Aqueous coating composition

Abstract

The present invention is directed to an aqueous coating composition comprising dispersed polymer particles comprising both (i) a polyurethane and (ii) a vinyl polymer, wherein said dispersed particles comprise the polyurethane and the vinyl polymer in a weight ratio of the polyurethane to the vinyl polymer in the range of from 20:80 to 85:15, the polyurethane-vinyl polymer hybrid has an acid value of at most 6 mg KOH / g of the polyurethane-vinyl polymer hybrid, and the polyurethane of the polyurethane-vinyl polymer hybrid comprises dispersing groups and the dispersing groups comprises sulfonate (-SO3-) groups in the salt form.

Description

[0001] AQUEOUS COATING COMPOSITION

[0002] The present invention relates to aqueous coating compositions comprising dispersed polymer particles comprising both (i) a polyurethane and (ii) a vinyl polymer, a process for preparing such a coating composition, use of the aqueous coating compositions for preparing coatings.

[0003] Aqueous polyurethane-vinyl polymer hybrid dispersions and their application in coatings are well known in the art. To prepare stable aqueous polyurethane-vinyl polymer hybrid dispersions, both the polyurethane and the vinyl polymer must be dispersed in water. This can be achieved by surfactants and / or by incorporating suitable groups such as ionic hydrophilic groups in the polyurethane. A very often used compound to provide stability to the aqueous dispersion are dihydroxy carboxylic acids, especially 2,2-dimethylol propionic acid. These are used as an anionic precursor and must be neutralized with base to impart dispersibility. The neutralization is usually done with volatile tertiary amines such as triethylamine and N,N-dimethyl ethanol amine, most often with triethylamine. Besides the demand for continuous improvement on the performance of coatings, legislation is however changing, and a large range of environmental related labels is available nowadays. Volatile tertiary amines generally are hazardous or even toxic and readily evaporate volatile organic compounds (VOC) during the film formation causing unacceptable environmental pollution and / or poor indoor air quality when used indoors. As a result, to fulfill these requirements for these environmental related labels it will no longer be possible to use raw materials often used ensuring stability of the coating composition like volatile tertiary amines. Alkali metal radicals can also be used to neutralize the anionic precursor, resulting in the presence of non-volatile metal salts in the coating composition. The inherent disadvantage of non-volatile metal salts is that these form salts that stay permanent present in the coating (compared to the volatile tertiary amine that evaporate from the coating forming back the unprotonated acid groups). The presence of permanent salt groups in the final coating result in an inherent water sensitivity and therefore the amount of acid groups should be as low as possible while still maintaining good storage stability and good processing without or only minor sediment formation during the process of synthesis. In general, when the acid value is reduced, the particle size increases to (sub-)micron size, which may lead to sediment formation during synthesis or even coagulation during synthesis and / or poor storage stability like settling behaviour of the large particles.

[0004] The object of the present invention is to improve the water resistance of coatings obtained from waterborne polyurethane-vinyl polymer hybrid dispersions neutralized with non-volatile metal salts, while still maintaining good storage stability and good processing without or with only minor sediment formation during the process of synthesis the polyurethane-vinyl polymer hybrid dispersion.

[0005] We now surprisingly found that we could synthesize polyurethane-vinyl polymer hybrids with even lower acid values than the pure urethane polymers and still maintaining small particles sizes resulting in an at least good storage stability for 4 weeks at room temperature and no to minor sediment formation during synthesis.

[0006] According to the present invention there is provided an aqueous coating composition comprising dispersed polymer particles comprising both (i) a polyurethane and (ii) a vinyl polymer, wherein said dispersed particles comprise the polyurethane and the vinyl polymer in a weight ratio of the polyurethane to the vinyl polymer in the range of from 20:80 to 85:15, the polyurethane-vinyl polymer hybrid has a calculated acid value of at most 6 mg KOH / g of the polyurethane-vinyl polymer hybrid, and the polyurethane of the polyurethane-vinyl polymer hybrid comprises, as dispersing groups, sulfonate (-SO3') groups in the salt form.

[0007] It has surprisingly been found that the aqueous coating compositions of the invention have an at least good storage-stability for 4 weeks at room temperature without the assistance of additional surfactants, are able to provide coatings with an at least good water resistance, can have a low sediment content even without filtration and do not need to contain volatile tertiary amines.

[0008] An additional advantage of the present invention is that the introduction of crosslinkable groups is not required to obtain coatings with an at least good water resistance. For instance, introduction of Schiff base crosslinking using carbonyl functionality (such as ketone functionality) in the polymer backbone of the polyurethane-vinyl polymer hybrid in combination with adipic dihydrazide may improve the water resistance of the coating. However, the use of low molecular weight hydrazide crosslinkers such as adipic dihydrazide is under pressure from environmental point of view, and its use may result in difficulties to comply to various environmental related labels, such as for example Eco-label.

[0009] In the context of the present invention, a polyurethane is a polymer obtained by polymerization of one or more polyols and one or more polyisocyanates, but it also includes those in which also monoamines and / or diamines are used as formation components, possibly as chain extenders. The polyurethanes that can be used in the present invention include polyurethanes as well as polyurethane-ureas. Preferably the polyurethane present in the waterborne coating composition of the present invention is a polyurethane-urea. Methods for preparing polyurethanes are known in the art and are described in for example the Polyurethane Handbook 2nd Edition, a Carl Hanser publication, 1994, by G. Oertel. For all upper and / or lower boundaries of any range given herein, the boundary value is included in the range given, unless specifically indicated otherwise. Thus, when saying from x to y, means including x and y and also all intermediate values.

[0010] The term "coating composition" encompasses, in the present invention, paint, coating, varnish, adhesive and ink compositions, without this list being limiting.

[0011] The waterborne coating composition according to the present invention is in the form of an aqueous polymer dispersion comprising dispersed polymer particles comprising at least one polyurethane, usually polyurethane-urea, and at least one vinyl polymer. The polyurethane and the vinyl polymer are present in the dispersed particles in a weight ratio of the polyurethane to the vinyl polymer of at least 20:80, preferably of at least 25:75, more preferably of at least 30:70, more preferably of at least 25:75, even more preferably of at least 30:70, most preferably of at least 35:65. The polyurethane and the vinyl polymer are present in the dispersed particles in a weight ratio of the polyurethane to the vinyl polymer of at most 85:15, preferably of at most 80:20, preferably of at most 75:25, more preferably of at most 70:30.

[0012] The dispersed particles comprising the polyurethane and the vinyl polymer are advantageously obtained by free radical polymerization of at least one vinyl monomer in the presence of at least one water-dispersed polyurethane thereby obtaining a hybrid of polyurethane and vinyl polymer (polyurethane-vinyl polymer hybrid). Accordingly, the vinyl polymer is advantageously formed in-situ by polymerizing the one or more vinyl monomers in the presence of a preformed aqueous polyurethane dispersion.

[0013] By a polyurethane-vinyl polymer hybrid (also referred herein as polyurethane-vinyl polymer) is meant that a vinyl polymer is prepared by the free-radical polymerization of vinyl monomer(s) in the presence of the polyurethane by forming an aqueous dispersion of said polyurethane resin and polymerising one or more vinyl monomers to form a vinyl polymer such that said vinyl polymer becomes incorporated in-situ into said aqueous dispersion by virtue of polymerising vinyl monomer(s) used to form the vinyl polymer in the presence of the polyurethane resin. Vinyl monomer is added before, during and / or after preparation of the polyurethane and the vinyl monomer is polymerized by adding a free radical yielding initiator to polymerize the vinyl monomer in the presence of the polyurethane. Suitable free radical yielding initiators are well known in the art and include mixtures partitioning between the aqueous and organic phases. Suitable free-radical-yielding initiators include inorganic peroxides such as ammonium persulphate, hydrogen peroxide, organic peroxides, such as benzoyl peroxide, alkyl hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide; dialkyl peroxides such as di-t-butyl peroxide; peroxy esters such as t-butyl perbenzoate and the like; mixtures may also be used. The peroxy compounds are in some cases advantageously used in combination with suitable reducing agents (redox systems) such as iso-ascorbic acid. Azo compounds such as azobisisobutyronitrile may also be used. Metal compounds such as Fe.EDTA (EDTA is ethylene diamine tetracetic acid) may also be usefully employed as part of the redox initiator system. The amount of initiator or initiator system to use is conventional, e.g. within the range of 0.05 to 6 wt.% based on the weight of vinyl monomer used.

