WO2004067582A1

WO2004067582A1 - Curable composition comprising a compound having radically polymerizable olefinically unsaturated groups, an oxidation-reduction enzyme, and a thiol-functional compound

Info

Publication number: WO2004067582A1
Application number: PCT/EP2004/000649
Authority: WO
Inventors: Keimpe Jan Van Den Berg; Edith Benningshof-Hulsbos
Original assignee: Akzo Nobel Coatings International BV
Current assignee: Akzo Nobel Coatings International BV
Priority date: 2003-01-28
Filing date: 2004-01-26
Publication date: 2004-08-12
Anticipated expiration: 2005-07-28

Abstract

The invention relates to a curable composition comprising a compound having at least one radically polymerizable olefinically unsaturated group and a molecular weight above 500 and an oxidation-reduction enzyme, characterized in that the composition additionally comprises a thiol-functional compound. The invention further relates to a process for curing the composition by actinic radiation, and to the use of the curable composition as adhesive and coating composition. The curable composition according to the invention cures sufficiently fast to be useful as a coating composition for finishing and refinishing of cars and large transportation vehicles. The composition does not require volatile and/or toxic monomers. Furthermore, a sufficient conversion of the curing reaction is generally obtained.

Description

CURABLE COMPOSITION COMPRISING A COMPOUND HAVING RADICALLY POLYMERIZABLE OLEFINICALLY UNSATURATED GROUPS, AN OXIDATION-REDUCTION ENZYME, AND A THIOL-FUNCTIONAL COMPOUND

The current invention relates to a curable composition comprising a compound having at least one radically polymerizable olefinically unsaturated group and a molecular weight above 500 and an oxidation-reduction enzyme, to a process of curing the composition, and to the use thereof as a coating or adhesive.

A composition of the above-mentioned type is known from European patent application EP 0 950 669-A. This publication discloses a method of catalytic cross-linking of a polymer having oxidatively cross-linkable functional groups, by contacting it with an oxidizing enzyme. This publication further describes a two- pack coating composition comprising a first container containing a polymeric component comprising a polymer having oxidatively cross-linkable functional groups and a second container containing a component comprising a catalytic amount of an oxidizing enzyme. In the examples phenolic, latent phenolic, and active methylene groups are employed as oxidatively cross-linkable functional groups. This publication mentions as additional oxidatively cross-linkable functional groups olefinically unsaturated functional groups such as vinyl, allyl acryloyl, as well as mercapto, sulfide, and phosphino groups. Compositions comprising a combination of olefinically unsaturated functional groups and mercapto-functional groups are not disclosed. A disadvantage of the compositions exemplified in EP 0 950 669-A is the relatively long time of 4 - 11 days required to achieve a good degree of cross- linking. For finishing and refinishing of cars and large transportation vehicles such a long curing time generally is not acceptable. It has also been found that a polymer having acrylic functional groups does not cure at all in the presence of an oxidizing enzyme alone.

European patent application EP 0 321 872-A discloses a process for the polymerization of radically polymerizable unsaturated monomers wherein the radical initiator is formed by a peroxide-generating enzyme. Oxidases are mentioned as suitable enzymes. Radical formation by decomposition of the formed peroxide can be induced by a reducing agent. A large number of suitable reducing agents are mentioned, including mercaptans, but only iron (11) chloride and ascorbic acid are specifically exemplified. A drawback to the process and the composition of EP 0 321 872-A is the need to employ radically polymerizable monomers, such as (meth)acrylate monomers. Such monomers have a molecular weight lower than 500 and are frequently toxic and volatile,, and additionally the monomers often have an offending smell. Furthermore, from the reported yields of polymer one has to conclude that the conversion generally is insufficient, which leads to the presence of free monomers in the polymer. As noted above for EP 0 950 669-A, a polymer having acrylic functional groups does not cure at all under the conditions described in EP 0 321 872-A. These properties detract from the suitability of the process and composition of EP 0 321 872-A for many applications, for example when used as a coating or adhesive composition.

The invention now provides a curable composition of the aforementioned type which is not restricted by the above-mentioned drawbacks. The curable composition of the current invention comprises a compound having at least one radically polymerizable olefinically unsaturated group and a molecular weight above 500 and an oxidation-reduction enzyme, characterized in that the composition additionally comprises a thiol-functional compound. The composition cures sufficiently fast to be useful as a coating composition for finishing and refinishing of cars and large transportation vehicles. The composition does not require volatile and/or toxic monomers. Furthermore, a sufficient conversion of the curing reaction is generally obtained with the curable composition according to the invention. The conversion can suitably be followed by determination of the decrease of radically polymerizable olefinically unsaturated groups, for example by means of infrared spectroscopy. Due to the non-volatility of the compound having at least one radically polymerizable olefinically unsaturated group and a molecular weight above 500, conversions which are unacceptably low in the polymerization of volatile monomers may be sufficient for curing the composition of the current invention.

Compounds having at least one radically polymerizable olefinically unsaturated group

Suitable compounds having at least one radically polymerizable olefinically unsaturated group have a molecular weight above 500, preferably above 700. When the compound having at least one radically polymerizable olefinically unsaturated group is an oligomer or polymer, the number average molecular weight suitably is in the range of 500 - 25,000, preferably 700 - 15,000. Above a molecular weight of 500 the volatility of compounds having at least one radically polymerizable olefinically unsaturated group is sufficiently low to prevent volatility and offending smell. Suitable radically polymerizable olefinically unsaturated groups are vinyl groups, vinyl aromatic groups, allyl groups, and electron-poor olefinically unsaturated groups. Examples of the latter types of groups are acryloyl groups, methacryloyl groups, and esters, anhydrides, amides, and imides of maleic, itaconic, and citraconic acid.

The preferred radically polymerizable olefinically unsaturated groups are electron-poor olefinically unsaturated groups. Particularly preferred are acryloyl- functional groups. In order to ensure cross-linking of the curable composition, it is preferred that the compound having at least one radically polymerizable olefinically unsaturated group and a molecular weight above 500 has a functionality of at least 2. In a particularly preferred embodiment the compound having at least one radically polymerizable olefinically unsaturated group is a polymer having a plurality of radically polymerizable olefinically unsaturated groups. It is to be understood that the term polymer includes oligomers. Examples of suitable polymers are polyaddition polymers, polyesters, polyurethanes, polyethers, and mixtures and hybrids thereof. Polyaddition polymers

Polyaddition polymers having radically polymerizable olefinically unsaturated groups are suitably prepared in a two-step process.

In a first step a polyaddition polymer is prepared according to generally known processes. As suitable polyaddition polymers may be mentioned the (co)polymers of ethylenically unsaturated monomers. The terms (meth)acrylate and (meth)acrylic acid below refer to methacrylate and acrylate, as well as methacrylic acid and acrylic acid, respectively. Examples of suitable ethylenically unsaturated monomers are (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isobomyl (meth)acrylate, dodecyl (meth)acrylate, and cyclohexyl (meth)acrylate; other (meth)acrylic monomers such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, and 3-methoxypropyl (meth)acrylate; hydroxyalkyl (meth)acrylates, e.g., 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, p-hydroxycyclohexyl (meth)acrylate, hydroxypolyethylene glycol (meth)acrylates, hydroxypolypropylene glycol (meth)acrylates, and the corresponding alkoxy derivatives thereof; epoxy (meth)acrylates, such as glycidyl (meth)acrylate; (meth)acrylamide, (meth)acrylonitrile and N-methylol (meth)acrylamide; and N-alkyl (meth)acrylamides, such as N-isopropyl (meth)acrylamide, N-tert. -butyl (meth)acrylamide, N-tert.-octyl (meth)acrylamide, N,N-dimethyl aminoethyl (meth)acrylate, and N,N-diethyl aminoethyl (meth)acrylate. These monomers may be used optionally in combination with comonomers such as mono- and diesters of maleate or fumarate, such as dibutyl maleate, dibutyl fumarate, 2- ethylhexyl maleate, 2-ethylhexyl fumarate, octyl maleate, isobornyl maleate, dodecyl maleate, cyclohexyl maleate, and the like, and/or with a vinyl derivative such as styrene, vinyl toluene, α-methyl styrene, vinyl naphthalene, vinyl chloride, vinyl acetate, vinyl pyrrolidone, vinyl laurate, vinylneododecanoate, N- vinyl formamide, and vinyl propionate, and/or with monomers containing one or more urea or urethane groups, for instance the reaction product of 1 mole of isocyanatoethyl methacrylate or α,α-dimethyl-isocyanatomethyl-3-isopropenyl benzene and 1 mole of butylamine, 1 mole of benzylamine, 1 mole of butanol, 1 mole of 2-ethylhexanol, and 1 mole of methanol, respectively. Mixtures of these monomers or adducts can also be used. Preferred (co)monomers are styrene and alkyl (meth)acrylates, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and mixtures thereof.

