Ink composition and printed matter

Abstract

This ink composition comprising a monomer (a) having at least one (meth)acrylate group and at least one vinyl ether group, a radically polymerizable monomer (b) having at least one (meth)acrylate group and not having a vinyl ether group, and a radical polymerization inhibitor (c), wherein: the moisture content is less than 1 mass% with respect to the total amount of the ink composition; the content of a sulfonic acid-based acid in the ink composition, as measured by ion chromatography, is at most 100 ppm; and when the intensity of a peak detected at 800-820 cm-1 and the intensity of a peak detected at 1,710-1,730 cm-1, as measured by FT-IR for the ink composition, are Ia0 and Ib0, respectively, the intensity of a peak detected at 800-820 cm-1 and the intensity of a peak detected at 1,710-1,730 cm-1, as measured by FT-IR for an ink composition after storing the ink composition under the conditions of 85ºC and 3 days, are Ia1 and Ib1, respectively, and the content of the monomer (a) with respect to the total amount of the ink composition is X mass%, the value calculated by {(Ia0 / Ib0-Ia1 / Ib1) / (Ia0 / Ib0)} / (X / 100) is at most 0.5.

Description

Ink Composition and Printed Matter

[0001] The present invention relates to an ink composition and a printed matter.

[0002] An ink composition containing a polymerizable compound is a composition used as an ink in a printing apparatus such as an inkjet printer, and is used in a printing method in which the ink composition is ejected onto a recording medium and cured by irradiation with active energy rays. According to such a printing method using an active energy ray-curable ink composition, it is possible to obtain a highly durable printed matter with excellent adhesion to a recording medium.

[0003] Regarding such ink compositions, for example, Patent Document 1 discloses a composition in which the content of a polymerizable compound, a photopolymerization initiator, and an organic sulfonic acid measured by a specific method is reduced to a specific amount or less. Further, Patent Document 2 discloses an inkjet ink that contains a pigment, a dispersant, a polymerizable compound, and a photopolymerization initiator, and has a total amount of strongly acidic substances not higher than a specific value.

[0004] JP 2020-59856 A JP 2005-200560 A

[0005] Conventionally, various ultraviolet-curable ink compositions have been studied and used in inkjet printing apparatuses. With the advancement of printing technology, inkjet printing apparatuses capable of high-speed and high-definition image formation have been developed. According to studies by the present inventors, a printing apparatus with a high ejection speed and a small nozzle diameter is used for high-speed and high-definition image formation, so that higher storage stability is required for the storage stability of the ink composition in order to suppress the deterioration of ejection performance. Accordingly, an object of the present invention is to provide an ink composition having high storage stability that is also suitable for high-speed and high-definition image formation.

[0006] The present inventor has conducted intensive studies and has completed the present invention. That is, the present invention includes the following preferred aspects. [1] An ink composition comprising: a monomer (a) having at least one (meth)acrylate group and at least one vinyl ether group; a radically polymerizable monomer (b) having at least one (meth)acrylate group and no vinyl ether group; and a radical polymerization inhibitor (c), wherein the water content is less than 1% by mass relative to the total amount of the ink composition, the content of sulfonic acid-based acid measured by ion chromatography for the ink composition is 100 ppm or less, and for the ink composition, FT-IR at 800 to 820 cm －１ Let the intensity of the peak detected at be I ａ０ , and the intensity of the peak detected at 1710 to 1730 cm －１ Let the intensity of the peak detected at be I ｂ０ , and for the ink composition after the ink composition is stored at 85°C for 3 days, FT-IR at 800 to 820 cm －１ Let the intensity of the peak detected at be I ａ１ , and the intensity of the peak detected at 1710 to 1730 cm －１ Let the intensity of the peak detected at be I ｂ１ , and when the content of the monomer (a) based on the total amount of the ink composition is defined as X% by mass, an ink composition wherein the value calculated by {(I ａ０ / I ｂ０ -I ａ１ / I ｂ１ ) / (I ａ０ / I ｂ０ )} / (X / 100) is 0.5 or less. [2] The ink composition according to [1], wherein the ink composition is a clear ink composition or a white ink composition. [3] The ink composition according to [1] or [2], wherein the amount of the color material in the ink composition is 0 to 15% by mass relative to the total amount of the ink composition. [4] The ink composition according to any one of [1] to [3], wherein the amount of the monomer (a) having at least one (meth)acrylate group and at least one vinyl ether group is 10 to 60% by mass relative to the total amount of the ink composition. [5] As the monomer (a) 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 represents a divalent organic group having 2 to 20 carbon atoms, R ３ represents a hydrogen atom or a monovalent organic group having 1 to 11 carbon atoms], the ink composition according to any one of [1] to [4], comprising the monomer (a1) represented by the formula. [6] The ink composition according to [5], wherein the monomer (a1) represented by the formula (I) is 2-(2-vinyloxyethoxy)ethyl (meth)acrylate. [7] The ink composition according to any one of [1] to [6], wherein the sulfonic acid-based acid is selected from the group consisting of methanesulfonic acid and p-toluenesulfonic acid. [8] The ink composition according to any one of [1] to [7], wherein the amount of the radical polymerization inhibitor (c) is 0.01 to 1 mass% relative to the total amount of the ink composition. [9] The ink composition according to any one of [1] to [8], wherein the radical polymerization inhibitor (c) is 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl free radical.

[10] The ink composition according to any one of [1] to [9], which is an ink composition for inkjet recording apparatuses.

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

[10] .

