CA2066988A1

CA2066988A1 - Preparation of an emulsifier-free polymer dispersion

Info

Publication number: CA2066988A1
Application number: CA 2066988
Authority: CA
Inventors: Heinz-Hilmar Bankowsky; Maria G. Rau; Karl-Heinz Schumacher
Original assignee: Individual
Current assignee: BASF SE
Priority date: 1991-04-27
Filing date: 1992-04-24
Publication date: 1992-10-28
Also published as: DE4113839A1; JPH05117310A; EP0511520A1

Abstract

- 25 - O.Z. 0050/42377 Abstract of the Disclosure: An emulsifier-free polymer dispersion is prepared by polymerization of ethylenically unsaturated monomers (A), which can be subjected to free radical polymerization, with the aid of a free radical initiator in aqueous medium which contains a polymer (B), by a process in which the monomers (A) are metered into the aqueous medium during polymerization. Dispersions prepared in this manner are used as an aqueous coating material and as an aqueous paper lacquer.

Description

2 ~ $
O.Z. 0050/42377 Preparation of an emulsifier-free polymer dis~ersion The present invention relates to a process for the preparation of an emulsifier-free po'ymer dispersion by polymerization of ethylenically unsaturated monomers S~A), which can be sub]ected to free radical polymeriza- i tion, with the aid of free radical initiators in an aqueous medium which contains a polymer (B). The present invention also rela~es to the polymer dispersions prepared in this manner and to their use as an agueous 10coating material or paper lacquer.
Aqueous polymer dispersions or latices are usually prepared by processes in which emulsifiers stabili~e the polymer particles. However, these emulsifiers give rise to certain disadvantages with 15regard to the preparation and use of such dispersions.
For example, undesirable foam formation occurs both during preparation and during processing of the dispersions. Furthermore, the emulsifiers frequently cause troublesome tack of ~he polymer film obtained from 20the dispersions and are often also responsible for the low water resistance of the film. Toxicological and ecological criteria likewise make it necessary to find aqueous dispersions which manage without such assistants.
In coating and lacquer formulations, the 25stabilizing effect of the emulsifiers is frequently reduced by undesirable interactions with the formulating agents (film-forming assistants, fillers, pigments, ionic resins and waxes), which may lead to a substantial deterioration in the performance characteristics ( for 30example gloss, shelf life and leveling). These stability problems occur in particular in the case of very finely divided dispersions having a correspondingly large total particle surface, where considerable amounts of emulsifier have to be added in order to achieve a 35coverage of the particle surface with emulsifier which is sufficient to effect stabilization.
To circumvent these problems, various attempts .
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, - - ~ - , - 2 - O.Z. 0050/42377 have been made with the aim of preparing emulsifier-free aqueous polymer dispersions.
For example, US-A-4 151 143 describes a two-stage preparation process for emulsifier-free dispersions, in which, in the first step, an anionic polymer is prepared by solution or mass polymerization. After this polymer has been dispersed in water rendered alkaline, mixtures of certain monomers which can be subjected to free radical polymerization are then added in a second stage, after which the mixture is polymerized as a batch in the presence of the pol~mer from stage 1. The dispersions prepared in this manner are intended to be used as components for coatings.
DE-A-31 23 598 describes emulsifier-free aqueous latices which are used for anodic electrocoating finishes. These polymer dispersions, too, are prepared by a method in which a batch is first prepared :Erom monomers and a carboxylated polymer. This batch is then polymerized. This is effected, inter alia, by a procedure in which the batch o~ monomers and carboxylated polymer is passed in the form of emulsion int.o heated water, the pol~meriza~ion initiator being introduced simultaneously.
Such latices prepared by the batch process can not be used for aqueous paper lacquers since in many cases the lacquers obtained do not have a sufficiently long shelf life or the gloss is insufficient. Moreover, the latices frequently exhibit a very large number of specks and have a high coagulum content.
US-A 4 465 803 describes a similar batch process for the preparation of emulsifier-free latices. There, monomers which can be subjected to free radical pol~merization are added, in an aqueous medium, to polymers functionalized in a specific manner. The batch is then polymerized. The latices ob~ained have the disadvantage that there are certain restrictions with regard to their use. For example, paper lacquers , ., . . : . . ~ :
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- 3 - O.Z. 0050/42377 obtained from such emulsifier-free latices frequently have disadvantageous gloss values.
