Radiation-curable inkjet ink composition and recording method

Abstract

To provide a radiation-curable inkjet ink composition and an inkjet recording method that offer excellent curability of the ink composition and abrasion resistance of the coating film, while reducing migration risk. [Solution] The radiation-curable inkjet ink composition comprises a polymerizable compound, a polymerization initiator, and a thioxanthone sensitizer having a molecular weight of 300 or more. The polymerizable compound comprises a monofunctional polymerizable compound and a difunctional polymerizable compound. The polymerization initiator comprises phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide. The monofunctional polymerizable compound comprises a hydroxyl group-containing monofunctional polymerizable compound, and the content of the difunctional polymerizable compound is 30% by mass or more of the total amount.

Description

[Technical Field]

[0001] The present invention relates to a radiation-curable inkjet ink composition and a recording method. [Background technology]

[0002] Inkjet recording methods, which enable the recording of high-resolution images with relatively simple equipment, are undergoing rapid development in various fields. In this context, various studies have been conducted on radiation-curable inkjet ink compositions. For example, Patent Document 1 discloses a photocurable inkjet ink composition that exhibits a specific viscosity and surface tension, comprising a thioxanthone compound having a photosensitizing effect, an ethylenically unsaturated bond-containing polymer photopolymerization initiator, a (meth)acrylate compound, a (meth)acrylamide compound and / or an aminobenzoate compound, and a surface modifier, in order to reduce migration risk. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-20850 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, when printing using the photocurable inkjet ink composition described in Patent Document 1, there was a problem in that it was difficult to improve the curability and abrasion resistance of the ink coating. In other words, there was a need for a radiation-curable inkjet ink composition that had excellent curability and abrasion resistance of the ink coating while reducing migration risk. [Means for solving the problem]

[0005] The radiation-curable inkjet ink composition comprises a hydroxyl group-containing monofunctional polymerizable compound, a difunctional polymerizable compound, a thioxanthone sensitizer having a molecular weight of 300 or more, and a polymerization initiator, wherein the polymerization initiator comprises phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide, and the content of the difunctional polymerizable compound is 30% by mass or more of the total amount. [Brief explanation of the drawing]

[0006] [Figure 1] This is a schematic diagram of the recording device used in this embodiment. [Figure 2] This table shows the composition and evaluation results of the ink compositions used in the examples. [Figure 3] A table showing the composition and evaluation results of the ink compositions related to the examples and comparative examples. [Modes for carrying out the invention]

[0007] The embodiments of the present invention (hereinafter referred to as "these embodiments") will be described in detail below, but the present invention is not limited thereto, and various modifications are possible without departing from its essence. In the following description, the radiation-curable inkjet ink composition may also be simply referred to as "ink composition".

[0008] 1. Radiation-curable inkjet ink composition The radiation-curable inkjet ink composition according to this embodiment comprises a hydroxyl group-containing monofunctional polymerizable compound, a difunctional polymerizable compound, a thioxanthone sensitizer having a molecular weight of 300 or more, and a polymerization initiator, wherein the polymerization initiator comprises phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide, and the content of the difunctional polymerizable compound is 30% by mass or more of the total amount of the ink composition.

[0009] While including a thioxanthone sensitizer with a molecular weight of 300 or more can reduce the migration risk in the coating film of the ink composition, a challenge arises in this case: the curability of the coating film of the ink composition may not be sufficient.

[0010] Therefore, by including phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide, which has excellent curability, and further including a hydroxyl group-containing monofunctional polymerizable compound that has excellent compatibility with thioxanthone sensitizers, the coating film of the ink composition becomes highly curable.

[0011] Furthermore, ink compositions containing a thioxanthone sensitizer with a molecular weight of 300 or more, phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide, and a hydroxyl group-containing monofunctional polymerizable compound tend to have difficulty improving the abrasion resistance of the ink film. Therefore, by including a difunctional polymerizable compound at a concentration of 30% by mass or more relative to the total amount of the ink composition, the abrasion resistance of the ink film is improved.

[0012] The following describes in detail each component of the radiation-curable inkjet ink composition of this embodiment.

[0013] 1.1. Polymerizable compounds The ink composition of this embodiment contains a polymerizable compound. The polymerizable compound is a concept that includes monofunctional polymerizable compounds having one polymerizable functional group and polyfunctional polymerizable compounds having two or more polymerizable functional groups. When the ink composition of this embodiment is irradiated with radiation, the polymerization reaction of the polymerizable compounds contained in the ink composition begins, and the ink composition hardens. Polymerizable compounds include monomers and oligomers. The polymerizable compounds can be used individually or in combination of two or more.

[0014] In this embodiment, the degree of polymerization of monomers in the oligomer is not particularly limited, but for example, it may be 2 to 100, 2 to 50, 2 to 25, 2 to 10, or 2 to 5. Here, the degree of polymerization refers to the number of monomers constituting the oligomer.

[0015] The content of the coincident compound is preferably 60% by mass or more and 95% by mass or less, 65% by mass or more and 90% by mass or less, and 70% by mass or more and 90% by mass or less with respect to the total amount of the ink composition.

[0016] 1.1.1. Monofunctional polymerizable compound The ink composition of the present embodiment contains a monofunctional polymerizable compound. Examples of the monofunctional polymerizable compound include a hydroxyl group-containing monofunctional polymerizable compound, a nitrogen-containing heterocyclic ring-containing monofunctional polymerizable compound, a monofunctional polymerizable compound having an alicyclic structure, and an aromatic group-containing monofunctional polymerizable compound. Here, when referring to "monofunctional", it means that the number of functional groups of the polymerizable double bond is one. The polymerizable compound is used alone or in combination of two or more.

