Ink composition

Abstract

[Problem] To provide an ink composition which has excellent re-solubility and dischargeability, suppresses odor, and can form a printed layer of high hardness. [Solution] An ink composition containing a pigment, a polymerizable compound, and a photopolymerization initiator, wherein the polymerizable compound contains at least an aminoacrylate (A), the photopolymerization initiator contains at least a hydrogen-extractive photopolymerization initiator (B), the amount of the aminoacrylate (A) contained in the ink composition is 10-30% by mass, and the amount of the hydrogen-extractive photopolymerization initiator (B) contained in the ink composition is 1.0-15.0% by mass.

Description

Ink composition

[0001] The present invention relates to an ink composition, and more particularly to an ink composition that has excellent resolubility and ejection properties, and furthermore, is odor-resistant and capable of forming a printed layer with high hardness.

[0002] When a photocurable ink composition is used for printing on a substrate, the ink composition is required to have additional properties in addition to photocurability depending on the application of the substrate. For example, in order to prevent scratches on the surface of the printed plastic substrate, the printed layer formed on the substrate is often required to have high hardness.

[0003] Photocurable ink compositions typically contain a polymerizable compound and a photopolymerization initiator. A radical polymerization initiator is preferred as the photopolymerization initiator. A commonly used method involves generating a polymerization initiating species (radicals) through light absorption by the photopolymerization initiator, causing a polymerization reaction of the polymerizable compound, and forming a film. α-Aminoacetophenone-type photopolymerization initiators (e.g., Omnirad 907 manufactured by IGM) and acylphosphine oxide-type photopolymerization initiators (e.g., Omnirad TPO manufactured by IGM) are known as photopolymerization initiators that have excellent photocuring properties and are suitable for use in ink compositions that can form highly hard printed layers.

[0004] However, α-aminoacetophenone-type photopolymerization initiators and acylphosphine oxide-type photopolymerization initiators are classified as Norrish Type I photopolymerization initiators (intramolecular cleavage-type photopolymerization initiators) that undergo a cleavage reaction within one molecule under light irradiation. Intramolecular cleavage-type photopolymerization initiators are substances that generate radicals through intramolecular cleavage, and these radicals initiate the polymerization of polymerizable compounds. However, the intramolecular cleavage also produces low-molecular-weight compounds, which poses odor problems.

[0005] Therefore, the present inventors have focused on a Norrish type II photopolymerization initiator as a radical polymerization initiator, in which an excited photopolymerization initiator undergoes a bimolecular reaction with another molecule (co-initiator) to generate an initiating radical.

[0006] Japanese Patent Laid-Open Publication No. 2021-161159 (Patent Document 1) describes an ink composition containing a photopolymerizable compound and a photopolymerization initiator, wherein the photopolymerizable compound contains a monofunctional polymerizable compound A and a polymerizable compound B, wherein the monofunctional polymerizable compound A is polymerized to produce a polymer having a glass transition temperature Tg of 25°C or higher and 60°C or lower, the polymerizable compound B has a repeating sequence having a structure containing an amino group and an ether group and is a polymerizable compound having two or more (meth)acrylate groups, and the photopolymerization initiator contains at least a hydrogen abstraction initiator. The examples of Patent Document 1 use JRCURE TPO (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide), an intramolecular cleavage type photopolymerization initiator, as the main photopolymerization initiator, but DETX (2,4-diethylthioxanthone), a hydrogen abstraction type photopolymerization initiator, is used in combination with this JRCURE TPO, and Genomer 5271 (amine acrylate) is used as polymerizable compound B. Therefore, although the ink composition described in Patent Document 1 is recognized as utilizing an intramolecular cleavage type photopolymerization initiator as the main photopolymerization initiator, the use of DETX and Genomer 5271 indicates that a Norrish Type II photopolymerization initiator is used as part of the radical polymerization initiator.

[0007] Japanese Patent Application Laid-Open No. 2021-161159

[0008] By using a Norrish type II photopolymerization initiator in the ink composition, the odor problem caused by using a Norrish type I photopolymerization initiator (intramolecular cleavage type photopolymerization initiator) can be resolved, but the hardness of the printed layer is not sufficient, and there is room for further investigation.

[0009] Therefore, an object of the present invention is to provide an ink composition that is excellent in resolubility and ejection properties, and further, that is odor-resistant and capable of forming a printed layer with high hardness.

[0010] As a result of extensive research into achieving the above object, the present inventors have found that by blending an aminoacrylate and a hydrogen abstraction photopolymerization initiator into an ink composition and adjusting the amounts of the aminoacrylate and hydrogen abstraction photopolymerization initiator contained in the ink composition to 10 to 30 mass % and 1.0 to 15.0 mass %, respectively, it is possible to provide an ink composition that has excellent resolubility and ejection stability, and furthermore, is capable of forming a printed layer with reduced odor and high hardness, and have thereby completed the present invention.

[0011] Therefore, the ink composition of the present invention is an ink composition containing a pigment, a polymerizable compound, and a photopolymerization initiator, wherein the polymerizable compound contains at least an aminoacrylate (A), the photopolymerization initiator contains at least a hydrogen abstraction photopolymerization initiator (B), the amount of the aminoacrylate (A) contained in the ink composition is 10 to 30 mass %, and the amount of the hydrogen abstraction photopolymerization initiator (B) contained in the ink composition is 1.0 to 15.0 mass %.

[0012] In a preferred embodiment of the ink composition of the present invention, the photopolymerizable compound includes a monofunctional polymerizable compound (C), a bifunctional polymerizable compound (D), and a tri- or higher functional polymerizable compound (E), and the monofunctional polymerizable compound (C), the bifunctional polymerizable compound (D), and the tri- or higher functional polymerizable compound (E) are polymerizable compounds different from the amino acrylate (A).

[0013] In another preferable embodiment of the ink composition of the present invention, the mass ratio (D / E) of the bifunctional polymerizable compound (D) to the tri- or higher functional polymerizable compound (E) contained in the ink composition is 30 / 70 to 80 / 20.

[0014] In another preferable embodiment of the ink composition of the present invention, the photopolymerization initiator includes an intramolecular cleavage-type photopolymerization initiator (F), and the amount of the intramolecular cleavage-type photopolymerization initiator (F) contained in the ink composition is 3.0 mass% or less.

[0015] In another preferable embodiment of the ink composition of the present invention, the mass ratio (B / F) of the hydrogen abstraction type photopolymerization initiator (B) to the intramolecular cleavage type photopolymerization initiator (F) contained in the ink composition is 2.0 or more.

[0016] In another preferable embodiment of the ink composition of the present invention, the mass ratio (A / B) of the aminoacrylate (A) to the hydrogen abstraction photopolymerization initiator (B) contained in the ink composition is 1.0 to 30.0.

[0017] According to the present invention, it is possible to provide an ink composition that has excellent resolubility and ejection stability, and further has reduced odor and is capable of forming a printed layer with high hardness.

[0018] The present invention will be described in detail below. The present invention relates to an ink composition containing a pigment, a polymerizable compound, and a photopolymerization initiator.

[0019] The ink composition of the present invention contains a polymerizable compound and a photopolymerization initiator, and is an ink composition that can be cured by irradiation with actinic energy rays such as ultraviolet rays, visible light, or electron beams, and is therefore suitable as an actinic energy ray-curable ink composition.

[0020] The polymerizable compound is a compound having a radically polymerizable functional group (for example, a polymerizable unsaturated group such as a carbon-carbon double bond constituting an acryloyl group, a methacryloyl group, a vinyl group, or an allyl group), and is capable of undergoing a polymerization reaction via the radically polymerizable functional group. A radically polymerizable carbon-carbon double bond is also called an "ethylenically unsaturated double bond." The polymerizable compound may be used alone or in combination of two or more types.

[0021] Polymerizable compounds are classified into monofunctional polymerizable compounds and polyfunctional polymerizable compounds. Here, examples of monofunctional polymerizable compounds include monofunctional polymerizable monomers having one functional group exhibiting radical polymerizability (for example, monofunctional polymerizable monomers having one polymerizable unsaturated group) and monofunctional polymerizable oligomers having one functional group exhibiting radical polymerizability (for example, monofunctional polymerizable oligomers having one polymerizable unsaturated group). Examples of polyfunctional polymerizable compounds include polyfunctional polymerizable monomers having two or more functional groups exhibiting radical polymerizability (for example, polyfunctional polymerizable monomers having two or more polymerizable unsaturated groups) and polyfunctional polymerizable oligomers having two or more functional groups exhibiting radical polymerizability (for example, polyfunctional polymerizable oligomers having two or more polymerizable unsaturated groups).

