AU604978B2

AU604978B2 - Thickeners for physically drying paints and coating materials and preparation of the thickeners

Info

Publication number: AU604978B2
Application number: AU23325/88A
Authority: AU
Inventors: Hans-Joachim Krause; Gernot Leib; Enrique Schweigger; Eckehardt Wistuba
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1987-10-02
Filing date: 1988-09-30
Publication date: 1991-01-03
Anticipated expiration: 2008-09-30
Also published as: AU2332588A; JPH01110514A; DE3862563D1; DE3733340A1; EP0313849B1; EP0313849A1; ATE62911T1

Abstract

The thickening agent (thickener) for physically drying paints and coatings which contain binders which are soluble in white spirit is a copolymer which forms a gel in white spirit and contains (a) from 7 to 15% by weight of acrylates and/or methacrylates of monoalkanols having 8 carbon atoms, (b) from 0.05 to 0.2% by weight of a crosslinking agent, (c) from 25 to 35% by weight of styrene and (d) from 49.8 to 67.95% by weight of at least one acrylate and/or methacrylate of monoalkanols having 4 carbon atoms, in copolymerised form, with the proviso that the total of the % by weight for (a) to (d) is always 100. The thickener is prepared by emulsion polymerisation of the parent monomers in the presence of alkylsulphonates as emulsifier.

Description

i i j r COMMONWEALTH OF AUSTRAL PATENTS ACT 1952-69 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: bo-plote Specification Lodged: c r t r e Accepted: Published: Reluted Art: This document contains the amendments made under Section 49 and is correct for printing.

Name of Applicant: BASF AKTIENGESELLSCHAFT D-6700 Ludwigshafen, Federal Republic of Germany.

Address of Applicant r r*Actual Inventor: Address for Service C t Address for Service: HANS-JOACHIM KRAUSE, GERNOT LEIB, ENRIQUE SCHWEIGGER and ECKEHARDT WISTUBA.

EDWD. WATERS SONS, 50 QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.

1 1 Complete Specification for the invention entitled: THICKENERS FOR PHYSICALLY DRYING PAINTS AND COATING MATERIALS AND PREPARATION OF THE THICKENERS.

us The following statement is a full description of this invention, including the best method of performing it known to 1.

f. W la- O.Z. 0050/39488 Thickeners for physically drying paints and coating materials and preparation of the thickeners European Patent 42,506 discloses gasoline-soluble copolymers of styrene, tert-butyl acrylate, isobutyl methacrylate and (meth)acryLates of alcohols of 10 to carbon atoms. The copolymers have a K value of from to 60 and are used as binders in gasoline-containing masonry paints or renders.

Thickeners frequently have to be incorporated into such solvent-containing, physically drying masonry paints or coating materials in order, for example, to permit the production of thicker coatings in a single o* operation and in order to prevent extensive penetration of the binder into highly acidic surfaces, for example 15 mineral building materials. However, the film-forming properties of the coatings, such as gloss, adhesion and weather resistance, should not be adversely affected by the addition of a thickener to the coating materials.

European Patent 22,982 discloses a thickener for physically drying paints and coating materials based on bint ders soluble in mineral spirit. The thickener is a 1 t C copolymer which forms a gel in mineral spirit and t"i contains, as copolymerized units, from 5 to 50% by weight of acrylates and/or methacrylates of monoalkanols of 8 to 18 carbon atoms, from 0.01 to 2% by weight of one or more polyolefinically unsaturated compounds which are copolymer- 6 izable with for example diacrylates of dihydric alcohols of 2 to 6 carbon atoms, from 0 to 60% by weight of styrene and/or vinyltoluene, from 0 to 80% by weight of one or more (meth)acrylates of monoalkanols of 4 to 7 carbon atoms and from 0 to 30% by weight of further copolymerizable olefinically unsaturated organic compounds not stated under to with the proviso that the sum of the percentages stated v. r' I- i C. t_ -i r. 2 O.Z. 0050/39488 under to is 100. The known thickeners substantially meet the requirements set but have the disadvantage that, because of the hydrophobic properties, the

C

8

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18 -alkyl (meth)acrylates are incorporated nonuniformly into the resulting polymer during the emulsion polymerization. This may lead to coagulation and to fluctuating thickening action of the copolymers. Another disadvantage is that paints containing the thickeners settle out on prolonged storage at -20 0 C. This precipitate is difficult to stir up.