[0007] According to the present invention, it is possible to provide an ink composition having high storage stability, which is also suitable for high-speed and high-definition image formation.

[0008] Hereinafter, embodiments of the present invention will be described in detail. The scope of the present invention is not limited to the embodiments described herein, and various modifications can be made without departing from the gist of the present invention.

[0009] The present invention provides an ink composition comprising: a monomer (a) having at least one (meth)acrylate group and at least one vinyl ether group; a radical polymerizable monomer (b) having at least one (meth)acrylate group and not having a vinyl ether group; and a radical polymerization inhibitor (c), wherein the water content is less than 1% by mass of the total amount of the ink composition; the content of sulfonic acid-based acids measured by ion chromatography of the ink composition is 100 ppm or less; and the FT-IR temperature of the ink composition is 800 to 820 cm⁻¹. －１ The intensity of the peak detected is I ａ０ Toshi, 1710-1730 cm －１ The intensity of the peak detected is I ｂ０ The ink composition, after being stored at 85°C for 3 days, was subjected to an FT-IR test of 800-820 cm⁻¹. －１ The intensity of the peak detected is I ａ１ Toshi, 1710-1730 cm －１ The intensity of the peak detected is I ｂ１ Let X be the mass % of monomer (a) based on the total amount of the ink composition, then {(I ａ０ / I ｂ０ -I ａ１ / I ｂ１ ) / (I ａ０ / I ｂ０ The ink composition is such that the value calculated by )} / (X / 100) is 0.5 or less.

[0010] (Polymerizable Compounds) The ink composition of the present invention contains polymerizable compounds which are monofunctional monomers and / or polyfunctional monomers. The polymerizable compounds in the present invention are compounds which undergo a polymerization reaction by 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 compounds 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.

[0011] The ink composition contains at least one monomer (a) having at least one (meth)acrylate group and at least one vinyl ether group as a polymerizable compound. Monomer (a) is a monomer that is radically polymerizable but also has a vinyl ether group which is a cationic polymerizable group. When an active energy ray curable composition contains a monomer containing a radically polymerizable group and a cationically polymerizable vinyl ether group, an ink composition with excellent reactivity and curability can be provided. Monomer (a) having at least one (meth)acrylate group and at least one vinyl ether group is not particularly limited as long as it is a monomer having a vinyl ether group and a radically polymerizable group. The ink composition may contain one type of monomer (a) or two or more types of monomer (a).

[0012] An example of monomer (a) having at least one (meth)acrylate group and at least one vinyl ether group is 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 Examples of monomers (a1) are represented by [where represents a hydrogen atom or a monovalent organic group having 1 to 11 carbon atoms].

[0013] 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.

[0014] 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 ２The - group may be replaced with -O- or similar. In that case, the number of carbon atoms in the replaced group should be between 2 and 20.

[0015] R ２ This is at least one -CH group in an alkylene group having 2 to 20 carbon atoms. ２ It is preferable that the - group is replaced by an -O- group (also referred to as a "C2- to C20 oxyalkylene group"). Examples of C2- to C20 oxyalkylene groups include at least one divalent group selected from the group consisting of oxyethylene, oxypropylene, and oxybutylene groups, as well as C2- to C20 polyoxyalkylenes in which one or more of these groups are repeated multiple times. In the case of a divalent group in which two or more oxyalkylene groups are repeated, the divalent groups may be randomly repeated or in blocks.

[0016] 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 The - group may also be replaced with -O- or similar groups. In that case, the number of carbon atoms in the replaced group should be between 3 and 20.

[0017] A divalent aromatic group having 6 to 10 carbon atoms is a group containing at least one aromatic ring. Examples of divalent aromatic groups having 6 to 10 carbon atoms include phenylene groups and naphthylylene groups. The above aromatic groups 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.

[0018] Examples of monovalent organic groups having 1 to 11 carbon atoms include alkyl groups having 1 to 11 carbon atoms, cycloalkyl groups having 3 to 10 carbon atoms, and monovalent aromatic groups having 6 to 10 carbon atoms.

[0019] C1-C11 alkyl groups may be linear or branched. Examples of C1-C11 alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, hexyl, heptyl, octyl, nonyl, and decyl groups. C1-C11 alkyl groups are preferably C1-C3 alkyl groups which may be substituted with phenyl groups, and methyl, ethyl, and benzyl groups are more preferably.

[0020] Examples of cycloalkyl groups having 3 to 10 carbon atoms include cyclopentane, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl groups. These cycloalkyl groups may be substituted with alkyl groups having 1 to 3 carbon atoms, for example.

[0021] Examples of monovalent aromatic groups having 6 to 10 carbon atoms include phenyl groups and naphthyl groups. These aromatic groups may be substituted with alkyl groups having 1 to 3 carbon atoms, for example.

[0022] R is a monomer (a1) represented by formula (I). １ represents a hydrogen atom or a methyl group, R ２ This is an alkylene group having 2 to 20 carbon atoms, or at least one -CH group in an alkylene group having 2 to 20 carbon atoms. ２ - A group in which the - group is replaced by -O- etc., R ３ Compounds in which the atom is a hydrogen atom or an alkyl group having 1 to 11 carbon atoms are preferred.

