WO2012130764A1

WO2012130764A1 - Use of an aqueous preparation for the coating of wood surfaces to achieve a natural-touch effect

Info

Publication number: WO2012130764A1
Application number: PCT/EP2012/055231
Authority: WO
Inventors: Marc Claudius Schrinner; Christoph Irle; Martin Melchiors; Maria ALMATÓ GUITERAS; Eva TEJADA
Original assignee: Bayer Materialscience Ag
Priority date: 2011-03-29
Filing date: 2012-03-23
Publication date: 2012-10-04

Abstract

The present invention relates to the use of an aqueous preparation for the coating of wood surfaces, characterized in that the aqueous preparation comprises: a hydroxyl-functional polyacrylate dispersion, a polyurethane dispersion, an at least partially hydrophilicized polyisocyanate and ≥0 weight-% to ≤10 weight-% of a matting agent, wherein the combined hydroxyl content of the hydroxyl-functional polyacrylate dispersion and the polyurethane dispersion is ≥1% to ≤12%.The invention further relates to a method of producing a coated wood surface,comprising the step of coating a wood surface with such an aqueous preparation and to a coated wood surface comprising an aqueous preparation whose use has been recited in the context of the use according to the invention.

Description

Use of an aqueous preparation for the coating of wood surfaces to achieve a natural-touch effect

The present invention relates to the use of an aqueous preparation comprising a polyacrylate dispersion, a polyurethane dispersion and a polyisocyanate for the coating of wood surfaces to achieve a natural-touch effect. The invention further relates to a method of producing a coated wood surface, comprising the step of coating a wood surface with such an aqueous preparation and to a coated wood surface comprising an aqueous preparation whose use has been recited in the context of the use according to the invention.

Aqueous coating compositions are increasingly being used instead of systems containing solvent with the objective of reducing emissions of organic solvents. Polyurethane dispersions comprise one important class of aqueous lacquer binders. D. Dieterich provides an overview in Prog. Org. Coatings 9, 281 (1981). Polyurethane dispersions combine the important properties of resistance to chemicals and mechanical stress. It is thus advantageous to use polyurethane dispersions, especially for coating surfaces exposed to severe mechanical stress. Polyurethane dispersions for coating wood are well known in the art. Examples include those described in WO 01/02455 Al , EP 1 845 120 Al , EP 1 350 824 A ! and EP I 717 284 Al . US 2006/0293468 A I provides aqueous coating materials. The materials comprise I) hydroxyl-free polyurethanes and/or p olyur eth ane-ur eas , II) ionically modified, hydroxyl-containing polyurethanes and/or p olyur ethane-ureas, and III) at least one crosslinker, characterized in that the components (I) and (II) comprise polycarbonate polyols which have at least 25% by weight of 1 ,4-butanediol as synthesis component. A process for preparing the coating materials, and their use as soft feel paint, is also provided.

Polyacrylate dispersions are for example described in US 7,863,372 which deals with aqueous secondary copolymer dispersions, to a process for preparing them and to their use for producing high-grade coatings, especially for wood. The dispersions comprise a copolymer (P) synthesized from a mixture of free-radically polymerizable monomers (M) comprising (Ml) cycloaliphatic esters of acrylic and/or methylacrylic acid and also (M2) vinyl esters of aliphatic carboxylic acids.

When wood is provided with a coating the haptic impression that a person touching the coated wood surface experiences may change. In particular, the wood surface may feel artificial and "plastic- like". This is unwelcome as it may lead to a decreased acceptance of the article, in particular i the article is a piece of furniture or a wooden floor covering. It would therefore be desirable to be able to coat such wooden objects of daily use in such a manner that one still has the impression of touching a natural wood surface without compromising other aspects of usability.

The present invention has the object of providing such a coating. Accordingly, this object has been achieved by the use of an aqueous preparation for the coating of wood surfaces, characterized in that the aqueous preparation comprises: a hydroxyl-functional polyacrylate dispersion, a polyurethane dispersion, an at least partially hydrophilicized polyisocyanate and

> 0 weight-% to < 10 weight-% of a matting agent, wherein the combined hydroxyl content of the hydroxyl-functional polyacrylate dispersion and the polyurethane dispersion is > 1% to < 12%.

In another embodiment the presently claimed invention relates to an aqueous preparation that comprises:

> 20 weight-% to < 50 weight-% a hydroxyl-functional polyacrylate dispersion, - > 20 weight-% to < 50 weight-% a polyurethane dispersion,

> 5 weight-% to < 20 weight-% an at least partially hydrophilicized polyisocyanate and

> 0 weight-% to < 10 weight-% of a matting agent, wherein the combined hydroxyl content of the hydroxyl-functional polyacrylate dispersion and the polyurethane dispersion is > 1% to < 12%. in another embodiment the presently claimed invention relates to an aqueous preparation that comprises:

> 20 weight-% to < 50 weight-% a hydroxyl-functional polyacrylate dispersion,

> 20 weight-% to < 50 weight-% a polyurethane dispersion,

> 5 weight-% to < 20 weight-% an at least partially hydrophilicized polyisocyanate and - > 0 weight-% to < 10 weight-% of a matting agent, > 0 weight- % to < 15 weight-% auxiliaries and additives selected from the group consisting of defoamers, wetting agents, thickeners, pigments, dispersing assistants, catalysts, anti- skinning agents, anti-settling agents and emulsifiers,

wherein the combined hydroxyl content of the hydroxyl-functional polyacrylate dispersion and the polyurethane dispersion is > 1% to < 12%.

A preferred range is > 20 weight-% to < 40 weight-% of a hydroxyl-functional polyacrylate dispersion and more preferred > 25 weight-% to < 35 weight-% of a hydroxyl-functional polyacrylate dispersion. A preferred range is > 20 weight-% to < 40 weight-% of a polyurethane dispersion.

A preferred range is > 10 weight-% to < 20 weight-% of an at least partially hydrophilicized polyisocyanate.

A preferred range is > I weight-% to < 10 weight-% of a matting agent and more preferred > 2 weight-% to < 7 weight-% of a matting agent. A preferred range is > 2 weight-% to < 14 weight-% of auxiliaries and additives selected from the group consisting of defoamers, wetting agents, thickeners, pigments, dispersing assistants, catalysts, anti-skinning agents, anti-settling agents and emulsifiers.

It has surprisingly been found that the combination of polymer dispersions according to the invention imparts a natural-touch feeling to wood surfaces while at the same time it offers a good combination of black heel mark resistance, dirt pick-up resistance and abrasion resistance. Hence the use of the afore-mentioned preparation is a use for the coating of wood surfaces, wherein the coated wood surface has a natural-touch feeling.

In the aqueous preparation the combined hydroxyl content of the hydroxyl-functional polyacrylate dispersion and the polyurethane dispersion is to be understood as the calculated content of OH groups, expressed in weight-%, of the dry polyacrylate and polyurethane polymers before OH group consuming reactions take place. The OH content of the solvents and in particular water is not included. The calculation of the OH content is based on the stoichiometries of the reactions for producing the polyacrylate and the polyurethane polymers. Preferred values for the hydroxyl content are > 1 % to < 10% and more preferred values are > 1 % to < 5%. The hydroxyl- functional polyacrylate dispersion may be prepared from acrylic acid or its derivatives and hydroxyl-containing co-monomers.

