EP0127055A1 - Method of finishing leather with a synthetic carboxylated rubber latex - Google Patents

Abstract

This invention relates to a process for finishing leather with a synthetic carboxylated rubber dispersion which may also contain up to 50% by weight of one or more oxides and / or hydroxides of 2 and / or 3-valent metals, the carboxylated Rubber dispersion is produced by the emulsion feed process with a conversion of more than 90% in such a way that it has a carboxylated rubber content of 20 to 60% by weight soluble in dimethylformamide at room temperature.

Description

The present invention relates to a process for finishing leather with a carboxylated rubber dispersion based on butadiene and / or isoprene and styrene and optionally oxides and / or hydroxides of 2 and / or 3-valent metals.

When finishing full-grain, sanded or split leather, its surface is treated with mixtures of binders and pigments in order to superficially close the pores of the leather. Aqueous polyacrylate dispersions, aqueous dispersions of vinyl acetate copolymers or aqueous dispersions of synthetic rubbers, i.e. Copolymers of 1,3-dienes, such as butadiene, isoprene or chloroprene, are used. The suitable pigments can be organic or inorganic in nature; come into question e.g. Iron oxide, titanium dioxide, kaolin, phthalocyanine or azo pigments. In addition, such dressings can contain thickeners, e.g. based on cellulose, such as carboxymethyl cellulose, polyvinyl alcohols, polyacrylic acid or their salts, casein or polymers of N-vinylpyrrolidone.

However, binders of the type mentioned are satisfactory when dressing split leather, e.g. for upper leather, not yet, because they show poor embossability, poor cold flexibility and insufficient dry and wet buckling strength.

Aqueous dispersions of synthetic rubber dispersions containing carboxyl groups have also been used as binders in the finishing of leather. In the process of GB-PS 822 231, a finish with improved hot ironing strength is achieved with the addition of zinc compounds, but with which the gloss, fullness and coverage as well as the grip are deteriorated and when different layers are applied due to insufficient adhesion of the layers to one another there is poor wet kink resistance . The dressings known from GB-PS 921 798 and 900 591 based on rubber dispersions containing polymerized carboxyl groups are also unsatisfactory in terms of their resistance to dry kinking.

Finally, US Pat. No. 3,330,597 discloses a process for finishing leather in which a carboxylated synthetic rubber latex is used which is not completely polymerized and in which the remaining monomers have been removed. The rubber is after the Batch-Wd / HB - Procedure (one-step process) by emulsion polymerization of 1 to 10 parts by weight of α, β-monoethylenically unsaturated aliphatic carboxylic acids and 90 to 99 parts by weight of a mixture of acyclic, conjugated dienes with 4 to 9 carbon atoms and vinylaromatic compounds with 8 to 12 Carbon atoms and / or (meth) acrylonitrile of a (meth) acrylonitrile content of a maximum of 50 parts by weight. The dressing agent contains 0.5 to 50% by weight, based on the rubber, of one or more oxides and / or hydroxides of divalent metals such as zinc oxide or magnesium hydroxide. Preparations of split leather, which are produced by this method, show good closure and coverage, grain scar, toughness, cold flexibility and adhesion as well as dry and wet buckling strength, but their embossability and stack stickiness still leave something to be desired.

• (A) 1 bis 10 Gew.-Teilen α,β-monoethylenisch ungesättigten, 3 bis 5 C-Atome enthaltenden Carbonsäuren und
• (B) 90 bis 99 Gew.-Teilen eines Gemisches aus
  • (a) 10 bis 90 Gew.-Teilen Butadien und/oder Isopren und
  • (b) 10 bis 90 Gew.-Teilen Styrol und/oder Acrylnitril, wobei die Menge an Acrylnitril im Gemisch bis zu 50 Gew.-Teile beträgt,

