Acyl phosphine oxide photoinitiators

Abstract

An acyl phosphine oxide photoinitiator having a structure according to Formula (I): Formula (I), wherein Ar represents an aryl group; R1 is selected from the group consisting of an aryl group, a heteroaryl group, an alkoxy group and an aryloxy group; R2, R4 and R6 are independently selected from the group consisting of an alkyl group and an alkoxy group; R3 and R5 are independently selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl group, an alkoxy group and an aryloxy group, with the proviso that at least one of R3 and R5 represents a substituent according to Formula (II): Formula (II), wherein R7 is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl, a heteroaryl group, and a -COR14 group; R8 is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl, a heteroaryl group, a free radical polymerizable ethylenically unsaturated group and a -C(R11)-CH2-NR12R13 group; X is selected from the group consisting of an oxygen and N-R9; n represents 0 or 1; and R9 is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group and an aryl group; R11 is selected from the group consisting of a hydrogen and a methyl group; R12 and R13 are independently selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group and an aralkyl group; and R14 is selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group, an alkaryl group, an aralkyl group, an aryl, and a heteroaryl group.

Description

DescriptionAcyl Phosphine Oxide PhotoinitiatorsTechnical Field

[0001] The present invention relates to acyl phosphine oxide photoinitiators and their use in low odour photocurable compositions, such as photocurable varnishes and (inkjet) inks.Background Art

[0002] Radiation curable technology has transitioned from mercury bulb-based exposure to LED exposure, with 385 nm and 395 nm LEDs being the primary light sources. This shift has significantly limited the variety of suitable photoinitiator classes available, with thioxanthones (type II initiators) and acyl phosphine oxides (type I initiators) being the most prominent. However, thioxanthones are not ideal for varnishes and white inks due to their tendency to yellow upon exposure, making acyl phosphine oxides the preferred photoinitiators for 385-395 nm LED exposure.

[0003] In recent years, concerns have arisen regarding the toxicology of standard commercially available acyl phosphine oxides. Additionally, these standard acyl phosphine oxides produce medium volatile degradation products, leading to an unpleasant background odour, which is particularly problematic in applications such as indoor decoration. Furthermore, the migration of standard acyl phosphine oxides restricts their use in food and packaging applications.

[0004] To address these limitations, significant research has been dedicated to designing functionalized acyl phosphine oxides. To mitigate the volatility of degradation products, the acyl fragment of acyl phosphine oxides must be functionalized. Several approaches have been disclosed in prior art.

[0005] WO2014129213 A1 and WO2014051026 A1 (Fujifilm Corporation) describe a method involving benzylic halogenation followed by further derivatization to produce mesityl-functionalized acyl phosphine oxides.However, this approach is limited by the selectivity of halogenation and the necessity for multistep synthesis.

[0006] WO2017086224 A1 (Fujifilm Corporation) outlines a Friedel-Crafts approach to functionalize standard acyl phosphine photoinitiators. A similar multistep Friedel-Crafts method is disclosed in EP4393720A1 (Arkema France). Friedel-Crafts reactions are known to generate significant waste and require special industrial precautions due to the corrosive nature of typical Friedel-Crafts catalysts.

[0007] A selective nitration approach is disclosed in WO2019243099 A1 and W02022106100 A1 (Agfa NV), which avoids highly corrosive chemistry but still necessitates multistep synthesis. Additional multistep synthesis methods have been disclosed in US20130328028 A (Cheil Industries, Inc.), JP2019183051 A1 (Konica Minolta, Inc.), WO2019071428 A1 (DIC Corporation), CN114507255 A (South China University of Technology), W02013091521 A1 (Shenzhen UV-ChemTech Co., Ltd.), and US20070027229 A1 (Ivoclar Vivadent A.-G.). Further approaches have been published by YinPing et al. in the European Polymer Journal (2022) and Progress in Organic Coatings (2022).

[0008] All these methods involve multistep synthesis, often combined with corrosive chemistry, generating substantial waste and limiting their applicability to high-end uses such as dental applications. These prior art methods lack economic viability for more general-purpose applications like indoor decoration and food packaging.

[0009] Therefore, there remains a need for new acyl phosphine oxide-based photoinitiators that are accessible via high-yield, preferably one-pot approaches from readily available starting materials. These new derivatives should not produce volatile degradation products and should be suitable for general-purpose applications.Summary of invention

[0010] A class of acyl phosphine oxide derivatives has been found that meet the above requirements, making them applicable for general-purpose uses.

[0011] It is an object of the present invention to provide a new class of acyl phosphine oxide photoinitiators.

[0012] It is also an object of the present invention to provide a method for the preparation of these acyl phosphine oxide photoinitiators.

[0013] It is a further object of the present invention to provide a photocurable composition comprising at least one acyl phosphine oxide according to the present invention, such as a photocurable ink or a photocurable inkjet ink.

[0014] Another object of the present invention is to provide a cured product with improved odour or less migration problems.

[0015] These and other objects and advantages of the present invention will become apparent from the detailed description given below.Description of embodimentsDefinitions

[0016] The term “alkyl group” means a functional group with all variants possible for each number of carbon atoms in the alkyl group, i.e. for one carbon atom: methyl, for two carbon atoms: ethyl, for three carbon atoms: n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl and tertiary-butyl; for five carbon atoms: n-pentyl, 1 ,1-dimethyl-propyl, 2,2-dimethylpropyl and 2- methyl-butyl, etc.Unless otherwise specified, a substituted or unsubstituted alkyl group is preferably a Ci to Ce-alkyl group, more preferably a Ci to C4-alkyl group and most preferably a methyl group or ethyl group.

[0017] The term “alkoxy group” means a functional group with all variants possible for each number of carbon atoms in the alkoxy group, i.e. for one carbon atom: methoxy, for two carbon atoms: ethoxy, for three carbon atoms: n-propoxy and isopropoxy; for four carbon atoms: n-butoxyl, isobutoxy and tertiary-butoxy; etc.Unless otherwise specified, an alkoxy-group is preferably a Ci to Ce- alkoxy group, wherein a methoxy group and an ethoxy group are particularly preferred.

[0018] Unless otherwise specified, an alkenyl group is preferably a C2 to Ce- alkenyl group.

[0019] Unless otherwise specified, an alkynyl group is preferably a C2 to Ce- alkynyl group.

[0020] The term “aryl group” means a monocyclic or polycyclic aromatic ring structure comprising only carbon atoms in the aromatic ring structure.

[0021] Unless otherwise specified, an aryl group is preferably a phenyl group (CeHs-), or a naphthyl group.

[0022] The term “aralkyl group” means an aryl group attached to an alkyl chain.Unless otherwise specified, an aralkyl group is preferably an aryl group attached to a Ci to Ce-alkyl chain, more preferably a benzyl group (C6H5CH2-), where a phenyl group (CeHs-) is attached to a methylene group (-CH2-).

[0023] The term “alkaryl group” means a functional group having one or more alkyl groups attached to an aryl group. Essentially, it is the opposite of an aralkyl group.Unless otherwise specified, an alkaryl group is preferably a group having one, two, three or more alkyl groups attached to a phenyl group or a naphthyl group, more preferably a tolyl group (CH3C6H4-), where a methyl group (CH3-) is attached to a phenyl group.

[0024] The term “heteroaryl group” means a monocyclic or polycyclic aromatic ring comprising carbon atoms and one or more heteroatoms in the ring structure, preferably 1 to 4 heteroatoms independently selected from nitrogen, oxygen, selenium and sulphur.Preferably, a heteroaryl group is a monocyclic ring, and more preferably a heteroaryl group is a five- or six-membered ring substituted by one, two or three oxygen atoms, nitrogen atoms, sulphur atoms, selenium atoms or combinations thereof.Preferred examples of heteroaryl groups include, but are not limited to, pyridinyl, pyridazinyl, pyrimidyl, pyrazyl, quinolyl, triazinyl, pyrrolyl, pyrazolyl, imidazolyl, (1,2,3,)- and (1 ,2,4)-triazolyl, pyrazinyl, pyrimidinyl, tetrazolyl, furyl, thienyl, isoxazolyl, thiazolyl, isoxazolyl, and oxazolyl.

[0025] The term “alkylene group” means a bivalent functional group derived from an alkane by removing two hydrogen atoms from one or two carbon atoms, thereby creating two points of attachment.Unless otherwise specified, an alkylene group is preferably a Ci to C20-alkylene group, more preferably a Ci to Cio-alkylene group and most preferably a Ci to Ce-alkylene group.

[0026] The term “arylene group” means a bivalent functional group derived from an aromatic hydrocarbon (arene) by removing a hydrogen atom from two ring carbon atoms.Unless otherwise specified, an arylene group is preferably a phenylene group.

[0027] The term “heteroarylene group” means a bivalent functional group derived from a heteroarene by removing a hydrogen atom from two ring atoms. Heteroarenes are aromatic compounds where one or more carbon atoms in a ring are replaced by heteroatoms such as nitrogen, oxygen, or sulphur. Preferred examples of heteroarylene groups include, but are not limited to, pyridinylene, pyridazinylene, pyrimidylene, pyrazylene, quinolylene, triazinylene, pyrrolylene, pyrazolylene, imidazolylene, (1,2,3,)- and (1,2,4)-triazolylene, pyrazinylene, pyrimidinylene, tetrazolylene, furylene, thienylene, isoxazolylene, thiazolylene, isoxazolylene, and oxazolylene.

[0028] The term “cycloalkylene group” means a bivalent group derived from a cycloalkane by removing two hydrogen atoms from one or two carbon atoms in the ring.Unless otherwise specified, a cycloalkylene group is preferably a cyclohexylene group.

[0029] The term “substituted”, in e.g. a substituted alkyl group, means that the group may be substituted by other atoms than the atoms normally present in such a group, for an alkyl group: carbon and hydrogen. For example, a substituted alkyl group may thus include a halogen atom or a thiol group, while an unsubstituted alkyl group contains only carbon and hydrogen atoms.

