GB2070632A - Tanning - Google Patents

Abstract

A tanning agent mixture comprises (1) an aluminum tanning agent and (2) a tanning agent based on a condensate of a C1 to C4 aliphatic aldehyde and one or more sulphonic and/or carboxylic acids containing the amino substituted benzene nucleus <IMAGE> where X=H, C1 to C4 alkyl, <IMAGE> or -CH2-COOH, and Y and Z are independently -H, -SO3H, -COOH, -CH3 or -CH2-SO3H, R=H or C1 to C4 alkyl and R%=H or C1-C3 alkyl with the proviso that at least one of the radicals X, Y or Z is or contains a sulphonic acid or carboxyl group.

Description

SPECIFICATION Tanning Agent Mixture, and Its Use U.S. Patent 1,222,033 discloses the use of condensates of aminonaphthalenesulfonic acids with formaldehyde as tanning agents. These products have a great tendency to form dark oxidation products on exposure to air, so that leather tanned with such agents can no longer be dyed or, at the very least, can no longer be dyed in brilliant hues.

U.S. Patent 3,852,374 discloses synthetic tanning agents prepared by condensing aromatic sulfonic acids with aldehydes, especially with formaldehyde. They give soft, well-filled leather and are simple to use. However, the leather tanned or retanned with these agents is difficult to dye in full shades with anionic dyes.

Further, British Patent 747,090 discloses synthetic tanning agents which are prepared by condensing aromatic amines with aldehydes, especially with formaldehyde. These products are free from sulfonic acid groups, so that they are absorbed efficiently on the leather on increasing the pH during tanning. However, they have not found acceptance in practice, presumably because of technical difficulties in use.

Aluminum tanning agents have been described in the very earliest tanning textbooks. It is also known that leather tanned with such agents can be dyed in deep hues. However, the levelness of the dyeings presents problems.

The present invention seeks to provide a tanning agent which is sufficiently water-soluble for industrial use, is devoid of objectionable intrinsic color and allows leather to be dyed, with conventional anionic dyes, in full and brilliant shades.

According to the present invention there is provided a tanning agent mixture which comprises a water-soluble mixture of I. from 0.5 to 30 parts by weight of a tanning agent which is a condensation product of from 0.1 to 6 molar proportions of one or more aliphatic aldehydes of 1 to 4 carbon atoms and 1 molar proportion of one or more sulfonic acids and/or carboxylic acids containing an aminosubstituted benzene nucleus and having the general formula

where X is H, C 4-alkyl,

or-CH2-C02-H, Ya and Z are independently H, -0S3H,-C 02H, -CH3 or -CH2-SQH, R is H or C,,-alkyl and R' is H or C,,-alkyl, with the proviso that at least one of the radicals X, Y and Z is or contains (as the case may be) a sulfonic acid group or carboxyl group, and II. one part by weight of an aluminum tanning agent.

Component I of the tanning agent mixture is prepared by condensing aromatic aminocarboxylic acids or, preferably, aminosulfonic acids of the above general formula with ClA aldehydes. Preferred compounds are those of the above formula where X is H or H(R')-SQH, Y is H or-CH3, Z is --SO,H or, if X is --CH(R3SO,H), is H, R is H and R' is H, after condensation with formaldehyde. The amount of aldehyde used is from 0.1 to 6, preferably from 0.2 to 3, moles per mole of acid of the above general formula. In the said acids, the amino group is always linked directly to the benzene nucleus whilst the carboxylic acid or sulfonic acid group may or may not be linked directly.

Examples of starting materials of the above general formula are the various isomeric anilinesulfonic acids and toluidinesulfonic acids, phenylaminomethanesulfonic acids, toluylaminomethanesulfonic acids and the corresponding compounds with carboxyl groups instead of the sulfonic acid groups. The corresponding compounds with two sulfonic acid groups or carboxyl groups, or with one sulfonic acid group plus one carboxyl group, may also be used. In principle, all isomers of the above compounds may be used. Particularly preferred compounds are 4-aminobenzenesulfonic acid (sulfanilic acid), 3-aminobenzenesulfonic acid (metanilic acid), o-toluylaminomethanesulfonic acid and anilinemethanesulfonic acid.

