WO2017158015A1

WO2017158015A1 - Aqueous coating composition

Info

Publication number: WO2017158015A1
Application number: PCT/EP2017/056111
Authority: WO
Inventors: Saskia Carolien Van Der Slot; Gerardus Cornelis Overbeek; Ronald Tennebroek; Alexander Wilhelmus Martinus Cornelis Donders; Frank Vaes
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: CN108779200A; EP3430062A1; WO2017158016A1

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, whereby 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 selected from the group consisting of hydrazine, hydrazine derivative and any mixture thereof, wherein the isocyanate-terminated polyurethane prepolymer is obtained by the reaction of at least one polyol with at least one polyisocyanate, whereby at least 30 wt.% of the polyisocyanate is aromatic polyisocyanate, (ii) the polyurethane-vinyl polymer hybrid is ketone functional and hydrazide (- C=ONHNH2) functional whereby the molar ratio of hydrazide groups to ketone groups in the polyurethane-vinyl polymer hybrid is from 0.05:1 to 1.5:1, (iii) the weight ratio of the polyurethane to the vinyl polymer in the polyurethane- vinyl polymer hybrid ranges from 90:10 to 35:65, and (iv) the amount of free hydrazine in the aqueous coating composition is at most 50 ppm.

Description

AQUEOUS COATING COMPOSITION

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

Over the years, the need for highly resistant coatings for wood applications, especially parquet, furniture and kitchen cabinets, is more and more growing. Such coatings must be chemically resistant, such as resistance to water and ethanol. Especially in flooring applications the resistance against several ethanol containing cleaning agents and ethanol is important. For furniture and kitchen cabinets, besides resistance against aggressive cleaning agents also a high resistance level against ethanol containing beverages/liquids is important. The coatings also need to have good mechanical properties such as black marking resistance and resistance to damage. 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. In general, polyurethane based binders have shown to combine good mechanical and chemical resistances. Therefore, polyurethane dispersions are well known in the coating industry. A major application for such coatings is as clear coatings for wood flooring.

Methods for preparing polyurethanes are known in the art and are described in for example the Polyurethane Handbook 2^nd Edition, a Carl Hanser publication, 1994, by G. Oertel. The polyurethane (A) may be prepared in a

conventional manner by reacting at least one organic polyisocyanate with at least one isocyanate-reactive component by methods well known in the prior art. Isocyanate- reactive groups include -OH, -SH, -NH-, and -NH2. Usually an isocyanate-terminated polyurethane prepolymer is first formed which is then chain extended with an active hydrogen containing compound. Often hydrazine or hydrazine derivatives as chain extending compound are applied, due to their high reactivity towards the isocyanate group and positive impact on the final performance level. However, in view of the toxicological profile of hydrazine, the amount of free hydrazine in the final coating compositions must be very low.

Besides the demand for continuous improvement on the

performance, legislation is changing and a large range of environmental related labels is available nowadays. The requirements of these eco-labels are getting more and more severe. As a result, raw materials often used for performance improvement are no longer possible to use in coating systems in order to fulfill the requirements for these environmental related labels (such as for example Eco-label).

Polyurethane 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, such as methylethyl ketone and/or acetone, 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 a polyurethane system, the Black Heel Mark Resistance (BHMR) is reduced to a non-acceptable level.

Introduction of Schiff base crosslinking using carbonyl functionality (such as ketone functionality) in either the polyurethane, vinyl polymer or both the polyurethane and vinyl polymer phases of the polyurethane-vinyl polymer hybrid in combination with adipic dihydrazide ADH has shown to significantly improve the mechanical properties of an urethane acrylic system, however the chemical resistances against water and ethanol still are insufficient when using ADH as crosslinker. In addition, the use of low molecular weight hydrazide crosslinkers such as adipic dihydrazide is under pressure from environmental point of view, and its use may result in difficulties to comply to various environmental related labels, such as for example Eco-label. Moreover, it has been found that the use of adipic dihydrazide in coating compositions may result in loss of warm wood coloration when applying the coating composition to a wooden substrate, in particular an oak substrate.