[0014] The polyurethane-vinyl polymer hybrid present in the aqueous coating composition of the present invention preferably has an acid value of at least 0.5 mg KOH / g of the polyurethane- vinyl polymer hybrid, more preferably of at least 0.8 mg KOH / g of the polyurethane-vinyl polymer hybrid, most preferably of at least 1 mg KOH / g of the polyurethane-vinyl polymer hybrid and preferably of at most 5 mg KOH / g of the polyurethane-vinyl polymer hybrid, or of at most 4.5 mg KOH / g the polyurethane-vinyl polymer hybrid, or of at most 4 mg KOH / g of the polyurethane-vinyl polymer hybrid, or of at most 3.5 mg KOH / g of the polyurethane-vinyl polymer hybrid or of at most 3 mg KOH / g of the polyurethane-vinyl polymer hybrid. As used herein, the acid value is calculated and is obtained by by multiplying the molar amount of acid groups present in 1 g solid polyurethane-vinyl polymer hybrid by 56100.

[0015] The z-average particle size of the dispersed particles present in the waterborne coating composition according to the invention is preferably at least 10 nm, more preferably at least 20 nm, more preferably at least 30 nm, more preferably at least 40 nm, even more preferably at least 50 nm. The z-average particle size of the dispersed particles present in the waterborne coating composition according to the invention is preferably at most 1000 nm, more preferably at most 800 nm, more preferably at most 500 nm, more preferably at most 400 nm, even more preferably at most 300 nm. The z-average particle size is determined with the method as described further herein.

[0016] In the present invention, the polyurethane of the polyurethane-vinyl polymer hybrid comprises dispersing groups and the dispersing groups comprises, consists essentially of, or consists of sulfonate (-SO3-) groups in the salt form. The dispersing groups preferably comprises, consists essentially of, or consists of -SO3'Cat+groups wherein Cat+represents a non-volatile metal cation, more preferably an alkali metal cation, even more preferably a sodium or potassium cation, most preferably a sodium cation. Said sulfonate (-SO3-) salt groups are present in the polyurethane of the polyurethane-vinyl polymer hybrid in an amount such as to result in that preferably at least 80%, more preferably at least 85%, more preferably at least 90%, more preferably at least 95% or at least 99% or even up to 100%, of the acid value of the polyurethane-vinyl polymer originates from sulfonate (-SO3-) groups. Said sulfonate dispersing groups are preferably introduced into the polyurethane of the polyurethane-vinyl polymer by chemically incorporating at least one sulfonate containing compound into said polyurethane, preferably by using a sulfonate containing compound as reactant after the polyurethane pre-polymer preparation, wherein the sulfonate containing compound is preferably a diaminosulphonate corresponding to the following general formula:

[0017] H2N-A-NH-B-SO3'Cat+wherein A and B individually represent an aliphatic hydrocarbon radical having from 2 to 6 carbon atoms, and Cat+represents a non-volatile metal cation, preferably an alkali metal cation, more preferably a sodium or potassium cation, most preferably a sodium cation. Preferably, A represents an aliphatic hydrocarbon radical having 2 carbon atoms and B represents an aliphatic hydrocarbon radical having 2 carbon atoms. A very suitable sulfonate containing compound is the sodium salt of 2-[(2- aminoethyl)amino]ethanesulfonic acid like the Vestamin® A95 obtainable from Evonik.

[0018] The glass transition temperature Tgof the at least one vinyl polymer of the polyurethane- vinyl polymer and the amount of the at least one vinyl polymer in the polyurethane-vinyl polymer are preferably chosen such that

[0019] Tg(°C) of the vinyl polymer x weight fraction of the vinyl polymer in the polyurethane-vinyl polymer is in the range from -45 to 50, preferably in the range from -40 to 40, more preferably in the range from -35 to 35, even more preferably in the range from -10 to 30. Thus, the glass transition temperature Tgof the at least one vinyl polymer of the hybrid and the amount of the at least one vinyl polymer in the polyurethane-vinyl polymer are preferably chosen such that the product obtained by multiplying the Tg(°C) of the vinyl polymer with the amount (weight fraction) of the vinyl polymer in the polyurethane-vinyl polymer is in the range from -45 to 50, preferably in the range from -40 to 40, more preferably in the range from -35 to 35, even more preferably in the range from -10 to 30. As used herein, the glass transition temperature is determined by calculation by means of the Fox equation. Thus, the Tg in Kelvin, of a copolymer having "n" copolymerised comonomers is given by the weight fractions W of each comonomer type and the Tg’s of the homopolymers (in Kelvin) derived from each comonomer (as listed, for example, in J. Brandrup, E.H. Immergut, Polymer handbook 4th edition p. VI 193) according to the equation: 1 / Tg= S(Wn / Tgn).

[0020] The calculated Tgin Kelvin may be readily converted to °C.

[0021] Preferably at least 80 wt.%, more preferably at least 95 wt.% and up to 100 wt.% of the total weight of vinyl monomers used are of a,p-mono-unsaturated vinyl monomers.

[0022] Examples of vinyl monomers include but are not limited to 1,3- butadiene; isoprene; styrene; a-methyl styrene; (meth)acrylic amides; vinyl ethers; vinyl esters such as vinyl acetate, vinyl propionate, vinyl laurate; vinyl esters of versatic acid such as VeoVa 9 and VeoVa 10 (VeoVa is a trademark of Resolution); heterocyclic vinyl compounds; alkyl esters of mono- olefinically unsaturated dicarboxylic acids such as di-n- butyl maleate and di-n-butyl fumarate; dialkylitaconates such as dimethyltaconate, diethylitaconate, dibutylitaconate and in particular, esters of acrylic acid or of methacrylic acid of formula CH2=CR4-COOR5 wherein R4 is H or methyl and R5 is optionally substituted alkyl of from 1 to 20 carbon atoms (more preferably from 1 to 8 carbon atoms) or cycloalkyl of from 3 to 20 carbon atoms (more preferably from 3 to 6 carbon atoms). Examples of such esters of acrylic acid or of methacrylic acid which are methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate (all isomers), octyl (meth)acrylate (all isomers), 2-ethylhexyl (meth)acrylate, isopropyl (meth)acrylate and n-propyl (meth)acrylate. Preferred monomers of formula CH2=CR4- COOR5 include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate (all isomers), octyl (meth)acrylate (all isomers), ethyl hexyl acrylate (all isomers) and isobornyl (meth)acrylate. In an embodiment, hydroxyl functional vinyl monomer(s) are used as part of the vinyl monomers, preferably the hydroxyl functional vinyl monomer(s) are used in an amount of from 1 to 20 wt.% or from 1 to 10 wt.% or from 2 to 8 wt.%, relative to the total amount of vinyl monomers. Suitable hydroxyl functional vinyl monomers include, for example, hydroxy(C1 -C4)alkyl (meth)acrylates, such as hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate and hydroxypropyl acrylate; preferably the hydroxy-functional vinyl monomer is hydroxyethyl methacrylate (HEMA).

