WO2017158016A1

WO2017158016A1 - Aqueous coating composition

Info

Publication number: WO2017158016A1
Application number: PCT/EP2017/056112
Authority: WO
Inventors: Saskia Carolien Van Der Slot; Gerardus Cornelis Overbeek; Ronald Tennebroek; Alexander Wilhelmus Martinus Cornelis Donders
Original assignee: Dsm Ip Assets B.V.
Priority date: 2016-03-15
Filing date: 2017-03-15
Publication date: 2017-09-21
Also published as: WO2017158015A1; EP3430062A1; CN108779200A

Abstract

The present invention relates to an aqueous coating composition comprising dispersed polyurethane-vinyl polymer hybrid particles wherein i. the polyurethane-vinyl polymer hybrid is obtained by free-radical polymerization of at least one vinyl monomer in the presence of a polyurethane, ii. the polyurethane is obtained by the reaction of at least (I) an isocyanate- terminated polyurethane prepolymer and (II) at least one active-hydrogen containing chain extending compound, wherein the isocyanate-terminated polyurethane prepolymer is obtained by the reaction of at least one polyol with at least one polyisocyanate, wherein from 50 to 100 wt.% of the total amount of the polyisocyanates used to form the polyurethane are aromatic polyisocyanates, iii. the polyurethane-vinyl polymer hybrid is ketone functional and contains from 50 to 1000 mmol of ketone groups per 1000 g polyurethane-vinyl polymer hybrid, preferably from 75 to 500 mmol of ketone groups per 1000 g polyurethane-vinyl polymer hybrid, more preferably from 150 to 400 mmol of ketone groups per 1000 g polyurethane-vinyl polymer hybrid, iv. the ketone groups of the polyurethane-vinyl polymer hybrid are present in the polyurethane and in the vinyl polymer, v. the weight ratio of the polyurethane to the vinyl polymer in the polyurethane- vinyl polymer hybrid ranges from 90:10 to 35:65, vi. the polyurethane-vinyl polymer hybrid has an acid value from 7 to 60 mg KOH/g polyurethane-vinyl polymer hybrid, preferably from 9 to 40 mg KOH/g polyurethane-vinyl polymer hybrid and most preferably from 12 to 25 mg KOH/g polyurethane-vinyl polymer hybrid, vii. the aqueous coating composition comprises a dihydrazide functional compound (containing two hydrazide groups (O=C-NHNH2)) with a molar mass below 1000 g/mole, viii. the molar ratio of hydrazide groups (present in the dihydrazide functional compound (vii)) to ketone groups is from 1.5 to 0.1 (preferably from 1.2 to 0.2, more preferably from 0.9 to 0.25).

Description

AQUEOUS COATING COMPOSITION

The present invention relates to an aqueous coating composition comprising a urethane-acrylic hybrid, a process for preparing such a composition and a coating obtained from such a composition.

It is well known in the coating industry that polyurethane binders can be applied to a variety of substrates to provide coatings with good mechanical and chemical resistances. A major application for such coatings is as clear coatings for wood flooring.

Over the years, the need for coatings with good mechanical properties for wood applications, especially parquet, furniture and kitchen cabinets, is more and more growing. The coatings need to have good black marking resistance and resistance to damage as well as good (micro) scratch resistance. Black heel marks occur especially in floor coatings when the heel or sole of a shoe leaves residue on the floor after a shoe scuffs (black marking) or scrapes (damage) the coating surface.

Urethane binders often require solvent in the production process in order to reduce the viscosity of the prepolymer to acceptable values. However, the legislation regarding the presence of VOC's (volatile organic components) in indoor applied binders is under pressure. The use of solvents containing VOC's in the urethane prepolymer preparation is therefore less and less preferred and a lot of effort and energy is required to remove such solvent after preparation. As described in WO- A-2006/002864, the use of vinyl monomers as diluent have shown to be a good alternative for solvent containing VOC's , leading to urethane acrylic hybrids. However, it has been found that by introducing a significant fraction of vinyl polymer in an urethane system, mechanical properties like Black Heel Mark Resistance and (micro) scratch resistance are reduced to a non-acceptable level .

The object of the present invention is to provide aqueous coating compositions of polyurethane-vinyl polymer hybrid particles which compositions can result in coatings with good mechanical properties, in particular the combination of (micro) scratch resistance and Black Heel Mark Resistance (BHMR) .

The object of the present invention has been achieved by providing an aqueous coating composition comprising dispersed polyurethane-vinyl polymer hybrid particles wherein (i) the polyurethane-vinyl polymer hybrid is obtained by free-radical polymerization of at least one vinyl monomer in the presence of a polyurethane,

(ii) the polyurethane is obtained by the reaction of at least (I) an isocyanate- terminated polyurethane prepolymer and (II) at least one active-hydrogen containing chain extending compound, wherein the isocyanate-terminated polyurethane prepolymer is obtained by the reaction of at least one polyol with at least one polyisocyanate, wherein from 50 to 100 wt.% of the total amount of the polyisocyanates used to form the polyurethane are aromatic polyisocyanates,

(iii) the polyurethane-vinyl polymer hybrid is ketone functional and contains from 50 to 1000 mmol of ketone groups per 1000 g polyurethane-vinyl polymer hybrid,

(iv) the ketone groups of the polyurethane-vinyl polymer hybrid are present in the polyurethane and in the vinyl polymer,

(v) the weight ratio of the polyurethane to the vinyl polymer in the

polyurethane-vinyl polymer hybrid ranges from 90:10 to 35:65,

(vi) the polyurethane-vinyl polymer hybrid has an acid value from 7 to 60 mg KOH/g polyurethane-vinyl polymer hybrid, preferably from 9 to 40 mg KOH/g polyurethane-vinyl polymer hybrid and most preferably from 12 to

25 mg KOH/g polyurethane-vinyl polymer hybrid,

(vii) the aqueous coating composition comprises a dihydrazide functional

compound (containing two hydrazide groups (0=C-NHNH2)) with a molar mass below 1000 g/mole,

(viii) the molar ratio of hydrazide groups (present in the dihydrazide functional compound (vii)) to ketone groups is from 1.5 to 0.1.