[0017] The total amount of the monofunctional polymerizable compound is preferably 5.0% by mass or more and 70.0% or less, 5.0% by mass or more and 60.0% by mass or less, 10.0% by mass or more and 50.0% by mass or less, and 15.0% by mass or more and 45.0% by mass or less with respect to the total amount of the ink composition. When the content of the monofunctional polymerizable compound is within the above range, the cured film of the ink composition is excellent in curability and flexibility. Specifically, the total amount of the monofunctional polymerizable compound is 5.0, 10.0, 15.0, 20.0, 25.0, 30.0, 35.0, 40.0, 45.0, 50.0, 55.0, 60.0, 65.0, 70.0% by mass with respect to the total amount of the polymerizable compound, and it may be within the range between any two of these values.

[0018] The total amount of the monofunctional polymerizable compound is preferably 5.0% by mass or more and 75.0% by mass or less, 5.0% by mass or more and 60.0% by mass or less, 10.0% by mass or more and 55.0% by mass or less, and 15.0% by mass or more and 45.0% by mass or less with respect to the total amount of the polymerizable compound. When the content of the monofunctional polymerizable compound is within the above range, the cured film of the ink composition tends to be excellent in curability and flexibility.

[0019] 1.1.1.1. Hydroxyl group-containing monofunctional polymerizable compound The ink composition of this embodiment contains a hydroxyl group-containing monofunctional polymerizable compound. This ensures sufficient curability even when the ink composition of this embodiment contains a thioxanthone sensitizer with a molecular weight of 300 or more and phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide, which will be described later. The reason for the improved curability of the ink composition is thought to be that the thioxanthone sensitizer with a molecular weight of 300 or more and phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide have high compatibility with the hydroxyl group-containing monofunctional polymerizable compound, resulting in a faster curing reaction of the ink composition.

[0020] The hydroxyl group-containing monofunctional polymerizable compound is not particularly limited as long as it contains a hydroxyl group, but from the viewpoint of further improving curability, it is preferable to include, for example, 4-hydroxybutyl (meth)acrylate, 1,4-cyclohexanedimethanol monoacrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate. In particular, it is more preferable from the viewpoint of improving curability to include 4-hydroxybutyl (meth)acrylate, 1,4-cyclohexanedimethanol monoacrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate. The ink composition may contain one type of hydroxyl group-containing monofunctional polymerizable compound, or it may contain two or more types of hydroxyl group-containing monofunctional polymerizable compounds.

[0021] In this specification, "(meth)acrylate" means at least one of acrylate and its corresponding methacrylate, and "(meth)acrylic" means at least one of acrylic and its corresponding methacrylic.

[0022] The content of the hydroxyl group-containing monofunctional polymerizable compound is preferably 2.0% to 50.0% by mass, 3.0% to 45.0% by mass, 5.0% to 40.0% by mass, 10.0% to 37.5% by mass, and 12.5% ​​to 35.0% by mass, relative to the total amount of the ink composition. Curability tends to be further improved when the content of the hydroxyl group-containing monofunctional polymerizable compound is within the above range. Specifically, the content of the hydroxyl group-containing monofunctional polymerizable compound may be 2.0, 5.0, 10.0, 12.5, 15.0, 20.0, 25.0, 30.0, 35.0, 37.5, 40.0, 45.0, or 50% by mass, or within a range between any two of these values.

[0023] The content of the hydroxyl group-containing monofunctional polymerizable compound is preferably 2.0% by mass or more and 60.0% by mass or less, 5.0% by mass or more and 50.0% by mass or less, and 10.0% by mass or more and 40.0% by mass or less, relative to the total amount of polymerizable compounds. When the content of the hydroxyl group-containing monofunctional polymerizable compound is within the above range, the curability tends to be further improved.

[0024] The content of the hydroxyl group-containing monofunctional polymerizable compound is preferably 2.0% by mass or more and 60.0% by mass or less, 5.0% by mass or more and 50.0% by mass or less, and 10.0% by mass or more and 40.0% by mass or less, relative to the total amount of monofunctional polymerizable compounds. When the content of the hydroxyl group-containing monofunctional polymerizable compound is within the above range, the curability tends to be further improved.

[0025] 1.1.1.2.Nitrogen-containing heterocycle-containing monofunctional polymerizable compound The ink composition of this embodiment may also contain a nitrogen-containing heterocyclic monofunctional polymerizable compound. This tends to result in excellent curability.

[0026] The ink composition of this embodiment preferably contains a nitrogen-containing heterocyclic monofunctional polymerizable compound, specifically a nitrogen-containing heterocyclic monofunctional polymerizable compound containing a vinyl group, or a nitrogen-containing heterocyclic monofunctional polymerizable compound containing an oxazolidinone group. It is particularly preferable to include N-vinylmethyloxazolidinone (VMOX) or acryloylmorpholine (ACMO). The ink composition of this embodiment tends to have improved curability when it contains VMOX or ACMO.

