Active energy ray-curable inkjet printing ink

Abstract

The present invention addresses the problem of providing an active energy ray-curable inkjet printing ink composition containing (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide as a photopolymerization initiator, the active energy ray-curable inkjet printing ink composition having sufficiently enhanced curability and preferably yielding a cured product having improved solvent resistance. As a solution, there is provided an active energy ray-curable inkjet printing ink composition having a viscosity of 5-80 cps at room temperature, wherein the ink composition contains 10 mass% or more of a monofunctional monomer with respect to the ink composition, 1-15 mass% of an amine-modified oligomer with respect to the ink composition, and (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide, and the ink composition contains a sensitizer when further containing a black pigment.

Description

Ink for Active Energy Ray Curing Inkjet Printing

[0001] The present invention relates to an ink for active energy ray curing inkjet printing, and more specifically, to an ink for active energy ray curing inkjet printing containing TMO ((2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide) as a photoinitiator.

[0002] An active energy ray curing type ink composition is an ink composition that can be cured by irradiating active energy rays such as ultraviolet rays and electron beams. The active energy ray curing type ink composition can be a solventless or low-solvent ink and has quick drying properties, so it can be printed on various printing substrates. That is, the active energy ray curing type ink composition can prevent ink bleeding even when printed on a printing substrate with low absorbency, etc.

[0003] Furthermore, it is also known to use an active energy ray curing type ink composition as an ink for inkjet printing. Patent Document 1 discloses an energy ray curing type inkjet ink composition containing a coloring material, a monofunctional monomer, a bifunctional oligomer, a photopolymerization initiator, and a surface tension adjuster.

[0004] An active energy ray curing type ink composition may contain a photoinitiator (photopolymerization initiator), depending on the type of active energy rays for curing. Photoinitiators can generally be roughly classified into several types, and examples thereof include compounds such as benzophenone-based, thioxanthone-based, acetophenone-based, and acylphosphine-based compounds.

[0005] As one of the photoinitiators, (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide (sometimes abbreviated as TMO) has been proposed, and its production method has also been studied (Patent Documents 2 and 3). In addition, an ink composition containing TMO has also been proposed; an ink containing TMO together with a modified epoxy resin acrylate prepolymer and a reactive diluent has been presented (Patent Document 4).

[0006] Japanese Patent Publication No. 2009-299057, Japanese Patent Publication No. 2002-531460, Japanese Patent Publication No. 2022-520286, CN118240419A

[0007] Photoinitiators can raise concerns about their chemical toxicity; for example, TPO (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide), an acylphosphine-based photoinitiator, has been linked to concerns about its biotoxicity. Furthermore, acylphosphine-based photoinitiators may result in insufficient curing properties, leading to inadequate hardness of the cured product; and may also cause discoloration (such as yellowing) of the cured product or insufficient viscosity stability of the ink composition.

[0008] Photopolymerization initiators may have low solubility (for example, low solubility in reactive diluents such as monofunctional monomers), and depending on the type, the solvent resistance of the cured product of the ink composition may not be sufficiently improved. Therefore, the present invention aims to sufficiently improve the curability of an active energy ray curable inkjet printing ink composition containing TMO as a photopolymerization initiator, and preferably improve the solvent resistance of the cured product.

[0009] The present invention relates to the following active energy ray-curable inkjet printing ink composition: [1] An active energy ray-curable inkjet printing ink composition having a viscosity of 5 cps or more and 80 cps or less at room temperature, comprising: 10% by mass or more of a monofunctional monomer relative to the ink composition; 1 to 15% by mass of an amine-modified oligomer relative to the ink composition; and (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide, and further comprising a black pigment, a sensitizer.

[0010] The present invention preferably relates to the following active energy ray curable inkjet printing ink compositions: [2] The ink composition according to [1], further comprising a sensitizer and a colorant. [3] The ink composition according to [1], comprising a white pigment or a transparent extender pigment, or not comprising a pigment component.

[0011] [4] The ink composition according to any one of [1] to [3], wherein the content of (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is 2 to 12% by mass relative to the ink composition. [5] The ink composition according to any one of [1] to [4], wherein the monofunctional monomer includes a monofunctional monomer with a molecular weight of 500 or less, and the content of the monofunctional monomer with a molecular weight of 500 or less is 10% by mass or more relative to the ink composition. [6] The ink composition according to any one of [1] to [5], wherein the monofunctional monomer includes a nitrogen-containing monofunctional monomer. [7] The ink composition according to any one of [1] to [6], wherein the ink composition further includes a polyfunctional monomer in an amount of 2% by mass or more relative to the total polymerizable components. [8] The ink composition according to any one of [1] to [7], wherein the ink composition does not contain diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide.

[0012] The inkjet printing ink composition of the present invention has the properties of an active energy ray curable ink, and can improve the solvent resistance of the cured product while solving problems that may occur with conventional ink compositions containing photoinitiators (improvement of curability, suppression of yellowing of cured products, and improvement of viscosity stability of the ink composition).

[0013] [1. Active Energy Ray Curable Inkjet Printing Ink Composition] The inkjet printing ink composition of the present invention (also simply referred to as "ink composition") is an ink composition that can be cured by exposure to active energy rays. Examples of active energy rays include ultraviolet light, electron beams, and visible light emitted from light-emitting diodes (LEDs) and various lamps and electrodes. From an environmental standpoint, it is preferable to use a light-emitting diode (LED) that generates ultraviolet light with an emission peak wavelength in the range of 350 to 420 nm as the light source for the active energy rays.

[0014] The ink composition of the present invention has a viscosity suitable for inkjet printing. Specifically, the viscosity at room temperature (25°C) is 5 cps or more, and may be 10 cps or more; on the other hand, it is 80 cps or less, preferably 60 cps or less, more preferably 40 cps or less, and may be 30 cps or less. The viscosity of the ink composition can be measured using an E-type viscometer under conditions of a temperature of 25°C and a rotor rotation speed of 20 rpm.

[0015] The inkjet printing ink composition of the present invention comprises A) a monofunctional monomer and an amine-modified oligomer as polymerizable components, and B) (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide as a photopolymerization initiator. The ink composition may also contain a polyfunctional monomer (other than the amine-modified oligomer) as a polymerizable component. The ink composition may also contain a colorant as needed, and in that case, it is preferable to contain a sensitizer. In particular, if the ink composition contains a black pigment, it contains a sensitizer.

[0016] [1-1. Photopolymerizable Components] The polymerizable components contained in the ink composition can be broadly classified into A) monofunctional monomers, B) reactive oligomers, and C) polyfunctional monomers.

[0017] [1-1A. Monofunctional Monomers] Monofunctional monomers as polymerizable components are typically compounds having one ethylenically unsaturated bond. Monofunctional monomers can be broadly classified into nitrogen-containing monofunctional monomers and other monofunctional monomers (unsaturated carboxylic acid compounds, alkyl (meth)acrylate compounds, hydroxyl group-containing (meth)acrylate compounds, halogen-containing (meth)acrylate compounds, ether group-containing (meth)acrylate compounds, carboxyl group-containing (meth)acrylate compounds, other (meth)acrylate compounds, and styrene compounds). In this specification, "(meth)acrylic" means "acrylic and / or methacrylic," and "(meth)acrylic acid" means "acrylic acid and / or methacrylic acid."