und Entfernen der restlichen Monomeren hergestellt und der noch 0 bis 50 Gew.%, bezogen auf den carboxylierten Kautschuk eines oder mehrerer Oxide und/oder Hydroxide 2- oder 3-wertiger Metalle zugesetzt worden ist, mit Vorteil zurichten kann, wenn der synthetische carboxylierte Kautschuklatex nach dem Emulsionszulaufverfahren bei einem Umsatz von mehr als 90 % hergestellt ist und einen in Dimethylformamid bei Raumtemperatur löslichen Polymerisatanteil von 20 bis 60 Gew.% aufweist. Wegen der verbesserten Verarbeitbarkeit, insbesondere der verminderten Stapelklebrigkeit kann mit derartigen carboxylierten Kautschuk-Dispersionen auch ohne Zusatz von Oxiden und/oder Hydroxiden 2- und/oder 3-wertiger Metalle gearbeitet werden. Es wird jedoch vorgezogen, derartige Oxide und/oder Hydroxide, insbesondere Zinkoxid, Zinkhydroxid, Magnesiumoxid und Magnesiumhydroxid mitzuverwenden, und diese in an sich üblicher Weise als Paste einzusetzen, die zusätzlich Netzmittel und gegebenenfalls weitere Zusätze enthält. Wegen der verminderten Stapelklebrigkeit können bei dem neuen Verfahren im Vergleich zu dem Verfahren des US-PS 3 330 597 im allgemeinen geringere Mengen an Oxiden und/oder Hydroxiden der genannten Art eingesetzt werden. Die Menge an Oxiden und/oder Hydroxiden 2- und/oder 3-wertiger Metalle liegt häufig im Bereich von 0 bis 50, meistens von 0,5 bis 50, vorzugsweise von 0,5 bis 10 Gew.%, bezogen auf den carboxylierten Kautschuk (fest).It has now been found that leather can be treated with a synthetic carboxylated rubber dispersion obtained by emulsion polymerization of

• (A) 1 to 10 parts by weight of α, β-monoethylenically unsaturated carboxylic acids containing 3 to 5 carbon atoms and
• (B) 90 to 99 parts by weight of a mixture
  • (a) 10 to 90 parts by weight of butadiene and / or isoprene and
  • (b) 10 to 90 parts by weight of styrene and / or acrylonitrile, the amount of acrylonitrile in the mixture being up to 50 parts by weight,

and removal of the remaining monomers and to which 0 to 50% by weight, based on the carboxylated rubber of one or more oxides and / or hydroxides of 2 or 3-valent metals, has been added, can be used to advantage if the synthetic carboxylated rubber latex is produced by the emulsion feed process with a conversion of more than 90% and has a polymer content of 20 to 60% by weight soluble in dimethylformamide at room temperature. Because of the improved processability, in particular the reduced stacking tack, such carboxylated rubber dispersions can also be used without the addition of oxides and / or hydroxides of 2 and / or 3-valent metals. However, it is preferred to use such oxides and / or hydroxides, in particular zinc oxide, zinc hydroxide, magnesium oxide and magnesium hydroxide, and to use them in a conventional manner as a paste which additionally contains wetting agents and optionally further additives. Because of the reduced stickiness of the stack, the new process can be compared to the process of US Pat. No. 3,330,597 in general NEN smaller amounts of oxides and / or hydroxides of the type mentioned are used. The amount of oxides and / or hydroxides of divalent and / or trivalent metals is often in the range from 0 to 50, usually from 0.5 to 50, preferably from 0.5 to 10% by weight, based on the carboxylated rubber (firmly).

The aqueous dispersions of the synthetic carboxylated rubber dispersions used for the dressings generally have a carboxylated rubber concentration of from 30 to 60, in particular from 35 to 55,% by weight. In the preparation by the emulsion feed process, as usual per se, part of the monomer mixture in emulsified form together with a corresponding part of the emulsifier and the polymerization initiator and regulator are introduced in an aqueous receiver, the receiver is heated to the polymerization temperature and, after the polymerization has started, the remaining monomer emulsion, which contains the emulsifier and generally regulator, and separately run an aqueous solution of the polymerization initiator according to consumption. The reaction is then generally allowed to continue, so that the conversion is over 90, usually 95 to 98%. The polymerization temperature is usually selected in the range from 45 to 65 ° C. and generally customary water-soluble radical-forming polymerization initiators, such as sodium and ammonium persulfate or redox catalysts such as tert-butyl perbenzoate / formaldehyde sulfoxylate / iron (II) sulfate and tert.- Butyl hydroperoxide / ascorbic acid / iron (II) sulfate used. Water-soluble persulfates of the type mentioned are preferred. The usual anionic and nonionic emulsifiers are suitable as emulsifiers, anionic emulsifiers being of particular interest. Sodium lauryl sulfate or alkylarylsulfonates with mostly 7 to 12 carbon atoms in the alkyl groups are preferably used as emulsifiers.