[0027] Furthermore, the ink composition of this embodiment may also contain nitrogen-containing heterocyclic monofunctional polymerizable compounds other than VMOX and ACMO. Examples of nitrogen-containing heterocyclic monofunctional polymerizable compounds other than VMOX and ACMO are not particularly limited, but include nitrogen-containing monofunctional vinyl monomers such as N-vinylcaprolactam, N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, and N-vinylpyrrolidone; nitrogen-containing monofunctional acrylate monomers such as N-(2-hydroxyethyl)acrylamide; nitrogen-containing monofunctional acrylamide monomers such as (meth)acrylamide, N-hydroxymethyl(meth)acrylamide, diacetoneacrylamide, N,N-dimethyl(meth)acrylamide, dimethylaminoethyl acrylate benzyl chloride quaternary salt, and oligomers thereof. The composition may contain one nitrogen-containing heterocyclic monofunctional polymerizable compound or two or more.

[0028] The content of the nitrogen-containing heterocycle-containing monofunctional polymerizable compound is preferably 10% to 50% by mass, 15% to 45% by mass, 20% to 40% by mass, or 20% to 35% by mass, relative to the total amount of the ink composition. When the content of the nitrogen-containing heterocycle-containing monofunctional polymerizable compound relative to the total amount of the ink composition is within the above range, the curability of the ink composition tends to improve. Specifically, the content of the nitrogen-containing heterocycle-containing monofunctional polymerizable compound may be 0.0, 5.0, 10.0, 12.5, 15.0, 20.0, 25.0, 30.0, 35.0, 37.5, 40.0, 45.0, or 50% by mass, or within a range between any two of these values.

[0029] The content of nitrogen-containing heterocycle-containing monofunctional polymerizable compounds is preferably 15% to 55% by mass, 20% to 50% by mass, 25% to 45% by mass, or 25% to 40% by mass, relative to the total amount of polymerizable compounds. When the content of nitrogen-containing heterocycle-containing monofunctional polymerizable compounds relative to the total amount of polymerizable compounds is within the above range, the curability of the ink composition tends to be further improved.

[0030] The content of nitrogen-containing heterocycle-containing monofunctional polymerizable compounds is preferably 20% to 65% by mass, 25% to 60% by mass, or 30% to 55% by mass, relative to the total amount of monofunctional polymerizable compounds. When the content of nitrogen-containing heterocycle-containing monofunctional polymerizable compounds relative to the total amount of monofunctional polymerizable compounds is within the above range, the curability of the ink composition tends to be further improved.

[0031] The molecular weight of the nitrogen-containing heterocycle-containing monofunctional polymerizable compound is preferably between 100 and 200, and between 110 and 180. Having the molecular weight of the nitrogen-containing heterocycle-containing monofunctional polymerizable compound within this range tends to improve the curability of the ink composition.

[0032] The glass transition temperature of homopolymers of nitrogen-containing heterocycle-containing monofunctional polymerizable compounds is preferably between 50°C and 200°C, and between 100°C and 175°C. When the glass transition temperature of the nitrogen-containing heterocycle-containing monofunctional polymerizable compound is within this range, blocking resistance tends to be improved.

[0033] 1.1.1.3. Monofunctional polymerizable compounds having an alicyclic structure The ink composition of this embodiment may contain a monofunctional polymerizable compound having an alicyclic structure. The monofunctional polymerizable compound having an alicyclic structure is not particularly limited, but examples include monomers having monocyclic hydrocarbon groups such as tert-butylcyclohexanol (meth)acrylate (TBCHA), 3,3,5-trimethylcyclohexyl (meth)acrylate (TMCHA), and 2-(meth)acrylic acid-1,4-dioxaspiro[4,5]decy-2-ylmethyl; monomers having unsaturated polycyclic hydrocarbon groups such as dicyclopentenyl (meth)acrylate and dicyclopentenyloxyethyl (meth)acrylate; and monomers having saturated polycyclic hydrocarbon groups such as dicyclopentanyl (meth)acrylate and isobornyl (meth)acrylate (IBXA).

[0034] Among these, isobornyl (meth)acrylate, tert-butylcyclohexanol acrylate, and trimethylcyclohexyl (meth)acrylate are preferred, with isobornyl acrylate being more preferred. Using monofunctional polymerizable compounds having such alicyclic structures tends to further improve blocking resistance or curability.

[0035] Furthermore, the content of monofunctional polymerizable compounds having an alicyclic structure is preferably 15% to 45% by mass, more preferably 20% to 40% by mass, and even more preferably 25% to 35% by mass, based on the total amount of the ink composition. Having a monofunctional monomer content having an alicyclic structure within the above range tends to improve blocking resistance or curability.

[0036] Furthermore, the content of monofunctional polymerizable compounds having an alicyclic structure is preferably 15% to 45% by mass, 20% to 40% by mass, and 25% to 35% by mass, relative to the total amount of polymerizable compounds. When the content of monofunctional polymerizable compounds having an alicyclic structure is within the above range, blocking resistance or curability tends to be further improved.

[0037] Furthermore, the content of monofunctional polymerizable compounds having an alicyclic structure is preferably 15% to 45% by mass, more preferably 20% to 40% by mass, and even more preferably 25% to 35% by mass, relative to the total amount of monofunctional polymerizable compounds. When the content of monofunctional polymerizable compounds having an alicyclic structure is within the above range, blocking resistance or curability tends to be further improved. Specifically, the content of monofunctional polymerizable compounds having an alicyclic structure may be 0.0, 5.0, 10.0, 12.5, 15.0, 20.0, 25.0, 30.0, 35.0, 37.5, 40.0, 45.0, or 50% by mass, and may be within the range of any two of these values.