It is an object of the present invention to provide a process for the preparation of aqueous, emulsifier-free polymer dispersions which do not have the disadvantages of the prior art and can be used for coatings and paper lac~uers of high quality.
We have found that this object is achieved by the process defined above, wherein the monomers (A) are metered into the aqueous medium during the polymerization.
We have also found the pol~mer dispersions prepared in this manner and their use as aqueous coating matarials or paper lacquer.
Preferred embodiments of the invention are described in the subclaims.
Emulsifiers are known to be amphiphilic molecules, ie. surfactants, which essentially consist of a hydrophilic moiety and a hydrophobic moiety. Suitable hydrophilic moieties are polyethylene oxide chains having not less than 5 ethylene oxide units, amines, ammonium groups, -COOR-, -S03R and -OS03R, where R is one equivalent of a cation or hydrogen. A hyrophobic moiety is, for example, a long-chain alkyl group, an alkaryl or aralkyl group of 8 to 30 carbon atoms or aryl. In rare cases, emulsifiers may have up to 3 hydrophilic and/or up to 3 hydrophobic moieties. For the purposes of the present invention, emulsifier-free means that no emulsifiers are added before or during the polymerization of monomers (A). This of course does not rule out the possibility that traces of emulsifiers, usually less than O.01% by weightr based on the sum of (A) and (B), are introduced by other ~tarting materials. However, emulsifiers in these small amounts have no adverse effects.
Suitable componen~s tA) of the novel polymer dispersions are in principle all ethylenically :: - : , . - . .
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- 4 - O.Z. 0050/42377 unsaturated monomers which can ~e subjected to free radical polymerization.
Particularly suitable monomers are those having a water solubility of up to 50 g/l at 25C, and combinations thereof.
Examples of suitable monomers are the esters of unsaturated monocarboxylic acids of 3 to 5 carbon atoms with alcohols of l to 20 carbon atoms, such as the acrylates, methacrylates and crotonates of, in particular, aliphatic or cycloaliphatic alcohols of 1 to carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, hexyl, 2-ethyl-hexyl, octyl, stearyl, cyclohexyl and methylcyclohexyl alcohol. However, the esters of the abovementioned acids with benzyl alcohol or phenol are also suitable for this purpose.
The monoesters of k ~ B-monoolefinically unsaturated monocarboxylic acids of 3 to 4 carbon atoms with satura~ed dihydric alcohols of 3 to 6 carbon atoms, for example 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate or 4-hydroxybutyl acrylate, are also suitable.
Glycidyl esters of acrylic and methacrylic acid, eg. glycidyl methacrylate, or the aminoalkyl esters of the two acids stated, for example N,N-diethylaminoethyl acrylate, N,N-dimethylaminoneopentyl acrylate or N,N-dimethylaminoethyl methacrylate, are also suitable.
Vinyl and allyl esters of carboxylic acids of 1 to 20 carbon atoms, such as allyl acetate, allyl propionate, vinyl formate, vinyl laurate, vinyl stearate and especially vinyl propionate and vinyl acetate, are also useful.
Vinyl ethers of alcohols of 1 to 8 carbon atoms are, for example, vinyl methyl ether, vinyl ethyl e~her, vinyl isopropyl ether and vinyl butyl ether.
Suitable vinylaromatic monomers of not more than carbon atoms are vinyltoluene, ~- and .
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- 5 - O.Z. 0050/42377 paramethylstyrene, ~-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene and preferably styrene.
The vinyl halides are chlorine , fluorine- o~
bromine-substituted ethylenically unsaturated compounds, preferably vinyl chloride and vinylidene chloride.
Examples of nitriles are acrylonitrile and meth-acrylonitrile. ~crylamide and mekhacrylamide are examples of amides.
Hydrocarbons having a polymerizable olefinic double bond are butadiene, isoprene, ethylene, propylene and isobukylene.
Monomers capable of crosslinking, such as butane-diol diacrylate, hexanediol diacrylate, tripropylene glycol diacrylate and trimethylolpropane triacrylate and trLmethacrylate, may also be used in minor amounts, for example from 1 to 10% by weight, based on the monomers used.
Minor amounts, for example not more than 5% by weight, based on the monomers used, of other auxiliary monomers, such as acrylic acid, methacrylic acid, maleic anhydride, vinylcarbazole, 1-(methacryloyloxyethyl)-imidazolidin-2-oneandl-(acry~oyloxyethyl)-imidazolidin-2-one (also referred to as ureido(meth)acrylake), may sometimes be used to impart certain proper-ties to the polymers.
Preferred monomers are methyl methacrylate, ethyl methacrylate, n-butyl, isobutyl and tert-butyl acrylate, n-butyl and tert-butyl methacrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n-lauryl acrylate, styrene and a mixture of two or more of these monomers, such as mixtures of from 20 to 80% by weight of methyl meth-acrylate and from 20 to 80% by weight of n-butyl acr~late, based in each case on the mixture, and in particular styrene ikself.
The component ~B) of khe polymer dispersion is pre~erably used as an aqueous solution. This is therefore preferably a convenkional water-soluble :-.