[0023] Preferably, at least 30 wt.%, more preferably at least 40 wt.%, more preferably at least 50 wt.%, even more preferably at least 60 wt.%, even more preferably at least 70 wt.% and even more preferably at least 80 wt.% of the total amount of vinyl monomer(s) used to prepare the vinyl polymer is selected from the group consisting of methyl methacrylate, butyl acrylate, butyl methacrylate, ethyl hexyl acrylate, octyl acrylate (preferably 2-octyl acrylate), styrene and mixtures of two or more of said monomers. Preferably, the vinyl monomer(s) used to prepare the vinyl polymer is selected from the group consisting of styrene, methyl methacrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, 2-ethyl hexyl acrylate, 2-octyl acrylate and mixtures thereof. More preferably at least 30 wt.%, preferably at least 50 wt.%, even more preferably at least 60 wt.% and more preferably at least 70 wt.% of the total amount of the vinyl monomer(s) used to prepare the vinyl polymer is styrene, methyl methacrylate, n-butyl acrylate, 2-ethyl hexyl acrylate, 2-octyl acrylate or any mixture of two or more of said monomers. Preferably less than 0.1 wt.% of the total amount of the vinyl monomer(s) used to prepare the vinyl polymer is acrylonitrile, more preferably the vinyl monomer(s) used to prepare the vinyl polymer does not comprise acrylonitrile.

[0024] The vinyl polymer of the polyurethane-vinyl polymer preferably has an acid value lower than 5 mg KOH / g solids of vinyl polymer, preferably less than 3 mg KOH / g solids of vinyl polymer, even more preferably less than 1 mg KOH / g solids of vinyl polymer.

[0025] The weight average molecular weight Mwof the polyurethane-vinyl polymer is preferably at least 10 kDalton, more preferably at least 20 kDalton, most preferably at least 40 kDalton, preferably at most 800 kDalton, more preferably at most 650 kDalton, most preferably at most 500 kDalton. As used herein, the weight average molecular weight is determined with the method as described further herein.

[0026] The polyurethane of the polyurethane-vinyl polymer is preferably obtained by the reaction of at least the following components (A1), (A2), (A4) and (A6) and optionally (A3) and (A5):

[0027] (A1) At least one polyisocyanate,

[0028] (A2) At least one isocyanate-reactive compound that contains at least one salt group which is capable to render the polyurethane dispersible in water,

[0029] (A3) Optionally at least one isocyanate-reactive compound containing at least one nonionic group,

[0030] (A4) At least one isocyanate-reactive polyol other than (A2) and (A3) having an OH number of from 25 to 300 mg KOH / g solids,

[0031] (A5) Optionally at least one isocyanate-reactive polyol other than (A2) and (A3) having an OH number higher than 300 mg KOH / g solids and lower than 1850 mg KOH / g solids, and

[0032] (A6) Water and / or at least one nitrogen containing chain extender compound.

[0033] Component (A1)

[0034] At least one polyisocyanate is used as component (A1). The amount of component (A1) is preferably in the range from 7 to 55 wt.%, more preferably in the range from 8 to 45 wt.%, more preferably in the range from 9 to 40 wt.%, relative to the total amounts of components used to prepare the polyurethane from which the building blocks from the polyurethane are emanated. If the polyurethane is obtained by the reaction of (A1), (A2), (A4) and (A6) and optionally (A3) and / or (A5), the total amounts of components used to prepare the polyurethane from which the building blocks from the polyurethane are emanated is the sum of the weight amounts of components (A1), (A2), (A4) and (A6) and, if applied, (A3) and (A5). Component (A1) comprises any suitable organic polyisocyanate including aliphatic, cycloaliphatic, araliphatic and / or aromatic polyisocyanates. Examples of suitable polyisocyanates include ethylene diisocyanate, 1 ,5-pentane diisocyanate, 1 ,6- hexamethylene diisocyanate (HDI), 2,2,4-trimethyl-1 ,6-hexamethylene diisocyanate, isophorone diisocyanate (IPDI), cyclohexane-1 ,4-diisocyanate, dicyclohexylmethane diisocyanate such as 4,4’-dicyclohexylmethane diisocyanate (4,4’-H12 MDI), p-xylylene diisocyanate, p-tetramethylxylene diisocyanate (p-TMXDI) (and its meta isomer m-TMXDI), 1 ,4-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4’- diphenylmethane diisocyanate (4,4’-MDI), polymethylene polyphenyl polyisocyanates, 2,4’- diphenylmethane diisocyanate, 3(4)-isocyanatomethyl-1 -methyl cyclohexyl isocyanate (IMCI) and 1 ,5-naphthylene diisocyanate.

[0035] Further examples are derivatives based on the afore mentioned diisocyanates having a uretdione, isocyanurate, carbodiimide, allophanate, biuret, iminooxadiazine dione and / or oxadiazine trione structure with two or more isocyanate groups. Mixtures of the polyisocyanates can be used as well. Preferably, the amount of polyisocyanates with more than two isocyanate groups is below 35 wt.%, more preferably below 20 wt.% and especially below 10 wt.% of the component (A1).

[0036] Component (A1) preferably consists of 1 ,5-pentane diisocyanate (CAS number 4538-42-5), hexamethylene diisocyanate (CAS number 822-06-0), isophorone diisocyanate (CAS number 4098-71-9), dicyclohexylmethane-4,4’-diisocyanate H12MDI (CAS number 5124-30- 1), 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4’-diphenylmethane diisocyanate (4,4’-MDI), 2,4’-diphenylmethane diisocyanate or any combination of any two or more thereof. More preferably, the at least one polyisocyanate according to (A1) comprises (i) 1 ,5- pentane diisocyanate and / or hexamethylene diisocyanate and (ii) isophorone diisocyanate and / or dicyclohexylmethane-4,4’-diisocyanate H12MDI.

[0037] Component (A2)

[0038] At least one isocyanate-reactive compound that contains at least one salt group of an acidic group, which is capable to render the polyurethane dispersible in water is used as component (A2). Component (A2) comprises, consists essentially of, or consists of at least one isocyanate-reactive compound that contains at least one sulfonate salt group. In general, the amount of component (A2) is in the range from 0.7 to 7 wt.%, preferably in the range from 0.8 to 6 wt.%, more preferably in the range from 1 to 4.5 wt.%, even more preferably in the range from 1 .3 to 4 wt.%, relative to the total amounts of components used to prepare the polyurethane from which the building blocks from the polyurethane are emanated.

[0039] Component (A2) preferably comprises, consists essentially of, or consists of at least one diamine sulfonate salt with the following formula H2N-A-NH-B-SO3'Cat+wherein A and B individually represent an aliphatic hydrocarbon radical having from 2 to 6 carbon atoms, and Cat+represents a non-volatile metal cation, preferably an alkali metal cation, more preferably a sodium or potassium cation, even more preferably a sodium cation. Usually an isocyanate- terminated polyurethane pre-polymer is then first formed by the reaction of components (A1) and (A4) and optionally (A3) and (A5) which is then further reacted with the diamine sulfonate salt (A2) and component (A6). A preferred diamine sulfonate salt is the sodium salt of 2-[(2-aminoethyl)amino]ethanesulfonic acid (CAS: 34730-59-1).

[0040] Optionally at least one isocyanate-reactive compound containing at least one non-ionic group which is capable to render the polyurethane dispersible in water, is used as component (A3).

[0041] The polyurethane may further be stabilized in the dispersion through non-ionic functionality incorporated into the polyurethane. Thus, the polyurethane may for a part be non-ionically stabilized by chemically incorporating non-ionic groups into the polyurethane to provide a part of the hydrophilicity required to enable the polyurethane to be stably dispersed in the aqueous dispersing medium. Preferred non-ionic water-dispersing groups are polyethylene oxide.

[0042] Preferred components (A3) are polyethylene glycols having at least 5 ethylene oxide repeating units, preferably at least 10, more preferably at least 15 ethylene oxide repeating units and preferably at most 120, more preferably at most 80 and even more preferably at most 40 ethylene oxide repeating units. More preferred components (A3) are

[0043] (methoxy-)polyethylene glycols having from 10 to 60 and preferably from 15 to 30 ethylene oxide repeating units. The isocyanate-reactive groups of component (A3) are preferably hydroxyl groups.

[0044] The polyurethane comprises component (A3) in an amount of preferably at most 10 wt.%, more preferably of at most 5 wt.%, more preferably of at most 3 wt.% and most preferably 0 wt.%, relative to the total amounts of components used to prepare the polyurethane from which the building blocks from the polyurethane are emanated.

