WO2021209543A1

WO2021209543A1 - Aqueous polymer dispersions

Info

Publication number: WO2021209543A1
Application number: PCT/EP2021/059767
Authority: WO
Inventors: Thomas Wolf; Hans-Juergen Denu; Joerg Alexander DIMMER; Immanuel WILLERICH; Xavier MOLLAT DU JOURDIN
Original assignee: Basf Se
Priority date: 2020-04-17
Filing date: 2021-04-15
Publication date: 2021-10-21
Also published as: CN115461385A; EP4136130A1

Abstract

The present invention relates to aqueous polymer dispersions, which are obtainable by a free radical aqueous emulsion polymerization of ethylenically unsaturated monomers M, which comprise a) 0.5 to 7.0% by weight, based on the total weight of monomers M, of a combination of a1 ) at least one monomer Ma1, selected from monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms and the salts thereof; a2) at least one monomer Ma2, selected from monoethylenically unsaturated dicarboxylic acids having 4 to 8 carbon atoms and the salts thereof; a3) at least one monomer Ma3, selected from monoethylenically unsaturated monosulfonic acids having 2 to 10 carbon atoms and the salts thereof; b1) 60 to 79.45% by weight, based on the total weight of monomers M, of at least one monomer Mb1, which is selected from nonionic monoethylenically unsaturated monomers having a solubility in deionized water of at most 60 g/L at 25°C and 1 bar, and whose homopolymers have a glass transition temperature Tg of at least 50°C; b2) 20 to 39.45% by weight, based on the total weight of monomers M, of at least one monomer Mb2, which is selected from nonionic monoethylenically unsaturated monomers having a solubility in deionized water of at most 60 g/L at 25°C and 1 bar, and whose homopolymers have a glass transition temperature Tg of at most 40°C; c) 0.05 to 2.0% by weight of at least one crosslinking monomer Mc; where the aqueous emulsion polymerization is carried out at least partly in the presence of a chain transfer compound. The invention also relates to a process for producing the aqueous polymer dispersions. The aqueous polymer dispersions are useful as binders in water-borne coating formulations, in particular as binder in water-borne coating formulations for shaped mineral articles.

Description

Aqueous polymer dispersions

The present invention relates to aqueous polymer dispersions, which are obtainable by a free radical aqueous emulsion polymerization of ethylenically unsaturated monomers M which comprise a) monoethylenically unsaturated monomers selected from acidic monomers, b1) nonionic monoethylenically unsaturated monomers Mb1 having a solubility in deionized water of at most 60 g/L at 25°C and 1 bar, whose homopolymers have a glass transition temperature Tg of at least 50°C and b2) nonionic monoethylenically unsaturated monomers Mb2 having a solubility in deionized water of at most 60 g/L at 25°C and 1 bar, whose homopolymers have a glass transition temperature Tg of at most 40°C.

The invention also relates to a process for producing the aqueous polymer dispersions. The aqueous polymer dispersions are useful as binders in water-borne coating formulations, in particular as binder in water-borne coating formulations for shaped mineral articles.

BACKGROUND ON THE INVENTION

Polymer dispersions of polymerized ethylenically unsaturated monomers M are commonly known, in particular as binder component. As a binder, in particular in coatings, one of the important requirements for such binders is that they provide high mechanical strength and hardness to the coating and, hence, provide good stability against mechanical impact and good blocking resistance. At the same time, the coating must be elastic in order to compensate mechanical stress. For exterior coatings, such as architectural coatings and coatings for shaped mineral articles, a low water-uptake and a good soil resistance and a good resistance against lichen and moss growth are also desirable.

Shaped mineral articles are shaped articles, which are essentially made of a mineral material, which comprises a mineral binder, in particular a cement binder. Specifically, a shaped article is an article, which is prepared from a hydraulically setting composition, e.g. a mortar, comprising a mineral binder, water, aggregates, and, if appropriate pigments, auxiliaries, by shaping the hydraulically setting composition followed by the hardening as a function of time, if appropriate, under exposure to elevated temperature. Mineral binders are finely divided inorganic substances, such as lime, gypsum, clay, fly ash, pozzolanic materials and/or cement, which are hydraulically setting, i.e. when they are mixed with water they undergo stone-like solidification as a function of time. In a mortar, the mineral binder will likewise harden or cure. Thereby, the mortar undergoes stone-like solidification as a function of time, in the air or else underwater, if appropriate with exposure to elevated temperature. Shaped mineral articles, more particularly of concrete roof tiles, may comprise several layers of mineral material comprising one or more mineral binders, where the different layers may have identical or different overall compositions (see e.g. DE 3932573 and GB 2,030,890).

Examples of shaped mineral articles for coating in accordance with the invention are concrete pipes of the kind used to transport waste water, concrete roof tiles, curbstones, steps, floor slabs, base slabs based on mineral binders, and also fiber cement slabs and fiber cement boards, respectively, i.e. flat shaped mineral articles filled with organic or inorganic fibers, such as polyester fibers or nylon fibers, for example.

A particular problem associated with shaped mineral articles is the incidence of efflorescence phenomena. These phenomena are probably attributable to the fact that the mineral binders comprise polyvalent cations, such as Ca²⁺ in an alkaline environment. Under exposure to water, the ionic constituents are leached out and migrate to the surface, where they react with the carbon dioxide from the air and cause the formation, on the surface of the shaped mineral articles, of white lime spots, which are unsightly and are relatively insoluble in water. The phenomenon of efflorescence may occur either during the actual hardening or curing of freshly prepared, shaped mineral articles, during the storage in packaging of the mineral articles or on exposure to weathering of shaped mineral articles, which have already hardened. In order to mitigate the aforementioned problems, the shaped mineral articles are frequently provided with a coating. For this purpose, use is generally made of water borne coating compositions, whose binder constituent is an aqueous polymer dispersion. Since efflorescence will already occur during the actual setting of the hydraulically setting composition, such a coating is typically applied to the shaped mineral article even before it has cured. After curing or setting, it is possible to carry out coating a second or further times with a paint or with a clearcoat material with subsequent drying in each case. However, the properties of the first generation varnishes were not particularly satisfactory with regard to their protection against efflorescence. Apart from that, coatings of this kind are easily soiled.

The protection of shaped mineral articles from the above-described efflorescence has been improved by means of coating materials based on styrene/acrylate dispersions or straight-acrylate dispersions, as described in EP 469295, DE 19514266, EP 821660 and DE 10343726. The prior-art coatings all have the disadvantage that their water absorption is comparatively high. This water absorption harbors the risk of leaching of low molecular mass constituents of the coating on prolonged weathering, such as of surface-active substances, which are frequently used in the preparation of the aqueous formulations. Water absorption is manifested, for example, in increased blushing or in embrittlement of the coating. Moreover, the absorption of water, owing to the associated swelling of the polymer, results in a reduction in a coating's mechanical stability and may also cause leaching of emulsifiers, which would result in an increase in the surface slippiness, which is likewise unwanted on grounds of safety. In the case of pigmented coatings, moreover, there is a risk of the perceived color undergoing adverse alteration as a result of the absorption of water of the coating.

EP 915071 discloses coating compositions for coating shaped mineral articles, where the coating composition contains an aqueous polymer dispersion as a binder, which is based on copolymers of ethylenically unsaturated monomers comprising more than 0.2% to 5% by weight of itaconic acid and which have reduced water-uptake.

WO 2009/080614 discloses aqueous polymer dispersions, which are prepared by a radical emulsion polymerization of monomers M comprising acidic monomers and monomers Mb1 and Mb2 by a gradient feed technique, where the different monomers, in particular the acidic monomers, are fed to the emulsion polymerization reaction with varying dosage rates. While the polymer dispersions result in a reduced water uptake, there is still room for improvement.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide binders for water-borne coating compositions, which are suitable for the exterior application, in particular for the coating of shaped mineral articles, such as concrete roof tiles, paving slabs and fiber cement coatings that provide low level of water absorption. Moreover, such coatings should not suffer deleterious alteration of their visual appearance even on prolonged exposure to moisture and/or sunlight. Moreover, it should be possible to formulate the binders as waterborne paints and varnishes that result in good coating properties, such as high mechanical strength, high protection against efflorescence, low tendency to whitening and good dirt/soiling resistance, resistance against lichen and moss growth and which show good filming properties. It was surprisingly found that the above-mentioned problems are solved by aqueous polymer dispersions, which are obtainable by free radical aqueous emulsion polymerization of ethylenically unsaturated monomers M comprising a) 0.5 to 7.0% by weight, based on the total weight of monomers M, of a combination of a1 ) at least one monomer Ma1 , selected from monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms and the salts thereof; a2) at least one monomer Ma2, selected from monoethylenically unsaturated dicarboxylic acids having 4 to 8 carbon atoms and the salts thereof; a3) at least one monomer Ma3, selected from monoethylenically unsaturated monosulfonic acids having 2 to 10 carbon atoms and the salts thereof; b1) 60 to 79.45% by weight, based on the total weight of monomers M, of at least one monomer Mb1, which is selected from nonionic monoethylenically unsaturated monomers having a solubility in deionized water of at most 60 g/L at 25°C and 1 bar, and whose homopolymers have a glass transition temperature Tg of at least 50°C; b2) 20 to 39.45% by weight, based on the total weight of monomers M, of at least one monomer Mb2, which is selected from nonionic monoethylenically unsaturated monomers having a solubility in deionized water of at most 60 g/L at 25°C and 1 bar, and whose homopolymers have a glass transition temperature Tg of at most 40°C; c) 0.05 to 2.0% by weight of at least one crosslinking monomer Me; where the aqueous emulsion polymerization is carried out at least partly in the presence of a chain transfer compound.

Therefore, a first aspect of the present invention relates to aqueous polymer dispersions, which are obtainable by a free radical aqueous emulsion polymerization of ethylenically unsaturated monomers M as defined herein, where the aqueous emulsion polymerization is carried out at least partly in the presence of a chain transfer compound.

A second aspect of the present invention is a process for preparing the aqueous polymer dispersion, which process comprises the free radical aqueous emulsion polymerization of the monomers M as defined herein, where the aqueous emulsion polymerization is carried out at least partly in the presence of a chain transfer compound.

Further aspects of the invention relate to the use of aqueous polymer dispersions as defined herein as binder or co-binder in water-borne coating compositions, in particular in architectural coating compositions and in coating compositions for shaped mineral articles.

The present invention also relates to waterborne coating compositions, which contain the aqueous polymer dispersion as described herein.

Further aspects of the present invention relates to a method for producing a permanent coating on a surface comprising applying the waterborne coating composition according to the present invention to a surface and allowing the composition to dry to produce the coating.

The aqueous polymer dispersions as described herein provides several benefits, in particular a low water-uptake of the coating, which is significantly lower compared to coatings containing binders according to prior art; high mechanical strength of the coating; good protection against efflorescence; good or even improved dirt/soiling resistance; good resistance against lichen and moss growth; good filming properties.

DETAILED DESCRIPTION OF THE INVENTION

Here and throughout the specification, the term “waterborne coating composition” means a liquid aqueous coating composition containing water as the continuous phase in an amount sufficient to achieve flowability.

Here and throughout the specification, the terms "wt.-%" and "% by weight" are used synonymously.

Here and throughout the specification, the indefinite article “a” comprises the singular but also the plural, i.e. an indefinite article in respect to a component of a composition means that the component is a single compound or a plurality of compounds. If not stated otherwise, the indefinite article “a” and the expression “at least one” are used synonymously.

Here and throughout the specification, the term “pphm” means parts by weight per 100 parts of monomers and corresponds to the relative amount in % by weight of a certain monomer based on the total amount of monomers M. Here and throughout the specification, the terms "ethoxylated" and "polyethoxylated" are used synonymously and refer to compounds having an oligo- or polyoxyethylene group, which is formed by repeating units O-CH2CH2. In this context, the term “degree of ethoxylation” relates to the number average of repeating units O-CH2CH2 in these compounds.

Here and throughout the specification, the term "non-ionic" in the context of compounds, especially monomers, means that the respective compound does not bear any ionic functional group or any functional group, which can be converted by protonation or deprotonation into a ionic group.

Here and throughout the specification, the terms “shaped mineral article” and “shaped mineral bodies” are used synonymously. These terms refer to shaped articles, which are essentially made of a mineral material and comprise a mineral binder, in particular a cement binder, and which are specifically described in the outset.

Here and throughout the specification, the prefixes C_n-C_m used in connection with compounds or molecular moieties each indicate a range for the number of possible carbon atoms that a molecular moiety or a compound can have. The term "Ci-C_n alkyl" denominates a group of linear or branched saturated hydrocarbon radicals having from 1 to n carbon atoms. The term "C_n/C_m alkyl" denominates a mixture of two alkyl groups, one having n carbon atoms, while the other having m carbon atoms.

Here and throughout the specification, the term "ethylenically unsaturated monomer" is understood that the monomer has at least one C=C double bond, e.g. 1 , 2, 3 or 4 C=C double bonds, which are radically polymerizable, i.e. which under the conditions of an aqueous radical emulsion are polymerized to obtain a polymer having a backbone of carbon atoms. Here and throughout the specification, the term “monoethylenically unsaturated” is understood that the monomer has a single C=C double bond, which is susceptible to radical polymerization under conditions of an aqueous radical emulsion polymerization.

For example, the term C1-C20 alkyl denominates a group of linear or branched saturated hydrocarbon radicals having from 1 to 20 carbon atoms, while the term C1-C4 alkyl denominates a group of linear or branched saturated hydrocarbon radicals having from 1 to 4 carbon atoms. Examples of alkyl include, but are not limited to methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, 2-methylpropyl (isopropyl), 1 , 1 -dimethylethyl (tert-butyl), pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1 -ethylpropyl, hexyl, 1,1-dimethylpropyl,

1.2-dimethylpropyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl,

1 ,1-dimethylbutyl, 1,2-dimethyl butyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl,

2.3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1 ,1,2-trimethylpropyl,

1.2.2-trimethylpropyl, 1 -ethyl-1 -methylpropyl, 1-ethyl-2-methylpropyl, heptyl, octyl, 2-ethylhexyl, nonyl, isononyl, decyl, undecyl, dodecyl, tridecyl, isotridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl docosyl and in case of nonyl, isononyl, decyl, undecyl, dodecyl, tridecyl, isotridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl docosyl their isomers, in particular mixtures of isomers, such as "isononyl", "isodecyl". Examples of Ci -C_halky I are for example methyl, ethyl, propyl, 1-methylethyl, butyl,

1 -methylpropyl, 2-methylpropyl or 1,1-dimethylethyl.

