Uv curable inkjet ink

Abstract

UV curable inkjet inks containing a free-radically polymerizable compound and a 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 UV-curable inkjet inks containing a photoinitiator, wherein the photoinitiator comprises a plurality of acylphosphine oxide moieties. Background Technology

[0002] Existing UV-curable inkjet technologies are based on LED curing and operate at 395nm for most printing systems. 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 provides high curing speed, but results in a considerable 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 395nm LEDs without the photo-yellowing issues. However, the industrial availability of acylphosphine oxides is limited, and there is increasing concern about their toxicology. The suitability of diacylphosphine oxides is often limited by their solubility in UV-curable formulations, further narrowing the choices for monoacylphosphine oxides as a particularly preferred photoinitiator for 395nm radiation-curable inkjet inks.

[0005] Besides toxicological issues and limitations in formulation latitude, 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 large-scale applications, such as interior decoration. If these migration issues could be resolved, the range of applications would be further broadened.

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

[0007] Functionalization of the mesityl fragment of acylphosphine oxide photoinitiators 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 oxalylamide-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 integrated into the structure to further optimize the surface curing of printed images and avoid the migration ability of skin-irritating acrylates. However, the use of supramolecular interactions often limits formulation freedom, which must be controlled by additional structural elements that do not have any further function for radiation curing. This results in an increase in the molecular weight of each photoinitiating moiety, affecting 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, a larger amount of photoinitiator must be added to further affect 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 UV LED-curable inkjet inks that exhibit high curability and fewer toxicological issues at 395 nm, while delivering cured products with minimal odor and migration problems. Summary of the Invention

[0011] It has now been found that the aforementioned problems with UV-curable inkjet inks can be largely solved by using 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 oxide can generate two radical species upon UV exposure, but its use is generally limited by its solubility in UV-curable inkjet inks. The acylphosphine oxide photoinitiator used in the UV-curable inkjet ink of this invention can also generate at least two radical species and exhibits good solubility. Crystallization of the photoinitiator is reduced by using a monoacylphosphine oxide moiety having a different chemical structure in the phosphine oxide moiety. It is believed that using a chemically distinct monoacylphosphine oxide moiety hinders the stacking into crystals.

[0013] Another advantage of using specific photoinitiators is that they allow for the preparation of low-odor UV-curable inkjet inks for indoor applications. Acylphosphine oxide photoinitiators generate two radical species upon UV exposure: phosphine oxide radicals and acyl radicals. While phosphine oxide radicals are almost completely incorporated into the polymerization network, this is not the case for acyl radicals. Unreacted acyl radicals typically form aldehydes, such as mesitaldehyde, resulting in an unpleasant odor in the cured product. By linking the monoacylphosphine oxide moieties to each other via their acyl groups, the molecular weight of the acyl radicals increases, thereby reducing the volatile degradation products of acylphosphine oxide photoinitiators. On the other hand, the likelihood of a photoinitiator generating multiple acyl radicals linked to each other and incorporated into the polymerization network also increases. The latter is beneficial for addressing migration issues.

[0014] Compared to photoinitiators with the same monoacylphosphine oxide moiety, a surprising improvement in surface cureability was observed when using a monoacylphosphine oxide moiety with a different chemical structure in the phosphine oxide moiety of the photoinitiator. Acylphosphine oxide photoinitiators typically exhibit good cureability for the inner portions of the polymerizable layer, but not for the surface portions, resulting in undesirable tackiness. UV-curable inkjet inks exhibited surface cureability comparable to or even better than when using the monoacylphosphine oxide photoinitiators TPO and TPO-L, which are commonly used in the inkjet industry.

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

[0016] definition The term "alkyl" refers to all possible variations for each number of carbon atoms in an alkyl group, 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.

[0017] 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 may include halogen atoms or thiol groups, while unsubstituted alkyl groups contain only carbon and hydrogen atoms.

[0018] Unless otherwise stated, the substituted alkyl group is preferably replaced by a component selected from aryl groups, heteroaryl groups, ester groups, amide groups, ether groups, thioether groups, ketone groups, aldehyde groups, sulfoxide groups, sulfone groups, sulfonate groups, sulfonamide groups, -Cl, -Br, -I, -OH, -SH, -CN and -NO2.

[0019] Unless otherwise specified, the substituted or unsubstituted alkyl groups are preferably C1 to C6-alkyl groups.

[0020] Unless otherwise specified, the substituted or unsubstituted alkenyl group is preferably a C2 to C6-alkenyl group.

[0021] Unless otherwise specified, the substituted or unsubstituted alkynyl group is preferably a C2 to C6 alkynyl group.

[0022] Unless otherwise specified, the substituted or unsubstituted alkoxy group is preferably a C1 to C6 alkyl group, with particularly preferred methoxy, ethoxy and propoxy groups.

[0023] The term aryl group refers to a monocyclic or polycyclic aromatic ring structure that contains only carbon atoms in the ring structure.

[0024] Unless otherwise specified, the aryl group is preferably a phenyl or naphthyl group, which may include one, two, three or more C1 to C6-alkyl groups, which may be substituted alkyl groups.

[0025] Unless otherwise specified, the substituted aryl group is an aryl group comprising one or more groups selected from aldehyde groups, -Cl, -Br, -I, -OH, -SH, -CN and -NO2.

[0026] The term heteroaryl group refers to a monocyclic or polycyclic aromatic ring comprising a carbon atom and one or more heteroatoms in the ring structure, preferably one to four heteroatoms, independently selected from nitrogen, oxygen, selenium, and sulfur. Preferably, the heteroaryl group is a monocyclic ring, and more preferably, the heteroaryl group is a five- or six-membered ring substituted with one, two, or three oxygen atoms, nitrogen atoms, sulfur atoms, selenium atoms, or combinations thereof.

[0027] Preferred examples of heteroaryl groups include, but are not limited to, pyridinyl, pyrimidyl, pyrazyl, quinolinyl, triazine, pyrroleyl, pyrazolyl, imidazolyl, (1,2,3)-triazolyl and (1,2,4)-triazolyl, pyrazinyl, pyrimidinyl, tetrazolyl, furanyl, thiophenyl, isoxazolyl, thiazolyl, isoxazolyl and oxazolyl.

[0028] UV-curable inkjet inks The UV-curable inkjet ink according to the present invention contains a free radical polymerizable compound and a photoinitiator, the photoinitiator comprising 2 to 6, preferably 2 to 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.

[0029] The photoinitiator preferably has a structure according to formula (1): [A] y – L – [B] x Equation (1) Where 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 the following substituents: hydrogen, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl groups, substituted or unsubstituted alkoxy groups, and substituted or unsubstituted aryl or heteroaryl groups; B represents the acylphosphine oxide portion of formula (1-2): Equation (1-2), Ar3 represents a substituted or unsubstituted aryl or heteroaryl group; R5 is selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted aryl groups, and substituted or unsubstituted alkoxy groups; R6, R7, and R8 are independently selected from the coupling position with L or from the following substituents: hydrogen, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkoxy groups, and substituted or unsubstituted aryl or heteroaryl groups; R9 represents a substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, and substituted or unsubstituted aryl or heteroaryl group.

[0030] In a preferred embodiment, x and y independently represent integers from 1 to 2, and in an even more preferred embodiment, both x and y are equal to 1. When x and y are equal to 1, a further improved solubility of the photoinitiator in UV-curable inkjet inks is observed.

[0031] In a preferred embodiment, the ratio of the molecular weights of A and B to that of L satisfies the following equation (Eq-1): (x * Mw(A) + y * Mw(B)) / Mw(L) ≥ 1.5.