The monomer mixture employed to prepare the polyaddition polymer must comprise monomers having functional groups for subsequent modification of the polymer in order to introduce the radically polymerizable olefinically unsaturated groups. Examples of monomers with functional groups for subsequent modification of the polymer are monomers having hydroxyl groups, epoxide groups, isocyanate groups, or carboxylic acid groups. The polyaddition polymer can be prepared by conventional methods of free radical initiated polymerization. Alternatively, advanced polymerization techniques, such as group transfer polymerization (GTP), atom transfer radical polymerization (ATRP), and reversible addition fragmentation chain transfer (RAFT) polymerization, can also be used for the preparation of polyaddition polymers. In a second step the polyaddition polymer thus prepared is modified in order to attach radically polymerizable olefinically unsaturated groups. Examples of such modification reactions are the esterification of hydroxyl groups of the polymer with radically polymerizable olefinically unsaturated carboxylic acids or isocyanates, the reaction of isocyanate groups of the polymer with radically polymerizable olefinically unsaturated alcohols or acids, the addition of radically polymerizable olefinically unsaturated carboxylic acids to epoxide groups of the polymer, and the addition of radically polymerizable olefinically unsaturated epoxide compounds to carboxylic acid groups of the polymer. Such reactions are generally known to the skilled person and are for example described in US 4,990,577. The polyaddition polymer resin can be water borne. Such polymers are suitably prepared by the generally known technique of aqueous emulsion polymerization. By emulsion polymerization is meant here the polymerization of monomer mixtures of ethylenically unsaturated monomers in water in the presence of a water-soluble or -insoluble initiator and, optionally, an emulsifier. The emulsion polymerization can be carried out as disclosed in EP-A-0 287 144 or GB-A-870 994.

Alternatively, the polyaddition polymer is prepared by the polymerization of suitable ethylenically unsaturated monomers as described above in an essentially non-aqueous environment, optionally in the presence of an organic solvent. Before or after the modification step to attach radically polymerizable olefinically unsaturated groups, the polyaddition polymer can be mixed with an aqueous medium, conveniently by adding water to the polyaddition polymer or, alternatively, by adding the polyaddition polymer to water, under agitation.

Use may be made of external emulsifiers. Suitable emulsifiers include anionic emulsifiers, such as carboxylate-, sulphonate-, and phosphonate-containing compounds, cationic emulsifiers such as amine/ammonium groups, and non- ionic emulsifiers based on alkylene oxide groups. The organic solvent content of the resulting emulsion or dispersion can be reduced by distillation, optionally under reduced pressure.

Polyesters

Polyesters having radically polymerizable olefinically unsaturated groups are also suitable for use in the composition according to the invention.

As suitable polyester resins may be mentioned the condensation products of a carboxylic acid or a reactive derivative thereof, such as the corresponding anhydride or lower alkyl ester with an alcohol.

Examples of suitable polycarboxylic acids or reactive derivatives thereof are tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyl hexahydrophthalic acid, methyl hexahydrophthalic anhydride, dimethyl cyclohexane dicarboxylate, 1 ,4- cyclohexane dicarboxylic acid, 1 ,3-cyclohexane dicarboxylic acid, phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, 5-tert. butyl isophthalic acid, trimellitic anhydride, maleic acid, maleic anhydride, fumaric acid, succinic acid, succinic anhydride, hydroxy succinic acid, dodecenyl succinic anhydride, dimethyl succinate, glutaric acid, adipic acid, dimethyl adipate, azelaic acid, dimer fatty acids, and mixtures thereof. Examples of suitable monocarboxylic acids include hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, 2- ethyl hexanoic acid, isononanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, isostearic acid, stearic acid, hydroxystearic acid, benzoic acid, tert. butyl benzoic acid, lactic acid, dimethylol propionic acid, and mixtures thereof.

Suitable alcohols include diols and triols and mixtures thereof, but higher- functionality polyols can also be used. Examples of lower-molecular weight diols, triols, and polyols include ethylene glycol, diethylene glycol, tetraethylene glycol, propane-1,2- and 1 ,3-diol, butane-1 ,4- and -1 ,3-diol, hexane-1 ,6-diol, octane-1 ,8-diol, neopentyl glycol, 1 ,4-bis-hydroxymethyl cyclohexane, 2-methyl- propane-1 ,3-diol, 2,2,4-trimethylpentane-1 ,3-diol, dipropylene glycol, polypropylene glycols, dibutylene glycol, polybutylene glycols, bisphenol-A and tetrabromo bisphenol-A, diols obtainable by hydrogenation of dimer fatty acids, glycerol, pentaerythritol, trimethylol propane, ditrimethylol propane, hexane- 1 ,2,6-triol, butane-1 ,2,4-triol, quinitol, mannitol, sorbitol, methyl glycoside, 1 ,4,3,6-dianhydrohexitols, the monoester of neopentylglycol and hydroxy pivalic acid, bis(hydroxyethyl) terephthalate, furan dimethanol, and the reaction products up to moiecular weight 400 of such polyols with propylene oxide and/or ethylene oxide.

Organic polymeric polyols can also be used in the preparation of the polyester.

They include diols and triols and mixtures thereof, but also higher-functionality polyols can be used, for example as minor components in admixture with diols.

The polymeric polyols suitably are selected from the group of polyester, polyester amides, polyethers, polythioethers, polycarbonates, polyacetals, polyolefins, and polysiloxanes.

Polyester polyols which can be used include hydroxyl-terminated reaction products of polyhydric alcohols, such as ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, 1 ,4-butane diol, 1 ,6-hexane diol, furan dimethanol, dimethylol cyclohexane, glycerol, trimethylol propane, pentaerythritol, and mixtures thereof, with polycarboxylic acids, especially dicarboxylic acids or their ester-forming derivatives, for example succinic, glutaric, and adipic acids, and their dimethyl esters, phthalic anhydride, hexahydrophthalic anhydride, dimethyl terephthalate, dimer fatty acids, and mixtures thereof. Polyesters obtained by the polymerization of lactones, for example caprolactone, in conjunction with a polyol, can also be used. Polyester amides can be obtained by the inclusion of aminoalcohols such as ethanolamine in the polyesterification mixtures. Suitable polyether polyols include polyalkylene oxide glycol, wherein the alkylene oxide may be selected from ethylene oxide and/or propylene oxide units.

Polythioether polyols which can be used include products obtained by condensing thiodiglycol either alone or with other glycols, dicarboxylic acids, formaldehyde, aminoalcohols or aminocarboxylic acids.

Polycarbonate polyols include products obtained by reacting diols, such as 1 ,3- propane diol, 1 ,4-butane diol, 1 ,6-hexane diol, 1 ,4-cyclohexane dimethanol, diethylene glycol or tetraethylene glycol, with diaryl carbonates, for example diphenyl carbonate, or with phosgene. Suitable polyolefin polyols include hydroxy-terminated butadiene homo- and copolymers.

In order to provide radically polymerizable olefinically unsaturated groups, suitable polymerizable carboxylic acids or alcohols can be built into the polyester. Examples of carboxylic acids having radically polymerizable olefinically unsaturated groups are acrylic acid, methacrylic acid, maleic acid, citraconic acid, itaconic acid, as well as their reactive derivatives. Alternatively, the radically polymerizable olefinically unsaturated groups can be introduced by a modification step as described above for polyaddition polymers.

