Aqueous polymer dispersions

Abstract

The present invention relates to an aqueous dispersion of a multiphase polymer, obtainable by a free-radically initiated aqueous emulsion polymerization, comprising an outer phase polymer A and an inner phase polymer B, wherein polymer A is a copolymer of i) 1-10 wt% acetoacetoxy(C 2-C 8)alkyl(meth)acrylate, ii) 10-35 wt% hydroxyalkyl(meth)acrylate, iii) 1-6 wt% an ethylenically unsaturated compound having at least one phosphorus-containing group, optionally iv) an ethylenically unsaturated carboxylic acid, and v) 50-80 wt% at least one ethylenically unsaturated compound distinct from the monomers i) to iv), and wherein polymer B is a copolymer of at least 1-10 wt% i), 10-30 wt% ii) and optionally iii) and / or iv), and 60-89 wt% v); with the proviso that: - either polymer B is obtainable by polymerizing monomers B in the presence of the polymer A or polymer A is obtainable by polymerizing monomers A in the presence of the polymer B, - the multiphase polymer has a calculated hydroxyl number from 45 to 155 mg KOH / g - the weight ratio of monomers B to monomers A is from 20:80 to 80:20, a process for producing an aqueous dispersion of a multiphase polymer by free-radically initiated aqueous emulsion polymerization and its use in a very wide variety of fields, in particular in anticorrosion coatings.

