acyl phosphine oxide photoinitiator

Abstract

An acylphosphine oxide photoinitiator having an ether, hydroxyl, or tertiary amine group attached to an amido group on the acyl group of the monoacylphosphine oxide moiety via a carbon chain of 1-3 carbon atoms. Also disclosed is the use of the acylphosphine oxide photoinitiator in photo-curable compositions and UV-curable inkjet inks.

Description

Technical Field

[0001] This invention relates to acylphosphine oxide photoinitiators and their use in photocurable compositions (e.g., UV-curable varnishes and (inkjet) inks). Background Technology

[0002] Existing UV-curable inkjet technologies are based on LED curing, which works for most printing systems at 395 nm. The number of industrially available photoinitiators suitable for curing at such wavelengths is quite limited. In most cases, for UV LED curing at 395 nm, one or more of the following acylphosphine oxide photoinitiators are used industrially: phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and ethyl(2,4,6-trimethylbenzoyl)phenylphosphine hypophosphite (TPO-L). However, there is increasing concern regarding the toxicology of BAPO, TPO, and TPO-L.

[0003] Of the three acylphosphine oxide photoinitiators, TPO-L has been concluded to have the lowest cytotoxicity. Published studies have also reached conclusions regarding the latter, such as ZENG, Boning et al., Cytotoxic and cytocompatible comparison among seven photoinitiators-triggered polymers in different tissue cells. Toxicology in vitro - DOI: 10.1016 / j.tiv.2021.105103. 2021 and KIM, Gi-Tae et al., Cytotoxicity, Color Stability and Dimensional Accuracy of 3D Printing Resin with ThreeDifferentPhotoinitiators. Polymers (Basel) - DOI: 10.3390 / polym14050979. 2022. TPO-L is increasingly being used in industry to replace BAPO and TPO; however, it has been observed that TPO-L has a slower curing rate compared to BAPO and TPO, which affects the efficiency and quality of the cured products.

[0004] One approach to addressing these issues is to explore alternative types of photoinitiators. Combinations of thioxanthone and amine-based co-initiators achieve high curing rates under 395 nm UV LEDs, but result in a significant yellowing of the cured layer, making them generally suitable for CMYK printing applications but not for varnishes and white inks, and sometimes also unsuitable for cyan and magenta inks.

[0005] Another approach is to design improved acylphosphine oxides, as they generally do not exhibit photo-yellowing issues. Diacylphosphine oxides are typically limited by their solubility in UV-curable formulations, leading to monoacylphosphine oxides being a particularly preferred photoinitiator for 395nm radiation-curable compositions, further narrowing the choices. In addition to toxicological concerns and limitations in formulation freedom, almost all available acylphosphine oxide initiators are prone to migration and the generation of volatile degradation products, resulting in odor. Odor, in particular, is a limiting factor for many high-volume applications such as interior decoration. If the migration problem can be solved, the range of applications will be further expanded.

[0006] Over the past decade, considerable research has been conducted in search of industrially available alternatives to acylphosphine oxides, with the aim of addressing the aforementioned issues.

[0007] Functionalization of the mesitylene segment of acylphosphine oxide photoinitiators, as disclosed in WO 2014 / 051026 (FUJIFILM), WO 2014 / 129213 (FUJIFILM), WO 2019 / 243039 (AGFA) and WO 2022 / 106099 (AGFA), is a potential solution to the problem of volatile degradation products.

[0008] WO 2019 / 243039 (AGFA) discloses urea and oxalamide-functionalized acylphosphine oxides, wherein additional supramolecular interactions are used to further control the volatility of degradation products.

[0009] In WO 2022 / 106099 (AGFA), additional tertiary amines are incorporated into the structure to further optimize the surface curing of printed images and avoid the migration of skin-irritating acrylates. However, the use of supramolecular interactions often restricts formulation freedom, which must be controlled by additional structural elements that do not possess any further radiation curing capabilities. This results in an increase in the molecular weight per photoinitiating moiety, affecting both the viscosity of the formulation and the curing rate for the same weight ratio in the formulation. To maintain the curing rate at an acceptable level, higher amounts of photoinitiator are added, further affecting the viscosity. The effect on viscosity limits the applicability of the disclosed photoinitiator in inkjet applications, where the viscosity of the formulation is particularly critical.

[0010] Therefore, there is still a need for photoinitiators that have high photoreactivity and formulation freedom without producing odor and without significantly affecting the viscosity of formulations (e.g., UV-curable inkjet inks). Summary of the Invention

[0011] It has now been found that the above problems can be largely solved by specific acylphosphine oxide photoinitiators (more particularly phosphine oxide photoinitiators having an ether group, hydroxyl group, or tertiary amine group on the acyl group of the monoacylphosphine oxide moiety via a carbon chain of 1-3 carbon atoms).

[0012] A remarkable improvement in surface curability was observed for certain acylphosphine oxide photoinitiators. Acylphosphine oxide photoinitiators typically exhibit good curability for the inner portions of the polymerizable layer but not for the surface portions, resulting in undesirable tackiness. The photoinitiator of this invention exhibits superior surface curability compared to TPO-L.

[0013] Another advantage of some photoinitiators according to the invention is that they can be used to prepare low-odor, photocurable compositions and inks. Acylphosphine oxide photoinitiators generate two types of free radicals upon UV exposure: phosphine oxide radicals and acyl radicals. While phosphine oxide radicals are almost completely incorporated into the polymer network, this is not the case for acyl radicals. Unreacted acyl radicals typically form aldehydes, such as trimethylbenzaldehyde, causing an unpleasant odor in the cured product. By linking two mono-acylphosphine oxide moieties to each other via their acyl groups, the molecular weight of the acyl radical is slightly increased, thus reducing the volatile degradation products of the acylphosphine oxide photoinitiator. On the other hand, when a photoinitiator generates multiple interconnected acyl radicals, the likelihood of them incorporating into the polymer network also increases. The latter is beneficial for addressing migration issues.

[0014] Therefore, one object of the present invention is to provide a new class of acylphosphine oxides that have increased formulation freedom for low-odor, photocurable compositions and exhibit good surface curing properties.

[0015] Another object of the present invention is to provide a radiation-curable composition, such as a UV-curable varnish for inkjet inks, comprising at least one photoinitiator according to the present invention.

[0016] These and other objects and advantages of the present invention will become apparent from the detailed description given below. Detailed Implementation

[0017] definition The term "alkyl" refers to all possible variants of an alkyl group for each number of carbon atoms, namely, 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 tert-butyl; for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethyl-propyl, and 2-methyl-butyl, etc.

[0018] In the context of substituted alkyl groups, the term "substituted" means that the alkyl group can be replaced by atoms other than those normally present in such groups (i.e., carbon and hydrogen). For example, substituted alkyl groups can include halogen atoms or thiol groups, while unsubstituted alkyl groups contain only carbon and hydrogen atoms.

[0019] Unless otherwise stated, the substituted alkyl group is preferably replaced by a group selected from the following: aryl, heteroaryl, ester, amide, ether, thioether, ketone, aldehyde, sulfoxide, sulfone, sulfonate, sulfonamide, -Cl, -Br, -I, -OH, -SH, -CN and -NO2.

[0020] Unless otherwise stated, substituted or unsubstituted alkyl groups are preferably C1-C6-alkyl groups.

[0021] Unless otherwise stated, the substituted or unsubstituted alkenyl group is preferably a C2-C6-alkenyl group.

[0022] Unless otherwise stated, the substituted or unsubstituted alkynyl group is preferably C2-C6-alkynyl.

[0023] Unless otherwise stated, substituted or unsubstituted alkoxy groups are preferably C1-C6-alkyl, with methoxy, ethoxy and propoxy groups being particularly preferred.

[0024] The term aryl refers to a monocyclic or polycyclic aromatic ring structure that contains only carbon atoms in its ring structure.

[0025] Unless otherwise stated, the aryl group is preferably phenyl or naphthyl, which may include one, two, three or more C1-C6-alkyl groups, which may be substituted alkyl groups.

[0026] Unless otherwise stated, a substituted aryl group is an aryl group comprising one or more groups selected from aldehyde, -Cl, -Br, -I, -OH, -SH, -CN and -NO2.

[0027] The term heteroaryl refers to a monocyclic or polycyclic aromatic ring containing a carbon atom and one or more heteroatoms (preferably 1-4 heteroatoms independently selected from nitrogen, oxygen, selenium, and sulfur) in its ring structure. Preferably, the heteroaryl is a monocyclic ring, and more preferably, the heteroaryl is a five- or six-membered ring substituted with one, two, or three oxygen atoms, nitrogen atoms, sulfur atoms, selenium atoms, or combinations thereof.

[0028] Preferred examples of heteroaryl groups include, but are not limited to, pyridinyl, pyrimidinyl, pyrazyl, quinolinyl, triazinyl, pyrroleyl, pyrazolyl, imidazolyl, (1,2,3)-triazolyl and (1,2,4)-triazolyl, pyrazinyl, pyrimidinyl, tetrazolyl, furanyl, thiophenyl, isoxazolyl, thiazolyl, isoxazolyl and oxazolyl.

[0029] Photoinitiator The photoinitiator according to the present invention is an acylphosphine oxide photoinitiator having an ether group, hydroxyl group, or tertiary amine group on an acyl group of a monoacylphosphine oxide moiety having an amide group connected to the acyl group via a carbon chain of 1, 2, or 3 carbon atoms.

[0030] The photoinitiator according to the present invention has a structure according to formula (1): Equation (1), in R1 is selected from substituted or unsubstituted alkyl, substituted or unsubstituted aryl, and substituted or unsubstituted alkoxy groups; R2 and R3 are independently selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl and substituted or unsubstituted aryl or heteroaryl; R4 is selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted aryl or heteroaryl, (meth)acrylate, vinyl ether, allyl ether, and monoacylphosphine oxide moiety according to formula (1-1). R5 and R6 are independently selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl and substituted or unsubstituted aryl or heteroaryl, and one of R5 and R6 may represent a monoacylphosphine oxide moiety according to formula (1-1), or R5 and R6 may represent atoms required to form a 5-8 membered ring. R7 is selected from substituted or unsubstituted aryl or heteroaryl groups and OR9; R8 indicates substituted or unsubstituted aryl or heteroaryl; R9 is selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, and substituted or unsubstituted aryl or heteroaryl. X is selected from O and NR 10 ; R 10 Selected from substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl and substituted or unsubstituted aryl or heteroaryl; n is an integer selected from 1 to 3; and The monoacylphosphine oxide portion according to formula (1-1) is: Equation (1-1), Where R 11 and R 12 It is independently selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl and substituted or unsubstituted aryl or heteroaryl; R* is the coupling site of R4, R5, or R6 with the photoinitiator; and m is an integer selected from 1 to 3.

