One-component aqueous coating composition

Abstract

A one-component waterborne coating composition comprising: a) an aqueous dispersion of polymer particles, which polymer particles comprise an anionic-stabilized copolymer having a Mw of at least 100,000 g / mol and self cross- linking functionality, wherein the copolymer is an acrylic copolymer, an acrylic-vinyl copolymer, or a polyurethane vinyl-acrylic copolymer; and b) an organosilane; wherein: the organosilane is unreactive towards carboxylic acid functionality; and the organosilane is present in an amount of at least 5 wt.% of the total solids of the coating composition; and a coated substrate comprising a substrate and a coating, which coating is obtained by applying said coating composition to the substrate and allowing the coating composition to dry.

Description

[0001] ONE-COMPONENT AQUEOUS COATING COMPOSITION

[0002] Field of the Invention

[0003] The present invention relates to a one-component aqueous coating composition. More specifically, it relates to a one-component waterborne coating composition comprising an aqueous acrylic polymer dispersion having improved chemical and mechanical properties.

[0004] Background

[0005] Aqueous coating compositions are well-known for application to many industrial substrates including ceramics, plastics, wood and metal. Articles such as wood trim, window frames and furniture are commonly coated with waterborne coatings. The cured coating must meet certain performance requirements, including hardness, adhesion, water and chemical resistance.

[0006] Aqueous polymer dispersions are commonly used as resins for paints and coatings. They are desirable because, compared with solvent-based paints and coatings, the resulting products have low volatile organic compound (VOC) content which is beneficial for environmental and health reasons. Moreover, legislation for these reasons continues to limit the permissible amount of VOC in products. Common aqueous polymer dispersions are those of acrylic or methacrylic copolymers, i.e. copolymers of acrylic monomers with other monomers, for example vinyl or styrene monomers or with polyurethane. The polymer particles are commonly multi-phase, for example in the form of core-shell wherein a core polymer has a different composition and properties to a shell polymer. For example, a shell polymer may have a lower molecular weight, lower Tgand a higher acid value than a core polymer.

[0007] Typically, when high chemical resistance and / or mechanical resistance are desired, the polymer is cross-linked. This is achieved using a cross-linking component, for example a polyisocyanate or carbodiimide. Because the cross-linking component is reactive with the polymer and / or water, the coating composition is provided in two parts which are mixed immediately prior to application; one containing an aqueous polymer dispersion and the other containing the cross-linking component, or “hardener”. Such a coating composition is known as a two component, 2 pack, or 2K coating composition. Common waterborne 2K systems are epoxy-amine, polyol-isocyanate and acidfunctional polymers with carbodiimide. A 2K aqueous coating system wherein the cross-linking component comprises a carbodiimide and an organofunctional alkoxysilane cross-linking component is known from WO2022 / 207135A1 , in which increased chemical resistance is attributed to the organofunctional alkoxysilane. A major drawback, however, of 2K systems is the added step of mixing the components prior to application within the correct conditions, amounts and timeframe.

[0008] One-component (1 K) waterborne systems are preferred over 2K systems for ease of use. However, 1 K aqueous polymer dispersions typically possess poorer chemical and physical properties than 2K systems, which is a feature of less cross-linking and may require high baking temperature. In order to overcome this, self cross-linking 1 K systems can be produced by adding a cross-linker to the 1 K system or using a reactive monomer in the polymerization. One of the most common 1 K self cross-linking waterborne systems is an acrylate polymer having a carbonyl-hydrazide cross-link, for example a ketone-dihydrazine cross-link, such as described in GB2503700A. The DAAM-ADH cross-link is a particular example. The chemical resistance of self-linking 1 K systems is however still less than that of comparable 2K systems and it is therefore desired to be improved.

[0009] A drawback of self cross-linking 1 K systems is that the higher level of addition of crosslinker tends to produce polymer dispersions having a have a lower storage stability (or shorter shelf-life) as the cross-linker may react with the polymer particles leading to gelling or setting. Gelling times of self cross-linking 1 K systems of weeks or days, or even immediate setting, have been reported.

[0010] It is known to add silane functionality to a polymer in low amounts by including an unsaturated silane monomer in the polymerization reaction. For example, EP2246403A1 and JP2002097368A2 describe polymers comprising alkoxysilane monomers. W02005 / 007715A1 describes incorporating low quantities of vinylethoxysilane into a (meth)acrylate monomer, while recognizing the short shelf-life of 1K waterborne compositions comprising alkoxysilane comonomers. US2020 / 024460A1 describes vinyl silane monomers as examples of adhesion promoting ethylenically unsaturated monomers. Typically, when added in amounts of 0.5 to 1 wt.% such organosilanes act effectively to promote adhesion to a substrate, without significantly reducing shelf-life, i.e. maintaining time to transport and store a product. However, organosilanes provide little cross-linking when dried at ambient temperatures. Larger quantities of organosilanes are not typically added because they cause instability, for example gelling, severe reduction of shelf-life, and in any case do not further improve adhesion.

[0011] Organosilanes are also known as highly reactive cross-linkers in 1K waterborne coating compositions. An example of a highly reactive organosilane cross-linker is given in US2007 / 0286959A1. It describes a coating composition for medical applications, which comprises a cross-linkable urethane polymer and an epoxy-silane cross-linker. Another example of an epoxy-silane cross-linker is provided in WO2005 / 121595A2 which describes a polymer dispersion, wherein an unsaturated cross-linking group is added to the polymer by reaction with an acid group. A secondary cross-linker and an additional cross-linker, for example an alkoxysilane, may be used.