[0018] The molecular weight of at least some of the monofunctional monomers used as polymerizable components is preferably 500 or less, more preferably 400 or less, and even more preferably 300 or less. Monofunctional monomers having a molecular weight below a certain level readily dissolve the photopolymerization initiator in the ink composition. The proportion of monofunctional monomers with a molecular weight of 500 or less is preferably at least 50% by mass, more preferably 60% by mass or more, even more preferably 70% by mass or more, and may be 80% by mass or more, or 90% by mass or more, based on the total amount of monofunctional monomers.

[0019] <Nitrogen-containing monofunctional monomers> Nitrogen-containing monofunctional monomers can improve the curability of ink compositions. Examples of nitrogen-containing monofunctional monomers include acryloylmorpholine, vinylmethyloxazolidinone, vinylcaprolactam, and selected from N,N-dimethylacrylamide, acrylonitrile, (meth)acrylamide, diethylacrylamide, N-vinylcarbazole, N-vinylacetamide, N-vinylpyrrolidone, N-vinylformamide, N-hydroxymethyl(meth)acrylamide, diacetoneacrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, lactone-modified flexible acrylates, etc. These nitrogen-containing monofunctional monomers can be used alone or in combination of two or more.

[0020] <Unsaturated Carboxylic Acid Compounds> Examples of unsaturated carboxylic acid compounds include (meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, fumaric acid, maleic acid, and other unsaturated carboxylic acids, as well as their salts and acid anhydrides.

[0021] <Alkyl (meth)acrylate compounds> Examples of alkyl (meth)acrylate compounds include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl acrylate, amyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, isooctyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, i Examples include sodecyl (meth)acrylate, isomiristyl (meth)acrylate, octadecyl (meth)acrylate, dicyclopentanyl (meth)acrylate, tridecyl (meth)acrylate, nonyl (meth)acrylate, hexadecyl (meth)acrylate, myristyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, norbornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, 1-adamantyl (meth)acrylate, 3,5,5-trimethylcyclohexyl acrylate, and 4-t-butylcyclohexyl (meth)acrylate.

[0022] <Hydroxyl group-containing (meth)acrylate compounds> Examples of hydroxyl group-containing (meth)acrylate compounds include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, hydroxypentyl (meth)acrylate, 2-hydroxy-3-methoxypropyl (meth)acrylate, 2-hydroxy-3-butoxypropyl (meth)acrylate, diethylene glycol mono(meth)acrylate, triethylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, dipropylene glycol mono(meth)acrylate, polypropylene Examples include polyalkylene glycol-modified (meth)acrylates such as ylene glycol mono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate, glycerin mono(meth)acrylate, 2-hydroxy-3-chloropropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-hydroxy-3-allyloxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, 2-ethylhexyl EO-modified (meth)acrylate, o-phenylphenol EO-modified (meth)acrylate, p-cumylphenol EO-modified (meth)acrylate, and nonylphenol EO-modified (meth)acrylate.

[0023] <Halogen-containing (meth)acrylate compounds> Examples of halogen-containing (meth)acrylate compounds include trifluoromethyl (meth)acrylate, 2,2,2-trifluoroethyl (meth)acrylate, 2,2,3,3-tetrafluoropropyl (meth)acrylate, 1H-hexafluoroisopropyl (meth)acrylate, 1H,1H,5H-octafluoropentyl (meth)acrylate, 1H,1H,2H,2H-heptadecafluorodecyl (meth)acrylate, 2,6-dibromo-4-butylphenyl (meth)acrylate, 2,4,6-tribromophenoxyethyl (meth)acrylate, and 2,4,6-tribromophenol 3EO (ethylene oxide)-added (meth)acrylate.

[0024] <Ether group-containing (meth)acrylate compounds> Examples of ether group-containing (meth)acrylate compounds include 1,3-butylene glycol methyl ether (meth)acrylate, methoxytriethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, methoxytripropylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, ethyl carbitol (meth)acrylate, 2-ethylhexyl carbitol (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, cresyl polyethylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, p-nonylphenoxyethyl (meth)acrylate, p-nonylphenoxypolyethylene glycol (meth)acrylate, glycidyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxy-polyethylene glycol (meth)acrylate, hexaethylene glycol monophenyl ether mono(meth)acrylate, and diethylene glycol monobutyl ether acrylate. Lilate, dipropylene glycol monomethyl ether (meth)acrylate, 3-methoxybutyl (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate (EO repeating units 400, 700, etc.), 2-(2-ethoxyethoxy)ethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 3-methoxybutyl acrylate, ethoxyethyl acrylate Phenoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, alkoxylated 2-phenoxyethyl (meth)acrylate (ethoxylated 2-phenoxyethyl (meth)acrylate, propoxylated 2-phenoxyethyl (meth)acrylate, etc.), alkoxylated nonylphenyl (meth)acrylate (ethoxylated (4) nonylphenol acrylate, etc.), 2-phenoxyethyl (meth)acrylate, paracumylphenoxyethylene glycol (meth)acrylate, methylphenoxyethyl acrylate,Examples include alkoxy and / or phenoxy (meth)acrylates such as ethoxylated succinic acid (meth)acrylate, ethoxylated tribromophenyl acrylate, and ethoxylated nonylphenyl (meth)acrylate.

[0025] <Carboxyl group-containing (meth)acrylate compounds> Examples of carboxyl group-containing (meth)acrylate compounds include β-carboxyethyl (meth)acrylate, monoacryloyloxyethyl succinate, ω-carboxypolycaprolactone mono(meth)acrylate, 2-(meth)acryloyloxyethyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hexahydrohydrogen phthalate, and 2-(meth)acryloyloxypropyl tetrahydrohydrogen phthalate.

[0026] <Other (meth)acrylate compounds> Other (meth)acrylate compounds include, for example, benzyl acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, acryloylmorpholine, morpholinoethyl (meth)acrylate, trimethylsiloxyethyl (meth)acrylate, diphenyl-2-(meth)acryloyloxyethyl phosphate, 2-(meth)acryloyloxyethyl acid phosphate, caprolactone-modified-2-(meth)acryloyloxyethyl phosphate Cethyl acid phosphate, 2-hydroxy-1-(meth)acryloxy-3-methacryloxypropane, acrylic acid phthalate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalate, 2-(meth)acryloyloxypropyl phthalate, tricyclodecane monomethylol (meth)acrylate, (meth)acrylate dimer, diethylaminoethyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl hexa Hydrophthalic acid, 2-ethylhexyl-diglycol (meth)acrylate, aminoethyl (meth)acrylate, ethyl carbitol acrylate, ethyl diglycol acrylate, dimethylaminoethyl acrylate benzyl chloride quaternary salt, tribromophenyl (meth)acrylate, 1,4-cyclohexanedimethanol mono(meth)acrylate, cresol (meth)acrylate, trimethylolpropane formal (meth)acrylate, neopentyl glycol (meth)acrylate Examples include fermented acid esters, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, 1-(meth)acryloylpiperidine-2-one, 2-(meth)acrylate-1,4-dioxaspiro[4,5]decy-2-ylmethyl, N-(meth)acryloyloxyethylhexahydrophthalimide, γ-butyrolactone (meth)acrylate, caprolactone-modified tetrahydrofurfuryl acrylate, imide acrylate, vinyl (meth)acrylate, maleimide, etc.