It is an object of the present invention to provide improved thickeners which can be prepared in a readily reproducible manner in industry, give stable paints even o. at low temperatures form two phases in nonaromatic gaso- 15 line/alkoxypropan-1-ol mixtures at -15 0 C and exhibit 4 thickening which is highly independent of the solvent.

We have found that this object is achieved, S according to the invention, by thickeners based on copolymers which contain, as copolymerized units, (meth)- ,t 20 acrylates, styrene and copolymerizable monomers possesst ing two or more ethylenically unsaturated double bonds, S* for physically drying paints and coating materials, if ,tt, the thickener is a copolymer which formsAin mineral spirit and contains, as copolymerized units, from 7 to 15% by weight of acrylates and/or methsti acrylates of monoalkanols of 8 carbon atoms, t from 0.05 to 0.2% by weight of monomers which are copolymerizable with (meth)acrylates and styrene and possess two or more ethylenically unsaturated double bonds, from 25 to 35% by weight of styrene and from 49.8 to 67.95% by weight of one or more acrylates and/or methacrylates of monoalkanols of 4 carbon atoms, with the proviso that the sum of the percentages by weight to is always 100.

The thickeners are prepared by a method in which 3 O.Z. 0050/39488 a monomer mixture consisting of from 7 to 15% by weight of acryLates and/or methacrylates of monoaLkanols of 8 carbon atoms, from 0.05 to 0.2% by weight of monomers which are copolymerizable with (meth)acryLates and styrene and possess two or more ethylenically unsaturated double bonds, from 25 to 35% by weight of styrene and from 49.8 to 67.95% by weight of one or more acrylates ano/or methacrylates of monoalkanoLs of 4 carbon atoms, the sum of the percentages by weight always being 100, is polymerized in aqueous emulsion which contains from 10 to S 55% by weight of the monomer mixture in emulsified form, 15 and the copolymer is then isolated from the polymer dispersion.

Binders for physically drying paints and coating

C

materials are disclosed in, for example, the abovementioned European Patent 42,506. Particularly suitable binders are polymers based on acrylates and methacrylates and copolymers of vinylaromatics and acrylates and/or methacrylates. An essential feature of these binders is that they are soluble in mineral spirit and have a K value (determined according to Fikentscher) of from 15 to tC On the other hand, the novel thickeners form, in esters, eg. ethyl acetate, and in very highly nonpolar solvents, such as mineral spirit, in from 10 to 30% concentration, homogeneous, highly viscous to solid gels.

These gels are very useful for thickening and regulating Sthe flow behavior of coating materials based on mineral spirit-soluble poly(meth)acrylates and copolymers of vinylaromatics and (meth)acrylates. It is also possible in some cases for these thickeners also to be used as the sole polymer binder. Even in nonpolar hydrocarbon mixtures, for example in mineral spirit having an aromatics content of 18% or Lower, the novel thickeners develop a 7

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4 O.Z. 0050/39488 powerful gel-forming action. They are therefore particularly suitable for use in coating materials which are prepared using environmentally compatible solvents or solvent mixtures having little odor. The thickeners according to the invention have good weather resistance and resistance to yellowing. They swell particularly rapidly in solvents and, in a solvent mixture, are therefore ready-to-use after stirring for only a few minutes.

The thickeners give very soft and speck-free gels. This property has a particularly advantageous effect on the quality and appearance of the coating materials prepared using the said gels. For example, coating.materials havt ing excellent leveling properties and coatings possessing high gloss can be produced.

15 The novel thickeners contain, as component acrylates and/or methacrylates of monoalkanols of 8 carlot bon atoms as copolymerized units. This group of monomers

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imparts lipophilic properties to the thickeners. They are, specifically, ethylhexyl acrylate, ethylhexyl meth- ,V ,20 acrylate, n-octyl acrylate and isooctyl acrylate, and the .corresponding esters of methacrylic acid. The lipophilic (meth)acrylates are copolymerized in the novel thickeners in an amount of from 7 to 15% by weight.

Examples of suitable monomers of group which are copolymerizable with (meth)acrylates and styrene and possess two or more ethylenically unsaturated double bonds, are acrylates and methacrylates of polyhydric, in particularly dihydric, alcohols of 2 to 6 carbon atoms, eg. ethyLene glycol diacrylate, butanediol diacrylate or 30 hexanediol diacrylate, and diacrylates of polyethylene glycols which contain from 2 to 34, preferably from 2 to 12, ethylene oxide units, such as diethylene glynol diacrylate or tetraethylene glycol diacrylate, or diacrylates of a polyethylene glycol having a molecular weight of 1,500.