The term "C5-C2o-cycloalky"” as used herein refers to a mono- or bicyclic cycloalkyl radical, which is unsubstituted or substituted by 1, 2, 3 or 4 Ci-C4-alkyl radicals, e.g. methyl groups, where the total number of carbon atoms of C5-C2o-cycloalkyl from 5 to 20. Examples of Cs-C2o-alkyl include, but are not limited to cyclopentyl, cyclohexyl, methylcyclohexyl, dimethylcyclohexyl, cycloheptyl, cyclooctyl, cyclododecyl, cyclohexadecyl, norbornyl (= bicyclo[2.2.1]heptyl) and isobornyl (= 1 ,7,7-trimethylbicyclo[2.2.1]heptyl).

The term C2-Cio-alkylene denominates a bivalent linear or branched saturated hydrocarbon radical having from 2 to 10 carbon atoms, in particular 2 to 6 or 2 to 4 carbon atoms (C2-C6-alkylene and C2-C4-alkylene, respectively) such as ethanediyl, propanediyl and butanediyl, where the radicals, which are bound to C2-C4-alkylene, are preferably bound not to the same carbon atoms of C2-Cio-alkylene, such as in

1.2-ethanediyl, 1,2-propanediyl, 1,2-butanediyl, 2,3-butanediyl, 2-methyl-1 ,2- propanediyl, 1,3-propanediyl, 1,4-butanediyl, 1,3-butandiyl, 2-methyl-1,3-propandiyl,

1 ,5-pentandiyl, 1 ,5-hexandiyl etc..

The term “phenylene” as used herein refers to a bivalent phenyl radical, such as

1.2-phenylene and 1,4-phenylene. Ci-C4-Alkylphenylene denominates phenylene, where the phenyl ring is substituted by an alkyl group.

The term “phenyl-C2-C4-alkylene” as used herein refers to a C2-C4-alkylene as defined herein, where 1 hydrogen atom has been replaced by a phenyl group.

According to the invention, the monomers M comprise a combination of at least one monomer Ma1 , at least one monomer Ma2 and at least one monomer Ma3: The monomers Ma1 are preferably selected from the group consisting of mono- ethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms, such as acrylic acid, methacrylic acid, crotonic acid, 2-ethylpropenoic acid, 2-propylpropenoic acid, 2-acryloxyacetic acid and 2-methacryloxyacetic acid. Particular preference is given to acrylic acid and methacrylic acid. In particular, the monomers Ma1 comprise acrylic acid. Preferably, the amount of acrylic acid is at least 50% by weight, in particular at least 70% by weight, based on the total amount of monomers Ma1. Especially, the monomers Ma1 are selected from the group consisting of acrylic acid and combinations thereof with methacrylic acid, where the amount of acrylic acid in said combinations is preferably at least 50% by weight, in particular at least 70% by weight, based on the total amount of monomers Ma1.

The total amount of monomers Ma1 is preferably in the range from 0.15 to 2.0% by weight, in particular 0.2 to 1.5% by weight, especially in the range from 0.2 to 1.0% by weight, based on the total amount of monomers M.

The monomers Ma2 are preferably selected from the group consisting of mono- ethylenically unsaturated dicarboxylic acids having 4 to 6 carbon atoms, such as itaconic acid, mesaconic acid, citraconic acid and fumaric acid. Preference is given to itaconic acid, mesaconic acid and citraconic acid. In particular, the monomers Ma2 comprise itaconic acid. Preferably, the amount of itaconic acid is at least 50% by weight, in particular at least 70% by weight, based on the total amount of monomers Ma2. Especially, itaconic acid is the sole monomer Ma2.

The total amount of monomers Ma2 is preferably in the range from 0.2 to 3.0% by weight, in particular 0.4 to 2.0% by weight, especially in the range from 0.5 to 1.5% by weight, based on the total amount of monomers M. The monomers Ma3 are selected from the group consisting of monoethylenically unsaturated sulfonic acids having 2 to 10 carbon atoms, in particular 2 to 8 carbon atoms such as vinylsulfonic acid, allylsulfonic acid, styrene sulfonic acid and monomers of the general formula (I)

where

X is NH or O,

R¹¹ is hydrogen or methyl,

R¹² is selected from the group consisting of C2-C6-alkylene, phenylene, phenyl-Ci-C2- alkylene and Ci-C2-alkylphenylene and where R¹² is in particular selected from the group consisting of C2-C6-alkylene, and the salts thereof, preferably the ammonium, sodium, potassium, magnesium and/or calcium salt thereof, especially the sodium or potassium salts thereof. In formula (I), X is preferably NH. In formula (I), R¹² is preferably C2-C6-alkylene, such as 1 ,2-ethylene, 1,3-propylene, 1,2-propylene, 1 -methyl-1 ,2-propylene, 1,4-butylene,

1 ,3-butylene etc..

In particular, the monomers Ma3 are selected from monomers of the formula (I) and the salts thereof, preferably the ammonium, sodium, potassium, magnesium and/or calcium salt thereof, especially the sodium or potassium salts thereof. Examples of monomers of the formula (I) include 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 2-methacrylamido-2-methylpropanesulfonic acid, 2-acrylamidobutanesulfonic acid, 3-acrylamido-3-methylbutanesulfonic acid, 2-acrylamido-2,4,4-trimethyl- pentanesulfonic acid, 2-methacrylamidobutanesulfonic acid, 3-methacrylamido-3- methylbutanesulfonic acid, 2-methacrylamido-2,4,4-trimethylpentanesulfonic acid,

2-sulfoethylacrylate, 3-sulfopropylacrylate, 2-sulfoethylmethacrylate,

3-sulfopropylmethacrylate and the salts thereof, in particular the ammonium, sodium, potassium, magnesium and/or calcium salt thereof, especially the sodium salt or potassium salt thereof.

Especially, the monomer Ma3 is 2-acrylamido-2-propanesulfonic acid (AMPS) and/or a salt thereof, in particular 2-acrylamido-2-propanesulfonic acid sodium salt (AMPS-Na) or a mixture consisting of at least 50% by weight, in particular at least 70% by weight of AMPS and/or at least one salt thereof, based on the total amount of monomers Ma3 and at least one further monomer Ma3 as defined herein.

The total amount of monomers Ma3, calculated as the sulfonic acid form, is preferably in the range from 0.15 to 2.0% by weight, in particular 0.3 to 1.2% by weight, especially in the range from 0.4 to 1.0% by weight, based on the total amount of monomers M.

The total amount of the combination of monomers Ma1 , Ma2 and Ma3 is in the range from 0.5 to 7.0% by weight, in particular in the range from 0.7 to 4.0% by weight and especially in the range from 1.1 to 3.0% by weight, based on the total amount of monomers M, based on the total weight of monomers M. Preferably, the monomers M comprise from 0.7 to 4.0% by weight, based on the total amount of monomers M, of a1) 0.2 to 1.5% by weight, based on the total amount of monomers M, of at least one monomer Ma1 ; a2) 0.4 to 2.0% by weight, based on the total amount of monomers M, of at least one monomer Ma2; a3) 0.3 to 1.2% by weight, based on the total amount of monomers M and calculated as the sulfonic acid form, of at least one monomer Ma3.

In particular, the monomers M comprise from 1.1 to 3.0% by weight, based on the total amount of monomers M, of a1) 0.2 to 1.0% by weight, based on the total amount of monomers M, of at least one monomer Ma1 ; a2) 0.5 to 1.5% by weight, based on the total amount of monomers M, of at least one monomer Ma2; a3) 0.4 to 1.0% by weight, based on the total amount of monomers M and calculated as the sulfonic acid form, of at least one monomer Ma3.

More preferably, the monomers M comprise from 0.5 to 7.0% by weight, based on the total amount of monomers M, of a1) 0.15 to 2.0% by weight, based on the total amount of monomers M, of at least one monomer Ma1, selected from acrylic acid and mixtures thereof with methacrylic acid; a2) 0.3 to 3.0% by weight, based on the total amount of monomers M, of at least one monomer Ma2, which comprises or is itaconic acid; a3) 0.2 to 1.5% by weight, based on the total amount of monomers M and calculated as the sulfonic acid form, of at least one monomer Ma3 which comprises or is 2-acrylamidopropyl-2-methylpropane sulfonic acid or a salt thereof.

Even more preferably, the monomers M comprise from 0.7 to 4.0% by weight, based on the total amount of monomers M, of a1) 0.2 to 1.5% by weight, based on the total amount of monomers M, of at least one monomer Ma1 , selected from acrylic acid and mixtures thereof with methacrylic acid; a2) 0.4 to 2.0% by weight, based on the total amount of monomers M, of at least one monomer Ma2, which comprises or is itaconic acid; a3) 0.3 to 1.2% by weight, based on the total amount of monomers M and calculated as the sulfonic acid form, of at least one monomer Ma3, which comprises or is 2-acrylamidopropyl-2-methylpropane sulfonic acid or a salt thereof. In particular, the monomers M comprise from 1.1 to 3.0% by weight, based on the total amount of monomers M, of a1) 0.2 to 1.0% by weight, based on the total amount of monomers M, of at least one monomer Ma1 ; a2) 0.5 to 1.5% by weight, based on the total amount of monomers M, of at least one monomer Ma2, which comprises or is itaconic acid; a3) 0.4 to 1.0% by weight, based on the total amount of monomers M and calculated as the sulfonic acid form, of at least one monomer Ma3, which comprises or is 2-acrylamidopropyl-2-methylpropane sulfonic acid or a salt thereof. The monomers M also comprise at least a monomer Mb1 as defined above, which is non-ionic, sparingly water soluble, i.e. it has a solubility in deionized water of at most 60 g/L, e.g. in the range from 0.1 to 60 g/L at 25°C and 1 bar, and characterized in that its homopolymer has a glass transition temperature Tg of at least 50°C, in particular in the range of 55 to 200°C, especially in the range from 60 to 180°C.

The total amount of monomers Mb1 is preferably in the range from 60.5 to 74.25% by weight, especially in the range from 61 to 70.82% by weight, based on the total amount of monomers M. The monomers M also comprise at least a monomer Mb2 as defined above, which is non-ionic, sparingly water soluble, i.e. it has a solubility in deionized water of at most 60 g/L, e.g. in the range from 0.1 to 60 g/L at 25°C and 1 bar, and characterized in that its homopolymer has a glass transition temperature Tg of at most 40°C, in particular in the range from -80 to +40°C.

The total amount of monomers Mb2 is preferably in the range from 25 to 38.75% by weight, especially in the range from 28 to 37.82% by weight, based on the total amount of monomers M. The actual Tg values for the homopolymers of monomers Mb1 and Mb2 are known and listed, for example, in Ullmann’s Encyclopadie der technischen Chemie [Ullmann's Encyclopedia of Industrial Chemistry], 5th ed., vol. A21 , p. 169, Verlag Chemie, Weinheim, 1992. Further sources of glass transition temperatures of homopolymers are, for example, J. Brandrup, E. H. Immergut, Polymer Handbook, 1st Ed., J. Wiley, New York 1966, 2nd Ed. J. Wiley, New York 1975, 3rd Ed. J. Wiley, New York 1989 and 4th Ed. J. Wiley, New York 2004. They can also be determined experimentally by the differential scanning calorimetry (DSC) method according to ISO 11357-2:2013, preferably with sample preparation according to ISO 16805:2003.

Suitable monomers Mb1 are monovinyl aromatic monomers, such as styrene, C1-C2- alkyl esters of methacrylic acid, such as methyl methacrylate and ethyl methacrylate, tert.-butyl methacrylate, tert.-butyl acrylate and mixtures thereof. In particular, the monomers Mb1 comprise at least one of the Ci-C2-alkyl esters of methacrylic acid and tert.-butyl acrylate. In particular, the monomer Mb1 comprises methyl methacrylate. Especially, the monomers Mb1 are selected from the group consisting of methyl methacrylate and combinations thereof with styrene or tert.-butyl acrylate, where the amount of methyl methacrylate in said combinations is preferably at least 50% by weight, in particular at least 70% by weight, based on the total amount of monomers Mb1. However, styrene may also be the sole monomer Mb1.

Suitable monomers Mb2 are Ci-C2o-alkyl esters of acrylic acid, except for tert.-butyl acrylate, C5-C2o-cycloalkyl esters of acrylic acid, C3-a Iky I esters of methacrylic acid, n-butyl methacrylate, Cs-C2o-a Iky I esters of methacrylic acid, C5-C2o-cycloalkyl esters of methacrylic acid and mixtures thereof.

Suitable Ci-C2o-alkyl esters of acrylic acid include, but are not limited to methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, n-decyl acrylate, isodecyl acrylate, 2-propylheptyl acrylate, lauryl acrylate, Ci2/Ci4-alkyl acrylate, Ci2-Cis-alkyl acrylate, isotridecyl acrylate, Ci₆/Cis-alkyl acrylate and stearyl acrylate.

Suitable C5-C2o-cycloalkyl esters of acrylic acid include, but are not limited to cyclohexylacrylate, norbornylacrylate and isobornylacrylate.

Suitable C3-alkyl esters of methacrylic acid and Cs-C2o-alkyl esters of methacrylic acid include, but are not limited to n-propyl methacrylate, isopropyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, n-decyl methacrylate, 2-propylheptyl methacrylate, lauryl methacrylate, Ci2/Ci4-alkyl methacrylate, Ci2-Cis-alkyl methacrylate, isotridecyl methacrylate, Ci₆/Cis-alkyl methacrylate and stearyl methacrylate. Suitable C5-Ci6-cycloalkyl esters of methacrylic acid include, but are not limited to cyclohexyl methacrylate, norbornyl methacrylate and isobornyl methacrylate.

Preferably, monomers Mb2 are C2-Cio-alkyl esters of acrylic acid, except for tert-butyl acrylate, and n-butyl methacrylate, where the C2-Cio-alkyl esters of acrylic acid are in particular selected from the group consisting of ethyl acrylate, n-butyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, 2-propylheptyl acrylate and mixtures thereof, such as mixtures of n-butyl acrylate and 2-ethylhexyl acrylate, mixtures of n-butyl acrylate and ethyl acrylate, mixtures of n-butyl acrylate and n-butyl methacrylate, mixtures of n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate, and mixtures of ethyl acrylate, n-butyl acrylate, n-butyl methacrylate and 2-ethylhexyl acrylate.