[0027] <Styrene-based compounds> Examples of styrene-based compounds include styrene, vinyltoluene, p-hydroxystyrene, p-chlorostyrene, p-bromostyrene, p-methylstyrene, p-methoxystyrene, p-t-butoxystyrene, p-t-butoxycarbonylstyrene, p-t-butoxycarbonyloxystyrene, 2,4-diphenyl-4-methyl-1-pentene, and divinylbenzene.

[0028] As a compound having one ethylenically unsaturated bond, "other compounds having one ethylenically unsaturated bond" other than the aforementioned compounds can be used. Examples of such compounds include vinyl acetate, vinyl monochloroacetate, vinyl benzoate, vinyl pivalate, vinyl butyrate, vinyl laurate, divinyl adipate, vinyl crotonate, vinyl 2-ethylhexanoate, three-membered ring compounds (e.g., vinylcyclopropanes, 1-phenyl-2-vinylcyclopropanes, 2-phenyl-3-vinyloxiranes, 2,3-divinyloxiranes, etc.), and cyclic ketene acetals (e.g., 2-methylene-1,3-dioxepane, posioxolanes, 2-methylene-4-phenyl-1,3-dioxepane, 4,7-dimethyl-2-methylene-1,3-dioxepane, 5,6-benzo-2-methylene-1,3-dioxepane, etc.).

[0029] These monofunctional monomers can be used individually or in combination of two or more.

[0030] The ink composition of the present invention contains polymerizable components, preferably containing 10% by mass or more, and more preferably 15% by mass or more, of monofunctional monomers relative to the ink composition; on the other hand, preferably 80% by mass or less, and more preferably 70% by mass or less. Monofunctional monomers are polymerizable components that can also function as diluents in the ink composition, and by containing 10% by mass or more of them relative to the ink composition, the photopolymerization initiator (TMO: (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide) can be sufficiently dissolved, ensuring the compatibility of the ink composition. Monofunctional monomers can also improve the foldability of the effect product of the ink composition.

[0031] The ink composition of the present invention preferably contains a nitrogen-containing monofunctional monomer as a polymerizable component; however, the content of the nitrogen-containing monofunctional monomer is preferably 20% by mass or more, more preferably 30% by mass or more, and may be 50% by mass or more, based on the total amount of monofunctional monomers. The nitrogen-containing monofunctional monomer readily dissolves the photopolymerization initiator and is therefore preferred as a monofunctional monomer in the ink composition of the present invention containing TMO, which is a photopolymerization initiator with low solubility.

[0032] [1-1B. Reactive Oligomers] The ink composition of the present invention contains a reactive oligomer as a polymerizable component. An oligomer is a component in which ethylenically unsaturated bonds contained within the molecule polymerize to become a high molecular weight component. Since oligomers are relatively high molecular weight components before polymerization, they can impart appropriate viscosity and elasticity to the ink composition. Furthermore, oligomers are relatively polar and may impart non-absorbent adhesion to the printing substrate to the cured ink composition. A reactive oligomer is an oligomer that contains one or more polymerizable functional groups (ethylenically unsaturated bonds) within the molecule.

[0033] The oligomer contained in the ink composition is preferably an amine-modified oligomer. An amine-modified oligomer is a reactive oligomer having two or more amino groups and functional groups that crosslink or polymerize upon irradiation with active energy rays within its molecule. Preferably, an amine-modified oligomer is a reactive oligomer having two amino groups and two functional groups that crosslink or polymerize upon irradiation with active energy rays within its molecule. Amine-modified oligomers are also sometimes referred to as reactive amine co-initiators, reactive amine synergists, acrylate-modified amine synergists, amine acrylates, etc.

[0034] The viscosity of the oligomer (preferably an amine-modified oligomer) is not limited, but it is particularly preferable that the viscosity at 25°C be 2000 cps or less in order to bring the overall viscosity of the photocurable inkjet printing ink composition within an appropriate range.

[0035] The content of amine-modified oligomers in the ink composition is 1% by mass or more, preferably 2% by mass or more, and more preferably 3% by mass or more, relative to the total amount of the ink composition; on the other hand, it is 15% by mass or less, preferably 13% by mass or less, and more preferably 10% by mass or less. By setting the content of amine-modified oligomers to 1% by mass or more, the curability of the ink composition can be improved, and the solvent resistance of the cured coating film can be improved. Furthermore, by setting the content of amine-modified oligomers to 15% by mass or less, the viscosity of the ink composition is suppressed, improving discharge stability while making it easier to ensure the stretchability of the cured printed film. The ink composition of the present invention contains TMO as a polymerization initiator, and TMO has relatively low solubility in reactive diluents (such as monofunctional monomers). Therefore, the curability of the ink composition of the present invention and the solvent resistance of its cured coating film may not be sufficiently improved, so these properties are improved by including amine-modified oligomers.

[0036] Amine-modified oligomers are also available from the market. Examples of amine-modified oligomers available on the market include CN371, CN373, CN383, CN386, CN501, CN550, and CN551 from Sartomer; EBECRYL80 and EBECRYL7100 from Daicel Ornex; GENOMER5142, GENOMER5161, and GENOMER5275 from RAHN; Miramer AS2010 and Miramer AS5142 from Miwon; and Etercure 641, Etercure 6410, Etercure 6411, Etercure 6412, Etercure 6413, and Etercure from Changxing Chemical Co., Ltd. Examples of preferred amine-modified oligomers include 6417, Etercure 6420, Etercure 6422, Etercure 6423, Etercure 6425, Etercure 6430, Etercure 645, and Etercure 647. Preferably, the oligomers are acrylic amine compounds such as CN371, CN373, CN383, and CN386 (manufactured by Sartomer), and even more preferably CN371, CN386 (manufactured by Sartomer), EBECRYL80 (manufactured by Daicel Ornex), etc., which have two or more photopolymerizable functional groups in the molecule.

[0037] [1-1C. Polyfunctional Monomers] Polyfunctional monomers as polymerizable components are monomers having two or more ethylenically unsaturated bonds, and for example, polyfunctional (meth)acrylate compounds and vinyl ether group-containing (meth)acrylate compounds can be used. The polyfunctional (meth)acrylate compounds may be bifunctional di(meth)acrylate compounds, trifunctional tri(meth)acrylate compounds, or polyfunctional (meth)acrylate compounds with more than two functions.