[0012] Accordingly, there is a need for a 1 K waterborne coating composition which has improved chemical resistance and physical properties and which also has a long pot life.

[0013] Summary of the invention

[0014] Accordingly, in a first embodiment the present invention provides a one-component waterborne coating composition comprising: a) an aqueous dispersion of polymer particles, which polymer particles comprise an anionic-stabilized copolymer having a Mwof at least 100,000 g / mol and self crosslinking functionality, wherein the copolymer is an acrylic copolymer, an acrylic-vinyl copolymer, or a polyurethane vinyl-acrylic copolymer; and b) an organosilane; wherein: the organosilane is unreactive towards carboxylic acid functionality; and the organosilane is present in an amount of at least 5 wt.% of the total solids of the coating composition.

[0015] In a second embodiment the present invention provides a coated substrate comprising a substrate and a coating, which coating is obtained by applying a coating composition as defined herein to the substrate and allowing the coating composition to dry.

[0016] Detailed description

[0017] As used herein self cross-linking functionality means that the polymer particles comprise reactive groups capable of bonding to each other. The self cross-linking functionality may be by direct reaction between reactive groups in the polymer, or it may comprise a cross-linking oligomer which bonds to reactive groups in the polymer. The function of self cross-linking is to increase hardness of the coating resulting from the coating composition. In 1 K waterborne coating compositions, self cross-linking functionality typically leads to chemical reaction after application and water and solvent evaporation.

[0018] An organosilane is a silane comprising at least one organic group. It may comprise one, two, three or four organic groups. The organosilane is unreactive towards carboxylic acid functionality. The organic group is therefore unreactive towards carboxylic acid functionality. Reaction of an organosilane with a carboxylic acid group present on an acrylic copolymer would likely lead to gelling of the polymer dispersion. Moieties which are reactive to carboxylic acid group include epoxy groups, amine groups and isocyanate groups. The organosilane does not comprise any of an epoxy group, an amine group or an isocyanate group. Groups which are unreactive to carboxylic acid functionality include alkyl, alkoxy and mercapto groups.

[0019] As used herein total solids of the coating composition means the total of all solid components present in the coating composition, which explicitly excludes water and any solvents present. Total solids of the coating composition excluding water and any solvents present includes all components of the coating composition which remain when the coating is applied to a substrate and is dried. It therefore includes reactive diluents, cross-linkers and any additives, for example pigments and fillers, which do not evaporate from the coating composition during drying. Accordingly, wt.% of the total solids of the coating composition means the weight expressed as a percentage of the total weight of the coating composition excluding water and any solvents present. It therefore corresponds to the wt.% of the coating resulting from the dried coating composition.

[0020] The anionic-stabilized copolymer is an acrylic copolymer, an acrylic-vinyl copolymer, or a polyurethane vinyl-acrylic copolymer.

[0021] Acrylic copolymers are well known in the art and are also referred to as acrylics, acrylate polymer, polyacrylate, or acrylic resin. These polymers are known for their transparency, resistance to breakage, and elasticity and are commonly used in paints and coatings. An acrylic copolymer is a polymer obtainable by polymerization, typically emulsion polymerization, of monomers comprising a mono-ethylenically unsaturated acrylic monomer, for example methacrylate and acrylate (respectively derivatives of methacrylic acid and acrylic acid).

[0022] Methacrylate includes an optionally branched alkyl ester of a C1-12 alcohol and methacrylic acid, for example methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, propyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate; hydroxyalkyl methacrylate, for example hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate; and cycloalkyl methacrylate, for example isobornyl methacrylate or cyclohexyl methacrylate. Acrylate includes an optionally branched alkyl ester of a C1-12 alcohol and acrylic acid, for example methyl acrylate, ethyl acrylate, isopropyl acrylate, propyl acrylate, n-butyl acrylate, t-butyl acrylate, octyl acrylate, 2-ethylhexyl acrylate; hydroxyalkyl acrylate, for example hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4- hydroxybutyl acrylate; and cycloalkyl acrylate, for example isobornyl acrylate, or cyclohexyl acrylate.

[0023] The acrylic monomers may comprise a polar functional group, for example an acrylamide, alkyleneoxide or a hydroxy functional group. Examples of suitable monomers comprising a hydroxy functional group are hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate.

[0024] An acrylic copolymer may be prepared from a mixture of monomers comprising a polar functional group and monomers free of such polar functional group, such as for example a mixture of hydroxyethyl acrylate and methyl methacrylate. Methyl methacrylate, styrene, ethyl acrylate, n-butyl methacrylate and n-butyl acrylate are nonacid functional monomers. Methacrylic acid and / or acrylic acid are acid-functional monomers.

[0025] The copolymer may be a pure acrylic copolymer in the sense that the polymers do not comprise any monomers other than (meth)acrylic monomers. Alternatively, the copolymer may be an acrylic-vinyl copolymer. An acrylic-vinyl copolymer comprises at least one of the acrylic monomers described above and further at least one other vinyl monomer. Vinyl monomers are any monomers comprising a C=C double bond. Examples of vinyl monomers include styrene, vinyl ester, unsaturated halide, diene, heterocyclic vinyl compounds, alkyl esters of mono-ethylenically unsaturated dicarboxylic acids, vinyl amide and nitrile.