[0031] In a preferred embodiment, X represents 0 and / or n, and m (if present) represents 1.

[0032] In a preferred embodiment, R4 is selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl and substituted or unsubstituted alkynyl, with substituted or unsubstituted alkyl being particularly preferred.

[0033] In a preferred embodiment, R5 and R6 are independently selected from hydrogen and substituted or unsubstituted alkyl groups, more preferably hydrogen and C1-C4 alkyl groups, and most preferably hydrogen and methyl groups.

[0034] The above preferred embodiments can be combined with each other without any limitation.

[0035] In a particularly preferred embodiment, the photoinitiator according to the invention is represented by formula (1-2) or (1-3): Equation (1-2), Equation (1-3), R4 to R6 and n are as defined for compounds according to formula (1).

[0036] In the most preferred embodiment, the photoinitiator according to the invention has a structure according to formula (2): Equation (2), Among them, R1 to R 12 X, n and m are as defined for compounds according to formula (1).

[0037] Preferred examples of the photoinitiators according to the present invention are given in Table 1 below, but are not limited thereto.

[0038] Table 1 Photocurable compositions The photocurable composition according to the present invention comprises the above-mentioned photoinitiator and a free radical polymerizable compound as essential components.

[0039] Any monomer, oligomer, and polymer capable of free radical polymerization can be used as a free radical polymerizable compound. The polymerizable compound can be any monomer and / or oligomer found in *Polymer Handbook Vol. 1+2, 4th Edition*, edited by J. BRANDRUP et al., Wiley-Interscience, 1999. Combinations of monomers and oligomers can also be used. Monomers and oligomers can have different degrees of functionality, and mixtures of monomers and oligomers with mono, di, tri, and higher functionalities can be used.

[0040] There are no restrictions on the type of free radical polymerizable chemical substance used in photocurable compositions. The free radical polymerizable chemical substance can be a polymerizable chemical substance based on (meth)acrylates, but it can also be a thiol-ene and / or thiol-acetylene polymerizable chemical substance. Since water and organic solvents can be present, it can also be polymerizable polymer particles, such as polymerizable latex.

[0041] A preferred aspect of the invention is a UV-curable inkjet ink comprising the above-described photocurable composition. The acylphosphine oxide initiator is preferably present in an amount between 1-25% by weight, more preferably between 3-22% by weight, and most preferably between 5-20% by weight, wherein the weight percentage is based on the total weight of the UV-curable inkjet ink. In the latter range, a suitable viscosity for inkjet printing is generally obtained.

[0042] UV-curable inkjet inks can be colorless, but preferably contain colorants. Colorless UV-curable inkjet inks can be used, for example, as primers to improve adhesion to substrates, or as varnishes to improve image gloss. The photoinitiator according to the invention provides improved curability compared to TPO-L without photo-yellowing. The latter is also observed in UV-curable inkjet inks containing cyan and white pigments.

[0043] UV-curable inkjet inks can include other components as needed, such as surfactants, dispersants, dispersants, stabilizers, UV absorbers, etc.

[0044] To achieve good jetting performance, UV-curable inkjet inks require 1000 seconds. -1 At a shear rate and at a spraying temperature between 30-70°C, preferably at 45°C, the viscosity at the spraying temperature is preferably less than 30.0 mPa·s, more preferably less than 20.0 mPa·s, and most preferably between 5.0-16.0 mPa·s.

[0045] The surface tension of the UV-curable 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. Within these ranges, good ink spreading is obtained on a wide range of substrates.

[0046] A single UV-curable inkjet ink can be used, but it is preferred to use a UV-curable inkjet ink kit containing multiple colored UV-curable inkjet inks according to the present invention.

[0047] For printing multicolor images, the UV-curable inkjet ink is preferably part of a UV-curable inkjet ink kit containing at least three, but most preferably at least four, UV-curable inkjet inks according to the invention. The inkjet ink kit is preferably a UV-curable CMYK or CRYK inkjet ink kit, and preferably also includes a UV-curable white inkjet ink to enhance color vibrancy. The inkjet ink kit can also be expanded with additional inks such as purple, green, red, blue, and / or orange to further broaden the color gamut of the image.

[0048] UV-curable inkjet ink kits can also be expanded through combinations of full-density and light-density inkjet inks. Combinations of dark and light inks and / or black and gray inks improve image quality by reducing graininess.

[0049] A UV-curable inkjet ink kit may also include one or more colorless UV-curable inkjet inks that can be used as primers and / or varnishes.

[0050] In a particularly preferred embodiment of the UV-curable inkjet ink kit, the ink kit according to the invention comprises: - Cyan UV-curable inkjet ink containing β-copper phthalocyanine pigment; - A red UV-curable inkjet ink containing pigments selected from the following: CI Pigment Red 57 / 1, CI Pigment Red 122, CI Pigment Red 144, CI Pigment Red 170, CI Pigment Red 175, CI Pigment Red 176, CI Pigment Red 187, CI Pigment Red 188, CI Pigment Red 202, CI Pigment Red 207, CI Pigment Red 242, CI Pigment Red 254, CI Pigment Red 272 and their mixtures; - A yellow, UV-curable inkjet ink containing pigments selected from the following: CI Pigment Yellow 74, CI Pigment Yellow 83, CI Pigment Yellow 97, CI Pigment Yellow 110, CI Pigment Yellow 120, CI Pigment Yellow 139, CI Pigment Yellow 138, CI Pigment Yellow 150, CI Pigment Yellow 151, CI Pigment Yellow 154, CI Pigment Yellow 155, CI Pigment Yellow 175, CI Pigment Yellow 180, CI Pigment Yellow 181, CI Pigment Yellow 194, CI Pigment Yellow 213, CI Pigment Yellow 214, and mixtures thereof; and - Black UV-curable inkjet ink containing carbon black pigment; preferably supplemented with white and / or colorless inkjet inks. Such ink kits are found to be particularly useful for reproducing wood grain patterns with minimal ink consumption, in addition to improved low odor and surface-curing properties. Low odor is essential when manufacturing interior furnishings for rooms and vehicles (e.g., furniture, wallpaper, doors, natural leather goods, fabrics, and decorative panels such as floor laminates).

[0051] When a more vibrant color is required, the red UV-curable inkjet ink is replaced by a magenta UV-curable inkjet ink containing a pigment selected from CI Pigment Violet 19 and its mixtures.

[0052] Compounds that can be polymerized by free radicals In a preferred embodiment of the UV-curable inkjet ink according to the present invention, the UV-curable inkjet ink comprises one or more free radical polymerizable monomers and / or oligomers.

[0053] Any monomer or oligomer capable of free radical polymerization can be used as a free radical polymerizable compound. The polymerizable compound can be any monomer and / or oligomer found in Polymer Handbook Vol. 1+2, 4th Edition, edited by J. BRANDRUP et al., Wiley-Interscience, 1999. Combinations of monomers and oligomers can also be used. Monomers and oligomers can have different degrees of functionality, and mixtures of monomers and oligomers with mono, di, tri, and higher functionalities can be used.

[0054] Monofunctional polymerizable compounds are typically used to enhance the flexibility of the cured layer, while polyfunctional polymerizable compounds are used to enhance the scratch resistance of the cured layer.

[0055] Monofunctional polymerizable compounds contain a single free radical polymerizable group selected from the following: acrylates, methacrylates, acrylamides, methacrylamides, styrene, maleates, fumarates, itaconic acid esters, vinyl ethers, vinyl esters, allyl ethers, and allyl esters.

[0056] Polyfunctional polymerizable compounds contain two, three or more free radical polymerizable groups selected from the following: acrylates, methacrylates, acrylamides, methacrylamides, styrene, maleates, fumarates, itaconic acid esters, vinyl ethers, vinyl esters, allyl ethers and allyl esters.

[0057] In a preferred embodiment, the monofunctional polymerizable compound is selected from acrylic acid, methacrylic acid, maleic acid (or its salts), maleic anhydride, and alkyl (meth)acrylates (linear, branched, and cycloalkyl), such as methyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; aryl (meth)acrylates, such as benzyl (meth)acrylate and phenyl (meth)acrylate; hydroxyalkyl (meth)acrylates, such as hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate; and (meth)acrylates having other types of functionality (e.g., ethylene oxide, amino, fluorine, polyoxyethylene, or phosphate substituted), such as glycidyl (meth)acrylate and propylene (meth)acrylate. Dimethylaminoethyl acrylate, trifluoroethyl acrylate, methoxy polyethylene glycol (meth)acrylate, and tripropylene glycol (meth)acrylate phosphate; allyl derivatives, such as allyl glycidyl ether; styrene derivatives, such as styrene, 4-methylstyrene, 4-hydroxystyrene, 4-acetylstyrene, and styrene sulfonic acid; (meth)acrylonitrile; (meth)acrylamide (including N-monosubstituted and N,N-disubstituted), such as N-benzyl (meth)acrylamide; maleimide, such as N-phenylmaleimide; vinyl derivatives, such as vinylcaprolactam, vinylpyrrolidone, vinylimidazole, vinylnaphthalene, and vinyl halides; vinyl ethers, such as vinyl methyl ether; vinyl esters of carboxylic acids, such as vinyl acetate, vinyl butyrate, and vinyl benzoate.

