The present invention refers to a hybrid cationic and free radical radiation, such as ultraviolet, curable coating or ink composition comprising at least one cyclo aliphatic epoxy resin or epoxide compound and/or oxetane resin or compound, at least one free radical polymerisable partially acrylated hydroxyfunctional compound, at least one free radical photoinitiator and at least one cationic photoinitiator. In a further aspect, the present invention refers to the use of said composition.

Cationic photopolymerisation is a ring opening polymerisation process of oxiranes and/or oxetanes initiated by a strong protonic acid generated by the photolysis of for instance onium salts, such as diaryliodonium and/or triarylsulphonium salts. Photosensitisers, such as thioxanthones and anthracene derivatives, as well as free radical photoinitiators can be used to enhance the activity of the onium salt. The living character of the polymerisation will continue to develop after for instance ultraviolet (UV) exposure, providing a beneficial post cure effect. This effect can be enhanced by a thermal treatment. The ring opening mechanism resulting in a low shrinkage and the outstanding adhesion on many substrates are some of the main features of cationic systems over free radical photopolymerisation. Furthermore, the oxonium ion and the carbocation are inactive towards oxygen which allows a high curing speed in air. Cationic radiation curing resins are typically used in printing inks, varnishes, coatings, rapid prototyping, electronic coatings, insulation coatings and in adhesives.

The main components of a cationic formulation are cycloaliphatic epoxy resins, epoxide compounds, such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, and/or oxetane resins and/or compounds, such as 3-ethyl-3-hydroxymethyl-oxetane, as main components. The ring opening of the three membered epoxide group and/or the four membered oxetane group can be accompanied by crosslinking with hydroxyl functional compounds like caprolactone polyols, polyether polyols, polyester polyols, such as dendritic polymers. These polyols act as chain transfer crosslinkers and flexibilisers and they can be used in concentration up to for instance 30% by weight.

A number of other components, such as epoxides, that is epoxy and epoxide resins and compounds having one or more three membered epoxide groups, vinyl ethers, Novolac resins, epoxidised oils, epoxidised polybutadiene, can be used to fine tune the end properties of a composition. The cationic photopolymerisation of epoxides, that is compounds and resins having one or more three membered epoxide groups, and oxetanes, that is compounds and resins having one or more four membered oxetane groups, can be combined, in a so called

hybrid formulation, with free radical polymerisation of for instance acrylate systems to build interpenetrating polymer networks.

It is with free radical initiated polymerisation systems difficult to get for instance excellent adhesion to substrates such as polyolefins. The high shrinkage during cure resulting in internal stress causing delamination between the coating and the substrate and the lack of groups that can chemically bond to the substrate are reasons to the poor adhesion. Adhesion of UV curable coating and inks are discussed in for instance "Adhesion of UV-Curable Coatings and Inks", John K. Braddock, Radtech Report, July/August 2002.

Hybrid cationic and free radical curing systems will have the benefit of dark cure effect. In hybrids the initial rate of dark cure is higher compared to a pure cationic system. The adhesion of hybrid formulations to difficult substrates like polyolefins is as good as for pure cationic formulations and much better than that of pure free radical curing systems based on acrylates.

Hydrid formulations and properties obtained therewith are disclosed and discussed in for instance "A Study of Epoxy Resin - Acrylated Polyurethane Semi-Interpenetrating Polymer Netsworks", Robert Vabarik et al, Journal of Applied Polymer Science vol. 68 (1998), pages 111-119, "UV-Initiated Free Radical and Cationic Photopolymerization of Acrylate/Ep oxide and Acrylate/Vinyl Ether Hybrid Systems with and without Photosensitizer" , Jung-Dae Cho et al, Journal of Applied Polymer Science vol. 93 (2004), pages 1473-1483 and "Internal Stress of Epoxy Modified with Acrylic Polymers Produced by In Situ UV Radiation Polymerization" , Yoshinobu Nakamura et al, Journal of Applied Polymer Science vol. 39 (1990), pages 1045-1060. Radiation curable hybrid pressure sensitive adhesives for bonding of optical discs are disclosed in WO 99/63017.