The object of the present invention is to provide aqueous coating compositions of polyurethane-vinyl polymer hybrid particles, which compositions contain low free hydrazine levels and which compositions can result in coatings with good chemical resistance, in particular water and ethanol resistance, in combination with good mechanical properties, in particular 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, whereby 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 selected from the group consisting of hydrazine, hydrazine derivative and any mixture thereof, wherein the isocyanate-terminated polyurethane prepolymer is obtained by the reaction of at least one polyol with at least one polyisocyanate, whereby at least 30 wt.% of the polyisocyanate is aromatic polyisocyanate,

(ii) the polyurethane-vinyl polymer hybrid is ketone functional and hydrazide (-C=ONHNH2) functional whereby the molar ratio of hydrazide end groups to ketone groups in the polyurethane-vinyl polymer hybrid is from 1 .5:1 to 0.05:1 ,

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

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

(iv) the amount of free hydrazine in the aqueous coating composition is at most 50 ppm (relative to the aqueous coating composition).

It has surprisingly been found that such a combination of good chemical resistance and good mechanical properties can be obtained with the aqueous coating compositions according to the invention. An additional advantage of the present invention is that when coating a wooden substrate, in particular an oak substrate, with the aqueous coating compositions according to the invention a warm wood coloration can be obtained.

US5141983 describes aqueous coating compositions obtained by polymerizing radical-polymerizable acrylic monomers containing a carbonyl group (ketone or aldehyde) or an amido group containing monomer in the presence of an aqueous polyurethane resin obtained by subjecting neutralized urethane prepolymer to chain extension with hydrazine or a hydrazine derivative. The preparation of the polyurethane is effected in the presence of methyl ethyl ketone as organic solvent, which may be removed as necessary. It has been found that the coating compositions of US5141983 result in coatings with poor ethanol resistance and also poor black heel marking resistance. It has furthermore been found that an additional disadvantage of the use of ketone functional solvents (such as methyl ethyl ketone) in the preparation of the polyurethane is that it results in unacceptable high free hydrazine levels.

WO2012173032 describes aqueous inkjet recording ink for lamination, which contains (a) a pigment and (b) an aqueous resin that contains an aqueous polyurethane resin (b-1 ) that is produced through a process wherein a chain extender composed of a hydrazine derivative is reacted and an acrylic copolymer (b-2) that contains a carbonyl group or an amide group. 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 hydrazide (-C=ONHNH2) functional whereby the molar ratio of hydrazide groups to ketone groups in the polyurethane-vinyl polymer hybrid is in the range from 0.05:1 to 1 .5:1. Preferably, the molar ratio of hydrazide groups to ketone groups in the polyurethane-vinyl polymer hybrid is in the range from 0.05:1 to 0.9:1 , more preferably in the range from 0.05:1 to 0.8:1 and even more preferably in the range from 0.07:1 to 0.7:1 . The molar ratio of hydrazide groups to ketone groups is preferably at least 0.1 , more preferably at least 0.15. Most preferably the hydrazide group is a semi carbazide group

(-NHC=ONHNH2).

Preferably, the amount of hydrazide end groups in the polyurethane- vinyl polymer hybrid is from 10 to 500 mmol of hydrazide groups per 1000 g polyurethane-vinyl polymer hybrid, preferably from 15 to 250 mmol per 1000 g polyurethane-vinyl polymer hybrid, more preferably from 20 to 150 mmol per 1000 g polyurethane-vinyl polymer hybrid. As used herein, the amounts of hydrazide groups and 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. For the sake of clarity, the hydrazide groups from compounds added after preparation of the polyurethane-vinyl polymer hybrid, such as for example the hydrazide groups from adipic dihydrazide (being a separate crosslinking agent) are not to be taking into account when determining the amount of hydrazide groups in the polyurethane-vinyl polymer hybrid.

The aqueous coating composition according to the invention comprises dispersed polyurethane-vinyl polymer hybrid particles whereby the polyurethane-vinyl polymer hybrid is ketone functional. The ketone groups may be present in the polyurethane and/or the vinyl polymer of the polyurethane-vinyl polymer hybrid. Preferably, ketone groups are present in at least the vinyl polymer of the polyurethane-vinyl polymer hybrid. 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 optionally (but preferably as described above) 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 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 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, preferably 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 methyl methacrylate and/or styrene. Even 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 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 of the polyurethane-vinyl polymer hybrid particles 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 selected from the group consisting of hydrazine, hydrazine derivative and any mixture thereof. The isocyanate-terminated polyurethane prepolymer is obtained by the reaction of at least one polyol with at least one polyisocyanate, whereby at least 30 wt.% of the total amount of polyisocyanate used in the preparation of the polyurethane is aromatic polyisocyanate, preferably at least 50 wt.%, more preferably at least 70 wt.% and even more preferably at least 90 wt.% of the polyisocyanate is aromatic polyisocyanate and even more preferably the polyisocyanate is aromatic polyisocyanate.