[0026] The acrylic-vinyl copolymer may comprise an acid-functional monomer, or a monomer bearing an acid-forming group, such as an anhydride, for example methacrylic anhydride or maleic anhydride, or an acid chloride. It may also have cross-linking functionality. Typically the acid-functional monomer is a carboxyl-functional acrylic monomer or other ethylenically unsaturated carboxyl bearing monomer, for example acrylic acid, methacrylic acid, maleic acid, itaconic acid or fumaric acid. A sulphonic acid-bearing monomer could also be used, for example styrene p-sulphonic acid (or correspondingly styrene p-sulphonyl chloride). An acid bearing monomer could be polymerised as the free acid or as a salt, for example the ammonium or alkali metal salt of ethylmethacrylate-2-sulphonic acid or 2-acrylamido-2-methylpropane sulphonic acid, or the corresponding free acids. Acid functional monomers can have cross-linking functionality. For example carboxylic acids can act as cross-linkers. Suitable examples of aqueous dispersions of acrylic-vinyl copolymers include Setaqua® 6756 (Allnex) and Neocryl® XK-98 (Covestro).

[0027] Styrene includes styrene itself, a-methlystyrene, o-, m- and p-methylstyrene, o-, m- and p-ethylstyrene, p-chlorostyrene and p-bromostyrene and t-butyl styrene. Vinyl ester includes vinyl acetate, vinyl alkanoate, vinyl propionate, vinyl laurate, vinyl esters of VersaticTM (Hexion) acids such as VeoVaTM 9 (Hexion) and neodecanoic acid (VeoVaTM 10 (Hexion)). Alkyl esters of mono-ethylenically unsaturated dicarboxylic acids include di-n-butyl maleate and di-n-butyl fumarate. Unsaturated halide includes vinyl halide, for example vinyl chloride and vinyl fluoride and vinylidene halide, for example vinylidene chloride. Diene includes 1,3-butadiene and isoprene. Vinyl amide includes N-vinyl pyrrolidone and N-vinyl caprolactam. Nitrile includes acrylonitrile and methacrylonitrile.

[0028] A polyurethane vinyl-acrylic copolymer is a hybrid of an acrylic-vinyl copolymer and a polyurethane. Such a hybrid may for example be formed by subjecting one or more of each of an acrylic monomer and vinyl monomer to free radical polymerisation conditions in the presence of a dispersion of an already chain-extended polyurethane using conventional techniques. This may for example be done by adding free radical initiators to a mixture of polyurethane dispersion and acrylic and vinyl monomer or, alternatively, by gradually adding acrylic and vinyl monomers to a polyurethane dispersion-containing initiator. Alternatively, a solution of isocyanate-terminated urethane-prepolymer in acrylic (and vinyl) comonomer is formed. The solution is then emulsified in an aqueous medium and the isocyanate-terminated prepolymer is chain extended. Subsequently, either acrylic and vinyl monomers can be added and the polymerisation thereof initiated or the polymerisation of the acrylic and vinyl monomers can be initiated and further acrylic and vinyl monomer can be added during polymerisation. Suitable examples of commercially available dispersions of polyurethane modified acrylic polymer include Daotan® VTW 6462 (Allnex); NeoPac E- 125 (Covestro) and Hybridur® 570 Dispersion (Evonik).

[0029] In one embodiment the organosilane is present in an amount of at least 7 wt.% of the total solids of the coating composition. Typically it is present in an amount of at least 8 wt.% of the total solids of the coating composition, for example at least 9 wt.%, at least 10 wt.%, at least 11 wt.% or at least 12 wt.% of the total solids of the coating composition. Sufficient organosilane is required to improve the physical and chemical properties of the coating. In one embodiment, the organosilane is present in an amount of at most 30 wt.% of the total solids of the coating composition. Typically it is present in an amount of at most 25 wt.% of the total solids of the coating composition, for example at most 22 wt.%, at most 20 wt.%, at most 18 wt.% or at most 15 wt.% of the total solids of the coating composition. The maximum amount of organosilane is typically determined by the point at which the composition loses stability. In one embodiment, the organosilane is present in an amount of from 7 wt.% to 30 wt.% of the total solids of the coating composition. Typically, the organosilane is present in an amount of from 9 wt.% to 25 wt.% of the total solids of the coating composition, for example from 11 to 20 wt.% or even from 12 to 15 wt.% of the total solids of the composition.

[0030] The organosilane is unreactive towards carboxylic acid functionality. In one embodiment, the organosilane is an alkylsilane, vinylsilane, mercaptoalkylsilane or tetraalkoxysilane. The organosilane typically comprises one or more of the following moieties: methoxy, ethoxy, propoxy, mercaptopropyl, methyl, ethyl, propyl, isobutyl, phenyl, vinyl and chloro. Examples of suitable organosilanes are mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, 3-ureidopropyltrimethoxysilane, 3- ureidopropyltriethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, methacryloxypropylmethyldimethoxysilane, methyltrimethoxysilane, methyltriisopropylsilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, tetramethoxysilane, tetraethoxysilane, ethyl polysilicate 40, tetrapropoxysilane, triethylsilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, n-octyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, propyl, methyl-diethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane, vinyl-triethoxysilane, vinyltris(2-methoxyethoxy)silane, vinylmethyldimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, cyclohexylmethyldimethoxysilane, diisobutyldimethoxysilane, diisopropyldimethoxysilane, dicyclopentyldimethoxysilane, octyl-trimethoxysilane and isobutylisopropyldimethoxysilane.

