The present invention relates to a composition comprising various synthetic retanning agents, a process for the treatment of pretanned leathers using this composition, and a material obtained by this process.

The retanning of pretanned leather to achieve greater fullness and a tighter grain is difficult. Since leather tanned with metal salts changes its properties adversely with respect to the tight-grained character in the pH range above 6-7, working in an acidic, aqueous medium will be better suitable in retanning, fatliquoring and dyeing. However, this is not possible according to the prior art.

The customary process steps of a leather tanned with metal salts comprise first washing and neutralization of a leather tanned with metal salts, which has a pH of about 4.5 to 6.5 in water. The leather is then treated in turn with retanning agents in a weakly alkaline, aqueous medium in order to achieve certain properties, such as, for example, tensile strength, fullness, hardness or softness. Thereafter, a leather pretreated in this manner is treated with anionic dyes in a fresh bath, preferably above the isoelectric point and often in the presence of penetration auxiliaries, in order thus to achieve complete dyeing of the leather and a good colour strength. The leather is then treated with fatliquoring agents which impart the desired softness, flexibility and strength to the leather. The dyeing process in the aqueous alkaline medium is complex owing to the different process steps and concomitantly used chemicals and gives rise to a large amount of wastewaters which make disposal expensive. The wet treatment of leather carried out in an alkaline, aqueous medium, including retanning, dyeing, fatliquoring and aftertreatment, is described, for example, in: "Bibliothek des Leders" [Library of leather], Volume 3 (tanning agents, tanning and retanning) [1985], Volume 4 (degreasing, fatliquoring and imparting of water repellency in leather production) [1987] & Volume 5 (The dyeing of leather) [1987] Umschau Verlag; and "Fundamentals of Leather Manufacturing", 1993, by E. Heidemann, published by Eduard Roether KG.

In order therefore to ensure complete uptake of all substances usually used in retanning, dyeing and fatliquoring, the leather is first neutralized and said process steps are carried out in separate liquors, the pH of which is not permitted to be below 4.0. As a rule, the pH should be adjusted in the range between 4.5 and 6.5. There is therefore still a need for more efficient and at the same time more economical process sequences in leather production. Thus, for example, DE 197 46 445 A1 describes storage-stable compositions (powders) which give homogeneous mixtures in aqueous solutions, these powders containing at least

one combination of retanning and fatliquoring agents. Vegetable tanning agents, aromatic syntans, resin tanning agents, reactive tanning agents and mineral and polymeric tanning agents are mentioned as retanning agents which may be used. The combination of retanning agents according to the present invention is not mentioned. The compositions according to DE 197 46 445 A1 may also contain further additives, including neutralizing agents, dye formulations or finishing agents. If the composition contains only retanning agents and fatliquoring agents, the steps of neutralization, dyeing and finishing are carried out in separate steps.

It was an object of the present invention to provide a process which starts after the pretanning and is intended to make the following steps of wet finishing up to the finished leather product substantially more efficient and more economical, in particular by avoiding the neutralization step, the leathers finally produced being qualitatively at least as good as the leather produced by customary processes.

It has now surprisingly been found that, with the use of a composition according to the invention in the process for the preparatory treatment of already pretanned leathers for the subsequent retanning, fatliquoring and dyeing, it is possible to dispense with the customary neutralization process and an increase of the pH to at least 4.5. Accordingly, substantially increased process economy can be achieved, in particular by virtue of the fact that it is possible to carry out all abovementioned treatment steps without change of liquor.

The invention firstly relates to a composition containing a) 1 - 95% by weight of a product of the reaction of a phenol and a sulphonating agent, the molar ratio (phenol):(SO ₃ ) being (1):(1.1-2.2), b) 1 - 95% by weight of a condensate of the reaction of a naphthalenesulphonic acid and formaldehyde, and c) 5 - 50% by weight c1) of a formaldehyde condensate of a dihydroxydiarylsulphonic acid with aryl- or (hydroxy)arylsulphonic acid and/or c2) of a urea/formaldehyde condensate of a phenol and phenolsulphonic acid, the sum of the components a), b), c1) and c2) being 100% by weight.