The monomers M also comprise at least one crosslinking monomer Me. Suitable crosslinking monomers are ethylenically unsaturated monomers, which bear at least one functionality, which is capable of reacting with itself or with other functional groups within the polymer formed by the polymerization of the monomers M, hereinafter monomers Mc1. Suitable crosslinking monomers are in particular multiethylenically unsaturated monomers having at least two, in particular 2 to 6 non-conjugated ethylenically unsaturated double bonds, hereinafter monomers Mc2. Suitable monomers are also monoethylenically unsaturated monomers having at least one further functional group, which is capable of reacting with itself or with a carboxylic acid group, hereinafter monomers Mc2, and mixtures of different monomers Me. Monomers Me may also be combinations of 2 or more different monomers Me, e.g. combinations of at least one monomer Mc1 and at least one monomer Mc2.

The total amount of monomers Me is preferably in the range from 0.05 to 1.5% by weight, especially in the range from 0.08 to 1.0% by weight, based on the total amount of monomers M.

The reactive group of the monomers Mc1 may be for example an oxiran group, e.g. a glycidyl group, or a silyl group bearing at least one Si-bound alkoxy group, including e.g. alkyldialkoxysilyl groups, such as methyldimethoxysilyl, ethyldimethoxysilyl, methyldiethoxysilyl and ethyldiethoxysilyl, and trialkoxysilyl groups, such as trimethoxysilyl and triethoxysilyl. In the context of silyl groups, the term alkyl refers in particular to alkyl having 1 to 4 carbon atoms. The term alkoxy refers to alkoxy groups having 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy and butoxy.

Examples of monomers Mc1 include, but are not limited to glycidyl esters of monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms, hereinafter monomers Mc1.1 , in particular glycidyl acrylate and glycidyl methacrylate; monoethylenically unsaturated monomers bearing at least one trialkoxysilyl group or at least one alkyldialkoxysilyl group, hereinafter monomers Mc1.2. Examples of these monomers Mc1.2 include vinyltrialkoxysilanes, e.g. vinyltrimethoxysilane, alkylvinyldialkoxysilanes, e.g., methylvinyldialkoxysilane. Examples of these monomers Mc1.2 also include alkyldialkoxysilylalkylesters of monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms, in particular alkyldialkoxysilylalkylesters of acrylic acid and alkyldialkoxysilylalkylesters of methacrylic acid, such as (meth)acryloyloxypropyl-methyldimethoxysilane and (meth)acryloyloxypropyl-methyldiethoxysilane, and trialkoxysilylalkylesters of monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms, in particular trialkoxysilylalkylesters of acrylic acid and trialkoxysilylalkylesters of methacrylic acid, such as (meth)acryloyloxypropyl-trimethoxysilane and (meth)acryloyloxypropyl-triethoxysilane and mixtures thereof.

Amongst monomers Mc1 , preference is given to monomers Mc1.2 and combinations of at least one monomer Mc1.2 with one or more of monomers Mc1.1.

Amongst the monomers Mc1.2, preference is given to trialkoxysilylalkylesters of monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms, in particular trialkoxysilylalkylesters of acrylic acid and trialkoxysilylalkylesters of methacrylic acid, such as (meth)acryloyloxypropyl-trimethoxysilane and (meth)acryloyloxypropyl-triethoxysilane, and mixtures thereof.

Examples of suitable monomers Mc2 include polyacrylic esters, polymethacrylic esters, polyallyl ethers or polyvinyl ethers of polyhydric alcohols having at least 2 OH groups, e.g. 2 to 6 OH groups, hereinafter monomers Mc2.1. The OH groups of the polyhydric alcohols may be completely or partly etherified or esterified, provided that on average they bear at least 2, e.g. 2 to 6 ethylenically unsaturated double bounds. Examples of the polyhydric alcohol components in such crosslinkers Mc2.1 include, but are not limited to, dihydric alcohols, such as 1,2-ethanediol, 1,2-propanediol, 1 ,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, but-2-ene-1,4-diol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol,

1 ,6-hexanediol, 1 ,10-decanediol, 1,2-dodecanediol, 1 ,12-dodecanediol, neopentyl glycol, 3-methylpentane-1,5-diol, 2,5-dimethyl-1,3-hexanediol, 2,2,4-trimethyl-1 ,3-pentanediol, 1 ,2-cyclohexanediol, 1 ,4-cyclohexanediol, 1 ,4-bis(hydroxymethyl)cyclohexane, hydroxypivalic acid neopentyl glycol monoester, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis[4-(2-hydroxypropyl)- phenyl]propane, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, 3-thiapentane-1 ,5- diol, and also polyethylene glycols, polypropylene glycols, block copolymers of ethylene oxide or propylene oxide, random copolymers of ethylene oxide and propylene oxide and polytetrahydrofurans having molecular weights of in each case 200 to 10000. Examples of polyhydric alcohols having more than two OH groups are trimethylolpropane, glycerol, pentaerythritol, 1,2,5-pentanetriol,

1 ,2,6-hexanetriol, cyanuric acid, sorbitan, sugars, such as sucrose, glucose, and mannose. The polyhydric alcohol components in such crosslinkers Mc2.1 having more than two OH groups can be alkoxylated with ethylene oxide or propylene oxide; monoesters of monoethylenically unsaturated C3-C6 monocarboxylic acids, in particular of acrylic acid or methacrylic acid, with monoethylenically unsaturated aliphatic or cycloaliphatic monohydroxy compounds, hereinafter monomers Mc2.2. Examples include vinyl acrylate, vinyl methacrylate, allyl acrylate, allyl methacrylate, cyclohex-2-enyl acrylate, cyclohex-2-enyl methacrylate, norbornenyl acrylate and norbornenyl methacrylate; straight-chain or branched, linear or cyclic, aliphatic or aromatic hydrocarbons, which possess at least two double bonds, which in the case of aliphatic hydrocarbons must not be conjugated, hereinafter monomers Mc2.3. Examples include divinylbenzene, divinyltoluene, 1,7-octadiene, 1,9-decadiene,

4-vinyl-1 -cyclohexene, trivinylcyclohexane or polybutadienes having molecular weights of 200 to 20000, in particular divinyl aromatic compounds, such as 1 ,3-divinyl benzene, 1,4-divinyl benzene.

Amongst monomers Mc2, preference is given to monomers Mc2.2, in particular to the acrylates and methacrylates, especially to allyl acrylate and allyl methacrylate.

In a particular group of embodiments, the monomers Me comprise at least one monomer Mc1.2, which is in particular selected from the group consisting of monoethylenically unsaturated monomers bearing at least one trialkoxysilyl group, in particular a trialkoxylsilylalkylester of a monoethylenically unsaturated monocarboxylic acid having 3 to 6 carbon atoms, and which is more particularly selected from the group consisting of trialkoxysilylalkylesters of acrylic acid and trialkoxysilylalkylesters of methacrylic acid, such as (meth)acryloyloxypropyl-trimethoxysilane and (meth)acryloyloxypropyl-triethoxysilane and mixtures thereof. In this particular group of embodiments, the monomer Mc1.2 may be the sole monomer Me. In this particular group of embodiments, the monomers Me may also be a combination of at least one monomer Mc1.2 and at least one monomer Me, which is different from the monomers Mc1.2, e.g. a monomer Mc1.1 or a monomer Mc2, in particular a monomer Mc2.2. Amongst the combination of at least one monomer Mc1.2 and at least one monomer Me, which is different from the monomers Mc1.2 particular preference is given to the combination of at least one monomer Mc1.2 with at least one monomer Mc1.1 , which is preferably selected from glycidyl acrylate and glycidyl methacrylate and to combinations of at least one monomer Mc1.2 with at least one monomer Mc2.2, which is preferably selected from allyl acrylate and allyl methacrylate.

In preferred groups 1 of embodiments, the monomers M comprise a) 0.7 to 4.0% by weight, based on the total amount of monomers M, of a combination of acidic monomers comprising a1) 0.2 to 1.5% by weight, based on the total amount of monomers M, of at least one monomer Ma1 , in particular at least one preferred monomer Ma1 ; a2) 0.4 to 2.0% by weight, based on the total amount of monomers M, of at least one monomer Ma2, in particular at least one preferred monomer Ma2; a3) 0.3 to 1.2% by weight, based on the total amount of monomers M and calculated as the sulfonic acid form, of at least one monomer Ma3, in particular at least one preferred monomer Ma3; b1 ) 60.5 to 74.25% by weight, based on the total amount of monomers M , of at least one monomer Mb1 , in particular at least one preferred monomer Mb1 ; b2) 25 to 38.75% by weight, based on the total amount of monomers M, of at least one monomer Mb2, in particular at least one preferred monomer Mb2; c) 0.05 to 1.5% by weight, based on the total amount of monomers M, of at least one monomer Me, in particular at least one preferred monomer Me, more preferably at least one monomer Mc1.2 or a combination of at least one monomer Mc1.2 and at least one of monomers Mc1.1 and/or at least one monomer Mc2.2.

In particularly preferred groups 2 of embodiments, the monomers M comprise a) 1.1 to 3.0% by weight, based on the total amount of monomers M, of a combination of acidic monomers comprising a1 ) 0.2 to 1.0% by weight, based on the total amount of monomers M , of at least one monomer Ma1 , in particular at least one preferred monomer Ma1 ; a2) 0.5 to 1.5% by weight, based on the total amount of monomers M, of at least one monomer Ma2, in particular at least one preferred monomer Ma2; a3) 0.4 to 1.0% by weight, based on the total amount of monomers M and calculated as the sulfonic acid form, of at least one monomer Ma3, in particular at least one preferred monomer Ma3; b1) 61 to 70.82% by weight, based on the total amount of monomers M, of at least one monomer Mb1 , in particular at least one preferred monomer Mb1 ; b2) 28 to 37.82% by weight, based on the total amount of monomers M, of at least one monomer Mb2, in particular at least one preferred monomer Mb2; c) 0.08 to 1.0% by weight, based on the total amount of monomers M, of at least one monomer Me, in particular at least one preferred monomer Me, more preferably at least one monomer Mc1.2 or a combination of at least one monomer Mc1.2 and at least one of monomers Mc1.1 and/or at least one monomer Mc2.2.

In very preferred groups 3 of embodiments, the monomers M comprise a) 0.5 to 7.0% by weight, based on the total amount of monomers M, of a combination of acidic monomers comprising a1) 0.15 to 2.0% by weight, based on the total amount of monomers M, of at least one monomer Ma1 , selected from acrylic acid and mixtures thereof with methacrylic acid; a2) 0.2 to 3.0% by weight, based on the total amount of monomers M, of at least one monomer Ma2, which comprises or is itaconic acid; a3) 0.15 to 2.0% by weight, based on the total amount of monomers M and calculated as the sulfonic acid form, of at least one monomer Ma3, which comprises or is 2-acrylamidopropyl-2-methylpropane sulfonic acid or a salt thereof; b1) 60 to 79.45% by weight, based on the total amount of monomers M, of at least one monomer Mb1 , in particular at least one preferred monomer Mb1 ; b2) 20 to 39.25% by weight, based on the total amount of monomers M, of at least one monomer Mb2, except for tert.-butyl acrylate, which is selected from C2-C10- alkyl esters of acrylic acid and n-butyl methacrylate, where the C2-Cio-alkyl esters of acrylic acid are in particular selected from the group consisting of ethyl acrylate, n-butyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, 2-propylheptyl acrylate and mixtures thereof, such as mixtures of n-butyl acrylate and 2-ethylhexyl acrylate, mixtures of n-butyl acrylate and ethyl acrylate, mixtures of n-butyl acrylate and n-butyl methacrylate, mixtures of n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate, and mixtures of ethyl acrylate, n-butyl acrylate, n-butyl methacrylate and 2-ethylhexyl acrylate; c) 0.05 to 2.0% by weight, based on the total amount of monomers M, of at least one monomer Me, in particular at least one preferred monomer Me, more preferably at least one monomer Mc1.2 or a combination of at least one monomer Mc1.2 and at least one of monomers Mc1.1 and/or at least one monomer Mc2.2.

In even more preferred groups 4 of embodiments, the monomers M comprise a) 0.7 to 4.0% by weight, based on the total amount of monomers M, of a combination of acidic monomers comprising a1 ) 0.2 to 1.5% by weight, based on the total amount of monomers M, of at least one monomer Ma1, selected from acrylic acid and mixtures thereof with methacrylic acid; a2) 0.4 to 2.0% by weight, based on the total amount of monomers M, of at least one monomer Ma2, which comprises or is itaconic acid; a3) 0.3 to 1.2% by weight, based on the total amount of monomers M and calculated as the sulfonic acid form, of at least one monomer Ma3, which comprises or is 2-acrylamidopropyl-2-methylpropane sulfonic acid or a salt thereof; b1) 60.5 to 74.25% by weight, based on the total amount of monomers M, of at least one monomer Mb1 , in particular at least one preferred monomer Mb1 ; b2) 25 to 38.75% by weight, based on the total amount of monomers M, of at least one monomer Mb2, which is selected from the group consisting of C2-Cio-alkyl esters of acrylic acid, except for tert.-butyl acrylate, and n-butyl methacrylate, where the C2-Cio-alkyl esters of acrylic acid are in particular selected from the group consisting of ethyl acrylate, n-butyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, 2-propyl heptyl acrylate and mixtures thereof, such as mixtures of n-butyl acrylate and 2-ethylhexyl acrylate, mixtures of n-butyl acrylate and ethyl acrylate, mixtures of n-butyl acrylate and n-butyl methacrylate, mixtures of n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate, and mixtures of ethyl acrylate, n-butyl acrylate, n-butyl methacrylate and 2-ethylhexyl acrylate; c) 0.05 to 1.5% by weight, based on the total amount of monomers M, of at least one monomer Me, in particular at least one preferred monomer Me, more preferably at least one monomer Mc1.2 or a combination of at least one monomer Mc1.2 and at least one of monomers Mc1.1 and/or at least one monomer Mc2.2.

In especially preferred groups 5 of embodiments, the monomers M comprise a) 1.1 to 3.0% by weight, based on the total amount of monomers M, of a combination of acidic monomers comprising a1 ) 0.2 to 1.0% by weight, based on the total amount of monomers M, of at least one monomer Ma1 , selected from acrylic acid and mixtures thereof with methacrylic acid; a2) 0.5 to 1.5% by weight, based on the total amount of monomers M, of at least one monomer Ma2, which comprises or is itaconic acid; a3) 0.4 to 1.0% by weight, based on the total amount of monomers M and calculated as the sulfonic acid form, of at least one monomer Ma3, which comprises or is 2-acrylamidopropyl-2-methylpropane sulfonic acid or a salt thereof; b1) 61 to 70.82% by weight, based on the total amount of monomers M, of at least one monomer Mb1, which comprises or is methyl methacrylate; b2) 28 to 37.82% by weight, based on the total amount of monomers M, of at least one monomer Mb2, which is selected from C2-Cio-alkyl esters of acrylic acid, except for tert.-butyl acrylate, and n-butyl methacrylate, where the C2-Cio-alkyl esters of acrylic acid are in particular selected from the group consisting of ethyl acrylate, n-butyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, 2-propylheptyl acrylate and mixtures thereof, such as mixtures of n-butyl acrylate and 2-ethylhexyl acrylate, mixtures of n-butyl acrylate and ethyl acrylate, mixtures of n-butyl acrylate and n-butyl methacrylate, mixtures of n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate, and mixtures of ethyl acrylate, n-butyl acrylate, n-butyl methacrylate and 2-ethylhexyl acrylate; c) 0.08 to 1.0% by weight, based on the total amount of monomers M, of at least one monomer Me, in particular at least one preferred monomer Me, more preferably at least one monomer Mc1.2 or a combination of at least one monomer Mc1.2 and at least one of monomers Mc1.1 and/or at least one monomer Mc2.2.