The polyurethane dispersion may be a dispersion of a hydroxyl-functional polyurethane and/ or or a non-hydroxyl-functional polyurethane. It is preferred that the polyurethane dispersion comprises a hydroxyl-functional polyurethane and more preferred that this dispersion is a hydroxyl-functional polyurethane dispersion without the presence of non-hydroxyl-functional polyur ethanes. With respect to UV stability, aliphatic polyurethanes are preferred for the dispersion.

Examples for matting agents, whose presence is optional, include silica particles.

The at least partially hydrophilicized polyisocyanate has two or more NCO groups per molecule and are based for example on isophorone diisocyanate, hexamethylene diisocyanate, 1,4- diisocyanatocyclohexane, bis(4-isocyanatocyclohexane)methane, 1 ,3 -diisocyanatobenzene, triisocyanatononane or the isomeric 2,4- and 2,6-TDI, and may further contain urethane, isocyanurate and/or biuret groups. Optionally the polyisocyanates may also be blocked.

Particular preference is given to the use of low-viscosity polyisocyanates of the abovementioned kind, based on aliphatic or cycloaliphatic isocyanates.

The polyisocyanates used as crosslinkers generally have a viscosity at 23 °C of 10 to 5000 mPas according to DIN EN ISO 3219 and may also be employed, if desired in order to adjust viscosity, in a blend with small amounts of inert solvents.

The copolymers of the invention are generally hydrophilic enough that even hydrophobic crosslinker resins can be dispersed without additional emulsifiers. However, this is not to rule out the use of external emulsifiers.

Water-soluble or dispersible polyisocyanates are obtainable for example by modification of carboxylate, sulphonate and/or polyethylene oxide groups and/or polyethylene oxide/polypropylene oxide groups. The polyisocyanates can be made hydrophilic by means for example of reaction with sub stoichi ometric amounts of monohydric, hydrophilic polyether alcohols. The preparation of hydrophilicized polyisocyanates of this kind is described for example in EP 0 540 985 Al (p. 3, 1.55 to p. 4, 1.5). Also highly suitable are the polyisocyanates containing allophanate groups that are described in EP 959 087 Al (p. 3, 1.39 to 51), which are prepared by reacting low-monomer-content polyisocyanates with polyethylene oxide polyether alcohols under allophanatization conditions. Also suitable are the water-dispersible polyisocyanate mixtures described in DE 100 078 21 Al (p. 2, 1.66 to p. 31.5), which are based on triisocyanatononane. Of particular suitability and preference are polyisocyanates hydrophilicized with ionic groups, especially sulphonate groups, of the kind described in DE 100 24 624 Al (p. 3 1 1.13 to 33), for example.

Also possible in principle, of course, is the use of mixtures of different crosslinker resins.

The ratio of the hydroxyl groups of the binder component to the isocyanate groups of the crosslinker is typically 3 : 1 to 1 :5, preferably 2: 1 to 1 :3 and with particular preference 1 : 1 to 1 :2.

The coating preparations can be used as they are or in combination with further auxiliaries and adjuvants known from coating technology, such as fillers and pigments, for example. They can be applied in known ways, such as by spreading, pouring, knifecoating, injecting, spraying, spincoating, rolling or dipping, for example. The present invention will be further described in connection with various embodiments. They may be combined freely unless the context clearly indicates otherwise. E v en when not explicitly mentioned, OH numbers as set forth below are determined according to DIN 53240/2 and acid numbers are determined according to DIN 53402.

The molecular weight (M_n, M_w) is determined by means of gel permeation chromatography (GPC). The samples were characterized in tetrahydrofuran eluent in accordance with DIN 55672-1. M„

(UV)=number-average molar weight (GPC, UV detection), result in g mol M_w (UV)=mass-average molar weight (GPC, UV detection), result in g/mol

In one embodiment of the use according to the invention the hydroxyl-functional polyacrylate dispersion is an aqueous secondary copolymer dispersion comprising a copolymer (P) synthesized from a mixture of free-radically polymerizable monomers (M) comprising Ml , M2, M3 , and, optionally, M4, M5 and M6, wherein (Ml) are cycloaliphatic esters of acrylic and/ or methylacrylic acid, (M2) are vinyl esters of branched, aliphatic carboxylic acids of the formula

wherein R¹ and R² are saturated alkyl groups containing together 6, 7, or 8 carbon ato:

(M3) are hydroxy-functional, free-radically polymerizable monomers, (M4) are carboxyl-functional, free-radically polymerizable monomers,

(M5) are hydroxyl- and carboxyl-free (meth)acrylic esters having CI to CI 8 hydrocarbon radicals in the alcohol moiety and/or vinyl aromatics, and

(M6) are monomers different from (Ml) to (M5); wherein said copolymer (P) has an OH number of > 35 mg KOH/g solids to < 200 mg KOH/g solids and an acid number of > 10 mg KOH/g solids to < 50 mg KOH/g solids.

As already mentioned, the Ol I number is determined according to DIN 53240/2. A preferred range is > 50 mg KOH/g solids to < 125 mg KOH/g solids and more preferred > 65 mg KOH/g solids to < 100 mg KOH/g solids. Likewise, preferred ranges for the acid number (DIN 53402) are > 15 mg KOH/g solids to < 30 mg KOH/g solids and more preferred > 20 mg KOH/g solids to < 25 mg KOI l/g solids.

For the purposes of the present invention, acrylic acid or methacrylic acid are also defined as (meth)acrylic acid.

Suitable monomers (Ml) are, for example, cyclohexyl (meth)acrylate, cyclohexyl (meth)acrylates ring-substituted with alkyl groups, 4-tert-butylcyclohexyl (meth)acrylate, norbornyl (meth)acrylate, isobomyl (meth)acrylate, preference being given to isobomyl acrylate and/or isobomyl methacrylate, and particular preference to isobomyl methacrylate. It is also possible to use mixtures comprising isobomyl acrylate and isobomyl methaciylate and other monomers (Ml). The monomers (Ml) other than isobomyl acrylate and isobomyl methacrylate may optionally be used in amounts of less than 10% by weight, based on the sum of (Ml) to (M5).

Suitable monomers (M2) are the esterification products of vinyl alcohol with linear or branched, aliphatic carboxylic acids such as, for example, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl octanoate, vinyl decanoate, vinyl dodecanoate (vinyl laurate) or vinyl stearate. Preferred are the vinyl esters of branched, aliphatic carboxylic acids of the general formula

wherein R^! and R² are saturated alkyl groups containing together 6, 7, or 8 carbon atoms, corresponding to the compounds VeoVa® 9, 10 and 1 1. As monomers (M2) it is preferred to use the vinyl monomers available commercially as VeoVa® Monomer 9, 1 0 and 1 1 (Hexion Specialty Chemicals B.V., Rotterdam, NL), with VeoVa® Monomer 9 being particularly preferred.

The stated monomers differ in terms of the glass transition temperature f their homopolymers: VeoVa® 9 has a T_g of 70 °C, VeoVa® 10 of -3 °C and VeoVa® 1 1 of -40 °C.

Suitable hydroxyl-functional monomers (M3) include ethylenically unsaturated, hydroxy!- containing monomers, such as hydroxyalkyl esters of unsaturated carboxylic acids, preferably hydroxyalkyl (meth)acrylates having 2 to 12, preferably 2 to 6, carbon atoms in the hydroxyalkyl radical. Examples of particularly preferred compounds are 2-hydroxyethyl (meth)acrylate, the isomeric hydroxypropyl (meth)acrylates, 2-, 3- and 4-hydroxybutyl (meth)acrylates, and the isomeric hydroxyhexyl (meth)acrylates.

