acyl phosphine oxide photoinitiator

Abstract

Photoinitiator comprising 2 to 6 monoacylphosphine oxide moieties, characterized in that the monoacylphosphine oxide moieties are connected to each other via their acyl groups and at least 2 monoacylphosphine oxide moieties have a different chemical structure in the phosphine oxide moiety.

Description

Technical Field

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

[0002] Photopolymerization is used in many applications, such as inks, adhesive optoelectronics, varnishes and coatings, dental applications, microelectronics, and 3D printing. The light source for photopolymerization technology is evolving from energy-intensive mercury lamps to safer light-emitting diodes (LEDs). Most UV LEDs operate at 395 nm, but the number of industrially available photoinitiators suitable for curing at such wavelengths is quite limited.

[0003] The combination of thioxanthone and amine-based co-initiators results in high curing speeds, but causes significant yellowing of the cured layer, making it suitable for many CMYK printing applications, but not for varnishes and white inks, and sometimes not for cyan and magenta inks.

[0004] Acylphosphine oxides have been found to be highly suitable for curing 395 nm LEDs without these photoyellowing issues. However, the industrial availability of acylphosphine oxides is limited, and there is growing concern about their toxicology. The suitability of bisacylphosphine oxides is generally limited by their solubility in UV-curable formulations, further narrowing the choices as monoacylphosphine oxides are particularly preferred photoinitiators for 395 nm radiation-curable compositions.

[0005] Besides the toxicological concerns and limitations of formulation range, 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. Furthermore, 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 limits the formulation range, 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 of each photoinitiating moiety, affecting both the viscosity of the formulation and the curing rate at the same weight ratio. To maintain the curing rate at an acceptable level, a higher amount of photoinitiator must be added, further affecting the viscosity. The effect on viscosity limits the applicability of the disclosed photoinitiators 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 range without producing odor and without significantly affecting formulation viscosity. Summary of the Invention

[0011] It has now been found that the above problems can be largely solved by photoinitiators comprising multiple monoacylphosphine oxide moieties, wherein the monoacylphosphine oxide moieties are linked to each other via their acyl groups (and therefore not via phosphine oxide groups), and at least two monoacylphosphine oxide moieties have different chemical structures in the phosphine oxide moieties.

[0012] Diacylphosphine oxides can generate two free radicals upon UV exposure, but their solubility is generally limited in UV-curable formulations. The acylphosphine oxide photoinitiator of the present invention also generates two free radicals and exhibits good solubility. Crystallization of the photoinitiator according to the present invention is reduced by using a monoacylphosphine oxide moiety having a different chemical structure in the phosphine oxide moiety. It is believed that the use of chemically distinct monoacylphosphine oxide moieties hinders the stacking into crystals.

[0013] Another advantage of the photoinitiators according to the invention is that they allow for the preparation of low-odor, photocurable compositions. 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 mesitylenebenzaldehyde, causing an unpleasant odor in the cured product. By linking the mono-acylphosphine oxide moieties to each other via their acyl groups, the molecular weight of the acyl radicals increases, 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] When a monoacylphosphine oxide moiety with a different chemical structure in the phosphine oxide moiety is used in the photoinitiator, a surprising improvement in surface curability is observed compared to photoinitiators with the same monoacylphosphine oxide moiety. Acylphosphine oxide photoinitiators typically exhibit good curability to the interior of the polymerizable layer, but not to the surface portion, leading to undesirable tackiness. The photoinitiator of the present invention exhibits surface curability comparable to or even better than that of the industrially commonly used monoacylphosphine oxide photoinitiators TPO and TPO-L.

[0015] Therefore, one object of the present invention is to provide a new class of acylphosphine oxides that has an increased formulation range for low-odor, photocurable compositions and exhibits good surface curing properties.

[0016] Another object of the present invention is to provide a mixture of acylphosphine oxide-based photoinitiators, wherein at least one photoinitiator in the mixture is a photoinitiator according to the present invention.

[0017] Another object of the present invention is to provide a radiation-curable composition, such as a UV-curable ink, comprising at least one photoinitiator according to the present invention.

[0018] When compared with photocurable compositions that include photoinitiators commonly used in industry, the use of photoinitiators according to the invention improves the surface curing of the photocurable composition and / or reduces the odor of the cured product of the photocurable composition.

[0019] These and other objects and advantages of the present invention will become apparent from the detailed description given below. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] Unless otherwise stated, the substituted alkyl group is preferably replaced by a group selected from the following: aryl, heteroaryl, ester group, amide group, ether group, thioether group, ketone group, aldehyde group, sulfoxide group, sulfone group, sulfonate group, sulfonamide group, -Cl, -Br, -I, -OH, -SH, -CN and -NO2.

[0023] Unless otherwise stated, substituted or unsubstituted alkyl groups are preferably C1-C6-alkyl groups.

[0024] Unless otherwise stated, the substituted or unsubstituted alkenyl group is preferably a C2-C6-alkenyl group.

[0025] Unless otherwise stated, the substituted or unsubstituted alkynyl group is preferably C2-C6-alkynyl.

[0026] Unless otherwise stated, substituted or unsubstituted alkoxy groups are preferably C1-C6-alkyl, with methoxy, ethoxy and propoxy groups being particularly preferred.

[0027] The term aryl refers to a monocyclic or polycyclic aromatic ring structure that contains only carbon atoms in its ring structure.

[0028] 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.

[0029] Unless otherwise stated, a substituted aryl group is an aryl group comprising one or more groups selected from aldehyde groups, -Cl, -Br, -I, -OH, -SH, -CN, and -NO2.

[0030] The term heteroaryl refers to a monocyclic or polycyclic aromatic ring containing a carbon atom and one or more heteroatoms, preferably 1 to 4 heteroatoms, in its ring structure, wherein the heteroatoms are independently selected from nitrogen, oxygen, selenium, and sulfur. 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.

[0031] Preferred examples of heteroaryl groups include, but are not limited to, pyridinyl, pyrimidyl, 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.

[0032] Photoinitiator The photoinitiator according to the invention comprises 2-6, preferably 2-4, more preferably 2 or 3, and most preferably 2 monoacylphosphine oxide moieties, wherein the monoacylphosphine oxide moieties are linked to each other via their acyl groups, and wherein at least 2 monoacylphosphine oxide moieties have different chemical structures in the phosphine oxide moieties.

