Ink composition and printed matter

Abstract

This ink composition comprises: a polyfunctional acylphosphine oxide-based initiator (a1) having a long-term oral toxicity DNEL to consumers in the REACH regulation of at least 100 μg / kg∙bw / day; a monoacylphosphine oxide-based initiator (a2) having a long-term oral toxicity DNEL to consumers in the REACH regulation of at least 100 μg / kg∙bw / day; a radically polymerizable monomer (b1) having at least one vinyl ether group and at least one (meth)acrylate group; a monofunctional radically polymerizable monomer (c1) having an aromatic ring and a hydroxyl group in the structure thereof; and a polyfunctional radically polymerizable monomer (c2) having an aromatic ring and a hydroxyl group in the structure thereof.

Description

Ink compositions and printed materials

[0001] This invention relates to an ink composition and printed materials.

[0002] The ink composition used as ink in printing devices such as inkjet printers is an active energy ray curable composition containing polymerizable compounds. This composition is used, for example, in a printing method in which it is ejected as ink onto a recording medium and cured by irradiation with active energy rays.

[0003] Such active energy ray curable compositions may use polymers having cationic polymerizable groups, or polymers having both radical polymerizable groups and cationic polymerizable groups. As an example of an active energy ray curable composition containing a polymer having both radical polymerizable groups and cationic polymerizable groups, Patent Document 1 discloses a radiation-curable inkjet composition containing a monomer represented by a specific formula having at least one vinyl ether group and at least one (meth)acrylate group. Patent Document 2 also discloses an ultraviolet-curable clear ink composition containing vinyl ether group-containing (meth)acrylic acid esters represented by a specific formula and a urethane oligomer.

[0004] Japanese Patent Publication No. 2017-186481 Japanese Patent Publication No. 2013-203873

[0005] The polymerization initiators used in conventional ink compositions, such as those disclosed in Patent Documents 1 and 2, cannot be said to be sufficiently safe raw materials. The present inventors have investigated how to provide a curable composition using safer raw materials. When they attempted to use a highly safe initiator in a composition containing a radical polymerizable monomer having at least one vinyl ether group and at least one (meth)acrylate group, they found that initiators (a1) and (a2) with a long-term oral toxicity DNEL (Derived No Effect Level) to consumers under the REACH regulation of 100 μg / kg bw / day or higher do not have sufficiently high solubility in the composition and may not be sufficiently stable. Furthermore, they found that the amount that can be incorporated may be limited from the viewpoint of solubility, and as a result, sufficient curability may not be obtained.

[0006] The present invention has been made in view of the above problems, and aims to provide an active energy ray curable composition containing a radical polymerizable monomer having at least one vinyl ether group and at least one (meth)acrylate group, and a highly safe initiator, which has high stability and high curability.

[0007] The present inventors have diligently studied to solve the above problems and have completed the present invention. The present invention includes the following preferred embodiments: [1] an ink composition comprising: a1 (a1) a polyfunctional acylphosphine oxide initiator having a long-term oral toxicity DNEL to consumers of 100 μg / kg bw / day or more under the REACH regulations; a2 (a2) a monoacylphosphine oxide initiator having a long-term oral toxicity DNEL to consumers of 100 μg / kg bw / day or more under the REACH regulations; b1 (b1) a radical polymerizable monomer having at least one vinyl ether group and at least one (meth)acrylate group; c1 (c1) a monofunctional radical polymerizable monomer having an aromatic ring and a hydroxyl group in its structure; and c2 (c2) a polyfunctional radical polymerizable monomer having an aromatic ring and a hydroxyl group in its structure. [2] The ink composition according to [1], wherein the content of the polyfunctional acylphosphine oxide initiator (a1) is 3% by mass or more based on the total amount of the ink composition. [3] The ink composition according to [1] or [2], wherein the total content of the polyfunctional acylphosphine oxide initiator (a1) and the monoacylphosphine oxide initiator (a2) is 5% by mass or more based on the total amount of the ink composition. [4] The ink composition according to any one of [1] to [3], wherein the amount of colorant in the ink composition is 0 to 0.01% by mass relative to the total amount of the ink composition. [5] The ink composition according to any one of [1] to [4], wherein the monoacylphosphine oxide initiator (a2) is not diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide. [6] The ink composition according to any one of [1] to [5], wherein the polyfunctional acylphosphine oxide initiator (a1) is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide. [7] The ink composition according to any one of [1] to [6], wherein the polyfunctional acylphosphine oxide initiator (a1) is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and the monoacylphosphine oxide initiator (a2) is ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.[8] The radical polymerizable monomer (b1) having at least one vinyl ether group and at least one (meth)acrylate group is a compound of formula (I): [In formula (I), R １ represents a hydrogen atom or a methyl group, R ２ R represents a divalent organic group with 2 to 20 carbon atoms. ３ An ink composition according to any one of [1] to [7], comprising a monomer (b1') represented by [I], where is a hydrogen atom or a monovalent organic group having 1 to 11 carbon atoms. [9] An ink composition according to [8], wherein the monomer (b1') represented by formula (I) is 2-(2-vinyloxyethoxy)ethyl (meth)acrylate.

[10] An ink composition according to any one of [1] to [9], wherein the amount of monofunctional radical polymerizable monomer in the ink composition is 10% by mass or less with respect to the total amount of the ink composition.