It is of course also possible to use the corresponding dimethyacrylates as monomers of group Other suitable crosslinking agents are vinyl esters of di ft fi t 4 t t C, t r iZ C "Cl 4* 5 O.Z. 0050/39488 ethyLenicaLy unsaturated C 3

-C

6 -carboxyLic acids, eg. vinyl acryLate, vinyl methacrylate or vinyL itaconate. Other suitable monomers of group are vinyl esters of saturated carboxylic acids containing two or more carboxy groups and di- and polyvinyl ethers of dihydric or polyhydric alcohols, eg. divinyl adipate, butanedioL divinyL ether and trimethyLoipropane trivinyl ether. ALLyL esters of ethylenically unsaturated carboxylic acids, eg.

allyl acrylate and altyL methacrylate, alLyl ethers of polyhydric alcohols, eg. pentaerythritol triallyl ether, triallyLsucrose and pentaaLlylsucrose, are also useful.

Other suitable monomers of this group are,.for example, methylenebisacrylamide, methyLenebismethacryLamide, divinyLethyleneurea, divinyLpropyleneurea, divinylbenzene, 15 divinyldioxane, tetraaLlylsiane and tetravinylsiLane.

Butanediol diacrylate and hexanediol diacrylate are preferably used. The monomers of group are copolymerized in an amount of from 0.05 to 0.2% by weight in the copoLymer.

Styrene is used as a monomer of component and is copoLymerized in amounts of from 25 to 35% by weight in the copolymer.

Suitable monomers are esters of acrylic acid or methacrylic acid with monohydric alcohols of 4 carbon 25 atoms, eg. n-butyL acrylate, isobutyl acrylate, tertbutyl acrylate, n-butyl methacrylate, isobutyl methacrylate and tert-butyl methacrylate. It is of course also possible to use mixtures of the stated monomers. The monomers of group are present in the thickeners in amounts of from 49.8 to 67.95% by weight.

The thickeners are prepared by the method of emulsion polymerization, in which a mixture of the monomers of groups to is copolymerized in aqueou emulsion in the presence of a polymerization initiator, at from 65 to 85 0 c. The emulsion polymerization method makes it possible to prepare copolymers having reproducible thickening properties. Another advantage is that ?c: i

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i 1 ni 4 *4W I 44 tr 4i t .1 tZ .11C I I' I I C -II I(

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4144 6 0.Z. 0050/39488 coagulate-free dispersions which form virtually no deposits on the polymerization apparatuses are obtained on a large industrial scale. A procedure in which from to 5% by weight, based on the total polymer dispersion formed, of a 10-55% strength by weight polymer dispersion prepared separately from the monomers to (d) are initially taken as a seed latex has proven a particularly advantageous preparation process. The polymer concentration in the seed latex is preferably from 25 to by weight. About 2-5% by weight of the monomer mixture to be polymerized are then added to the polymer dispersion initially taken as a seed latex, if necessary after the addition of water and emulsifiers. The initially taken mixture is then heated to 65-85 0 C under a nitro- 15 gen atmosphere and polymerization is initiated by adding an initiator. The monomers to and from 0.25 to 2.5% by weight, based on the monomer mixture, of a polymerization initiator are then added continuously or a little at a time to the initially taken mixture and poly- 20 merized therein in the stated temperature range. The polymerization initiators used are compounds which form free radicals. Water-soluble polymerization initiators, in particular sodium peroxydisulfate, potassium peroxydisulfate or ammonium peroxydisulfate, or mixtures of 25 these are preferably used. From 0.4 to 1.5% by weight, based on the monomer mixture to be polymerized, of an initiator are preferably employed.

As is usual in emulsion polymerizations, emulsifiers are used. The sodium salts of C 12

-C

18 -alkylsulfonates have proven particularly useful here. The emulpre bCrwiy Ymore sifiers are used in amounts of~from 0.15 to 3,Apreferably from 0.6 to 2.4, by weight, based on monomers. The emulsifiers can either be added to the initially taken mixture, added to the reaction mixture as a separate feed or introduced into the polymerization apparatus together with the initiator. The polymerization initiators are preferably introduced into the initially taken i 1( rift. 1L ~I____ILLiTr.- i I;r; i 7 O.Z. 0050/39488 mixture in the polymerization apparatus in the form of a 15-28% strength aqueous solution in amounts of from 0.4 to 0.8% by weight, based on the weight of the total ready-prepared polymer dispersion, at from 70 to 75 0

C.

