Agents for the production of leather

The present invention relates to an aqueous composition for the tanning of pelts or tanning, fatliquoring and dyeing of leather, a process for the tanning of pelts or tanning, fatliquoring and dyeing of leather and the leather treated by the process.

Chrome-free tanning has become more important in recent years, particularly for the area of automotive leather. However, it is particularly difficult to produce leather with an intense dyeing which was tanned exclusively by an anionic method, with either vegetable or synthetic tanning agents. The anionic character of the tanned leather then evidently does not enable the leather to fix the dye as desired in sufficient concentration. Frequently, the tanner is therefore forced to increase the amount of dyes, tanning agents and fatliquoring agents. This results in substantially poorer liquor exhaustion. Another disadvantage of chrome-free tanning is the substantially higher cost factor.

DE 28 56 628 describes a process for dyeing grain leather with anionic dyes for both anionically and cationically tanned leather, which is characterized in that the dyeing process is effected in the presence of two neutral surfactants in addition to the anionic dye. These surfactants are oxyethylated aliphatic alcohols and oxyethylated primary amines, which are present in a weight ratio of 4:1 to 1 :4. In the case of anionically tanned or retanned leather, the dye is first allowed to run for 5 to 90 minutes in the dye liquor separated from the tanning, and the surfactant mixture is then added which leads to a deepening of the colour. The subsequent fatliquoring of the leather can be effected in the presence of the surfactant mixture mentioned.

Since, as mentioned, chrome-free tanning has become more important in recent years, particularly in the area of automotive leather, there is considerable demand for more economical and more cost-efficient processes for the production of leather.

It was surprisingly found that complete dyeing and a regular distribution of both tanning agents and fatliquoring agents are possible by the use of stable and approximately neutral solutions of compositions containing specific synthetic tanning agents and surfactants.

This permits a generally improved liquor exhaustion, and the customary liquor change can be dispensed with. Thus, greater efficiency is achieved with respect to the amounts of

tanning agents, dyes and fatliquoring agents used, and the economic advantages achieved thereby have a positive effect particularly in the case of chrome-free tanning, which is more expensive per se. Thus, a means for the treatment and production of leather is present which is suitable in particular for the production of chrome-free wet-white leathers, but can also advantageously be used for the production of wet-blue leathers.

The invention firstly relates to an aqueous solution of

A) 20-90% by weight of water and, dissolved therein,

B) 10-80% by weight of a composition containing

B1) a tanning aromatic compound having at least one sulpho group or a salt thereof,

B2) an aliphatic amine having a degree of oxyethylation of 5 to 80 and 8 to 20 carbon atoms and optionally

B3) an aliphatic alcohol having a degree of oxyethylation of 5 to 80 and 8 to 20 carbon atoms, the solution having a pH of more than 6.0.

The tanning agents in the form of component B1) are known, cf. for example Ullmanns Enzyklopadie der technischen Chemie [Ullmann's Encyclopaedia of Industrial Chemistry], vol. 16, (4), 138 to 140 (1979), and can be prepared by processes as described in the references stated there.

For example, the following may be mentioned as possible aromatic compounds: naphthalene, biphenyl, terphenyl, phenols, cresols, 4,4'-dihydroxydiphenyl sulphone, β-naphthol, dihydroxybenzenes, resorcinol, 2,2'-bis(hydroxyphenyl)propane and diaryl ethers, such as diphenyl ether and ditolyl ether, which are sulphonated in a known manner.

These sulphonated aromatic compounds can be subjected, alone or in combination with a further aromatic, optionally likewise sulphonated compound, to a condensation with formaldehyde and/or urea.