[0038] 1.1.1.4. Monofunctional polymerizable compounds containing aromatic groups The ink composition of this embodiment may or may not contain an aromatic group-containing monofunctional polymerizable compound. The aromatic group-containing monofunctional polymerizable compound is not particularly limited as long as it contains an aromatic group, but examples include phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, alkoxylated 2-phenoxyethyl (meth)acrylate, ethoxylated nonylphenyl (meth)acrylate, alkoxylated nonylphenyl (meth)acrylate, p-cumylphenol EO modified (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate. Among these, from the viewpoint of further improving low-temperature storage, it is preferable to include phenoxyethyl (meth)acrylate and benzyl (meth)acrylate.

[0039] The content of the aromatic group-containing monofunctional polymerizable compound is preferably 0.0% to 40.0% by mass, 3.0% to 35.0% by mass, 5.0% to 30.0% by mass, and 10.0% to 25.0% by mass, relative to the total amount of the ink composition. When the content of the aromatic group-containing monofunctional polymerizable compound is within the above range, low-temperature storage tends to be improved. Specifically, the content of the aromatic group-containing monofunctional polymerizable compound may be 0.0, 5.0, 10.0, 15.0, 20.0, 25.0, 30.0, 35.0, or 40.0% by mass, or within a range between any two of these values.

[0040] The content of the aromatic group-containing monofunctional polymerizable compound is preferably 0.0% to 40.0% by mass, 3.0% to 35.0% by mass, 5% to 30.0% by mass, and 10.0% to 27.5% by mass, relative to the total amount of polymerizable compounds. When the content of the aromatic group-containing monofunctional polymerizable compound is within the above range, low-temperature storage tends to be improved. Specifically, the content of the aromatic group-containing monofunctional polymerizable compound may be 0.0, 5.0, 10.0, 15.0, 20.0, 25.0, 30.0, 35.0, or 40.0% by mass, and may be within the range of any two of these values.

[0041] The content of the aromatic group-containing monofunctional polymerizable compound is preferably 0.0% to 40.0% by mass, 3.0% to 35.0% by mass, 5% to 30.0% by mass, and 10.0% to 27.5% by mass, relative to the total amount of monofunctional polymerizable compounds. When the content of the aromatic group-containing monofunctional polymerizable compound is within the above range, low-temperature storage tends to be improved. Specifically, the content of the aromatic group-containing monofunctional polymerizable compound may be 0.0, 5.0, 10.0, 15.0, 20.0, 25.0, 30.0, 35.0, or 40.0% by mass, and may be within the range of any two of these values.

[0042] 1.1.2. Multifunctional polymerizable compound The polyfunctional polymerizable compounds in this embodiment include difunctional polymerizable compounds containing two polymerizable functional groups and trifunctional or higher polymerizable compounds containing three or more polymerizable functional groups.

[0043] 1.1.2.1. Bifunctional polymerizable compound In this embodiment, the ink composition contains a difunctional polymerizable compound. The difunctional polymerizable compound is not particularly limited, but examples include diethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1, Examples include 6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, ethylene oxide (EO) adduct di(meth)acrylate of bisphenol A, propylene oxide (PO) adduct di(meth)acrylate of bisphenol A, neopentyl glycol di(meth)acrylate of hydroxypivalate, and polytetramethylene glycol di(meth)acrylate. These difunctional polymerizable compounds can be used individually or in combination of two or more. The term "difunctional" refers to a compound with two functional groups in its polymerizable double bond.

[0044] In particular, when one or more of the following are included: dipropylene glycol di(meth)acrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, and 1,6-hexanediol di(meth)acrylate, the abrasion resistance of the ink coating tends to be superior, and is therefore more preferable.

[0045] The bifunctional polymerizable compound may include a compound represented by the following formula (1) such as 2-(2-vinyloxyethoxy)ethyl acrylate. By including such a vinyl ether group-containing (meth)acrylate, the viscosity of the ink composition decreases, and the ejection stability tends to be further improved. In addition, the curability of the ink composition is further improved, and the recording speed can be increased with the improvement of the curability. CH2=CR

[0047] , , , 3 , 2 , 2 -COOR 2 -O-CH=CH-R 3 ··· (1) (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.)

[0046] In the above formula (1), as the divalent organic residue having 2 to 20 carbon atoms represented by R 2 , there are linear, branched or cyclic alkylene groups having 2 to 20 carbon atoms which may be substituted, alkylene groups having 2 to 20 carbon atoms which may be substituted and have an oxygen atom due to an ether bond and / or an ester bond in the structure, and divalent aromatic groups having 6 to 11 carbon atoms which may be substituted. Among these, alkylene groups having 2 to 6 carbon atoms such as an ethylene group, an n-propylene group, an isopropylene group, and a butylene group, and alkylene groups having 2 to 9 carbon atoms which have an oxygen atom due to an ether bond in the structure such as an oxyethylene group, an oxy-n-propylene group, an oxyisopropylene group, and an oxybutylene group are preferable. Further, from the viewpoint of further reducing the viscosity of the composition and further improving the curability of the composition, R 2 is more preferably a compound having a glycol ether chain in which it is an alkylene group having 2 to 9 carbon atoms having an oxygen atom due to an ether bond in the structure such as an oxyethylene group, an oxy-n-propylene group, an oxyisopropylene group, and an oxybutylene group.

