WO2005058993A2

WO2005058993A2 - A polyurethane and vinyl polymer based recyclable aqueous coating composition

Info

Publication number: WO2005058993A2
Application number: PCT/GB2004/005194
Authority: WO
Inventors: Rajasingham Satgurunathan; Marc Roelands; Martin Van Ginkel
Original assignee: Dsm Ip Assets B.V.
Priority date: 2003-12-17
Filing date: 2004-12-08
Publication date: 2005-06-30
Also published as: WO2005058993A3; GB0329168D0; EP1694733A2

Abstract

A recyclable aqueous coating composition comprising a combination of a polyurethane polymer (A), a vinyl polymer (B) having a Tg ≥ 20°C, a Mw > 50,000 and an acid value < 40mgKOH/g and a vinyl polymer (C) having a Tg ≥ 70°C, a Mw from 15,000 to 50,000 and an acid value ≥ 40 mgKOH/g where the ration of (A)+(B):(C) is in the range of from 95:5 to 65:35.

Description

A POLYURETHANE AND VINYL POLYMER BASED RECYCLABLE AQUEOUS COATING COMPOSITION

The present invention relates to a recyclable aqueous coating composition comprising a polyurethane polymer and at least two different vinyl polymers, a recycled aqueous coating composition, a method for recycling such an aqueous composition and the use of such an aqueous coating composition in spray applications. Efficient coating of automobiles, automobile parts and other larger objects, for example wooden furniture, prepared on an industrial basis, normally requires the coating composition to be applied using a spray application process. Typically Venjakob spray machines are used for spray coating wood. Such spray application processes generate a significant amount of overspray and therefore the spray process is usually conducted in a spray booth. The overspray is usually considered as waste and requires disposal, which can cause environmental problems. There are a number of methods disclosed in the art for dealing with overspray. WO 82/02543 discloses a method for recycling paint overspray by forming a slurry of the overspray and centrifugally separating the slurry into liquid and solid components where the liquid may be reused for collecting overspray and the solid may be disposed or used as a base. US 4,607,592 discloses a process and a device for recovering paint overspray where the overspray is collected and flushed with water, then subsequently filtered to separate the water from the paint components. The physical characteristics of the paint components are measured and compared with fresh paint, adjusted to match and then the reclaimed paint is mixed into fresh paint for spraying. WO 92/19686 discloses a process for treating overspray where the overspray is collected with water, separated into a concentrated and a dilute phase, and then separating the dilute phase electrophoretically into a water fraction and a concentrated fraction. The water fraction is then further separated into a recyclable water and a concentrated fraction. All the concentrated fractions are then mixed and adjusted with other components to generate a composition substantially as the original composition. The processes discussed above all require separation processes where the water is separated out in a number of stages before the solid components are recycled. There is no disclosure with regard to the maintenance of the physical properties of the recycled compositions. Important properties to be maintained after recycling are the physical appearance, hardness, blocking and chemical resistance of any resultant coating. WO 99/16805, JP 71242855, JP 7048537 and JP 7048538 generally describe aqueous polyurethane vinyl polymer dispersions however they do not discuss the recyclability of such dispersions. We have found that by tailoring aqueous coating compositions, in particular polyurethane polymer and vinyl polymer based aqueous coating compositions, it is possible to recycle the composition in more of the same composition without requiring any separation stages and yet still maintain the physical properties of a coating derived from the recycled composition when compared with a coating formed from the original composition. According to the present invention there is provided a recyclable aqueous coating composition comprising components: (1 ) at least a polyurethane polymer (A); (2) at least a vinyl polymer (B) having a Tg > 20°C, a weight average molecular weight > 50,000 Daltons and an acid value < 40 mgKOH/g; and (3) at least a vinyl polymer (C) having a Tg > 70°C, a weight average molecular weight in the range of from 15,000 to 50,000 Daltons and an acid value > 40 mgKOH/g; wherein the weight ratio of polyurethane polymer (A) and vinyl polymer (B) together to vinyl polymer (C) is in the range of from 95:5 to 65:35, preferably in the range of from 92:8 to 70:30, more preferably in the range of from 92:8 to 75:25 and especially in the range from 92:8 to 80:20. Preferably the weight ratio of polyurethane polymer (A) to vinyl polymer (B) is in the range of from 10:90 to 95:5, preferably 10:90 to 25:75, more preferably 10:90 to 60:40 and especially in the range of from 15:85 to 50:50. The recyclable aqueous coating composition of the invention is recycled by redispersing any overspray resulting from application of the coating composition to a substrate, of for example an article, in more of the original recyclable composition in a weight ratio of 1 :99 to 30:70, more preferably 5:95 to 20:80 and especially 8:92 to 15:85. Preferably the overspray is recycled within 50 minutes, more preferably within 40 minutes and most preferably within 30 minutes of application of the coating composition. For the purpose of the present invention the term overspray is intended to include any excess of the recyclable aqueous coating composition obtained as a result of applying the composition to a substrate, irrespective of the method of application, examples of which are described herein. For the purpose of the present invention by the term recycled is meant collection of the overspray and redispersion of the overspray in more of the original recyclable composition. In a second embodiment of the invention there is provided a recycled aqueous coating composition comprising: (a) 70 to 99 wt%, more preferably 80 to 95 wt% and especially 85 to 92 wt% of the recyclable aqueous coating composition of the invention; and (b) 1 to 30 wt%, more preferably 5 to 20 wt% and especially 8 to 15 wt% of overspray; where (a) + (b) = 100%. The recyclable aqueous coating composition of the invention may be a dispersion, emulsion or solution of polyurethane polymer (A), vinyl polymer (B) and vinyl polymer (C) in a liquid medium. For the purpose of the invention a liquid medium is one which comprises > 50%, more preferably > 65% and most preferably > 80% of water. The liquid medium may also comprise a range of organic solvents known in the art and includes those described herein. The aqueous composition of the invention will typically comprise colloidally dispersed particles of polyurethane polymer (A), vinyl polymer (B) and vinyl polymer (C) i.e. will typically be in the form of an aqueous polymer latex. Polyurethane polymer (A), vinyl polymer (B) and/or vinyl polymer (C) may bear water-dispersing groups. Such water-dispersing groups may be ionic and/or non-ionic water-dispersing groups. Preferred ionic water-dispersing groups are anionic water- dispersing groups. Preferred anionic water-dispersing groups are carboxylic, phosphoric and/or sulphonic acid groups. The anionic water-dispersing groups are preferably fully or partially in the form of a salt. Conversion of for example a potentially anionic water-dispersing group to the salt form (i.e. anionic water-dispersing group) may be effected by neutralisation with a base, preferably during the preparation of the recyclable aqueous coating 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, N,N-dimethylethanolamine or dimethyl amino ethyl methacrylate. Suitable inorganic bases include alkali hydroxides and carbonates, for example lithium hydroxide, sodium hydroxide, or potassium hydroxide. A quaternary ammonium hydroxide, for example N⁺(CH₃)₄(OH), can also be used. Generally a base is used which gives counter ions that may be desired for the composition. For example, preferred counter ions include Li⁺, Na⁺, K\ NH₄ ⁺ and substituted ammonium salts. Cationic water-dispersing 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). Preferred non-ionic water-dispersing groups are polyalkylene oxide groups, more preferably polyethylene oxide groups. A small segment of the polyethylene oxide group can be replaced by propylene segments and/or butylene oxide segments, however the polyethylene oxide group should still contain ethylene oxide as a major component. When the water-dispersing group is polyethylene oxide, preferably the polyethylene oxide group has a molecular weight from 175 to 5000 Daltons, more preferably from 350 to 2200 Daltons, most preferably from 660 to 2200 Daltons. Polyurethane polymer (A), vinyl polymer (B) and/or vinyl polymer (C) may bear crosslinking groups. Polyurethane polymer (A), vinyl polymer (B) and/or vinyl polymer (C) may be crosslinkable without the requirement for added compounds which react with crosslinking groups on the polyurethane polymer (A), vinyl polymer (B) and/or vinyl polymer (C) to achieve crosslinking, although these can still be employed if desired. Optionally the aqueous coating composition of the present invention comprises at least 5 one post-added crosslinker in the range from 0 to 35 wt% based on the total polymer (A) + (B) + (C) solids. Polyurethane polymer (A), vinyl polymer (B) and/or vinyl polymer (C) may crosslink at ambient temperature by a number of mechanisms including but not limited to autoxidation, Schiff base crosslinking and silane condensation. By crosslinking by