Suitable carboxyl-functional free-radically polymerizable monomers (M4) are olefinically unsaturated monomers containing carboxylic acid or carboxylic anhydride groups, such as acrylic acid, methacrylic acid, β-carboxyethyl acrylate, crotonic acid, fumaric acid, maleic anhydride, itaconic acid or monoalkyl esters of dibasic acids or anhydrides, such as maleic acid monoalkyl esters, for example. Acrylic acid and/or methacrylic acid are preferred.

Hydroxyl- and carboxyl-free monomers (M5) employed are acrylates and methacrylates having 1 to 18 carbon atoms in the alcohol moiety of the ester group. The alcohol moiety is preferably aliphatic and may be linear or branched. Examples of suitable monomers of component (M5) are methyl, ethyl, n-propy!. isopropyl, n-butyl, isobutyl, tert-butyl, the isomeric pentyl, hexyl, 2-ethylhexyl, octyl, dodecyl, hexadecyl and octadecyl (meth)acrylates. Particularly suitable vinyl aromatics are styrene, optionally substituted styrenes and vinyltoluenes. Preferred monomers (M5) are methyl, n-butyl, isobutyl, tert-butyl (meth)acrylate and also 2-ethylhexyl acrylate and styrene. Suitable monomers (M6) are acetoacetoxyethyl meth acrylate, acrylamide, acrylonitrile, vinyl ethers, methacrylonitrile or vinyl acetates. In addition it is possible to make use, proportionally, of monofunctional polyalkylene oxides having molecular weights of 200 to 3000 g/mol, preferably 350 to 1000 g mol, or esterified (meth)acrylic acid, which are suitable as nonionic, hydrophilic groups. Suitable alkylene oxides include, preferably, ethylene oxide or mixtures of ethylene oxide and propylene oxide. Preferably, however, the hydrophilicization of the copolymers takes place by ionic groups means monomers (M4). The proportions of the synthesis components (Ml) to (M6) are chosen such that the copolymer (P) has an OH number of 35 to 200 mg KOH/g, preferably of 50 to 125 mg KOH/g solids and an acid number of 10 to 50 mg KOH/g, preferably 15 to 30 mg KOH/g solids.

The preparation of the copolymer (P) can in principle be carried out by means of conventional free- radical polymerization processes in organic phase. The copolymer (P) is preferably prepared in a multi-stage operation of the kind already described in EP 0 947 557 Al (p. 31.2-p. 41.15) or in EP 024 184 Al (p. 21.53-p. 41.9). in this operation first a hydrophobic monomer mixture (MI), free from acid groups or with a low acid group content, is metered in, and then, at a later point in time in the polymerization, a more hydrophilic monomer mixture (Mil), containing acid groups, is metered in, the more hydrophilic monomer mixture (Mil) containing acid groups containing no monomers of type (Ml) and (M2).

Preferably the copolymer (P) is synthesized from monomers (M) selected from the group containing

(Ml) > 10% to < 30% by weight of cycloaliphatic esters of acrylic acid and/or methacrylic acid or mixtures thereof, (M2) > 7.5% to < 40% by weight vinyl esters of branched, aliphatic carboxylic acids of formula:

wherein R^! and R are saturated alkyl groups containing together 6, 7, or 8 carbon atoms,

(M3) > 14% to < 36% by weight of hydroxy-functional, free-radically polymerizable monomers,

(M4) > 1 % to < 4.5% by weight of carboxyl-functional, free-radically polymerizable monomers,

(M5) > 18% to < 62% by weight of hydroxyl- and carboxyl-free (meth)acrylic esters having CI to CI 8 hydrocarbon radicals in the alcohol moiety and/ or vinyl aromatics,

(M6) > 0% to < 40% by weight of further monomers, different from (Ml) to (M5), the copolymers (P) containing > 22.5% to < 50% by weight of monomer units (Ml) plus (M2), and the sums of components (Ml) to (M6) adding up to < 100% by weight.

Before, during or after the dispersion of the copolymers (P) in water, the acid groups present are converted at least proportionally into their salt form by addition of suitable neutralizing agents. Suitable neutralizing agents are organic amines or water-soluble inorganic bases, such as soluble metal hydroxides, metal carbonates or metal hydrogen carbonates, for example, such as sodium hydroxide or potassium hydroxide, for example.

With respect to the preparation of the above-mentioned aqueous secondary copolymer dispersions, by way of example in a first step a hydrophobic monomer mixture M(I) comprising the monomers (Ml) 16.5% to 33.5% by weight, (M2) 12.5% to 44.5% by weight, and further comprising the monomers (M3) 10% to 35% by weight, (M4) 0% to 2.5% by weight, (M5) 10% to 61% by weight and (M6) 0% to 40% by weight is polymerized.

Subsequently, in a second stage the polymer obtained is admixed with a hydrophilic monomer mixture M(II) containing the monomers (M3) 20% to 60% by weight, (M4) 10% to 45% by weight, (M5) 30% to 70% by weight and (M6) 0% to 40% by weight and the components are reacted to a copolymer (P), and the resultant copolymer (P), containing acid groups, is transferred to the aqueous phase. At least 40 mol % of the carboxyl groups are neutralized before or during dispersion.

An example for another process is where in a first step a mixture (V) composed of 30% to 70% by weight of one or more monomers (M2) and 70% to 30% by weight of an organic solvent are charged to a reactor and subsequently in a second step a hydrophobic monomer mixture M(I) comprising the monomers (Ml) 22.5% to 36.5% by weight, (M2) 0% to 33.5% by weight, and further comprising the monomers (M3) 10% to 35% by weight, (M4) 0% to 2.5% by weight, (M5) 10% to 67.5% by weight and (M6) 0% to 40% by weight is polymerized. In a further stage the resulting polymer is admixed with a hydrophilic monomer mixture Μ(Π) containing the monomers (M3) 20% to 60% by weight, (M4) 10% to 45% by weight, (M5) 30% to 70% by weight and (M6) 0% to 40% by weight, and the components are reacted to a copolymer (P), and the resultant copolymer (P), containing acid groups, is transferred to the aqueous phase. At least 25 mol % the carboxyl groups are neutralized before or during dispersion. The number-average molecular weight M_n of the copolymer (P) can be controlled through a specific choice of the operating parameters, such as of the molar monomer/initiator ratio, for example, of the reaction time or of the temperature, and is situated in general at between 500 g/mol and 30000 g/mol, preferably between 1000 g/mol and 15000 g/mol, more preferably between 1500 g/mol and 10000 g/mol It is further preferred that the copolymer P has an average molecular weight (GPC) M„ of > 3000 to < 7000 g/mol, an average molecular weight (GPC) M_w of > 10000 to < 25000 g/mol and a molecular weight distribution M_w/M_n of > 2.5 to < 4.0. The acid number (DIN 53240) of the copolymer P in 100% form may also be in the range of > 12 to < 30 mg KOH/g.

Likewise, it is preferred that the copolymer P has a hydroxyl group content of > 1% to < 8%. The hydroxyl group content of the copolymer (P) in 100% form is preferably 1 % to 5% by weight, preferably 1.5% to 4.5% by weight and with particular preference 1.75% to 3.5% by weight. The calculation of the OH content is based on the stoichiometries of the reaction for forming the copolymer and is expressed in weight-%.