[0030] Unless otherwise specified, a substituted functional group of the functional groups listed above is preferably substituted by one or more constituents selected from the group consisting of an ester group, an amide group, an ether group, a thioether group, a ketone group, an aldehyde group, asulfoxide group, a sulfone group, a sulfonate ester group, a sulphonamide group, -Cl, -Br, -I, -OH, -SH, -CN and -NO2.Acyl Phosphine Oxide Photoinitiators

[0031] An acyl phosphine oxide photoinitiator in accordance with the invention has a structure according to Formula (I):Formula (I),whereinAr represents an aryl group, preferably a substituted or unsubstituted phenyl group;R1 is selected from the group consisting of a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted alkoxy group and a substituted or unsubstituted aryloxy group, with a phenyl group and a Ci to Ce alkoxy group being the most preferred;R2, R4 and Re are independently selected from the group consisting of a substituted or unsubstituted alkyl group and a substituted or unsubstituted alkoxy group;R3 and R5 are independently selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, a substituted or unsubstituted aryl group, substituted or unsubstituted alkoxy group and a substituted or unsubstituted aryloxy group, with the proviso that at least one of R3 and R5 represents a substituent according to Formula (II):Formula (II),wherein R? is selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, a substituted or unsubstituted aryl, a substituted or unsubstituted heteroaryl group, and a -COR14 group;Rs is selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, a substituted or unsubstituted aryl, a substituted or unsubstituted heteroaryl group, a free radical polymerizable ethylenically unsaturated group and a -C(Rn)-CH2-NR12 13 group;X is selected from the group consisting of an oxygen and N-R9;n represents 0 or 1 ; andR9 is selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group and a substituted or unsubstituted aryl group;R11 is selected from the group consisting of a hydrogen and a methyl group, a hydrogen being more preferred;R12 and R13 are independently selected from the group consisting of a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group and a substituted or unsubstituted aralkyl group; andR14 is selected from the group consisting of a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted alkaryl group, asubstituted or unsubstituted aralkyl group, a substituted or unsubstituted aryl, and a substituted or unsubstituted heteroaryl group.

[0032] In a preferred embodiment, R2, R4 and Re represent a substituted or unsubstituted alkyl group, an unsubstituted alkyl group being more preferred, a methyl group being particularly preferred.

[0033] In an even further preferred embodiment, R3 and R5 are independently selected from the group consisting of a hydrogen and a functional group according to Formula (II), with the proviso that at least one of R3 and R5 represents a substituent according to Formula (II).

[0034] In another preferred embodiment, R1 is selected from the group consisting of an unsubstituted aryl group and a substituted or unsubstituted alkoxy group, an unsubstituted alkoxy group being more preferred, a phenyl group and a Ci to Ce alkoxy group being the most preferred.

[0035] In a preferred embodiment n represents 0.

[0036] In another preferred embodiment, R7 represents a hydrogen. In a particularly preferred embodiment, Ar represents a substituted or unsubstituted phenyl group.

[0037] In a preferred embodiment, Rs represents a free radical polymerizable ethylenically unsaturated group including a free radical polymerizable functional group selected from the group consisting of an acrylate group, a methacrylate group, an acrylamide group, a methacrylamide group, a styrene group, a maleate group, a fumarate group, an itaconate group, a vinyl ether group, a vinyl ester group, an allyl ether group and an allyl ester group. More preferably Rs represents a free radical polymerizable ethylenically unsaturated group including an acrylate group or a methacrylate group.

[0038] Some or all of the above preferred embodiments may be combined with each other because this results in less odour.

[0039] In a particularly preferred embodiment of the acyl phosphine oxide photoinitiator according to Formula (I), several and preferably all of the conditions a) to f) are fulfilled, wherein a) R1 represents a phenyl group or a Ci to Ce alkoxy group; b) R2, R4 and Re represent a methyl group; c) R7 represents a hydrogen;d) Ar represents a phenyl group; e) X represents oxygen;and f) n represents 0.

[0040] In one embodiment, the acyl phosphine oxide photoinitiator preferably has a structure according to Formula (III):Formula (III), wherein Rio is selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group and a substituted or unsubstituted aryl or heteroaryl group.

[0041] In a preferred embodiment of the acyl phosphine oxide photoinitiator according to Formula (III), 2, 3 or all of the conditions a) to d) are fulfilled, wherein a) Ri is a substituted or unsubstituted alkoxy group, a Ci to Ce alkoxy group being more preferred for solubility reasons; b) Rio is a hydrogen or a substituted or unsubstituted alkyl group; c) Rn is a hydrogen; and d) R12 and R13 represent a substituted or unsubstituted alkyl group.

[0042] In another embodiment, the acyl phosphine oxide photoinitiator preferably has a structure according to Formula (IV):whereinR15 is selected from the group consisting of the group consisting of a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group and an -COR14 group;R16 a substituted or unsubstituted alkyl group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted alkaryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aryl or heteroaryl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group and -NR17R18 group; R17 and R18 are independently selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group and a substituted or unsubstituted aryl or heteroaryl group.

[0043] In a preferred embodiment of the acyl phosphine oxide photoinitiator according to Formula (IV), 2 or 3 of the conditions a) to c) are fulfilled, wherein a) R1 is a substituted or unsubstituted alkoxy group, a Ci to Ce alkoxy group being more preferred for solubility reasons; b) R15 is a hydrogen; c) R16 is a substituted or unsubstituted alkyl group.

[0044] Preferred examples of acyl phosphine oxide photoinitiators according to the present invention are given in Table 1 without being limited thereto.Table 1<>>"> < < > > <"

[0045] Another aspect of the invention is a photocurable composition comprising a free radical polymerizable compound and at least one acyl phosphine oxide as described above.

[0046] The photocurable composition may be a colourless composition such as a colourless photocurable ink or inkjet ink, but preferably it contains a colorant, more preferably a colour pigment. Colourless photocurable (inkjet) inks may be used, for example, as a protective varnish or as a primer to improve adhesion of a printed image to a substrate.

[0047] In addition to a colorant, the photocurable composition may include other ingredients as desired, such as surfactants, dispersants, dispersion synergists, stabilizers, UV absorbers and the like.

[0048] A preferred embodiment is a photocurable ink comprising a photocurable composition according to the invention. The photocurable ink preferably contains a colour pigment.

[0049] A preferred embodiment is a photocurable inkjet ink comprising a photocurable composition according to the invention. The photocurable inkjet ink preferably contains a colour pigment.

[0050] For having a good ejecting ability, the viscosity of the photocurable inkjet ink at the jetting temperature is preferably smaller than 30.0 mPa.s, more preferably smaller than 20.0 mPa.s, most preferably between 5.0 and 16.0 mPa.s at a shear rate of 1000 s1and at a jetting temperature between 30 and 70°C, preferably at a jetting temperature of 45°C.

[0051] The surface tension of the photocurable inkjet ink is preferably in the range of 20 mN / m to 35 mN / m at 25°C, more preferably in the range of about 22 mN / m to about 30 mN / m at 25°C. In these ranges, good ink spreading is obtained on a wide range of substrates.

[0052] While a single photocurable inkjet ink can be used, it is preferable to use a photocurable inkjet ink set containing multiple differently colored inkjet inks in accordance with the invention.

[0053] For printing multi-colour images, the photocurable inkjet ink is preferably part of a photocurable inkjet ink set containing at least three but most preferably at least four photocurable inkjet inks in accordance with the invention. Such an inkjet ink set is preferably a photocurable CMYK or CRYK inkjet ink set, preferably further including a photocurable white inkjet ink, for example, for enhancing colour vibrancy. This inkjet ink set may also be extended with extra inks such as violet, green, red, blue, and / or orange to further enlarge the colour gamut of the image.

[0054] The photocurable inkjet ink set can be enhanced by combining full density inkjet inks with light density inkjet inks. Full density inkjet inks match the colour of their light density counterparts but contain more (of the same) colorant. Full and light-density inks are sometimes referred to as dark andlight colour inks, respectively. The combination of such dark and light colour inks, such as black and grey inks, improves the image quality by a lowered graininess.

[0055] The photocurable inkjet inks described in the invention have a reduced odour, making them highly suitable for indoor decoration applications. Low odour is essential when manufacturing indoor decorative articles for rooms and vehicles, such as furniture, wallpaper, doors, natural leather articles, textile fabrics and decorative panels such as flooring laminate panels.

[0056] For reproducing wood patterns with a glossy finish, a CRYK ink set is preferred over a CMYK ink set, particularly for achieving a large color gamut and good metamerism. In a preferred embodiment of such a Photocurable inkjet ink set, the ink set includes: a cyan Photocurable inkjet ink containing a beta-copper phthalocyanine pigment; a red Photocurable inkjet ink containing a pigment selected from the group consisting of C.L Pigment Red 57 / 1, C.L Pigment Red 122, C.L Pigment Red 144, C.L Pigment Red 170, C.L Pigment Red 175, C.L Pigment Red 176, C.L Pigment Red 187, C.L Pigment Red 188, C.L Pigment Red 202, C.L Pigment Red 207, C.L Pigment Red 242, C.L Pigment Red 254, C.L Pigment Red 272 and mixed crystals thereof; a yellow Photocurable inkjet ink containing a pigment selected from C.L Pigment Yellow 74 C.L Pigment Yellow 83, C.L Pigment Yellow 97, C.L Pigment Yellow 110, C.L Pigment Yellow 120, C.L Pigment Yellow 139, C.L Pigment Yellow 138, C.L Pigment Yellow 150, C.L Pigment Yellow 151 , C.L Pigment Yellow 154, C.L Pigment Yellow 155, C.L Pigment Yellow 175, C.L Pigment Yellow 180, C.L Pigment Yellow 181 , C.L Pigment Yellow 194, C.L Pigment Yellow 213, C.L Pigment Yellow 214 and mixed crystals thereof; and a black photocurable inkjet ink containing a carbon black pigment; preferably complemented by a white photocurable inkjet ink and / or a colourless photocurable inkjet ink. For an improvement in graininess, the ink set may contain full- and light-density photocurable inkjet inks.