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 polyol used to prepare the isocyanate-terminated polyurethane prepolymer usually comprises a polyol containing ionic and/or potentially ionic water- dispersing groups. The amount of polyol containing ionic or potentially ionic water- dispersing groups relative to the total amount of components used to prepare the polyurethane is from 1 to 15 wt.%, preferably from 3 to 12 wt.% and even more preferably from 4 to 10 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 N,N- 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⁺, Nh 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 0.7 to 5.0, more preferably from 0.8 to 3.0 and even more preferably from 0.85 to 1 .2.

The polyol used to prepare the isocyanate-terminated polyurethane prepolymer usually further comprises another polyol. The amount of other polyol relative to the total amount of components used to prepare the polyurethane is from 30 to 79 wt.%, preferably from 45 to 75 wt.% and even more preferably from 50 to 70 wt.%. 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.

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 selected from the group consisting of hydrazine, hydrazine derivative and any mixture thereof and 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. 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 from 1 .0 to 1.25, more preferably from 1 .05 to 1 .2.

The amount of free hydrazine present in the aqueous coating composition of the present invention is preferably at most 15 ppm, more preferably at most 10 ppm, more preferably at most 5 ppm and even more preferably at most 3 ppm. As used herein, the amount of free hydrazine in the aqueous coating composition is determined as described herein.

The polyurethane and the vinyl polymer in the hybrid particles 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. In a preferred embodiment of the present invention, the aqueous coating composition is substantially free of a dihydrazide functional compound

(containing two hydrazide groups (-C=ONHNH2)) with a molar mass below 1000 g/mole, more preferably the aqueous coating composition is substantially free of a dihydrazide functional compound with a molar mass below 500 g/mole, even more preferably the aqueous coating composition is substantially free of a dihydrazide functional compound with a molar mass below 250 g/mole, especially preferably the aqueous coating composition is substantially free of adipic dihydrazide. Substantially free means that the aqueous coating composition contains less than 1000 ppm, preferably less than 800 ppm, more preferably less than 600 ppm, more preferably less than 400 ppm, more preferably less than 200 ppm of the dihydrazide functional compound (relative to the aqueous coating composition). In a more preferred embodiment of the present invention, the aqueous coating composition is free of a dihydrazide functional compound (containing two hydrazide groups (-C=ONHNH2)) with a molar mass below 1000 g/mole, more preferably the aqueous coating composition is free of a dihydrazide functional compound with a molar mass below 500 g/mole, even more preferably the aqueous coating composition is free of a dihydrazide functional compound with a molar mass below 250 g/mole, especially preferably the aqueous coating composition is free of adipic dihydrazide.

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 from 25 to 40 wt.% (relative to the aqueous coating composition).

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 the invention comprising the following steps:

I. preparing an isocyanate-terminated polyurethane prepolymer by

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

(a) from 20 to 60 wt.% of at least one organic polyisocyanate ,

whereby at least 30 wt.% of the polyisocyanate is aromatic polyisocyanate

(b) from 1 to 15 wt.%, preferably from 3 to 12 wt.% and even more preferably from 4 to 10 wt% of an isocyanate-reactive polyol containing ionic and/or potentially ionic water-dispersing groups,

(c) from 30 to 79, preferably from 30 to 77 wt.% and even more preferably from 30 to 76 wt.% of at least one isocyanate-reactive polyol other than (b),

(d) optionally (but preferably) adding vinyl monomer in step I;

II. either blending the isocyanate-terminated polyurethane prepolymer with an aqueous phase comprising neutralization agent and chain extending compound selected from the group consisting of hydrazine, hydrazine derivative and any mixture thereof, 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 selected from the group consisting of hydrazine, hydrazine derivative and any mixture thereof;

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 III and the amount of vinyl monomer added in the process is 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 and whereby the amounts of components (a), (b), and (c) are given relative to the total amount of components used to prepare the polyurethane.

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.

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 selected from the group consisting of hydrazine, hydrazine derivative and any mixture thereof. 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 selected from the group consisting of hydrazine, hydrazine derivative and any mixture thereof.