The aqueous carboxylated rubber dispersions contain 1 to 10, preferably 1 to 5 parts by weight of (, .beta.-monoethylenically unsaturated 3 to 5 carbon atoms containing carboxylic acids, such as acrylic acid, methacrylic acid, maleic acid and / or itaconic acid, polymerized, acrylic acid being preferred The polymers contain butadiene or isoprene or mixtures of these in copolymerized form as monomers (a), butadiene polymers being preferred. The proportion of butadiene and / or isoprene is preferably between 40 and 60 parts by weight. The polymers should contain at least 10 parts Styrene may also contain up to 50 parts by weight of acrylonitrile in copolymerized form. The total amount of styrene and acrylonitrile should not exceed 90 parts by weight. Of the monomers (b), up to 25 parts by weight can be added by others copolymerizable monomers must be replaced, but the proportion of water-soluble mono together do not exceed 10% by weight of the polymer. Examples of additional water-soluble monomers are acrylamide, methacrylamide, N-methylol-acrylamide and -methacrylamide, vinylsulfonic acid or its water-soluble salts and allylsulfonic acid and its water-soluble salts. Other water-insoluble monomers are, for example, acrylic and methacrylic esters, such as methyl acrylate and methacrylate, ethyl acrylate, n-butyl acrylate and methacrylate, tert-butyl acrylate, isobutyl acrylate and methacrylate and 2-ethylhexyl acrylate and methacrylate, vinyl acetate and vinyl acetate, such as vinyl acetate and also vinyl halides, such as vinyl chloride and vinylidene chloride, and also hydroxyalkyl acrylates and methacrylates, such as 2-hydroxyethyl acrylate and methacrylate, 1,4-butanediol monoacrylate and 3-hydroxypropyl acrylate.

In the preparation of the aqueous carboxylated rubber dispersions, regulators are usually used in amounts which are conventional per se and which are 0.3 to 1% by weight, based on the amount of the monomers. As such, e.g. Tetrabromethane, dialkyldixanthate and preferably alkyl mercaptans, such as especially dodecyl mercaptan, in question. By suitably coordinating the polymerization temperature, the composition of the monomers, the type and amount of the emulsifier and the type and amount of the regulator, the polymerization can be controlled in a conventional manner such that the proportion of the carboxylated rubber obtained (solid) which is soluble in dimethylformamide at room temperature is 20 to 60, preferably 25 to 50% by weight of the polymer. Although no chain terminators are generally used in the production of the rubber dispersions, the new process gives leather formulations with very high buckling strengths in the dry and wet state which, despite improved embossability and reduced stacking tackiness, do not lag behind the buckling strengths of the process according to the US -PS 3 330 597 finished leather stand back.

In the production of mixtures for leather finishing, customary wetting agents, usually in amounts of 20 to 60% of their weight, can be added to the oxides or hydroxides of the divalent or trivalent metals, nonionic wetting agents being preferred. In addition, organic solvents, for example methyl, ethyl, n-propyl and iso-propyl alcohol or ethyl glycol monoethyl ether or ketones, such as acetone and methyl ethyl ketone, natural or synthetic oils, such as claw oil, peanut oil or Turkish red oil, in free and / or emulsified form and also Defoamers can be added. Mixtures of this type are preferably used in the form of pastes in the process according to the invention. In addition, commercially available opaque color pastes can also be used when dressing leather. With the new process, full-grain, sanded and in particular split leather or leather fiber materials can be finished. The finishing agents can be applied to the leather in a manner known per se using the aqueous synthetic rubber dispersions containing carboxyl groups, pigment preparations of the type mentioned above and other additives. Casting, knife coating, brushing, spraying, brushing or plush processes can be used for this. The amount of finishing agent depends on the type and pretreatment of the leather and can be easily determined by preliminary tests.

Priming is usually carried out in one or more orders and good hot-melted intermediate ironing or scar embossing results in a good fusion and thus a good finish of the primer.