10 autoxidation is meant that crosslinking results from an oxidation occurring in the presence of air and usually involves a free radical mechanism and is preferably metal- catalysed resulting in covalent crosslinks. Suitably autoxidation is provided for example by fatty acid groups containing unsaturated bonds (by which is meant the residue of such fatty acids which have

15 become incorporated into for example polyurethane polymer (A) by reaction at their carboxylic acid groups) or by (meth)allyl functional residues, β-keto ester groups or β- keto amine groups. Preferably autoxidation is provided at least by fatty acid groups containing unsaturated bonds. By Schiff base crosslinking is meant that crosslinking takes place by the reaction

-0 of carbonyl functional groups, where by a carbonyl functional group herein is meant an aldo or keto group and includes an enolic carbonyl group such as is found in an acetoacetyl group. Such a carbonyl functional group may react with a carbonyl-reactive amine and/or hydrazine (or blocked amine and/or blocked hydrazine) functional group. By silane condensation is meant the reaction of alkoxy silane or -SiOH groups in

.5 the presence of water, to give siloxane bonds by the elimination of water and/or alkanols (for example methanol) during the drying of the aqueous coating composition. Other crosslinking mechanisms known in the art include those provided by the reaction of epoxy groups with amino, carboxylic acid or mercapto groups, the reaction of mercapto groups with ethylenically unsaturated groups such as fumarate and acryloyl

30 groups, the reaction of masked epoxy groups with amino or mercapto groups, the reaction of isothiocyanates with amines, alcohols or hydrazines, the reaction of amines (for example ethylenediamine or multifunctional amine terminated polyalkylene oxides) with β-diketo (for example acetoacetoxy or acetoamide) groups to form enamines. The use of blocked crosslinking groups, such as blocked isocyanate groups, may be

35 beneficial. Preferably any crosslinking is by autoxidation of unsaturated functional groups and/or Schiff base crosslinking. The term polyurethane polymer as used herein includes one polyurethane polymer as well as more than one polyurethane polymer. Polyurethane polymer (A) may

\0 comprise a range of polyurethane polymers known in the art. Preferably polyurethane polymer (A) bears water-dispersing groups, more preferably anionic and/or non-ionic water-dispersing groups. Preferably polyurethane polymer (A) is the reaction product of: I) an isocyanate-terminated polyurethane prepolymer having an acid value of > 20 mgKOH/g of prepolymer obtained from the reaction of components comprising: (i) at least one organic polyisocyanate; (ii) at least one isocyanate-reactive compound bearing ionic and/or potentially ionic water-dispersing groups; (iii) at least one isocyanate-reactive compound not comprised by ii); and II) at least one active-hydrogen chain extending compound. Preferably the weight average molecular weight of polyurethane polymer (A) is in the range of from 50,000 to 1 ,000,000 Daltons, more preferably in the range of from

