EP0470465A1 - Process of retanning leather previously subjected to mineral tanning with aromatic sulphonic acids - Google Patents

Abstract

Process for retanning mineral tanned leathers, characterised in that the retanning agents used are sulphonic acids and/or their salts of the general formula <IMAGE> where R is hydrogen, -CH3 or the radicals <IMAGE> X is hydrogen, an alkali metal, in particular sodium, potassium or lithium, ion or an ammonium ion, and n is 1, 2, 3 or 4.

Description

worin

• R für Wasserstoff, -CH₃ oder die Reste
  
• X für Wasserstoff, ein Alkali-, insbesondere Natrium-, Kalium- oder Lithium-lon, oder für ein Ammonium-lon und
• n für 1, 2, 3, oder 4 stehen.

The invention relates to a process for retanning minerally, in particular with chrome tanning agents, tanned leather with sulfonic acids and / or their salts of the general formulas

wherein

• R represents hydrogen, -CH ₃ or the radicals
  
• X for hydrogen, an alkali, in particular sodium, potassium or lithium ion, or for an ammonium ion and
• n stands for 1, 2, 3, or 4.

The mono- and disulfonic acids of phenol, cresols, hydroxydiphenylene and naphthols and their alkali and ammonium salts are preferably used.

Commonly used as retanning agents and as auxiliaries for leveling chemical and / or physical irregularities in the leather surface are, for example, formaldehyde condensation products of β-naphthalenesulfonic acid (DE-PS 290 965), diphenyl and ditolyl ether sulfonic acids (US Pat. No. 2,315,951) and terphenyl sulfonic acids (US-PS 3 906 037) and their ammonium or alkali salts. So-called exchange tanning agents, which are predominantly present as phenol-containing formaldehyde condensation products of aromatic sulfonic acids or their salts, are customary as retanning and / or leveling agents for chrome leather (GB-PS 1 291 784 and DT-PS 611 671).

The disadvantage of these higher molecular weight anionic retanning and leveling agents is that, in interaction with anionic dyes, they preferentially attach to the leather surface and block binding possibilities for anionic dyes here. This inevitably leads to the dyes predominantly setting deeper in the leather.

In this way, very uniform surface colorations are obtained, but in comparison to the dyeing without anionic leveling agents, they are highly lightened. The range of dyes is only partially used for surface coloring. So if a high level of coloration is required, losses in color strength caused by the use of anionic retanning agents and leveling agents have to be accepted.

There are gradual differences in the lightening effect on dyeings between the different types of tanning agents and leveling agents, which may depend, among other things, on the ratio of leveling agents or retanning agents to dye and dye-specific, but they consistently cause high color loss on leather, that can reach 50 - 80% compared to leathers that are dyed under comparable conditions but without retanning or leveling agent treatment.

If the leather surface is reloaded cationically by means of cationic auxiliaries or mineral tanning agents to produce deep dyeings on heavily retanned leathers, similarity deficiencies often arise as in the dyeing of the pure leather which has not been treated with anionic tanning agents, retanning agents or leveling aids to be watched.

It has surprisingly been found that the sulfonic acids of the formulas (I) and (11) or their salts, which have not been condensed to form larger molecules with formaldehyde like anionic synthetic tanning agents and leveling agents, are particularly suitable as retanning agents. They offer the advantage that the leather retanned with it or the leather treated before or during dyeing results in deep and brilliant surface dyeings with anionic dyes with excellent levelness. The color depth results similar to pure chrome leather that has not been treated with retanning agents and / or leveling agents.

Suitable retanning agents of the formulas (I) and (11), which allow a deep and brilliant coloration of the leather with optimal use of the dye range, are preferably partially or completely neutralized with sodium hydroxide or ammonia with phenolsulfonic acids. They can e.g. produce by allowing 2 moles of sulfuric acid monohydrate to act on sulfonation at 110-130 C, preferably 120 ° C, for 1 hour on 1 mole of technical phenol and then neutralizing the reaction mixture to the desired final pH and converting it into powder by spray drying or formed as a liquid product with approx. 40% active substance.

The sulfonic acids and their salts of the formula (I) or (11) are optimally effective for levelness, brilliance and depth of the coloration of the leather, if they are mixed with anionic dyes in amounts of 2-10%, preferably 3-, before or during the coloration. 6% (based on the so-called fold weight of the leather) act on the leather and let it open. They are particularly good at leveling the color and compensating for the different dyeability of damaged and undamaged areas within individual skins or skins if they are applied to the leather before the dye is added and the dye can then be evenly applied to the leveled leather.

• 40 - 80 Gewichtsteilen eines 33 % basischen Chromsulfat,
• 40 - 20 Gewichtsteilen des Natriumsalzes.

The compounds of formula (I) or (11) can also be used in combination with other tanning agents and auxiliaries on leather. For example, they can be combined with chrome tanning agents, which in practice are often used together with synthetic tanning agents for retanning to increase the fullness and shape the leather character. Expediently, additions of base agents and / or neutralizing agents, such as sodium sulfite, sodium carbonate or alkali metal or alkaline earth metal salts of organic carboxylic acids such as formic acid, acetic acid or technical dicarboxylic acid mixtures, are also added to the combination to the chromium tannin portion. If, for example, improvement in leather fullness and softness and at the same time good dyeability is required, the following combination has proven itself

• 40-80 parts by weight of a 33% basic chromium sulfate,
• 40-20 parts by weight of the sodium salt.

Mixtures of the sulfonic acids and / or their salts, in particular the sodium or ammonium salts, with mono- or polybasic, preferably dibasic, carboxylic acids, e.g. Formic, acetic, propionic, succinic, glutaric, adipic, and / or their alkali (Na, K, Li), ammonium or alkaline earth salts (Mg, Ca, Sr, Ba).