From 20 to 40% by weight of the monomer mixture, from 0.7 to 2.8% by weight of a 40% strength emulsifier solution of the sodium salt of a C 12

-C

18 -paraffinsulfonate and from 0.4 to 0.8% by weight of the 15-28% strength initiator solution, the percentages being based on the weight of the total ready-prepared polymer dispersion, are added uniformly in the course of from 3 to 8 hours, the two last-mentioned solutions being diluted beforehand with o *o water to 3-10% by weight. After the monomer addition is complete and the total amount of initiator has been t15 metered in, the reaction mixture can be further polymerized for up to 2.5 hours at from 70 to 800C.

The copolymers are then isolated from the disper- Ssion. This can be done using the methods stated in European Patent 22,982. However, the copolymers are prefer- ,'a20 ably precipitated from the polymer dispersion at from t ci Sst to 65 C by adding from 0.5 to 1.5% by weight, based on the copolymers, of aluminum sulfate. Precipitation of the dispersion is preferably effected in dilute form while stirring at from 50 to 60 C, the solids content of the polymers present in the dispersion being from 5 to E preferably from 7.5 to 12.5, by weight.

STo remove the aluminum ions, 5% strength aqueous sodium hydroxide solution is added to the precipitated polymer while stirring at from 50 to 70UC, preferably 60 0 C, so that the pH is from 7 to 8.5. In order to achieve particularly optimum particle size of the pre- i cipitated polymer, the polymer suspension is aftertreated for from 0.2 to 2 hours at from 80 to 95 0 C. This aftertreatient is preferably carried out at 90+2oC.

Heating of the precipitated polymer suspension can be carried out by passing steam into the suspension or by heating the reactor jacket. This aftertreatment gives a -i I ii r 1~ 8 O.Z. 0050/39488 particularly advantageous copolymer particle size, which is advantageous for the subsequent filtration and drying and for the swelling properties of the copolymer. The particle size of the polymer is, for example, as follows: 1,000 pm: 800-1,000 pm: 630-800 pm: 6.9% and 100 um: 74.9%.

The precipitated polymer is then filtered off, washed with water and dried at from 30 to 60 0 C, preferably from 45 to 55 0 C. Drying is preferably carried out in a through-circulation drier, a fluidized-bed drier or a flash drier. The novel thickeners can also be used as sole binders in paints and coating materials. However, •i t they are preferably used in combination with known polymer binders having a similar monomer composition, in S 15 paints and coating materials. Examples of suitable polymer binders which may be combined with the novel thickeners are copolymers based on (meth)acrylates or styrene and (meth)acrylates, whic are soluble in mineral spirit (according to DIN 51,632) and in aromatics, such as toluene and xylene, and esters. The novel thickeners can be used, preferably in combination with further compatible binders, to prepare swollen gels for a variety of coating materials and adhesives, by dissolution or swelling in a conventional coating solvent, eg. a gasoline hydrocarbon, an aromatic hydrocarbon, an ester or a ketone. For the preparation of such coating materials, pigments, fillers, metallic or mineral materials and further coating raw materials, such as plasticizers, can be incorporated in a known manner into the solution or into the gels. The desired flow behavior of the coating materials can readily be obtained in a simple manner by changing the proportion of the novel thickeners in the total binder of the coating, as well as by the selection and amount of the pigments and fillers. For example, it is possible to prepare coating materials which have plastic, pseudoplastic, thixotropic or rheopectic flow behavior to different extents or combinations of these phenomena.

.ri- 9 O.Z. 0050/39438 The pigment volume concentrations of the coating materials are from 15 to 75%. The binder content of the coating materials is from 5 to 45% by weight. The thickeners are used in an amount of from 1 to 25% by weight in the coating materials. The novel thickeners therefore permit the preparation of coating materials which contain mineral spirit and possess excellent performance characteristics, for example good sprayability, rollability and brushability. The coating materials which contain the novel thickeners show no settling out of pigment, no, or reduced, running on vertical surfaces and little or no migration of the binder into absorbent surt tt faces, have good Leveling properties and give highly c t t glossy films in top coats. The thickeners according to the invention are preferably used for the preparation of solvent-containing masonry paints which have particularly good leveling properties and hence permit the formation of uniform film thicknesses.

