CA1066856A - Leather dressing - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention relates to an aqueous dispersion for the final dressing of leather, which consists essentially of a mixture of a) an aqueous emulsion of a nitrocellulose solution in organic solvents which are immiscible with water, liquid at the use temperature and sufficiently volatile at 100 to 150°C containing 3 to 20% by weight based on the solution, of nitrocellulose and 10 to 100% by weight, based on nitro-cellulose, of a plasticizer and further containing a non-ionic emulsifier, and b) an aqueous dispersion of a polyurethane-ionomer with 0.02 to 0.2 percent of salt-like groups and wherein the ratio of a) to b), based on the weights of the aqueous emulsions or dispersions, is from 1:0.1 to 1:10.

Description

O.Z. 30,0~3 ~0~;g;1~356 LEATHER DRESSING

The object of a leather dressing ls to gi~e the finished leather a particular appearance and particular resistance characterls-tics~ The dressing influences the shade~ the gloss, the e~enness and the resistanc of the leather to external mechanical and optical factors, both during the manufacture of the leather article and during its use.
It is known to coat leather with unmodified natural mater_ ials or natural materials which have been modlfied by physico- ;
chemical reactions. Thus9 for example, dressings containing casein which has been dissolved under alkaline conditions can be rendered water-insoluble by appropriate treatmen~ with acids ~ -and formaldehyde. Nevertheless, such dressings remain water-swellable an~ therefore sensitive to moisture.
Dressings cu~taining nitrocellulose always contain plasti-cizers. Hence, when using nitrocellulose dressings there is `
always the possibility that the plasticizer required to produce a supple and soft coating may ~igrate into the primer or lnto the leather itself,!~r migrate to ~he surface, which makes the dressing brittle and cracked and can in many cases e~en cause ; 2a it to flake of.
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O,Z. 30,023 ~066~35~; -; The use of polymer dispersions as dressings is virtually nil, since they do not have suf~icient rub resistance and scratch resistance, coupled with adequate elasticity, for a ; ~inal dressing, whilst nitrocellulose lacquers do possess these properties, Furthermore, the thermoplastic behavior of the poly-mers restricts their uses.
On the other hand it is known (German Patent 1,171~393) to coat fibrous structures with a mixture of a copolymer con-taining hydroxyl groups, and based on diol monoacrylates and 10 further copolymerizable compounds, and of reaction products of toluidinediisocyanates with polyalcohols (polyurethanes) which ~
contain an excess o~ reactive isocyanate groups, and to cross- -link the components at 60 to 160C. Without such a heat treat-ment, however, the drying times of such coatings are so long .:..
i that materials treated therewith can only be stacked after a considerable time. On the other hand, it is known that leather cannot be exposed to such high temperatures because they denature the collagen fibera of the leather.
A further deve1opment is ~erman Published Specification ~ -20 1,794,263, which uses, as polyisocyanates, particular hi~h moleoular~weight~isocyanurate isocyanates which are applied together with ethylenically unsaturated copolymerizable compounds, contsining hydroxyl ~roups, to the leather and are crosslinked thereon. Whi1st this dressing must be regarded as a major ad-vanoe, it is, beoause of the~relatively expensive process an~
t~hB~sxpensive~products which i~gives, pro~ably only of interest or leather srtioles which~themselves5 as made-up leather goods, ustify a su~ioiently high price which is sufficiently above :
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o z. 30,023 1~ 6 6 ~ S
that of the coating.
The industry therefore continues to seek to manufacture leather dressings with inexpensive nitrocellulose lacquer emulsionsO In addition, however, the outstanding properties of polyurethanes which have become known from polyurethane chemistry should also be utilized ln leal;her coating.

However, as is known, and as German Patent 1,171,393 teaches, polyurethane coatings are britt~e and tend to crack and can only be applied successfully to leather at fairly high 10 temperature In recent times, novel polyurethane modifications were discovered which at first sight appeared suitable for use as final leather dres'sings in industry. These mater;als are the group of compounds described, for example,in Angewandte Chemie ' 82 (1970), pages 53 et seq., as "Polyurethane ionomers'l.
Such ionomers are obtained by providing the customary components~ such as~polyisocyanates and polyalcohols or poly-ester alcohols, with quaternized or anionic groups, so that the polyurethanes formed therefrom are in due course in the form of 20 salts. These salt-like polyurethanes, so-called polyurethane-ionomers, possess excellent dispersibility in water and are .
accordingly outstandingly suitable for use as dispersion `coating agents ~or a great diversity of purposes.