[0038] Examples of difunctional monomers include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, pentyl glycol di(meth)acrylate, neopentyl glycol Di(meth)acrylate, hydroxypivalyl hydroxypivalate di(meth)acrylate, hydroxypivalyl hydroxypivalate dicaprolactone di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,2-hexanediol di(meth)acrylate, 1,5-hexanediol di(meth)acrylate, 2,5-hexanediol di(meth)acrylate, 1,7-heptanediol di(meth)acrylate, 1,8-octanediol di(meth)acrylate, 1,2-octanediol di(meth)acrylate acrylate, 1,9-nonanediol di(meth)acrylate, 1,2-decanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, 1,2-dodecanediol di(meth)acrylate, 1,14-tetradecanediol di(meth)acrylate, 1,2-tetradecanediol di(meth)acrylate, 1,16-hexadecanediolic acid di(meth)acrylate, 1,2-hexadecanediolic acid di(meth)acrylate, 2-methyl-2,4-pentanediol All di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, 2-methyl-2-propyl-1,3-propanediol di(meth)acrylate, 2,4-dimethyl-2,4-pentanediol di(meth)acrylate, 2,2-diethyl-1,3-propanediol di(meth)acrylate, 2,2,4-trimethyl-1,3-pentanediol di(meth)acrylate, dimethylol octanedi(meth)acrylate, 2-ethyl-1,3-hexanediol di(meth)acrylate, 2,5-dimethyl-2,5-Hexanediol di(meth)acrylate, 2-methyl-1,8-octanediol di(meth)acrylate, 2-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, 2,4-diethyl-1,5-pentanediol di(meth)acrylate, 1,2-Hexanediol di(meth)acrylate, 1.5-Hexanediol di(meth)acrylate, 2.5-Hexanediol di(meth)acrylate, 2-methyl-2,4-pentanedi(meth)acrylate, 2.4-diethyl-1,5-pentanediol di(meth)acrylate, tricyclodecanedimethylol di(meth)acrylate, tricyclodecanedimethylol dicaprolactone di(meth)acrylate, bis Examples include phenol A tetraethylene oxide adduct di(meth)acrylate, bisphenol F tetraethylene oxide adduct di(meth)acrylate, bisphenol S tetraethylene oxide adduct di(meth)acrylate, hydrogenated bisphenol A tetraethylene oxide adduct di(meth)acrylate, hydrogenated bisphenol F tetraethylene oxide adduct di(meth)acrylate, hydrogenated bisphenol A di(meth)acrylate, hydrogenated bisphenol F di(meth)acrylate, bisphenol A tetraethylene oxide adduct dicaprolactone di(meth)acrylate, and bisphenol F tetraethylene oxide adduct dicaprolactone di(meth)acrylate.

[0039] Examples of trifunctional monomers include trimethylolpropane EO-modified tri(meth)acrylate, glycerin tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane tricaprolactone tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolhexane tri(meth)acrylate, trimethyloloctan tri(meth)acrylate, and pentaerythritol tri(meth)acrylate.

[0040] Examples of monomers with four or more functionalities include pentaerythritol tetra(meth)acrylate, pentaerythritol tetracaprolactone tetra(meth)acrylate, diglycerin tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ditrimethylolpropane tetracaprolactone tetra(meth)acrylate, ditrimethylolethane tetra(meth)acrylate, ditrimethylolbutane tetra(meth)acrylate, and ditrimethylol Examples include hexanetetra(meth)acrylate, ditrimethyloloctanetetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tripentaerythritol hexa(meth)acrylate, tripentaerythritol hepta(meth)acrylate, tripentaerythritol octa(meth)acrylate, and tripentaerythritol polyalkylene oxide hepta(meth)acrylate.

[0041] The polyfunctional monomer may be a vinyl ether group-containing (meth)acrylate compound; examples include (meth)acrylate-2-vinyloxyethyl, (meth)acrylate-3-vinyloxypropyl, (meth)acrylate-1-methyl-2-vinyloxyethyl, (meth)acrylate-2-vinyloxypropyl, (meth)acrylate-4-vinyloxybutyl, (meth)acrylate-1-methyl-3-vinyloxypropyl, (meth)acrylate-1-vinyloxymethylpropyl, (meth)acrylate-2-methyl-3-vinyl Xyxypropyl, 3-methyl-3-vinyloxypropyl (meth)acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth)acrylate, 3-vinyloxybutyl (meth)acrylate, 1-methyl-2-vinyloxypropyl (meth)acrylate, 2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl (meth)acrylate, 5-vinyloxypentyl (meth)acrylate, 6-vinyloxyhexyl (meth)acrylate, 4-vinyloxymethylcyclohexylmethyl (meth)acrylate , (meth)acrylate-3-vinyloxymethylcyclohexylmethyl, (meth)acrylate-2-vinyloxymethylcyclohexylmethyl, (meth)acrylate-p-vinyloxymethylphenylmethyl, (meth)acrylate-m-vinyloxymethylphenylmethyl, (meth)acrylate-o-vinyloxymethylphenylmethyl, (meth)acrylate-2-(vinyloxyethoxy)ethyl, (meth)acrylate-2-(vinyloxyisopropoxy)ethyl, (meth)acrylate-2-(vinyloxyethoxy)propyl, (meth)acrylate Examples include (t) 2-(vinyloxyethoxy)isopropyl acrylate, (meth) 2-(vinyloxyisopropoxy)propyl meth) acrylate, (meth) 2-(vinyloxyisopropoxy)isopropyl meth) acrylate, (meth) 2-(vinyloxyethoxyethoxy)ethyl meth) acrylate, (meth) 2-(vinyloxyisopropoxyethoxy)ethyl meth) acrylate, (meth) 2-(vinyloxyisopropoxyisopropoxy)ethyl meth) acrylate, etc.

[0042] The ink composition of the present invention may or may not contain a polyfunctional monomer. From the viewpoints of the abrasion resistance and solvent resistance of the printed cured product, it preferably contains 2% by mass or more, more preferably 3% by mass or more, still more preferably 4% by mass or more of a polyfunctional monomer based on the total of the polymerizable components; on the other hand, it preferably contains 80% by mass or less, more preferably 60% by mass or less, still more preferably 40% by mass or less of a polyfunctional monomer. By setting the content of the polyfunctional monomer to 2% by mass or more, the abrasion resistance and solvent resistance of the cured printed film can be improved; on the other hand, when it exceeds 80% by mass, the flexibility (stretchability) of the cured printed film tends to decrease.

[0043] [1-2. Photoinitiator] The ink composition of the present invention contains a photoinitiator. The photoinitiator generates active species such as radicals upon irradiation with active energy rays and initiates the photopolymerization of the active energy ray-curable composition.

[0044] The ink composition of the present invention contains (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide as a photoinitiator. (2,4,6-Trimethylbenzoyl)bis(p-tolyl)phosphine oxide is a compound represented by the following structural formula and may be abbreviated as "TMO".