[11] An ink composition according to any one of [1] to

[10] , wherein the amount of trifunctional or polyfunctional radical polymerizable monomer in the ink composition is 10% by mass or less with respect to the total amount of the ink composition.

[12] An ink composition according to any one of [1] to

[11] , wherein the amount of quintupliable or polyfunctional radical polymerizable monomer in the ink composition is 0.5 to 10% by mass with respect to the total amount of the ink composition.

[13] The ink composition according to any one of [1] to

[12] , wherein the amount of monomer (b1) having at least one vinyl ether group and at least one (meth)acrylate group is 30 to 50% by mass with respect to the total amount of the ink composition.

[14] The ink composition according to any one of [1] to

[13] , wherein the total amount of monofunctional radical polymerizable monomer (c1) having an aromatic ring and a hydroxyl group in its structure, and polyfunctional radical polymerizable monomer (c2) having an aromatic ring and a hydroxyl group in its structure is 10 to 20% by mass with respect to the total amount of the ink composition.

[15] The ink composition according to any one of [1] to

[14] , which is an ink composition for an inkjet recording device.

[16] A printed article comprising a cured product of the ink composition according to any one of [1] to

[15] .

[0008] The present invention provides an active energy ray curable composition comprising a radical polymerizable monomer having at least one vinyl ether group and at least one (meth)acrylate group, and a highly safe initiator, thereby providing an active energy ray curable composition having high stability and high curability.

[0009] The embodiments of the present invention will be described in detail below. However, the scope of the present invention is not limited to the embodiments described herein, and various modifications can be made without departing from the spirit of the invention.

[0010] The ink composition of the present invention comprises a polyfunctional acylphosphine oxide initiator (a1) with a long-term oral toxicity DNEL (Derived No Effect Level) of 100 μg / kg bw / day or higher under REACH regulations, a monoacylphosphine oxide initiator (a2) with a long-term oral toxicity DNEL (Derived No Effect Level) of 100 μg / kg bw / day or higher under REACH regulations, a radical polymerizable monomer (b1) having at least one vinyl ether group and at least one (meth)acrylate group, a monofunctional radical polymerizable monomer (c1) having an aromatic ring and a hydroxyl group in its structure, and a polyfunctional radical polymerizable monomer (c2) having an aromatic ring and a hydroxyl group in its structure.

[0011] (Polyfunctional Acylphosphine Oxide Initiator (a1)) The polyfunctional acylphosphine oxide initiator (a1) contained in the ink composition is a polyfunctional acylphosphine oxide initiator with a long-term oral toxicity DNEL (Derived No Effect Level) to consumers under the REACH regulation of 100 μg / kg bw / day or higher. A polyfunctional acylphosphine oxide initiator is a phosphine oxide initiator having two or more acyl groups (preferably two or more phenylacyl groups). Such a polyfunctional acylphosphine oxide initiator (a1) is an initiator with extremely high safety.

[0012] The Derived No Effect Level (DNEL) for long-term oral toxicity to consumers under REACH regulations indicates the level of exposure at which a chemical substance does not cause adverse effects on humans (consumers). Specifically, it is the value obtained by dividing the no-observed-adverse-effect level (NOAEL) obtained from toxicity tests for general toxicity, reproductive toxicity, mutagenicity, and carcinogenicity, as shown in the OECD test guidelines, by the product of uncertainty factors. The DNEL can be measured specifically according to the method described in ECHA's "Guidance on information requirements and chemical safety assessment Chapter R.8".

[0013] Examples of polyfunctional acylphosphine oxide initiators (a1) are not particularly limited, but include phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide. The ink composition of the present invention may contain one type of polyfunctional acylphosphine oxide initiator (a1), or it may contain two or more types of polyfunctional acylphosphine oxide initiators (a1).

[0014] The content of the polyfunctional acylphosphine oxide initiator (a1) is preferably 1 to 8% by mass, more preferably 3 to 7% by mass, and even more preferably 4 to 6% by mass, based on the total amount of the ink composition, from the viewpoint of safety, stability, and curability of the ink composition.

[0015] Polyfunctional acylphosphine oxide initiators with a long-term oral toxicity DNEL (Derived No Effect Level) to consumers under REACH regulations less than 100 μg / kg bw / day do not fall under the category of polyfunctional acylphosphine oxide initiator (a1) in the present invention. While it is preferable that such initiators are not included in the ink compositions of this disclosure, such polyfunctional initiators may be included in addition to the polyfunctional acylphosphine oxide initiator (a1). The amount of a polyfunctional acylphosphine oxide initiator that does not fall under the category of a polyfunctional acylphosphine oxide initiator (a1) and whose long-term oral toxicity DNEL (Derived No Effect Level) to consumers under the REACH regulation is less than 100 μg / kg bw / day is preferably 0 to 1% by mass, more preferably 0 to 0.5% by mass, and even more preferably 0 to 0.1% by mass, relative to the total amount of the ink composition of the present invention.

[0016] (Monoacylphosphine oxide initiator (a2)) The monoacylphosphine oxide initiator (a2) contained in the ink composition is a monoacylphosphine oxide initiator (monofunctional acylphosphine oxide initiator) with a long-term oral toxicity DNEL (Derived No Effect Level) to consumers under the REACH regulation of 100 μg / kg bw / day or higher. A monoacylphosphine oxide initiator is a phosphine oxide initiator having one acyl group (preferably one phenylacyl group). Such a monoacylphosphine oxide initiator (a2) is a highly safe initiator.