[0047] In the above formula (1), R 3As monovalent organic residues having 1 to 11 carbon atoms, suitable options include linear, branched, or cyclic alkyl groups having 1 to 10 carbon atoms, which may be substituted, and aromatic groups having 6 to 11 carbon atoms, which may be substituted. Among these, alkyl groups having 1 to 2 carbon atoms, such as methyl or ethyl groups, and aromatic groups having 6 to 8 carbon atoms, such as phenyl and benzyl groups, are preferably used.

[0048] If any of the above organic residues are groups that may be substituted, the substituents can be divided into groups containing carbon atoms and groups that do not contain carbon atoms. First, if the substituent is a group containing carbon atoms, that carbon atom is counted in the number of carbon atoms of the organic residue. Examples of groups containing carbon atoms include, but are not limited to, carboxyl groups and alkoxy groups. Next, examples of groups that do not contain carbon atoms include, but are not limited to, hydroxyl groups and halo groups.

[0049] Specific examples of the compounds of formula (1) are not particularly limited, but include, for example, 2-vinyloxyethyl (meth)acrylate, 3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl (meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl (meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate, 1-vinyloxymethylpropyl (meth)acrylate, 2-methyl-3-vinyloxypropyl (meth)acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth)acrylate, (methyl-2-vinyloxyethyl (meth)acrylate, (methyl-2-vinyloxyethyl (meth)acrylate) (Meth) 3-vinyloxybutyl acrylate, (meth) 1-methyl-2-vinyloxypropyl acrylate, (meth) 2-vinyloxybutyl acrylate, (meth) 4-vinyloxycyclohexyl acrylate, (meth) 6-vinyloxyhexyl acrylate, (meth) 4-vinyloxymethylcyclohexylmethyl acrylate, (meth) 3-vinyloxymethylcyclohexylmethyl acrylate, (meth) 2-vinyloxymethylcyclohexylmethyl acrylate, (meth) p-vinyloxymethylphenylmethyl acrylate, (meth) m-vinyloxymethylphenyl methyl, o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(2-vinyloxyethoxy)ethyl methacrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxy)propyl (meth)acrylate, 2-(vinyloxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate, 2-(vinyloxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyethyl) Xyethoxy)ethyl, (meth)acrylate 2-(vinyloxyethoxyisopropoxy)ethyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)ethyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)ethyl, (meth)acrylate 2-(vinyloxyethoxyethoxy)propyl, (meth)acrylate 2-(vinyloxyethoxyisopropoxy)propyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)propyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)propyl,(meth)acrylate 2-(vinyloxyethoxyethoxy)isopropyl, (meth)acrylate 2-(vinyloxyethoxyisopropoxy)isopropyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)isopropyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)isopropyl, (meth)acrylate 2-(vinyloxyethoxyethoxyethoxy)ethyl, (meth)acrylate 2-(vinyloxyethoxyethoxyethoxyethoxy) Examples include ethyl acrylate, 2-(isopropenoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate, polyethylene glycol monovinyl ether (meth)acrylate, and polypropylene glycol monovinyl ether (meth)acrylate. Among these specific examples, 2-(2-vinyloxyethoxy)ethyl acrylate is particularly preferred due to its ease of balancing the curability and viscosity of the composition. In this embodiment, 2-(2-vinyloxyethoxy)ethyl acrylate may also be referred to as VEEA.

[0050] The content of the difunctional polymerizable compound is 30% by mass or more of the total amount of the ink composition. Preferably, it is 35.0% by mass or more and 90.0% by mass or less, 40.0% by mass or more and 80.0% by mass or less, 45.0% by mass or more and 75.0% by mass or less, and 50.0% by mass or more and 70.0% by mass or less. Being within the above range tends to result in superior viscosity properties and curability. Specifically, the content of the difunctional polymerizable compound may be 30.0, 35.0, 40.0, 45.0, 50.0, 55.0, 60.0, 65.0, 70.0, 75.0, 80.0, 85.0, or 90.0% by mass, and may be within the range of any two of these values.

[0051] The content of the difunctional polymerizable compound is preferably 35.0% to 90.0% by mass, 40.0% to 80.0% by mass, 45.0% to 75.0% by mass, or 50.0% to 70.0% by mass, relative to the total amount of polymerizable compounds. Being within these ranges tends to result in superior viscosity properties and curability. Specifically, the content of the difunctional polymerizable compound may be 30.0, 35.0, 40.0, 45.0, 50.0, 55.0, 60.0, 65.0, 70.0, 75.0, 80.0, 85.0, or 90.0% by mass, and may also be within a range between any two of these values.

[0052] 1.1.2.2. Polymerizable compounds with three or more functions The ink composition of this embodiment may or may not contain a polyfunctional polymerizable compound with three or more functions. The polyfunctional polymerizable compound with three or more functions is not particularly limited, but examples include trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, dipentaerythritol polyacrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylated dipentaerythritol polyacrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxytri(meth)acrylate, caprolactone-modified trimethylolpropane tri(meth)acrylate, pentaerythritol ethoxytetra(meth)acrylate, and caprolactam-modified dipentaerythritol hexa(meth)acrylate. Furthermore, when referring to "three or more functional groups," it means that the number of polymerizable double bond functional groups is three or more.

[0053] The content of the trifunctional or polyfunctional (meth)acrylate is preferably 0.0% to 20.0% by mass, 1.5% to 15.0% by mass, 3.0% to 12.5% ​​by mass, and 5.0% to 10.0% by mass, relative to the total amount of the ink composition. When the content is within the above range, the curing properties tend to be excellent.