The component a) of the composition is the product of the reaction of a phenol and a sulphonating agent, the molar ratio (phenol):(SO ₃ ) being (1):(1.1-2.2). The component a) is already known, for example from EP 0 554 218 A1, which describes the advantageous use of the component a) for pickling pelts. A preferably used sulphonating agent for the preparation

of component a) is SO ₃ or especially oleum. Oleum is a solution of SO ₃ in concentrated sulphuric acid. Thus, reaction products of phenol and oleum are particularly suitable, the molar ratio (phenol):(SO ₃ ) being especially (1):(1.4-1.8). The reaction products are usually present in the form of mixtures, substantially sulphonated diphenoldisulphonic acid being obtained in the abovementioned reaction, corresponding to the following formula (I):

in which n and m are each O, 1 or 2, provided that the sum of n and m is 1 or 2. Phenolsulphonic acid is also formed as a byproduct.

The composition according to the invention contains 1 - 95% by weight, preferably 10 - 60% by weight, particularly preferably 15 - 55% by weight, particularly preferably 20 - 50% by weight, of component a).

For the preparation of component b), naphthalene is sulphonated according to the known prior art and the sulphonated product is condensed with formaldehyde at elevated temperature with elimination of water to give the desired product. The sulphonation is preferably effected analogously to component a) with the aid of oleum according to the following reaction scheme for naphthalenesulphonic acid by way of example:

The composition according to the invention contains 1 - 95% by weight, preferably 20 - 80% by weight, particularly preferably 30 - 70% by weight, particularly preferably 40 - 60% by weight, of component b).

For the preparation of component c1 ) known from the prior art, an aryl- or (hydroxy)arylsulphonic acid is condensed with dihydroxydiphenyl sulphone in the presence of formaldehyde with elimination of water, and the product obtained is neutralized, for example

- A -

with an ammonia solution.

The dihydroxydiphenyl sulphone used is preferably 4,4'-dihydroxydiphenyl sulphone. Naphthalenesulphonic acid is particularly preferably used.

For the preparation of component c2) known from the prior art, phenol and sulphonated phenol are condensed with urea and/or formaldehyde.

The composition according to the invention contains 5 - 50% by weight, preferably 5 - 40% by weight, particularly preferably 5 - 30% by weight, particularly preferably 10 - 25% by weight of component c1) and/or c2). Mixtures of different c1) and/or c2) components can also be used as component c), the abovementioned weight data being applicable for the mixtures. A component c1) is preferably used as component c), particularly preferably the formaldehyde condensate of 4,4'-dihydroxydiphenyl sulphone and naphthalenesulphonic acid.

The abovementioned condensates are present in the form of the free acids and can be partly or completely neutralized by suitable alkalis and/or ammonia in aqueous solution.

The composition according to the invention can be prepared by simply combining the components described above. For this purpose, water is initially introduced into a vessel, for example into a sulphonation flask, and components a), b) and c) are stirred in at room temperature in succession, clear, generally brown solutions being obtained.

About 50% strength solutions are regarded as being suitable in practice, i.e. there are 50 parts by weight of the composition according to the invention per 50 parts by weight of water. Such a composition, i.e. for example adjusted to a concentration of 50%, is added to the liquor in an amount of 1 - 20, preferably 3 - 12, particularly preferably 5 - 10, % by weight, based on the shaved weight of the leather. If the composition according to the invention is adjusted to a different concentration, the amounts used should be appropriately adapted.

The composition according to the invention is used in leather production after the pickling and the pretanning but before the retanning, dyeing and fatliquoring. As a result of the use of the composition according to the invention, it is possible to dispense with the step of neutralization of the tanned leather, and the customary agents for retanning, fatliquoring and dyeing can be added as usual, but without a liquor change being necessary for this purpose. There are therefore substantial economic advantages through the overall shorter process duration and the lower water demand.

The quality of the leathers obtained is particularly convincing, and said leathers are substantially fuller and stronger than leathers produced by conventional processes. The good tight-grained character (particularly in the case of stronger leathers) and better embossability of the finished leather are further achievable positive results. It may be possible to explain this by the fact that the possibility of a "one-pot process" not only permits a simplified distribution but also a particularly good distribution of the retanning agents, colorants and fatliquoring agents, so that, for example, particularly complete dyeing is also observable.