[0045] Component (A4)

[0046] Component (A4) is at least one isocyanate-reactive polyol other than (A2) and (A3) having an OH number of from 25 to 300 mg KOH / g solids. As used herein, the hydroxy value of a component is measured by titration a known mass of component according to ASTM D4274 and is expressed as mg KOH / g. The amount of (A4) is preferably in the range from 38 to 92.3 wt.%, more preferably in the range from 49 to 91.2 wt.%, more preferably in the range from 55.5 to 90 wt.%, relative to the total amounts of components used to prepare the polyurethane from which the building blocks from the polyurethane are emanated. Such polyols may be selected from any of the chemical classes of polyols that can be used in polyurethane synthesis. In particular the polyol may be a polyester polyol, a polyesteramide polyol, a polyether polyol, a polythioether polyol, a polycarbonate polyol, a polyacetal polyol, a polyvinyl polyol and / or a polysiloxane polyol. Preferably, the polyol is selected from polyester(amide) polyol, polyether polyol or polycarbonate polyol or any combination thereof. More preferably, the polyol is selected from polyester(amide) polyol, polyether polyol or polycarbonate polyol or any combination thereof. Even more preferably, the polyol is selected from polyester polyol, polyether polyol or polycarbonate polyol or any combination thereof.

[0047] Component (A5)

[0048] Component (A5), which is optionally used, is at least one isocyanate-reactive polyol other than (A2) and (A3) having an OH number higher than 300 mg KOH / g solids and lower than 1850 mg KOH / g solids. If used, component (A5) is one or more compound with structural formula HO-R-OH, wherein R is a (cyclo)aliphatic carbon group having from 2 to 12 carbons, preferably from 2 to 8 carbons. Non-limited examples are neopentylglycol (NPG), cyclohexanedimethanol (CHDM), butanediol, hexanediol, trimethylolpropane and any mixture thereof. The amount of (A5), if present, is preferably in the range from 0.5 to 12 wt.%, more preferably in the range from 1 to 10 wt.%, more preferably in the range from 2 to 8 wt.%, relative to the total amounts of components used to prepare the polyurethane from which the building blocks from the polyurethane are emanated.

[0049] Component (A6)

[0050] Water and / or at least one nitrogen containing chain extender compound is used as chain extender component (A6). For water extension, two NCO groups will form one urea bond. First a NCO group reacts with water to form an unstable carbamic acid intermediate that decomposes to CO2 and an amine group, which amine group will then react with another NCO group to form a urea group. However, water extension is very slow compared to chain extension using a nitrogen containing chain extender. Therefore, if a nitrogen containing chain extender compound is applied, it is assumed that the isocyanate groups of the polyurethane pre-polymer first react with the nitrogen containing chain extender and that during and / or after dispersion the isocyanate groups still present on the polyurethane pre-polymer react with water to form a urea group.

[0051] Examples of suitable nitrogen containing chain extenders include amino-alcohols, primary or secondary diamines or polyamines (including compounds containing a primary amino group and a secondary amino group), hydrazine and substituted hydrazines. Examples of such chain extender compounds useful herein include 2-(methylamino)ethylamine, aminoethyl ethanolamine, aminoethylpiperazine, diethylene triamine, and alkylene diamines such as ethylene diamine and 1,6-hexamethylenediamine, and cyclic amines such as isophorone diamine. Also compounds such as hydrazine, azines such as acetone azine, substituted hydrazines such as, for example, dimethyl hydrazine, 1,6-hexamethylene-bis-hydrazine, carbodihydrazide, hydrazides of dicarboxylic acids, such as adipic acid dihydrazide, oxalic acid dihydrazide, and isophthalic acid dihydrazide, Hydrazides made by reacting lactones with hydrazine, bis-semi-carbazide, and bis-hydrazide carbonic esters of glycols may be useful. Water-soluble nitrogen containing chain extenders are preferred.

[0052] Preferably the nitrogen containing chain extender compound is selected from the group consisting of amino-alcohols, primary amines, secondary diamines, hydrazine, substituted hydrazines, substituted hydrazides and any combination of any two or more thereof.

[0053] Where the chain extender is other than water, for example, a hydrazine, it may be added to the aqueous dispersion of the isocyanate-terminated polyurethane pre-polymer or, alternatively, it may already be present in the aqueous medium when the isocyanate- terminated polyurethane pre-polymer is dispersed therein. The chain extension may be conducted at convenient temperatures from about 5 °C to 95 °C or, more preferably, from about 10 °C to 60 °C.

[0054] The total amount of nitrogen containing chain extender compound employed, if used, should be such that the ratio of active hydrogens in the chain extender to isocyanate groups in the polyurethane pre-polymer preferably is in the range from 0.1 :1 to 2:1, more preferably from 0.6:1 to 1.4:1 and especially preferred from 0.8 to 1.2. Preferably, component (A6) is water or water and at least one nitrogen containing chain extender with a NHX(wherein x is 1 or 2) functionality of 2 or 3, more preferably with a NHXfunctionality of 2, wherein for a hydrazide the NH groups connected to the carbonyl groups are not considered chain extending groups. More preferably, component (A6) comprises at least one nitrogen containing chain extender with a NHX(wherein x is 1 or 2) functionality of 2 or 3, more preferably with a NHXfunctionality of 2, wherein for a hydrazide the NH groups connected to the carbonyl groups are not considered chain extending groups. Even more preferably, component (A6) is water and at least one nitrogen containing chain extender with a NHX(wherein x is 1 or 2) functionality of 2 or 3, more preferably with a NHXfunctionality of 2, wherein for a hydrazide the NH groups connected to the carbonyl groups are not considered chain extending groups. The nitrogen containing chain extender is preferably selected from the group consisting of diamines and / or dihydrazides.

[0055] The amount of tertiary amine in the aqueous coating composition of the present invention is at most 0.3 wt.%, more preferably at most 0.2 wt.%, even more preferably at most 0.1 wt.% and most preferably the aqueous coating composition is free of tertiary amines.

[0056] The aqueous coating composition of the present invention may comprise water-miscible organic solvent. The amount of water-miscible organic solvent in the aqueous coating composition of the present invention is preferably at most 10000 ppm, more preferably at most 5000 ppm, more preferably at most 2000 ppm, most preferably at most 1000 ppm. The water-miscible organic solvent preferably is acetone and / or methyl ethyl ketone. The aqueous coating composition of the present invention preferably does not comprise tin. In case tin is present, the amount of tin in the aqueous coating composition of the present invention is preferably at most 2 ppm.

[0057] The aqueous coating composition of the present invention preferably comprises the dispersed particles comprising the polyurethane and the vinyl polymer in an amount of from 20 to 60 wt.%, preferably from 25 to 55 wt.%, more preferably from 30 to 52 wt.%, most preferably from 35 to 50 wt.%.

[0058] The aqueous coating composition of the present invention preferably comprises at most 5 wt.% of surfactant, preferably at most 3 wt.% of surfactant, more preferably at most 1 wt.% of surfactant, more preferably at most 0.5 wt.% of surfactant and most preferably at most 0.2 wt.% of surfactant and especially preferred is free of surfactants.

[0059] The aqueous coating composition according to the present invention preferably has a solids content of at least 15 wt.%, more preferably of at least 20 wt.%, more preferably of at least 25 wt.%, more preferably of at least 30 wt.%, more preferably of at least 35 wt.%, more preferably of at least 40 wt.%, most preferably of at least 45 wt.% and preferably of at most 70 wt.%, more preferably of at most 65 wt.%, even more preferably of at most 60 wt.% or of at most 55 wt.%.