In the aforementioned groups 1 to 5 of embodiments, the monomer Mc1.2 is preferably selected from the group consisting of trialkoxysilylalkylesters of acrylic acid and trialkoxysilylalkylesters of methacrylic acid, such as (meth)acryloyloxypropyl- trimethoxysilane and (meth)acryloyloxypropyl-triethoxysilane and mixtures thereof.

In the aforementioned groups 1 to 5 of embodiments, the monomer Mc1.1 is preferably selected from the group consisting of glycidyl acrylate and glycidyl methacrylate.

In the aforementioned groups 1 to 5 of embodiments, the monomer Mc2.2 is preferably selected from the group consisting of vinyl acrylate, vinyl methacrylate, allyl acrylate, allyl methacrylate, cyclohex-2-enyl acrylate, cyclohex-2-enyl methacrylate, norbornenyl acrylate and norbornenyl methacrylate and especially from the group consisting of allyl acrylate and allylmethacrylate.

Usually, the total weight of monomers Ma1 , Ma2, Ma3, Mb1 , Mb2 and Me amount to at least 95% by weight, in particular at least 98% by weight, especially at least 99% or 100% by weight of the total amount of monomers M. A skilled person will immediately appreciate that the figures given for the weight of monomers Ma1 , Ma2, Ma3, Mb1 ,

Mb2 and Me will not exceed 100% by weight. Optionally, the monomers M further comprise at least one nonionic monoethylenically unsaturated monomer Md, which is different from the aforementioned monomers Mb1, Mb2 and Me, and which preferably has a functional group selected from a carboxamide group, a hydroxyl group, an urea group and a keto group. Examples for monomers Md having a carboxamide group are primary amides of monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms, such as acrylamide and methacrylamide;

N-C1-C10 alkyl amides of monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms, in particular N-C1-C10 alkyl amides of acrylic acid or methacrylic acid, such as N-methyl acrylamide, N-ethyl acrylamide, N-propyl acrylamide, N-isopropyl acrylamide, N-butyl acrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, N-propyl methacrylamide, N-isopropyl methacrylamide and N-butyl methacrylamide. Examples for monomers Md having a hydroxyl group are hydroxyl-C2-C4-alkyl esters of monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms, in particular of acrylic acid or methacrylic acid, such as 2-hydroxyethyl acrylate, 2- or 3-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2- or 3-hydroxypropyl methacrylate and 4-hydroxybutyl methacrylate.

Examples for monomers Md having a urea group are 2-(2-oxo-imidazolidin-1-yl)ethyl acrylate, 2-(2-oxo-imidazolidin-1-yl)ethyl methacrylate, which are also termed 2-ureido (meth)acrylate, N-(2-acryloxyethyl)urea, N-(2-methacryloxyethyl)urea, N-(2-(2-oxo- imidazolidin-1 -yl)ethyl) acrylamide, N-(2-(2-oxo-imidazolidin-1-yl)ethyl) methacrylamide, 1-allyl-2-oxoimidazolin and N-vinylurea.

Examples for monomers Md having a keto group are acetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate, acetoacetoxybutyl methacrylate, 2-(acetoacetoxy)ethyl methacrylate, diacetoneacrylamide (DAAM), diacetoneacrylamide and diacetonemethacrylamide.

Usually, the amount of monomers Md will not exceed 5% by weight, in particular 2% by weight, especially 1% by weight, based on the total amount of monomers M. In particular, the monomers M do not contain a monomer, which is different from monomers Ma1 , Ma2, Ma3, Mb1, Mb2 and Me.

According to the invention, the aqueous polymer dispersions are prepared in the presence of at least one chain transfer compound.

In general, chain transfer compounds are understood to mean compounds that transfer free radicals, thereby stop the growth of the polymer chain or control chain growth in the polymerization, and which thus reduce the molecular weight of the resulting polymers. Usually, chain transfer compounds possess at least one readily abstractable hydrogen atom. Preferably, the abstractable hydrogen is part of a mercapto group, i.e. a group SH, also termed “thiol group”.

The chain transfer compound is in particular selected from the group consisting of Ci-C₂o-alkyl esters of SH-substituted C₂-C₆ alkanoic acids, hereinafter C₂-C₆ thioalkanoic acids (chain transfer compounds T.1), in particular Ci-C₂o-alkyl esters of mercaptoacetic acid (= thioglycolic acid) ), such as methyl thioglycolate, ethyl thioglycolate, n-butyl thioglycolate, n-hexyl thioglycolate, n-octyl thioglycolate, 2-ethylhexyl thioglycolate and n-decylthioglycolate, and Ci-C₂o-alkyl esters of mercaptopropionic acid, such as methyl mercaptopropionate, ethyl mercaptopropionate, n-butyl mercaptopropionate, n-hexyl mercaptopropionate, n-octyl mercaptopropionate, 2-ethylhexyl mercaptopropionate and n-decyl mercaptopropionate;

Ci-C₂o-alkyl mercaptans (chain transfer compounds T.2), in particular to C₆-C₁₆- alkyl mercaptans, for example 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 the isomeric compounds thereof, n-octanethiol and the isomeric compounds thereof, n-nonanethiol and the isomeric compounds thereof, n-decanethiol and the isomeric compounds thereof, n-undecanethiol and the isomeric compounds thereof, n-dodecanethiol and the isomeric compounds thereof, such as tert.- dodecanethiol, n-tridecanethiol and isomeric compounds thereof;

OH-substituted C2-C2o-alkyl mercaptans (chain transfer compounds T.3), for example 2-hydroxyethanethiol and 2-hydroxypropanethiol; - aromatic thiols (chain transfer compounds T.4), such as benzenethiol, ortho-, meta- or para-methylbenzenethiol, and mixtures thereof.

Examples of further chain transfer compounds, which may be used instead of the chain transfer compounds T.1 to T.4 or in combination therewith are aliphatic and/or araliphatic halogen compounds, 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, but also aliphatic and/or aromatic aldehydes, such as acetaldehyde, propionaldehyde and/or benzaldehyde, hydrocarbons having readily abstractable hydrogen atoms, for example toluene and thiol compounds different from T.1 to T.4, e.g. thiol compounds described in Polymer Handbook, 3rd edition, 1989, J. Brandrup and E.H. Immergut, John Wiley & Sons, section II, pages 133 to 141.

Particular preference is given to chain transfer compounds T.1 and T2, in particular to C4-Ci6-alkyl esters of SH-substituted C2-C4 alkanoic acids, especially to C4-Ci6-alkyl esters of mercaptoacetic acid, to C4-Ci6-alkyl esters of mercaptopropionic acid, to C₆-Ci₆-alkyl mercaptans and to mixtures thereof.

The amount of chain transfer compound is preferably in the range of 0.05 to 1.2% by weight, in particular in the range from 0.1 to 0.9% by weight, especially in the range from 0.15 to 0.6% by weight, based on the total weight of the monomers M. In general, the polymers in the aqueous polymer dispersions of the present invention, which are formed from the polymerized monomers M have a glass transition temperature T_g in the range from 25 to 70°C, in particular in the range from 28 to 50°C, especially in the range from 30 to 45°C. In case of a multi-stage polymer containing two or more polymers or polymer phases, respectively, with different glass transition temperatures, the glass transition temperatures of the individual polymer phases may be outside the ranges given here. However, the weight average glass transition temperature T_g(av), as calculated by the equation

Tg(av) = (Tg(1 )*wi + Tg(2)^*w₂ .... Tg(n)^*w_n) is in the range from 25 to 70°C, in particular from 28 to 50°C, especially in the range from 30 to 45°C. In the equation T_g(1), T_g(2) to T_g(n) indicate the individual glass transition temperatures in °C or K of the individual polymers 1 , 2 to n, while wi, w₂ to w_n indicate the amount in % by weight of the individual polymers 1 , 2 to n.

The actual glass transition temperature depends on the composition of monomers M, which form the polymer in the polymer dispersion, i.e. from the type and relative amount of monomers Ma1, Ma2, Ma3, Mb1, Mb2, Me and optional monomers Md, if present. A theoretical glass transition temperature can be calculated from the composition monomer M used in the emulsion polymerization. The theoretical glass transition temperatures are usually calculated from the composition of monomers by the Fox equation: 1/Tg(F) = Xi/Tgi + x₂/Tg₂ + .... x_n/Tg_n.

In this equation, xi, x₂. x_n are the mass fractions of the different monomers 1 , 2. n, and Tgi, Tgi . Tg_n are the actual glass transition temperatures in Kelvin of the homopolymers synthesized from only one of the monomers 1, 2. n at a time. Tg(F) is the theoretical glass transition temperature according to Fox. The Fox equation has been described by T. G. Fox in Bull. Am. Phys. Soc. 1956, 1 , page 123 and can also be found in Ullmann's Encyclopadie der technischen Chemie [Ullmann's Encyclopedia of Industrial Chemistry], vol. 19, p. 18, 4th ed., Verlag Chemie, Weinheim, 1980. The actual Tg values for the homopolymers of most monomers are known and listed in the references cited above.

Usually, the theoretical glass temperature Tg* calculated according to Fox as described herein and the experimentally determined glass transition temperature as described herein are similar or even same and do not deviate from each other by more than 5 K, in particular they deviate not more than 2 K. Accordingly, both the actual and the theoretical glass transition temperatures of the polymer can be adjusted by choosing proper monomers Mi, M₂ ... M_n and their mass fractions xi, xi . x_n in the monomer composition so to arrive at the desired glass transition temperature Tg(1) and Tg(2), respectively. It is common knowledge for a skilled person to choose the proper amounts of monomers Mi, M₂ ... M_n for obtaining a copolymer and/or copolymer phase with the desired glass transition temperature. Consequently, the monomers M are chosen, such that a theoretical glass transition temperature Tg(F) according to Fox is achieved, which is in the range of 25 to 70°C, in particular in the range of 28 to 50°C, especially in the range of 30 to 45°C. For the purposes of the invention, it has been found beneficial, if the particles of the polymer contained in the polymer latex have a Z-average particle diameter in the range from 80 to 500 nm, in particular in the range from 80 to 300 nm, as determined by quasi-elastic light scattering.

If not stated otherwise, the size of the particles as well as the distribution of particle size is determined by quasi-elastic light scattering (QELS), also known as dynamic light scattering (DLS). The measurement method is described in the ISO 13321:1996 standard. The determination can be carried out using a High-Performance Particle

Sizer (HPPS). For this purpose, a sample of the aqueous polymer latex will be diluted, and the dilution will be analyzed. In the context of QELS, the aqueous dilution may have a polymer concentration in the range from 0.001 to 0.5% by weight, depending on the particle size. For most purposes, a proper concentration will be 0.01% by weight. However, higher or lower concentrations may be used to achieve an optimum signal/noise ratio. Measurement configuration: HPPS from Malvern, automated, with continuous-flow cuvette and Gilson autosampler. Parameters: measurement temperature 20.0°C; measurement time 120 seconds (6 cycles each of 20 s); scattering angle 173°; wavelength laser 633 nm (HeNe); refractive index of medium 1.332 (aqueous); viscosity 0.9546 mPa-s. The measurement gives an average value of the second order cumulant analysis (mean of fits), i.e. Z average. The "mean of fits" is an average, intensity-weighted hydrodynamic particle diameter in nm.

The hydrodynamic particle diameter can also be determined by hydrodynamic chromatography fractionation (HDC), as for example described by H. Wiese,

"Characterization of Aqueous Polymer Dispersions" in Polymer Dispersions and Their Industrial Applications (Wiley-VCH, 2002), pp. 41-73. For further details, reference is made to the examples and the description below. The particle size distribution of the polymer particles contained in the polymer dispersion is in particular monomodal or almost monomodal, which means that the distribution function of the particle size has a single maximum. However, the particle size distribution of the copolymer particles contained in the polymer latex may also be polymodal, in particular bimodal, which means that the distribution function of the particle size has at least two maxima. Preferably, said first maximum is in the range of 50 to 180 nm, and said second maximum is in the range of 200 to 400 nm.

Preferably, the final polymer dispersion has a pH of at least pH 7, e.g. in the range of pH 7 to pH 12, prior to the use in the coating composition. The aqueous polymer dispersions of the present invention generally have solids contents in the range of 30 to 75% by weight, preferably in the range of 40 to 65% by weight, in particular in the range of 45 to 60% by weight.

The polymer dispersion can be confectioned with a film-forming auxiliary, also termed filming auxiliary. It is well known that the filming auxiliary lowers the minimum film forming temperature of the polymer dispersion. The minimum film forming temperature, hereinafter MFFT, is the lowest temperature at which the polymer particles of the polymer dispersion coalesce and form a coherent film. The MFFT is typically determined by applying the polymer dispersion as a thin film to a metal plate with a defined temperature gradient - see DIN ISO 2115: 2001-04.

Therefore, an aspect of the present invention relates to the polymer dispersion as described herein, which contain at least one filming auxiliary.

The amount of filming auxiliary is typically chosen, such that a MFFT in the range of 0 to 15°C results. Preferably, the amount of filming auxiliary is in the range from 2 to 25% by weight, in particular from 5 to 20% by weight, based on the total amount of polymer formed by the polymerized monomers M.