[0017] The method for measuring the long-term oral toxicity DNEL (Derived No Effect Level) to consumers under the REACH regulation is as described above.

[0018] Examples of monoacylphosphine oxide initiators (a2) are not particularly limited, but include ethoxyphenyl (2,4,6-trimethylbenzoyl)phosphine oxide. The ink composition of the present invention may contain one type of monoacylphosphine oxide initiator (a2), or it may contain two or more types of monoacylphosphine oxide initiators (a2).

[0019] The content of the monoacylphosphine oxide initiator (a2) is preferably 0.1 to 15% by mass, more preferably 2 to 10% by mass, and even more preferably 3 to 7% by mass, based on the total amount of the ink composition, from the viewpoint of safety, stability, and curability of the ink composition.

[0020] Monoacylphosphine oxide initiators with a long-term oral toxicity DNEL (Derived No Effect Level) to consumers under REACH regulations less than 100 μg / kg bw / day are preferably not included in the ink composition of this disclosure, but such monoacylphosphine oxide initiators may be included in addition to monoacylphosphine oxide initiator (a2). The amount of monoacylphosphine oxide initiators that do not fall under monoacylphosphine oxide initiator (a2) and have a long-term oral toxicity DNEL to consumers under REACH regulations less than 100 μg / kg bw / day is preferably 0 to 1% by mass, more preferably 0 to 0.5% by mass, even more preferably 0 to 0.1% by mass, and even more preferably 0 to 0.05% by mass, relative to the total amount of the ink composition of the present invention. Among monoacylphosphine oxide initiators that do not fall under monoacylphosphine oxide initiator (a2) and have a long-term oral toxicity DNEL to consumers less than 100 μg / kg bw / day under the REACH regulations, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide is an example.

[0021] In a preferred embodiment of the present invention, from the viewpoint of more effectively achieving the effects of the present invention, the total content of the polyfunctional acylphosphine oxide initiator (a1) and the monoacylphosphine oxide initiator (a2) is preferably 5% by mass or more, more preferably 5.3% by mass or more, and even more preferably 5.5% by mass or more, based on the total amount of the ink composition. According to the ink composition of the present invention, high stability and high curability can be achieved even when relatively large amounts of the polyfunctional acylphosphine oxide initiator (a1) and the monoacylphosphine oxide initiator (a2), which are usually considered to be compounds with low solubility, are included.

[0022] (Other Initiators) The ink composition may contain other initiators other than polyfunctional acylphosphine oxide initiators and monoacylphosphine oxide initiators. The other initiators are preferably those with a long-term oral toxicity DNEL to consumers under the REACH regulations of 100 μg / kg bw / day or higher, in which case the amount of initiator is not particularly limited.

[0023] (Polymerizable Monomers) In this specification, polymerizable monomers are compounds that undergo a polymerization reaction upon irradiation with active energy rays and have the function of curing compositions containing them. Examples of active energy rays include visible light, near-ultraviolet light, ultraviolet light, electron beams, alpha rays, gamma rays, and X-rays, among which ultraviolet light and electron beams are preferred. In a preferred embodiment of the present invention, the ink composition of the present invention is preferably a photocurable ink composition, and more preferably an ultraviolet curable ink composition. Specifically, polymerizable monomers are preferably compounds having at least one ethylenically double bond selected from the group consisting of acryloyl group, methacryloyl group, vinyl group, allyl group, and vinyl ether group, and more preferably compounds having at least one ethylenically double bond selected from the group consisting of acryloyl group, methacryloyl group, and vinyl ether group. In this specification, compounds having at least one acryloyl group and / or methacryloyl group, and compounds having at least one acryloyl ester group and / or methacryloyl ester group are referred to as (meth)acrylic compounds. In a preferred embodiment of the present invention, the ink composition of the present invention preferably contains a (meth)acrylic compound. In this specification, "(meth)acrylic compound" is a general term for "acrylic compound" and "methacrylic compound." "(meth)acrylic acid" is a general term for "acrylic acid" and "methacrylic acid," and "(meth)acrylate" is a general term for "acrylate" and "methacrylate." The notations "(meth)acrylamide" and "(meth)acryloyloxy" have the same meaning.

[0024] The radical polymerizable monomer (b1) ink composition contains a radical polymerizable monomer (b1) having at least one vinyl ether group and at least one (meth)acrylate group. An example of a polymerizable monomer (b1) having at least one vinyl ether group and at least one (meth)acrylate group is formula (I): [In formula (I), R １ represents a hydrogen atom or a methyl group, R ２R represents a divalent organic group with 2 to 20 carbon atoms. ３ Examples of monomers represented by [where represents a hydrogen atom or a monovalent organic group having 1 to 11 carbon atoms] include monomers represented by formula (I) (b1), which have at least one vinyl ether group and at least one (meth)acrylate group, and are also referred to herein as monomer (b1').

[0025] Examples of divalent organic groups having 2 to 20 carbon atoms in formula (I) include alkylene groups having 2 to 20 carbon atoms, cycloalkylene groups having 3 to 20 carbon atoms, and divalent aromatic groups having 6 to 10 carbon atoms.