2 ~ 2 - 6 - O.Z. 005~/42377 polymer. In contrast to polymer dispersions, polymer solutions have an LT value of more than 99% at 25C. The LT value, a measure of the light transmittance of an aqueous phase, is determined at a dil~tion to a solids content of 0.01% by weight, using a commercial photometer (at a wavelength of 0.54b ~m) for a path length of 25 mm relative to water, to which an LT value of 100% is assigned.
Random copolymers of from 5 to 70% by weight, in particular from 40 to 70~ by weight of styrene and from 30 to 95, in particular from 30 to 60, % by weight of (meth)acrylic acid, usually having a weight average molecular weight of from 1,000 to 100,000, preferably from 1,000 to 20,000, are suitable. In order to ensure adequate water solubility, these compounds are partially or completely neutralized with bases, such as ammonia, amines or alkali metal or alkaline earth metal hydroxides.
Copolymers of from 40 to 60% by weight of maleic acid and from 60 to 40% by weight of diisobutene and copolymers of from 5 to g5~ by weight of maleic acid and from 5 to 95% by weight of (meth)acrylic acid or of from 50 to 90% by weight of maleic acid and from 10 to 50~ by weight of methyl. vinyl ether can also be used to advantage. The average molecular weights of these copolymers are in general from 1,000 to 20~,000.
Copolymers of from 10 to 50% by weight of (meth)acrylamide and from 50 to 90% by weight of vinylpyrrolidone, whose molecular weight may be from 5,000 to 200,000, are also suitable. To obtain advantageous water solubility, these compounds too can be partially or completely neutralized with the above-mentioned bases.
Poly(meth)acrylic acids or poly-2-acrylamido-2 methylpropanesulfonic acids, which may contain up to 60%
by weight, based on the polymer, of acrylates and methacrylates of alcohols of 1 to 4 carbon atoms, - . . . ~ - . , .
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7 - O.Z. 0050/42377 acrylamide or methacrylamide as polymerized units and generally have an average molecular weight of from 2,000 to 500,000, are also suitable. To obtain sufficient water solubility, these polymers too may be partially or completely neutralized with the abovementioned bases.
Other suitable polymers B are water-soluble polyvinylpyrrolidones having average molecular weights of, usually, from 1,000 to 350,000, polyethylene oxides having average molecular weights of in general from 2,000 to 100,000, poly(meth)acrylamides having average molecular weights of, usually, from 20,000 to 200,000, polyvinyl acetates which have been partly hydrolyzed to polyvinyl alcohol and have average molecular weights of, usually, from 2,000 to 100,000 and, if desired, lS ethoxylated hydroxyalkylcellulose where the alkyl radical is of 1 to 3 carbon atoms and which has a degree of ethoxylation of not more than 4 ethylene oxide units per anhydroglucose unit. Examples of these are NatrosolV 250 LR or 250 L from Hercules GmbH, Hamburg. The viscosity of 2P6 strength aqueous solutions of such polymers at 20C ~s-tandard viscosity) is in general less than 350 mPas.
Preferred polymers are the stated polyvinyl-pyrrolidones, polyethylene oxides, poly-2-acrylamido-2-methylpropanesulfonic acids with not more than 5 r preferably 0, % by weight of polymerized comonomers, polyacrylamides and in particular the copolymers of styrene and acrylic acidr particularly successful results being obtained with copolymers which are composed of from 55 to 65~ by weight of styrene and 35 to 45% by weight of acrylic acid and have an average molecular weight of from 1,000 to 5,000.
These polymers are well known ~o the skilled worker and are commercially available and therefore need not be described further.
The novel polymerization process is carried out in an aqueous medium, preferably without the addition of .