Description

2501821Aqueous polymer dispersionsDescriptionThe present invention relates to an aqueous dispersion of a multiphase polymer, a process for producing an aqueous dispersion of a multiphase polymer by free-radically initiated aqueous emulsion polymerization and its use in a very wide variety of fields, in particular in anticorrosion coatings.Aqueous dispersions of a multiphase polymer containing phosphorus groups are known as binders for anti-corrosion coatings.EP-A 1193298 discloses aqueous multiphase polymers as binders for direct-to-metal applications. EP1193298 teaches multiphase polymers containing in their first phase a strong acid monomer such as phosphoethyl methacrylate for anticorrosion compositions and high-gloss coatings. Some of the polymers have methacrylic acid or alternatively acetoacetoyxyethyl methacrylate polymerized in the second phase.EP-A 2426155 discloses dispersions of multistage dispersion polymers comprising phosphoric acid-containing monomers in copolymerized form and the use thereof in coating compositions. It teaches polymers that contain phosphoethyl methacrylate polymerized in both polymer phases. The addition of methacrylic acid in the first phase improves the srub resistance of the polymer. The thus obtained polymer dispersion particles are said to be advantageously suitable titanium dioxide-containing coating compositions.WO2019 / 091889 teaches the production of multiphase dispersion polymers containing phosphorus groups as binders for direct-to-metal applications. The use of a phosphorus-containing dispersant and phosphorus-containing monomers in the first polymerization stage results in less corrosion of the steel reactor in which polymerization takes place.All these dispersions are used as one-component coatings. Their disadvantage is that they are often not high-gloss and have limited chemical resistance.Two-component paints generally have better chemical resistance but require the additional application of a primer. Multiple painting processes with different coating compositions are technically more complex and require longer drying times.The task underlying the invention was to find new aqueous dispersions of muliphase polymers that exhibit both high gloss and good mechanical and chemical resistance. Furthermore, if they are formulated as a two-component PU coating, they should not require an additional primer and, if necessary, a multiple layer application of a single composition according to the invention should be sufficient.2501822We have found that these objects are achieved, surprisingly, by an aqueous dispersion of a multiphase polymer obtainable by a free-radically initiated aqueous emulsion polymerization, comprising an outer phase polymer A and an inner phase polymer B, wherein polymer A is a copolymer of1 to 10% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate (monomers A1),10 to 35% by weight of at least one hydroxyalkyl(meth)acrylate (monomers A2),1 to 6% by weight of at least one ethylenically unsaturated compound having at least one phosphorus- containing group (monomers A3),0 to 10% by weight of at least one ethylenically unsaturated carboxylic acid (monomers A4),50% to 80% by weight of at least one ethylenically unsaturated compound distinct from the monomers A1 to A4(monomers A5),and the amounts of the monomers A sum to 100% by weight (total monomer amount A), and wherein polymer B Is a copolymer of1 to 10% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate (monomers B1),10 to 30% by weight of at least one hydroxyalkyl(meth)acrylate (monomers B2),O to 0.1% by weight of at least one ethylenically unsaturated compound having at least one phosphorus- containing group (monomers B3),0 to 0.5% by weight of at least one ethylenically unsaturated carboxylic acid (monomers B4),60% to 89% by weight of at least one ethylenically unsaturated compound distinct from the monomers B1 to B4(monomers B5),and the amounts of the monomers B sum to 100% by weight (total monomer amount B),with the proviso thateither polymer B is obtainable by polymerizing monomers B in the presence of the polymer A or polymer A is obtainable by polymerizing monomers A in the presence of the polymer B,the multiphase polymer has a calculated hydroxyl number from 45 to 155 mg KOH / g,the weight ratio of monomers B to monomers A is from 20:80 to 80:20.The present invention further relates to a process for producing the aqueous dispersion, the use of the aqueous polymer dispersion as a binder in aqueous coating compositions, in particular in anticorrosion coating compositions for metal surfaces, and aqueous two-component coating compositions comprising the dispersion of the multiphase polymer.Production of the aqueous polymer dispersions obtainable by the process according to the invention by two-stage aqueous emulsion polymerization may employ the following ethylenically unsaturated monomers A1, A2, A3, A4, A5, B1, B2, B3, B4 and B5.2501823In the following, compounds derived from acrylic acid and methacrylic acid are partly shortened by inserting the syllable "(meth)" in the compound derived from the acrylic acid.Monomer A1 and B1 are independently of each other acetoacetoxy(C2-C8)alkyl(meth)acrylate advantageously acetoacetoxy(C2-C4)alkyl(meth)acrylate. The alkyl radikal of acetoacetoxy(C2-C8)alkyl(meth)acrylate is linear, branched or cyclic.Suitable monomers A1 and B1 are acetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate, acetoacetoxyneopentyl methacrylate, acetoacetoxybutyl methacrylate and 2-(acetoacetoxy)ethyl methacrylate.The amounts of monomer A1 is 1 to 10% by weight, advantageously 2 to 8% by weight and especially advantageously 2 to 7% by weight in each case based on the total monomer amount A.The amounts of monomer B1 is 1 to 10% by weight, advantageously 2 to 8% by weight and especially advantageously 2 to 7% by weight in each case based on the total monomer amount B.Monomers A2 are independently of each other hydroxyalkyl(meth)acrylate, preferably more particularly, all hydroxyalkyl, advantageously hydroxy-C2-Cio-alkyl, preferably hydroxy-C2-C4-alkyl, and particularly advantageously hydroxy-C2-C3-alkyl acrylates and / or methacrylates; for the purposes of this specification, the alkoxylated hydroxyalkyl acrylates and / or methacrylates, i.e., those reacted with alkylene oxides (essentially ethylene oxide and propylene oxide), are also to be regarded as monomers A2. With advantage, the hydroxyalkyl-containing monomers A2 are selected from the group comprising diethylene glycol monoacrylate, 4-hydroxybutyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl acrylate, diethylene glycol monomethacrylate, 4-hydroxybutyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxypropyl methacrylate, and 2-hydroxyethyl methacrylate. Used with more particular advantage are 2-hydroxyethyl acrylate and / or 2-hydroxyethyl methacrylate, with 2-hydroxyethyl methacrylate being particularly preferred.The amounts of monomers A2 are 10 to 35% by weight, advantageously 15 to 30% by weight and especially advantageously 17 to 27% by weight in each case based on the total monomer amount A.Monomers A3 are ethylenically unsaturated compound having at least one phosphorus-containing group. Examples thereof are vinylphosphonic acid, 3-phospho-2-hydroxypropyl(meth)acrylate, and / or a (meth)acryl(poly)oxyalkylene phosphate, wherein the (meth)acryl (poly)oxyalkylene phosphate has the following formula I:H2C=CH(H / CH3)-C(=O)-[AO]x-O-P(=O)(-OR2)(OR2), Formula (I)wherein2501824AO: represents oxyethylene [-OCH2CH2-], oxypropylene [-OCH(CH3)CH2-], oxybutylene [-OCH(C2H5)CH2-] or mixtures thereof, wherein oxyethylene and / or oxypropylene are preferred, andx: represents a number between 1 and 30, wherein numbers between 1 and 20 are preferred and numbers between 1 and 10 are very particularly preferredR2: represents independently H or a group R2a-(AO)x-, wherein R2” is (meth)acryl and AO and x have one of the definitions specified above, wherein, however, R2advantageously represents H,Explicitly mentioned (meth)acryl (poly)oxyalkylene phosphates are compounds of the following formulae:and especially preferablyThe abovementioned preferred (meth)acryl (poly)oxyalkylene phosphates are commercially available, for example as Sipomer® PAM-100, Sipomer® PAM-200, Sipomer® PAM-300 or Sipomer® PAM-4000 from Solvay / Rhodia and 2-(methacryloyloxy)ethylphosphate from Sigma-Aldrich / Merck KgaA. Some other examples of P containig ethylenically unsaturated monomer are Maxemul® 6106, Maxemul® 6112, Maxemul® 5010, Maxemul® 5011 from Croda.The monomers A3 of course also comprise the fully or partly neutralized water-soluble salts, in particular the alkali metal salts or ammonium salts, of the abovementioned acids.The total amount of monomers A3 is > 1% and 56% by weight, advantageously > 1% and 55% by weight and particularly advantageously > 1% and 54% by weight in each case based on the total monomer amount A.Employable monomers A4 Include any ethylenically unsaturated carboxylic acid especially a,P-monoethylenically2501825unsaturated C3- to Ce-mono- or -dicarboxylic acids. Examples of C3- to Ce-mono- or -dicarboxylic acids, preferably C3- or C4-mono- or -dicarboxylic acids, are acrylic acid, methacrylic acid, ethyl acrylic acid, itaconic acid, allyl acetic acid, crotonic acid, vinyl acetic acid, vinyl lactic acid, fumaric acid, maleic acid, 2-methyl maleic acid. However, the monomers A4 also comprise the anhydrides of corresponding a,P-monoethylenically unsaturated dicarboxylic acids, for example maleic anhydride or 2-methylmaleic anhydride.The monomers A4 of course also comprise the fully or partly neutralized water-soluble salts, in particular the alkali metal salts or ammonium salts, of the abovementioned acids.Particularly advantageously employed monomers A4 are acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid and / or crotonic acid.The total amount of the monomers A4 is >0% and 510% by weight, advantageously > 0.1% and 55% by weight and particularly advantageously > 1% and 55% by weight in each case based on the total monomer amount 1.Employable monomers A5 include all ethylenically unsaturated compounds distinct from the monomers A1, A2, A3 and A4, for example alkyl (meth)acrylates (monomer A5-0), wherein these preferably comprise alkyl (meth)acrylates whose linear or branched alkyl radical has 1 to 20 carbon atoms, particularly preferably 1 to 10 carbon atoms and very particularly preferably 1 to 8 carbon atoms. It should be noted in this context that “(meth)acrylic acid” compounds or “(meth)acrylate” compounds is generally to be understood as comprehending both the relevant acrylic acid compounds and the relevant methacrylic acid compounds.Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, 2-methylbutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-propylheptyl (meth)acrylate, n-decyl (meth)acrylate, undecyl (meth)acrylate and n-dodecyl (meth)acrylate.Also advantageously contemplated as monomers A5 are alkyl (meth)acrylates with a cycloaliphatic structure (monomers A 5-0) preferably isobornyl methacrylate, isophoryl methacrylate, cyclohexyl methacrylate, 4-tert-butylcyclohexyl (meth)acrylate, dicyclopentadiene acrylate and / or adamantyl acrylate preferred are isobornyl methacrylate and / or cyclohexyl methacrylate.Also advantageously contemplated as monomers A are vinylaromatics (monomers A5-0) having up to 20 carbon atoms.The vinylaromatics having up to 20 carbon atoms are optionally substituted aromatic systems having a vinyl group in conjugation with the aromatic ring system.2501826Such substituted vinylaromatics often have one or more, preferably one, linear or branched alkyl groups having 1 to 10 carbon atoms, often 1 to 6 carbon atoms and preferably 1 to 4 carbon atoms on the aromatic or on the vinyl group. If the substituent is on the aromatic, the substituent may preferably be in the ortho or para position, particularly preferably in the para position, to the vinyl group.Suitable vinylaromatic compounds include in particular vinyltoluene, vinylnaphthalene, a- and p-methylstyrene, a-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene and / or styrene, wherein, however, styrene and / or a-methylstyrene are particularly preferred.However, the monomers A5 also comprise ethylenically unsaturated nitriles having up to 20 carbon atoms, such as in particular fumaric acid dinitrile, acrylonitrile and methacrylonitrile, preferably acrylonitrile and methacrylonitrile and particularly preferably acrylonitrile, vinyl esters of carboxylic acids comprising up to 20 carbon atoms, in particular vinyl laurate, vinyl stearate, vinyl propionate, vinyl versatate, vinyl butyrate and vinyl acetate, but preferably vinyl acetate, vinyl and vinylidene halides having up to 10 carbon atoms, such as in particular chlorine-, fluorine- or bromine-substituted ethylenically unsaturated compounds, preferably vinyl chloride and vinylidene chloride and vinyl ethers of alcohols comprising 1 to 10 carbon atoms, such as advantageously methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, sec-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether and n-octyl vinyl ether, wherein vinyl ethers of alcohols comprising 1 to 4 carbon atoms are preferred.Additionally functionalized ethylenically unsaturated compounds A5-1 are employable according to the invention also include organic compounds having at least two nonconjugated ethylenically unsaturated groups, such as for example 1,2-, 1,3- and 1 ,4-butanediol diacrylate, 1,2- and 1 ,3-propylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1 ,2-ethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, pentaerythritol tri- and tetra(meth)acrylate, allyl methacrylate, 1,2-, 1,3- and 1,4-divinylbenzene and mixtures thereof. These compounds are particularly preferably selected from the group consisting of divinylbenzene, 1 ,4-butanediol diacrylate and allyl methacrylate.Further functionalized ethylenically unsaturated compounds A5-1 employable according to the invention are selected from the group consisting of 2-ureidoethyl (meth)acrylate, 2-ureidoethyl (meth)acrylamide, diacetone acrylamide (DAAM), diacetone methacrylamide and (meth)acrylamide. Preferred among this group are 2-ureidoethyl (meth)acrylate and (meth)acrylamide particularly preferred is 2-ureidoethyl (meth)acrylate.However, the functionalized ethylenically unsaturated compounds A5-1 employable according to the invention further include compounds having a (meth)acrylate group and an epoxy group. Examples especially include glycidyl acrylate and glycidyl methacrylate, preferably glycidyl methacrylate.2501827Likewise included among the functionalized ethylenically unsaturated compounds A5-1 employable according to the invention are also ethylenically unsaturated compounds having at least one silicon-containing group, for example vinyltriacetoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane or vinyltriethoxysilane.It is particularly advantageous when the at least one monomer A5-1 is to an extent of > 0% and < 20% by weight selected from the group comprising 2-ureidoethyl methacrylate, diacetone acrylamide, glycidyl methacrylate, 3-(methacryloyloxy)propyltrimethoxysilane, vinyltriethoxysilane and (meth)acrylamide.In one specific embodiment of the present invention, ethylenically unsaturated compounds A5-2 having a nonionic oligoalkylene ether moiety, and / or an ionic moiety derived from an organically bound carboxylic or sulphonic acid group, are additionally employed in the course of the radical emulsion polymerization. Due to the oligoalkylene ether moiety, these monomers are employable as emulsifiers, so called reactive emulsifier. These are generally compounds which carry at least one radically polymerizable group, preferably selected from the group consisting of allyl, acrylate, methacrylate, and vinyl ether, and at least one emulsifying group, preferably selected from the group indicated above.These emulsifiers are, for example, incorporable emulsifiers with the brand names Bisomer® MPEG 350 MA from Laporte, Hitenol® BC-20 (APEO), Hitenol® BC-2020, Hitenol® KH-10 or Noigen® RN-50 (APEO) from Dai-lchi Kogyo Seiyaku Co., Ltd., , Adeka® Reasoap® PP-70, Adeka® Reasoap® NE-10, Adeka® Reasoap® NE-20, Adeka® Reasoap® NE-30, Adeka® Reasoap® NE-40, Adeka® Reasoap® SE-10N, Adeka® Reasoap® SE-1025A, Adeka® Reasoap® SR-10, Adeka® Reasoap® SR-1025, Adeka® Reasoap® SR-20, Adeka® Reasoap® ER-10, Adeka® Reasoap® ER-20, Adeka® Reasoap® ER-30, Adeka® Reasoap® ER-40 from Adeka, Pluriol® A 010 R, Pluriol® A 12 R, Pluriol® A23 R, Pluriol® A 46 R, Pluriol® A 750 R, Pluriol® A 950 R, Pluriol® A 590 I, Pluriol® A 1190 I, Pluriol® A 590 V, Pluriol® A 1190 V, Pluriol® A 5890 V, Pluriol® A 308 R and DAA ES 8761 from BASF SE, Latemul® S 180 A and Latemul® S 180 from Kao, Eleminol® JS-2 from Sanyou Kasel, Aquaion® HS-1025 from Daiichi Kogyou Seiyaku and C12-AMPS from Lubrizol.The amount of the optionally employed ethylenically unsaturated compounds A5-2 is < 5 wt%, advantageously < 3 wt%, and especially advantageously > 0.3 and 52 wt%, based in each case on total monomer A. According to a preferred embodiment > 0.3 and 2 wt% based on total monomer A of ethylenically unsaturated compounds A5-2 are employed.The total amount of monomers A5 is > 50% and < 80% by weight, advantageously > 60% and < 80% by weight and particularly advantageously > 60% and 575% by weight in each case based on the total amount of monomer A.Preferably, more than 80% by weight of monomer A5, most preferable more than 90% by weight of monomer A5 is selected from the group consisting of n-butyl acrylate, n-butyl methacrylate, iso-butyl methacrylate, isobutyl acrylate, isopentyl (meth)acrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, n-heptyl acrylate, styrene and methyl methacrylate.2501828According a preferred embodiment, up to 10% by weight of monomer A5 is selected from the group consisting of 2-ureidoethylmethacrylate, glycidyl methalcrylate, 3-(methacryloyloxy)propyltrimethoxysilane, vinyltriethoxysilane, and (meth)acrylamide and / or up to 10% by weight of monomer B5 is selected from the group consisting of 2-ureidoethylmethacrylate, glycidyl methalcrylate, 3-(methacryloyloxy)propyltrimethoxysilane, vinyltriethoxysilane, and (meth)acrylamide.Preferably the type and the amounts of the monomers A1 to A5 are chosen such that the polymer A obtained therefrom after the polymerization has a glass transition temperature TgAmeasured according to DIN EN ISO 11357-2 (2013-09) [differential scanning calorimetry, midpoint temperature, heating rate 20 K / min] in the range >35°C and 5 110°C, advantageously > 45°C and < 85°C and especially advantageously > 50°C and < 75°C. It should be noted that the glass transition temperatures of the first step are determined by the abovementioned method. This means that if the monomers B1 to B5 are polymerized in the first step, the glass transition temperature of polymer B is determined using this method. The glass transition temperature of the second polymerization step is not always easy to determine, as the curves sometimes overlap.It is known to those skilled in the art that according to Fox (T.G. Fox, Bull. Am. Phys. Soc. 1956 [Ser. II] 1, page 123 and according to Ullmann's Encyclopedia of Industrial Chemistry, vol. 19, page 18, 4th edition, Verlag Chemie, Weinheim, 1980) the glass transition temperature of at most weakly crosslinked copolymers may be estimated to a good approximation using the following formula:1 / Tg = xi / Tg1+ x2 / Tg2+ .... xn / Tg",wherein Xi, X2, .... Xn are the mass fractions of the monomers 1, 2, .... n and Tg1, Tg2, .... Tgnare the glass transition temperatures in degrees Kelvin of the respective polymers composed only of one of the monomers 1, 2, .... n. The glass transition temperatures of these homopolymers of most ethylenically unsaturated monomers are known (or may be determined experimentally in a simple manner known per se) and are recited for example in J. Brandrup, E.H. Immergut, Polymer Handbook 1st Ed. J. Wiley, New York, 1966, 2nd Ed. J. Wiley, New York, 1975 and 3rd Ed. J. Wiley, New York, 1989, and also in Ullmann's Encyclopedia of Industrial Chemistry, page 169, Verlag Chemie, Weinheim, 1992.Preferably, the inner phase polymer B is produced in a first stage and then the outer phase polymer A is produced in a second stage.Employed in the second polymerization stage are advantageously2 to 8% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate (monomers A1 ), preferably selected from the group consisting of acetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate, acetoacetoxyneopentyl methacrylate, acetoacetoxybutyl methacrylate and 2-(acetoacetoxy)ethyl methacrylate,250182915 to 30% by weight of at least one hydroxyalkyl(meth)acrylate selected from the group consisting of - hydroxyethyl acrylate and 2-hydroxyethyl methacrylate (monomers A2,1 to 5% by weight of at least one ethylenically unsaturated compound having at least one phosphorus- containing group (monomers A3), preferably selected from the group consisting of0 to 5% by weight of at least one ethylenically unsaturated carboxylic acid (monomers A4), preferably selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid and / or crotonic acid60% to 80% by weight of at least one ethylenically unsaturated compound distinct from the monomers A1 to A4 (monomers A5),and the amounts of the monomers A sum to 100% by weight.Additionally, the monomers A5 are preferably distributed into60% to 70% by weight selected from the group consisting of n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, styrene and / or methyl methacrylate (monomer A5-0) and> 0% and < 10% by weight of ethylenically unsaturated