In another embodiment of the use according to the invention the polyur ethane dispersion comprises:

I) hydroxyl-free polyur ethanes and/or polyurethane-ureas and/or

II) ionically modified, hydroxyl- and/or amino-containing polyur ethanes and/ or polyurethane-ureas, and

III) at least one crosslinker, wherein the components (I) and (II) comprise polycarbonate polyols which have at least 25% by weight of 1 ,4-butanediol as a synthesis component.

In the non-functional PU polymers (I), the synthesis components are preferably selected from the group of components:

AA1) polyisocyanates,

AA2) polymeric polyols having a number-average molecular weight of M_n 200 to 8000 g/mol, which comprise polycarbonate polyols having at least 25% by weight of 1,4-butanediol as synthesis component

AA3) low molecular weight compounds of molar weight M_n 62 to 400 g/mol possessing in total two or more hydroxyl and/or amino groups,

AA4) compounds possessing one hydroxyl or amino group,

AA5) isocyanate-reactive, ionic or potentially ionic compounds, and

AA6) isocyanate-reactive, nonionic, hydrophilic compounds.

Suitable polyisocyanates of component AA1 ) are the aromatic, araliphatic, aliphatic or cycloaliphatic polyisocyanates which are known per se to the skilled person, have an NCO functionality of preferably > 2 and may also contain iminooxadiazinedione, isocyanurate, uretdione, urethane, allophanate, biuret, urea, oxadiazinetrione, oxazolidinone, acylurea and/or carbodiimide structures. They may be used individually or in any desired mixtures of one another.

Examples o f suitable polyisocyanates are hexamethylene diisocyanate ( I I D! ), isophorone diisocyanate (IPDI), the isomeric dicyclohexylmethane 4,4'-diisocyanate or mixtures thereof with any desired isomer content and 1 ,4-cyclohexyl diisocyanate.

An example of a non-modified polyisocyanate having more than 2 NCO groups per molecule that may be mentioned is, for example, 4-isocyanatomethyl-l ,8-octane diisocyanate (nonane triisocyanate). Preference is given to polyisocyanates or polyisocyanate mixtures of the aforementioned kind that contain exclusively aliphatically and/or cycloaliphatically attached isocyanate groups.

Particular preference is given to hexamethylene diisocyanate, isophorone diisocyanate, the isomeric dicyclohexylmethane 4,4'-diisocyanate and also mixtures thereof.

Hydroxyl-containing polycarbonate polyols meeting the definition of component AA2) are obtainable by reacting carbonic acid derivatives, e.g. diphenyl carbonate, dimethyl carbonate or phosgene, with diols. The hydroxyl-functional poly-carbonate polyols AA2) to be used according to the invention have an average hydroxyl functionality of 1.6 to 4, preferably 1.8 to 3, and more preferably 1.9 to 2.3 and a number-average molecular weight of 240 to 8000 g/mol, preferably of 500 to 3000 g/mol, more preferably of 750 to 2500 g/mol. The polycarbonate polyols are preferably prepared according to the preparation process described in EP 1 404 740 Al (pp. 6-8, Examples 1 -6) and EP 477 508 A I (p. 5, Example 3).

Examples of suitable diols include 1 ,3- and 1 ,4-butanediol, 1,6-hexanediol, 1 ,8-octanediol, 1, 12- dodecanediol, neopentyl glycol, 1 ,4-bishydroxymethylcyclohexane, 2-inethy - 1.^-propanediol and trimethyipentane-l ,3-diol, the fraction of 1 ,4-butanediol being at least 25% by weight of the diol components used.

Preferably the diol component contains 45% to 100% by weight of 1 ,4-butanediol and 0% to 55% by weight of 1 ,6-hexanediol, more preferably 60% to 1 00% by weight of 1 ,4-butanediol and 0% to 40% by weight of 1,6-hexanediol.

The hydroxyl polycarbonates are preferably linear, but may also be branched where appropriate as a result of the incorporation of polyfunctional components, particularly low molecular weight polyols. Particularly preferred components AA2) are based on mixtures of 1 ,4-butanediol and 1,6-hexanediol and have an average hydroxyl functionality of 1.9 to 2.05.

Polyester polyols which have a molecular weight M_n of 400 to 6000 g/moi, more preferably of 600 to 3000 g/mol, can likewise be used by way of example as polymeric polyols AA2). Their hydroxyl number is generally 22 to 400 mg KOH/g, preferably 50 to 200 mg KOH/g and more preferably 80 to 160 mg KOH/g, and they have an 01 1 functionality of 1 .5 to 6, preferably of 1.8 to 4 and more preferably of 1.9 to 3.3.

Highly suitable examples are the conventional polycondensates of diols and also optionally polyols and dicarboxylic and also optionally polycarboxylic acids or hydroxycarboxylic acids or lactones. Instead of the free polycarboxylic acids it is also possible to use the corresponding polycarboxylic anhydrides or corresponding polycarboxylic esters of lower alcohols to prepare the polyesters. Examples of suitable diols are ethylene glycol, butane- 1,4-diol, hexane-l,6-diol, neopentyl glycol. As polyols for optional use as well, mention may be made here, for example, of trimethylolpropane, glycerol or pentaerythritol. Preferred suitable dicarboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, or adipic acid. Anhydrides of these acids are also suitable, where they exist. F r the purposes of the present invention, consequently, the anhydrides are embraced by the term "acid" . Monocarboxylic acids as well, such as benzoic acid and hexanecarboxylic acid, can be used provided that the average functionality of the polyol is greater than 2. As a polycarboxylic acid which can also be used optionally, in relatively small amounts, mention may be made here of trimellitic acid.

Further suitable components AA2) are the polylactone and polyether polyols known from polyurethane chemistry, insofar as they correspond to the abovementioned criteria with respect to functionality and molecular weight. The fraction of the hydroxypolycarbonates in the sum of the polyols from AA2) used to prepare the polymers (I) and (II), respectively, is 35 to 100% by weight, preferably 45 to 100% by weight and more preferably 65 to 100% by weight.

The low molecular weight polyols AA3) that are used for synthesizing the polyurethane resins generally have the effect of a stiffening and/or a branching of the polymer chain. The molecular weight is preferably situated between 62 and 200 g/mol. Suitable polyols may contain aliphatic, alicyclic or aromatic groups. Mention may be made here, by way of example, of the low molecular weight polyols having up to about 20 carbon atoms per molecule, such as ethylene glycol, diethylene glycol, 1 ,4-butanediol, 1 ,3-butylene glycol, cyclobexanediol, 1,4-cyclohexanedimethanol, 1,6- hexanediol, and also trimethylolpropane, glycerol or pentaerythritol.

Diamines or polyamines and also hydrazides can likewise be used as AA3), examples being ethylenediamine, 1 ,2- and 1,3-diaminopropane, 1 ,4-diaminobutane, 1,6-diaminohexane, is ophor onediamine, an isomer mixture of 2,2,4- and 2,4,4-trimethylhexamethylenediamine, 2- methylpentamethylenediamine, diethylenetriamine, 1 ,3- and 1 ,4-xylylenediamine, α,α,α',α'- tetrametbyl-1,3- and - 1 ,4-xylylenediamine and 4,4-diaminodicyclohexylmethane, dimethylethylenediamine, hydrazine or adipic dihydrazide. Suitability as AA3) is also possessed in principle by compounds containing active hydrogen with a different reactivity towards NCO groups, such as compounds which in addition to a primary amino group also contain secondary amino groups or in addition to an amino group (primary or secondary) also contain OH groups.