Suitable film-forming auxiliaries are solvents, also termed non-permanent plasticizers, and permanent plasticizers. Permanent plasticizers typically have a lower solubility in water and a lower volatility than non-permanent plasticizers. In contrast to permanent plasticizers, non-permanent plasticizers will evaporate from the coating and principally serve for a better coalescence of the binder particles at low temperature. Suitable filming auxiliaries providing non-permanent plasticization are, for example, i) hydrocarbons, such as white spirit and pine oil, ii) C2-C4-alkandiols, also termed C2-C4-alkylene glycols, di-C2-C4-alkylene glycols, tri-C2-C4-alkylene glycols and their mono-Ci-C₆-alkylethers, such as propylene glycol, ethylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol hexyl ether, diethylene glycol monomethyl ether, diethylene glycol monopropyl ether, dipropylene glycol methyl ether, dipropylene glycol n-butyl ether, propylene glycol tert— butyl ether, tripropylene glycol methyl ether, butyl diglycol (= 2-(2-(butoxy)ethoxy)ethanol)) and 1-methoxy-2-propanol; iii) mono- and diesters of C2-Cs-alkandiols, of di-C2-C4-alkylene glycols and of tri-C2- C4-alkylene glycols with C2-C4-alkanoic acids, such as acetic acid, propionic acid, butyric acid and isobutyric acid, and the monoesters of the mono-Ci-C₆- alkylethers of C2-C4-alkandiols, of di-C2-C4-alkylene glycols and of tri-C₂-C₄- alkylene glycols with C2-C4-alkanoic acids, such as butyl glycol acetate, butyl glycol diacetate, ethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate and 2,2,2-trimethyl-1 ,3-pentanediol monoisobutyrate (Texanol®); iv) di-Ci-C₆-alkylesters of aliphatic dicarboxylic acids having 4 to 8 carbon atoms such as dibutyl adipate, diisobutyl adipate, diisobutyl succinate, diisobutyl glutarate and diisobutyl maleate; v) the glycol ethers and esters, commercially available, for example, from BASF SE under the Solvenon® and Lusolvan® and Loxanol® names, and from Dow under the Dowanol® trade name.

Suitable external plasticizers of low volatility include the following: dimethyl phthalate, dibutyl phthalate, dioctyl phthalate and other esters of phthalic acid, propoxylated m-cresol having a number-average degree of propoxylation of 6, propoxylated p-cresol having a number-average degree of propoxylation of 6, and also mixtures of these two oligo(propylene glycol) cresol ethers, oligo(propylene glycol) cresol ethers having a number-average degree of propoxylation of 3, oligo(propylene glycol) cresol ethers having a number-average degree of propoxylation of 12, and also oligo(propylene glycol) phenyl ethers and oligo(propylene glycol) alkylphenyl ethers having a number- average degree of propoxylation of 3 to 12, aromatic glycol ethers, ethyl p-toluenesulfonate, alkyl esters of aromatic sulfonic acids, tributoxyethyl phosphate, tri-n-butyl phosphate, and other phosphoric esters.

Preference is given to filming auxiliaries, which are different from hydrocarbons. Preference is also given to non-permanent plasticizers. Particular preference is given to filming auxiliaries from groups ii) to v).

The aqueous polymer dispersion can be prepared by a free radical aqueous emulsion polymerization of the monomers M. According to the invention, the aqueous emulsion polymerization is carried out at least partly in the presence of a chain transfer compound as disclosed herein.

As the chain transfer compound is consumed in the free-radical aqueous emulsion polymerization, the expression “at least partially” is well understood that during at least a certain time period of the polymerization, which is preferably at least 10% of the total duration of the polymerization reaction, chain transfer compound is present in the polymerization reaction mixture. For example, the total amount of chain transfer compound may be added initially to the polymerization reaction or it may be added in the course of the polymerization reaction in or more portions or continuously. In particular, the major amount of the chain transfer compound, i.e. at least 50% by weight, preferably at least 70% by weight of the total amount of chain transfer compound is added in the course of the polymerization reaction. The addition rate of the chain transfer compound is preferably chosen; so that the major amount of the chain transfer compound, i.e. at least 50% by weight, preferably at least 70% by weight of the total amount of chain transfer compound is continuously added within a time period of the polymerization reaction; which is at least 10% of the total time of the polymerization reaction. As mentioned before, preference is given to chain transfer compounds having a mercapto group, in particular to chain transfer compounds of the groups T.1 to T.4 described above. Particular preference is given to chain transfer compounds T.1 and T2, in particular to C4-Ci6-alkyl esters of SH-substituted C2-C4 alkanoic acids, especially to C4-Ci6-alkyl esters of mercaptoacetic acid, to C4-Ci6-alkyl esters of mercaptopropionic acid, to C₆-Ci₆-alkyl mercaptans and to mixtures thereof.

The amount of chain transfer compounds is preferably in the range of 0.05 to 1.2% by weight, in particular in the range from 0.1 to 0.9% by weight, especially in the range from 0.15 to 0.6% by weight, based on the total weight of the monomers M.

Preferably, the free-radical aqueous emulsion polymerization is carried out as a free radical aqueous multistep emulsion polymerization. A free-radical aqueous multistep emulsion polymerization is a free-radical aqueous emulsion polymerization, which is carried out in at least two successive polymerization steps, where in each step a portion M’ of the monomers M is polymerized in a free-radical emulsion polymerization, where the second and any further polymerization step is carried out in the polymer dispersion obtained in the previous step.

In the free radical multistep emulsion polymerization the monomer composition of the portion M’ polymerized in the respective polymerization step may be identical or different. Preferably, in one of the polymerization steps of the free radical multistep emulsion polymerization, hereinafter step (i), the relative proportion of the total amount of all acidic monomers, i.e. monomers Ma1, Ma2 and Ma3, in the portion of monomers M polymerized in said polymerization step (i), hereinafter the monomers M(i), is higher is higher than the relative proportion of the total amount of all acidic monomers polymerized in any other polymerization step. In particular, the relative proportion of the total amount of all acidic monomers present in the monomers M(i) is at least 1% by weight higher, with respect to the total amount of monomers M(i), than the relative proportion of the total amount of all acidic monomers present in the monomers of the other polymerization steps. In particular, the total amount of acidic monomers Ma1,

Ma2 and Ma3 present in the monomers M(i) is in the range of 2 to 10% by weight, in particular 2.5 to 8% by weight, especially 3 to 7% by weight, based on the total amount of monomers M(i) polymerized in said polymerization step. In particular, the relative proportion of the total amount of all acidic monomers Ma1 , Ma2 and Ma3 present in the monomers polymerized in the other polymerization step(s) is at most 2% by weight, in particular at most 1.5% by weight and especially at most 1 % by weight, based on the total amount of monomers polymerized in the other polymerization step(s). In particular, at least 40% by weight, e.g. 40 to 100% by weight, especially 50 to 95% by weight of the total amount of acidic monomers Ma1 , Ma2 and Ma3 contained in the monomers M are polymerized in said polymerization step (i).

Principally, the chain transfer compound may be present in any of the polymerization steps of the free radical multistep emulsion polymerization. Preferably, at least a portion of the chain transfer compound is present in the step (i) of the multistep emulsion polymerization. In particular, at least 40% by weight, especially at least 50% by weight of the total amount of the chain transfer compound is present in step (i) of the free radical aqueous multistep emulsion polymerization. Especially, the total amount or at least 85% of the total amount of the chain transfer compound is present in step (i) of the free radical aqueous multistep emulsion polymerization.

Preferably, the total amount of monomers M(i) polymerized in the step (i) does not exceed 60% by weight, in particular 50% by weight of the total amount of monomers M and is in particular in the range from 10 to 60% by weight and in particular in the range from 15 to 50% by weight, based on the total amount of monomers M. Consequently, the total amount of monomers polymerized in any other steps is preferably at least 40% by weight, in particular at least 50% by weight, and is in particular in the range from 40 to 90% by weight and in particular in the range from 50 to 85% by weight, based on the total amount of monomers M.

Step (i) may be the first step of the free radical multistep emulsion polymerization or any other step of the free radical multistep emulsion polymerization. In a particular group (1) of embodiments, step (i) is the first step of the free radical multistep emulsion polymerization. In another particular group (2) of embodiments, step (i) is the second step of the free radical multistep emulsion polymerization.

In the particular (1) group of embodiments, the multistep emulsion polymerization preferably comprises: i. a first step (1 ), where monomers M(1 ) are polymerized under the conditions of a free radical aqueous emulsion polymerization, where the monomers M(1) comprise at least one monomer Ma1 , at least one monomer Ma2, at least one monomer Ma3, at least one monomer Mb1 , at least one monomer Mb2 and at least one monomer Me, and ii. a second step (2), where monomers M(2) are polymerized under the conditions of a free radical aqueous emulsion polymerization, where the monomers M(2) comprise at least one monomer Mb1 and at least one monomer Mb2 and optionally at least one further monomer selected from the group consisting of the monomers Ma1 , Ma2, Ma3 and Me.

In the group (1) of embodiments, step (1) corresponds to step (i). The above disclosure with respect to the relative amounts of acidic monomers present in the monomers M(i), the presence of chain transfer agent in step (i) and the relative amount of monomers M(i) with respect to the total amount of monomers M apply to step (1) in the same way. The multistep emulsion polymerization of the group (1) of embodiments may of course comprise one or more further subsequent steps (3), (4) . (n.)

In the particular (2) group of embodiments, the multistep emulsion polymerization preferably comprises: i. a first step (1 ’), where monomers M(1 ’) are polymerized under the conditions of a free radical aqueous emulsion polymerization, where the monomers M(T) comprise at least one monomer Mb1 and at least one monomer Mb2 and optionally at least one further monomer selected from the group consisting of the monomers Ma1 , Ma2, Ma3 and Me, and ii. a second step (2’), where monomers M(2’) are polymerized under the conditions of a free radical aqueous emulsion polymerization, where the monomers M(2’) comprise at least one monomer Ma1 , at least one monomer Ma2, at least one monomer Ma3, at least one monomer Mb1 , at least one monomer Mb2 and at least one monomer Me.

In the group (2) of embodiments, step (2’) corresponds to step (i). The above disclosure with respect to the relative amounts of acidic monomers present in the monomers M(i), the presence of chain transfer agent in step (i) and the relative amount of monomers M(i) with respect to the total amount of monomers M apply to step (2’) in the same way. The multistep emulsion polymerization of the group (2) of embodiments may of course comprise one or more further subsequent steps (3’), (4’) . (n’). The free-radically initiated aqueous emulsion polymerization is triggered by means of a free-radical polymerization initiator (free-radical initiator). These may, in principle, be peroxides or azo compounds. Of course, redox initiator systems are also useful. Peroxides used may, in principle, be inorganic peroxides, such as hydrogen peroxide or peroxodisulfates, such as the mono- or di-alkali metal or ammonium salts of peroxodisulfuric acid, for example the mono- and disodium, -potassium or ammonium salts, or organic peroxides, such as alkyl hydroperoxides, for example tert-butyl hydroperoxide, p-menthyl hydroperoxide or cumyl hydroperoxide, and also dialkyl or diaryl peroxides, such as di-tert-butyl or di-cumyl peroxide. Azo compounds used are essentially 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile) and 2,2'-azobis(amidinopropyl) dihydrochloride (AIBA, corresponds to V-50 from Wako Chemicals). Suitable oxidizing agents for redox initiator systems are essentially the peroxides specified above. Corresponding reducing agents, which may be used are sulfur compounds with a low oxidation state, such as alkali metal sulfites, for example potassium and/or sodium sulfite, alkali metal hydrogensulfites, for example potassium and/or sodium hydrogensulfite, alkali metal metabisulfites, for example potassium and/or sodium metabisulfite, formaldehydesulfoxylates, for example potassium and/or sodium formaldehydesulfoxylate, alkali metal salts, specifically potassium and/or sodium salts of aliphatic sulfinic acids and alkali metal hydrogensulfides, for example potassium and/or sodium hydrogensulfide, salts of polyvalent metals, such as iron(ll) sulfate, iron(ll) ammonium sulfate, iron(ll) phosphate, ene diols, such as dihydroxymaleic acid, benzoin and/or ascorbic acid, and reducing saccharides, such as sorbose, glucose, fructose and/or dihydroxyacetone.

Preferred free-radical initiators are inorganic peroxides, especially peroxodisulfates.

In general, the amount of the free-radical initiator used, based on the total amount of monomers M, is 0.05 to 2 pphm, preferably 0.1 to 1 pphm, based on the total amount of monomers M.

The amount of free-radical initiator required for the emulsion polymerization of monomers M can be initially charged in the polymerization vessel completely.

However, it is also possible to charge none of or merely a portion of the free-radical initiator, for example not more than 30% by weight, especially not more than 20% by weight, based on the total amount of the free-radical initiator and then to add any remaining amount of free-radical initiator to the free-radical polymerization reaction under polymerization conditions. Preferably, at least 70%, in particular at least 80%, especially at least 90% or the total amount of the polymerization initiator are added to the free-radical polymerization reaction under polymerization conditions. Addition may be done according to the consumption, batchwise in one or more portions or continuously with constant or varying flow rates during the free-radical emulsion polymerization of the monomers M.

Generally, the term "polymerization conditions" is 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. Advantageously, the type and amount of the free-radical initiator, polymerization temperature and polymerization pressure are selected, such that a sufficient amount of initiating radicals is always present to initiate or to maintain the polymerization reaction.

Preferably, the radical emulsion polymerization of the monomers M is performed by a so-called feed process (also termed monomer feed method), which means that at least 80%, in particular at least 90% or the total amount of the monomers M to be polymerized are metered to the polymerization reaction under polymerization conditions during a metering period P. Addition may be done in portions and preferably continuously with constant or varying feed rate. The duration of the period P may depend from the production equipment and may vary from e.g. 20 minutes to 12 h. Frequently, the duration of the period P will be in the range from 0.5 h to 8 h, especially from 1 h to 6 h. In a multistep emulsion polymerization step, the total duration of all steps is typically in the above ranges. The duration of the individual steps, is typically shorter.

Preferably, at least 70%, in particular at least 80%, especially at least 90% or the total amount of the polymerization initiator is introduced into emulsion polymerization the in parallel to the addition of the monomers.

The aqueous radical emulsion polymerization is usually performed in the presence of one or more suitable surfactants. These surfactants typically comprise emulsifiers and provide micelles, in which the polymerization occurs, and which serve to stabilize the monomer droplets during aqueous emulsion polymerization and also growing polymer particles. The surfactants used in the emulsion polymerization are usually not separated from the polymer dispersion, but remain in the aqueous polymer dispersion obtainable by the emulsion polymerization of the monomers M.

The surfactant may be selected from emulsifiers and protective colloids. Protective colloids, as opposed to emulsifiers, are understood to mean polymeric compounds having molecular weights above 2000 Daltons, whereas emulsifiers typically have lower molecular weights. The surfactants may be anionic or nonionic or mixtures of non-ionic and anionic surfactants.

Anionic surfactants usually bear at least one anionic group, which is typically selected from phosphate, phosphonate, sulfate and sulfonate groups. The anionic surfactants, which bear at least one anionic group are typically used in the form of their alkali metal salts, especially of their sodium salts or in the form of their ammonium salts.

