More in particular the invention relates to high solid coating compositions derived from epoxy compounds and an ethylenically unsaturated acid, which can be cured by ultraviolet light, optionally in combination with a heat source e. g. infrared light, after application on the desired substrate.

In order to obtain such high solids coating formulations, it is normally necessary to employ appropriate acrylate resins, having low viscosities, i. e. low molar masses.

In addition to the still increasing pressure from environmental and health authorities, to reduce the emission of organic compounds, e. g. solvents, additives, when a coating composition is applied and processed for drying or curing, there is still an economical aim to improve the adhesion of said coating compositions, on different substrates such as metals, wood or polymers, or combinations thereof, in order to be able to manufacture high quality, coated industrial products.

It will be appreciated that there is an aim to improve the adhesion to in particular low surface tension polymer surfaces such as polypropylene and ethylene propylene copolymers of the until now used coating compositions, which have been derived from adducts of a. diglycidylether of diphenylolpropane, such as EPON 828, and acrylic acids, and di-and tri-acrylates of polyols,

such as propylene glycols trimethylol propane, hexane diol and/or aminoacrylates (EPON is a trademark).

Another property which had to be improved in respect of the"high solids"character, was the viscosity of the major ingredients.

Another object of the invention was to develop solvent free high solid coating compositions, derived from less different ingredients, which moreover should be as cheap as possible.

As a result of extensive research and experimentation, such a coating composition aimed at and a copolymer binder to be used in it have been surprisingly found now.

Accordingly, the present invention relates to a low viscosity copolymer binder, containing hydroxyl groups, obtainable by copolymerization in the absence of solvents or in the presence of small amounts of inert organic solvent, of at least: 1) an adduct of (A) one or more diglycidylesters of a, a, a', a'- branched aliphatic dicarboxylic acids, containing 8 to 18 carbon atoms in the acid residue and preferably from 10 to 14 carbon atoms (DTADGE) and, (B) acrylic acid, optionally a-alkyl-substituted, wherein the alkyl substituent contains from 1 to 4 carbon atoms and preferably 1, the molar ratio of A and B being in the range of from 0.9 to 1.1 to 1.1 to 0.9 and preferably close to 1.0, or an adduct of (C) one or more a, a, a', a'-branched aliphatic dicarboxylic acids (DTA), and (D) glycidyl acrylate, wherein the acryl acid residue has optionally been substituted by an alkyl from 1 to 4 carbon atoms and preferably 1 carbon atom, the molar

ratio of (C) and (D) being in the range of from 0.9 to 1.1 and preferably close to 1.0, and optionally 2) one or more ethylenically unsaturated comonomers, other than component 1, in the presence of a free radical polymerization photo- initiator (3), and under irradiation with UV and optionally IR light.

Depending on the specific type of adduct and optional additional comonomers and type of initiator the polymerization is be carried out at a temperature in the range from 40 to 80 °C and preferably from 60 to 70 °C.

Relatively high temperatures in this range can be reached by the use of additional IR light sources, e. g. from 5 to 10 IR lamps of 600 W, providing additional heat for reaching desired temperatures in the coating layer.

It will be appreciated that the specific temperature applied and the energy input UV of irradiation will be mainly dependent on the selected type of initiator and its concentration.

Suitable UV irradiation densities for the curing of the compositions of the present invention are in the range of from 50 to 1700 J/m2.

Preferably UV irradiation densities used in the range of from 200 to 1200 J/m2 and more preferably from 500 to 1000 J/m2.

According to preferred embodiments of the present invention, the adduct component (1) is initially prepared from (A) and (B), in about equimolar amounts, in the presence of a catalyst, known in the art for this purpose, such as stannous octoate, in an amount of from 0.01 to 0.20 wt%, and preferably 0.05 to 0.10 wt%, relative to the weight of component A, and in the presence of a polymerization inhibitor, such as hydroquinone derivatives in an amount of from 100 to 200 ppm relative to the weight of component A, at a

temperature in the range of from 50 °C to 200 °C, and preferably from 80 °C to 100 °C.

The preferred component (B) is acrylic acid.