In a special embodiment, the polyester resin is present as an aqueous solution or dispersion. Suitable measures to facilitate the dispersion or dissolution of the organic polyester resin in water with the aid of an external emulsifier or by ionic and/or non-ionic stabilizing groups built into the polyester are the same as will be described below for polyurethanes.

Polyethers

As suitable polyether resins may be mentioned the polymers of cyclic ethers such as ethylene oxide, propylene oxide, other epoxides, oxetane, and tetrahydrofuran. Suitable hybrid resins are described in WO 01/90265, which is included in this application by reference. The radically polymerizable olefinically unsaturated groups can be introduced by a modification step as described above for polyaddition polymers.

Polyurethanes

Polyurethanes can be prepared according to generally known methods by reacting a) an organic polyisocyanate, b) one or more polyalcohols selected from b1) polyalcohols containing 2 to 6 hydroxyl groups and having a number average molecular weight up to 400 and b2) polymeric polyols having a number average molecular weight between about 400 and about 3,000, c) at least one isocyanate-reactive and/or isocyanate-functional compound bearing at least one radically polymerizable olefinically unsaturated group, d) optionally compounds containing at least two isocyanate-reactive groups, such as diamines or dithiols, e) optionally compounds having ionic and/or non-ionic stabilizing groups, and f) optionally compounds having one isocyanate-reactive group. The polyurethane can be prepared in a conventional mariner by reacting a stoichiometric amount or an excess of the organic polyisocyanate with the other reactants under substantially anhydrous conditions at a temperature between about 30°C and about 130°C until the reaction between the isocyanate groups and the isocyanate-reactive groups is substantially complete. The reactants are generally used in proportions corresponding to a ratio of isocyanate groups to isocyanate-reactive (usually hydroxyl) groups of from about 1 :1 to about 6:1 , preferably about 1:1. If an excess of the organic polyisocyanate is used, an isocyanate-terminated prepolymer can be prepared in a first step. In a second step, at least one isocyanate-reactive group containing compound c) can be added.

The organic polyisocyanate a) used in making the polyurethane resin can be an aliphatic, cycloaliphatic or aromatic di-, tri- or tetra-isocyanate that may be ethylenically unsaturated or not. Examples of diisocyanates include 1 ,2- propylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, 2,3-butylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 2,2,4-trimethyl hexamethylene diisocyanate, dodecamethylene diisocyanate, ω,ω'-dipropylether diisocyanate, 1 ,3-cyclopentane diisocyanate, 1 ,2-cyclohexane diisocyanate, 1 ,4-cyclohexane diisocyanate, isophorone diisocyanate, 4-methyl-1 ,3-diisocyanatocyclohexane, trans-vinylidene diisocyanate, dicyclohexyl methane-4,4'-diisocyanate (Desmodur^® W), toluene diisocyanate, 1 ,3-bis(isocyanatomethyl) benzene, xylylene diisocyanate, α.α. '.α'-tetramethyl xylylene diisocyanate (TMXDI^®), 1,5-dimethyl-2,4~bis(2- isocyanatoethyl) benzene, 1 ,3,5-triethyl-2,4-bis(isocyanatomethyl) benzene, 4,4'-diisocyanato-diphenyl, 3,3'-dichloro-4,4'-diisocyanato-diphenyl, 3,3'- diphenyl-4,4'-diisocyanato-diphenyl, S.S'-dimethoxy^^'-diisocyanato-diphenyl, 4,4'-diisocyanato-diphenyl methane, 3,3'-dimethyl-4,4'-diisocyanato- diphenylmethane, and diisocyanatonaphthalene. Examples of triisocyanates include 1 ,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, 1 ,8- diisocyanato-4-(isocyanatomethyl) octane, and lysine triisocyanate. Adducts and oligomers of polyisocyanates, for instance biurets, isocyanurates, allophanates, uretdiones, urethanes, and mixtures thereof are also included. Examples of such oligomers and adducts are the adduct of 2 molecules of a diisocyanate, for example hexamethylene diisocyanate or isophorone diisocyanate, to a diol such as ethylene glycol, the adduct of 3 molecules of hexamethylene diisocyanate to 1 molecule of water (available under the trademark Desmodur N of Bayer), the adduct of 1 molecule of trimethylol propane to 3 molecules of toluene diisocyanate (available under the trademark Desmodur L of Bayer), the adduct of 1 molecule of trimethylol propane to 3 molecules of isophorone diisocyanate, the adduct of 1 molecule of pentaerythritol to 4 molecules of toluene diisocyanate, the adduct of 3 moles of m-α,α,α',α'-tetramethyl xylene diisocyanate to 1 mole of trimethylol propane, the isocyanurate trimer of 1 ,6-diisocyanatohexane, the isocyanurate trimer of isophorone diisocyanate, the uretdion dimer of 1 ,6-diisocyanatohexane, the biuret of 1 ,6-diisocyanatohexane, the allophanate of 1,6-diisocyanatohexane, and mixtures thereof. Furthermore, (co)polymers of isocyanate-functional monomers such as α,α'-dimethyl-m-isopropenyl benzyl isocyanate are suitable for use. The polyisocyanate can comprise hydrophilic groups, for example covalently bonded hydrophilic polyether moieties, which facilitate the formation of aqueous dispersions.

It is preferred that use be made of an aliphatic or cycloaliphatic di- or triisocyanate containing 8-36 carbon atoms. Suitable polyalcohols b1) and b2) which can be used in the preparation of the polyurethane have been mentioned above in the description of suitable building blocks for polyesters.

As isocyanate-reactive compounds bearing at least one radically polymerizable olefinically unsaturated group c) may be used hydroxyalkyl (meth)acrylates, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4- hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and polypropylene glycol mono-(meth)acrylate. Amino-functional compounds, such as 2-(tert- butylamino)ethyl methacrylate, are equally suitable, Also compounds bearing at least one radically polymerizable olefinically unsaturated group and a thiol group as isocyanate-reactive group can be used.

Superior results are generally obtained with the addition products of difunctional or polyfunctional epoxy compounds and (meth)acrylic acid. As examples of suitable difunctional or polyfunctional epoxy compounds, which as such may be solid or liquid, may be mentioned the diglycidyl or polyglycidyl ethers of (cyclo)aliphatic or aromatic hydroxyl compounds, such as ethylene glycol, glycerol, cyclohexane diol, and mononuclear or polynuclear difunctional or trifunctional phenols and bisphenols such as bisphenol-A and bisphenol-F; epoxidized aliphatic and/or cycloaliphatic alkenes, such as dipentene dioxide, dicyclopentadiene dioxide, and vinyl cyclohexene dioxide. Thus far good results have been obtained with difunctional epoxides selected from the group of hydrogenated bisphenol-A diglycidyl ether, 1 ,4-butanediol diglycidyl ether, 1 ,6- hexanediol diglycidyl ether, and neopentylglycol diglycidyl ether.

Compounds having one isocyanate-reactive group f) may optionally be used in the preparation of the polyurethane as a chain stopper to limit the molecular weight of the polyurethane. Suitable compounds are well known in the art and include monoalcohols, monoamines, and monothiols. The polyurethanes can contain organic solvents for reduction of the viscosity. Suitable solvents are aromatic hydrocarbons such as toluene and xylene; alcohols such as ethanol, isopropanol, /7-butanol, 2-butanol, hexanol, benzyl alcohol, and ketones such as methylethy! ketone, methylisobutyl ketone, methylamyl ketone, and ethylamyl ketone; esters such as butyl acetate, butyl propionate, ethoxyethyl propionate, ethylglycol acetate, butylglycol acetate, and methoxypropyl acetate; ethers such as 2-methoxypropanol, 2-methoxybutanol, ethylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dioxolane or mixtures thereof. Examples of other suitable solvents are N-methyl-2-pyrrolidone, dimethyl carbonate, propylene carbonate, butyrolactone, and caprolactone.