In the Examples which follow, parts and percentages are by weight, unless stated otherwise. The K values of the soluble polymers were measured according to H. Fikentscher in tetrahydrofuran at 25 0 C and at a polymer concentration of 1% by weight (cf. Cellulose Chemie, 13 (1932), 48-64 and 71-74; K k.10 3 The LT value is determined by first distributing 10 g of a 50% strength dispersion in 490 g of water. 10 g of this are taken and made up to 1 L with water. The light transmittance is determined in a cell having a path length of 25 mm, in comparison with water (100%).

EXAMPLE 1 Preparation of a seed latex 730 g of water, 1.16 g of sodium C 12

-C

18 -alkylsulfonate and 38.8 g of a monomer mixture which consists of 150 g of isobutyl methacrylate, 110 g of styrene, 81.1 g of tert-butyl acrylate, 46.5 g of ethylhexyl acrylate and 0.5 g of hexanediol diacrylate are initially taken in a stirred kettle equipped with a thermometer, a

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7RLiCI i- -i;ilil i _Lill i~ 10 O.Z. 0050/39488 reflux condenser and feed vessels as well as apparatuses for working under nitrogen. The initially taken mixture is stirred and heated to 72 0 C under a nitrogen atmosphere. As soon as 72 0 C is reached, an aqueous solution of 2.3 g of ammonium persulfate in 60 g of water is added and the mixture is heated to 75 0 C. At this temperature, a start is then made with simultaneously metering in the remainder of the monomer mixture and a solution of g of sodium C 12

-C

18 -alkyLsulfonate and 2.3 g of ammonium persulfate in 114.7 g of water uniformly in the course of 5 hours. After the addition of the monomers and initiator, the reaction mixture is polymerized for a further 2.5 hours at 75 0 C. The seed latex thus obtained has the following characteristics: 15 Solids content: 30.4% 4 ft 4f ft t f I I%

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I If t t I IC I IC i I' i 1.7 LT value: 81% Surface tension: 43 dyn/cm Coagulate content: Preparation of the polymer dispersion The procedure is the same as that for the preparation of the seed latex according to with the only exception that 10.6 g of the 30.4% strength polymer dispersion, whose preparation was described under 25 are also initially taken in the stirred kettle. In this case, a polymer dispersion having a solids content of 31.2%, a pH of 1.6, a surface tension of 32 dyn/cm and an LT value of 38% is obtained.

Precipitation of the polymer dispersion 1,300 g of water are initially taken in a heatable kettle equipped with a stirrer. 83 g of a 2% strength aqueous aluminum sulfate solution are dissolved therein, while stirring. The initially taken solution is then heated to 55C, and 665 g of the polymer dispersion according to are added in the course of 1 hour at this temperature. During.this procedure, the polymer is precipitated. If the mixture is not stirred, the .1 a i 1 i 11 O.Z. 0050/39488 polymer settles out on the bottom of the kettle.

The stirred mixture is heated to 60 0 C and 35 g of 5% strength aqueous sodium hydroxide solution are added. The pH of the reaction mixture is then 8.1. After 15 minutes, the reaction mixture is heated to 90 0

C

and stirred at this temperature for 15 minutes. It is then cooled, and the copolymer is filtered off. The filter cake is washed with three times 300 ml of water and then dried at 50 0 C in a through-circulation drier for 24 hours. The thickener thus obtained has the foil .ing characteristics: Appearance: White powder c Particle size: 75% smaller than 100 pm Swellable in: Mineral spirit, butyl acetate Viscosity in mineral spirit 15% strength: 450 mPa.s 20% strength: 1,060 mPa.s 25% strength: 1,340 mPa.s 30% strength: 3,540 mPa.s EXAMPLE 2 Preparation of a gasoline-soluble masonry paint 63 g of gasoline-soluble copolymer of styrene, tert-butyl acrylate, isobutyl methacrylate and lauryl acrylate (obtained according to Example 1 of European Patent 42,506) are dissolved in 117 g of a mixture of mineral spirit having a boiling range of from 155 to 1850C t and an aromatic hydrocarbon containing about 70% of trimethylbenzenes and having a boiling range of from 160 to 182 0 C, in a weight ratio of 2 1. 179 g of a strength solution of the thickener which is prepared according to Example 1 and is dissolved in mineral spirit having a boiling range of from 155 to 185 0 C and an aromatic hydrocarbon containing about 70% of trimethylbenzenes and having a boiling range of 160 to 182 0 C, in a weight ratio of 2 1, are then added to this solution.