To improve the fullness and softness of the leather, one or more of the following compounds may additionally be present during condensation of the above aminosulfonic acids or aminocarboxylic acids: phenols, phenolsulfonic acids, naphthalenesulfonic acids and their methyl derivatives and/or dicyandiamide, biuret, melamine and especially urea. The total amount of these additionally used compounds should be not more than 90 percent by weight, preferably not more than 70% by weight, based on the aromatic aminosulfonic acids or aminocarboxylic acids.

The sulfonic acid or carboxylic acid, containing one or more amino groups and containing a benzene nucleus, can be employed, in the reaction with the aldehyde of 1 to 4 carbon atoms, either directly as the monomer or, preferably, after a precondensation with formaldehyde. The precondensation is advantageously carried out using a molar ratio of amino-containing sulfonic acid or carboxylic acid to formaldehyde of from 1:0.5 to 1 :6, preferably from 1:1 to 1:6, especially from 1:1 to 1:3, in aqueous solution at from 50 to 1 000C, preferably from 80 to 1 000C, at a pH of from 1 to 8. From 1 to 6 moles of sodium bisulfite may additionally be present, in order to introduce sulfonic acid groups.

Predominantly, aminomethanesulfonic acids are thereby formed.

If, for example, anilinesulfonic acids are used as the starting materials and a precondensation with formaldehyde is not employed, the tanning agent may be prepared as follows: An aqueous solution, preferably of about 30% strength, of, for example, formaldehyde is added, whilst stirring, to an aqueous solution of the anilinesulfonic acid at from 30 to 600C and at pH 1-8, preferably 4.5-6. The mixture is then stirred at 40--1000C until the desired degree of condensation has been reached; this requires from Q to 24, preferably from 1 to 12, hours. The degree of condensation can be discerned, for example, from the increasing viscosity of the reaction mixture.

The preparation of the tanning agent component I is carried out similarly if instead of an aniline-sulfonic acid a formaldehyde condensation product of an amino-containing benzenesulfonic acid or benzenecarboxylic acid is employed for the condensation with the Cs 4- aldehyde.

In an alternative advantageous procedure, for example, a mixture of a) the reaction product of aniline or toluidine with from 1 to 6 moles of formaldehyde and from 1 to 6 moles of sodium bisulfite is heated with b) an aqueous solution, containing free formaldehyde, of a condensation product of formaldehyde with from 0.3 to 1 mole of urea and from 0.1 to 0.3 mole of melamine per mole of formaldehyde, in the weight ratio of component a) to component b) (each calculated as solids) of from 1:0.5 to 1:5, preferably from 1:1 to 1:3, in aqueous solution at a pH of from 3.5 to 8 for from 1 to 10 hours at 60--1000C.

If, in preparing component I of the tanning agent mixture, it is desired to carry out a cocondensation with phenol, cresol, their sulfonic acids or naphthalenesulfonic acids, urea, biuret, dicyandiamide and/or melamine, it is advisable first to precondense either the aniline component or the other component with small amounts of aidehyde and only then to carry out the cocondensation. It is particularly advantageous first to carry out a precondensation in the case of both components of the co-condensation.

In addition to formaldehyde, which is preferred, suitable aldehydes include acetaldehyde, propionaldehyde and n- and i-butyraldehyde.

Instead of free formaldehyde it is of course also possible to employ formaldehyde donors, e.g.

paraformaldehyde or condensates or adducts of urea or melamine with formaldehyde.

Examples of suitable phenols are phenol itself, cresol, xylenol p,p'-dihydroxydiphenylsulfone and p,p'-dihydroxydiphenylmethane. Phenol is preferred. Examples of suitable phenolsulfonic acids and naphthalenesulfonic acids are the sulfonic acid mixtures which are obtained on sulfonation of phenol, cresol, xylenol and naphthalene. The sulfonation products of phenol and of naphthalene are preferred.