The invention furthermore relates to a process for the treatment of wetwhite, wetblue or vegetable pretanned leather as a substrate, characterized in that - for the purpose of said treatment - a composition according to the invention in the form of an aqueous solution is added to the aqueous liquor and said composition is allowed to act on the pretanned leather.

In the case of the leather to be treated, the choice both with regard to the starting material in relation to leather type and origin or animal species and with regard to the product or intended use of the leather obtained is not critical.

The leather can be produced in all machines suitable for wet finishing, i.e. drum, dosamat, tanning machine or mixer.

The invention furthermore relates to a process for the pretreatment and wet finishing of pretanned leather, comprising the steps a) treatment of the leather with the composition according to the invention, b) aftertreatment of the leather which comprises one or more of the steps retanning, dyeing and fatliquoring by addition of appropriate conventional agents known from the prior art, characterized in that all process steps are effected in a common liquor and without neutralization.

The production of leather by the process according to the invention is effected, for example, by initially introducing pretanned leather at 10 - 50°C, preferably 20 - 40°C, particularly preferably at 25 - 30 ⁰ C, into 50 to 300% of water, preferably 50 - 150%, particularly preferably 50 - 100%, of water, based on the weight of the substrate. After some operating time, a pH of about 3 to not more than 4 results, depending on the type of pretanning, and about 2.8 - 3.8 are typical and a range of 2.8 - 3.4 is particularly typical. The temperature of the liquor is now adjusted to about 30 ⁰ C. The composition according to the invention is now added as 50% strength aqueous solution in an amount of 1 - 20, particularly preferably 5 -

10, % by weight to the liquor. After the addition, the pH decreases by about 0.5 to about 2.5 to not more than 3.5, depending on the starting value. With unchanged liquor temperature of about 30 ⁰ C, the agent is allowed to act on the leather for the duration of 30 to 60 minutes with circulation. As a rule, 30 to 45 minutes are sufficient.

After the end of the pretreatment of the substrate with the composition according to the invention, retanning agent, fatliquoring agent and dyes are now added in succession without liquor change and without neutralization of the aqueous acidic liquor, and these are allowed to act on the substrate in the presence of the agent according to the invention.

Specifically, for example, retanning agent and dyes are added in succession, and these are allowed to act on the substrate at about 30 ⁰ C, for example for 2 hours. 100% of water heated to 60 ⁰ C are then added to the liquor, and the liquor temperature is increased to 50°C with addition of the fatliquoring agent and treatment is effected for about one hour. 1 - 2% of formic acid are now added and treatment is continued for a further 40 min. After a final value of pH 3.5 - 3.8 has been reached, the liquor is discharged, washing is effected for about 10 min with 200% of cold water altogether and the leather is finished in the usual manner.

Even if, in contrast to the prior art, no neutralizing agents are used, the wet finishing of the substrate can be effected with the use of the known retanning agents, fatliquoring agents and dyes, as known from the prior art and for the most part commercially available. Only some of the agents known per se are therefore mentioned below by way of example and in a non- limiting manner:

Suitable retanning agents are in principle the agents known from the prior art and for the most part commercially available: chromium, aluminium, iron or zirconium salts, such as chlorides and sulphates, as mineral tanning agents; polymeric tanning agents, such as polyacrylates or copolymers containing acrylates, polyurethanes and polybutadienes; reactive tanning agents, such as aldehydes, isocyanates, alkyl sulphochlorides, relatively high molecular weight alkanesulphonates, aromatic tanning agents and vegetable tanning agents may be mentioned by way of example and in a non-limiting manner. Preferred retanning agents are polymeric tanning agents, synthetic aromatic tanning agents and vegetable tanning agents.

Suitable fatliquoring agents are in principle the agents known from the prior art and for the most part commercially available. The most customary ones are agents which are based on animal, vegetable or synthetic fats, oils and waxes, and which are generally present in a form

modified so that they are soluble or at least emulsifiable in water.