However, they are not suitable for leather since poly-~ ~ -urethane~ionomers are moisture-sensitive, that is to say the film becomes tacky on exposure to atmospheric moisture.
The invention relates to aqueous disper~ ~s~ ~or the final dressing of Ieather, which essentially consist of a ~: 7 '~ ~
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~66856 mixture of a) an aqueous emulsion of a nitrocellulose solution in organic solvents which are immiscible with water, liquid at the use -tempera-ture and sufficiently volatile at 100 -to 150C
contAining 3 to 20~ by weight based on the solution, of nitrocellulose and 10 to 100% by weight, based on nitro-cellulose, of a plasticizer and further con-taining a : -non-ionic emulsifier, and b) an aqueous dispersion of a polyurethane-:ionomer wi-th 0.02 to 0.2 percent of salt-like groups and wherein the ratio of a) to b), based on the weights of the aqueous emulsions or dispersions, is from 1:0.1 to 1:10.
Examples of solvents which may be mentioned are higher -.::
ketones such as diisopropyl ketone or dibutyl ketone, methyl- . .
hexanone, cyclohexanone, isophorone, esters such as ethyl acetate, butyl acetate, amyl acetate or cyclohexyl acetate, ethyl glycol acetate or butyl ~lycol acetate or hydrocarbons such as : :
~: toluene, xylenes tetrahydronaphthalene or decahydronaphthalene or paraffins of low molecular weight t such as solvent naphtha.
20 : : As is known, nltrocellulose is marketed, for safety ..
reasons, as a paste with water or lower alcohols such as methanol, :
ethanol, propanol or butanol, preferably in weight ratios from .
1.7:1 to 2:1, and is also dissolved, in this form, in the solvents mentioned.
; The plasticizers usedjinto the solutions may be selected Erom the group~consisting of:

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~OG61~ o o z . 30,023 phthalic acid esters, in particular dimethyl ph~halate, diethyl phthalate, dibutyl phthalate, diamyl phthalate, d;octyl phthalate, dinonyl phthalate, di~2-ethylhexyl phthalate or dicyclohexyl phthalate, butyl, amyl or octyl esters of sebacic acid or adipic acid, butyl stearate, tributyl phosphate, phenyl phosphate or cresyl phosphate and pressed or blown castor oil.
Finally, nitrocellulose solutions can `also contain surface-coating resins which are compatible with nitrocellulose, such as Dammar resin, rosins, ketone resins or sulfonamide resins, modified phenolic resinsy maleic acid resins~ urea-formaldehyde resins or melamine-formaldehyde resins.
The nitrocellulose solutions contain emulsifiers, and in particular preferably the emulsifiers described, for example, in German Published Specification 2,203,554. For the purposes of the invention, the emulsifiers are non-ionic and examples are ethoxylation products (with degrees of ethoxylation from 4 to 10) of al-cohols of 10 to 30 carbon atoms and al~ylphenols such as nonylphenol, In addition, ethoxylated castor oils~ of which the degree of ethoxylation is suitably from 20 to 60, should be mentioned above all.
In special cases, the nitrocellulose solutions contain from 25 to 150 per cent by weight of emulsifiers, based on dry nitrocellulose.
On ~he other hand~ the emulsifier can also be present in the aqueous phase, but from an industriàl point of ~iew it is of particular interest if the emulsifler is dissolved in the i~ :
~ nitrocellulose solution prior to emulsification.
~: _5_ ' ~66~356 The water used as the second phase of the nitro-cellulose emulsion can be entirely devoid of chemicals but at times stabili~ers axe desirable; amongst the most important oE
these are casein, gelatine, methylcellulose or carboxymethyl-cellulose.
Suitable ratios of water to solvent, or solvent mixture, containing the nitrocellulose ar~ disclosed in the relevant literature, for example in A. Kraus, Handbuch der ~itrocellulose~
lacke, Verlag W. Pansegrau, Berlin-Wilmersdorf, 1952. The :10 technique o~ emulsification is simple and comprises, for example, bringing the organic and aqueous phases together and effecting mutual distribution by mechanical agitation.
Component b) is a polyurethane-ionomer dispersion as describedJ for example, in Canadian Patent 794,411. Within the scope of the present invention, possible star-ting materials for the manufacture of these ionomers are, as a first group, compounds .
carrying at least 2 active hydrogen atoms. These compounds should be at least predominantly linear and have a molecular weight from 300 to 10,000, preferably 500 to 4,000 They 20 : include, for example, polyethers, polyesters, polyesteramides, polyacetals and polythioethersO Examplas of polyethers which may be mentioned are the polymerization products of tetra-hydrofuran, propylene oxide and ethylene oxide, and copoly-- .
~ merization products or graft polymerization products of these - .~: .
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compounds, for example addition products of alkylene oxide and polystyrene. Further possible starting material5 are 9ingle polyether9, or mixtures of polyethers, which are ob-tained for example, by condensation of, say, hexanediols, : . . .