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- 8 - O.Z. on50/423~ 8 organic solvents, by a feed procedure. Organic solvents are understood as meaning those which are inert in the polymerization of the monomers A. From 10 to 95, preferably from 45 to 90, % by weight of monomers A and from 5 to ~, preferably from 10 to 55, % by weight of the polymer B are used, the percentages in each case being based on the total amount of A and B.
The monomers are generally subjected to free radical polymerization at a pH of from 3 to 11 and at a reaction temperature of from 20 to 95C, preferably from 40 to 90C. In general, from 0.1 to 5% by weight, based on the monomers used, of conventional, water-soluble initiators for the emulsion polymerization are used as free radical ini~iators for the free radical polymeriza-tion. The initiators, for example hydrogen peroxide,sodium peroxodisulfate or ammonium peroxodisulfate, may be used alone or in a known manner with small amounts, such as from 0.001 to 0.1% by weight, based on the monomers used, of reducing agents, such as ascorbic acid, sodium pyrosulfite, Rongalit~ from B~SF AG, thiourea or hydrazine, or hea~y metal salts, such as sulfates or halides of iron, of cobalt, of nickel, of titanium or of vanadium.
Conventionally used regulators, such as n-dodecyl ~5 mercaptan, tert-dodecyl mercaptan, thioglycol and thio-glycerol, may furthermore be used for regulating the molecular weight. These substances are generally in added in amounts of from 0.1 to 2% by weight, based on the monomers used.
In the novel feed process, the polymer B, preferably as an aqueous ~olution, and usually not more than 60, preferably from 1 to 50, in particular from 20 to 40, % by weight of the total amoullt of the free radical initiator used are added to the initially taken aqueous medium. If necessary, other known assistants, such as buffer substances or regulators, may be added in conventional amounts. The reducing agent which may be :~ :. . :

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_ 9 - O.~. 005U/42377 used can be metered in.
After heating to the desired reaction temperature, the remaining amount of free radical initiator and the monomers A are metered in in a S conventional manner in separate feeds. From 30 to 300, preferably from 30 to 180, minutes are required for the component A and from 10 to 60, preferably from 15 to 40, minutes or longer are required for the residual amount of the free radical initiator. After the end of the addition of the polymerization initiator, polymerization is allowed to continue for a further 30-150 minutes at the reaction temperature.
The free radical initiator can be metered in or some of the free radical initiator can be initially taken in a preerred manner. The amount of initially taken initiator and the feed rate of the initiator and monomers are advantageously chosen so that there is no accumulation of unconverted monomers in the reaction vessel, for example more than 1% by weight, based on the total amount of the monomers used. This can be determined by the skilled worker in a simple manner, for example by sampling or in preliminary experiments. The polymerization process has the advantage that the heat of reaction is evolved not in surges but uniformly in a controlled manner and can be readily removed. Only small heat exchangers are required for this purpose.
The polymer dispersions having a solids content of from 15 to 55, in particular from 30 to 50~ % by weight, measured according to DIN 53,189, are obtained.
With the abovementioned inorganic bases, such as the alkali metal and alkaline earth metal hydroxides, ammonia or organic bases, such as amines, the aqueous emulsifier-free polymer dispersions can be brought to the desired pH.
The main particle diameter of the polymer dispersions, determined by the method of dynamic light scattering ~accordlng to B.J. Berne, R. Pecora, Dynamic :,. , : ,. .