[0031] In one embodiment, the organosilane may be for example isobutyl-trimethoxysilane, 3- mercaptopropyl-trimethoxysilane, methyl-trimethoxysilane, methyl-triisopropylsilane, propyl, methyl-diethoxysilane, vinyl-trimethoxysilane, vinyl-triethoxysilane, octyltrimethoxysilane, tetraethoxysilane, tetramethoxysilane (tetramethyl-orthosilicate) or methacryloxypropyltrimethoxysilane.

[0032] The anionic-stabilized copolymer may comprise one or more functional monomers for imparting cross-linking functionality. Typically, this is not an acid monomer. Examples include hydroxy and epoxy functional (meth)acrylates such as hydroxy-(C1-12) alkyl methacrylate, in particular 2-hydroxyethyl methacrylate, glycidyl methacrylate, and the corresponding acrylates; keto- and aldehyde-functional monomers, in particular acrolein, methacrolein, and methylvinyl ketone; acetoacetoxy esters of hydroxy-(C1-12) alkyl acrylates and methacrylates, in particular acetoacetoxyethyl acrylate or methacrylate; and keto- or aldehyde-containing amides, in particular diacetone acrylamide (DAAM).

[0033] In one embodiment the self cross-linking functionality is obtainable by polymerization of a ketone functional monomer with a hydrazine cross-linker. In one embodiment the hydrazine cross-linker is adipic acid dihydrazide (ADH). For example, the incorporation of diacetone acrylamide (DAAM) into the polymer is typically accompanied by the addition of adipic acid dihydrazide (ADH) as a cross-linker into the dispersion which, on drying of the dispersion reacts with the keto-functionality to cross-link the polymer. DAAM-ADH is a well-established cross-linking system for acrylic polymers. In another embodiment, the self cross-linking functionality is obtainable by polymerization of a silane- or silanol-functional monomer.

[0034] The acrylic copolymer has a weight average molecular weight Mwof at least 100,000 g / mol. Typically it has a Mwof at least 250,000 g / mol, for example above 400,000 g / mol. Mwcan be measured by gel permeation chromatography.

[0035] The copolymer is an anionic-stabilized copolymer. This means that the polymer comprises an anionic functionality.

[0036] In one embodiment the anionic-stabilized polymer comprises at least 40 wt.%, for example at least 50 wt.% or at least 60 wt.% of one or more acrylate or methacrylate monomers.

[0037] Styrene monomers commonly lead to poor UV resistance in the resulting coating. Typically, the copolymer comprises less than 4 wt.% styrene, more preferably less than 3 wt.% styrene, even more preferably less than 2 wt.% styrene, still more preferably less than 1 wt.% styrene, even more preferably the polymers are free of styrene. Reference herein to styrene is to any styrene as defined above.

[0038] The dispersion of polymer particles is in aqueous medium. Accordingly, it comprises a continuous phase which is aqueous. The polymer particles form a discrete phase. In its simplest form the aqueous medium is water.

[0039] In one embodiment the polymer particles are multiphase polymer particles comprising a first polymer phase and a second polymer phase, wherein the first polymer phase comprises the anionic-stabilized copolymer having a Mwof at least 100,000 g / mol and self cross-linking functionality. Typically, the anionic-stabilized copolymer has a Mwof at least 200,000 g / mol, for example at least 400,000 g / mol or at least 600,000 g / mol. Typically the anionic-stabilized copolymer has a Mwof at most 5,000,000 g / mol, for example at most 3,000,000 g / mol.

[0040] The second polymer phase may comprise a polymer having a molecular weight of less than that of the anionic-stabilized polymer and a solubility in water of at least 1g / 100mL. Typically the second phase polymer has a Mwof less than 40,000 g / mol, for example less than 30,000 g / mol. The second phase polymer typically has a Mwof at least 500.

[0041] In one embodiment the multiphase polymer particles are core-shell polymer particles, wherein the core comprises the first polymer phase and the shell comprises the second polymer phase. Therefore the core comprises the anionic-stabilized copolymer having a Mwof at least 100,000 g / mol and self cross-linking functionality. Correspondingly, the shell may comprise a polymer having a Mwof less than 50,000 g / mol and a solubility in water of at least 1g / 100mL.

[0042] An example of a core-shell particles is one wherein a shell polymer comprises one or more alkyl-methacrylate; one or both of alkyl-acrylic acid and acrylic acid; and one or both of diacetone acrylamide and acetoacetoxy ethyl methacrylate. Typically, it comprises methyl methacrylate; methacrylic acid; diacetone acrylamide and optionally butyl methacrylate. Typically, the shell vinyl polymer comprises at least 50 wt.% alkyl methacrylate, for example methyl methacrylate and butyl methacrylate.

[0043] In one embodiment the core polymer comprises an alkyl-methacrylate; an alkylacrylate; and one or both of diacetone acrylamide and acetoacetoxy ethyl methacrylate. Typically, it comprises butyl methacrylate, butyl acrylate and diacetone acrylamide. Typically, the second vinyl polymer comprises at least 50 wt.% alkyl methacrylate, for example butyl methacrylate.

[0044] An example core polymer comprises 3 to 12 wt.% methacrylic acid and / or acrylic acid, 1 to 10 wt.% of diacetone acrylamide and / or acetoacetoxy ethyl methacrylate, 50 to 90 wt.% methyl methacrylate, 0 to 30 wt.% of one or more of ethyl acrylate, n-butyl methacrylate and n-butyl methacrylate and 0 to 40 wt.% styrene.