[0032] 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 conforms to these equations, excellent formulation freedom is achieved because a low impact on viscosity and good solubility in radiation-curable inkjet inks is observed.

[0033] In a preferred embodiment, the linking group L contains no more than 15 carbon atoms. In the most preferred embodiment, L contains no more than 12 carbon atoms. With such a linking group, excellent formulation freedom is again achieved, as a low impact on viscosity and good solubility in radiation-curable inkjet inks is observed.

[0034] The molecular weight of the photoinitiator according to formula (1) is preferably between 700 and 2,500 g / mol, more preferably between 750 and 2,000 g / mol, and most preferably between 800 and 1,500 g / mol. Within these ranges, the photoinitiator according to formula (1) can be used appropriately in conventional amounts in UV-curable inkjet inks without significantly affecting the viscosity of the ink.

[0035] In a preferred embodiment, L comprises at least one ether functional group or a tertiary amine group. Surprisingly, higher curing sensitivity is typically observed when the linking group L contains at least one ether functional group or a tertiary amine group.

[0036] In a preferred embodiment, 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.

[0037] In a preferred embodiment, A represents the acylphosphine oxide moiety, wherein Ar1 and Ar2 represent phenyl groups, R1 and R3 represent methyl groups, R2 represents hydrogen, and R4 represents the coupling position with L; and / or B represents the acylphosphine oxide moiety, wherein Ar3 represents phenyl groups, R5 and R7 represent methyl groups, R6 represents hydrogen, R8 represents the coupling position with L, and R9 represents an ethyl group.

[0038] The above preferred embodiments can be combined with each other without any limitation.

[0039] In another preferred embodiment of the UV-curable inkjet ink, the photoinitiator according to formula (1) (where x and y represent integers 1) is a portion of the photoinitiator mixture used in the UV-curable inkjet ink, 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 the 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 between 20 and 80 mol% of the photoinitiator according to formula (1-a), more preferably at least 30 mol% and most preferably at least 40 mol% of the photoinitiator according to formula (1-a). Within these ranges, improved surface curing of inkjet printed images has been observed compared to ALA or BLB.

[0040] In another preferred embodiment of the UV-curable inkjet ink according to the invention, the photoinitiator is a compound 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)-valent 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 the following substituents: hydrogen, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl 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), Ar3 represents a substituted or unsubstituted aryl or heteroaryl group; R5 is selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted aryl groups, and substituted or unsubstituted alkoxy groups; R6, R7, and R8 are independently selected from the coupling position with N or from the following substituents: hydrogen, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkoxy groups, and substituted or unsubstituted aryl or heteroaryl groups; R9 represents a substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, and substituted or unsubstituted aryl or heteroaryl group.

[0041] In a preferred embodiment, 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 in UV-curable inkjet inks is observed.

[0042] In a preferred embodiment, 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, excellent formulation freedom is achieved because a low impact on viscosity and good solubility in radiation-curable inkjet inks is observed.

[0043] In a preferred embodiment, L1 contains at least one ether functional group or a tertiary amine group. Surprisingly, higher curing sensitivity is typically observed when the linking group L contains at least one ether functional group or a tertiary amine group.

[0044] In a preferred embodiment, 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.

[0045] In a preferred embodiment, A represents the acylphosphine oxide moiety, wherein Ar1 and Ar2 represent phenyl groups, R1 and R3 represent methyl groups, R2 represents hydrogen, and R4 represents the coupling position with N; and / or B represents the acylphosphine oxide moiety, wherein Ar3 represents phenyl groups, R5 and R7 represent methyl groups, R6 represents hydrogen, R8 represents the coupling position with L, and R9 represents an ethyl group.

[0046] The above-mentioned preferred embodiments can be combined with each other, and there are no limitations on UV-curable inkjet inks.

[0047] In a further preferred embodiment, the photoinitiator according to formula (2) (where x and y represent integers 1) is part of a photoinitiator mixture used in UV-curable inkjet inks, 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 defined for the 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'. The mixture preferably contains 20 to 80 mol% of a photoinitiator according to formula (2-a), more preferably at least 30 mol% and most preferably at least 40 mol% of a 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'.

[0048] Preferred examples of photoinitiators for UV-curable inkjet inks according to the present invention are given in Table 1 below, but are not limited thereto.

[0049] Table 1 .

[0050] In another preferred embodiment, the photoinitiator used in the UV-curable inkjet ink according to the invention comprises 2 to 6, preferably 2 to 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 by linking groups, wherein at least two monoacylphosphine oxide moieties have different chemical structures in the phosphine oxide moieties, and wherein the linking groups include radical polymerizable groups. The radical polymerizable groups result in a polymerizable photoinitiator.

[0051] The free radical polymerizable group is 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 group is selected from acrylates and methacrylates, with acrylates being particularly preferred.

[0052] The advantage of linking groups that include polymerizable groups is that they further increase the likelihood that acyl groups containing degradation products will be integrated into the polymer network after UV curing without causing migration problems or unpleasant odors.

[0053] Preferred examples of polymerizable photoinitiators according to the present invention are given in Table 2 below, but are not limited thereto.

[0054] Table 2 .

[0055] The aforementioned acylphosphine oxide initiator is preferably present in an amount of 1 to 25 wt%, more preferably 2 to 18 wt%, and most preferably 3 to 15 wt%, based on the total weight of the UV-curable inkjet ink.

[0056] The aforementioned acylphosphine oxide initiators can be added as pure compounds, but are preferably added as photoinitiator mixtures. The manufacture of the aforementioned acylphosphine oxide initiators ALB or A'-L1-B' yields photoinitiator mixtures containing ALB, ALA, and BLB as described above, and photoinitiator mixtures containing A'-L1-B', A'-L1-A', or B'-L1-B' as described above. These photoinitiator mixtures can be used in the UV-curable inkjet inks of the present invention without any separation of the acylphosphine oxide initiators ALB or A'-L1-B' by, for example, chromatographic techniques. A major advantage of using photoinitiator mixtures in UV-curable inkjet inks is the economic benefit of not requiring expensive purification or separation techniques. These examples demonstrate that when a considerable amount of the acylphosphine oxide initiator ALB or A'-L1-B' is used, preferably when the molar ratio of A to B or A' to B' is between 3:1 and 1:3, more preferably between 2:1 and 1:2, more preferably between 1.1:1 and 1:1.1, and most preferably at a molar ratio of 1, there are no disadvantages of curability or odor.

[0057] A preferred method for preparing such a photoinitiator mixture comprises the following steps: a) mixing 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; and b) reacting the two monoacylphosphine oxide compounds with a compound in which the two monoacylphosphine oxide compounds are attached via the primary amine group or the group according to formula (M-1); Among them, the groups according to formula (M-1) are: Equation (M-1), Wherein Z represents the carbon atom of the aromatic ring in the acyl moiety, and R represents a C1 to C6 alkyl group, preferably an ethyl group. Preferred monoacylphosphine oxide compounds having a primary amine group attached to the acyl moiety are P-(3-amino-2,4,6-trimethylbenzoyl)-P-phenylphosphine ethyl ester and 3-[(diphenylphosphinyl)carbonyl]-2,4,6-trimethylbenzenamine.

[0058] UV-curable inkjet inks can be colorless, but they preferably contain colorants. Colorless UV-curable inkjet inks can be used, for example, as a primer to improve adhesion to the substrate, or as a varnish to improve image gloss.

[0059] UV-curable inkjet inks may include other components as needed, such as surfactants, dispersants, dispersant synergists, stabilizers, UV absorbers, etc.