[0057] When more vibrant colours are desired, the red photocurable inkjet ink is replaced by or supplemented with a magenta photocurable inkjet ink. Thismagenta ink preferably contains a pigment selected from the group consisting of C.L Pigment Violet 19 and its mixed crystals.

[0058] The above-described acyl phosphine oxide photoinitiator is preferably present in an amount between 1 and 30 wt%, more preferably 2 and 25 wt%, most preferably between 5 and 20 wt%, with the wt% based on the total weight of the photocurable composition or (inkjet) ink.

[0059] The photocurable composition or (inkjet) ink preferably contains 10 to 95 wt% of free radical polymerizable compounds, with the wt% based on the total weight of the photocurable composition or (inkjet) ink. For better curability, a range of 20% to 90% by mass is more preferable.Free Radical Polymerizable Compounds

[0060] There is no limitation on the type of free radical polymerizable compounds used in the photocurable compositions and (inkjet) inks of the invention as long as it is a compound that can be made to undergo a polymerization reaction by means of an initiating species generated from the acyl phosphine oxide photoinitiator by the application of UV radiation.

[0061] The free radical polymerizable compound is preferably an ethylenically unsaturated compound. The free radical polymerizable chemistry may be a (meth)acrylate based polymerizable chemistry, but may for instance also be a thiol-ene and / or thiol-yne polymerizable chemistry. Suitable polymerizable monomers may be any monomer found in the Polymer Handbook Vol 1 + 2, 4th edition, edited by J. BRANDRUP et al., Wiley- Interscience, 1999.

[0062] In this invention, preferably a mixture of free radical polymerizable monomers and oligomers is utilized. These monomers and oligomers can have varying degrees of functionality, including mono-, di-, tri-, and higher functionality monomers. Such a mixture allows for fine-tuning the viscosity of the photocurable composition based on the properties of the acyl phosphine oxide photoinitiator, which is especially relevant for photocurable inkjet inks.

[0063] A monofunctional monomer is typically used to enhance the flexibility of a cured layer, while a polyfunctional monomer is employed to improve its scratch resistance.

[0064] A monofunctional monomer contains a single free radical polymerizable group preferably selected from the group consisting of an acrylate, a methacrylate, an acrylamide, a methacrylamide, a styrene group, a maleate, a fumarate, an itaconate, a vinyl ether, a vinyl ester, an allyl ether and an allyl ester.

[0065] A polyfunctional polymerizable compound contains two, three or more free radical polymerizable groups preferably independently selected from the group consisting of an acrylate, a methacrylate, an acrylamide, a methacrylamide, a styrene group, a maleate, a fumarate, an itaconate, a vinyl ether, a vinyl ester, an allyl ether and an allyl ester.

[0066] In the present specification, both or either one of 'acrylate' and 'methacrylate' are sometimes referred to as '(meth)acrylate', and both or either one of 'acrylic' and 'methacrylic' are sometimes referred to as '(meth)acrylic'.

[0067] Examples of the (meth)acrylate used as the free radical polymerizable monomer include a monofunctional (meth)acrylate, a difunctional (meth)acrylate, a trifunctional (meth)acrylate, a tetrafunctional (meth)acrylate, a pentafunctional (meth)acrylate, and a hexafunctional (meth)acrylate.

[0068] In a preferred embodiment, the monofunctional monomers are selected from hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, tert-octyl (meth)acrylate, isoamyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, cyclohexyl (meth)acrylate, 4-n-butylcyclohexyl (meth)acrylate, bornyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, 2- ethylhexyldiglycol (meth)acrylate, butoxyethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 4-bromobutyl (meth)acrylate, cyanoethyl (meth)acrylate, benzyl (meth)acrylate, butoxymethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, an alkoxymethyl (meth)acrylate, an alkoxyethyl (meth)acrylate, 2-(2-methoxyethoxy)ethyl (meth)acrylate, 2-(2- butoxyethoxy)ethyl (meth)acrylate, 2,2,2-trifluoroethyl (meth)acrylate, 1 H ,1 H,2H,2H-perfluorodecyl (meth)acrylate, 4-butylphenyl (meth)acrylate, phenyl (meth)acrylate, 2,4,5-trimethylphenyl (meth)acrylate, 4-chlorophenyl (meth)acrylate, phenoxymethyl (meth)acrylate, phenoxyethyl (meth)acrylate, glycidyl (meth)acrylate, glycidyloxybutyl (meth)acrylate, glycidyloxyethyl (meth)acrylate, glycidyloxypropyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, a hydroxyalkyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2 -hydroxy butyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylate, trimethoxysilylpropyl (meth)acrylate, trimethylsilylpropyl (meth)acrylate, polyethylene oxide monomethyl ether (meth)acrylate, oligoethylene oxide monomethyl ether (meth)acrylate, polyethylene oxide (meth)acrylate, oligoethylene oxide (meth)acrylate, an oligoethylene oxide monoalkyl ether (meth)acrylate, a polyethylene oxide monoalkyl ether (meth)acrylate, dipropylene glycol (meth)acrylate, a polypropylene oxide monoalkyl ether (meth)acrylate, an oligopropylene oxide monoalkyl ether (meth)acrylate, 2-(meth)acryloyloxyethylsuccinic acid, 2-(meth)acryloyloxyhexahydrophthalic acid, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, butoxydiethylene glycol (meth)acrylate, trifluoroethyl (meth)acrylate, perfluorooctylethyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, ethylene oxide(EO)-modified phenol (meth)acrylate, EO-modified cresol (meth)acrylate, EO-modified nonylphenol (meth)acrylate, propylene oxide(PO)-modified nonylphenol (meth)acrylate, EO-modified 2-ethylhexyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, (3-ethyl-3-oxetanylmethyl) (meth)acrylate, and phenylethylene glycol (meth)acrylate; allyl derivatives such as allyl glycidyl ether; styrenics such as styrene, 4-methylstyrene, 4-hydroxystyrene, 4-acetostyrene, and styrenesulfonic acid; (meth)acrylonitrile; (meth)acrylamides (including N-mono and N,N-disubstituted) such as N-benzyl (meth)acrylamide; maleimides such as N-phenyl maleimide; vinyl derivatives such as vinylcaprolactam, vinylpyrrolidone, vinylimidazole, vinylnapthalene, andvinyl halides; vinylethers such as vinylmethyl ether; vinylesters of carboxylic acids such as vinylacetate, vinylbutyrate, and vinyl benzoate.

[0069] In a preferred embodiment, the polyfunctional acrylates are selected from difunctional (meth)acrylates including 1 ,6-hexanediol di(meth)acrylate, 1 ,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 2,4-dimethyl-1 ,5-pentanediol di(meth)acrylate, butylethylpropanediol di(meth)acrylate, ethoxylated cyclohexanemethanol di(meth)acrylate, polyethylene glycol di(meth)acrylate, oligoethylene glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, 2-ethyl-2- butylbutanediol di(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate, EO-modified bisphenol A di(meth)acrylate, bisphenol F polyethoxydi(meth)acrylate, polypropylene glycol di(meth)acrylate, oligopropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 2- ethyl-2-butylpropanediol di(meth)acrylate, 1 ,9-nonane di(meth)acrylate, propoxylated ethoxylated bisphenol A di(meth)acrylate, tricyclodecane di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and PO-modified neopentyl glycol di(meth)acrylate; from trifunctional (meth)acrylates including trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, an alkylene oxidemodified tri(meth)acrylate of trimethylolpropane, pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, trimethylolpropane tris((meth)acryloyloxypropyl) ether, an isocyanuric acid alkylene oxidemodified tri(meth)acrylate, propionic acid dipentaerythritol tri(meth)acrylate, tris((meth)acryloyloxyethyl) isocyanurate, hydroxypivalaldehyde-modified dimethylolpropane tri(meth)acrylate, sorbitol tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, and ethoxylated glycerol triacrylate;from tetrafunctional (meth)acrylates including pentaerythritol tetra(meth)acrylate, sorbitol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol propionate tetra(meth)acrylate, and ethoxylated pentaerythritol tetra(meth)acrylate;from pentafunctional (meth)acrylates including sorbitol penta(meth)acrylate and dipentaerythritol penta(meth)acrylate; andfrom hexafunctional (meth)acrylates including dipentaerythritol hexa(meth)acrylate, sorbitol hexa(meth)acrylate, an alkylene oxidemodified hexa(meth)acrylate of phosphazene, and c-caprolactone- modified dipentaerythritol hexa(meth)acrylate.

[0070] A particularly preferred polyfunctional acrylate is a polymerizable compound having two different polymerizable groups, such as a vinylether group and an acrylate group. Preferred vinylether (meth)acrylates are those disclosed in US 6310115 (AGFA) and in columns 3 and 4 of US 67679890 B (NIPPON SHOKUBAI).A particularly preferred compound is 2- (2’-vinyloxyethoxy)ethyl acrylate (VEEA). VEEA is especially to achieve a high curing degree.

[0071] A preferred photocurable inkjet ink for indoor decoration applications comprises the above-described acyl phosphine oxide photoinitiator and a mixture of free radical polymerizable monomers comprising of: a) 7 - 70 wt%, preferably 15 - 60 wt% and most preferably 25 - 50 wt% of 2- (2’- vinyloxyethoxy)ethyl acrylate b) 1 - 65 wt% , preferably 20 - 60 wt% of one or more polymerizable compounds selected from the group consisting of monofunctional acrylates and difunctional acrylates; and c) 0 - 55 wt% of one or more polymerizable compounds selected from the group consisting of trifunctional acrylates, tetrafunctional acrylates, pentafunctional acrylates and hexafunctional acrylates,wherein all weight percentages of a, b and c are based upon the total weight of the polymerizable composition of the photocurable inkjet ink. In general, the cured products of these photocurable inkjet inks exhibit a more pleasant odour.

[0072] Acrylates of the aforementioned monofunctional or polyfunctional monomers are preferred over their methacrylate counterparts due to their generally higher curing speed.

[0073] In a preferred embodiment, the photocurable composition or (inkjet) ink includes an N-vinyllactam, such as N-vinylcaprolactam. Another particularly preferred monomer is vinyl methyl oxazolidinone, available as VMOX from BASF. These monomers are favored because they provideexcellent ink curability and adhesion of the cured film to a recording medium.

