AU596222B2 - Crosslinking of casein films in leather finishing - Google Patents

Abstract

1. A process for crosslinking casein films in leather finishing, wherein the casein is applied in layers together with a water-soluble condensate of melamine and/or urea with formaldehyde and, if appropriate, glyoxal and any methylol groups present may be etherified with a lower alcohol, drying is effected at from 20 to 80 degrees C after each application, and crosslinking is carried out by from one to three heat treatments in the absence of an acidic catalyst at from 140 to 200 degrees C for from 0.1 to 5 seconds in each case.

Description

Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 COMPLETE

SPECIFICXFION

(ORIGINAL)

I t. Class Application Number: Lodged: i96222 Complete $p,,cif ication Lodged: Accepted: Published: Priority: 14 Related Art: Name of A~pllcant: *Address of Applicant Actual Inventor.

Address for Service: BASF AKTIENGESELLSCHAFT D-6700 Ludwigshafen, Federal Republic of Germany KARL FISCHER, GUENTER ECKERT and DIETRICH LACH EDWD. WATERS SONS, 30 QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.

Comp~ete Specification for the invention entitled: CROSSLINKIIN OF CASEIN FILMS IN LEATHER FINISHING The following statement Is a full description of this Invention, including the Lest method of performing It known to us O.Z. 0050/38712 Crosslinking of casein films in leather finp shing The present invention relates to a process for crosslinking casein films, applied, for example, as bottoming and seasoning layers in leather finishing, wherein crosslinking the casein is carried out with the aid of a water-soluble condensate of melamine and/or urea with formaldehyde and, if appropriate, glyoxal and any methylol groups present can be etherified with a lower alcohol, the procedure being effected without the use of an acidic catalyst.

It is known that leather, in particular sheep, pig and goat skins and calfskins, whose finish is intended to have high gloss and a natural handle, is finished using casein as a binder. However, the casein applied has little resistance to water and this does not adequately protect the leather from damage. For this reason, the *casein film applied to the leather is crosslinked with, for' example, formaldehyde solution, which makes it suft r ficiently resistant to moisture, particularly when fixing is catalyzed with acetic acid. The use of fornaLadehyde is disadvantageous since it entails a considerable odor nuisance and irritation of the mucous membranes.

German Laid-Open Application DOS 3,332,571 describes a process for finishing leather with casein films, in which the crosslinking component used for the casein is no longer formaldehyde but hexamethylolmelamine hexamethyl ether in the presence of formic acid and/or a complex of tartaric acid and boric acid as an acidic catalyst.

This process not only results in less environmental pollution but also in better resistance of the casein film to moisture in comparison with formaldehyde. From German Laid-Open Application DOS 3,332,571, it is clear that an acidic catalyst which is applied in a special operation has to be used for the crosslinking in rrder to obtain useful results.

Furthermore, German Laid-Open Application DOS 3,127,598 discloses a process for fixing, ie. crosslinking, T7-

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i ii di iij~t 2 O.Z. 0050/38712 casein seasons, in which the crosslinking agents used are alkoxymethylated ureas and the acidic catalysts employed are preferably oxalic acid and in particular sulfuric acid. The main disadvantage of this process is the use of the corrosive sulfuric acid which has a pronounced skin-irritant effect.

Neither process has become established in practice. Handling of sulfuric acid as a crossLinking catalyst is not advisable owing to its corrosiveness. The tartaric acid/boric acid complexes may in certain circumstances form a white coating on the Leather surface, while the results obtained with formic acid as an acidic catalyst are generally Less satisfactory compared with tartaric acid/boric acid complexes under otherwise identical process conditions.

We have found, surprisingly, that the use of acidic catalysts for crosslinking casein films can be completely dispensed with if a very particular procedure is adopted.

Aqueous mixtures of casein and formaldehyde; con- 20 densates, with or without the conventional additives, are applied to the leather in a conventional manner and dried, and crosslinking is carried out at elevated temperatures, for example simply by plating. Glazing can then be carried out in a conventional manner.

The present application accordingly relates to a process for crosslinking casein films in Leather finishing, in particular for the production of glazed leather, wherein the casein is applied in layers together with a water-soluble condensate of melamine and/or urea with formaldehyde and, if appropriate, glyoxal, and any methylol groups present may be etherified with a lower alcohol, drying is effected at from 20 to 80 0 C after each application, and crosslinking is carried out by from nne to three heat treatments in the absence of an acidic catalyst, at from 140 to 200 0 C, preferably from 165 to 180 0 C, for from 0.1 to 5 sec, preferably from 0.5 to 3 sec, in each case.