[0026] The alkylene group having 2 to 20 carbon atoms may be linear or branched. Examples of alkylene groups having 2 to 20 carbon atoms include ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, and hexadecylene. The number of carbon atoms in the alkylene group having 2 to 20 carbon atoms is preferably 2 to 20, more preferably 2 to 15, and even more preferably 2 to 9. At least one -CH group in the alkylene group ２ The - group may be replaced by -O-, -COO-, aromatic groups, etc. In that case, the number of carbon atoms in the replaced group should be between 2 and 20.

[0027] A cycloalkylene group having 3 to 20 carbon atoms is a group containing at least one cyclic structure. Examples of cycloalkylene groups having 3 to 20 carbon atoms include cyclopropylene, cyclobutylene, cyclopentylene, cyclohexylene, cycloheptylene, cyclooctylene, cyclononylene, cyclodecylene, cycloundecylene, and cyclohexadecylene. The above cycloalkylene groups may be substituted with one or more alkyl groups having 1 to 3 carbon atoms. The number of carbon atoms in the cycloalkylene group having 3 to 20 carbon atoms is preferably 4 to 15, more preferably 5 to 12. At least one -CH group in the above cycloalkylene group ２- group may also be replaced with -O-, -COO-, or the like. In that case, the number of carbon atoms in the group after replacement may be 3 to 20.

[0028] The divalent aromatic group having 6 to 10 carbon atoms is a group containing at least one aromatic ring. Examples of the divalent aromatic group having 6 to 10 carbon atoms include a phenylene group and a naphthylene group. The above aromatic group may be substituted with one or more alkyl groups having 1 to 3 carbon atoms. The number of carbon atoms in the aromatic group having 6 to 10 carbon atoms is preferably 4 to 8, more preferably 5 to 7.

[0029] Examples of the monovalent organic group having 1 to 11 carbon atoms include an alkyl group having 1 to 11 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, and a monovalent aromatic group having 6 to 10 carbon atoms.

[0030] The alkyl group having 1 to 11 carbon atoms may be linear or branched. Examples of the alkyl group having 1 to 11 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group, hexyl group, heptyl group, octyl group, nonyl group, and decyl group. The alkyl group having 1 to 11 carbon atoms is preferably an alkyl group having 1 to 3 carbon atoms which may be substituted with a phenyl group, and more preferably a methyl group, an ethyl group, and a benzyl group.

[0031] Examples of the cycloalkyl group having 3 to 10 carbon atoms include a cyclopentane group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group. The cycloalkyl group may be substituted with, for example, an alkyl group having 1 to 3 carbon atoms.

[0032] Examples of the monovalent aromatic group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group. The aromatic group may be substituted with, for example, an alkyl group having 1 to 3 carbon atoms.

[0033] As the polymerizable monomer represented by formula (I), R １ represents a hydrogen atom or a methyl group, and R ２is an alkylene group having 2 to 20 carbon atoms, or at least one -CH in an alkylene group having 2 to 20 carbon atoms ２ - group is a group substituted with -O- or -COO-, and R ３ is preferably a compound that is a hydrogen atom or an alkyl group having 1 to 11 carbon atoms.

[0034] The radically polymerizable monomer (b1) having at least one vinyl ether group and at least one (meth)acrylate group may be used alone or in combination of two or more. As the radically polymerizable monomer (b1) having at least one vinyl ether group and at least one (meth)acrylate group, a monomer selected from the group consisting of 2-(2-vinyloxyethoxy)ethyl acrylate (VEEA) and 2-(2-vinyloxyethoxy)ethyl methacrylate (VEEM) is preferable from the viewpoint of dilutability.

[0035] The content of the radically polymerizable monomer (b1) having at least one vinyl ether group and at least one (meth)acrylate group is preferably 30 to 50% by mass, more preferably 33 to 45% by mass, and even more preferably 35 to 40% by mass, based on the total amount of the ink composition, from the viewpoints of improving the curability of the ink composition and the solvent resistance of the resulting cured film.

[0036] Radically polymerizable monomer (c1) The ink composition contains a monofunctional radically polymerizable monomer (c1) having an aromatic ring and a hydroxyl group in its structure. The radically polymerizable monomer (c1) has a structure having an aromatic ring and a hydroxyl group, and is a monofunctional monomer having one polymerizable group, for example, one ethylenic double bond preferably selected from the group consisting of an acryloyl group, a methacryloyl group, a vinyl group, an allyl group and a vinyl ether group.

[0037] Examples of the monofunctional radically polymerizable monomer (c1) having an aromatic ring and a hydroxyl group in its structure include 2-hydroxy-3-phenoxypropyl acrylate.

[0038] The content of the monofunctional radical polymerizable monomer (c1) is preferably 1 to 10% by mass, more preferably 3 to 10% by mass, and even more preferably 5 to 10% by mass, based on the total amount of the ink composition, from the viewpoint of improving the solubility of the ink composition and the solvent resistance of the resulting cured film.

[0039] The radical polymerizable monomer (C2) ink composition contains a polyfunctional radical polymerizable monomer (C2) having an aromatic ring and a hydroxyl group in its structure. The radical polymerizable monomer (C2) is a polyfunctional monomer having a structure with an aromatic ring and a hydroxyl group, and also having two or more ethylenically double bonds selected from the group consisting of two polymerizable groups, for example, preferably acryloyl, methacryloyl, vinyl, allyl, and vinyl ether groups.