It has surprisingly been found that with the aqueous coating compositions according to the invention it is possible to obtain a coating with good mechanical properties, in particular Black Heel Mark Resistance (BHMR) and (micro) scratch resistance.

US2009/0137734 discloses aqueous dispersions of polyurethane/acrylic polymer hybrid made by forming a mixture of urethane prepolymer or polymer, acrylic monomer or polymer, ketone functional molecule/oligomers, and hydrazine functional molecule/oligomers. EP1814925 EP1814925 describes aqueous coating compositions comprising polyurethane vinyl polymer hybrid dispersions. None of these patent publications describe the aqueous coating compositions according to the present invention.

The aqueous coating composition according to the invention comprises dispersed polyurethane-vinyl polymer hybrid particles whereby the polyurethane-vinyl polymer hybrid is ketone functional and contains from 50 to 1000 mmol of ketone groups per 1000 g polyurethane-vinyl polymer hybrid, preferably from 75 to 500 mmol of ketone groups per 1000 g polyurethane-vinyl polymer hybrid, more preferably from 150 to 400 mmol of ketone groups per 1000 g polyurethane-vinyl polymer hybrid. In the present invention, the ketone groups are present in the polyurethane and in the vinyl polymer of the polyurethane-vinyl polymer hybrid. As used herein, the amount of ketone groups in the polyurethane-vinyl polymer hybrid are determined by calculation as known in the art. For the sake of clarity, the calculations are illustrated in the experimental part of the description. The summed amount of the amount of ketone group containing vinyl monomers used to prepare the vinyl polymer of the polyurethane-vinyl polymer hybrid and the amount of ketone group containing components used to prepare the polyurethane of the polyurethane-vinyl polymer hybrid is chosen such that the desired amount of ketone groups in the polyurethane-vinyl polymer hybrid is obtained. The molar amount of ketone groups in the vinyl polymer to the total molar amount of ketone groups in the polyurethane-vinyl polymer hybrid is preferably from 40% to 95%, more preferably from 55% to 90% and most preferred from 70% to 85%.

The ketone groups are introduced in the vinyl polymer by

copolymerizing ketone group containing vinyl monomers with at least one vinyl monomer not containing ketone groups (further referred to as other vinyl monomer). Suitable vinyl monomers comprise one or more polymerisable ethylenically unsaturated groups. The vinyl monomers used to prepare the vinyl polymer of the polyurethane- vinyl polymer hybrid thus consist of vinyl monomer(s) not containing ketone groups (i.e. other vinyl monomer(s)) and ketone group containing vinyl monomer(s). It is preferred to use vinyl monomers not containing isocyanate or isocyanate-reactive groups. Free acid functional vinyl monomers such as methacrylic acid should preferably not be employed since they may destabilize the dispersion. The ketone group containing vinyl monomers are preferably selected from the group consisting of acrolein, diacetone acrylamide, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone, diacetone acrylate, acetonitrile acrylate and any mixture thereof. More preferably the ketone groups are introduced in the vinyl polymer by copolymerizing of diacetone acrylamide with at least one other vinyl monomer.

The dispersed polyurethane-vinyl polymer hybrid particles present in the aqueous coating composition of the present invention is obtained by free-radical polymerization of vinyl monomer in the presence of a polyurethane. As described above, at least a part of the vinyl monomer is a ketone group containing vinyl monomer which is copolymerized with at least one other vinyl monomer. In this preferred embodiment, at least 30 wt.%, more preferably at least 50 wt.%, more preferably at least 70 wt.% and even more preferably 100 wt.% of the total amount of the other vinyl monomer(s) used to prepare the vinyl polymer is selected from the group consisting of methyl methacrylate, butyl acrylate, butyl methacrylate, acrylonitrile, styrene and mixtures of two or more of said monomers. Preferably, the other vinyl monomer used to prepare the vinyl polymer is selected from the group consisting of methyl methacrylate, butyl acrylate, butyl methacrylate, styrene and mixtures thereof. More preferably at least 30 wt.%, preferably at least 50 wt.% and more preferably at least 70 wt.% of the total amount of the other vinyl monomer(s) used to prepare the vinyl polymer is selected from styrene and/or methyl methacrylate.

The vinyl monomer(s) are polymerized using a conventional free radical yielding initiator system. Suitable free radical yielding initiators 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.

Preferably the glass transition temperature T_g of the vinyl polymer of the polyurethane-vinyl polymer hybrid is from -10 °C to 1 10 °C, preferably from 20 °C to 1 10 °C, whereby the T_g is measured by differential scanning calorimetry (DSC) taking the inflection point in the thermogram as the T_g value. The polyurethane present in the aqueous coating composition of the present invention is obtained by the reaction of at least (I) an isocyanate-terminated polyurethane prepolymer and (II) at least one active-hydrogen containing chain extending compound. The isocyanate-terminated polyurethane prepolymer is obtained by the reaction of at least one polyol with at least one polyisocyanate, whereby from 50 to 100 wt.% of the total amount of the polyisocyanates used in the preparation of the polyurethane are aromatic polyisocyanates, preferably from 75 to 100 wt.% of the total amount of the polyisocyanates used to form the polyurethane are aromatic

polyisocyanates, preferably 100 wt.% of the total amount of the polyisocyanates used to form the polyurethane are aromatic polyisocyanates.

