DE3306374A1 - METHOD FOR TANNING SKIN WITH A HIGH BASIC CHROME TANNER - Google Patents

Abstract

1 process for tanning hides, characterized in that a highly basic chromium sulfate tanning material which contains 57 to 63 equivalent% OH groups and the remaining sulfate residues of which are replaced in an amount of up to 10 equivalent% by an organic acid residue is used for the tanning, used.

Description

The invention relates to a method for tanning hides with a highly basic chromium sulfate tanning agent which has a basicity of 57 to 63% and which can be masked by up to 10% by the remainder of an organic acid, for tanning hides.

It is known, for example from DE-AS 23 34 636, to use basic chromium salts in tannery. A common tanning agent is, for example, a chromium-III-sulfate with 33% basicity, whereby chromium-III-sulfates can also be used, which are masked by formate residues, since with these complexes an even higher basicity, up to 50%, can be used. can be adjusted.

In practice up to now a maximum of 50% basic, uniform chromium salts have been used as tanning agents. The basicity of the chromium salts indicates the mol% of hydroxyl groups that are bound to the trivalent chromium cation, with 3-hydroxyl groups corresponding to a basicity of 100%.

The old rule in practice is that for a fast through-tanning of hides, the basicity should be low, for example 33%, and an increase should only be made in the course of the tanning process. Chrome tanning agents with a higher basicity are already available on the market. However, these are not uniform, but rather represent mixtures of low-basic chromium salts with, for example, dolomite, calcium carbonate and / or magnesium oxide. They are adjusted in such a way that the basicity increases during the tanning process.

A process for tanning hides has now been found in which a highly basic, uniform chromium sulphate tanning agent which contains 57 to 63 equivalent% OH groups and the remaining sulphate radicals in an amount of up to 10 equivalent% is replaced by an organic acid radical for the tanning process are, can use.

Organic acids or acid anions for the production of a masked, highly basic chromium sulfate are lower alkanecarboxylic acids, in particular formic and acetic acid, but also dicarboxylic acids, such as adipic acid, and aromatic carboxylic acids, in particular phthalic acid. Of the acids mentioned, acetic acid and formic acid are particularly preferred.

The invention overcomes the general prejudice that chromium (III) sulfates with more than 50% basicity cannot be used advantageously in tanning. The surprising advantage of the process according to the invention is that, despite the high basicity, even thick hides can be tanned through relatively quickly without difficulty and without special measures.

The tanning agent to be used according to the invention can be prepared in a conventional manner by adjusting the basicity, for example with sodium hydroxide solution and, if necessary, conversion with the corresponding masking agent in the form of the acid or a salt from a sulfuric acid chromium (III) salt solution. Such tanning agents can also be obtained, for example, from a chromium (III) salt solution obtained by reducing chromate / dichromate solutions with sulfite or sulfur dioxide or another reducing agent, e.g. methanol, and corresponding adjustment with a base and masking agent.

In the particularly preferred embodiments, the basicity is set to about 60% and the degree of masking is about 5% and the chromium dioxide content, calculated on dry weight, is about 23-25%.

The chromium salt solutions prepared in the manner described above can readily be used as chromium tanning solutions. They can also be dried in a spray dryer or other dryer to a powder that is shelf-stable and clearly soluble in water again when used. A chromium sulfate tanning agent in powder form which can be used according to the invention and which is obtained in this way contains 15 to 30% by weight of chromium oxide.

The tanning according to the invention also takes place in the same way as it has been done so far with conventional chromium salts.

The general procedure is that a delimed and pecked pelt is then in the same or a fresh liquor in an amount of 30 to 100% based on the pelt weight, with a chromium oxide supply of 0.5 to 2.5, preferably 1, 4 to 1.8% by weight, based on the pelt weight, drummed for about 3 to 10 hours and then further processed in the well-known manner. The chromium sulfate tanning agents to be used according to the invention can also be used, like the previous chrome tanning agents, in conjunction with other vegetable or synthetic tanning agents. They can also be modified, for example according to DE-AS 23 34 636, with water-soluble mono- or polyglycols.