[0040] Examples of polyfunctional radical polymerizable monomers (c2) having an aromatic ring and a hydroxyl group in their structure include bisphenol A glycerolate diacrylate.

[0041] The content of the monofunctional radical polymerizable monomer (C2) is preferably 0.5 to 10% by mass, more preferably 1 to 8% by mass, and even more preferably 3 to 6% by mass, based on the total amount of the ink composition, from the viewpoint of improving the solubility and dilution of the initiator in the ink composition.

[0042] In the ink composition, the total amount of monofunctional radical polymerizable monomer (c1) having an aromatic ring and a hydroxyl group in its structure, and polyfunctional radical polymerizable monomer (c2) having an aromatic ring and a hydroxyl group in its structure, is preferably 10 to 20% by mass, more preferably 12 to 18% by mass, and even more preferably 14 to 16% by mass, relative to the total amount of the ink composition, from the viewpoint of improving the solubility of the initiator.

[0043] The ink composition may contain other monofunctional radical polymerizable monomers or other polyfunctional radical polymerizable monomers that do not fall under radical polymerizable monomers (b1), (c1), and (c2).

[0044] Other monofunctional radical polymerizable monomers include, for example, amyl (meth)acrylate, isoamyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, isomiristyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, tridecyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, neopentyl glycol (meth)acrylate benzoate, butoxyethyl (meth)acrylate, ethoxy-diethylene glycol (meth)acrylate, methoxy-triethylene glycol (meth)acrylate, methoxy-polyethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, pheno Examples include oxyethyl (meth)acrylate, phenoxy-polyethylene glycol (meth)acrylate, 2-(2-ethoxyethoxyethyl acrylate)nonylphenol ethylene oxide adduct (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 3,5,5-trimethylcyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalic acid, 1,4-cyclohexanedimethanol mono(meth)acrylate, and ethoxylated nonylphenyl (meth)acrylate. These monofunctional monomers may be used individually or in combination of two or more.

[0045] Among monofunctional monomers, those with a viscosity of less than 10 mPa·s at 25°C are preferred. Examples of monofunctional monomers that are preferred are tetrahydrofurfuryl acrylate (THFA), isobornyl acrylate (IBXA), phenoxyethyl acrylate (PEA), 3,5,5-trimethylcyclohexyl acrylate (TMCHA), 4-tert-butylcyclohexyl acrylate (TBCHA), 2-(2-ethoxyethoxyethyl acrylate), and 2-ethylhexyl (meth)acrylate, as they have low viscosity of less than 10 mPa·s at 25°C.

[0046] Other polyfunctional radical polymerizable monomers include difunctional monomers and trifunctional or higher monomers that do not fall under the radical polymerizable monomers (b1), (c1), and (c2) described above. It is preferable that the ink composition of the present invention contains trifunctional or higher monomers from the viewpoint of improving coating film strength.

[0047] Examples of polyfunctional monomers include monomers having two or more (meth)acrylate groups.

[0048] Examples of difunctional monomers include 2-hydroxy-3-acryloyloxypropyl (meth)acrylate, hydroxypivalyl hydroxypivalate di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 2,methyl-1,3-butylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 3,methyl-1,5-pentanediol di(meth)acrylate, ethoxylated 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, propoxylated neopentyl glycol di(meth)acrylate, polyethylene glycol #200 di(meth)acrylate Examples include acrylate, polyethylene glycol #400 di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol #400 di(meth)acrylate, polypropylene glycol (#700) di(meth)acrylate, glycerin di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol #600 di(meth)acrylate, polyethylene glycol #1000 di(meth)acrylate, ethoxylated polypropylene glycol #700 di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, tricyclodecanedimethanol diacrylate, and the like.

[0049] Examples of monomers with three or more functions include ethoxylated (20) trimethylolpropane triacrylate, propoxylated (3) trimethylolpropane triacrylate, trimethylolpropane tri(meth)acrylate (TMPTA), pentaerythritol tri(meth)acrylate (PETA), tris(2-hydroxyethyl) isocyanurate tri(meth)acrylate, glyceryl tri(meth)acrylate, dipentaerythritol hydroxypenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and ethylene oxide modified, propylene oxide modified, and caprolactone modified forms thereof. These polyfunctional monomers can be used individually or in combination of two or more.

[0050] The amount of monofunctional radical polymerizable monomer in the ink composition is preferably 10% by mass or less of the total amount of the ink composition, from the viewpoint of improving the strength of the coating film. The amount of monofunctional radical polymerizable monomer mentioned above also includes the amount of monofunctional radical polymerizable monomer (c1) having an aromatic ring and a hydroxyl group in its structure.

[0051] In the ink composition, the amount of other monofunctional radical polymerizable monomers that do not fall under the monofunctional radical polymerizable monomer (c1) having an aromatic ring and a hydroxyl group in its structure is preferably 0 to 10% by mass, more preferably 0 to 7% by mass, and even more preferably 0 to 5% by mass, relative to the total amount of the ink composition, from the viewpoint of improving the strength of the coating film.

[0052] The amount of polyfunctional radical polymerizable monomer in the ink composition is preferably 50 to 90% by mass, more preferably 60 to 85% by mass, and even more preferably 70 to 80% by mass, relative to the total amount of the ink composition, from the viewpoint of improving the solvent resistance of the resulting cured film. The amount of the above polyfunctional radical polymerizable monomer also includes the amount of a radical polymerizable monomer (b1) having at least one vinyl ether group and at least one (meth)acrylate group, and a polyfunctional radical polymerizable monomer (c2) having an aromatic ring and a hydroxyl group in its structure.