Ketone containing solvents such as acetone and/or methyl ethyl ketone may be used in the process according to the invention for lowering the viscosity of the prepolymer to acceptable values. However, at least steps I and II of the process according to the invention are effected in the absence of ketone containing solvent such as acetone and/or methyl ethyl ketone since the ketone functional solvent also is reactive towards the preferred chain extension agent hydrazine and therefore leads to unacceptably high free hydrazine levels in the waterborne coating composition. The process for preparing the aqueous coating composition according to the invention is preferably effected in the absence of ketone containing solvent such as acetone and/or methyl ethyl ketone.

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, but may be applied.

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 -3 and results are as shown in Table 6.

Components and abbreviations used:

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

diphenylmethane diisocyanate available from Huntsman

Isophorone diisocyanate available from BASF UK ltd

Dimethylolpropionic acid available from Perstorp polyols

Ketone functional polyol ketone-functional polyester polyol PEC-205, 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- available from Eastman Chemical bv

Cyclohexanedimethanol

poly THF-1000 Polytetramethylene ether glycol, OH-number = 1 12.5 mg

KOH/g available from BASF

Catalyst Tin (II) dioctoaat available from Air Products

Amitol M21 Ν,Ν-Dimethylethanolamine available from Chemproha bv Hydrazine Hydrazine hydrate available from Arkema

Defoamer Tegofomex 805, available from Evonik Degussa

Inhibitor 2,6-Di-tert-butyl-4-methylphenol available from Avecia Inc

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 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 -C5

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

C 1 C2 C3 C4

Urethane Prepolymer synthesis

1 Rubinate 9279 72.83 72.00 73.42

2 Isophorone diisocyanate 74.39

3 Dimethylol propionic acid 16.26 16.39 16.38 16.18

4 poly-tetrahydrofuran 1000 64.00 53.94 64.50 61 .81

5 Ketone functional polyol 12.06

6 1 ,4-cyclohexanedimethanol 6.27 6.32 6.32 6.25

7 Methyl methacrylate 47.81 48.21 48.19 47.59

8 Styrene 9.71 9.79 9.79 9.67

9 Inhibitor 0.12 0.12 0.10 0.10

10 catalyst 0.06

Dispersion process

11 Water 623.41 617.85 626.43 625.26

12 Disponyl AFX 4030 15.96 16.10 16.08 15.88

13 Defoamer 1 .28 1 .29 1 .29 1 .27

14 hydrazine (64%) 5.04 4.22 6.91 7.60

15 Amitol M21 1 1 .03 1 1 .14 1 1 .62 10.98

Vinyl polymerisation process

16 Methyl methacrylate 58.55

17 Styrene 71 .57 60.04 1 1 .62 58.92

18 Butylacrylate 30.28 31 .37 28.97 30.78

19 Diacetone acrylic amide 12.10 0.72 1 1 .87

20 t-Butylhydroxy peroxide (70%) 0.52 0.32 0.37 0.52

21 isoascorbic acid (100%) 0.32 0.21 0.27 0.32

22 Libratex AS-10 16.58 16.74 16.74 16.51

23 Fe(lll)(EDTA) (1 %) 2.07 2.09 0.79 2.07

24 Preservative solution 5.00 5.08 1 .51 1 .99

25 adipic acid dihydrazide 2.63 Procedure for obtaining the aqueous coating compositions of Comparative

Experiments C1 -C4

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 keep the temperature of the reactor vessel for 2 hours at 87°C. After 2 hours the weight% NCO was determined from the urethane prepolymer reaction mixture using titration.

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 22 to the dispersion reactor followed by 16, 17, 18 and 19. After 60 minutes add 20 and 23 followed by the addition of 21 over a period of 45 minutes. Cool the reaction mixture to room temperature, and add 24 and 25.

Table 2: Recipes for obtaining the aqueous coating composition of Comparative Experiments C5

Procedure for obtaining the aqueous coating compositions of Comparative Experiment C5

Add 1 and 6 to a reactor vessel with stirring equipment and mix. Add a mixture of 2, 3, 4 and 5 to the reactor vessel. After addition, keep the temperature of the reactor vessel for 2 hours at 58°C. After 2 hours the weight% NCO was determined from the urethane prepolymer reaction mixture using titration.