[0045] TMO is one of the acylphosphine-based photoinitiators, but is considered to be less toxic compared to TPO (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide), which is another acylphosphine-based photoinitiator. That is, TPO is designated as reproductive toxicity category 1B, but TMO is not so designated.

[0046] TMO has lower solubility compared to TPO and is relatively difficult to dissolve in the ink composition. Therefore, in the active energy ray-curable ink composition containing TMO, it is necessary to adjust the composition of the photopolymerizable components so that TMO is easily compatible. Therefore, the ink composition of the present invention contains 10% by mass or more of a monofunctional monomer with respect to the ink composition.

[0047] In addition, the active energy ray-curable ink composition containing TPO sometimes had insufficient solvent resistance of its cured product. On the other hand, by combining TMO and an amine-modified oligomer, the solvent resistance of the cured product of the ink composition can be improved.

[0048] The content of TMO in the ink composition of the present invention is preferably 2% by mass or more, more preferably 4% by mass or more, still more preferably 6% by mass or more, with respect to the total of the ink composition; on the other hand, it is preferably 16% by mass or less, and still more preferably 14% by mass or less.

[0049] The ink composition of the present invention may contain other photoinitiators together with TMO. Examples of other photoinitiators include acylphosphine oxide-based compounds, triazine-based compounds, aromatic ketone-based compounds, aromatic onium salt-based compounds, organic peroxides, thioxanthone-based compounds, thiophenyl-based compounds, anthracene-based compounds, hexaaryl bisimidazole-based compounds, ketoxime ester-based compounds, borate-based compounds, azinium-based compounds, metallocene-based compounds, active ester-based compounds, halogenated hydrocarbon-based compounds, alkylamine-based compounds, iodonium salt-based compounds, sulfonium salt-based compounds, and the like. However, the ink composition of the present invention preferably does not contain TPO specified in Reproductive Toxicity Category 1B.

[0050] [1-3. Colorant or Pigment] The ink composition of the present invention can contain a colorant. A colorant is a component that imparts a color other than white to the ink composition, and imparts black or a color. The colorant may be a pigment or a dye, but is preferably a pigment (colored pigment). Further, the ink composition of the present invention may contain a pigment. It is a component added to impart coloring power, hiding power, etc. to the ink composition; pigments can be roughly classified into white pigments, (non-white) colored pigments, transparent extender pigments, metal powders, etc. Further, pigments can be roughly classified into organic pigments and inorganic pigments.

[0051] The ink composition of the present invention may contain a white pigment or a transparent extender pigment, or it may not contain a pigment; in other words, the ink composition of the present invention may be a white ink or a transparent ink. When the cured product of a white ink or a transparent ink turns yellow, the change in color is often noticeable (easily visible). When an ink composition containing a photopolymerization initiator is cured, the cured product may turn yellow; however, TMO, which is a photopolymerization initiator contained in the ink composition of the present invention, has the characteristic of being less likely to cause yellowing of the cured product. For this reason, it may be preferable that the ink composition of the present invention be a white ink or a transparent ink. Furthermore, if the ink composition of the present invention contains a white pigment or a transparent extender pigment, or if it does not contain a pigment, it may not be necessary to include a sensitizer.

[0052] On the other hand, the ink composition of the present invention may contain a coloring agent; that is, the ink composition of the present invention may be a black ink or a colored ink. As described below, if the ink composition contains a coloring agent, it is preferable to include a sensitizer.

[0053] Examples of white pigments include titanium dioxide (Pigment White 7, etc.), aluminum oxide, zinc oxide, zinc sulfide, antimony oxide, and zirconium oxide, but titanium dioxide is preferred. White pigments may be surface-treated with various materials such as alumina and silica. Examples of transparent extender pigments include silicon dioxide (silica), barium sulfate, aluminum oxide (alumina), calcium carbonate, magnesium carbonate, etc., but silica or alumina is preferred.

[0054] Examples of coloring pigments include dye lake pigments, azo, benzimidazolone, phthalocyanine, quinacridone, anthraquinone, dioxazine, indigo, thioindico, perylene, perinone, diketopyrrolopyrrole, isoindolinone, nitro, nitroso, flavanthrone, quinophthalone, pyranthrone, and indanthrone organic pigments, as well as various inorganic pigments.

[0055] Examples of preferred coloring pigments include yellow pigments such as disazo yellow (pigment yellow 12, pigment yellow 13, pigment yellow 14, pigment yellow 17, pigment yellow 1), Hansa yellow, pigment yellow 150, and pigment yellow 155; magenta pigments such as brilliant carmine 6B, lake red C, watching red, quinacridone, pigment red 122, and pigment red 254; cyan pigments such as phthalocyanine blue, phthalocyanine green, alkali blue, and pigment blue 15:4; colored pigments such as red iron oxide, antimony red, cadmium yellow, cobalt blue, Prussian blue, ultramarine, iron black, chromium oxide green, carbon black (pigment black 7, etc.), and graphite; and metal powders such as aluminum paste and bronze powder.

[0056] Examples of yellow pigments include C. I. Pigment Yellow (PY) 1, 2, 3, 12, 13, 14, 16, 17, 42, 73, 74, 75, 81, 83, 87, 93, 95, 97, 98, 108, 109, 114, 120, 128, 129, 138, 139, 150, 151, 155, 166, 180, 184, 185, and 213.

[0057] Examples of magenta pigments include C. I. Pigment Red (PR) 5, 7, 12, 22, 38, 48:1, 48:2, 48:4, 49:1, 53:1, 57, 57:1, 63:1, 101, 102, 112, 122, 123, 144, 146, 149, 168, 177, 178, 179, 180, 184, 185, 190, 202, 209, 224, 242, 254, 255, 270, and C. I. Pigment Violet 19.

[0058] Examples of cyan pigments include C.I. Pigment Blue (PB) 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 18, 22, 27, 29, and 60.

[0059] Examples of black pigments include carbon black (C.I. Pigment Black 7). As described later, if the ink composition of the present invention contains a black pigment, it further contains a sensitizer. Ink compositions containing black pigments may not have sufficient curability when irradiated with active energy rays, so a sensitizer is included to improve the curability of the ink composition.

[0060] The pigment content in the ink composition varies depending on the type of pigment and the desired degree of coloring, and is not particularly limited: in the case of black pigment or coloring pigment, it is, for example, about 1.0 to 10.0% by mass of the total ink composition; in the case of white pigment or extender pigment, it may be, for example, about 1.0 to 20.0% by mass of the total ink composition.

[0061] [1-4. Sensitizers] The ink composition of the present invention may contain a sensitizer, which can improve the curability of the ink composition. When the ink composition of the present invention contains a black pigment, it is preferable to contain a sensitizer, and when it contains a coloring agent (a coloring agent other than white), it is preferable to contain a sensitizer. This is because when the ink composition is irradiated with active energy rays, the coloring agent contained in the ink composition may block the active energy rays, making it difficult to cure the ink composition. Sensitizers can generally be broadly classified into non-polymeric sensitizers and polymeric sensitizers. The ink composition of the present invention may contain either type of sensitizer, but polymeric sensitizers are sometimes preferred because they can suppress migration from the coating film.