80,000 to 500,000 Daltons. The weight average molecular weight is preferably measured by Gel Permeation Chromatography (GPC) using tetrahydrofuran (THF) as a solvent and polystyrene standards. 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; and these methods are included herein by reference. Polyurethane polymer (A) may be prepared in a conventional manner by reacting an organic polyisocyanate with a compound bearing isocyanate-reactive groups. Isocyanate-reactive groups include -OH, -SH, -NH-, and -NH₂. In some preparations an isocyanate-terminated polyurethane prepolymer is first formed which is then chain extended with an active- hydrogen containing compound. Component (i) includes but is not limited to aliphatic, cycloaliphatic, araliphatic and/or aromatic polyisocyanates. Examples of suitable polyisocyanates include ethylene diisocyanate, 1 ,6-hexamethylene diisocyanate, isophorone diisocyanate, cyclohexane-1 ,4-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, p-xylylene diisocyanate, α,α'-tetramethylxylene diisocyanate, 1 ,4-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanates, 2,4'-diphenylmethane diisocyanate, 3(4)-isocyanatomethyl-1 -methyl cyclohexyl isocyanate and 1 ,5-naphthylene diisocyanate. Mixtures of polyisocyanates and also polyisocyanates which have been modified by the introduction of urethane, allophanate, urea, biuret, carbodiimide, uretonimine, urethdione or isocyanurate residues can be used. Preferably the isocyanate-terminated polyurethane prepolymer comprises 5 to 70 wt%, more preferably 20 to 70 wt% and most preferably 25 to 65 wt% of component (i). Preferably at least 40 wt%, more preferably at least 60 wt% and most preferably at least 80 wt% of component (i) comprises at least one aliphatic polyisocyanate, this term (for the sake of clarity) being intended to mean compounds in which all the isocyanate groups are directly bonded to aliphatic or cycloaliphatic groups, irrespective of whether aromatic groups are also present. The isocyanate-reactive compound will normally consist of an organic polyol component, which may bear other reactive groups. By a polyol component is also meant to include compounds with one or more isocyanate-reactive groups such as primary or secondary amines. Water-dispersing groups are preferably introduced by employing at least one isocyanate-reactive compound (or less preferably an isocyanate-functional compound) bearing a non-ionic and/or ionic water-dispersing groups as a reactant in the preparation of the isocyanate-terminated polyurethane prepolymer or polyurethane polymer (A). Preferably component (ii) comprises anionic or potentially anionic water-dispersing groups. Examples of compounds bearing anionic water-dispersing groups include carboxyl group containing diols and triols, for example dihydroxy alkanoic acids such as 2,2-dimethylolpropionic acid (DMPA) and/or 2,2-dimethylolbutanoic acid (DMBA). Preferably the isocyanate-terminated polyurethane prepolymer comprises 4.5 to 25 wt% and more preferably 8 to 20 wt% of component (ii). Preferably the acid value of the isocyanate-terminated polyurethane prepolymer is > 30 mgKOH/g prepolymer. A preferred upper level for the acid value of the isocyanate-terminated polyurethane prepolymer is 100 mgKOH/g prepolymer. Preferably the acid value of the isocyanate-terminated polyurethane prepolymer is in the range of from 40 to 80 mgKOH/g, more preferably 40 to 70 mgKOH/g prepolymer. Component (iii) may be any other isocyanate-reactive compound, for example component (iii) may bear non-ionic water-dispersing groups as described above. Examples of preferred compounds bearing non-ionic water-dispersing groups include methoxy polyethylene glycol (MPEG) with molecular weights of for example 350, 550, 750, 1000 and 2000, as described in EP 0317258. Component (iii) may bear crosslinking groups as described above. Crosslinking groups are preferably introduced by employing at least one isocyanate-reactive compound (or less preferably an isocyanate-functional compound) bearing a crosslinking group as a reactant in the preparation of the isocyanate-terminated polyurethane prepolymer or polyurethane polymer (A). Component (iii) may be an isocyanate-reactive compound bearing no water- dispersing groups or crosslinking groups. Such compounds preferably contain at least one (more preferably at least two) isocyanate-reactive groups, and are more preferably polyols. The polyols particularly include diols and triols and mixtures thereof but higher functionality polyols may be used, for example as minor components in admixture with diols. Preferred polyol molecular weights are from 250 to 6000, more preferably from 500 to 3000. The polyols may be members of any of the chemical classes of polyols used or proposed to be used in polyurethane formulations. In particular the polyols may be polyesters, polyesteramides, polyethers, polythioethers, polycarbonates, polyacetals, polyolefins or polysiloxanes. Polyester polyols which may be used include hydroxyl-terminated reaction products of polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, 1 ,4-butanediol, 1 ,6-hexanediol, furan dimethanol, cyclohexane dimethanol, glycerol, trimethylolpropane or pentaerythritol, or mixtures thereof, with 5 polycarboxylic acids, especially dicarboxylic acids or their ester-forming derivatives, for example succinic, glutaric and adipic acids or their methyl esters, phthalic anhydrides or dimethyl terephthalate. Polyesters obtained by the polymerisation of lactones, for example caprolactone, in conjunction with a polyol may also be used. Polyesteramides may be obtained by the inclusion of amino-alcohols such as 0 ethanolamine in polyestehfication mixtures. Polyesters which incorporate carboxy groups may be used, for example polyesters synthesised by esterification of DMPA and/or DMBA with diols, provided that the esterification is carried out at temperatures below 200°C to retain the carboxy functionality in the final polyester. Polyether polyols which may be used include products obtained by the 5 polymerisation of a cyclic oxide, for example ethylene oxide, propylene oxide or tetrahydrofuran or by the addition of one or more such oxides to polyfunctional initiators, for example water, methylene glycol, ethylene glycol, propylene glycol, diethylene glycol, cyclohexane dimethanol, glycerol, trimethylopropane, pentaerythritol or Bisphenol A. Especially useful polyether polyols include polyoxypropylene diols and triols, poly !0 (oxyethylene-oxypropylene) diols and triols obtained by the simultaneous or sequential addition of ethylene and propylene oxides to appropriate initiators and polytetramethylene ether glycols obtained by the polymerisation of tetrahydrofuran. Low molecular weight compounds containing at least one (more preferably at least two) isocyanate-reactive groups and having a weight average molecular weight up !5 to 500, preferably in the range of 40 to 250 can also be used. Examples include ethyleneglycol, neopentyl glycol, 1-propanol, and 1 ,4-cyclohexyldimethanol. Preferably the isocyanate-terminated polyurethane prepolymer comprises 5 to 90.5 wt% of component (iii). Components (i), (ii) and (iii) preferably add up to 100%. When an isocyanate-terminated polyurethane prepolymer is prepared, it is SO conventionally formed by reacting a stoichiometric excess of the organic polyisocyanate with the isocyanate-reactive compounds under substantially anhydrous conditions at a temperature between about 30°C and about 130°C until reaction between the isocyanate groups and the isocyanate-reactive groups is substantially complete; the reactants for the prepolymer are generally used in proportions corresponding to a ratio of isocyanate 55 groups to isocyanate-reactive groups of from about 1.4:1 to about 2.9:1 , preferably from about 1.5:1 to 2.5:1. If desired, catalysts such as dibutyltin dilaurate and stannous octoate, zirconium or titanium based catalysts may be used to assist in the polyurethane polymer (A) formation. An organic solvent may optionally be added before or after prepolymer or

