EP0470465B1 - Process of retanning leather previously subjected to mineral tanning with aromatic sulphonic acids - Google Patents

Description

worin

R

für Wasserstoff, -CH₃ oder die Reste

X

für Wasserstoff, ein Alkali-, insbesondere Natrium-, Kalium- oder Lithium-Ion, oder für ein Ammonium-Ion 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

for hydrogen, -CH₃ or the radicals

X

for hydrogen, an alkali, in particular sodium, potassium or lithium ion, or for an ammonium ion and

n

stand 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.

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 are common as retanning agents and as auxiliaries for leveling chemical and / or physical irregularities in the leather surface (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 common practice 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 fact that the dyes predominantly bind deeper in the leather.

In this way, very uniform surface colorations are obtained, but compared to the dyeing without anionic leveling agents, they are very bright. The range of dyes is only partially used for surface coloring. 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, a lack of equality often arises as in the dyeing of the pure leather that has not been treated with anionic tanning agents, retanning agents or leveling aids to be watched.

EP-A-24014 discloses a similar process using sulfonic acids which differ from the present ones in that there is no OH group.

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

Suitable retanning agents of the formulas (I) and (II), 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 1 mole of technical phenol at 110-130 ° C, preferably 120 ° C, for 2 hours for sulfonation and then neutralizing the reaction mixture to the desired final pH and spray-drying in powder transferred or formed as a liquid product with approx. 40% active substance.

The sulfonic acids and their salts of the formula (I) or (II) 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 compensate 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 equalized leather.

40 - 80

Gewichtsteilen eines 33 % basischen Chromsulfat,

40 - 20

Gewichtsteilen des Natriumsalzes.

The compounds of formula (I) or (II) can also be applied to leather in combination with other tanning agents and auxiliaries. 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, soda or alkali 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 proves itself

40-80

Parts by weight of a 33% basic chromium sulfate,

40-20

Parts by weight of the sodium salt.

Mixtures have also proven to be particularly suitable for simultaneous neutralization and leveling retanning the sulfonic acids and / or their salts used according to the invention, in particular the sodium or ammonium salts with mono- or polybasic, preferably dibasic, carboxylic acids, for example 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 acid), as is for example a by-product in the production of adipic acid, 30-60 parts by weight of sodium and / or ammonium salts containing phenolsulfonic acid.

example 1

Chromium leather from cowhide or calfskin, which is manufactured in the usual way, folded to 1.6-1.8 mm and neutralized to pH 3.8-4.2, is at 100% liquor in a rotating tanning barrel 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 in the course of 2 hours and then neutralized after cooling and diluting to pH 6.5-6.8 with ammonia 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 usual 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, the result is a full soft leather with extremely brilliant and deep surface coloring.

In terms of color depth, this leather corresponds to leather dyed with the same amount of dye without pretreatment, but this 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 produced according to US Pat. No. 3,906,037, Example 3, instead of the phenol salt, has a strongly lightened, pale color.

Example 2

Chromium cowhide, folded to 1.6-1.8 mm thickness and neutralized to pH 3.6-3.8, is treated for 10 minutes with 4% of a phenolsulfonate 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 treatment mentioned above, 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 (CI 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.

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 is pre-greased for 15 minutes with 2.5% of a sulfited leather greasing agent based on trans in 100% of a 40 ° C warm liquor and then treated in the same liquor for 10 minutes with 1% of an ammonia solution which contains 2.5% by weight NH₃ . Then 2.5% of the anionic metal complex dye Acid Brown 85 (CI 34 900) are added together with 2% of a potassium phenol sulfonate and 2% of a sweetened chestnut extract and are dyed and retanned for 90 minutes at the same time. After this treatment, 100% water at 70 ° C. is added and the mixture is left to act for 10 minutes before being acidified in the same liquor with 1.5% of a formic acid solution (up to pH 3.8) for 40 minutes, which is 8.5 percent by weight contains pure formic acid. After draining the liquor, a new bath in 100% liquor at 55 ° C over-dyed with another 1.5% of the same dye as in the pretreatment and then greased with a fat mixture based on wool fat and chlorinated paraffin sulfonate. Finally, aftertreatment with 2.5% sweetened chestnut wood extract and acidified again with 0.5% of a formic acid solution which contains 8.5% by weight of pure formic acid. With a final pH value of 3.8, the leathers are rinsed in the normal manner and stored on trestle overnight. After wilting, vacuum drying for 1/2 minute at 80 ° C and 50% counter pressure, hanging drying, conditioning, tunnels and another vacuum drying for 1/2 minute at 80 - 90 ° C. After that, with a residual moisture content of 18-20%, the grain side is sanded in 3 - 4 passages with 220-230 grit sanding paper, depending on the texture of 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 mole of phenol at 120 ° C. for 120 minutes and neutralization with potassium hydroxide.

Claims (3)

1. Process for retanning mineral-tanned leathers, characterized in that the retanning agents used are sulphonic acids and/or salts thereof of the general formula

   

   wherein

   R   represents hydrogen, -CH₃ or the radicals

   

   X   represents hydrogen, an alkali metal ion, especially sodium, potassium or lithium ion, or an ammonium ion and

   n   represents 1, 2, 3 or 4.
2. Process according to Claim 1, characterized in that the retanning agents used are phenolmonosulphonic or phenoldisulphonic acids and/or alkali metal salts or ammonium salts thereof.
3. Process according to Claim 1 or 2, characterized in that the retanning agents used are ammonium salts of phenolsulphonic acids.