In a special embodiment, the polyurethane is present in the form of an aqueous dispersion or solution. It is then appropriate to facilitate the dispersion or dissolution of the organic polyurethane resin in water with the aid of external emulsifiers as mentioned above for the preparation of polyaddition polymers, or by ionic and/or non-ionic stabilizing groups built into the polyurethane. Suitable ionic stabilizing groups can be derived from carboxylic acid groups, sulphonic acid groups, phosphorous acid groups, phosphoric acid groups, and phosphonic acid groups.

Carboxylic acid groups can be introduced into the polyurethanes by the co- reaction of hydroxycarboxylic acids. Dimethylol propionic acid, hydroxypivalic acid, and hydroxystearic acid are preferred. Sulphonate groups or sulphonic acid groups can be introduced into a polyurethane, for example by reaction of isocyanates and hydroxyl- or amine- functional compounds comprising at least one sulphonic acid group or sulphonate group, for example 2-hydroxethane sulphonic acid, the sodium salt of 2-aminoethane sulphonic acid, 3-cyclohexylamino-1 -propane sulphonic acid, the reaction product of an aminoalkylsulphonic acid or its salt with an epoxide- functional compound, the reaction product of sodium 5-sulphoisophthalic acid with an equivalent excess of diols, triols or epoxy compounds. Hydroxyl- terminated oligoesters of sodium 5-sulphoisophthalic acid are particularly suitable. Such oligoesters may contain reacted units of polycarboxylic acids such as adipic acid, phthalic acid, isophthalic acid, hexahydrophthalic anhydride, trimellitic anhydride, etc. It is preferred that more than 50% of the sulphonic acid groups and carboxylic acid groups of the polyurethane binder are neutralized with a base. Advantageously, the neutralizing agent is ammonia and/or an amine. Tertiary amines are preferred. Examples of suitable tertiary amines include trimethyl amine, triethyl amine, triisopropyl amine, tributyl amine, triethanol amine, triisopropanol amine, N,N-dimethyl ethanol amine, N,N-dimethyl isopropyl amine, N,N-diethyl ethanol amine, 1-dimethylamino-2-propanol, 3-dimethyl amino-1-propanol, 2-dimethylamino-2-methyl-1-propanol, N-methyl diethanol amine, N-ethyl diethanol amine, N-butyl diethanol amine, N,N-dimethyl cyclohexylamine, N,N'-dimethyl piperazine, N-methyl piperidine, N-methyl morpholine, and N-ethyl morpholine. Suitable primary amines are for example isopropyl amine, butyl amine, ethanolamine, 3-amino-1-propanol, 1-amino-2- propanol, 2-amino-2-methyl-1-propanol or 2-amino-2-methyl-1 ,3-propane diol. Secondary amines that can be used are for example morpholine, diethyl amine, dibutyl amine, N-methyl ethanolamine, diethanol amine, or diisopropanol amine. Also mixtures of these amines may optionally be used.

Equally suitable for use as neutralizing agents are alkali metal hydroxides such as sodium hydroxide or potassium hydroxide. Neutralization can be carried out prior to, during or after the polyurethane formation. The polyurethane resin present as an aqueous dispersion can also comprise non-ionic stabilizing groups. Non-ionic stabilizing groups can comprise C₁-C₄ alkoxy polyalkylene oxide groups. The preferred alkylene oxide groups are ethylene oxide groups, but propylene oxide groups or mixtures of ethylene oxide groups and propylene oxide groups are useful as well. For example, the alkylene oxide groups may be C₁-C₄ alkoxy ethers of polyalkylene glycols represented by formula I:

wherein R1 is a hydrocarbon group with 1 to 4, preferably 1 or 2, carbon atoms; R2 is a methyl group; x is between 0 and 40, preferably between 0 and 20, most preferably between 0 and 10; y is between 0 and 50, and x+y is between 2 and 50, preferably between 2 and 25. Examples are C₁-C₄ alkoxy polyC₂(C₃)alkylene oxide glycol and/or C₁-C₄ alkoxy polyC₂(C₃)alkylene oxide 1 ,3-diol, wherein polyC₂(C3)alkylene oxide stands for polyethylene oxide, optionally comprising propylene oxide units. Suitably, the polyurethane comprises 2.5 to 15 wt.% C₁-C₄ alkoxy polyalkylene oxide groups with a number average molecular weight of 500 to 3,000.

Suitable compounds comprising C₁-C₄ alkoxy polyalkylene oxide groups contain at least one isocyanate-reactive group. Examples are methoxy polyC₂(C₃)alkylene oxide glycols and methoxy polyC₂(C₃)alkylene oxide-1 ,3- diols, such as Tegomer^® D-3123 (PO/EO = 15/85; Mn = 1 ,180), Tegomer^® D- 3409 (PO/EO = 0/100; Mn = 2,240), and Tegomer^® D-3403 (PO/EO = 0/100; Mn = 1 ,180) available from Goldschmidt AG, Germany, and MPEG 750 and MPEG 1000. Polyester polyols comprising polyalkylene oxide groups can be used as well. The introduction of the compounds comprising C₁-C₄ alkoxy polyalkylene oxide groups and at least one isocyanate-reactive group into the polyurethane can be conducted in the course of the polyurethane preparation. A further suitable class of non-ionic stabilizing groups for water borne polyurethane resins is formed by polyoxazolines. Mixing the polyurethane resin with an aqueous medium can be done conveniently by adding water to the polyurethane solution or, alternatively, by adding the polyurethane solution to water, under agitation of the water and the polyurethane solution. The organic solvent content of the resulting emulsion or dispersion can be reduced by distillation, optionally under reduced pressure. The curable composition of the invention preferably is water borne. Accordingly, it is also preferred that the polymer having radically polymerizable olefinically unsaturated groups is present as a water borne or water-dilutable formulation. It is particularly preferred that the polymer having radically polymerizable olefinically unsaturated groups is an acryloyl-functional polyurethane, especially in the form of a water borne polyurethane dispersion.

Oxidation-reduction enzymes

Oxidation-reduction enzymes are enzymes which catalyze oxidation-reduction reactions. Such enzymes are also known as oxidoreductases. Suitable oxidation-reduction enzymes for use in the present invention are those which are generally known in the art. Examples are oxidoreductases of classes 1.1.1. to 1.97 according to the International Enzyme Nomenclature such as defined by the Committee of the International Union of Biochemistry and Molecular Biology. Specific examples include laccase, cellobiose-quinone-1- oxidoreductase, bilirubin oxidase, cytochrome oxidase, glucose oxidase, catechol oxidase (tyrosinase), galactose oxidase, glycolat oxidase, hexose oxidase, L-gulonolacton oxidase, L-sorbose oxidase, catalase, monophenol monooxygenase, polyphenol oxidase, superoxide dismutase, ferroxidase, pyridoxol-4 oxidase, L-ascorbate oxidase, O-aminophenol oxidase, alcohol oxidase, and peroxidases. The composition according to the invention can also comprise a combination of two or more oxidation-reduction enzymes, for example to adapt the curing properties of the composition to particular needs. Preferred oxidation-reduction enzymes are peroxidases and laccases. Laccases catalyze the oxidation of a range of reducing agents with a concomitant reduction of oxygen to water. A suitable laccase is a microbial laccase produced by submerged fermentation of a genetically modified microorganism such as described in WO 94/26925. Peroxidases sometimes have a lower pH dependency of their enzymatic activity than other enzymes. As specific examples of peroxidases may be mentioned cytochrome-C peroxidase, iodide peroxidase, glutathione peroxidase, chloride peroxidase, ^• L-ascorbate peroxidase, phospholipid-hydroperoxide-glutathione peroxidase, manganese peroxidase, diaryl propan peroxidase (lignin peroxidase), soybean peroxidase, pea peroxidase, guar beans peroxidase, garbanzo beans peroxidase, runner beans peroxidase, rice peroxidase, cotton peroxidase, horseradish peroxidase, and a peroxidase produced by submerged fermentation of a genetically modified Aspergillus sp. as described in United States Patent US 5,958,724. The last two peroxidases are particularly preferred.

The composition according to the invention suitably comprises 0.001 to 5, preferably 0.01 to 1 weight-% of oxidation-reduction enzyme, calculated on the non-volatile content of the composition. It is preferred that the oxidation- reduction enzyme is added to the composition in the form of a solution in a buffer, such as a phosphate buffer.