10 final polymer formation to control the viscosity. An organic solvent may optionally be added at any stage of the isocyanate-terminated polyurethane prepolymer and/or polyurethane polymer (A) preparation to control the viscosity. Suitable solvents which may be used include acetone, methylethylketone, dimethylformamide, diglyme, N- methylpyrrolidinone, N-ethyl pyrrolidinone, ethyl acetate, ethylene and propylene glycol diacetates, alkyl ethers of ethylene and propylene glycol diacetates, alkyl ethers of ethylene and propylene glycol monoacetates, toluene, xylene and sterically hindered alcohols such as t-butanol and diacetone alcohol. The preferred organic solvents are water-miscible solvents such as N-methylpyrrolidinone, acetone and dialkyl ethers of glycol acetates or mixtures of N-methylpyrrolidinone and methyl ethyl ketone. The solvent may also include reactive diluents such as olefinically unsaturated monomers, which may be polymerised in situ to prepare a vinyl polymer. Optionally no organic solvents are added. An aqueous polyurethane polymer (A) dispersion may also be prepared, if the prepolymer/chain extension route was employed, by neutralising and dispersing the isocyanate-terminated polyurethane prepolymer (optionally carried in an organic solvent) in an aqueous medium such as water and chain extending the prepolymer with active- hydrogen containing chain extender in the aqueous phase. Neutralisation, dispersion and chain extension may be carried out in any order and may be carried out simultaneously. The isocyanate-terminated polyurethane prepolymer may be dispersed in water using techniques well known in the art. Preferably, the isocyanate-terminated polyurethane prepolymer is added to the water with agitation or, alternatively, water may be stirred into the isocyanate-terminated polyurethane prepolymer. Alternatively, although less preferably, the isocyanate-terminated polyurethane prepolymer may be chain extended to form the polyurethane polymer (A) while dissolved in an organic solvent (usually acetone) followed by the addition of water to the polyurethane polymer (A) solution until water becomes the continuous phase and the subsequent removal of solvent (e.g. by distillation) to form an aqueous dispersion (the well-known "acetone process"). Active-hydrogen containing chain extenders, which may be reacted with the isocyanate-terminated polyurethane prepolymer, include amino-alcohols, primary or secondary diamines or polyamines, hydrazine, and substituted hydrazines. Examples of such chain extenders useful herein include alkylene diamines such as ethylene diamine and cyclic amines such as isophorone diamine. Also materials such as hydrazine, azines such as acetone azine, substituted hydrazines such as, for example, dimethyl hydrazine, 1 ,6-hexamethylene-bis-hydrazine, carbodihydrazine, hydrazides of dicarboxylic acids and sulphonic acids such as adipic acid mono- or dihydrazide, oxalic acid dihydrazide, isophthalic acid dihydrazide, hydrazides made by reacting lactones with hydrazine such as gammahydroxylbutyric hydrazide, bis-semi- carbazide, and bis-hydrazide carbonic esters of glycols may be useful. Water itself may be effective as an indirect chain extender. Another suitable class of chain extenders are the so-called "Jeffamine" compounds with a functionality of 2 or 3 (available from Huntsman). These are PPO or PEO-based di or triamines, e.g. "Jeffamine" T403 and "Jeffamine" D-400. Where the chain extender is other than water, for example a polyamine or hydrazine, it may be added to the aqueous dispersion of the isocyanate-terminated polyurethane prepolymer or, alternatively, it may already be present in the aqueous medium when the isocyanate-terminated polyurethane prepolymer is dispersed therein. The isocyanate-reactive component may also include a chain terminator, for example one or more organic mono-ols. Optionally a combination of a chain extenders and a chain terminators may be used. Examples of chain terminators are mono- functional isocyanate-reactive compounds such as mono-alcohols, mono-amines, mono- hydrazines and mono-mercaptanes. The preparation of polyurethane polymer (A) may also be carried out by a technique comprising in-line mixing, as described in Research Disclosure (2002), 475, p772-774. Any other known methods for preparing polyurethane dispersions such as a ketamine/ketazine process or a hot process as described in "Progress in Organic Coatings", D. Dietrich, 9, 1981 , p 281) may also be utilised. The term vinyl polymer as used herein includes one vinyl polymer as well as more than one vinyl polymer. Vinyl polymer (B) and vinyl polymer (C) are homo- or copolymers derived from free-radically polymerisable olefinically unsaturated monomers, which are also usually referred to as vinyl monomers, and can contain polymerised units of a wide range of such monomers, especially those commonly used to make binders for the coatings industry. Examples of vinyl monomers which may be used to form vinyl polymer (B) and vinyl polymer (C) include but are not limited to vinyl monomers such as 1 ,3-butadiene, isoprene; trifluoro ethyl (meth)acrylate (TFEMA); dimethyl amino ethyl (meth)acrylate (DMAEMA); polyalkylene glycol di(meth)acrylates such as 1 ,3-butyleneglycol diacrylate, ethyleneglycol diacrylate; divinyl benzene; styrene, α-methyl styrene, (meth)acrylic amides and (meth)acrylonitrile; vinyl halides such as vinyl chloride; vinylidene halides such as vinylidene chloride; vinyl ethers; vinyl esters such as vinyl acetate, vinyl propionate, vinyl laurate; vinyl esters of versatic acid such as VeoVa 9 and VeoVa 10 (VeoVa is a trademark of Resolution); heterocyclic vinyl compounds; alkyl esters of mono-olefinically unsaturated dicarboxylic acids such as di-n-butyl maleate and di-n- butyl fumarate and in particular, esters of acrylic acid and methacrylic acid of formula CH₂=CR¹-COOR² wherein R¹ is H or methyl and R² is optionally substituted alkyl or cycloalkyl of 1 to 20 carbon atoms (more preferably 1 to 8 carbon atoms) examples of which are methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate (all isomers), octyl (meth)acrylate (all isomers), 2-ethylhexyl (meth)acrylate, isopropyl (meth)acrylate and propyl (meth)acrylate. Preferred monomers of formula CH₂=CR¹-COOR² include butyl (meth)acrylate (all isomers), methyl (meth)acrylate, octyl (meth)acrylate (all isomers) and ethyl (meth)acrylate. Particularly preferred vinyl monomers include (meth)acrylate monomers and styrene based monomers. The vinyl monomers may include vinyl monomers carrying functional groups such as crosslinker groups and/or water-dispersing groups as described above and/or other functional vinyl monomers as exemplified below. Such functionality may be introduced directly in the vinyl polymer by free-radical polymerisation, or alternatively the functional group may be introduced by a reaction of a reactive vinyl monomer, which is subsequently reacted with a reactive compound carrying the desired functional group. Some functional groups may perform than one function, for example (meth)acrylic acid is usually used as a water-dispersing monomer however it may also act as a crosslinking monomer. Such variations are known to those skilled in the art. Preferred vinyl monomers providing ionic or potentially ionic water-dispersing groups include but are not limited to (meth)acrylic acid, itaconic acid, maleic acid, β- carboxyethyl acrylate, monoalkyl maleates (for example monomethyl maleate and monoethyl maleate), citraconic acid, styrenesulphonic acid, vinylbenzylsulphonic acid, vinylsulphonic acid, acryloyloxyalkyl sulphonic acids (for example acryloyloxymethyl sulphonic acid), 2-acrylamido-2-alkylalkane sulphonic acids (for example, 2-acrylamido- 2-methylethanesulphonic acid), 2-methacrylamido-2-alkylalkane sulphonic acids (for example 2-methacrylamido-2-methylethanesulphonic acid), mono(acryloyloxyalkyl) phosphates (for example mono(acryloyloxyethyl)phosphate) and mono(methacryloyl- oxyalkyl) phosphates (for example, mono(methacryloyloxyethyl)phosphate). Non-ionic water-dispersing groups may be in-chain, pendant or terminal groups. Preferred vinyl monomers providing non-ionic water-dispersing groups include alkoxy polyethylene glycol (meth)acrylates, preferably having a number average molecular weight of from 350 to 3000. Examples of such monomers which are commercially available include ω-methoxypolyethylene glycol (meth)acrylate and diethylene glycol mono vinyl ether. Preferably vinyl polymer (B) has an acid value in the range of from 0 to 39, more preferably 0 to 30 and especially 0 to 25 mgKOH/g. Preferably vinyl polymer (C) has an acid value in the range of from 40 to 200, more preferably 50 to 100 mgKOH/g. Preferably vinyl polymer (C) is alkali soluble. By alkali soluble is meant that at least 50%, more preferably at least 75% of vinyl polymer (C) is dissolved within a composition at a pH in the range of from 7.5 to 9.0. Vinyl polymer (B) and vinyl polymer (C) may possess functional groups for imparting latent crosslinkability to the composition (so that crosslinking takes place for example after the aqueous composition is subsequently dried) either when combined with an externally added crosslinking agent and/or by reaction with each other and/or by reaction with polyurethane polymer (A). Such crosslinking methods include those described above such as autoxidation, Schiff base crosslinking and silane condensation. Examples of suitable vinyl monomers include acrylic and methacrylic monomers having at least one free carboxyl, hydroxyl, epoxy, acetoacetoxy, or amino group, such as acrylic acid and methacrylic acid, glycidyl 5 acrylate, glycidyl methacrylate, aceto acetoxy ethyl methacrylate, allyl methacrylate, tetraethylene glycol methacrylate, divinyl benzene, t-butylamino ethyl methacrylate and dimethylamino ethyl methacrylate. Amino functionality may be incorporated by preparing a vinyl polymer comprising vinyl monomers such as acrylic acid or methacrylic acid and subsequently converting at least a proportion of the carboxylic acid groups to amino