[0062] Examples of non-polymeric sensitizers include anthracene-based sensitizers such as 9,10-dibutoxyanthracene, 9,10-diethoxyanthracene, 9,10-dipropoxyanthracene, and 9,10-bis(2-ethylhexyloxy)anthracene; and thioxanthone-based sensitizers such as 2,4-diethylthioxanthone, 2-isopropylthioxanthone, and 4-isopropylthioxanthone. The sensitizer is preferably a thioxanthone-based sensitizer.

[0063] Examples of polymeric photosensitizers include thioxanthone polymeric photosensitizers, acylphosphine polymeric photosensitizers, and other polymeric photosensitizers. Examples of thioxanthone polymeric photosensitizers include Omnipol TX ((2-carboxymethoxythioxanthone)-(polytetramethylene glycol 250) diester) (number average molecular weight: 660) (manufactured by IGM Resins B.V.) and Genopol TX-1 (number average molecular weight: 820) (manufactured by RaHN). An example of an acylphosphine polymeric photosensitizer is SpeedCure 7010 (molecular weight 1839) (manufactured by Lambson). Furthermore, other polymeric sensitizers include oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propane) (Lamberti, "ESACURE KIP 150", "ESACURE 1"), polyethylene glycol 200-di(β-4(4-(2-dimethylamino-2-benzyl)butanonylphenyl)piperazine) (IGM, "Omnipol 910"), (carboxymethoxymethoxybenzophenone)-(polyethylene glycol 250) diester (IGM, "Omnipol BP"), and others.

[0064] The sensitizer content in the ink composition is preferably 0.3 parts by mass or more, and more preferably 1.0 part by mass or more, when the total amount of polymerizable components is 100 parts by mass; on the other hand, it is preferably 10 parts by mass or less, and more preferably 9 parts by mass or less.

[0065] [1-5. Other Components] The ink composition of the present invention may further contain polymerization inhibitors, pigment dispersants, leveling agents, and other additives.

[0066] [1-5A. Polymerization Inhibitors] The ink composition of the present invention may contain a polymerization inhibitor. Polymerization inhibitors can suppress unintended polymerization reactions (such as polymerization reactions that occur without irradiation with active energy rays). Examples of polymerization inhibitors include hydroquinone, dibutylhydroxytoluene, hydroquinone monomethyl ether, and phenothiazine. The content of the polymerization inhibitor in the ink composition is, for example, about 0.01 to 5.0% by mass.

[0067] [1-5B. Pigment Dispersant] If the ink composition of the present invention contains a pigment, it may further contain a pigment dispersant for dispersing the pigment. The pigment dispersant is preferably a polymer-based pigment dispersant, and more preferably a pigment dispersant containing a basic group. Examples of pigment dispersants containing a basic group include polymer-based pigment dispersants such as basic group-containing polyester pigment dispersants, basic group-containing acrylic pigment dispersants, basic group-containing urethane pigment dispersants, and basic group-containing carbodiimide pigment dispersants, as well as anionic surfactants.

[0068] Polymeric pigment dispersants are not particularly limited, but may be linear polymers having a pigment-affinity moiety consisting of basic groups at least at the ends of the main chain (one or both ends) by a block or graft structure. Polymeric pigment dispersants may contain 2 to 3,000 basic groups per molecule and may have a number-average molecular weight of 1,000 to 1,000,000.

[0069] The pigment dispersant content in the ink composition is preferably 1.0 to 200.0 parts by mass, based on a total pigment amount of 100 parts by mass.

[0070] [1-5C. Leveling Agents (Surface Modifiers)] The ink composition of the present invention may contain leveling agents. Leveling agents can also improve the ejection stability of the ink composition. Examples of leveling agents include nonionic surfactants, cationic surfactants, anionic surfactants, betaine surfactants, and silicone-based surfactants.

[0071] Specific examples of silicone-based surfactants used as leveling agents include polyether-modified silicone oils such as hydroxyl-containing polyether-modified polydimethylsiloxane and polyether-modified polydimethylsiloxane, polyester-modified polydimethylsiloxane and polyester-modified methylalkylpolysiloxane. Silicone-based surfactants are also available from the market as BYK-307, BYK-315, BYK-315N, BYK-331, BYK-333, BYK-347, BYK-348, BYK-349, BYK-345, BYK-377, BYK-378, BYK-3455 (BYK Corporation), etc.

[0072] The content of the surface modifier in the ink composition is preferably in the range of 0.05 to 2.50% by mass relative to the ink composition.

[0073] [1-5D. Other Additives] Examples of other additives include solvents, UV absorbers, antioxidants, defoamers, preservatives, fungicides, rust inhibitors, thickeners, humectants, pH adjusters, and other various additives. The solvent is preferably present in the ink composition at 10.0% by mass or less, more preferably at 5.0% by mass or less, even more preferably at 2.0% by mass or less, and may not be present at all.

[0074] [2. Preparation of Ink Composition] The ink composition of the present invention can be prepared according to conventionally known methods. For example, the components can be dispersed and mixed using a disperser such as a wet circulation mill, bead mill, ball mill, sand mill, attritor, roll mill, DCP mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, high-pressure homogenizer (microfluidizer, nanomizer, ultimateizer, Genus PY, DeBEE2000, etc.), or pearl mill, and the viscosity can be adjusted as necessary to obtain the ink composition.

[0075] Furthermore, if the ink composition contains a pigment, a base ink composition (also called a pigment dispersion) can be obtained in advance by mixing the pigment, a pigment dispersant, and a portion of the polymerizable components, and the remaining portion of the above components can be added to it to prepare the ink composition to achieve the desired composition.

[0076] [3. Inkjet Printing of Ink Compositions] The ink composition of the present invention can be used for printing with an inkjet printing apparatus. The type of inkjet printing apparatus that can be used is not particularly limited and may be a line head type (single pass type) or a serial head type (multi-pass type). A continuous type inkjet printing apparatus may also be used, in which case a conductivity imparting agent can be added to adjust the conductivity of the ink composition.

[0077] The ink composition is supplied to the printer head of an inkjet printing device, and the printer head ejects the ink composition onto the substrate to be printed. The ejection of the ink composition from the printer head onto the substrate (printing of an image) should be performed such that the thickness of the coating on the substrate is, for example, 1 to 60 μm.

[0078] The ink composition that lands on the substrate to be printed is exposed to and cured by active energy rays. Examples of active energy rays include ultraviolet light, electron beams, and visible light emitted from light-emitting diodes (LEDs), various lamps, and electrodes. From an environmental perspective, it is preferable to use light-emitting diodes (LEDs) that generate ultraviolet light with an emission peak wavelength in the range of 350 to 420 nm as the light source.

[0079] The substrate to be printed on is not particularly limited, and is not limited to any substrate to which a conventionally known photocurable inkjet printing ink composition can be applied. Examples of substrates include plastics, paper, capsules, gels, metal foils, glass, wood, and cloth. The cured coating film of the ink composition of the present invention has excellent abrasion resistance and stretchability. Therefore, it is sometimes preferable to print the ink composition of the present invention on a flexible substrate, such as a plastic film.