It is true that leather dyed with this component I alone can also be dyed in deep hues, but the brilliance of the dyeing is not entirely satisfactory.

The solution obtained can be mixed direct with an aqueous solution of an aluminum tanning agent, the mixture being employed for tanning or retanning. Alternatively, the tanning agent can be isolated in a conventional manner, for example by salting out or spray-drying, and then be mixed with dry aluminum tanning agent, or a solution of the aluminum tanning agent may be added to the above solution of the organic tanning agent, after which the mixture obtained is spray-dried.

In principle, any aluminum tanning agent may serve as component 11 of the tanning agent mixture. Aluminum tanning agents were even known in antiquity, and are described in relevant textbooks, for example in H. Herfeld, Grundlagen der Lederherstellung, Verlag Theodor Steinkopf, Dresden and Leipzig 1950, pages 307-314, and I. and H. Möllering, Verfahren der Gerberei Chemie, Wissenschaftliche Verlagsgesellschaft mbH, Stuttgart, 1954, pages 190-200. Hence, the aluminum tanning agents do not require more detailed description here.They not only include the tanning agents based on aluminum alone but also those which in addition to aluminum may contain other metals, for example zirconium, zinc or chromium, and/or may contain synthetic tanning agents.

The weight ratio of tanning agent I to aluminum tanning agent II in the mixture is from 0.5:1 to 30:1, preferably from 2:1 to 6:1.

Tanning agents are employed in liquors of varying length. The thinner the leather, the longer the liquor must be, to prevent the leather from tearing during drumming. The liquor length may, depending on the type of leather and its thickness, be up to about 400%, based on shaved weight.

According to the prior art, the use of aluminum tanning agents in relatively long liquors must always be expected to give a precipitate of aluminum hydroxide, and hence cause uneven uptake of the tanning agent, resulting in uneven dyeings. Surprisingly, this occur substantially less in the case of the tanning agent mixture according to the invention. It is true that even with this combination cloudiness of the liquor due to precipitation of aluminum hydroxide may occur, but only on greater dilution, and after a longer time, than in the absence of the tanning agents The stability of the aqueous solution of the, mixture of tanning agents (I) and (II) (which mixture can of course also be prepared by mixing the aqueous solutions of the individual components) can be improved further by adding small amounts of compounds which form water soluble complexes with aluminum. For the purposes of the present invention, small amounts generally means up to 0.6, but preferably less than 0.3, mole of complexing agent per mole of aluminum tanning agent. The use of larger amounts causes the risk of color shifts when dyeing with metal complex dyes.

Preferred complexing agents (component III) are tartaric acid, citric acid and aminopolycarboxylic acids. Examples of the latter are nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, p- hydroxyethylaminodiacetic acid, N,N-di-(P- hydroxyethyl)-glycine, 1,3propylenediaminetetraacetic acid, 1,2propylenediaminetetraacetic acid, N-(p- hydroxyethyl )-ethylenediam inetriacetic acid, 2 hydroxypropylene- 1 ,3-diaminetetraacetic acid, di (p-aminoethyl)-ether-tetraacetic acid, glycol-bis (ss-aminoethyl)-ether-tetraacetic acid and cyclohexylene-1 ,2-diaminetetraacetic acid; their alkali metal salts and alkaline earth metal salts may also be used.

The tanning agent mixtures according to the invention may consist of components I and II (with or without Ill), as the sole tanning constituents, or these components may comprise more than 70 percent by weight, preferably more than 90 percent by weight, of the tanning constituents. Of course, the tanning agent mixtures according to the invention can be mixed with other constituents (which may even be used in substantial amounts), for example sodium sulfate, water-soiuble high polymers to act as lubricants, and buffers, such as salts of formic, acetic, propionic, oxalic, malonic, glutaric, adipic or phosphoric acid. Mineral-pretanned hides preferably means chrome-tanned hides.