0 groups (as part of amino ester groups) by an imination reaction using an alkylene imine such as ethylene imine or propylene imine. Preferably vinyl polymer (C) bears carbonyl functional groups. Such carbonyl functional groups in a vinyl polymer are normally chain-pendant and/or terminal groups. Preferably the weight average molecular weight (Mw) of vinyl polymer (B) is in

5 the range of from 60,000 to 6,000,000 Daltons, more preferably in the range of from 100,000 to 3,000,000 Daltons and most preferably in the range of from 120,000 to 2,500,000 Daltons. Preferably vinyl polymer (C) has a weight average molecular weight in the range of from 15,000 to 40,000 Daltons, more preferably 20,000 to 40,000 Daltons and most

!0 preferably 20,000 to 35,000 Daltons. The Tg of a polymer herein stands for the glass transition temperature and is well known to be the temperature at which a polymer changes from a glassy, brittle state to a rubbery state. Tg values of polymers may be determined experimentally using techniques such as Differential Scanning Calorimetry (DSC) or calculated theoretically

!5 using the well-known Fox equation where the Tg (in Kelvin) of a copolymer having "n" copolymehsed comonomers is given by the weight fractions "W" and the Tg values of the respective homopolymers (in Kelvin) of each comonomer type according to the equation "1/Tg = + W₂/Tg₂ + W_n/Tg_n". The calculated Tg in Kelvin may be readily converted to °C.

^'0 The calculated Tg of vinyl polymer (B) is preferably in the range of from 20 to 140°C and more preferably in the range of from 30 to 100°C. Preferably the calculated Tg of vinyl polymer (C) is in the range of from 70 to 140°C, more preferably 80 to 120°C and most preferably 80 to 110°C. Vinyl polymer (B) and vinyl polymer (C) may be present in the composition of the