[0023] Examples of monomers (a1) represented by formula (I) include vinyloxyalkyl (meth)acrylate, vinyloxycycloalkyl (meth)acrylate, alkylvinyloxyalkyl (meth)acrylate, vinyloxyalkylcycloalkylalkyl (meth)acrylate, vinyloxyalkylarylalkyl (meth)acrylate, vinyloxyalkoxyalkyl (meth)acrylate, vinyloxyalkoxyalkoxyalkyl (meth)acrylate, and vinyloxyalkoxyalkoxyalkoxyalkyl (meth)acrylate. Monomers (a1) represented by formula (I) may be used individually or in combination of two or more types.

[0024] Examples of vinyloxyalkyl (meth)acrylates include 2-vinyloxyethyl (meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl (meth)acrylate, and 2-vinyloxybutyl (meth)acrylate.

[0025] Examples of vinyloxycycloalkyl (meth)acrylates include vinyloxycyclohexyl (meth)acrylate.

[0026] Examples of alkylvinyloxyalkyl (meth)acrylates include 2-methyl-3-vinyloxypropyl (meth)acrylate and 1-methyl-2-vinyloxypropyl (meth)acrylate.

[0027] Examples of vinyloxyalkylcycloalkylalkyl (meth)acrylates include 3-vinyloxymethylcyclohexylmethyl (meth)acrylate.

[0028] Examples of vinyloxyalkylarylalkyl (meth)acrylates include p-vinyloxymethylphenylmethyl (meth)acrylate.

[0029] Examples of vinyloxyalkoxyalkyl (meth)acrylates include 2-(2-vinyloxyethoxy)ethyl acrylate (VEEA), 2-(2-vinyloxyethoxy)ethyl methacrylate (VEEM), 2-(vinyloxyisopropoxy)propyl (meth)acrylate, and 2-(vinyloxyisopropoxy)isopropyl (meth)acrylate.

[0030] Examples of vinyloxyalkoxyalkyl (meth)acrylates include vinyloxyethoxyethoxyethyl (meth)acrylate.

[0031] Examples of vinyloxyalkoxyalkoxyalkyl (meth)acrylates include vinyloxyethoxyethoxyethoxyethyl (meth)acrylate.

[0032] As the monomer (a1) represented by formula (I), 2-(2-vinyloxyethoxy)ethyl (meth)acrylate is preferred because it has low viscosity, low odor, minimizes skin irritation, has a high flash point, excellent reactivity and curability, and the coating film formed by curing has excellent adhesion.

[0033] The content of monomer (a) having at least one (meth)acrylate group and at least one vinyl ether group is preferably 10 to 60% by mass, more preferably 20 to 50% by mass, and even more preferably 30 to 45% by mass, relative to the total amount of the ink composition, from the viewpoint of adjusting the viscosity of the ink composition by acting as a diluent when using a high viscosity monomer as the other polymerizable monomer, from the viewpoint of improving the stability of the ink composition, and from the viewpoint of reactivity and adhesion.

[0034] The ink composition further comprises a radical polymerizable monomer (b) as a polymerizable compound, which has at least one (meth)acrylate group and no vinyl ether group. The radical polymerizable monomer (b) may be a monofunctional monomer or a polyfunctional monomer, as long as it has at least one (meth)acrylate group and no vinyl ether group.

[0035] Examples of monofunctional monomers include 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, and methoxydipropylene glycol (meth) Acrylate, phenoxyethyl (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-hydroxy-3-phenoxypropyl (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, ethoxylated nonylphenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, benzyl (meth)acrylate, ω-carboxy-polycaprolactone mono(meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, butyl (meth)acrylate, propyl (meth)acrylate, isobutyl (meth)acrylate, ethyl (meth)acrylate, stearyl (meth)acrylate, lar Examples include monomers having a (meth)acryloyl group such as uryl (meth)acrylate, dimethylacrylamide, diethylacrylamide, 2-hydroxyethylacrylamide, dimethylaminopropylacrylamide, and acryloylmorpholine; monomers having a vinyl group such as N-vinyl-2-caprolactam, N-vinyl-2-pyrrolidone, N-vinyloxazolidinone, and N-vinylmethyloxazolidinone; and monomers having a vinyl ether group such as hexyl vinyl ether, phenyl vinyl ether, and cyclohexyl vinyl ether. These monofunctional monomers may be used individually or in combination of two or more.

[0036] 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 include 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. In addition, 2-hydroxy-3-phenoxypropyl acrylate (HPPA) and cyclic trimethylolpropane formal acrylate (CTFA) are preferred from the viewpoint of improving adhesion to the substrate.

[0037] 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, and 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, 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, tetraethylene glycol di(meth)acrylate, polyethylene monomers having a (meth)acryloyl group such as glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, bisphenol A PO adduct di(meth)acrylate, neopentyl glycol di(meth)acrylate hydroxypivalate, polytetramethylene glycol di(meth)acrylate, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether,Examples include monomers having a vinyl ether group, such as dipropylene glycol divinyl ether, butylene glycol divinyl ether, dibutylene glycol divinyl ether, neopentyl glycol divinyl ether, cyclohexanediol divinyl ether, cyclohexanedimethanol divinyl ether, norbornyl dimethanol divinyl ether, and isobainyl divinyl ether; monomers having a (meth)acryloyl group and a vinyl ether group, such as 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate, and 2-(vinyloxyisopropoxy)isopropyl (meth)acrylate; and monomers having an acryloyl group and an allyl group, such as 2-(allyloxymethyl)methyl acrylate and 2-(allyloxymethyl)ethyl acrylate.