Preferred anionic surfactants are anionic emulsifiers, in particular those, which bear at least one sulfate or sulfonate group. Likewise, anionic emulsifiers, which bear at least one phosphate or phosphonate group may be used, either as sole anionic emulsifiers or in combination with one or more anionic emulsifiers, which bear at least one sulfate or sulfonate group. Examples of anionic emulsifiers, which bear at least one sulfate or sulfonate group, are, for example, the salts, especially the alkali metal and ammonium salts, of alkyl sulfates, especially of Cs-C22-alkyl sulfates, the salts, especially the alkali metal and ammonium salts, of sulfuric monoesters of ethoxylated alkanols, especially of sulfuric monoesters of ethoxylated C8-C22- alkanols, preferably having an ethoxylation level (EO level) in the range from 2 to 40, the salts, especially the alkali metal and ammonium salts, of sulfuric monoesters of ethoxylated alkylphenols, especially of sulfuric monoesters of ethoxylated C4-Ci8-alkylphenols (EO level preferably 3 to 40), the salts, especially the alkali metal and ammonium salts, of alkylsulfonic acids, especially of C8-C22-alkylsulfonic acids, the salts, especially the alkali metal and ammonium salts, of dialkyl esters, especially di-C4-Ci8-alkyl esters of sulfosuccinic acid, - the salts, especially the alkali metal and ammonium salts, of alkylbenzenesulfonic acids, especially of C4-C22-alkylbenzenesulfonic acids, and the salts, especially the alkali metal and ammonium salts, of mono- or disulfonated, alkyl-substituted diphenyl ethers, for example of bis(phenylsulfonic acid) ethers bearing a C4-C24-alkyl group on one or both aromatic rings. The latter are common knowledge, for example from US-A-4,269,749, and are commercially available, for example as Dowfax® 2A1 (Dow Chemical Company).

Also suitable are mixtures of the aforementioned salts. Examples of anionic emulsifiers, which bear a phosphate or phosphonate group, include, but are not limited to the following salts, are selected from the following groups: - the salts, especially the alkali metal and ammonium salts, of mono- and dialkyl phosphates, especially Cs-C22-alkyl phosphates, the salts, especially the alkali metal and ammonium salts, of phosphoric monoesters of C2-C3-alkoxylated alkanols, preferably having an alkoxylation level in the range from 2 to 40, especially in the range from 3 to 30, for example phosphoric monoesters of ethoxylated Cs-C22-alkanols, preferably having an ethoxylation level (EO level) in the range from 2 to 40, phosphoric monoesters of propoxylated Cs-C22-alkanols, preferably having a propoxylation level (PO level) in the range from 2 to 40, and phosphoric monoesters of ethoxylated-co- propoxylated Cs-C22-alkanols, preferably having an ethoxylation level (EO level) in the range from 1 to 20 and a propoxylation level of 1 to 20, the salts, especially the alkali metal and ammonium salts, of phosphoric monoesters of ethoxylated alkylphenols, especially phosphoric monoesters of ethoxylated C4-Ci8-alkylphenols (EO level preferably 3 to 40), the salts, especially the alkali metal and ammonium salts, of alkylphosphonic acids, especially C8-C22-alkylphosphonic acids and the salts, especially the alkali metal and ammonium salts, of alkylbenzenephosphonic acids, especially C4-C22-alkylbenzenephosphonic acids.

Further suitable anionic surfactants can be found in Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], volume XIV/1 , Makromolekulare Stoffe [Macromolecular Substances], Georg-Thieme-Verlag, Stuttgart, 1961 , p. 192- 208.

Preferably, the surfactant comprises at least one anionic emulsifier, which bears at least one sulfate or sulfonate group. The at least one anionic emulsifier, which bears at least one sulfate or sulfonate group, may be the sole type of anionic emulsifiers. However, mixtures of at least one anionic emulsifier, which bears at least one sulfate or sulfonate group, and at least one anionic emulsifier, which bears at least one phosphate or phosphonate group, may also be used. In such mixtures, the amount of the at least one anionic emulsifier, which bears at least one sulfate or sulfonate group, is preferably at least 50% by weight, based on the total weight of anionic surfactants used in the process of the present invention. In particular, the amount of anionic emulsifiers, which bear at least one phosphate or phosphonate group does not exceed 20% by weight, based on the total weight of anionic surfactants used in the process of the present invention.

Preferred anionic surfactants are anionic emulsifiers, which are selected from the following groups, including mixtures thereof: the salts, especially the alkali metal and ammonium salts, of alkyl sulfates, especially of Cs-C22-alkyl sulfates, the salts, especially the alkali metal salts, of sulfuric monoesters of ethoxylated alkanols, especially of sulfuric monoesters of ethoxylated Cs-C22-alkanols, preferably having an ethoxylation level (EO level) in the range from 2 to 40, of sulfuric monoesters of ethoxylated alkylphenols, especially of sulfuric monoesters of ethoxylated C4-Ci8-alkylphenols (EO level preferably 3 to 40), of alkylbenzenesulfonic acids, especially of C4-C22-alkylbenzenesulfonic acids, and of mono- or disulfonated, alkyl-substituted diphenyl ethers, for example of bis(phenylsulfonic acid) ethers bearing a C4-C24-alkyl group on one or both aromatic rings.

Particular preference is given to anionic emulsifiers, which are selected from the following groups, including mixtures thereof: the salts, especially the alkali metal and ammonium salts, of alkyl sulfates, especially of Cs-0₂₂-alkyl sulfates, the salts, especially the alkali metal salts, of sulfuric monoesters of ethoxylated alkanols, especially of sulfuric monoesters of ethoxylated Cs-C22-alkanols, preferably having an ethoxylation level (EO level) in the range from 2 to 40, of mono- or disulfonated, alkyl-substituted diphenyl ethers, for example of bis(phenylsulfonic acid) ethers bearing a C4-C24-alkyl group on one or both aromatic rings.

As well as the aforementioned anionic surfactants, the surfactant may also comprise one or more nonionic surface-active substances, which are especially selected from nonionic emulsifiers. Suitable nonionic emulsifiers are e.g. araliphatic or aliphatic nonionic emulsifiers, for example ethoxylated mono-, di- and trialkylphenols (EO level: 3 to 50, alkyl radical: C4-C10), ethoxylates of long-chain alcohols (EO level: 3 to 100, alkyl radical: Cs-Cze), and polyethylene oxide/polypropylene oxide homo- and copolymers. These may comprise the alkylene oxide units copolymerized in random distribution or in the form of blocks. Very suitable examples are the EO/PO block copolymers. Preference is given to ethoxylates of long-chain alkanols, in particular to those, where the alkyl radical C8-C30 having a mean ethoxylation level of 5 to 100 and, among these, particular preference to those having a linear C12-C20 alkyl radical and a mean ethoxylation level of 10 to 50 and also to ethoxylated monoalkylphenols.

In a particular embodiment of the invention, the surfactants used in the process of the present invention comprise less than 20% by weight, especially not more than 10% by weight, of nonionic surfactants, based on the total amount of surfactants used in the process of the present invention, and especially do not comprise any nonionic surfactant. Preferably, the surfactant will be used in such an amount that the amount of surfactant is in the range from 0.2 to 5% by weight, especially in the range from 0.3 to 3% by weight, based on the monomers M to be polymerized. In a multistep emulsion step emulsion polymerization, the surfactant will be used in such an amount that the amount of surfactant is usually in the range from 0.2 to 5% by weight, especially in the range from 0.3 to 3% by weight, based on the total amount of monomers polymerized in the respective steps, e.g. in steps M(i) and M(ii) respectively.

Preferably, the major portion, i.e. at least 80% of the surfactant used, is added to the emulsion polymerization in parallel to the addition of the monomers. In particular, the monomers are added as an aqueous emulsion to the polymerization reaction, which contains at least at least 80% of the surfactant used in the emulsion polymerization.

It has been found advantageous to perform the free-radical emulsion polymerization of the monomers M in the presence of a seed latex. A seed latex is a polymer latex, which is present in the aqueous polymerization medium before the polymerization of monomers M is started. The seed latex may help to better adjust the particle size or the final polymer latex obtained in the free-radical emulsion polymerization of the invention.

Principally, every polymer latex may serve as a seed latex. For the purpose of the invention, preference is given to seed latices, where the particle size of the polymer particles is comparatively small. In particular, the Z average particle diameter of the polymer particles of the seed latex, as determined by dynamic light scattering (DLS) at 20°C (see below), is preferably in the range from 10 to 80 nm, in particular from 10 to 50 nm. Preferably, the polymer particles of the seed latex is made of ethylenically unsaturated monomers, which comprise at least 95% by weight, based on the total weight of the monomers forming the seed latex, of one or more monomers Mb1 and/or Mb2 as defined above. For this, the seed latex is usually charged into the polymerization vessel before the polymerization of the monomers M is started. In particular, the seed latex is charged into the polymerization vessel followed by establishing the polymerization conditions, e.g. by heating the mixture to polymerization temperature. It may be beneficial to charge at least a portion of the free-radical initiator into the polymerization vessel before the addition of the monomers M is started. However, it is also possible to add the monomers M and the free-radical polymerization initiator in parallel to the polymerization vessel. The amount of seed latex, calculated as solids, may frequently be in the range from 0.05 to 5% by weight, in particular from 0.1 to 3% by weight, based on the total weight of the monomers in the monomer composition M to be polymerized.

If the free-radical aqueous emulsion polymerization is carried out as a free-radical multistep aqueous emulsion polymerization the invention, the second step is carried out subsequent to the first step. The second step may be carried out immediately after the monomer composition of the first step has been completely added to the emulsion polymerization of first step, i.e. the polymerization of monomers to be polymerized in the second step is immediately started after the addition of monomers polymerized in the first step has been completed. However, it is also possible to allow the polymerization of the first step to continue after the addition of monomers to be polymerized in the first step has been completed, before the polymerization of monomers to be polymerized in the second step is started. In the second and any further step of the multistep emulsion polymerization, the monomers may be added all at once to the polymer dispersion obtained in the first step. However, the free-radical emulsion polymerization of the monomers to be polymerized in the second step is preferably performed by a feed process as described above. This means that at least 80%, in particular at least 90% or the total amount of the monomers in the monomers to be polymerized in the second and any further steps are metered to the polymerization reaction under polymerization conditions during a metering period P’. The duration of each of the periods P and P’ may depend from the production equipment and may vary from e.g. 10 minutes to 8 h. Frequently, the duration of each of the periods P and P’ will be in the range from 20 minutes to 7 h, especially from 30 minutes to 5 h.

The free-radical aqueous emulsion polymerization of the invention can be carried out at temperatures in the range from 0 to 170°C. Temperatures employed are generally in the range from 50 to 120°C, frequently 60 to 120°C and often 70 to 110°C. The free- radical aqueous emulsion polymerization of the invention can be conducted at a pressure of less than, equal to or greater than 1 atm (atmospheric pressure), and so the polymerization temperature may exceed 100°C and may be up to 170°C. Polymerization of the monomers is normally performed at ambient pressure, but it may also be 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 emulsion polymerizations are conducted 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 of the invention is conducted at ambient pressure (about 1 atm) with exclusion of oxygen, for example under an inert gas atmosphere, for example under nitrogen or argon.

The free-radical emulsion polymerization of the invention is usually effected in an aqueous polymerization medium, which, as well as water, comprises at least one surface-active substance, so-called surfactants, for stabilizing the emulsion of the monomers and the polymer particles of the polymer latex. Suitable surfactants are mentioned hereinabove.

Apart from that, the conditions required for the performance of the free radical emulsion polymerization are sufficiently familiar to those skilled in the art, for example from the prior art cited at the outset and from "Emulsionspolymerization" [Emulsion Polymerization] in Encyclopedia of Polymer Science and Engineering, vol. 8, pages 659 ff. (1987); D. C. Blackley, in High Polymer Latices, vol. 1 , pages 35 ff. (1966); H. Warson, The Applications of Synthetic Resin Emulsions, chapter 5, pages 246 ff. (1972); D. Diederich, Chemie in unserer Zeit 24, pages 135 to 142 (1990); Emulsion Polymerization, Interscience Publishers, New York (1965); DE-A 4003422 and Dispersionen synthetischer Hochpolymerer [Dispersions of Synthetic High Polymers],

F. Holscher, Springer-Verlag, Berlin (1969)].

It is frequently advantageous, when the aqueous polymer dispersion obtained on completion of polymerization of the monomers M is subjected to an after-treatment to reduce the residual monomer content. This after-treatment is effected either chemically, for example by completing the polymerization reaction using a more effective free-radical initiator system (known as postpolymerization), and/or physically, for example by stripping the aqueous polymer dispersion with steam or inert gas. Corresponding chemical and physical methods are familiar to those 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 DE-A 19847115. The combination of chemical and physical aftertreatment has the advantage that it removes not only the unconverted ethylenically unsaturated monomers, but also other disruptive volatile organic constituents (VOCs) from the aqueous polymer dispersion. As the polymer contained in the aqueous polymer dispersion contains acidic groups from the monomers Ma1 , Ma2 and Ma3 and optionally from the polymerization initiator, the aqueous polymer dispersion obtained by the process of the invention is frequently neutralized prior to formulating it as a coating composition. The neutralization of acid groups of the polymer is achieved by neutralizing agents known to the skilled of the art after polymerization and/or during the polymerization. For example, the neutralizing agent may be added in a joint feed with the monomers to be polymerized, or in a separate feed. Suitable neutralizing agents include organic amines, alkali hydroxides, ammonium hydroxides. In particular, neutralization is achieved by using ammonia or alkali hydroxides, such as sodium hydroxide or potassium hydroxide.

Preferably, the final polymer dispersion has a pH of at least pH 7, e.g. in the range of pH 7 to pH 12, prior to the use in the coating composition.

The aqueous polymer dispersions of the present invention are particularly useful as binders or co-binders in water-borne coating compositions, in particular in architectural coating compositions and in coating compositions for mineral shaped bodies.

The waterborne coating compositions typically contain the aqueous polymer dispersion of the present invention and thus contain the polymer resulting from the polymerization of the monomers M in the form of fine particles and also the surface-active substances used in the emulsion polymerization, such as emulsifiers and/or protective colloids.

The waterborne coating compositions typically comprise not more than 50%, more particularly not more than 20%, and especially not more than 10% by weight, based on the total weight of the coating composition, of water-miscible solvents. With very particular preference the formulations of the invention comprise no organic solvents besides water, aside from typical frost preventatives and film-forming auxiliaries.