Optional comonomers (2) may be selected from di-or tri-acrylates of polyols, such as tripropylene glycol diacrylate, trimethylol propane triacrylate, bis-phenylol propane acrylate, hexane diol diacrylate, and relatively small amounts of silicone acrylates, such as EBECRYL 350 (EBECRYL is a trademark) and/or amino acrylate (e. g.

EBECRYL 7100) in total amounts of from 10-80 wt%, relative to the total weight of comonomers.

Additional suitable comonomers as component (2) are selected from, alkyl acrylates and hydroxy alkyl acrylates, wherein the alkyl ester group contains from 1 to 4 carbon atoms and wherein the acrylate residue can be optionally a-substituted by an alkyl group of from 1 to 4 carbon atoms; vinyl aromatic comonomers having from 8 to 20 carbon atoms and preferably styrene.

It has been surprisingly found, that coating compositions derived from the (co) polymer binders as specified hereinbefore, show a very attractive adhesion to metal, wood, paper and polymer substrates, and in particular to poly (propylene), poly (ethylene), optionally mixed with propylene-, ethylene-, alkadiene-copolymers (EPDM) or alkadiene-vinyl aromatic block copolymers.

Another surprising advantage provided by the hereinbefore specified (co) polymer binders was the attractive low viscosity, which enables the use of less or no diluent comonomers in comparison to prior art compositions.

According to preferred embodiments of the present invention, the concentration of photo-initiator is in the range of from 1 to 8 wt%, and preferably from 2 to 7 wt%, relative to the weight of the total (co) monomer composition and most preferably from 3 to 6 wt%.

In most preferred embodiments of the invention the polymerization temperature is in the range of from 60 to 70 °C.

It will be appreciated that the curable low viscosity binders of the present invention, may contain, in addition to the hereinbefore defined adducts, acrylate comonomers in amounts of from 10 to 80 wt%, relative to the weight of the total composition and preferably from 20 to 70 wt% and more preferably from 30 to 60 wt%.

Under usual conditions, the copolymerisation is carried out without any solvent. However under certain specific conditions, also covered by the present invention, the use of small amounts of inert organic solvent may be desired (i. e. amounts of at most 5 wt%, relative to the weight of the complete comonomer composition).

The diglycidyl esters of a, a, a', a'-branched aliphatic dicarboxylic acids (DTADGE) used for the (co) polymers binders of the present invention (component A) are more in particular diglycidylesters of a, (x, a', a'-tetraalkylalkanedicarboxylic acids, containing from 8 to 18 carbon atoms in the acid moiety, and more preferably from 10 to 14 carbon atoms. Most preferred starting components A are selected from diglycidylesters of and technical mixtures thereof straightly obtainable from commercial manufacturing processes.

The a, a, a', a'-branched aliphatic dicarboxylic acids (DTA) used as components (c), are more in particular those, containing from 8 to 18 carbon atoms in the acid moiety and preferably from 10 to 14 carbon atoms. More preferred as diacids are those produced as technical mixtures straightly obtained from commercial manu- facturing processes.

Suitable photo-initiators, which can be used for the manufacture of the high solid copolymer systems according

to the present invention are soluble in the starting (co) monomer (s) compositions.

Such photo-initiators are e. g. those composed of (a) an aromatic ketone, (b) optionally one or more tertiary amines, at least one carbon of which, situated in the alpha position with regard to the nitrogen atom, carries at least one hydrogen atom, and (c) at least one aromatic or non-aromatic alpha dione.

Aromatic ketones which can be used include acetophenone, propiophenone, 2-phenyl-acetophenone, 2-chloro-2-phenyl-acetophenone, 2,2-dichloro-2-phenyl- acetophenone, 2-butyloxy-2-phenylacetophenone, 2,2-dimethyoxy-2-phenylacetophenone, 2,2-diethoxy- acetophenone, 2-methylol-2-methoxy-2-phenyl-acetophenone, 2-hydroxy-2-phenyl-acetophenone, benzophenone, 4-tri- chloromethylbenzophenone, indenone, 1,3-indandione, fluoreone, xanthone, thioxanthone, 2-chlorothioxanthone, anthraquinone, 2-ethylanthraquinone, 1,6-hexanediol acrylate o-benzoylbenzoate and the like.