15 invention as a blend of preformed polymers or as a sequentially formed composition of the polymers by preparing one of the vinyl polymers in the presence of the other. In another aspect of the invention, vinyl polymer (B) and/or vinyl polymer (C) may be multistage polymers prepared by sequential polymerisation, by which it is meant that that the polymers comprises at least two distinct Tg values. A gradient polymerisation process, where the vinyl monomer composition of the monomer feed is varied continuously, may also be used to prepare vinyl polymer (B) and/or vinyl polymer (C). Vinyl polymer (B) and/or vinyl polymer (C) may also be an oligomer-supported polymer, by which is meant a low molecular weight polymer with a typical Mw of 5,000 to 50,000, more preferably 15,000 to 50,000 Daltons (usually described as an oligomer) is first prepared as a stabilising agent for the second phase of the vinyl polymer preparation. It is also possible to prepare a vinyl polymer in the presence of polyurethane polymer (A) thus forming a polyurethane/vinyl polymer hybrid. Alternatively the isocyanate-terminated prepolymer may be dispersed in an aqueous phase containing vinyl polymer (B) and/or vinyl polymer (C) and then chain extended to give polyurethane polymer (A). Preferably polyurethane polymer (A) and vinyl polymer (B) are in the form of a hybrid, where preferably vinyl polymer (B) is prepared in the presence of polyurethane polymer (A) and optionally in the presence of vinyl polymer (C). All of the vinyl monomer to be polymerised to form a hybrid may be present at the commencement of the polymerisation, or the vinyl monomer may be added to the reaction medium during the course of the polymerisation (in one or more stages or continuously). For example, when the aqueous dispersion of the isocyanate-terminated polyurethane prepolymer is formed in the process to make the polyurethane polymer (A) as described above some or all of the vinyl monomer for the vinyl polymer (B) may be added during the prepolymer preparation prior to its dispersion into water (and therefore may act as a reactive diluent), or all of the vinyl monomer may be added subsequent to dispersion (or some or all of the vinyl monomer may have already been added to the water prior to the dispersion of the prepolymer therein). The vinyl monomers tend to swell (i.e. become absorbed in) the polyurethane polymer (A) particles which when polymerised result in a hybrid of the polyurethane polymer (A) and vinyl polymer (B) in which at least part of the vinyl polymer (B) (and usually most of the vinyl polymer (B)) is located within the polyurethane polymer (A) particles. Preferably vinyl polymer (C) is preformed and then blended with polyurethane polymer (A) before or after the preparation of vinyl polymer (B). Vinyl polymer (B) and vinyl polymer (C) are preferably prepared by free-radical polymerisation, although in some circumstances anionic polymerisation may be utilised. The free-radical polymerisation can be performed by techniques well known in the art, for example, emulsion polymerisation, solution polymerisation, suspension polymerisation or bulk polymerisation. Vinyl polymer (C) is preferably formed by an emulsion or by a bulk polymerisation process. Bulk polymerisation of vinyl monomers is described in detail in EP 0,156,170, WO 82/02387 and US 4,414,370, which are incorporated herein by reference. In general in a bulk polymerisation process a mixture of two or more vinyl monomers are charged continuously into a reactor zone containing molten vinyl oligomer having the same ratio of vinyl monomers as the vinyl monomer mixture. The free-radical polymerisation may be carried out as a batch, step-wise, gradient or as a semi-continuous polymerisation process to make a single or a multistage polymer. Free-radical polymerisation of vinyl monomers will require the use of a free- radical-yielding initiator to initiate the vinyl polymerisation. Suitable free-radical-yielding initiators include K, Na or ammonium persulphate; hydrogen peroxide; percarbonates; organic peroxides, such as acyl peroxides including 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 Na or K pyrosulphite or bisulphite, and iso-ascorbic acid. Metal compounds such as Fe.EDTA (EDTA is ethylene diamine tetracetic acid) may also be usefully employed as part of the redox initiator system. Azo functional initiators may also be used. Preferred azo initiators include azobis(isobutyronitrile) and 4,4'-azobis(4-cyanovaleric acid). The amount of initiator or initiator system used is conventional, e.g. within the range 0.05 to 6 wt % based on the total weight of vinyl monomers used. Preferred initiators include ammonium persulphates, sodium persulphates, potassium persulphates, azobis(isobutyronitrile) and/or 4,4'-azobis(4-cyanovaleric acid). Molecular weight control may be provided by catalytic chain transfer agents as described below, or may be provided by using chain transfer agents such as mercaptans and halogenated hydrocarbons, for example mercaptans such as n-dodecylmercaptan, n-octylmercaptan, t-dodecylmercaptan, mercaptoethanol, iso-octyl thioglycolate, C₂ to C₈ mercapto carboxylic acids and esters thereof such as 3-mercaptopropionic acid and 2- mercaptopropionic acid; and halogenated hydrocarbons such as carbon tetrabromide and bromotrichloromethane. In catalytic chain transfer polymerisation (CCTP) a free-radical polymerisation is carried out using a catalytic amount of a selected transition metal complex acting as a catalytic chain transfer agent (CCTA), and in particular a selected cobalt chelate complex. For example, N.S. Enikolopyan et al, J.Polym.Chem.Ed, Vol 19, 879 (1981 ), discloses the use of cobalt II porphyrin complexes as chain transfer agents in free- radical polymerisation, while US 4,526,945 discloses the use of dioxime complexes of cobalt II for such a purpose. US 4,680,354, EP 0,196,783, EP 0,199,436 and EP 0,788,518 describe the use of certain other types of cobalt II chelates as chain transfer agents for the production of polymers of olefinically unsaturated monomers by free- radical polymerisation. WO 87/03605 on the other hand claims the use of certain cobalt III chelate complexes for such a purpose, as well as the use of certain chelate complexes of other metals such as iridium and rhenium. Preferably < 0.1 wt %, more preferably < 0.08 wt %, especially < 0.04 wt % and most especially < 0.03 wt % of catalytic chain transfer agents, based on the weight of vinyl monomer, is used. Combinations of conventional chain transfer agents and catalytic chain transfer agents may also be used. Surfactants can be utilised in order to assist in the dispersion of the polyurethane polymer (A), vinyl polymer (B) and/or vinyl polymer (C) in water (even if they are self- dispersible). Suitable surfactants include but are not limited to conventional anionic, cationic and/or non-ionic surfactants and mixtures thereof such as Na, K and NH₄ salts of dialkylsulphosuccinates, Na, K and NH₄ salts of sulphated oils, Na, K and NH₄ salts of alkyl sulphonic acids, Na, K and NH₄ alkyl sulphates, alkali metal salts of sulphonic acids; fatty alcohols, ethoxylated fatty acids and/or fatty amides, and Na, K and NH₄ salts of fatty acids such as Na stearate and Na oleate. Other anionic surfactants include alkyl or (alk)aryl groups linked to sulphonic acid groups, sulphuric acid half ester groups (linked in turn to polyglycol ether groups), phosphonic acid groups, phosphoric acid analogues and phosphates or carboxylic acid groups. Cationic surfactants include alkyl or (alk)aryl groups linked to quaternary ammonium salt groups. Non-ionic surfactants include polyglycol ether compounds and preferably polyethylene oxide compounds as disclosed in "Non-Ionic Surfactants - Physical Chemistry" edited by M.J. Schick, M. Decker 1987. The amount of surfactant used is preferably 0 to 10% by weight, more preferably 0 to 5% by weight, still more preferably 0 to 3% by weight and especially 0.1 to 2% by weight based on the weight of the vinyl monomers. The recyclable aqueous coating composition of the invention typically has a solids content of from about 20 to 60 wt%, more usually from 25 to 50 wt% and especially 25 to 40 wt%. The recyclable aqueous coating composition of the invention is particularly useful for providing the principle component of coating compositions (e.g. protective or decorative coating compositions) for which purpose it may be further diluted with water and/or organic solvents, or it may be supplied in a more concentrated form by evaporation of water and/or organic components of the liquid medium. As a coating composition, it may be applied to a variety of substrates including wood (in particular porous wood), board, metals, stone, concrete, glass, cloth, leather, paper plastics, foam and the like, by any conventional method including brushing, dipping, flow coating, spraying and the like, and more preferably by spraying. The aqueous composition once applied may be allowed to dry naturally at ambient temperature or the drying process may be accelerated by the application of heat. The recyclable aqueous composition of the invention may contain conventional ingredients, some of which have been mentioned above; examples include pigments (for example titanium dioxide, iron oxide, chromium based compounds and/or metal pthalocyanine compounds), dyes, emulsifiers, surfactants, plasticisers, thickeners, heat stabilisers, levelling agents, anti-cratehng agents, fillers, sedimentation inhibitors, UV absorbers, antioxidants, drier salts, water-soluble and/or water-insoluble co-solvents, wetting agents, defoamers, fungicides, bactenocides, waxes and the like introduced at any stage of the production process or subsequently. It is possible to include an amount of antimony oxide in the dispersions to enhance the fire retardant properties. The recyclable aqueous coating composition of the invention preferably contains less than 15 wt % of organic solvents and more preferably less than 10 wt % based on total solids weight of polymer (A) + (B) + (C). The aqueous coating composition of the invention may be substantially solvent-free. By a substantially solvent-free aqueous composition is meant that the composition must contain less than 1.5 wt % of organic solvents based on total polymer solids, more preferably less than 0.5 wt %, and most preferably no solvent at all. (In this specification organic plasticisers are intended to be within the scope of the term "solvent"; these, like coalescent solvents, are also used in the art to decrease the minimum film forming temperature (MFFT) although strictly speaking they are not solvents). If desired the aqueous composition of the invention can be used in combination with other polymer compositions which are not according to the invention. In a third embodiment of the present invention is provided a method for recycling a recyclable aqueous coating composition according to the present invention comprising steps: (X) coating a substrate with the composition; (Y) collecting any overspray of the composition; and (Z) redispersing the overspray, in the original composition in a weight ratio of 1 :99 to 30:70. The recyclable aqueous coating composition of the invention has the advantage that when it is recycled that the physical properties of a resultant coating are maintained.