Particularly suitable tanning agents are: a) Condensates of naphthalenesulphonic acid and formaldehyde; b) Formaldehyde condensates of 4,4'-dihydroxydiphenylsulphones with (hydroxy )arylsulphonic acids; c) Formaldehyde condensates of aromatic hydroxyl compounds containing sulpho groups with aralkyl halides;

d) Urea-formaldehyde condensates of phenols and phenol sulphonic acids; e) Reaction products of phenol and a sulphonating agent, such as oleum, the molar ratio (phenol):(SO ₃ ) being (1):(0.8-2.2); f) Condensates of sulphonated diaryl ethers and formaldehyde; g) Condensates of sulphonated di- or terphenyls and formaldehyde; h) Condensates of 4,4'-dihydroxydiphenyl sulphone and sulphonated 4,4'- dihydroxydiphenyl sulphone with formaldehyde; i) Formaldehyde condensates of diaryl ether sulphonic acid and 4,4'-dihydroxydiphenyl sulphone; j) Formaldehyde condensates of phenol with aryl sulphonic acids or hydroxyarylsulphonic acids; and k) Formaldehyde condensates of dioxydiaryl sulphones with sulphites.

The component B1) is preferably selected from the abovementioned tanning agents b), e), h) and k).

The oxyethylated aliphatic amines in the form of a component B2) are alkylamine ethoxylates of the following general formula (I). They are obtained by ethoxylation of aliphatic primary amines. The data for the chain length n and degree of ethoxylation m in the following general formula (I) for alkylamine ethoxylates are mean values. The component B2) is therefore a compound of the general formula (I):

in which R denotes a linear or branched hydrocarbon radical having 8-20 C atoms and m denotes 5-80.

Alkylamine ethoxylates of linear aliphatic primary amines, such as, for example, octyl-, nonyl-, tridecyl-, oleyl-, or stearylamine, whose hydrocarbon radical R has 12 to 18 C atoms, the degree of ethoxylation m being 5 to 12, are preferably used.

The oxyethylated aliphatic alcohols in the form of a component B3) are alkyl alcohol ethoxylates of the following general formula (II). These are prepared by ethoxylation of industrial fatty alcohols from fat hydrogenation or from alkanols of petrochemical (oxo alcohols) origin. Several moles of ethylene oxide are subjected to an addition reaction with

one mole of fatty alcohol or oxo alcohol by preferably alkaline catalysis. Adducts having more than 80 ethylene oxide units are possible. This leads to a distribution between polyethylene glycol ethers of different degrees of ethoxylation (EO degree). Homologues are defined as those AEOs which differ in the length of the alkyl radical and ethoxymers are defined as those AEOs which differ in the number of ethoxy units. The data for the chain length n and EO degree m in the following general formula for alkyl alcohol ethoxylates are therefore mean values.

The component B3) is therefore a compound of the general formula (II):

R4 L O- - + J mOH ( ^v II) ' in which R denotes a linear or branched hydrocarbon radical having 8-20 C atoms and m denotes 5-80.

Alkyl alcohol ethoxylates of linear aliphatic fatty alcohols, whose hydrocarbon radical R has 12 to 18 C atoms and in which the EO degree m is 5 to 12 are preferably used.

The composition according to the invention contains, as a proportion of B), a component B1) in an amount of 5-95% by weight, preferably 20-90% by weight, particularly preferably 40- 90% by weight, especially preferably 55-90% by weight.

The composition according to the invention thus furthermore contains, as a proportion of B) and summing to 100% by weight, the component B2) in an amount of 95-5% by weight, preferably 80-10% by weight, particularly preferably 60-10% by weight, especially preferably 10-45% by weight.

In the composition according to the invention, the component B2) can be partially replaced by the optional component B3). Use of the component B3) is not decisive for the improved dyeing according to the invention and regular distribution of tanning agents and fatliquoring agents and improved liquor exhaustion. However, it was found that an emphatically brilliant dyeing can be achieved with the use of component B3).

If this special colour effect is desired, it is sufficient in practice if 1-30, preferably 5-20, particularly preferably 5-15, % by weight of the component B2) is replaced by a component B3).

It is also possible to use mixtures of in each case 2 or more than 2 of the respective components as component B1), B2) and B3).