[0033] The photoinitiator preferably has a structure according to formula (1): [A] y –L–[B] x Equation (1), in x and y independently represent integers from 1 to 3; L represents an x+y valence linker with no more than 25 carbon atoms; A represents the acylphosphine oxide portion according to formula (1-1): Equation (1-1), Ar1 and Ar2 independently represent substituted or unsubstituted aryl or heteroaryl groups; R1 is selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted aryl groups, and substituted or unsubstituted alkoxy groups; R2, R3, and R4 are independently selected from the coupling position with L or from substituents selected from hydrogen, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkoxy groups, and substituted or unsubstituted aryl or heteroaryl groups. B represents the acylphosphine oxide portion according to formula (1-2): Equation (1-2), Wherein Ar3 represents a substituted or unsubstituted aryl or heteroaryl group; R5 is selected from substituted or unsubstituted alkyl, substituted or unsubstituted aryl, and substituted or unsubstituted alkoxy groups; R6, R7, and R8 are independently selected from the coupling position with L or from the substituents selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkoxy, and substituted or unsubstituted aryl or heteroaryl groups; R9 represents a substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, and substituted or unsubstituted aryl or heteroaryl group.

[0034] In a preferred embodiment of the photoinitiator according to formula (1), x and y independently represent integers from 1 to 2, and in even more preferred embodiments, both x and y are equal to 1. When x and y are equal to 1, further improved solubility is observed in the photocurable composition.

[0035] In a preferred embodiment, the ratio of the molecular weights of A and B to L satisfies the following equation (Eq-1): (x*Mw(A)+y*Mw(B)) / Mw(L)≥1.5 (Eq-1).

[0036] In a more preferred embodiment, the ratio is 2 or greater. In the most preferred embodiment, the ratio is 2.5 or greater. When the photoinitiator according to the invention conforms to these equations, an excellent formulation range is obtained due to the low effect on viscosity and good solubility observed in the radiation-curable composition.

[0037] In a preferred embodiment of the photoinitiator according to formula (1), the linking group L comprises no more than 15 carbon atoms. In the most preferred embodiment, L comprises no more than 12 carbon atoms. With such a linking group, an excellent formulation range is again obtained due to the low effect on viscosity and good solubility observed in the radiation-curable composition.

[0038] The molecular weight of the photoinitiator according to formula (1) is preferably 700-2,500 g / mol, more preferably 750-2,000 g / mol, and most preferably 800-1,500 g / mol. Within these ranges, the photoinitiator according to formula (1) can be suitably used in conventional amounts in UV-curable inkjet inks without significantly affecting the viscosity of the ink.

[0039] In a preferred embodiment of the photoinitiator according to formula (1), L comprises at least one ether functional group or a tertiary amine group. Surprisingly, higher curing sensitivity is generally observed when the linking group L contains at least one ether functional group or a tertiary amine group.

[0040] In a preferred embodiment of the photoinitiator according to formula (1), the linking group L may consist of one or more segments selected from -CH2-, -CHMe-, -CMe2-, -O-CH2-CH2-, -CH2-O-CH2-, -O-CH2-CH2-O- and -C(=O)-CH2-CH2-C(=O)-; wherein the segments may appear multiple times in the linking group L.

[0041] In a preferred embodiment of the photoinitiator according to formula (1), A represents the acylphosphine oxide moiety, wherein Ar1 and Ar2 represent phenyl, R1 and R3 represent methyl, R2 represents hydrogen, and R4 represents the coupling position with L; and / or B represents the acylphosphine oxide moiety, wherein Ar3 represents phenyl, R5 and R7 represent methyl, R6 represents hydrogen, R8 represents the coupling position with L, and R9 represents ethyl.

[0042] The above preferred embodiments can be combined with each other without any limitation.

[0043] In a further preferred embodiment, the photoinitiator of formula (1) where x and y represent integers 1 is part of a photoinitiator mixture, wherein the mixture comprises photoinitiators according to formulas (1-a), (1-b), and (1-c), wherein groups A, B, and L are as defined for a photoinitiator according to formula (1), wherein Formula (1-a) is ALB, formula (1-b) is ALA, and formula (1-c) is BLB. The mixture preferably contains 20-80 mol% of a photoinitiator according to formula (1-a), more preferably at least 30 mol%, and most preferably at least 40 mol% of a photoinitiator according to formula (1-a). Within these ranges, improved surface curing of inkjet-printed images has been observed compared to ALA or BLB.

[0044] In a further preferred embodiment, the photoinitiator according to the invention is a photoinitiator according to formula (2): Equation (2), in n and m independently represent 0 or 1; x and y independently represent integers from 1 to 3; L1 represents a (x+y) valence linker group having no more than 25 carbon atoms; X and Y independently represent O or NH; A1 represents the acylphosphine oxide portion according to formula (2-1): Equation (2-1), Ar1 and Ar2 independently represent substituted or unsubstituted aryl or heteroaryl groups; R1 is selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted aryl groups, and substituted or unsubstituted alkoxy groups; R2, R3, and R4 are independently selected from the coupling position with N or from substituents selected from hydrogen, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkoxy groups, and substituted or unsubstituted aryl or heteroaryl groups. B1 represents the acylphosphine oxide portion according to formula (2-2): Equation (2-2), Wherein Ar3 represents a substituted or unsubstituted aryl or heteroaryl group; R5 is selected from substituted or unsubstituted alkyl, substituted or unsubstituted aryl, and substituted or unsubstituted alkoxy groups; R6, R7, and R8 are independently selected from the coupling position with N or from the substituents selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkoxy, and substituted or unsubstituted aryl or heteroaryl groups; R9 represents a substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, and substituted or unsubstituted aryl or heteroaryl group.

[0045] In a preferred embodiment of the photoinitiator according to formula (2), n and m are 0, and x and y independently represent integers from 1 to 2. In the most preferred embodiment, n and m are 0, and x and y are equal to 1. When x and y are equal to 1, improved solubility is observed in the photocurable composition.

[0046] In a preferred embodiment of the photoinitiator according to formula (2), the linking group L1 contains no more than 15 carbon atoms. In the most preferred embodiment, L1 contains no more than 12 carbon atoms. With such a linking group, an excellent formulation range is obtained due to the low effect on viscosity and good solubility observed in the radiation-curable composition.