The photo-initiating action of these aromatic ketones is greatly improved by tertiary amines having at least one hydrogen atom on the carbon atom next to the nitrogen atom. Tertiary amines which can be used include trimethylamine, triethanolamine, N-methyldiethanolamine, N, N'-dimethyl-ethanolamine, dimethylstearylamine, N, N-dimethylaniline and N, N'-di (2-hydroxyethyl)-aniline.

The photo-initiating action of the above-mentioned aromatic ketones can also be greatly improved by the addition of at least one aromatic or non-aromatic alphadione, examples of which include biacetyl, glyoxal, inane-1, 2-dione, p-chlorophenyl-glyoxal, benzil, camphoquinone and the like.

Photo-initiator compositions derived from the components (a), (b) and (c) contain from 0.5 to 95 wt% of

(a), from 0 to 99 wt% of (b), and from 0 to 90 wt% of (c).

It will be appreciated by a person skilled in the art that it may be advantageous in certain cases, to associate, in one and the same molecule, the tertiary amine function, at least one carbon atom of which, in the alpha position with regard to the nitrogen atom, carries at least one hydrogen atom, with the aromatic ketone function, for example 2-isopropyloxy-2- (4-dimethyl- aminophenyl)-propiophenone, 4-dimethylaminobenzophenone, 4,4'-bis-(dimethylamino)-benzophenone, N-methylacridone, 2-diethylamino-9-fluorenone, 7-diethylamino-4-methyl- coumarin and the like. It is also possible to associate, in one and the same molecule, the tertiary amine function, at least one carbon atom of which, in the alpha position with regard to the nitrogen atom, carries at least one hydrogen atom, with at least one acrylic or methacrylic radical, for example the monoacrylates, diacrylates and triacrylates or methacrylates of triethanolamine, N-methyl-diethanolamine, N, N'-dimethyl- ethanolamine or N, N'-di (2-hydroxyethyl)-aniline; or the mixed esters of acrylic acid and beta-dimethylamino- propionic acid with polyols, such as 1,4-butanediol, trimethylolpropane or the like.

The hereinbefore specified photo-initiators can be applied in concentrations of 1 to 25 wt% of the weight of the total composition.

Other examples of suitable photo-initiators or free radical photo-initiators, known from"Photo-initiators and Photosensitizers of Polymerization; A short review, Vol. 6, European Coatings Journal, pp. 412-419 (1996)".

More specific examples are oligo (2-hydroxy-2-methyl- 1- (4- (1-methylvinyl) phenyl) propanone), 2-hydroxy-2- methyl-1-phenyl-1-propanone, 2,4,6-trimethylbenzophenone, 4-methylbenzophenone, 2,2-dimethoxy-1,2-diphenylethanone,

2-butoxy-1, 2-diphenylethanone, 2- (2-methyl propoxy)-1, 2- diphenylethanone, benzophenone, 2-alpha hydroxy ketone, other alpha hydroxy ketones, other benzophenone derivatives or mixtures thereof.

Other photo-initiators (i. e., photo-polymerization initiators) compatible and suitable for use with the inks of the present invention are well known in the art.

Additional examples of suitable photo-initiators are listed in U. S. Patent No. 4,670,295 (Quin et al.) and U. S. Patent No. 4,680,368 (Nakamoto et al.).

A preferred photo-initiators is ESACURE KIP-100F (ESACURE is a trademark) that is commercially available from Sartomer. This photo-initiator (ESACURE KIP-100F) is a liquid mixture of 70% by weigh of oligo (2-hydroxy-2- methyl-l- (4- (l-methylvinyl) phenyl) propanone with a M. W. = 204. 7 grams/mole per repeating unit and 30% by weight of 2-hydroxy-2-methyl-1-phenyl-1-propanone with a M. W. = 164. 2 grams/mole.

Said photo-initiators are preferably used in amounts of from 0.05 to 5 wt% relative to the weight of the total composition, and more preferably from 0.1 to 0.5 wt%.