The object of the present invention is the use of a partially acrylated, methacrylated and/or β-methyl acrylated hydroxyfunctional product in a hybrid cationic and free radical, such as ultraviolet (UV), curing system. Said partially acrylated product can crosslink, by free radical polymerisation of the aciylate group(s) and by chain transfer reaction of the hydroxyl group(s) in a cationic polymerisation between the networks formed by polymerisation of acrylate groups and that of the cationic polymerisation. This ensures crosslinking of all potentially reactive compounds compared to a physical blend of fully acrylated products and epoxides, oxetanes, vinyl ethers and polyols. This imparts a lower amount of products that can be extracted from the cured film, which is beneficial in the developing of low migrating system, such as food packaging printing inks, coatings and laminating adhesives. Hybrid formulations typically have excellent adhesion to polyolefins.

The present invention accordingly refers to a hybrid cationic and tree radical radiation curable, such as a UV curable, coating, such as a varnish, paint or enamel, or ink composition comprising at least one cycloaliphatic epoxide compound or cycloaliphatic epoxy resin and/or at least one oxetane resin or compound having one or more oxetane rings, at least one free radical photopolymerisable compound having an acrylate, methacrylate and/or β-methyl acrylate functionality of at least 1 and a hydroxyl functionality of at least 1, at least one cationic photoinitiator, and at least one free radical photoinitiator.

Said cycloaliphatic epoxide compound or epoxy resin is in preferred embodiments of the present invention 4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, 3,4-epoxy- - 1 -methyl -cyclohexylmethyl-3 ,4-epoxy- 1 -methylcyclohexane carboxylate, 6-methyl~3 ,4- ~epoxycyclohexylmethyl-6-methyl-3,4-epoxycyclohexane carboxylate, 3,4~epoxy-3-methyl- cyclohexylmethyl-3,4-epoxy-3-methylcyclohexane carboxylate and/or 3,4-epoxy-5-methyl- cyclohexylmethyl-3 ,4-epoxy-5 -methylcyclohexane carboxylate.

Said oxetane resin or compound is in embodiments of the present invention preferably and suitably a 3-methyl-3-(hydroxymethyl)oxetane, 3-ethyl-3-(hydroxymethyl)oxetane or 3,3-di(hydroxymethyl)oxetane, a 3-ethyl-3-phenoxymethyloxetane, a bis(l-ethyl- (3-oxetanil))methyl)ether, a 3-ethyl-3-(2-ethylhexyloxy)methyl)oxetane, a l,4-bis((3-ethyl- -3-oxetanylmethoxy)methyl)benzene, a phenol Novolak oxetane and/or a 3-ethyl-(triethoxysilylpropoxy)methyl)oxetane. Said oxetane include species such as hydroxyfunctional oxetanes of trimethylolethane, trimethylolpropane, pentaerythritol, ditrimethylolethane, ditrimethylolpropane and dipentaerythritol.

Said compound having an acrylate, methacrylate and/or β-methyl acrylate functionality of at least 1 and a hydroxyl functionality of at least 1 is in likewise preferred embodiments an acrylic, a methacrylic and/or a β-methyl acrylic ester of a diol, triol or polyol, such as a 5,5-dihydroxyalkyl-l,3-dioxane, a 2-carboxy-2-alkyl-l,3-propanediol, a 2-hydroxy- -1,3-propanediol, a 2-hydroxy-2-alkyl- 1,3 -propanediol, a 2-alkyl-l,3-propanediol, a 2,2-dialkyl-l,3-propanediol, a 2-alkyl-2-hydroxyalkyl-l,3-propanediol, a 2,2-dihydroxy- alkyl-l,3-propanediol or a dimer, trimer or polymer of a said 1,3-propanediol or 1,3-dioxane. Further suitable embodiments of said diol, triol or polyol include adducts between at least one alkylene oxide, such as ethylene oxide, propylene oxide, butylene oxide, butadiene monoxide, cyclohexene oxide and/or phenylethylene oxide and a said 1,3-propanediol or 1,3-dioxane or a dimer, trimer or polymer thereof. Said diols, triols and polyols can suitably be exemplified by mono, di, tri or polyethylene glycols, mono, di, tri or polypropylene glycols, mono, di, tri or polybutylene glycols, polytetramethylene glycol, 2,2-dimethylolpropionic acid, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,6-cyclohexanedimethanol, 5,5~dihydroxymethyl-l,3- -dioxane, 2-methyl-l,3-propanediol, 2-propyl-2-rnethyl-l,3-propanediol, 2,2-diethyl-l,3-