Prepare in a dispersion reactor a mixture of 7, 8, 9, 10 and 1 1. Add the urethane mixture from the reactor vessel to the dispersion reactor maintaining the temperature at 25°C. Charge 19 to the dispersion reactor followed by 12, 13, 14, 15 and 16. After 60 minutes add 20 and 17 followed by the addition of 18 over a period of 45 minutes. Cool the reaction mixture to room temperature, evaporate the acetone under reduced pressure and add 21 .

Examples 1 -4

Table 3: Recipes for obtaining the aqueous coating compositions of Examples 1 -4

Procedure for obtaining the aqueous coating compositions of Examples 1 -4

Add 1 , 6, 7, and 8 to a reactor vessel with stirring equipment and mix. Add a mixture of 2, 3, 4 and 5 to the reactor vessel. After addition, remain the temperature of the reactor vessel for 2 hours at 87°C. After 2 hours the weight% NCO was determined from the reaction mixture using titration.

Prepare in a dispersion reactor a mixture of 9, 10, 1 1 , 12 and 13. Add the urethane mixture to the dispersion reactor maintaining the temperature at 25°C. Charge 19 to the dispersion reactor followed by 14, 15 and 16. After 60 minutes add 20 and 17 followed by the addition of 18 over a period of 45 minutes. Cool the reaction mixture to room temperature and add 21 . The following formulae were used for calculating the characteristics as reported in Table 4 and 5.

Calculation of mmol -NCO end groups present in the isocyanate-terminated

polyurethane prepolymer =

(((Weight reaction mixture prepolymer synthesis in g)^*(wt.%NCO/100))/eq. weight NCO (=42))^*1000.

Calculation of mmol -NH2 end groups (present in the chain extender) added to the isocyanate-terminated polyurethane prepolymer =

((Weight chain extender in g)/(molecular weight chain extender))^* number of functional groups in the chain extender^*1000.

Calculation of mmol hydrazide groups present in the polyurethane-vinyl polymer hybrid (mmol -NH2 end groups (present in the chain extender) added to the isocyanate- terminated polyurethane prepolymer)- (mmol -NCO end groups present in the isocyanate-terminated polyurethane prepolymer).

Calculation of mmol keton groups present in the polyurethane-vinyl polymer hybrid = ((Weight ketone functional raw material in g)/(molecular weight ketone functional raw material))^*number of ketone groups per molecule^*1000

Calculation of mmol hydrazide end groups/kg polyurethane-vinyl polymer hybrid = (mmol hydrazide groups present in the polyurethane-vinyl polymer hybrid)/

(weight 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/kg polyurethane-vinyl polymer hybrid =

(mmol ketone groups present in the polyurethane-vinyl polymer hybrid)/(weight polyurethane-vinyl polymer hybrid weight in kg)

Calculation of weight ratio of polyurethane to vinyl polymer in the polyurethane-vinyl polymer hybrid =

(Total weight monomers, chain extending compound and neutralizing agent to prepare the polyurethane in g)/(weight vinyl monomers in g)

Calculations for example 1

Calculation of mmol -NCO end groups present in the isocyanate-terminated polyurethane prepolymer

Weight reaction mixture prepolymer synthesis = 216.41 g

Wt.%NCO = 4.02%

Equivalent weight NCO = 42 g/mol

((216.41 ^* 0.0402)/42)^*1000 = 207 mmol Calculation of mmol -NH2 end groups (present in the chain extender) added to the isocyanate-terminated polyurethane prepolymer

Weight chain extender = 5.44 ^* 0.64 =3.48 g

Molecular weight chain extender = 32.04 g/mol

Number of functional groups in the chain extender = 2

((5.44^*0.64 )/32.04)^*2^*1000= 217 mmol

Calculation of mmol hydrazide end groups present in the polyurethane-vinyl polymer hybrid

217 - 207 = 10 mmol Calculation of mmol ketone groups present in the polyurethane-vinyl polymer hybrid Weight ketone functional raw material = 1 1 .89 g

Molecular weight ketone functional raw material = 169.22 g/mol

Number of ketone groups per molecule = 1

(1 1.89/169.22 )^*1 ^* 1000 = 70 mmol

Calculation of mmol hydrazide groups/kg polyurethane-vinyl polymer hybrid = Weight polyurethane vinyl polymer hybrid = 0.333 kg

mmol hydrazide groups 10 mmol

10/0.333= 30 mmol/kg

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

Weight polyurethane vinyl polymer hybrid = 0.333 kg

mmol ketone groups 70 mmol

70/0.333 = 210 mmol

Total weight monomers, chain extending compound and neutralizing agent to prepare the polyurethane= 173.42 g

Weight vinyl monomers = 159.13 g

173.42/159.13 = 52/48

Table 4: Further characterization of the aqueous coating compositions of Comparative Experiments C1 -C5.

