PROCESS AND COMPOSITIONS FOR PIGMENT-DYEING OF LEATHER In the production of dyed leather by exhaust dyeing from aqueous dyebath with water soluble dyes the dyes may distribute in various regularity and depth in and/or on the substrate depending on the kind and quality of the substrate, especially where the substrate may be of irregular structure or show some defects, and on the kind of dyeing method and dyestuff employed, so that there may result dyeings of correspondingly irregular aspect and/or unsatisfactory levelness. As a consequence, any defects or structure variations of the substrate may be insufficiently hidden or even become more visible by the dyeing. A possible way for improving the aspect of the dyeing is the application of pigments, which may be applied on the previous dyeing by exhaust dyeing or in a finish. If the pigments are applied in the finishing stage by employing a pigmented finish composition, the resulting dyed and pigment-finished leather will have a less natural aspect and the own characteristic aspect of the leather will at least in part be hidden by the pigmented finish. If the pigment is applied on the previous dyeing by an exhaust pigment-dyeing procedure by bath pigmentation from an aqueous medium there occurs the further problem that, depending on the substrate and pigment, the pigment-dyeing may again be of unsatisfactory regularity, especially where there are employed pigment mixtures of different colours, in particular if there are employed combinations of organic pigments with inorganic pigments; in this case it may also become more difficult or even impossible to achieve a good reproducibility of a certain desired shade, or more particularly to match the shade of the previous dyeing.

In US patent 4914764 there is described a pigment-dyeing of leather with extremely fine particle size pigment compositions containing certain novolak alkoxylate derivatives or with pigments of larger particle size, followed by post-fixation. Post- fixation is carried out with a formaldehyde-derived resin or with a polyurethane. There is also described a pre-fixation before pigment-dyeing and, where the substrate has been previously dyed, the dyed substrate is subjected to a priming and/or pre-fixation before pigment-dyeing. Pre-fixation is carried out with a formaldehyde-derived resin or with a polyurethane ; for priming there are mentioned polyurethanes and certain (meth) acrylic, vinylic and maleic polymers and polydiallyldimethylammonium chloride. By this

process, in particular following pre-fixation, the pigment-dyeing may be insufficiently level so that a substantial amount of a levelling agent is necessary. This way of proceeding may imply several applications of resin layers, e. g. for any priming and/or pre-fixation and for one or more post-fixations, which may add up to any optional subsequent finishing and thus to the final weight and handle of the produced leather.

Similarly, also in EP-A-414117 there has been proposed to employ pigment dispersions of finest particle size, i. e. of average particle size < 100 nm. In the exemplified dyeing processes each dyeing stage is concluded with a fixation with a nitrogen-containing formaldehyde condensation product. Due to the very small particle size of the pigments, which is of a comparable degree of magnitude to the porosity of the substrate, a portion of the employed pigment may penetrate the leather substrate or"drown"in the substrate, at least on the flesh side or split side of grain or split grain leather, which results in a loss of yield of the pigment-dyeing.

In DE-A-19709181 there is described a pigment-dyeing of dyed leather, in which, before pigmenting, the leather is pre-treated with colloidal silica. The employed colloidal silica particles are of a very small particle size between 5 and 135 nm, in particular between 5 and 90 nm, and also in this case a portion of the very small particles, being of a comparable degree of magnitude to the pores of the substrate, may "drown"in the substrate, at least on the flesh side or split side of a grain or split grain leather. In the exemplified dyeings the pigment-dyeing is then subjected to fixation with a melamine resin. Due to the mentioned difference of dyeing behaviour on the two sides of grain or split grain leather, these methods may leed to pigment-dyeings in which on a grain or split grain leather flesh side or split side and grain side are pigment-dyed in a different depth, which if the substrate has been previously dyed with anionic dyes, may even result in a different shade of the two sides of the dyed and pigment-dyed leather.

In a single example (example 4) of DE-A-19709181 there is also described a process in which silica-treatment is carried out in combination with the fixation with melamine, after pigment-dyeing, while before pigment-dyeing the leather is first pre-treated with a chrome-syntan and then with an acrylamide-based polymer ; in this example there is no silica pre-treatment and the pigment-dyeing is carried out subsequently to the treatment

with the acrylamide based polymer. Also in this method the dyeing behaviour on the two sides of grain or split grain leather would be different, resulting in a corresponding difference of the two sides of the pigment-dyed or dyed and pigment-dyed leather.

According to another variant, leather is dyed with a mixture of black pigment and anionic dye, as described in US patents 5007941 and 5152801. This variant does not contemplate the above problem of improving the quality of a previous dyeing with water soluble dyes and in particular of colour matching of a previous dyeing with soluble dyes, and is limited to black pigments and corresponding mixtures.

In EP 0344555 A2 there is described a pigment-dyeing of tanned leather in the presence of alkoxylated amines. This document is not concerned with any particular pre- treatment of the pigment-dyeing, and illustrates the process in two generic recipes A and B. In recipe A the leather is first retanned and washed, then it is treated in a bath consisting of 200 % of water and 1 % of ammonia (this is a solution of 5 g/l ammonia <BR> <BR> with a pH of about 11) -by this treatment the pH of the leather may reach nearly neutral pH values-and the pigments for pigment-dyeing and the dyeing assistants (oleylamine + 10 mols of ethylene oxide, and tallow fat alcohol + 80 mols of ethylene oxide) are given into this bath. In recipe B the leather is first subjected to a multiple retanning first with a polymer tanning agent based on acrylic acid/acrylonitrile, then with an amphoteric tanning agent based on a condensation product of phenolsulphonic acid and formaldehyde and then with a resin tanning agent based on a condensation product of melamine and formaldehyde, and then washed; dyeing is carried out with a bath containing pigments, acid dyes and the same dyeing assistants as in recipe A. Also these methods may leed to pigment-dyeings in which on a grain leather or split grain leather the flesh side or split side and the grain side are dyed in a different depth, which with a mixture of acid dyes with the pigments, may even result in a different shade of the two sides of the dyed leather. This document also does not contemplate the above problem of improving the quality of a previous dyeing with water soluble dyes and in particular of colour matching of a previous dyeing with soluble dyes.

GB-A-380351 describes alkoxylated amines as surfactants with several uses, one use being as dispersing agents for most various substances, inorganic pigments being also

generically mentioned among many other substances. This document mentions also the possibility of using the alkoxylated amines as dyeing assistant with water soluble dyes (vat dyes, azo dyes) on textiles. Pigmentation or bath-pigmentation of leather are neither mentioned nor suggested and there is also no mention or suggestion of any composition that would be suitable for bath-pigmentation of leather or, more particularly, of leather that would have been pre-treated in any particular way.

It has now been found that by the below defined process there may be obtained pigment-dyeings of outstanding colour yield, levelness and reproducibility of the pigment-dyeing, with satisfactory surface penetration, and also of satisfactory hiding properties with respect of any irregular previous dyeings of the substrate, while priming or pre-fixation with resins may be avoided and any post-fixation with a resin may also be avoided or reduced to a minimum, and there may be produced dyed leather of very regular colour in which grain side and flesh side or split side are dyed in very similar or even practically the same tone, while the typical leather structure is substantially maintained and visible, to provide a coloured leather with a high colour yield and pleasant aspect and handle.