[0047] In a preferred embodiment of the photoinitiator according to formula (2), L1 comprises at least one ether functional group or a tertiary amine group. Surprisingly, higher curing sensitivity is generally observed when the linking group L contains at least one ether functional group or a tertiary amine group.

[0048] In a preferred embodiment of the photoinitiator according to formula (2), the linking group L1 may consist of one or more segments selected from -CH2-, -CHMe-, -CMe2-, -O-CH2-CH2-, -CH2-O-CH2-, -O-CH2-CH2-O- and -C(=O)-CH2-CH2-C(=O)-; wherein the segments may appear multiple times in the linking group L1.

[0049] In a preferred embodiment of the photoinitiator according to formula (2), A represents the acylphosphine oxide moiety, wherein Ar1 and Ar2 represent phenyl, R1 and R3 represent methyl, R2 represents hydrogen, and R4 represents the coupling position with N; and / or B represents the acylphosphine oxide moiety, wherein Ar3 represents phenyl, R5 and R7 represent methyl, R6 represents hydrogen, R8 represents the coupling position with L, and R9 represents ethyl.

[0050] The above preferred embodiments can be combined with each other without any limitation.

[0051] In a further preferred embodiment, the photoinitiator of formula (2) where x and y represent integers 1 is part of a photoinitiator mixture, wherein the mixture comprises photoinitiators according to formulas (2-a), (2-b), and (2-c), wherein the group A' is A-NH-C(=O)-(X). n -, B' is B-NH-C(=O)-(Y) m - and L1 is as defined for a photoinitiator according to formula (2), wherein formula (2-a) is A'-L1-B', formula (2-b) is A'-L1-A', and formula (2-c) is B'-L1-B'. The mixture preferably contains 20-80 mol% of the photoinitiator according to formula (2-a), more preferably at least 30 mol%, and most preferably at least 40 mol% of the photoinitiator according to formula (2-a). Within these ranges, improved surface curing of inkjet-printed images has been observed compared to using only A'-L1-A' or B'-L1-B'.

[0052] Preferred examples of photoinitiators according to the present invention are given in Table 1 below, but are not limited thereto.

[0053] Table 1 In another preferred embodiment, the photoinitiator according to the invention comprises 2-6, preferably 2-4, more preferably 2 or 3, and most preferably 2 monoacylphosphine oxide moieties, wherein the monoacylphosphine oxide moieties are linked to each other via their acyl groups through linking groups, wherein at least two monoacylphosphine oxide moieties have different chemical structures in the phosphine oxide moieties, and wherein the linking groups include radically polymerizable groups. Radically polymerizable groups result in a polymerizable photoinitiator.

[0054] The free radical polymerizable groups are preferably selected from acrylates, methacrylates, acrylamide, methacrylamide, styrene groups, maleate esters, fumarate esters, itaconic acid esters, vinyl ethers, vinyl esters, allyl ethers, and allyl esters. In a preferred embodiment, the free radical polymerizable groups are selected from acrylates and methacrylates, with acrylates being particularly preferred.

[0055] The advantage of linking groups that include polymerizable groups is that they further increase the likelihood that acyl-containing degradation products will be integrated into the polymer network after UV curing, without causing migration problems or unpleasant odors.

[0056] Preferred examples of polymerizable photoinitiators according to the present invention are given in Table 2 below, but are not limited thereto.

[0057] Table 2 PA-1 PA-2 PA-3 PA-4 Photocurable compositions The photocurable composition according to the present invention comprises the above-mentioned photoinitiator and a free radical polymerizable compound as essential components.

[0058] 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, Volumes 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.

[0059] 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.

[0060] Radiation-curable compositions may include other photoinitiators, which may be Norrish type I initiators 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 forming radicals by abstracting hydrogen from a second compound, which becomes the actual initiating radical. This second compound is referred to as a polymerization synergist or co-initiator. Suitable photoinitiators are disclosed in CRIVELLO, JV et al., VOLUME III: Photoinitiators for FreeRadical Cationic, 2nd ed., BRADLEY, G. (ed.), London, UK: John Wiley and Sons Ltd, 1998, pp. 287-294.

[0061] To further increase photosensitivity, the free radical curable composition may additionally contain one or more co-initiators, also known as polymerization synergists, typically amine synergists.

[0062] 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).

[0063] Another preferred embodiment is a photocurable (inkjet) ink comprising a photocurable composition according to the invention. The (inkjet) ink preferably contains a colorant, more preferably a colored pigment.

[0064] Based on the total weight of the photocurable composition or ink, the photocurable composition or photocurable (inkjet) ink according to the present invention preferably contains 1-25% by weight, more preferably 2-20% by weight, of the photoinitiator of the present invention.

[0065] Photocurable compositions or photocurable (inkjet) inks may contain other additives, such as surfactants, dispersants, dispersants, stabilizers, UV absorbers, etc.

[0066] Cured products Another aspect of the invention is the curing of a photocurable composition according to the invention via UV LED curing. Compared to photocurable compositions comprising conventionally used acylphosphine oxides TPO and TPO-L, the cured product exhibits an improvement in the amount of migratable material and a reduction in unpleasant odor.

[0067] Manufacturing method A method for manufacturing a photoinitiator mixture including the photoinitiator according to the present invention comprises the following steps: a) Two monoacylphosphine oxide compounds having different chemical structures in the phosphine oxide moiety and each having a primary amine group or a group according to formula (M-1) attached to the acyl moiety are mixed in a molar ratio of 3:1 to 1:3; and b) React the two monoacylphosphine oxide compounds with a compound in which the two monoacylphosphine oxide compounds are linked via a primary amine group or a group according to formula (M-1); The group according to formula (M-1) is: Equation (M-1), Where Z represents the carbon atom of the aromatic ring in the acyl moiety, and R represents C1-C6-alkyl, preferably ethyl.