[0022] In the ink composition of the present invention, the polymerizable compound preferably contains both a monofunctional polymerizable compound and a polyfunctional polymerizable compound, and more preferably contains a monofunctional polymerizable compound, a bifunctional polymerizable compound, and a trifunctional or higher functional polymerizable compound. A bifunctional polymerizable compound is a polyfunctional polymerizable compound having two functional groups that exhibit radical polymerizability, and a trifunctional or higher functional polymerizable compound is a polyfunctional polymerizable compound having three or more functional groups that exhibit radical polymerizability.

[0023] The amount of polymerizable compounds contained in the ink composition of the present invention is preferably 50 to 98% by mass, and more preferably 70 to 96% by mass. The amount of monofunctional polymerizable compounds contained in the ink composition of the present invention is preferably 10 to 60% by mass, and more preferably 20 to 40% by mass. The amount of polyfunctional polymerizable compounds contained in the ink composition of the present invention is preferably 40 to 85% by mass, and more preferably 45 to 75% by mass. The amount of bifunctional polymerizable compounds contained in the ink composition of the present invention is preferably 20 to 65% by mass, and more preferably 30 to 55% by mass. The amount of tri- or higher functional polymerizable compounds contained in the ink composition of the present invention is preferably 5 to 40% by mass, and more preferably 10 to 30% by mass.

[0024] In the ink composition of the present invention, the polymerizable compound contains at least an aminoacrylate. The aminoacrylate is a compound having an amino group and an acryloyl group and / or a methacryloyl group. Here, the amino group is defined as —NH ２ or a functional group having the structure -NH ２ It refers to a functional group in which one or two hydrogen atoms are substituted with an organic group (for example, a hydrocarbon group). In the present invention, an aminoacrylate is a compound having one or more amino groups and one or more radically polymerizable functional groups, wherein one or more of the radically polymerizable functional groups is an acryloyl group or a methacryloyl group. In this specification, aminoacrylate is referred to as component (A) and is also referred to as "aminoacrylate (A)."

[0025] The ink composition of the present invention uses at least a Norrish type II photopolymerization initiator in which an excited-state photopolymerization initiator undergoes a bimolecular reaction with another molecule (co-initiator) to generate initiating radicals. Here, the aminoacrylate (A) is a substance that acts as a co-initiator that reacts with the excited-state photopolymerization initiator. On the other hand, the aminoacrylate (A) is also a compound having a functional group that exhibits radical polymerizability, and therefore is classified as a polymerizable compound in the present invention. Note that the present invention uses a hydrogen abstraction photopolymerization initiator that becomes excited upon absorption of light and reacts with the co-initiator (component (A) in the present invention) to generate initiating radicals. In this specification, the hydrogen abstraction photopolymerization initiator is referred to as component (B), and is also referred to as "hydrogen abstraction photopolymerization initiator (B)."

[0026] Amine-based materials have a radical chain transfer effect, which can lower the molecular weight of the polymer formed. However, when an aminoacrylate (A) is used together with a hydrogen-abstraction photopolymerization initiator (B), even if the polymerization reaction terminates due to radical chain transfer, repolymerization is possible from around the amino group in the chain, making it easier to form a high-molecular-weight polymer, resulting in excellent photocurability and high hardness. According to the present invention, as described below, by adjusting the amounts of aminoacrylate (A) and hydrogen-abstraction photopolymerization initiator (B) contained in the ink composition within a specific range, an ink composition can be provided that has excellent photocurability and is capable of forming a printed layer with high hardness. Furthermore, the ink composition of the present invention uses a Type II photopolymerization initiator in which an excited photopolymerization initiator undergoes a bimolecular reaction with another molecule (co-initiator) to generate an initiating radical. Therefore, compared to ink compositions that use an intramolecular cleavage photopolymerization initiator as the main photopolymerization initiator, the odor caused by the use of the photopolymerization initiator can be reduced.

[0027] The amount of aminoacrylate (A) contained in the ink composition of the present invention is 10 to 30% by mass, and preferably 15 to 25% by mass. If the amount of aminoacrylate (A) is less than 10% by mass, it is difficult to form a highly hard printed layer, and if the amount of aminoacrylate (A) exceeds 30% by mass, the viscosity of the ink composition increases, tending to deteriorate the ejection properties of the ink composition.

[0028] The aminoacrylate (A) preferably has one or more radically polymerizable functional groups, and more preferably has two to four radically polymerizable functional groups.

[0029] The aminoacrylate (A) can be obtained by reacting (meth)acrylic acid or (meth)acrylate with an amine compound. Examples of methods for preparing the aminoacrylate (A) include an esterification reaction between (meth)acrylic acid or (meth)acryloyl chloride and an alkanolamine, an addition reaction between a (meth)acrylic acid ester of a polyhydric alcohol and a monoamine or diamine, and an addition reaction between a (meth)acrylate and an alkanolamine.

[0030] Examples of alkanolamines that can be used to prepare the aminoacrylate (A) include N,N-dimethylethanolamine, diethanolamine, triethanolamine, diisopropanolamine, N-methyldiethanolamine, and 2-amino-2-methyl-1-propanol.

[0031] The (meth)acrylic acid ester of a polyhydric alcohol that can be used to prepare the aminoacrylate (A) can be prepared, for example, by reacting (meth)acrylic acid with an alcohol having two or more hydroxyl groups. Examples of the alcohol having two or more hydroxyl groups include 1,6-hexanediol, glycerin, trimethylolpropane, trimethylolethane, and pentaerythritol.

[0032] Examples of monoamines that can be used in the preparation of the aminoacrylate (A) include methylamine, n-butylamine, n-hexylamine, 2-ethylhexylamine, cyclohexylamine, ethanolamine, and benzylamine.

[0033] Examples of diamines that can be used to prepare the aminoacrylate (A) include ethylenediamine, tetramethylenediamine, 1,5-pentamethylenediamine, and hexamethylenediamine.

[0034] The amino acrylate (A) may also be called a reactive amine coinitiator, a reactive amine synergist, an acrylate-modified amine synergist, an amine acrylate, or the like.

[0035] Examples of commercially available aminoacrylates (A) include "Aron DA (dimethylaminoethyl acrylate)" (product name) manufactured by Toagosei Co., Ltd., "MIRAMER AS5142" (trade name) manufactured by MIWON Co., Ltd., "CN371 NS" (trade name), "CN550" (trade name), and "CN551 NS" (trade name) manufactured by Arkema, "EBECRYL 7100," "EBECRYL 80," "EBECRYL 81" (trade name), and "EBECRYL 83" (trade name) manufactured by Cytec, and "GC1100Z" and "GC1000W" (trade name) manufactured by Qualipoly Chemical Corporation.

[0036] The amino acrylate (A) may be used alone or in combination of two or more kinds.

[0037] In the ink composition of the present invention, the polymerizable compound preferably includes, in addition to the amino acrylate (A), a monofunctional polymerizable compound that does not fall under the amino acrylate (A), a bifunctional polymerizable compound that does not fall under the amino acrylate (A), and a tri- or higher functional polymerizable compound that does not fall under the amino acrylate (A). In this specification, a monofunctional polymerizable compound that does not fall under the amino acrylate (A) is referred to as component (C) and is also referred to as a "monofunctional polymerizable compound (C)," a bifunctional polymerizable compound that does not fall under the amino acrylate (A) is referred to as component (D) and is also referred to as a "bifunctional polymerizable compound (D)," and a tri- or higher functional polymerizable compound that does not fall under the amino acrylate (A) is referred to as component (E) and is also referred to as a "tri- or higher functional polymerizable compound (E)."