compound selected form the group consisting of 2- ureidoethyl (meth)acrylate, diacetone acrylamide, glycidyl methacrylate, 3- (methacryloyloxy)propyltrimethoxysilane, vinyltriethoxysilane, and (meth)acrylamide (monomer A5-1)> 0% and 55% by weight of ethylenically unsaturated compounds having a nonionic oligoalkylene ether moiety, and / or an ionic moiety derived from an organically bound carboxylic or sulphonic acid group (monomer A5-2)and the amounts of monomers A5-0, monomers A5-1 and monomers A5-2 sum to the amount of monomers A5.Employed in the second polymerization stage are advantageously2 to 7% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate selected from the group consisting of acetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate, acetoacetoxyneopentyl methacrylate, acetoacetoxybutyl methacrylate and 2-(acetoacetoxy)ethyl methacrylate(monomers A1),17 to 27% by weight of 2-hydroxyethyl acrylate and / or 2-hydroxyethyl methacrylate (monomers A2), 1 to 4% by weight of H2C=C(CH3)-C(=O)-[OCH(CH3CH2)]4-7-O-P(=O)(-OH)2 (monomer A3)1 to 5% by weight of acrylic acid and / or methacrylic acid a (monomers A4),60% to 75% by weight of at least one ethylenically unsaturated compound distinct from the monomers A1 to A4 and selected from the group consisting of methyl methacrylate, styrene and / or 2- ethylhexyl acrylate (monomers A5),> 0% and 55% by weight of ethylenically unsaturated compounds having a nonionic oligoalkylene ether moiety,25018210and / or an ionic moiety derived from an organically bound carboxylic or sulphonic acid group (monomer A5-2)and the amounts of the monomers A sum to 100% by weight.Contemplated monomers B2 include all of the abovementioned monomers A2. The amounts of monomers B2 are 10 to 30% by weight, advantageously 10 to 25% by weight and especially advantageously 10 to 23% by weight in each case based on the total monomer amount B.Contemplated monomers B3 include all of the abovementioned monomers A3. The amounts of monomers B3 are 5 0.1% by weight, advantageously < 0.05% by weight and especially advantageously < 0.01% by weight in each case based on the total monomer amount B.Contemplated monomers B4 include all of the abovementioned monomers A4. The amounts of monomers B4 are 5 0.5% by weight, advantageously < 0.1% by weight and especially advantageously < 0.01% by weight in each case based on the total monomer amount B.However, advantageously no monomers B3 and B4 whatsoever are employed.Contemplated monomers B5 in principle include all of the abovementioned monomers A5, wherein, however, the proportion of the functionalized ethylenically unsaturated monomers B5-1 is 55.0% by weight, advantageously 51% by weight and especially advantageously 50.1% by weight in each case based on the total amount of monomers B5.Particularly advantageously more than 80% by weight of monomer B5, most preferable more than 90% by weight of monomer B5 are selected from the group comprising n-butyl acrylate, n-butyl methacrylate, isobutyl methacrylate, isobutyl acrylate, tert-butyl acrylate, tert-butyl methacrylate, isopentyl acrylate, isopentyl methacrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, n-heptyl acrylate, styrene and methyl methacrylate. The monomers B5 are particularly advantageously selected to an extent of 100% by weight from the group comprising n-butyl acrylate, n-butyl methacrylate, iso-butyl methacrylate, isobutyl acrylate, isopentyl acrylate, isopentyl methacrylate, 2-ethylhexyl acrylate, n-heptyl acrylate, 2-octyl acrylate, styrene and methyl methacrylate.According to the invention the type and the amounts of the monomers B1 to B5 are chosen such that the polymer B obtained therefrom has a glass transition temperature TgBby Fox in the range from 0 to 35°C. Additionally the amounts of the monomers A1 to A5 are chosen such that the polymer A obtained therefrom after the polymerization has a glass transition temperature TgAby Fox in the range from >35 to 110°C, advantageously from 40°C to 100°C and particularly advantageously from > 50°C and 580°C and which is at least 15°C above the glass transition temperature TgBof polymer B.25018211Employed in polymerization stage B are advantageously2 to 8% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate selected from the group consisting of acetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate, acetoacetoxyneopentyl methacrylate, acetoacetoxybutyl methacrylate and2-(acetoacetoxy)ethyl methacrylate (monomers B1),10 to 25% by weight of at least one hydroxyalkyl(meth)acrylate selected from the group consisting of - hydroxyethyl acrylate and 2-hydroxyethyl methacrylate (monomers B2),0 to 0.05% by weight of at least one ethylenically unsaturated compound having at least one phosphorus- containing group (monomers B3), preferably selected from the group consisting ofO to 0.1% by weight of at least one ethylenically unsaturated carboxylic acid (monomers A4), preferably selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid and / or crotonic acid67% to 85% by weight of at least one ethylenically unsaturated compound distinct from the monomers B1 to B4, preferably selected from the group consisting of n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, styrene and / or methyl methacrylate (monomers B5)and particularly preferably2 to 7% by weight of acetoacetoxyethylmethacrylat (monomers B 1 ),10 to 23% by weight of 2-hyd roxyethy I acrylate and / or 2-hyd roxyethy I methacrylate (monomers B2), 0 to 0.05% by weight of H2C=C(CH3)-C(=O)-[OCH(CH3CH2)]4-7-O-P(=O)(-OH)2and / or H2C=C(CH3)-C(=O)- OCH2CH2-O-P(=O)(-OH)2(monomer B3)O to 0.1% by weight of acrylic acid and / or methacrylic acid a (monomers B4),50% to 80% by weight of at least one ethylenically unsaturated compound distinct from the monomers B1 to B4 (selected from the group consisting of methyl methacrylate, styrene and / or 2- ethylhexyl acrylate (monomers B5),the weight ratio of monomers B to monomers A is from 20:80 to 80:20, preferably from 50:50 to 80 :20 by weight and advantageously from 55:45 to 70:30.Preferred is the aqueous dispersion of a multiphase polymerwherein the polymer A is a copolymer of2 to 8% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate (monomers A1), 15 to 30% by weight of at least one hydroxyalkyl(meth)acrylate (monomers A2),1 to 5% by weight of at least one ethylenically unsaturated compound having at least one25018212phosphorus-containing group (monomers A3),0 to 5% by weight of at least one ethylenically unsaturated carboxylic acid (monomers A4), 60% to 80% by weight of at least one ethylenically unsaturated compound distinct from the monomers A1 to A4 (monomers A5),wherein the amounts of the monomers A sum to 100% by weight (total monomer amount A), and wherein polymer B is a copolymer of2 to 8% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate (monomers B1), 10 to 25% by weight of at least one hydroxyalkyl(meth)acrylate (monomers B2),0 to 0.05% by weight of at least one ethylenically unsaturated compound having at least one phosphorus-containing group (monomers B3),O to 0.1% by weight of at least one ethylenically unsaturated carboxylic acid (monomers B4), 67% to 85% by weight of at least one ethylenically unsaturated compound distinct from the monomers B1 to B4 (monomers B5),wherein the amounts of the monomers B sum to 100% by weight (total monomer amount B).The present invention further relates to a process for producing the aqueous dispersion of a multiphase polymer by free-radically initiated aqueous emulsion polymerization, the process comprising:free-radically polymerizing, in an aqueous medium and in the presence of a chain transfer agent,in a polymerization stage A1 to 10% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate (monomers A1),10 to 35% by weight of at least one hydroxyalkyl(meth)acrylate (monomers A2),1 to 6% by weight of at least one ethylenically unsaturated compound having at least one phosphorus- containing group (monomers A3),0 to 10% by weight of at least one ethylenically unsaturated carboxylic acid (monomers A4),% to 80% by weight of at least one ethylenically unsaturated compound distinct from the monomers A1 to A4(monomers A5), preferably more than 80% by weight of monomer A5, is selected from the group consisting of n-butyl acrylate, n-butyl methacrylate, iso-butyl methacrylate, isobutyl acrylate, isopentyl acrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, n-heptyl acrylate, styrene and methyl methacrylate,and the amounts of the monomers A sum to 100% by weight,and in a polymerization stage B1 to 10% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate (monomers B1),10 to 30% by weight of at least one hydroxyalkyl(meth)acrylate (monomers B2),O to 0.1% by weight of at least one ethylenically unsaturated compound having at least one phosphorus- containing group (monomers B3),0 to 0.5% by weight of at least one ethylenically unsaturated carboxylic acid (monomers B4),2501821360% to 89% by weight of at least one ethylenically unsaturated compound distinct from the monomers B1 to B4 (monomers B5), preferably more than 80% by weight of monomer B5, is selected from the group consisting of n-butyl acrylate, n-butyl methacrylate, iso-butyl methacrylate, isobutyl acrylate, isopentyl acrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, n-heptyl acrylate, styrene and methyl methacrylate and the amounts of the monomers B sum to 100% by weight,• and wherein either monomers B are polymerized in the presence of the polymer A or monomers A are polymerized in the presence of the polymer B,• the monomers are chosen to result in a calculated hydroxyl number of the multiphase polymer from 45 to 155 mg / g• and the weight ratio of monomers B to monomers A is from 20:80 to 80:20.The conduct of free-radically initiated emulsion polymerizations of ethylenically unsaturated compounds (monomers) in an aqueous medium has already been widely described and is therefore well known to the person skilled in the art [in this regard see Emulsions polymerisation [Emulsion Polymerization] in Encyclopedia of Polymer Science and Engineering, volume 8, pages 659 ff. (1987); D.C. Blackley, in High Polymer Latices, volume 1, pages 35 ff. (1966); H. Warson, The Applications of Synthetic Resin Emulsions, chapter 5, pages 246 ff. (1972); D. Diederich, Chemie in unsererZeit 24, pages 135 to 142 (1990); Emulsion Polymerisation, Interscience Publishers, New York (1965); DE-A 4003422 and Dispersionen synthetischer Hochpolymerer [Dispersions of Synthetic High Polymers], F. Hblscher, Springer-Verlag, Berlin (1969)]. The free-radically initiated aqueous emulsion polymerization is typically affected by dispersing the monomers, generally with inclusion of dispersing aids, such as emulsifiers and / or protective colloids, in aqueous medium and polymerizing them using at least one water-soluble free-radical polymerization initiator. Frequently, the residual contents of unconverted monomers in the aqueous polymer dispersions obtained are reduced using chemical and / or physical methods likewise known to a person skilled in the art [see for example EP-A 771328, DE-A 19624299, DE-A 19621027, DE-A 19741184, DE-A 19741187, DE-A 19805122, DE-A 19828183, DE-A 19839199, DE-A 19840586 and 19847115], the polymer solids content is adjusted to a desired value by diluting or concentrating, or further customary added substances, for example foam- or viscosity-modifying additives, are added to the aqueous polymer dispersion. The process according to the invention differs from this general procedure merely in that it is performed in two stages while observing the recited limiting parameters and the specific monomer compositions and a specific pH management.According to the invention it should be noted that the abovementioned monomers A1 to A5 may be employed individually or else as mixtures. Further it should be noted that the abovementioned monomers B1 to B5 may be employed individually or else as mixtures. Of the monomers B1 to B5 in each case the total amounts or portions may be initially charged in the aqueous polymerization medium before initiation of the polymerization reaction and any remaining portions may be added under polymerization conditions. However, it is also possible for the total amounts of the monomers B to be added to the aqueous polymerization medium under polymerization conditions.25018214In a preferred embodiment in the first polymerization stage at least a portion < 10% by weight of the total monomer amount B is initially charged in the aqueous polymerization medium before initiation of the polymerization reaction and the remaining residual amount is added to the aqueous polymerization medium under polymerization conditions while in the second polymerization stage the total amount of the monomers A1 to A5 (total monomer amount A) is added to the aqueous polymerization medium under polymerization conditions. The monomers A1 to A5 and B1 to B5 may each be added to the aqueous polymerization medium in individual streams, as a monomer mixture or in the form of an aqueous monomer emulsion discontinuously or continuously at constant or varying flow rates.However, it is particularly advantageous when the monomers of the first and the second polymerization stage are employed as monomer mixtures, especially advantageously as aqueous monomer emulsions each of them in its stage. Advantageously at least > 90% by weight and especially advantageously > 95% by weight or the total amounts of the monomer mixtures of the first stage are added as aqueous monomer emulsions under polymerization conditions and > 95% by weight or the total amounts of the monomer mixtures the second polymerization stages are added to the aqueous polymerization medium as aqueous monomer emulsions under polymerization conditions in the second stage.The polymerization is conducted in the presence of compounds which form free radicals (initiators). These may be peroxides, azo compounds or redox initiator systems. All these types of initiators are well known to the skilled person in the art and are described for example in WO 201991889, page 11.Initiation of the polymerization reaction is understood to mean the start of the polymerization reaction of the monomers present in the polymerization vessel after the free-radical initiator has formed free radicals. The polymerization reaction can be initiated by addition of free-radical initiator to the aqueous polymerization mixture in the polymerization vessel under polymerization conditions. However, it is also possible to add a portion or the total amount of the free-radical initiator to the aqueous polymerization mixture comprising the initially charged monomers in the polymerization vessel under conditions unsuitable for inducing a polymerization reaction, for example at low temperature, and then establish polymerization conditions in the aqueous polymerization mixture. Polymerization conditions are generally understood to mean those temperatures and pressures under which the free-radically initiated aqueous emulsion polymerization proceeds at sufficient polymerization rate. They depend particularly on the free-radical initiator used. It is advantageous when the type and amount of the free-radical initiator, the polymerization temperature and the polymerization pressure are selected such that the free-radical initiator has a half-life of < 3 hours and especially advantageously < 1 hour, and there are always sufficient starter free-radicals available to initiate and to maintain the polymerization reaction.A contemplated reaction temperature for the free-radically initiated aqueous emulsion polymerization is the entire range from 0°C to 170°C. Temperatures employed are generally 50 to 120°C, preferably 60 to 110°C and especially preferably 60 to 100°C. The free-radically initiated aqueous emulsion polymerization may be performed at a pressure25018215of less than, equal to or greater than 1 atm [1.013 bar (absolute), atmospheric pressure], and so the polymerization temperature may exceed 100°C and may be up to 170°C. In the presence of monomers A1 to B3 with a low boiling point, the emulsion polymerization is preferably performed under elevated pressure. In this case, the pressure may assume values of 1.2, 1.5, 2, 5, 10, 15 bar (absolute) or even higher values. If the emulsion polymerization is performed under reduced pressure, pressures of 950 mbar, frequently of 900 mbar and often 850 mbar (absolute) are established. Advantageously, the free-radical aqueous emulsion polymerization is performed at 1 atm with exclusion of oxygen, especially under an inert gas atmosphere, for example under nitrogen or argon.According to the invention the total amount of the free-radical initiator may be initially charged in the aqueous reaction medium before initiation of the polymerization reaction. However, it is also possible optionally to initially charge only a portion of the free-radical initiator in the aqueous reaction medium before initiation of the polymerization reaction and then add the total amount / any remaining residual amount in the first and / or second polymerization stage continuously or discontinuously according to consumption under polymerization conditions during the free-radically initiated emulsion polymerization. It is of course possible to use different free-radical initiators in different amounts in the first and in the second polymerization stage. In a preferred embodiment a portion of the free-radical initiators is initially charged in the aqueous reaction medium before initiation of the polymerization reaction and the remaining residual amount is added simultaneously with the monomer addition during the first and the second polymerization stage.The total amount of free-radical initiators is generally > 0.05% and < 5% by weight, preferably > 0.1% and < 3% by weight and particularly preferably > 0.1% and 51.5% by weight in each case based on the total monomer amount.To adjust the weight-average molecular weights of the polymers formed in the first and in the second polymerization stage, free-radical chain-transferring compounds (chain transfer agents) may be employed. Employed compounds are essentially aliphatic and / or araliphatic halogen compounds, such as, for example, n-butyl chloride, n-butyl bromide, n-butyl iodide, methylene chloride, ethylene dichloride, chloroform, bromoform, bromotrichloromethane, dibromodichloromethane, carbon tetrachloride, carbon tetrabromide, benzyl chloride, benzyl bromide, organic thio compounds, such as primary, secondary or tertiary aliphatic thiols, such as ethanethiol, n-propanethiol, 2-propanethiol, n-butanethiol, 2-butanethiol, 2-methyl-2-propanethiol, n-pentanethiol, 2-pentanethiol, 3-pentanethiol, 2-methyl-2-butanethiol, 3-methyl-2-butanethiol, n-hexanethiol, 2-hexanethiol, 3-hexanethiol, 2-methyl-2-pentanethiol, 3-methyl-2-pentanethiol, 4-methyl-2-pentanethiol, 2-methyl-3-pentanethiol, 3-methyl-3-pentanethiol, 2-ethylbutanethiol, 2-ethyl-2-butanethiol, n-heptanethiol and its isomeric compounds, n-octanethiol and its isomeric compounds, n-nonanethiol and its isomeric compounds, n-decanethiol and its isomeric compounds, n-undecanethiol and its isomeric compounds, n-dodecanethiol and its isomeric compounds, n-tridecanethiol and its isomeric compounds, substituted thiols, for example 2-hydroxyethanethiol, aromatic thiols, such as benzenethiol, ortho-, meta-, or paramethylbenzenethiol, mercaptoalkanoic acid and derivatives thereof, such as 6-methylheptyl 3-mercaptopropionate or 2-ethylhexyl 2-mercaptoethanoate, 2-ethylhexyl 3-mercaptopropionate, isooctyl 3-mercaptopropionate and all further sulfur compounds described in the polymer handbook 3rd edition, 1989, J. Brandrup and E.H. Immergut, John Wiley25018216& Sons, Section II, pages 133 to 141 , but also aliphatic and / or aromatic aldehydes, such as acetaldehyde, propionaldehyde and / or benzaldehyde, unsaturated fatty acids, such as oleic acid, dienes having nonconjugated double bonds, such as divinyl methane or vinylcyclohexane or hydrocarbons having easily abstractable hydrogen atoms, such as toluene for example. However, it is also possible to use mixtures of mutually nondisruptive representatives of the abovementioned chain transfer agents.According to the invention the total amount of the chain transfer agent may be initially charged in the aqueous reaction medium before initiation of the polymerization reaction. However, it is also possible optionally to initially charge only a portion of the chain transfer agent in the aqueous reaction medium before initiation of the polymerization reaction and then add the total amount / any remaining residual amount in the first and / or second polymerization stage continuously or discontinuously as required under polymerization conditions during the free-radically initiated emulsion polymerization. It is of course possible to use different chain transfer agents in different amounts in the first and in the second polymerization stage.The total amount of chain transfer agent is generally > 0% and < 5% by weight, preferably > 0.5% and < 3.5% by weight and particularly preferably > 1% and 53% by weight in each case based on the total monomer amount.According to a preferred embodiment of the invention the aqueous emulsion polymerization is performed in the presence of at least one phosphorus-containing dispersing aid. Suitable phosphorus-containing dispersing aids in principle include all dispersing aids comprising at least one phosphorus-containing group.Suitable phosphorus-containing dispersing aids include for example mono- and / or diesters of phosphoric acid with alkoxylated and / or non-alkoxylated Ce- to Cao-fatty alcohols, as disclosed, for example, in WO 2009 / 17757, sections