[0068] Preferred monoacylphosphine oxide compounds having a primary amine group attached to the acyl moiety are P -(3-amino-2,4,6-trimethylbenzoyl)- P -Ethyl phenylphosphine and 3-[(diphenylphosphino)carbonyl]-2,4,6-trimethylaniline. Example

[0069] method 1. TLC-MS Molecular weight was determined using TLC-MS according to the following procedure. TLC was performed under the conditions given in the synthesis examples. The TLC was conducted using materials from Agilent Technologies. TM 1100 HPLC pump with AmaZon TM SL mass spectrometer (provided by BRUKER DALTONICS) coupled with CAMAG TM TLC-MS interface analysis was performed. First, a blank spectrum was obtained by eluting the spots on the TLC plate where no compound was present with a 0.01 mol ammonium acetate solution in methanol. Then, a second spectrum of the compound to be analyzed was obtained by eluting the spots of the compound under consideration with a 0.01 mol ammonium acetate solution in methanol. The spectrum of the compound to be analyzed was obtained by subtracting the first spectrum from the second spectrum.

[0070] 2. Curing properties The photocurable composition was coated onto a PET175 substrate using a bar 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 curing performance, no more than 3 passes are preferred.

[0071] According to Table 3, surface curing is checked by wiping the surface of the cured sample five times with a Q-tip.

[0072] Table 3 Surface curing fraction observe 0 No visible damage 1 Surface gloss change 2 Clear surface damage 3 The coating was damaged 4 Almost completely removed coating 5 Remove the coating completely 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 (2,4,6-trimethylbenzoyl diphenylphosphine oxide, CASRN75980-60-8).

[0073] Evaluation is conducted by assigning scores based on the criteria in Table 4.

[0074] Table 4 Odor score standard No improvement The lack of improved odor was discernible compared to samples containing TPO. improve The improved odor was discernible compared to samples containing TPO. 4. Average particle size The average particle size of the pigment particles was determined by photon correlation spectroscopy at 633 nm using a 4 mW HeNe laser on diluted samples of the pigment dispersion. The particle size analyzer used was a Malvern™ nano-S, available from Goffin-Meyvis. Samples were prepared by adding one drop of dispersion to a cuvette containing 1.5 mL of ethyl acetate and mixing until a homogeneous sample was obtained. The measured particle size was the average of three consecutive measurements, consisting of six 20-second runs.

[0075] Material Unless otherwise stated, all materials used in the following examples are readily available from standard sources such as Sigma-Aldrich (MERCK) and Acros Organics (THERMOFISHER SCIENTIFIC). Any water used is softened water.

[0076] Amino-TPO-L was prepared according to the method described in WO 2017 / 191043 (AGFA GRAPHICS). P -(3-amino-2,4,6-trimethylbenzoyl)-P - Ethyl phenylphosphinate (CASRN2143083-29-6).

[0077] Amino-TPO is 3-[(diphenyloxyphosphino)carbonyl]-2,4,6-trimethylaniline (CASRN2771298-79-2) prepared according to the method described in WO 2022 / 106100 (AGFA).

[0078] TPO-oxam (CASRN2771298-80-5) is a TPO derivative having the following structure and prepared according to paragraph

[0082] of WO 2022 / 106099 (AGFA): .

[0079] TPO-L-oxam (CASRN2404565-44-0) is a TPO-L derivative having the following structure and prepared according to paragraph

[0220] of WO2019 / 243039 (AGFA): .

[0080] Diethylene glycol bis(chloroformate) is supplied by ABCR GmbH.

[0081] Adipic acid chloride, 3,3,5-trimethyl-hexamethylene-1,6-diisocyanate, and bis(3-aminopropyl)methylamine were supplied by TCI Europe.

[0082] 3,6-Dioxa-1,8-Octadiamine was provided by Aldrich.

[0083] Glutaryl dichloride and diethanolyl dichloride are supplied by TCI Europe.

[0084] TPO (CASRN75980-60-8) is manufactured by IGM under the Omnirad brand. TM TPO is provided.

[0085] TPO-L (CASRN84434-11-7) is manufactured by IGM under the Omnirad brand. TM TPO-L is available.

[0086] Silwet TM L7500 is a silicone-based wetting agent supplied by Momentive Performance Materials GmbH.

[0087] Genomer TM 2253 is an acrylated amine oligomer supplied by Rahn.

[0088] VEEA is 2-(2-vinyloxyethoxy)ethyl acrylate, a bifunctional monomer available from NIPPON SHOKUBAI, Japan.

[0089] DPGDA is dipropylene glycol diacrylate, available from ARKEMA as Sartomer. TM SR508 obtained.

[0090] PET175 is a 175 pm thick uncoated polyethylene terephthalate sheet, available from AGFA-GEVAERT NV as Astera™ type UR175.334.

[0091] The comparative photoinitiator COMPINI-1 was prepared as follows: Dissolve 6.63 g (20 mmol) of amino-TPO-L in 40 ml of ethyl acetate. Add a solution of 3.3 g (24 mmol) of potassium carbonate in 50 ml of water to the amino-TPO-L ethyl acetate solution. P -(3-amino-2,4,6-trimethylbenzoyl)- P ethyl phenylphosphine 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, at which point 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. COMPINI-1 gradually crystallized from the medium upon treatment of the residue with isopropyl acetate 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 provided by MERCK) was separated. 254 TLC 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.

[0092] The comparative photoinitiator COMPINI-2 was prepared as follows: 7.27 g (20 mmol) of amino-TPO 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 amino-TPO, at which point amino-TPO 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-2 (melting point: 158 °C, dissolved in TLC silica gel 60 F provided by MERCK) was separated. 254 TLC analysis on the plate, eluent: dichloromethane / methanol 95 / 5, R f : 0.14).

[0093] The comparative photoinitiator COMPINI-3 was prepared as follows: 7.27 g (20 mmol) of amino-TPO was added to 40 mL of ethyl acetate. A solution of 2.9 g (21 mmol) of potassium carbonate in 20 mL of water was added, and the reaction mixture was stirred. After 3 minutes, 1.92 g (10.2 mmol) of adipic acid chloride was added, at which point the temperature rose to 29 °C. The reaction was allowed to continue at room temperature for 16 hours. COMPINI-3 was separated by filtration, washed with 50 mL of ethyl acetate, and dried. 8.4 g (yield: 100%) of COMPINI-3 was separated (in a Uniplate provided by MILES SCIENTIFIC). TM TLC analysis on Analtech HPTL-RP18F plate: eluent MeOH / 0.5 M NaCl 70 / 30, R f : 0.1).