[0058] In a more preferred embodiment, the monofunctional polymerizable compound is selected from monoacrylates and vinyl lactams, such as N-vinylcaprolactam. Particularly preferred monofunctional polymerizable compounds are selected from isoamyl acrylate, stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate, isoamyl acrylate, isostearyl acrylate, 2-ethylhexyl-diethylene glycol acrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethylhexahydrophthalic acid, butoxyethyl acrylate, ethoxydiethylene glycol acrylate, methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycol acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydroxyethyl acrylate, and 2-ethylhexyl acrylate. 2-Hydroxypropyl acrylate, 2-Hydroxy-3-phenoxypropyl acrylate, Vinyl ether acrylate, 2-Acryloyloxyethyl succinic acid, 2-Acryloyloxyethyl phthalic acid, 2-Acryloyloxyethyl-2-hydroxyethyl-phthalic acid, lactone-modified flexible acrylate, tert-butylcyclohexyl acrylate, caprolactone acrylate, cyclic trimethylolpropane formal acrylate, cyclic trimethylolpropane formal acrylate, ethoxylated nonylphenol acrylate, isodecanyl acrylate, isooctyl acrylate, octyldecyl acrylate, alkoxylated phenolic acrylate, tridecyl acrylate, and acryloylmorpholine.

[0059] In a preferred embodiment, the monofunctional polymerizable compound includes N-vinyllactam, such as N-vinylcaprolactam. Another particularly preferred monomer is vinylmethyloxazolidinone, available from BASF as VMOX. N-vinylcaprolactam and vinylmethyloxazolidinone are preferred monomers because they provide good ink curability and adhesion of the cured film to the recording medium.

[0060] Preferred multifunctional acrylates include triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, dimethyloltricyclodecane diacrylate, bisphenol A EO (ethylene oxide) adduct diacrylate, and bisphenol A PO (Propylene oxide) adduct diacrylate, hydroxyneopentate neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, alkoxylated dimethyloltricyclodecane diacrylate and polytetramethylene glycol diacrylate, trimethylolpropane triacrylate, EO-modified trimethylolpropane triacrylate, tri(propylene glycol) triacrylate, caprolactone-modified trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxytetraacrylate, dipentaerythritol hexaacrylate, di(trimethylolpropane) tetraacrylate, glycerol propoxytetraacrylate and caprolactam-modified dipentaerythritol hexaacrylate.

[0061] Other suitable difunctional acrylates include alkoxylated cyclohexanone dimethyl diacrylate, alkoxylated hexanediol diacrylate, dioxanediol diacrylate, dioxanediol diacrylate, cyclohexanone dimethyl diacrylate, diethylene glycol diacrylate, and neopentyl glycol diacrylate.

[0062] Other multifunctional acrylates include propoxylated glycerol triacrylate and propoxylated trimethylolpropane triacrylate, di-trimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate, ethoxylated pentaerythritol tetraacrylate, methoxylated diol acrylates and acrylates.

[0063] Preferred multifunctional acrylates include dipropylene glycol diacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, cyclohexanediol diacrylate, polyethylene glycol 200 diacrylate, 3-methyl-1,5-pentanediol diacrylate, pentaerythritol tetraacrylate, trimethylolpropane triacrylate, and dipentaerythritol pentaacrylate.

[0064] Multifunctional polymerizable compounds may have two distinct polymerizable groups, such as a vinyl ether group and an acrylate group. Preferred vinyl ether acrylates are those disclosed in US 6310115 (AGFA). Particularly preferred compounds are 2-(2'-vinyloxyethoxy)ethyl acrylate (VEEA). Other suitable vinyl ether acrylates are those disclosed in columns 3 and 4 of US 67679890 B (NIPPON SHOKUBAI).

[0065] The use of multifunctional polymerizable compounds having two distinct polymerizable groups (e.g., vinyl ether groups and acrylate groups) allows for the manufacture of low-migration, UV-curable inkjet inks for inkjet printing on food packaging and toys. Preferred UV-curable inkjet inks for inkjet printing on food packaging materials comprise the aforementioned photoinitiator or photoinitiator mixture and a polymerizable composition consisting of: a) 25-100% by weight of one or more polymerizable compounds A having at least one acrylate group and at least one second polymerizable group selected from vinyl ether groups, allyl ether groups, and allyl ester groups; b) 0-55% by weight of one or more polymerizable compounds B selected from monofunctional and difunctional acrylates; and c) 0-55% by weight of one or more polymerizable compounds C selected from trifunctional, tetrafunctional, pentafunctional, and hexafunctional acrylates, provided that if the weight percentage of compound B is >24% by weight, then the weight percentage of compound C is >1% by weight. Furthermore, all weight percentages of A, B, and C are based on the total weight of the polymerizable composition of the UV-curable inkjet ink.

[0066] Instead of monofunctional or polyfunctional acrylates, their methacrylate analogues can also be used. For certain applications, acrylates are preferred over acrylates. For example, when the substrate is textiles worn directly on human skin, the use of acrylates may cause skin sensitization.

[0067] Another preferred alternative radical curing chemistry is so-called thiol-ene and thiol-yne chemistry. In such chemistry, a combination of at least one polyfunctional thiol compound and at least one polyfunctional polymerizable compound is used. The polyfunctional polymerizable compound is preferably a polyfunctional monomer or oligomer having a plurality of polymerizable groups selected from: vinyl, acrylamide, methacrylamide, vinyl carbonate, vinyl ether, vinyl ester, vinyl carbamate, allyl ether, allyl ester, and ynyl. Particularly preferred are polymerizable compounds including allyl ether, vinyl carbonate, and ynyl groups.

[0068] The synthesis of such monomers is disclosed in relevant literature, such as in HURD, Charles D. Vinylation and the Formation of Acylals. Journal of American Chem. Soc. 1956, Vol. 78, No. 1, pp. 104-106; LOBELL, M. et al., Synthesis of hydroxycarboxylic acid vinyl esters. MP Synthesis.1994, Vol. 4, pp. 375-377; LEE, TY et al., Synthesis, Initiation, and Polymerization of Photoinitiating Monomer. Macromolecules. 2005, Vol. 38, No. 18, pp. 7529-7531; ATTA, AM et al., New vinyl ester resins based on rosin for coating applications. React. Funct. Polym. 2006, Vol. 66, pp. 1596–1608; WO 01 / 00634A (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, Volume 3, pp. 123-125.

[0069] Preferred polymerizable oligomers and polymers are urethanes, polyesters, polyethers, polycarbonates, polyurethanes, polyureas, and linear oligomers having the following polymerizable groups: acrylates, methacrylates, vinyl groups, acrylamides, methacrylamides, vinyl carbonates, vinyl ethers, vinyl ester-vinyl urethane groups, and their corresponding olefin and alkyne compounds.

[0070] Particularly preferred monomers are selected from di- or low-functional allyl ethers, di- or low-functional allyl esters, di- or low-functional vinyl ethers, di- or low-functional vinyl esters, and di- or low-functional norbornene derivatives. Typical allyl ethers may be selected from pentaerythritol tetraallyl ether, glycerol triallyl ether, 1,6-hexanediol diallyl ether, cyclohexanediethanol diallyl ether, trimethylolpropane triallyl ether, dipentaerythritol hexaallyl ether, and their ethoxylated and propoxylated derivatives. Typical vinyl ethers may be selected from pentaerythritol tetravinyl ether, glycerol trivinyl ether, 1,6-hexanediol divinyl ether, cyclohexanediethanol divinyl ether, trimethylolpropane trivinyl ether, dipentaerythritol hexavinyl ether, and their ethoxylated and propoxylated derivatives. Typical allyl esters include diallyl bisaccharide, diallyl terephthalate, triallyl trimellitate, tetraallyl pyromellitic acid, triallyl citrate, and diallyl glutarate. Typical vinyl esters include divinyl bisaccharide, divinyl terephthalate, trimellitate, tetravinyl pyromellitic acid, trivinyl citrate, and divinyl glutarate.

[0071] Other photoinitiators and co-initiators UV-curable inkjet inks may include other photoinitiators, which may be Norrish Type I and / or Norrish Type II initiators. Norrish Type I initiators are initiators that split upon excitation, immediately generating initiating radicals. Norrish Type II initiators are photoinitiators activated by photochemical radiation and form radicals by abstracting hydrogen from a second compound, which then becomes the actual initiating radical. This second compound is called a polymerization synergist or co-initiator.

[0072] Suitable Norrish type I and Norrish type II photoinitiators are disclosed in CRIVELLO, JV et al., VOLUME III: Photoinitiators for Free Radical Cationic, 2nd ed., edited by BRADLEY, G., London, UK: John Wiley and Sons Ltd, 1998, pp. 276-293.

[0073] Acylphosphine oxide photoinitiators in UV-curable inkjet inks can be combined with photoinitiators selected from thioxanthone compounds, α-hydroxyalkylbenzene compounds, and carbazole compounds. Such combinations can further improve the curing speed.

[0074] To further enhance photosensitivity, UV-curable inkjet inks may contain one or more co-initiators, also known as polymerization synergists, typically amine synergists.

[0075] Suitable examples of amine synergists can be classified into three groups: 1) Tertiary fatty amines, such as methyldiethanolamine, dimethylethanolamine, triethanolamine, triethylamine, and N-methylmorpholine; (2) Aromatic amines, such as amyl p-dimethylaminobenzoate, 2-n-butoxyethyl 4-(dimethylamino)benzoate, ethyl 2-(dimethylamino)benzoate, ethyl 4-(dimethylamino)benzoate, and 2-ethylhexyl 4-(dimethylamino)benzoate; and (3) Amines esterified with (meth)acrylate, such as dialkylaminoalkyl esters of (meth)acrylate (e.g., diethylaminoethyl acrylate) or N-morpholinoalkyl esters of (meth)acrylate (e.g., N-morpholinoethyl acrylate).

[0076] Based on the total weight of the UV-curable inkjet ink, the UV-curable inkjet ink according to the present invention preferably contains a total amount of 1-25% by weight, more preferably 2-20% by weight of a photoinitiator.

[0077] UV-curable inkjet inks may contain other additives, such as surfactants, dispersants, dispersants, stabilizers, UV absorbers, organic solvents, and water.

[0078] Colorant UV-curable inkjet inks may contain colorants. Colorants can be dyes, pigments, or combinations thereof. Organic and / or inorganic pigments can be used. Colorants are preferably pigments or polymeric dyes, with organic colored pigments being the most preferred. Organic colored pigments generally allow for a much wider color gamut. However, for white and black, inorganic pigments, such as titanium dioxide and carbon black, are preferred.