C1 C2 C3 C4 C5 wt.% NCO 4.43 3.66 4.43 4.22 4.63

Degree of chain extension 0.88 0.88 1 .20 1 .4 1 .05 mmol -NCO end groups polyurethane

229 191 231 217 221 prepolymer

mmol -NH2 end groups from hydrazine 201 169 276 304 232 mmol hydrazide end groups after chain

0 0 45 87 10 extension

mmol ketone groups 0 92 4 70 93

Calculated solids content of the polymer

33.30 35.4 33.43 33.33 35.33 in the coating composition (wt.%) mmol hydrazide end group/kg

n.a. n.a. 136 260 31 polyurethane-vinyl polymer hybrid

mmol ketone fgroup/kg polyurethane- n.a. 275 13 210 275 vinyl polymer hybrid

Molar ratio hydrazide /ketone in the

n.a. n.a. 10.46 1 .24 0.1 1 polyurethane-vinyl polymer hybrid

Weight ratio polyurethane to vinyl

polymer in the polyurethane-vinyl 52/48 52/48 53/47 52/48 52/48 polymer hybrid

Table 5: Further characterization of the aqueous coating compositions of Examples 1 -4

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 stain resistances

The stain resistance is tested by placing cotton pads on the coating surface. Soak each pad with the appropriate chemical (water, 48% ethanol in water or coffee) and cover with a petri dish. The spots are allowed to soak for 16 hours. After 16 hours the petri dishes and cotton pads are removed. The spots are examined for damage and rated after recovery for 4 hours. 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 damaged,

o Rate the coating for scuff damage.

Determination of free hydrazine content

The method for measuring the free hydrazine content method is based on a combined dilution/derivatisation step of hydrazine with acetone. The large excess of acetone ensures rapid reaction and stability of the derivate. The acetone azine- derivate is formed instantaneous, no catalyst or heating is needed. The derivate is analyzed by full evaporation Headspace Gas Chromatography (HSGC) followed by detection with a Flame Ionization Detector (FID) while making use of n-butylacetate as internal standard.

Internal standard solution: 10 mg butylacetate and dilute it with 100 ml acetone Sample preparation: 250 mg of polymer dispersion is added to a GC vial. Add 1 .2 g of internal standard. Transfer 35 μΙ to a headspace vial.

Sample is measured on a gas chromatograph equipped with

• Carrier gas He or h

• Head Space auto sampler

• Programmed Temperature Vaporisation injection port (PTV)

• Column:

o SGE BP-20, 25 m x 0.25 mm i.d., df 1 .Ομηη or similar

• Flame Ionization Detector

The quantification limit of this method is considered to be 3 ppm, the detection limit of this method is 0.5 ppm. The test results are listed in Table 6.

Table 6

The coating composition of comparative experiment C1 , in which a polyurethane-vinyl polymer hybrid is used, results in a coating having no mechanical properties. By introducing ketone functionality and crosslinking with adipic dihydrazide ADH

(comparative experiment C2), the mechanical properties are improved, but the stain resistance is poor and there is loss of warm wood coloration required for e.g. flooring applications. Comparative Experiments C3 shows that similar to the use of ADH, high amount of hydrazide endgroups result in poor ethanol resistance and also in poor mechanical properties and warm wood coloration is also not obtained. Comparative Experiment C4 shows that using aliphatic isocyanate results in poor ethanol resistance and also in poor mechanical properties and warm wood coloration is also not obtained. In Comparative Experiment C5 the residual level of free hydrazine is much too high. The coating compositions of Examples 1 -4 surprisingly combine mechanical properties, chemical resistance, wood coloration and compliance to environmental related paint labels.

