier application is substantially promoted by these tools in the sense of the invention, so that the Teaching according to the invention also extends to the field of leather finishing already mentioned in the earlier application.

The supersaturated aqueous solutions of the formate salts described in accordance with the invention and to be used in accordance with the invention contain aluminum triformate in combination with in particular sodium formate. Salt mixtures of this type can be started easily of the inexpensive sodium aluminate solutions and their reaction with formic acid. The formate salt solids content in the aqueous concentrates is at least about 35% by weight, preferably at least about 40% by weight. In the embodiments of particular interest according to the invention, the formate salt contents are above 50% by weight and in particular in the range from about 55 to 60% by weight.

Although the mixing ratios of aluminum triformate to sodium formate can fundamentally fluctuate within a wide range, as is disclosed in the previously mentioned older application DE 40 10 930, however, mixing ratios of aluminum triformate to sodium formate are preferred for the teaching according to the invention , which are in the range of about 0.5 to 2, based on the weight ratio of the two components as oxide, ie based on the weight ratio of Al₂O₃ to Na₂O.

The proportions of formic acid on the one hand and formate-forming metal components on the other - in particular, therefore, aluminum and sodium - are chosen in the preferred production in a practically stoichiometric ratio. Control of the pH of the supersaturated aqueous concentrates is expedient or necessary to ensure the storage stability of the supersaturated solutions in the sense according to the invention. In the preferred embodiment, the pH values of the concentrates are weakly acidic values and in particular in the range not above pH 5. The pH range from about 3 to 4 can be particularly suitable with regard to the degree of acidity of the aqueous concentrates.

The stabilizing agents according to the invention are, on the one hand, the 1,2,3,4-butanetetracarboxylic acid already highlighted, but also acid-stable, water-soluble and / or water-swellable polymer compounds, with xanthan gum being of particular importance here comes to. The stabilizing agents are expediently used in amounts below 5% by weight, based on the aqueous concentrate, and in particular in amounts of about 0.1 to about 2% by weight in the aqueous concentrate. It may be expedient to add these stabilizers in the form of aqueous solutions - for example about 10% by weight aqueous solutions - or also after pre-swelling in, for example, isopropanol in the formate salt-containing active substance mixture.

Particularly suitable for the use of the concentrates according to the invention as mineral tanning agents for the production of chromium-free or low-chromium leathers and furs is the use of the butanetetracarboxylic acid as a stabilizer, which here is preferably present in amounts of about 0.5 to 1% by weight on aqueous concentrate - to which formate salt concentrates can be added. Aqueous active substance preparations of this type show a practically unlimited storage stability even when the formate salt concentrations are at or above 50% by weight.

The stabilizing agent, for example butane tetracarboxylic acid, can be added in the course of the preparation of the aqueous concentrates, for example before the final heating of the primary reaction mixture for the preparation of the supersaturated aqueous solutions. Likewise, the stabilizer can also be added subsequently to the finished concentrates in a final process step.

The forms of mineral tanning agents based on aluminum triformate described in accordance with the invention are notable for the tanning and dressing of leathers and skins by outstanding application-related advantages. Here, for example, the good meterability, the easy distribution of the mineral tannin in the tanning liquor, the neutral odor, above all are to be listed But also the good Al₂O₃ absorption of the skin. Extensive comparative tests, which will be dealt with in the examples, have shown that when using comparatively lower aluminum triformate concentrations in the tanning liquors, comparable results are obtained with regard to the product properties as are known from the previously known processes for mineral aluminum tanning with those described corresponding products can be set on a solid basis. Associated with this, however, is moreover a significantly better exhaustion of the liquors, whereby not only the percentage exhaustion of the liquor is significantly increased compared to the methods according to the prior art, in particular the residual aluminum content in the liquor can be significantly reduced by the teaching according to the invention.

Details can be found in the following examples.

Examples

In the following Examples 1 and 2, the preparation of characteristic representatives for the supersaturated concentrated formate salt solutions to be used according to the invention is first described.

example 1

To 1210 g of an 85% aqueous formic acid (or 1030 g of pure formic acid), 2000 g of sodium aluminate (14.3% by weight Na₂O and 11.3% by weight Al₂O₃) were added dropwise within 30 minutes. A temperature increase of up to 80 ° C and precipitation occurred. The mixture was then heated under reflux until a clear solution was obtained. The yellow product solution contained 23.0 wt .-% (or 24.3 wt .-%) aluminum triformate (corresponding to 7.3 wt .-% Al₂O₃ or 7.6 wt .-% Al₂O₃) and 19.5 wt. -% (or 20.7% by weight) sodium formate.