[0080] Examples of plastics constituting the substrate to be printed include one or more selected from the group consisting of polyester polymers (e.g., polyethylene terephthalate (PET), polyethylene naphthalate, etc.), cellulosic polymers (e.g., diacetylcellulose, triacetylcellulose (TAC), etc.), polycarbonate polymers, polyacrylic polymers (e.g., polymethyl methacrylate, etc.), vinyl chloride polymers, polyolefin polymers (e.g., polyethylene, polypropylene, polyolefin polymers having a cyclic or norbornene structure, ethylene-propylene copolymer polymers, etc.), polyamide polymers (e.g., nylon, aromatic polyamide polymers, etc.), polystyrene polymers (e.g., polystyrene, acrylonitrile-styrene copolymer polymers, etc.), polyimide polymers, polysulfone polymers, polyethersulfone polymers, polyetherketone polymers, polyphenylsulfide polymers, polyvinyl alcohol polymers, polyvinylidene chloride polymers, polyvinyl butyral polymers, polyarylate polymers, polyoxymethylene polymers, and polyepoxy polymers, as well as blends of these polymers.

[0081] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention shall not be construed as being limited based on the description of the examples.

[0082] A. Preparation of Ink Compositions The raw materials used in the preparation of the ink compositions of each example and comparative example shown in Tables 1 to 4 are shown below.

[0083] A-1. Pigments: Pigment Yellow 150, Pigment Red 122, Pigment Red 254, Pigment Blue 15:4, Pigment Black 7, Pigment White 7, AEROXIDE® ALU-C: Alumina microparticles (Evonik), AEROSIL® R9200: Silica microparticles (Evonik)

[0084] A-2. Pigment dispersants: • Solsperse 56000: Pigment dispersion resin, amine value 39 mg KOH / g (Lubrizol) • BYKJET 9151: Pigment dispersion resin (BYK) • Solsperse 36000: Pigment dispersion resin, acid value 45 mg KOH / g (Lubrizol) • Adisper PB821: Pigment dispersion resin (Ajinomoto Fine Techno Co., Ltd.)

[0085] A-3. Monofunctional monomers: 4HBA (4-hydroxybutyl acrylate) Molecular weight: 144.2 Benzyl acrylate Molecular weight: 162.2 VCAP (N-vinylcaprolactam) Molecular weight: 139.2 Acryloylmorpholine Molecular weight: 141.17

[0086] A-4. Oligomer CN371NS: Amine-modified oligomer (Sartomer Co., Ltd.) Miramer PE-210: Bisphenol A epoxy acrylate (Miwon Co., Ltd.)

[0087] A-5. Polyfunctional monomers: Trimethylolpropane(EO)3triacrylate (Miramer M3130, Toyo Chemicals Co., Ltd.), Dipropylene glycol diacrylate, 1,6-Hexanediol diacrylate

[0088] A-6. Photopolymerization initiators: TMO: (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide; TPO: diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; BAPO: phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; TPOL: (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide

[0089] A-7. Sensitizers: DETX: 2,4-diethylthioxanthone; Speedcure 7010: High molecular weight thioxanthone (Sartomer Co.)

[0090] A-8. Other Additives: • Irgastab UV22: Polymerization inhibitor (BASF) • Lunacure 500: Polymerization inhibitor (DKSH) • BYK-377: Silicone-based surface modifier (BYK) • ESACURE A198: Aminobenzoate compound (IGM RESINS B.V.)

[0091] Inkjet printing ink compositions for each example and comparative example were prepared by blending and stirring each component according to the formulations shown in Tables 1 to 4.

[0092] B. Evaluation of Ink Compositions and Their Cured Coatings (Printed Materials) The ink compositions and their cured products produced in each example and comparative example were evaluated for the following items, and the evaluation results are shown in Tables 1 to 4.

[0093] B-1. Viscosity of the ink composition The viscosity (cps) of the ink composition immediately after preparation was measured using an E-type viscometer (product name: RE100L viscometer, manufactured by Toki Sangyo Co., Ltd.) at a temperature of 25°C and a rotor rotation speed of 20 rpm.

[0094] B-2. Solvent Resistance of Cured Coating Films The cured coating films of each ink composition printed on a PVC board (T938, manufactured by Takiron CI Co., Ltd.) were evaluated using a Japan Society for the Promotion of Science (JSPS) fastness tester (manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd.). The degree to which the coating film was removed was visually observed when the coating film was rubbed with a bleaching cloth containing 30% ethanol water 5 times, and evaluated according to the following criteria: ○: No removal of coating film △: Scratches on the surface of the coating film ×: Clear removal of coating film observed

[0095] B-3. ​​Bendability of Cured Coating Films (Printed Materials) The cured coating films of each ink composition printed on PET (E5100, manufactured by Toyobo Co., Ltd.) were bent at a bending angle of 180 degrees, and the state of cracking was visually inspected. ○: No cracks such as fine cracks appear in the coating film △: Fine cracks appear in the coating film ×: Clear cracks appear in the coating film

[0096] B-4. LED Curability (Surface Curability) of Ink Compositions Each ink composition was applied to the surface of a PET film using a bar coater No. 4 to obtain each coated product. Then, an LED irradiation device (398 nm, 500 mJ / cm²) was used. 2LED light was irradiated using a cotton swab. After light irradiation, the ink-coated film was lightly rubbed with a cotton swab, and the condition of the film and the cotton swab was evaluated. ○: No swab marks were left on the film △: Some swab marks were left on the film ×: Ink was left on the cotton swab

[0097] B-5. Compatibility of Photopolymerization Initiators In the ink compositions of each example and comparative example, each component excluding the pigment and pigment dispersant was stirred and mixed in a disperser at room temperature, and the time until the photopolymerization initiator dissolved was measured and evaluated according to the following evaluation criteria. ○: Dissolves within 1 hour △: Dissolves in 1 to 2 hours ×: Does not dissolve even after 2 hours or more

[0098] B-6. The cured coatings of each ink composition printed on a yellowish-white PVC board were color-measured using an X-Rite eXact spectrophotometer (manufactured by x-rite), and evaluated according to the following criteria based on their b* values: ○: b* value is less than 0. ×: b* value is 0 or greater.