Other suitable commercially available photo- initiators include, but are not limited to 1-hydroxy cyclohexyl phenyl ketone (IRGACURE 184); n5-2, 4-cyclo- pentadien-1-yl) (1, 2,3,4,5, 6-n)- (l-methyl ethyl) benzene)- iron (+)-hexafluorophosphate (-1) (IRGACURE 261); 2-benzyl-2-n-dimethylamino-1- (4-morpholinophenyl)-1- butanone (IRGACURE 369); 1-hydroxycyclohexyl phenyl ketone (50% by weight) plus benzophenone (50% by weight) (IRGACURE 500); bis (2,6-dimethoxy benzoyl)-2,4,4-tri- methylpentyl phosphineoxide (DMBAPO) (25% by weight) plus 2-hydroxy-2-methyl-1-phenyl-propan-1-one (HMMP) (75% by weight) (IRGACURE 1700); 4- (2-hydroxyethoxy) phenyl (2- hydroxy propyl) ketone (IRGACURE 2959); 2,4,6-trimethyl benzoyl diphenyl phosphineoxide (TPO) (50% by weight)

plus 2-hydroxy-2-methyl-1-phenyl-propan-1-one (HMPP) (50% by weight) (DAROCUR 4265); 2,2-dimethoxy-2-phenyl- acetophenone (BDK) (IRGACURE 651) ; bis (n5-2, 4-cyclo- pentadien-1-yl); bis (2,6-difluoro-3- (lH-pyrrol-l- yl) phenyl) titanium (CGI-784); 2-methyl-l- (4- (methyl- thio) phenyl)-2-morpholino propan-1-one (MMMP) (IRGACURE 907); 2-hydroxy-2-methyl-1-phenyl-propan-1-one (HMPP) DAROCUR 1173); or mixtures thereof (IRGACURE and DAROCUR are trademarks).

Said photo-initiators are preferably used in concentrations of from 0.05 to 5 wt% and more preferably from 0.1 to 0.5 wt% relative to the weight of the total composition.

Preferred curable binder compositions according to the present invention are those wherein adducts of diglycidylesters of a, a, a', a'-branched aliphatic dicarboxylic acids (DTADGE) and acrylic acid in an about 1: 1 molar ratio have been used in combination with tripropylene glycol diacrylate, trimethylol propane triacrylate, hexanedioldiacrylate, optionally mixed with minor amounts of aminoacrylatee, e. g. EBECRYL 7100 and/or silicone acrylate (e. g. EBECRYL 350).

It will be appreciated that another aspect of the present invention is formed by irradiation curable coating compositions, comprising at least one comonomer (1) and optionally comonomer (2), and a free radical polymerization photo-initiator as specified hereinbefore, and optionally one or more of the usual auxiliaries such as dyes, coloring agents, stabilisers and the like.

The invention moreover relates to irradiation cured coating films on a substrate, comprising a copolymer binder as specified hereinbefore.

Said coating compositions have been surprisingly found to provide an excellent adhesion to pure

poly (propylene), pure poly (ethylene) poly (propylene) mixed with ethylenepropylene diene rubber (EPDM), poly (propylene) mixed with optionally hydrogenated with alkadiene-vinyl aromatic block copolymers and non-treated or pretreated metal surfaces but also to wooden or paper substrates and in particular wooden construction elements for the building industry.

The curing of said coating compositions is preferably carried out by means of UV, visible light, optionally in combination with IR radiation.

According to a more preferred embodiment the coated articles are transported on a conveyor moving under fixed irradiation sources with an adjusted speed.

It will be appreciated that the present invention also relates to articles, coated with compositions comprising at least one (co) polymer binder according to the invention, in a cured or uncured state.

It is true that from US patent No. 4,877,838 were known high-solids, thermosetting coating composition, containing low mol weight hydroxy functional acrylic copolymer, linear low molecular weight hydroxy functional polyester polymer and a hydroxy ester functional epoxy ester diluent, produced by copolymerizing ethylenically unsaturated monomers containing glycidyl or oxirane functional monomers, such as acrylic, methacrylic or vinyl derivatives of glycidol.

Said diluent could be prepared from a diglyciyl ester of 2,2-dimethyl-4-methylene glutarate and a saturated or unsaturated fatty acids. However not any indication was given to irradiation curing and to any adhesion to metal or plastic to be improved, whereas organic solvents were used in significant amounts during preparation of the respective ingredients, and which had to be stripped off to increase the polymer solids content.