To increase the aluminum triformate concentration, a more concentrated aluminate solution was used in further work. It was used under the trade name "DYNAFLOCK L" from the company Hüls AG sodium aluminate solution with 19 wt .-% Na₂O and 25 wt .-% Al₂O₃. In the neutralization reaction of this aluminate solution with formic acid under the conditions mentioned above, it was found that no clear products were initially to be produced. However, further experiments then showed that the desired storage-stable, clear, highly supersaturated aqueous solutions could also be obtained by carefully controlling the temperature control. In detail, the following was true:

When the concentrated aluminate solution was added dropwise to formic acid, a white, gelatinous and easily mobile precipitate was obtained in the first step. To obtain a clear product solution later, it was necessary to remove the heat of reaction. Avoid internal piston temperatures above approximately 25 ° C. The dropping rate was therefore dependent on the effectiveness of the cooling. After the addition of the aluminate had ended, the crude product solution had to be heated at 60 ° C. in order to dissolve the precipitate until a clear solution was obtained. After the subsequent cooling to room temperature, the product solution remained clear. Details are shown in Example 2 below.

Example 2

To 2260 g of an 85% aqueous formic acid, 2000 g of DYNAFLOCK L (sodium aluminate solution: 19% by weight Na₂O and 25% by weight Al₂O₃; Hüls AG) were added dropwise with vigorous stirring while cooling with cold water. The dropping rate depended on the temperature of the reaction solution, which should not exceed 25 ° C. The mixture was then stirred at 60 ° C. until a clear solution was obtained (about 10 minutes). The clear, colorless solution contained 37.3% by weight aluminum triformate (corresponding to 11.75% by weight Al₂O₃) and 19.6% by weight sodium formate.

By adding 1,2,3,4-butanetetracarboxylic acid (BTCA) a permanent stabilization of the supersaturated solution could be achieved. BTCA was used in amounts of 0.1 to 1.5% by weight, based on the aqueous concentrate, as a pure substance or in the form of an aqueous solution, preferably as a 10% by weight aqueous solution. BTCA levels of 0.5 to 0.7% by weight led to stable, easily movable systems. A 1.0 wt% BTCA level provided a pseudoplastic system. Storage tests under changing climate conditions (-30 to 60 ° C) with the BTCA-stabilized solutions showed that these withstood the extreme temperature fluctuations for more than 6 weeks.

In a series of application studies, the concentrates according to the invention were used as tanning agents and compared with commercial products based on basic aluminum chloride or solid, fine-crystalline aluminum triformate.

The comparative products were the basic aluminum chloride complex salt sold by the applicant under the trade name "Pellutax ALP" with an aluminum content (Al₂O₃) of 16 to 18% by weight and a basicity of approx. 20%, as well as the product sold by Zschimmer and Schwarz " Novaltan AL "(about 23% Al₂O₃) used.

Details of the comparison tests are given below. In summary, the following can be said in advance:

When using the examined mineral tanning agents on pickled German sheepskins, no differences were found with regard to the evaluation criteria of feel, softness, fullness and color of wool and leather. The aluminum tannins stabilized according to the invention with BTCA initially contained significantly less active substance (aluminum compounds). However, these agents were better available for the tanning process. This resulted in cheaper fleet wasting. The difference between the aluminum triformate range in the fleet and the aluminum absorbed by the sheepskin is smaller than that of the comparison products.

The tanning trials

Together with the commercial products mentioned, two tanning agents based on aluminum triformate / sodium formate, designed as liquid products according to the invention, stabilized with BTCA. The formate mixture EP-1 according to the invention produced according to Example 2 contained - based on the aqueous concentrate - 0.5% by weight of BTCA. The formate mixture EP-2 according to the invention produced according to Example 2 contained - based on aqueous concentrate - 1.0% by weight of BTCA. The two products were each stabilized with a 10% by weight aqueous BTCA solution.

The mineral tannins to be compared were used in the same amount by weight. In detail, the following was true: The tests were carried out with German pickled fur sheepskins. Before tanning, the corresponding skin halves were shaved to a wool height of 20 mm, then trimmed and the weights of the skin halves adjusted.

In order to complete the test series and to test the behavior of the tannins on leather as well, the corresponding pimple pelvis halves, which originated from the same raw material and were specially softened, shredded, unwrapped, ashed, stained, degreased and wound in the same series, ran in the same series were. The weights of the spots were set to the same value. The basis for the calculation of the fleet quantity was the pimple weight of the skins. The liquor ratio was 1:10. The use of the chemicals was fixed at g / l and calculated accordingly.

1. Pellutax ALP

17 Gew.-% Al₂O₃

2. Novaltan AL

23,5 Gew.-% Al₂O₃

3. EP-1

11,2 Gew.-% Al₂O₃
0,5 Gew.-% 1,2,3,4 Butantetracarbonsäure

4. EP-2

10,6 Gew.-% Al₂O₃
1 Gew.-% 1,2,3,4 Butantetracarbonsäure

The following products were tested against each other in equal quantities:

1. Pellutax ALP

17 wt .-% Al₂O₃

2. Novaltan AL

23.5 wt .-% Al₂O₃

3. EP-1

11.2 wt .-% Al₂O₃
0.5% by weight 1,2,3,4 butane tetracarboxylic acid

4. EP-2

10.6 wt .-% Al₂O₃
1% by weight 1,2,3,4 butanetetracarboxylic acid

Tanning: liquor ratio 1:10, calculated on pimple weight, min. Means minutes.