[0074] In a preferred embodiment, the photocurable composition or (inkjet) ink contains contain at least one of N-vinyl caprolactam, vinyl methyl oxazolidinone and (2’-vinyloxyethoxy)ethyl acrylate. The mixture of free radical polymerizable monomers may also include a (meth)acrylamide compound selected from the group consisting of (meth)acrylamide, N- methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-propyl (meth)acrylamide, N-n-butyl (meth)acrylamide, N-t-butyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N- methylol (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, and (meth)acryloyl morpholine.

[0075] The mixture of free radical polymerizable monomers in the photocurable composition or (inkjet) ink may be supplemented by polymerizable oligomers and / or polymerizable polymers. In the present disclosure, the oligomer has preferably a weight-average molecular weight of 500 or more and 20,000 or less, and the polymer has preferably a weight-average molecular weight of more than 20,000.

[0076] Preferred free radical polymerizable oligomers and polymers are polyurethanes, polyesters, polyethers, polycarbonates, poly-carbamates, polyureas and straight-chain oligomers having the following polymerizable groups: acrylate, methacrylate, vinyl, acrylamide, methacrylamide, vinyl carbonate, vinyl ether, vinylester- vinyl carbamate groups, as well as their corresponding alkene and alkyne compounds.

[0077] A urethane (meth)acrylate oligomer is particularly preferred for free radical polymerization due to its excellent abrasion resistance, flexibility, and chemical resistance in the resulting cured product.

[0078] The urethane (meth)acrylate oligomer may be a compound having one or more urethane bonds and having one or more (meth)acrylate groups.

[0079] It is preferable to use a bifunctional urethane (meth)acrylate oligomer to have a weight-average molecular weight between 3,000 and 20,000 to ensure optimal abrasion resistance, flexibility, and chemical resistance in the cured product.

[0080] As the bifunctional urethane (meth)acrylate oligomer, a commercially available product may be used. Examples of the commercially available product include CN963B80 and CN9001 (manufactured by ARKEMA and SHIKO UV-3200B, SHIKO UV-3300B, SHIKO UV-3310B, and SHIKO UV- 6630B (all manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.).

[0081] The content of the urethane (meth)acrylate oligomer in the photocurable composition and (inkjet) ink according to the present disclosure is preferably 1 % by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and particularly preferably 5% by mass or more and 10% by mass or less with respect to the total mass of the composition from the viewpoint of the abrasion resistance, flexibility, and chemical resistance of the obtained cured product.

[0082] Another preferred alternative free radical curing chemistry is the so-called thiol-ene and thiol-yne chemistry. In such a chemistry, a combination of at least one polyfunctional thiol monomer and at least one polyfunctional polymerizable monomer is used. The polyfunctional polymerizable monomer is preferably a polyfunctional monomer having a plurality of polymerizable groups selected from a group consisting of a vinyl group, an acrylamide group, a methacrylamide group, a vinyl carbonate group, a vinyl ether group, a vinyl ester group, a vinyl carbamate group, an allyl ether groups, an allyl ester group and an alkyne group. Particularly preferred are polymerizable compounds including allyl ether groups, vinyl carbonate groups and alkyne groups.

[0083] Synthesis of such monomers is disclosed in the relevant literature, for example in HURD, Charles D.. Vinylation and the Formation of Acylals. Journal Am. Chem.Soc. 1956, vol.78, no.1, p.104_106. ; LOBELL, M., et al. Synthesis of hydroxycarboxylic acid vinyl esters. MP Synthesis. 1994, vol.4, p.375-377. ; LEE, T. Y., et al. Synthesis, Initiation, and Polymerization of Photoinitiating Monomer. Macromolecules. 2005, vol.38, no.18, p.7529-7531. ; ATTA, A.M., etal. New vinyl ester resins based on rosin for coating applications. React. Funct. Po / ym.. 2006, vol.66, p.1596- 1608. ; WO 01 / 00634 A (WRIGHT CHEM CORP) ; and ROHR, Markus,et al. Solvent-free ruthenium-catalysed vinylcarbamate synthesis from phenylacetylene and diethylamine in ‘supercritical’ carbon dioxide. Green Chemistry. 2001, vol.3, p.123-125.Other Photoinitiators and Co-initiators

[0084] The acyl phosphine oxide photoinitiator can be used as a single photoinitiator in the photocurable composition or (inkjet) ink. Alternatively, it may be combined with other photoinitiators and / or a-co-initiators to form a photoinitiating system in the photocurable composition or (inkjet) ink.

[0085] The other photoinitiator(s) may be a Norrish type I initiator and / or a Norrish type II initiator. A Norrish Type I initiator is a photoinitiator which cleaves after excitation, yielding the initiating radical immediately. A Norrish type II- initiator is a photoinitiator which is activated by actinic radiation and forms free radicals by hydrogen abstraction from a second compound that becomes the actual initiating free radical. This second compound is called a polymerization synergist or co-initiator.

[0086] Suitable Norrish type I and II photo-initiators are disclosed in CRIVELLO, J.V., et al. VOLUME III: Photoinitiators for Free Radical Cationic & Anionic Photopolymerisation. 2nd edition. Edited by BRADLEY, G.. London, UK: John Wiley and Sons Ltd, 1998. p.287-294.

[0087] The acyl phosphine oxide photoinitiator may be combined with a photoinitiator selected from the group consisting of another acyl phosphine oxide initiator a thioxanthone initiator, an a-hydroxyalkylphenone initiator and a carbazole initiator. Such combinations can improve curing speed further.

[0088] In order to increase the photosensitivity further, a co-initiator may be added, which preferably is an amine synergist.

[0089] Suitable examples of amine synergists can be categorized in three groups:1) tertiary aliphatic amines such as methyldiethanolamine, dimethylethanolamine, triethanolamine, triethylamine and N- methylmorpholine;(2) aromatic amines such as amylparadimethylaminobenzoate, 2-n- butoxyethyl-4-(dimethylamino) benzoate, 2-(dimethylamino)ethylbenzoate, ethyl-4-(dimethylamino)benzoate, and 2-ethylhexyl-4-(dimethylamino)benzoate; and(3) (meth)acrylated amines such as dialkylamino alkyl(meth)acrylates (e.g., diethylaminoethylacrylate) or N-morpholinoalkyl-(meth)acrylates (e.g. , N-morpholinoethyl-acrylate).

[0090] The total amount of photoinitiator used is preferably an amount of 1 to 30 wt%, more preferably 2 to 20 wt%, and most preferably 5 to 15 wt%, based on the total weight of the photocurable composition or (inkjet) ink. Preferably, the acyl phosphine oxide photoinitiator of the invention constitutes 60% to 100% of the total photoinitiator.

[0091] The total amount of coinitiator used is preferably an amount of 1 to 20 wt%, more preferably 2 to 15 wt%, and most preferably 5 to 10 wt%, based on the total weight of the photocurable composition or (inkjet) ink.Colorants

[0092] The photocurable composition may contain a colorant. The colorant may be a dye, a pigment or a combination thereof. Organic and / or inorganic pigments may be used. The colorant is preferably a pigment or a polymeric dye, most preferably an organic colour pigment. Organic colour pigments generally allow to obtain a much broader colour gamut.However, for the colours white and black, preferably inorganic pigments such as titanium dioxide respectively carbon black are used.

[0093] The pigments may be black, white, cyan, magenta, yellow, red, orange, violet, blue, green, brown, mixtures thereof, and the like. This colour pigment may be chosen from those disclosed by HERBST, Willy, et al. Industrial Organic Pigments, Production, Properties, Applications. 3rd edition. Wiley - VCH , 2004. ISBN 3527305769.

[0094] A preferred pigment for a photocurable cyan (inkjet) ink according to the invention is a beta-copper phthalocyanine pigment, with C.L Pigment Blue 15:3 or 15:4 being particularly preferred for minimal light fading of the cured product.

[0095] The pigments mentioned above for the red and tallow inks in CRYK ink set may also be used for (inkjet) inks in a different ink set.

[0096] The pigment in a magenta photocurable (inkjet) ink is preferably C.L Pigment Violet 19 or a mixed crystal thereof.

[0097] In a black photocurable (inkjet) ink according to the invention, the pigment is preferably a carbon black pigment. Suitable black pigments include carbon blacks such as Pigment Black 7 (e.g. Carbon Black MA8TMfrom MITSUBISHI CHEMICAL), Regal™ 400R, Mogul™ L, Elftex™ 320 from CABOT Co., or Carbon Black FW18, Special Black 250, Special Black 350, Special Black 550, Printex™ 25, Printex™ 35, Printex™ 55, Printex™ 90, Printex™ 150T from EVONIK. In a preferred embodiment, the carbon black pigment used is a pigment having less than 0.15% of toluene- extractable fraction using the method as described in section III, paragraph 5 of the Resolution AP(89) 1 dated 13 September 1989 published by the Council of Europe.

[0098] It is also possible to include mixtures of pigments in the photocurable (inkjet) ink. For example, in some inkjet ink application a neutral black inkjet ink is preferred and can be obtained, for instance, by mixing a black pigment and a cyan and / or magenta pigment into the ink. Also pigments may be combined to enlarge the colour gamut of an ink set.

[0099] An inkjet ink set may also include one or more spot colours. Silver and gold are often desired colours for making a product more attractive by giving it an exclusive appearance.

[0100] Suitable pigments include mixed crystals of the above preferred pigments.Mixed crystals are also referred to as solid solutions. For example, under certain conditions different quinacridones mix with each other to form solid solutions, which are quite different from both physical mixtures of the compounds and from the compounds themselves. In a solid solution, the molecules of the components enter into the same crystal lattice, usually, but not always, that of one of the components. The x-ray diffraction pattern of the resulting crystalline solid is characteristic of that solid and can be clearly differentiated from the pattern of a physical mixture of the same components in the same proportion. In such physical mixtures, the x-ray pattern of each of the components can be distinguished, and the disappearance of many of these lines is one of the criteria of the formation of solid solutions. A commercially available example is Cinquasia™ Magenta L 4540 from SUN CHEMICAL.