Thiol-functional compounds

Thiol-functional compounds that can suitably be used in the composition according to the invention include dodecyl mercaptan, mercapto ethanol, 1 ,3- propanedithiol, 1 ,6-hexanedithiol, methylthioglycolate, 2-mercaptoacetic acid, 2- mercaptopropionic acid, 3-mercaptopropionic acid, mercaptosuccinic acid, cysteine, and mixtures thereof.

Also suitable are esters of a thiol-functional carboxylic acid with a polyol, such as esters of 2-mercaptoacetic acid, 3-mercaptopropionic acid, 2- mercaptopropionic acid, 11-mercaptoundecanoic acid, and mercaptosuccinic acid. Examples of such esters include pentaerythritol tetrakis (3- mercaptopropionate), pentaerythritol tetrakis (2-mercaptoacetate), trimethylol propane tris (3-mercaptopropionate), trimethylol propane tris (2- mercaptopropionate), trimethylol propane tris (2-mercaptoacetate), and mixtures thereof. A further example of such a compound consists of a hyperbranched polyol core based on a starter polyol, e.g. trimethylol propane and dimethylol propionic acid, which is subsequently esterified with 3- mercaptopropionic acid and isononanoic acid. These compounds are described in European patent application EP-A-0 448 224 and international patent application WO 93/17060. The polyols to be esterified with a thiol-functional carboxylic acid can also comprise non-ionic stabilizing groups, such as described above for polyurethane resins. Examples of such polyols are ethoxylated pentaerythritol and ethoxylated trimethylol propane. The presence of non-ionic stabilizing groups can facilitate the incorporation of the thiol- functional compound in the event that the composition according to the invention is water borne.

Addition products of H2S to epoxy-functional compounds also give thiol- functional compounds. These compounds may have a structure of the following formula T[(O-CHR-CH₂-O)nCH₂CHXHCH2YH]_m, with T being a m-valent organic moiety wherein m is an integer between 1 and 10, R being hydrogen or methyl, n being an integer between 0 and 20, X and Y being oxygen or sulphur, with the proviso that X and Y are not equal. An example of such a compound is commercially available from Cognis under the trademark Capcure® 3/800. Other syntheses to prepare thiol-functional compounds involve: the reaction of an aryl or alkyl halide with NaHS to introduce a pendant mercapto group into the alkyl and aryl compounds, respectively; the reaction of a Grignard reagent with sulphur to introduce a pendant mercapto group into the structure; the reaction of a polymercaptan with a polyolefin according to a nucleophilic reaction, an electrophilic reaction or a radical reaction; the reaction of disulphides; and other routes such as mentioned in Jerry March, Advanced Organic Chemistry, 4^th edition, 1992, page 1298.

In another embodiment of the invention the thiol groups of the thiol-functional compound can be covalently attached to a resin. Such resins include thiol- functional polyurethane resins, thiol-functional polyester resins, thiol-functional polyaddition polymer resins, thiol-functional polyether resins, thiol-functional polyamide resins, thiol-functional polyurea resins, and mixtures thereof. Thiol- functional resins can be prepared by the reaction of H2S with an epoxy group or an unsaturated carbon-carbon bond-containing resin, the reaction between a hydroxyl-functional resin and a thiol-functional acid, and by the reaction of an isocyanate-functional polymer and either a thiol-functional alcohol or a di- or polymercapto compound.

A thiol-functional polyurethane resin can be the reaction product of a di-, tri- or tetrafunctional thiol compound with an isocyanate-terminated polyurethane and preferably is the reaction product of a diisocyanate compound and (a) diol- functional compound(s). Suitable thiol-functional polyurethane resins are obtainable by first preparing an isocyanate-functional polyurethane from diols, diisocyanates, and optionally building blocks containing groups which facilitate the stabilization of the resin in an aqueous dispersion, followed by reaction of the isocyanate-functional polyurethane with a polyfunctional thiol in a base- catalyzed addition reaction. Other thiol-functional polyurethane resins are known and described, e.g., in German patent publication DE-A-26 42 071 and European patent application EP-A-0 794 204.

The thiol-functional resin can be a polyester prepared from (a) at least one polycarboxylic acid or reactive derivatives thereof, (b) at least one polyol, and (c) at least one thiol-functional carboxylic acid. The polyesters preferably possess a branched structure. Branched polyesters are conventionally obtained through condensation of polycarboxylic acids or reactive derivatives thereof, such as the corresponding anhydrides or lower alkyl esters, with polyalcohols, when at least one of the reactants has a functionality of at least 3. Examples of suitable thiol-functional carboxylic acids have been mentioned above. Optionally, monocarboxylic acids and monoalcohols may be used in the preparation of the polyesters. Preferably, C₄-C₁₈ monocarboxylic acids and C₆- C₁₈ monoalcohols are used. Examples of the Cβ-Cis monoalcohols include cyclohexanol, 2-ethylhexanol, stearyl alcohol, and 4-tert. butyl cyclohexanol.

The thiol-functional resin can be a thiol-functional polyaddition polymer, for example a poly(meth)acrylate. Such a poly(meth)acrylate is derived from hydroxyl-functional (meth)acrylic monomers, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, and other ethylenically unsaturated polymerizable monomers as described above for the polyaddition polymer preparation. The thiol group is introduced by esterification of (part of) the hydroxyl groups of the acrylate copolymer with one or more of the thiol-functional carboxylic acids described above. Alternatively, glycidyl methacrylate is introduced into the polymer to prepare an epoxy-functional poly(meth)acrylate. The epoxy groups are then reacted with suitable thiol-functional carboxylic acids such as mentioned above. Alternatively, the thiol group can be introduced by reacting an isocyanate- functional polyacrylate with a thiol-functional alcohol, e.g., mercapto ethanol. The polyaddition polymer can be prepared by conventional methods as described above, for instance by the slow addition of appropriate monomers to a solution of an appropriate polymerization initiator, such as an azo or peroxide initiator.

It is preferred that the thiol-functional compound has a thiol-functionality in the range of 2 to 10, more preferably 3 to 10.

Particularly preferred thiol-functional compounds are pentaerythritol tetrakis(3- mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate), and Capcure^® 3/800, or mixtures thereof.

The amount of thiol-functional compound in the composition according to the invention suitably is selected such that the molar ratio of radically polymerizable olefinically unsaturated groups to thiol groups is in the range 1 :10 to 30:1. Preferably, the molar ratio of radically polymerizable olefinically unsaturated groups to thiol groups is in the range 1:2 to 10:1.

Optional components of the composition

Mediators

In a preferred embodiment, the composition according to the invention additionally comprises a mediator. Mediators are compounds which lead to a broader substrate specificity of the enzyme, make the enzyme action less dependent on pH profiles, and improve the access to insoluble substrates. Mediators thus enhance the overall activity of the enzyme. Mediators having at least one NO-, NOH, or HRN-OH group, such as hydroxylamines, hydroxylamine derivatives, hydroxamic acids or derivatives thereof can be used. These compounds are described in detail in International Patent Application WO 97/48786, pp. 11 - 25. Further examples of suitable mediators are described in United States patent US 5,912,405. Preferred mediators are methyl syringate, ethyl syringate, propyl syringate, butyl syringate, and phenothiazine-10-propionic acid. When the composition comprises a mediator, the mediator concentration generally ranges from 0.1 to 1,000 μmol/l, preferably from 10 to 500 μmol/l.