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~066~S6 oO z . 30,023 diol, heptanediol or octanediol, optionally with addition of 10 to 30% of lower ~lycols. Propoxylated or ethoxylated (or mixed alkoxylated~ glycols and amines can also be used.
Amongst the polythioethers, self-condensation products of thiodiglycol, or condensation products of thiodi~lycol ~ with other ~lycols, inter alia also glycols containing tertiary `` amino ~roups (for example dihydroxyethylaniline) should be mentioned in particular.

Polyacetals which can be used are especially the water-insoluble ~ypes, for example obtained ~rom hexanediols and formaldehyde or 4,4'-dihydroxyethoxydiphenyldimethylmethane ~ and formaldehyde.
`~ Polyesters and polyester-amides obtained by conventional methods from polyhydric alcohols and polybasic carboxylic acids, with the optional use of diamines and aminoalcohols, should also be mentioned.
is also possible to start from polyhydroxy compounds hich already contain urethane or urea groupsO Of course~
mixtures of di~erent polyhydroxy compounds can also be used;
20~ ~for;example, hydrophilic polyethers, polyethylene glycols, polyest~ers and polyesters~and polyacetals will only be used aS~constituentS in~mixtures with hydrophobic polyhydroxy com-pounds.;Natura1 polyols such as castor oil or carbohydrates oan~ a~lso be us~ed. ~ -Examples of the second group which are employed in accordance~with conventional method together with the examples of~the ~irst group, are polyisooyanates, preferably diiso oyan~ates~

0 Z 30,023 ~06~8~
cyanates~
Suitable diisocyanates are all aliphatic and aromatic diisocyanates, such as, ~or example, 1,5 napththylened .. ... .
cyanate, 4~ diphenylmethanedii50cyanate3 4,ll-diphenyldimethyl-methanediisocyanate, dl- and tetra-a~kyldiphenylrnetilanediiso-cyanate, 4,ll-dibenzyldiisocyanate, 1,3-phenylenediisocyanate, 1~4-phenylenediisocyanate~ toluylenediisocyanate, chlorinated and brominated diisocyanates, diisocyanates containing phos-phorus, butane-1,4-diisocyanateg hexane-1,6-diisocyanate, dicyclohexylmethanediisocyanate and cyclohexane-1,4-diiso-cyanate. Special mention should be made o~ partially masked diisocyanates which permit the formation of self-crosslinking polyurethanes, for example dimeric toluylenediisocyanate, and polyisocyanates which have been partially or completely reacted with, for example, phenol-tert.-butanol-phthalimide-caprolac-tam, which, if they are completely masked, do not initially participate in the reaction and are simply admixed. Chain ~ lengtheners, containing reactive H atoms, which can optionally i be used, are the conventional glycols, such as ethylene glycol, diethyleneglycol, triethylene glycol and tetraethylene glycol, '~ 1,2-butanediol, 1,3-butanediol, neopentyl glycol, dihydroxy- -~ hydroquinone, ethoxyhydro~uinone, and also diamines, for ~ ~
, example ethylenediamine, hexamethylenediamine, benzidine and di- -aminophenylmethane~ aminoalcohols and water ~ydrazine and ammonia are also suitable~
To convert the polyurethane, obtained from the said materials 9 into ionomers J compounds are re~uired, as a third : -, , . , ., . :, . , ; , . , ~.............. . .