[0060] To achieve good jetting capability, the viscosity of the UV-curable inkjet ink at the jetting temperature is preferably less than 30.0 mPa·s, more preferably less than 20.0 mPa·s, and most preferably between 5.0 and 16.0 mPa·s, at a shear rate of 1000 s⁻¹. -1 Furthermore, the spray temperature is between 30°C and 70°C, preferably at 45°C.

[0061] The surface tension of UV-curable inkjet inks 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.

[0062] A single UV-curable inkjet ink can be used, but it is preferred to use a group of UV-curable inkjet inks containing a variety of colored UV-curable inkjet inks according to the present invention.

[0063] For printing multicolor images, UV-curable inkjet inks are preferably part of a UV-curable inkjet ink set, which, according to the invention, contains at least three, but most preferably at least four, UV-curable inkjet inks. The inkjet ink set is preferably a UV-curable CMYK or CRYK inkjet ink set, and preferably also includes a UV-curable white inkjet ink for enhancing color vibrancy. This inkjet ink set can also be expanded with additional inks (e.g., purple, green, red, blue, and / or orange) to further broaden the color gamut of the image.

[0064] UV-curable inkjet ink sets 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.

[0065] The UV-curable inkjet ink kit may also include one or more colorless UV-curable inkjet inks used as primers and / or varnishes.

[0066] In a particularly preferred embodiment of the UV-curable inkjet ink assembly, the ink assembly according to the present invention comprises: - Cyan UV-curable inkjet ink contains β-copper phthalocyanine pigment; - 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; - 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, the inks are supplemented with white inkjet inks and / or colorless inkjet inks. This ink set has been found to be particularly effective in reproducing wood patterns with minimal ink consumption, in addition to improved low odor and surface curing properties. Low odor is essential when manufacturing interior decoration items for rooms and vehicles, such as furniture, wallpaper, doors, natural leather goods, textiles, and decorative panels, such as floor laminates.

[0067] When a more vibrant color is desired, red UV-curable inkjet inks are replaced by magenta UV-curable inkjet inks containing pigments selected from CI pigment violet 19 and its mixed crystals.

[0068] Free radical polymerizable compounds There are no limitations on the type of free radical polymerizable compound used in the UV-curable inkjet inks of this invention. The free radical polymerizable chemistry can be a polymerizable chemistry based on (meth)acrylates, but it can also be a thiol-ene and / or thiol-acetylene polymerizable chemistry. Since water and organic solvents may be present, it can also be polymerizable polymer particles, such as polymerizable latex.

[0069] 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.

[0070] 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, fourth 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 functionalities, and mixtures including combinations of mono, di, tri, and higher functional monomers and oligomers can be used.

[0071] 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.

[0072] Monofunctional polymerizable compounds contain a single radical polymerizable group selected from acrylates, methacrylates, acrylamide, methacrylamide, styrene groups, maleates, fumarates, itaconic acid esters, vinyl ethers, vinyl esters, allyl ethers, and allyl esters.

[0073] Multifunctional polymerizable compounds contain two, three or more free radical polymerizable groups selected from acrylates, methacrylates, acrylamides, methacrylamides, styrene groups, maleates, fumarates, itaconic acid esters, vinyl ethers, vinyl esters, allyl ethers and allyl esters.

[0074] 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 ester substitution), 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-mono- and N,N-di-substituted), 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.

[0075] 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, 2-hydroxypropyl acrylate, and 2-hydroxyethyl acrylate. -3-Phenoxypropyl ester, 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.

[0076] In a preferred embodiment, the monofunctional polymerizable compound includes N-vinyllactam, such as N-vinylcaprolactam. Another particularly preferred monomer is vinylmethyloxazolidinone, available from BASF at VMOX. The monomers N-vinylcaprolactam and vinylmethyloxazolidinone are preferred because they provide a cured film with good ink cureability and adhesion for the recording medium.

[0077] 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.

[0078] Other suitable difunctional acrylates include alkoxylated cyclohexanone dimethyl diacrylate, alkoxylated hexanediol diacrylate, dioxanediol diacrylate, cyclohexanediol diacrylate, diethylene glycol diacrylate, and neopentyl glycol diacrylate.

[0079] Other multifunctional acrylates include propoxylated glycerol triacrylate and propoxylated trimethylolpropane triacrylate, di(trimethylolpropane)tetraacrylate, dipentaerythritol pentaacrylate, ethoxylated pentaerythritol tetraacrylate, methoxylated ethylene glycol acrylate, and acrylates.

[0080] Preferred multifunctional acrylates include dipropylene glycol diacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, cyclohexanone dimethyl acrylate, polyethylene glycol 200 diacrylate, 3-methyl-1,5-pentanediol diacrylate, pentaerythritol tetraacrylate, trimethylolpropane triacrylate, and dipentaerythritol pentaacrylate.

[0081] Multifunctional polymerizable compounds can have two different polymerizable groups, such as vinyl ether groups and acrylate groups. 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).

[0082] Using multifunctional polymerizable compounds that have two distinct polymerizable groups, such as 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, said polymerizable composition comprising: 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.

[0083] 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.

[0084] Another preferred alternative radical curing chemistry is so-called thiol-ene and thiol-yne chemistry. In such chemistry, a combination of at least one multifunctional thiol compound and at least one multifunctional polymerizable compound is used. The multifunctional polymerizable compound is a multifunctional monomer or oligomer having multiple polymerizable groups selected from vinyl groups, acrylamide groups, methacrylamide groups, ethylene carbonate groups, vinyl ether groups, vinyl ester groups, urethane groups, allyl ether groups, allyl ester groups, and yne groups. Particularly preferred are polymerizable compounds comprising allyl ether groups, ethylene carbonate groups, and yne groups.

[0085] The synthesis of such monomers has been 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, Volume 66, Pages 1596–1608; WO 01 / 00634 A (WRIGHT CHEM CORP); and ROHR, Markus et al. Solvent-free ruthenium-catalysed vinylcarbamate synthesis from phenylacetylene and diethylamine in 'supercritical' carbon dioxide. Green Chemistry. 2001, Volume 3, pp. 123-125.

[0086] Preferred polymerizable oligomers and polymers are polyurethanes, polyesters, polyethers, polycarbonates, polyurethanes, polyureas, and linear oligomers having polymerizable groups such as acrylates, methacrylates, vinyl groups, acrylamides, methacrylamides, vinyl carbonates, vinyl ethers, vinyl ester-vinyl carbamate groups, and their corresponding olefin and alkyne compounds.

[0087] Particularly preferred monomers are selected from di- or low-functionalized allyl ethers, di- or low-functionalized allyl esters, di- or low-functionalized vinyl ethers, di- or low-functionalized vinyl esters, and di- or low-functionalized 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.

[0088] 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 cleave upon excitation, immediately generating initiating radicals. Norrish Type II initiators are photoinitiators that are activated by photochemical radiation and form radicals by abstracting hydrogen from a second compound that becomes the actual initiating radical. This second compound is called a polymerization synergist or co-initiator.

[0089] Suitable Norrish type I and II photoinitiators are disclosed in CRIVELLO, JV et al., Volume 3: Photoinitiators for Free Radical Cationic and Anionic Photopolymerization, 2nd ed., edited by BRADLEY, G. London, UK: John Wiley and Sons Ltd, 1998. pp. 287-294.

[0090] Acylphosphine oxide photoinitiators in UV-curable inkjet inks can be combined with photoinitiators selected from thioxanone compounds, α-hydroxyalkylphenyl ketone compounds, and carbazole compounds. Such combinations can further improve the curing speed.

[0091] To further enhance photosensitivity, UV-curable inkjet inks may contain one or more co-initiators, also known as polymerization synergists, typically amine synergists.