[0006] ,

[0007] and

[0034] to

[0065] or in WO 2009 / 115607, page 4, lines 22 to 34 and page 25, line 31 to page 26, line 14. It should be noted that in the context of the present document explicit reference is to be made to these literature citations and accordingly the phosphorus-containing dispersing aids disclosed therein should be considered as a constituent of this document.However, it is particularly advantageous in the context of the present document to employ phosphorus-containing dispersing aids selected from compounds of formula IIR1-(AO)m-O-P(=O)(OR2)(OH) Formula (II)whereinm represents an integer of 0 to 30, preferably 5 to 25 and especially preferably 5 to 20,AO represents oxyalkylene, as defined for the compounds of general formula I,R1represents Ce-Cso-alkyl, preferably C8-C22-alkyl and especially preferably Cn-Ci4-alkyl and25018217R2represents H or a group -(A0)m-R2a, wherein R2” is as defined for R1and AO and m have one of the definitions specified above, wherein, however, R2advantageously represents H and the alkali metal or ammonium salts of the abovementioned compounds of formula II.The abovementioned phosphorus-containing dispersing aids are familiar to those skilled in the art and commercially available, for example as Maphos® 24 T (BASF BTC), Maphos® 10 T (BASF BTC), Amphisol® A (DSM Nutritional Products Europe Ltd.), Colafax® CPE (Colonial Chemical, Inc.). Crodafos® MCA (Croda Inc.), Crodafos® CES (Croda Inc.), Crodafos® HCE (Croda Inc.), Crodafos® 1435 (Croda Inc.), Crodafos® CS 20 Acid (Croda Inc.), Crodafos® CP (Croda Inc.), Hostaphat® CC100 (Clariant International Ltd.), Rhodafac® RS-410 (Solvay S.A.) Rhodafac® RS-610 (Solvay S.A.), Rhodafac® RS-610 / A25 (Solvay S.A.), Rhodafac® RS-610 E (Solvay S.A.), Rhodafac® RS-710 (Solvay S.A.), Rhodafac® RS-710 E (Solvay S.A.) or Lutensit® A-EP (BASF SE).The amount of the at least one phosphorus-containing dispersing aid employed according to a preferred embodiment is > 0.5% by weight, advantageously > 0.5% and < 4.0% by weight, preferably > 0.5% and < 2.0% by weight and particularly preferably > 0.7% and 51.5% by weight in each case based on the total monomer amount.According to a preferred embodiment the total amount of the phosphorus-containing dispersing aid may be initially charged in the aqueous reaction medium before initiation of the polymerization reaction. However, it is also possible optionally to initially charge only a portion of the phosphorus-containing dispersing aid in the aqueous reaction medium before initiation of the polymerization reaction and then add the total amount / any remaining residual amount in the first or in the first and the second polymerization stage continuously or discontinuously as required under polymerization conditions during the free-radically initiated emulsion polymerization. It is of course possible to use different phosphorus-containing dispersing aids in different amounts in the first and in the second polymerization stage. Advantageously > 50% by weight of the at least one phosphorus-containing dispersing aid are added to the aqueous reaction medium during the polymerization reaction as a constituent of the aqueous monomer emulsion. However, it should be noted that at least a portion of the at least one phosphorus-containing dispersing aid is already present during the first polymerization stage. It is advantageous when the amount of the at least one phosphorus-containing dispersing aid is > 0.5% by weight and advantageously > 0.8% by weight at all times during the aqueous emulsion polymerization in each case based on the total amount of monomers A1 to B3 added to the aqueous polymerization mixture at the time in question.Optionally also employable in addition to the at least one phosphorus-containing dispersing aid are further protective colloids and / or emulsifiers typically used for performing free-radical aqueous emulsion polymerizations.Suitable protective colloids are, for example, polyvinyl alcohols, cellulose derivatives or copolymers comprising vinyl pyrrolidone. A detailed description of further suitable protective colloids may be found in Houben-Weyl, Methoden der organischen Chemie, vol. XIV / 1, Makromolekulare Stoffe, pages 411 to 420, Georg-Thieme-Verlag, Stuttgart, 1961. It is of course also possible to use mixtures of emulsifiers and / or protective colloids. Additional dispersing aidsemployed are preferably exclusively emulsifiers which unlike the protective colloids have relative molecular weights of typically below 1000. They may be either anionic, cationic, or nonionic. When mixtures of surface-active substances are used, the individual components must of course be compatible with one another and this may be checked using a few preliminary experiments if there is any doubt. Anionic emulsifiers are generally compatible with one another and with nonionic emulsifiers. The same also applies to cationic emulsifiers, whereas anionic and cationic emulsifiers are mostly not compatible with one another. Commonly used emulsifiers are, for example, ethoxylated mono-, di- and trialkylphenols (degree of ethoxylation: 3 to 50, alkyl radical: C4 to C12), ethoxylated fatty alcohols (degree of ethoxylation: 3 to 50; alkyl radical: C8 to C36) and alkali metal and ammonium salts of alkyl sulfates (alkyl radical: C8 to C12), of sulfuric monoesters of ethoxylated alkanols (degree of ethoxylation: 4 to 30, alkyl radical: C12 to C18) and ethoxylated alkylphenols (degree of ethoxylation: 3 to 50, alkyl radical: C4 to C12), of alkylsulfonic acids (alkyl radical: C12 to C18) and of alkylarylsulfonic acids (alkyl radical: C9 to C18). Further suitable emulsifiers are found in Houben-Weyl, Methoden der organischen Chemie, vol. XIV / 1, Makromolekulare Stoffe, pages 192 to 208, Georg-Thieme-Verlag, Stuttgart, 1961.Further surface-active substances that have proven suitable include compounds of general formula IIIFormula (III)wherein R3and R4represent hydrogen atoms or C4- to C24-alkyl and are not simultaneously hydrogen atoms, and M1and M2may be alkali metal ions and / or ammonium ions. In general formula III R3and R4preferably represent linear or branched alkyl radicals having 6 to 18 carbon atoms, especially having 6, 12 or 16 carbon atoms, or hydrogen, wherein R3and R4are not both simultaneously hydrogen atoms. M1and M2are preferably sodium, potassium or ammonium, wherein sodium is particularly preferred. Particularly advantageous compounds of general formula III are those in which M1and M2are sodium, R3is a branched alkyl radical having 12 carbon atoms and R4is a hydrogen atom or R3. Technical grade mixtures comprising a proportion of 50% to 90% by weight of the monoalkylated product, for example Dowfax® 2A1 (brand of Dow Chemical Company), are frequently used. The compounds of general formula III are common knowledge, for example from US-A 4269749, and are commercially available.If additional dispersing aids are employed in addition to the at least one phosphorus-containing dispersing aid it is advantageous to employ anionic and / or nonionic and especially advantageously anionic surfactants.The total amount of optional dispersing aids is generally > 0% and < 3.0% by weight, preferably > 0% and < 2.0% by weight and particularly preferably > 0.1% and 50.5% by weight in each case based on the total monomer amount.According to the invention the total amount of optional dispersing aid is added continuously or discontinuously as required in the first and / or second polymerization stage under polymerization conditions during the free-radically initiated emulsion polymerization. However, it is also possible optionally to initially charge the total amount or a portion of the optionally employed dispersing aid in the aqueous reaction medium before initiation of the polymerization reaction and add any remaining residual amount during the first and / or the second polymerization stage continuously or discontinuously.It should further be noted that the free-radically initiated aqueous emulsion polymerization in the first polymerization stage may optionally also be performed in the presence of a polymer seed, for example in the presence of 0.01% to 10% by weight, frequently of 0.05% to 7.0% by weight and often of 0.1% to 4.0% by weight of a polymer seed in each case based on the total amount of monomers.The process according to the invention is advantageously performed such that the second polymerization stage is only commenced once the total monomer amount of first polymerization stage has been converted to an extent of > 80% by weight, advantageously > 90% by weight, as is easily determinable using calorimetric measurements familiar to those skilled in the art.It is advantageous according to the invention when the pH of the aqueous polymerization mixture during both the first and the second polymerization stages is in the range 3 and 8 and especially advantageously in the range > 4.0 and 56.5, measured at room temperature. According to the invention pH measurement or pH testing is carried out such that via a small bypass conduit a small amount of the aqueous polymerization mixture is continuously discharged from the polymerization vessel and cooled to 20°C to 25°C (room temperature), the pH thereof is determined by means of a calibrated pH electrode and the aqueous polymerization mixture is then returned to the polymerization vessel. It is of course also possible to take a small sample of the aqueous polymerization mixture, cool it to room temperature, measure the pH and subsequently return the sample to the aqueous polymerization mixture.According to the invention pH adjustment may be carried out using any customary bases, such as alkali metal, alkaline earth metal or ammonium hydroxides or carbonates or hydrogencarbonates, for example NaOH, KOH, NH4OH, Ca(OH)2, Na2CO3, K2CO3, (NH4)CO3, NaHCO3, KHCO3or NH4HCO3. Likewise suitable as bases are ammonia and primary, secondary or tertiary organic amines and aminoalcohols, for example methylamine, ethylamine, 1 -propylamine, 2-propylamine, 1-n-butylamine, 2-n-butylamine, 2-methyl-1 -propylamine, 2-methyl-2-propylamine etc., dimethylamine, diethylamine, di-n-propylamine, diisopropylamine, di-n-butylamine, di-2-methylpropylamine etc., trimethylamine, triethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, tri-2-methylpropylamine, N,N-dimethylethanolamine, N,N-dimethylisopropanolamine, N,N-dimethylaminoethoxyethanol etc., but also mixed amines, such as N-methyl-N-ethylamine, N,N-dimethyl-N-ethylamine etc. Preferred bases are N,N-dimethylethanolamine, N,N-dimethylisopropanolamine and N,N-dimethylaminoethoxyethanol, 2-Dimethylamino-2-methylpropanol, 3-amino-3-methyl-2-butanol, N,N-dimethylmethoxypropylamine and N-methylmorpholine.20The aqueous polymer dispersion obtained after the second polymerization stage comprises polymer particles having a weight-average particle diameter in the range > 50 and 5500 nm, advantageously in the range > 50 and 5200 nm and especially in the range > 80 and 5150 nm. According to the invention determination of the weight-average particle diameter is generally carried out according to ISO 13321 with a High-Performance Particle Sizer from Malvern at 22°C and a wavelength of 633 nm.Preferably, the multiphase polymer according to the invention has a weight average molecular weight in the range from 5000 to 50000 g / mol determined by size exclusion chromatography (SEC).The present aqueous polymer dispersions are notable for high stability and minimal formation of coagulum.It should also be noted that the aqueous polymer dispersions obtainable by the process according to the invention and the polymer powders obtainable therefrom by drying are advantageously employable as a binder in the production of adhesives, sealants, renders, paper coating slips, fiber nonwovens, flexible roof coatings and paints and also in sand consolidation, as a component in the production of textile or leather auxiliaries and impact modifiers or for modification of mineral binders and plastics.The aqueous polymer dispersions according to the invention / the polymer powders thereof are especially advantageously suitable as binders in aqueous anticorrosion compositions for metal surfaces, wherein this is to be understood as also including the surfaces of metal alloys. If multilayer systems are employed the aqueous polymer dispersions according to the invention / the polymer powders thereof may be employed as binders in one or more layers.The aqueous polymer dispersions of the invention advantageously be used as binders for two-component coating compositions, as for example for varnishes, protective coatings, traffic markings, decorative coatings, paints, and other coatings.Suitable auxiliaries may be added for the various uses, such as, for example, flow control agents, thickeners, defoamers, fillers, pigments, pigment dispersing assistants, etc.The coatings may be obtained by applying the coating compositions to suitable substrates, such as wood, concrete, metal, glass, plastic, ceramics, plasters, stone, asphalt, textiles, and coated, primed, or weathered substrates.With particular advantage, however, the two-component coating compositions of the invention are suitable for coating metals and metal alloys, especially in light, medium, or heavy-duty corrosion control, and also for producing high-gloss coatings.25018221For the two-component coating compositions, besides the aqueous dispersion of the multiphase polymer of the invention, a further, crosslinker component is required, which advantageously comprises polyisocyanates, melamineformaldehyde resins and / or urea-formaldehyde resins, all known for these purposes to the skilled person.Also comprised in accordance with the invention, therefore, are aqueous coating compositions which in addition to the aqueous polymer dispersion of the invention further comprise at least one component selected from the group comprising polyisocyanate, melamine-formaldehyde resin, and urea-formaldehyde resin.Preferred is an aqueous two-component coating composition comprisinga) the aqueous dispersion of the multiphase polymer according to the invention (as a first component), and b) a polyisocyanate as the second component.The polyisocyanates which can be used in the two-component coating compositions of the invention are prepared by polymerization of monomeric aromatic, aliphatic and / or cycloaliphatic isocyanates, preferably of aliphatic and / or cycloaliphatic (in this specification, in abbreviated form, (cyclo)aliphatic isocyanates, and more preferably of aliphatic isocyanates.Aromatic isocyanates are those which comprise at least one aromatic ring system, in other words not only purely aromatic compounds but also araliphatic compounds. The former are isocyanates where the isocyanato groups are attached directly to aromatic ring systems, whereas in the case of the latter the isocyanato groups are attached to alkylene groups, but the compounds also comprise aromatic ring systems, as in the case of Tetramethylxylylene diisocyanate (TMXDI), for example.Cycloaliphatic isocyanates are those which comprise at least one cycloaliphatic ring system.Aliphatic isocyanates are those which comprise exclusively linear or branched carbon chains, i.e., acyclic compounds.The monomeric isocyanates are preferably diisocyanates, which carry precisely two isocyanate groups. They can, however, in principle also be monoisocyanates, having one isocyanate group.In principle, higher isocyanates having on average more than 2 isocyanate groups are also contemplated. Suitability therefor is possessed for example by triisocyanates such as triisocyanatononane, 2’-isocyanatoethyl2,6-diisocyanatohexanoate, 2,4,6-triisocyanatotoluene, triphenylmethane triisocyanate or 2,4,4’-triisocyanatodiphenyl ether, or the mixtures of diisocyanates, triisocyanates, and higher polyisocyanates that are obtained, for example, by phosgenation of corresponding aniline / formaldehyde condensates and represent methylene-bridged polyphenyl polyisocyanates.25018222These monomeric isocyanates do not contain any substantial products of reaction of the isocyanate groups with themselves.The monomeric isocyanates are preferably isocyanates having 4 to 20 C atoms. Examples of typical diisocyanates are aliphatic diisocyanates such as tetramethylene diisocyanate, pentamethylene 1,5-diisocyanate, hexamethylene diisocyanate (1,6-diisocyanatohexane), octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate, derivatives of lysine diisocyanate (e.g., methyl 2,6-diisocyanatohexanoate or ethyl 2,6-diisocyanatohexanoate), trimethylhexane diisocyanate or tetramethylhexane diisocyanate, cycloaliphatic diisocyanates such as 1,4-, 1,3- or 1,2-diisocyanatocyclohexane, 4,4’- or 2,4’-di-(isocyanatocyclohexyl)methane, 1-isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl)cyclohexane (isophorone diisocyanate), 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane or 2,4- or 2, 6-diisocyanato-1 -methylcyclohexane, and also 3 (or 4), 8 (or 9)-bis(isocyanatomethyl)tricyclo[5.2.1.026]decane isomer mixtures, and also aromatic diisocyanates such as tolylene 2,4- or 2,6-diisocyanate and the isomer mixtures thereof, m- or p-xylylene diisocyanate, 2,4’- or 4,4’-diisocyanatodiphenylmethane and the isomer mixtures thereof, phenylene 1 ,3- or 1 ,4-diisocyanate, 1 -chlorophenylene 2,4-diisocyanate, naphthylene 1,5-diisocyanate, diphenylene 4,4’-diisocyanate, 4,4’-diisocyanato-3,3’-dimethylbiphenyl, 3-methyldiphenylmethane 4,4’-diisocyanate, tetramethylxylylene diisocyanate, 1,4-diisocyanatobenzene or diphenyl ether4,4’-diisocyanate.Particular preference is given to hexamethylene 1 ,6-diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, isophorone diisocyanate, and 4,4’- or 2,4’-di(isocyanatocyclohexyl)methane, very particular preference to isophorone diisocyanate and hexamethylene 1,6-diisocyanate, and especial preference to hexamethylene 1,6-diisocyanate.Mixtures of said isocyanates may also be present.Isophorone diisocyanate is usually in the form of a mixture, specifically a mixture of the cis and trans isomers, generally in a proportion of about 60:40 to 90:10 (w / w), preferably of 70:30 to 90:10.Dicyclohexylmethane 4,4’-diisocyanate may likewise be in the form of a mixture of the different cis and trans isomers.As diisocyanates it is possible to use not only those diisocyanates obtained by phosgenating the corresponding amines but also those prepared without the use of phosgene, i.e. , by phosgene-free processes. According to EP-A-126299 (US 4596678), EP-A-126300 (US 4596679), and EP-A-355443 (US 5087739), for example, (cyclo)aliphatic diisocyanates, such as hexamethylene 1,6-diisocyanate (HDI), isomeric aliphatic diisocyanates having 6 carbon atoms in the alkylene radical, 4,4’- or2,4’-di(isocyanatocyclohexyl)methane, and 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane (isophorone diisocyanate or IPDI), for example, can be prepared by reacting the (cyclo)aliphatic diamines with, for example, urea and alcohols to give (cyclo)aliphatic biscarbamic esters and subjecting said esters to thermal cleavage into the corresponding diisocyanates and alcohols. The synthesis takes place usually continuously in a circulation process and optionally in the presence of N-unsubstituted carbamic esters, dialkyl carbonates, and other by-products recycled from the reaction process. Diisocyanates obtained in this25018223way generally contain a very low or even unmeasurable fraction of chlorinated compounds, which Is advantageous, for example, In applications In the electronics Industry.In one embodiment of the present Invention the Isocyanates used have a total hydrolyzable chlorine content of less than 200 ppm, preferably of less than 120 ppm, more preferably less than 80 ppm, very preferably less than 50 ppm, In particular less than 15 ppm, and especially less than 10 ppm. This can be measured by means, for example, of ASTM specification D4663-98. Of course, though, monomeric isocyanates having a higher chlorine content can also be used, of up to 500 ppm, for example.It will be appreciated that it is also possible to employ mixtures of those monomeric isocyanates which have been obtained by reacting the (cyclo)aliphatic diamines with, for example, urea and alcohols and cleaving the resulting (cyclo)aliphatic biscarbamic esters, with those diisocyanates which have been obtained by phosgenating the corresponding amines.The polyisocyanates which can be formed by oligomerizing the monomeric isocyanates are generally characterized as follows:The average NCO functionality of such compounds is in general at least 1.8 and can be up to 8, preferably 2 to 5, and more preferably 2.4 to 4.The isocyanate group content after oligomerization, calculated as NCO = 42 g / mol, is generally from 5% to 25% by weight unless otherwise specified.The polyisocyanates are preferably compounds as follows:1) Polyisocyanates containing isocyanurate groups and derived from aromatic, aliphatic and / or cycloaliphatic diisocyanates. Particular preference is given in this context to the corresponding aliphatic and / or cycloaliphatic isocyanatoisocyanurates and in particular to those based on hexamethylene diisocyanate and isophorone diisocyanate. The isocyanurates present are, in particular, trisisocyanatoalkyl and / or trisisocyanatocycloalkyl isocyanurates, which constitute cyclic trimers of the diisocyanates, or are mixtures with their higher homologs containing more than one isocyanurate ring. The isocyanatoisocyanurates generally have an NCO content of 10% to 30% by weight, in particular 15% to 25% by weight, and an average NCO functionality of 2.6 to 8. The polyisocyanates containing isocyanurate groups may to a minor extent also comprise urethane groups and / or allophanate groups, preferably with a bound-alcohol content of less than 2% by weight, based on the polyisocyanate.2) Polyisocyanates containing uretdione groups and having aromatically, aliphatically and / or cycloaliphatically attached isocyanate groups, preferably aliphatically and / or cycloaliphatically attached, and in particular those25018224derived from hexamethylene diisocyanate or isophorone diisocyanate. Uretdione diisocyanates are cyclic dimerization products of diisocyanates.The polyisocyanates containing uretdione groups are obtained frequently in a mixture with other polyisocyanates, more particularly those specified under 1). Polyisocyanates containing uretdione groups typically have functionalities of 2 to 3.For this purpose the diisocyanates can be reacted under reaction conditions under which not only uretdione groups but also the other polyisocyanates are formed, or the uretdione groups are formed first of all and are subsequently reacted to give the other polyisocyanates, or the diisocyanates are first reacted to give the other polyisocyanates, which are subsequently reacted to give products containing uretdione groups.3) Polyisocyanates containing biuret groups and having aromatically, cycloaliphatically or al iphatically attached, preferably cycloaliphatically or al iphatically attached, isocyanate groups, especially tris(6- isocyanatohexyl)biuret or its mixtures with its higher homologs. These polyisocyanates containing biuret groups generally have an NCO content of 18% to 24% by weight and an average NCO functionality of 2.8 to 6.4) Polyisocyanates containing urethane groups and / or allophanate groups and having aromatically, aliphatically or cycloaliphatically attached, preferably aliphatically or cycloaliphatically attached, isocyanate groups, of the kind obtained, for example, by reaction of excess amounts of diisocyanate, such as of hexamethylene diisocyanate or of isophorone diisocyanate, with mono- or polyhydric alcohols. These polyisocyanates containing urethane groups and / or allophanate groups generally have an NCO content of 12% to 24% by weight and an average NCO functionality of 2.0 to 4.5.Polyisocyanates of this kind containing urethane groups and / or allophanate groups may be prepared without catalyst or, preferably, in the presence of catalysts, such as ammonium carboxylates or ammonium hydroxides, for example, or allophanatization catalysts, such as bismuth, cobalt, cesium, Zn(ll) orZr(IV) compounds, for example, in each case in the presence of monohydric, dihydric or polyhydric, preferably monohydric, alcohols.These polyisocyanates containing urethane groups and / or allophanate groups occur frequently in hybrid forms with the polyisocyanates specified under 1).5) Polyisocyanates comprising oxadiazinetrione groups, derived preferably from hexamethylene diisocyanate or isophorone diisocyanate. Polyisocyanates of this kind comprising oxadiazinetrione groups are accessible from diisocyanate and carbon dioxide.6) Polyisocyanates comprising iminooxadiazinedione groups, derived preferably from hexamethylene diisocyanate or isophorone diisocyanate. Polyisocyanates of this kind comprising iminooxadiazinedione groups are preparable from diisocyanates by means of specific catalysts.7) Uretonimine-modified polyisocyanates.8) Carbodiimide-modified polyisocyanates.9) Hyperbranched polyisocyanates, of the kind known for example from DE-A 10013186 or DE-A 10013187.10) Polyurethane-polyisocyanate prepolymers, from di- and / or polyisocyanates with alcohols.11 ) Polyurea-polyisocyanate prepolymers.12) The polyisocyanates 1)-11 ), preferably 1), 3), 4), and 6), described under the abovementioned points, can be converted, following their preparation, into polyisocyanates containing biuret groups or urethane / allophanate groups and having aromatically, cycloaliphatically or aliphatically attached, preferably (cyclo)aliphatically attached, isocyanate groups. The formation of biuret groups, for example, is accomplished by addition of water or by reaction with amines. The formation of urethane groups and / or allophanate groups is accomplished by reaction with monohydric, dihydric or polyhydric, preferably monohydric, alcohols, in the presence optionally of suitable catalysts. These polyisocyanates containing biuret groups or urethane / allophanate groups generally have an NCO content of 10% to 25% by weight and an average NCO functionality of 3 to 8.13) Hydrophilically modified polyisocyanates, i.e., polyisocyanates which as well as the groups described under 1) to 12) also comprise groups which result formally from addition of molecules containing NCO-reactive groups and hydrophilizing groups to the isocyanate groups of the above molecules. The latter groups are nonionic groups such as alkylpolyethylene oxide and / or ionic groups derived from phosphoric acid, phosphonic acid, sulfuric acid or sulfonic acid, and / or their salts.14) Modified polyisocyanates for dual cure applications, i.e., polyisocyanates which as well as the groups described under 1) to 13) also comprise groups resulting formally from addition of molecules containing NCO- reactive groups and UV-crosslinkable or actinic-radiation-crosslinkable groups to the isocyanate groups of the above molecules. These molecules are, for example, hydroxyalkyl (meth)acrylates and other hydroxy-vinyl compounds.In one preferred embodiment of the present invention, the polyisocyanates are hydrophilically modified polyisocyanates or mixtures of hydrophilically modified and nonmodified polyisocyanates.In a particularly preferred embodiment at least 50% by weight, particularly preferred 60% by weight of the polyisocyanates are nonmodified polyisocyanates. Even more preferably at least 75% by weight, most preferably at least 90% by weight of the polyisocyanates are nonmodified polyisocyanates.In one particularly preferred embodiment, the polyisocyanate comprises polyisocyanates based on 1,6-hexamethylene diisocyanate.In one further particularly preferred embodiment, the polyisocyanate comprises a mixture of polyisocyanates, very preferably of 1,6-hexamethylene diisocyanate and of isophorone diisocyanate.In one particularly preferred embodiment, the polyisocyanate is a mixture comprising low-viscosity polyisocyanates, preferably polyisocyanates comprising isocyanurate groups, having a viscosity of 600 to 1500 mPa*s, more particularly below 1200 mPa*s, low-viscosity urethanes and / or allophanates having a viscosity of 200 to 1600 mPa*s, more particularly 600 to 1500 mPa*s, and / or polyisocyanates comprising iminooxadiazinedione groups.In this specification, unless noted otherwise, the viscosities reported are determined at 23°C in accordance with DIN EN ISO 3219 / A.3 in a cone / plate system with a shear rate of 1000 s1.The process for preparing the polyisocyanates may take place as described in WO 2008 / 68198, especially from page 20 line 21 to page 27 line 15 therein, which is hereby made part of the present specification by reference.The reaction can be discontinued, for example, as described therein from page 31 line 19 to page 31 line 31, and working up may take place as described therein from page 31 line 33 to page 32 line 40, which in each case is hereby made part of the present specification by reference.The reaction can alternatively also be discontinued as described in WO 2005 / 087828 from page 11 line 12 to page 12 line 5, which is hereby made part of the present specification by reference.In the case of thermally labile catalysts it is also possible, furthermore, to discontinue the reaction by heating the reaction mixture to a temperature above at least 80°C, preferably at least 100°C, more preferably at least 120°C. Generally, it is sufficient for this purpose to heat the reaction mixture, in the way which is necessary at the working-up stage in order to separate the unreacted isocyanate by distillation.In the case both of thermally non-labile catalysts and of thermally labile catalysts, the possibility exists of terminating the reaction at relatively low temperatures by addition of deactivators. Examples of suitable deactivators are hydrogen chloride, phosphoric acid, organic phosphates, such as dibutyl phosphate or diethylhexyl phosphate, carbamates such as hydroxyalkyl carbamate, or organic carboxylic acids.27These compounds are added neat or diluted in a suitable concentration as necessary to discontinue the reaction.As second component it is also possible to use blocked polyiscocyanate compounds, for thermally cured polyurethane coatings.As a second component in two-component coating compositions, it is also possible to use melamine-formaldehyde resins and urea-formaldehyde resins, especially for thermally cured / baked coatings.Melamine-formaldehyde resins can be characterized according to fields of application (molding compounds, glues, impregnating resins, coating materials), alkylating compounds (etherification with butanol, methanol, mixed etherification) or, as listed here, according to the ratio of triazine to formaldehyde to etherifying alcohol:1. fully to highly methylolated and fully alkylated to highly alkylated resins (HMMM grades)2.1 partly methylolated and highly alkylated resins (high imino grades)2.2. partly methylolated and partly alkylated resins (methylol grades)3. resins with a low degree of methylolation (melamine-formaldehyde condensates)The first major group, that of the fully etherified melamine-formaldehyde resins, in which the so-called molar melamine:formaldehyde:alcohol incorporation ratio is theoretically 1 :6:6, in practice generally 1 :>5.5:>5.0, and usually 1 :>5.5:>4.5, is distinguished by extremely good high-solids behavior (relatively low viscosity at high solids content). In this group of crosslinkers, the free formaldehyde is readily reducible, owing to the low viscosity of the amino resin. At the present time it is possible to achieve a free formaldehyde content of < 0.3% by weight. The commercial products usually comprise methanol as the alcohol, although grades with mixed etherification, or fully butylated grades, are also known.The fully etherified melamine-formaldehyde resins are employed in practice preferably in can coatings and coil coatings worldwide, and in NAFTA also for all coats of the automotive coat system.The low thermal reactivity under baking conditions, such as 20 minutes at 140°C, necessitates catalysis with strong acids for these fully etherified melamine-formaldehyde resins. This results in very rapid curing, and a homogeneous co-network as a result of transetherification with the binder, accompanied by the release of the etherifying alcohols. With this strong-acid catalysis, very short cure times are possible, as with partly methylolated melamine-formaldehyde resins. Crosslinking may be accompanied by formaldehyde emission which goes well beyond the free formaldehyde and is due to the redissociation of methylol groups.The second major group, that of the partly etherified melamine-formaldehyde resins, which in practice usually have a molar melamine:formaldehyde:alcohol incorporation ratio of 1 :3 to 5.4:2 to 4.3, is distinguished by a much higher thermal reactivity than that of the first group, without acid catalysis. The production of these crosslinkers is25018228accompanied by self-condensation, which leads to a higher viscosity (lower high-solids behavior) and so makes it more difficult to remove the free formaldehyde at distillation. For these products, a free formaldehyde content of 0.5% to 1.5% by weight is standard, although there are also products having a free formaldehyde content of 0.3% to 3% by weight. Here again, methylated and butylated grades and also grades with mixed etherification are widely encountered as commercial products. Etherification with further alkylating substances is described in the literature and available in the form of specialty products.High-imino grades and methylol grades, each as a subgroup, both feature incomplete methylolation, i.e. , molar formaldehyde incorporation ratios of less than 1 :5.5. The high-imino grades differ from the methylol grades, however, in a high degree of alkylation, i.e., the fraction of etherified methylol groups as a proportion of the formaldehyde equivalents incorporated, of usually up to 80% by weight, whereas the figure for the methylol grades is generally < 70% by weight.Applications for the partly methylolated melamine-formaldehyde resins extend across all fields of use, including combinations with HMMM grades, for adaptation of reactivity, where curing temperatures of 100 to 150°C are called for. Additional catalysis using weak acids is possible and is common practice.Besides the reaction of the melamine-formaldehyde resins with the two-stage polymer of the aqueous polymer dispersion of the invention, there is a substantially increased proportion of