The aromatic polyisocyanate can be a mixture of aromatic

polyisocyanates. An aromatic polyisocyanate (for the sake of clarity) being intended to mean compounds in which all of the isocyanate groups are directly bonded to an aromatic group, irrespective of whether aliphatic groups are also present. Examples of suitable aromatic polyisocyanates include but are not limited to p-xylylene diisocyanate, 1 ,4-phenylene diisocyanate, 2,4- toluene diisocyanate, 2,6- toluene diisocyanate, 4,4'- methylene bis(phenyl isocyanate), 2,4'-methylene bis(phenyl isocyanate). Preferably, the aromatic polyisocyanate is 2,4- toluene diisocyanate, 2,6- toluene diisocyanate, 4,4'-methylene bis(phenyl isocyanate), 2,4'-methylene bis(phenyl isocyanate) and any mixture thereof.

The polyurethane-vinyl polymer hybrid has an acid value from 7 to 60 mg KOH/g polyurethane-vinyl polymer hybrid, preferably from 9 to 40 mg KOH/g polyurethane-vinyl polymer hybrid and most preferably from 12 to 25 mg KOH/g polyurethane-vinyl polymer hybrid. The acid value is determined by acid/base titration: A specific amount of sample, dissolved in a suitable solvent (or solvent mixture), is titrated with an alcoholic potassium hydroxide solution of known concentration. The equivalence point of the potentiometric titration is determined by means of a

titroprocessor. The acid number is calculated based on the equivalence point.

The polyol used to prepare the isocyanate-terminated polyurethane prepolymer comprises a polyol containing ionic and/or potentially ionic water-dispersing groups having a molecular weight of from 100 to 500 g/mol (further referred to as component (b)). The amount of polyol containing ionic or potentially ionic water- dispersing groups having a molecular weight of from 100 to 500 g/mol relative to the total amount of components used to prepare the polyurethane is preferably from 6 to 15.6 wt.%, more preferably from 6 to 12 wt.%. As used herein, potentially anionic dispersing group means a group which under the relevant conditions can be converted into an anionic group by salt formation (i.e.deprotonating the group by a base).

Preferred ionic water-dispersing groups are anionic water-dispersing groups. Preferred anionic water-dispersing groups are carboxylic, phosphoric and/or sulphonic acid groups. Examples of such compounds include carboxyl containing diols, for example dihydroxy alkanoic acids such as 2,2-dimethylol propionic acid (DMPA) or 2,2- dimethylolbutanoic acid (DMBA). Alternatively sulfonate groups may be used as potentially anionic water-dispersing groups. The anionic water-dispersing groups are preferably fully or partially in the form of a salt. Conversion to the salt form is optionally effected by neutralisation of the polyurethane prepolymer with a base, preferably during the preparation of the polyurethane prepolymer and/or during the preparation of the aqueous composition of the present invention. If the anionic water-dispersing groups are neutralised, the base used to neutralise the groups is preferably ammonia, an amine or an inorganic base. Suitable amines include tertiary amines, for example triethylamine or Ν,Ν-dimethylethanolamine. Suitable inorganic bases include alkali hydroxides and carbonates, for example lithium hydroxide, sodium hydroxide, or potassium hydroxide. A quaternary ammonium hydroxide, for example N⁺(CH3)4(OH), can also be used. Generally a base is used which gives counter ions that may be desired for the composition. For example, preferred counter ions include Li⁺, Na⁺, K⁺, NH4⁺ and substituted ammonium salts. Cationic water dispersible groups can also be used, but are less preferred. Examples include pyridine groups, imidazole groups and/or quaternary ammonium groups which may be neutralised or permanently ionised (for example with dimethylsulphate). A very suitable polyol containing ionic or potentially ionic water-dispersing groups is dimethylol propionic acid (DMPA). The neutralising agent is preferably used in such an amount that the molar ratio of the ionic and potentially ionic water dispersing groups to the neutralizing groups of the neutralising agent are in the range of from 0.5 to 2.0, more preferably from 0.7 to 1.5 and even more preferably from 0.85 to 1.2.

The isocyanate-terminated polyurethane prepolymer is prepared using from 0 to 10 wt.%, preferably from 3 to 8 wt.% of at least one isocyanate-reactive polyol containing non-ionic water-dispersing groups (further referred to as component (c)). Preferred non-ionic waterdispersing groups are polyalkylene oxide groups, more preferably polyethylene oxide groups. A small segment of the polyethylene oxide group can be replaced by propylene oxide segment (s) and/or butylene oxide segment (s), however the polyethylene oxide group should still contain ethylene oxide as a major component. The preferred ethylene oxide chain length is > 4 ethylene oxide units, preferably > 8 ethylene oxide units and most preferably > 15 ethylene oxide units. Preferably the polyethylene oxide group has a Mw from 175 to 5000

Daltons, more preferably from 350 to 2200 Daltons, most preferably from 660 to 2200 Daltons.

The isocyanate-terminated polyurethane prepolymer is prepared using from 2 to 40 wt. % of isocyanate reactive polyol containing ketone groups not comprised by (b) or (c) (further referred to as component (d)). The ketone groups of the polyurethane are introduced in the polyurethane by incorporation of ketone group containing isocyanate reactive compounds selected from the group consisting of dihydroxy acetone, diacetone alcohol, or via isocyanate reactive ketone group containing polyols with a Mw from 500 to 5000 Daltons bearing ketone groups.