The tanning agents according to the invention may be employed for tanning or, preferably, for retanning under the conventional conditions for the respective processes. The tanning agent may be added as such, as a solution or as a suspension to the tanning liquor, in which it dissolves. The liquor length may be from 30 to 1,000%, preferably from 100 to 400%, based on the shaved weight of the leather to be tanned or retanned. The pH during retanning is usually from 4.0 to 6.5, preferably from 4.5 to 5.5, whilst during tanning it is usually from 3.0 to 5.0, preferably from 3.5 to 4.5. The temperature is usually from 20 to 600C, preferably from 35 to 500C. The retanning time is usually from 15 to 120 minutes, preferably from 30 to 60 minutes.

The tanning times are usually from 4 to 24 hours, and from 20 to 40%, based on pelt weight, of tanning agent is usually employed. For retanning, from 0.5 to 10%, preferably from 1 to 5%, based on shaved weight, of the tanning agent is usually employed. The tanning agent may be added together with or, preferably, before the dye. The advantages of the novel process manifest themselves particularly when using anionic dyes.

In the Examples, parts and percentages are by weight.

Example 1 470 parts of phenol and 550 parts of 96% strength sulfuric acid were stirred for 4 hours at 950C. The mixture was then diluted with 250 parts of water and cooled to 600C. 300 parts of urea were then added and 750 parts of 30% strength formaldehyde solution were run in over 6 hours at 5O-550C. The batch was then stirred for a further 2 hours at 600C, after which it was brought to pH 2.0 with 450 parts of 50% strength sodium hydroxide solution. In the text which follows, this solution is referred to as component a.

Parallel to component a, a second product (component b) was prepared as follows: 500 parts of 30% strength formaldehyde solution and 93 parts of aniline were added to 520 parts of sodium bisulfite in 210 parts of water. After the mixture had been stirred for 3 hours at 900 C, 48 parts of urea were added and 1 60 parts of 30% strength formaldehyde solution were then introduced dropwise in the course of 1 hour, at 500C. The batch was then stirred for 4 hours at 900C.

Components a and b were mixed and the mixture was stirred for a further 4 hours at 900C.

It was then brought to pH 3.0 with 1 50 parts of formic acid and 2,970 parts of a 37% strength solution of a commercial 20% basic aluminum tanning agent, containing 18% of Al203, based on solids, were added. The solution obtained was spray-dried.

The tanning agent powder obtained was tested in comparison with a commercial combination tanning agent which consisted of a conventional tanning agent based on phenolsulfonic acid and aluminum tanning agent.

On dissolving 5 parts of the tanning agent according to the invention in 100 parts of water, a clear solution was obtained, which did not change even after standing for 24 hours. In contrast, the commerical combination tanning agent precipitated from the solution after only a few minutes.

The leather retanned according to the inventon was dyed with 0.5%, based on shaved weight, of Acid Brown 216 (C.I. No. 34,906). The dyeing was substantially deeper and more level than that of the comparative leather which had been treated with the commercial combination tanning agent.

Example 2 1 75 parts of ethylenediaminetetraacetic acid were added to the tanning agent solution of Example 1 before spray-drying. Leather retanned with the resulting tanning agent gave a dyeing which was somewhat more level still than that of the leather of Example 1.

Example 3 The procedure of Example 2 was followed, except that instead of the ethylenediaminetetraacetic acid 220 parts of citric acid were employed. The tanning agent gave a leather which had very good dyeing characteristics.

Example 4 360 parts of 30% strength formaldehyde solution were run into 374.4 parts of sodium bisulfite, with stirring, the rate of addition being such that the temperature rose to 95-970C, 74.4 parts of aniline were then added and the mixture was stirred for a further 2 hours at 1000C. Thereafter, 32.7 parts of urea were added, following which 103 parts of a 30% strength formaldehyde solution were introduced dropwise in the course of 1 hour at 500C.The mixture was then stirred for 4 hours at 900C, and was subsequently brought to pH 4 with 8 parts of formic acid. Finally, 1,550 parts of a 20% strength solution of a commercial 65% basic aluminum tanning agent, containing 23%, based on solids, of Awl203, and 87.6 g of ethylenediaminetetraacetic acid were added, and the resulting solution was spray-dried.