The aqueous polymer dispersions of the present invention can be used as coating compositions as they are. The coating compositions may, however, contain typical formulation auxiliaries. The total amount of typical formulation auxiliaries is usually in the range from 0.1 to 30% by weight, in particular in the range from 0.5 to 10% by weight of the waterborne coating composition. Conventional formulation auxiliaries include, but are not limited to pigment dispersants, wetting agents, rheology modifying agents, leveling agents, biocides, defoamers antifreeze agents, flow promoters, and the aforementioned film-forming auxiliaries. Further suitable formulation auxiliaries and components are e.g. described by J. Bieleman in “Additives for Coatings”, Wiley-VCH, Weinheim 2000; by T. C. Patton in “Paint Flow and Pigment Dispersions”, 2. Edition, John Wiley & Sons 1978; and by M. Schwartz and R. Baumstark in “Water based Acrylates for Decorative Coatings”, Curt R. Vincentz Verlag, Flanover 2001.

The waterborne coating compositions of the invention may also, furthermore, comprise inorganic fillers and/or pigments. Typical pigments are, for example, titanium dioxide, preferably in the rutile form, barium sulfate, zinc oxide or lithopones (zinc sulfide + barium sulfate). For decorative purposes, the formulations may also comprise colored pigments, examples being iron oxides, carbon black, graphite, zinc yellow, zinc green, ultramarine, manganese black, antimony black, manganese violet, Paris blue or Schweinfurt green. The formulations may also comprise pigments, which reflect IR radiation, i.e. IR reflecting pigments, such as pigments based on Fe/Cr mixed oxides and titanium based mixed oxides, such as antimony nickel titanium oxides. Suitable fillers comprise aluminosilicates, such as feldspars, silicates, such as kaolin, talc, mica, magnesite, alkaline earth metal carbonates, such as calcium carbonate, in the form for example of calcite or chalk, magnesium carbonate, dolomite, alkaline earth metal sulfates, such as calcium sulfate, silicon dioxide, etc.

The proportion of the pigments and fillers in the waterborne coating compositions can be described in a manner known per se via the pigment volume concentration (PVC). The PVC describes the ratio of the volume of pigments (VP) and fillers (VF) relative to the total volume, consisting of the volumes of binder (VB), pigments (VP) and fillers (VF) in a dried coating film in percent: PVC = (VP + VF) x 100 / (VP + VF + VB). Preferably, the PVC will not exceed a value of 60 and is specifically in the range from 0 to 50.

The waterborne coating compositions of the invention may also comprise crosslinking additives. Such additives include the following: aromatic ketones, e.g., alkyl phenyl ketones, which, if appropriate, have one or more substituents on the phenyl ring, or benzophenone and substituted benzophenones as photoinitiators. Photoinitiators suitable for this purpose are known, for example, from DE-A 3827975 and EP-A 417 568. Suitable compounds with a crosslinking action are also water-soluble compounds having at least two amino groups, examples being dihydrazides of aliphatic dicarboxylic acids in accordance with DE-A 39 01 073, if the polymer formed by the polymerized monomers M comprises, in copolymerized form, monomers comprising carbonyl groups. The waterborne coating compositions of the invention include, for example, clearcoat (transparent varnish) formulations, surface coating formulations, such as paints, renders or coating systems.

According to one preferred embodiment of the present invention, waterborne coating compositions are formulated as a clearcoat material. In that case, they generally comprise, based on their total weight, 10% to 60%, preferably 40% to 55%, by weight of at least one polymer formed by polymerized monomers M and 0.1 % to 30%, preferably 0.5% to 10%, by weight of typical auxiliaries, more particularly defoamers and/or film-forming auxiliaries.

Another embodiment of the present invention relates to waterborne coating compositions in the form of pigmented and/or filled formulations. In this case, the total amount of the polymer formed by polymerized monomers M in the aqueous formulation is in the range from 10 to 60% by weight, preferably in the range from 20 to 40% by weight; the auxiliaries’ content is in the range from 0.1 to 30% by weight and preferably in the range from 0.5 to 10% by weight, and the content of fillers and/or pigments is in the range from 10 to 60% by weight and more particularly from 10% to 40% by weight. Preferably, the PVC is in the range from 2 to 50. Furthermore, besides the film-forming assistants and the defoamers, pigmented formulations will preferably also comprise a dispersant and/or wetting agent.

The clearcoat materials and pigmented paints of the invention may comprise further typical auxiliaries, such as wetting agents, in-can and in-film preservatives, thickeners, defoamers, flow promoters, and antifreeze agents, for example, in the amounts that are typical per se.

The present invention also relates to the use of the waterborne coating compositions of the present invention for permanently coating substrates and accordingly to a method for producing a permanent coating on a surface of a substrate. The method comprises

(a) applying the waterborne coating composition according to the invention to a surface to be coated, and

(b) allowing the composition to dry to produce the permanent coating.

The waterborne coating compositions can be applied to surfaces and/or substrates to be coated in a customary manner, such as, for example, by applying the waterborne coating composition with brushes or rolls, by spraying, by dipping, by rolling, by curtain coating or by bar coating. The coating of surfaces and/or substrates is effected in such a way that the surface and/or substrate is first coated with a composition of the invention and then the aqueous composition is subjected to a drying step. The drying step is typically carried out at temperatures in the range of +5 to +80°C and in particular in the range of +10 to +70°C. Typically, temperatures of +5 to+ 25°C will be sufficient to achieve an acceptable permanent coating. However, higher temperatures will accelerate the drying speed, and temperatures of up to +80°C or up to +70°C may also be suitable.

Principally, the waterborne coating compositions of the present invention can be applied to any substrate, which is conventionally coated by waterborne coating compositions. The waterborne coating compositions can be applied to surfaces, such as, for example, metal, asphalt, concrete, fiber cement boards, stone, ceramic, minerals, wood, plastic, polymer, and glass. The waterborne coating compositions can be applied to interior or exterior surfaces, such as, for example, an architectural surface, such as a roof, a wall, a floor and a ceiling.

The waterborne coating compositions of the present invention are particularly suitable for coating of mineral substrates including stone walls and concrete surfaces and especially suitable for coating surfaces of shaped mineral articles, such as concrete roof tiles and fiber cement boards.

The coating of shaped mineral articles by waterborne coating compositions is well known, e.g. from the prior art discussed at the outset, and from EP 1069093 and EP 3498783. In case of coating shaped mineral articles, the application rate of the aqueous polymer formulation to be applied for preservation is typically 50 to 700 g/m² (calculated wet). Application may take place in a conventional manner, by spraying, troweling, knife coating, rolling or pouring including curtain coating. The method of the invention can be employed with both ready-cured and freshly prepared ("green") shaped mineral articles. It is especially suitable for preserving shaped mineral articles comprising cement as a mineral binder (cast concrete). In a particularly advantageous way, it prevents efflorescence on concrete roof tiles. The latter are usually produced from cement mortars, whose consistency permits ultimate shaping. They are generally hardened at temperatures between 40 and 80°C. Typically, hardening is carried out at a relative humidity in the range of 30 to 90%. After shaping (by extrusion, for example), but generally prior to hardening, the concrete roof tiles are coated superficially with a waterborne coating composition of the invention, and then stored for 6 to 12 h in curing chambers, in which typically the abovementioned temperature and humidity conditions prevail. Within this time, they cure, and at the same time the coating composition forms a permanent film. In some cases, a further application is performed with coating composition, after the curing operation, with subsequent drying. Then, drying may be carried out at temperatures described above, e.g. in the range from 5 to 50°C. EXAMPLES

Hereinafter the following abbreviations are used:

% b.w. % by weight

AA acrylic acid

AMA allyl methacrylate

AMPS: 2-acrylamido-2-methylpropane sulfonic acid

AM acrylamide

DLS: dynamic light scattering

EHTG 2-ethylhexyl thioglycolate

EO: ethylene oxide

HDC: hydrodynamic chromatography

HDC-PS: particle size determined by HDC

HPPS: High Performance Particle Sizer

IA itaconic acid

MAA: methacrylic acid n.d. not determined n.o. not observed

/7-BUA /7-butyl acrylate

PDI: polydispersity index rpm: rotations per minute

SC: solids content

SDS: sodium dodecyl sulfate (sodium lauryl sulfate)

/-DMK tert- dodecyl mercaptan

MEMO 3-(trimethoxy silyl)propyl methacrylate

WU: water uptake

Z-PS: particle size determined by DLS

1. Analytics and characterization

1.1 Characterization of the dispersions i) Solids contents of the polymer dispersions were measured according to the standard method DIN EN ISO 3251: 2008-06. ii) pH values of the polymer dispersions were measured according to the standard method DIN EN 1262:2004-01. iii) The glass transition temperature was determined by the DSC method (Differential Scanning Calorimetry, 20 K/min, midpoint measurement, DIN 53765:1994-03) by means of a DSC instrument (Q 2000 series from TA instruments). iv) Particle Size Distribution of Polymer Dispersion by DLS The particle diameter of the polymer latex was determined by dynamic light scattering (DLS, also termed quasi-elastic light scattering) of an aqueous polymer dispersion diluted with deionized water to 0.001 to 0.5% by weight at 22°C by means of a HPPS from Malvern Instruments, England. What is reported is the cumulant Z average diameter calculated from the measured autocorrelation function (ISO Standard 13321). v) Particle Size Distribution of Polymer Dispersion by HDC Measurements were carried out using a PL-PSDA particle size distribution analyzer (Polymer Laboratories, Inc.). A small amount of sample of the polymer latex was injected into an aqueous eluent containing an emulsifier, resulting in a concentration of approximately 0.5 g/l. The mixture was pumped through a glass capillary tube of approximately 15 mm diameter packed with polystyrene spheres. As determined by their hydrodynamic diameter, smaller particles can sterically access regions of slower flow in capillaries, such that on average the smaller particles experience slower elution flow. The fractionation was finally monitored using an UV-detector, which measured the extinction at a fixed wavelength of 254 nm. vi) The minimum film forming temperature (MFFT) was determined in accordance with DIN ISO 2115:2001-04 using a Kofler heating bank.

1.2 Application testing: i) Films of the conditioned latex dispersion as described in the examples above were cast on polyethylene foil using a doctor blade with 600 pm gap width. The resulting films were dried for 24 hours at room temperature. After this, the films were separated from the polyethylene foil and dried at 60°C for three days in the oven. Using a gauge, two specimen, each in the dimension of 5cm^*4cm, were cut out of the film. The specimen were immersed in a reservoir of deionized water for 72 h in a stainless steel mesh. Afterwards, the specimen were removed from the stainless steel mesh and dried to constant weight in an oven at 60°C and weighted (Wd_ry). Then, the specimen were put into a reservoir of deionized water again also in a stainless steel mesh for 24 hours, taken out of the reservoir and the mesh and dried with a towel to remove all adhering water droplets and weighted again immediately (w_wet). The water uptake in percent (%) was calculated by the formula 100.

2. Materials used for preparing the polymer dispersions Seed latex S1 : acrylic seed particles having a solid content of 33% by weight and a Z-average particle size of 30 nm as determined by DLS Emulsifier E1: sodium dodecylsulfate - Emulsifier E2: sodium salt of a C12/14 alcohol ether sulfate having about 2 EO units

Emulsifier E3: sodium salt of a C12/14 alcohol ether sulfate having about 4 EO units

Coalescent agent CA1 : 2-(2-butoxyethoxy)ethanol - Coalescent agent CA2: dibutyl adipate

If not stated otherwise, the water used in the production examples was deionized water. 3. Production of polymer dispersions

Example 1:

A polymerization vessel equipped with a stirrer and three separate feeding lines was charged as followed:

Initial charge #0:

402.78 g water 19.69 g seed latex S1

In a first addition vessel was prepared feed/emulsion #1 by mixing the following components:

Feed/emulsion #1

6.46 g itaconic acid 6.33 g acrylic acid 1.88 g 2-acrylamido-2-methylpropane sulfonic acid 0.38 g 3-(trimethoxy silyl)propyl methacrylate 0.95 g emulsifier E1 2.86 g emulsifier E2 238.75 g methyl methacrylate 133.51 g /7-butyl acrylate 3.17 g tert- dodecyl mercaptan 214.30 g water In a second addition vessel was prepared feed/emulsion #2 by mixing the following components:

Feed/emulsion #2

4.39 g 2-acrylamido-2-methylpropane sulfonic acid 0.89 g 3-(trimethoxy silyl)propyl methacrylate 2.22 g emulsifier E1 6.65 g emulsifier E2 554.88 g methyl methacrylate 322.01 g /7-butyl acrylate 273.04 g water

In a third addition vessel was prepared the following feed/initiator solution # 3 by dissolving:

Feed/initiator solution #3:

3.83 g sodium peroxodisulfate in 50.79 g water In a fourth addition vessel was prepared the following feed/oxidation solution # 4 by dissolving:

Feed/oxidation solution #4:

1.26 g te t-butyl hydroperoxide in 11.34 g of water

In a fifth addition vessel was prepared the following feed/reduction solution # 5 by dissolving:

Feed/reduction solution #5: 0.72 g sodium bisulfite in 7.68 g of water mixed with 0.43 g of acetone

The initial charge #0 was heated up to polymerization temperature of 83°C under stirring with 150 rpm. Then after reaching the reaction temperature of 83°C, feed/emulsion #1 was fed into the reaction vessel in the course of 60 minutes. In parallel, starting at the same time as feed/emulsion #1 but from a spatially separated feeding vessel, 30% b.w. of feed/initiator solution #3 was fed into the reaction vessel in the course of 60 minutes. After the end of the addition of feed/emulsion #1 , feed/emulsion #2 was fed into the reaction vessel in the course of 140 minutes. In parallel, starting at the same time as feed/emulsion #2 but from a spatially separated feeding vessel, 70%wt of feed/initiator solution #3 was fed into the reaction vessel in the course of 140 minutes.

After the end of the addition of feed/emulsion #2 and feed/initiator solution #3, the reaction vessel was stirred for an additional 20 minutes after which a solution of 2.16 g of sodium hydroxide in 37.23 g of water was added in the course of 20 minutes. After the end of the addition of the aqueous solution of sodium hydroxide, starting at the same time but from two spatially separated feeding vessels, feed/oxidation solution #4 and feed/reduction solution #5 were fed into the reaction vessel at 83°C in the course of 60 minutes. After the end of the addition of feed/oxidation solution #4 and feed/reduction solution #5, 4.44 g of sodium hydroxide, dissolved in 76.22 g of water and 230.69 g of water were added to the reaction vessel and the vessel was cooled to 25°C.

The particle diameter as measured by dynamic light scattering was 168 nm. The pH value of the final dispersion was approximately 9.0.

After one day, 180 g of coalescent agent CA1 was added to the dispersion and the mixture allowed to equilibrate for 24 hours. The solids content of the final dispersion was approximately 47%.