In the new dressing process, the viscosity of the application can be regulated in a conventional manner by means of thickeners, an increase in viscosity leading to a reduction in the penetration capacity and thereby to a higher filling effect, which is of particular interest when dressing split leather and leather fiber materials.

As a final finish on leather prepared according to the invention, e.g. Conventional polyurethane varnishes, collodion varnishes or collodion varnish emulsions as well as aqueous polyacrylate or polyurethane dispersions, which can be applied by spraying and casting processes.

The leathers prepared according to the new process dry very quickly and show excellent dry and wet kink resistance, good cold flexibility and embossability as well as very good rub-through resistance and adhesion from layer to layer and very good fullness. They also show greatly reduced stack gluing in comparison to the dressings according to US Pat. No. 3,330,597. This is surprising because of the virtually complete polymerization in the preparation of the binder dispersion with regard to the disclosure of US Pat. Nos. 3,330,597 and GB Pat. Nos. 921,798 and 900,591.

• Aus einer 30 Xigen wäßrigen Dispersion des carboxylierten Kautschuks wird ein Film gegossen und dieser nach dem Trocknen im Klimaraum bei 25°C und 70 % relativer Luftfeuchtigkeit 48 Stunden gelagert. Ein 1 cm² großes Stück des erhaltenen Films wird 24 Stunden in Dimethylformamid (über einem 4 A-Molekularsieb getrocknet) aufbewahrt, das Dimethylformaldehyd über einen Quarzfilter abgegossen und der Rückstand im Trockenschrank bei 120°C 5 Stunden getrocknet. Aus der Masse des in einem Exsikkator abgekühlten Dimethylformamid-Rnckstands wird der gelöste Anteil berechnet.

The soluble proportions of the carboxylated rubber indicated below are determined as follows:

• A film is cast from a 30% aqueous dispersion of the carboxylated rubber and, after drying in a climatic room, it is stored for 48 hours at 25 ° C. and 70% relative atmospheric humidity. A 1 cm ² piece of the film obtained is stored for 24 hours in dimethylformamide (dried over a 4 A molecular sieve), the dimethylformaldehyde is poured off through a quartz filter and the residue is added to the drying cabinet Dried at 120 ° C for 5 hours. The dissolved fraction is calculated from the mass of the dimethylformamide residue cooled in a desiccator.

The parts and percentages given in the following examples relate to the weight, unless stated otherwise. The parts by volume given in relation to the parts by weight are like the liter to the kilogram.

I. Manufacture of the aqueous dispersions of the carboxylated rubbers Dispersion 1

In an autoclave equipped with a stirrer of 160 parts by volume, 7.5 parts of water, 0.09 parts of sodium peroxodisulfate and 7.5 parts of an emulsion, prepared from 30.9 parts of water, 15 parts of butadiene, 8.1 parts of acrylonitrile, 5.1 Parts of styrene, 0.9 parts of acrylic acid, 0.18 parts of tert-dodecyl mercaptan, 0.3 parts of sodium lauryl sulfate, 0.9 parts of methacrylamide and 0.3 parts of the sodium salt of dodecylbenzenesulfonic acid. The mixture is heated to 55 ° C. and polymerized for 10 minutes. Then you add the rest of the emulsion evenly within 3 hours. Polymerization is then carried out at 55 ° C. until the solids content is 42% (approximately 94% conversion of the monomers). The dispersion 1 obtained is freed of residual monomers while passing nitrogen through. The polymer contained therein has a soluble content of 23%.

Dispersion 2

5 parts of water, 0.01 part of sodium lauryl sulfate, 0.04 part of sodium pyrophosphate, 0.005 part of sodium salt of ethylenediaminetetraacetic acid, 0.0025 part of sodium formaldehyde sulfoxylate dihydrate and 2 parts of an emulsion consisting of 5.4 parts are placed in an autoclave equipped with a stirrer and having 50 parts by volume Parts of butadiene, 1 part of acrylonitrile, 3 parts of styrene, 0.3 parts of acrylic acid, 0.3 parts of methacrylamide, 0.06 parts of tert-dodecyl mercaptan, 0.1 part of sodium lauryl sulfate and 8.2 parts of water and 0.5 part by volume of one Solution of 0.08 parts of sodium peroxodisulfate in 2 parts of water presented. The mixture is heated to 60 ° C. and polymerized for 30 minutes. The remaining monomer emulsion and the remaining peroxodisulfate solution are then fed in uniformly within 2 hours. The polymerization is continued at 60 ° C. until the solids content is about 38% (conversion about 95%, based on the monomers). After the remaining monomers have been driven off from the dispersion 2 obtained, its solids content is 40%. The soluble fraction of the polymer is 38%.