self-crosslinking on the part of the melamine-formaldehyde resin with itself. The consequence is a reduced elasticity in the system as a whole, and this must be compensated by appropriate selection of the co-component. Set against this is the advantage of reduced total formaldehyde emission from the coatings produced from the system.The structure of the melamine-formaldehyde resins which can be employed in accordance with the invention is advantageously as follows:As mentioned earlier, melamine-formaldehyde resins are frequently characterized by way of the molar melamine:formaldehyde:alcohol incorporation ratio. The alcohol here is preferably selected from the group consisting of methanol, ethanol, isobutanol and n-butanol or mixtures thereof, and more preferably selected from the group consisting of methanol and n-butanol.Melamine-formaldehyde resins which can be used in accordance with the invention may have a molar incorporation ratio of 1 : (2 to 6) : (1 to 6), though in individual cases, as a result of the formation of oligoformal chains, the formaldehyde incorporation ratio may even be up to 8.Preferred molar incorporation ratios are 1 : (3 to 6) : (1.5 to 6).25018229For methyl-etherified melamine-formaldehyde resins, molar incorporation ratios of 1 : (3.6 to 5.7) : (2.1 to 4.7) are particularly preferred; very much preferred are molar incorporation ratios of 1 : (5 to 6) : (3.5 to 6), more particularly 1 : (5 to 6) : (4 to 5).For n-butyl-etherified melamine-formaldehyde resins, molar incorporation ratios of 1 : (3.2 to 5.7) : (1.3 to 4) are particularly preferred; very much preferred are molar incorporation ratios of 1 : (5 to 6) : (3.5 to 6), more particularly 1 : (5 to 6) : (3.5 to 4.5).The melamine-formaldehyde resins that can be used may have not only one melamine group per polycondensate but, indeed, two or more melamine groups, preferably up to six, more preferably up to four, very preferably up to three, and more particularly up to two.The structure of urea-formaldehyde resins which can be used in accordance with the invention is advantageously as follows:The molar urea:formaldehyde:alcohol incorporation ratio is 1 : (1 to 4) : (0.3 to 3), preferably 1 : (1 to 3) : (0.4 to 2), more preferably 1 : (1.5 to 2.5) : (0.5 to 1.5), and very preferably 1 : (1.6 to 2.1) : (0.6 to 1.3).The alcohol here is preferably selected from the group consisting of methanol, ethanol, isobutanol, and n-butanol or mixtures thereof, more preferably selected from the group consisting of methanol and n-butanol.The aqueous coating composition of the invention, comprising the aqueous polymer dispersion of the invention and at least one component selected from the group comprising polyisocyanate, melamine-formaldehyde resin and ureaformaldehyde resin, is especially suitable in one particular embodiment as a binder for paints and as a binder for varnishes.Where the aforementioned aqueous compositions are used for producing varnishes and paints, these aqueous compositions preferable further comprise pigments, fillers and / or anticorrosion agents.Pigments used in this case may in principle be all organic and / or inorganic white and / or chromatic pigments familiar to the skilled person, with a particle size 518 mesh.The most important white pigment on the basis of its high refractive index (rutile: 2.70 and anatase: 2.55) and its high hiding power, is titanium dioxide in its various modifications. However, both zinc oxide and zinc sulfide as well are used as white pigments. These white pigments may be employed in surface-coated form or uncoated form.In addition to white pigments, for color design, any of a very wide variety of chromatic pigments comprise to the skilled person may be used, examples being the somewhat more reasonably priced inorganic iron, cadmium,25018230chromium and lead oxides and / or sulfides, lead molybdate, cobalt blue or carbon black, and also the somewhat more expensive organic pigments, examples being phthalocyanines, azo pigments, quinacridones, perylenes or carbazoles.It will be appreciated that the aqueous compositions may, in addition to the pigments, also comprise what are called fillers, familiar to the skilled person. Fillers are essentially inorganic materials in powder form, having a particle size < 18 mesh, with a refractive index lower than that of the pigments (white fillers, according to DIN 55943 and DIN 55945, have refractive index values < 1.7). The fillers in powder form are often naturally occurring minerals, such as calcite, chalk, dolomite, kaolin, talc, mica, diatomaceous earth, barytes, quartz or talc / chlorite intergrowths, for example, or else synthetically produced inorganic compounds, such as precipitated calcium carbonate, calcined kaolin or barium sulfate, and fumed silica, for example. A preferred filler used is calcium carbonate, in the form of the crystalline calcite or of the amorphous chalk.Anticorrosion agents contemplated include, in accordance with the invention, corrosion inhibitors or anticorrosion pigments, in particular.Examples of corrosion inhibitors are set out in "Corrosion Inhibitors, 2nd Edition. An Industrial Guide", Ernest W. Flick, Ed: William Andrew Inc ISBN: 978-0-8155-1330-8. Preferred corrosion inhibitors are hexamine, benzotriazole, phenylenediamine, dimethylethanolamine, polyaniline, sodium nitrite, cinnamaldehyde, condensation products of aldehydes and amines (imines), chromates, nitrites, phosphates, hydrazine, and ascorbic acid.Examples of anticorrosion pigments are modified zinc orthophosphates (for example, HEUCOPHOS® ZPA, ZPO, and ZMP), polyphosphates (for example HEUCOPHOS® ZAPP, SAPP, SRPP, and CAPP), WSA - Wide Spectrum Anticorrosives (for example HEUCOPHOS® ZAMPLUS and ZCPPLUS) and modified silicate pigments (for example HEUCOSIL® CTF, Halox® 750), from Heubach GmbH, for example, and also barium borophosphate (for example Halox® 400), barium phosphosilicates (for example Halox® BW-111, Halox® BW-191), calcium borosilicates (for example Halox® CW-291, CW-22 / 221, CW-2230), calcium phosphosilicate (for example Halox® CW-491), strontium phosphosilicate (for example Halox® SW-111) or strontium zinc phosphosilicate (for example, Halox® SZP-391), from Halox®.The application of the aqueous composition, especially aqueous coating materials, especially advantageously paints and varnishes, to a substrate may take place in a known way, as for example by spraying, trowling, knifecoating, brushing, rolling, roller coating, or pouring. The coating thickness is generally in a range from about 10 to 500 pm, and preferably 30 to 200 pm. The volatile constituents of the aqueous composition are removed subsequently by drying. This operation may if desired be repeated one or more times.Drying is familiar to the skilled person and takes place for example in a tunnel oven or by flashing. Drying may also take place by means of NIR radiation, with NIR radiation here referring to electromagnetic radiation in the wavelength25018231range from 760 nm to 2.5 pm, preferably from 900 to 1500 nm. Drying may take place at a temperature from ambient temperature to 100°C over a period of a few minutes to several days.The aqueous compositions, more particularly the paints and varnishes comprising anticorrosion agents, are suitable advantageously for the coating of metallic surfaces. These may in principle be the surfaces of any desired metals. More particularly, however, they are those metals or alloys which are typically used as metallic construction materials and which require protection from corrosion.For corrosion control, the aqueous compositions are used to treat, as substrates, the surfaces of iron, steel, Zn, Zn alloys, Al or Al alloys. These metallic, advantageously grease-free surfaces may be uncoated, may be coated with zinc, aluminum or alloys thereof, may be hot dip galvanized, electroplated with zinc, sherardized, or precoated with primers. In addition, it is also well known to the person skilled in the art that, to reinforce the adhesion of the paint, and hence improve corrosion resistance, different types of treatments are employed for the metal and alloy surfaces which are either inorganic, organic or inorganic-organic hybrid chemistries, such as, for example, either an iron- or zinc-phosphating, chromating, oxalate or anodizing process, titanium / zirconium- or silane-based technologies. Also possible is to clean the metal / alloy surfaces by the physical / mechanical methods such as sand blasting or abrasive cleaning.The surfaces in question are, in particular, those of iron, steel, zinc, zinc alloys, aluminum or aluminum alloys. Steel may comprise the typical alloying components known to the skilled worker. The surfaces in question may be surfaces of structures composed entirely of the stated metals or alloys. Alternatively they may be the surfaces of structures coated with Zn, Zn alloys, Al or Al alloys, the structures being able to be composed of other materials, for example of other metals, alloys, polymers or composites. In one preferred embodiment of the invention the surfaces are those of untreated steel or of galvanized and / or aluminized steel.Zinc alloys or aluminum alloys are known to the skilled worker. Typical constituents of zinc alloys comprise, in particular, Al, Pb, Si, Mg, Sn, Cu or Cd. Typical constituents of aluminum alloys comprise, in particular, Mg, Mn, Si, Zn, Cr, Zr, Cu or Ti. The term "zinc alloy" is also intended to include Al / Zn alloys in which Al and Zn are present in approximately equal quantity. The skilled worker selects the nature and amount of alloying constituents in accordance with the desired end application. Zn or aluminum coatings can be applied to steel by means for example of hot dip methods, such as hot dip galvanizing, or by means of sherardizing. Where the component is stationary or the geometry of the component does not permit otherwise, corresponding coats can also be applied by means of thermal spraying (spray galvanizing, spray aluminizing).By means of the aqueous polymer dispersions of the invention, more particularly the aqueous compositions of the invention, it is possible advantageously to provide corrosion protection to metallic surfaces, which in the course of service are in contact with atmospheric air, although the surfaces in question may also be those which in the course of service are in contact with water, soil or other corrosive media.25018232The metallic surfaces to be protected against corrosion by means of the aqueous polymer dispersions of the invention, in particular the aqueous compositions of the invention, may in principle be any desired surfaces.Preferably, though, they are the surfaces of metallic structures or metal constructions and / or their required components. Metal constructions and structures are typically joined from construction-grade steel, such as steel girders, steel pipes or steel panels, by riveting, welding or screwing, to form corresponding constructions. In one embodiment of the invention the coated articles may be stationary metallic constructions such as, for example, buildings, bridges, power masts, tanks, containers, buildings, pipelines, power plants, chemical plants, ships, cranes, posts, bulkheads, valves, pipes, tanks, fittings, flanges, couplings, halls, roofs, and construction-grade steel. Even more preferably, the metallic surfaces to be protected are of transportation vehicles, e.g. commercial vehicles, trains or ACE (Agriculture, construction and earthmoving equipment) or even automotive coatings including OEM and repair / refinish coatings. In the case of this embodiment, corrosion control coatings are typically applied by spreading or spraying on site. This corrosion control may be either first-time control or a renovation. The drying and curing of such corrosion control coatings takes place under atmospheric conditions, in other words at ambient temperature, and in the presence of air and typical atmospheric humidity. The relative atmospheric humidity may have any desired value, but is preferably between 10% and 80% and more preferably between 30% and 70%. Depending on the degree of protection required, the protection of surfaces against corrosion by means of corrosion control paints is also referred to as light, medium, and heavy duty corrosion control.The aqueous polymer dispersions of the invention and more particularly the aqueous compositions of the invention can be used as or in preparations for the treatment of metallic surfaces.In light, medium or heavy duty corrosion control this can be accomplished by means, for example, of spray application or spread application, the paint being subsequently cured under atmospheric conditions. It is of course also possible to apply two or more paints or coatings, identical or different in composition, in succession. The overall thickness (dry) of corrosion control paints of this kind is determined by the skilled worker in accordance with the desired properties of the corrosion control coat. It amounts, for example, to at least 25 pm, in general to at least 40 pm, preferably at least 50 pm, more preferably at least 60 pm, and very preferably at least 80 pm, in particular at least 100 pm, especially at least 125 pm, often at least 150 pm, and even at least 175 pm or at least 200 pm. The upper limit for the overall coat thickness, i.e., the thickness of all applied corrosion control coats together, is 2 mm, preferably less than 1.5 mm, more preferably less than 1 mm, very preferably less than 800 pm, and in particular less than 500 pm.The coating composition of the invention can be applied in any desired way, as for example by spreading or spraying.The present invention further relates to a process for coating metal surfaces, wherein the aqueous coating composition according to the invention is applied to a metal surface and subsequently dried.25018233The curing method is guided by the nature of the crosslinker and takes place as a general rule under atmospheric conditions.The temperature needed for curing is guided in particular by the crosslinker employed. Highly reactive crosslinkers can be cured at lower temperatures than less reactive crosslinkers.The term "atmospheric corrosion control" means in the context of this specification that the coating material, which comprises at least one polymer dispersion of the invention, has a coat thickness after drying of at least 40 pm, preferably at least 50 pm, more preferably at least 60 pm, and very preferably at least 80 pm, and a coat thickness of up to 2 mm, preferably less than 1.5 mm, more preferably less than 1 mm, very preferably less than 800 pm, and in particular less than 500 pm, the coating material curing following application to the surface under typical ambient conditions, i.e. , for instance, at ambient temperature or at room temperature, in the presence of air and also typical atmospheric humidity, without the use of additional apparatus or installations. Typical cure temperatures, depending on the ambient environment, are more than 0 to 40°C, preferably 5 to 35°C, more preferably 10 to 30°C, and very preferably 15 to 25°C in the presence of air and typical atmospheric humidity. The relative atmospheric humidity may be whatever is desired, and is preferably between 10% and 80% and more preferably between 30% and 70%. It is clear to the skilled person that the time to complete curing of one and the same binder system may differ according to the ambient conditions that are actually prevailing.In a further embodiment, the aqueous polymer dispersions and aqueous compositions of the invention may be used in clearcoats and in so-called direct-to-metal coatings; in the case of the clearcoat materials, in general no pigments and no anticorrosion agents are used. Clearcoat materials are applied as a single coat to the metal and find application especially when chemical resistance or gloss is required in addition to a corrosion control effect. It will be appreciated that the polymer dispersions and aqueous compositions of the invention can also be used in what are called topcoat materials. These topcoat materials, however, generally comprise pigments. For clearcoat and topcoat materials, typical dry film thicknesses are 15 to 200 pm, preferably 20 to 100 pm, and more preferably 20 to 80 pm.The aqueous compositions of the invention applied to a substrate, and paints or varnishes based thereon, are baked at a temperature between room temperature and 200°C, preferably 30 to 150°C, even more preferably 60 to 100°C and most preferably 60 - 80°C over a period from 1 minute to 120 minutes, preferably 10 to 60 minutes even more preferable 15 min to 40 min.With particular preference the aqueous polymer dispersions and aqueous compositions of the invention are used in anticorrosion agents which are employed in corrosiveness categories C2 (to DIN EN ISO 12944) or higher, preferably in corrosiveness categories C3 or higher, and more preferably in corrosiveness categories C4 or higher.The corrosiveness categories in accordance with DIN EN ISO 12944, based on the mass loss per unit area or on the thickness reduction after the first year of ambient storage, are defined as follows for unalloyed steel and for zinc:25018234C2 (low corrosivity): unalloyed steel: mass loss > 10- 200 g / m2thickness decrease > 1.3 - 25 pmzinc: mass