Reactive diluents

The composition of the present invention optionally comprises one or more reactive diluents. Compounds suitable as reactive diluents generally are ethylenically unsaturated compounds. As representative examples of such may be mentioned the compounds disclosed in EP-A-0 965 621. The reactive diluent preferably has a molecular weight of from about 80 to about 800, more preferably about 100 to about 400. Compounds meeting the molecular weight requirement are suitable for lowering the viscosity of the composition. Preferably, reactive diluents are used in an amount of 5 to 50 weight-% on solid, resin, more preferably 10 to 40 weight-%. Examples of monofunctional reactive diluents are the ethylenically unsaturated monomers described above for the preparation of polyaddition polymers. Preferred reactive diluents are those having more than one radically polymerizable olefinically unsaturated group. Such compounds ordinarily are the esters of acrylic or methacrylic acid and a polyhydric alcohol. Further suitable reactive diluents are urethane acrylates, melamine acrylates, epoxy- acrylic acid adducts, and reactive diluents containing polyethylene oxide. Examples of the aforesaid difunctional diluents are ethylene glycol diacrylate and dimethacrylate; isopropylene and propylene glycol diacrylate and dimethacrylate. Similarly, the diol diacrylates and dimethacrylates of butane, pentane, hexane, heptane, and so forth up to and including thirty-six carbon diols are useful in the present clear coats as reactive diluents. Of particular interest are 1 ,4-butane diol diacrylate, 1 ,6-hexane diol diacrylate, diethylene glycol diacrylate, trimethylol propane triacrylate, and pentaerythritol tetraacrylate. Thus far good results have been obtained with reactive diluents selected from the group of 3-methoxypropyl-, benzyl-, octyl-, 2-hydroxy-ethyl citraconimide, (meth)acrylate esters of butane diol, hexane diol, and trimethylol propane, the diacrylate ester of butane diol diglycidyl ether, ethoxylated trimethylol propane triacrylate, and the reaction product of α,α,α',α'-tetramethyl xylylene diisocyanate (TMXDI^®) with 4-hydroxybutyl acrylate and/or the esterification product of 1 mole of 2-hydroxyethyl acrylate and 2 moles of caprolactone, and/or methoxy polyethyleneoxide glycol having a molecular weight between 300 and 1 ,000.

Radical-generating compound

The composition according to the invention optionally comprises a radical- generating compound. The radical-generating compound may be selected from peroxide, peroxide derivatives, thermolabile azo compounds, and photoinitiators. Such radical-generating compounds are generally known in the art. As examples of photoinitiators which can be used may be mentioned benzoin ether (Esacure^® ex Fratelli Lamberti), benzyl dimethyl ketone acetal (Irgacure^® 651 ex Ciba), 1-hydroxycyclohexyl phenyl ketone (Irgacure^® 184 ex Ciba), 2-hydroxy-2-methyl-1 -phenyl propane-1-one (Darocur^® 1173 ex Ciba), 1- (4-isopropyl phenyl)-2-hydroxy-2-methyl propane-1-one (Darocur^® 1116 ex Ciba), diethoxyacetophenone (DEAP^® ex Upjohn), methyl thioxanthone (Quantacur^® ex Shell), 2,4,6-trimethylbenzoyl diphenyl phosphine oxide (Lucirin TPO^® ex BASF), and bisphosphine oxides such as CGI^® 819 and CGI^® 403 ex Ciba. Hydrogen peroxide and solutions thereof are preferred as radical-generating compounds.

In a special embodiment, the radical-generating compound is formed in situ by a peroxide-generating enzyme. Suitable enzymes are oxidases such as have been mentioned above. The peroxide-generating enzyme is suitably employed in combination with a substrate suitable for the particular enzyme. Examples of substrates are those described in EP 0 321 872-A. It is preferred to use a combination of glucose oxidase and glucose as substrate.

Organic co-solvent

As mentioned above, the composition according to the invention preferably is water borne. However, the water borne composition may optionally comprise one or more organic solvents, with the proviso that the volatile organic content (VOC) of the ready-for-use composition does not exceed 420 g/l. As suitable organic solvents may be mentioned dimethyl dipropylene glycol, methyl ether of diacetone alcohol, ethyl acetate, butyl acetate, ethyl glycol acetate, butyl glycol acetate, ethylene glycol monobutyl ether, 1 ,2- or 1 ,3-propylene glycol monomethyl ether, 1-methoxy-2-propyl acetate, butyl propionate, ethoxy ethyl propionate, toluene, xylene; methylethyl ketone, methyl isobutyl ketone, methyl amyl ketone, ethyl amyl ketone, dioxolane, N-methyl-2-pyrrolidone, dimethyl carbonate, propylene carbonate, butyrolactone, caprolactone, and mixtures thereof. The components of the composition according to the invention are advantageously mixed prior to use, i.e. they form parts of a multi-component system. For instance, in a two-component system one component may comprise the radically polymerizable olefinically unsaturated compound, the thiol-functional compound, and optionally a mediator, and the second component may comprise the oxidation-reduction enzyme. Alternatively, one component may comprise the radically polymerizable olefinically unsaturated compound and the oxidation-reduction enzyme, and the second component may comprise the thiol-functional compound and optionally a mediator. It is also possible to make use of a three-component system. Thus, the first component may comprise the radically polymerizable olefinically unsaturated compound, the second component may comprise the thiol-functional compound and optionally a mediator, and the third component may comprise the enzyme. Other multi-component systems are also within the scope of the invention, as long as the individual components exhibit the required stability.

The thiol groups of the thiol-functional compound are susceptible to various side reactions under alkaline conditions. On the one hand, these side reactions may desirably contribute to the curing of the composition. On the other hand, said side reactions may undesirably deplete the thiol groups of the composition, thereby aggravating the enzymatic cure of the composition. The depletion of thiol groups by said side reactions can be avoided when the curable composition does not comprise a significant amount of free base. If the curable composition is water borne, it is preferred that the pH of the composition is below 8.5, more preferably below 7, with a particular preference for a pH below 6.5.

The composition can advantageously be used as a coating or adhesive composition. Accordingly, the composition can additionally comprise conventional additives such as solvents, pigments, fillers, leveling agents, emulsifiers, anti-foaming agents and rheology control agents, reducing agents, antioxidants, HALS-stabilizers, UV-stabilizers, water traps such as molecular sieves, and anti-settling agents.

Application of the composition onto a substrate can be via any method known to the skilled person, e.g., via rolling, spraying, brushing, flow coating, dipping, and roller coating. Preferably, the composition such as described is applied by spraying.

The composition of the present invention can be applied to any substrate. The substrate may be, for example, metal, e.g., iron, steel, and aluminium, plastic, wood, glass, synthetic material, paper, leather, or a coating layer. The compositions of the current invention show particular utility as clear coats (over base coats, water borne and solvent borne), base coats, pigmented top coats, primers, and fillers. The compositions are suitable for coating objects such as bridges, pipelines, industrial plants or buildings, oil and gas installations, or ships. The compositions are particularly suitable for finishing and refinishing automobiles and large transportation vehicles, such as trains, trucks, buses, and airplanes.

The applied composition can be cured very effectively at a temperature of, e.g., 0-80°C. It is assumed that curing of the composition occurs mainly by polymerization of the compound having at least one radically polymerizable olefinically unsaturated group, the polymerization being initiated substantially by the action of the enzyme. In an alternative process, the applied composition according to the invention can be at least partly cured under the influence of actinic radiation, preferably ultraviolet radiation and/or visible light. Accordingly, the invention also relates to a process for curing the composition of the invention, which comprises the steps of applying the composition to a substrate, optionally evaporating solvents and/or diluents, and exposing the applied composition to actinic radiation to at least partly cure the composition. In a preferred embodiment of the process, the composition comprises a radical-generating photoinitiator as described above. The advantage of the process according to the invention resides in the possibility to achieve a relatively fast initial cure of the applied composition by exposure to actinic radiation. Unlike in the case of conventional actinic radiation curable compositions, for example as known from International patent application WO 02/34808, the degree of curing induced by the radiation is not critical, because curing under the action of the enzyme will continue even in the absence of actinic radiation. Further, during radiation curing of compositions applied to shaped objects shadow areas are frequently exposed to lower levels of actinic radiation or they are not exposed to actinic radiation at all. With conventional radiation curing processes this leads to uncured or undercured areas. This drawback is avoided by the process according to the invention, because also the shadow areas will eventually be sufficiently cured under the influence of the enzyme.

Suitable sources of actinic radiation to be used in the process according to the invention are commercially available. As examples fluorescent tubes, deuterium halogen light sources, laser light sources, mercury vapor lamps, mercury-xenon lamps, UV light emitting diodes (UV-LEDs), and metal halide lamps may be mentioned. In addition to lamps which continuously provide actinic radiation, it is also possible to use discontinuous sources of actinic radiation, such as Xenon flash lamps or pulsed lasers.