The invention is illustrated in more detail in the following examples, however without restricting its scope to these specific embodiments.

Example 1 Synthesis of the adduct of Acrylic acid and DTADGE (DTADGE-AA adduct): Initial Reactor Charge (parts by weight, in g) Acrylic acid 33. 72 DTADGE 80 DABCO T9 catalyst (0.07 wt% on DTADGE) 0.056 MMHQ (monomethylether of hydro- quinone) as inhibitor (185 ppm on DTADGE) 0.0148 (DABCO is a trademark) A mixture of 1: 1 equivalent diglycidylester of ditertiary acid (DTADGE) and acrylic acid, together with 0.07 wt% DABCO T9 (a commercial grade of stannous octoate) on the total DTADGE content is made. The reaction is performed under air flow to recycle the inhibitor. 185 ppm 4-Methoxy phenol (MMHQ) is added.

The reactor charge is heated slowly under constant stirring to-80 °C, where a big exotherm appears. The temperature will increase to 100 °C and this temperature is maintained, until the exotherm is stabilised and a final epoxy group content (EGC) is reached of 17 meq/kg.

The viscosity of the DTADGE-AA adduct is 13500 mPas at 20 °C.

Example 2 Synthesis of the adduct of Glycidyl Methacrylate (GMA) and ditertiary acid (DTA) (GMA-DTA adduct):

Initial Reactor Charge (parts by weight, in g) DTA 80 GMA 105 DABCO T9 catalyst (0.07 wt% on GMA) 0.0735 MMHQ (monomethylether of hydroquinone) as inhibitor (185 ppm on GMA) 0.0194 A mixture of 1: 1 equivalent ditertiary acid (DTA) and glycidyl methacrylate, together with 0.07 wt% DABCO T9 (a commercial grade of stannous octoate) on the total GMA content is made. The reaction is performed under air flow to recycle the inhibitor. 185 ppm 4-Methoxy phenol (MMHQ) is added.

The reactor charge is heated slowly under constant stirring to-80 °C, where an exotherm appears. The temperature will increase to 100 °C and this temperature is maintained, until the exotherm is stabilised.

Thereafter the temperature was increased to 120 °C as this reaction went slower than the DTADGE-AA reaction. A final epoxy group content (EGC) is reached of 162 meq/kg The viscosity of the GMA-DTA adduct is 11250 mPas at 21 °C.

Examples 3-9 and Comparative Examples A-C Use of the DTADGE-AA and GMA-DTA adducts of examples 1 and 2 in UV cure.

The properties of the tested coating compositions were compared with a presently commercially applied composition, which has generally been regarded as the optimal one up to now by persons skilled in the art.

Such a composition (comparative comp. A) normally comprises: Epoxy acrylate (E828-AA adduct) (EBECRYL 600) 37.5% by weight Tripropylene glycol diacrylate (TPGDA) 25%

Trimethylol propane triacrylate (TMPTA) 10% Hexanedioldiacrylate (HDDA) 8% Aminoacrylate (EBECRYL 7100) 13% IRGACURE 500 (mix of benzophenone and IRGACURE 184) 5.5% Silicone acrylate (EBECRYL 350) 1% This recipe has to be used ideally at a temperature of 60 °C (heat given by one or more IR lamps of 600 W each).

Speed of the conveyor = 40/50 m/min.

Lamp of 80 W (bulb H lamp).

The following compositions were prepared, using the DTADGE-AA adduct or the GMA-DTA adduct of examples 1 and 2 respectively.

Example 3 A composition (III) was prepared comprising: DTADGE-AA adduct 37.5% by weight tripropylene glycol diacrylate (TPGDA) 25% trimethylol propane triacrylate (TMPTA) 10% hexanediol acrylate (HDDA) 8% aminoacrylate (EBECRYL 7100) 13% silicone acrylate (EBECRYL 350) 1% IRGACURE 500 5.5% Example 4 A composition (IV) was prepared comprising: DTADGE-AA adduct 58.5% by weight TMPTA 10% TPGDA 12% EBECRYL 7100 13% IRGACURE 500 5.5% EBECRYL 350 1% Example 5 A composition (V) was prepared comprising : DTADGE-AA adduct 94.5% by weight IRGACURE 500 5.5%