loss > 0.7- 5 g / m2thickness decrease > 0.1 - 0.7 pmC3 (medium corrosivity): unalloyed steel: mass loss > 200 - 400 g / m2thickness decrease > 25-50 pmzinc: mass loss > 5- 15 g / m2thickness decrease > 0.7 - 2.1 pmC4 (high corrosivity): unalloyed steel: mass loss > 400 - 650 g / m2thickness decrease > 50 -80 pmzinc: mass loss > 15- 30 g / m2thickness decrease > 2.1 - 4.2 pmC5-I / M (very high): unalloyed steel: mass loss > 650 - 1500 g / m2thickness decrease > 80 - 200 pmzinc: mass loss > 30- 60 g / m2thickness decrease > 4.2 - 8.4 pmImportantly it is easily possible (by freeze or spray drying, for example) to obtain, from the aqueous polymer dispersions of the invention, the corresponding polymer powders. These inventively accessible polymer powders can likewise be employed as binders in the production of adhesives, sealants, synthetic resin renders, papercoating slips, nonwoven fiber webs, flexible roof coatings, and paints and varnishes, and also in sand consolidation, as a component in the production of textile assistants or leather assistants, and impact modifier, or for the modification of mineral binders and plastics.The present invention further provides coating compositions comprising- at least one aqueous polymer dispersion of the invention as binder,- optionally at least one other binder, different from the aqueous polymer dispersion of the invention,- optionally at least one crosslinker selected from the group consisting of polyisocyanates, melamine-formaldehyde resins, and urea-formaldehyde resins,- optionally at least one pigment, and- optionally at least one corrosion inhibitor.The optionally employed other binders different from the aqueous polymer dispersions of the invention may be, for example, water-based, water-dilutable, water-miscible polyacrylate polyols, polyester polyols, polyether polyols, polyurethane polyols; polyurea polyols; polyester polyacrylate polyols; polyester polyurethane polyols; polyurethane25018235polyacrylate polyols, polyurethane-modified alkyd resins; fatty acid modified polyester polyurethane polyols, copolymers with allyl ethers, graft polymers of the stated groups of substances with, for example, different glass transition temperatures, and also mixtures of the stated binders. Preferred are polyacrylate polyols, polyester polyols, and polyurethane polyols.Preferred hydroxyl numbers of these other binders, measured in accordance with DIN 53240-2 (by potentiometry), are 40 to 350 mg KOH / g and preferably 80 to 180 mg KOH / g resin solids for polyester polyols, and 15 to250 mg KOH / g and preferably 80 to 160 mg KOH / g resin solids for polyacrylate polyols, and also 10 to150 mg KOH / g and preferably 20 to 100 mg KOH / g resin solids for polyurethane polyols.These other binders may additionally have an acid number in accordance with DIN EN ISO 3682 (by potentiometry) of up to 200 mg KOH / g, preferably up to 150 and more preferably up to 100 mg KOH / g binder.Particularly preferred other binders are polyacrylate polyols, polyetherpolyol and polyesterols.Polyacrylate polyols preferably have a number-average molecular weight Mnof at least 500 g / mol, more preferably at least 1200 g / mol. The molecular weight Mnmay in principle have no upper limit, or be preferably up to 50000 g / mol, more preferably up to 20000 g / mol, very preferably up to 10000 g / mol, and more particularly up to 5000 g / mol.The number-average molecular weights are determined by gel permeation chromatography, which is familiar to the skilled person, using suitable calibration compounds.Further other binders are, for example, polyester polyols of the kind obtainable by condensing polycarboxylic acids, more particularly dicarboxylic acids, with polyols, more particularly diols. In order to ensure that the polyester polyol has a functionality appropriate for the polymerization use is also made in part of triols, tetrols, etc., and of tribasic acids, etc.Polyester polyols are known for example from Ullmann’s Enzyklopadie der technischen Chemie, 4th edition, volume 19, pages 62 to 65. It is preferred to use polyester polyols obtained by reacting dihydric alcohols with dibasic carboxylic acids. In place of the free polycarboxylic acids it is also possible to use the corresponding polycarboxylic anhydrides or corresponding polycarboxylic esters of lower alcohols or mixtures thereof to prepare the polyester polyols. The polycarboxylic acids may be aliphatic, cycloaliphatic, aromatic or heterocyclic and may optionally be substituted, by halogen atoms, for example, and / or unsaturated.The aqueous compositions comprising the dispersions according to the invention formulated as primer or topcoat show excellent properties. The coatings show very good adhesion and very good corrosion protection.The invention is to be illustrated using the following, nonlimiting examples.25018236ExamplesExample 1 (Dispersion 1)A polymerization vessel equipped with feeding devices and temperature regulation was charged at room temperature under a nitrogen atmosphere with287.8 g of deionized water and5.5 g of a 25% by weight aqueous solution of a phosphorus-containing dispersing aid (Rhodafac®RS610 / A25)and this initial charge was heated to 85°C with stirring. When this temperature had been reached, 21.9 g of feed 1 were added, after waiting for 2 min, 29.3 g of 1.5% strength by weight aqueous solution of ammonium peroxodisulfate were added and the reaction mass is stirred for further 5 min at the abovementioned temperature. Then remining amount of Feed 1 and 29.3 g of 1.5% strength by weight aqueous solution of ammonium peroxodisulfate were added to the reactor over the course of 105 minutes at constant flow rate. After that 13.7 water added to the reactor through rinsing the addition vessel. Thereafter, the polymerization mixture was left to react for another 15 minutes at 85°C. Subsequently, feed 2 and was metered in continuously over the course of 65 minutes at a constant flow rate. Simultaneously 29.3 g of 1.5% strength by weight aqueous solution of ammonium peroxodisulfate was also added at constant rate in 65 minutes. After that 31.4 g water added to the reactor through rinsing the addition vessel. After the end of feed 2, the polymerization mixture was left to react at 85°C for a further 105 minutes. After 75 min of end of Feed 2, 5.5 g of Surfynol 465 (non-ionic surfactant) was added to the polymerization mixture in 5 min. Then the reactor mass was cooled to 60°C and 32.1 g of 30% strength by weight aqueous solution of N,N dimethylisopropanolamine was added. Thereafter the aqueous polymer dispersion obtained was cooled to room temperature and filtered through a 50 pm filter.Feed 1 (homogeneous mixture comprising monomers B):110.0 g deionized water,7.7 g of a 25% by weight aqueous solution of a phosphorus-containing dispersing aid (Rhodafac® RS610 / A25)5.5 g Surfynol 465 (non-ionic surfactant)74.3 g styrene (20.8 wt.-%),121.0 g iso-butyl methacrylate (33.8 wt-%),88.0 g 2-ethylhexyl acrylate (24.6 wt.-%)16.50 g acetoacetoxyethyl methacrylate, (4.6 wt.-%)58.9 g 2-hydroxyethyl methacrylate (16.2 wt-%)4.4 g isooctyl 3-mercaptopropionate25018237Feed 2 (homogeneous mixture comprising monomers A):55.0 g deionized water,11.0 g of Adeka Reasoap SR 1025 (25% by weight aqueous solution of a reactive surfactant, 1.4 wt.-%) 2.8 g Surfynol 46535.8 g styrene (18.6 wt.-%),82.5 g iso-butyl methacrylate (42.9 wt.-%),13.2 g methyl methacrylate (6.9 wt.-%)44.9 g 2-hydroxyethyl methacrylate (22.9 wt.-%)8.8 g acetoacetoxyethyl methacrylate, (4.6 wt.-%)3.85 g 2-hydroxyethyl methacrylate phosphate (2.0 wt.-%)4.4 g methacrylic acid, and (2.3 wt.-%)5.0 g isooctyl 3-mercaptopropionate,The resulting polymer dispersion had a solids content of 47.7 wt%. The mean particle diameter of the dispersion particles obtained was 115 nm. The calculated hydroxyl number of the dispersion polymer was 78 mg of KOH / g. The weight-average molecular weight of the multiphase polymer was 25800 g / mol.The solids contents of the obtained aqueous polymer dispersions were generally determined by drying a defined amount of the aqueous polymer dispersion (about 0.8 g) to constant weight at a temperature of 160°C using a Mettler Toledo HR73 moisture analyzer. Two measurements were carried out in each case. The value reported in the examples is the average of these two measurements.The pH was generally determined using a calibrated InPro® 325X pH electrode from Mettler-Toledo GmbH.The hydroxyl number is defined according to DIN EN ISO 4629-1:2016-12.The calculated hydroxyl number is defined as the ratio of the theoretical mass of potassium hydroxide (in mg) equivalent to the moles of hydroxyl groups theoretically present in a gram of the multiphase polymer, supposing that all monomers used are converted to the polymer (100% conversion).Performance tests:Determination of fineness of grind in pigment dispersionThe fineness of grind was determined according to DIN EN ISO 1524 using a Hegman Grindometer. A fineness of 10 pm or less is considered to be good for glossy paints.Gloss / HazeThe gloss of cured paint films was measured using a Byk-lnstruments’ micro-TRI-gloss instrument according to DIN EN ISO 2813. The dry film thickness and substrate will be provided in the context of the test results. A waterbased25018238paint with a gloss of 60 at 60° angle is considered glossy, below 60 it is considered semi-glossy, above 80 it is considered high-glossAdhesionThe painted and cured sheets are tested for paint adhesion to the metal substrate using the cross-cut test according to DIN EN ISO 2409. A cross-cut test result of GT0 is rated very good, GT1 is good, GT2 acceptable.Wet adhesion of cured paint on metal substrates was done similar to DIN EN ISO 2812-4 (Version A) using distilled water. After 24 h exposure the water was removed and immediately afterwards a cross-cut test according to DIN EN ISO 2409 was performed on the wetted area. After 24 h of recovery at room temperature the cross-cut test was repeated at another spot of the previously wetted paint film. Besides the cross-cut rating a good result is the absence of blisters ( 0 (SO) according to DIN EN ISO 4628-2) and rust (Ri 0 according to DIN EN ISO 4628-3).Film thicknessThe dry film thickness of the cured coating films was determined according to DIN EN ISO 2808 using an Eddy-current gauge.HardnessThe hardness of the cured coating films was measured according to DIN EN ISO 1522 (pendulum hardness according to Konig in oscillations).Determination of resistance to liquidsThis test was done according to DIN EN ISO 2812-3: filter paper was dipped into liquid substances and placed on top of the panels (horizontal orientation). At the end of the test period the filter paper was removed, and the test panels wiped dry and cleaned with water or solvents that do not attack the coating. The exposed area was immediately assed for blistering (ISO 4628-2) and visible changes to the surfaces were rated according to ISO 4628-1. A test result of 0 is considered excellent, 1-2 good, 3 acceptable, 4-5 bad.(Neutral) Salt Spray Test:To test the anticorrosion properties a salt spray test according to DIN EN ISO 9227. The test specimens shall be placed in the cabinet so that they are not in the direct line of travel of the spray from the atomizer. The upper part of the cabinet is designed in a way that drops of sprayed solution formed on its surface do not fall on the specimens being tested. The test specimens shall be arranged so that they do not contact with the cabinet and so that surfaces to be tested are exposed to free circulation of spray. The sodium chloride concentration of the sprayed solution collected was 50 g / l ± 5 g / l. The specific gravity range for a 50 g / l ± 5 g / l solution is 1.029 to 1.036 at 25 °C. The pH of the salt solution was adjusted to 6.5 to 7.2 at 25 ± 2 °C (corrections were done by adding hydrochloric acid or sodium hydroxide accordingly). The test temperature was 35 ± 2°C.25018239A straight scratch or scribe mark through the coating to the substrate was made in accordance with ISO 17872 using a scratch stylus according to Sikkens with a 0.5 mm thick blade. The vertical scribe was made of the length of at least 9 cm and 3 cm from bottom edge of the test panel. Then, uncoated areas of the panels were careful sealed using self-adhesive tape and placed in the cabinet as described above. The test panels were periodically examined for any sign of blisters or corrosion at the time interval of 48 h, 96 h, 168 h, 240 h, 480 h and 720 h or longer if the coating is still good after 720 h. At the end of the test period, the test specimens were removed from the cabinet, the residues of spray solution were carefully removed from their surfaces by gently rinsing the test panel in clean running water. The panels are evaluated for• Crosscut adhesion according to DIN EN ISO 2409• Degree of blistering according to DIN EN ISO 4628-2, size 0-5, quantity (density): 0-5• Corrosion around scribe• Delamination (mm)• Rust Creepage (mm)• Flaking (mm)The conditioning of the panel before the test is described in test results.Resistance to humidity:The resistance of the coating to humidity was tested according to DIN EN ISO 6270-2. The conditioning of the test panels before testing is described in the test results. The panels’ uncoated areas are sealed using self-adhesive tape. The test panels were then placed at an angle > 60° in the chamber, making sure they do not touch each other and maintaining following distances:distance from the walls: not less than 100 mmdistance from the water surface: not less than 200 mmdistance between the samples: not less than 20 mmThe chamber was maintained stable at 40 + / - 3°C temperature and 100% humidity with dewing of the samples at constant condensation-water climate. The test panels were periodically examined at the time interval of 48 h, 96 h, 168 h, 240 h, 480 h, 720 h or further until the first signs of blisters were observed on the panel. After the test was completed, the panels were examined for• Crosscut adhesion according to DIN EN ISO 2409, immediately (Oh) and after 24 h recovery at ambient temperature• Degree of blistering according to DIN EN ISO 4628-2, size 0-5, quantity (density): 0-5 immediately (Oh) and after 24 h recovery at RT• Any signs of corrosion25018240Preparation of formulations:Example 2: Preparation and application of 2K polyurethane coating using inventive example 1preparation of White pigment paste (PP1)Using following composition, the pigment paste is produced by dispersing the Titanium dioxide and barium sulfate (Blanc fixe) in the remaining liquid medium in the following composition. Pigments were dispersed using a dissolver with a Teflon disc and 2 mm glass beads to the fineness of <10 micron.Composition of pigment paste (PP1)Preparation of Component A using inventive dispersion 1 (A1)To prepare the component A for the 2K polyurethane coating, dispersion in inventive example 1 along with other the solvents and additives, were added to the pigment paste (PP1) as per the following formulation and sequence. The component A with solid content of 55% was obtained.25018241Preparation of component B1 (Crosslinker)Under mixing, Basonat® HI 2000, was dissolved in Rhodiasolv ® RPDE (from Solvay) to give a 65 wt% homogeneous solution.Where, Basonat® HI 2000 (from BASF) is a low viscous HDI-based polyisocyanate, which is without any modification with hydrophilic group.Preparation and application of 2K polyurethane coating (C1)Under mixing in high-speed dissolver, at 600 rpm, to 100 g of component A1, 18.2 g component B1 was added. The mixture was then stirred at 1200 - 1300 rpm for 3 minutes and 5 g water was added and mixed to give a ready to apply paint system, which can be applied after waiting for 30 min. The cold rolled steel panels (Gardobond OC) were uniformly coated by this paint system by using a box type drawdown applicator to give dry film thickness of approximately 50 - 60 pm. After application, panels were given flash-off at ambient condition for 30 minutes and forced dried in oven at 60°C for 2 h. The test panels for chemical resistance were further matured for 24 h at ambient condition before the test. For Humidity test and neutral salt spray test, the panels were seasoned for 48h at 60°C before the test to ensure the fully matured curing of coating as it would be in field condition after several days.25018242Application test results of C1 : Gloss, Adhesion and HardnessThe films showed very glossy coatings with excellent adhesion.Application test results of C1 : resistance to liquidsNote: test result of 0 is considered excellent, 1-2 good, 3 acceptable, 4-5 badThe coating made in this invention demonstrated excellent chemical resistance properties.Application test results of C1 : humidity ResistanceThe Humidity test was stopped at the time when the film started showing blisters, therefore the durations in the following table indicate the end of the test.25018243The inventive coating could stand up to 720 h in humidity test, which is very good performance for water-based coatings.Application test results of C1 : Corrosion resistance - neutral salt spray test (SST)The inventive coating demonstrated very good corrosion resistance up to 720 h of the test with a formulation free of any anticorrosive pigments.