[0045] The shell polymer may have an acid number of at least 20 and therefore comprises sufficient acid-functional monomers to achieve such an acid number. The shell polymer may be derived from a monomer system which contains from 1 to 45 wt.% of acid functional monomers (typically from 3 to 30 wt.%; preferably from 3 to 20 wt.% of acid functional monomers); from 0.5 to 20 wt.% of cross-linking monomers (typically from 1 to 15 wt.%; particularly from 1 to 10 wt.% of cross-linking monomers); and from 98.5 to 50 wt.% of non-acid functional, non-cross-linking comonomers (typically from 96 to 65 wt.%; preferably from 96 to 75 wt.% non-acid functional, non-cross-linking comonomers).

[0046] In one embodiment one or both of the core polymer and the shell polymer each further comprises a monomer comprising a cross-linkable moiety. Typically both the core polymer and the shell polymer each comprise a monomer comprising a cross-linkable moiety.

[0047] In one embodiment, the core has a glass transition temperature, Tgc, and the shell has a glass transition temperature Tgs, wherein Tgc is at least 40°C greater than Tgs. Tpically, Tgc is at least 60°C greater than Tgs, for example at least 80°C greater.

[0048] Glass transition temperature, Tg, of a copolymer is calculated according to the Flory Fox equation using the weight fraction of each comonomer and Tg’s of the homopolymers (in degrees Kelvin) derived from each comonomer. This may be done, for example, as reported in Fox, T.G.; Flory, P.J. (1950), "Second-order transition temperatures and related properties of polystyrene", Journal of Applied Physics, 21 (6): 581-591.

[0049] The coating composition preferably has a solids volume content of at least 35 vol.%, more preferably in the range of from 36 to 50 vol.%. In case the coating composition is a varnish without inorganic pigments resulting in a transparent or translucent coating, it preferably has a solids volume content of at most 45 vol.%, more preferably in the range of from 36 to 42 vol.%. In case the coating composition comprises one or more inorganic pigments, it may have a higher solids volume content, for example in the range of from 38 to 50 vol.%, more preferably of from 40 to 48 vol.%.

[0050] In terms of weight, the coating composition preferably has a solids content of more than 30 wt.%. More preferably, the solids content is between 35 and 50 wt.% for a clear coating composition (without inorganic pigments), even more preferably between 37 and 47 wt.%, still more preferably between 39 and 43 wt%. In case the coating composition comprises one or more inorganic pigments, the solids content is more preferably between 50 and 61 wt.%, still more preferably between 53 and 59 wt.%.

[0051] The coating composition may comprise a cosolvent. However, preferably no organic solvents are used, since low or no-VOC content is desired.

[0052] A coalescing solvent lowers the effective glass transition temperature of the coating composition such that the coating composition forms a film at ambient conditions. Any coalescing solvent known to be suitable for use in aqueous coating compositions comprising an acrylic polymer dispersion as a binder may be used. The coalescing solvent should not react with the organosilane. Such coalescing solvents are well known in the art and commercially available. Suitable coalescing solvents include glycol ethers, dibasic esters, ester alcohols. Preferred coalescing solvents are ester functional. Examples of suitable commercially available coalescing solvents include Coasol™ (di-isobutyl succinate, di-isobutyl glutarate and di-isobutyl adipate), Lusolvan™ FBH (di-isobutyl ester of a mixture of dicarboxylic acids), Lusolvan™ PP (di-isobutyl ester of a mixture of dicarboxylic acids), Loxanol™ EFC 300 (linearic ester), Butyl Carbitol™, Butyl Cellosolve, Dowanol™ EPh (ethylene glycol phenyl ether), Dowanol™ PPh (propylene glycol phenyl ether), Dowanol™ TPnB (tripropylene glycol n-butyl ether), Dowanol™ DPnB, DBE-9™ (a mixture of refined dimethyl glutarate and dimethyl succinate), Eastman DB™ solvent, Eastman EB™ (ethylene glycol monobutyl ether), Texanol™ (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate), DAPRO™ FX 511.

[0053] In one embodiment, the coating composition further comprises one or more of a color pigment, extender pigment, coalescing solvent, co-solvent, surfactant, plasticizer, pH modifier, defoaming agent, thickener, leveling agent, matting agent, anti-setting agent and biocide.

[0054] The coated substrate is obtained by applying a coating composition to the substrate and allowing the coating composition to dry. The layer may be applied using any suitable technique known in the art, for example by brush, roller or spaying. Drying may be supplemented by applying radiation, for example UV or electron beam radiation, or applying heat to effect curing of the coating. Typically curing is carried out at ambient temperature. Preferably, the composition is free from cross-linking reagents which require curing at elevated temperatures or by applying radiation. The substrate may be any suitable substrate, such as for example wood, polymer, composite, metal or mineral substrate. The substrate may be a primed or bare substrate. A single layer or multiple successive layers of coating composition may be applied to the substrate.

[0055] The one-component waterborne coating composition may be produced by forming an aqueous dispersion of polymer particles; adding to the aqueous dispersion of polymer particles an organosilane; and further optionally adding one or more additives. A suitable two-stage emulsion polymerization process for forming a dispersion of polymer particles is described in US2003 / 0153676A1. Typically, the aqueous dispersion of polymer particles is produced by preparing a monomer mixture comprising an acrylic monomer and carrying out emulsion polymerization of the monomer mixture in water. Typically, at least one surfactant and at least one initiator are used. In case the polymer particles are multiphase polymer particles, typically the process of preparation of the particles is as follows:

[0056] (a) preparing a first monomer mixture;

[0057] (b) carrying out emulsion polymerization of the first monomer mixture in water to form an aqueous dispersion of a first polymer;

[0058] (c) preparing a second monomer mixture;

[0059] (d) carrying out emulsion polymerization of the second monomer mixture in the presence of the aqueous dispersion of the first polymer to form an aqueous dispersion of polymer particles.