[0099] B-7. Pencil Hardness of Cured Coatings Tests were conducted on cured coatings printed on substrates in accordance with JIS K 5600-5-4:1999, General Test Methods for Paints. The hardness of the hardest pencil that did not exhibit cohesive failure was defined as the pencil hardness. ○: 2H or higher △: B to H ×: 2B or lower

[0100] B-8. Viscosity Stability of Ink Compositions After allowing each ink composition obtained in the examples and comparative examples to stand for 3 weeks at an ambient temperature of 60°C, the viscosity was measured using an E-type viscometer, and the viscosity increase rate (%) was calculated using the following formula. Viscosity stability was evaluated according to the following evaluation criteria: Viscosity increase rate (%) = ((Viscosity value after standing for 3 weeks at 60°C / Viscosity value after standing for 3 weeks at 25°C) × 100) - 100. ○: Viscosity increase rate less than 10% △: Viscosity increase rate between 10% and 20% ×: Viscosity increase rate greater than 20%

[0101]

[0102]

[0103] As shown in Comparative Examples 1 and 2 of Table 2, the ink compositions containing TPO as a photopolymerization initiator did not exhibit sufficient solvent resistance in their cured coatings. Furthermore, as shown in Comparative Examples 3 and 4 of Table 2, the ink compositions containing TPOL, or a combination of TPOL and BAPO, as a photopolymerization initiator, did not exhibit sufficient solvent resistance in their cured coatings, nor did they exhibit sufficient LED curability or pencil hardness. The viscosity stability of the ink compositions also deteriorated. As shown in Comparative Example 4, the ink composition containing a combination of TPOL and BAPO as a photopolymerization initiator showed yellowing in its cured coating. In contrast, the examples containing TMO as a photopolymerization initiator (Table 1) obtained satisfactory evaluations in all evaluation items.

[0104] As shown in Comparative Example 5 in Table 2, ink compositions that did not contain amine-modified oligomers showed reduced LED curability and insufficient solvent resistance, despite containing other oligomers. Thus, even when TMO is included as a photopolymerization initiator, ink compositions that do not contain the reactive oligomer amine-modified oligomer cannot achieve both LED curability and solvent resistance. Furthermore, as shown in Comparative Example 6 in Table 2, ink compositions with a low monofunctional monomer content (3% by mass relative to the ink composition) did not have sufficient compatibility with the photopolymerization initiator, resulting in insufficient LED curability of the cured coating film. In addition, the flexibility of the cured coating film was also reduced in Comparative Example 6. In contrast, each example (Table 1) containing amine-modified oligomers and a predetermined amount of monofunctional monomers obtained sufficient evaluations for each evaluation item.

[0105] As can be seen from the comparison with Examples 1-5, 6, 7, and 8 in Table 1, sufficient evaluations were obtained for each evaluation item whether the pigment included a white pigment or a transparent extender pigment, or whether it did not contain any pigment.

[0106] As can be seen from the comparison between Example 1 and Example 2 in Table 1, the TMO content is adjustable, and by combining it with other photopolymerization initiators, sufficient evaluation can be obtained for each evaluation item.

[0107] As can be seen from the comparison between Example 1 and Examples 3 and 4 in Table 1, the content of the amine-modified oligomer can be adjusted, for example, by balancing it with the polyfunctional monomer.

[0108] As can be seen from the comparison between Example 1 and Example 5 in Table 1, the content of monofunctional monomers (especially nitrogen-containing monomers) can be adjusted.

[0109]

[0110]

[0111] As shown in Comparative Examples 7 and 8 of Table 4, the ink compositions containing TPO as a photopolymerization initiator did not exhibit sufficient solvent resistance in their cured coatings. Furthermore, as shown in Comparative Examples 9 and 10 of Table 4, the ink compositions containing TPOL, or a combination of TPOL and BAPO, as a photopolymerization initiator, did not exhibit sufficient solvent resistance in their cured coatings, nor did they exhibit sufficient LED curability or pencil hardness. The viscosity stability of the ink compositions also deteriorated. In contrast, Examples 9 to 17 (Table 3), which contained TMO as a photopolymerization initiator, obtained practically sufficient evaluations in all evaluation items.

[0112] As shown in Comparative Example 11 of Table 4, when a black pigment was included, the ink composition without a sensitizer showed reduced LED curability and hardness of the cured coating film.

[0113] As shown in Comparative Example 12 of Table 4, ink compositions that did not contain amine-modified oligomers exhibited reduced LED curability despite containing other oligomers. Furthermore, as shown in Comparative Example 13 of Table 4, ink compositions with a low monofunctional monomer content (3% by mass relative to the ink composition) did not adequately match the photopolymerization initiator, resulting in insufficient LED curability of the cured coating film. In addition, Comparative Example 13 also showed reduced flexibility of the cured coating film. In contrast, Examples 9 to 17 (Table 3), which contained amine-modified oligomers and a predetermined amount of monofunctional monomers, obtained practically sufficient evaluations for each evaluation item.

[0114] As can be seen from the comparison with Examples 9-14, 15, 16, and 17 in Table 3, sufficient evaluations were obtained for each evaluation item whether the pigment included black pigment or various color pigments.

[0115] As can be seen from the comparison between Example 9 and Example 10 in Table 3, the TMO content is adjustable, and by combining it with other photopolymerization initiators or appropriately selecting sensitizers, sufficient evaluation can be obtained for each evaluation item.

[0116] As can be seen from the comparison between Example 9 and Examples 11 and 12 in Table 3, the content of the amine-modified oligomer can be adjusted, for example, by balancing it with the polyfunctional monomer. Also, as can be seen from the comparison between Example 9 and Example 13 in Table 3, the content of the monofunctional monomer (especially nitrogen-containing monofunctional monomer) can also be adjusted, for example, by balancing it with the polyfunctional monomer. Furthermore, as can be seen from the comparison between Example 9 and Example 14 in Table 3, the content of the sensitizer can also be adjusted to some extent.

[0117] The active energy ray-curable inkjet printing ink composition of the present invention contains TMO, which has low biotoxicity, as a photopolymerization initiator, and can therefore be used as an ink composition with high biological safety. Furthermore, it exhibits excellent ink properties and cured film properties as an active energy ray-curable inkjet printing ink composition, and in particular, has excellent solvent resistance. Therefore, it can be applied to various applications of conventional active energy ray-curable inkjet printing ink compositions and is expected to be applied to new applications.

Claims

1. An active energy ray curable ink for inkjet printing having a viscosity of 5 cps or more and 80 cps or less at room temperature, comprising: 10% by mass or more of a monofunctional monomer relative to the ink composition; 1 to 15% by mass of an amine-modified oligomer relative to the ink composition; and (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide, and further comprising a black pigment, a sensitizer.

2. The ink composition according to claim 1, further comprising a sensitizer and a coloring agent.

3. The ink composition according to claim 1, which contains a white pigment or a transparent extender pigment, or which does not contain a pigment component.

4. The ink composition according to any one of claims 1 to 3, wherein the content of (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is 2 to 12% by mass relative to the ink composition.

5. The ink composition according to any one of claims 1 to 3, wherein the monofunctional monomer comprises a monofunctional monomer with a molecular weight of 500 or less, and the content of the monofunctional monomer with a molecular weight of 500 or less is 10% by mass or more relative to the ink composition.

6. The ink composition according to any one of claims 1 to 3, wherein the monofunctional monomer includes a nitrogen-containing monofunctional monomer.

7. The ink composition according to any one of claims 1 to 3, further comprising 2% by mass or more of polyfunctional monomers relative to the total amount of polymerizable components.

8. The ink composition according to any one of claims 1 to 3, wherein the ink composition does not contain diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide.

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