• a) vor Zugabe des Al-Gerbstoffes;
• b) 30 Min. nach Zugabe des Al-Gerbstoffes;
• c) 4 Stunden nach Zugabe des Al-Gerbstoffes;
• d) 14 Stunden nach Zugabe des Al-Gerbstoffes;
• e) 4 Stunden nach Abstumpfen des Al-Gerbstoffes

gemessen. Die Werte sind aus nachstehender Tabelle 1 ersichtlich.

The liquor pH of the various tanning procedures was electrometric

• a) before adding the Al tanning agent;
• b) 30 minutes after the addition of the Al tanning agent;
• c) 4 hours after adding the Al tanning agent;
• d) 14 hours after the addition of the Al tanning agent;
• e) 4 hours after the Al tanning agent has been blunted

measured. The values are shown in Table 1 below.

In a large number of comparative tests, the product properties were assessed in accordance with Table 4 below. The following applies to the numerical values in this table: grade 10 = very good, grade 1 = very bad

The assessment of the fur skins and leather showed no quality differences in terms of feel, softness, fullness and whiteness of the leather and the wool. Compared to Pellutax ALP, the good binding and absorption of the fur leather to Al₂O₃ of the two products according to the invention were found to be advantageous. When using Pellutax ALP (17 wt .-% Al₂O₃), no more Al₂O₃ was stored in the fur leather despite the higher concentration. The Al₂O₃ content of the fur skins, which were tanned with the products EP-1 and EP-2 according to the invention, was above the values achieved for the goods produced with Pellutax ALP.

Claims (13)

1. The use of at least substantially storage-stable, supersaturated and acidified aqueous solutions of mixtures of aluminium triformate with alkali metal and/or alkaline earth metal formate as a concentrated formulation of an aqueous solution of a mineral tanning agent based on aluminium triformate for the chrome-free or low-chrome tanning of leather and/or skins.
2. The use claimed in claim 1, characterized in that mixtures of aluminium triformate with sodium formate which have been produced in particular by reaction of aqueous sodium aluminate solution with formic acid are present.
3. The use claimed in claims 1 and 2, characterized in that the solids contents of the formate salt mixtures in the aqueous concentrates are at least 35% by weight, preferably at least 40% by weight and, more preferably, above 50% by weight.
4. The use claimed in claims 1 to 3, characterized in that the mixing ratios of aluminium triformate to sodium formate are in the range from 0.5 to 2:1, based on the ratio by weight of Al₂O₃ to Na₂O.
5. The use claimed in claims 1 to 4, characterized in that the aqueous concentrates have pH values of not more than 5 and preferably in the range from pH 3 to 4.
6. The use claimed in claims 1 to 5, characterized in that they are formulated as storable, supersaturated and at least substantially separation-free and readily water-dilutable concentrates which are liquid at room temperature and which have preferably been produced by reaction of an aqueous aluminate liquor with formic acid.
7. The use claimed in claims 1 to 6, characterized in that the water-containing concentrates contain acid-resistant stabilizers which are preferably present in the water-containing concentrate in quantities below 5% by weight and, more preferably, in quantities of 0.1 to 2% by weight.
8. The use claimed in claims 1 to 7, characterized in that butane tetracarboxylic acid and/or acid-stable water-soluble and/or water-swellable polymer compounds, preferably butane tetracarboxylic acid, are used as stabilizers.
9. The use claimed in claims 7 and 8, characterized in that the water-containing concentrates contain butane tetracarboxylic acid in quantities of 0.5 to 1% by weight, based on water-containing concentrate.
10. The use claimed in claims 1 to 9, characterized in that the water-containing concentrates are prepared by addition of an aqueous aluminate liquor with cooling to formic acid in a stoichiometric ratio, the temperature of the reaction mixture preferably not exceeding 25°C, subsequent heating of the reaction product to a temperature in the range from about 60 to 80°C, followed by cooling, the stabilizer, preferably butane tetracarboxylic acid, being added before or after the heating step.
11. Storage-stable, supersaturated and acidified aqueous solutions of aluminium triformate in admixture with sodium formate with solids contents of the formate salt mixtures of at least 35% by weight and preferably at least 40% by weight which contain small quantities of butane tetracarboxylic acid and xanthan gum as stabilizers.
12. Supersaturated aluminium triformate solutions as claimed in claim 11, characterized in that they have pH values of not more than 5 and preferably in the range from pH 3 to 4.
13. The use of the supersaturated aluminium triformate solutions claimed in claims 11 to 12 as water-dilutable aluminium triformate solutions already dissolved in water for use as tanning auxiliaries with a fixing and/or tanning effect in the tanning and/or finishing of leather and skins.