The polyurethane resins I) and II) may also, where appropriate, include units AA4), which in each case are located at the chain ends and finish the said ends. These units are derived on the one hand from monofunctional compounds reactive towards NCO groups, such as monoamines, particularly mono-secondary amines or monoalcohols.

By ionically and potentially ionically hydrophilicizing compounds AA5) are meant all compounds which contain at least one isocyanate-reactive group and also at least one functionality, such as - COOY, -SO3Y, -POf OYh (Y for example = 1 1. NH₄ ⁺, metal cation), -NR₂, -NR.-Γ (R=H, alkyl, aryl), which on interaction with aqueous media enters into a pi 1 -dependent dissociation equilibrium and in that way can have a negative, positive or neutral charge. Preferred isocyanate-reactive groups are hydroxy! or amino groups.

Suitably ionically or potentially ionically hydrophilicizing compounds meeting the definition of component AA5) are, for example, mono- and dihydroxycarboxylic acids, mono- and diaminocarboxylic acids, mono- and dihydroxysulphonic acids, mono- and diaminosulphonic acids and also mono- and dihydroxyphosphonic acids or mono- and diaminophosphonic acids and their salts such as dimethylolpropionic acid, dimethylolbutyric acid, hydroxypivalic acid, N-(2- aminoethyl)-P-alanine, 2-(2-aminoethylamino)ethanesulphonic acid, ethylenediaminepropylsulphonic or -butylsulphonic acid, 1 ,2- or l ,3-propylenediamine-.p.-ethylsulphonic acid, malic acid, citric acid, glycolic acid, lactic acid, glycine, alanine, taurine, lysine, 3,5-diaminobenzoic acid, an adduct of aliphatic diamines such as, for example, ethylenediamine (EDA) or isophoronediamine, I PDA and acrylic acid (EP 0 916 647 Al, example 1) and the alkali metal and/or ammonium salts thereof; the adduct of sodium bisulphite with but-2-ene-l,4-diol, polyethersulphonate, the propoxylated adduct of 2-butenediol and Nal lSO-.. described for example in DE 2 446 440 Al (page 5-9, formula I-III), and compounds which contain units which can be converted into cationic groups, amine-based units for example, such as N-methyldiethanolamine, as hydrophilic synthesis components. It is additionally possible to use cyclohexylamino-propanesulphonic acid (CAPS) such as in WO 01/88006 Al, for example, as a compound meeting the definition of component AA5). To synthesize the component (I), preferred compounds AA5) are those which possess carboxyl or carboxylate and/or sulphonate groups and/or ammonium groups. Particularly preferred ionic compounds AA5) are those containing carboxyl and/or sulphonate groups as ionic or potentially ionic groups, such as the salts of N-(2-aminoethyl)-P-alanine, of 2-(2- aminoethylamino)ethanesulphonic acid or of the adduct of IPDI and acrylic acid (EP 0 916 647 Al, example 1) and also of dimethylolpropionic acid.

Suitable non-ionically hydrophilicizing compounds meeting the definition of component AA6) are, for example, polyoxyalkylene ethers which contain at least one hydroxyl or amino group. These polyethers include a fraction of 30% to 100% by weight of units deriv ed from ethylene oxide.

The polyalkylene oxide polyether alcohols are either straight polyethylene oxide polyethers or mixed polyalkylene oxide polyethers at least 30 mol %, preferably at least 40 mol %, of whose alkylene oxide units are composed of ethylene oxide units. Preferred non-ionic compounds are monofunctional mixed polyalkylene oxide polyethers containing at least 40 mol % ethylene oxide units and not more than 60 mol % propylene oxide units.

For the PU polymers (I) it is preferred to use a combination f ionic and non-ionic hydrophilicizing agents meeting the definitions of components AA5) and AA6). Particularly preferred combinations are those of non-ionic and anionic hydrophilicizing agents.

It is preferred to use 5% to 45% by weight of component AAl), 50% to 90% by weight of component AA2), 1% to 30% by weight of the sum of compounds AA3) and AA4), 0 to 12% by weight of component AA5), 0 to 15% by weight of component AA6), the sum of AA5) and AA6) being 0.1 % to 27% by weight and the sum of all components adding to 100% by weight.

It is particularly preferred to use 10% to 40% by weight of component AAl), 55% to 85% by weight of component AA2), 1% to 25% by weight of the sum of compounds AA3) and AA4), 0 to 10% by weight of component AA5), 0 to 10% by weight of component AA6), the sum of AA5) and AA6) being 0.1% to 20% by weight and the sum of all components adding to 100% by weight. Very particular preference is given to using 15% to 40% by weight of component AAl), 60% to 85% by weight of component AA2), 1% to 20% by weight of the sum of compounds AA3), 0 to 8% by weight of component AA5), 0 to 10% by weight of component AA6), the sum of AA5) and AA6) being 0.1 % to 18% by weight and the sum of all components adding to 100% by weight.

The process for preparing the aqueous PU dispersion (I) can be carried out in one or more stages in homogenous phase or, in the case of multi-stage reaction, partly in disperse phase. Following complete or partial polyaddition of AA1)-AA6) there is a dispersing, emulsifying or dissolving step. This is followed optionally by a further polyaddition or modification in disperse phase.

The aqueous PU dispersions (I) can be prepared using all of the prior art methods, such as the prepo!ymer mixing method, acetone method or melt dispersing method, for example. The PU dispersion (I) is prepared preferably by the acetone method. The solids content of the PU dispersion (I) is generally 25% to 65%, preferably 30% to 60% and more preferably 40% to 60%.

The ionically modified, hydroxyl-containing polyur ethanes and/ or polyurethane-ureas (II) contain 5% to 45% by weight of component AA1), 50% to 94.5% by weight of components AA2), 0% to 15% by weight of component AA3), 0.5% to 12% by weight of component AA5), 0% to 15% by weight of component AA6), the sum of all components adding up to 100% by weight.

The ionically modified, hydroxyl-containing polyur ethanes and/or polyurethane-ureas (II) preferably contain 7.5% to 35% by weight of component AA1), 60% to 90% by weight of components AA2), 0% to 10% by weight of components AA3), 2.5% to 7.5% by weight of component AA5), 0% to 12.5% by weight of component AA6), the sum of all components adding up to 100% by weight. The ionically modified, hydr oxyl- containing polyur ethanes and/or polyurethane-ureas (II) very preferably contain 10% to 25% by weight of component II.1), 65% to 85% by weight of components AA2), 1.5% to 5% by weight of component AA3), 3% to 7% by weight of component AA5), 0% to 10% by weight of component AA6), the sum of all components adding up to 100% by weight.

Suitable components AA3) are only compounds which are OH-functional. Components AA4) are not used for the synthesis of polymers (II).

The ionically modified, hydroxyl-containing polyur ethanes and/or polyurethane-ureas (II) preferably feature purely ionic hydrophilicization in accordance with the definition of components AA5). These coating materials comprise the ionically modified, hydroxyl-containing polyurethanes and/or polyurethane-ureas (II), which in the course of preparation are either converted into the aqueous form, and are therefore present as a dispersion, or alternatively are present as a solution in an optionally water -miscible solvent which is inert towards isocyanate groups.