The isocyanate-terminated polyurethane prepolymer is prepared using from 0 to 64 wt.%, preferably from 5 to 50 wt.% of at least one isocyanate- reactive polyol not comprised by (b), (c) or (d). Such polyol 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.

The aqueous coating composition of the present invention comprises a dihydrazide functional compound (containing two hydrazide groups (0=C-NHNH2)) with a molar mass below 1000 g/mole, preferably with a molar mass below 500 g/mole, more preferably with a molar mass below 250 g/mole, especially preferably the dihydrazide functional compound is adipic dihydrazide.

The molar ratio of hydrazide groups (present in the dihydrazide functional compound (vii)) to ketone groups is from 1.5 to 0.1 , preferably from 1 .2 to 0.2, more preferably from 0.9 to 0.25. As used herein, the molar ratio of hydrazide groups (present in the dihydrazide functional compound (vii)) to ketone groups is determined by calculation as known in the art. For the sake of clarity, the calculation is illustrated in the experimental part of the description

The at least one active-hydrogen containing chain extending compound that is reacted with the polyurethane prepolymer to obtain the polyurethane of the polyurethane-vinyl polymer hybrid is preferably selected from the group consisting of hydrazine, ethylene-1 ,2-dihydrazine, propylene-1 ,3-dihydrazine, butylene- 1 ,4-dihydrazine, and any mixture thereof. More preferably, the active-hydrogen containing chain extending compound is hydrazine. Another preferred active-hydrogen containing chain extending compound is water. The molar ratio of active hydrogens in the chain extending compound to isocyanate groups in the polyurethane prepolymer (also referred to as the degree of chain extension) is preferably in the range from 0.75 to 0.99 stoichiometric amount and more preferably from 0.8 to 0.93 stoichiometric amount.

The polyurethane and the vinyl polymer in the polyurethane and the vinyl polymer hybrid are present in a weight ratio of polyurethane to vinyl polymer ranging from 90:10 to 35:65, preferably from 80:20 to 40:60, more preferably from

65:35 to 45:55. As used herein, the weight ratio of polyurethane to vinyl polymer in the polyurethane-vinyl polymer hybrid is calculated as known in the art and is further illustrated in the experimental part.

The aqueous coating composition according to the invention may comprise co-solvent preferably in an amount of less than 10 wt.% of co-solvent by weight of solids, more preferably less than 7 wt.% of co-solvent by weight of solids, even more preferably less than 5 wt.% of co-solvent by weight of solids, even more preferably less than 2 wt.% of co-solvent by weight of solids and most preferably 0 wt.% of co-solvent by weight of solids. A co-solvent, as is well known in the coating art, is an organic solvent employed in an aqueous composition to ameliorate the drying characteristics thereof, and in particular to lower its minimum film forming temperature. The co-solvent may be incorporated during preparation of the polyurethane-vinyl polymer hybrid or may have been added during formulation of the aqueous

composition. Non-limiting examples of co-solvents , include the mono- and di-alkyl ethers or esters of (di- or tri-)ethylene and (di- or tri-)propylene glycols like propylene glycol n-butyl ether (PnB), Dipropylene glycol n-butyl ether (DPnB), Dipropylene glycol methyl ether acetate (DPMA), Tripropylene glycol methyl ether (TPM), Propylene glycol methyl ether (PM), Propylene glycol methyl ether acetate (PMA), Dipropylene glycol methyl ether (DPM) and mixtures thereof. The amount of co-solvent 1 -methyl-2- pyrrolidinone in the aqueous coating composition is preferably less than 10 wt.% by weight of solids, preferably less than 5 wt.%, more preferably less than 0.5 wt.% and even more preferably is 0 wt.%.

The aqueous coating composition according to the invention comprises the dispersed polyurethane-vinyl polymer hybrid particles preferably in an amount of from 20 to 55 wt.%, more preferably in an amount of from 25 to 50 wt.% and most preferably in an amount of from 25 to 40 wt.% (relative to the aqueous coating composition).

The aqueous coating composition of the present invention preferably has pH of is at least 7, preferably from 7.5 to 8 since such compositions give less discoloration of wooden substrate.

The aqueous composition of the invention may contain conventional ingredients, examples include pigments, dyes, emulsifiers, surfactants, associative thickeners, heat stabilizers, matting agents, inhibitors, UV absorbers, antioxidants, drier salts, wetting agents, defoamers, fungicides, bacteriocides and the like introduced at any stage of the production process or subsequently.

The aqueous coating composition according to the invention typically has a solids content of from 20 to 50 % by weight, more usually from 25 to 48 % by weight and especially from 30 to 45 % by weight.