[0060] Typically, the first monomer mixture is a dispersion in an aqueous continuous phase. Typicality, an initiator is present in either or both of steps (b) and (d). Typically, a surfactant is present in either or both of steps (b) and (d). Typically, either or both of steps of steps (b) and (d) are carried out at elevated temperature; typically under inert atmosphere, for example nitrogen or argon and typically under stirring. Typically, a base is added after either or both of steps (b) and (d) to, at least partly, neutralize acid groups present in the polymer(s).

[0061] The process for producing a dispersion of polymer particles is typically a semi- continuous emulsion polymerization (where reagents are fed to the reactor over a defined time period) or a batch process (where all reagents are present in the reactor at the beginning of the reaction). Alternatively, the process may be a continuous process. Each of steps (b) and (d) may be independently semi-continuous, batch or continuous. Preferably both steps (b) and (d) are semi-continuous.

[0062] The process of the present invention may further comprise a step (e) purifying the aqueous dispersion of polymer particles. Purification may comprise multiple steps and is typically carried out by techniques known in the art, for example it may include one or more of oxidation and reduction steps and filtration.

[0063] The first vinyl polymer can be described as an ‘alkali soluble resin’ (ASR). The first polymer will dissolve and / or form micelles when it is neutralized in water, for example when neutralisation is carried out directly after step (b). When the second polymerization step (d) is performed, the first polymer can act as a surfactant for the second monomer mixture and form a shell of the second vinyl polymer. The resulting polymer particles are soluble shell polymer particles, with the first polymer acting as a soluble shell for the second polymer. The resulting polymer particles are present as an aqueous dispersion. Therefore, in one embodiment, the first polymer at least partially encapsulates the second polymer. The resulting polymer particles are known as coreshell polymer particles.

[0064] An organosilane is added to the aqueous dispersion of polymer particles. Typically, addition is under inert atmosphere and typically under stirring. To produce a coating composition, additives are typically added to the aqueous dispersion of polymer particles by known techniques. Suitable additives, for example one or more of a color pigment, extender pigment, coalescing solvent, co-solvent, surfactant, plasticizer, pH modifier, defoaming agent, thickener, leveling agent, matting agent, anti-setting agent and biocide are typically added to the aqueous dispersion of polymer particles.

[0065] A coated substrate is obtained by applying a coating composition to the substrate and allowing the coating composition to dry. The layer may be applied using any suitable technique known in the art, for example by brush, roller or spaying. Drying may be supplemented by applying radiation, for example UV or electron beam radiation, or applying heat to effect curing of the coating. Typically, curing is carried out at ambient temperature. Preferably, the composition is free from high temperature cross-linking reagents or radiation-curing cross-linking agents. The substrate may be any suitable substrate, such as for example wood, polymer, composite, metal or mineral substrate. The substrate may be a primed or bare substrate. A single layer or multiple successive layers of coating composition may be applied to the substrate.

[0066] The invention is further illustrated by means of the following non-limiting examples.

[0067] Raw Materials

[0068] Polymer dispersions:

[0069] Setaqua® 6756 supplied by Allnex, self cross-linking polymer stabilized acrylic core-shell emulsion, solids 40%, MFFT 15°C, Acid value 28 mgKOH / g solids.

[0070] Neocryl® XK-98, supplied by Covestro, self cross-linking acrylic core shell emulsion, solids 44%, MFFT is 7°C, Acid value 30 mgKOH / g solids.

[0071] Setaqua® 6802, supplied by Allnex, alkali swellable acrylic core-shell emulsion, solids 24%, Tg(DSC) is 68°C, Acid value 19 mgKOH / g solids.

[0072] Daotan® VTW 6462, supplied by Allnex, aliphatic urethane acrylic hybrid emulsion, self cross-linking. Solids 36°C, MFFT is below 5°C, Acid value less than 5 mgKOH / g solids.

[0073] Bahydrol® A2651 , supplied by Covestro, hydroxyfunctional polyacrylic secondary dispersion, solids 40%, Tg(DSC) is 54°C, Acid value 10 mg KOH / g solids.*

[0074] Neocryl® XK-82, supplied by Covestro, Styrene acrylic emulsion, solids 40%, Tg

[0075] DSC is 50°C.*

[0076] *Not self cross-linking.

[0077] The following organosilanes under the Dynasylan® trade name were supplied by Evonik GmbH:

[0078] Dynasylan® IBTMO lisobutyl-trimethoxysilane

[0079] Dynasylan® MTMO (3-mercaptopropyl-trimethoxysilane)

[0080] Dynasylan® MEMO (methyl-trimethoxysilane)

[0081] Dynasylan® VTMO (vinyl-trimethoxysilane)

[0082] Dynasylan® VTEO (vinyl-triethoxysilane)

[0083] Dynasylan® OCTMO (octyl-trimethoxysilane) Dynasylan® TMOS (tetramethyl-orthosilicate)

[0084] Dynasylan® AMEO (3-aminopropyltriethoxysilane)*

[0085] Dynasylan® DAMO (N-2-Aminoethyl-3-aminopropyltrimethoxysilane)* Dynasylan® GLYMO ([3-(2,3-Epoxypropoxy)propyl]trimethoxysilane)* Dynasylan® GLYEO ([3-(2,3-Epoxypropoxy)propyl]triethoxysilane)*

[0086] *Reactive with acid-functional groups.