[0054] The content of the polyfunctional (meth)acrylate with three or more functions is preferably 0.0% to 20.0% by mass, 1.5% to 15.0% by mass, 3.0% to 12.5% ​​by mass, and 5.0% to 10.0% by mass, relative to the total amount of polymerizable compounds. When the content is within the above range, the curing properties tend to be excellent.

[0055] 1.2. Polymerization Initiators The ink composition of this embodiment contains a polymerization initiator. By irradiating the polymerization initiator with radiation, the polymerization initiator generates active species. The generated active species promote the reaction of polymerizable compounds contained in the ink composition. The polymerization initiator contains phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide. By including phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide, the ink composition exhibits excellent curability even in ink compositions with a low migration risk that contain a thioxanthone sensitizer with a molecular weight of 300 or more. The polymerization initiator can be used alone or in combination of two or more types.

[0056] Other polymerization initiators besides phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide may be included as polymerization initiators. These other polymerization initiators are not particularly limited, but may include, for example, aromatic ketones, hydroxyketones, acylphosphine compounds, aromatic onium salt compounds, organic peroxides, thio compounds such as thioxanthones, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having carbon-halogen bonds, and alkylamine compounds. Examples of polymerization initiators include phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide alone, or phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide, and one of these may be used alone, or two or more may be used in combination.

[0057] The polymerization initiator content is preferably 1.0% to 20.0% by mass, 2.0% to 17.5% by mass, 3.0% to 15.0% by mass, 4.0% to 12.5% ​​by mass, and 4.5% to 10.0% by mass, relative to the total amount of the ink composition. When the polymerization initiator content is within the above range, curability tends to be improved and the risk of migration can be reduced. Specifically, the polymerization initiator content may be 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 12.5, 13.0, 14.0, 15.0, 17.5, or 20.0% by mass, or within a range between any two of these values.

[0058] The content of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide is preferably 1.0% to 15.0% by mass, 1.5% to 12.5% ​​by mass, 2.0% to 10.0% by mass, 2.0% to 8.0% by mass, and 2.5% to 7.5% by mass, relative to the total amount of the ink composition. By having a phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide content within the above ranges, the risk of migration is reduced, and the curability of the coating film tends to be further improved. Specifically, the content of phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide may be 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 7.5, 8.0, 10.0, 12.5, or 15.0% by mass relative to the total amount of the ink composition, and may be within a range between any two of these values.

[0059] The content of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide is preferably 20.0% to 80.0% by mass, 30.0% to 70.0% by mass, 35.0% to 65.0% by mass, 37.5% to 62.5% by mass, and 40.0% to 60.0% by mass, relative to the total amount of polymerization initiator. By having a phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide content within the above range, the risk of migration is reduced, and the curability of the coating film tends to be further improved. Specifically, the content of phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide may be 5.0, 10.0, 15.0, 20.0, 25.0, 30.0, 35.0, 37.5, 40.0, 50.0, 60.0, 65.0, 70.0, or 80.0% by mass relative to the total amount of polymerization initiator, and may be within the range of any two of these values.

[0060] The polymerization initiator of this embodiment may include other polymerization initiators other than phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide. Other polymerization initiators are not particularly limited, but examples include acylphosphine compounds such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide and ethylphenyl(2,4,6-trimethylbenzoyl)phosphine.

[0061] The content of other polymerization initiators is preferably 1.0% by mass or more and 15.0% by mass or less, 2.0% by mass or more and 12.5% ​​by mass or less, 3.0% by mass or more and 10.0% by mass or less, or 3.5% by mass or more and 8.5% by mass or less, relative to the total amount of the ink composition.

[0062] The content of other polymerization initiators is preferably 10.0% by mass or more and 70.0% by mass or less, 15.0% by mass or more and 60.0% by mass or less, 20.0% by mass or more and 55.0% by mass or less, and 30.0% by mass or more and 45.0% by mass or less, relative to the total amount of polymerization initiators.

[0063] 1.3.1. Thioxanthone sensitizers with a molecular weight of 300 or more The ink composition of this embodiment contains a thioxanthone sensitizer having a molecular weight of 300 or more. The thioxanthone sensitizer having a molecular weight of 300 or more contains a thioxanthone structure in its molecule. The thioxanthone sensitizer having a molecular weight of 300 or more can be used alone or in combination of two or more types.

[0064] Thioxanthone sensitizers with a molecular weight of 300 or more absorb radiation and become excited when irradiated, coming into contact with the photoinitiator and promoting its decomposition. This can further improve the curability of the ink composition, and by including a thioxanthone sensitizer with a molecular weight of 300 or more, the risk of migration of the ink composition can be reduced.

[0065] Thioxanthone sensitizers with a molecular weight of 300 or more are not particularly limited, but include 1,3-di({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxy)-2,2-bis({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxymethyl)propane (Sartomer, Speed ​​Cure® 7010, CAS No. 1003567-83-6), alpha-[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]omega-[[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]oxy]poly(oxy-1,4-butanediyl) (IGM Resins BV, Omnipol® TX, CAS No. 1003567-83-6), alpha-[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]oxy]poly(oxy-1,4-butanediyl) (IGM Resins BV, Omnipol® TX, CAS It is preferable to include No. 813452-37-8).