[0092] Suitable examples of amine potentiators can be divided into three groups: 1) Tertiary aliphatic 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) (meth)acrylated amines, such as dialkylaminoalkyl (meth)acrylates (e.g., diethylaminoethyl acrylate) or N-morpholinoalkyl-(meth)acrylates (e.g., N-morpholinoethyl acrylate).

[0093] The UV-curable inkjet ink according to the present invention preferably contains a total amount of photoinitiator in an amount of 1 to 25% by weight, more preferably 2 to 20% by weight, based on the total weight of the UV-curable inkjet ink.

[0094] UV-curable inkjet inks may contain other additives, such as surfactants, dispersants, dispersant synergists, stabilizers, UV absorbers, organic solvents, and water.

[0095] 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 (e.g., titanium dioxide and carbon black, respectively) are preferred.

[0096] Pigments can be black, white, cyan, magenta, yellow, red, orange, purple, blue, green, brown, or mixtures thereof. These colored pigments can be selected from those disclosed by HERBST, Willy et al., Industrial Organic Pigments, Production, Properties, Applications. 3rd ed. Wiley-VCH, 2004. ISBN 3527305769.

[0097] Preferred pigments for cyan inkjet inks are β-copper phthalocyanine pigments, with CI pigment blue 15:3 or 15:4 being particularly preferred.

[0098] 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. The pigments in 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.

[0099] The pigment in the magenta UV-curable inkjet ink is preferably CI pigment violet 19 or a mixture thereof.

[0100] The preferred purple pigments are CI pigments 23, 32 and 37.

[0101] The particularly preferred orange pigments are CI Pigment Orange 5, 13, 16, 34, 40, 43, 59, 66, 67, 69, 71 and 73.

[0102] The preferred green pigments are CI Pigment Green 7 and 36.

[0103] The preferred brown pigments are CI pigments Brown 6 and 7.

[0104] 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); Regal ® 400R, Mogul ® L, Elftex ® 320 from CABOT Co.; or Carbon Black FW18, Special Black 250, Special Black 350, Special Black 550, Printex ® 25. Printex ® 35. Printex ® 55. Printex® 90. Printex ® 150T, from DEGUSSA. In a preferred embodiment, the carbon black pigment used is a pigment having less than 0.15% toluene extractable fraction using the method described in Part III, paragraph 5 of Resolution AP(89) 1, published by the European Commission on 13 September 1989.

[0105] 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 the ink set. Inkjet ink sets can also include one or more spot colors. Silver and gold are often used as desired colors to make products more attractive by giving them a unique appearance.

[0106] 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) 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 pattern of each component can be distinguished, and the disappearance of many of these spectral lines is one of the criteria for the formation of a solid solution. A commercially available example is Cinquasia from Sunchemical. TM Magenta L 4540.

[0107] 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 jet nozzles. It is also desirable to use small particles for maximum color intensity and to slow down sedimentation.

[0108] 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 less desirable because of reduced lightfastness, but mainly because very small pigment particles or individual pigment molecules may still be extracted in food packaging applications.

[0109] The number-average pigment particle size was best 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, and 635 nm wavelength, with the graph representing the correction function.

[0110] 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.

[0111] Titanium dioxide is preferably used for 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 utilization of features and select them according to their intended use. Using the anatase form with 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.

[0112] For the surface treatment of titanium dioxide, aqueous or vapor-phase treatments can be applied, and alumina-silica treatment agents are commonly used. Titanium dioxide treated with alumina or alumina-silica is preferably combined with an organic surface treatment.

[0113] The number-average particle size of titanium dioxide or other white pigments is preferably 50 to 500 nm, more preferably 150 to 400 nm, and most preferably 200 to 300 nm to achieve the best trade-off between hiding power and dispersion stability. When the average diameter is less than 50 nm, sufficient hiding power cannot be obtained, and when the average diameter exceeds 500 nm, the ink's storage capacity and ejection suitability tend to deteriorate. The number-average particle size is preferably determined by photon correlation spectroscopy at a wavelength of 633 nm using a 4 mW HeNe laser on diluted samples of pigmented inkjet inks. A suitable particle size analyzer is a Malvern. TM Nano-S is available from Goffin-Meyvis. Samples can be prepared by adding a drop of ink to a cuvette containing 1.5 mL of ethyl acetate and mixing until a homogeneous sample is obtained. The particle size is measured as the average of three consecutive measurements consisting of six 20-second runs.

[0114] 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 are pigments that can be dispersed in a dispersion medium without a dispersant.

[0115] Based on the total weight of the pigment dispersion, the pigment is preferably used in the concentrated pigment dispersion for the preparation of inkjet ink in an amount of 10 to 40% by weight, more preferably 15 to 30% by weight.

[0116] In colored inkjet inks, the pigment is preferably present in an amount of 0.1 to 13.0% by weight. Based on the total weight of the inkjet ink, dark inkjet inks preferably contain 1.5 to 13.0% by weight, more preferably 1.8 to 6.0% by weight of colored pigment, while based on the total weight of the inkjet ink, light inkjet inks preferably contain 0.1 to 1.3% by weight, more preferably 0.3 to 1.2% by weight of colored pigment.

[0117] 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% to 25.0% by weight of white pigment.

[0118] dispersant UV-curable inkjet inks preferably contain dispersants to further improve pigment dispersion properties. For high printing reliability, polymeric dispersants are preferred. These dispersants improve the reliability of inkjet printing methods due to their typically low settling velocities, especially when they contain secondary or tertiary amine groups.

[0119] 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: • Statistical polymerization of monomers (e.g., monomers A and B polymerize into ABBAABAB); • Alternating polymerization of monomers (e.g., monomers A and B polymerize into ABABABAB); • Monomers that undergo gradient (gradual) polymerization (e.g., monomers A and B polymerize into AAABAABBABBBB); • Block copolymers (e.g., monomers A and B polymerized into AAAAABBBBBB), where the block lengths (2, 3, 4, 5 or even more) of each block are important for the dispersing ability of the polymer dispersant; • Graft copolymers (graft copolymers consist of a polymer backbone and polymer side chains attached to the backbone); and • These polymers can be in mixed forms, such as block gradient copolymers.

[0120] The polymer dispersant preferably has a number average molecular weight Mn between 500 and 30,000, more preferably between 1,500 and 10,000.

[0121] 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.

[0122] 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.

[0123] Examples of commercial 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, from EVONIK; • EDAPLAN TM Dispersant, from MÜNZING CHEMIE; • ETHACRYL TM Dispersant, from LYONDELL; • GANEX TM Dispersant, from ISP; • DISPEX TM and EFKA TM Dispersant, from BASF; • DISPONER TM Dispersant, from DEUCHEM.

[0124] Particularly preferred polymer dispersants include Solsperse TM Dispersant, from LUBRIZOL; Efka TM Dispersant, from BASF; Disperbyk TM Dispersant, from BYK CHEMIE GMBH; and Ajisper TM The dispersant is from AJINOMOTOFINE-TECHNO Co. A particularly preferred dispersant is Solsperse. TMDispersants of 32000, 35000 and 39000, from LUBRIZOL and Disperbyk from BYK CHEMIE GMBH. TM 162.

[0125] Dispersants can be used alone or in combination of two or more.

[0126] The polymeric dispersant is preferably used in an amount of 10 to 200 wt%, more preferably 20 to 100 wt%, and most preferably 50 to 90 wt%, based on the weight of the pigment.