2 ~ f;l ~l3 ~ 10 - O.Z. 0050/42377 Light Scattering, John Wiley & Sons~ New York, 1976), may be from 20 to 1,000 nm, in particular from 40 to 1,000 nm .
The aqueous emulsifier-free polymer dispersions obtainable by the novel process have a long shelf life and are ready for shipment and use without further treatment. They can be prepared without organic solvents. They are particularly suitable for aqueous coating materials and in particular as high quality aqueous paper lacquers. In the paper lacquers, they result in a very long shelf lie and extremely high gloss of the applied and dried paper lacquers.
Aqueous coating materials frequently contain further conventional components, in general from 15 to 25% by weight of pigments, such as TiO2, from 5 to 25% by weight of fillers, such as cha~k or silicates, from 0.1 ~o 1~ by weight of pigmant distributors, from 0.2 to 1%
by weight of antifoams, from 0.05 to 0.2% by weight of preservatives and not more than about 10% by w~ight o~
film-forming assistants, plasticizers and thickeners, in addition to the polymer dispersions as binders, which are generally present in amounts of from 25 to 60% by weight, based on the aqueous coating material.
Aqueous paper lacquers contain further conven-tional components in addition to the polymer dispersions.Examples are film-forming assistants, such as propylene glycol and butylglycol, plasticizers, such as di-n-butyl phthalate, surface tension regulators, such as isopropanol, and waxes, in each case in amounts of, usually, from 1 to 10% by weight, based on the aqueous paper lacquer. Furthermora, from 10 to 50% strength by weight aqueous solutions of the abovementioned polymers B, such as the stated styrene/acrylic acid copolymers, may be present in amounts o~ from 10 to 50% by weight in the aqueous paper lacquer.
In the Examples which follow, percentages, parts and ratios are by weight, unless stated otherwise. The ., . ", ., , , , ~ . .

2 ~
~ O.Z. 0050/42377 following abbreviations are used:
n-BA: n-Butyl acrylate i-BA: Isobutyl acrylate t-BA: tert-Butyl acrylate n-HA: n-Hexyl acrylate 2-EHA: 2-Ethylhexyl acryla-te n-LA: n-Lauryl acrylate MMA: Methyl methacrylate EMA: Ethyl methacrylate n-BMA: n-Butyl methacrylate t-BMAo tert-Butyl methacrylate S: Styrene SC. Solids content M: Weight average molecular weight General preparation method for Examples 1 to 20 In a 3 l four-necked flask which was equipped with a reflux condenser, 2 feed vessels, a thermometer, a pilot stirrer and a gas inlet and outlet, the amount, stated in Table 2, of a 22.5% strength ammoniacal solution (pH lO) of a copolymer B of 60~ by weight of styrene and 40% by weight of acrylic acid and having an average molecular weight of 1,200 was initially taken and, after the reaction vessel had heen flushed with nitrogen, was heated to 85C. 54 g of 1.5% strength aqueous ammonium peroxodisulfate solution were added and 220 g of the monomer or monomer mixture A were then run in at 85C in the course of 1 hour while stirring. At the same time, in a separate~ feed, 126 g of a 1.5%
strength ammonium peroxodisulfate solution were added dropwise, but in this case the time for the dropwise addition was increased by 30 minutes to a total o~ 1.5 hours. A~ter the end o the two feeds, the reaction was allowed to continue for a further 1 hour at 85C, after which the mixture was cooled to room temperature.
The polymer dispersions obtained by this preparation method are coagulum-free and have the following data:

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- 12 -O.Z. 0050/42377 T ~ LE 2 Example Monomer A Solution of pH SC (%) Parti~le copolymer Bdiamete~
g (nm) 1 n-BA 802 9.0 39.0 143 2 i~BA 391 8.7 38.7 113 3 t-BA 391 9.0 40.0 110 4 n-HA 391 8.9 39.6 127 2-E~A 391 9.1 39.7 136 6 n-LA 391 9.0 39.9 193 7 ~MA 802 9.6 39.7 96 8 MMA 978 9.6 41.6 75 -`