[0087] Test methods

[0088] Viscosity

[0089] Viscosity was visually checked by lightly shaking the sample and observing the appearance. As used below *** means viscosity remained low (a thin semi-transparent liquid); ** means increased viscosity; * means an irreversible gel is formed which can not be liquified by shaking.

[0090] MEK double rub

[0091] Coatings were applied to the substrate by drawdown to yield a film as described and allowed to dry for one day. A cotton wool ball was dipped in methyl ethyl ketone (MEK) and rubbed across the surface of the dried coating film until the coating failed (e.g. dissolved, was damaged) according to ASTM D5402. The number of MEK double rubs is a measure of chemical resistance and an indication of the degree of cross-linking of the coating.

[0092] Water resistance / Ethanol resistance

[0093] Resistance to each of ethanol and water was independently tested following ISO 2812- 4, by soaking a filter paper with water or ethanol and leaving on the surface for a period (1 hour for ethanol and 24 hours for water). After removing the filter paper, the surface was wiped and the surface appearance judged directly. After 30-60 minutes the surface was reassessed. The appearance of the substrate was observed and rated according to a scale of 0 to 5, where 0 is worst and 5 is best: 5 = no mark (all angles); 4 = little mark (visible at 1 angle); 3 = clear visible mark (visible all angles and easy damageable); 2 = strong mark and damaged after wiping; 1 = dissolved or strong blistering, partly removed during wiping; 0 = dissolved completely removed by wiping.

[0094] Scratch Resistance

[0095] Hardness of the applied films was determined according to ASTM D3363 with pencils with different hardness, 6B being very soft, with increasing hardness via 5B, 4B, 3B, 2B, B, F, H, 2H, etc.

[0096] Preparation of Examples

[0097] The compositions of the Examples and Comparative Examples were each made by mixing with a Speedmixer® (a bladeless mixing system that uses a dual asymmetric centrifuge) an organosilane (where present) with a polymer dispersion, to yield 20 g coating composition.

[0098] Examples 1 to 6 and Comparative Examples 1 to 5

[0099] In Examples 1 to 6 and Comparative Examples 1 to 5 the polymer dispersion used was Setaqua® 6756. The compositions were prepared as described above. In Comparative Example 1 , no organosilane was added to the polymer dispersion. In the remaining cases 12.5 wt.% organosilane was added based on the solids content of the polymer dispersion, which equates to 5 wt.% organosilane based on the total weight of the polymer dispersion. Viscosity was visually checked directly after preparation of the composition and after 1 weeks’ storage and after 6 weeks’ storage. Each of the compositions, after 1 weeks’ storage and after 6 weeks’ storage, was drawn down, directly after mixing on tin plates with a drawdown bar giving around 50 pm dry film. After 1 day of drying, chemical resistance was tested by carrying out MEK double rubs. The results are presented in Table 1. Table 1

[0100] *** viscosity remained low

[0101] ** viscosity increased

[0102] * gelled

[0103] - not tested

[0104] Comparative Examples 2 to 5 gelled either directly or after storing for one week, and therefore are unsuitable for storage. This indicates the detrimental effect of the organosilanes used in Comparative Example 2 to Comparative Example 5 on storage stability. Examples 1 to 6 and Comparative Example 1 remained viscous after 6 weeks. Examples 1 to 6 had a chemical resistance of over 130 M EK double rubs after storing the composition for 1 week; whereas Comparative Example 1 had a chemical resistance of only 100 M EK double rubs after storage for one week; indicating the improvement in chemical resistance due to addition of the organosilanes of the Examples.

[0105] The compositions of Examples 7 to 11 and Comparative Examples 6 to 17 were produced with the polymer dispersion and type and amount of organosilane indicated in Table 2. The compositions were each stored for 7 days, and were then drawn down, directly after mixing on tin plates with a drawdown bar giving around 50 pm dry film. After 1 day of drying, chemical resistance was tested by carrying out MEK double rubs; ethanol resistance; water resistance and pencil hardness were measured as described above. The results are given in Table 2.

[0106] Table 2

[0107] X denotes that the appearance of the films lacked transparency, had cracks and / or the presence of gel particles. Accordingly, no meaningful test results could be obtained.

[0108] Comparative Examples 8 and 9 (respectively, no organosilane and 4 wt.% MTMO) did not form a cohesive film, whereas Example 11 (20% MTMO) formed a cohesive film which had high chemical resistance (MEK double rubs) and good water resistance.

[0109] This indicates that with Setaqua® 6802 formation of a film is possible with an amount of MTMO above 4 wt.%.

[0110] Comparing Examples 9 and 10 with Comparative Examples 6 and 7, shows that in Daotan® 6462 polymer dispersion, the higher the amount of VTEO (organosilane) from 0 to 2.8 to 14 wt.% the higher the chemical resistance (MEK double rubs, ethanol resistance) and water resistance. However, a higher amount of VTEO of 27 wt.% does not provide any higher performance over 14 wt.% VTEO content. Comparative Examples 10, 11 and 12 and Example 12, indicate a similar trend for the amount of VTEO with Neocryl® XK-98 polymer dispersion. When the amount of VTEO present is higher (comparing 0 to 2.3 to 4.5 wt.%) the chemical resistance (MEK double rubs) is slightly higher but other parameters are not improved. At 11.5 wt.% VTEO measurably higher chemical and water resistance are shown.