[0079] Pigments can be black, white, cyan, magenta, yellow, red, orange, purple, blue, green, brown, or mixtures thereof. The colored pigment can be selected from those disclosed in HERBST, Willy et al., Industrial Organic Pigments, Production, Properties, Applications. 3rd ed. Wiley-VCH, 2004. ISBN 3527305769.

[0080] Preferred pigments for cyan inkjet inks are β-copper phthalocyanine pigments, with CI pigment blue 15:3 or 15:4 being particularly preferred.

[0081] For red inkjet inks, the preferred pigments are selected from CI Pigment Red 57 / 1, CI Pigment Red 122, CI Pigment Red 170, CI Pigment Red 175, CI Pigment Red 176, CI Pigment Red 187, CI Pigment Red 188, CI Pigment Red 207, CI Pigment Red 242, CI Pigment Red 254, CI Pigment Red 272 and their mixtures.

[0082] The pigments in the yellow UV-curable inkjet inks are preferably selected from CI Pigment Yellow 74, CI Pigment Yellow 83, CI Pigment Yellow 97, CI Pigment Yellow 110, CI Pigment Yellow 120, CI Pigment Yellow 138, CI Pigment Yellow 150, CI Pigment Yellow 151, CI Pigment Yellow 154, CI Pigment Yellow 155, CI Pigment Yellow 175, CI Pigment Yellow 180, CI Pigment Yellow 181, CI Pigment Yellow 185, CI Pigment Yellow 194, CI Pigment Yellow 213, CI Pigment Yellow 214 and their mixtures.

[0083] The pigment in the magenta UV-curable inkjet ink is preferably CI pigment violet 19 or a mixture thereof.

[0084] The preferred purple pigments are CI pigments 23, 32 and 37.

[0085] The particularly preferred orange pigments are CI Pigment Orange 5, 13, 16, 34, 40, 43, 59, 66, 67, 69, 71 and 73.

[0086] The preferred green pigments are CI Pigment Green 7 and 36.

[0087] The preferred brown pigments are CI pigments Brown 6 and 7.

[0088] In black UV-curable inkjet inks, carbon black pigments are preferred. Suitable black pigments include carbon black, such as Pigment Black 7 (e.g., Carbon Black MA8 from MITSUBISHI CHEMICAL). ® ); obtained from CABOT Co.'s Regal ® 400R, Mogul ® L, Elftex ® 320; or Carbon Black FW18, Special Black 250, Special Black 350, Special Black 550, Printex from DEGUSSA. ® 25. Printex ® 35. Printex® 55. Printex ® 90. Printex ® 150T. In a preferred embodiment, the carbon black pigment used is a pigment having a toluene extractable fraction of less than 0.15% as described in paragraph 5 of Part III of Resolution AP(89)1, published by the Council of Europe on 13 September 1989.

[0089] Inkjet inks can also include mixtures of pigments. For example, in some inkjet ink applications, neutral black inkjet inks are preferred, and can be obtained, for example, by mixing black and cyan pigments into the ink. Pigments can also be combined to expand the color gamut of an ink kit. Inkjet ink kits can also include one or more spot colors. Silver and gold are often desired colors to make products more attractive by giving them a unique look.

[0090] Suitable pigments include mixed crystals of the particularly preferred pigments described above. Mixed crystals are also called solid solutions. For example, under certain conditions, different quinacridones are mixed to form a solid solution, which is very different from both a physical mixture of compounds and the compounds themselves. In a solid solution, the molecules of the components enter the same crystal lattice, usually but not always, into the lattice of one of the components. The X-ray diffraction pattern of the resulting crystalline solid is characteristic of the solid and can be clearly distinguished from the pattern of a physical mixture of the same components in the same proportion. In such a physical mixture, the X-ray patterns of each component can be distinguished, and the disappearance of many of these lines is one of the criteria for the formation of a solid solution. A commercially available example is Cinquasia from SUN CHEMICAL. TM Magenta L 4540.

[0091] The pigment particles in inkjet inks should be small enough to allow the ink to flow freely through the inkjet printing apparatus, especially at the nozzle. It is also desirable to use small particles to maximize color intensity and slow down sedimentation.

[0092] The number-average pigment particle size is preferably between 0.050 and 1 µm, more preferably between 0.070 and 0.300 µm, and particularly preferably between 0.080 and 0.200 µm. Most preferably, the number-average pigment particle size is not greater than 0.150 µm. An average particle size smaller than 0.050 µm is not ideal for reducing lightfastness, but this is mainly because very small pigment particles or individual pigment molecules may still be extracted in food packaging applications.

[0093] The number-average pigment particle size was preferably determined using a Brookhaven Instruments Particle Sizer BI90Plus based on the principle of dynamic light scattering. The ink was then diluted, for example, with ethyl acetate to a pigment concentration of 0.002% by weight. The BI90Plus measurement settings were: 5 runs at 23°C, 90° angle, 635 nm wavelength, and a graph = correction function.

[0094] In the case of white inkjet inks, it is preferable to use pigments with a refractive index greater than 1.60, more preferably greater than 2.00, more preferably greater than 2.50, and most preferably greater than 2.60. White pigments can be used alone or in combination.

[0095] Preferably, titanium dioxide is used in pigments with a refractive index greater than 1.60. Titanium dioxide exists in anatase, rutile, and brookite crystalline forms. Anatase has a relatively low density and is easily ground into fine particles, while rutile has a relatively high refractive index and exhibits high covering power. Any of these can be used in this invention. It is preferred to maximize the use of features and select them according to their intended use. Using anatase, which has low density and small particle size, can achieve excellent dispersion stability, ink storage stability, and sprayability. At least two different crystalline forms can be used in combination. The combined use of anatase and rutile, which exhibits high tinting strength, can reduce the total amount of titanium dioxide, resulting in improved ink storage stability and sprayability.

[0096] For the surface treatment of titanium dioxide, aqueous or vapor-phase treatments can be applied, and alumina-silica treatment agents are commonly used. Alumina-treated or alumina-silica-treated titanium dioxide can be used, preferably in combination with organic surface treatments.

[0097] To achieve an optimal trade-off between hiding power and dispersion stability, the number-average particle diameter of titanium dioxide or other white pigments is preferably 50-500 nm, more preferably 150-400 nm, and most preferably 200-300 nm. Sufficient hiding power cannot be obtained when the average diameter is less than 50 nm, and the storage stability and ejection suitability of the ink tend to deteriorate when the average diameter exceeds 500 nm. The number-average particle diameter is best determined by photon correlation spectroscopy using a 4 mW HeNe laser at a wavelength of 633 nm on diluted samples of colored inkjet inks. A suitable particle size analyzer is a Malvern. TM Nano-S is available from Goffin-Meyvis. Samples can be prepared by adding one drop of ink to a cuvette containing 1.5 mL of ethyl acetate and mixing until a homogeneous sample is obtained. The particle size measured is the average of three consecutive measurements consisting of six 20-second runs.

[0098] Typically, pigments are stabilized in a dispersion medium by dispersants such as polymeric dispersants or surfactants. However, the surface of pigments can be modified to obtain so-called "self-dispersible" or "self-dispersible" pigments, which can be dispersed in a dispersion medium without a dispersant.

[0099] Based on the total weight of the pigment dispersion, the pigment is preferably used in the concentrated pigment dispersion for the preparation of inkjet inks at an amount of 10-40% by weight, more preferably 15-30% by weight.

[0100] In colored inkjet inks, the pigment is preferably present in an amount of 0.1-13.0% by weight. Based on the total weight of the inkjet ink, dark inkjet inks preferably contain 1.5-13.0% by weight, more preferably 1.8-6.0% by weight of colored pigment, while based on the total weight of the inkjet ink, light inkjet inks preferably contain 0.1-1.3% by weight, more preferably 0.3-1.2% by weight of colored pigment.

[0101] Based on the total weight of the inkjet ink, the white inkjet ink preferably contains more than 13.0% by weight, more preferably 15.0-25.0% by weight of white pigment.

[0102] dispersant UV-curable inkjet inks preferably contain dispersants to further improve pigment dispersion properties. For high printing reliability, polymeric dispersants are preferred. Such dispersants improve the reliability of inkjet printing methods due to their typically lower settling velocities, especially when they contain secondary or tertiary amine groups.

[0103] Typical polymer dispersants are copolymers of two monomers, but can contain three, four, five, or even more monomers. The properties of a polymer dispersant depend on both the properties of the monomers and their distribution in the polymer. Copolymer dispersants preferably have the following polymer composition: • Statistically polymerized monomers (e.g., monomers A and B polymerize to form ABBAABAB); • Alternating polymerization of monomers (e.g., monomers A and B polymerize to form ABABABAB); • Monomers that undergo gradient polymerization (e.g., monomers A and B polymerize into AAABAABBABBBB); • Block copolymers (e.g., monomers A and B polymerized into AAAAABBBBBB), in which the block length of each block (2, 3, 4, 5 or even more) is important for the dispersing ability of the polymer dispersant; • Graft copolymers (graft copolymers consist of a polymer backbone and polymer side chains attached to that backbone); and • Mixed forms of these polymers, such as block gradient copolymers.

[0104] The polymer dispersant preferably has a number average molecular weight Mn between 500 and 30,000, and more preferably between 1,500 and 10,000.

[0105] The polymer dispersant preferably has a weight-average molecular weight (Mw) of less than 100,000, more preferably less than 50,000, and most preferably less than 30,000.

[0106] The polymer dispersant preferably has a polydispersity PD of less than 2, more preferably less than 1.75, and most preferably less than 1.5.

[0107] Commercial examples of polymer dispersants are as follows: ·DISPERBYK TM The dispersant is available from BYK CHEMIE GMBH; SOLSPERSE TM The dispersant is available from LUBRIZOL; ·TEGO TM DISPERS TM Dispersant, obtained from EVONIK; ·EDAPLAN TM Dispersant, obtained from MÜNZING CHEMIE; ·ETHACRYL TM Dispersant, obtained from LYONDELL; ·GANEX TM Dispersant, obtained from ISP; DISPEX TM and EFKA TM Dispersant, obtained from BASF; ·DISPONER TM Dispersant, derived from DEUCHEM.