[0038] Examples of monomers with three or more functionalities include ethoxylated (20) trimethylolpropane triacrylate, propoxylated (3) trimethylolpropane triacrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, tris(2-hydroxyethyl) isocyanurate tri(meth)acrylate, glyceryl tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol ethoxytetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and di Examples include monomers having a (meth)acryloyl group, such as pentaerythritol hexa(meth)acrylate and its ethylene oxide modified, propylene oxide modified, and caprolactone modified forms; monomers having a vinyl ether group, such as glycerin trivinyl ether, glycerin ethylene oxide adduct trivinyl ether (6 moles of ethylene oxide added); trimethylolpropane trivinyl ether, trivinyl ether ethylene oxide adduct trivinyl ether (3 moles of ethylene oxide added); pentaerythritol trivinyl ether; and ditrimethylolpropane hexavinyl ether. These polyfunctional monomers can be used individually or in combination of two or more.

[0039] Among the polyfunctional monomers mentioned above, ethoxylated (20) trimethylolpropane triacrylate, propoxylated (3) trimethylolpropane triacrylate, and trimethylolpropane triacrylate (TMPTA) are preferred because they have relatively low viscosity, while pentaerythritol triacrylate (PETA), pentaerythritol tetraacrylate (PETTA), dipentaerythritol pentaacrylate (DPPA), and dipentaerythritol hexaacrylate (DPHA) are preferred from the viewpoint of improving the curability of the coating film.

[0040] In the ink composition, the radical polymerizable monomer (b) preferably includes an amine-modified radical polymerizable monomer. When the ink composition includes an amine-modified radical polymerizable monomer, polymerization inhibition by oxygen in the air can be suppressed, and the curing speed (curability) and film strength can be improved during ultraviolet irradiation, especially when low-energy ultraviolet irradiation using light-emitting diodes (LEDs). The amine-modified polymerizable compound is preferably a polymerizable compound having at least one amino group (primary, secondary, or tertiary amine skeleton) in its molecule. Examples of such polymerizable compounds include amino (meth)acrylate, amine-modified polyether (meth)acrylate, amine-modified polyester (meth)acrylate, amine-modified epoxy (meth)acrylate, and amine-modified urethane (meth)acrylate. These can be used alone or in combination of two or more. The content of the above amine-modified polymerizable monomer is not particularly limited, but is preferably 1 to 30% by mass, more preferably 3 to 20% by mass, and even more preferably 5 to 15% by mass, based on the total amount of the ink composition. Examples of amine-modified polymerizable compounds include EBECRYL 80, 81, and 7100 (all manufactured by Daicel Ornex), CN371NS, CN550, and CN551 (all manufactured by Sartomer), and Laromer PO94F (all manufactured by BASF).

[0041] From the viewpoint of improving the strength of the coating film, the amount of monofunctional radical polymerizable monomer in the ink composition is preferably 0 to 15% by mass, more preferably 0 to 10% by mass, and even more preferably 0 to 5% by mass, relative to the total amount of the ink composition.

[0042] The amount of polyfunctional radical polymerizable monomer in the ink composition is preferably 10 to 90% by mass, more preferably 20 to 85% by mass or less, and even more preferably 30 to 80% by mass, relative to the total amount of the ink composition, from the viewpoint of ink curability. The amount of polyfunctional radical polymerizable monomer also includes the amount of monomer (a) having at least one vinyl ether group and at least one (meth)acrylate group, and radical polymerizable monomer (b) having two or more (meth)acrylate groups and no vinyl ether group.

[0043] In the ink composition, the amount of polyfunctional radical polymerizable monomers other than monomer (a) is preferably 10 to 80% by mass, more preferably 20 to 70% by mass or less, and even more preferably 25 to 60% by mass, relative to the total amount of the ink composition, from the viewpoint of ink curability and coating film strength.

[0044] The amount of trifunctional or polyfunctional radical polymerizable monomers in the ink composition is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, relative to the total amount of the ink composition, from the viewpoint of ink curability and coating film strength. The above amount of trifunctional or polyfunctional radical polymerizable monomers includes the amounts 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. The amount of trifunctional or polyfunctional radical polymerizable monomers may be 0.5 to 30% by mass, more preferably 2 to 20% by mass, and even more preferably 5 to 10% by mass, relative to the total amount of the ink composition, from the viewpoint of ink curability and coating film strength.

[0045] The amount of five- or more polyfunctional radical polymerizable monomers in the ink composition is preferably 0.5 to 10% by mass, more preferably 2 to 10% by mass, and even more preferably 4 to 9% by mass, relative to the total amount of the ink composition, from the viewpoint of ink viscosity, ink curability, and coating film strength.

[0046] Radical polymerization inhibitor (c) Among the polymerizable compounds, monomer (a) having at least one (meth)acrylate group and at least one vinyl ether group is a monomer with very high reactivity, and it was sometimes difficult to provide an ink composition containing monomer (a) with sufficient stability. In addition, the polymerizable compounds may contain residual sulfonic acid used in the production of the polymerizable compounds, and it has been found that such acids worsen the storage stability of the ink. Furthermore, even if the sulfonic acid is reduced, sufficient storage stability and sufficient coating film strength may not be obtained. This is thought to be because even if the cationic polymerization of the vinyl ether group is reduced by the sulfonic acid, a small amount of cationic polymerization occurs, leading to competitive polymerization between cationic polymerization and radical polymerization, which causes a decrease in storage stability.