In the novel process, the aqueous solution of the i 3 O.Z. 0050/38712 casein together with the condensates used for cross inking, in the form of an aqueous mixture or solution, is applied to the Leather in a conventional manner, preferably by spraying. This mixture contains from 0.75 to 7.5% by weight of casein and from 0.7 to 13, preferably from 2.5 to 8.0, by weight of condensate.

This mixture may contain the conventional additives, with or without further assistants, as used in the finishing of Leather. After each appLication, drying is carried out at from 20 to 80 0

C.

From 50 to 125 g, preferably from 60 to 100 g, of mixture per m 2 of leather are advantageously applied per application, ie. from 0.7 to 25.7, preferably from 0.9 to 20.5, g/m 2 of leather, based on the dry weight of the casein and of the crosslinking agent used.

As a rule, from one to six layers are applied as 00 o o ~0 oUo bottoming and then from one to three layers as season.

.s UsuaLLy, two layers are applied to the leather as bottoming, drying being carried out after each application.

oooo 20 Thereafter, two layers are applied as season and are then dried in the same way.

The mixtures applied as bottoming and as season differ in their composition as a rule only in that the :o bottoming forms a softer film which is more highly pigmen- 25 ted than the seasoning, which in turn forms a fairly hard film and thus gives a relatively high gloss.

aoor Thus, intermediate plating at elevated temperatures, for example after application of the individual bottnming layers, is not necessary.

°o 30 After the final drying, crosslinking is initiated Sin practice by hot plating once, twice or three times under the conditions stated above.

The solutions or mixtures to be applied are prepared using the commercial colloidal casein solutions containing from 8 to 25% by weight of casein.

The condensates of melamine and/or urea qith formaldehyde and, if appropriate, glyoxal, which are used as I

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0O o .l o o C 0 i 4 O.Z. 0050/38712 crossLinking agents and some or all of whose methylol groups may be etherified, are the conventional commercial solutions or reaction mixtures of these condensates or their dry powder. The condensates used should give clear or slightly cloudy colloidal solutions in water or in 1:1 Tixtures of water and n-propanol. The commercial aqueous solutions having solids contents of from 30 to by wright are preferably used.

The condensates used as crosslinking agents can, for example, bj characterized as follows.

Condensate's based on urea are reaction mixtures obtained by reacting 1 mole of urea with from 1.6 to 4, preferably from 1.8 to 2.8, moles of formaldehyde. If necessary, the merhylol groups present can be etherified by reaction with methanol or ethanol.

These condensates can readily be incorporated into a finishing mixture with casein without a reaction with the casein occurring immediately. Their crossLinked finishing films have a high gloss.

20 We have found that this gloss can be further increased if urea/formaLdehyde/gLyoxaL condensates are used. Advantage'-s condensates are the reaction products of 1 mole of ur'ea with from 2 to 3.5 moles of formaldehyde and from 0.1 to 1.5 moles of glyoxal. A condensate of 1 mole of urea, 3 moles of formaldehyde and 0.5 mole of glyoxal is very particularly preferred.

Among the melamine derivatives, condensates of 1 mole of melamine and from 2 to 6, preferably from 2.2 to 5.5, moles of formaldehyde have proven particularly usefuL. For gloss production, it is advantageous if the methylol groups are present in ethrified form, in particular as the methyl ether. Hence, the reaction products of 1 mole of melamine, from 2.2 to 6 moles of formaldehyde and from 2.2 to 6 moles of rrmi hanol are particularly preferred. Specific examples of these are hexamethylolmelamine hexamethyl ether and the condensate of 1 mole of meLamine, 5.5 moles of formaldehyde and

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I-.

5 O.Z. 0050/38712 moles of methanol, as available commercially in their aqueous soLutions having a solids content of from 30 to by weight or in powder form.

These crosslinking agents not only impart high gLoss to the finishing film but can also be readily incorporated into the finishing mixture at room temperature, particularly when the aqueous solutions are used. If difficulties are experienced in dissolving the powder form, warm water at about 40 0 C or a mixture of from 1 to 4 parts of water and 1 part of n-propanol is advantageously used.

Melamine/urea/formaldehyde condensates obtained by reacting 1 mole of melamine, from 0.1 to 0.6 mole of urea and from 2.5 to 3.8 moles of formaldehyde and, if appropriate, from 0.5 to 3.8 moles of methanol for etherification have also proven useful.

Other examples are melamine/formaldehyde/glyoxal oo condensates of 1 mole of melamine, from 1.4 to 3.5 moles 'og of formaldehyde and from 0,2 to 1 mole of glyoxal.