9 EMA 391 9.0 39.4 77 lS 10 n-B~ 802 8.6 39.6 78 11 t- 'JMA 391 9.2 39.9 Sl 12 50% S, 50% n-BA 802 9.2 39.4 116 13 5~% NMA, 50% n-BA 802 9.1 39.6 131 14 50X ~MA, 50% n-BA 978 9.3 41.0 98 50% NMA, 50X n-BA 182 9.2 42.9 140 ; 17 S 802 9.0 45.3 100 18 S 684 9.0 45.4 105 19 S 489 8.9 44.9 111 S 400 8.9 40.6 135 General preparation methods for Examples 21 to 33 ; In a 3 1 four-necked flask which was equipped with a reflux condenser~, 2 feed vessels, a thermometer, :a pilot stirrer and a gas inlet and outlet, the amount, stated in Table 3, of the aqueous solution of polymex B
was initially taken and, after the reaction vessel had been flushed with nitrogen, was heated to 85C. 54 g of a 1.5% strength a~ueous ammonium peroxodisulfate solution were added and 220 g of styrene were then run in at 85C
: 35 in the course of 1 hour while stirring. At the same :
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- 13 - O.Z. 0050/42377 time, in a separate feed, 126 g of a 1.5% strength ammonium peroxodisulfate solution were added dropwise, but in this case the time for the dropwise addition was increased by 30 minutes to a total of 1.5 hours. After the end of the two feeds, the reaction was allowed to continue for a further hour at o5C, after which the mixture was cooled to room temperature.
The polymer dispersions obtained by this preparation method are coagulum-free and have the following data:

Example Monomer B Solution of Dispersion obtained polymer B used SC Particle Amount (g) (%)1) (%) diameter (~m) _.___ _ 21 Copolymer 293 30 43.3 103 50% of methyl meth-acrylate 35X of methyl acrylate 15% of acrylic acid 22 Polyethylene oxide 601 30 39.1 177 M ~ 9,000 23 Polyvinylpyrrolidone 733 30 40.0 130 M ~ 40,000 : 25 24 Poly-2-acrylamido- 495 20 35.2 400 2-methanesulfonic acid, Na salt M ~ 42,000 Copolymer of 600 30 39.1 250 50% of maleic acid :
50% of diisobutylene Na salt M ~ 1,200 :
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~ - 14 - O.Z. 0050/42377 Concentration of the solution TA13LE 3 ( continued) Example Monomer BSolution of Dispersion obtained polymer B used SC Particle A~ount (g) (%)1) (X) diameter (~m) . . . _ ~ _ _ _ 26 Copolymer of lO00 11 23.9 1000 88% of polyvinyl alcohol 12% of polyvinyl acetate M ~ 26,000 (Mowiol~ 4/88 from Hoechst AG, Frankfurt) 27 Cellulose hydroxy 2000 5.5 13.9 183 ethyl ether containing 2.5 ethylene oxide units lS per anhydroglucose unit (Natrosol 250 LR) 28 Polyacrylamide S18 20 35.3 405 M ~ 120,000 .
29 Copolymer of 1100 10 21.3 395 70% of vinylpyrrolidone 30% of methacrylamide M ~ 100,000 :' Copolymer of 440 25 39.5 420 : 50% of maleic acid and 50% of acrylic acid :
M ~ 3,000 31 Copolymer of 30% oE 470 23.5 32.0 465 : maleic acid and 70%
: of acrylic acid Na salt M - 70,000 : : :~
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- 15 - O.Z. 0050/42377 Concentration oE the solution TABLE 3 (continued) ~xample Monomer B Solution of Dispersion obtained - polymer B used SCParticle Amount (g) (%)1) (%) diameter (~) 32 Copolymer of 440 25 39.01000 67% of maleic acid and 33% of methyl vinyl ether M = 70,000 33 Polyethylene oxide 601 3038.3 81 = 6,800 Concentration oE the solutiorl ~eneral method for Examples 34 to 36 The procedure described for Examples 21 to 33 is followed, but using a mixture of 802 g of a 22.5%
strength by weight aqueous solution of the ammonium salt of a copolymer of 60% hy weight of styrene and 40% by weight of acrylic acid (M = 1,200) and 15 g of a 30%
strength by weight aqueous solution of a polyethylene oxide (M - 9,OOO) as polymer B and 220 g of the monomer A stated in Table 4 of the monomer mixture A.
Example Monomer A Dispersion obtained :: SCParticle diameter (%)(~m) 34 ~MA 40.678 50% MMA/50% n-BA 40.9102 36 S 46.5~06 In the prior art batch preparation process, 220 g of a random copolymer of 60% of styrene and 40% of acrylic acid, having an average molecular weight of :: :

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- 16 - O.Z. ~050/42377 1,200, wexe dissolved in 758 g of a 3% strength aqueous ammonia solution. 220 g of styrene were emulsified in this resin solution at 85C. 180 g of a 1.5~ streng-th ammonium peroxodisulfate solution were then added dropwise to the emulsion at 85C in the course of 1 hour while stirring. The batch coagulated completely during the addition of ~he initiator.