An aqueous solution according to the invention consists of

A) 20-90, preferably 35-65, particularly preferably 45-60, % by weight of water and, dissolved therein,

B) 10-80, preferably 35-65, particularly preferably 40-55, % by weight of a composition described above.

About 40-50% strength solutions of the compositions according to the invention are regarded as being suitable in practice.

A composition according to the invention can be prepared by simply combining the components described above. For this purpose, the initially prepared component B1) is initially introduced into a vessel as an aqueous solution which is optionally adjusted with a base to a slightly basic pH of about 7.0 to 8.0, and subsequently aqueous solutions of the component B2) and optionally B3) are stirred in, clear, pale or brown solutions being obtained.

As mentioned, the solutions are, if required, adjusted to an approximately neutral to moderately basic pH with the aid of bases, such as ammonia or alkali. The pH of the solution which is established in this manner should be above 6.0 and should not exceed 9.0. Preferred pH values are above 6.5, in particular above 6.8, and should not exceed a value of 8.5. The particularly preferred pH range extends from 7.0 to 8.0.

The tanning agents in the form of the component B1) are therefore always used predominantly, as a rule completely, in the form of their salts, especially lithium, potassium or ammonium salts or in particular their sodium salts. Ammonium salts are understood as meaning salts which are derived from ammonia or primary, secondary and tertiary amines.

A feature essential to the invention is therefore the circumstance that the naturally acidic compounds (free sulphonic acids) in the form of the component B1) are adjusted to an approximately neutral to moderately basic pH, and that furthermore a component B1) neutralized in this manner, together with a fatty amine in the form of the component B2), gives

a clear and surprisingly storage-stable solution. The addition of an optional component B3) changes nothing about this.

The compositions according to the invention in the form of the solutions described above can advantageously be used in principle with all substrates for leather production. The following may be mentioned:

- pickled hide; pre-tanned wet-white leather, treated for example, with aldehyde derivatives, such as, for example, glutardialdehyde or formaldehyde, or hydroxyalkylphosphine compounds, such as, for example, tetrakis(hydroxymethyl)phosphonium sulphate;

- leather treated with vegetable tanning agents; or

- chrome-tanned leather (wet-blue).

Depending on substrate and intended use, the following amounts of the solutions according to the invention are suitable for use, for example for a 40-50% strength solution of composition as described above, and based on the shaved weight of the hide or of the leather:

For pickled hide, the use of 2-10% by weight of a solution according to the invention for pretanning after the preliminary treatment with aldehydes or vegetable tanning agents is expedient. A wet-white leather pre-tanned in this manner is very suitable for further processing with tanning agents, for example with a solution according to the invention or other tanning agents, for the production of leathers free of heavy metals.

For the production of leathers free of heavy metals, in particular chrome-free wet-white leathers, 30-40% by weight altogether of a solution according to the invention are expedient for the main tanning, dyeing and fatliquoring on already pre-tanned leather in the presence of aldehydes or vegetable tanning agents. A substantial effect according to the invention is based on the possibility firstly of carrying out the steps of tanning, dyeing and fatliquoring without changing the liquor, and on the fact that secondly a very good liquor exhaustion is achieved and optimal dyeing can be achieved.

For chrome-tanned wet-blue leather, 4-10% by weight of a composition according to the invention are sufficient for retanning and for deepening the colour in dyeing with dyes.

The invention therefore furthermore relates to a process for the pretanning of pelts or retanning of wet-white, wet-blue or vegetable-pretanned leather as a substrate,

characterized in that a solution according to the invention is added to the aqueous liquor and said liquor is allowed to act on the substrate. Depending on the substrate, the solution according to the invention penetrates completely into the leather within 1 to 3 hours.

Depending on the aim, it is advisable to add the solution according to the invention during the pretanning but after the treatment with aldehyde. If the solution according to the invention is used during the retanning, it should be used firstly before the dyes and secondly together with the fatliquoring agents in order to achieve a deepening of colour and an improvement in the bath exhaustion.