In order to avoid any risk involved in handling UV radiation of very short wavelength (UV-B and/or UV-C radiation), especially for use in automotive refinishing shops preference is given to lamps which produce the less injurious UV-A radiation and/or visible light.

The amount of actinic radiation necessary to at least partly cure the reactive components will of course depend on the light intensity, the angle of exposure to and the distance from the radiation, and the thickness of the coating to be applied, as well as the presence or absence of a radical-generating photoinitiator. For any given composition the best method of determining the amount and duration of the radiation required is by experimental determination of the amount of radically polymerizable olefinically unsaturated groups not cured following exposure to the radiation source.

The invention will be elucidated further with reference to the following examples.

In the examples the following abbreviations are used:

Penta-(SH)₄". Pentaerythritol tetrakis(3-mercaptopropionate)

PPA: Phenothiazine-10-propionic acid PUR: Polyurethane n.d.: not determined

In the examples the following compounds are used:

Peroxidase A is a peroxidase produced by submerged fermentation of a genetically modified Aspergillus sp. such as described in US 5,958,724. Laccase A is a microbial laccase produced by submerged fermentation of a genetically modified microorganism such as described in WO 94/26925. Laccase B differs from Laccase A only in that the activity is reduced by the factor 2.

Preparation of acryloyl-functional PUR dispersion A

a) Preparation of a polyester comprising polyethylene oxide groups

A 3 I 4-neck flask fitted with a variable speed stirrer, thermocouples in combination with a controller, a distillation column, a reflux condenser, a nitrogen sparge, and a heating mantle was charged with a mixture composed of 332 g of hexahydrophthalic anhydride and 1 ,614 g of polyethylene glycol monomethyl ether of an average molecular weight of 750. The mixture was heated to 170°C for 30 minutes, cooled to 140°C, and 269 g of dirtrimethylol propane) were added, followed by 132 g of xylene and 3.3 g of a 85% aqueous phosphoric acid solution. The mixture was heated to 235°C, and water was azeotropically distilled off until the acid value of the reaction mixture was below 5 mg KOH/g. The mixture was then cooled to 180°C, and xylene was distilled off at reduced pressure. The resulting polyester diol solidified at room temperature and had an acid value of 3.9 mg KOH/g and a hydroxyl value of 59 mg KOH/g.

b) Preparation of an acryloyl-functional diol

A 2-litre 4-neck flask, which was fitted with a variable speed stirrer, a thermo- couple, a dry air sparge via the head space, a dip tube, and a heating mantle was charged with 573 g of hydrogenated bisphenol-A diglycidyl ether (Eponex^®1510 ex Resolution Performance Products), 17.5 g of acrylic acid, and 0.56 g of 2,6-ditert. butyl p-cresol. The mixture was heated to 95°C while bubbling with dry air. A mixture of 157.7 g of acrylic acid, 0.56 g of 2,6-ditert. butyl p-cresol, and 0.75 g of chromium 2-ethylhexanoate was added drop-wise in approximately 3 hours. The temperature of the reaction mixture was maintained between 95 and 100°C. Stirring at this temperature was continued until the acid value of the reaction mixture had dropped below 5 mg KOH/g. The prepared adduct was cooled and diluted with 97 g of dry 2-butanone.

c) Preparation of acryloyl-functional polyurethane dispersion A

A 3 I 4-neck flask fitted with a variable speed stirrer, thermocouples in combination with a controller, a condenser, a dry air sparge, and a heating mantle was charged with a mixture composed of 273.2 g of acryloyl-functional diol Ab), 146.7 g of polyester Aa), 12.26 g of trimethylol propane, 99.1 g of 4- hydroxybutyl acrylate, 260.8 g of bis(4-isocyanotocyclohexyl) methane (Desmodur^® W ex Bayer), 1.50 g of 2,6-ditert.butyl-p-cresol, and 250 g of 2- butanone. The mixture was heated to 45°C and stirred until homogeneous, while bubbling with dry air. Then 0.94 g of tin(ll) octanoate was added after one hour of stirring. The reaction mixture was stirred for approximately six hours at 80°C until the isocyanate content was < 0.1 wt.%. Then, 3 ml of ethanol 100% was added, and stirring was continued for about 30 minutes. The reaction mixture was cooled to 45°C. After dilution of the reaction mixture with 154 g of 2-butanone the stirrer speed was increased, and 1 ,125 g of water were added at a rate of 12 ml/min. After all the water had been added, a distillation head and a vacuum pump were connected to the flask and the pressure was gradually lowered until all 2-butanone was distilled off. A white emulsion with the following characteristics was obtained: solids content 44%, acryloyl equivalent weight 535 g/equivalent on solids, Mn 2686, Mw 11153, pH 5.5, and particle size 120 nm.

For the preparation of curable compositions 0.5 g of the surface active additive Byk 346 ex Byk Chemie was added to 100 g of acryloyl-functional PUR dispersion A.

Preparation of acryloyl-functional PUR dispersion B

a) Preparation of polyester diol from hexane diol and hexahydrophthalic anhydride

A 2-litre 4-neck flask was fitted with a variable speed stirrer, a thermocouple in combination with a controller, a packed distillation column, a nitrogen inlet, and a heating mantle. In the flask were placed 874.4 g of 1 ,6-hexanediol, 759.7 g of hexahydrophthalic anhydride, and 0.42 g of dibutyltin oxide. The reaction mixture was heated with stirring and with nitrogen flow at 250°C for 4 hours and 75 g of water were distilled off. The reaction mixture was cooled down to 105°C and the remaining water was distilled off at reduced pressure. The resulting polyester diol had an acid value of 3.2 mg KOH/g and a hydroxyl value of 172 mg KOH/g, GPC data Mn: 963 g/mol, Mw: 1,500 g/mol. b) Preparation of acryloyl-functional polyurethane dispersion B A 10-liter reactor was fitted with a condenser, a thermocouple, a dropping funnel stirrer, a dry air inlet tube reaching into the reaction mixture, and oil bath heating. The reactor was loaded with 1411.3 g of bis(4-isocyanatocyclohexyl) methane (Desmodur W ex Bayer), 3.2 g of tin octoate, and 800 g of dry 2- butanone. To this solution was added in 2 hours at about 60°C a mixture composed of 1 ,416.3 g of the acryloyl-functional diol Ab) described above, 1 ,212.3 g of polyester comprising the polyethylene oxide groups Aa) described above, 976.6 g of the polyester diol Ba) prepared from hexane diol and hexahydrophthalic anhydride, 284.2 g of 4-hydroxybutyl acrylate, 10.4 g of 2.6- ditert. butyl-p-cresol, and 1 ,400 g of dry 2-butanone. Then another 3.2 g of tin octoate were added and the reaction mixture was stirred at 80°C for 4 hours (isocyanate content < 0.15%). The residual isocyanate was quenched by the addition of ethanol. To 3,619 g of this resin, loaded in a 10-liter reactor, were added 900 g of acetone and then 4,200 g of water were added drop-wise at 50°C within 3 hours with stirring. Stirring was continued for 1 hour and then acetone and 2-butanone were distilled off from the dispersion at reduced pressure. A white emulsion with the following characteristics was obtained: solids content 43%, acryloyl equivalent weight 781 g/equivalent on solids, Mn 3,700 g/mol, Mw 19,200 g/mol, particle size 75 nm.

For the preparation of curable compositions 0.5 g of the surface-active additive Byk 346 ex Byk Chemie was added to 100 g of acryloyl-functional PUR dispersion B.

Preparation of curable compositions

Curable compositions were prepared from the acryloyl-functional PUR dispersions A and B described above. Table 1 summarizes comparative compositions C1 - C4. Tables 2 - 5 summarize the curable compositions according to the invention. The amounts of components listed in the tables are given in parts by weight. The components were added to the acryloyl-functional PUR dispersion described above in the order mentioned in the tables. The components were mixed by stirring with an electrical laboratory stirrer. The curable compositions were applied on polyethylene terephthalate foils or on steel panels using a drawing bar or a paint spray gun. The layer thickness of the dried films was 70 to 90 μm when applied with a drawing bar and 25 to 60 μm when applied by spraying.