-propanediol, 2-ethyl-2-methyl-l,3-propanediol, 2-butyl-2-ethyl-l,3-propanediol, neopentyl glycol, dimethylolpropane, 1,1-dimelliylolcyclohexane, glycerol, 1,1-dimethylolnorbornane, 1,1-dimethylolnorbornene, trimethylolethane, trimethylolpropane, diglycerol, ditrimethylol- ethane, dilrimethylolpropane, pentaerytliritol, dipentaerythritol, anliydroenneaheptitol, tetramethylolcyclohexanol, sorbitol, mannitol and adducts between at least one said alkylene oxide and a said diol, triol or polyol.

Further preferred embodiments of said diol, triol or polyol are found among dendritic polyester and polyether polyols, such as dendritic polymers disclosed in for instance WO 93/17060, WO 93/18079, WO 96/07688, WO 96/12754, WO 99/00439, WO 99/00440, WO 00/56802 and WO 02/40572 which disclosures in their entirety by reference is herein included.

Yet further suitable and preferred embodiments of said diol, triol or polyol are polycarbonate diols, triols and polyols obtained from a for instance at least one above said diol, triol or polyol and at least one carbon dioxide source, such as dimethyl carbonate, diethyl carbonate and/or urea.

Said at least one cationic photoinitiator is in preferred embodiments of the present invention an iodonium, a sulphonium, a halonium, a sulphoxonium, a diazonium, a thioxanthonium and/or a metallocene salt and said free radical photoinitiators is likewise preferably benzoin or a benzoin derivative, acetophenone, benzil or a benzil ketal, an anthraquinone, triphenylphosphine, a benzoylphosphine oxides, a benzophenone, a thioxanthone, a xanthones, an acridine derivative, a phenazene derivative and/or a quinoxaline derivative.

The radiation curable composition according to the present invention may furthermore and additionally to said components comprise at least one organic or inorganic pigment, filler and/or colorant, at least one sensitiser, such as l-chloro-4-propoxy-thioxanthone, sensitising said at least one cationic photoinitiator thus increasing its reactivity and/or at least one stabiliser, selected from for instance hydrocarbon carboxylic acid salts of group IA or DA metals, such as sodium bicarbonate, potassium bicarbonate and/or rubidium carbonate.

In a further aspect the present invention refers to the use of a radiation curable composition as disclosed above in decorative and/or protective coatings, such as lacquers, varnishes, paints and enamels, in inks, such as printing inks and screen inks and in rapid prototyping.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilise the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever. In the following Examples 1 and 2 refer to

synthesis of partially acrylated hydroxyfonctional products used in embodiments of the present invention and Examples 3-8 to preparation and evaluation of hybrid radiation curable compositions, coatings and inks, according to embodiments of said invention. Said embodiment compositions are compared with free radical and cationic radiation curable compositions. Evaluation results are given in Tables 1-3.

Example 1

250 g of an ethoxylated pentaerythritol (Polyol PP50 , Perstorp Specialty Chemicals AB, Sweden), 122 g of acrylic acid, 0.558 g of 4-methoxyphenol, 3.72 g of methane sulphonic acid,

260 g of toluene and 6 drops of nitrobenzene was charged in a 1 litre three-necked round-bottomed reaction flask equipped with a Dean-Stark water trap, an air flow inlet, a heating device and a thermometer. The reaction mixture was heated to 124°C and the temperature was maintained until the reaction was completed and the calculated amount of reaction water (25 ml) was collected. The reaction mixture was subsequently neutralised with NaOH (40% aq) to a pH of 6.8. Separation was after addition of acetone performed over night in a separatory funnel. The product was then washed with water and evaporated to a non- volatile content of 99% by weight. Yielded product was a partially acrylated Polyol PP50 having an acrylate concentration of 5.4 mmole/g and hydroxyl value of 105 mg KOH/g.