The present invention further relates to a process for preparing an aqueous coating composition according to any of the preceding claims comprising the following steps

I: preparing an isocyanate-terminated polyurethane prepolymer by

reacting at least components (a), (b), (d) and optionally (c) and (e):

(a) from 20 to 60 wt.%, more preferably from 25 to 50 wt% of at least one organic polyisocyanate, wherein from 50 to 100 wt.% of the total amount of the polyisocyanates used to form the polyurethane are aromatic polyisocyanates,

(b) from 6 to 15.6 wt.%, preferably from 6 to 12 wt.% of an

isocyanate-reactive polyol containing ionic and/or potentially ionic water-dispersing groups having a molecular weight of from 100 to 500 g/mol,

(c) from 0 to 10 wt.%, preferably from 3 to 8 wt.% of at least one isocyanate-reactive polyol containing non-ionic water-dispersing groups,

(d) from 2 to 40 wt. %, more preferably from 3 to 20 wt%, most preferably from 4 to 10 wt% of isocyanate reactive polyol containing ketone groups not comprised by (b) or (c),

(e) from 0 to 64 wt.%, preferably from 5 to 50 wt.% of at least one isocyanate-reactive polyol not comprised by (b), (c) or (d),

(f) adding from 0 to 35wt.% of vinyl monomer in step I, where the amounts of (a), (b), (c), (d) and (e) are given relative to the total amount of components used to prepare the isocyanate-terminated polyurethane prepolymer from which the building blocks from the isocyanate-terminated polyurethane prepolymer are emanated, and where the amount of (f) is given relative to (a) to (f);

II either blending the isocyanate-terminated polyurethane prepolymer with an aqueous phase comprising neutralization agent and chain extending compound, or either neutralizing the isocyanate-terminated polyurethane prepolymer by adding neutralizing agent to the isocyanate- terminated polyurethane prepolymer and subsequently adding the neutralized isocyanate-terminated polyurethane prepolymer to water comprising chain extending compound;

III. optionally (but preferably) adding vinyl monomer; and

IV. adding a radical initiator to polymerize the vinyl monomer,

whereby vinyl monomer is added in step I and/or step III and the amount of vinyl monomer added in the process is preferably such that the weight ratio of the polyurethane to the vinyl polymer in the polyurethane-vinyl polymer hybrid ranges from 90:10 to 35:65.

Some or all of the vinyl monomers may be present at the

commencement of the preparation of the isocyanate-terminated prepolymer, or some or all of the vinyl monomers may be added during the course of the preparation, or some or all of the vinyl monomers may be added after having prepared the isocyanate- terminated prepolymer or some or all of the vinyl monomers may be added to the aqueous phase in which the urethane prepolymer is dispersed or some or all of the vinyl monomers may be added to the aqueous dispersion of the chain extended polyurethane (so after step II) in which case the vinyl monomer(s) swell into the chain extended polyurethane particles. The vinyl monomers are not polymerised until after chain extension has been carried out; thus step IV is preferably effected after step I and step II and in case step III is not optional, step IV is effected before step III, together with step III and/or after step III. At least a part of the vinyl monomers added in the process according to the invention contain ketone groups. The amount of vinyl monomers containing ketone groups added in the process of the invention is preferably such that the molar amount of ketone groups in the vinyl polymer to the total molar amount of ketone groups in the polyurethane-vinyl polymer hybrid is from 40% to 95%, more preferably from 55% to 90% and most preferred from 70% to 85%. In a preferred embodiment of the process of the present invention, neutralizing and chain extending the isocyanate-terminated polyurethane prepolymer is effected by blending of the isocyanate-terminated polyurethane prepolymer with an aqueous phase comprising neutralization agent and chain extending compound. In a more preferred embodiment of the process of the invention, said blending is effected by adding the isocyanate-terminated polyurethane prepolymer to an aqueous phase comprising neutralization agent and chain extending compound.

The aqueous composition of the invention is particularly useful for providing the principle component of coating compositions (e.g. protective or decorative coating compositions) especially for coating compositions on substrates made from wood, metal, plastic, concrete, glass and any combination thereof and in particular for coating compositions on wood substrates, especially oak substrates. Preferred substrates are floor, furniture and kitchen cabinets, in particular wooden floor, wooden furniture and wooden kitchen cabinets. There is further provided according to the present invention a coating obtained by (i) applying an aqueous coating composition according the invention to a substrate and (ii) drying the aqueous coating composition by evaporation of volatiles to obtain a coating, whereby no additional chemical crosslinking reaction is needed after having applied the coating composition on the substrate like for example UV curing and/or curing with the aid of a crosslinker. The aqueous coating composition according to the present invention allows to obtain a coating solely by drying the aqueous coating composition by evaporation of volatiles; a crosslinker and/or external curing trigger such as UV-radiation is not needed.

The present invention therefore also relates to a substrate having a coating obtained by (i) applying an aqueous coating composition according to the invention to a substrate in particular as described above and (ii) drying the aqueous coating composition by evaporation of volatiles.

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.

Examples and Comparative Experiments

The following examples and comparative experiments were prepared and coatings were obtained and tested. The composition of the examples is shown in Tables 1 and 2 and results are as shown in Table 3. Components and abbreviations used:

Rubinate 9279 Blend of 41 wt % toluene diisocyanate and 59 wt %

diphenylmethane diisocyanate available from Huntsman

Dimethylolpropionic acid available from Perstorp polyols

Ketone functional polyol ketone-functional polyester polyol, available from DSM, which has a hydroxyl value of 80 mg KOH/g and an acid value of < 5 mg KOH/g. The ketone functionality is 1.7 milli-equivalents ketone groups per g polyol.