Example 15 in Table 2 was carried out by the batch procedure ~cf. Comparative Exa~ple 1~.
40.3 g of the copolymer of 60% of styrene and 40%
of acrylic acid in 141 g of a 3~ strength aqueou~ ammonia solution formed the initially taken mixture in which 220 g of monomers, consisting of 110 g of n-BA and 110 g of MMA, were emulsified.
The batch coagulated during the addition of the initiator.

In the feed preparation process described in DE-A-31 23 598, 90 g of a random copolymer of 60% of styrene and 40% of acrylic acid, having an average molecular weight of 1,200, ware dissolved in 210 g of a 4% strength aqueous ammonia solution. 220 g of styrene were emulsified in this solution at room temperature, after which the emulsion obtained was passed, while stirring, into 160 g of water which had been initially taken and heated to 85C. At the same time, 100 g of a 1.5%
strength ammonium peroxodisulfate solution were added dropwise in the course of 1.5 hours to the initially taken mixture at 85C. After the end of ~he feeds, polymerization was allowed to continue for a further 1 hour at 85C, and a finely divided, bluish white dispersion having a solids conten~ of 40% was obtained.
The dispersion contained 1.3% of coagulum (based on the total solids content) and, in the form of a film applied to a glass sheet, exhibited many specks.
Determination of the speck content:

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- 17 - O.Z. 0050/42377 The aqueous dispersion was spread over a glass sheet in a layer thickness of 200 ~m and dried for 24 hours at room tempera-ture. Thereafterr the specks visible with the naked eye were visually e~aluated in an area of 6 x 20 cm and were assigned to a scale of ratings which ranged from 0 (speck-free) to 3 (very large number of specks). The Table below shows the results:
Example No. Ratinq Comp. Example 3 3 The Examples which follow describe the formulations for aqueous paper lacquers in which the emulsifier-free polymer dispersions are present as binders.
A water-soluble pol~mer can be used as a cobinder for paper lacquers. A copolymer of from 55 to 65% by weight of styrene and from 35 to 45% by weight of acrylic acid, having a molecular weight of from lrOOO to 5,000, proved to be particularly suitable, and in some cases up to 50% by weight of the styrene may be replaced with ~-methylstyrene. The abovementioned water-soluble poly-acrylic and polymethacrylic acids are also suitable.
General method for formulation I:
Parts by weight Component 56a) Aqueous solution of a copolymer (35%
strength by weight) 27 Polymer dispersion (SC = 45%) 9 Aqueous polyethylene wax emulsion, 35%
strength, as assistant for increasing the scratch-resistance 7b) Water ~ Antifoam - :. . . ,: . .
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- 18 ~ O.Z. 0050~42377 ~): Solution consisting of Parts by weight Component Copolymer of 60% of styrene and 40% of acrylic acid (M = 1,200) 13 Concentrated NH3 3 Butylglycol as film-forming assistant 49 Water o b~: Where the polymer content of th~ dispersion fluctuated, the amount was ad~usted accordingly.
The individual components were mixed with one another with continuous stirring. It was advantageous to prepare the polymer dispersion and wax emulsion together beforehand and to avoid coagulation of the wax particles.
The formulation II used a novel dispersion as the sole binder. Only a few commercial aqueous dispersions could be processed in this manner to give an acceptable paper lacquer.
General method for formulation II:
Parts by weight Component 74 Polymer disparsion, SC = 45 4 Isopropanol as assistant for reducing the sur~ace tension 2 Propylene glycol as film-forming assistant 8 Di-n-butyl phthalate as plasticizer 2 Polyethylene wa~ emulsion, 35%
strength, as assistant for higher scratch-resistance 10~ Water Testing the paper lacquers 1. Viscosity: Measured according to DIN 53,211 using a DIN 4 mm cup at 23C, stated in seconds.
2. Shelf life: The lacquer was stored at 50C in a closed vessel in a drying oven. A test was carried out to determine whether the lacquer thickened or : ~ :