Claims

25018244CLAIMS1. An aqueous dispersion of a multiphase polymer obtainable by a free-rad ically initiated aqueous emulsion polymerization, comprising an outer phase polymer A and an inner phase polymer B, wherein polymer A is a copolymer of1 to 10% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate (monomers A1), 10 to 35% by weight of at least one hydroxyalkyl(meth)acrylate (monomers A2),1 to 6% by weight of at least one ethylenically unsaturated compound having at least one phosphorus-containing group (monomers A3),O to 10% by weight of at least one ethylenically unsaturated carboxylic acid (monomers A4), 50% to 80% by weight of at least one ethylenically unsaturated compound distinct from the monomers A1 to A4 (monomers A5),and the amounts of the monomers A sum to 100% by weight (total monomer amount A), and wherein polymer B is a copolymer of1 to 10% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate (monomers B1), 10 to 30% by weight of at least one hydroxyalkyl(meth)acrylate (monomers B2),O to 0.1% by weight of at least one ethylenically unsaturated compound having at least one phosphorus-containing group (monomers B3),0 to 0.5% by weight of at least one ethylenically unsaturated carboxylic acid (monomers B4), 60% to 89% by weight of at least one ethylenically unsaturated compound distinct from the monomers B1 to B4 (monomers B5),and the amounts of the monomers B sum to 100% by weight (total monomer amount B),with the proviso thateither polymer B is obtainable by polymerizing monomers B in the presence of the polymer A or polymer A is obtainable by polymerizing monomers A in the presence of the polymer B, the multiphase polymer has a calculated hydroxyl number from 45 to 155 mg KOH / g,the weight ratio of monomers B to monomers A is from 20:80 to 80:20.

2. The aqueous dispersion of a multiphase polymer according to claim 1 , wherein the monomers A4 are selected from the group consisting of are acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid and / or cratonic acid.250182453. The aqueous dispersion of a multiphase polymer according to either of claims 1 and 2, wherein the monomers A3 employed are vinylphosphonic acid, 3-phospho-2-hydroxypropyl(meth)acrylate, and / or a (meth)acryl(poly)alkoxy phosphate and / or salt thereof.

4. The aqueous dispersion of a multiphase polymer according to any of claims 1 to 3, wherein more than 80% by weight of monomer A5, is selected from the group consisting of n-butyl acrylate, n-butyl methacrylate, isobutyl methacrylate, isobutyl acrylate, tert-butyl acrylate, tert-butyl methacrylate, isopentyl acrylate, isopentyl methacrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, n-heptyl acrylate, styrene and methyl methacrylate and / or more than 80% by weight of monomer B5, is selected from the group consisting of n-butyl acrylate, n-butyl methacrylate, iso-butyl methacrylate, isobutyl acrylate, isopentyl acrylate, isopentyl methacrylate, 2-ethylhexyl acrylate, n-heptyl acrylate, 2-octyl acrylate, styrene and methyl methacrylate.

5. The aqueous dispersion of a multiphase polymer according to any of claims 1 to 4, wherein the polymer A is a copolymer of2 to 8% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate (monomers A1), 15 to 30% by weight of at least one hydroxyalkyl(meth)acrylate (monomers A2),1 to 5% by weight of at least one ethylenically unsaturated compound having at least one phosphorus-containing group (monomers A3),0 to 5% by weight of at least one ethylenically unsaturated carboxylic acid (monomers A4), 60% to 80% by weight of at least one ethylenically unsaturated compound distinct from the monomers A1 to A4 (monomers A5),wherein the amounts of the monomers A sum to 100% by weight (total monomer amount A), and wherein polymer B is a copolymer of2 to 8% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate (monomers B1), 10 to 25% by weight of at least one hydroxyalkyl(meth)acrylate (monomers B2),0 to 0.05% by weight of at least one ethylenically unsaturated compound having at least one phosphorus-containing group (monomers B3),O to 0.1% by weight of at least one ethylenically unsaturated carboxylic acid (monomers B4), 67% to 85% by weight of at least one ethylenically unsaturated compound distinct from the monomers B1 to B4 (monomers B5),wherein the amounts of the monomers B sum to 100% by weight (total monomer amount B).

6. The aqueous dispersion of a multiphase polymer according to any of claims 1 to 5, wherein up to 10% by weight of monomer A5 is selected from the group consisting of 2-ureidoethyl (meth)acrylate, ureidoethyl (meth)acrylamide, glycidyl methacrylate, 3-(methacryloyloxy)propyltrimethoxysilane, vinyltriethoxysilane, and (meth)acrylamide and / or up to 10% by weight of monomer B5 is selected from the group consisting of 2-25018246ureidoethyl (meth)acrylate, ureidoethyl (meth)acrylamide, glycidyl methacrylate, 3- (methacryloyloxy)propyltrimethoxysilane, vinyltriethoxysilane, and (meth)acrylamide.

7. The aqueous dispersion of a multiphase polymer according to any of claims 1 to 6, wherein the weight average molecular weight of the multiphase polymer is 5000 - 50000 g / mol determined by size exclusion chromatography (SEC).A process for producing an aqueous dispersion of a multiphase polymer by free-radically initiated aqueous emulsion polymerization in the presence of a chain transfer agent,in a polymerization stage A1 to 10% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate (monomers A1), 10 to 35% by weight of at least one hydroxyalkyl(meth)acrylate (monomers A2),1 to 6% by weight of at least one ethylenically unsaturated compound having at least one phosphorus-containing group (monomers A3),0 to 10% by weight of at least one ethylenically unsaturated carboxylic acid (monomers A4), 50% to 80% by weight of at least one ethylenically unsaturated compound distinct from the monomers A1 to A4 (monomers A5),and the amounts of the monomers A sum to 100% by weight,and in a polymerization stage B1 to 10% by weight of at least one acetoacetoxy(C2-C8)alkyl(meth)acrylate (monomers B1), 10 to 30% by weight of at least one hydroxyalkyl(meth)acrylate (monomers B2),O to 0.1% by weight of at least one ethylenically unsaturated compound having at least one phosphorus-containing group (monomers B3),0 to 0.5% by weight of at least one ethylenically unsaturated carboxylic acid (monomers B4), 60% to 89% by weight of at least one ethylenically unsaturated compound distinct from the monomers B1 to B4 (monomers B5),and the amounts of the monomers B sum to 100% by weight,• and wherein either monomers B are polymerized in the presence of the polymer A or monomers A are polymerized in the presence of the polymer B,• the monomers are chosen to result in a calculated hydroxyl number of the multiphase polymer from 45 to 155 mg / g• and the weight ratio of monomers B to monomers A is from 20:80 to 80:20.

9. The process according to claim 8, wherein the polymerization stages 1 and 2 are performed at a pH in the range > 3 and < 8 measured at room temperature.2501824710. A process according to claim 8 or 9, wherein the aqueous polymerization is performed in the presence of at least one phosphorus-containing dispersing aid.

11. The use of the dispersion of a multiphase polymer according to any of claims 1 to 7 as a binder in an aqueous coating composition.

12. The use of the dispersion of a multiphase polymer according to any of claims 1 to 7 as a binder in aqueous anticorrosion coating compositions for metal surfaces.

13. An aqueous two-component coating composition comprisinga) First component comprising the aqueous dispersion of the multiphase polymer according to any of claims 1 to 7, andb) Second component comprising a polyisocyanate, a melamine-formaldehyde resins and / or a ureaformaldehyde resins, preferably a polyisocyanate.

14. An aqueous coating composition according to claim 13, wherein the molar ratio of the isocyanate groups in the polyisocyanate component to the hydroxyl groups in the polyacrylate component is in the range from 0.2:1 to 5:1.

15. An aqueous coating composition according to claim 13 or 14, wherein the composition further comprises pigments, fillers and / or anticorrosion agents.

16. A process for coating a substrate, by applying the coating composition according to any of claims 13 to 15 to the substrate selected from the group consisting of wood, concrete, metal, glass, plastic, ceramics, plasters, stone, asphalt and textiles, and coated, primed, or weathered substrates and preferably metal.

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