The ionically modified, hydr oxyl- containing polyurethanes and/or polyurethane-ureas (II) can be prepared by the customary prior art processes. The polyurethanes and/or polyurethane-ureas (II) differ from the PU polymers (I) in particular in the type of preparation and the type of hydrophilicizing. They contain carboxylic acid groups and/or sulphonic acid groups, preferably carboxylic acid groups, which may have been at least fractionally neutralized, as hydrophilic groups. For the preparation of the PU polymers (II) preference is therefore given as component AA5) to those possessing carboxyl and/or carboxylate groups. Particularly preferred ionic compounds AA5) are dihydroxycarboxylic acids, with especial preference being given to α,α-dimethylolalkanoic acids, such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid or dihydroxysuccinic acid, for example.

To prepare the ionically modified, hydroxyl-containing polyurethanes and/or polyurethane-ureas (II) it is usual to introduce, initially, components AA2), AA3), AA5) and optionally AA6), optionally together with a suitable catalyst and, where required, in an appropriate solvent, into a vessel. Added to this mixture at a temperature of 0 to 140 °C, preferably 70 to 135 °C and more preferably at 90 to 130 °C is a polyisocyanate component AA1), after which the components are left to react until the reaction product is isocyanate-free. The amounts of components AAl) to AA6) employed are calculated such that for each equivalent of hydroxyl groups there is 0.45 to 0.95, preferably 0.55 to 0.90, more preferably 0.65 to 0.85 equivalent (eq) of isocyanate groups.

The preparation of the ionically modified, hydroxyl-containing polyurethanes and/or polyurethane- ureas (II) takes place preferably without the addition of organic solvents.

The acid groups incorporated in the prepolymer are at least fractionally neutralized. This can be done during or else after prepolymer preparation but also during or after dispersing in water, by adding suitable neutralizing agents (see also with regard to PU dispersion (I)). Examples of suitable neutralizing agents are triethylamine, triethanolamine, dimethylethanolamine, ethyldiisopropylamine or diis opropy lethy lamine . The neutralizing agent is generally used in a molar ratio with respect to the acid groups of the prepolymer of 0.3: 1 to 1.3: 1 , preferably of 0.6: 1 to 1.1 : 1.

Thereafter the hydroxyl-functional polyurethane is converted into an aqueous dispersion by addition of water or by introduction into water.

The resins of the PU polymers (II) that are obtainable in accordance with the procedure described above possess a number-average molecular weight M„ of 1000 to 30 000 g/mol, preferably of 1500 to 10 000 g/mol, an acid number of 10 to 80, preferably of 15 to 40 mg KOH/g and a hydroxyl group content of 0.5% to 6% by weight, preferably of 1.0% to 4%.

The PU dispersions (I) and (II) may furthermore comprise all additives that are known for PI I dispersions such as, for example, antioxidants, light stabilizers and/or other auxiliaries and additives as well as fillers.

Also present are crosslinkers (III). Depending on the choice of crosshnker it is possible to prepare both one-component paints and two-component paints. By one-component paints for the purposes of the present invention are meant coating compositions wherein binder component and crosshnker component can be stored together without a crosslinking reaction taking place to any marked extent or any extent detrimental to the subsequent application. By two-component paints are meant for the purposes of the present invention coating compositions wherein binder component and crosshnker component have to be stored in separate vessels owing to their high reactivity. The two components are mixed only shortly before application, when they react generally without additional activation. Examples of suitable crosslinkers (III) include blocked or non-blocked polyisocyanate crosslinkers, amide- and amine- ormaldehyde resins, phenolic resins, aldehyde resins and ketone resins, such as for example phenol-formaldehyde resins, resoles, furan resins, urea resins, carbamate resins, triazine resins, melamine resins, benzoguanamine resins, cyanamide resins or aniline resins. Preference is given to polyisocyanates.

As crosshnker component (III) it is particularly preferred to use polyisocyanates having free isocyanate groups, since the resultant aqueous polyurethane paints display a particularly high level of paint properties. Examples of suitable crosslinkers (III) include paint polyisocyanates such as polyisocyanates containing uretdione, biuret, isocyanurate or iminooxadiazinedione groups and formed from hexamethylene diisocyanate, l -isocyanato-3,3,5-trimethyl-5- isocyanatomethylcyclohexane or bis(4-isocyanatocyclohexane)methane. The PU polymers (I) and (II) as described here are generally sufficiently hydrophilic, so that the dispersibility even of hydrophobic crosslinkers from component (III) is ensured. If d esired, however, it is also possible to add external emulsifiers such as are known to the skilled person.

Additionally, however, it is also possible in component (III) to use water-soluble or dispersible polyisocyanates such as are obtainable, for example, by modification with carboxylate, suiphonate and/or polyethylene oxide groups and/or polyethylene oxide/polypropylene oxide groups.

Also possible in principle, of course, is the use of mixtures of different crosshnker resins of the aforementioned kind in component (III). Likewise prov ided by the present invention is a process for preparing the aqueous coating materials of the invention, characterized in that the PU polymers (Ϊ) and also the PU polymers (II) are dispersed in water and mixed with the crosslinker (III).

The ratio of the crosslinker (III) to the compounds of components (II) that are reactive with it is to be chosen so as to result in a ratio of crosslinker-reactive groups from (II) (e.g. OH groups) to the reactive groups of the crosslinker (NCO groups in the case of isocyanates) of 0.5: 1.0 to 3.5 : 1.0, preferably 1.0: 1.0 to 3.0: 1.0 and more preferably of 1.0: 1.0 to 2.5: 1.0.

The mixture of components (I) and (II) contains preferably 5% to 95% by weight (with respect to solid resin), more preferably 25% to 75% by weight (with respect to solid resin) of component (II), and the amount of (I) is to be chosen such that the total amounts of (I) and (II) add up to 100% by weight (with respect to solid resin).

As customary paint auxiliaries and additives, the substances known to the skilled person may be present in the coating materials of the invention, such as defoamers, wetting agents, thickeners, pigments, dispersing assistants, catalysts, anti-skinning agents, anti-settling agents and/or emulsifiers, and also additives which enhance the desired soft feel effect. The point in time during preparation at which the additives/auxiliaries are added to the coating materials of the invention or incorporated into them is unimportant.

Preferably the polycarbonate polyols contain > 60% to < 100% by weight of 1 ,4-butanediol and > 0% to < 40% by weight of 1 ,6-hexandiol as synthesis components, the sum of 1 ,4-butanediol and 1,6-hexanediol adding up to < 100% by weight. It is also preferred that the polycarbonate polyols have an average hydroxyl functionality of > 1.6 to < 4.

In another embodiment of the use according to the invention the at least partially hydrophilicized polyisocyanate is an aliphatic polyisocyanate. Preferably the at least partially hydrophilicized polyisocyanate is based on 1,6-hexamethylene diisocyanate. The term "based on" is to be understood that 1 ,6-hexamethylene diisocyanate has been used in the reaction to form the polyisocyanate even if the NCO groups are partially converted into other functional groups such as isocyanurate groups or biuret groups in the course of the reaction.

The present invention further relates to a method of producing a coated wood surface, comprising the step of coating a wood surface with an aqueous preparation whose use has been recited as stated above. Another aspect of the present invention is a coated wood surface comprising an aqueous preparation whose use has been recited as stated above.