[0060] In a preferred embodiment of the invention, the waterborne coating composition comprises dispersed particles comprising a polyurethane and a vinyl polymer in a weight ratio of the polyurethane to the vinyl polymer in the range from 20:80 to 85:15, wherein the polyurethane-vinyl polymer hybrid has an acid value of at most 6 mg KOH / g of the polyurethane-vinyl polymer hybrid, wherein at least 80 % of the acid value of the polyurethane-vinyl polymer hybrid originate from sulfonate (-SO3-) groups, wherein component (A2) comprises, consists essentially of, or consists of at least one diamine sulfonate salt with the following formula H2N-A-NH-B-SO3' Cat+wherein A and B individually represent an aliphatic hydrocarbon radical having from 2 to 6 carbon atoms, preferably A and B are ethylene radicals, and Cat+represents an alkali metal cation, preferably a sodium or potassium cation, more preferably a sodium cation, wherein said dispersed particles comprising the polyurethane and the vinyl polymer have a z- average particle size in the range of from 10 to 1000 nm, whereby the z-average particle size is determined with the method as described herein, wherein the aqueous coating composition of the present invention preferably comprises at most 5 wt.% of surfactant, more preferably at most 3 wt.% of surfactant, more preferably at most 1 wt.% of surfactant, more preferably at most 0.5 wt.% of surfactant and most preferably at most 0.2 wt.% of surfactant and especially preferred is free of surfactants, wherein the amount of (A1) is at least 7 wt% and at most 55 wt%, based on total weight of polyurethane polymer, wherein the amount of (A2) is at least 0.7 wt% and at most 7 wt%, based on total weight of polyurethane polymer, wherein the amount of (A4) is at most 92.3 wt.% and at least 38 wt% based on total weight of polyurethane polymer, and wherein the weight average molecular weight Mwof the polyurethane-vinyl polymer hybrid is at least 10 KDalton and at most 800 KDalton. In another preferred embodiment of the invention, the waterborne coating composition comprises dispersed particles comprising a polyurethane and a vinyl polymer in a weight ratio of the polyurethane to the vinyl polymer in the range from 20:80 to 85:15, wherein the polyurethane-vinyl polymer hybrid has an acid value of at most 6 mg KOH / g of the polyurethane-vinyl polymer hybrid, wherein at least 80 % of the acid value of the polyurethane-vinyl polymer hybrid originate from sulfonate (-SO3-) groups, wherein component (A2) comprises, consists essentially of, or consists of at least one diamine sulfonate salt with the following formula H2N-A-NH-B-SO3' Cat+wherein A and B individually represent an aliphatic hydrocarbon radical having from 2 to 6 carbon atoms, preferably A and B are ethylene radicals, and Cat+represents an alkali metal cation, preferably a sodium or potassium cation, more preferably a sodium cation, wherein said dispersed particles comprising the polyurethane and the vinyl polymer have a z- average particle size in the range of from 10 to 1000 nm, whereby the z-average particle size is determined with the method as described herein, wherein the aqueous coating composition of the present invention preferably comprises at most 5 wt.% of surfactant, more preferably at most 3 wt.% of surfactant, more preferably at most 1 wt.% of surfactant, more preferably at most 0.5 wt.% of surfactant and most preferably at most 0.2 wt.% of surfactant and especially preferred is free of surfactants, wherein the amount of (A1) is at least 7 wt% and at most 55 wt%, based on total weight of polyurethane polymer, wherein the amount of (A2) is at least 0.7 wt% and at most 7 wt%, based on total weight of polyurethane polymer, wherein the amount of (A4) is at most 91.8 wt.% and at least 24 wt% based on total weight of polyurethane polymer, wherein the amount of (A5) is at least 0.5 wt.% and at most 12 wt.%, and wherein the weight average molecular weight Mwof the polyurethane-vinyl polymer hybrid is at least 10 KDalton and at most 800 KDalton.

[0061] The present invention further relates to a process for preparing the aqueous coating composition of the present invention, wherein the process comprises at least the following steps:

[0062] 1) Preparing a polyurethane pre-polymer by reacting (A1) At least one polyisocyanate, and

[0063] (A4) At least one isocyanate-reactive polyol other than (A2) and (A3) having an OH number of from 25 to 300 mg KOH / g solids, and optionally

[0064] (A3) at least one isocyanate-reactive compound containing at least one non-ionic group, and / or

[0065] (A5) at least one isocyanate-reactive polyol other than (A2) and (A3) having an OH number higher than 300 mg KOH / g solids and lower than 1850 mg KOH / g solids,

[0066] 2) Preparing a polyurethane by reacting the polyurethane pre-polymer, preferably in water-miscible organic solvent, more preferably in acetone, with (1) at least one isocyanate-reactive compound that contains at least one salt group which is capable to render the polyurethane dispersible in water (A2), wherein component (A2) comprises, consists essentially of, or consists of at least one isocyanate-reactive compound that contains at least one sulfonate salt group, and (2) optionally (but preferably) with at least one nitrogen-containing chain-extender compound (A6),

[0067] 3) Adding the polyurethane to water or adding water to the polyurethane to obtain a waterborne dispersion and removing the water-miscible organic solvent (which is preferably acetone) during or after the dispersion step,

[0068] 4) Adding one or more vinyl monomers during and / or after step 3), preferably after step 3), and

[0069] 5) Preparing a vinyl polymer by polymerizing the one or more vinyl monomers in the presence of the polyurethane, thereby obtaining the polyurethane-vinyl polymer hybrid.

[0070] The amount of water-miscible organic solvent added in step 2) is preferably at least 30 wt.%, preferably at least 40 wt.%, more preferably at least 50 wt.%, relative to the total amounts of components used to prepare the polyurethane from which the building blocks from the polyurethane are emanated.

[0071] The present invention further relates to a coating obtained by (i) applying the aqueous coating composition of the present invention or obtained with the process of the present invention to at least part of a surface of a substrate, and (ii) causing or allowing the volatiles present in the coating composition to be removed.

[0072] The present invention is now illustrated by reference to the following examples. Unless otherwise specified, all parts, percentages and ratios are on a weight basis. Components and abbreviations used

[0073] H12MDI = Dicyclohexylmethane-4,4'-diisocyanate available from Covestro

[0074] HDI Hexamethylenediisocyanate available from Covestro

[0075] IPDI Isophorondiisocyanate available from Covestro

[0076] DMPA Dimethylolpropionic acid available from Perstorp polyols

[0077] PPG1000 = Polypropyleneglycol from BASF, OHV = 110.5 mg KOH / g

[0078] Priplast 3192 = Polyester diol supplied by Croda, OHV = 56 mg KOH / g

[0079] Polyester diol = Polyester diol based on hexanediol, adipic acid, NPG, ethylene glycol and caprolactone, OHV=112 mg KOH / g pTHF2000 = Polytetrahydrofuran from BASF, OHV = 56 mg KOH / g

[0080] Ymer N120 = Nonionic diol available from perstorp, OHV = 120 mg KOH / g

[0081] NPG = Neopentyl glycol

[0082] AAS = Sodium N-(2-aminoethyl)aminoethanesulfonate

[0083] EDA = Ethylene diamine from BASF

[0084] DEA = Diethanolamine available from Aldrich

[0085] BA = n-butylacrylate

[0086] MMA = Methylmethacrylate available from Dow Chemical

[0087] BHT = Butylated hydroxyl toluene (inhibitor) available from Merisol

[0088] TEA = Triethylamine available from Arkema

[0089] BYK-011 = Defoamer [29%] available from BYK

[0090] Hydrazine = Hydrazine solution in water [16%] available from Arkema

[0091] IAA = Isoascorbic acid available from Brenntag Volkers Benelux BV tBHPO = tert-Butyl hydroperoxide, available from Akzo Nobel Chemicals BV

[0092] FeEDTA = Iron-ethylenediaminetetracetic acid complex, 1% in water

[0093] BiND = Bismuth neodecanoate

[0094] Tinoctoate = Catalyst available from Brenntag Volkers Benelux BV

[0095] Bismuthneodecanoate =Catalyst available from Reaxis

[0096] BDG = Butyldiglycol

[0097] Methods:

[0098] Viscosity was determined with a Brookfield DV-I viscometer (spindle S61, 60 rpm, 23°C).