[0038] The monofunctional polymerizable compound (C) is preferably a monofunctional polymerizable monomer, and specific examples thereof include isoamyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, and ethyl carbitol (meth)acrylate. acrylate, 2-(2'-vinyloxyethoxy)ethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-t-butylcyclohexyl (meth)acrylate, cyclohexyl (meth)acrylate, N-(meth)acryloylmorpholine, tetrahydrofurfuryl (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, γ-butyrolactone (meth)acrylate, N-vinylcaprolactam, N-(meth)acryloyloxyethylhexahydrophthalimide, 1-(meth)acryloylpyrrolidin-2-one, 1-(meth)acryloylpiperidin-2-one, N-vinyl-2-pyrrolidone, N-vinylimidazole, dimethylacrylamide, hydroxyethyl (meth)acrylamide , diethyl acrylamide, isopropyl acrylamide, dimethylaminopropyl (meth)acrylamide, diacetone acrylamide, N-n-butoxymethyl acrylamide, N-isobutoxymethyl acrylamide, N-methoxymethyl acrylamide, N-methylolacrylamide, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, benzyl (meth)acrylate, neopentyl glycol (meth)acrylic acid benzoate, Isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, γ-(meth)acryloxypropyltrimethoxysilane, γ-(meth)acryloxypropyltriethoxysilane, γ-(meth)acryloxypropylmethyldimethoxysilane, γ-(meth)acryloxypropylmethyldiethoxysilane, γ-(meth)acryloxypropylmethyldipropoxysilane, γ-(meth)acryloxypropylmethyldipropoxysilane ) acryloxybutylphenyldimethoxysilane, γ-(meth)acryloxypropyldimethylmethoxysilane, γ-(meth)acryloxypropyldiethylmethoxysilane, β-(meth)acryloxyethyltrimethoxysilane, β-(meth)acryloxyethyltriethoxysilane, polyoxyethylene mono(meth)acrylate, polyoxypropylene mono(meth)acrylate, polyoxybutylene mono(meth)acrylate, and the like, as well as compounds modified with alkylene glycol. Among these, monofunctional polymerizable monomers with elongated alkyl chains or alkylene glycol chains are preferred because their increased molecular weight reduces odor compared to before chain elongation.

[0039] As described above, the amount of the monofunctional polymerizable compound (C) contained in the ink composition of the present invention is preferably 10 to 60 mass %, and more preferably 20 to 40 mass %. The monofunctional polymerizable compound (C) may be used alone or in combination of two or more types.

[0040] The bifunctional polymerizable compound (D) includes bifunctional polymerizable monomers and bifunctional polymerizable oligomers. Examples of the polymerizable monomer corresponding to the bifunctional polymerizable compound (D) include 1,3-butylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,5-pentanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,7-heptanediol di(meth)acrylate, 1,8-octanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, 2-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, 2-methyl-1,8-octanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, dipropyl ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, PO (propylene oxide)-modified neopentyl glycol di(meth)acrylate, cyclohexanedimethanol diacrylate, tricyclodecane dimethanol diacrylate, dimethylol-tricyclodecane di(meth)acrylate, dicyclopentanyl diacrylate, bisphenol A di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, and the like.

[0041] Examples of the tri- or higher functional polymerizable compound (E) include tri- or higher functional polymerizable monomers and tri- or higher functional polymerizable oligomers. Examples of the polymerizable monomer corresponding to the trifunctional or higher polymerizable compound (E) include trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, ethoxylated glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, EO-modified diglycerin tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, EO-modified dipentaerythritol hexa(meth)acrylate, and glycerin tri(meth)acrylate.

[0042] The polymerizable oligomer corresponding to the bifunctional polymerizable compound (D) or the trifunctional or higher polymerizable compound (E) is preferably an acrylic oligomer, which is an oligomer having an acryloyl group or a methacryloyl group as a radically polymerizable functional group.

[0043] The number of functional groups of the polymerizable oligomer is preferably 2 to 6, and the molecular weight of the polymerizable oligomer is preferably 800 to 20000. The molecular weight of the polymerizable oligomer is a weight average molecular weight in terms of polystyrene.

[0044] Specific examples of the acrylic oligomer include polyurethane acrylic oligomer [acrylic oligomer having a plurality of urethane bonds (—NHCOO—)], polyester acrylic oligomer [acrylic oligomer having a plurality of ester bonds (—COO—)], polyepoxy acrylic oligomer [acrylic oligomer having a plurality of epoxy groups], silicone acrylic oligomer [acrylic oligomer having a plurality of siloxane bonds (—SiO—)], polybutadiene acrylic oligomer [acrylic oligomer having a plurality of butadiene units], and the like.

[0045] Further, the following acrylic oligomers are known: Beamset 550B, Beamset 575, Beamset AQ-19 (manufactured by Arakawa Chemical Industries, Ltd.), AH-600, UA-306H, UA-306T, UA-306I, UA-510H, UF-8001G (manufactured by Kyoeisha Chemical Co., Ltd.), CN929, CN959, CN962, CN963, CN964, CN965NS, CN966NS, CN980NS, CN981NS, CN982, CN983NS, CN985, CN996NS, CN2920, CN2921, CN8881NS, CN8883NS, CN9001NS, CN973, CN978NS, CN970, CN971, CN972, CN975NS, CN2270, CN2271, CN2273, CN2274 (manufactured by Arkema), U-6LPA, U-10HA, U-10PA, UA-1100H, U-15HA, UA-33H, U-200PA, UA-160TM, UA-290TM, UA-4200, UA-4400, UA-122P (manufactured by Shin-Nakamura Chemical Co., Ltd.), New Frontier R-1235, R-1220, RST-402, R-1304, R-1214, R-1302XT, GX-8801A, R-1603, R-1150D (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), EBECRYL230, EBECRYL270, EBECRYL280 / 15IB, EBECRYL284, EBECRYL4858, EBECRYL8210, EBECRYL8307, EBECRYL8402, EBECRYL8409, EBECRYL8411, EBECRYL8804, EBECRYL8807, EBECRYL9270, KRM7735, EBECRYL4820, EBECRYL8311, EBECRYL8701, EBECRYL8210, EBECRYL8405, KRM8528 (manufactured by Daicel Allnex Co., Ltd.), UV-1700B, UV-6300B, UV-7550B, UV-7600B, UV-7605B, UV-7610B, UV-7630B, UV-7640B, UV-7650B, UV-6630B, UV-7000B, UV-7510B, UV-3000B, UV-3200B, UV-3300B, UV-3310B, UV-3700B, UV6640B (manufactured by Mitsubishi Chemical Corporation),Aronix M-6100, M-6250, M-6500, M-7100, M-7300K, M-8030, M-8060, M-8100, M-8530, M-8560, M-9050 (manufactured by Toagosei Co., Ltd.)

[0046] The amount of the bifunctional polymerizable compound (D) contained in the ink composition of the present invention is preferably 20 to 65% by mass, and more preferably 30 to 55% by mass. The bifunctional polymerizable compound (D) may be used alone or in combination of two or more.

[0047] The amount of the tri- or higher functional polymerizable compound (E) contained in the ink composition of the present invention is preferably 5 to 40 mass %, and more preferably 10 to 30 mass %. The tri- or higher functional polymerizable compound (E) may be used alone or in combination of two or more.

[0048] When the ink composition of the present invention contains a bifunctional polymerizable compound (D) and a tri- or higher functional polymerizable compound (E), the mass ratio (D / E) of the bifunctional polymerizable compound (D) to the tri- or higher functional polymerizable compound (E) contained in the ink composition is preferably 30 / 70 to 80 / 20, and more preferably 50 / 50 to 75 / 25. By blending the bifunctional polymerizable compound (D) and the tri- or higher functional polymerizable compound (E) in the above-specified mass ratio, it is possible to increase the hardness of the printed layer while maintaining adhesion to the substrate.

[0049] In the ink composition of the present invention, the polymerizable compound preferably contains a monofunctional polymerizable monomer having a heterocycle or an aromatic ring, and the monofunctional polymerizable monomer having a heterocycle is preferably one in which the heterocycle contains an oxygen atom. By using a monofunctional polymerizable monomer having a heterocycle or an aromatic ring, it is possible to improve pigment dispersion stability. Furthermore, from the viewpoint of improving pigment dispersion stability, the amount of the monofunctional polymerizable monomer having a heterocycle and / or an aromatic ring contained in the ink composition of the present invention is preferably 2 to 60% by mass, and more preferably 5 to 40% by mass. The monofunctional polymerizable monomer having a heterocycle or an aromatic ring may be used alone or in combination of two or more types.