[0101] Pigment particles in inkjet ink should be sufficiently small to permit free flow of the ink through the inkjet-printing device, especially at the ejecting nozzles. It is also desirable to use small particles for maximum colour strength and to slow down sedimentation. The numeric average pigment particle size is preferably between 0.050 and 1 pm, more preferably between 0.070 and 0.300 pm and particularly preferably between 0.080 and 0.200 pm.

[0102] The numeric average pigment particle size of pigment particles is best determined with a Brookhaven Instruments Particle Sizer BIOOplus based upon the principle of dynamic light scattering. The ink is then diluted, for example, with ethyl acetate to a pigment concentration of 0.002 wt%. The measurement settings of the BIOOplus are: 5 runs at 23°C, angle of 90°, wavelength of 635 nm and graphics = correction function.

[0103] In the case of a photocurable white (inkjet) ink according to the invention, preferably a pigment with a refractive index greater than 1.60, preferably greater than 2.00, more preferably greater than 2.50 and most preferably greater than 2.60 is used. The white pigments may be employed singly or in combination.

[0104] In a coloured inkjet ink the pigment is preferably present in an amount of 0.1 to 13.0 wt%. A dark colour inkjet ink preferably contains 1.5 to 13.0 wt%, more preferably 1.8 to 6.0 wt% of colour pigment based on the total weight of the inkjet ink, while a light colour inkjet ink preferably contains 0.1 to 1.3 wt%, more preferably 0.3 to 1.2 wt% of colour pigment based on the total weight of the inkjet ink.

[0105] A white inkjet ink preferably contains more than 13.0 wt%, more preferably 15.0 to 25.0 wt% of a white pigment based on the total weight of the inkjet ink.Dispersants

[0106] The photocurable (inkjet) ink preferably contains a dispersant for further improving pigment dispersion properties. For obtaining high printing reliability, the dispersant is preferably a polymeric dispersant. Such dispersant improves the reliability of an inkjet printing process due to agenerally smaller sedimentation speed, especially when the dispersant contains secondary or tertiary amine groups.

[0107] Typical polymeric dispersants are copolymers of two monomers but may contain three, four, five or even more monomers. The properties of polymeric dispersants depend on both the nature of the monomers and their distribution in the polymer. Copolymeric dispersants preferably have the following polymer compositions:• statistically polymerized monomers (e.g. monomers A and B polymerized into ABBAABAB);• alternating polymerized monomers (e.g. monomers A and B polymerized into ABABABAB);• gradient (tapered) polymerized monomers (e.g. monomers A and B polymerized into AAABAABBABBB);• block copolymers (e.g. monomers A and B polymerized into AAAAABBBBBB) wherein the block length of each of the blocks (2, 3, 4, 5 or even more) is important for the dispersion capability of the polymeric dispersant;• graft copolymers (graft copolymers consist of a polymeric backbone with polymeric side chains attached to the backbone); and • mixed forms of these polymers, e.g. blocky gradient copolymers.

[0108] The polymeric dispersant has preferably a number average molecular weight Mn between 500 and 30000, more preferably between 1500 and 10000.

[0109] The polymeric dispersant has preferably a weight average molecular weight Mw smaller than 100,000, more preferably smaller than 50,000 and most preferably smaller than 30,000.

[0110] The polymeric dispersant has preferably a polydispersity PD smaller than 2, more preferably smaller than 1.75 and most preferably smaller than 1.5.

[0111] Commercial examples of polymeric dispersants are the following:DISPERBYK™ dispersants available from BYK CHEMIE GMBH;SOLSPERSE™ dispersants available from LUBRIZOL; TEGO™ DISPERS™ dispersants from EVONIK; EDAPLAN™ dispersants from MUNZING CHEMIE; ETHACRYL™ dispersants from LYONDELL;GANEX™ dispersants from ISP; DISPEX™ and EFKA™ dispersants from BASF; and DISPONER™ dispersants from DEUCHEM.

[0112] The dispersants may be used alone or in combination of two or more kinds thereof.

[0113] The polymeric dispersant is preferably used in an amount of 10 to 200 wt%, more preferably 20 to 100 wt%, most preferably 50 to 90 wt% based on the weight of the pigment.Dispersion Synergists

[0114] The photocurable (inkjet) ink may include a dispersion synergist to further improve the dispersion stability by a polymeric dispersant and thus also the printing reliability as less pigment can sediment in the nozzle of a print head upon stand-by of an inkjet device.

[0115] A dispersion synergist usually consists of an anionic part and a cationic part. The anionic part of the dispersion synergist exhibiting a certain molecular similarity with the colour pigment and the cationic part of the dispersion synergist consists of one or more protons and / or cations to compensate the charge of the anionic part of the dispersion synergist.

[0116] The dispersion synergist is preferably added in a smaller amount than the polymeric dispersant(s). The ratio of polymeric dispersant / dispersion synergist depends upon the pigment and should be determined experimentally. Typically, the ratio wt% polymeric dispersant / wt% dispersion synergist is selected between 2:1 to 100:1, preferably between 2:1 and 20:1.

[0117] Suitable dispersion synergists that are commercially available include Solsperse™ 5000 and Solsperse™ 22000 from LUBRIZOL. Suitable dispersion synergists for a diketopyrrolo-pyrrole pigment, a quinacridone pigment or a mixed crystal thereof include those disclosed in EP 1790698 A (AGFA GRAPHICS) , EP 1790696 A (AGFA GRAPHICS) , WO 2007 / 060255 (AGFA GRAPHICS) and EP 1790695 A (AGFA GRAPHICS) .

[0118] In dispersing C.L Pigment Blue 15:3, the use of a sulfonatedCu-phthalocyanine dispersion synergist, e.g. Solsperse™ 5000 from LUBRIZOL is preferred.Stabilizers

[0119] The photocurable (inkjet) ink may also contain a stabilizer, often referred to as a polymerization inhibitor. Due to the fact that an ink contains the polymerization inhibitor, a polymerization reaction before curing, such as during storage or transport, can be prevented. It can also improve the printing reliability. For example, a UV LED photocurable inkjet ink in a print head of an inkjet device is usually kept at a higher temperature such as 45 to 55°C.

[0120] Suitable polymerization inhibitors include phenol type antioxidants, hindered amine light stabilizers, phosphor type antioxidants, benzoquinone, hydroquinone and derivatives, such as hydroquinone monomethyl ether commonly used in (meth)acrylate monomers.

[0121] Examples of the phenolic polymerization inhibitor include, but are not limited to the following substances, p-methoxy phenol, cresol, t-butyl catechol, di-t-butyl-p-cresol, hydroquinone monomethylether, a-naphthol, 3,5-di-t-butyl-4-hydroxytoluene, 2,6-di-t-butyl-4-methylphenol, 2,2'- methylene-bis(4-methyl-6-t-butylphenol), 2,2'-methylene-bis(4-ethyl-6- butylphenol), and 4,4'-thio-bis(3-methyl-6-t-butylphenol) and pyrogallol.

[0122] Suitable commercial inhibitors are, for example, Sumilizer™ GA-80, Sumilizer™ GM and Sumilizer™ GS produced by Sumitomo Chemical Co. Ltd.; Genorad™ 16, Genorad™ 18 and Genorad™ 20 from Rahn AG; Irgastab™ UV10 and Irgastab™ UV22, Tinuvin™ 460 and CGS20 from Ciba Specialty Chemicals; Floorstab™ UV range (UV-1, UV-2, UV-5 and UV-8) from Kromachem Ltd, Additol™ S range (S100, S110, S120 and S130) from Cytec Surface Specialties.

[0123] A preferred polymerization inhibitor is Irgastab™ UV10 from BASF. Other examples of polymerization inhibitor include TEMPO, TEMPOL, and Al cupferron.

[0124] The polymerization inhibitors may be used alone or in combination of two or more kinds thereof. In a preferred embodiment, the polymerization inhibitor is a mixture of different types of polymerization inhibitors.

[0125] Preferred polymerization inhibitors are mixtures of an oxyl free radicalbased polymerization inhibitor, a phenol-based polymerization inhibitor, and an amine-based polymerization inhibitor.

[0126] Suitable examples are given in EP 2851402 A (FUJIFILM) . The polymerization inhibitor is preferably present in an amount of 0.1 to 5 wt% based on the total weight of the free radical curable (inkjet) ink. Below 0.1 wt%, the undesired polymerization is insufficiently inhibited and above 5 wt% the curing speed is heavily reduced.Surfactants

[0127] The photocurable inkjet ink may contain a surfactant. The surfactant can be anionic, cationic, non-ionic, or zwitter-ionic. The surfactant is preferably present in an amount of 0.1 to 3 wt% based on the total weight of the free radical curable inkjet ink. At higher concentrations than 3 wt%, the adhesion may deteriorate rapidly, while usually insufficient spreading of the ink is observed at concentration lower than 0.1 wt%.

[0128] The total quantity of surfactant is preferably less than 3 wt% based on the total weight of the ink and more preferably less than 1.5 wt% based on the total weight of the photocurable inkjet ink to prevent foaming of the ink in its container. Such foaming has a negative impact on the printing reliability.

[0129] Preferred surfactants are selected from fluoro surfactants (such as fluorinated hydrocarbons) and silicone surfactants. The silicone surfactants are preferably siloxanes and can be alkoxylated, polyester modified, polyether modified, polyether modified hydroxy functional, amine modified, epoxy modified and other modifications or combinations thereof. Preferred siloxanes are polymeric, for example polydimethylsiloxanes.

[0130] Preferred commercial silicone surfactants include BYKTM333 and BYKTMUV3510 from BYK Chemie and Tegoglide™ 410 from EVONIK.

[0131] In a preferred embodiment, the surfactant is a polymerizable compound.

[0132] Preferred polymerizable silicone surfactants include a (meth)acrylated silicone surfactant. Most preferably the (meth)acrylated silicone surfactant is an acrylated silicone surfactant, because acrylates are more reactive than methacrylates.