[0047] The ink composition further contains at least one radical polymerization inhibitor (c) to suppress the decrease in storage stability of the ink composition due to the progression of polymerization reactions during storage as described above. Examples of radical polymerization inhibitors (c) include hydroquinone, methoquinone, hydroxylamine aluminum, and 2,2,6,6-tetramethylpiperidine 1-oxyl free radical. The ink composition may contain one radical polymerization inhibitor or two or more radical polymerization inhibitors. From the viewpoint of the stability of the ink composition, the radical polymerization inhibitor is preferably selected from the group consisting of methoquinone, hydroxylamine aluminum, and 2,2,6,6-tetramethylpiperidine 1-oxyl free radical, more preferably selected from the group consisting of methoquinone and 2,2,6,6-tetramethylpiperidine 1-oxyl free radical, and even more preferably 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl free radical.

[0048] The amount of radical polymerization inhibitor in the ink composition is preferably 0.01 to 1% by mass, more preferably 0.02 to 0.7% by mass, and even more preferably 0.05 to 0.5% by mass, relative to the total amount of the ink composition, from the viewpoint of the stability of the ink composition and the strength of the coating film.

[0049] The content of sulfonic acid-based acids in the ink composition of the present invention, as measured by ion chromatography, is 100 ppm or less. When the content of sulfonic acid-based acids in the ink composition exceeds 100 ppm, cationic polymerization, which can proceed in small amounts in the ink composition, is more likely to trigger radical polymerization, and as a result, monomer (a) acts as a bifunctional monomer and polymerizes in three dimensions. As a result, it has been found that this may lead to a significant decrease in storage stability and a decrease in coating film strength. The content of sulfonic acid-based acids, as measured by ion chromatography, is preferably 90 ppm or less, more preferably 85 ppm or less, and even more preferably 80 ppm or less. The smaller the content of sulfonic acid-based acids, the better; it should be 0 ppm or more. The content of sulfonic acid-based acids is measured by ion chromatography, specifically, using the ink composition as a measurement sample, it can be measured using an ion chromatograph under the conditions of an anion chromatograph using an aqueous extract of the acid component.

[0050] Sulfonic acid-based acids are acids having at least one sulfonic acid group, and examples include alkyl sulfonic acids such as methanesulfonic acid, and aromatic sulfonic acids such as benzenesulfonic acid and p-toluenesulfonic acid. Such sulfonic acid-based acids are used as catalysts during monomer synthesis and are often present as impurities in the raw material monomers. From the viewpoint of improving storage stability, sulfonic acid-based acids are preferably selected from the group consisting of methanesulfonic acid and p-toluenesulfonic acid, and by reducing the amount of these sulfonic acids, an ink composition having a value α within the range described later can be prepared.

[0051] Water Content of Ink Composition The water content of the ink composition is less than 1% by mass relative to the total amount of the ink composition, from the viewpoint of the stability of the ink composition. In an ink composition comprising a monomer (a) having at least one (meth)acrylate group and at least one vinyl ether group, and a radical polymerizable monomer (b) having at least one (meth)acrylate group and not having a vinyl ether group, it has been found that, from the viewpoint of improving storage stability, it is important to include a radical polymerization inhibitor (c) and to keep the content of sulfonic acid-based acids to 100 ppm or less, but it is also important to keep the water content of the ink composition to less than 1% by mass. It has been found that if the water content is 1% by mass or more, the ionization of sulfonic acid-based acids is promoted and cationic polymerization of vinyl ether groups proceeds, so sufficient storage stability cannot be obtained. Therefore, from the viewpoint of improving storage stability, the water content of the ink composition is preferably 0.8% by mass or less, more preferably 0.6% by mass or less, and even more preferably 0.5% by mass or less.

[0052] Furthermore, the ink composition of the present invention contains a radical polymerization inhibitor (c), and the water content and sulfonic acid content are within the above range, and the FT-IR of the ink composition is 800 to 820 cm⁻¹. －１ The intensity of the peak detected is I ａ０ Toshi, 1710-1730 cm －１ The intensity of the peak detected is I ｂ０ The ink composition, after being stored at 85°C for 3 days, was subjected to an FT-IR test of 800-820 cm⁻¹. －１ The intensity of the peak detected is I ａ１ Toshi, 1710-1730 cm －１ The intensity of the peak detected is I ｂ１ Let X be the mass % of monomer (a) based on the total amount of the ink composition, then {(I ａ０ / I ｂ０ -I ａ１ / I ｂ１ ) / (I ａ０ / I ｂ０The ink composition is such that the value calculated by the formula )} / (X / 100) is 0.5 or less. The value calculated by the above formula is also referred to as value α in this specification. Here, FT-IR is 800 to 820 cm －１ The peaks detected are thought to originate from the C=CH out-of-plane bending vibrations in the acrylic group of monomer (a) having at least one (meth)acrylate group and at least one vinyl ether group, and radical polymerizable monomer (b). Therefore, their intensity is considered to represent the relative amount of acrylic double bonds. Also, 1710–1730 cm －１ The peak detected is derived from the C=O stretching vibration of the acrylic ester in the ink composition, and therefore its intensity is considered to represent the initial amount of acrylic groups relatively. Furthermore, when the ink composition is stored at 85°C for 3 days, polymerization reactions can proceed in the acrylic groups, and the 800-820 cm⁻¹ peaks relatively represent the amount of acrylic double bonds. －１ As the detected peak intensity decreases, it can be said that the polymerization reaction has progressed. On the other hand, at 1710–1730 cm⁻¹ －１ The peak detected is generally considered not to change under the above storage conditions. Therefore, (I in the above formula) ａ０ / I ｂ０ -I ａ１ / I ｂ１ This value (I) relatively indicates the change in the amount of polymerization that occurred when the acrylic groups present in the ink composition before storage were stored at 85°C for 3 days. This change is then expressed as the original ratio (I ａ０ / I ｂ０ When dividing by (a), and considering that the amount of change will naturally increase if the amount of monomer (a) is large and the acid component is not sufficiently suppressed, the value obtained by subtracting the effect of the amount of monomer is the value α. From the viewpoint of storage stability, the value α is 0 to 0.5, preferably 0 to 0.45.