The invention relates to the defined pigment-dyeing (bath pigmentation) process on leather, suitable compositions therefor, and the pigment-dyed substrates.

The invention thus firstly provides a process for the production of pigment-dyed leather (Lp) wherein a tanned leather (L) is retanned at a pH < 4.5 with (SM) a combined retanning agent, which is a combination of (S) a syntan or syntan precursor with (M) a basic metal tanning agent, and is pigment-dyed in an aqueous dyebath with at least one pigment (P) in the form of (A) and aqueous dispersion of (P) a colour pigment, in which the average particle size of the dispersed particles is < 5 urn, in the presence of

(B) a surface active aliphatic mono-, di-or triamine containing a Cl2-3o-hydrocarbon radical and at least one polyethyleneglycolether chain, or an amphoteric derivative thereof, atapH<4. 5.

As (L) are suitable any kinds of leather as are conventionally dyed from aqueous medium, particularly grain leather (e. g. nappa from sheep, goat or cow, leather from pig, horse or colt and box-leather from calf or cow), suede leather (e. g. velours from sheep, goat or calf and hunting leather), split velours (e. g. from cow, horse, colt or calf skin), buckskin and nubuk leather. The leather may have been tanned by any conventional tanning method, in particular vegetable, mineral, synthetic or combined tanned (e. g. chrome tanned, zirconium tanned, aluminium tanned, semi-chrome tanned, glutaraldehyde tanned or phosphonium tanned). If desired, the leather may also be re- tanned; for re-tanning there may be used any tanning agent conventionally employed for re-tanning, e. g. mineral, vegetable or synthetic tanning agents [e. g. chromium, zirconyl or aluminium derivatives, quebracho, chestnut or mimosa extracts, aromatic syntans, polyurethanes, (co) polymers of (meth) acrylic acid compounds or melamine/, dicyanodiamide/and/or urea/formaldehyde resins]. Preferably (L) is a chrome tanned leather. According to a preferred feature (L) is a tanned grain leather or nubuk leather.

The leathers may be of various thicknesses, thus, there may be used very thin leathers, such as book-binder's leather or glove-leather (nappa), leather of medium thickness, such as upholstery leather, shoe upper leather, apparel (clothing) leather and leather for handbags, or also thick leathers, such as bottom leather, furniture leather, leather for suitcases, for belts and for sport articles. Before treatment with (SM), in particular after tanning (and optionally retanning) and before any intermediate dyeing, the pH of the leather is advantageously set to values in the range of 4 to 6.5 (the leather is "neutralized"). Depending on the kind of the leather, there may be chosen an optimum pH range, e. g. for grain leather and nubuk pH values in the range of 4 to 6, for suede leather and split velours and for very thin leathers pH-values in the range of 4.5 to 6.5, for intermediately dried suede leathers and intermediately dried split velours the pH

may range in the scope of 5 to 6.5. For the adjustment of the pH-value of the leather there may be employed conventional assistants; for tanned leather of acidic character the pH may be adjusted by addition of suitable bases, e. g. ammonia, ammonium bicarbonate or alkali metal salts of weak acids, e. g. sodium formate, sodium acetate, sodium bicarbonate, sodium carbonate or sodium sulphite, of which sodium formate and sodium bicarbonate are preferred. Sodium carbonate and sodium bicarbonate are usable in particular as second bases for the exact adjustment of the superficial pH-value of the leather. Mineral tanned leather may, if desired, also be masked, e. g. with alkali metal formate, oxalate or polyphosphate or e. g. with titanium/potassium oxalate.

According to a particular feature of the invention (L) is a tanned leather that-optionally after an intermediate retannage-has also been dyed with one or more water soluble dyes (F). As a water soluble dye there is meant a dye that is dissolved in the form of a true solution under application conditions, e. g. that gives a true solution in water at a concentration of 3 g/1, at a pH of 7 and at 20°C. The dyes (F) may be any water soluble dyes as are known to be employable for dyeing tanned leather, in particular (Fl) anionic dyes (e. g. as known in the art, e. g. from the Colour Index, as acid dyes, direct dyes and/or leather dyes), (F2) cationic dyes (e. g. as known in the art, e. g. from the Colour Index, as basic dyes, where indicated for leather), and (F3) sulphur dyes in water soluble form (in particular leuco sulphur dyes, condense sulphur dyes and solubilized sulphur dyes or Bunte salt dyes, e. g. as known in the art, e. g. from the Colour Index). Preferably (F) is (Fl).

The dyeing with water soluble dyes (F) may be carried out in a manner known per se suitably in an aqueous medium and under conventional temperature and pH conditions, The dyeing with anionic dyes (FI) may be carried out in a manner known per se, suitably in an aqueous medium and under conventional temperature and pH conditions, in particular in the temperature range of 20 to 80°C, preferably 25 to 70°C, milder temperature conditions, in particular in the range of 25 to 40°C, being preferred for the achievement of deeper penetrations. The pH-values of the dye-bath may, in general, range broadly, mainly from pH 7 to pH 4; in general the dyeing may be advantageously begun at higher pH-values and concluded at lower pH-values. Preferably the dyeing is

carried out at pH-values ! 4.5, in particular in the pH-range of 6 to 4.5, and for the conclusion of the dyeing procedure the pH-value is lowered (e. g. by addition of an acid conventional in the leather dyeing technique, such as acetic acid or formic acid) preferably to values in the range between 4 and 3.

The dyeing with cationic dyes (F2) may be carried out under conventional temperature and pH conditions, advantageously in the temperature range of 10 to 70°C, preferably 25 to 70°C ; the pH-values are advantageously within the range of 2.5 to 4.5, preferably 3 to 4, and to complete the dyeing procedure, the pH of the dye bath is advantageously raised by base addition, preferably to values > 4, more preferably ! 4.5, in particular in the range of 4 to 6, more preferably 4.5 to 5.5, for fixation. Any conventional bases may be used for this purpose, e. g. those mentioned above for"neutralization"of tanned leather, or sodium carbonate, preferably sodium carbonate or ammonium hydroxide, or also amines, e. g. fatty amines or their derivatives, as conventionally employed as leather softeners or fixing agents for anionic dyeings. After the addition of the dye and optionally of any dyeing assistants and before any addition of a base, the treatment of the substrate in the dye bath is continued until the desired penetration is achieved.

The dyeing with sulphur dyes in water soluble form (F3) may be carried out analogously to the dyeing with the anionic dyes (FI).

An optimum dyeing-duration for a given combination of substrate, dye, assistant and dyeing method may be assessed by means of a few preliminary tests and is e. g. within 15 and 120 minutes, mostly within 30 and 90 minutes.

The dye (F) -concentration referred to the leather may vary broadly, depending on the substrate, the dye, the dyeing method and the desired colouristic effect, and may range, if desired, up to the saturation level of the substrates. The total amount of the dye may e. g. be in the range of 0.02 to 5 % by weight, based on the wet weight of the substrate (i. e. about 0.04 to 10 %, based on the dry weight of the substrate). The dyeing may be carried out in one or more stages, e. g. in two stages, optionally with insertion of charge reversal of the substrate by means of conventional cationic assistants for dyeings with

anionic dyes, or respectively with conventional anionic assistants for dyeings with cationic dyes.