The present invention furthermore relates to the leathers produced by the process according to the invention or tanned using a composition according to the invention.

Examples

A1) Example 1 : Agents consisting of the components B1), B2) and B3) 1200 parts of a molten reaction product of phenol and oleum (20%), the molar ratio (phenol):(SO ₃ ) being 1 : 1.0 to 1.1 , are dissolved in 288 parts of water and adjusted to a pH of 7.3 to 7.5 with 557 parts of 50% strength sodium hydroxide solution, and then 194 parts of 37% strength formaldehyde solution are added and condensation is then effected at 105°C until (about 6 hours) a sample which - diluted with a little water - remains clear on acidification with dilute sulphuric acid to a pH of 3.5. A solution of 1100 parts of water, 175 parts of tallow fatty amine ethoxylate with 8 mol of ethylene oxide and 20 parts of isodecyl alcohol with 7 mol of ethylene oxide is then added to the reaction mass. A clear, pale solution which has a pH of 7.0 to 8.0 is obtained. The solids content is about 48% by weight and is outstandingly suitable for the tanning of leather.

A2) Example 2: Agent consisting of the components B1) and B2)

1200 parts of a molten reaction product of phenol and oleum (20%), the molar ratio

(phenol):(SO ₃ ) being 1 :0.8 to 0.9, are melted at 90 ⁰ C with 42 parts of water, and 14.4 parts of urea are added. After cooling to 55°C, 38.5 parts of a 37% strength formaldehyde solution are added dropwise in the course of 2 hours and stirring is effected for about a further 4 hours until the condensate has dissolved in water to give a clear solution. The reaction product obtained is adjusted to a pH of 7.3 to 7.5 with 38 parts of 50% strength sodium hydroxide solution.

A solution of 415 parts of water and 265 parts of tallow fatty amine ethoxylate with 8 mol of

ethylene oxide is then added to the reaction mass. A clear, pale solution which has a pH of 7.0 to 8.0 is obtained. The solids content is about 45% by weight and is outstandingly suitable for the retanning of dark dyeings.

A3) Example 3: Agent consisting of the components B1), B2) and B3): 100 parts of naphthalenesulphonic acid are heated with 55.8 parts of a molten reaction product of phenol and oleum (20%), the molar ratio (phenol):(SO ₃ ) being 1 :1.40 to 1.45, and 100 parts of water and 30 parts of formaldehyde to 105 °C to 110°C for about 3 hours until the condensate dissolves in water to give a clear solution. Thereafter, the solution is adjusted to a pH of 7.0 to 8.0 with 80 parts of a 25% strength ammonia solution, and a solution of 100 parts of water, 30 parts of tallow amine with 6 mol of ethylene oxide and 5 parts of isodecyl alcohol with 7 mol of ethylene oxide is added. A clear, brown solution which has a pH of 7.0 to 8.0 is obtained. The solids content is about 43%. The solution is outstandingly suitable for the retanning of chrome-free leather.

A4) Example 4: Agent consisting of the components B1) and B2):

135 parts of dihydroxydiphenyl sulphone (59% strength) are heated with 43.5 parts of formaldehyde (37% strength) and 26 parts of sodium sulphite in a closed reactor for about 3 hours to 130 ⁰ C until the condensate dissolves in water to give a clear solution. 75 parts of water and 20 parts of tallow fatty amine ethoxylate with 8 mol of ethylene oxide are then added. A clear, brown solution which has a pH of 7.0 to 8.0 is obtained. The solids content is about 45%. The solution is outstandingly suitable for the tanning and retanning of chrome-free leather.