Example 2:

The polymer of inventive example 2 was prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1, feed/emulsion #2 and coalescent agent as indicated in table 1 below and but, after the end of the addition of feed/emulsion #2 and feed/initiator solution #3, the reaction vessel was stirred for an additional 20 minutes after which a solution of 4.69 g of sodium hydroxide in 41.61 g of water was added in the course of 20 minutes.

Examples 3, 4, 5, 6 and 9:

The polymers of inventive examples 3, 4, 5, 6 and 9 were prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1, feed/emulsion #2 and coalescent agent as indicated in table 1 below.

Example 7:

The polymer of inventive example 7 was prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1, feed/emulsion #2 and coalescent agent as indicated in table 1 below but after the end of the addition of feed/emulsion #2 and feed/initiator solution #3, the reaction vessel was stirred for an additional 20 minutes after which a solution of 2.79 g of sodium hydroxide in 48.18 g of water was added in the course of 20 minutes.

Example 8: The polymer of inventive example 8 was prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1 , feed/emulsion #2 and coalescent agent as indicated in table 1 below and the feed/emulsion #1 and feed/emulsion #2 were both fed subsequently into the reactor over the course of 100 minutes each. Feed/initiator solution #3 was fed continuously, starting together with feed/emulsion #1 , over the course of 200 minutes. After the end of the addition of feed/emulsion #2 and fee/initiator solution #3, the reaction vessel was stirred for an additional 20 minutes after which a solution of 2.79 g of sodium hydroxide in 48.18 g of water was added in the course of 20 minutes. Example 10:

The polymer of inventive example 10 was prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1, feed/emulsion #2 and coalescent agent as indicated in table 1 below and but after the end of the addition of feed/emulsion #2 and feed/initiator solution #3, the reaction vessel was stirred for an additional 20 minutes after which a solution of 2.41 g of sodium hydroxide in 41.61 g of water was added in the course of 20 minutes. After the end of the addition of feed/oxidation solution #4 and feed/reduction solution #5, 3.55 g of sodium hydroxide, dissolved in 60.98 g of water, was added to the reaction vessel. Example 11:

The polymer of inventive example 11 was prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1, feed/emulsion #2 and coalescent agent as indicated in table 1 below and but after the end of the addition of feed/emulsion #2 and feed/initiator solution #3, the reaction vessel was stirred for an additional 20 minutes after which a solution of 2.41 g of sodium hydroxide in 41.61 g of water was added in the course of 20 minutes. After the end of the addition of feed/oxidation solution #4 and feed/reduction solution #5, 4.31 g of sodium hydroxide, dissolved in 74.04 g of water, was added to the reaction vessel. Example 12:

The polymer of inventive example 12 was prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1, feed/emulsion #2 and coalescent agent as indicated in table 1 below and but the initial charge contained 6.28 g of AMPS. After the end of the addition of feed/emulsion #2 and feed/initiator solution #3, the reaction vessel was stirred for an additional 20 minutes after which a solution of 2.03 g of sodium hydroxide in 35.04 g of water was added in the course of 20 minutes. After the end of the addition of feed/oxidation solution #4 and feed/reduction solution #5, 3.81 g of sodium hydroxide, dissolved in 65.33 g of water, was added to the reaction vessel.

Example 13:

The polymer of inventive example 13 was prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1 , feed/emulsion #2 and coalescent agent as indicated in table 1 below; and feed/initiator solution #3 was prepared by dissolving 1.90 g of sodium peroxodisulfate in 50.79 g of water.

Example 14:

The polymer of inventive example 14 was prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1 , feed/emulsion #2 and coalescent agent as indicated in table 1 below; and after the end of the addition of feed/emulsion #2 and feed/initiator solution #3, the reaction mixture was stirred for an additional 20 minutes after which a solution of 2.41 g of sodium hydroxide in 41.61 g of water was added in the course of 20 minutes.

Examples 15 and 16:

The polymers of inventive examples 15 and 16 were prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1 , feed/emulsion #2 and coalescent agent as indicated in table 1 below; and the initial charge contained 8.49 g of itaconic acid. After the end of the addition of feed/emulsion #2 and feed/initiator solution #3, the reaction mixture was stirred for an additional 20 minutes after which a solution of 2.41 g of sodium hydroxide in 41.61 g of water was added in the course of 20 minutes. Examples 17, 18 and 19:

The polymers of inventive examples 17, 18 and 19 were prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1, feed/emulsion #2 and coalescent agent as indicated in table 1 below; and after the end of the addition of feed/emulsion #2 and feed/initiator solution #3, the reaction mixture was stirred for an additional 20 minutes after which a solution of 2.41 g of sodium hydroxide in 41.61 g of water was added in the course of 20 minutes.

Example 20: The polymer of inventive example 20 was prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1, feed/emulsion #2 and coalescent agent as indicated in table 1 below but, the precharge contained 18.62 of seed latex S1 , feed/emulsion #1 was added simultaneously with 44.36%wt of feed/initiator solution #3 within 100 minutes and afterwards feed/emulsion #2 was added simultaneously with 55.64%wt of feed/initiator solution #3 within 120 minutes. After the end of the addition of feed/emulsion #2 and feed/initiator solution #3, the reaction vessel was stirred for an additional 30 minutes after which a solution of 6.32 g of sodium hydroxide in 108.54 g of water was added in the course of 80 minutes.

Table 1 also includes the feed/emulsion #1 , feed/emulsion #2 and coalescent agent of example 1. The properties of the polymer dispersions obtained, such as particle diameter as measured by dynamic light scattering, pH-value of the final dispersion and solids contents of the final dispersion are also given in table 1.

Table 1:

Solids content of the final dispersion

Table I (continuation):

Solids content of the final dispersion

# The initial charge contained 6.28 g of AMPS.

## The initial charge contained 8.49 g of IA. 5 a) Determined before addition of coalescent agent.

Comparative examples C1-C5 Comparative examples C1 and C2:

The polymers of C1 and C2 were prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1 , feed/emulsion #2 and coalescent agent as indicated in table 2 below, and the initial charge #0 contained 32.20 g of S1 and 9.36 g of 2-acrylamido-2-methylpropane sulfonic acid. Feed/emulsion #1 was fed into the reactor vessel in the course of 60 minutes. Feed/emulsion #2 was fed into the reactor vessel in the course of 120 minutes. Feed/initiator solution #3 was fed into the reactor vessel in the course of 180 minutes. After the end of the addition of feed/oxidation solution #4 and feed/reduction solution #5, 0.51 g of ammonia, dissolved in 1.52 g of water, was added to the reaction vessel.

Comparative example C3: The polymer of C3 was prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1 , feed/emulsion #2 and coalescent agent as indicated in table 2 below, and the initial charge #0 contained 39.02 g of S1 and 378.09 g of water. Feed/emulsion #1 and feed/emulsion #2 were each fed subsequently into the reactor over the course of 120 minutes. After the end of the addition of feed/emulsion #2 and feed/initiator solution #3, the reaction mixture was stirred for an additional 20 minutes after which a solution of 4.03 g of sodium hydroxide in 96.72 g of water was added in the course of 20 minutes. After the end of the addition of feed/oxidation solution #4 and feed/reduction solution #5, 4.17 g of sodium hydroxide, dissolved in 204.33 g of water, was added to the reaction vessel.

Comparative example C4:

The polymer of C4 was prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1 , feed/emulsion #2 and coalescent agent as indicated in table 2 below and after the end of the addition of feed/emulsion #2 and feed/initiator solution #3, the reaction mixture was stirred for an additional 20 minutes after which a solution of 1.65 g of sodium hydroxide in 28.47 g of water was added in the course of 20 minutes. After the end of the addition of feed/oxidation solution #4 and feed/reduction solution #5, 3.04 g of sodium hydroxide, dissolved in 52.27 g of water, was added to the reaction vessel.

Comparative example C5:

The polymer of C4 was prepared in analogy to the protocol given in inventive example 1 but using the feed/emulsion #1 , feed/emulsion #2 and coalescent agent as indicated in table 2 below, and after the end of the addition of feed/emulsion #2 and feed/initiator solution #3, the reaction mixture was stirred for an additional 20 minutes after which a solution of 2.41 g of sodium hydroxide in 41.61 g of water was added in the course of 20 minutes. The properties of the comparative polymer dispersions obtained, such as particle diameter as measured by dynamic light scattering, pH-value of the final dispersion and solid contents of the final dispersion are also given in table 2.

Table 2

Solids content of the final dispersion

4. Results of application testing 4.1 Water uptake

The polymer dispersions of inventive examples 1 to 20 and comparative examples C1 to C5 were formulated with the coalescent agent as described in table 1 and table 2, respectively. These formulations were used to prepare the test specimen as described above. The results are summarized in table 3 below.

Table 3: Water uptake of films obtained from examples 1 to 13 and 20 and comparative examples C1 to C5, respectively

Claims

An aqueous polymer dispersion obtainable by a free radical aqueous emulsion polymerization of ethylenically unsaturated monomers M, where the monomers M comprise a) 0.5 to 7.0% by weight, based on the total weight of monomers M, of a combination of a1 ) at least one monomer Ma1 , selected from monoethylenically unsaturated monocarboxyl ic acids having 3 to 6 carbon atoms and the salts thereof; a2) at least one monomer Ma2, selected from monoethylenically unsaturated dicarboxylic acids having 4 to 8 carbon atoms and the salts thereof; a3) at least one monomer Ma3, selected from monoethylenically unsaturated monosulfonic acids having 2 to 10 carbon atoms and the salts thereof; b1) 60 to 79.45% by weight, based on the total weight of monomers M, of at least one monomer Mb1 , which is selected from nonionic monoethylenically unsaturated monomers having a solubility in deionized water of at most 60 g/L at 25°C and 1 bar, and whose homopolymers have a glass transition temperature Tg of at least 50°C; b2) 20 to 39.45% by weight, based on the total weight of monomers M, of at least one monomer Mb2, which is selected from nonionic monoethylenically unsaturated monomers having a solubility in deionized water of at most 60 g/L at 25°C and 1 bar, and whose homopolymers have a glass transition temperature Tg of at most 40°C; c) 0.05 to 2.0% by weight of at least one crosslinking monomer Me; where the aqueous emulsion polymerization is carried out at least partly in the presence of a chain transfer compound.

2. The aqueous polymer dispersion of claim 1 , where the monomers M comprise 0.6 to 6% by weight, in particular 1.0 to 4.0% by weight, based on the total amount of monomers M , of a combination of a1) 0.15 to 2.0% by weight, based on the total amount of monomers M, of at least one monomer Ma1 ; a2) 0.2 to 3.0% by weight, based on the total amount of monomers M, of at least one monomer Ma2; a3) 0.15 to 1.5% by weight, based on the total amount of monomers M, of at least one monomer Ma3.

3. The aqueous polymer dispersion of any one of the preceding claims, where the monomers Ma1 are selected from acrylic acid, methacrylic acid and mixtures thereof, the monomer Ma2 is selected from the group consisting of itaconic acid, mesaconic acid and citraconic acid, and is especially itaconic acid, and the monomer Ma3 is 2-acrylamido-2-methylpropane sulfonic acid or its sodium salt.

4. The aqueous polymer dispersion of any one of the preceding claims, where the monomers M comprise 0.05 to 1.5% by weight, in particular 0.08 to 1.0% by weight, based on the total amount of monomers M, of at least one crosslinking monomer Me.

5. The aqueous polymer dispersion of any one of the preceding claims, where the crosslinking monomers Me are selected from the group consisting of multiethylenically unsaturated monomers having at least two non-conjugated ethylenically unsaturated double bonds and monoethylenically unsaturated monomers having at least one further functional group, which is capable of reacting with itself or with a carboxylic acid group and mixtures thereof.

6. The aqueous polymer dispersion of any one of the preceding claims, where the monomers Mb1 are selected from the group consisting of Ci-C2-alkyl esters of methacrylic acid, tert.-butyl acrylate, tert.-butyl methacrylate, monovinyl aromatic monomers and mixtures thereof.

7. The aqueous polymer dispersion of any one of the preceding claims, where the monomers Mb2 are selected from the group consisting of Ci-C2o-alkyl esters of acrylic acid, except for tert.-butyl acrylate, C5-C2o-cycloalkyl esters of acrylic acid, C3-a Iky I esters of methacrylic acid, n-butyl methacrylate, C5-C2o-alkylesters of methacrylic acid, C5-C2o-cycloalkyl esters of methacrylic acid and mixtures thereof.

8. The aqueous polymer dispersion of any one of the preceding claims, where the chain transfer compound has a mercapto group.

9. The aqueous polymer dispersion of any one of the preceding claims, where the amount of chain transfer compound is in the range from 0.05 to 1.2% by weight, in particular from 0.1 to 0.9% by weight, based on the total amount of monomers M.

10. The aqueous polymer dispersion of any one of the preceding claims, where the free radical aqueous emulsion polymerization is carried out as a free radical aqueous multistep emulsion polymerization.

11. The aqueous polymer dispersion of claim 10, where at least 40% by weight of the total amount of all monomers Ma1 , Ma2 and Ma3 of the monomers M are contained in the monomers polymerized in one step of the free radical aqueous multistep emulsion polymerization.

12. The aqueous polymer dispersion of claim 11 , where at least 40% by weight of the total amount of the chain transfer agent is present in said step of the free radical aqueous multistep emulsion polymerization.

13. The aqueous polymer dispersion of any one of claims 11 or 12, where in said step the amount of monomers polymerized is 10 to 50% by weight, based on the total amount of monomers M polymerized in the free radical aqueous multistep emulsion polymerization.

14. The aqueous polymer dispersion of any one of the preceding claims, which additionally contains a film-forming auxiliary.

15. A process for preparing an aqueous polymer dispersion of any one of the preceding claims, which comprises the free radical aqueous emulsion polymerization of the monomers M, where the aqueous emulsion polymerization is carried out at least partly in the presence of a chain transfer compound.

16. The process of claim 15, where the free radical aqueous emulsion polymerization is carried out as a free radical aqueous multistep emulsion polymerization as defined in any one of claims 10 to 13.

17. The use of an aqueous polymer dispersion according to any one of claims 1 to 14 as binder or co-binder in water-borne coating compositions, in particular in architectural coating compositions and in coating compositions for shaped mineral bodies.

18. A water-borne coating composition containing the aqueous polymer dispersion according to any one of claims 1 to 14.

19. A method of producing a permanent coating on a surface comprising

(a) applying a coating composition according to claim 18 to the surface, and

(b) allowing the coating composition to dry to produce the permanent coating.