[0133] In a preferred embodiment, the (meth)acrylated silicone surfactant is a polyether modified (meth)acrylated polydimethylsiloxane or a polyester modified (meth)acrylated polydimethylsiloxane.

[0134] Preferred commercially available (meth)acrylated silicone surfactants include: Ebecryl™ 350 , a silicone diacrylate from Cytec; the polyether modified acrylated polydimethylsiloxane BYKTMLIV3500, BYKTMLIV3510 and BYKTMLIV3530, the polyester modified acrylated polydimethylsiloxane BYK™ LIV3570, all manufactured by BYK Chemie; Tego™ Rad 2100, Tego™ Rad 2200N, Tego™ Rad 2250N, Tego™ Rad 2300, Tego™ Rad 2500, Tego™ Rad 2600, Tego™ Rad 2700, and Tego™ RC711 all manufactured by EVONIK. Another preferred silicone is Silwet™ L7500 from OSI SPECIALITIES BENELUX NV; Silaplane™ FM7711 , Silaplane™ FM7721 , Silaplane™ FM7731 , Silaplane™ FM0711 , Silaplane™ FM0721 , Silaplane™ FM0725, Silaplane™ TM0701 , Silaplane™ TM0701T all manufactured by CHISSO Corporation; and DMS-R05, DMS-R11, DMS- R18, DMS-R22, DMS-R31, DMS-U21 , DBE-U22, SIB1400, RMS-044, RMS-033, RMS-083, UMS-182, UMS-992, UCS-052, RTT-1011 and UTT- 1012 all manufactured by GELEST Inc..

[0135] Particularly preferred surfactants for the photocurable inkjet ink are Silmer™ surfactants from SILTECH CORPORATION, such as Silmer™ ACR Di-1508.Preparation of Photocurable Inks and Inkjet Inks

[0136] The preparation of photocurable (inkjet) inks is well-known to the skilled person.

[0137] The average particle size and distribution of a colour pigment is an important feature for inkjet inks. The inkjet ink may be prepared by precipitating or milling the pigment in the dispersion medium in the presence of a dispersant.

[0138] Mixing apparatuses may include a pressure kneader, an open kneader, a planetary mixer, a dissolver, and a Dalton Universal Mixer. Suitable milling and dispersion apparatuses are a ball mill, a pearl mill, a colloid mill, a high-speed disperser, double rollers, a bead mill, a paint conditioner, andtriple rollers. The dispersions may also be prepared using ultrasonic energy or using a microfluidizer.

[0139] Different types of materials may be used as milling media, such as glasses, ceramics, metals, and plastics. In a preferred embodiment, the grinding media can comprise particles, preferably substantially spherical in shape, e.g. beads consisting essentially of a polymeric resin or yttrium stabilized zirconium oxide beads.

[0140] In the process of mixing, milling and dispersion, each process is performed with cooling to prevent build-up of heat and as much as possible under light conditions in which actinic radiation has been substantially excluded.

[0141] The (inkjet) ink may contain more than one pigment, and may be prepared using separate dispersions for each pigment, or alternatively several pigments may be mixed and co-milled in preparing the dispersion.

[0142] The dispersion process can be carried out in a continuous, batch or semibatch mode.

[0143] The preferred amounts and ratios of the ingredients of the mill grind will vary depending upon the specific materials and the intended applications. The contents of the milling mixture comprise the mill grind and the milling media. The mill grind comprises pigment, polymeric dispersant and a liquid carrier. For inkjet inks, the pigment is usually present in the mill grind at 5 to 50 wt%, excluding the milling media. The weight ratio of pigment over polymeric dispersant is preferably 20:1 to 1 :2, more preferably 2:1 to 1 :1.

[0144] The optimal milling time can vary and depends upon the pigment, mechanical means and residence conditions selected, the initial and desired final particle size, etc. In the present invention pigment dispersions with an average particle size of less than 100 nm may be prepared.

[0145] After milling is completed, the milling media is separated from the milled particulate product (in either a dry or liquid dispersion form) using conventional separation techniques, such as by filtration, sieving through a mesh screen, and the like. Often the sieve is built into the mill, such as for a bead mill. The milled pigment concentrate is preferably separated from the milling media by filtration.

[0146] In general, it is desirable to make the Inkjet inks in the form of a concentrated pigment dispersion, which is subsequently diluted to the appropriate concentration for use in the inkjet printing system. This technique permits preparation of a greater quantity of pigmented ink from the equipment. By dilution, the inkjet ink is adjusted to the desired viscosity, surface tension, colour, hue, saturation density, and print area coverage for a particular application.Cured Products and Printed Articles

[0147] Another aspect of the invention is a cured product formed by UV curing the photocurable composition or (inkjet) ink in accordance with the invention on a substrate.

[0148] The cured product is preferably a printed article comprising a cured composition derived from the photocurable composition as described above.

[0149] There are no specific limitations on the nature of the printed articles, which can be either 3D-printed or printed on a substrate.

[0150] In a preferred embodiment, the printed article is selected from printed packaging, printed leather articles, and printed interior decoration articles.

[0151] More preferably, the printed article is produced using inkjet printing technology, which facilitates customization and personalization.

[0152] Printed packaging includes articles made from corrugated cardboard or folded carton.

[0153] Preferred printed leather articles are those made from natural leather.

[0154] Printed interior decoration articles include laminate products such as luxury vinyl tiles. However, the photocurable (inkjet) inks may also be directly printed on an article such as furniture or doors.

[0155] There are no limitations on the substrates for printing UV-curable (inkjet) inks; they can be plastic, metal, wood, or cellulose-based.Inkjet Printing Methods

[0156] An inkjet printing method comprising the steps of:a) jetting an image with a photocurable inkjet ink according to claim 9 or 10 on a substrate; andb) curing the jetted image by UV light emitting diodes having an emission wavelength of 360 nm or larger.

[0157] The UV curing is preferably performed by UV LEDs having an emission wavelength larger than 360 nm, preferably larger than 370 nm and most preferably between 390 and 400 nm.

[0158] The photocurable inkjet ink is jetted by one more print heads ejecting small droplets in a controlled manner through nozzles onto a substrate moving relative to the print head(s).

[0159] A preferred print head for the inkjet printing system is a piezoelectric head.Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied thereto. The application of a voltage changes the shape of the piezoelectric ceramic transducer in the print head creating a void, which is then filled with inkjet ink. When the voltage is again removed, the ceramic expands to its original shape, ejecting a drop of ink from the print head. Piezoelectric print heads have proven to be the most reliable print heads in industrial printing.

[0160] A preferred piezoelectric print head is a so-called push mode type piezoelectric print head, which has a rather large piezo-element capable of ejecting also high viscous inkjet ink droplets. Such a print head is available from RICOH as the GEN5s print head.

[0161] A more preferred piezoelectric print head is a so-called through-flow piezoelectric drop-on-demand print head. Such a print head is, for instance available from TOSHIBA TEC as the CF1ou print head or from FUJIFILM DIMATIX as Samba™ G3L and G5L printheads. Through-flow print heads are preferred because they enhance the reliability of inkjet printing due to the ink circulation within the print head.

[0162] The inkjet print head preferably scans back and forth in a transversal direction across the moving ink-receiver surface. The inkjet print head may not print on the way back, but bi-directional printing is preferred for obtaining a high areal throughput. For maximizing high areal throughput, another printing method may be used that is known as a “single pass printing process”, which can be performed by using page wide inkjet print heads or multiple staggered inkjet print heads that cover the entire width ofthe ink-receiver surface. In a single pass printing process the inkjet print heads usually remain stationary and the ink-receiver surface is transported under the inkjet print heads.

[0163] However, the inkjet printing of the photocurable inkjet inks is more preferably performed in a multi-pass printing mode. Multi-pass printing is a very suitable technique to reduce banding in ink-jet printing or mask nozzle failure which may occur in single pass inkjet printings. Dots of ink, when still in liquid form, tend to run together due to surface tension. This is referred to as coalescence. To print a high-quality image, it is important to print individual round dots. But to achieve full saturated colours, the dots must overlap to completely cover the substrate. By only printing a portion of the image data so as to avoid simultaneously printing adjacent dots during each printing cycle, coalescence may be largely avoided.Additionally, by avoiding all horizontal adjacencies, the transverse speed of the printing mechanism can be increased up to two times the rated print speed of the print head. In a preferred embodiment, the number of passes used is to 2 to 6 passes, more preferably no more than 4 passes.

[0164] An advantage of using a multi-pass printing mode is that the photocurable inkjet inks are cured in consecutive passes, rather than in a single pass which would require a curing device with a high UV output. The print head lifetime is also larger for multi pass printing. While in single pass printing one side shooter is sufficient to replace the whole print head, in multi pass printing side shooters and even failings can be tolerated. Also the cost of a multi-pass printer is usually much lower, especially for wide format substrates.

[0165] For facilitating curing, the inkjet printer may include one or more oxygen depletion units. The oxygen depletion units place a blanket of nitrogen or other relatively inert gas (e.g. CO2), with adjustable position and adjustable inert gas concentration, in order to reduce the oxygen concentration in the curing environment. Residual oxygen levels are usually maintained as low as 200 ppm, but are generally in the range of 200 ppm to 1200 ppm.Preparation Methods of Acyl Phosphine Oxide Photoinitiators

[0166] A preferred method for the preparation of the acyl phosphine oxides according to the invention has as synthesis scheme:whereinRi is selected from the group consisting of an aryl group, a heteroaryl group, an alkoxy group and an aryloxy group;R? is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl, a heteroaryl group, and a -CORu group; Rs is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl, a heteroaryl group, a (meth)acrylate group, a free radical polymerizable ethylenically unsaturated group and a -C(Rn)-CH2-NRi2Ri3 group; X is selected from the group consisting of an oxygen and N-Rg; n represents 0 or 1 ; and Rg is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group and an aryl group; Rn is selected from the group consisting of a hydrogen and a methyl group; R12 and R13 are independently selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group and an aralkyl group; and R14 is selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group, an alkaryl group, an aralkyl group, an aryl, and a heteroaryl group.