[0094] The comparative photoinitiator COMPINI-4 was prepared as follows: 6.63 g (20 mmol) of amino-TPO-L was added to 40 mL of ethyl acetate. A solution of 2.9 g (21 mmol) of potassium carbonate in 20 mL of water was added, and the reaction mixture was stirred. 1.92 g (10.2 mmol) of adipic acid chloride was added over 3 minutes, at which point the temperature was raised to 32 °C. The reaction was allowed to continue for 2 hours. An additional 0.5 g (2.7 mmol) of adipic acid chloride was added, and the reaction was allowed to continue for 30 minutes. The organic fraction was separated, washed with 40 mL of 0.5 M sodium chloride solution, and evaporated under reduced pressure. 7.4 g (yield: 96%) of COMPINI-4 (in a Uniplate provided by MILES SCIENTIFIC) was separated. TM TLC analysis on Analtech HPTL-RP18F plate: eluent MeOH / 0.5 M NaCl 70 / 30, R f (0.25).

[0095] PB15:4 is used for Sunfast TM Blue 15:4 is an abbreviation for CI Pigment Blue 15:4 from SUN CHEMICAL CORPORATION.

[0096] DB162 is used in the polymer dispersant Disperbyk. TM The abbreviation 162 is available from BYK CHEMIE GMBH, which removes the solvent mixture of 2-methoxy-1-methylethyl acetate, xylene, and n-butyl acetate. This 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.

[0097] INHIB is a mixture of polymerization inhibitors having a composition according to Table 5: Table 5 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) from ALDRICH CHEMICAL Co.

[0098] Cupferron TM AL is N-nitrosophenylhydroxylamine aluminum from WAKO CHEMICALS LTD.

[0099] Example 1 This embodiment illustrates the synthesis of the photoinitiator according to the present invention.

[0100] Synthesis of INIMIX-1 containing ASYM-2 3.31 g (10 mmol) of amino-TPO-L and 3.63 g (10 mmol) of amino-TPO were added to 40 mL of ethyl acetate. A solution of 3.3 g (24 mmol) of potassium carbonate in 40 mL of water was added, at which point the acylphosphine oxide was completely dissolved. After 5 minutes, a solution of 1.74 g (10.3 mmol) of glutaryl dichloride in 5 mL of ethyl acetate was added, while stirring vigorously. The temperature was kept below 25°C. The reaction was continued at room temperature for one hour. TLC was performed using a Silicagel 60 F TLC system provided by Merck. 254 Eluent: Ethyl acetate, R f (Amino-TPO): 0.25, R f (Amino-TPO L): 0.43) Analyze the reaction mixture. Add an additional 0.17 g (1 mmol) of glutaryl dichloride and allow the reaction mixture to continue at room temperature for 16 hours. Separate the organic fraction, extract with 40 mL of 0.5 M NaCl aqueous solution, dry to MgSO4, and evaporate under reduced pressure. Elute using a gradient from dichloromethane to dichloromethane / methanol 95 / 5, and perform preparative column chromatography on Graceresolver. TM Residual amino-TPO and amino-TPO-L were removed on an 80 g SiOH 40 µm 60 Å column. 4 g (yield: 51%) of INIMIX-1 was isolated (on a Uniplate provided by MILESSCIENTIFIC). TM Analtech HPTLC-RP18F plate TLC analysis: eluent MeOH / 0.5 MNaCl 70 / 30, R f Symmetric-TPO-L: 0.27, R f ASYM-2: 0.19, R f Symmetry-TPO: 0.13). The structure of ASYM-2 was confirmed using TLC-MS.

[0101] Synthesis of INIMIX-2, INIMIX-3 and INIMIX-4 containing ASYM-5 Table 6 sample xgamino-TPO ygamino-TPO-L Yield INIMIX-2 3.63 g (10 mmol) 3.31 g (10 mmol) 7.6 g (96 %) INIMIX-3 5.45 g (15 mmol) 1.66 g (5 mmol) 6.5 g (82 %) INIMIX-4 1.82 g (5 mmol) 4.97 g (15 mmol) 7.5 g (95 %) x g of amino-TPO L and y g of amino-TPO (Table 6) were added to 40 mL of ethyl acetate. A solution of 3.3 g (24 mmol) of potassium carbonate in 40 mL of water was added, at which point the acylphosphine oxide was completely dissolved. After 5 minutes, a solution of 1.76 g (10.4 g) of diethanolamide dichloro in 5 mL of ethyl acetate was added, with vigorous stirring. The temperature was kept below 25 °C. The reaction was continued at room temperature for one hour. TLC analysis confirmed complete conversion (using a Silicagel 60 F TLC unit provided by MERCK). 254 Eluent: Ethyl acetate, R f (Amino-TPO): 0.25, R f (Amino-TPO L): 0.43). The ethyl acetate phase was separated, extracted with 40 mL of 0.5 M NaCl aqueous solution, dried over MgSO4, and evaporated under reduced pressure. Analysis was performed using TLC (on a Uniplate provided by MILES SCIENTIFIC). TM Analtech HPTLC-RP18F plate TLC analysis: eluent MeOH / 0.5 M NaCl 70 / 30, R f Symmetric TPO-L: 0.28, R f ASYM-5: 0.20, R f The separated INIMIX-2 to INIMIX-4 were analyzed by symmetry-TPO (0.13). The structure of ASYM-5 was confirmed by TLC-MS.

[0102] Synthesis of INIMIX-5 containing ASYM-1 3.31 g (10 mmol) of amino-TPO-L and 3.63 g (10 mmol) of amino-TPO were dissolved in 46 g of ethyl acetate. A solution of 3.04 g (12.5 mmol) of potassium carbonate in 20 mL of water was added, and the reaction mixture was stirred. After 30 minutes, a solution of 2.67 g (11 mmol) of diethylene glycol bis(chloroformate) in 5 mL of ethyl acetate was added, while the temperature was increased from 22°C to 25°C. The reaction was allowed to continue for one hour. An additional 0.23 g (1 mmol) of diethylene glycol bis(chloroformate) was added, and the reaction was allowed to continue for another hour. The organic fraction was separated, washed with 40 mL of 0.5 M sodium chloride solution, and evaporated under reduced pressure. 8.7 g (yield: 100%) of INIMIX-5 (in a Uniplate provided by MILES SCIENTIFIC) was separated. TMTLC analysis on Analtech HPTL-RP18F plate: eluent MeOH / 0.5 M NaCl 70 / 30, R f Symmetric-TPO: 0.08, R f ASYM-1: 0.11, R f Symmetrical TPO-L: 0.28).