The dyes (F) may, if desired, be employed in combination with conventional dyeing assistants, mainly non-ionic and/or, for (Fi) and/or (F3), also anionic products (in particular surfactants, preferably hydrophilic polysaccharide derivatives, polyoxyethylated alkylphenols or alcohols, lignosulphonates or sulpho group-containing aromatic compounds).

Before treatment with (SM) the dyed substrates may, if desired, be fat-liquored. More particularly a fat-liquoring may, if desired, be carried out before and/or after the dyeing with (F), in particular also in the same liquor, preferably after fixation of the (F)-dyeing, or in a fresh bath. For fat-liquoring after the dyeing process with (F) the fat-liquoring agent is advantageously added after fixation; in particular after the dyeing process with (Fi), the fat-liquoring agent is advantageously added after the pH of the liquor has been lowered, preferably to values between 3 and 4, in a fresh bath and is preferably completed by addition of an acid, e. g. as mentioned above, to set the pH in the range of 3 to 4.

For the fat-liquoring step there may be used any conventional natural animal, vegetable or mineral fat, fatty oil or wax, or chemically modified animal or vegetable fat or oil, which include in particular tallow, fish oils, neats-foot oil, olive oil, castor oil, rapeseed oil, cottonseed oil, sesame oil, corn oil and Japanese tallow, and chemically modified products thereof (e. g. hydrolysis, transesterification, oxidation, hydrogenation or sulphonation products), bees-wax, Chinese wax, carnauba wax, montan wax, wool fat, birch oil, mineral oils with boiling range within 300 and 370°C (particularly the so- called"heavy alkylates"), soft paraffin, medium paraffin, vaseline and methyl esters of C14-22-fatty acids. By the term"sulphonation"for the fat-liquoring agents, there is meant generally the introduction of the sulpho group including also the formation of a sulphato group (="sulphating") and the introduction of a sulpho group by reaction with a sulphite or S02 (="sulphiting").

Synthetic leather fat-liquoring agents, including esters, in particular partial esters of polybasic acids (e. g. phosphoric acid) with optionally oxyethylated fatty alcohols, as are known to improve hydrorepellency of the leather, may be added e. g. after pigmentation with (A).

Preferably (L) is (LF), i. e. a tanned leather that has been retanned, dyed with at least one water soluble dye (F) and fatliquored, more preferably (LF1), i. e. a tanned leather that has been retanned, dyed with at least one water soluble anionic dye (Fi) and fatliquored.

After conclusion of the dyeing procedure, and any fat-liquoring and including any base or acid addition, the substrate (LF) or (LFI) may be washed or rinsed and may be dried or preferably, without intermediate drying, directly be subjected to the treatment with (SM).

The combined retanning agents (SM) may be any conventional such products which are mixtures, salts and/or complexes of a syntan or syntan precursor (S) with a suitable basic metal tanning agent (M).

The syntans or syntan precursors (S) expediently are selected from (Si) synthetic tanning agents of aromatic character, in particular aromatic polycondensates preferably containing sulpho groups and which may comprise hydroxy groups linked to aromatic nuclei, in particular in the form of phenolic and/or naphtholic constituents, and (S2) precursors of (Sl), in particular sulpho-group-containing precondensates of the starting aromatic compounds, e. g. to an average of 1.2 to 6 aromatic rings in the precondensed precursors.

Representative polycondensates (Si) or their precondensed precursors (S2) are those deriving from the corresponding starting compounds, e. g. from phenol, cresol, sulphophenols, naphthols, sulphonaphthols, toluene and sulphonaphthalenes, which are selected so that the resulting polycondensate (S1) or precursor (S2) contains sulpho

groups and/or the polycondensate or precursor precondensate may have been further sulphonated, and preferably contains also hydroxy groups. They may be condensed or precondensed in a conventional manner, in particular directly by formation of-SO2-,- O-and/or-OSO2-bridges or alternatively by condensation over an aldehyde, typically formaldehyde, to form-CH2-bridges. Preferably (S), in particular (sol) and (S2), are sulpho-group-containing condensation products or/and products of the condensation of sulpho-group-containing, preferably phenolic, compounds with formation of an S02 bridge, and may optionally contain further aromatic components. As (S) there may in particular be mentioned sulpho-group-containing condensation products of phenols, cresols, naphthalene and/or naphthols and optionally toluene, at least a part of which contains sulpho groups, and optionally with ligninsulphonic acid and/or with dihydroxydiphenylsulphone. Preferably the precondensates or polycondensates are further sulphonated in order to be water soluble in alkali metal salt form. Among the mentioned polycondensates and precondensates those produced by direct condensation are preferred over those produced by condensation with an aldehyde. Among the mentioned condensation products, the sulpho-group-containing phenolic precondensates (S2), especially those produced by direct condensation i. e. without any aldehyde, are preferred as (S).

As complex forming, basic metal tanning agent (M) suitable for complex formation with (S) there may be employed any conventional basic metal salt tanning agents, e. g. basic chromium, aluminium, iron, molybdenum, titanium or zirconium salts, in particular chromium sulphates, aluminium sulphates, alums, iron sulphates, zirconium sulphates, titanium sulphates and/or molybdenum sulphates of basic character, with a basicity as efficient per se for tannage. Basic metal sulphates suitable as (M) mostly have a basicity corresponding to a metal oxide content in the range of 15 to 40 %, preferably 20 to 36 %. Among these are preferred aluminium-based tanning agents and chromium-based tanning agents, particularly basic aluminium sulphates, basic alums and especially basic chrome sulphates. Basic metal tanning agents, in particular the mentioned basic sulphates, are known in the art and described in detail in the specialised literature. According to an alternative feature the basic metal salts may also be employed in conventional masked form, where they are masked with organic carboxylic

acids, preferably with 1 to 12 carbon atoms, typically with formic, acetic, oxalic or phthalic acid.

The combined retanning agents (SM) are known or may be produced in a manner known per se, by combining (S) with (M) in aqueous solution, e. g. by mixing (S) with (M) in dissolved salt form, optionally with heating (e. g. to > 70°C up to the boil), by which the basic metal salt (M) forms a complex with (S), which, depending on the kind of involved compounds (S) and (M), may be more or less labile. The combination of (M) with sulpho-group-containing (S) may also involve salt formation of (M) with sulphonic acid groups present in (S). The produced (SM) may be isolated and/or dried in a manner known per se, e. g. by salting out and filtration, and the filter cake may if desired or required be dried, e. g. by evaporation of the excess water, or the liquid solution may be directly dried e. g. by spray-drying.

The components (S) and (M) are combined with each other preferably in such a ratio as to result in a combined product (SM) with a basicity, expressed in metal oxide content derived from (M), corresponding to a metal oxide content in the range of 8 to 20 % by weight, more preferably 10 to 15 % by weight of (SM). When (M) is a basic aluminium sulphate or a basic alum, the basicity of the corresponding (SM) preferably corresponds to an Al203-content in the range of 10-13 %. When (M) is a basic chrome sulphate, the basicity of the corresponding (SM) preferably corresponds to a Cr203-content in the range of 11-14 %.