The present invention will be further described with reference to the following examples without wishing to be limited by them. Glossary:

PAC ! : aqueous hydroxyl-functional secondary polyacrylate copolymer dispersion with a calculated hydroxyl content of 3% for the solvent-free material; 41 weight-% solids.

PUD 1 : aliphatic hydroxy-functional polycarbonate ester polyur ethane dispersion comprising 1,4- butanediol as a synthesis component; ca. 55 weight-% solids. PUD 2: aqueous hydroxy-functional polyester-polyur ethane dispersion; ca. 38 weight-% solids.

PUD 3: aqueous aliphatic, anionic p oly ester-p olyur ethane dispersion; ca. 37 weight-% solids.

PUD 4: aqueous aliphatic, anionic fatty acid-modified polyurethane dispersion; ca. 5 weight-% solids.

PUD 5: aqueous aliphatic polyurethane dispersion; ca. 50 weight-% solids. PAC 2: aqueous core-shell styrene acrylate dispersion; ca. 40 weight-% solids.

Defoamer: mixture of foam-breaking polysiloxanes and hydrophobic particles in polyglycol.

Wetting agent 1 : poly ether modified Siloxane

Wetting agent 2: polyether siloxane copolymer.

Wax emulsion: non-ionic emulsion of a modified paraffin wax PU pigment: polyurethane pigment, 100% dry powder.

Matting agent: silica matting agent; >99.8% S1O2.

PI 1 : hydrophilic, aqueous polyisocyanate based on 1,6-hexamethylene diisocyanate; 80% in methoxypropylacetate.

Example 1 : five formulations "Comp. 1 -5 " were prepared as comparative examples and one formulation "Invention 1" was prepared according to the present invention. The components are listed in the table below. Values given for the amount of the components are expressed as weight- parts. The viscosities stated were measured using a DIN 4 cup (r = 2 mm, L = 4 mm. ho = 75 mm, V = 100 mm³) and are stated in seconds.

Comp. 1 Comp.2 Comp. 3 Comp. 4 Comp. 5 Invention 1

% OH resin 3 1.8 3 - - 1.7

PAC 1 59.2 - - - - 32.1

PUD 1 - 49.2 - - - 23.2

PUD 2 - - 63.6 - - -

PUD 3 - - - 68.9 - -

PAC 2 - - - - 62.4 -

Water 13.1 27.3 9.0 5.4 10.4 18.6

Defoamer 0.6 0.6 0.6 0.6 0.6 0.6

Wetting 0.7 0.7 0.7 0.7 0.7 0.7 agent 1

Wetting 0.3 0.3 0.3 0.3 0.3 0.3 agent 2

Wax 2.0 2.0 2.0 2.0 2.0 2.0 emulsion

PU pigment 5.6 5.6 5.6 5.6 5.6 5.6

Matting 3.2 3.2 3.2 3.2 3.2 3.2 agent

Sub-Total 84.2 89.4 84.2 86.6 87.3 86.4 "A"

PIC 1 16 10.6 15.8 13.4 13.4 13.6

Total 100 100 100 100 100 100 "A+B" % solids 47 47 47 47 47 47

NCO/OH 1 .5 1.5 1.5 - - 1.5

Viscosity 24" 23" 49" 53" 26" 22"

"A"

Viscosity n. d. n. d. n. d. n. d. n. d. 41 "

"A+B"

W at er t o 7% 7% 1-2%

adjust

viscosity

"A+B"

The formulation of comparative example 5 showed a strong increase in viscosity. After 10 minutes it could not be applied anymore. Viscosity is given in seconds as efflux time in DIN 4 mm cup.

Example 2: the formulations of example 1 were tested according to DIN EN 12720 and evaluated immediately and after three days. Substrates used were sanded m el a mine foil (for chemical resistances), glass panels (for hardness) and black plexiglass (for gloss and scratch determinations). The formulations were mixed manually and applied using 200 microns wet application. Ageing was performed for 16 hours at 50 °C for me! a mine and glass panels and for 24 hours at room temperature for the plexiglass panels. The results are stated in the following table.

Comp. 1 Comp. 2 Comp. 3 Comp. 4 Comp. 5 Invention 1

Haze 2.1 1.1 4.4 22 35 2.2

Gloss 60 85° 1/4.8 0.6/3 1.5/4.3 4.7/22 6.7/20 0.9/3.7

After Haze 4.3 1 .4 6.3 28 38.6 4

Scratch

Gloss 60 85° 1.3/7.1 0.6/3.8 1.7/6.1 5.3/27.3 6.8/19.5 1.2/6

(50 db 5€-

% increase gloss 30%/ 0%/ 13%/ 12.7%/ 1.5% 33%/ note)

60785°

48% 26% 42% 24% -2.5% 62%

Hardness Konig 16 h 50 °C 104" 32.7" 116" 104" 115" 63"

Coffee 6h 3-4/5 2/2 3-4/5 2/2 2-3/3 2-3/2-3 16 h 4-5/5 2/2 5/5 2/2 2/2 2-3/2-3

Red Wine 6 h 2-3/3 2/2 2/2-3 2/2 2/2 2/2

16 h 2-3/2-3 2/2 2/2 2/2 2/2 2/2

Water 6 h 5/5 5/5 5/5 5/5 5/5 5/5

16 h 5/5 5/5 5/5 5/5 5/5 5/5

Mustard 6 h 2/2 2/2 2/2-3 2/2 2/2 2/2

16 h 2/2 2/2 2/2 2/2 2/2 2/2

Ethanol 1 h 5/5 5/5 4-5/5 4/4 3/3-4 4-5/4-5

The samples were evaluated by visual inspection by an experienced technician and graded on a scale of 1 to n, wherein 1 denotes a low resistance and 5 denotes a high resistance (according to DIN EN 12720). Film hardness was determined by Konig pendulum according to DIN EN ISO 1522. Gloss was determined according to DIN EN ISO 2813.

Example 3 : the formulations of example 1 were tested for their popping limit on glass and wood substrates. The popping limit is understood as the dry film thickness up to which no disturbances in the coating film due to gas bubbles can be observed. If the coating is applied with a dry film thickness above the popping limit, disturbances in the coating film due to gas bubbles occur. Specimens were aged at 23 °C and 50% relative humidity. The results are stated in the following table.

Comp. 1 Comp. 2 Comp. 3 Comp. 4 Comp. 5 Invention 1

Glass

g/m² 300 >500 200 500 - 400

Remarks Big bubble Bubble craters

formation formation

Wood

g/m² tricolor >300* - >300* - - 500 g/m² beech 500 - >300* - - 500 * : The popping limit has only been tested up to the mentioned thickness. Therefore, one can only infer that the popping limit higher than the given value.

Example 4: the formulations of example 1 were tested for their ability to confer a natural touch- feeling to coated wood surfaces. The coatings were applied with a spray gun to the stated amount of 300 g/m² and aged at 23 °C and 50% relative humidity. An experienced technician then tested the haptic impression and graded it on a scale of 1 to 5, wherein a value of 1 means a very artificial impression and 5 means a very natural impression. The results are stated in the following table.

Example 5 : the formulations of example I were tested for their black heel mark resistance (BHMR) on tricolor wood. The coatings were applied with a spray gun to the stated amount of 300 g/m² and aged at 23 °C and 50% relative humidity. An experienced technician then performed the tests and graded the results on a scale of 1 to 5, wherein a value of 1 means a very low resistance and a value of 5 means a very high resistance. The results are stated in the following table.