The process with the highly basic salts enables the chrome tanning to be carried out in a simplified and safe manner while at the same time ensuring good chromium absorption and fixing, which, compared to conventional tanning processes, offers the possibility of reducing the amount of chromium oxide offered without reducing the chromium oxide content in the finished leather.

The following examples explain the production and use of the new chrome tanning agents.

Chrome tanning, examples on peeled, peeled pelt, percentages on the pelt weight:

example 1

Pelt split to 3 mm.

Pimples and tanning:

60% water 25 ° C

5% table salt, tumble for 10 minutes,

Addition of 0.4% formic acid 85% (diluted 1: 5)

0.5% sulfuric acid 98% (diluted 1:10)

Milling for 2 hours, pH of the liquor: 3.6

Addition of 1.8% chromium oxide in the form of a chromium sulfate tanning

fabric powder,

60% basic, 5 equivalent% with acetate

remains masked,

6 hours of walking

pH of the liquor: 3.6

Example 2

Pelt split to 3 mm.

Pimples and tanning:

60% water 25 ° C

5% table salt, tumble for 10 minutes,

0.4% formic acid 85% (diluted 1: 5)

0.5% sulfuric acid 98% (diluted 1:10)

Milling for 2 hours, pH of the liquor: 3.6

+ 1.6% chromium oxide in the form of a chromium sulfate tanning

fabric powder,

60% basic, 7 equivalent% with acetate residues

masked

Walk for 2 hours,

+ 0.5% adipic acid disodium salt

Walk for 4 hours,

pH of the liquor: 3.8

Temperature of the liquor: 45 ° C

Example 3

Pelts split to 3 mm.

Pimples: 80% water 25 ° C

6% table salt, mill for 5 minutes,

+ 1.4% sulfuric acid 98% (diluted 1:10)

Milling for 2 hours, pH of the liquor: 2.2

+ 1% sodium formate

Drumming for 1 hour, pH of the liquor: 3.4

Drain the liquor

Tanning: 80% water at 25 ° C

1.5% chromium oxide in the form of a chromium sulfate

tannin 62%

basic, 5 equivalent% with acetate residues

masked,

5 hours of walking

pH of the liquor: 3.5

Example 4

Unsplit nakedness.

Pimples and tanning:

50% water 25 ° C

6% table salt, tumble for 10 minutes,

+ 0.8% formic acid 85% (diluted 1: 5)

Fulling for 2 hours, pH value of the liquor: 3.5

+ 0.2% sulfuric acid 98% (diluted 1:10)

Fulling for 15 minutes, pH value of the liquor: 2.9

+ 1.5% chromium oxide in the form of a chrome tanning

substance 60% basic,

5 equivalent% masked with formate residues

Walk for 8 hours,

pH of the liquor: 3.4

Temperature: 45 ° C

Example 5

Sheepskins, limed and rinsed.

Pimples: 100% water 25 ° C

10% table salt, tumble for 10 minutes,

+ 0.4% formic acid 85% (diluted 1: 5)

0.2% sulfuric acid 98% (diluted 1:10)

Drumming for 30 minutes, pH value of the liquor: 4.2

+ 1.4% chromium oxide in the form of a chromium sulfate tanning

fabric

58% basic, 8 equivalent% with acetate

remains masked,

6 hours of walking

pH of the liquor: 4.0

Temperature: 35 ° C

Example 6

Chromium plating of seamed cowhide

Percentages on the folded weight

50% water 50 ° C

1.5% chromium oxide in the form of a chromium tanning agent

60% basic,

5 equivalent% masked with acetate residues,

Walk for 2 hours.

Claims (1)

Process for tanning hides, characterized in that a highly basic chromium sulfate tanning agent which contains 57 to 63 equivalent% OH groups and the remaining sulfate residues of which up to 10 equivalent% are replaced by an organic acid residue is used for the tanning .