Level very deep hues were obtainable by leather retanned with the tanning agent obtained.

Example 5 20.8 parts of technical-grade naphthalenesulfonic acid and 10 parts of 30% strength formaldehyde solution were stirred for 30 minutes at 1000C. A mixture of 100 parts of component a and 1 5 parts of 30% strength sodium hydroxide solution was then run in slowly at 500C. 20 parts of formaldehyde solution were subsequently added dropwise and the batch was stirred for 1 hour at 1000C. Finally, 100 parts of the aluminum tanning agent described in Example 1 were added and the solution was spray-dried.

The leather treated with this tanning agent also had very good dyeing characteristics.

Claims (11)

Claims

1. A tanning agent mixture which comprises a water-soluble mixture of i. from 0.5 to 30 parts by weight of a tanning agent which is a condensation product of from 0.1 to 6 molar proportions of one or more aliphatic aldehydes of 1 to 4 carbon atoms and 1 molar proportion of one or more sulfonic acids and/or carboxylic acids containing an aminosubstituted benzene nucleus and having the general formula

where X is H, C,4-alkyl,

or-CH2-C02-H, Y and Z are independently H, -S03H, -C02H, -CH3 or -CH2-SO3H,RisH or C1.4-alkyi and R' is H or C,3-alkyl, with the proviso that at least one of the radicals X, Y and Z is or contains (as the case may be) a sulfonic acid group or carboxyl group, and II. one part by weight of an aluminum tanning agent.

2. A tanning agent mixture as claimed in claim 1, wherein the tanning agent I has been obtained by condensing the aliphatic aldehyde(s) with the carboxylic acid(s) and/or sulfonic acid(s) in aqueous solution for from 1/2 to 24 hours at a pH of from 1 to 8 at from 30 to 1000C.

3. A tanning agent mixture as claimed in claim 1 or 2, wherein the condensation to produce the tanning agent I has been carried out in the presence of urea, biuret, dicyandiamide, melamine, a phenol, a phenolsulfonic acid or a naphthalenesulfonic acid.

4. A tanning agent mixture as claimed in claim 3, wherein the total amount of the urea or other specified compound is not more than 10 percent by weight of the aromatic aminosulfonic acid or aminocarboxylic acid used in the condensation to produce the tanning agent I.

5. A tanning agent mixture as claimed in any of claims 1 to 4, wherein component I has been prepared by heating a mixture of a) a reaction product of aniline or toluidine with from 1 to 6 moles of formaldehyde and from 1 to 6 moles of sodium bisulfite, with b) an aqueous solution, containing free formaldehyde, of a condensate of formaldehyde with from 0.3 to 1 mole of urea and from 0.1 to 0.3 mole of melamine, in the weight ratio of a) to b) (based on solids) of from 1:0.5 to 1 :5, in aqueous solution, at a pH of from 3.5 to 8, for from 1 to 10 hours at from 60 to 1 OO"C.

6. A tanning agent mixture as claimed in any of claims 1 to 5 which contains up to 0.6 mole, per mole of aluminum treating agent II, of a compound Ill which forms a water-soluble complex with aluminum.

7. A tanning agent mixture as claimed in claim 6, wherein the compound Ill is tartaric acid, citric acid or an aminopolycarboxylic acid.

8. A tanning agent mixture as claimed in claim 1 and substantially as described in any of the foregoing Examples.

9. A process for tanning or retanning a pickled or mineral-pretanned hide with an aqueous solution of a tanning agent, wherein an aqueous solution of a tanning agent mixture as claimed in any of claims 1 to 8 is employed.

1 0. Hides which have been chrome-tanned and then re-tanned by a process as claimed in claim 9.

11. Dyed leather goods obtained from hides tanned or retanned by a process as claimed in claim 9.