[0050] Examples of monofunctional polymerizable monomers having a heterocycle include N-acryloylmorpholine, N-methacryloylmorpholine, γ-butyrolactone (meth)acrylate, N-vinylcaprolactam, N-acryloyloxyethylhexahydrophthalimide, N-methacryloyloxyethylhexahydrophthalimide, 1-acryloylpyrrolidin-2-one, 1-methacryloylpyrrolidin-2-one, 1-acryloylpiperidin-2-one, 1-methacryloylpiperidin-2-one, N-vinyl-2-pyrrolidone, N-vinylimidazole, tetrahydrofurfuryl (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, and cyclic trimethylolpropane formal (meth)acrylate. Among these, tetrahydrofurfuryl (meth)acrylate is particularly preferred.

[0051] Examples of monofunctional polymerizable monomers having an aromatic ring include benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxy-polyethylene glycol (meth)acrylate, etc. Among these, phenoxyethyl (meth)acrylate is particularly preferred.

[0052] When the ink composition of the present invention contains a monofunctional polymerizable monomer having a heterocycle or an aromatic ring, the amount of the monofunctional polymerizable monomer having a heterocycle or an aromatic ring is preferably 10 mass % or more of the total amount of the monofunctional polymerizable compound (C) contained in the ink composition, and it is more preferable that the monofunctional polymerizable compound (C) contained in the ink composition is composed solely of the monofunctional polymerizable monomer having a heterocycle or an aromatic ring.

[0053] The photopolymerization initiator has the effect of initiating polymerization of the above-mentioned polymerizable compound when irradiated with active energy rays. The photopolymerization initiator used in the ink composition of the present invention is classified as a radical polymerization initiator. In the ink composition of the present invention, the photopolymerization initiator includes at least a hydrogen abstraction photopolymerization initiator (B). The hydrogen abstraction photopolymerization initiator (B) corresponds to a Norrish type II photopolymerization initiator in which the excited photopolymerization initiator undergoes a bimolecular reaction with another molecule (co-initiator) to generate an initiating radical. In the field of photopolymerization initiators, Norrish Type II photopolymerization initiators are also called bimolecular photopolymerization initiators, and a combination of a photopolymerization initiator that becomes excited upon absorption of light and a co-initiator that reacts with the excited photopolymerization initiator is sometimes called a Norrish Type II photopolymerization initiator. However, in the present invention, the aminoacrylate (A) that acts as the co-initiator is classified as a polymerizable compound, and a photopolymerization initiator that becomes excited upon absorption of light and reacts with the co-initiator (component (A) in the present invention) to generate an initiating radical is called a hydrogen abstraction photopolymerization initiator (B). For classification of photopolymerization initiators, see, for example, "Photopolymerization Initiators," Chapter 1, Section 3 (pages 93-103) of "Dictionary of Optical Application Technology and Materials," published by Industrial Technology Service Center Co., Ltd. on April 26, 2006.

[0054] The hydrogen abstraction type photopolymerization initiator (B) has a photopolymerization initiation mechanism different from that of a Norrish type I photopolymerization initiator (intramolecular cleavage type photopolymerization initiator), and therefore can solve the odor problem associated with the use of a Norrish type I photopolymerization initiator (intramolecular cleavage type photopolymerization initiator).

[0055] The amount of hydrogen abstraction photopolymerization initiator (B) contained in the ink composition of the present invention is 1.0 to 15.0% by mass, preferably 2.0 to 10.0% by mass, and more preferably 3.0 to 8.0% by mass. If the amount of hydrogen abstraction photopolymerization initiator (B) is less than 1.0% by mass, a sufficient amount of radicals for the curing reaction is not generated, and a printed layer with high hardness is not obtained. Furthermore, the hydrogen abstraction photopolymerization initiator (B) dissolved in the ink composition may precipitate, for example, during low-temperature storage. However, if the amount of hydrogen abstraction photopolymerization initiator (B) is 15.0% by mass or less, the precipitated hydrogen abstraction photopolymerization initiator (B) can be redissolved by storing the ink composition at room temperature (approximately 23°C) for a certain period of time (e.g., about one day). Therefore, the ink composition of the present invention has excellent resolubility. On the other hand, when the amount of the hydrogen abstraction type photopolymerization initiator (B) exceeds 15.0 mass %, the hydrogen abstraction type photopolymerization initiator (B) precipitates from an ink composition, and the precipitate remains even when stored at room temperature (approximately 23°C) for a certain period of time (for example, about one day).

[0056] Furthermore, the mass ratio (A / B) of the aminoacrylate (A) to the hydrogen abstraction photopolymerization initiator (B) contained in the ink composition of the present invention is preferably 1.0 to 30.0, and more preferably 1.0 to 10.0. By setting the mass ratio (A / B) to 1.0 or more, a printed layer with high hardness is easily formed, and by setting the mass ratio (A / B) to 30.0 or less, an ink composition with excellent ejection properties is easily prepared.

[0057] The hydrogen abstraction photopolymerization initiator (B) is a photopolymerization initiator that becomes excited by absorbing light and causes a bimolecular reaction with the aminoacrylate (A), and is preferably an anthraquinone-type photopolymerization initiator, a benzophenone-type photopolymerization initiator, a thioxanthone-type photopolymerization initiator, or the like. Examples of anthraquinone-type photopolymerization initiators include 2-methylanthraquinone, etc. Examples of benzophenone-type photopolymerization initiators include benzophenone, etc. Examples of thioxanthone-type photopolymerization initiators include 2,4-diethylthioxanthone, 2-isopropylthioxanthone, and 2-chlorothioxanthone. The hydrogen abstraction photopolymerization initiator (B) may be used alone or in combination of two or more.

[0058] In the ink composition of the present invention, the photopolymerization initiator preferably contains, in addition to the hydrogen abstraction photopolymerization initiator (B), a small amount of an intramolecular cleavage photopolymerization initiator, to the extent that odor problems do not occur. In this specification, the intramolecular cleavage photopolymerization initiator is referred to as component (F) and is also referred to as the "intramolecular cleavage photopolymerization initiator (F)." The use of the intramolecular cleavage photopolymerization initiator (F) in addition to the hydrogen abstraction photopolymerization initiator (B) can increase the curing rate. The amount of the intramolecular cleavage photopolymerization initiator (F) contained in the ink composition of the present invention is preferably 3.0% by mass or less, and more preferably 0.5 to 2.0% by mass. The intramolecular cleavage photopolymerization initiator (F) may be used alone or in combination of two or more types.

[0059] The intramolecular cleavage type photopolymerization initiator (F) includes a benzoin type photopolymerization initiator, a benzil ketal type photopolymerization initiator, an α-hydroxyacetophenone type photopolymerization initiator, an α-aminoacetophenone type photopolymerization initiator, an acylphosphine oxide type photopolymerization initiator, an oxime ester type photopolymerization initiator, and the like.

[0060] Specific examples of the intramolecular cleavage type photopolymerization initiator (F) include: benzoin type photopolymerization initiators such as 2,2-dimethoxy-1,2-diphenylethan-1-one (2,2-dimethoxy-2-phenylacetophenone); benzyl ketal type photopolymerization initiators such as α,α-dimethoxy-α-phenylacetophenone (Irgacure 651 (BASF product name)); and α-hydroxyacetophenone type photopolymerization initiators such as 1-hydroxy-cyclohexyl-phenyl-ketone (Omnirad 184 (IGM Resins B.V. product name)) and 2-hydroxy-2-methyl-1-phenylpropan-1-one (Omnirad 1173 (IGM Resins B.V. product name)). Examples of photopolymerization initiators include 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methylpropanone (Omnirad 2959 (IGM Resins B.V. product name)), 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methylpropanone (Omnirad 2959 (IGM Resins B.V. product name)), etc.; examples of α-aminoacetophenone type photopolymerization initiators include 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholino)-1-propanone (Irgacure 907 (BASF product name)), 2-benzyl-2-dimethylamino-1-[4-(4-morpholino)phenyl]-1-butanone (Irgacure 369 (BASF product name)), etc.; examples of acylphosphine oxide type photopolymerization initiators include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (Omnirad 819 (IGM Resins B.V. product name)), etc.; Examples of photopolymerization initiators include 1,2-octanedione, 1-[4-(phenylthio)-2-(O-benzoyloxime)] (product name of BASF)), 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime) (product name of BASF)), and the like.