[0167] Sulfonic acids and sulfuric acid are the preferred acidic conditions, with sulfonic acids being more favored, and methane sulfonic acid being the most preferred.

[0168] In a preferred embodiment of the preparation method, 1 , 2, 3, 4, or all of the conditions a) to f) are fulfilled, wherein a) Ri represents a phenyl group or a Ci to Ce alkoxy group; b) R? represents a hydrogen; c) Ar represents a phenyl group; d) X represents oxygen;and e) n represents 0.EXAMPLESMeasurement MethodsTLC-MS

[0169] The molecular mass was determined using TLC-MS, according to the following procedure. A TLC was run under circumstances given in the synthetic examples. The TLC was analyzed using a CAMAG™ TLC-MS interface coupled to an AmaZon™ SL mass spectrometer (supplied by BRUKER DALTONICS) via an Agilent™ 1100 HPLC pump. First a blank spectrum was taken by eluting a spot on the TLC plate where no compounds are present with a 0.01 molar solution of ammonium acetate in methanol. A second spectrum of the compound to be analyzed was taken by eluting the spot of the compound under consideration with a 0.01 molar solution of ammonium acetate in methanol. The first spectrum was subtracted from the second spectrum, giving the spectrum of the compound to be analyzed.Curability

[0170] The curability was checked by wiping the surface of the cured samples five times with a Q-tip. A sample was considered fully cured if it had a score “A ” according to Table 2.Table 2Materials

[0171] All solvents and reagents were supplied by standard fine chemical suppliers such as TCI Europe, unless otherwise specified.

[0172] Ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate (TPO-L) was supplied by IGM as Omnirad™ TPO-L.

[0173] (2,4,6-Trimethylbenzoyl)diphenylphosphine oxide (TPO) was supplied by IGM as Omnirad™ TPO.

[0174] N-(hydroxymethyl)prop-2-enamide and N-hydroxymethyl-phtalimide were supplied by TCI Europe.

[0175] 1-(hydroxymethyl)pyrrolidin-2-one, N-hydroxymethyl-succinimide and N- (hydroxymethyl)-2-phenyl-acetamide were supplied by ABCR.

[0176] Silwet™ L7500 is a silicone based wetting agent supplied by Momentive Performance Materials GmbH.

[0177] Genomer™ 2253 is an acrylated amine oligomer supplied by Rahn.

[0178] VEEA™ is 2-(2-vinyloxyethoxy)ethyl acrylate, a difunctional monomer available from NIPPON SHOKUBAI, Japan.

[0179] PET175 is a 175 pm thick unsubbed polyethylene terephthalate sheet available as Astera™ type UR175.334 from AGFA-GEVAERT NV.EXAMPLE 1

[0180] This example illustrates the synthesis of the acyl phosphine oxide photoinitiator AM-1.Synthesis

[0182] 0.2 g (0.2 mol) N-(hydroxymethyl)prop-2-enamide was dispersed in 140 ml methane sulfonic acid while cooling the mixture to 5°C. The addition of methane sulfonic acid to N-(hydroxymethyl)prop-2-enamide was strongly exothermic at the start of the addition. 63.3 g ( 0.2 mol) ethyl (2,4,6- trimethylbenzoyl)phenylphosphinate was added slowly to 120 ml methanesulfonic acid while maintaining the temperature at 5°C. The ethyl (2,4,6- trimethylbenzoyl)phenylphosphinate solution was added to the N- (hydroxymethyl)prop-2-enamide suspension over 20 minutes while maintaining the temperature between 0 and 5°C. The reaction mixture was allowed to warm to room temperature upon which N-(hydroxymethyl)prop- 2-enamide gradually dissolved. The reaction was allowed to continue at room temperature for 16 hours. The reaction mixture was added slowly to 2 liter water at 0°C. The mixture was extracted with 1 liter ethyl acetate. The ethyl acetate fraction was washed with a NaHCOs solution in water until the aqueous phase had a pH of 7. The aqueous phase was extracted with an additional 500 ml ethyl acetate. The pooled ethyl acetate fractions were dried over MgSCM and evaporated under reduced pressure. The oily residue gradually solidified and was treated with 150 ml methyl tert.butyl ether, upon which AM-1 crystallized. AM-1 was isolated by filtration and dried. 49.8 g (y : 62%) of AM-1 was isolated (TLC analysis on MERCK TLC Silica gel 6OF254 , eluent methylene chloride / methanol 95 / 5, Rf : 0.27, m.p. : 143°C). The structure of AM-1 was further confirmed using TLC-MS.EXAMPLE 2

[0183] This example illustrates the synthesis of the acyl phosphine oxide photoinitiator AM-2.Synthesis

[0184]

[0185] 1 g (10 mmol) N-(hydroxymethyl)prop-2-enamide was dispersed in 5 ml methane sulfonic acid while cooling the mixture to 5°C. 3.48 g (10 mmol) (2,4,6-trimethylbenzoyl)diphenylphosphine oxide was added in portion while maintaining the temperature below 5°C. 2 ml methane sulfonic acid was added and the mixture was allowed to warm to room temperature. The reaction was allowed to continue for 72 hours at room temperature. The reaction mixture was added to 100 ml water at 0°C. The crude AM-2 precipitated from the medium and was isolated by filtration. The crude AM- 2 was purified by preparative column chromatography on a Prochrom™ LC80 column (Kromasil™ Si 60 A 10 pm as stationary phase and a gradient elution form ethyl acetate to ethyl acetate / methanol 90 / 10). 1.4 g (y : 33%) of AM-1 was isolated (TLC analysis on MERCK TLC Silica gel 6OF254, eluent : ethyl acetate, Rf : 0.51, m.p. : 192°C). The structure of AM- 2 was further confirmed using TLC-MS.EXAMPLES

[0186] This example illustrates the synthesis of the acyl phosphine oxide photoinitiator AM-3.Synthesis

[0187]

[0188] 65 ml methane sulfonic acid was gradually added to a mixture of 15.82 g (50 mmol) ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate and 7.25 g (63 mmol) 1-(hydroxymethyl)pyrrolidin-2-one while maintaining the temperature below 25°C. The reaction was allowed to continue at room temperature for 16 hours. 1 g (8.7 mmol) 1-(hydroxymethyl)pyrrolidin-2- one was added and the reaction was allowed to continue for an additional two hours at room temperature. 0.5 g (4.35 mmol) 1 -(hydroxymethyl) pyrrolidin-2-one was added and the reaction was allowed to continue for 90 minutes at room temperature. The reaction mixture was added to 400 ml water at 0°C and extracted with 200 ml ethyl acetate. The organic fraction was washed with a solution of 3 g NaHCOs in 200 ml water, dried over MgSCU and evaporated under reduced pressure. 16.3 g (y : 79 %) of AM-3 was isolated (TLC analysis on MERCK TLC Silica gel 6OF254, eluent : methylene chloride / methanol 95 / 5, Rf : 0.28). The structure of AM-3 was further confirmed using TLC-MS.EXAMPLE 4

[0189] This example illustrates the synthesis of the acyl phosphine oxide photoinitiator AM-4.Synthesis

[0190]

[0191] 64.82 ml methane sulfonic acid was gradually added to a mixture of 15.82 g (50 mmol) ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate and 10.41 g (63 mmol) N-(hydroxymethyl)-2-phenyl-acetamide while maintaining the temperature below 25°C. The reaction was allowed to continue at room temperature for 16 hours. The reaction mixture was added to 400 ml water at 0°C and extracted with 200 ml ethyl acetate. The organic fraction was washed with a solution of 3 g NaHCOs in 200 ml water, dried over MgSCM and evaporated under reduced pressure. The crude AM-4 was purified by preparative column chromatography on a Prochrom™ LC80 column (Kromasil™ Si 60 A 10 pm as stationary phase, eluent : methylene chloride / ethyl acetate 50 / 50). 15.8 g (y : 68%) of AM-4 was isolated (TLC analysis on MERCK TLC Silica gel 6OF254, eluent : ethyl acetate, Rf :0.54). The structure of AM-4 was further confirmed using TLC-MS.EXAMPLES

[0192] This example illustrates the synthesis of the acyl phosphine oxide photoinitiator AM-5.Synthesis

[0194] 2 g (5 mmol) AM-1 was added to 20 ml ethanol. 0.43 g (5 mmol) piperidine was added. AM-1 dissolved upon the addition of piperidine. The reaction mixture was heated to 35°C and the reaction was allowed to continue at 35°C for 20 hours. An additional 0.08 g (0.94 mmol) piperidine was added and the reaction was allowed to continue for two hours at 76°C. The solvent was evaporated under reduced pressure and the crude AM-5 was purified by preparative column chromatography, using Kromasil™ 18 100A, 10 pm as stationary phase and a gradient elution from methanol / 0.2 M ammonium acetate 90 / 10 to methanol. 1.2 g (y : 49 %) of AM-5 was isolated isolated (TLC analysis on a UNIPLATE Analtech™ HPTLC- RP18F plate, eluent methanol / 1 M NaCI 70 / 30, Rf : 0.3). The structure of AM-5 was further confirmed using TLC-MS.EXAMPLE 6

[0195] This example illustrates the synthesis of the acyl phosphine oxide photoinitiator AM-6.Synthesis

[0196]

[0197] 2 g (5 mmol) AM-1 was added to 20 ml ethanol. 0.61 g (6 mmol) dipropyl amine was added. AM-1 dissolved upon the addition of dipropyl amine. The reaction mixture was heated to 76°C and the reaction was allowed to continue at 76°C for 40 hours. The solvent was evaporated under reduced pressure and the crude AM-6 was purified by preparative column chromatography, using Kromasil™ 18 100A, 10 pm as stationary phase and a gradient elution from methanol / 0.2 M ammonium acetate 90 / 10 to methanol. 1.3 g (y : 52 %) of AM-6 was isolated isolated (TLC analysis on a UNIPLATE AnaltechTM HPTLC-RP18F plate, eluent methanol / 1 M NaCI 70 / 30, Rf : 0.3). The structure of AM-6 was further confirmed using TLC- MS.EXAMPLE 7