Example 6: the formulations of example 1 were subjected to a dirt pick-up test. The substrates were applied to a beech wood substrate to the stated amount of 300 g/m² and aged at 50 °C and for 30 minutes. The dirt pick-up test solution was a 1 : 1 mixture of water and ethanol together with 1.25% Microlith® black C-WA pigment. An experienced technician then performed the tests and graded the results on a scale of I to 5, wherein a value of 1 means a very low dirt pick-up resistance and a value of 5 means a very high dirt pick-up resistance. The results are stated in the following table. Comp. 1 Comp. 2 Comp. 3 Comp. 4 Comp. 5 Invention 1

300 g/m² 1 3 3 I 2 5

Example 7: substrates coated with the formulations of example 1 were subjected to a Taber® CS 10 abrasion test (I O force). This abrasion wheel has a medium abrading action, like that of normal handling, cleaning or polishing. It is a popular wheel for coatings, plastics, textiles, leather, and paper products. The results are stated in the following table as mg.

In summary, coatings for wood substrates using the formulation according to the invention offer the best combination of a naturally-feeling touch, black heel mark resistance, dirt pick-up resistance and abrasion resistance. Abrasion resistance was determined according to DIN EN ISO 2470-1. Example 8:

Other polyurethane dispersions in combination with the polyacryiate PAC 1 were used to prepare formulations. The formulation "Invention 1 " is also listed for better reference. The components are listed in the table below. Values given for the amount of the components are expressed as weight- parts. The viscosities stated were measured using a DIN 4 cup (r = 2 mm, L = 4 mm, ho = 75 mm. V = 100 mm³) and are stated in seconds.

Invention 1 Invention 2 Invention 3 Invention 4

% Ol 1 resin 1.7 1.4 1 .4 1.7

PAC 1 32.1 32.1 32.1 32.1 PUD 1 23.2 - - -

PUD 3 - 34.5 - -

PUD 4 - - 36.5 -

PUD S - - - 25.5

Water 18.6 7.3 5.3 16.3

Defoamer 0.6 0.6 0.6 0.6

Wetting 0.7 0.7 0.7 0.7 agent 1

Wetting 0.3 0.3 0.3 0.3 agent 2

Wax 2.0 2.0 2.0 2.0 emulsion

PU pigment 5.6 5.6 5.6 5.6

Matting 3.2 3.2 3.2 3.2 agent

Sub-Total 86.4 86.4 86.4 86.4 "A"

PIC I 13.6 13.6 13.6 13.6

Total 100 100 100 100 "A+B"

% solids 47 47 47 47

Viscosity 22" 24" 30" 21 " "A"

Viscosity 41 " 54" 84" 30" "A+B"

W at e r t o 1 -2% 5%

adjust

viscosity

"A+B" Example 9: the formulations o example 8 were tested according to DIN EN 12720 and evaluated immediately and after three days. Substrates used were sanded melamine foil (for chemical resistances), glass panels (for hardness) and black plexiglass (for gloss and scratch determinations). The formulations were mixed manually and applied using 200 microns wet application. Ageing was performed for 16 hours at 50 °C for me la mine and glass panels and for 24 hours at room temperature for the plexiglass panels. The results are stated in the following table.

Example 10: the formulations of example 8 were tested for their popping limit on glass and wood substrates. The popping limit is understood as the dry film thickness up to which no disturbances in the coating film due to gas bubbles can be observed. If the coating is applied with a dry film thickness above the popping limit, disturbances in the coating film due to gas bubbles occur. Specimens were aged at 23 °C and 50% relative humidity. The results are stated in the following table.

Example 11 : the formulations of example 8 were tested for their ability to confer a natural touch- feeling to coated wood surfaces. The coatings were applied with a spray gun to the stated amount of 300 g/m² and aged at 23 °C and 50% relative humidity. An experienced technician then tested the haptic impression and graded it on a scale of 1 to 5, wherein a value 1 means a very artificial impression and 5 means a very natural impression. The results are stated in the following table.

Invention 1 Invention 2 Invention 3 Invention 4

300 g/m² 5 4-5 4-5 5

Remarks - - - -

Claims

I . Use of an aqueous preparation for the coating of wood surfaces, characterized in that the aqueous preparation comprises: a hydroxyl-functional polyacrylate dispersion, - a polyurethane dispersion, an at least partially hydrophilicized polyisocyanate and

2. Use according to claim 1 , characterized in that the aqueous preparation comprises:

> 20 weight-% to < 50 weight-% a hydroxyl-functional polyacrylate dispersion,

> 20 weight-% to < 50 weight-% a polyurethane dispersion,

> 0 weight-% to < 10 weight-% of a matting agent, wherein the combined hydroxyl content of the hydroxyl-functional polyacrylate dispersion and the polyurethane dispersion is > 1% to < 12 %.

3. Use according to claim 1 or 2, wherein combined hydroxyl content of the hydroxyl-functional polyacrylate dispersion and the polyurethane dispersion is > 1 % to < 10 %.

4. Use according to claim 1 or 2, wherein the polyurethane dispersion comprises a hydroxyl- functional polyurethane.

5. Use according to claim 1 or 2, wherein the hydroxyl-functional polyacrylate dispersion is an aqueous secondary copolymer dispersion comprising a copolymer (P) synthesized from a mixture of free-radically polymerizable monomers (M) comprising Ml, M2, M3, and, optionally, M4, M5 and M6, wherein (Ml) are cycloaliphatic esters of acrylic and/ or methylacrylic acid, (M2) are vinyl esters of branched, aliphatic carboxylic acids of the formula

wherein \V and R are saturated alkyl groups containing together 6, 7, or 8 carbon atoms,

(M5) are hydroxyl- and carboxyl-free (meth)acryiic esters having CI to CI 8 hydrocarbon radicals in the alcohol moiety and/or vinyl aromatics, and

6. Use according to claim I or 2, wherein the polyur ethane dispersion comprises:

I) hydroxyl-free polyurethanes and/or poiyurethane-ureas and/or

II) ionically modified, hydroxyl- and/or amino-containing polyurethanes and/ or polyurethane-ureas, and III) at least one crosslinker, wherein the components (I) and (II) comprise polycarbonate polyols which have at least 25% by weight of 1 ,4-butanediol as a synthesis component.

7. Use according to claim 6, wherein the polycarbonate polyols contain > 60% to < 100% by weight of 1,4-butanediol and > 0% to < 40% by weight of 1,6-hexandiol as synthesis components, the sum of 1 ,4-butanediol and 1 ,6-hexanediol adding up to < 100% by weight.

8. Use according to claim 6, wherein the polycarbonate polyols have an average hydroxyl functionality of > 1.6 to < 4.

9. Use according to claim 1 , wherein the at least partially hydrophilicized polyisocyanate is an aliphatic polyisocyanate.

10. Use according to claim 9, wherein the at least partially hydrophilicized polyisocyanate is based on 1,6-hexamethylene diisocyanate.

11. A method of producing a coated wood surface, comprising the step of coating a wood surface with an aqueous preparation whose use has been recited in one or more of claims 1 to 10.

12. A coated wood surface comprising an aqueous preparation whose use has been recited in one or more of claims 1 to 10.