1 ,4-Cyclohexanedimethanol available from Eastman Chemical bv

Desmodur W Dicyclohexylmethane-4,4"-diisocyanate available from

Covestro

Catalyst Tin (II) dioctoaat available from Air Products

poly THF-1000 Polytetramethylene ether glycol, OH-number = 112.5 mg

KOH/g available from BASF

Amitol M21 Ν,Ν-Dimethylethanolamine available from Chemproha bv

Hydrazine Hydrazine hydrate available from Arkema

Defoamer Tegofomex 805, available from Evonik Degussa

Disponyl AFX4030 Nonionic surfactant available from Cognis

Methyl methacrylate available from Arkema

Styrene available from BASF UK ltd

n-Butyl acrylate available from BASF UK ltd

Diaceton acryl amide available from Novasol

Isoascorbic acid available from Brenntag Volkers Benelux bv

tert-Butyl hydroperoxide available from Akzo Nobel Chemicals bv

Fe(lll)(EDTA) Iron-ethylenediaminetetracetic acid complex, 1 % in water Inhibitor 2,6-Di-tert-butyl-4-methylphenol available from Avecia Inc Acetone dimethyl ketone available from Aldrich

Libratex AS-10 Nonionic surfactant available from Librachemicals LTD Preservative Proxel ultra 10, 10% 1 ,2-Benzisothiazolin-3-one solution available for Arch

Adipic acid dihydrazide Available from Novasol

Dowanol DPnB Dipropylene glycol n-butyl ether available from Dow Chemical

Company Comparative Experiments C1 -C4 and Example 1

Table 1 : Recipes for obtaining the aqueous coating compositions of Comparative Experiments C1 -C4 and Example 1

C1 C2 C3 C4 Ex 1

Urethane Prepolymer

synthesis

1 Rubinate 9279 72.8 66.1 72.1 71.8

2 Desmodur W 82.7

3 Dimethylol propionic acid 16.3 16.1 16.1 16.1 16.4

4 poly-tetrahydrofuran 1000 64.0 19.0 63.4 41 .2 53.8

5 Ketone functional polyol 50.6 1 1 .9 12.0

6 1 ,4-cyclohexanedimethanol 6.3 6.2 6.2 6.2 6.3

7 Methyl methacrylate 47.8 47.4 47.3 47.4 48.1

8 Styrene 9.7 9.6 9.6 9.6 9.8

9 inhibitor 0.1 0.1 0.1 0.1 0.1

10 catalyst 0.05

Dispersion process

11 water 623.4 622.2 622.9 621 .2 615.8

12 Disponyl AFX 4030 15.9 15.8 15.8 15.8 16.0

13 Defoamer 1 .3 1 .3 1 .3 1 .3 1 .3

14 hydrazine (64%) 5.0 3.8 4.6 4.3 4.2

15 Amitol M21 1 1 .0 9.9 9.8 10.9 1 1.1

Vinyl polymerisation

process

16 Styrene 71 .6 71 .1 55.2 58.7 59.9

17 Butylacrylate 30.3 30.7 30.6 30.7 31.3

18 Diacetone acrylic amide 15.2 1 1 .8 12.1 t-Butylhydroxy peroxide

19 (70%) 0.5 0.5 0.5 0.5 0.3

20 isoascorbic acid (100%) 0.3 0.3 0.3 0.3 0.2

21 Libratex AS-10 16.6 16.4 16.4 16.4 16.7

22 Fe(lll)(EDTA) (1 %) 2.1 2.1 2.1 2.1 2.1

23 Preservative solution 5.0 5.6 5.6 5.6 5.1

24 adipic acid dihydrazide 5.0 5.0 5.0 5.8

Calculated solids content of 33.52 the polymer in the coating

composition (wt.%) 33.30 32.92 32.84 33.00 Procedure for obtaining the aqueous coating compositions of Comparative

Experiments C1 -C4 and Example 1

Add 1 , 2, 7, 8, 9 and 10 to a reactor vessel with stirring equipment and mix. Add a mixture of 3, 4, 5 and 6 and keep the temperature of the reactor vessel for 2 hours at 87°C.

Prepare in a dispersion reactor a mixture of 1 1 , 12, 13, 14 and 15. Add the urethane mixture from the reactor vessel to the dispersion reactor maintaining the temperature at 25°C. Charge 21 to the dispersion reactor followed by 16, 17 and 18. After 60 minutes add 19 and 22 followed by the addition of 20 over a period of 45 minutes. Cool the reaction mixture to room temperature, and add 23 and 24.

Table 2: Further characterization of the aqueous coating compositions of Comparative Experiments C1 -C4 and Example 1

Table 2

modification Ketone in Ketone in Total ketone Molar polyurethane vinyl polymer (mmol/kg ratio

(mmol/kg (mmol/kg polyurethane- hydrazide polyurethane- polyurethane- vinyl polymer groups vinyl polymer vinyl polymer hybrid) from hybrid) hybrid) ADH / ketone

Polyurethane-vinyl

polymer hybrid

without Schiff base

C1 crosslinking

Polyurethane-vinyl

polymer hybrid with

ketone in the

C2 polyurethane 265 265 0.66

Polyurethane-vinyl

polymer hybrid with

ketone in the vinyl

C3 polymer 274 274 0.64

C4 Aliphatic

polyurethane-vinyl

polymer hybrid with

ketone in the

polyurethane and

the vinyl polymer 62 21 1 273 0.64

Polyurethane-vinyl

polymer hybrid with

ketone in the

polyurethane and

Ex1 the vinyl polymer 62 213 275 0.72

The following formulae were used for calculating the characteristics as reported in Table 2.

Calculation of mmol ketone groups in polyurethane/kg polyurethane-vinyl polymer hybrid =

((Weight ketone functional components used for preparing the polyurethane in g)/(molecular weight ketone functional components used for preparing the

polyurethane)^*number of ketone groups per molecule ^* 1000)/(weight of the polyurethane-vinyl polymer hybrid in kg)

The weight polyurethane-vinyl polymer hybrid in this calculation is defined as the sum of all raw materials that form together the polymer composition. Hence, in this calculation isocyanates, polyols, chain extending compound, neutralizing agent and vinyl monomers are included. Water, surfactant, defoamers, preservatives and other additives used in the process for preparing the polyurethane-vinyl polymer hybrid are excluded in this calculation.