[0053] In the ink composition, the amount of other polyfunctional radical polymerizable monomers that do not fall under radical polymerizable monomer (b1) and radical polymerizable monomer (c2) is preferably 20 to 60% by mass, more preferably 30 to 50% by mass, and even more preferably 35 to 45% by mass, relative to the total amount of the ink composition, from the viewpoint of improving the solvent resistance of the resulting cured film.

[0054] The amount of trifunctional or polyfunctional radical polymerizable monomers in the ink composition is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less, relative to the total amount of the ink composition, from the viewpoint of improving dilutability and the solvent resistance of the resulting cured film. The amount of trifunctional or polyfunctional radical polymerizable monomers mentioned above includes the amount of radical polymerizable monomers (b1) having at least one vinyl ether group and at least one (meth)acrylate group, and polyfunctional radical polymerizable monomers (c2) having an aromatic ring and a hydroxyl group in their structure, if these are trifunctional or more.

[0055] The amount of five- or more polyfunctional radical polymerizable monomers in the ink composition is preferably 0.5 to 10% by mass, more preferably 1 to 7% by mass, and even more preferably 2 to 5% by mass, relative to the total amount of the ink composition, from the viewpoint of improving dilutability and the solvent resistance of the resulting cured film. The above amount of five- or more polyfunctional radical polymerizable monomers also includes the amount of five- or more polyfunctional radical polymerizable monomers (b1) having at least one vinyl ether group and at least one (meth)acrylate group, and polyfunctional radical polymerizable monomers (c2) having an aromatic ring and a hydroxyl group in their structure.

[0056] From the viewpoint of curability and durability of the coating film, the amount of polymerizable monomer contained in the ink composition is preferably 50 to 99.9% by mass, more preferably 60 to 99.5% by mass, and even more preferably 70 to 99% by mass, relative to the total amount of the ink composition.

[0057] The polyfunctional acylphosphine oxide initiator (a1) and monoacylphosphine oxide initiator (a2) contained in the ink composition of the present invention are highly safe initiators. However, highly safe initiators often have low solubility with other monomers, making it difficult to ensure stability when incorporated into an ink composition. Furthermore, when the amount of initiator added is limited to ensure stability, sufficient curability may not be obtained. According to the ink composition of the present invention, by incorporating the highly safe polyfunctional acylphosphine oxide initiator (a1) and monoacylphosphine oxide initiator (a2), along with the radical polymerizable monomers (b1), (c1), and (c2) described above, it has become possible to achieve an ink composition with high stability and excellent curability, even when using highly safe initiators, such as those with low solubility.

[0058] (Other components) In addition to the components listed above, the ink composition of the present invention may further contain known general additives such as colorants, polymerization inhibitors, polymerizable oligomers, surface modifiers, surfactants, leveling agents, defoamers, antioxidants, pH adjusters, charge imparters, bactericides, preservatives, deodorants, charge modifiers, wetting agents, anti-skinning agents, fragrances, diluents, and thickeners.

[0059] The ink composition may contain a colorant. The colorant is a material that imparts color to the ink composition, and specific examples include white pigments such as titanium dioxide, organic pigments, and inorganic pigments. From the viewpoint of transparency, it is preferable that the amount of colorant in the ink composition be small. For example, the amount of colorant is preferably 0 to 0.01% by mass, more preferably 0 to 0.005% by mass, and even more preferably 0 to 0.001% by mass, relative to the total amount of the ink composition.

[0060] (Ink Composition) The viscosity of the ink composition of the present invention is, from the viewpoint of printability, for example, 2 to 60 mPa·s, preferably 3 to 40 mPa·s, more preferably 4 to 35 mPa·s, and even more preferably 5 to 30 mPa·s. The viscosity of the ink composition can be measured using an E-type viscometer, a B-type viscometer, or the like.

[0061] (Method for Manufacturing Ink Composition) The method for manufacturing the ink composition of the present invention is not particularly limited as long as an ink composition satisfying the above characteristics can be obtained, but for example, it can be manufactured using conventionally known preparation methods. For example, it can be manufactured by adding polymerizable monomers and, if necessary, other components such as polymerization initiators, surface modifiers, and gelation inhibitors, and mixing them uniformly using a stirrer. Specific examples of stirrers include three-way motors, magnetic stirrers, dispersers, and homogenizers. The ink composition may also be mixed using a mixer such as a line mixer. Furthermore, the ink composition may be mixed using a disperser such as a bead mill or a high-pressure jet mill in order to further refine the particles in the ink composition.

[0062] The ink composition may contain a solvent as a dispersion medium for its components, or it may be solvent-free and use a polymerizable compound with a low molecular weight as the dispersion medium. In terms of curing the ink composition after application to a recording medium, it is preferable that the ink composition be solvent-free. This is because if solvent remains in the formed image, the solvent resistance of the image will decrease, or problems with VOCs (Volatile Organic Compounds) from the residual solvent will arise. From this viewpoint, it is preferable to use a polymerizable compound as the dispersion medium, and among these, to select a polymerizable compound with low viscosity, from the viewpoint of improved dispersibility and handling properties of the ink composition. The solvent content in the ink composition is preferably 0 to 5% by mass, more preferably 0 to 1% by mass.