[0061] The mass ratio (B / F) of the hydrogen abstraction type photopolymerization initiator (B) to the intramolecular cleavage type photopolymerization initiator (F) contained in the ink composition of the present invention is preferably 2.0 or more, and more preferably 4.0 or more.

[0062] The pigment used in the ink composition of the present invention is not particularly limited, and any known pigment that is normally used in inks can be used.

[0063] Specific examples of pigments include C.I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 9, 10, 12, 13, 14, 15, 16, 17, 24, 32, 34, 35, 36, 37, 41, 42, 43, 49, 53, 55, 60, 61, 62, 63, 65, 73, 74, 75, 77, 81, 83, 87, 93, 94, 95, 97, 98, 99, 100, 101, 104, 105, 106, 108, 109, 110, 111, 113, 114, 116, 117, 119, 120, 123, 124, 126, 127, 128, 129, 130, 133, 138, 139, 150, 151, 152, 153, 154, 155, 165, 167, 168, 169, 170, 172, 173, 174, 175, 176, 179, 180, 181, 182, 183, 184, 185, 191, 193, 194, 199, 205, 206, 209, 212, 213, 214, 215, 219, C. I. Pigment Orange 1, 2, 3, 4, 5, 13, 15, 16, 17, 19, 20, 21, 24, 31, 34, 36, 38, 40, 43, 46, 48, 49, 51, 60, 61, 62, 64, 65, 66, 67, 68, 69, 71, 72, 73, 74, 81,C. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 21, 22, 23, 31, 32, 38, 41, 48, 48:1, 48:2, 48:3, 48:4, 48:5, 49, 52, 52:1, 52:2, 53:1, 54, 57:1, 58, 60:1, 63, 64:1, 68, 81:1, 83, 88, 89, 95, 101, 104, 105, 108, 112, 114, 119, 122, 123, 136, 144, 146, 147, 149, 150, 164, 166, 168, 169, 170, 171, 172, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 187, 188 , 190, 193, 194, 200, 202, 206, 207, 208, 209, 210, 211, 213, 214, 216, 22 0, 220, 221, 224, 226, 237, 238, 239, 242, 245, 247, 248, 251, 253, 254, 2 55, 256, 257, 258, 260, 262, 263, 264, 266, 268, 269, 270, 271, 272, 279, C. I. Pigment Violet 1, 2, 3, 3:1, 3:3, 5:1, 13, 15, 16, 17, 19, 23, 25, 27, 29, 31, 32, 36, 37, 38, 42, 50, C. I. Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:5, 15:6, 16, 17:1, 24, 24:1, 25, 26, 27, 28, 29, 36, 56, 60, 61, 62, 63, 75, 79, 80, C. I. Pigment Green 1, 4, 7, 8, 10, 15, 17, 26, 36, 50, C. I. C.I. Pigment Brown 5, 6, 23, 24, 25, 32, 41, 42, C.I. Pigment Black 1, 6, 7, 9, 10, 11, 20, 26, 28, 31, 32, 34, C.I. Pigment White 1, 2, 4, 5, 6, 7, 11, 12, 18, 19, 21, 22, 23, 26, 27, 28, aluminum flakes, glass flakes, pearl pigments and hollow particles.

[0064] The amount of pigment contained in the ink composition of the present invention is, for example, 1 to 20% by mass. The pigment may be used alone or in combination of two or more types.

[0065] The ink composition of the present invention may further contain a pigment dispersant as needed to disperse the pigment. The content of the pigment dispersant in the ink composition is, for example, 0.1 to 5 mass %. The pigment dispersants may be used alone or in combination of two or more.

[0066] Specific examples of pigment dispersants include ANTI-TERRA-U, ANTI-TERRA-U100, ANTI-TERRA-204, ANTI-TERRA-205, DISPERBYK-101, DISPERBYK-102, DISPERBYK-103, DISPERBYK-106, DISPERBYK-108, DISPERBYK-109, DISPERBYK-110, DISPERBYK-111, DISPERBYK-112, DISPERBYK-116, DISPERBYK-130, DISPERBYK-140, DISPERBYK-142, DISPERBYK-145, DISPERBYK-161, DISPERBYK-162, DISPERBYK-163, DISPERBYK-164, DISPERBYK-166, DISPERBYK-167, DISPERBYK-168, DISPERBYK-170, DISPERBYK-171, DISPERBYK-174, DISPERBYK-180, DISPERBYK-182, DISPERBYK-183, DISPERBYK-184, DISPERBYK-185, DISPERBYK-2000, DISPERBYK-2001, DISPERBYK-2008, DISPERBYK-2009, DISPERBYK-2020, DISPERBYK-2025, DISPERBYK-2050, DISPERBYK-2070, DISPERBYK-2096, DISPERBYK-2013, DISPERBYK-2150, DISPERBYK-2155, DISPERBYK-2163, DISPERBYK-2164, BYK-P104, BYK-P104S, BYK-P105, BYK-9076, BYK-9077, BYK-220S, BYKJET-9150, BYKJET-9151 (all manufactured by BYK Japan), Solsperse3000, Solsperse5000, Solsperse9000, Solsperse11200, Solsperse13240, Solsperse13650, Solsperse13940, Solsperse16000, Solsperse17000, Solsperse18000, Solsperse20000, Solsperse21000,Solsperse24000SC, Solsperse24000GR, Solsperse26000, Solsperse27000, Solsperse28000, Solsperse32000, Solsperse32500, Solsperse32550, Solsperse32600, Solsperse33000, Solsperse34750, Solsperse35100, Solsperse35200, Solsperse36000, Solsperse36600, Solsperse37500, Solsperse38500, Solsperse39000, Solsperse 41000, Solsperse 54000, Solsperse 55000, Solsperse 56000, Solsperse 71000, Solsperse 76500, Solsperse J180, Solsperse J200, Solsperse X300 (all manufactured by Lubrizol Corporation), Disparlon DA-7301, Disparlon DA-325, Disparlon DA-375, Disparlon DA-234 (all manufactured by Kusumoto Chemicals Co., Ltd.), FLOWLEN AF-1000, FLOWLEN DOPA-15B, FLOWLEN DOPA-15BHFS, FLOWLEN DOPA-17HF, FLOWLEN DOPA-22, FLOWLEN DOPA-33, FLOWLEN G-600, FLOWLEN G-700, FLOWLEN G-700AMP, FLOWLEN G-700DMEA, FLOWLEN G-820, FLOWLEN G-900, FLOWLEN GW-1500, FLOWLEN KDG-2400, FLOWLEN NC-500, FLOWLEN WK-13E (all manufactured by Kyoeisha Chemical Co., Ltd.), TEGO Dispers 610, TEGO Dispers 610S, TEGO Dispers 630, TEGO Dispers 650, TEGO Dispers652, TEGO Dispers655, TEGO Dispers662C, TEGO Dispers670, TEGO Dispers685, TEGO Dispers700, TEGO Dispers710, TEGO Dispers740W, LIPOTIN A, LIPOTIN BL, LIPOTIN DB, LIPOTIN SB (manufactured by Evonik Degussa),Examples of the polyisoprene include PB821, PB822, PN411, PA111 (manufactured by Ajinomoto Fine-Techno Co., Inc.), Texahole 963, Texahole 964, Texahole 987, Texahole P60, Texahole P61, Texahole P63, Texahole 3250, Texahole SF71, Texahole UV20, Texahole UV21 (manufactured by Cognis), BorchiGen SN88, BorchiGen 0451 (manufactured by Borchius).

[0067] The ink composition of the present invention may further contain a surface conditioner from the viewpoint of improving wettability, etc. The surface conditioner refers to a substance that has a hydrophilic moiety and a hydrophobic moiety in its molecular structure and that can adjust the surface tension of the ink composition by adding it.