Calculation of mmol ketone groups in vinyl polymer /kg polyurethane-vinyl polymer hybrid =

((Weight ketone functional vinyl monomer in g)/(molecular weight ketone functional vinyl monomer) ^* number of ketone groups per molecule ^* 1000)/(weight of the polyurethane vinyl polymer hybrid in kg)

Calculation of mmol ketone groups in polyurethane-vinyl polymer hybrid/kg polyurethane-vinyl polymer hybrid =

(mmol ketone groups in vinyl polymer /kg polyurethane-vinyl polymer hybrid) + (mmol ketone groups in polyurethane/kg polyurethane-vinyl polymer hybrid)

Calculation of mmol hydrazide groups from the dihydrazide functional compound /kg polyurethane-vinyl polymer hybrid =

((Weight dihydrazide functional compound in g) /(molecular weight dihydrazide functional compound)^*number of hydrazide groups per molecule ^* 1000)/(weight of the polyurethane vinyl polymer hybrid in kg) Calculation of molar ratio of hydrazide groups from the dihydrazide functional compound/ketone groups in the polyurethane-vinyl polymer hybrid =

(mmol hydrazide groups from the dihydrazide functional compound /kg polyurethane- vinyl polymer hybrid)/(mmol ketone groups in polyurethane-vinyl polymer hybrid /kg polyurethane-vinyl polymer hybrid)

Calculations for comparative C3

Calculation of mmol ketone in vinyl polymer /kg polyurethane-vinyl polymer hybrid Weight ketone functional vinyl monomer in g = 15.2 g

Molecular weight ketone functional vinyl monomer (DAAM) = 169.22 mol/g

Number ketone groups per molecule = 1

Weight of polyurethane vinyl polymer hybrid in kg =0.328 kg

^■= ((15.2/169.22)^*1 ^*1000)/0.328=274 mmol ketone/kg polyurethane vinyl polymer hybrid

Weight ketone functional components used for preparing the polyurethane = 0 g

^■=> 0 mmol ketone groups in polyurethane/kg polyurethane-vinyl polymer hybrid

^■=> 274 + 0 = 274 mmol ketone in polyurethane-vinyl polymer hybrid /kg polyurethane vinyl polymer hybrid

Weight ADH in g = 5.0 g

Molecular weight ADH = 174.20 g/mol

Number of hydrazide groups per molecule = 2

Weight of polyurethane vinyl polymer hybrid in kg =0.328 kg

^■= ((5.0/174.20)^*2^*1000)/0.328=175 mmol hydrazide/ kg polyurethane vinyl polymer hybrid Calculation of molar ratio of hvdrazide groups from the dihydrazide functional compound/ketone groups in the polyurethane-vinyl polymer hybrid

mmol hydrazide from the dihydrazide functional compound /kg polyurethane-vinyl polymer hybrid = 175 mmol/kg

mmol ketone in the polyurethane-vinyl polymer hybrid /kg polyurethane-vinyl polymer hybrid = 274 mmol/kg

175/274=0.64

Coating preparation on oak

94.34 weight parts of the aqueous coating compositions as described above are mixed with 5.66 weight parts of Dowanol DPnB.

The so obtained aqueous coating composition is brushed on an oak panel to obtain a wet film and the coating is allowed to dry on a flat surface for a minimum of 2 hours. Slightly sand the panel with sanding paper till all grain raising is gone. After sanding apply the second layer with a brush. Again allow the coating to dry for a minimum of 2 hours on a flat surface. After drying, age the panel at room temperature for 1 week. Performance and wood coloration is tested after ageing.

Testing black heel mark resistance

The black heel mark resistance is tested by striking the coated surface with a heel, hit the coating with the heel (manual force). Wipe the affected area with a tissue (very soft, just to remove the loose rubber parts) to determine how much carbon black can be removed.

Black Marking: After wiping with a tissue, rate the degree of dirt or carbon black which remains.

Damage:

o Rub the coating with your finger to remove as much black as possible o If enough black can be removed to easily see the coating surface, check for permanent damage.

o Rate the coating for scuff damage. Testing Micro scratch resistance

The micro scratch resistance is tested by applying a coating layer of 80 micron wet by wire rod on a Leneta test cards and dry for 24 hours on a flat surface. Age cards for 1 week at room temperature. Determine micro scratch resistance using a felt-pad on the black parts of the test panels using Satra Rub tester using 24.5N weight on top of the rub tester. Check gloss level after every (increasing) 500 revolutions. Gloss level of the coating should not change.

Table 3

Only with the coating composition of the invention a coating with good micro scratch resistance and Black Heel Mark Resistance can be obtained.

Claims

An aqueous coating composition comprising dispersed polyurethane-vinyl polymer hybrid particles wherein

(i) the polyurethane-vinyl polymer hybrid is obtained by free-radical polymerization of at least one vinyl monomer in the presence of a polyurethane,

(ii) the polyurethane is obtained by the reaction of at least (I) an isocyanate-terminated polyurethane prepolymer and (II) at least one active-hydrogen containing chain extending compound, wherein the isocyanate-terminated polyurethane prepolymer is obtained by the reaction of at least one polyol with at least one polyisocyanate, wherein from 50 to 100 wt.% of the total amount of the polyisocyanates used to form the polyurethane are aromatic polyisocyanates,

(v) the weight ratio of the polyurethane to the vinyl polymer in the polyurethane-vinyl polymer hybrid ranges from 90:10 to 35:65,

(vi) the polyurethane-vinyl polymer hybrid has an acid value from 7 to 60 mg KOH/g polyurethane-vinyl polymer hybrid,

(vii) the aqueous coating composition comprises a dihydrazide

functional compound (containing two hydrazide groups (0=C- NHNh )) with a molar mass below 1000 g/mole,

The aqueous coating composition according to claim 1 , wherein the polyurethane-vinyl polymer hybrid contains from 75 to 500 mmol of ketone groups per 1000 g polyurethane-vinyl polymer hybrid.