Example 6 A composition (VI) was prepared comprising: GMA-DTA adduct 37.5% by weight TPGDA 25% TMPTA 10% HDDA 8% EBECRYL 7100 13% EBECRYL 350 1% IRGACURE 500 5.5% Comparative Example B A composition (B) was prepared comprising: EBECRYL 600 38% by weight TPGDA 25% TMPTA 10% HDDA 8% EBECRYL 7100 13% IRGACURE 651 5% EBECRYL 350 1% Example 7 A composition (VII) was prepared comprising: GMA-DTA adduct 38% by weight TPGDA 25% TMPTA 10% HDDA 8% EBECRYL 7100 13% IRGACURE 651 5% EBECRYL 350 1% Comparative Example C A composition (C) was prepared comprising: EBECRYL 600 37.5% by weight TPGDA 25% TMPTA 10% HDDA 8% EBECRYL 7100 13% ITX (isopropylthioxanthone) 5.5%

EBECRYL 350 1% Example 8 A composition (IX) was prepared comprising: GMA-DTA adduct 37.5% by weight TPGDA 25% TMPTA 10% HDDA 8% EBECRYL 7100 13% ITX 5.5% EBECRYL 350 1% The compositions III-IX and comparative compo- sitions A-C were tested on different substrates pure polypropylene, modified polypropylene mixed with ethylene propylene diene rubber (EPDM) and metal Q-panels.

A temperature of in average of 60 °C was aimed when applying heat from 9 IR lamps of 600 W each.

The UV irradiation was delivered by a 120 W bulb H lamp, providing an irradiation energy density of 800 J/m2 while the conveyer speed was 5.4 m/min.

At the moment that a panel on the conveyor had fully entered the area of the lamps, these were switched off which was found to represent a reproducible method.

The results have been listed in the following tables.

The König hardness is given as indication.

Difficulties were experienced during measurements due to the low surface tension of the coatings which made the pendulum slide. The surface tension was too low.

Pencil hardness could not be measured in a reproducible, reliable way, due to the loss of adhesion.

Table 1 Substrate: PP with high concentration of EPDM Composition Adhesion König hardness (s) ISO 2409* ISO 1522 (E) 1 mm 2 mm A 4 2 97 3 0 1 73 4 0 0 90 5 0 0 65 B na 5 95 7 na 2 76 *Rating: 0 = excellent adhesion, the edges of the cuts are completely smooth; none of the squares of the coating is detached, 5 = total loss of adhesion.

Table 2 Substrate: metal Q-panel (ASTM) Compo-Adhesion, König Erichsen Direct MEK sition 1 mm, hardn. Slow pen. Impact/ (double ISO 2409 (s) (mm) Reverse rubs) ISO Impact 1520 (E) (inch/lb) ISO 6272 (E) no TAPE TAPE A 5 5 87 4 <20/<20 >100 3 0 4 55 5 80/60 >100 4 0 3 65 6.5 100/100 >100 5 0 5 70 7 100/100 >100 6 3 5 87 5.2 60/40 >100 B 5 5 na 4.3 40/20 >100 7 1 1 66 5.2 80/30 >100 C 5 5 na 3.3 30/10 >100 8 1 4 na 6 >120/>120 >100

Table 3 Substrate: PP with low concentration EPDM Composition Adhesion, 2 mm, ISO 2409 no TAPE A 5 6 2 B 5 7 5 C 5 8 5 Table 4 Substrate: pure PP Composition Adhesion ISO 2409 König hardness (s) 1 mm 2 mm A 5 5 na* 3 5 5 na 4 5 4 77 5 5 4 66 * : not applicable A trial was also done on carbon black containing PP.

Here the adhesion was as bad as on pure PP, but a slightly better adhesion was seen when the epoxy acrylate was replaced by the DTADGE-AA adduct.

Conclusion: On metal substrates and polypropylene with a certain amount of EPDM a clear improvement of adhesion can be observed using the adduct of DTADGE and AA or GMA and DTA. Adhesion of DTADGE-AA adduct is slightly better than the GMA-DTA adduct.