[0066] The molecular weight of the thioxanthone sensitizer with a molecular weight of 300 or more is preferably 350 or more, 500 or more, 700 or more, and 1000 or more. Furthermore, the molecular weight is preferably 5000 or less, 4500 or less, 4000 or less, and 3000 or less. When the molecular weight is within this preferred range, the curability and viscosity of the ink composition are excellent. Specifically, the molecular weight may be 300, 350, 500, 600, 700, 800, 900, 1000, 2000, 2500, 3000, 3500, 4000, 4500, or 5000, and may also be within the range of any two of these values.

[0067] The content of the thioxanthone sensitizer having a molecular weight of 300 or more is preferably 0.1% to 20% by mass, 0.5% to 15% by mass, 1% to 10% by mass, 1.5% to 8% by mass, or 1% to 5% by mass, relative to the total amount of the ink composition. Being within the above range tends to result in superior viscosity characteristics and curability. Specifically, the content of the thioxanthone sensitizer having a molecular weight of 300 or more may be 0.1, 0.3, 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12.5, 15, or 20% by mass, and may be within the range of any two of these values.

[0068] The content of the thioxanthone sensitizer having a molecular weight of 300 or more is preferably 10.0% to 70.0% by mass, 20.0% to 60.0% by mass, 30.0% to 50% by mass, and 35.0% to 45% by mass, relative to the total amount of phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide. Being within the above range tends to result in superior viscosity properties and curability. Specifically, the content of the thioxanthone sensitizer having a molecular weight of 300 or more may be 10.0, 15.0, 20.0, 25.0, 30.0, 35.0, 40.0, 45.0, 50.0, 55.0, 60.0, 65.0, or 70.0% by mass, relative to the total amount of phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide, and may be within the range of any two of these values.

[0069] The content of the thioxanthone sensitizer having a molecular weight of 300 or more is preferably 5.0% by mass or more and 50.0% by mass or less, 10.0% by mass or more and 40.0% by mass or less, 15.0% by mass or more and 37.5% by mass or less, and 20.0% by mass or more and 35.0% by mass or less, relative to the total amount of polymerization initiator. Being within the above range tends to result in superior viscosity properties and curability. Specifically, the content of the thioxanthone sensitizer having a molecular weight of 300 or more may be 5.0, 10.0, 12.5, 15.0, 20.0, 25.0, 30.0, 35.0, 40.0, 45.0, or 50.0% by mass, relative to the total amount of polymerization initiator, and may be within the range of any two of these values.

[0070] 1.3.2. Other Sensitizers The ink composition of this embodiment may contain other sensitizers (hereinafter referred to as "other sensitizers") other than thioxanthone sensitizers having a molecular weight of 300 or more. "Other sensitizers" is a concept that includes sensitizers with a molecular weight of less than 300 and sensitizers that do not contain a thioxanthone structure.

[0071] Other sensitizers include thioxanthone sensitizers with a molecular weight of less than 300, amine compounds (aliphatic amines, amines containing aromatic groups, piperidines, reaction products of epoxy resins and amines, triethanolamine triacrylate, etc.), urea compounds (allylthiourea, o-tolylthiourea, etc.), sulfur compounds (sodium diethyldithiophosphate, soluble salts of aromatic sulfinic acid, etc.), nitrile compounds (N,N-diethyl-p-aminobenzonitrile, etc.), phosphorus compounds (tri-n-butylphosphine, sodium diethyldithiophospide, etc.), nitrogen compounds (Michler ketone, N-nitrisohydroxylamine derivatives, oxazolidine compounds, tetrahydro-1,3-oxazine compounds, condensates of formaldehyde or acetaldehyde and diamines, etc.), and chlorine compounds (carbon tetrachloride, hexachloroethane, etc.).

[0072] Other sensitizers are preferably present in amounts of 0.1% to 20% by mass, 0.5% to 15% by mass, 1% to 10% by mass, 1.5% to 8% by mass, and 1% to 5% by mass, relative to the total amount of the ink composition. Being within these ranges tends to result in superior curability. Specifically, the content of the difunctional polymerizable compound may be 0.1, 0.3, 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12.5, 15, or 20% by mass, and may be within the range of any two of these values.

[0073] 1.4 Polymerization Inhibitors The ink composition may contain polymerization inhibitors. Polymerization inhibitors are not particularly limited, but examples include hydroquinones such as hydroquinone, hydroquinone monomethyl ether (MEHQ), 1-o-2,3,5-trimethylhydroquinone, and 2-tert-butylhydroquinone; catechols such as catechol, 4-methylcatechol, and 4-tert-butylcatechol; phenol, butylhydroxytoluene, butylhydroxyanisole, p-methoxyphenol, cresol, pyrogallol, 3,5-di-t-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-t-butylphenol), and 2,2'-methylenebis(4-ethyl-6-butylphenol). Examples of polymerization inhibitors include phenols such as 4,4'-thiobis(3-methyl-6-t-butylphenol), compounds having a 2,2,6,6-tetramethylpiperidine-N-oxyl skeleton, such as 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl, compounds having a 2,2,6,6-tetramethylpiperidine skeleton, such as 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, compounds having a 2,2,6,6-tetramethylpiperidine-N-alkyl skeleton, and hindered amines having a 2,2,6,6-tetramethylpiperidine-N-acyl skeleton. These polymerization inhibitors can be used individually or in combination of two or more.

[0074] The polymerization inhibitor content is preferably 0.05% by mass or more and 3.0% by mass or less, 0.07% by mass or more and 2.0% by mass or less, or 0.1% by mass or more and 1.0% by mass or less, relative to the total amount of the ink composition.