[0127] Dispersing synergists UV-curable inkjet inks may include dispersant synergists to further improve dispersion stability via polymeric dispersants, and thus also improve printing reliability because less pigment can deposit in the nozzles of the printhead when the inkjet unit is in standby mode.

[0128] Dispersing synergies typically consist of anionic and cationic moieties. The anionic moieties of dispersing synergies exhibit a certain 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.

[0129] The dispersing synergist is preferably added in a smaller amount than the polymeric dispersant(s). The polymeric dispersant / dispersing synergist ratio depends on the pigment and should be determined experimentally. Typically, the ratio of polymeric dispersant by weight % to dispersing synergist by weight % is selected from between 2:1 and 100:1, preferably between 2:1 and 20:1.

[0130] Commercially available suitable dispersants include Solsperse from LUBRIZOL. TM 5000 and Solsperse TM 22000.

[0131] Suitable dispersing synergists for diketopyrrolopyrrole pigments, quinacridone pigments or mixed crystals thereof include those disclosed in EP 1790698 A (AGFA GRAPHICS), EP 1790696 A (AGFA GRAPHICS), WO 2007 / 060255 (AGFA GRAPHICS) and EP 1790695 A (AGFA GRAPHICS).

[0132] When dispersing CI Pigment Blue at a ratio of 15:3, sulfonated Cu-phthalocyanine dispersing synergists are used, such as Solsperse from LUBRIZOL. TM 5000 is the preferred value.

[0133] stabilizer UV-curable inkjet inks can also contain polymerization inhibitors. The presence of polymerization inhibitors in the ink prevents polymerization reactions from occurring before curing, such as during storage or transportation. It also improves printing reliability because the UV LEDs in the printhead of the inkjet unit are typically maintained at higher temperatures, such as 45 to 55°C.

[0134] Suitable polymerization inhibitors include phenolic antioxidants, hindered amine light stabilizers, phosphorus antioxidants, benzoquinone, hydroquinone and its derivatives, such as hydroquinone monomethyl ether, which is commonly used in (meth)acrylate monomers.

[0135] Examples of phenol 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.

[0136] Suitable product 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, 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), from Kromachem Ltd; Additol TM The S series (S100, S110, S120, and S130) are from Cytec Surface Specialties.

[0137] The preferred polymerization inhibitor is Irgastab from BASF. TMUV10. Other examples of polymerization inhibitors include TEMPO, TEMPOL, and the Al copper-iron reagent.

[0138] Polymerization inhibitors can be used alone or in combination of two or more of them.

[0139] 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 2851402 A (FUJIFILM).

[0140] Based on the total weight of the free radical curable inkjet ink, the polymerization inhibitor is preferably present in an amount of 0.1 to 5 wt%. Below 0.1 wt%, undesirable polymerization cannot be adequately inhibited, and above 5 wt%, the curing rate is severely reduced.

[0141] surfactants UV-curable inkjet inks may contain surfactants. Surfactants can be anionic, cationic, nonionic, or amphoteric. Based on the total weight of the free radical curable inkjet ink, the surfactant is preferably present in an amount of 0.1 to 3 wt%. At concentrations above 3 wt%, adhesion deteriorates rapidly, while insufficient ink spreading is typically observed at concentrations below 0.1 wt%.

[0142] The total amount of surfactant is preferably less than 3 wt% based on the total weight of the ink, and more preferably less than 1.5 wt% based on the total weight of the UV-curable inkjet ink, to prevent the ink from foaming in its container. Such foaming has a negative impact on printing reliability.

[0143] 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 polymerized, such as polydimethylsiloxane.

[0144] Preferred commercial silicone surfactants include BYK from BYK Chemie. TM 333 and BYK TM UV3510 and Tegoglide from EVONIK TM 410.

[0145] In a preferred embodiment, the surfactant is a polymerizable compound.

[0146] Preferred polymerizable silicone surfactants include (meth)acrylated silicone surfactants. Most preferably, the (meth)acrylated silicone surfactant is an acrylated silicone surfactant, because acrylates are more reactive than methacrylates.

[0147] In a preferred embodiment, the (meth)acrylated silicone surfactant is a polyether-modified (meth)acrylated polydimethylsiloxane or a polyester-modified (meth)acrylated polydimethylsiloxane.

[0148] Preferred commercially available (meth)acrylated silicone surfactants include: Ebecryl TM 350, silicone diacrylate, 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 BYK Chemie; 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, all manufactured by EVONIK. Another preferred silicone is OSI SPECIALITIES BENELUX NV's Silwet. TM L7500; 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.

[0149] The preferred surfactant for free radical inkjet inks is Silmer from SILTECH CORPORATION. ® Surfactants, such as Silmer ® ACR Di-1508.

[0150] Preparation of UV-curable inkjet inks The preparation of UV-curable inkjet inks is well known to technicians.

[0151] 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.

[0152] Mixing equipment may include pressure kneaders, open kneaders, planetary mixers, dissolvers, and Dalton universal mixers. Suitable grinding and dispersing equipment includes ball mills, pearl mills, colloid mills, high-speed dispersers, two-roll mills, bead mills, paint conditioners, and three-roll mills. Dispersions may also be prepared using ultrasonic energy or microfluidics.

[0153] 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.

[0154] 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 where photochemical radiation has been largely eliminated.

[0155] 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.

[0156] The dispersion process can be carried out in continuous, intermittent, or semi-intermittent modes.

[0157] The preferred amounts and ratios of the mill grind components will vary depending on the specific material and intended application. The contents of the mill mixture include mill grind and abrasive media. The mill grind comprises pigment, polymeric dispersant, and liquid carrier. For inkjet inks, pigment is typically present in the mill grind at 5 to 50% by weight, 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.

[0158] 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.

[0159] 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.

[0160] 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 pigmented ink from the equipment. Through dilution, the inkjet ink is adjusted to the viscosity, surface tension, color, hue, saturation density, and print coverage desired for a specific application.

[0161] Cured products Another aspect of the present invention is the curing of a UV-curable inkjet ink formed by UV LED curing. Compared with conventionally used acylphosphine oxide TPO and TPO-L UV inkjet inks, the cured product exhibits improved migration capacity and reduced unpleasant odor.

[0162] Inkjet printing method The inkjet printing method according to the present invention preferably includes the following steps: a) An image printed with UV-curable inkjet ink onto a substrate; and b) The image is cured by UV light-emitting diodes.

[0163] UV curing is preferably performed by a UV LED with an emission wavelength greater than 360 nm, preferably greater than 370 nm, and most preferably between 390 nm and 400 nm.

[0164] UV-curable inkjet ink is ejected in a controlled manner through nozzles from one or more printheads (or more) onto a substrate that moves relative to the printheads (or more). A piezoelectric printhead is the preferred printhead for an inkjet printing system. 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 voids that are 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. Piezoelectric printheads have proven to be the most reliable printheads in industrial printing.

[0165] 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.

[0166] The preferred piezoelectric printhead is the so-called through-flow piezoelectric drop-on-demand printhead. Such printheads are available from TOSHIBA TEC as CF1ou printheads. Through-flow printheads are preferred because they enhance the reliability of inkjet printing due to ink circulation within the printhead.

[0167] The inkjet printhead preferably scans laterally back and forth above the moving ink-receiver surface. The printhead may not print on the return stroke, but bidirectional printing is preferred for achieving high area throughput. To maximize area throughput, another printing method known as "single-pass printing" 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-receiver surface. In single-pass printing, the printhead typically remains stationary, and the ink-receiver surface is conveyed below the printhead.

[0168] However, inkjet printing with UV-curable inkjet inks is performed in a multi-pass printing mode. 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 printing 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. In addition, by avoiding all horizontal adjacency, the lateral speed of the printing unit can be increased to twice the rated printing speed of the print head. In a preferred embodiment, the number of passes used is 2 to 6, more preferably no more than 4.