[0108] Particularly preferred polymer dispersants include Solsperse from LUBRIZOL. TM Dispersant, Efka from BASF TM Dispersant, Disperbyk, obtained from BYK CHEMIE GMBH TM Dispersant and Ajisper from AJINOMOTO FINE-TECHNOCo TM Dispersant. A particularly preferred dispersant is Solsperse from LUBRIZOL. TM Dispersants 32000, 35000 and 39000 and Disperbyk from BYK CHEMIE GMBHTM 162.

[0109] Dispersants can be used alone or in combination of two or more.

[0110] Based on the weight of the pigment, the polymer dispersant is preferably used in an amount of 10-200% by weight, more preferably 20-100% by weight, and most preferably 50-90% by weight.

[0111] Dispersing synergists UV-curable inkjet inks may include dispersing synergists to further improve dispersion stability via polymeric dispersants, and thus also improve printing reliability, as less pigment may deposit in the nozzles of the printhead when the inkjet unit is in standby mode.

[0112] Dispersing synergists typically consist of anionic and cationic moieties. The anionic moieties of dispersing synergists exhibit some molecular similarity to colored pigments, while the cationic moieties consist of one or more protons and / or cations to compensate for the charge of the anionic moieties.

[0113] The dispersing synergist is preferably added in a smaller amount than one or more polymeric dispersants. The ratio of polymeric dispersant to dispersing synergist depends on the pigment and should be determined experimentally. Typically, the ratio of polymeric dispersant by weight % to dispersing synergist by weight % is between 2:1 and 100:1, preferably between 2:1 and 20:1.

[0114] Commercially available suitable dispersants include Solsperse from LUBRIZOL. TM 5000 and Solsperse TM 22000.

[0115] Suitable dispersing synergists for diketylpyrrolo-pyrrole pigments, quinacridone pigments or their mixtures include those disclosed in EP 1790698A (AGFA GRAPHICS), EP 1790696A (AGFA GRAPHICS), WO 2007 / 060255 (AGFA GRAPHICS) and EP 1790695A (AGFA GRAPHICS).

[0116] When dispersing CI pigment blue at a ratio of 15:3, it is preferable to use a sulfonated Cu phthalocyanine dispersing synergist, such as Solsperse from LUBRIZOL. TM 5000.

[0117] stabilizer UV-curable inkjet inks can also contain polymerization inhibitors. The presence of polymerization inhibitors prevents polymerization reactions before curing, such as during storage or transportation. This also improves printing reliability because the UV LEDs in the printhead of the inkjet printer are used. UV-curable inkjet inks are typically maintained at higher temperatures, such as 45-55°C.

[0118] Suitable polymerization inhibitors include phenolic antioxidants, hindered amine light stabilizers, phosphorus antioxidants, benzoquinone, hydroquinone and its derivatives, such as hydroquinone monomethyl ether commonly used in (meth)acrylate monomers.

[0119] Examples of phenolic polymerization inhibitors include, but are not limited to, the following substances: p-methoxyphenol, cresol, tert-butylcatechol, di-tert-butyl-p-cresol, hydroquinone monomethyl ether, α-naphthol, 3,5-di-tert-butyl-4-hydroxytoluene, 2,6-di-tert-butyl-4-methylphenol, 2,2'-methylene-bis(4-methyl-6-tert-butylphenol), 2,2'-methylene-bis(4-ethyl-6-butylphenol), and 4,4'-thio-bis(3-methyl-6-tert-butylphenol) and pyrogallol.

[0120] Suitable commercial inhibitors include, for example, Sumilizer. TM GA-80, Sumilizer TM GM and Sumilizer TM GS, manufactured by Sumitomo Chemical Co. Ltd.; Genorad TM 16. Genorad TM 18 and Genorad TM 20, derived from RahnAG; Irgastab TM UV10 and Irgastab TM UV22, Tinuvin TM 460 and CGS20, from Ciba Specialty Chemicals; Floorstab TM UV series (UV-1, UV-2, UV-5, and UV-8), obtained from Kromachem Ltd; Additol TM The S series (S100, S110, S120 and S130) are from Cytec Surface Specialties.

[0121] The preferred polymerization inhibitor is Irgastab, obtained from BASF. TM UV10. Other examples of polymerization inhibitors include TEMPO, TEMPOL, and the Al copper-iron reagent.

[0122] Polymerization inhibitors can be used alone or in combination of two or more of them.

[0123] In a preferred embodiment, the polymerization inhibitor is a mixture of different types of polymerization inhibitors. Preferred polymerization inhibitors are mixtures of alkyl radical-based polymerization inhibitors, phenol-based polymerization inhibitors, and amine-based polymerization inhibitors. Suitable examples are given in EP 2851402A (FUJIFILM).

[0124] Based on the total weight of the free radical curable inkjet ink, the polymerization inhibitor is preferably present in an amount of 0.1-5% by weight. Below 0.1% by weight, undesirable polymerization cannot be adequately suppressed, while above 5% by weight, the curing rate is significantly reduced.

[0125] surfactants UV-curable inkjet inks may contain surfactants. Surfactants can be anionic, cationic, nonionic, or amphoteric surfactants. Based on the total weight of the free-radical curable inkjet ink, the surfactant is preferably present in an amount of 0.1-3% by weight. At concentrations above 3% by weight, adhesion may deteriorate rapidly, while at concentrations below 0.1% by weight, insufficient ink spreading is typically observed.

[0126] Based on the total weight of the ink, the total amount of surfactant is preferably less than 3% by weight, and more preferably less than 1.5% by weight based on the total weight of the UV-curable inkjet ink, to prevent the ink from foaming in its container. Such foaming has a negative impact on printing reliability.

[0127] Preferred surfactants are selected from fluorinated surfactants (e.g., fluorinated hydrocarbons) and silicone surfactants. Silicone surfactants are preferably siloxanes and may be alkoxylated, polyester-modified, polyether-modified, polyether-modified hydroxyl-functionalized, amine-modified, epoxy-modified, and other modified or combinations thereof. Preferred siloxanes are polymers, such as polydimethylsiloxane.

[0128] Preferred commercial silicone surfactants include BYK from BYK Chemie. TM 333 and BYK TM UV3510 and Tegoglide from EVONIK TM 410.

[0129] In a preferred embodiment, the surfactant is a polymerizable compound.

[0130] Preferred polymerizable silicone surfactants include (meth)acrylated silicone surfactants. Most preferably, (meth)acrylated silicone surfactants are acrylated silicone surfactants because acrylates are more reactive than methacrylates.

[0131] In a preferred embodiment, the (meth)acrylated silicone surfactant is a polyether-modified (meth)acrylated polydimethylsiloxane or a polyester-modified (meth)acrylated polydimethylsiloxane.

[0132] Preferred commercially available (meth)acrylated silicone surfactants include: Ebecryl TM 350, an organosilicon diacrylate derived from Cytec; polyether-modified acrylated polydimethylsiloxane BYK TM UV3500, BYK TM UV3510 and BYK TM UV3530, polyester-modified acrylated polydimethylsiloxane BYK TM UV3570, all manufactured by BYKChemie; Tego TM Rad 2100, Tego TM Rad 2200N, Tego TM Rad 2250N, Tego TM Rad 2300, Tego TM Rad 2500, Tego TM Rad 2600, Tego TM Rad 2700 and Tego TM RC711 is manufactured by EVONIK. Another preferred silicone is Silwet. TM L7500, derived from OSI SPECIALITIES BENELUX NV; Silaplane TM FM7711, Silaplane TM FM7721, Silaplane TM FM7731, Silaplane TM FM0711, Silaplane TM FM0721, Silaplane TM FM0725, Silaplane TM TM0701, Silaplane TMTM0701T, 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.

[0133] The preferred surfactant for free radical inkjet inks is Silmer, derived from SILTECH CORPORATION. ® Surfactants, such as Silmer ® ACR Di-1508.

[0134] Preparation of UV-curable inkjet inks The preparation of UV-curable inkjet inks is well known to those skilled in the art.

[0135] The average particle size and distribution of colored pigments are important characteristics of inkjet inks. Inkjet inks can be prepared by precipitating or grinding pigments in a dispersion medium in the presence of a dispersant.

[0136] Mixing apparatus may include pressure kneaders, open kneaders, planetary mixers, dissolvers, and Dalton Universal Mixers. Suitable grinding and dispersing apparatus includes ball mills, pearl mills, colloid mills, high-speed dispersers, two-roll mills, bead mills, coating conditioners, and three-roll mills. Dispersions may also be prepared using ultrasonic energy or microfluidizers.

[0137] Different types of materials can be used as abrasive media, such as glass, ceramics, metals, and plastics. In a preferred embodiment, the abrasive media may comprise particles, preferably in a substantially spherical shape, such as beads composed substantially of polymer resin or yttrium-stabilized zirconia beads.

[0138] During the mixing, grinding, and dispersing processes, each process is carried out under cooling to prevent heat accumulation and, as far as possible, under light conditions that largely eliminate photochemical radiation.

[0139] Inkjet inks can contain more than one pigment and can be prepared using separate dispersions for each pigment, or alternatively, several pigments can be mixed and co-ground during the preparation of the dispersions.

[0140] The dispersion process can be carried out in continuous, intermittent, or semi-intermittent modes.

[0141] The preferred amounts and ratios of the components in the abrasive will vary depending on the specific material and the intended application. The contents of the abrasive mixture include the abrasive particles and the abrasive media. The abrasive particles contain pigments, polymeric dispersants, and liquid carriers. For inkjet inks, pigments are typically present in the abrasive particles at a weight of 5-50% excluding the abrasive media. The weight ratio of pigment to polymeric dispersant is preferably 20:1 to 1:2, more preferably 2:1 to 1:1.

[0142] The optimal grinding time can vary and depends on the pigment, the mechanical means and the selected residence conditions, the initial and desired final particle size, etc. In this invention, pigment dispersions with an average particle size of less than 100 nm can be prepared.

[0143] After grinding, conventional separation techniques, such as filtration or sieving, are used to separate the grinding media from the ground particulate product (in dry or liquid dispersion form). Typically, sieves are incorporated into the mill, such as a bead mill. Filtration is preferred for separating the ground pigment concentrate from the grinding media.