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, whereby 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 selected from the group consisting of hydrazine, hydrazine derivative and any mixture thereof, wherein the isocyanate-terminated

polyurethane prepolymer is obtained by the reaction of at least one polyol with at least one polyisocyanate, whereby at least 30 wt.% of the polyisocyanate is aromatic polyisocyanate,

(ii) the polyurethane-vinyl polymer hybrid is ketone functional and hydrazide (-C=ONHNH2) functional whereby the molar ratio of hydrazide groups to ketone groups in the polyurethane-vinyl polymer hybrid is from 0.05:1 to 1 .5:1 ,

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

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

(iv) the amount of free hydrazine in the aqueous coating composition is at most 50 ppm.

The aqueous coating composition according to claim 1 , wherein the amount of hydrazide groups is from 15 to 250 mmol per 1000 g polyurethane-vinyl polymer hybrid.

The aqueous coating composition according to any of the preceding claims, wherein the molar ratio of hydrazide groups to ketone groups is from 0.05:1 to 0.9:1 .

The aqueous coating composition according to claim 1 or 2, wherein the molar ratio of hydrazide groups to ketone groups is from 0.07:1 to 0.7:1 .

The aqueous coating composition according to any of the preceding claims, wherein the hydrazide groups (-C=ONHNH2) are semicarbazide (- NHC=ONHNH2) groups.

The aqueous coating composition according to any of the preceding claims, wherein the polyurethane and/or the vinyl polymer contains ketone groups. The aqueous coating composition according to any of the preceding claims, wherein at least the vinyl polymer contains ketone groups.

The aqueous coating composition according to any of the preceding claims, wherein the ketone groups are introduced in at least the vinyl polymer by copolymerizing of diacetone acrylamide.

The aqueous coating composition according to any of the preceding claims, wherein the 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 aqueous coating composition according to any of the preceding claims, wherein the active-hydrogen containing chain extending compound is selected from the group consisting of hydrazine, ethylene-1 ,2-dihydrazine, propylene-

1 ,3-dihydrazine, butylene-1 ,4-dihydrazine, and any mixture thereof

The aqueous coating composition according to any of claims 1 -9, wherein the active-hydrogen containing chain extending compound is hydrazine.

The aqueous coating composition according to any of the preceding claims, wherein the amount of free hydrazine in the aqueous coating composition is at most 15 ppm.

The aqueous coating composition according to any of claims 1 -1 1 , wherein the amount of free hydrazine in the aqueous coating composition is at most 10 ppm.

The aqueous coating composition according to any of claims 1 -1 1 , wherein the amount of free hydrazine in the aqueous coating composition is at most 5 ppm.

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 claims 1 -14, wherein the weight ratio of the polyurethane to the vinyl polymer in the polyurethane- vinyl polymer hybrid ranges from 65:35 to 45:55.

The aqueous coating composition according to any of the preceding claims, wherein the aqueous coating composition is free of adipic dihydrazide.

An aqueous coating composition according to any of the preceding claims, wherein the aqueous coating composition comprises less than 5 wt.% of co- solvent. An aqueous coating composition according to any of claims 1 -17,

wherein the aqueous coating composition comprises less than 2 wt.% of co- solvent by weight of solids.

An 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) and (c):

(a) from 20 to 60 wt.% of at least one organic polyisocyanate , whereby at least 30 wt.% of the polyisocyanate is aromatic polyisocyanate

(b) from 1 to 15 wt.% of an isocyanate-reactive polyol containing ionic and/or potentially ionic water-dispersing groups,

(c) from 30 to 79 wt.% of at least one isocyanate-reactive polyol other than (b),

(d) optionally adding vinyl monomer in step I;

II. either blending the isocyanate-terminated polyurethane prepolymer with an aqueous phase comprising neutralization agent and chain extending compound selected from the group consisting of hydrazine, hydrazine derivative and any mixture thereof, 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 selected from the group consisting of hydrazine, hydrazine derivative and any mixture thereof;

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 III and the amount of vinyl monomer added in the process is 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 and whereby the amounts of components (a), (b), and (c) are given relative to the total amount of components used to prepare the polyurethane.

A process according to claim 21 , wherein the process is effected in the absence of ketone containing solvent.

A substrate having a coating obtained by (i) applying an aqueous coating composition according to any one of claims 1 to 20 or obtained according to claim 21 or 22 to a substrate and (ii) drying the aqueous coating composition by evaporation of volatiles.

A substrate according to claim 23, wherein the substrate is selected from the group consisting of wood, metal, plastic, concrete, glass and any combination thereof.

A substrate according to claim 23, wherein the substrate is oak.