[0053] The ink composition may contain a colorant. Examples of colorants include carbon black, titanium dioxide, copper phthalocyanine pigments, azo pigments, quinacridone pigments, isoindoline pigments, benzimidazolon pigments, naphthol pigments, fluorescent pigments, various lake pigments, various inorganic pigments, and various dyes. From the viewpoint of improving storage stability, the amount of colorant in the ink composition is preferably 0 to 8% by volume, more preferably 0 to 7% by volume, and even more preferably 0 to 6% by volume, relative to the total volume of the ink composition.

[0054] From the viewpoint of improving storage stability, the ink composition is preferably a clear ink composition or a white ink composition.

[0055] (Other components) In addition to the components listed above, the ink composition of the present invention may further contain known general additives such as polymerization initiators, polymerizable oligomers, surface modifiers, surfactants, leveling agents, defoamers, antioxidants, pH adjusters, deodorants, wetting agents, fragrances, diluent solvents, and thickeners.

[0056] The ink composition of the present invention may contain a polymerization initiator, such as a photopolymerization initiator. Examples of photopolymerization initiators include acylphosphine oxide compounds, alkylphenone compounds, thioxanthone compounds, and benzophenone compounds. The ink composition may contain one type of polymerization initiator or two or more types. From the viewpoint of improving the stability of the ink composition, the polymerization initiator is preferably a photopolymerization initiator.

[0057] Examples of acylphosphine oxide compounds include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide (TPO-L), bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, and 2,4,6-trimethylbenzoyl-phosphine oxide. The polymerization initiator is preferably an acylphosphine oxide compound.

[0058] Examples of alkylphenone compounds include α-aminoalkylphenones and benzyl methyl ketals, specifically 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1, 2-methyl-1-[4-(methoxythio)-phenyl]-2-morpholinopropan-2-one, and 2,2-dimethoxy-1,2-diphenylethane-1-one. These may be used individually or in combination. Examples of alkylphenone compounds available on the market include Irgacure 369, Irgacure 907, and Irgacure 651 from Ciba Corporation.

[0059] Examples of thioxanthone compounds include thioxanthone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, and 1-chloro-4-propoxythioxanthone. These may be used individually or in combination. Examples of thioxanthone compounds available on the market include KAYACURE DETX-S from Nippon Kayaku Co., Ltd. and Chivacure ITX from Double Bond Chemical Co., Ltd.

[0060] Examples of benzophenone compounds include benzophenone, 4-methylbenzophenone, and 4-benzoyl-4'-methyldiphenyl sulfide.

[0061] The content of the photopolymerization initiator in the ink composition is preferably 1 to 20% by mass, more preferably 2 to 18% by mass, based on the total amount of the ink composition.

[0062] In addition to the above, the ink composition may further contain conventionally known photopolymerization initiators such as arylalkyl ketones, oxime ketones, acylphosphine oxides, acylphosphonates, S-phenyl thiobenzoate, titanocene, aromatic ketones, benzyl, quinone derivatives, and ketocoumarins.

[0063] Examples of these photopolymerization initiators include, for example, ethyl (2,4,6-trimethylbenzoyl)-phenylphosphenate and 1-hydroxycyclohexyl-phenyl-ketone 1,2-octanedione-[4-(phenylthio)-2-(o-benzoyloxime)].

[0064] Examples of acylphosphine oxide compounds available on the market include Omnirad TPO and Omnirad TPO-L, manufactured by IGM Resins.

[0065] The viscosity of the ink composition of the present invention is, from the viewpoint of having high ejection performance, storage stability, and high film strength suitable for high-speed, high-definition image formation, 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 33 mPa·s. The viscosity of the ink composition can be measured using an E-type viscometer, a B-type viscometer, or the like.

[0066] The ink composition of the present invention may be a white ink composition, or it may be used as a multi-color ink set consisting of multiple color ink compositions.

[0067] Method for Manufacturing the 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 a conventionally known preparation method. For example, if a pigment is included, a mixture is prepared by premixing the pigment (e.g., titanium dioxide), some or all of a polymerizable compound (polymerizable oligomer if included), and a pigment dispersant, and this mixture is dispersed using a disperser to prepare a primary dispersion.

[0068] For the dispersion of the colorant, dispersion devices such as bead mills, ball mills, sand mills, attritors, roll mills, jet mills, homogenizers, paint shakers, kneaders, agitators, Henschel mixers, colloid mills, ultrasonic homogenizers, pearl mills, and wet jet mills can be used, and mixers such as line mixers may also be used. Furthermore, after dispersion of the colorant, classification treatment may be performed using a centrifuge, filter, cross-flow, etc., to remove coarse particles of the colorant. When dispersing the colorant, a dispersant may be added. In addition, when adding the colorant, it is possible to use a synergist (pigment derivative) appropriate for each colorant as a dispersion aid as needed. As pigment derivatives, phthalocyanine derivatives and azo derivatives such as EFKA-745 (manufactured by EFKA Corporation), Solspers 5000, 12000, and 22000 (all manufactured by Lubrizol Corporation) can also be used. A solvent may be added as a dispersion medium for various components such as colorants, or a polymerizable compound with low molecular weight may be used as a dispersion medium without a solvent. In terms of curing the ink composition of the present invention after application to a recording medium, it is preferable that the ink composition be solvent-free. This is because if a 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 a dispersion medium, and among these, to select a polymerizable compound with low viscosity, from the viewpoint of improving dispersion suitability and the handling properties of the ink composition.