The curing reaction of the compositions was monitored by infrared spectroscopy (IR). For this purpose the intensity of the signal due to the carbon-carbon double bond of the acryloyl group at 810 cm^"1 was related to a reference signal 777 cm^"1, which remained unchanged during curing. Corresponding formulations without oxidation reduction enzymes were used to determine the ratio of the above-mentioned signals in the absence of any curing reaction. Thus, approximate conversions of the curing reaction were calculated from the infrared spectroscopy data.

Film properties were determined visually and by exposure of the cured film to cotton wool soaked with 2-butanone. The film properties were judged "OK" when the film was clear, homogeneous and without cracks, and when the film did not dissolve upon exposure to cotton wool soaked with 2-butanone.

The comparative compositions of Table 1 do not comprise a thiol-functional compound. None of these compositions exhibits any conversion of the acryloyl functionality after 3 days. Nor does composition C3, which comprises a mediator and a radical-generating compound but no thiol-functional compound, cure at all.

From Table 2 it can be concluded that all compositions comprising a thiol- functional compound exhibit a reasonable degree of curing. From experiments 3 and 4 one can conclude that the addition of a radical-generating compound such as hydrogen peroxide increases the conversion of the curing reaction. Comparing experiments 3 and 5 indicates that the use of a peroxidase solution in a phosphate buffer is advantageous over the use of a peroxidase as such. Experiments 6 - 8 demonstrate that high conversions of the curing reaction can be achieved within 15 minutes. From experiments 7 and 8 it can be concluded that peroxidase A and horseradish peroxidase are about equally effective to induce curing. The cured polymers of experiments 7, 8, and 9 were treated with 2-butanone after 3 days of curing. These samples were found to be insoluble in 2-butanone, indicating a good degree of curing. Experiment 9 further demonstrates the suitability of laccase as an oxidation-reduction enzyme and of methyl syringate as a mediator. Experiment 13 of Table 3 demonstrates that laccase as an oxidation-reduction enzyme in combination with PPA as a mediator is effective, too. In experiments 15 and 16 of Table 3 alternative thiol-functional compounds have been used. In experiments 15 and 16 the quantity of the thiol-functional compounds was such that like the samples of experiments 12 - 14, these samples contain an equimolar amount of thiol groups. It can be concluded that the thiols of experiments 15 and 16 also induce the curing reaction. However, pentaerythritol tetrakis(3-mercaptopropionate) appears to be more effective to achieve a high conversion.

Table 4 presents the film properties of compositions applied by spraying on steel panels and/or foils at room temperature and 50% relative humidity. The compositions of experiments 18 and 19 of Table 4 are analogous to those of experiments 10 and 12 of Table 3, respectively. Experiments 18 and 19 of

Table 4 show that neither the technique of application (spaying or drawing bar) nor the type of substrate affects the film properties. Lowering the mediator content (experiment 20 of Table 4 compared to experiment 19 of Table 4) lowers the double bond conversion. Increasing the amount of thiol in the formulation (experiment 22 of Table 4 compared to experiment 20 of Table 4) can lead to an improvement of the coating properties of the films. Experiments

23 and 24 of Table 4 involve the use of laccase B, which has an activity reduced by factor two compared to the laccase A used in experiments 9 and 13 of Table 2 and Table 3, respectively. Good film properties were obtained particularly for experiment 24 of Table 4, as both the appearance and the resistance to 2-butanone of the film are acceptable.

Table 5 summarizes experiments with compositions which were cured with and without exposure to UV-A radiation. The compositions were applied to steel panels and allowed to dry for 30 minutes at room temperature before exposure to UV-A radiation. Irradiation was carried out for 10 minutes with a Philips TL 10

UV lamp with reflector. The distance between the lamp and the coated substrate was 10 cm. Experiment 28 illustrates a composition including a conventional photoinitiator, laccase A and methyl syringate as mediator. The indicated film properties of the UV cured compositions were determined immediately after irradiation, whereas the indicated film properties of the non-

UV cured compositions were determined after 3 days of curing at room temperature. Experiments 25, 27, and 28 demonstrate that satisfying film properties can be attained immediately after exposure to actinic radiation, while equally satisfying properties can also be attained without exposure to radiation after a couple of days.

Table 1 : Comparative examples, compositions were applied by draw bar to polyethylene terephthalate foils

1) 0.5 weight-% solution in phosphate buffer of pH 7

2) 0.2 weight-% solution in butylglycol

3) 0.35 weight-% solution in water

Table 2: Curable compositions according to the invention, applied by draw bar to polyethylene terephthalate foils

1) 0.5 weight-%) solution in phosphate buffer of pH 7

2) 0.2 weight-% solution in butylglycol

3) 0.35 weight-% solution in water

4) 10 weight-% solution in water

5) 0.1 weight-% solution in butylglycol

6) Film properties of Experiment 9 were satisfactory

Table 3: Curable compositions according to the invention, applied by draw bar to polyethylene terephthalate foils

9\

1) 0.5 weight-%) solution in phosphate buffer of pH 7

2) 0.2 weight-%) solution in butylglycol

3) 0.35 weight-%) solution in water

Table 4: Curable compositions according to the invention, applied by spraying onto polyethylene terephthalate f and/or steel panels

-4

* Laccase B has a lower activity than Laccase A used in Experiments 9, 13, and 28

** Determined after 4 hours

1) 0.5 weight-%) solution in phosphate buffer of pH 7

2) 0.2 weight-%) solution in butylglycol

3) 0.1 weight-%) solution in butylglycol

4) 0.35 weight-%) solution in water

Table 5: Curable compositions according to the invention, applied by spraying onto steel panels

oe

1) 0.5 weight-% solution in phosphate buffer of pH 7

2) 0.2 weight-%) solution in butylglycol

3) 0.35 weight-%) solution in water

4) 0.5 weight-%) solution in phosphate buffer of pH 4

5) 0.1 weight-%) solution in butyl glycol

6) Determined after 3 days

Claims

1. A curable composition comprising a compound having at least one radically polymerizable olefinically unsaturated group and a molecular weight above 500 and an oxidation-reduction enzyme, characterized in that the composition additionally comprises a thiol-functional compound.

2. A curable composition according to claim 1 , characterized in that the thiol- functional compound has a thiol functionality in the range of 2 to 10.

3. A curable composition according to claim 1 or 2, characterized in that the thiol- functional compound is selected from pentaerythritol tetrakis(3-mercapto propionate), trimethylolpropane tris(3-mercaptopropionate), and Capcure^® 3/800.

4. A curable composition according to any one of the preceding claims, characterized in that the oxidation-reduction enzyme is selected from a peroxidase and a laccase.

5. A curable composition according to any one of the preceding claims, characterized in that the composition additionally comprises a radical- generating compound.

6. A curable composition according to claim 5, characterized in that the radical- generating compound is hydrogen peroxide.

7. A curable composition according to any one of preceding claims 1 to 4, characterized in that it comprises a combination of glucose oxidase and glucose capable of producing hydrogen peroxide.

8. A curable composition according to any one of the preceding claims, characterized in that the composition is water borne.

9. A curable composition according to claim 8, characterized in that the compound having at least one radically polymerizable olefinically unsaturated group is an acryloyl-functional water borne polyurethane dispersion.

10. A curable composition according to any one of the preceding claims, characterized in that the composition additionally comprises a mediator.

11.A curable composition according to claim 10, characterized in that the mediator is selected from methyl syringate, ethyl syringate, and phenothiazine-10- propionic acid.

12. A process for curing a composition according to any one of the preceding claims, comprising the steps of a) applying the composition to a substrate, b) optionally evaporating solvents and/or diluents, and c) exposing the applied composition to actinic radiation to at least partly cure the composition.

13. Use of the curable composition according to any one of the preceding claims as a coating or adhesive composition.

4. Use according to claim 13 as a coating in the finishing and refinishing of automobiles and large transportation vehicles.