[0063] The ink composition of the present invention is preferably an ink composition for an inkjet recording device, used in a printing method using an inkjet recording device. The printing method using an inkjet recording device is not particularly limited, but examples include a charge control method that ejects ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that utilizes the vibration pressure of a piezoelectric element, an acoustic inkjet recording method that utilizes radiation pressure that converts an electrical signal into an acoustic beam and irradiates the ink, and a thermal inkjet recording method that heats the ink to form bubbles and utilizes the pressure generated. The above inkjet recording methods include a method that ejects many low-concentration inks called photo inks in minute volumes, a method that improves image quality by using multiple inks of substantially the same hue but different densities, and a method that uses colorless and transparent ink.

[0064] In this embodiment, the irradiation means may include ultraviolet irradiation means such as mercury lamps, metal halide lamps, and LED lamps. For the ink composition of this embodiment, the integrated ultraviolet light intensity is 200 mJ / cm². ２ The following low-energy options can also be used.

[0065] It is preferable to irradiate the ink composition with energy rays between 1 and 1,000 ms after ejecting the ink composition onto the recording medium. If the elapsed time is less than 1 ms, the distance between the head and the light source becomes too close, and there is a risk that the energy rays may directly irradiate the head, leading to unforeseen problems. On the other hand, if the elapsed time exceeds 1,000 ms, when using other colors such as cyan, magenta, and yellow in addition to the ink composition of the present invention, ink bleeding tends to occur, and the image quality tends to deteriorate.

[0066] In this way, a printed article containing a cured product of the ink composition of the present invention can be obtained. The present invention also provides a printed article containing a cured product of the ink composition of the present invention. The ink composition of the present invention can be used in a printing method using an inkjet recording device, for example, the inkjet recording device may include a heating unit for heating the ink composition and a filter for filtering the ink composition. With such an inkjet recording device, heating reduces the ink viscosity and has the effect of stabilizing head ejection.

[0067] The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0068] First, Table 1 shows the components used in the following examples and comparative examples.

[0069]

[0070] [Example 1] A curable composition was prepared using the components shown in Table 2. Specifically, the components shown in Table 2 were weighed into a 20cc glass bottle and dissolved by stirring in an ultrasonic cleaner at 45°C for 30 minutes to obtain a curable composition. The initiators "819" and "TPO-L" used in this example both have a long-term oral toxicity DNEL to consumers of 100 μg / kg bw / day or more under the REACH regulations, and correspond to the polyfunctional acylphosphine oxide initiator (a1) and monoacylphosphine oxide initiator (a2) in the present invention, respectively. The DNEL value of initiator 819 is 1500, and the DNEL value of initiator TPO-L is 500.

[0071] [Examples 2-12 and Comparative Examples 1-16] Curable compositions were obtained in the same manner as in Example 1, except that the components shown in Tables 2-4 were used. In Comparative Examples 4, 5, and 6 were evaluated as having poor low-temperature precipitation properties, so other items were not evaluated.

[0072] [Viscosity] The viscosity of the curable compositions of the examples and comparative examples was measured using a Toki Sangyo R100 viscometer (TVE-22L) at a temperature of 25°C and a rotation speed of 20 rpm. The viscosity (mPa·s) results for the examples and comparative examples were as follows: Example 1: 23.36, Example 4: 20.59, Example 5: 21.66, Example 6: 22.98, Example 7: 22.88, Example 8: 27.05, Example 9: 26.04, Example 10: 20.01, Example 11: 24.09, Example 12: 19.73, Comparative Example 1: 19.74, Comparative Example 2: 24.23, Comparative Example 3: 22.52, Comparative Example 8: 14.91, Comparative Example 9: 13.36, Comparative Example 10: 15.8, Comparative Example 11: 16.49, Comparative Example 12: 17.16, Comparative Example 13: 21.41, Comparative Example 14: 16.38, Comparative Example 15: 17.05, and Comparative Example 16: 20.37.

[0073] [Low-Temperature Precipitation] The curable compositions of the examples and comparative examples were stored at -20°C for 30 days, and the presence or absence of precipitates was checked and evaluated according to the following criteria. ○: No precipitation after 30 days of storage at -20°C ×: Precipitation after 30 days of storage at -20°C

[0074] [Curing properties for thick and thin films] Ink was applied to a PET film using a bar coater, and the printed film was cured with an LED lamp. The printed film was applied so that the thick film was 8 μm thick with a #3 bar coater, and the thin film was 1.5 μm thick with a #0.6 bar coater. The curing conditions were: LED lamp wavelength: 395 nm, illuminance: 1000 mW / cm². ２ The irradiation energy per pass (1P) was set at 37 mJ / cm². ２ The irradiation was repeated, and the number of passes required for complete curing was measured. Complete curing was determined when the coating film could be rubbed with a dry cotton swab without load, and no abrasion occurred. The results were evaluated according to the following criteria: (Criteria for evaluating thick-film curing ability) ○: 8P (or 296 mJ / cm²) ２ ) No abrasions were observed at the time of irradiation. △: 16P (or 592 mJ / cm²) ２ ) No abrasions were observed at the time of irradiation. ×: 16P (or 592 mJ / cm²) ２Even after irradiation, abrasions occurred. (Evaluation criteria for thin film curing ability) ○: 18P (or 666 mJ / cm²) ２ ) No abrasions were observed at the time of irradiation. △: 30P (or 1110 mJ / cm²) ２ ) No abrasions were observed at the time of irradiation. ×: 30P (or 1110 mJ / cm²) ２ Even after irradiation, abrasions occurred.