[0099] Average particle size PS and polydispersity index Pdi PS:

[0100] The intensity average particle size, z-average, and the polydispersity index PDi PS have been determined by photon correlation spectroscopy using a Malvern Zetasizer Nano ZS. Samples were diluted in demineralized water to a concentration of approximately 0.1 g dispersion / liter. Measurement temperature 25°C. Angle of laser light incidence 173°. Laser wavelength 633 nm.

[0101] Sulfur content of the dispersions was measured by elemental analysis, via digestion or combustion sample preparation, using an Inductively Coupled Plasma Optical Emission Spectrometer from Spectro (ICP-OES) carried out by Currents GmbH u. Co. OHG, DE- 51368 Leverkusen.

[0102] Acid value of the hybrid

[0103] The acid value of the polyurethane-vinyl polymer hybrid (mg KOH / g hybrid) refers to the amount of acid groups present in the polyurethane-vinyl polymer hybrid and was calculated as follows:

[0104] Molar amount of acid groups present in 1 g solid polyurethane-vinyl polymer hybrid x 56100, i.e. , the product obtained by multiplying 56100 by the molar amount of acid groups present in 1 gram of solid polyurethane-vinyl polymer hybrid.

[0105] £H

[0106] The pH was measured using a Metrohm pH meter.

[0107] Solids

[0108] The solid content of the dispersion was measured on a HB43-S halogen moisture analyzer from Mettler Toledo at a temperature of 75°C.

[0109] Size exclusion chromatography in NMP

[0110] The number average molecular weight Mn, weight average molecular weight Mwand molecular weight distribution was determined with Size exclusion chromatography (SEC), using three PLgel 10 pm Mixed-B columns at 70°C on a Waters Alliance e2695 LC system with a Waters 2414 DRI detector. N-Methylpyrrolidone (NMP) and 10 mM lithiumbromide (Li Br) was used as eluent with a flow of 1 mL / min. The samples were dissolved in the eluent using a concentration of 5 mg polymer per mL solvent. The solubility was assessed with a laser pen after 24 hours stabilization at room temperature; if any scattering was visible the samples were filtered first and 100 pl sample solution was injected. The MMD (molecular mass distribution) results were calculated with 12 narrow polystyrene standards from 370 to 1.071.000 Da. In general, a series of average molecular weights can be defined by the equation: M= SNiMn+1 / SNiMin, whereby: n=0 gives M= Mn; n = 1 gives M = Mw, n = 2 gives M = Mz.The higher averages are increasingly more sensitive to high molecular weight polymers. Nj is the number of molecules with molecular weight Mj.

[0111] Sediment before filtration (centrifuge method)

[0112] When the viscosity of the dispersion is higher than 50 mPa.s (Brookfield viscosity) the dispersion is 1 :1 diluted with water. 100 ml of the (diluted) dispersion is placed in a centrifuge flask with a 0.2 ml tip and is centrifuged for 15 min at 276G. Subsequently the centrifuge flask is taken out of the centrifuge and the sediment is read from the tube tip of the centrifuge flask. Each mark on the tube tip represents 0.05 ml or 0.05% sediment.

[0113] Storage stability 4 weeks

[0114] A jar of at least 370 ml was filled right up to the brim and the sample was visually evaluated after 4 weeks storage at room temperature.

[0115] Excellent: no or only very minor changes in viscosity and particle size without formation of any sediment

[0116] Good: minor changes in viscosity and particle size without formation of any sediment

[0117] Fair: formation of a slight amount of sediment in the dispersion

[0118] Poor: formation of substantial sediment in the dispersion

[0119] Very poor: coagulation and / or phase separation of the dispersion

[0120] The following (comparative) examples were prepared and coatings were obtained and tested. The compositions of the examples and results are as shown in the tables below.

[0121] Examples 1-2

[0122] Example 1 : Preparation of a polyurethane-vinyl polymer hybrid dispersion

[0123] Stage 1 : A 1000 cm3flask equipped with a thermometer and overhead stirrer was charged with IPDI (21.1 g), pTHF2000 (135.9 g) and BiND (0.02 g). The mixture was heated to 95°C and kept at 95°C for 2.5 hours until the NCO-content of the resultant isocyanate-terminated prepolymer was just below the theoretical value, in this case 1.36% (theoretical 1.45%). Then the mixture was cooled to 70°C and acetone (235.5 g) was added. The mixture was stirred until a homogeneous solution was obtained and the temperature was adjusted to 40°C.

[0124] Subsequently, a solution of AAS (2.71 g) and EDA (0.31 g) in water (17.1 g) was added in 15 minutes to the reactor. The mixture was stirred for an additional 10 minutes. Then, deionised water (281.8 g) was added to disperse the prepolymer, and the dispersion was stirred for 10 minutes.

[0125] The dispersion was transferred to a 2L rotavap flask, BYK-011 (0.02 g) was added and vacuum distillation was started to remove the acetone until below 0.5%.

[0126] Stage 2: The radical polymerisation for producing a polyurethane vinyl hybrid dispersion was carried out as follows:

[0127] A 1000 cm3flask equipped with a thermometer and overhead stirrer was charged with 141.2 g of the dispersion prepared in Stage 1 , deionised water (58.11 g), BA (10.5) and MMA (15.7 g). After mixing for 30 minutes, a 10% tert-butylhydroperoxide solution in water (1.31 g) and a 1 % FeEDTA solution in water (0.13 g) was added followed by feeding in a 1 % iso-ascorbic acid solution (pH adjusted to approximately 8 with ammonia) in water (7.85 g) over a period of 10 minutes, the mixture was allowed to exotherm to a reaction temperature of 30-40°C. The funnel was rinsed with deionised water (15.3 g).

[0128] The resultant polyurethane vinyl hybrid dispersion was filtered through 75 micron filter cloth and the specifications are given in Table 5 below. Mw is 147 KDalton and the polydispersity (Mw / Mn) is 16.1. Because the acid value of sulfonate groups like NaSOs can not be measured by the standard titration methods like DIN EN ISO 2114, elemental analysis of sulfur was conducted by ICP-OES. The sulfur content was 2000 ppm sulfur on solids, which corresponds with the calculated acid value of the sulfonate groups present in the polyurethane-vinyl polymer hybrid.

[0129] Table 1 specifies the components and its amounts applied for preparing the polyurethane and corresponding polyurethane-vinyl polymer hybrid resin dispersions according to Examples 1 to 2 using the process as described for Example 1. Unless specified otherwise, the amounts of the different components are expressed in grams. The specifications of the resulting compositions are represented in Table 5 and the film properties in Table 6.

[0130] The acid value of the polyurethane-vinyl polymer hybrid was calculated as follows:

[0131] 1 . Determining weight % of acid groups present in the polyurethane prepared in stage 1 , i.e., weight % of AAS present in the polyurethane prepared in stage 1 :

[0132] (2.71x100)7(21.1 + 135.9+2.71+0.31)=1.69 wt% s / s.

[0133] 2. Determining weight amount (gram) of solid polyurethane-vinyl polymer hybrid prepared in stage 2:

[0134] 2.1 . Determining weight amount of solid PU prepared in stage 1 and used in stage 2: 141.2 g of the Pll dispersion prepared in stage 1 with 43.3% solids content is used in stage 2, i.e., = 0.433 x 141.2 = 61.1 gram of which (160.02 / 160.0458) % is solid PU and (0.0258 / 160.0458) % is the remaining solid content of the PU dispersion.

[0135] 2.2. Determining weight amount of solid polyurethane-vinyl polymer hybrid prepared in stage 2 is the sum of the weight amount of solid PU prepared in stage 1 and used in stage 2 and the weight amount of the vinyl monomers added in stage 2, i.e.,

[0136] [61.1 x (160.02 / 160.0458)] (solid PU) + 10.5 g (BA) + 15.7 g (MMA) = 87.3 g of solid polyurethane-vinyl polymer hybrid.

[0137] 3. Determining amount of acid groups present in the polyurethane prepared in stage 1 and used in stage 2, i.e., amount of AAS present in the polyurethane prepared in stage 1 and used in stage 2:

[0138] (1.69 / 100) x 61.1 x (160.02 / 160.0458) = 1.03 g.