[0069] Next, the remaining polymerizable compound, polymerization inhibitor, and other components such as photopolymerization initiators, surface modifiers, and gelling inhibitors, as needed, are added to the primary dispersion and mixed uniformly using a stirrer. Specific examples of stirrers include three-way motors, magnetic stirrers, dispersers, and homogenizers. Alternatively, the ink composition may 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 to further refine the particles in the ink composition. In the production of an ink composition, for example, if the ink composition is a clear ink composition, a crude ink composition may be produced by mixing each component without preparing a primary dispersion.

[0070] 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. Because the ink composition of the present invention has high storage stability, it also has stable ejection properties and can be suitably used as an ink composition for high-speed, high-definition inkjet recording devices that use a high ink ejection frequency and a small diameter nozzle. 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 uses the vibration pressure of a piezoelectric element, an acoustic inkjet recording method that uses 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 uses 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 transparent ink.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0075] First, Table 1 shows the components used to prepare the ink compositions in the following examples and comparative examples.

[0076]

[0077] (Preparation of polymerizable monomer (b) and measurement of sulfonic acid content) Polymerizable monomer (b1): SR508NS-1 ("SR508NS" manufactured by Arkema) was mixed with basic activated alumina "MP Alumina B-Super1" in a 1:1 ratio, stirred for 1 hour, and then the basic activated alumina was removed to remove the acidic components contained in the raw material SR508NS. Next, the amount of sulfonic acid-based acids contained in the obtained SR508NS after acid removal treatment (also referred to as "polymerizable monomer (b1)" and "SR508NS-1") was measured using ion chromatography under the following measurement conditions. The results showed that the amount of methanesulfonic acid was 10 ppm and the amount of p-toluenesulfonic acid was 0 ppm. The sample and ultrapure water were placed in a sealed container in a 1:10 ratio, heated and extracted at 100°C for 2 hours, and after cooling, solid-phase extraction was performed using a hydrophilic filter to prepare the measurement solution. Next, the amount of sulfonic acid in the measurement solution was quantified using ion chromatography (IC) under the following conditions. The methanesulfonic acid content was measured by anion chromatography. An ICS-1600 (manufactured by Dionex) was used, and detection was performed using an electrical conductivity detector. The p-toluenesulfonic acid content was measured at 35°C using column AS12A (4 mmφ × 200 mm) with a flow rate of 1.5 mL / min, an injection volume of 25 μL, and eluent 3 mM sodium bicarbonate. The p-toluenesulfonic acid content was measured by anion chromatography. An Integrion RFIC (Thermo Fisher Scientific) was used, and detection was performed using an electrical conductivity detector. At 30°C, column AS20A (4 mmφ × 200 mm) was used with a flow rate of 1.0 mL / min, an injection volume of 25 μL, and a gradient setting (min / potassium hydroxide solution, 0 min / 5 mM → 5 min / 5 mM → 15 min / 30 mL → 20 min / 55 mL), and the mobile phase composition was continuously changed to elute and measure the content. In this example, the amount of inorganic acid was measured as described above, but the amount of inorganic acid may also be measured by ion chromatography analysis of the obtained curable composition.

[0078] Polymerizable monomer (b2): SR508NS-2 To 99.9900 g of SR508NS-1 prepared as described above, 0.0100 g of methanesulfonic acid was added to obtain a polymerizable monomer with a methanesulfonic acid content of 110 ppm and a p-toluenesulfonic acid content of 0 ppm. This polymerizable monomer is also referred to as polymerizable monomer (b2) or SR508NS-2.

[0079] Polymerizable monomers (b3) and (b4): SR508NS-3 and SR508NS-4. Polymerizable monomers (b3) (SR508NS-3) and polymerizable monomers (b4) (SR508NS-4) were obtained in the same manner as the preparation method for polymerizable monomer (b2), except that methanesulfonic acid was added in an amount that resulted in a methanesulfonic acid content of 310 ppm or 410 ppm, with the amounts of methanesulfonic acid and p-toluenesulfonic acid shown in Table 2.

[0080] Polymerizable monomer (b5): SR238NS The amount of sulfonic acid-based acids was measured using the above ion chromatography conditions for 1,6-hexanediol diacrylate (Arkema "SR238NS") obtained as a raw material. The amounts of methanesulfonic acid and p-toluenesulfonic acid are shown in Table 2.

[0081] Polymerizable monomers (b6) and (b7): SR899NS-1, SR899NS-2 Dipentaerythritol hexaacrylate (Arkema "SR899NS") obtained as a raw material was measured for sulfonic acid-based acids under the above ion chromatography conditions. The amounts of methanesulfonic acid and p-toluenesulfonic acid are shown in Table 2. This dipentaerythritol hexaacrylate is also referred to as polymerizable monomer (b6) and SR899NS-1. Next, 0.0490 g of methanesulfonic acid was added to 99.9510 g of polymerizable monomer (b6) to adjust the amount of methanesulfonic acid to 500 ppm and the amount of p-toluenesulfonic acid to 0 ppm. This polymerizable monomer is also referred to as polymerizable monomer (b7) and SR899NS-2.