[0169] 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 in single-pass printing, a single shooter is sufficient to replace the entire printhead, in multi-pass printing, the shooter can be tolerated, and even if it fails. Furthermore, multi-pass printers are generally much less expensive, especially for wide-format substrates.

[0170] To facilitate curing, inkjet printers may include one or more oxygen-consuming units. These units contain a blanket of nitrogen or other relatively inert gases (such as CO2), with adjustable position and inert gas 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

[0171] 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 via 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 spots on a TLC plate containing no compound with 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 considered compound with the same solution. The spectrum of the compound to be analyzed was obtained by subtracting the first spectrum from the second spectrum.

[0172] 2. Curability UV-curable inkjet ink was applied to a PET175 substrate using a bar coater and a 20μm winding bar. Samples were obtained from Aktiprint. TM The mini duo LED curing stage cures at full power and a linear curing speed of 10 m / min. The number of passes required to achieve complete curing (including surface curing) is taken 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.

[0173] According to Table 3, surface curing is checked by wiping the surface of the cured sample five times with a cotton swab (Q-tip).

[0174] Table 3 .

[0175] 3. Odor In the curability test, the odor was evaluated directly by two people after UV LED curing and compared with a sample containing TPO (2,4,6-trimethylbenzoyl diphenylphosphine oxide, CASRN75980-60-8).

[0176] The assessment is conducted by assigning scores based on the criteria in Table 4.

[0177] Table 4 .

[0178] 4. Average particle size The average particle size of the pigment particles was determined by photon correlation spectroscopy on diluted samples of the pigment dispersion at a wavelength of 633 nm using a 4 mW HeNe laser. The particle size analyzer used was a Malvern from Gofin-Meyvis. TM The nano-S sample can be prepared by adding one drop of dispersion to a cuvette containing 1.5 mL of ethyl acetate and mixing until a homogeneous sample is obtained. The particle size is the average of three consecutive measurements consisting of six 20-second runs.

[0179] Material All materials used in the following examples are available from standard sources such as Sigma-Aldrich (MERCK) and AcrosOrganics (THERMOFISHER SCIECNTIFIC) unless otherwise stated. Any water used is deionized water.

[0180] Amino-TPO-L is an ethyl P-(3-amino-2,4,6-trimethylbenzoyl)-P-phenylphosphinate (CASRN2143083-29-6), prepared according to the method described in WO 2017 / 191043 (AGFA GRAPHICS).

[0181] Amino-TPO is 3-[(diphenylphosphino)carbonyl]-2,4,6-trimethylaniline (CASRN2771298-79-2), prepared according to the method described in WO 2022 / 106100 (AGFA).

[0182] TPO-oxam (CASRN2771298-80-5) is a TPO derivative having the following structure and prepared according to paragraph

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

[0183] 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): .

[0184] Diethylene glycol bis(chloroformate) is supplied by ABCR GmbH.

[0185] Adipicoyl chloride, 3,3,5-trimethyl-hexamethylene-1,6-diisocyanate, and bis(3-aminopropyl)methylamine were supplied by TCI Europe.

[0186] 3,6-Dioxa-1,8-Octadiamine was supplied by Aldrich.

[0187] Glutaryl dichloride and diethylene glycol dichloride are supplied by TCI Europe.

[0188] TPO (CASRN75980-60-8) is manufactured by IGM under the Omnirad brand. TM TPO supply.

[0189] TPO-L (CASRN84434-11-7) is manufactured by IGM under the Omnirad brand. TM TPO-L available.

[0190] Silwet TM L7500 is a silicone-based wetting agent supplied by Momentive Performance Materials GmbH.

[0191] Genomer TM 2253 is an acrylated amine oligomer supplied by Rahn.

[0192] VEEA is 2-(2-ethyleneoxyethoxy)ethyl acrylate, a bifunctional monomer available from NIPPON SHOKUBAI, Japan.

[0193] DPGDA is dipropylene glycol diacrylate, which can be used as a sartomer. TM SR508 was obtained from ARKEMA.

[0194] PET175 is a 175 μm thick unsubbed polyethylene terephthalate sheet, which can be used as an Astera... TM Type UR175.334 is obtained from AGFA-GEVAERT NV.

[0195] The following is a comparison of the photoinitiator COMPINI-1: 6.63 g (20 mmol) of amino-TPO-L 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-L, in which ethyl P-(3-amino-2,4,6-trimethylbenzoyl)-P-phenylphosphine ester 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 with vigorous stirring. 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 grams (y: 53%) of COMPINI-1 (melting point: 132 °C, in TLC SILICAGEL 60 RP-18 F supplied by MERCK) were separated. 254 TLC analysis was performed on an S-plate with the following eluents: MeOH / 0.5M NaCl: 70 / 30, R. f = 0.21). The structure of COMPINI-1 was further confirmed using TLC-MS.

[0196] The following is a comparison of the photoinitiator COMPINI-2: 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, wherein 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 with vigorous stirring. 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 (y: 67%) of COMPINI-2 (melting point: 158 °C, in TLC SILICAGEL 60 F supplied by MERCK) was separated. 254 TLC analysis was performed on the plate using dichloromethane / methanol 95 / 5 as the eluent. f = 0.14) The 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. 1.92 g (10.2 mmol) of adipoyl chloride was added over 3 minutes, while the temperature was raised 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 (y: 100%) of COMPINI-3 (in Uniplate supplied by MILESSCIENTIFIC) was separated. TM TLC analysis was performed on Analtech HPTL-RP18F plates: eluent MeOH / 0.5M NaCl 70 / 30, R f = 0.1).

[0197] The following is a comparison of the photoinitiator COMPINI-4: 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, while 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 (y: 96%) of COMPINI-4 (in Uniplate supplied by MILES SCIENTIFIC) was separated. TM TLC analysis was performed on an Analtech HPTL-RP18F plate: eluent MeOH / 0.5M NaCl 70 / 30, R f = 0.25).

[0198] PB15:4 is used for Sunfast TM Blue 15:4 is an abbreviation for Blue 15:4 pigment from Sun Chemical Corporation's CI pigment blue 15:4.

[0199] DB162 is a polymer dispersant, Disperbyk, available from BYK CHEMIE GMBH. TM The abbreviation 162 refers to the solvent mixture containing 2-methoxy-1-methylethyl acetate, xylene, and n-butyl acetate. This polymeric dispersant is a polyester-polyurethane dispersant based on caprolactone and toluene diisocyanate, having an amine value of 13 mg KOH / g, a Mn of approximately 4,425, and a Mw of approximately 6,270.

[0200] INHIB is a mixture that forms polymerization inhibitors, and its composition is shown in Table 5: Table 5 .

[0201] BHT is an abbreviation for 2,6-di-tert-butyl-4-methylphenol (CASRN128-30-0) from ALDRICH CHEMICAL Co.

[0202] Cupferron TM AL is aluminum N-nitrosophenylhydroxylamine from WAKO CHEMICALS LTD.

[0203] Example 1 This embodiment illustrates the synthesis of the photoinitiator according to the present invention.