[0198] This example illustrates the synthesis of the acyl phosphine oxide photoinitiator AM-7.Synthesis

[0199]

[0200] 2.4 g (6 mmol) AM-1 was added to 20 ml ethanol. 0.26 g (3 mmol) piperazine was added. The mixture was heated to 76°C and the reaction was allowed to continue for 20 hours at 76°C. The solvent was removed under reduced pressure. The crude AM-7 was purified by preparative column chromatography on a Buchi NP-Flash column (Graceresolve™ 80 g SiOH 40pm 60A), using multiple gradient elution from methylene chloride over ethylacetate to methanol. 0.9 g (y : 33%) of AM-7 was isolated (TLC analysis on a UNIPLATE Analtech™ HPTLC-RP18F plate, eluent methanol / 1 M NaCI 80 / 20, Rf : 0.3). The structure of AM-4 was further confirmed using TLC-MS.EXAMPLES

[0201] This example illustrates the synthesis of the acyl phosphine oxide photoinitiator AM-8.Synthesis

[0202]

[0203] 2.4 g (6 mmol) of AM-1 was added to 20 ml ethanol. 0.63 g (3 mmol) 1 ,3- dipiperidylpropane was dissolved in 5 ml ethanol and added to the reaction mixture. The reaction mixture was heated to 75°C and the reaction was allowed to continue for 20 hours at 75°C. The solvent was removed under reduced pressure and the crude AM-8 was purified using preparative column chromatography on a Buchi NP-Flash column (Graceresolve™ 80 g SiOH 40pm 60A), using multiple gradient elution from methylene chloride over ethylacetate to methanol. 1.1 g (y : 36%) of AM-8 was isolated. The structure of AM-8 was further confirmed using TLC-MS.EXAMPLE 9

[0204] This example illustrates the synthesis of the acyl phosphine oxide photoinitiator AM-12.Synthesis

[0206] 12.65 g (40 mmol) ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate and 6.2 g (48 mmol) N-hydroxymethyl-succinimid were mixed. 51.9 ml methane sulfonic acid was added dropwise while maintaining the temperature below 30°C. The reaction was allowed to continue for 16 hours at 35°C. The reaction mixture was added to 400 ml water and the precipitated residue was isolated. The residue was treated with 300 ml water. The aqueous phase was neutralized to pH=7 and extracted with 200 ml ethyl acetate. The organic fraction was dried over MgSCM and evaporated under reduced pressure. The crude AM-12 was purified using preparative column chromatography on a Buchi NP-Flash column (Graceresolve™ 80 g SiOH 40pm 60A), using a gradient elution from methylene chloride to ethyl acetate. 6.4 g (y : 37%) of AM-12 was isolated (TLC analysis on Merck TLC Silica gel 6OF254, eluent : ethyl acetate, Rf : 0.41). The structure of AM-12 was further confirmed using TLC-MS.EXAMPLE 10

[0207] This example illustrates the synthesis of the acyl phosphine oxide photoinitiator AM-16.Synthesis

[0209] 12.65 g (40 mmol) ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate and 8.51 g (48 mmol) N-hydroxymethyl-phthalimide were mixed. 51.9 ml methane sulfonic acid was added dropwise while maintaining the temperature below 30°C. The reaction was allowed to continue for 2 hours at 25°C. The reaction mixture was added dropwise to 400 ml water at 0°C. The crude AM-16 precipitated from the medium and was isolated by filtration. The crude AM-16 was treated with 400 ml water that was neutralized to pH = 7 using NaHCOs. AM-16 was isolated by filtration and dried. 19.6 g of AM-16 was isolated, which proved to be a mixture of a mono-substituted and disubstituted compound (TLC analysis on Merck TLC Silica gel 6OF254, eluent : methylene chloride / ethyl acetate 90 / 10, the mono-substituted compound : Rf = 0.14, the di-substituted compound : Rf = 0.28). The structural assignment of the compounds was done using TLC-MS.EXAMPLE 11

[0210] This example demonstrates the curing efficiency and odour performance of the acyl phosphine oxide photoinitiators, as compared to the reference photoinitiator TPO-L.Preparation Photocurable Inkjet Inks

[0211] The comparative example COMP-1 and the inventive examples INV-1 to INV-5 were prepared according to Table 3. The weight% (wt%) were based on the total weight of the LED curable inkjet inks.Table 3Evaluation and Results

[0212] The inventive examples INV-1 to INV-5 and the comparative example COMP-1 were coated on a PET175 substrate using a bar coater and a 10 pm wired bared. The samples were cured on a Aktiprint™ mini duo LED curing station at full power and a linear curing speed of 10m / min. All samples were cured in one pass.

[0213] A second set of samples, including the comparative example COMP-1 and the inventive examples INV-1 to INV-5, were coated and covered with a PET175 substrate to retain potential volatiles during curing. The samples were cured using an Aktiprint™ mini duo LED curing station at full power, with a linear curing speed of 10 m / min in a single pass. After curing, the samples were stored in the dark for one hour. Subsequently, the covers were removed, and the odour of each sample was evaluated on a scale from 0 to 5, where 0 indicates no noticeable odour and 5 indicates a very pronounced odour. The results are summarized in Table 4.Table 4

[0214] Table 4 clearly shows that the acyl phosphine oxide photoinitiators of the present invention exhibit a very faint or no noticeable odour, whereas the comparative initiator still has a distinctly noticeable odour.

Claims

ClaimsClaim 1. An acyl phosphine oxide photoinitiator having a structure according to Formula (I):Formula (I), whereinAr represents an aryl group;Ri is selected from the group consisting of an aryl group, a heteroaryl group, an alkoxy group and an aryloxy group;R2, R4 and Re are independently selected from the group consisting of an alkyl group and an alkoxy group;R3 and R5 are independently selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl group, an alkoxy group and an aryloxy group, with the proviso that at least one of R3 and R5 represents a substituent according to Formula (II):Formula (II),wherein R7 is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl, a heteroaryl group, and a -COR14 group;Rs is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl, a heteroaryl group, a free radical polymerizable ethylenically unsaturated group and a -C(Rn)-CH2-NRi2Ri3 group;X is selected from the group consisting of an oxygen and N-R9;n represents 0 or 1 ; andR9 is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group and an aryl group;R11 is selected from the group consisting of a hydrogen and a methyl group; R12 and R13 are independently selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group and an aralkyl group; andR14 is selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group, an alkaryl group, an aralkyl group, an aryl, and a heteroaryl group.Claim 2. The acyl phosphine oxide photoinitiator according to claim 1 , wherein 1 , 2, 3, 4, 5 or all of the conditions a) to f) are fulfilled, wherein a) R1 represents a phenyl group or a Ci to Ce alkoxy group; b) R2, R4 and Re represent a methyl group; c) R7 represents a hydrogen; d) Ar represents a phenyl group; e) X represents oxygen;and f) n represents 0.Claim 3. The acyl phosphine oxide photoinitiator according to claim 1 having a structure according to Formula (III):Formula (III),wherein R10 is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl and a heteroaryl group.Claim 4. The acyl phosphine oxide photoinitiator according to claim 3, wherein 1 , 2, 3 or all of the conditions a) to d) are fulfilled, wherein a) Ri is a Ci to Ce alkoxy group; b) Rio is a hydrogen or an alkyl group; c) Rn is a hydrogen; d) R12 and R13 represent an alkyl group.Claim 5. The acyl phosphine oxide photoinitiator according to claim 1 having a structure according to Formula (IV):Formula (IV),whereinR15 is selected from the group consisting of the group consisting of an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group and an -COR14 group;R16 an alkyl group, an alkenyl group, an alkynyl group, an alkaryl group, an aralkyl group, an aryl or heteroaryl group, an alkoxy group, an aryloxy group and -NR17R18 group;R17 and R18 are independently selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group and an aryl or heteroaryl group.Claim 6. The acyl phosphine oxide photoinitiator according to claim 5, wherein 1 , 2 or 3 of the conditions a) to c) are fulfilled, wherein a) R1 is a Ci to Ce alkoxy group; b) R15 is a hydrogen; c) R16 is an alkyl group.Claim 7. The acyl phosphine oxide photoinitiator according to claim 1 selected from the group consisting ofClaim 8. A photocurable composition comprising a free radical polymerizable compound and at least one acyl phosphine oxide according to any one of claims 1 to 7.Claim 9. A photocurable inkjet ink comprising a photocurable composition according to claim 8.Claim 10. The photocurable inkjet ink according to claim 9 containing a colour pigment.Claim 11. A printed article comprising a cured composition derived from the photocurable composition of claim 8.Claim 12. The printed article according to claim 11 obtained using inkjet printing technology.Claim 13. An inkjet printing method comprising the steps of:a) jetting an image with a photocurable inkjet ink according to claim 9 or 10 on a substrate; andb) curing the jetted image by UV light emitting diodes having an emission wavelength of 360 nm or larger.Claim 14. A method for the preparation of the acyl phosphine oxides according to any one of claims 1 to 7, having as synthesis scheme:whereinRi is selected from the group consisting of an aryl group, a heteroaryl group, an alkoxy group and an aryloxy group;R? is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl, a heteroaryl group, and a -COR14 group;Rs is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl, a heteroaryl group, a (meth)acrylate group, a free radical polymerizable ethylenically unsaturated group and a -C(Rn)-CH2-NRi2Ri3 group;X is selected from the group consisting of an oxygen and N-R9;n represents 0 or 1 ; andR9 is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group and an aryl group;R11 is selected from the group consisting of a hydrogen and a methyl group; R12 and R13 are independently selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group and an aralkyl group; andR14 is selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group, an alkaryl group, an aralkyl group, an aryl, and a heteroaryl group.Claim 15. The method according to claim 14, wherein 1, 2, 3, 4, or all of the conditions a) to e) are fulfilled, whereina) R1 represents a phenyl group or a Ci to Ce alkoxy group;b) R? represents a hydrogen; c) Ar represents a phenyl group; d) X represents oxygen;and e) n represents 0.

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