The aqueous coating composition according to claim 1 , wherein the polyurethane-vinyl polymer hybrid contains from 150 to 400 mmol of ketone groups per 1000 g polyurethane-vinyl polymer hybrid. The aqueous coating composition according to any of the preceding claim, wherein the molar ratio of hydrazide groups (present in the dihydrazide functional compound (vii)) to ketone groups is from 1.2 to 0.2.

The aqueous coating composition according to any of the preceding claim, wherein the molar ratio of hydrazide groups (present in the dihydrazide functional compound (vii)) to ketone groups is from 0.9 to 0.25.

The aqueous coating composition according to any of the preceding claims, wherein the molar amount of ketone groups in the vinyl polymer to the total molar amount of ketone groups in the polyurethane-vinyl polymer hybrid is from 40% to 95%.

The aqueous coating composition according to any of the preceding claim, wherein the ketone groups are introduced in the vinyl polymer by

copolymerizing of diacetone acrylamide.

The aqueous coating composition according to any of the preceding claims, wherein the weight ratio of the polyurethane to the vinyl polymer in the polyurethane-vinyl polymer hybrid ranges from 90:10 to 35:65.

The aqueous coating composition according to any of the preceding claims, wherein the weight ratio of the polyurethane to the vinyl polymer in the polyurethane-vinyl polymer hybrid ranges from 80:20 to 40:60.

The aqueous coating composition according to any of preceding claims, wherein from 75 to 100 wt.% of the total amount of the polyisocyanates used to form the polyurethane are aromatic polyisocyanates.

The aqueous coating composition according to any of preceding claims, wherein the aromatic polyisocyanate is selected from the group consisting of

2,4- toluene diisocyanate, 2,6- toluene diisocyanate, 4,4'-methylene bis(phenyl isocyanate), 2,4'-methylene bis(phenyl isocyanate) and any mixture thereof.

The aqueous coating composition according to any of preceding claims, wherein the active-hydrogen containing chain extending compound is hydrazine.

The aqueous coating composition according to any of preceding claims, wherein the molar ratio of active hydrogens in the chain extending compound to isocyanate groups in the polyurethane prepolymer is in the range from 0.75 to 0.99 stoichiometric amount. The aqueous coating composition according to any of preceding claims, wherein the aqueous coating composition comprises less than 5 wt.% of co- solvent.

The aqueous coating composition according to any of preceding claims, wherein the aqueous coating composition comprises less than 2 wt.% of co- solvent by weight of solids.

The aqueous coating composition according to any of preceding claims, wherein the amount of 1 -methyl-2-pyrrolidinone in the aqueous coating composition is less than 0.5 wt.%.

The aqueous coating composition according to any of the preceding claims wherein the dispersed polyurethane-vinyl polymer hybrid particles are present in the aqueous coating composition in an amount of from 20 to 55 wt.% (relative to the aqueous coating composition)

A process for preparing an aqueous coating composition according to any of the preceding claims comprising the following steps

I. preparing an isocyanate-terminated polyurethane prepolymer by

reacting at least components (a), (b), (c), (d) and (e):

(a) from 20 to 60 wt.% of at least one organic polyisocyanate, wherein from 50 to 100 wt.% of the total amount of the polyisocyanates used to form the polyurethane are aromatic polyisocyanates,

(b) from 6 to 15.6 wt.% of an isocyanate-reactive polyol containing ionic and/or potentially ionic water-dispersing groups having a molecular weight of from 100 to 500 g/mol,

(c) from 0 to 10 wt.% of at least one isocyanate-reactive polyol

containing non-ionic water-dispersing groups,

(d) from 2 to 40 wt. % of isocyanate reactive polyol containing ketone groups not comprised by (b) or (c),

(e) from 0 to 64 wt.% of at least one isocyanate-reactive polyol not comprised by (b), (c) or (d),

(f) adding from 0 to 35wt.% of vinyl monomer in step I,

where the amounts of (a), (b), (c), (d) and (e) are given relative to the total amount of components used to prepare the isocyanate-terminated polyurethane prepolymer from which the building blocks from the isocyanate-terminated polyurethane prepolymer are emanated, and where the amount of (f) is given relative to (a) to (f); II. either blending the isocyanate-terminated polyurethane prepolymer with an aqueous phase comprising neutralization agent and chain extending compound or either neutralizing the isocyanate-terminated polyurethane prepolymer by adding neutralizing agent to the isocyanate-terminated polyurethane prepolymer and subsequently adding the neutralized isocyanate-terminated polyurethane prepolymer to water comprising chain extending compound;

III. optionally adding vinyl monomer; and

IV. adding a radical initiator to polymerize the vinyl monomer,

whereby vinyl monomer is added in step I and/or step III.

A substrate having a coating obtained by (i) applying an aqueous coating composition according to any one of claims 1 to 17 or obtained with the process according to claim 18 to a substrate and (ii) drying the aqueous coating composition by evaporation of volatiles.

A substrate according to claim 19, wherein the substrate is selected from the group consisting of wood, metal, plastic, concrete, glass and any combination thereof.

A substrate according to claim 20, wherein the substrate is wood, composite, concrete or vinyl.