Such physical properties include but are not limited to film appearance, blocking, hardness and chemical resistance of the resultant coating. Preferably the film appearance is maintained after recycling. Film appearance is usually diminished when using a recycled composition as when the overspray dries, particles are formed which no longer redissolve in the original composition. These particles may be visible without requiring magnification and are detrimental to the film appearance. Preferably a film prepared from the recycled composition of the invention has < 5 particles per 150 cm². Kόnig hardness as used herein is a standard measure of hardness, being a determination of how the viscoelastic properties of a coating formed from the dispersion slows down a swinging motion deforming the surface of the coating and is measured according to DIN 53157 using an Erichsen hardness equipment. Preferably the hardness of a coating obtained from a recycled aqueous coating composition of the invention is within ± 20s, more preferably within ± 10s of the hardness of a coating obtained from the original composition. Blocking is the well-known phenomenon of coated substrates which are in contact tending to unacceptably adhere to each other, for examples doors and windows in their respective frames, particularly when under pressure, as for example in stacked panels. Preferably the blocking of a coating obtained from a recycled aqueous coating composition of the invention is substantially identical to the blocking of a coating obtained from the original composition. Chemical resistance as used herein is defined as the resistance to direct contact with chemicals such as hand cream, coffee, detergent and alcohol. Preferably the chemical resistance of a coating obtained from a recycled aqueous coating composition of the invention is substantially identical to the chemical resistance of a coating obtained from the original composition. In a fourth embodiment of the present invention there is provided a coating obtained from a recyclable aqueous coating composition or a recycled coating composition according to any one of the preceding claims. In a fifth embodiment of the present invention there is provided the use of a recyclable aqueous coating composition or a recycled aqueous coating composition according to the present invention in spray applications. In a sixth embodiment of the present invention there is provided the use of a recyclable aqueous coating composition or a recycled aqueous coating composition according to the present invention for coating wood. The present invention is now illustrated but in no way limited by reference to the following examples. Unless otherwise specified all parts, percentages and ratios are on a weight basis.

Polyurethane polymer (A), vinyl polymer (B) Polyurethane polymer (A) and vinyl polymer (B) were provided by NeoPac E111 , a polyurethane/acrylic hybrid polymer dispersion available from NeoResins, Avecia BV (solids 35 wt%, pH 8.2). The acid value of the polyurethane polymer (A) component was about 63 mgKOH/g and the molecular weight (Mw) was > 200,000 Daltons. The polyurethane polymer (A) component was prepared from aliphatic isocyanates. The Tg of the vinyl polymer (B) component was 52°C, the Mw was approximately 500,000 and the acid value was 0 mgKOH/g.

Synthesis of Vinyl Polymer (C)1 The ingredients used for the preparation of vinyl polymer (C)1 are listed in Table 1 below. Table 1

Ingredients 1 to 3 were charged to a 21 3-necked round bottom flask, equipped with a stirrer and a thermometer under a nitrogen atmosphere. The contents of the reactor were heated up to 85°C. An emulsified feed containing ingredients 6 to 11 was prepared in a feeding vessel. The emulsified feed was fed into the reactor (at 85°C) over 90 minutes. Simultaneously the initiator feed (ingredients 4 to 5) was fed into the reactor

I0 over 90 minutes. The reaction temperature was maintained at 83 to 87°C during the feeds. On completion of the feeds, the batch was maintained at 85°C for a further period of 30 minutes. After this ingredients 12 and 13 were added over a period of 5 minutes. The temperature was maintained for another 30 minutes at 85°C. Finally the reactor was cooled to 50°C and a mixture of ingredients 14 and 15 was added, followed by an

15 addition of ingredients 16 and 18 to the reactor over a period of 45 minutes. The reactor content was cooled to 25°C and filtered through 200 mesh filter cloth to remove any coagulum formed during the reaction. The solids content of the resultant latex was 25 wt%. The calculated Tg was 104°C, the Mw as measured by GPC was 30,000 Daltons and the acid value was 65 mgKOH/g.

Vinyl Polymer (C)2 NeoCryl BT-101 (available from Avecia BV), a 40 wt% solids solution with a pH of about 1.6 to 2.6 was diluted with water to 15 wt% and neutralised with ammonia to a pH of 9.0 to 9.5. The calculated Tg of NeoCryl BT-101 was 105°C, the Mw as measured by GPC was 25,000 Daltons and the acid value was 150mg KOH/g.

Example 1 = E1 The resultant latex of vinyl polymer (C)1 [14 g] was blended with NeoPac E111 [100 g] to give Example 1.

Example 2 = E2 The resultant latex of vinyl polymer (C)1 [24.71 g] was blended with NeoPac E111 [100g] to give Example 2.

Example 3 = E3 Vinyl polymer solution (C)2 [25.92g] was blended with NeoPac E111 [100g] to give Example 3.

Comparative Example 1 = CE1 NeoPac E111 without any vinyl polymer (C) was used as comparative example 1.

Comparative Vinyl Polymer (C)3 A 20 wt% solids solution in water of Joncryl E07 (available as solid flake from S.C. Johnson) was prepared and neutralised with ammonia to a pH of 9 to 9.5. From the product literature it is known that Joncryl E07 is an α-methylstyrene-styrene-acrylic acid copolymer dispersion with a Mw of about 9,000 to 10,500 Daltons and an acid value of about 220 to 235 mgKOH/g. The Tg as measured by DSC was about 130°C.

Comparative Vinyl Polymer (C) 4 NeoCryl BT-24 (available from Avecia BV) a 45 wt% solids solution with a pH of about 4.9 to 5.5 was diluted with water to 22 wt% and neutralised with ammonia to a pH of 8.5 to 9.0. The calculated Tg of NeoCryl BT-24 was 29°C, the Mw as measured by GPC was 25,000 Daltons and the acid value was 71 mg KOH/g.

Comparative Example 2 = CE2 Vinyl polymer solution (C)3 [19.4g] was blended with NeoPac E111 [100g] to give comparative Example 2. Comparative Example 3 = CE3 Vinyl polymer solution (C)4 [28.07g] was blended with NeoPac E111 [100g] to give comparative example 3.

Formulation

Clear Formulation for test coatings The following formulation shown below in Table 2 was used for all of the examples: Table 2

Preparation method Ingredients 2 to 6 were pre mixed and adjusted to a pH value of 8.0 using aqueous ammonia. The premix was then added to ingredient 1 while stirring, after which ingredients 7 to 11 were then added in and mixed at high speed.

Collection and recycling of overspray

Step (1) 6.5 +/- 0.5 g of formulated test sample (original material E1 , E2, E3, CE1 , CE2 or CE3) was spray coated on to a cooled (4°C) glass plate by using a conventional air assisted spray equipment and the resultant film was allowed to dry for 10 minutes at a temperature of 20 +/- 2°C and 50% relative humidity.

Step (2) The semi-dried film prepared in step (1 ) was removed using a scraping tool and collected into a bottle. Step (3) Within 20 minutes from the end of step (1 ) [i.e. drying of the film for 10 minutes] 4 +/- 0.5 g of the semi-dried film collected in step (2) was mixed with 36 +/- 0.5 g of original material to obtain recycled material, which was used for the tests described below.