Suitable dyes are all customary natural and synthetic leather dyes, such as anionic or cationic dyes, metal complex or direct dyes, anionic, metal complex and sulphur dyes being particularly preferred. Preferably used dyes are anionic dyes and metal complex dyes.

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

Examples

A1) Component a)

136.5 parts of phenol (1.45 mol) are melted at 45°C. 193.4 parts of oleum (20%) (2.08 mol of SO ₃ ) are slowly added to this melt so that the reaction temperature does not exceed 160 ⁰ C. The reaction mixture is now stirred under reduced pressure at 20 mmHg and 160°C for 6 hours, and at the same time the water formed is removed azeotropically together with small proportions of phenol from the reaction mixture. The mixture is then cooled to about 40°C under atmospheric pressure. 243 parts of a molten mixture which contains the desired sulphonic acid as the main component are obtained.

A2) Component b)

61 parts of naphthalene are melted at 80 ⁰ C. 59 parts of oleum (20%) are slowly added to this melt so that the reaction temperature does not exceed 150°C. The reaction mixture is now stirred at 150 ⁰ C for 4 hours. After cooling to 110 ⁰ C, 55 parts of water are slowly added and 30 parts of formaldehyde (37%) are added dropwise in the course of 2 hours. The reaction mixture is now stirred at 105°C for 2 hours and adjusted to a 45% strength solution.

A3) Component c1)

195 parts of component b) (45% strength solution) are stirred together with 23 parts of 4,4'- dihydroxydiphenyl sulphone at 95°C, and 20 parts of formaldehyde (37%) are added dropwise thereto in the course of 2 hours. The reaction mixture is now stirred at 105°C for a further 2 hours. After cooling to 60 ⁰ C, the pH is adjusted to 3.5 with ammonia (25%) and acidification is also effected with 16 parts of 85% formic acid. The solution is adjusted to 50%.

A4) Component c2)

82 parts of the reaction product of a phenol and a sulphonating agent, the molar ratio (phenol):(SO ₃ ) being (1):(1.2), are mixed at 65 - 75°C with 32 parts of water and 15 parts of urea. Thereafter, 31 parts of formaldehyde (37%) are added dropwise in the course of 4 hours and stirring is then continued for 1 hour. After cooling to 60°C, the pH is adjusted to 3.5 with ammonia (25%) and acidification is also effected with 12 parts of formic acid (85%) and 6.5 parts of acetic acid (80%). The solution is adjusted to 50%.

B1) Preparation of a 50% strength composition comprising the components a), b), c1) 500 ml of water are initially introduced into a sulphonation flask at room temperature, and initially 120 g of component a) (24% by weight), 270 g of component b) (54% by weight) and 110 g (22% by weight) of component c1) are added with vigorous stirring. After some time, a clear, brown solution which has a pH of 0.5 is obtained.

B2) Preparation of a 50% strength composition comprising the components a), b), c2) 500 ml of water are initially introduced into a sulphonation flask at room temperature, and initially 250 g of component a), 200 g of component b) and 50 g of component c2) are added with vigorous stirring. After some time, a clear, brown solution which has a pH of 0.7 is obtained.

C) Use example

Stated percentages are based on the salted weight of the leather hides or skins. A piece of wetblue or wetwhite 0.9 - 1.6 mm thick shaved cattle leather is introduced into a drum containing 150% of water. After an operating time of 10 minutes, the water has a pH of 3 to 3.5, depending on the type of pretanning. 7% of the 50% strength composition of example B1) are added, the pH decreasing to a value between 2.5 and 3.0 (depending on the initial value), and treatment is effected for 40 minutes (at 30°C). Thereafter, conventional retanning agents and dyes are added and treatment is effected for a further 2 hours, whereby the pH may increase slightly by 0.5 to 1. 100% of water heated to 60°C are now added and the liquor temperature is increased to 50 ⁰ C with addition of conventional fatliquoring agents and treatment is effected for 1 hour. 1-2% of formic acid are now added and treatment is effected for a further 40 min. After an end value of pH 3.5 - 3.8 has been reached, the liquor is discharged, washing is effected for about 10 min with 200% of cold water altogether and the leather is finished in a conventional manner.

The leather obtained is substantially fuller and stronger than leather produced in a conventional manner, with prior neutralization.