[0082] The amounts of sulfonic acids in VEEA and CN371NS, as listed in Table 1, were measured under the ion chromatography conditions described above. The results are shown in Table 2.

[0083]

[0084] [Example 1] An ink composition was prepared using the components shown in Table 3. Specifically, the components shown in Table 3 were weighed into a 50cc glass bottle and dissolved by stirring in an ultrasonic cleaner at 45°C for 60 minutes to obtain the ink composition.

[0085] [Examples 2-10 and Comparative Examples 1-3] Ink compositions were obtained in the same manner as in Example 1, except that the components shown in Table 3 were used.

[0086] (Amount of sulfonic acid) The total amount of sulfonic acid in the obtained ink composition was calculated by multiplying the acid concentration contained in each polymerizable monomer by its respective blending ratio and summing the results. It was confirmed that components other than monomer (b) shown in Table 2 in the ink composition do not contain sulfonic acid.

[0087] (Viscosity) The viscosity of the ink composition was measured using a viscometer TV-100EL (manufactured by Toki Sangyo Co., Ltd.) under conditions of a liquid temperature of 25°C, and this was recorded as the initial viscosity. Next, the ink composition was stored at 85°C for 3 days, and the viscosity of the stored ink composition was measured under the same conditions as the initial viscosity, and this was recorded as the viscosity after the storage test. From the obtained results, the viscosity change rate, which represents how much the viscosity changed before and after the storage test, was calculated.

[0088] (Moisture content) The moisture in the ink was vaporized using a moisture vaporizer ADP-611 (manufactured by Kyoto Electronics Manufacturing Co., Ltd.), and the moisture content (water content) in the ink composition was measured using a moisture meter MKC-710 (manufactured by Kyoto Electronics Manufacturing Co., Ltd.).

[0089] (Reactive double bond retention ratio: {(A-B) / A} / C)) The FT-IR spectrum of the ink composition was measured by ATR using an FT-IR iZ10 (Thermo Fisher). The obtained spectrum was measured at 800–820 cm⁻¹. －１ The intensity of the peak detected is I ａ０ Toshi, 1710-1730 cm－１ The intensity of the peak detected is I ｂ０ Next, the ink composition was stored at 85°C for 3 days, and the FT-IR spectrum of the stored ink composition was measured in the same manner. The obtained spectrum was measured at 800–820 cm⁻¹. －１ The intensity of the peak detected is I ａ１ Toshi, 1710-1730 cm －１ The intensity of the peak detected is I ｂ１ This was determined. Furthermore, the monomer (a) content based on the total amount of the ink composition was set to X mass%. At this time, the following formula {(I ａ０ / I ｂ０ -I ａ１ / I ｂ１ ) / (I ａ０ / I ｂ０ The value obtained by )} / (X / 100) was calculated. The results are shown in Table 3.

Claims

1. An ink composition comprising: a monomer (a) having at least one (meth)acrylate group and at least one vinyl ether group; a radically polymerizable monomer (b) having at least one (meth)acrylate group and no vinyl ether group; and a radical polymerization inhibitor (c), wherein the water content is less than 1 mass% relative to the total amount of the ink composition, the content of sulfonic acid-based acid measured by ion chromatography for the ink composition is 100 ppm or less, and for the ink composition, 800 to 820 cm by FT-IR －１ Let the intensity of the peak detected at be I ａ０ , and 1710 to 1730 cm －１ Let the intensity of the peak detected at be I ｂ０ , and for the ink composition after storing the ink composition at 85°C for 3 days, 800 to 820 cm by FT-IR －１ Let the intensity of the peak detected at be I ａ１ , and 1710 to 1730 cm －１ Let the intensity of the peak detected at be I ｂ１ , and when the content of the monomer (a) based on the total amount of the ink composition is defined as X mass%, the value calculated by {(I ａ０ / I ｂ０ -I ａ１ / I ｂ１ ) / (I ａ０ / I ｂ０ )} / (X / 100) is 0.5 or less, the ink composition.

2. The ink composition according to claim 1, wherein the ink composition is a clear ink composition or a white ink composition.

3. The ink composition according to claim 1 or 2, wherein the amount of colorant in the ink composition is 0 to 15% by mass relative to the total amount of the ink composition.

4. The ink composition according to any one of claims 1 to 3, wherein the amount of monomer (a) having at least one (meth)acrylate group and at least one vinyl ether group is 10 to 60% by mass with respect to the total amount of the ink composition.

5. As the monomer (a) 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 4, comprising a monomer (a1) represented by [where represents a hydrogen atom or a monovalent organic group having 1 to 11 carbon atoms].

6. The ink composition according to claim 5, wherein the monomer (a1) represented by formula (I) is 2-(2-vinyloxyethoxy)ethyl (meth)acrylate.

7. The ink composition according to any one of claims 1 to 6, wherein the sulfonic acid is selected from the group consisting of methanesulfonic acid and p-toluenesulfonic acid.

8. The ink composition according to any one of claims 1 to 7, wherein the amount of the radical polymerization inhibitor (c) is 0.01 to 1% by mass relative to the total amount of the ink composition.

9. The ink composition according to any one of claims 1 to 8, wherein the radical polymerization inhibitor (c) is a 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl free radical.

10. An ink composition according to any one of claims 1 to 9, which is an ink composition for an inkjet recording device.

11. A printed article comprising a cured product of an ink composition according to any one of claims 1 to 10.

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