A5) Example 5: Agent consisting of the components B1), B2) and B3): Sodium hydroxide solution (30% strength) and 88 parts of formaldehyde solution (37% strength) are carefully added to 400 parts of a molten reaction product of phenol and oleum (20%), the molar ratio (phenol):(SO ₃ ) being 1 :0.80 to 0.90, and condensation is then effected at 100 ⁰ C to 105°C until (about 6 hours) a sample, diluted with a little water, remains clear on acidification with dilute sulphuric acid to a pH of 3.5. A solution of 240 parts of water, 35 parts of tallow fatty amine ethoxylate with 8 mol of ethylene oxide and 9 parts of isodecyl alcohol with 7 mol of ethylene oxide is then added to the reaction mass. A clear, pale solution which has a pH of 7.0 to 8.0 is obtained. The solids content is about 48% by weight and is outstandingly suitable for the pretanning, tanning and retanning of leather.

B) Use examples

The stated percentages relate to the salted weight of the leather hides or skins.

Example B1) Use for the pretanning of pelts

100 parts of a pickled calf pelt are first treated with 2.5% of a 25% strength glutardialdehyde solution for 6 hours at 25°C in a rotating drum and then stirred for a further 2 hours with 5% of the composition according to preparation example Al The pH is then adjusted to 4.0 with pulverized sodium bicarbonate or sodium formate.

The leather thus treated (wet-white leather) is dewatered and is shaved to the desired thickness. This pre-tanned leather is outstandingly suitable for further processing with mineral, vegetable or synthetic tanning agents for the production of leather free of heavy metals.

Example B2) Use for wet-white leather

200% of water at 30 ⁰ C and 0.5 % of formic acid are acidified together with the hide pre- tanned with 1 % of glutardialdehyde (cut to 0.9-1.0 mm) for the duration of 15 minutes. 6% of the product from example A5 are then added and said product is allowed to act for 20 minutes.

4% of the prepared fatliquoring agent (an about 50% strength aqueous solution of a fatli- quoring agent based on sulphited natural and synthetic fats) are then added and, after 20 minutes, 25% of the product from example A5 are added.

The dyeing is carried out with 2.2% of commercially available dye, such as C.I. Acid Black 210 and mixtures of this dye with other C.I. Acid Black dyes as secondary components. The dyes are allowed to act for 240 minutes. The mixture is acidified with 0.8% of formic acid after 60 minutes until complete exhaustion of the liquor. The bath is discharged and the leather is washed for 10 minutes with water at 50 ⁰ C.

3% of product, according to example A5, is added for 20 minutes. For the fatliquoring, 200% of water at 50°C and 3% of product according to example A5 are introduced into the drum, and the run time is 20 minutes. 12% of the fatliquoring agent are added and, after 60 minutes, the mixture is acidified with 1% of formic acid for 45 minutes until complete exhaustion of the liquor.

The leather thus obtained has good fullness and has a deep black brilliant hue.

Example B3) Use for wet-blue leather

The wet-blue leather (cut to 1.0-1.2 mm) is rinsed, washed and neutralized to pH 5.5 in 150% of water containing a sodium bicarbonate/sodium formate mixture, in the usual manner.

The preparatory fatliquoring (an about 50% strength aqueous solution of a fatliquoring agent based on sulphited natural and synthetic fats) is applied, the fatliquoring agent is discharged and the leather is washed for 10 minutes with 200% of water at 30°C. For the retanning, 100% of water at 30 ⁰ C and 10% of commercially available phenol sulphonic acids as a tanning agent together with 4% of vegetable extract (tara extract) and 3% of fatliquoring agent (an about 50% aqueous solution of a fatliquoring agent based on sulphited natural and synthetic fats) are introduced into the drum, and the run time is 30 minutes. Retanning is effected with 6% of product according to example A2 for 20 minutes. Thereafter, 2.5% of C.I. Acid Black 210 is added and dyeing is effected; the process may take up to 60 minutes before the desired dyeing is achieved. After the fatliquoring, discharge is effected in the usual manner and 6% of commercially available phenol sulphonic acids as a tanning agent together with 2% of a vegetable extract are added for 45 minutes.

200% of water at 50°C are added and, after 30 minutes, 2% of formic acid are introduced for 40 minutes.

The leather thus obtained has a level black dyeing in an optimal hue and fastness.