[0075] [Solvent resistance (ethanol resistance) in thick and thin films] Ink was applied to a PET film using a bar coater, and the printed film was cured with an LED lamp. The printed film was applied so that the thick film was 8 μm thick with a #3 bar and the thin film was 1.5 μm thick with a #0.6 bar. The curing conditions for evaluation of thick films were an irradiation energy of 450 mJ / cm². ２ For evaluation of the cured material in thin film, an irradiation energy of 750 mJ / cm² was used. ２ A material cured using [method / method] was used. The resulting coating film was rubbed back and forth 10 times without load using a cotton swab soaked in an ethanol aqueous solution. The upper limit of the concentration of the ethanol aqueous solution at which no abrasion occurred on the coating film was measured. The results were evaluated according to the following criteria: (Evaluation criteria for solvent resistance in thick and thin films) ◎: No abrasion occurred with an 80% ethanol aqueous solution. ○: Abrasion occurred with an 80% ethanol aqueous solution, but not with a 50% ethanol aqueous solution. △: Abrasion occurred with a 50% ethanol aqueous solution, but not with a 10% ethanol aqueous solution. ×: Abrasion occurred with a 10% ethanol aqueous solution.

[0076]

[0077]

[0078]

Claims

1. An ink composition comprising: a1 (a) a polyfunctional acylphosphine oxide initiator with a long-term oral toxicity DNEL to consumers of 100 μg / kg bw / day or higher under the REACH regulations; a2 (a) a monoacylphosphine oxide initiator with a long-term oral toxicity DNEL to consumers of 100 μg / kg bw / day or higher under the REACH regulations; b1 (b) a radical polymerizable monomer having at least one vinyl ether group and at least one (meth)acrylate group; c1 (c) a monofunctional radical polymerizable monomer having an aromatic ring and a hydroxyl group in its structure; and c2 (c) a polyfunctional radical polymerizable monomer having an aromatic ring and a hydroxyl group in its structure.

2. The ink composition according to claim 1, wherein the content of the polyfunctional acylphosphine oxide initiator (a1) is 3% by mass or more based on the total amount of the ink composition.

3. The ink composition according to claim 1 or 2, wherein the total content of the polyfunctional acylphosphine oxide initiator (a1) and the monoacylphosphine oxide initiator (a2) is 5% by mass or more, based on the total amount of the ink composition.

4. The ink composition according to any one of claims 1 to 3, wherein the amount of colorant in the ink composition is 0 to 0.01% by mass relative to the total amount of the ink composition.

5. The ink composition according to any one of claims 1 to 4, wherein the monoacylphosphine oxide initiator (a2) is not diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

6. The ink composition according to any one of claims 1 to 4, wherein the polyfunctional acylphosphine oxide initiator (a1) is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

7. The ink composition according to any one of claims 1 to 4, wherein the polyfunctional acylphosphine oxide initiator (a1) is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and the monoacylphosphine oxide initiator (a2) is not diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

8. The ink composition according to any one of claims 1 to 6, wherein the polyfunctional acylphosphine oxide initiator (a1) is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and the monoacylphosphine oxide initiator (a2) is ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

9. As the radical polymerizable monomer (b1) having at least one vinyl ether group and at least one (meth)acrylate group, formula (I): [In formula (I), R １ represents a hydrogen atom or a methyl group, R ２ R represents a divalent organic group with 2 to 20 carbon atoms. ３ The ink composition according to any one of claims 1 to 8, comprising a monomer (b1') represented by [where represents a hydrogen atom or a monovalent organic group having 1 to 11 carbon atoms].

10. The ink composition according to claim 9, wherein the monomer (b1') represented by formula (I) is 2-(2-vinyloxyethoxy)ethyl (meth)acrylate.

11. The ink composition according to any one of claims 1 to 10, wherein the amount of monofunctional radical polymerizable monomer in the ink composition is 10% by mass or less with respect to the total amount of the ink composition.

12. The ink composition according to any one of claims 1 to 11, wherein the amount of trifunctional or polyfunctional radical polymerizable monomer in the ink composition is 10% by mass or less with respect to the total amount of the ink composition.

13. The ink composition according to any one of claims 1 to 12, wherein the amount of five- or more polyfunctional radical polymerizable monomers in the ink composition is 0.5 to 10% by mass relative to the total amount of the ink composition.

14. The ink composition according to any one of claims 1 to 13, wherein the amount of monomer (b1) having at least one vinyl ether group and at least one (meth)acrylate group is 30 to 50% by mass with respect to the total amount of the ink composition.

15. The ink composition according to any one of claims 1 to 14, wherein the total amount of monofunctional radical polymerizable monomer (c1) having an aromatic ring and a hydroxyl group in its structure, and polyfunctional radical polymerizable monomer (c2) having an aromatic ring and a hydroxyl group in its structure, is 10 to 20% by mass of the total amount of the ink composition.

16. An ink composition for an inkjet recording device, according to any one of claims 1 to 15.

17. A printed article comprising a cured product of an ink composition according to any one of claims 1 to 16.

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