[0144] Typically, it is desirable to prepare inkjet inks in the form of concentrated pigment dispersions, which are then diluted to a suitable concentration for use in inkjet printing systems. This technique allows for the preparation of larger quantities of colored ink from the equipment. By dilution, the inkjet ink is adjusted to the viscosity, surface tension, color, hue, saturation density, and printing area coverage required for a specific application.

[0145] Cured products Another aspect of the invention is the curing of a UV-curable inkjet ink formed according to the invention via UV LED curing. Compared to conventionally used UV-curable compositions containing acylphosphine oxide TPO-L, this cured product exhibits an improved amount of migratable material and a reduction in unpleasant odor.

[0146] Inkjet printing method The inkjet printing method according to the present invention preferably includes the following steps: a) Printing images onto a substrate using UV-curable inkjet inks as defined above; and b) Use a UV light-emitting diode with an emission wavelength of 360 nm or greater for curing.

[0147] In a preferred embodiment of the inkjet printing method, images are printed in a single pass in a single-pass inkjet unit or in a double pass in a multi-pass inkjet unit. The improved UV LED curing sensitivity of inkjet inks allows for high-speed printing without the need for large, expensive curing units.

[0148] UV curing is preferably performed using a UV LED with an emission wavelength greater than 360 nm, preferably greater than 370 nm, and most preferably between 390 and 400 nm.

[0149] UV-curable inkjet ink is sprayed in a controlled manner through nozzles onto a substrate that moves relative to one or more printheads, ejecting small droplets. A piezoelectric printhead is the preferred printhead for inkjet printing systems. Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied. The application of voltage alters the shape of the piezoelectric ceramic transducer in the printhead, creating a void, which is then filled with inkjet ink. When the voltage is removed again, the ceramic expands back to its original shape, ejecting ink droplets from the printhead. In industrial printing, piezoelectric printheads have proven to be the most reliable printheads.

[0150] The preferred piezoelectric printhead is the so-called push-mode piezoelectric printhead, which has a fairly large piezoelectric element that is also capable of ejecting high-viscosity ink droplets. Such a printhead is available from RICOH with the GEN5s printhead.

[0151] The preferred piezoelectric printhead is the so-called flow-through piezoelectric on-demand inkjet printhead. Such printheads are available from TOSHIBA TEC with CF1 printheads. Flow-through printheads are preferred because they enhance the reliability of inkjet printing due to ink circulation within the printhead.

[0152] The inkjet printhead preferably scans laterally back and forth across the moving ink-receiving surface. The printhead may not print on its return journey, but bidirectional printing is preferred for achieving high area throughput. To maximize high area throughput, an alternative printing method known as the "single-pass printing method" can be used, which can be achieved by using a page-width inkjet printhead or multiple staggered inkjet printheads covering the entire width of the ink-receiving surface. In the single-pass printing method, the inkjet printhead typically remains stationary while the ink-receiving surface is conveyed beneath it.

[0153] However, UV-curable inkjet inks are used in multi-pass printing. Multi-pass printing is a technique used to reduce banding in inkjet printing. When ink droplets are still in liquid form, they tend to flow together due to surface tension. This is called coalescence. For high-quality images, it is important to print individual dots. However, to achieve fully saturated colors, the dots must overlap to completely cover the substrate. Coalescence can be largely avoided by printing only a portion of the image data to avoid printing adjacent dots simultaneously during each printing cycle. Furthermore, by avoiding all horizontal adjacency, the lateral speed of the printing machine can be increased to twice the rated printing speed of the print head. In a preferred embodiment, the number of passes used is 2-6, more preferably no more than 4.

[0154] The advantage of using multi-pass printing is that UV-curable inkjet inks are cured in a continuous pass, rather than in a single pass requiring a curing unit with high UV output. Printhead life is also longer with multi-pass printing. While a single side ejector is sufficient for an entire printhead in single-pass printing, multiple side ejectors and even failures can be tolerated in multi-pass printing. Furthermore, multi-pass printers are generally much less expensive, especially for wide-format substrates.

[0155] To facilitate curing, inkjet printers may include one or more oxygen-consuming units. These units contain a cover of nitrogen or other relatively inert gases (such as CO2) with adjustable position and concentration to reduce the oxygen concentration in the curing environment. Residual oxygen levels are typically maintained as low as 200 ppm, but are generally in the range of 200 ppm to 1200 ppm. Example

[0156] method 1. TLC-MS The molecular weight was determined using TLC-MS according to the following procedure. TLC was performed under the conditions given in the synthesis examples. CAMAG was used. TM TLC-MS interface for analyzing TLC, this interface is provided by Agilent TM 1100 HPLC pump with AmaZon TM An SL mass spectrometer (supplied by BRUKER DALTONICS) was coupled. First, a blank spectrum was obtained by eluting the spots on a TLC plate where no compound was present using a solution of 0.01 mol ammonium acetate in methanol. Then, a second spectrum of the compound to be analyzed was obtained by eluting the spots of the compound under consideration using the same solution. The spectrum of the compound to be analyzed was obtained by subtracting the first spectrum from the second spectrum.

[0157] 2. Curing properties The photocurable composition was applied to a PET175 substrate using a doctor blade coater and a 20 µm wire-wound bar. Samples were obtained from Aktiprint. TM Curing is performed at full power and a linear curing speed of 10 m / min on the mini duo LED curing station. The number of passes required to achieve complete curing (including surface curing) is used as a measure of curing speed, with a maximum of 10 passes. For good curability, it is preferable to require no more than 3 passes.

[0158] According to Table 2, surface curing is checked by wiping the surface of the cured sample five times with a cotton swab.

[0159] Table 2 Surface curing fraction observe 0 No visual impairment 1 Changes in surface gloss 2 Clear surface damage 3 The coating was damaged 4 Almost completely remove the coating 5 The coating was completely removed during wiping. 3. Odor After UV LED curing, two people directly evaluated the odor in the curability test and compared it with a sample containing TPO-L (CASRN84434-11-7).

[0160] Evaluation is conducted by assigning scores based on the following criteria in Table 3.

[0161] Table 3 Odor score standard A Compared to samples containing TPO-L, an odorless improvement can be identified. B Some improvements in the ability to detect unpleasant odors compared to samples containing TPO-L. C A noticeable improvement in odor was discernible compared to samples containing TPO-L. 4. Average particle size The average particle size of the pigment dispersion was determined by photon correlation spectroscopy using a 4mW HeNe laser at a wavelength of 633 nm on diluted samples. The particle size analyzer used was a Malvern, available from Goffin-Meyvis. TM nano-S. The sample was prepared by adding one drop of the dispersion to a cuvette containing 1.5 mL of ethyl acetate and mixing until a homogeneous sample was obtained. The particle size was measured as the average of three consecutive measurements consisting of six 20-second runs.

[0162] Material Prepared according to the method described in WO 2017 / 191043 (AGFA GRAPHICS) P -(3-amino-2,4,6-trimethylbenzoyl)- P - Ethyl phenyl hypophosphite (CASRN2143083-29-6).

[0163] 3-[(diphenyloxyphosphino)carbonyl]-2,4,6-trimethylaniline (CASRN2771298-79-2) was prepared according to the method described in WO 2022 / 106100 (AGFA).

[0164] Glutaroyl dichloride, diglycoloyl dichloride, and 2-ethoxyacetyl chloride are supplied by TCI Europe.

[0165] Methoxyacetyl chloride is supplied by ABCR GmbH.

[0166] TPO-L (CASRN84434-11-7) is supplied by IGM as Omnirad TPO-L.

[0167] Silwet TM L7500 is a silicone-based wetting agent supplied by Momentive Performance Materials GmbH.

[0168] Genomer TM 2253 is an acrylated amine oligomer supplied by Rahn.

[0169] VEEA is 2-(2-vinyloxyethoxy)ethyl acrylate, a bifunctional monomer available from NIPPON SHOKUBAI, Japan.

[0170] DPGDA is dipropylene glycol diacrylate, which can be used as a sartomer. TM SR508 was obtained from ARKEMA.

[0171] PET175 is a 175 pm thick unsubbed polyethylene terephthalate sheet, available from AGFA-GEVAERT NV as Astera™ type UR175.334.

[0172] COMPINI-1 is a contrast photoinitiator prepared as follows: 6.63 g (20 mmol) P -(3-Amino-2,4,6-trimethylbenzoyl) P Ethyl phenylphosphinate was dissolved in 40 ml of ethyl acetate. A solution of 3.3 g (24 mmol) potassium carbonate in 50 ml of water was added to... P -(3-Amino-2,4,6-trimethylbenzoyl) P In an ethyl acetate solution of ethyl phenylphosphine, here P -(3-amino-2,4,6-trimethylbenzoyl)- P 1-Ethyl phenylphosphinate was completely dissolved. The reaction mixture was cooled to 5°C, and 1.74 g (10.3 mmol) of glutaryl dichloride was added dropwise over five minutes while the mixture was vigorously stirred. The temperature was kept below 10°C during the addition. The cooling was removed, and the reaction was allowed to continue at room temperature for two hours. The ethyl acetate phase was separated, extracted with 50 ml of 0.5 M sodium chloride aqueous solution, and dried over MgSO4, where COMPINI-1 began to crystallize from the medium. MgSO4 was removed by adding 400 ml of water. Undissolved COMPINI-1 was separated and treated with 200 ml of isopropyl acetate for one hour. After treatment of the residue with isopropyl acetate, COMPINI-1 gradually crystallized from the medium and was separated by filtration as a white crystalline compound. 4 g (yield: 53%) of COMPINI-1 (melting point: 132°C, in TLC silica gel 60 RP-18 F supplied by Merck) was separated. 254TLC analysis on S plate, eluent MeOH / 0.5 M NaCl: 70 / 30, R f (0.21). The structure of COMPINI-1 was further confirmed using TLC-MS.