In addition, 72 g of chloroparaffin, 179 g of titanium dioxide (rutile), 287 g of calcium carbonate filler, 72 g of potassium aluminum silicate filler and 31 g of finely _L L'a 4 i_ 12 0.Z. 0050/39488 divided silica are added, with thorough mixing of the components. The masonry paint thus obtained has a pigment volume concentration of 60%. The particle diameters of the pigments (1 Im) and fillers (5-150 pm) used are in the ranges usual for the paint industry.

The leveling properties of the paint are very good. This evaluation was obtained by applying 100 g of the paint with a brush to a vertical surface (kraft paper). After a drying time of 30 minutes, the quality of the surface was evaluated in terms of brush strokes and running of the paint. There were no visible brush strokes (good leveling) and the paint did not run.

The weather resistance of the coatings is very Sgood. The paint has a viscosity of 4,200 mPa.s.

The paint was homogeneous (no sediment) after a storage time of 7 days at I I f H t u ft ft .j c. .i i: i,

Claims

1. A thickener based on copolymers which contain, as copolymerized units, (meth)acrylates, styrene and copoly- meriz-able monomers possessing two or more ethylenically unsaturated double bonds, for physically drying paints and coating materials, wherein the thickener is a copoly- mer which forms a gel in mineral spirit and contains, as copolymerized units, from 7 to 15% by weight of acrylates and/or meth- acrylates of monoalkanols of 8 carbon atoms, Cb) from 0.05 to 0.2% by weight of monomers which are copolymerizable with (meth)acryLates and styrene and possess two or more ethylenically unsaturated double bonds, from 25 to 35% by weight of styrene and from 49.8 to 67.95% by weight of one or more acryl- ates and/or methacrylates of monoalkanols of 4 carbon atoms, with the proviso that the sum of the percentages by weight to is always 100.

2. A process for the preparation of a thickener as claimed in claim 1, wherein a monomer mixture consisting of from 7 to 15% by weight of acrylates and/or meth- acrylates of monoalkanols of 8 carbon atoms, from 0.05 to 0.2% by weight of monomers which are copolymerizable with (meth)acrylates and styrene and possess two or more ethylenically unsaturated double bonds, from 25 to 35% by weight of styrene and from 49.8 to 67.95% by weight of one or more acryl- ates and/or methacrylates of monoalkanols of 4 carbon atoms, the sum of the percentages by weight always being 100, is polymerized in aqueous emulsion in the presence of a C 12 -C 18 -alkylsulfonate as an emulsifier to give a poly- mer dispersion having a solids content of from 10 to B: i- r 14 O.Z. 0050/39488 by weight, and the copolymer is then isolated from the polymer dispersion.

3. A process as claimed in claim 2, wherein from to 5% by weight, based on the total polymer dispersion formed, of a 10-55% strength by weight polymer dispersion prepared separately from the monomers to are initially taken as a seed Latex, and the monomers to and from 0.25 to 2.5% by weight, based on the monomer mixture of sodium peroxydisulfate, potassium peroxydisuL- fate and/or ammonium peroxydisulfate are then added con- tinuously or a little at a time to this polymer dispersion at from 65 to 85 0 C and are polymerized therein. f"

4. A process as claimed in claim 2 or 3, wherein from 0.15 to 3% by weight, based on the monomers, of a sodium C 12 -C 18 -alkylsulfonate are used as an emulsifier for the r preparation of aqueous monomer emulsion.

A process as claimed in claim 2 or 3 or 4, where- in the copolymer is precipitated from the polymer disper- sion at from 35 to 65 0 C by adding from 0.5 to 1.5% by e weight, based on the copolymer, of aluminum sulfate.

6. A process as claimed in claim 2 or 3 or 4 or wherein the copolymer precipitated from the polymer dis- S persion is aftertreated, at a pH of from 7 to 8.5 and at from 50 to 70 0 C by adding a base.

7. A process as claimed in claim 2, wherein the co- t polymer precipitated from the polymer dispersion is after- treated at from 80 to DATED THIS 29th day of September, 1988 BASF AKTIENGESELLSCHAFT EDWD. WATERS SONS, PATENT ATTORNEYS, QUEEN STREET, MELBOURNE. VIC. 3000.