Test for assessing the film appearance of the coating The formulated original test samples and the recycled material of each example prepared in step (3) above, were cast onto a 10cm x 15cm glass plate using a Bird applicator at a wet film thickness of 80 micron and allowed to stand for 2 minutes at a temperature of 20+/- 2°C and a relative humidity of 50%. On standing for 2 minutes the appearance of the whole wet film was visually assessed for the number of particles present in the film and the results are given in Table 3 below. Film appearance was measured by the number of particles per glass plate (i.e. per 150 cm²) and values were given to the film appearance as follows: 0 to 5 particles = few = good 6 to 20 particles = medium = adequate 21 + particles = dense = poor

Test methods of coating obtained As the maintenance of film appearance was considered more important than the maintenance of hardness or blocking, recycled materials which did not maintain their film appearance were not tested for hardness, blocking or hand cream resistance, and this is shown in Table 3 below as a *.

Kόnig Hardness This method is based on DIN 53157 (although it is not an exact copy of it). It assesses the damping behaviour of a coating, which is influenced by the elastic and viscoelastic properties of the coating. Clean glass plates were coated with 80μm wet films of the above described formulated original test samples and recycled material. They were dried at room temperature for four hours. The coated glass plates were placed at an oven at 50°C for 16 hours. The coated substrates were conditioned at room temperature (20 + 5°C) and at a relative humidity of 50% for 24 hours, before the hardness was determined with an Erichsen type 299/300 equipment for hardness measurements. The results are shown in Table 3 below.

Block Resistance This measurement is done in order to determine whether two layers of a coating will stick together under influence of temperature and pressure. A 100μm wet film of each formulated original test samples and recycled material were applied onto a Leneta Opacity test chart (form 2C). The coating was dried at room temperature for 5 minutes and then placed in the oven at 60°C for 20 minutes. Immediately after this the test chart was cut into pieces of 3.3 x 5 cm. Two pieces of each coating were put onto each other with the coated sides towards each other, so that they formed a cross. These test strips were then placed in a Blocking tester (ex Koehler Instrument Company) with a pressure of 3 kg/cm². The Blocking tester was placed in the oven for 4 hours at 60°C. After that the Blocking tester was taken out of the oven. The test strips were taken out of the Blocking tester and kept at room temperature for 30 minutes. After that the two pieces were separated from each other by hand. The damage to the coated substrates was determined. A rating of 0 means that the film was severely damaged; 5 means that the film was not affected at all. The results are shown in Table 3 below. Hand Cream Resistance testing method The formulated original test samples and recycled materials were applied (100 micron wet film thickness) on a wood (Mahogany) panel and allowed to dry in an oven at 50°C for 16 hours. The panel was removed from the oven and allowed to cool at room temperature for 1 hour. Following this, a spot ( about 1 cm²) of hand cream (Atrix) was placed on the coating and covered with a piece of filter paper and watch glass. This assembly was placed in an oven at 40°C for 2 hours. After this period the spot was gently wiped with a tissue and the film was assessed for its integrity. This was rated between 0 to 5, where 0 = film totally destroyed and 5 = film fully intact without any defects. The results are shown in Table 3 below.

Table 3

Claims

1. A recyclable aqueous coating composition comprising components: (1) at least a polyurethane polymer (A); (2) at least a vinyl polymer (B) having a Tg > 20°C, a weight average molecular weight > 50,000 Daltons and an acid value < 40 mgKOH/g; and (3) at least a vinyl polymer (C) having a Tg > 70°C, a weight average molecular weight in the range of from 15,000 to 50,000 Daltons and an acid value > 40mgKOH/g; wherein the weight ratio of polyurethane polymer (A) and vinyl polymer (B) together to vinyl polymer (C) is in the range of from 95:5 to 65:35.

2. A recyclable aqueous coating composition according to claim 1 wherein polyurethane polymer (A) is the reaction product of:

(I) an isocyanate-terminated polyurethane prepolymer having an acid value of > 20 mgKOH/g of prepolymer obtained from the reaction of components comprising: (i) at least one organic polyisocyanate; (ii) at least one isocyanate-reactive compound bearing ionic and/or potentially ionic water-dispersing groups; (iii) at least one isocyanate-reactive compound not comprised by (ii); and II) at least one active-hydrogen chain extending compound.

3. A recyclable aqueous coating composition according to claim 2 wherein at least 40 wt% of component (i) comprises at least one aliphatic polyisocyanate.

4. A recyclable aqueous coating composition according to any one of the preceding claims wherein the weight average molecular weight of polyurethane polymer (A) is in the range of from 50,000 to 1 ,000,000 Daltons.

5. A recyclable aqueous coating composition according to any one of the preceding claims wherein vinyl polymer (C) is alkali soluble.

6. A recyclable aqueous coating composition according to any one of the preceding claims wherein vinyl polymer (C) bears carbonyl functional groups.

7. A recyclable aqueous coating composition according to any one of the preceding claims wherein vinyl polymer (B) is prepared in the presence of polyurethane polymer (A).

8. A recyclable aqueous coating composition according to any one of the preceding claims wherein vinyl polymer (C) is blended with polyurethane polymer (A) and vinyl polymer (B).

9. A recyclable aqueous coating composition according to any one of the preceding claims containing less than 15 wt% of organic solvents based on the total solid weight of (A) + (B) + (C).

10. A recyclable aqueous coating composition according to any one of the preceding claims having a solids content of from about 20 to 60 wt%.

11. A recyclable aqueous coating composition according to any of the preceding claims which is recycled by redispersing any overspray resulting from application of the coating composition to a substrate, in more of the original recyclable composition in a weight ratio of 1 :99 to 30:70.

12. A recyclable aqueous coating composition according to claim 11 wherein the overspray is recycled within 40 minutes of application of the recyclable aqueous coating composition.

13. A recycled aqueous coating composition comprising: (a) 70 to 99 wt% of the recyclable aqueous coating composition according to any one of claims 1 to 12; and (b) 1 to 30 wt% of overspray; where (a) + (b) = 100%.

14. A recycled aqueous coating composition according to claim 13 wherein a film prepared from the recycled composition has < 5 particles per 150 cm².

15. A recycled aqueous composition according to claim 13 wherein the hardness of a coating prepared from the recycled aqueous coating composition is within + 20s of the hardness of a coating prepared from the original recyclable aqueous coating composition.

16. A method for recycling a recyclable aqueous coating composition according to any one of claims 1 to 12 comprising steps: (X) coating a substrate with the composition; (Y) collecting the overspray of the composition; and (Z) redispersing the overspray, in the original composition in a weight ratio of 1 :99 to 30:70.

17. A coating obtained from a recyclable aqueous coating composition according to any one of claims 1 to 12.

18. A coating obtained from a recycled aqueous coating composition according to claim 13.

19. Use of a recyclable aqueous coating composition according to any one of claims 1 to 12 in spray applications.

20. Use of a recycled aqueous coating composition according to claim 13 in spray applications.

21. Use of a recyclable aqueous coating composition according to any one of claims 1 to 12 for coating wood.

22. Use of a recycled aqueous coating composition according to claim 13 for coating wood.