[0173] COMPINI-2 is a contrast photoinitiator prepared as follows: 6.6 g (20 mmol) P -(3-Amino-2,4,6-trimethylbenzoyl) P Ethyl phenylphosphinate was suspended in 40 ml of ethyl acetate. A solution of 3.3 g (24 mmol) of potassium carbonate in 50 ml of water was added. After adding the potassium carbonate solution, P -(3-amino-2,4,6-trimethylbenzoyl)- P Ethyl phenylphosphinate was dissolved. The reaction mixture was cooled to 5°C. 2.5 g (32 mmol) of acetyl chloride was added over five minutes while the mixture was vigorously stirred and the temperature was maintained between 5 and 10°C. The cooling was removed, and the reaction mixture was allowed to gradually reach room temperature. The ethyl acetate phase was separated, extracted with 50 mL of 0.5 M sodium chloride aqueous solution, dried over MgSO4, and evaporated under reduced pressure. 7.1 g (yield: 95%) of COMPINI-2 was separated. The solution was then processed on TLC silica gel 60 RP-18 F supplied by Merck. 254 COMPINI-2 was analyzed by TLC on an S plate (eluent: MeOH / 0.5 M NaCl, R f (0.4). The structure of COMPINI-2 was further confirmed using TLC-MS.

[0174] COMPINI-3 is a contrast photoinitiator prepared as follows: 7.27 g (20 mmol) of 3-[(diphenyloxyphosphino)carbonyl]2,4,6-trimethylaniline was dissolved in 40 mL of ethyl acetate. A solution of 3.3 g (24 mmol) of potassium carbonate in 50 mL of water was added to the ethyl acetate solution of 3-[(diphenyloxyphosphino)carbonyl]2,4,6-trimethylaniline, where 3-[(diphenyloxyphosphino)carbonyl]2,4,6-trimethylaniline was completely dissolved in ethyl acetate. The reaction mixture was cooled to 10 °C, and 1.74 g (10.3 mmol) of glutaryl dichloride was added dropwise over five minutes while the mixture was vigorously stirred. The temperature was kept below 12 °C during the addition. The cooling was removed, and the reaction was continued at room temperature for one hour. COMPINI-3 crystallized from the medium and separated by filtration. The crystallized COMPINI-3 was washed with ethyl acetate and dried. 5.9 g (yield: 67%) of COMPINI-3 (melting point: 158 °C) was isolated in TLC silica gel 60 F supplied by Merck. 254 TLC analysis on the plate, eluent: dichloromethane / methanol 95 / 5, R f (0.14).

[0175] PB15:4 is used for Sunfast TM Blue 15:4 is an abbreviation for a CI pigment derived from Sunchemical Corporation.

[0176] DB162 is used in the polymer dispersant Disperbyk. TM The abbreviation 162 is available from BYKCHEMIE GMBH, which removes the solvent mixture of 2-methoxy-1-methylethyl acetate, xylene, and n-butyl acetate. The polymer dispersant is a polyester-polyurethane dispersant based on caprolactone and toluene diisocyanate, with an amine value of 13 mg KOH / g, Mn of approximately 4,425, and Mw of approximately 6,270.

[0177] INHIB is a mixture that forms a polymerization inhibitor with the composition according to Table 4: Table 4 Components weight% DPGDA 82.4 p-Methoxyphenol 4.0 BHT 10.0 <![CDATA[Cupferron TM AL]]> 3.6 BHT is an abbreviation for 2,6-di-tert-butyl-4-methylphenol (CASRN128-30-0), derived from ALDRICHCHEMICAL Co.

[0178] Cupferron TM AL is N-nitrosophenylhydroxylamine aluminum, obtained from WAKO CHEMICALS LTD.

[0179] Example 1 This embodiment illustrates the synthesis of the photoinitiator according to the present invention.

[0180] Synthesis of photoinitiator INI-1 6.63 g (20 mmol) P -(3-Amino-2,4,6-trimethylbenzoyl) P Ethyl phenylphosphinate was dissolved in 40 ml of ethyl acetate. A solution of 3.3 g (24 mmol) potassium carbonate in 40 ml of water was added to... P -(3-Amino-2,4,6-trimethylbenzoyl) P The mixture was cooled to 2°C, and 2.66 g (24 mmol) of methoxyacetyl chloride was added dropwise over 10 minutes while the mixture was vigorously stirred. The temperature was kept below 10°C during the addition. The cooling was removed, and the reaction was allowed to continue at room temperature for 30 minutes. The ethyl acetate phase was separated, extracted with 50 mL of 0.5 M sodium chloride aqueous solution, dried over MgSO4, and evaporated under reduced pressure. 7.6 g (yield: 94%) of INI-1 was separated as a viscous oil (on TLC silica gel 60 F supplied by Merck). 254 TLC analysis on plate, eluent: ethyl acetate, R f (0.23). The structure of INI-1 was further confirmed using TLC-MS.

[0181] Synthesis of photoinitiator INI-2 7.27 g (20 mmol) of 3-[(diphenyloxyphosphino)carbonyl]2,4,6-trimethylaniline was dissolved in 40 mL of ethyl acetate. A solution of 3.3 g (24 mmol) of potassium carbonate in 40 mL of water was added to the ethyl acetate solution of 3-[(diphenyloxyphosphino)carbonyl]2,4,6-trimethylaniline, where 3-[(diphenyloxyphosphino)carbonyl]2,4,6-trimethylaniline was completely dissolved in ethyl acetate. The reaction mixture was cooled to 10 °C. 1.76 g (10.3 mmol) of diethanolamide was added dropwise over 2 minutes while the mixture was vigorously stirred. The temperature was kept below 12 °C during the addition. The cooling was removed, and the reaction was continued at room temperature for two hours. The ethyl acetate phase was separated, extracted with 50 mL of 0.5 M sodium chloride aqueous solution, dried over MgSO4, and evaporated under reduced pressure. 7.9 g of crude INI-2 was separated. INI-2 was purified by preparative column chromatography on a Prochrom LC80 column on Kromasil Si 60 Å 10 µm silica, using a gradient elution from ethyl acetate to ethyl acetate / methanol 96 / 4. 3.85 g (yield: 47%) of INI-2 was separated (on TLC silica gel 60 F supplied by Merck). 254 On-plate TLC analysis, eluent: dichloromethane / methanol 95 / 5, R f (0.19).

[0182] Synthesis of photoinitiator INI-3 7.27 g (20 mmol) of 3-[(diphenyloxyphosphino)carbonyl]2,4,6-trimethylaniline was dissolved in 40 mL of ethyl acetate. A solution of 3.3 g (24 mmol) of potassium carbonate in 50 mL of water was added to the ethyl acetate solution of 3-[(diphenyloxyphosphino)carbonyl]2,4,6-trimethylaniline, where 3-[(diphenyloxyphosphino)carbonyl]2,4,6-trimethylaniline was completely dissolved in ethyl acetate. The reaction mixture was cooled to 10 °C. 3 g (24 mmol) of 2-ethoxyacetyl chloride was added dropwise over 2 minutes while the mixture was vigorously stirred. The temperature was kept below 12 °C during the addition. The cooling was removed, and the reaction was continued at room temperature for one hour. The ethyl acetate phase was separated, extracted with 50 mL of 0.5 M sodium chloride aqueous solution, and dried over MgSO4. INI-3 partially crystallized on MgSO4. MgSO4 was treated with 100 mL of dichloromethane. Ethyl acetate and dichloromethane fractions were combined and evaporated under reduced pressure. 8 g (yield: 89%) of INI-3 was separated (on a TLC silica gel 60F supplied by Merck). 254 TLC analysis on plate, eluent: ethyl acetate, Rf 0.23; Melting point: 50℃).

[0183] Synthesis of photoinitiator INI-4 6.63 g (20 mmol) P -(3-Amino-2,4,6-trimethylbenzoyl) P Ethyl phenylphosphinate was dissolved in 40 ml of ethyl acetate. A solution of 3.3 g (24 mmol) of potassium carbonate in 50 ml of water was added to the ethyl acetate phase. P -(3-Amino-2,4,6-trimethylbenzoyl) P 1-Ethyl phenylphosphite was completely dissolved. The reaction mixture was cooled to 10°C, and 1.76 g (10.3 mmol) of diethanolyl dichloride was added dropwise over 2 minutes while the mixture was vigorously stirred. The temperature was kept below 12°C during the addition. The cooling was removed, and the reaction was continued at room temperature for one hour. The ethyl acetate phase was separated, extracted with 50 mL of 0.5 M sodium chloride aqueous solution, dried over MgSO4, and evaporated under reduced pressure. 7.4 g (yield: 97%) of INI-2 was separated as a grayish-white solid (melting point: 90°C, on TLC silica gel 60 RP-18 F supplied by Merck). 254 TLC analysis on S-plate, eluent: MeOH / 0.5 M NaCl 70 / 30: R f : 0.2).

[0184] Synthesis of photoinitiator INI-6 6.63 g (20 mmol) P -(3-Amino-2,4,6-trimethylbenzoyl) P Ethyl phenylphosphinate was dissolved in 40 ml of ethyl acetate. A solution of 3.3 g (24 mmol) of potassium carbonate in 50 ml of water was added to the ethyl acetate phase. P -(3-Amino-2,4,6-trimethylbenzoyl) P1-Ethyl phenylphosphite was completely dissolved. The reaction mixture was cooled to 10°C, and 3 g (24.5 mmol) of 2-ethoxyacetyl chloride was added dropwise over 2 minutes while the mixture was vigorously stirred. The temperature was kept below 12°C during the addition. The cooling was removed, and the reaction was continued at room temperature for one hour. The ethyl acetate phase was separated, extracted with 50 mL of 0.5 M sodium chloride aqueous solution, dried over MgSO4, and evaporated under reduced pressure. 8.3 g (yield: 100%) of INI-6 was separated as a yellow, viscous oil (on TLC silica gel 60 F supplied by Merck). 254 TLC analysis on plate, eluent: ethyl acetate, R f (0.35).

[0185] Example 2 This embodiment illustrates that, compared to the common industrial acylphosphine oxide TPO-L, the photoinitiator according to the present invention provides good formulation freedom and improved curing sensitivity.

[0186] Preparation of UV LED Curable Inkjet Ink Comparative Examples COMP-1 to COMP-4 and Examples INV-1 to INV-5 of the present invention were prepared by mixing the components according to Tables 5 and 6. Weight percentages (wt%) are based on the total weight of the LED-curable inkjet inks. The weight % of the photoinitiator was selected such that the molar amount of the acylphosphine oxide moiety was the same in all UV-curable inkjet inks.