[0139] Thus, the solid PU prepared in stage 1 and used in stage 2 contains 1.03 grams of acid groups and consequently also the resulting polyurethane-vinyl polymer hybrid prepared in stage 2 contains 1.03 grams of acid groups.

[0140] 4. Determining the acid value of the polyurethane-vinyl polymer hybrid prepared in stage 2:

[0141] Molar mass AAS = 190.2 g / mol,

[0142] [(1 .03 / 190.2) / 87.3] x 56100 = 3.5 mg KOH / g.

[0143] The calculated sulfur content originating from the SO3 group in AAS per gram of solid polyurethane-vinyl polymer hybrid is:

[0144] [(1.03 / 190.2) / 87.3] (molar amount of AAS per gram of solid polyurethane-vinyl polymer hybrid) x 32.065 g / mol (molar mass sulfur) x 106= 1989 ppm sulfur per gram of solid polyurethane- vinyl polymer hybrid. This calculated sulfur content corresponds well with 2000 ppm of sulfur on solids, being the measured content by ICP-OES.

[0145] Table 1

[0146] Example 3

[0147] Stage 1 : A 1000 cm3flask equipped with a thermometer and overhead stirrer was charged with IPDI (34.39 g), NPG (4.67 g), Priplast 3192 (116.61 g) and BiND (0.02 g). The mixture was heated to 95°C and kept at 95°C for 2 hours. The NCO-content of the resultant isocyanate-terminated prepolymer was 2.38% (theoretical 2.78%). Then the mixture was cooled to 70°C and acetone (233.54 g) was added. The mixture was stirred until a homogeneous solution was obtained and the temperature was adjusted to 40°C.

[0148] At 40°C, a solution of AAS (3.25 g), EDA (1.05 g) in water (21.0 g) was added to the reactor in 15 minutes, and was stirred for an additional 10 minutes. Then, deionised water (274.0 g) was added to disperse the prepolymer, and the dispersion was stirred for 10 minutes.

[0149] The dispersion was transferred to a 2L rotavap flask, BYK-011 (0.02 g) was added and vacuum distillation was started to remove the acetone until below 0.5%.

[0150] Stage 2: The radical polymerisation for producing a polyurethane vinyl hybrid dispersion was carried out as follows:

[0151] A 1000 cm3flask equipped with a thermometer and overhead stirrer was charged with 188.7 g of the dispersion prepared in Stage 1 , deionised water (24.2 g) and MMA (20.0 g). After mixing for 30 minutes, a 10% tert-butylhydroperoxide solution in water (1.0 g) and a 1% FeEDTA solution in water (0.10 g) was added followed by feeding in a 1% iso-ascorbic acid solution (pH adjusted to approximately 8 with ammonia) in water (6.0 g) over a period of 10 minutes, the mixture was allowed to exotherm to a reaction temperature of 30-40°C. The funnel was rinsed with deionised water (10.1g).

[0152] The resultant polyurethane vinyl hybrid dispersion was filtered through 75 micron filter cloth and the specifications are given in Table 5 below and the film properties in Table 6.

[0153] Examples 4-7

[0154] In Examples 4-7, the process described for Example 3 was repeated except that the monomer polymerization to prepare the ll / A hybrid was split into two separate steps. In the first step only 50% of the monomers was added and polymerized using 50% of the tBHPO, FeEDTA and iAA solutions. After cooling down to 25°C the residual amount of monomers was added. Subsequently, the reactor content was mixed for 1 hour and the remaining amount of tBHPO and FeEDTA were added followed by feeding the rest of the iAA solution. The quantities and components are specified below in Table 2. Unless specified otherwise, the amounts of the different components are expressed in grams. The specifications of the resulting compositions are represented in Table 5 and the film properties in Table 6. Table 2

[0155] Comparative Example A

[0156] Stage 1 : A 1000 cm3flask equipped with a thermometer and overhead stirrer was charged with IPDI (21.2 g), pTHF2000 (136.4 g) and BiND (0.02 g). The mixture was heated to 95°C and kept at 95°C for 2.5 hours. The NCO-content of the resultant isocyanate- terminated prepolymer was 1.36% (theoretical 1.45%). Then the mixture was cooled to 70°C and acetone (236.3 g) was added. The mixture was stirred until a homogeneous solution was obtained and the temperature was adjusted to 40°C.

[0157] Subsequently, a solution of AAS (1.90 g) and EDA (0.54 g) in water (13.8 g) was added in 15 minutes to the reactor. The mixture was stirred for an additional 10 minutes. Then, deionised water (285.3 g) was added to disperse the prepolymer, and the dispersion was stirred for 10 minutes.

[0158] The dispersion was transferred to a 2L rotavap flask, BYK-011 (0.02 g) was added and vacuum distillation was started to remove the acetone until the dispersion reached a solid content of above 40%. If possible, the resultant polyurethane dispersion was filtered through 75 micron filter cloth and the specifications are given in Table 5 below, the film properties in Table 6.

[0159] Comparative Example B

[0160] In comparative example B, the process described for comparative example A was repeated except that different quantities and different constituents were used. These quantities and components are specified below in Table 3. Unless specified otherwise, the amounts of the different components are expressed in grams. The specifications of the resulting compositions are represented in Table 5, the film properties in Table 6.

[0161] Table 3: Compositions of the polyurethane dispersions of Comparative examples A to B with similar acid values compared to examples 1 and 2.

[0162] Comparative Examples C-D

[0163] In comparative examples C-D, the process described for Example 1 was repeated except that different quantities and different constituents were used. These quantities and components are specified below in Table 4. Unless specified otherwise, the amounts of the different components are expressed in grams. The specifications of the resulting compositions are represented in Table 5 and the film properties in Table 6.

[0164] Table 4: Compositions of the polyurethane and corresponding polyurethane-vinyl polymer hybrid dispersions of comparative examples C-D Table 5: Specifications of Examples 1 to 7 Table 5 continued: Specifications of Comparative Examples A to D

[0165] Application of formulations

[0166] The examples prepared as described above were cast onto a Leneta test chart using a wire rod at a wet film thickness of 100 micron. For Ex. 1-2, 1% of BYK 346 was added (on total binder). Ex. 3, 6 and 7 also contained 5wt% BDG on total formulation.

[0167] The cast films were then allowed to dry at room temperature for 1 hour, followed by ageing of the coatings at 50°C for 16 hours. The coatings were allowed to cool to room temperature for 1 hour.

[0168] The stain resistance of the coated cards towards the following stains were then assessed: water, ethanol (48%), coffee and red wine. In all cases, a spot (1 cm2) of the respective stain was placed on the coating and covered with a piece of filter paper and a watch glass. All mentioned spots were left for six hours. After these periods, the spot was gently wiped off with a tissue. After 24 hrs at room temperature the films were assessed for their integrity. This was rated between 1 to 5, where

[0169] 5 Film fully intact without any defects or deterioration,

[0170] 4 Only very minor damage or hazing of the film,

[0171] 3 Clear hazing, deterioration or minor dissolving of the film,

[0172] 2 Film dissolved at some spots,

[0173] 1 Film entirely dissolved.

[0174] The results for the clear coatings are shown in Tables 6. As used herein, a coating with an at least good water resistance is a coating with a water resistance with a rating of at least 3, preferably with a rating of at least 4.

[0175] Table 6: Water resistances of the polyurethane-vinyl polymer hybrid dispersions Examples 1 to 7

[0176] Table 6 continued: Water resistances of comparatives A and B, the pure polyurethane dispersions of examples 1 and 2 with similar acid values, and comparatives C and D, the polyurethane-vinyl polymer hybrid dispersions with high acid values.