[0068] Specific examples of surface conditioners that can be used in the ink composition of the present invention include anionic surface conditioners such as dialkyl sulfosuccinates, alkyl naphthalene sulfonates, and fatty acid salts; nonionic surface conditioners such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, and polyoxyethylene-polyoxypropylene block copolymers; cationic surface conditioners such as alkylamine salts and quaternary ammonium salts; acrylic surface conditioners, silicone surface conditioners, and fluorine-based surface conditioners. Silicon-based surface conditioners and acrylic surface conditioners are particularly preferred, and commercially available products from BYK, Evonik, Dow Corning Toray, and other companies can be used. Furthermore, in the case of silicone-based surface conditioners, it is preferable that the silicone-based surface conditioner is a polyether-modified silicone oil having an HLB of 7.6 to 12.

[0069] The amount of the surface conditioner can be appropriately selected depending on the purpose of use, but is preferably 0.01 to 1 mass % in the ink composition. The surface conditioner may be used alone or in combination of two or more types.

[0070] Specific examples of the surface conditioner include BYK-300, BYK-302, BYK-306, BYK-307, BYK-310, BYK-313, BYK-315N, BYK-320, BYK-322, BYK-323, BYK-325, BYK-326, BYK-330, BYK-331, BYK-333, BYK-342, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, BYK-350, BYK-354, BYK-355, BYK-356, BYK-358N, BYK-361N, BYK-370, BYK-375, BYK-377, BYK-378, BYK-381, BYK-392, BYK-394, BYK-399, BYK-3440, BYK-3441, BYK-3455, BYK-3550, BYK-3560, BYK-3565, BYK-3760, BYK-DYNWET 800N, BYK-SILCLEAN 3700, BYK-SILCLEAN 3701, BYK-SILCLEAN 3720, BYK-UV3500, BYK-UV3505, BYK-UV3510, BYK-UV3530, BYK-UV3535, BYK-UV3570, BYK-UV3575, BYK-UV3576 (manufactured by BYK Chemie Japan Co., Ltd. as above), TEGO Flow 300, TEGO Flow 370, TEGO Flow 425, TEGO Flow ATF 2, TEGO Flow ZFS 460, TEGO Glide 100, TEGO Glide 110, TEGO Glide 130, TEGO Glide 406, TEGO Glide 410, TEGO Glide 411, TEGO Glide 415, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, TEGO Glide 450, TEGO Glide 482, TEGO GlideA 115, TEGO GlideB 1484, TEGO GlideZG 400 (manufactured by Evonik Japan Co., Ltd. as above),501W ADDITIVE, FZ-2104, FZ-2110, FZ-2123, FZ-2164, FZ-2191, FZ-2203, FZ-2215, FZ-2222, FZ-5609, L-7001, L-7002, L-7604, OFX-0193, OFX-0309 FLUID, OFX-5211 FLUID, SF 8410 FLUID, SH3771, SH 3746 FLUID, SH 8400 FLUID, SH 8700 FLUID, Y-7006 (all manufactured by Dow Corning Toray Co., Ltd.), Examples of such copolymers include KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-640, KF-642, KF-643, KF-644, KF-945, KF-6004, KF-6011, KF-6012, KF-6015, KF-6017, KF-6020, KF-6204, X-22-2516, and X-22-4515 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0071] The ink composition of the present invention may contain an ultraviolet absorber. The ultraviolet absorber has the effect of absorbing ultraviolet rays and preventing deterioration caused by ultraviolet rays. Examples of the ultraviolet absorber include cyanoacrylate-based compounds, benzophenone-based compounds, benzoate-based compounds, benzotriazole-based compounds, hydroxyphenyltriazine-based compounds, benzylidene camphor-based compounds, and inorganic fine particles.

[0072] Specific examples of the ultraviolet absorber include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-dodecyloxybenzophenone-2-hydroxy-4-benzyloxybenzophenone, bis(5-benzoyl-4-hydroxy-2-methoxyphenyl)methane, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2-hydroxy-4-methoxy-2'-carboxybenzophenone, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-[2'-hydroxy-3',5'-bis(α,α-(dimethylbenzyl)phenyl]benzotriazole, 2-(2'-hydroxy-3',5'-di-t-butylphenyl)benzotriazole, 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-t-amylphenyl)benzotriazole, 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole, 2,2'-methylene-bis[4-(1,1,3,3-tetramethylbutyl)-6-(2N-benzotriazol-2-yl)phenol], condensation product of methyl-3-[3-t-butyl-5-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]propionate with polyethylene glycol, 2-(2-hydroxyphenyl)benzotriazole, Examples thereof include 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2,6-di-t-butylphenyl-3',5'-di-t-butyl-4'-hydroxybenzoate, and hexadecyl-3,5-di-t-butyl-4-hydroxybenzoate.

[0073] The amount of ultraviolet absorber contained in the ink composition of the present invention is preferably within a range of 0.1 to 15% by mass, more preferably 0.5 to 10% by mass, and even more preferably 1 to 5% by mass. If the amount of ultraviolet absorber is too large, the film may not be sufficiently cured. Although one type of ultraviolet absorber may be used alone or two or more types may be used in combination, it is preferable that the ultraviolet absorber contains at least two types of ultraviolet absorbers. By using multiple types of ultraviolet absorbers with different structures, the effect of the ultraviolet absorbers can be maintained longer.

[0074] The ink composition of the present invention may contain a radical scavenger. The radical scavenger can scavenge free radicals and improve light stability. In addition, substances that react with free radicals and have the function of preventing polymerization reactions (so-called polymerization inhibitors) are also included in radical scavengers.

[0075] Examples of the radical scavenger include hindered amine compounds, hydroquinone compounds, phenol compounds, phenothiazine compounds, nitroso compounds, and N-oxyl compounds, and it is particularly preferable to use a nitroso compound and a phenol compound in combination.

[0076] Specific examples of the radical scavenger include hindered amine compounds such as bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, 1-{2-(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy)ethyl}-2,2,6,6-tetramethylpiperidine, and 8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro{4.5}decane-2,4-dione; phenol; o-, m-, or p-cre phenolic compounds such as 2-t-butyl-4-methylphenol, 6-t-butyl-2,4-dimethylphenol, 2,6-di-t-butyl-4-methylphenol, 2-t-butylphenol, 4-t-butylphenol, 2,4-di-t-butylphenol, 2-methyl-4-t-butylphenol, and 4-t-butyl-2,6-dimethylphenol; hydroquinone, hydroquinone monomethyl ether, methylhydroquinone, 2,5-di-t-butylphenol; hydroquinone compounds such as benzoquinone, 2-methyl-p-hydroquinone, 2,3-dimethylhydroquinone, trimethylhydroquinone, 4-methylbenzcatechin, t-butylhydroquinone, 3-methylbenzcatechin, 2-methyl-p-hydroquinone, 2,3-dimethylhydroquinone, trimethylhydroquinone, t-butylhydroquinone, benzoquinone, t-butyl-p-benzoquinone, and 2,5-diphenyl-p-benzoquinone; nitroso-based compounds such as N-nitroso-N-phenylhydroxylamine ammonium and N-nitroso-N-phenylhydroxylamine aluminum salt; and N-oxyl-based compounds such as 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-oxo-2,2,6,6-tetramethyl-piperidine-N-oxyl, and 4-methoxy-2,2,6,6-tetramethyl-piperidine-N-oxyl.

[0077] The amount of radical scavenger contained in the ink composition of the present invention is preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. If the amount of radical scavenger is too large, it may cause poor curing. The lower limit of the content of radical scavenger is, for example, 0.01% by mass or more, preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more. The radical scavengers may be used alone or in combination of two or more.

[0078] The ink composition of the present invention may contain a resin. The resin has the role of forming a film on the substrate while capturing solid components such as pigments, and contributes to improving the adhesion of the ink composition to the substrate.

[0079] Specific examples of resins include polyvinyl acetate, vinyl chloride-vinyl acetate copolymers, vinyl chloride resins, chlorinated rubber, chlorinated polyethylene resins, chlorinated polypropylene resins, chlorinated ethylene-vinyl acetate resins, acrylic resins, polystyrene resins, polyamide resins, polyurethane resins, polyolefin resins, silicone resins, fluororesins, epoxy resins, polyester resins, ketone resins, phenolic resins, polyvinyl alcohol, polyvinyl alcohol derivatives (anion-modified polyvinyl alcohol, etc.), cellulose, cellulose derivatives (hydroxymethyl cellulose, hydroxyethyl cellulose, cellulose acetate, etc.), rosin resins, alkyd resins, alginic acid, alginic acid derivatives (propylene glycol alginate, etc.), and the like. Modified versions of these resins are also included. For example, in the case of resins having hydroxyl groups, modifications such as hydroxyalkyl etherification and carboxylic acid modification can be mentioned.