The treatment of (L), preferably of (LF) or (LFI), with (SM) may be carried out in one ore more stages, at least one of which is immediately preceding the pigment-dyeing stage, and may be carried out under conditions analogous to conventional retanning conditions, in an aqueous bath, e. g. at temperatures in the range of 30 to 60°C, preferably 35 to 45°C, and under acidic conditions at pH < 4.5, preferably at a pH in the range of 3.5 to 4.5, more preferably 3.8 to 4.2. The concentration of (SM) is expediently chosen in such a range as to provide a satisfactory influence on the subsequent treatment with (A) and (B), especially with a view to the resulting (SM)-and (M) -content of the treated substrate. The concentration of (SM) referred to the wet substrate is e. g. in the range of 0.5 to 6 %, preferably 1 to 4 % by weight, more preferably in the range of 2 to

3 % by weight in each treatment stage. With a view to the (M) -content of (SM) and of the treated leather, the concentration of (SM) referred to the substrate is suitably chosen accordingly, e. g. so that the concentration of metal oxide of (M) referred to the wet weight of the substrate is e. g. in the range of 0.06 to 0.7 %, preferably 0.12 to 0.5 % by weight, more preferably in the range of 0.24 to 0.36 % by weight in each corresponding treatment stage. The more suitable range may vary with various factors, such as kind of substrate, kind of (M) and of (S), kind and concentration of (A) and of (B) and selected process conditions. Where (M) is an aluminium-based mineral tanning agent, in particular a basic aluminium sulphate or alum, the A1203-concentration referred to the wet leather substrate preferably is in the range of 0.2 to 0.7 % per (SM)-treatment stage.

Where (M) is a chrome-based mineral tanning agent, in particular a basic chromium sulphate, the Cr203-concentration referred to the wet leather substrate preferably is in the range of 0.2-0. 6 % per (SM)-treatment stage. The treatment with (SM) may be carried out for a time similar to the duration of a retanning treatment or even shorter, e. g. in the range of 15 to 45 minutes, preferably 20 to 35 minutes.

According to a particular feature of the process of the invention, before dyeing with (F), a retanning may also be carried out with (SM). This previous treatment is suitably followed by neutralisation preferably to a pH as described above. Dyeing with (F) may then be carried out as described above.

As pigments (P) there may be employed any colour pigments (including also black pigments and white pigments), in particular as conventionally employed in the art of leather pigmenting, e. g. as defined and listed in the Colour Index, or as mentioned (independently from their particle size) in the above cited documents US 4914764 and EP-A-414117. More particularly, there may be employed inorganic pigments, mainly metal oxides and/or salts, for example chrome pigments (e. g. chromium oxide green), nickel-chromium compounds, spinels (e. g. cobalt blue), iron oxides and iron oxide- based pigments (e. g. ochre, umber and sienna browns), ultramarines, titanium dioxide, zinc oxide, barium sulphate and carbon black, organic pigments, for example azo pigments, phthalocyanine pigments, dioxazine pigments, perylene tetracarboxylic acid pigments, quinacridone pigments, triphenylmethane pigments, indigo and thioindigo pigments, polymethine pigments, diketopyrrolopyrrol pigments and anthraquinone

pigments, laked pigments and metal complex pigments (e. g. cobalt, nickel or copper phthalocyanine).

The pigments (P) are expediently of a particle size as suitable for the production of aqueous dispersions, mostly as corresponds to primary particles e. g. of an average particle size < 2, um, preferably zu 1 um, e. g. in the range of 0.01 to 1, um, mostly in the range of 0.01 to 0.8 um. Where the average particle size of the primary particles is very small, e. g. below 50 nm, it is also possible to employ secondary particles or agglomerates, so long as the particle size of the agglomerates is within the above range, preferably < 1, um. Preferably the particles (P) are substantially not agglomerated, even if some pigments in primary particle size form may have a more or less pronounced tendency to spontaneous agglomeration. Preferably the particles of (P) are on average 10nm As primary particles (P) there may be employed known pigment particles of the defined particle size, or particles that may be produced in the defined particle size according to known methods or analogously to methods known per se, e. g. by desolubilisation (precipitation, crystallisation) from aqueous true or colloidal solutions, preferably sols, or by disaggregation of corresponding larger particles (in particular of aggregates of colloidal particles) e. g. by grinding, milling, or subjecting to vibration, ultrasonic treatment or shearing (e. g. in a homogeniser) and, if required or desired, selecting a defined particle size range e. g. by sieving and screening.

Optionally the pigments (P) may be extended with extenders (E) in particular as conventionally employed for the production of extended pigments and as mentioned e. g. in the Colour Index (4th ed. ) or in Kirk-Othmer Encyclopaedia of Chemical Technology, or may be compounded with conventional agents such as casein or hydrophilic cellulose derivatives, e. g. hydroxyethylcellulose.

Extender (E) comprise in general known non-coloured inorganic substances as conventionally employed as extender pigments in pigment compositions or as opacifying agents for plastic material or lacquers, and may also comprise colourless inorganic substances or white pigments.

The inorganic extender (E) may be any such substance, naturally occurring and optionally physically modified, or synthetically produced, and preferably as employed in particular in compounded pigments or extended pigments. (E) may include mineral substances and synthetically produced inorganic substances, in particular oxides such as silica and alumina, and inorganic salts, e. g. silicates, aluminates, sulphates and carbonates, of low valence metal ions, mainly of alkali metal ions, alkaline earth metal ions or earth metal ions, especially of sodium, potassium, magnesium, calcium, barium and/or aluminium. The following may be mentioned as examples: calcium carbonate in various forms (mineral natural form or synthetic precipitated and/or crystallised forms, e. g. rhombohedral, scalenohedral, prismatic or spherical calcite, clustered or discrete acicular aragonite), various sulphates (calcium sulphates such as gypsum or anhydrite, barium sulphates, calcium sulphoaluminate), various forms of silica (e. g. amorphous silica such as diatomite, precipitated or fumed silica, or silica xerogel), sodium silico- aluminate, various silicates (e. g. clays, e. g. china clay, attapulgite, bentonite or montmorillonite), and various alumina hydrates (such as boehmite and pseudo boehmite). Their particle size may range in conventional scopes, in particular of primary particles as described above for (P).

If (P) is extended with (E), the weight ratio of (E) to (P) may range in conventional scopes as may be desired for a defined pigment, depending on its particular properties, such as e. g. colour intensity of the pigment (P) and particle size and chemical constitution of the pigment (P) and of the extender (E), e. g. in the scope of 20 to 400 parts by weight, mostly 40 to 250 parts by weight of (E) for every 100 parts by weight of (P).

The aqueous pigment dispersion (A) may comprise a conventional dispersant or wetting agent as commercially available, e. g. polyphosphates, polyacrylic acid salts, anionic casein, sulphosuccinate derivatives, lignosulphonates, fatty acid salts (soaps) or ethyleneoxide adducts to fatty alcohols, in a suitable low concentration as usual e. g. < 10 % by weight, preferably < 5 % by weight, for the process of the invention lower dispersant concentrations being preferred e. g. zu 2 % by weight. The pigments (P) and also the further additives-each separately, or together in the form of a compounded,

extended and/or dispersed pigment-may be employed in the forms as commercially available, in particular (P) may be employed e. g. in the form of a concentrated aqueous slurry or dispersion, e. g. with a pigment content in the range of 5 to 70 % by weight, preferably 10 to 50 % by weight, or even in dry form. Extended pigments also may be employed e. g. in the form of a concentrated aqueous slurry or dispersion as commercially available, e. g. with a solids content in the range of 10 to 70 % by weight, preferably 12 to 50 % by weight, or for the production of (A) even in dry form. The concentration of (P) may be chosen as desired, expediently according to the characteristic properties of the pigment, e. g. as may suit a gamut of a defined standard colour depth.