[0187] Table 5 weight % COMP-1 COMP-2 COMP-3 COMP-4 TPO-L 7.8 - - - COMPINI-1 - 9.2 - - COMPINI-2 - - 9.1 - COMPINI-3 - - - 9.9 <![CDATA[Genomer TM 2253]]> 8.9 8.9 8.9 8.9 <![CDATA[Silwet TM L7500]]> 1.0 1.0 1.0 1.0 VEEA 82.3 80.9 81 80.2 Table 6 weight % INV-1 INV-2 INV-3 INV-4 INV-5 INI-1 9.7 - - - - INI-2 - 9.9 - - - INI-3 - - 10.7 - - INI-4 - - - 9.2 - INI-6 - - - - 10 <![CDATA[Genomer TM 2253]]> 8.9 8.9 8.9 8.9 8.9 <![CDATA[Silwet TM L7500]]> 1.0 1.0 1.0 1.0 1.0 VEEA 80.4 80.2 79.4 80.9 80.1 Results and Evaluation The curability and odor of UV-curable inkjet inks COMP-1 to COMP-4 and INV-1 to INV-5 were determined. The results are shown in Table 7.

[0188] Table 7 sample Number of times Surface curing odor COMP-1 4 0 refer to COMP-2 10 5 C COMP-3 10 3 B COMP-4 10 5 C INV-1 2 0 B INV-2 2 0 C INV-3 3 0 B INV-4 2 0 C INV-5 2 0 B It should be immediately clear from Table 7 that only the UV-curable inkjet inks INV-1 to INV-5 exhibit improved curability. The only difference between the UV-curable inkjet inks COMP-1 and INV-4 is the presence of ether groups in the photoinitiator of UV-curable inkjet ink INV-4. The same is true when comparing the UV-curable inkjet inks COMP-3 and INV-2. The ether functional groups in the photoinitiators of UV-curable inkjet inks INV-1 and INV-5 also provide improved curability compared to structurally similar photoinitiators in UV-curable inkjet inks COMP-1 and COMP-3.

[0189] The UV-curable inkjet inks INV-2 and INV-4 showed a significant improvement in odor when the photoinitiator was a compound according to formula (2). It is believed that by linking the two monoacylphosphine oxide moieties together via their acyl groups, the molecular weight of the acyl radicals is slightly increased, thus reducing the volatile degradation products of the acylphosphine oxide photoinitiator and also increasing the likelihood of incorporation into the polymerization network, as a single photoinitiator generates multiple interconnected acyl radicals. The latter also helps to address migration issues.

[0190] Example 3 This embodiment illustrates inkjet printing of photocurable inkjet inks including photoinitiators according to the present invention.

[0191] Preparation of concentrated cyan dispersion DISP-C A concentrated cyan pigment dispersion was prepared by mixing the components according to Table 8 for 30 minutes using a DISPERLUX™ disperser from DISPERLUX SARL, Luxembourg. The container was then connected to a Bachofen DYNOMILL™ ECM Poly mill with an internal volume of 8.2 L, filled with 42% yttria-stabilized zirconia beads. The mixture was circulated in the mill at a flow rate of approximately 8 L / min for a residence time of 38 min. After milling, the dispersion was separated from the beads using a 1 µm filter. The average particle size of the pigment in the concentrated cyan pigment dispersion DISP-C was measured to be 89 nm.

[0192] Table 8 Components weight% PB15:4 25 DB162 10 INHIB 1 DPGDA 64 Preparation of Cyan Inkjet Ink Using Dimatix TM 10 pl printhead, from Synaps, obtained from AGFA TMComparative ink C-1 and the ink I-1 of this invention were jetted onto an OM135 / AP. A jetting frequency of 5 kHz and a jetting voltage of 31 V were used. The jetting temperature of each inkjet ink was adjusted until all nozzles were jetting, as shown in Table 9 below.

[0193] Table 9 Inkjet ink Injection temperature (°C) C-1 35 I-1 45 Printed samples were cured using a Fusion DRSE-120 conveyor equipped with a Unijet™ i24511 UV LED module from USHIO. The conveyor transported the samples on a conveyor belt at a speed of 20 m / min under UV lamps. The UV LEDs were used at full power. After one pass, the degree of curing was evaluated by wiping the samples 10 times with a cotton swab, and surface damage was assessed. Surface damage was scored according to Table 10. Table 10 Surface curing fraction observe 0 No visual impairment 1 The change in surface gloss did not leave any ink marks on the cotton swab. 2 Clear surface damage, with clear ink stains on the cotton swab. 3 The entire ink layer was destroyed. 4 Almost completely removes the ink layer 5 Remove the ink layer completely during wiping. The surface damage evaluation of COMP-1 ink and INV-1 ink of the present invention is summarized in Table 11.

[0194] Table 11 Inkjet ink Surface damage C-1 1 I-1 1 This evaluation clearly shows that, compared to standard acylphosphine oxide photoinitiators, the ink I-1 containing acylphosphine oxide photoinitiator according to the present invention can be easily sprayed using a standard piezoelectric printhead without loss of curing sensitivity. Furthermore, no photo-induced yellowing problem was observed.

Claims

1. An acylphosphine oxide photoinitiator having an ether group, hydroxyl group, or tertiary amine group on an acyl group of a monoacylphosphine oxide moiety connected via a carbon chain of 1-3 carbon atoms.

2. The acylphosphine oxide photoinitiator according to claim 1, wherein it is a compound according to formula (1): Equation (1), where R1 is selected from alkyl, aryl, and alkoxy groups; R2 and R3 are independently selected from hydrogen, alkyl, alkenyl, alkynyl, and aryl or heteroaryl; R4 is selected from hydrogen, alkyl, alkenyl, alkynyl, aryl or heteroaryl, (meth)acrylate, vinyl ether, allyl ether and monoacylphosphine oxide moiety according to formula (1-1); R5 and R6 are independently selected from hydrogen, alkyl, alkenyl, alkynyl and aryl or heteroaryl, and one of R5 and R6 may represent the monoacylphosphine oxide moiety according to formula (1-1), or R5 and R6 may represent the atoms required to form a 5-8 membered ring; R7 is selected from aryl or heteroaryl and OR9; R8 indicates aryl or heteroaryl; R9 is selected from hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl; X is selected from O and NR 10 ; R 10 Selected from alkyl, alkenyl, ynyl, aryl, or heteroaryl groups; n is an integer selected from 1 to 3; and The monoacylphosphine oxide portion according to formula (1-1) is: Equation (1-1), Where R 11 and R 12 It is independently selected from hydrogen, alkyl, alkenyl, ynyl, and aryl or heteroaryl; R* is the coupling site of R4, R5, or R6 with the photoinitiator; and m is an integer selected from 1 to 3.

3. The acylphosphine oxide photoinitiator according to claim 2, having a structure according to formula (1-2) or (1-3): Equation (1-2), Equation (1-3), R4 to R6 and n are as defined for compounds according to formula (1).

4. The acylphosphine oxide photoinitiator according to claim 1 or 2, having a structure according to formula (2): Equation (2), Among them, R1 to R 12 X, n and m are as defined for compounds according to formula (1).

5. The acylphosphine oxide photoinitiator according to claim 1 or 2, wherein the photoinitiator is selected from: ， ， ， ， ， ， ， ， ， ， ， ， and 。 6. A photocurable composition comprising, as necessary components, a photoinitiator according to any one of claims 1-5 and a free radical polymerizable compound.

7. A UV-curable inkjet ink comprising the photocurable composition of claim 6.

8. A UV-curable inkjet ink, wherein, based on the total weight of the UV-curable inkjet ink, the UV-curable inkjet ink comprises, in an amount of 5-20% by weight, the photoinitiator according to any one of claims 1-5.

9. The UV-curable inkjet ink as claimed in claim 7 or 8, further comprising a colored pigment.

10. The UV-curable inkjet ink of claim 9, wherein the colored pigment is a cyan pigment or a white pigment.

11. A UV-curable inkjet ink kit comprising one or more UV-curable inkjet inks according to any one of claims 7-10.

12. The UV-curable inkjet ink kit according to claim 11, comprising: - Cyan UV-curable inkjet ink containing β-copper phthalocyanine pigment; - Red or magenta UV-curable inkjet ink containing pigments selected from the following: CI Pigment Red 57 / 1, CI Pigment Red 122, CI Pigment Red 144, CI Pigment Red 170, CI Pigment Red 175, CI Pigment Red 176, CI Pigment Red 187, CI Pigment Red 188, CI Pigment Red 202, CI Pigment Red 207, CI Pigment Red 242, CI Pigment Red 254, CI Pigment Red 272, CI Pigment Violet 19 and their mixtures; - A yellow UV-curable inkjet ink containing pigments selected from the following: CI Pigment Yellow 74, CI Pigment Yellow 83, CI Pigment Yellow 97, CI Pigment Yellow 110, CI Pigment Yellow 120, CI Pigment Yellow 139, CI Pigment Yellow 138, CI Pigment Yellow 150, CI Pigment Yellow 151, CI Pigment Yellow 154, CI Pigment Yellow 155, CI Pigment Yellow 175, CI Pigment Yellow 180, CI Pigment Yellow 181, CI Pigment Yellow 194, CI Pigment Yellow 213, CI Pigment Yellow 214, and mixtures thereof; and - Black UV-curable inkjet ink containing carbon black pigment; optionally supplemented by white UV-curable inkjet ink containing titanium dioxide pigment and / or colorless UV-curable inkjet ink.

13. A cured product, wherein the cured product is formed by curing one or more UV-curable inkjet inks as defined in any one of claims 7-12 by UV LED.

14. An inkjet printing method comprising the following steps: a) Spraying an image onto a substrate using one or more UV-curable inkjet inks as defined in any one of claims 7-12; and b) The sprayed image is cured by a UV light-emitting diode with an emission wavelength of 360 nm or greater.

15. The inkjet printing method of claim 14, wherein the image is printed in a single pass in a single-pass inkjet apparatus or in a double pass in a multi-pass inkjet apparatus.

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