[0111] Comparing Examples 7 and 8 there is no measurable difference in measured properties between a content of VTEO (organosilane) in Setaqua® 6756 (polymer dispersion) of between 12.5 wt.% and 25 wt.%.

[0112] Comparative Examples 13 and 14 indicate no difference in measured properties with Bayhydrol® A2651 whether 12.5 wt.% of MTMO or no organosilane is present. Both Comparative Examples gave generally poor results.

[0113] These results confirm that the nature of the polymer dispersion and the identity of the organosilane are important in determining properties. Further, there is a minimum threshold of organosilane required to achieve a film with good chemical and water resistance; and a maximum threshold over which no improvement is shown. 16 and 17

[0114] The composition of Example 13 was identical to that of Example 7. The composition of Example 14 was made by addition to Setaqua®6756 of 12.5 wt.% (based on the solids content of the polymer dispersion) of MTMO. The composition of Comparative Example 16 was made by addition of 12.5 wt.% VTEO (based on the solids content of the polymer dispersion) to respectively Bayhydrol® A2651 and Neocryl® XK-82. The compositions of Examples 13 and 14 and Comparative Examples 16 and 17 were stored at a temperature 20 to 24°C in plastic containers and checked at different time intervals on visual viscosity and wet appearance (container) and drawdown on thin plate (after filtration through a 125 pm paint strainer). The composition of Example 15 is identical to that of Example 13. It was produced one year after Example 13, stored for one week and compared to Example 13. The results are given in Table 3. Table s

[0115] *** viscosity remained low / no particles in container / drawdown

[0116] ** viscosity increased * gelled / particles in container / drawdown

[0117] - not tested

[0118] All compositions had adequate viscosity and appearance one week after production. Example 13 maintained low viscosity and an absence of particles for one year of storage and Example 14 for 6 months of storage. This indicates a long shelf-life of the compositions. Comparative Examples 16 and 17 showed particle formation in the container after only one month. After 6 months particle formation was shown in the container and drawdown. This indicates an inadequate shelf-life.

Claims

CLAIMS1. A one-component waterborne coating composition comprising: a) an aqueous dispersion of polymer particles, which polymer particles comprise an anionic-stabilized copolymer having a Mw, measured by gel permeation chromatography, of at least 100,000 g / mol and self cross-linking functionality, wherein the copolymer is an acrylic copolymer, an acrylic-vinyl copolymer, or a polyurethane vinyl-acrylic copolymer; and b) an organosilane; wherein: the organosilane is unreactive towards carboxylic acid functionality; and the organosilane is present in an amount of at least 5 wt.% of the total solids of the coating composition.

2. A coating composition according to claim 1, which comprises the organosilane in an amount of from 7 wt.% to 30 wt.% of the total solids of the coating composition.

3. A coating composition according to claim 1, which comprises the organosilane in an amount of from 9 wt.% to 25 wt.% of the total solids of the coating composition.

4. A coating composition according to any one of claims 1 to 3, wherein the organosilane is an alkyl-silane, vinyl silane, mercaptoalkylsilane or tetraalkoxysilane.

5. A coating composition according to claim 4, wherein the organosilane is isobutyl-trimethoxysilane, 3-mercaptopropyl-trimethoxysilane, methyltrimethoxysilane, vinyl-trimethoxysilane, vinyl-triethoxysilane, octyltrimethoxysilane, tetramethyl-orthosilicate, tetraethoxysilane, tetramethoxysilane or methacryloxypropyltrimethoxysilane.

6. A coating composition according to any one of claims 1 to 5, wherein the self cross-linking functionality is obtainable by polymerization of a ketone functional monomer with a hydrazine cross-linker.

7. A coating composition according to claim 6, wherein the hydrazine cross-linker is adipic acid dihydrazide (ADH).

8. A coating composition according to any one of claims 1 to 5, wherein the self cross-linking functionality is obtainable by polymerization of a silane- or silanol- functional monomer.

9. A coating composition according to any one of claims 1 to 8, wherein the polymer particles are multiphase polymer particles, comprising a first polymer phase and a second polymer phase, wherein the first polymer phase comprises the anionic-stabilized copolymer having a Mw, measured by gel permeation chromatography, of at least 100,000 g / mol and self cross-linking functionality.

10. A coating composition according to claim 9, wherein the second polymer phase comprises a polymer having a molecular weight of less than that of the anionic- stabilized copolymer and a solubility in water of at least 1g / 100mL.

11. A coating composition according to claim 9 or claim 10, wherein the multiphase polymer particles are core-shell polymer particles, wherein the core comprises the first polymer phase and the shell comprises the second polymer phase.

12. A coating composition according to claim 11 , wherein the core has a glass transition temperature, Tgc, calculated according to the Flory Fox equation, and the shell has a glass transition temperature Tgs, calculated according to the Flory Fox equation, wherein Tgc is at least 20°C greater than Tgs.

13. A coating composition according to any one of claims 1 to 12, further comprising one or more of a color pigment, extender pigment, coalescing solvent, co-solvent, surfactant, plasticizer, pH modifier, defoaming agent, thickener, leveling agent, matting agent, anti-setting agent, and biocide.

14. A coated substrate comprising a substrate and a coating, which coating is obtained by applying a coating composition as defined in any one of claims 1 to 13 to the substrate and allowing the coating composition to dry.

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