[0204] 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, in which the acylphosphine oxide was completely dissolved. Under vigorous stirring, a solution of 1.74 g (10.3 mmol) of glutaryl dichloride in 5 mL of ethyl acetate was added over five minutes. The temperature was kept below 25 °C. The reaction was allowed to continue at room temperature for one hour. The reaction mixture was analyzed by TLC (using a TLC Silicagel 60 F supplied by MERCK). 254 Eluent: Ethyl acetate, R f (Amino-TPO): 0.25, R f (Amino-TPO L: 0.43). 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 sodium chloride aqueous solution, dry to MgSO4 and evaporate under reduced pressure. Perform preparative column chromatography on Graceresolve. TM Residual amino-TPO and amino-TPO-L were removed on an 80g SiOH 40µm 60Å column using a gradient elution from dichloromethane to dichloromethane / methanol 95 / 5. 4g (y: 51%) of INIMIX-1 (in Uniplate supplied by MILES SCIENTIFIC) was separated. TM TLC analysis was performed on an Analtech HPTLC-RP18F plate: eluent MeOH / 0.5M NaCl 70 / 30, R f Symmetric-TPO-L: 0.27, R f ASYM-2: 0.19, R f Symmetrical - TPO: 0.13). The structure of ASYM-2 was confirmed using TLC-MS.

[0205] Synthesis of INIMIX-2, INIMIX-3 and INIMIX-4 containing ASYM-5 Table 6 .

[0206] x g of amino-TPO and y g of amino-TPO-L (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, in which the acylphosphine oxide was completely dissolved. Under vigorous stirring, a solution of 1.76 g (10.4 g) of diethylene glycol dichloro in 5 mL of ethyl acetate was added over five minutes. The temperature was kept below 25 °C. The reaction was allowed to continue at room temperature for one hour. TLC analysis confirmed complete conversion (using a TLC instrument supplied by MERCK, SILICAGEL 60 F). 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 sodium chloride aqueous solution, dried over MgSO4 and evaporated under reduced pressure. The separated INIMIX-2 to INIMIX-4 (Uniplate supplied by MILES SCIENTIFIC) were analyzed by TLC. TM TLC analysis was performed on an Analtech HPTLC-RP18F plate: eluent MeOH / 0.5M NaCl 70 / 30, Rf symmetric TPO-L: 0.28, R f ASYM-5: 0.20, R f Symmetrical - TPO: 0.13). The structure of ASYM-5 was confirmed using TLC-MS.

[0207] 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 (y: 100%) of INIMIX-5 (Uniplate supplied by MILES SCIENTIFIC) was separated. TM TLC analysis was performed on an Analtech HPTL-RP18F plate: eluent MeOH / 0.5M NaCl 70 / 30, R f Symmetric-TPO: 0.08, R f ASYM-1: 0.11, Rf Symmetrical TPO-L: 0.28).

[0208] Synthesis of INIMIX-6 containing ASYM-4 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 10 minutes, a solution of 2.2 g (11.5 mmol) of adipic acid chloride in 5 mL of ethyl acetate was added, while maintaining the temperature below 25 °C. The reaction was allowed to continue 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 (y: 97%) of INIMIX-6 (in Uniplate supplied by MILES SCIENTIFIC) was separated. TM TLC analysis was performed on an Analtech HPTL-RP18F plate: eluent MeOH / 0.5M NaCl 70 / 30, R f Symmetric-TPO: 0.09, R f ASYM-4: 0.15, R f Symmetrical TPO-L: 0.23).

[0209] 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 INIMIX-7 phase was separated from the mixture. The INIMIX-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 fraction used for washing was pooled and evaporated under reduced pressure. Both fractions still contained considerable amounts of impurities and were pooled. INIMIX-7 was analyzed by preparative column chromatography in Büchi. TM Purification was performed on an NP-Flash column using a gradient elution from ethyl acetate to ethyl acetate / methanol 75 / 25. 4.6 g (y: 50%) of INIMIX-7 (in Uniplate supplied by MILES SCIENTIFIC) was separated. TM TLC analysis was performed on an Analtech HPTL-RP18F plate: eluent MeOH / 0.5M NaCl 80 / 20, R fSymmetrical TPO: 0.12; R f ASYM-8: 0.18; R f Symmetrical TPO-L: 0.25).

[0210] Synthesis of INIMIX-8 containing ASYM-12 4.31 g (10 mmol) of TPO-L-oxam and 4.63 g (10 mmol) of TPO-oxam were added to 90 mL of acetonitrile. A solution of 1.53 g (10 mmol) of 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. INIMIX-8 was analyzed by preparative column chromatography in Büchi. TM Purification was performed on an NP-Flash column using a gradient elution from ethyl acetate to ethyl acetate / methanol 75 / 25. 3.5 g (y: 37%) of INIMIX-8 (in Uniplate supplied by MILES SCIENTIFIC) was separated. TM TLC analysis was performed on an Analtech HPTL-RP18F plate: eluent MeOH / 1M NaCl 80 / 20, R f Symmetrical TPO: 0.26; R f ASYM-12: 0.33; R f Symmetrical TPO-L: 0.41).

[0211] Synthesis of INIMIX-9 containing ASYM-13 4.31 g (10 mmol) of TPO-L-oxam and 4.63 g (10 mmol) of 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 INIMIX-9 was analyzed by preparative column chromatography in Büchi. TM Purification was performed on an NP-Flash column using a gradient elution from ethyl acetate to ethyl acetate / methanol 75 / 25. 2.6 g (y: 27%) of INIMIX-9 (in Uniplate supplied by MILES SCIENTIFIC) was separated. TMTLC analysis was performed on an Analtech HPTL-RP18F plate: eluent MeOH / 1M NaCl 80 / 20, R f Symmetrical TPO: 0.25; R f ASYM-13: 0.31; R f Symmetrical TPO-L: 0.39.

[0212] Example 2 This embodiment illustrates that the photoinitiator according to the present invention achieves an optimal balance between formulation freedom and curing sensitivity, wherein the curing sensitivity is close to that of common industrial acylphosphine oxide initiators TPO and TPO-L.

[0213] Preparation of LED Curable Inkjet Ink Comparative Examples C-1 to C-4 and Examples I-1 to I-9 of the present invention were prepared according to the mixed components in Tables 7 and 8. Weight % (wt%) is based on the total weight of the LED-curable inkjet inks. The wt% of the photoinitiator was selected such that the molar amount of the acylphosphine oxide moiety was the same in all UV-curable inkjet inks.

[0214] Table 7 .

[0215] Table 8 .

[0216] Results and Evaluation The cureability and odor of UV-curable inkjet inks C-1 to C-4 and I-1 to I-9 were determined. The results are shown in Table 9.

[0217] Table 9 .

[0218] By comparing cured products C-1 to C-4 with I-1, it can be seen that only UV-curable inkjet ink I-1 exhibits good curability and improved cured product odor. UV-curable inkjet inks C-1 and C-2, containing common TPO and TPO-L respectively, also show 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, more specifically two TPO-L moieties and one TPO moiety, respectively. The photoinitiator ASYM-2 of UV-curable inkjet ink 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 (food-like) curability.

[0219] By including ether functional groups in the linking groups, as exemplified by photoinitiator ASYM-5 in UV-curable inkjet inks I-2 to I-4, curability can be further improved compared to ASYM-2 in UV-curable inkjet ink I-1. The amount of photoinitiator ASYM-5 in UV-curable inkjet inks I-2 to I-4 appears to have no effect on curability as long as it is present.

[0220] Compared to UV-curable inkjet inks I-6 and I-7, which lack ether functionality in their linking groups, UV-curable inkjet inks I-5 and I-9 have been shown to improve curability by including one or more ether groups in their linking groups.

[0221] The UV-curable inkjet ink I-8 indicates that including tertiary amine groups in the linking groups can also improve curability.

[0222] No photochromism was observed for inkjet inks C-1 to C-4 and I-1 to I-9.