Dispersion 3

In an autoclave equipped with a stirrer of 160 parts by volume, 12 parts of water, 0.075 parts of tert-butyl hydroperoxide (80% strength), 0.03 parts of sodium pyrophosphate and 15 parts by volume of an emulsion of 31 parts of water, 15 parts of isoprene and 8.1 parts of acrylonitrile , 5.1 parts of styrene, 0.9 parts of methacrylamide, 0.9 parts of acrylic acid, 0.18 parts of tert-dodecyl mercaptan, 0.45 parts of sodium lauryl sulfate and 0.45 parts of sodium dodecylbenzenesulfonate and heated to 60 ° C. Then 1 part of a solution of 0.015 part of sodium salt of ethylenediaminetetraacetic acid, 0.0075 part of iron (II) sulfate heptahydrate and 0.03 part of sodium formaldehyde sulfoxylate dihydrate in 3 parts of water is added and the mixture is polymerized for 1/4 hour. The remainder of the monomer emulsion and the reducing agent solution are then added within 4 hours and postpolymerization is carried out at 60 ° C. up to a solids content of 38.5% (97% conversion). After the remaining monomers have been driven off from the dispersion 3 obtained under reduced pressure, its solids content is 39.5%. The soluble proportion of the carboxylated polymer is 52%.

Comparative dispersion (a)

In an autoclave equipped with a stirrer of 50 parts by volume, 1 part of water, 0.03 parts of potassium peroxodisulfate, 2.5 parts by volume of an emulsion of 10.4 parts of water, 5 parts of butadiene, 2.7 parts of acrylonitrile, 1.7 parts of styrene, 0 , 3 parts of acrylic acid, 0.3 part of methacrylamide, 0.3 part of sodium lauryl sulfate, 0.3 part of sodium salt of dodecylbenzenesulfonic acid, 0.092 part of sodium sulfate and 0.03 part of tert-dodecyl mercaptan and 0.2 part by volume of a solution of 0.0002 part of sodium formaldehyde sulfoxylate , 0.0008 parts of iron nitrate and 0.0006 parts of sodium salt of ethylenediaminetetraacetic acid in 2 parts of water and the mixture was heated to 70.degree. After 1/4 hour of polymerization, the rest of the monomer emulsion and the solution of the reducing agent are added within 4 hours. Polymerization is then carried out at 70 ° C. to a solids content of approximately 42% (approximately 95% conversion). The comparative dispersion (a) obtained is freed from residual monomers. The carboxylated polymer contained therein has a soluble content of 17%.

Comparative dispersion (b)

In an autoclave equipped with a stirrer of 160 parts by volume, 7.5 parts of water, 0.09 parts of sodium peroxodisulfate and 2.5 parts by volume of a mixture consisting of 31.3 parts of water, 15 parts of butadiene, 8.1 parts of acrylonitrile, 5.1 Parts styrene, 0.9 parts acrylic acid, 0.9 parts methacrylamide, 0.45 parts sodium lauryl sulfate, 0.45 parts sodium salt of dodecylbenzenesulfonic acid and 0.45 parts tert-dodecylmer submitted to captan. The mixture is heated to 55 ° C. and polymerized for 10 minutes. The rest of the monomer emulsion is then fed in uniformly within 2 hours. The mixture is then polymerized at 55 ° C. to a solids content of about 42% (conversion about 94%). The comparative dispersion (b) obtained is freed of residual monomers by passing nitrogen through it. The carboxylated polymer contained therein has a soluble fraction of 73%.