il ~)66~6 group, which contain at least one active hydrogen atom which reacts with isocyanate groups or at least one isocyanate gxoup and at least one group capable of salt formation. ~le groups capable of salt formation can be anionic or cationic;
in the present invention~ cationic groups are preferred.
However, it i5 also possible to dispense ~ith the third group if the starting compounds with active hydrogen atoms, or ~he diisoryanates, contain such groupings, capable of salt formationg in the molecule.
For the purposes of the invention, compounds which can be used as the third group are above all those which in addition ~ -to the active hydrogen atoms or isocyana~e groups contain, as groups capable of salt formation~ amino groups which can be neutrali~ed with acids or can be quaternized by means of alkyl-' ating agents.
As such compounds, hydroxyalkylated aliphatic~ cyclo-aliphatic~ aromatic and heterocyclic amines should be mentioned particularly3 examples being N,N-dimethylethanolaminea N~N'-diethylethanolamine9 N~N'-dibutyle~hanolamine, l~dimethyl7 aminopropanol-2~ N~N~-methyl- ~-hydroxyethylaniline9 NsN~
methyl ~ -hydroxypropylaniline, N~N'-ethyl- B -hydroxyethyl- ~ -.
aniline~ N9NI-butyl- ~-hydroxyethylaniline~ N_hydroxyethyl-p~peridine, N-hydroxye~hylmorphollne, ~ hydroxye~hylpyridine and ~ -hydroxyethylquinoline~ In additlonS al~oxylated ali-phatic~ cycloaliphatic, aromatic and het~rocyclic primary amines~ arninoalcohols, diaminesa triamines and amides can be usad.

` 0~ z 30,023 ~6~5~;

Alkylating agents for the quaterni2ation reaction can be, for example, organic halogen compounds or esters of strong acids, are known in the art and can be derived from any com-pounds which are capable or such quaterni~ation reactions.
Chloroethanol, bromoethanol, chlorobutanol, bromopropanol, trichloroacetyltriethylenetetramine and l,3-dichloropropanol-2 should be mentioned particularly.
The proportion of salt-like g~oups should in general be from 0.02 to 0.2%~ and ln most cases approx. 0.1%, of the dry polyurethane composition. A polyurethane composition con~
verted to the form of a salt in this way is co~patible with water in all proportions and can be ronver~ed into an aqueous dispersion in accordance with the methods customary in the chemistry of elastic and plastic polymers. A preferred embodi-ment is to dilute the polyurethane co~position which carries salt-like groups9 and is dissolved in a polar solvent, with from about 70 to 150% of water, based on the weight of the polyure-thane composYtion3 and--then to distil off most or all of the -or~anic solvent under reduced pressureO On dilution with waeer~
a homogeneous molecularly disperse solution is produced in the : first instance; on further addition of waeer ehis becomes opaque and changes to a colloidally disperse solution. In the course of removing the organic solYen~9 ehe particle si~e in-creases further so that ultimately a coarse stable latex is ; produced, which in general has a solids content of from 30 to 70% by weight.
A polyurethane-ionomer disperison thus obtained is then ~10~

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mixed with the nitrocellulose lacquer emu:Lsion, described above, in weight ratios preferably from 1:1 to 20 ~ rati~
of 1:1 to 1~5 is of particular interest for industrial purposesO
The weight ratios are based on the finished dispersions. In preparing the m:ixtures, emulsifiers can be used, above all emulsifiers of the type described eaxlier in connection with the preparation of the nitrocellulose emulsions. However, frequently the proportion of emulsifiers already present in the nitrocellulose emulsions suffices for preparing the mixture.
.10 If emulsifiers are used, their proportion is in general from 0.1 to 1% by weight, based on the mixtureO
Application of the mixtures to the leather is simple and is effected by first diluting the mixtures with water again in a ratio from 1:1 to 1:1.5 and spraying the diluted mixture onto pretanned leather, so that a dressing becomes superfluous.
In general, from 50 g to 100 g, preferably about 50 g, based on solids and calculated per square meter of leather surface, is applied, but larger or smaller amounts can be eciually success- .
ful, depending on the quality of leather. iIn the case of full-grain leathers, in particular, physical resistance characteris-tics are obtained which are normally only achievable with the expensive so-called "eas~-care" systems which are applied from organic solutions (compare the procedure in German ~ublished : Specification 1,79~,263).
; The Ex~nples which now follow describe the use of the ;~ ~ dispersions according to the invention and provide details of the leathers obtained.

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A) Preparation of the nitrocellulose lacquer emulsions.

18 parts by weight of an ester-solubl~ nitrocellulose of viscosity 3/4 seconds, which has been moistened with iso-propyl alcohol so that the proportions by weight are 12 parts of dry nitrocellulose and 6 parts of isopropyl alcohol, are stirred with 5 parts by waight of castor oilg 4 parts by weight of dloctyl phthalate, 4 parts by weight of an ethoxylated castor oil, 25 parts by weight of ethylhexyl acetate, 25 pa~ts by weight of diisobutyl ketone and 19 parts by weight of toluene uDtil a clear solution is obtained.
52 parts by weight of this surface~coating solution are intimately mixed with 48 parts by weight of ~ater, using a high speed turbine mixer, thereby giving a homogeneous emulsion.