[0103] Synthesis of INIMIX-6 containing ASYM-4 3.31 g (10 mmol) amino-TPO-L and 3.63 g (10 mmol) amino-TPO were dissolved in 46 g ethyl acetate. A solution of 3.04 g (12.5 mmol) potassium carbonate in 20 mL of water was added, and the reaction mixture was stirred. A solution of 2.2 g (11.5 mmol) adipic acid chloride in 5 mL of ethyl acetate was added over 10 minutes, while maintaining the temperature below 25 °C. The reaction was continued at room temperature for 16 hours. The organic fraction was separated, washed with 40 mL of 0.5 M sodium chloride solution, and evaporated under reduced pressure. 7.8 g (yield: 97%) of INIMIX-6 (in Uniplate provided by MILES SCIENTIFIC) was obtained. TM TLC analysis on Analtech HPTL-RP18F plate: eluent MeOH / 0.5 M NaCl 70 / 30, R f Symmetric-TPO: 0.09, R f ASYM-4: 0.15, R f Symmetrical TPO-L: 0.23).

[0104] Synthesis of INIMIX-7 containing ASYM-8 3.63 g (10 mmol) of amino-TPO and 3.31 g (10 mmol) of amino-TPO-L were dissolved in 30 mL of acetonitrile. 2.21 g (10 mmol) of 3,3,5-trimethyl-hexamethylene-1,6-diisocyanate was added, and the reaction mixture was heated to 63 °C for 20 hours. The reaction mixture was cooled to room temperature, and the INMIX-7 phase was separated from the mixture. The INMIX-7 phase was washed with 30 mL of acetonitrile, 40 mL of ethyl acetate, and 60 mL of methyl tert-butyl ether, and dried. The organic fractions used for washing were combined and evaporated under reduced pressure. Both fractions still contained significant amounts of contaminants and were combined. Preparative column chromatography was performed using a gradient elution from ethyl acetate to ethyl acetate / methanol 75 / 25 in Büchi. TMINIMIX-7 was purified on an NP-Flash column. 4.6 g (yield: 50%) of INIMIX-7 was isolated (on a Uniplate provided by MILES SCIENTIFIC). TM TLC analysis on Analtech HPTL-RP18F plate: eluent MeOH / 0.5 M NaCl 80 / 20, R f Symmetrical TPO: 0.12; R f ASYM-8: 0.18; R f Symmetrical TPO-L: 0.25).

[0105] Synthesis of INIMIX-8 containing ASYM-12 4.31 g (10 mmol) TPO-L-oxam and 4.63 g (10 mmol) TPO-oxam were added to 90 mL of acetonitrile. A solution of 1.53 g (10 mmol) bis(3-aminopropyl)methylamine in 5 mL of acetonitrile was added, and the mixture was heated to 80 °C. The reaction was continued at 80 °C for 20 hours. After cooling to room temperature, a precipitate formed. The precipitate was removed by filtration, and the solvent was evaporated under reduced pressure. 8.4 g of crude INIMIX-8 was separated. Preparative column chromatography was performed using a gradient elution from ethyl acetate to ethyl acetate / methanol 75 / 25 in Büchi. TM INIMIX-8 was purified on an NP-Flash column. 3.5 g (yield: 37%) of INIMIX-8 was isolated (on a Uniplate provided by MILES SCIENTIFIC). TM TLC analysis on Analtech HPTL-RP18F plate: eluent MeOH / 1 M NaCl 80 / 20, R f Symmetric TPO: 0.26; R f ASYM-12: 0.33; R f Symmetrical TPO-L: 0.41).

[0106] Synthesis of INIMIX-9 containing ASYM-13 4.31 g (10 mmol) TPO-L-oxam and 4.63 g (10 mmol) TPO-oxam were added to 90 mL of acetonitrile. A solution of 1.56 g (10 mmol) of 3,6-dioxa-1,8-octanediamine in 5 mL of acetonitrile was added, and the mixture was heated to 75 °C. The reaction was continued at 80 °C for 20 hours. The reaction mixture was concentrated to 20 mL and refluxed for another 20 hours. The solvent was removed under reduced pressure, and the mixture was eluted using a gradient from ethyl acetate to ethyl acetate / methanol 75 / 25, and the solution was analyzed by preparative column chromatography in Büchi. TM INIMIX-9 was purified on an NP-Flash column. 2.6 g (yield: 27%) of INIMIX-9 was isolated (on a Uniplate provided by MILES SCIENTIFIC). TM TLC analysis on Analtech HPTL-RP18F plate: eluent MeOH / 1 M NaCl 80 / 20, R f Symmetrical TPO: 0.25; R f ASYM-13: 0.31; R f Symmetrical TPO-L: 0.39).

[0107] Example 2 This embodiment illustrates that the photoinitiator according to the present invention achieves an optimal balance between formulation range and curing sensitivity, wherein the curing sensitivity is close to that of common industrial acylphosphine oxide initiators TPO and TPO-L.

[0108] Preparation of LED-curable compositions Comparative Examples C-1 to C-4 and Examples I-1 to I-9 of the present invention were prepared by mixing the components according to Tables 7 and 8. Weight % (wt%) is based on the total weight of the LED-curable compositions. The weight % of the photoinitiator was selected such that the molar amount of the acylphosphine oxide moiety was the same in all the photocurable compositions.

[0109] Table 7 Weight % of each component C-1 C-2 C-3 C-4 I-1 I-2 TPO 8.5 - - - - - TPO-L - 7.8 - - - - COMPINI-1 - - 9.2 - - - COMPINI-2 - - - 9.9 - - INIMIX-1 - - - - 9.5 - INIMIX-2 - - - - - 9.6 <![CDATA[Genomer TM 2253]]> 8.9 8.9 8.9 8.9 8.9 8.9 <![CDATA[Silwet TM L7500]]> 1.0 1.0 1.0 1.0 1.0 1.0 VEEA 81.6 82.3 80.9 80.2 80.6 80.5 Table 8 Weight % of each component I-3 I-4 I-5 I-6 I-7 I-8 I-9 INIMIX-3 9.7 - - - - - - INIMIX-4 - 9.4 - - - - - INIMIX-5 - - 10.4 - - - - INIMIX-6 - - - 9.8 - - - INIMIX-7 - - - - 10.6 - - INIMIX-8 - - - - - 11.6 - INIMIX-9 - - - - - - 11.6 <![CDATA[Genomer TM 2253]]> 8.9 8.9 8.9 8.9 8.9 8.9 8.9 <![CDATA[Silwet TM L7500]]> 1.0 1.0 1.0 1.0 1.0 1.0 1.0 VEEA 80.4 80.7 79.7 80.3 79.5 78.5 78.5 Results and Evaluation The curability and odor of the photocurable compositions C-1 to C-4 and I-1 to I-9 were determined. The results are shown in Table 9.