Dicyanodiamide/formaldehyde and biuret/formaldeoo 20 hyde condensates can also be used. It is also possible to employ mixtures of the abovementioned condensates.

All of the crosslinking agents stated effect good crosslinking, which can be demonstrated by testing the wet S rub fastness (according to IUF 450) and the flexibility a sa .o 25 (according to IUP 20) of the leather obtained.

As a rule, the crosslinking agent is used in the a° form of its 30-70% strength by weight aqueous solutions or in powder form for ti.e preparation of the solutions or mixtures to be applied. The crosslinking agents are 30 used in amounts of from 7 to 130, preferably from 25 to very particularly preferably from 40 to 65, parts, based on the dry weight of the crosslinking agents, per 7.5-75 parts of casein in 1,000 parts of finishing mixture.

The finishing mixtures may contain the conventional additives, for example soluble dyes and/or pigment preparations for imparting color, oil emulsions or wax -6 O.Z. 0050/38712 emulsions for improving the plating behavior and the handle, and, if required, further assistants as may be used in the finishing of leather.

The particularly noteworthy advantages of finishing by the novel process are the following: application of an acidic catalyst can surprisingly be avoided; this has the advantage that the leather contains a smaller amount of acid, which may accelerate embrittlement of the leather.

The machines used are protected since less corrosive sub-, stances are employed, and environmental pollution is reduced.

In contrast to the general opinion that an acidic catalyst has to be used for crosslinking casein, good crosslinking is achieved; this can be demonstrated by the high wet rub fastnesses and good flexibilities.

Glazed Leathers are preferably produced, glazing being effected after hot plating, ie. after crosslinking of the applied layers has been carried out. This is particularly advantageous because the crosslinked layers show no 1 20 tendency to smear during glazing. If necessary, glazing can be followed by a final plating.

c t The Examples below illustrate the process according to the invention. Parts are by weight, unless stated otherwise.

EXAMPLE 1 parts of a 70% strength by weight aqueous solution of a melamine resin, obtained by condensation of 1 mole of melamine, 5.5 moles of formaldehyde and 5.5 moles of methanol, are stirred into 660 parts of water. Thereafter, 195 parts of a commercial 20% strength by weight casein solution, 20 parts of peanut oil emulsified with Su an anionic emulsifier, 5 parts of a wax emulsified with a nonionic emulsifier, 30 parts of a liquid formulation of the dye C.I. Acid Black 63 and 30 parts of an aqueous pigment preparation of C.I. Pigment Black 7 are added with further stirring.

This bottoming mixture is sprayed onto a goat 7 O.Z. 0050/38712 Leather by 2 spray appLications by means of a compressed air gun, in a total amount of 150 g/m which corresponds to 12.2 g/m 2 of solid, based on casein and crosslinking agent. After each spray application, drying is carried out at 65 0 C. The leather is then polished on a stone roller.

The bottomed Leather prepared in this manner is then sprayed with a season having the foLLowing composit ion: 680 parts of water, parts of the abovementioned aqueous melamine resin solution, 200 parts of a 15% strength by weight aqueous casein soLution, 30 parts of peanut oil emulsified with an anionic emulsifier, and parts of a liquid formulation of Acid Black 63.

This mixture is sprayed on the leather in 2 applications, drying being carried out at 65°C after each appLication. The total amount applied is 120 g/m ie. 10.3 9g m 2 of solid, based on casein and crosslinking agent.

CrosslYnking is then carried out on a continuous plating machine at 1700C. The contact time is 0.5 sec.

Thereafter, glazing is carried out and plating is repeated in the same manner at 170 0 C in order to increase the gLoss.

The finished leather surface exhibits the desired smooth handle and high gloss. The crosslinked film possesses extremely good wet rub fastness, measured according to IUF 450, and flexibility, measured according to IUP EXAMPLE 2 parts of a 75% strength by weight aqueous soluk tion of a formaldehyde/glyoxaL/urea condensate of 1 moLe of urea, 2,5 moles of formaLdehyde and 1 mole of glyoxal are diluted with 700 parts of water. Thereafter, 180 parts of an 18% strength by weight casein solution, 20 parts of pulyglycol ether as a plasticizer, 20 parts of a Liquid formulation of C.I. Acid Black 63 and 20 parts of an 8 O.Z. 0050/38712 aqueous pigment preparation of C.I. Pigment Black 7 are added.

This mixture is applied in 3 applications on a calf Leather, with the aid of a plush pad, as bottoming in a total amount of 150 g/m corresponding to 11.6 g/ m 2 of solid, based on casein and crosslinking agent.