[0080] The amount of resin contained in the ink composition of the present invention is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. If the amount of resin is too large, it may cause poor curing. The resin may be used alone or in combination of two or more types.

[0081] The ink composition of the present invention may contain, as other components, additives such as a silane coupling agent, an antioxidant, a plasticizer, an anti-rust agent, a solvent, an antibacterial agent, an antiviral agent, a viscosity adjuster, a filler, an antifoaming agent, a charge control agent, a stress relaxation agent, a penetrating agent, a light-guiding material, a glittering material, a magnetic material, and a fluorescent material, if necessary.

[0082] The ink composition of the present invention can be used as various color inks such as cyan ink, magenta ink, yellow ink, black ink, orange ink, green ink, violet ink, light cyan ink, and light magenta ink.

[0083] The ink composition of the present invention can be prepared by mixing various components appropriately selected as needed. In addition, it is preferable to filter the ink composition using a filter in order to prevent clogging of the nozzles of the head due to impurities, etc.

[0084] The ink composition of the present invention preferably has a viscosity at 40°C of 5 to 25 mPa·s, more preferably 5 to 20 mPa·s. When the ink viscosity at 40°C is within the above-specified range, good jetting properties can be obtained. The ink viscosity can be measured using a cone-plate viscometer. The temperature at which the ink is jetted is preferably 30°C to 50°C.

[0085] The ink composition of the present invention preferably has a surface tension of 20 to 35 mN / m, more preferably 23 to 33 mN / m, at 25° C. When the ink surface tension at 25° C. is within the above-specified range, good jetting properties can be obtained. The ink surface tension can be measured by a plate method.

[0086] As a printing method for the ink composition of the present invention, various printing methods such as gravure printing, offset printing, flexographic printing, screen printing, coater printing, and inkjet printing can be used, with inkjet printing being particularly preferred. Various inkjet printers can be used for inkjet printing. Examples of inkjet printers include inkjet printers that eject the ink composition using a charge control system or a piezoelectric system. Large-format inkjet printers, specifically inkjet printers designed for printing on products produced on industrial lines, can also be suitably used.

[0087] The layer formed by printing using the ink composition of the present invention is cured by irradiation with active energy rays such as ultraviolet rays. Examples of light sources for active energy rays include high-pressure mercury lamps, metal halide lamps, and LED lamps. The wavelength of the active energy rays irradiated to cure this layer preferably overlaps with the absorption wavelength of the photopolymerization initiator, and the dominant wavelength of the active energy rays is preferably 350 to 400 nm. The cumulative light intensity of the active energy rays is 100 to 2000 mJ / cm. ２ It is preferable that the temperature is in the range of

[0088] The ink composition of the present invention can be used to achieve a surface finish such as a glossy finish, a matte finish, etc. by appropriately selecting the ejection conditions for inkjet printing and the subsequent curing conditions. For example, if the ink composition spreads and then hardens over time, it will have a glossy finish, and if the ink droplets harden while remaining in a lens shape, it will have a matte finish.

[0089] Substrates on which printing is performed with the ink composition of the present invention include, for example, plastic substrates such as epoxy resin, ABS resin, polycarbonate, polyvinyl chloride, polystyrene, acrylic resin, for example, polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyolefin, for example, polypropylene (PP), etc., metal substrates such as steel, zinc-plated steel, tin-plated steel, stainless steel, magnesium alloy, aluminum, aluminum alloy, titanium, titanium alloy, etc., inorganic substrates other than metals such as cement, mortar, concrete, slate, gypsum, calcium silicate, glass, ceramic, calcium carbonate, marble, artificial marble, etc., wood substrates such as wood, paper substrates, composite substrates combining two or more of these substrates, etc. Further, examples of composite substrates include composite substrates such as wood fiber-reinforced cement boards, fiber-reinforced cement boards, fiber-reinforced cement / calcium silicate boards, metal substrates that have been subjected to various surface treatments, for example, oxidation treatment, and plastic substrates the surface of which is coated with an inorganic substance (for example, plastic substrates coated with glass).

[0090] The substrate may have various shapes, for example, two-dimensional substrates such as films, sheets, and plates, and three-dimensional substrates that are complex three-dimensional objects, etc. The surface of the substrate may be smooth or may have irregularities.

[0091] The surface of the substrate may be subjected to pretreatment such as degreasing, chemical conversion treatment, or polishing, or may be coated with a sealer or primer.

[0092] Specific examples of the substrate include plastic materials such as PVC sheet, tarpaulin, pladan (plastic cardboard), and acrylic sheet; papers such as coated paper (specifically, resin-coated paper), art paper, cast paper, lightly coated paper, fine paper, synthetic paper, and inkjet paper; wooden building materials made from wood such as veneer, plywood, particle board, and medium-density fiberboard (MDF); inorganic building materials such as ceramic siding board, flexible board, calcium silicate board, gypsum slag barite board, wood chip cement board, pulp cement board, precast concrete board, lightweight aerated concrete (ALC) board, and gypsum board; metal building materials such as aluminum, iron, and stainless steel, PCM steel plate, tile, and glass plate.

[0093] A substrate on which printing is performed with the ink composition of the present invention may have a layer formed from a white ink disposed on part or the entire surface. By providing a layer formed from a white ink, a printed layer with good color development can be formed. The layer formed from the white ink may contain a white pigment, other pigments, resins, ultraviolet absorbers, radical scavengers, antioxidants, plasticizers, rust inhibitors, algae inhibitors, fungicides, antibacterial agents, antiviral agents, fillers, charge control agents, light-guiding materials, luster materials, magnetic materials, phosphors, waxes, etc.

[0094] Here, examples of the white ink include various inks such as organic solvent-based inks that use an organic solvent as the main solvent, water-based inks that use water as the main solvent, and photocurable inks that use a polymerizable compound, but photocurable inks are preferred. Components that can be used in photocurable inks include the components that can be used in the ink composition of the present invention described above.

[0095] As the printing means for the white ink, various printing means such as gravure printing, offset printing, flexographic printing, screen printing, coater printing, and inkjet printing can be used, with inkjet printing being particularly preferred.

[0096] An additional layer (e.g., a coating film or a printed film) may be formed on the layer formed by printing using the ink composition of the present invention. For example, a coating film formed from a paint or a printed film formed from an ink may be formed. The additional layer may contain a resin, a pigment, an ultraviolet absorber, a radical scavenger, an antioxidant, a plasticizer, an anti-rust agent, an anti-algae agent, an anti-fungal agent, an antibacterial agent, an antiviral agent, a filler, a charge control agent, a light-guiding material, a luster material, a magnetic material, a phosphor, wax, etc.

[0097] Examples of paints and inks used to form additional layers include organic solvent-based paints and inks that use an organic solvent as the main solvent, water-based paints and inks that use water as the main solvent, photocurable paints and inks that use a polymerizable compound, powder paints, and various other paints and inks. Here, examples of components that can be used in the case of photocurable inks include the components that can be used in the ink composition of the present invention described above.

[0098] The means for forming the additional layer is not particularly limited. For example, in the case of paint, various coating means such as air spray, airless spray, roll coater, flow coater, and electrostatic coating can be used. In addition, in the case of ink, various printing means such as gravure printing, offset printing, flexographic printing, screen printing, coater printing, and inkjet printing can be used.

[0099] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0100] <Preparation of Ink Compositions> Mixtures containing the components shown in Tables 1 to 5 in the amounts (parts by mass) shown in Tables 1 to 5 were stirred and dissolved to homogenize, and then filtered to prepare the actinic ray-curable ink compositions shown in Examples 1 to 28 and Comparative Examples 1 to 4.