If desired, a solubiliser (G), in particular a hydrotrope, may also be present, e. g. urea or a low molecular, preferably C2-6, aliphatic polyol (e. g. a diol or triol) or ether thereof, such as glycerol, mono-or di-C2-3-alkylene glycol or a mono-or di-C2-3-alkylene glycol mono-(Cl-alkyl)-ether. The solubiliser (G) may be present in a low proportion, as sufficient for improving the rheological behaviour of the pigment, e. g. in a proportion in the range of 1 to 25 parts by weight of (G) for every 100 parts by weight of (P).

Preferably, however, no solubiliser (G) is employed.

If desired or required, a preservative (H) in particular an agent for improving the stability against micro-organisms, mainly an additive for combating the harmful activity of micro-organisms, may also be present in (A). For combating the harmful activity of microorganirms there may be used conventional agents (H), especially bacterial growth inhibiting agents or/and biocides, mainly fungicides. There may be used commercially available products which may be used in the recommended concentrations, e. g. in a concentration of 0. 001 to 0.1 % by weight of active substance referred to the aqueous composition (A).

For the dyeing process of the invention the pigment compositions (A) may be used in concentrated form (Ac), e. g. with a solids content in the range of 10 to 70 % by weight, preferably 20 to 60 % by weight, and be directly stirred into the dyeing liquor, or the concentrated aqueous dispersions (Ac) may be pre-diluted with water e. g. to 5 to 10 times their volume, to stock dispersions (As), e. g. with a solids concentration in the

range of from 1 to 14 %, preferably 2 to 7 % by weight, which may then be metered into the dyeing vessel for dyeing.

The surface active product (B) is an aliphatic mono-, di-or triamine that contains a lipophilic, preferably aliphatic hydrocarbon radical with 12 to 30 carbon atoms, preferably directly linked to a nitrogen, and at least one polyethyleneglycolether chain, or is an amphoteric derivative thereof. The lipophilic radical may be any such aliphatic radical as conventionally occurring in surface active amines, and may be saturated or ethylenically unsaturated; it may be derived from natural fats or oils or even from synthetic alcohols. It may be linear or branched. Preferably the lipophilic radicals are linear derivatives from natural fats or oils, representative such radicals being e. g. lauryl, cetyl, myristyl, oleyl, palmitoleyl, linoleyl, stearyl, arachidyl, behenyl, tetracosyl and triacontyl and technical mixtures such as coconut fatty radicals and tallow fatty radicals and their hydrogenated derivatives. The fatty radicals with 16 to 24 carbon atoms are preferred, especially the saturated ones. Preferably the amines (B) contain only one such lipophilic hydrocarbon radical per molecule.

In the di-or triamines, the amine nitrogens are preferably linked to a saturated aliphatic bridge and are preferably at a distance of two or three carbon atoms from each other.

The bridging groups are preferably ethylene or propylene.

The polyethyleneglycolether chains may be linked to the amino nitrogens directly or over a preferably aliphatic bridge, e. g. over oxypropylene or oxybutylene or over 2- hydroxy-oxypropylene. Preferably the polyethyleneglycolether chains are directly linked to the amino nitrogens. They may be further unsubstituted or terminated with an anionic group e. g. a carboxymethyl group, a phosphato group or preferably a sulphato group.

Preferred optionally amphoteric aminocompounds (B) are of the following average formula

wherein R signifies an aliphatic C12-3o-hydrocarbon radical, X signifies hydrogen,-CH2-COOM',-P03M'2 or-S03M', M'signifies a cation, m signifies 2 or 3, r signifies 0,1 or 2, each of n, p and q is at least 1, and p+q+nr=20to 100.

R preferably signifies a lipophilic radical as set out above. r preferably signifies 0 or 1. m preferably signifies 3 or, if r = 2, also 2 and 3.

X preferably signifies hydrogen or-SO3M', more preferably hydrogen.

The total number of oxyethylene groups present on average in the molecule, i. e. p + q + n-r, is preferably in the range of 25 to 80, more preferably 30 to 70.

The above formula (1) shows the carboxy, phosphonate or sulpho group in salt form.

Under alkaline to weakly acidic conditions M'preferably is an alkali metal or ammonium cation as may derive from the addition of a water soluble base for pH adjustment and salt formation or directly from the synthesis of the phosphate, carboxymethylate or sulphate, e. g. sodium, potassium or ammonium. Under strongly acidic conditions, e. g. at pH < 4, compounds of formula (1) in which at least one X is a phosphonate, carboxymethylate or sulpho group may at least in part also be in the form of the corresponding inner salt.

The compounds (B) are known or may be produced analogously to known methods.

Some representative compounds of formula (I) and their production are described e. g. in DE-A-3837199.

Pigment-dyeing according to the invention with (A) in the presence of (B) is carried out immediately after a treatment with (SM) more particularly, if the treatment with (SM) is carried out in more than one stage, immediately after the last stage of the treatment with (SM). Treatment with (SM) involves at least in part also a retannage taking place at an acidic pH zu 4.5, but after the last treatment with (SM) before bath-pigmentation with (A) in the presence of (B), no raising of the pH above 4.5 is inserted for any retannage fixation. That at least one treatment with (SM) is"immediately"preceding pigment- dyeing with (A) in the presence of (B), or that pigment-dyeing according to the invention with (A) in the presence of (B) is carried out"immediately"after a treatment with (SM) or"immediately"after the last treatment stage with (SM) means that no other treatment agent is inserted between this treatment with (SM) and the following pigment-dyeing with (A) in the presence of (B). This means in particular that (A) and (B) may be directly added into the used or exhausted treatment bath of the (last) pre- treatment with (SM), or after the (last) pre-treatment with (SM) the exhausted pre- treatment bath may be drained and (A) and (B) may be added in a fresh bath. If desired, the substrate pre-treated with (SM) may even be rinsed with water, but preferably no such rinsing is carried out and (A) and (B) are added directly into the used (exhausted) pre-treatment bath or the exhausted bath is drained without rinsing and (A) and (B) are added in a fresh bath.

The pigment-dyeing with (A) in the presence of the pigment-dyeing assistant (B) is carried in an aqueous medium. In particular no other dyes are present together with pigments (P) in (A) and this dye bath, especially no water soluble dyes, no disperse dyes and no vat dyes. The liquor-to-goods ratio referred to the wet substrate may be in a range as suitable per se for drumming, e. g. in the range of 100 to 500 %, preferably 120 to 300 %. The pH is preferably in the range of 3.5 to 4.5, more preferably 3.8 to 4.2.

The temperature is e. g. in the range of 30 to 60°C, preferably 35 to 45°C, milder temperature conditions, in particular in the range of 38 to 40°C, being preferred. The treatment may be carried out for a time as suitable or/and desired for the particular

substrate, the employed pigment (P) and amine (B), the dyeing conditions and the desired colour result. The pigment-dyeing time may e. g. be within 10'and 60', preferably within 20'and 40'. For the conclusion of the pigment-dyeing procedure an acid, suitably as conventional per se in the leather dyeing technique, such as acetic acid or formic acid, is added preferably to lower slightly the pH to values zu 4, e. g. in the range of 3 to 4, preferably between 3.2 and 3.8. The treatment with the acid may be carried out e. g. for 10'to 90', preferably 20'to 60'. Then the treated leather may be rinsed with water.