Claims

Claims1 . An aqueous coating composition comprising dispersed polymer particles comprising both (i) a polyurethane and (ii) a vinyl polymer, wherein said dispersed particles comprise the polyurethane and the vinyl polymer in a weight ratio of the polyurethane to the vinyl polymer in the range of from 20:80 to 85:15, said dispersed particles comprising the polyurethane and the vinyl polymer are obtained by free radical polymerization of at least one vinyl monomer in the presence of at least one water-dispersed polyurethane thereby obtaining a hybrid of polyurethane and vinyl polymer (polyurethane-vinyl polymer hybrid), the polyurethane-vinyl polymer hybrid has an acid value of at most 6 mg KOH / g of the polyurethane-vinyl polymer hybrid, the polyurethane of the polyurethane-vinyl polymer hybrid comprises dispersing groups and the dispersing groups comprises sulfonate (-SO3-) groups in the salt form, and at least 80 % of the acid value of the polyurethane-vinyl polymer hybrid originates from sulfonate (-SO3-) groups.

2. The aqueous coating composition according to claim 1 , wherein the polyurethane- vinyl polymer hybrid has an acid value of at least 0.5 mg KOH / g, preferably of at least 0.8 mg KOH / g, most preferably of at least 1 mg KOH / g of the polyurethane-vinyl polymer hybrid and preferably of at most 5 mg KOH / g of the polyurethane-vinyl polymer hybrid, or of at most 4.5 mg KOH / g the polyurethane-vinyl polymer hybrid, or of at most 4 mg KOH / g of the polyurethane-vinyl polymer hybrid, or of at most 3.5 mg KOH / g of the polyurethane-vinyl polymer hybrid or of at most 3 mg KOH / g of the polyurethane-vinyl polymer hybrid.

3. The aqueous coating composition according to claim 1 or 2, wherein said dispersed particles comprising the polyurethane and the vinyl polymer have a z- average particle size in the range of from 10 to 1000 nm, more preferably in the range from 30 to 500 nm, even more preferably in the range from 40 to 400 nm and most preferably in the range from 50 to 300 nm, whereby the z-average particle size is determined with the method as described in the description.

4. The aqueous coating composition according to anyone of the preceding claims, wherein the polyurethane and the vinyl polymer are present in said dispersed particles in a weight ratio of the polyurethane to the vinyl polymer in the range of from 25:75 to 80:20, more preferably from 30:70 to 75:25, even more preferably from 35:65 to 70:30.

5. The aqueous coating composition according to anyone of the preceding claims, wherein the polyurethane of the polyurethane-vinyl polymer hybrid comprises dispersing groups and the dispersing groups comprises, consists essentially of, or consists of -SOs'Caf groups wherein Cat+represents a non-volatile metal cation, more preferably an alkali metal cation, even more preferably a sodium or potassium cation, most preferably a sodium cation.

6. The aqueous coating composition according to anyone of the preceding claims, wherein at least 85%, more preferably at least 90%, even more preferably at least 95% or at least 99% or at least 100% of the acid value of the polyurethane-vinyl polymer hybrid originates from sulfonate (-SO3-) groups.

7. The aqueous coating composition according to anyone of the preceding claims, wherein the vinyl polymer has a glass transition temperature Tgand wherein the amount of the vinyl polymer in the polyurethane-vinyl polymer hybrid and the glass transition temperature Tgof the vinyl polymer are chosen such that the product obtained by multiplying the Tg(°C) of the vinyl polymer with the weight fraction of the vinyl polymer in the polyurethane-vinyl polymer hybrid is in the range from -45 to 50, preferably in the range from -40 to 40, more preferably in the range from -35 to 35, even more preferably in the range from -10 to 30, wherein the glass transition temperature is calculated using the Fox equation.

8. The aqueous coating composition according to anyone of the preceding claims, wherein at least 30 wt.%, more preferably at least 50 wt.% and even more preferably at least 80 wt.% of the total amount of vinyl monomer(s) used to prepare the vinyl polymer is selected from the group consisting of methyl methacrylate, butyl acrylate, butyl methacrylate, ethyl hexyl acrylate, octyl acrylate (preferably 2-octyl acrylate), isobornyl acrylate, isobornyl methacrylate, styrene and mixtures of two or more of said monomers.

9. The aqueous coating composition according to anyone of the preceding claims, wherein the polyurethane comprises isocyanate-reactive compound containing at least one non-ionic group in an amount of at most 5 wt.%, more preferably of at most 3 wt.% and most preferably 0 wt.%, relative to the total amounts of components used to prepare the polyurethane from which the building blocks from the polyurethane are emanated.

10. The aqueous coating composition according to anyone of the preceding claims, wherein the vinyl polymer of the polyurethane-vinyl polymer hybrid has an acid value lower than 5 mg KOH / g solids of vinyl polymer, preferably less than 3 mg KOH / gsolids of vinyl polymer, even more preferably less than 1 mg KOH / g solids of vinyl polymer.

11. The aqueous coating composition according to anyone of the preceding claims, wherein the polyurethane is the reaction product of at least the following components:(A1) At least one polyisocyanate,(A2) At least one isocyanate-reactive compound that contains at least one salt group which is capable to render the polyurethane dispersible in water,(A3) Optionally at least one isocyanate-reactive compound containing at least one non-ionic group,(A4) At least one isocyanate-reactive polyol other than (A2) and (A3) having an OH number of from 25 to 300 mg KOH / g solids,(A5) Optionally at least one isocyanate-reactive polyol other than (A2) and (A3) having an OH number higher than 300 mg KOH / g solids and lower than 1850 mg KOH / g solids, and(A6) Water and / or at least one nitrogen containing chain extender compound, wherein component (A2) comprises, consists essentially of, or consists of at least one isocyanate-reactive compound that contains at least one sulfonate salt group.

12. The aqueous coating composition according to claim 11 , wherein component (A2) comprises, consists essentially of, or consists of at least one diamine sulfonate salt with the following formula H2N-A-NH-B-SO3'Cat+, wherein A and B individually represent an aliphatic hydrocarbon radical having from 2 to 6 carbon atoms, preferably A and B are ethylene radicals, and Cat+represents a non-volatile metal cation, preferably an alkali metal cation, more preferably a sodium or potassium cation, more preferably a sodium cation.

13. The aqueous coating composition according to anyone of the preceding claims, wherein the dispersed particles comprising the polyurethane and the vinyl polymer are present in the aqueous coating composition in an amount of from 20 to 60 wt.%, preferably from 25 to 55 wt.%, more preferably from 30 to 52 wt.%, most preferably from 35 to 50 wt.%.

14. A process for preparing the aqueous coating composition according to any one of the preceding claims, wherein the process comprises at least the following steps:1) Preparing a polyurethane pre-polymer by reacting(A1) At least one polyisocyanate, and(A4) At least one isocyanate-reactive polyol other than (A2) and (A3) having an OH number of from 25 to 300 mg KOH / g solids, andoptionally(A3) at least one isocyanate-reactive compound containing at least one non-ionic group, and / or(A5) at least one isocyanate-reactive polyol other than (A2) and (A3) having an OH number higher than 300 mg KOH / g solids and lower than 1850 mg KOH / g solids,2) Preparing a polyurethane by reacting the polyurethane pre-polymer, preferably in water-miscible organic solvent, more preferably in acetone, with (1) at least one isocyanate-reactive compound that contains at least one salt group which is capable to render the polyurethane dispersible in water (A2), wherein component (A2) comprises, consists essentially of, or consists of at least one isocyanatereactive compound that contains at least one sulfonate salt group, and (2) optionally with at least one nitrogen-containing chain-extender compound (A6),3) Adding the polyurethane to water or adding water to the polyurethane to obtain a waterborne dispersion and removing the water-miscible organic solvent (which is preferably acetone) during or after the dispersion step,4) Adding one or more vinyl monomers during and / or after step 3), preferably after step 3), and5) Preparing a vinyl polymer by polymerizing the one or more vinyl monomers in the presence of the polyurethane, thereby obtaining the polyurethane-vinyl polymer hybrid.

15. The process according to claim 14, wherein step 2) is effected in the presence of water-miscible organic solvent, preferably acetone, wherein the amount of water- miscible organic solvent in step 2) is preferably at least 30 wt.%, relative to the total amounts of components used to prepare the polyurethane from which the building blocks from the polyurethane are emanated.

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