[0101] The details of the components shown in Tables 1 to 5 are given below. 1) Monarch 1000 (manufactured by Cabot Corporation), carbon black (Pigment Black 7) 2) Heliogen Blue L7101F (manufactured by Sun Chemical Co.), β-modified copper phthalocyanine (Pigment Blue 15:4) 3) Fastogen Super Magenta RG (manufactured by DIC Corporation), quinacridone pigment (Pigment Red 122) 4) Pigment Yellow E4GN (manufactured by Lanxess), nickel azomethine complex (Pigment Yellow 150) 5) Light Acrylate THF-A (manufactured by Kyoeisha Chemical Co., Ltd.), tetrahydrofurfuryl acrylate 6) Light Acrylate PO-A (manufactured by Kyoeisha Chemical Co., Ltd.), phenoxyethyl acrylate 7) Light Acrylate 1,6HX-A (Kyoeisha Chemical Co., Ltd.), 1,6-hexanediol diacrylate 8) DPGDA (Daicel Allnex Corporation), dipropylene glycol diacrylate 9) Light Acrylate PE-4A (Kyoeisha Chemical Co., Ltd.), pentaerythritol tetraacrylate 10) Light Acrylate DPE-6A (Kyoeisha Chemical Co., Ltd.), dipentaerythritol hexaacrylate 11) EBECRYL 7100 (Daicel Allnex Corporation), bifunctional aminoacrylate 12) EBECRYL 80 (Daicel Allnex Corporation), tetrafunctional amine-modified highly reactive polyether acrylate 13) Q-1301 (Fujifilm Wako Pure Chemical Industries, Ltd.), N-nitrosophenylhydroxyamine aluminum salt 14) Yoshinox BHT (API Corporation), butylated hydroxytoluene 15) MEHQ (manufactured by Tokyo Chemical Industry Co., Ltd.), 4-methoxyphenol 16) SpeedCure DETX (manufactured by Arkema), 2,4-diethylthioxanthone 17) SpeedCure 2-ITX (manufactured by Arkema), 2-isopropylthioxanthone 18) Omnirad 819 (former Irgacure 819) (manufactured by IGM Resins B.V.), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide 19) BYK-UV 3500 (manufactured by BYK-Chemie), silicone-based surface conditioner

[0102] <Preparation of Printed Material> The ink composition prepared was applied to a commercially available PET film (HK-33WF manufactured by Higashiyama Film Co., Ltd.: 70 mm x 150 mm x 188 μm thick) using a bar coater #5, and then exposed to actinic energy rays (LED 385 nm) at 1000 mW / cm ２ , 1000 mJ / cm ２ The resulting printed matter was used to evaluate odor and hardness.

[0103] <Resolubility> The prepared ink composition was stored at 5°C for 7 days, and then stored at 23°C for 1 day, after which the ink composition was filtered through a SUS mesh filter (pore size: 5 µm). The presence or absence of precipitates on the SUS mesh filter after filtration was visually confirmed to evaluate the resolubility of the ink composition. The evaluation criteria were as follows. The results are shown in Tables 1 to 5. (Evaluation criteria) ○: No precipitates ×: Presence of precipitates

[0104] <Odor> A sensory test of the odor of printed matter (immediately after production) was conducted by 10 panelists in a room at a room temperature of 23°C and 50% RH. Evaluation was made on a three-point scale: "no odor," "slight odor," and "odor." "no odor" was given 0 points, "slight odor" was given 1 point, and "odor" was given 2 points, and the odor was evaluated by adding up the scores given by each panelist. The evaluation criteria were as follows. The results are shown in Tables 1 to 5. Printed matter rated "good" is a printed matter with reduced odor. (Evaluation criteria) Good: Total score of 10 panelists is 5 points or less. Bad: Total score of 10 panelists is 6 points or more.

[0105] <Ejectability> Using an inkjet recording device equipped with a piezo-type inkjet nozzle, the nozzle was filled with the ink composition of each Example or Comparative Example. The temperature during ink ejection was set to 50°C, and a solid pattern image (recording resolution 720 x 600 dpi) was printed on the surface of a commercially available PET film (HK-33WF, manufactured by Higashiyama Film Co., Ltd.: 70 mm x 150 mm x 188 μm thick). The ejectability of each ink composition was evaluated. The evaluation criteria were as follows. The results are shown in Tables 1 to 5. Ink compositions rated "Good" are ink compositions with excellent ejectability. (Evaluation Criteria) Good: No omissions, resulting in a good printed image. Bad: Omissions occurred, resulting in color unevenness in the printed image.

[0106] <Hardness of Printed Layer> The pencil hardness of the printed matter produced by the above method was measured in accordance with JIS K 5600-5-4:1999. The evaluation criteria were as follows. The results are shown in Tables 1 to 5. Printed matter rated "Good" is a printed matter with high hardness. (Evaluation Criteria) Good: Pencil hardness of 2H or more Bad: Pencil hardness of H or less

[0107]

[0108]

[0109]

[0110]

[0111]

[0112] In the table, the item “hydrogen abstraction type photopolymerization initiator (B) / intramolecular cleavage type photopolymerization initiator (F)” indicates the mass ratio (B / F) of the hydrogen abstraction type photopolymerization initiator (B) to the intramolecular cleavage type photopolymerization initiator (F) contained in the ink composition, the item “aminoacrylate (A) / hydrogen abstraction type photopolymerization initiator (B)” indicates the mass ratio (A / B) of the aminoacrylate (A) to the hydrogen abstraction type photopolymerization initiator (B) contained in the ink composition, and the item “bifunctional polymerizable compound (D) / tri- or higher functional polymerizable compound (E)” indicates the mass ratio (D / E) of the bifunctional polymerizable compound (D) to the tri- or higher functional polymerizable compound (E) contained in the ink composition.

[0113] The ink compositions of Examples 1 to 28 were inks with excellent resolubility and ejection properties, and furthermore, these ink compositions were capable of forming a highly hard printed layer with reduced odor. On the other hand, when the amount of aminoacrylate in the ink composition was less than 10% by mass (Comparative Example 1), a highly hard printed layer was not obtained, and when the amount of aminoacrylate in the ink composition was more than 30% by mass (Comparative Example 2), the ink ejection properties were poor. Furthermore, when the amount of hydrogen abstraction photopolymerization initiator contained in the ink composition was less than 1.0% by mass (Comparative Example 3), a highly hard printed layer was not obtained, and when the amount of hydrogen abstraction photopolymerization initiator contained in the ink composition was more than 15.0% by mass (Comparative Example 4), the resolubility was poor.

Claims

1. An ink composition comprising a pigment, a polymerizable compound, and a photopolymerization initiator, wherein the polymerizable compound comprises at least an aminoacrylate (A), and the photopolymerization initiator comprises at least a hydrogen abstraction type photopolymerization initiator (B), the amount of the aminoacrylate (A) contained in the ink composition is 10 to 30 mass %, and the amount of the hydrogen abstraction type photopolymerization initiator (B) contained in the ink composition is 1.0 to 15.0 mass %.

2. The ink composition according to claim 1, wherein the photopolymerizable compound comprises a monofunctional polymerizable compound (C), a bifunctional polymerizable compound (D) and a trifunctional or higher functional polymerizable compound (E), and the monofunctional polymerizable compound (C), the bifunctional polymerizable compound (D) and the trifunctional or higher functional polymerizable compound (E) are polymerizable compounds different from the amino acrylate (A).

3. The ink composition according to claim 2, wherein a mass ratio (D / E) of the bifunctional polymerizable compound (D) to the tri- or higher functional polymerizable compound (E) contained in the ink composition is 30 / 70 to 80 / 20.

4. The ink composition according to claim 1, wherein the photopolymerization initiator comprises an intramolecular cleavage type photopolymerization initiator (F), and the amount of the intramolecular cleavage type photopolymerization initiator (F) contained in the ink composition is 3.0 mass % or less.

5. The ink composition according to claim 4, wherein a mass ratio (B / F) of the hydrogen abstraction type photopolymerization initiator (B) to the intramolecular cleavage type photopolymerization initiator (F) contained in the ink composition is 2.0 or more.

6. The ink composition according to claim 1, wherein a mass ratio (A / B) of the aminoacrylate (A) to the hydrogen abstraction type photopolymerization initiator (B) contained in the ink composition is 1.0 to 30.0.

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