Example 2

250 g of Boltorn ^® H2003 (dendritic polyether polyol, Perstorp Specialty Chemicals AB, Sweden), 69 g of acrylic acid, 0.5 g of 4-methoxyphenol, 3.5 g of methane sulphonic acid and

26O g of toluene was charged in a 1 litre three-necked round-bottomed reaction flask equipped with a Dean-Stark water trap, an air flow inlet, a heating device and a thermometer. The reaction temperature was between initially 90 ⁰ C and finally 122°C and the reaction was stopped when the calculated amount of water (17 ml) was collected. The reaction mixture was subsequently neutralised with NaOH (8% aq) to pH of 6.8. Separation was after addition of acetone performed over night in a separation funnel. The product was washed with water and evaporated to a non- volatile content 99% by weight. Yielded product was a partially acrylated

Boltorn " H2003 having an acrylate concentration of 2.9 mmole/g and hydroxyl number of 82 mg KOH/g.

Example 3

Radiation curable compositions, clear coatings, according to embodiments of the present invention and comprising the products obtained in Examples 1 and 2 (Embodiment

Formulations 3 and 4) were prepared and compared with a free radical photopolymerisable clear coating (Formulation 1) and with a cationic photopolymerisable clear coating (Formulation 2). Components and amounts in parts are given below.

*1 : Cyclo aliphatic epoxy resin (Dow Chemicals, USA).

*2: Epoxy acrylate oligomer (Cytec Surface Specialties, Belgium).

*3: Propoxylated glycerol triacrylate (Cytec Surface Specialties, Belgium).

*4: Tripropylene glycol diacrylate (Cytec Surface Specialties, Belgium).

*5: Caprolactone polyol (Dow Chemicals, USA).

*6: 3-Ethyl-3-hydroxymethyloxetane (Perstorp Specialty Chemicals AB, Sweden).

*7: Photoinitiator (Dow Chemicals, USA).

*8: Isopropyl-thioxanthone (Lambson, UK)

*9: Free radical photoinitiator (Ciba, Switzerland)

*10: Wetting agent (Byk Chemie, Germany)

*11 : Free radical photoinitiator (Ciba, Switzerland)

*12: Amine acrylate (Cytec Surface Specialties, Belgium)

Example 4

The radiation curable compositions prepared in Example 3 were applied on plastic substrates at a thickness of 6 μm wet film. The coatings were cured in air by being passed once under a 80 W/cm UV lamp at a speed of 16 m/min and characterised by methyl ethyl ketone (MEK) double rubs and adhesion to polyethylene (PE) and oriented polypropylene (OPP) with tape test (scale 0-5, 0 best). The PE and OPP films did not have a fresh corona treatment. The reactivity was determined as the maximum curing speed for surface cure after one pass under the lamp. The result is given in Table 1 below.

Adhesion test method; An adhesive tape was superposed on the coated surface of the polyolefm film and was pressed with fingers to firmly bond them. The adhesive tape was then peeled rapidly from one direction at an angle of 90 degrees. The amount of coating separated from the film and bonded to the adhesive tape visually evaluated according to following scale

0: No Coating/ink was transferred to the adhesive tape,

1: <5 % of the coating/ink transferred to the adhesive tape,

2: 5-25 % of the coating/ink transferred to the adhesive tape,

3: 25-50 of the coating/ink transferred to the adhesive tape,

4: 50-95 of the coating/ink transferred to the adhesive tape, and

5: > 95 % of the ink/coating transferred to the adhesive tape.

The adhesion test was made 24 hours after cure on films conditioned in 23 ⁰ C and 50% relative humidity.