The ratio of (A) and (B) may be chosen in a broad range, as may be required or preferred for a defined pigment-dyeing process and may be optimized by means of a few preliminary tests. Preferably the weight ratio of (P) to (B) is in the range of 50/100 to 1000/100, more preferably 200/100 to 800/100. (A) and (B) may be added separately into the drum or also together. According to a particular feature of the invention they may be added in the form of a pigment-dyeing composition (C), which is an aqueous dispersion comprising (A) and (B) preferably in a weight ratio of (P) to (B) in the range of 50/100 to 1000/100, more preferably 200/100 to 800/100, and which may be concentrated or pre-diluted analogously as mentioned above for (A). The invention thus further provides a concentrated pigment-dyeing composition (Cc) and a pre-diluted pigment-dyeing composition (Cs), which are aqueous dispersions consisting essentially of (Ac) and (B) or (As) and (B) and any added water, in the stated weight ratio of (P) to (B) and in the above stated concentration, particular features of this aspect of the invention being represented by concentrated aqueous compositions (Cc) with a dry substance content in the range of 10 to 70 % by weight, and by pre-diluted aqueous compositions (Cs) which correspond to compositions (Cc) pre-diluted with water to 5 to 10 times their volume, to stock dispersions (Cs). The process for the production of the concentrated or pre-diluted compositions (Cc) or (Cs) is characterised in that an aqueous dispersion (Ac) or (As) or a mixture of aqueous dispersions (Ac) or (As) is mixed with the surface active pigment-dyeing assistant (B) and-if required-with water. More particularly, the process for the production of the concentrated compositions (Cc) is characterised in that an aqueous dispersion (Ac) or a mixture of aqueous dispersions (Ac) is mixed with the surface active pigment-dyeing assistant (B) and-if required- with water, and the process for the production of the pre-diluted compositions (Cs) is

characterised in that an aqueous dispersion (As) or a mixture of aqueous dispersions (As) is mixed with the surface active pigment-dyeing assistant (B) and-if required- with water, or concentrated compositions (Cc) are diluted with water, to 5 to 10 times the volume of (Cc).

The topping with (T) may be carried out under bath lengths, temperature conditions and treatment times in the same ranges as described above for the pigment-dyeing, preferably after having lowered the pH by acid addition, e. g. bath lengths in the range of 100 to 500 %, preferably 120 to 300 %, pH preferably in the range of 3.2 to 4.2, more preferably 3.5 to 3.9, temperature e. g. in the range of 20 to 60°C, preferably 25 to 50°C, more preferably 30 to 40°C, and in a treatment time as suitable or/and desired for the particular substrate, employed substances and conditions and desired result, e. g. within 10'and 60', preferably within 20'and 40'.

After the pigment-dyeing with (A) and (B) the dyeing may if desired be topped with a non-ionic or weakly anionic polymer (T) of retanning properties. (T) is preferably mainly or only aliphatic and any anionic groups present in (T) are preferably carboxylic groups. Suitable polymers (T) are in particular acrylic or maleic (co) polymers (e. g. polyacrylates and copolymers of acrylic or maleic acid with C2-4-alkylene and/or styrene) and optionally at least in part hydrolysed vinylacetate (co) polymers (e. g. partially hydrolysed copolymers of vinyl acetate with C2-4-alkylene and/or styrene).

Retanning agents of this kind are known in the art and described in the specialised literature and also available in various commercial forms on the market, e. g. the carboxylic (co) polymers in the form of aqueous solutions of their alkali metal salts, mostly sodium salts, and the non-ionic ones e. g. in the form of aqueous dispersions.

Alternatively to the topping or in addition thereto a conventional leather softener, in particular a cationic leather softener may, if desired, be applied in a final step, particularly if a fat-liquoring has been carried out with a sulphonated fat-liquoring agent. Preferably however no such softener aftertreatment is carried out.

The treated substrate may then be further treated in conventional manner, e. g. rinsed or washed, drained and dried and, after drying, mechanically finished as usual.

The pigment-dyeing process of the invention is suitably carried out in the drum, as a drum-dyeing, in particular as a part of a sequence of leather treatments in the drum in the dyehouse.

By the process of the invention there may be obtained pigment-dyeings of outstanding colour yield, levelness and reproducibility of the pigment-dyeing, even with mixtures of the above mentioned pigments (P), in particular even with mixtures of inorganic and organic pigments (P), with satisfactory surface penetration, and also satisfactory hiding properties with respect of any eventually irregular previous dyeings, e. g. with (Fi), of the substrate. The dyes (F) and their application parameters may in particular be chosen in such a way that a good dye- (F)-penetration into the leather is achieved and the pigments (P) and respectively (P) are chosen so as to give a pigment-dyeing of the same shade as the (F) -dyeing. According to the invention there may in particular be produced dyed leather of very regular colour in which grain side and flesh side or split side are dyed in very similar or even practically the same tone, even with mixtures of the above mentioned pigments (P), while the typical leather structure is substantially maintained and visible. Thus according to a particular, advantageous feature of the invention the above pigment-dyeing process is also suitable for colour matching, i. e. leather (LF) that has been dyed with one or more water soluble dyes (F) may be pigment-dyed according to the invention with a mixture of two or more pigments (P), each in the form of (A), to give a pigment-dyed leather (Lp) in which the shade of the pigment-dyeing matches the shade of the previous dyeing with the water soluble dyes. The process of the invention is particularly suitable for the pigment-dyeing of leather in deep shades-especially deeper than a dyeing corresponding to 1/1 standard depth on wool-, on which the above mentioned properties are particularly pronounced.

By the process of the invention the characteristic properties of the dyes are substantially not impaired, but in particular as for fastnesses, colour yield and brilliancy of shade, provide optimum dyeings, and also the characteristic properties of the leather such as handle, fastnesses, tear resistance and bending resistance can be maintained to a high degree or even be improved. Particularly worth mention are light fastness, fastness to perspiration and fastness to dry or wet rubbing of the pigment-dyeings of the invention.

If desired, the leather pigment-dyed according to the invention may be subjected to subsequent treatments, e. g. it may be hydrophobized or finished with a resilient polymer-coating or gloss-topping (e. g. for improving other properties such as water repellency or oil repellency).

In order not to cover or hide the valuable leather dyeing structure as may be obtained according to the invention, it is preferred not to apply any softener to the dyeing, and as for any finish (polymer-coating or gloss topping) it is preferred either not to apply any finish at all or to apply only a thin and transparent finish (e. g. such as a non-pigmented polyurethane or alkyd resin finish, as known per se in the art). If such a finish is applied, it is preferred not to hide or impair by any ironing or embossing of the finished leather the typical leather structure, which is substantially maintained and visible upon the pigment-dyeing process of the invention.