[0110] Table 9 Cured products Photoinitiator Number of times Surface curing Odor of cured products C-1 TPO 1 0 Reference C-2 TPO-L 3 0 No improvement C-3 COMPINI-1 10 5 improve C-4 COMPINI-2 10 5 improve I-1 ASYM-2 2 0 improve I-2 ASYM-5 1 0 improve I-3 ASYM-5 1 0 improve I-4 ASYM-5 1 0 improve I-5 ASYM-1 1 0 improve I-6 ASYM-4 2 0 improve I-7 ASYM-8 3 0 improve I-8 ASYM-12 1 0 improve I-9 ASYM-13 1 0 improve By comparing cured products C-1 to C-4 and I-1, it can be seen that only the photocurable composition I-1 exhibits good curability and improved odor of the cured product. Photocurable compositions C-1 and C-2, containing commonly used TPO and TPO-L respectively, also exhibit good curability, but the cured products have an unpleasant odor. The photoinitiators COMPINI-1 and COMPINI-2 can be called "symmetric" acylphosphine oxides because they both contain two identical acylphosphine oxide moieties, and more specifically, two TPO-L moieties and one TPO moiety, respectively. The photoinitiator ASYM-2 of the photocurable composition I-1 can be called "asymmetric" acylphosphine oxides because it contains one TPO-L moiety and one TPO moiety. Surprisingly, although COMPINI-1, COMPINI-2, and ASYM-2 have the same linking groups, only the asymmetric acylphosphine oxide ASYM-2 provides good curability.

[0111] Compared to ASYM-2 in photocurable composition I-1, curability can be further improved by including ether functional groups in the linking groups, as shown by photoinitiator ASYM-5 in photocurable compositions I-2 to I-4. The amount of photoinitiator ASYM-5 in photocurable compositions I-2 to I-4 appears to have no effect on curability as long as it is present.

[0112] Compared to photocurable compositions I-6 and I-7, which lack ether functional groups in their linking groups, photocurable compositions I-5 and I-9 demonstrate improved curability by including one or more ether groups in their linking groups.

[0113] The photocurable composition I-8 demonstrates that including tertiary amine groups in the linking groups also improves curability.

[0114] No photo-yellowing problem was observed for the photocurable compositions C-1 to C-4 and I-1 to I-9.

[0115] Example 3 This embodiment illustrates that the advantages of the photoinitiator according to the present invention can also be obtained for different monomers in the photocurable composition.

[0116] Preparation of LED-curable compositions Comparative Examples C-5 and C-6, as well as Examples I-10 of the present invention, were prepared by mixing the components according to Table 10. Weight % (wt%) is based on the total weight of the LED-curable compositions. The weight % of the photoinitiator was selected such that the molar amount of the acylphosphine oxide moiety was the same in all the photocurable compositions.

[0117] Table 10 Weight % of each component C-5 C-6 I-10 COMPINI-3 10.2 - - COMPINI-4 - 9.4 - INIMIX-6 - - 9.8 DPGDA 79.9 80.7 80.3 <![CDATA[Genomer TM 2253]]> 8.9 8.9 8.9 <![CDATA[Silwet TM L7500]]> 1.0 1.0 1.0 Results and Evaluation The curability of photocurable compositions C-5, C-6, and I-10 was determined. The results are shown in Table 11.

[0118] Table 11 Cured products Number of times C-5 >10 C-6 10 I-10 1 As can be clearly seen from Table 11, the asymmetric phosphine oxide in photocurable composition I-10 provides superior curability compared to photocurable compositions C-5 and C-6 containing similar symmetric phosphine oxides.

[0119] Example 4 This embodiment illustrates inkjet printing of photocurable inkjet inks including the photoinitiator according to the present invention.

[0120] Preparation of concentrated cyan dispersion DISP-C Concentrated cyan pigment dispersions were prepared using a DISPERLUX™ disperser from DISPERLUX SARL, Luxembourg, by mixing the components according to Table 12 for 30 minutes. 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 minutes. 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 found to be 89 nm.

[0121] Table 12 Components weight% PB15:4 25 DB162 10 INHIB 1 DPGDA 64 Preparation of Cyan Inkjet Ink Comparative inkjet ink COMP-1 and the inkjet inks INV-1 to INV-3 of the present invention were prepared by mixing concentrated cyan pigment dispersion DISP-C with the components shown in Table 13. Weight percentages (wt%) are based on the total weight of the inkjet inks.

[0122] Table 13 Weight % of each component COMP-1 INV-1 INV-2 INV-3 TPO-L 10 - - - INIMIX-4 - 10 - - INIMIX-5 - - 10 - INIMIX-6 - - - 10 DISP-C 15 15 15 15 <![CDATA[Genomer TM 2253]]> 9 9 9 9 VEEA 65 65 65 65 <![CDATA[Silwet TM L7500]]> 1 1 1 1 Evaluation of cyan inkjet ink Using Dimatix TM 10 pl printhead, from Synaps of AGFA TMComparative ink COMP-1 and the inks of the present invention INV-1 to INV-3 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 14 below.

[0123] Table 14 Inkjet ink Injection temperature (°C) COMP-1 35 INV-1 42 INV-2 42 INV-3 41 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 under UV lamps at a speed of 20 m / min. 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 Q-tip and assessing surface damage. Surface damage was scored according to Table 15. Table 15 Surface curing fraction observe 0 No visible damage 1 The surface gloss changed, and no ink marks were left on the Q-tip. 2 Clear surface damage, with clear ink contamination on the Q-tip. 3 All ink layers were destroyed 4 Almost completely removes the ink layer 5 Remove the ink layer completely during wiping. The surface damage evaluation of the comparative ink COMP-1 and the inks INV-1 to INV-3 of the present invention is summarized in Table 16.