18.5 parts by weight of an ester-soluble nitrocellulose of viscosity 3/4 seconds; which has been moistened with water, corresponding to 12 parts by weight of dry nltrocellulose and 6.5 parts by weight of water, are stirred with 4.5 par~s by welght of blown castor oil, 4 pares by weight of dibutyl phthal-ate, 25 par~s by weight of ethylhexyl acetate, 18 parts of ~ethylhexanone. 25 parts by weight of xylene and 5 parts by weight of ethoxylated cas~or oil until solution is comple~e.
65 parts by weight of this surface-coating solutlon are mixed wi~h 35 parts by weight of water, using a high speed stirrer, to glve a homogeneous emulslon whlch can readily be diluted further with water~

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~ O.z. 30,023 8~;

20 parts by weight of an ester~soluble nitrocelluLose of viscosity 3/~ seconds which has been ~oistened with n-butyl alcohol, corresponding to 13 parts by weight of dry nitro-cellulo~e and 7 parts by weight of butyl alcohol~ are stirred with 6 parts by weight of castor oil~ 4 part:s b~ weigh~ of dioctyl adipate~ 2 pa~ts by weight of nonylbenzene ethoxyla~.e, 4 parts by weight of ethoxylated castor oil, 40 parts by weight of butylglycol acetate and 24 parts by weight of toluene until solution is completeO :
53 parts by weight o this solution are emulsified in ~ :
47 parts by weight of water.
B~ Preparation of the polyurethane-ionomer dispersions = e~ .
- 387 g ~002 mole~ of a polyester of adipic acid, hexane-diol and neopentyl glycoi) having an OR number of 58~ are degassed for one hour at 120 C and 20 mm Hg~ cooled ~o 80 C
and reacted for.two hours with 174.2 g ~1 mole~ of toluylene~
diisocyanate in which the ratio of the 2,4 and 2~6 isomers is ~0:20. The melt was cooled to 56C and diluted with 685 g of acetone, and a solution of 29.8 g (0.25 mole) of N-methyldi- `~
ethanolamine and 49957 g (0055 mole) of 1~4-butanediol in 100 g :.
of acetone was added drop~ise over the course of two hours.
The reaction was continued for a f~rther two hours at 56 CJ At ~he end of the reaction, the solution wns csoled~ ~nd a solu~ion of 250 ml of N/l hydrochloric acid in 550 ml of water was added :

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~ 00Z~ 30~023 ~0 6 ~

dropwise at room temperature whilst stirrin~ vigorouslyO A~ter adding a further 500 ml Or water, the acetone was strlpped of~ in vacuoO Approx. 1,950 ~ o~ a stable dispersion of 33%
solids content remain.

Ani_nic dis~ers_on 484 g (0.25 mole) of the polyester used above were degassed as described and reacted with 88 g (0 505 mole) of 80/20 toluyl-enediisocyanate for two hours at 80C. The melt was cooled and diluted with 1,400 g of acetone, and a solution of 15O04 g (0.25 mole) of ethylenediamine~ 30.5 g (0.25 mole) of propane-sulfone and 100 g of 10% strength sodium hydroxide so:Lution in100 ml of water was added at room temperature. A~ter 30 minutes, ~-720 g of water were added dropwise whilst stirring vigorously.
After removing the acetone by vacuum distillation, an anionic --~
dispersion of 40~ solids content is obtained.

The polyurethane-monomer dispersions were combined with nitrocellulose lacquer emulsions by the following method:
~ 100 parts of polyurethane dispersion ; ~ according to Example 4~
50 - 100 parts o~ a nitrocellulose lacquer emulsion according to Example 1 and ~; 0~5 - 1 part of ethoxylated castor oil, degree o~f eth~xylation approx. 30.
Method of mixing: the emulsifier is first stirred into ~ : . .
the nitrocellulose lacquer emulsion, and this mixture is then -14- ~ -:

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added to the polyurethane-ionomer dispersion whilst stirring vigorouslyO
This mixture is then diluted with water in the ratio o~ 1:1 and sprayed onto to a previously dyed leather, so that a dressing becomes super.~luous. Particularly in the case o~ full-grained leathers, physical resistance characteristics which are normally only ~achievab:le with so cal:led "easy-care" systems applied ~rom organic solutions are o~tained, A full-grained sideleather produced in accordance with the above instructions has the ~ollowing resistance characteristics:

Dry rub resistance: 5,000 ) ) by the Satra Wet rub resistance: 2,000 ) method Brittle point: -30C
.
Adhesion: 600 ptcm Flexometer: 50,000 folds : Swellin~ resistance: 5 x = O ) by the Veslic : : : 10 x - 1 ~ method ; : 2 kp/10%
: elongation ;

: COMPARATIVE EXAMPLE : .
Conventional dressings:(200 parts o~ emulsion according :.
to Example i, but only nitrocellulose) have the following ; ;:
physical propertîes:

:~ Dry rub~resistance: 1,000 ): :
by the ~r.a .
Wet~rub resistance: iOO ~ method .:
~: - . .

~6~6 ~ z o 30,023 Brittle po;nt- -5 t~ -10C
Adhes;on: 300 p/cm Flexometer: 50,000 ~olcls Swellin~ resistance: 5 x accordi.ng to the Veslic method~

2 kp/5% elongation The comparison of these two methods o~ dres~ing the leather shows that the new process gives substantially better resistance characteristics.

A nappa side leather which has been previously dyed with a dye is coated with a mixture of 100 parts of a polyurethane-ionomer dispersion accordin~
to Rxample 5, 100 parks of nitrocellulose emulsion according to Example 2 and 200 parts of water ,~ by repeated spraying in the conventional.manner~ and dried.
A leather with excellent resistance characteristics is obtained without major ~.odification of the natural .
character of the leather. The product was tested in accordance with Example 6 and an~logous results were obtainedO

100 parts o~ polyurethane-ionomer dispersion according to Rxample 4, 50 parts of nitrocellulose emulsion according to Example 3 and 150 parts of water.
~, .
Cross-spraying twice again gives leather with outstanding i~ , .

' ~ ` , ' O~z. 30,023 685Si resistance characteristics. The test results are analo~ous to Example 60 100 parts of polyurethane-ionomer dispersion according to Example L~, 200 parts o~ nitrocellulose emulsion according to Exarnple 1 and 300 parts o~ water, The mixture is repeatedly sprayed onto dyed ~ull-grained leather. The test is analogous to Example 6.

lo A mixture of 100 parts of polyurethane-ionomer dispersion according to Example 5, -300 parts of a nitrocellulose emulsion according t-o ~ :
Example 2 and --200 parts of water -;~
is applied to normal dyed polyurethane imitatlon leather or ~ -PVC imitation leather~ by repeated spraying, A polyurethane : or PVC imitation leather having a very leather-like hand and very good resistance characteristics is obtained. The test 20 is analogous to Example 6. :~

In addition3 the mixtures mentioned abo~e (Example 7 to ;~
9) can al~o be applied to leather which has been primed in : .
the~onventional way. For example, a polyacrylate dispersion ~ :
~;~: ; o~ 20% solids content obtainable by conventional methods is .~` ' "
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. . . , ~ . , -~66~5~ .Z 30,023 applied to a bu~ed chrome slde leather by spray;ng once, the leather is dried and pressed at 70C/100 atmospheres and is then sprayed once analogously to Exampl~ 7-9~ Here again, a leather with good resistance characteristics (dry rub resistance, wet rub resistance and crease resistance) and with a pleasant hand is obtainedO The test is analogous to ~xample 6~

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Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An aqueous dispersion for the final dressing of leather, which consists essentially of a mixture of a) an aqueous emulsion of a nitrocellulose solution in organic solvents which are immiscible with water, liquid at the use temperature and sufficiently volatile at 100 to 150°C
containing 3 to 20% by weight based on the solution, of nitrocellulose and 10 to 100% by weight, based on nitro-cellulose, of a plasticizer and further containing a non-ionic emulsifier, and b) an aqueous dispersion of a polyurethane-ionomer with 0.02 to 0.2 percent of salt-like groups and wherein the ratio of a) to b), based on the weights of the aqueous emulsions or dispersions, is from 1:0.1 to 1:10.

2. An aqueous dispersion as claimed in claim 1, wherein the ratio of a) to b) is 1:1 to 2.

3. An aqueous dispersion as claimed in claim 1, wherein the component a) contains from 25 to 150% by weight, based on dry nitrocellulose, of non-ionic emulsifiers.

4. An aqueous dispersion as claimed in claim 1, wherein the component b) is an aqueous polyurethane-ionomer dispersion with from 30 to 70% by weight solids content, and wherein the polyurethane composition contains from 0.02 to 0.2 of salt-like groups, based on solids.