In the following Examples parts and percentages are by weight. The temperatures are indicated in degrees Celsius."C. I." stands for"Colour Index". The employed products are commercially available products. The water soluble dyes are used in blended form containing about 30 % of the respective dye and the blending agent being Glauber's salt (sodium sulphate). The pigments are used in the form of aqueous dispersions in an anionic casein solution with a pigment content in the range of 10-50 % and a viscosity in the range of 400 to 2000 mPa s, and are (Pi) C. I. Pigment Black 7, (P2), C. I. Pigment Red 120, (P3) C. I. Pigment Brown 43, (P4) C. I. Pigment Blue 15: 3, (P5) C. I. Pigment Green 7, (P6) C. I. Pigment Orange 72, (P7) C. I. Pigment Red 101, (Pg) C. I. Pigment Red 170, (Pg) C. I. Pigment White 6, (Plo) C. I. Pigment Yellow 42, (Pll) C. I. Pigment Yellow 81, (P12) C. I. Pigment Yellow 83, (Pi3) C. I. Pigment Yellow 155. The employed syntan (SM1) is a phenolic syntan precondensate, which is a condensation product of sulphophenol, that has been combined with basic chrome sulphate (of 33.4 % basicity) by heating to the boil, to form a complex with a Cr203 content of 12.5 %. The employed compounds of formula (B) are of the average formulae: <BR> <BR> /(CH2-CH2-O) pl SO3NH4<BR> Ri N\ (By<BR> (CH2-CH2-O) ql S03NH4

in which Ri is tallow fatty alkyl and pl + ql = 55, in which R2 is behenyl and n2 + p2 + q2 = 35 EXAMPLE 1 a) 100 parts of chrome-tanned calf leather of 1.4-1. 6 mm thickness (grain leather) for shoe uppers are wetted back with 300 parts of water, 0.3 parts of a 85 % formic acid solution and 0.2 parts of the adduct of 10 moles of ethylene oxide to 1 mol of nonylphenol at 40°C during 30 minutes. The bath is then drained off and the leather is treated for 45 minutes with 100 parts of water at 40°C, 4 parts of Syntan (SM1) and 0.5 parts of a cationic fat-liquoring agent (an emulsion of fatty acid aminoamides) then 1 part of sodium phthalate are added and treatment is continued for further 45 minutes. The pH is 3.9 and the bath is allowed to dwell overnight. Then the bath is drained off and 150 parts of water at 30°C, 3 parts of potassium acetate solution (30 %) and 1 part of sodium formate are added and drumming is carried on for 45 minutes. 4 parts of protein emulsion (20 %) and 0.5 parts of fatliquoring agent (sulphited fish oil) are added and drumming is continued at 30°C for 30 minutes, then 6 parts of pyrogallol-based retanning agent, 4 parts of phenolic syntan, 2 parts of C. I. Acid Brown 425 and 1 part of C. I.

Acid Brown 432 are added and drumming is continued for 60 minutes. 100 parts of water at 60°C are then added and after 60 minutes formic acid is added in two subsequent additions of 0.7 parts of an 85 % formic acid solution, at an interval of 20 minutes. After 20 minutes the pH is 3.7. The bath is drained off and the leather is washed with 300 parts of water at 60°C. For fatliquoring 150 parts of water at 60°C, 3 parts of sodium polyacrylate, 4 parts of heavy alkylate, 2.5 parts of sulphated vegetable and mineral oil and 0.5 parts of sulphited fish oil are added

and drumming is carried on for 60 minutes. 0.8 parts of 85 % formic acid are added and after 30 minutes the bath is drained off. b) 200 parts of water at 40°C and 3 parts of syntan (SMl) are added and drumming is continued. After 30 minutes the pH is 3.9, and the bath is drained off. c) For pigment-dyeing 200 parts of water at 40°C, 0.5 parts of (Bl), 2.5 parts of (P3), 0.5 parts of (P2) and 0.5 parts (Pi) are added and drumming is continued for 30 minutes. Then 0.5 parts of 85 % formic acid solution are added and treatment is continued for 30 minutes, by which the pH is lowered from 3.9 to 3.7. 0.7 parts of a 50 % solution of partially hydrolysed vinyl acetate/ethylene copolymer solution (retanning agent) are added and drumming is continued for 30 minutes, then the bath is drained off and the leather is washed with 300 parts of water for 20 minutes then the bath is drained and the leather is dried and cured as conventional.

There is obtained a leather very evenly dyed in a brown shade, practically of the same tone on both sides and also in the cut edge.

EXAMPLE 2 To 100 parts of chrome-tanned bovine leather of 1.8-2. 0 mm thickness (grain leather) for shoe uppers or handbags pretreated analogously as in part a) of Example 1 150 parts of water at 40°C and 2 parts of (SM1) are added and drumming is carried on for 60 minutes. 0.5 parts of (Bl), 2.5 parts of (P3), 0.5 parts of (P2) and 0.5 parts (Pi) are added and drumming is continued for 30 minutes. Then 0.5 parts of 85 % formic acid solution are added and treatment is continued for 30 minutes, by which the pH is lowered to 3.2- 3.3. The bath is drained off. 150 parts of water at 40°C and 0.6 parts of a 50 % solution of partially hydrolysed vinyl acetate/ethylene copolymer solution (retanning agent) are added and drumming is continued for 45 minutes, then the bath is drained off and the leather is washed with 300 parts of water for 20 minutes then the bath is drained off and the leather is dried and cured as conventional. There is obtained a leather very evenly dyed in a brown shade, practically of the same tone on both sides and also in the cut edge.

EXAMPLE 3 To 100 parts of chrome-tanned nappa leather of 1. 0-1. 1 mm thickness for upholstery (furniture, automobile, aircraft), gloves or clothing pretreated analogously as in part a) of Example 1 200 parts of water at 45°C and 4 parts of (SMl) are added and drumming is carried on for 40 minutes. 1.5 parts of (Bl), 2.5 parts of (P3), 0.5 parts of (P2) and 0.5 parts (PI) are added and drumming is continued for 20 minutes. Then 1.5 parts of 85 % formic acid solution are added and treatment is continued for 30 minutes, by which the pH is lowered to 3.2. The bath is drained off. 150 parts of water at 45°C and 3.5 parts of a 20 % solution of maleic acid/styrene copolymer solution (retanning agent) are added and drumming is continued for 45 minutes, then the bath is drained off and the leather is washed with 300 parts of water for 20 minutes then the bath is drained off and the leather is dried and cured as conventional. There is obtained a leather very evenly dyed in a brown shade, practically of the same tone on both sides and also in the cut edge.

EXAMPLE 4 a) 100 parts of chrome-tanned calf leather of 1.4-1. 6 mm thickness (grain leather) for shoe uppers are wetted back with 300 parts of water, 0.3 parts of a 85 % formic acid solution and 0.2 parts of the adduct of 10 moles of ethylene oxide to 1 mol of nonylphenol at 40°C during 30 minutes. Then the bath is drained off and 150 parts of water at 30°C and 2.5 parts of sodium formate are added and drumming is carried on for 45 minutes. 4 parts of protein emulsion (20 %) and 0.5 parts of fatliquoring agent (sulphited fish oil) are added and drumming is continued at 30°C for 30 minutes, then 4 parts of mimosa retanning agent, 2 parts of C. I. Acid Brown 425 and 1 part of C. I. Acid Brown 432 are added and drumming is continued for 60 minutes. 100 parts of water at 60°C are then added and after 60 minutes formic acid is added in two subsequent additions of 0.7 parts of an 85 % formic acid solution, at an interval of 20 minutes. After 20 minutes the pH is 3.7.