[0124] Table 16 Inkjet ink Surface damage COMP-1 1 INV-1 1 INV-2 1 INV-3 1 This evaluation clearly shows that, compared to standard acylphosphine oxide photoinitiators, inks containing the 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. A photoinitiator comprising 2-6 monoacylphosphine oxide moieties, characterized in that... The monoacylphosphine oxide moieties are linked to each other via their acyl groups, and at least two monoacylphosphine oxide moieties have different chemical structures in the phosphine oxide moieties.

2. The photoinitiator of claim 1, wherein the photoinitiator comprises two or three monoacylphosphine oxide moieties.

3. The photoinitiator of claim 1 or 2, wherein the linking groups between the monoacylphosphine oxide moieties include radically polymerizable groups.

4. The photoinitiator according to claim 1 or 2, having a structure according to formula (1): [A] y –L–[B] x Equation (1), in x and y independently represent integers from 1 to 3; L represents a (x+y) valence linker group with no more than 25 carbon atoms; A represents acylphosphine oxide according to formula (1-1): Equation (1-1), in Ar1 and Ar2 independently represent substituted or unsubstituted aryl or heteroaryl groups; R1 is selected from substituted or unsubstituted alkyl, substituted or unsubstituted aryl, and substituted or unsubstituted alkoxy groups; and R2, R3, and R4 are independently selected from the coupling position with L or from the substituents selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy, and substituted or unsubstituted aryl or heteroaryl. B represents the acylphosphine oxide portion according to formula (1-2): Equation (1-2), Ar3 represents substituted or unsubstituted aryl or heteroaryl groups; R5 is selected from substituted or unsubstituted alkyl, substituted or unsubstituted aryl, and substituted or unsubstituted alkoxy groups; R6, R7, and R8 are independently selected from the coupling position with L or from substituents selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy, and substituted or unsubstituted aryl or heteroaryl; and R9 represents a substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, and substituted or unsubstituted aryl or heteroaryl.

5. The photoinitiator as claimed in claim 4, wherein the ratio of the molecular weights of A and B to L satisfies the following equation: (x*Mw(A)+y*Mw(B)) / Mw(L)≥1.

5.

6. The photoinitiator according to claim 1 or 2, having a structure according to formula (2): Equation (2), in n and m independently represent 0 or 1; x and y independently represent integers from 1 to 3; L1 represents a (x+y) valence linker group having no more than 25 carbon atoms; X and Y independently represent O or NH; A1 represents the acylphosphine oxide portion according to formula (2-1): Equation (2-1), Ar1 and Ar2 independently represent substituted or unsubstituted aryl or heteroaryl groups; R1 is selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted aryl groups, and substituted or unsubstituted alkoxy groups; R2, R3, and R4 are independently selected from the coupling position with N or from substituents selected from hydrogen, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkoxy groups, and substituted or unsubstituted aryl or heteroaryl groups. B1 represents the acylphosphine oxide portion according to formula (2-2): Equation (2-2), Wherein Ar3 represents a substituted or unsubstituted aryl or heteroaryl group; R5 is selected from substituted or unsubstituted alkyl, substituted or unsubstituted aryl, and substituted or unsubstituted alkoxy groups; R6, R7, and R8 are independently selected from the coupling position with N or from the substituents selected from hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkoxy, and substituted or unsubstituted aryl or heteroaryl groups; R9 represents a substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, and substituted or unsubstituted aryl or heteroaryl group.

7. The photoinitiator according to any one of claims 4-6, wherein the linking group L or L1 comprises at least one ether functional group or a tertiary amine group.

8. The photoinitiator of claim 1, wherein the photoinitiator is selected from: ， ， ， ， ， Average n=2, ， ， ， ， ， ， ， ， ， ,and 。 9. A photoinitiator mixture comprising at least one photoinitiator according to claim 4 or 6, wherein the photoinitiator of formula (1) where x and y represent integers 1 is part of a mixture comprising photoinitiators of formulas (1-a), (1-b) and (1-c), wherein groups A, B and L are as defined for the photoinitiator of formula (1), wherein formula (1-a) is ALB, formula (1-b) is ALA, and formula (1-c) is BLB; and wherein the mixture comprises 20-80 mol% of the photoinitiator of formula (1-a); Alternatively, the photoinitiator of formula (2), in which x and y represent integers 1, is part of a photoinitiator mixture comprising photoinitiators according to formulas (2a), (2-b), and (2-c), wherein the group A' is A-NH-C(=O)-(X). n -, B' is B-NH-C(=O)-(Y) m - and L1 is as defined for a photoinitiator according to equation (2), where Formula (2-a) is A'-L1-B', formula (2-b) is A'-L1-A', and formula (2-c) is B'-L1-B'; and the mixture contains 20-80 mol% of a photoinitiator according to formula (2-a).

10. A photocurable composition comprising, as necessary components, any one of claims 1-8, a photoinitiator and a free radical polymerizable compound.

11. The photocurable composition of claim 10, comprising the photoinitiator mixture of claim 9.

12. A photocurable ink comprising a pigment and the photocurable composition of claim 10 or 11.

13. A cured product, wherein the cured product is formed by curing the photocurable composition of any one of claims 10-12 by UV LED.

14. A method for manufacturing a photoinitiator mixture comprising the photoinitiator according to any one of claims 1-8, comprising the following steps: a) Two monoacylphosphine oxide compounds having different chemical structures in the phosphine oxide moiety and each having a primary amine group or a group according to formula (M-1) attached to the acyl moiety are mixed in a molar ratio of 3:1 to 1:

3. and b) React the two monoacylphosphine oxide compounds with a compound in which the two monoacylphosphine oxide compounds are linked via a primary amine group or a group according to formula (M-1); The group according to formula (M-1) is: Equation (M-1), Wherein Z represents the carbon atom of the aromatic ring in the acyl moiety, and R represents a C1-C6-alkyl group, preferably ethyl.

15. Use of the photoinitiator according to any one of claims 1-8 for improving the surface curing of a photocurable composition and / or reducing the odor of the cured product of the photocurable composition.

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