After each plush application, drying is carried out at 0 C. After the first application, the leather is polished on a store roller.

The bottomed calf leather prepared in this manner is then seasoned with a mixture of 680 parts of water, parts of the aqueous formaldehyde/glyoxal/urea resin solution used for bottoming, 220 parts of a 20% strength by weight aqueous casein solution, 30 parts of polyglycol ether and 10 parts of a liquid formulation of C.I. Acid Black 63.

This seasoning mixture is applied to the calf leather by three plush appLications with intermediate drying at 65 0 C in each case. The total amount applied is g/m 2 corresponding to 7 g/m 2 of solid, based on casein t and crosslinking agent.

Plating is then carried out twice on a continuous plating machine at 170°C during a contact time of 1 sec.

The calf leather is then smoothed on a hydraulic plating press at 120 0

C.

The seasoned leather surface finished in this manner exhibIts the desired smooth handle, very high gloss, adequate wet rub fastness and good flexibility.

EXAMPLES 3 TO 9 S 30 In the Examples below, the procedure described in EKai rple 1 is followed. As shown in the Table, the 'i closslinking agents, the plating temperature, the contact t'ime and the amount of crosslinking agent used are varied whereas the casein and additives remain unchanged.

i 9 O.Z. 0050/38712

TABLE

Exam- Crosslinking agent (composition in moles) Amounts Plating pLe Melamine Urea Formaldehyde GLyoxal MethanoL used 1 temp.

Bottom/ °C season 3 1 5.5 5.5 35/35 150 4 1 2.5 1 22.5/37.5 160 1 3.5 50/50 170 6 1 2.2 20/40 180 7 1 0.5 3.5 3.5 50/80 185 8 1 0.2 2.8 2.8 40/50 170 9 1 0 2 0.5 22.5/36 185 TABLE (Continued) Exam- Contact Web rub fastness Flexibility Gloss pLe time (IUF 450) (IUP sec 3 2x 2 good good high 4 2x2 satisfactory good very high 2x 2 very good satisfactory silky 6 3x1 good good high 7 3x1 good good high 8 3x1 good good high 9 3x1 adequate good high 1 Based on parts of condensate as solid in bottoming and seasoning mixture per 1,000 parts according to Example 1,

Claims (6)

1. A process for crosslinking casein films in leather finishing, wherein the leather is coated with an aqueous mixture which contains from 0.75 to 7.5% by weight of casein and from 0.7 to 13% by weight of a water-soluble condensate of melamine and/or urea with formaldehyde and/or of a water-soluble condensate obtained by reacting melamine and/or urea with formaldehyde and etherified with a lower alcohol, in an amount of from 50 to 125 g/m 2 the coating is dried at from 20 to 80 0 C, the coating procedure is repeated from 1 to 8 times after each coating has dried, and crosslinking is then carried out by from one to three heat treatments in the absence of an acidic catalyst at from 140 *a to 200 0 C for from 0.1 to 5 sec in each case.

2. A process as claimed in claim 1, wherein a condensate obtained by reacting 1 mole of urea and from 1.6 to 4 moles of formaldehyde is used.

3. A process as claimed in claim 1, wherein a condensate obtained by reacting 1 mole of urea, from 2.0 to moles of formaldehyde and from 0,1 to 1.5 moles of glyoxal is used.

4. A process as claimed in claim 1, wherein a condensate obtained by reacting 1 mole of melamine and from 2 to 6 moles of formaldehyde and/or a condensate obtained by reacting 1 mole of melamin and from 2 to 6 moles of formaldehyde and etherified with from 2.2 to 6 moles of methanol, is used.

I 11 A process as claimed in claim 1, wherein a condensate obtained by reacting 1 mole of melamine, from 0.1 to 0.6 mole of urea and from 2.5 to 3.8 moles of formaldehyde and/or a condensate obtained by reacting 1 mole of melaine, from 0.1 to 0.6 mole of urea and from 2.5 to 3.8 moles of formaldehyde and etherified with from 0.5 to 3.8 moles of methanol, is used.

6. A process as claimed in claim 1, wherein a condensate obtained by reacting 1 mole of melmine, from 1.4 tc, 3.5 moles of formaldehyde and from 0.2 to 1 mole of glyoxal is used. DATED this 9th day of January, 1990 4 o4 BASF AKTIENGESELLSCHAFT WATERMARK PATENT TRADEMARK ATTORNEYS, 2nd Floor, "The Atrium", 290 Burwood Road, Hawthorn, Victoria, 3122, 4 AUSTRALIA. LCG/LPS:EK(1 :26) ~i LCG/lP~iEKils26