The bath is drained off and the leather is washed with 300 parts of water at 60°C.

For fatliquoring 150 parts of water at 60°C, 3 parts of sodium polyacrylate, 4 parts of heavy alkylate and 2.5 parts of sulphated vegetable and mineral oil are added

and drumming is carried on for 50 minutes. 0. 8 parts of 85 % formic acid are added and after 30 minutes the bath is drained off. b) 200 parts of water at 40°C and 3 parts of syntan (SM1) are added and drumming is continued. After 30 minutes the pH is 3.9, and the bath is drained off. c) For pigment-dyeing 200 parts of water at 40°C, 0.5 parts of (B2), 2.5 parts of (P3), 0.5 parts of (P2) and 0.5 parts (Pi) are added and drumming is continued for 30 minutes. Then 0.5 parts of 85 % formic acid solution are added and treatment is continued for 30 minutes, by which the pH is lowered from 3.9 to 3.7. 0.7 parts of a 50 % solution of partially hydrolysed vinyl acetate/ethylene copolymer solution (retanning agent) are added and drumming is continued for 30 minutes, then the bath is drained off and the leather is washed with 300 parts of water for 20 minutes then the bath is drained and the leather is dried and cured as conventional.

There is obtained a leather very evenly dyed in a brown shade, practically of the same tone on both sides and also in the cut edge.

EXAMPLE 5 a) 100 parts of chrome-tanned cow leather of 1.1-1. 2 mm thickness (grain leather) for car upholstery are wetted back with 300 parts of water, 0.3 parts of a 85 % formic acid solution and 0.2 parts of the adduct of 10 moles of ethylene oxide to 1 mol of nonylphenol at 40°C during 30 minutes. Then the bath is drained off and 150 parts of water at 30°C, 3 parts of sodium bicarbonate and 1 part of sodium formate are added and drumming is carried on for 45 minutes. 3 parts of sodium polyacrylate and 1 part of fatliquoring agent (sulphited natural oil) are added and drumming is continued at 30°C for 30 minutes, then 4 parts of pyrogallol-based retanning agent (Tara), 2 parts of C. I. Acid Brown 425 and 1 part of C. I. Acid Brown 432 are added and drumming is continued for 60 minutes. 100 parts of water at 60°C are then added and after 60 minutes formic acid is added in two subsequent additions of 0.7 parts of an 85 % formic acid solution, at an interval of 20 minutes. After 20 minutes the pH is 3.7. The bath is drained off and the leather is washed with 300 parts of water at 60°C. For fatliquoring 150 parts of water at

60°C, 3 parts of sodium polyacrylate, 12 parts of sulphited vegetable and mineral oil and 4 parts of sulphited fish oil are added and drumming is carried on for 60 minutes. 0.8 parts of 85 % formic acid are added and after 30 minutes the bath is drained off. b) 200 parts of water at 40°C and 3 parts of syntan (SM1) are added and drumming is continued. After 30 minutes the pH is 3.9, and the bath is drained off. c) For pigment-dyeing 200 parts of water at 40°C, 0.5 parts of (B2), 2.5 parts of (P3), 0.5 parts of (P2) and 0.5 parts (P1) are added and drumming is continued for 30 minutes. Then 0.5 parts of 85 % formic acid solution are added and treatment is continued for 30 minutes, by which the pH is lowered from 3.9 to 3.7. 0.7 parts of a 50 % solution of partially hydrolysed vinyl acetate/ethylene copolymer solution (retanning agent) are added and drumming is continued for 30 minutes, then the bath is drained off and the leather is washed with 300 parts of water for 20 minutes then the bath is drained and the leather is dried and cured as conventional.

There is obtained a leather very evenly dyed in a brown shade, practically of the same tone on both sides and also in the cut edge.

EXAMPLE 6 a) 100 parts of chrome-tanned cow leather of 1.1-1. 2 mm thickness (grain leather) for upholstery are wetted back with 300 parts of water, 0.3 parts of a 85 % formic acid solution and 0.2 parts of the adduct of 10 moles of ethylene oxide to 1 mol of nonylphenol at 40°C during 30 minutes. Then the bath is drained off and 150 parts of water at 30°C, 1.5 parts of sodium bicarbonate and 2.5 parts of sodium formate are added and drumming is carried on for 45 minutes. 4 parts of protein emulsion (20 %) and 0.5 parts of fatliquoring agent (sulphited fish oil) are added and drumming is continued at 30°C for 30 minutes, then 4 parts of mimosa retanning agent, 4 parts of phenolic syntan, 2 parts of C. I. Acid Brown 425 and 1 part of C. I.

Acid Brown 432 are added and drumming is continued for 60 minutes. 100 parts of water at 60°C are then added and after 60 minutes formic acid is added in two subsequent additions of 0.7 parts of an 85 % formic acid solution, at an interval of

20 minutes. After 20 minutes the pH is 3.7. The bath is drained off and the leather is washed with 300 parts of water at 60°C. For fatliquoring 150 parts of water at 60°C, 3 parts of sodium polyacrylate, 8 parts of heavy alkylate, 3 parts of sulphated vegetable and mineral oil and 4 parts of a combined fat liquor containing sulphated natural oil and phospholipides are added and drumming is carried on for 60 minutes. 0.8 parts of 85 % formic acid are added and after 30 minutes the bath is drained off. b) 200 parts of water at 40°C and 3 parts ofsyntan (SMi) are added and drumming is continued. After 30 minutes the pH is 3.9, and the bath is drained off. c) For pigment-dyeing 200 parts of water at 40°C, 0.5 parts of (B2), 2.5 parts of (P3), 0.5 parts of (P2) and 0.5 parts (Pi) are added and drumming is continued for 30 minutes. Then 0.5 parts of 85 % formic acid solution are added and treatment is continued for 30 minutes, by which the pH is lowered from 3.9 to 3 7. 0.7 parts of a 50 % solution of partially hydrolysed vinyl acetate/ethylene copolymer solution (retanning agent) are added and drumming is continued for 30 minutes, then the bath is drained off and the leather is washed with 300 parts of water for 20 minutes then the bath is drained and the leather is dried and cured as conventional.

There is obtained a leather very evenly dyed in a brown shade, practically of the same tone on both sides and also in the cut edge.

EXAMPLES 7-9 The procedure described in Examples 1-3 is repeated, with the difference that in Examples 1 and 2 the 0.5 parts of (Bi) are replaced by 0.5 parts of (B2), and in Example 3 the 1.5 parts of (Bl) are replaced by 1.5 parts of (B2). There are obtained in each case leathers very evenly dyed in a brown shade, practically of the same tone on both sides and also in the cut edge.

By replacing in the above Examples 1 to 9 the employed pigment mixture of (Pi), (P2) and (P3), by any of (P4), (P5), (P6), (P7), (Ps), (Ps), (Plo) (Pll), (Pl2) or (Pi3) or by a suitable mixture of two or more thereof or a mixture of one or more thereof with any of

(Pi), (P2) and/or (P3), and predyeing the leather with corresponding acid dyes (leather dyes) or mixtures giving the same shade, corresponding dyeings are obtainable which are practically of the same tone on both sides and also in the cut edge.

In the above Examples the employed dispersions of pigments (P) and the surface active compound (B1) or (B2) are advantageously mixed with each other before feeding into the drum in step c).