For example, a mixture may be mentioned which contains 70-40 parts by weight of sodium salts of a technical dicarboxylic acid mixture (mixture of succinic, glutaric and adipic acids), e.g. in the production of adipic acid is necessarily a by-product which contains 30-60 parts by weight of sodium and / or ammonium salts of phenolsulfonic acid.

example 1

Chromium leather made from cowhide or calfskin, which is manufactured in the usual way, folded to 1.6-1.8mm and neutralized to pH 3.8-4.2, is at 100% liquor in a rotating tanning drum with 6% of a pH 6.5-6.8 adjusted phenolsulfonic acid ammonium salt, which is formed when 2 moles of sulfuric acid monohydrate act on 1 mole of phenol at 120 ° C for 2 hours and then neutralized with ammonia after cooling and diluting to pH 6.5-6.8 and spray dried into powder or formed as a liquid product with approx. 40% active substance.

After this pretreatment of the leather, dyeing is carried out in the customary manner with 1% of the copper complex of a monoazo dye from DE-PS 670 935, example 1.

Following the dyeing, greasing is carried out in the dye bath in the customary manner and then treated with 1.5% formic acid in order to achieve the best possible absorption of the dye and the greasing.

After drying and tensioning the leather, a full, soft leather with extraordinarily brilliant and deep surface coloring results.

In terms of color depth, this leather corresponds to leather dyed without the aid of a pretreatment with the same amount of dye, but which results in significantly lower levelness.

A chrome leather, which was treated under the same conditions with the Na salt of the terphenylsulfonic acid-formaldehyde condensate, which was prepared according to US Pat. No. 3,906,037, Example 3, instead of the phenol salt, has a strongly lightened, pale color.

Example 2

In normal operation, 1.6-1.8 mm thick folded and neutralized to pH 3.6-3.8 chrome cowhide are treated with 4% of a phenolsulfonate for 10 minutes to initiate retanning in a 100% warm liquor. To prepare the sulfonate, 2 mols of sulfuric acid monohydrate are allowed to act on 1 mol of phenol at 120 ° C. in the course of 2 hours with vigorous stirring, the mixture is cooled, diluted, neutralized with sodium hydroxide solution and converted into powder form by spray drying.

After the above treatment, intensive retanning follows in the same bath, each with 2% of a phenolic tanning agent, a resin tanning agent based on dicyandiamide and a vegetable tanning agent, preferably Mimosa extract. After 45 minutes the tannins are completely absorbed and the liquor can be drained. Then, as usual, dyeing is continued in a fresh liquor with 2% of the anionic metal complex dye Acid-Brown 85 (C.I. 34 900). Greasing and further completion are also customary in the company. The finished leather results in full brilliant and equally level coloring in the cattle box character.

Improvements in the dyeability, especially the depth of color, the brilliance and the levelness, are particularly evident when a comparative experiment is carried out in which the condensation product of diphenyl ether sulfonic acid and formaldehyde obtained according to US Pat. No. 2,315,951, example 1, is used instead of the sodium salt.

Example 3

To produce nubuck leather, chrome leather, which is folded and neutralized to pH 6.0 (cut color with bromothymol blue yellow to yellow-green), is first washed with 300% water at 40 ° C. After draining the wash liquor, pre-greased for 15 minutes with 2.5% of a sulfite-based leather greasing agent based on trans in 100% of a liquor at 40 ° C. and then treated in the same liquor for 10 minutes with 1% of an ammonia solution containing 2.5% by weight of NH ₃ contains. Then 2.5% of the anionic metal complex dye Acid Brown 85 (CI 34 900) are added together with 2% of a potassium phenolsulfonate and 2% of a sweetened chestnut extract and dyed and retanned for 90 minutes at the same time. After this treatment, 100% water at 70 ° C. is added and the mixture is allowed to act for 10 minutes before acidifying in the same liquor for 40 minutes with 1.5% of a formic acid solution (up to pH 3.8) which is 8.5% pure by weight Contains formic acid. After draining the liquor, overdyeing in a new bath in 100% liquor of 55 C with a further 1.5% of the same dye as in the pretreatment and then greasing with a fat mixture based on wool fat and chloroparaffin sulfonate. Finally, aftertreated with 2.5% sweetened chestnut wood extract and acidified again with 0.5% of a formic acid solution containing 8.5% by weight of pure formic acid. With a final pH value of 3.8, the leathers are rinsed in the normal way and stored overnight on the trestle. After wilting, vacuum drying for 1/2 minute at 80 C and 50% counter pressure, drying is carried out, conditioning, tunnels and another vacuum drying for 1/2 minute at 80 - 90 C. Then, with a residual moisture content of 18-20%, the grain side becomes 220 -230-grit sandpaper sanded in 3 - 4 passages depending on the grain.

This way of working results in full and soft nubuck leather, which is characterized by high brilliance and levelness of coloration and very fine, even sanding.

The above-mentioned potassium phenol sulfonate is prepared by reacting 98 g of sulfuric acid monohydrate with 1 mol of phenol at 120 ° C. for 120 minutes and neutralization with potassium hydroxide.

Claims (3)

1. A process for retanning mineral-tanned leathers, characterized in that sulfonic acids and / or their salts of the general formula are used as retanning agents

wherein R represents hydrogen, -CH ₃ or the radicals

X for hydrogen, an alkali, in particular sodium, potassium or lithium ion, or for an ammonium ion and n stands for 1, 2, 3 or 4,
be used. 2. The method according to claim 1, characterized in that phenol mono- or disulfonic acids and / or their alkali or ammonium salts are used as retanning agents. 3. The method according to claim 1 or 2, characterized in that ammonium salts of phenolsulfonic acids are used as retanning agents.