Example 5

Radiation curing compositions, printing inks, according to embodiments of the present invention and comprising the product obtained in Examples 1 and 2 (Embodiment Formulations 7 and 8) were prepared and compared with a free radical photopolymerisable printing ink (Formulation 5) and a cationic photopolymerisable printing ink (Formulation 6). All inks were prepared at 50 ⁰ C in a high speed dispersing equipment. Components and amounts in parts are given below.

*1 : Cycloaliphatic epoxy (Dow Chemicals, USA).

*2: 3-Ethyl-3-hydroxymethyloxetane (Perstorp Specialty Chemicals AB, Sweden).

*3 : Ethoxylated pentaerythritol tetraacrylate (Cytec Surface Specialties, Belgium).

*4: Polyester acrylate oligomer (Cytec Surface Specialties, Belgium).

*5: Hexandiol diacrylate (Cytec Surface Specialties, Belgium).

*6: Caprolactone polyol (Dow Chemicals, USA).

*7: Dispersing agent (Noveon, Germany).

*8: Organic pigment (Sun Chemicals, USA).

*9: Photoinitiator (IGM resins, Holland).

*10: Solvent for Omnicat 550 (Hϋls, Germany).

*11-13: Free radical photoinitiators (Ciba, Switzerland). * 14- 15 : Free radical photoinitiators (Lambson, UK). *16: Wetting agent (Byk Chemie GmbH, Germany).

Example 6

The radiation curing compositions, printing inks, prepared in Example 5 were applied with Echocel hand proofer with anilox roller 700 cells/inch on plastic substrates. The coatings were cured in air by being passed once under an 80 W/cm UV lamp at a speed of 10 m/min and characterised by ethanol double rubs and adhesion to polyethylene (PE) and oriented polypropylene (OPP) with tape test (adhesion test method as in Example 4). The PE and OPP

films did not have a fresh corona treatment. The reactivity was determined as the maximum curing speed for surface cure after one pass under the lamp. The result is given in Table 2 below.

Example 7

Radiation curing compositions, screen inks, according to embodiments of the present invention and comprising the product obtained in Examples 2 (Embodiment Formulations 11 and 12) were prepared and compared with a free radical photopolymerisable screen inlc (Formulation 9) and a cationic photopolymerisable screen inlc (Formulation 10). AU inks were prepared at 50 ⁰ C in a high speed dispersing equipment. Components and amounts thereof are listed below.

*1: Cycloaliphatic epoxy resin (Dow Chemicals, USA).

*2: 3-Ethyl-3-hydroxymethyloxetane (Perstorp Specialty Chemicals AB, Sweden).

*3: Epoxy acrylate oligomer (Cytec Surface Specialties, Belgium).

*4: Hexandiol diacrylate (Cytec Surface Specialties, Belgium).

*5: Ethoxylated trimethylolpropane triacrylate (Cytec Surface Specialties, Belgium).

*6: Caprolactone polyol (Dow Chemicals, USA).

*7: Dispersing agent (Noveon, England).

*8: T1O2 (Kronos Titan, Norway).

*9: Photoinitiator (CBA, Switzerland).

*10: Senitiser (Lambson Ltd, UK).

*11-14: Free radical photoinitiators (Ciba, Switzerland).

Example 8

The radiation curing compositions, screen inks, prepared in Example 7 were applied on plastic substrates at a film thickness of 12 μm wet film. The screen inks were cured in air by being passed twice under a 160 W/cm UV lamp at a speed of 30 m/min and characterised by methyl ethyl ketone (MEK) double rubs, adhesion to polyethylene (PE) and oriented polypropylene (OPP) with tape test (adhesion test method as in Example 4) and Erichsen flexibility according to ASTM E-643. The PE and OPP films did not have a fresh corona treatment. The result is given in Table 3 below.

Table 1

* Tests performed on freshly corona treated polyethylene and oriented polypropylene.

Table 2

Tests performed on freshly corona treated polyethylene and oriented polypropylene.

Table 3