[0223] Example 3 This embodiment illustrates that the advantages of the photoinitiator according to the present invention are also obtained for different monomers in UV-curable inkjet inks.

[0224] Preparation of LED Curable Inkjet Ink Comparative Examples C-5 and C-6, as well as Example I-10 of the present invention, were prepared by mixing components according to Table 10. Weight % (wt%) is based on the total weight of the LED-curable inkjet ink. The wt% of the photoinitiator was selected such that the molar amount of the acylphosphine oxide moiety was the same in all UV-curable inkjet inks.

[0225] Table 10 .

[0226] Results Evaluation The cureability and odor of UV-curable inkjet inks C-5, C-6, and I-10 were determined. The results are shown in Table 11.

[0227] Table 11 .

[0228] It should be immediately clear from Table 11 that the asymmetric phosphine oxide in UV-curable inkjet ink I-10 provides superior curability compared to UV-curable inkjet inks C-5 and C-6, which contain similar symmetric phosphine oxides.

[0229] Example 4 This embodiment illustrates inkjet printing using UV-curable inkjet inks comprising the photoinitiator according to the present invention.

[0230] Preparation of concentrated cyan dispersion DISP-C A concentrated cyan pigment dispersion was prepared by mixing the components according to Table 12 for 30 minutes using a DISPERLUX™ disperser from DISPERLUX SARL, Luxembourg. The container was then connected to a Bachofen DYNOMILL. TM An ECM Poly mill with an internal volume of 8.2 liters was used, filled with 42% 0.4 mm yttrium-stabilized zirconia beads. The mixture was circulated through the mill at a flow rate of approximately 8 liters / minute with a residence time of 38 minutes. After milling, the dispersion was separated from the beads using a 1-micron filter. The average particle size of the pigment particles in the concentrated cyan pigment dispersion DISP-C was found to be 89 nanometers.

[0231] Table 12 .

[0232] 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 using concentrated cyan pigment dispersion DISP-C and mixed with the components shown in Table 13. Weight percentages (wt%) are based on the total weight of the inkjet inks.

[0233] Table 13 .

[0234] Evaluation of cyan inkjet ink Using Dimatix TM 10 pl printhead, from Synaps of AGFATM Comparative ink COMP-1 and the inks INV-1 to INV-3 of this invention were jetted onto an OM135 / AP. A jetting frequency of 5 kHz was used in conjunction with a jetting voltage of 31 V. The jetting temperature of each inkjet ink was adjusted until all nozzles were inkjet, as shown in Table 14 below.

[0235] Table 14 .

[0236] Unijet uses a UV LED module from USHIO. TM The i24511 Fusion DRSE-120 conveyor cures printed samples, transporting them along a conveyor belt at a speed of 20 m / min to the area under a UV lamp. The UV LED is used at full power. After a one-pass operation, the degree of curing is assessed by wiping the sample 10 times with a cotton swab and evaluating surface damage. Surface damage is scored according to Table 15. Table 15 .

[0237] The surface damage assessments of ink COMP-1 and the inks INV-1 to INV-3 of this invention are summarized in Table 16.

[0238] Table 16 .

[0239] This assessment clearly demonstrates that the UV-curable ink according to the present invention can be easily jetted using a standard piezoelectric printhead, and there is no loss of curing sensitivity compared to UV-curable inkjet inks containing a standard acylphosphine oxide photoinitiator. No photoyellowing problem was also observed.

Claims

1. A UV-curable inkjet ink containing a free radical polymerizable compound and a photoinitiator, wherein the photoinitiator comprises 2 to 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 UV-curable inkjet ink according to claim 1, wherein the photoinitiator comprises 2 or 3 monoacylphosphine oxide moieties.

3. The UV-curable inkjet ink according to claim 1 or 2, wherein the linking groups between the monoacylphosphine oxide portions include free radical polymerizable groups.

4. The UV-curable inkjet ink according to any one of claims 1 to 3, wherein the photoinitiator has a structure according to formula (1): [A] y –L–[B] x Equation (1) Where x and y independently represent integers from 1 to 3; L represents a (x+y)-valent linker group having 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 groups, substituted or unsubstituted aryl groups, and substituted or unsubstituted alkoxy groups; and R2, R3, and R4 are independently selected from the coupling position with L or from the following substituents: hydrogen, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl 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), Ar3 represents substituted or unsubstituted aryl or heteroaryl groups; R5 is selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted aryl groups, and substituted or unsubstituted alkoxy groups; R6, R7, and R8 are independently selected from the coupling position with L or from the following substituents: hydrogen, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl groups, substituted or unsubstituted alkoxy groups, and substituted or unsubstituted aryl or heteroaryl groups; and R9 represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, and a substituted or unsubstituted aryl or heteroaryl group.

5. The UV-curable inkjet ink according to claim 4, wherein the ratio of the molecular weight of one side A and B to that of the other side L satisfies the following equation: (x * Mw(A) + y * Mw(B)) / Mw(L) ≥ 1.

5.

6. The UV-curable inkjet ink according to any one of claims 1 to 3, wherein the photoinitiator has 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)-valent 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 the following substituents: hydrogen, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl 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), Ar3 represents a substituted or unsubstituted aryl or heteroaryl group; R5 is selected from substituted or unsubstituted alkyl groups, substituted or unsubstituted aryl groups, and substituted or unsubstituted alkoxy groups; R6, R7, and R8 are independently selected from the coupling position with N or from the following substituents: hydrogen, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkoxy groups, and substituted or unsubstituted aryl or heteroaryl groups; R9 represents a substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, and substituted or unsubstituted aryl or heteroaryl group.

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

8. The UV-curable inkjet ink according to claim 1, wherein the photoinitiator is selected from: Average n=2, and 。 9. The UV-curable inkjet ink according to claim 4 or 6, wherein the photoinitiator of formula (1) where x and y represent integers 1 is a portion comprising a mixture of photoinitiators according to formulas (1-a), (1-b) and (1-c), wherein groups A, B and L are as defined for the photoinitiator according to formula (1), wherein formula (1-a) is ALB, formula (1-b) is ALA, and formula (1-c) is BLB; and wherein the mixture comprises between 20 and 80 mol% of the photoinitiator according to formula (1-a); Or, the photoinitiator of formula (2) representing the integer 1 according to x and y is a part of a photoinitiator mixture containing 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 defined for the 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 to 80 mol% of a photoinitiator according to formula (2-a).

10. The UV-curable inkjet ink according to any one of claims 1 to 9, wherein the polymerizable composition of the UV-curable inkjet ink comprises: 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; and All weight percentages of A, B, and C are based on the total weight of the polymerizable composition of the UV-curable inkjet ink.

11. The UV-curable inkjet ink according to any one of claims 1 to 10, further comprising pigment.

12. A UV-curable inkjet ink kit comprising one or more UV-curable inkjet inks according to any one of claims 1 to 10.

13. The UV-curable inkjet ink assembly according to claim 12, comprising: - Cyan UV-curable inkjet ink contains β-copper phthalocyanine pigment; - Red or magenta UV-curable inkjet inks 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 mixtures thereof; - 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 their mixtures. and - Black UV-curable inkjet ink containing carbon black pigment; optionally supplemented with white UV-curable inkjet ink and / or colorless UV-curable inkjet ink.

14. A cured product, wherein the cured product is formed by curing one or more UV-curable inkjet inks according to any one of claims 1 to 13 by UV LED.

15. An inkjet printing method, comprising the following steps: a) Spraying an image onto a substrate having a UV-curable inkjet ink according to any one of claims 1 to 13; as well as b) Images of jetting cured by UV light-emitting diodes with an emission wavelength of 360 nm or greater.

Images