Comparative dispersion (c)

18 parts of water, 5 parts of butadiene, 2.7 parts of acrylonitrile, 1.7 parts of styrene, 0.3 parts of methacrylic acid, 0.3 parts of methacrylamide, 0.05 parts of tert. Dodecyl mercaptan, 0.2 part of sodium sulfonate of a mixture of long-chain paraffin hydrocarbons with an average chain length of 15 carbon atoms as emulsifier, and 0.0025 part of sodium formaldehyde sulfoxylate dihydrate and 0.005 part of tert-butyl hydroperoxide and heated to 35 ° C. A reducing agent solution of 0.0025 part of sodium formaldehyde sulfoxylate dihydrate and 0.1 part of ethoxylated octylphenol (25 ethylene oxide residues) in 0.9 part of water is then added within 2 hours and the mixture is polymerized at 35 ° C. to a solids content of 30.4% (turnover about 86 Z) after. The comparative dispersion (c) obtained is freed from residual monomers under reduced pressure. The carboxylated polymer dissolves completely in dimethylformamide.

II. Leather finishing Examples 1 to 3 and Comparative Examples (a) to (c)

For the preparation of split leather, 100 parts of a commercially available pigment preparation each with 600 parts of the above-described dispersions 1, 2, 3, (a), (b) and (c), 200 parts of water and 40 parts of a zinc oxide paste each in column 7, below, of the composition indicated in US Pat. No. 3,330,597. The mixture is applied to split leather with the plush board in an amount of 12 g / m ² , the application is ironed at 80 ° C. and then sprayed until completely covered with another mixture. After drying, mint at 80 ° C and 200 bar with a 2 sec delay. Finally, a usual finish based on a nitro emulsion varnish is applied.

To assess the stacking, the leathers are dried after the last spray application, with the coated side on top of one another and stored under a load of 5 kg / cm ² at 40 ° C. for 18 hours.

• Note 1 = Abschälen der Filmschichten beim Auseinanderziehen der Leder
• Note 2 = starkes Kleben, starke Beschädigung der Oberflächen
• Note 3 = Kleben, leichte Beschädigung der Oberflächen
• Note 4 leichtes Kleben ohne Beschädigung der Oberflächen
• Note 5 = kein Kleben, keine Beschädigung der 0berflächen.

The behavior to be observed is assessed as follows:

• Note 1 = peeling off the film layers when pulling the leather apart
• Grade 2 = strong sticking, severe damage to the surfaces
• Grade 3 = gluing, slight damage to the surfaces
• Note 4 light gluing without damaging the surfaces
• Grade 5 = no sticking, no damage to the surfaces.

The assessment of the wet kink resistance and dry kink resistance of the finished leather is carried out in the usual way using a Bally flexometer.

The values observed for the individual dressings are compiled in Table 1 for the examples according to the invention and in Table 2 below for the comparative examples.

If the dispersions 1, 2 and 3 are used according to the dressing method described in Examples 1 to 3, but in each case without the zinc oxide dispersion being used, dressings with split leather that have practically the same physical fastness properties are obtained if the procedure is otherwise the same little loss in processing properties, ie a drop of 1 to 2 notes when stacking.

Claims (3)

1. A method of finishing leather with a synthetic carboxylated rubber dispersion by emulsion polymerization of (A) 1 to 10 parts by weight of one or more β-monoethylenically unsaturated carboxylic acids containing 3 to 5 carbon atoms and (B) 90 to 99 parts by weight of a mixture (a) 10 to 90 parts by weight of butadiene and / or isoprene and (b) 10 to 90 parts by weight of styrene and / or acrylonitrile, the amount of acrylonitrile in the mixture being up to 50 parts by weight, and removing the remaining monomers and 0 to 50% by weight, based on the carboxylated rubber, of one or more oxides and / or hydroxides of 2 and / or 3-valent metals has been added, characterized in that the carboxylated rubber - Dispersion is prepared by the emulsion feed process with a conversion of more than 90% in such a way that it has a carboxylated rubber content of 20 to 60% by weight soluble in dimethylformamide at room temperature. 2. The method according to claim 1, characterized in that in the synthetic rubber used up to 25 parts by weight of the copolymerized water-insoluble monomers are replaced by other copolymerizable monomers, the proportion of water-soluble additional monomers in total not more than 10% by weight, based on the carboxylated rubber. 3. The method according to claim 1 or 2, characterized in that the treatment of the leather is carried out with a rubber dispersion and a paste which consists of a mixture of metal oxides and / or hydroxides, wetting agents and optionally other additives.