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~ 19 - O.ZO 0050/42377 whether its viscosity increased greatly.
Testing of the paper coating The lacquer was applied with a 6 ~m knife coater to white and black contrast paper and cardboard and was dried at room temperature. The gloss was measured using a multi-gloss reflectometer at an angle of 60C.
The results are shown in Tables 5 and 6.
It is clear that tha dispersions prepared according to the invention have a wide range of uses.
Thus, when used as paper lacquers in many formulations on many papers, they have a balanced property profile between the shelf life of the aqueous lacquer and surface properties of the dry coating, such as gloss, on various substrates.

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- 21 - O . Z . 0050/42377 ~, a~ o~ ,1 o ~ Ln X ~ ~~ ~ ~ Ln w v U~ O ~ d' ~r I A ~1 Ul Ll v ~ ~ D ~ O r~
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- 22 - O.Z. 0050/42377 Example 5 of US-~ 4 465 803 was repeated. With this dispersion as a binder, an aqueous paper lacquer was prepared as described abo~e using formulation I. The gloss is shown in Table 7.

Example 5 of US-A 4 465 803 was repeated.
However, 207 g of n-butyl methacrylate and 0.5 g of ammonium persulfate were not added before heating ~o lQ 80C, and 100 g of water were also retained. After the initially taken mixture had been heated, 207 g of n-butyl methacrylate were metered in continuously in the course of 60 minutes and 0.5 g of ammonium persulfate, dissol~ed in 100 g of water, were metered in continuously in the course of 90 minutes, and the mixture was then kept at this temperature for 1.5 hours.
With this dispersion as a binder, an aqueous paper lacquer was prepared as described above using formulation I. The gloss values in Table 7 show the clear superiority of the novel dispersion o~er the dispersion prepared by the prior art batch process.

Paper lacquer formulations according to formulation I
Comparative Example 4 Dispersion 37 Gloss Cardboard 23 31 60C Paper (white) 43 54 6 ~m Paper (black) 51 59 , ~ . ~ . .. .

.. . . ~ .
. .

Claims

1. A process for the preparation of an emulsifier-free polymer dispersion by polymerization of ethylenically unsaturated monomers (A), which can be subjected to free radical polymerization, with the aid of a free radical initiator in an aqueous medium which contains a polymer (B), wherein the monomers (A) are metered into the aqueous medium during the polymerization.

2. A process as claimed in claim 1, wherein monomers are metered in continuously.

3. A process as claimed in claim 1, wherein from 5 to 90% by weight of the monomers (A) and from 10 to 95%
by weight of the polymer (B), based in each case on the sum of (A) and (B), are used.

4. A process as claimed in claim 1, wherein the free radical initiator is metered in during the polymerization.

5. A process as claimed in claim 1, wherein not more than 60% by weight of the free radical initiator used is initially taken in the aqueous medium and the remainder is metered in during the polymerization.

6. A process as claimed in claim 1, wherein esters of alcohols of 1 to 20 carbon atoms, amides or nitriles of monocarboxylic acids of 3 to 5 carbon atoms, vinyl esters or allyl esters of carboxylic acids of 1 to 20 carbon atoms, vinyl ethers of alcohols of 1 to 8 carbon atoms, vinylaromatic monomers of not more than 20 carbon atoms, vinyl halides or hydrocarbons having a polymerizable double bond are used as monomers (A).

7. A process as claimed in claim 1, wherein the polymer (B) is dissolved in the aqueous medium.

8. An emulsifier-free polymer dispersion, preparable by a process as claimed in claim 1.

9. A method of using an emulsifier-free polymer dispersion as claimed in claim 8 as the aqueous coating material.

- 24 - O.Z. 0050/42377

10. A method of using emulsifier-free polymer dispersion as claimed in claim 8 as an aqueous paper lacquer.