[0075] 1.5. Surfactants The ink composition may contain a surfactant. The surfactant is not particularly limited, but examples include acetylene glycol-based surfactants, fluorine-based surfactants, and silicone-based surfactants. From the viewpoint of achieving the effects of the present invention more effectively and reliably, the surfactant is preferably a silicone-based surfactant.

[0076] Examples of silicone-based surfactants include BYK(registered trademark)-UV3500, UV3570, and BYK350 (product names, BYK Chemie Japan Co., Ltd.).

[0077] The surfactant content is not particularly limited relative to the total amount of the ink composition, but is, for example, 0.1 to 1.0% by mass.

[0078] 1.6. Colorants The ink composition of this embodiment may or may not contain a colorant. If a colorant is included, examples of colorants include dyes and pigments.

[0079] The dyes are not particularly limited, but examples include acid dyes, direct dyes, reactive dyes, and basic dyes. Specific examples of dyes include, for example, CI (Colour Index Generic Name) Acid Yellow 17, 23, 42, 44, 79, 142; CI Acid Red 52, 80, 82, 249, 254, 289; CI Acid Blue 9, 45, 249; CI Acid Black 1, 2, 24, 94; CI Food Black 1, 2; CI Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173. Examples include CI Direct Red 1, 4, 9, 80, 81, 225, 227; CI Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202; CI Direct Black 19, 38, 51, 71, 154, 168, 171, 195; CI Reactive Red 14, 32, 55, 79, 249; and CI Reactive Black 3, 4, 35. These dyes can be used individually or in combination of two or more.

[0080] The pigments are not particularly limited, but examples include inorganic pigments and organic pigments. Examples of inorganic pigments are carbon blacks such as furnace black, lamp black, acetylene black, and channel black, as well as iron oxide and titanium dioxide. Examples of organic pigments include azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and chelate azo pigments, polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments, dye chelates, dye lakes, nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments. These pigments can be used individually or in combination of two or more.

[0081] While not particularly limited, examples of carbon black include No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200B, etc. (all manufactured by Mitsubishi Chemical Corporation), Raven® 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc. (all manufactured by Carbon Columbia), Rega1® 400R, Rega1 330R, Rega1 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch® 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch Examples include the 1400 (manufactured by CABOT JAPAN KK), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex® 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black 4A, and Special Black 4 (all manufactured by Degussa).

[0082] While not particularly limited, examples of white pigments include CI Pigment White 6, 18, and 21.

[0083] Yellow pigments are not particularly limited, but examples include CI Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 155, 167, 172, and 180.

[0084] The magenta pigment is not particularly limited, but examples include CI Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48(Ca), 48(Mn), 57(Ca), 57:1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, or CI Pigment Violet Numbers 19, 23, 32, 33, 36, 38, 43, and 50 can be cited.

[0085] While not particularly limited, examples of cyan pigments include CI Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, 66, and CI Bat Blue 4, 60.

[0086] In addition, pigments other than magenta, cyan, and yellow are not particularly limited, but examples include CI Pigment Green 7, 10, CI Pigment Brown 3, 5, 25, 26, and CI Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, and 63.

[0087] The amount of colorant is not particularly limited relative to the total amount of the ink composition, but for example, 1.0% by mass or more and 10.0% by mass or less, and 3.0% by mass or more and 8.0% by mass or less are preferred.

[0088] Alternatively, the ink composition of this embodiment may be a clear ink composition. A clear ink composition is an ink composition that does not contain or substantially contains colorants. In this embodiment, "substantially colorant-free" is not particularly limited, but preferably, for example, the colorant content is 0.50% by mass or less, 0.25% by mass or less, 0.10% by mass or less, 0.05% by mass or less, 0.01% by mass or less, 0.001% by mass or more and 0.500% by mass or less, 0.001% by mass or more and 0.250% by mass or less, 0.001% by mass or more and 0.100% by mass or less, 0.001% by mass or more and 0.050% by mass or less, or 0.001% by mass or more and 0.010% by mass or less, relative to the total amount of the ink composition.

[0089] 1.7. Other ingredients The ink composition of this embodiment may contain, in addition to the components described above, other known components that can be used in conventional ink compositions. These other components are not particularly limited, but examples include slip agents, solubilizers, viscosity modifiers, pH adjusters, antioxidants, preservatives, and corrosion inhibitors. These other components may be used individually or in combination of two or more.

[0090] 2. Method for manufacturing the ink composition The method for manufacturing the ink composition of this embodiment is not particularly limited, but for example, each of the above components may be added to a mixing tank simultaneously and mixed, or each component may be added to a mixing tank sequentially and mixed. After mixing each component, filtration or degassing may be performed as needed.

[0091] 3. Recording media The recording medium used for recording the ink composition of this embodiment is not particularly limited, but examples include absorbent recording media, low-absorbent recording media, and non-absorbent recording media.

[0092] Absorbent recording media are not particularly limited, but examples include plain paper such as electrophotographic paper with high permeability of ink compositions, inkjet paper (inkjet-specific paper equipped with an ink-absorbing layer composed of silica particles or alumina particles, or an ink-absorbing layer composed of a hydrophilic polymer such as polyvinyl alcohol (PVA) or polyvinylpyrrolidone (PVP)), and fabrics.

[0093] Low-absorption recording media are not particularly limited, but examples include art paper, coated paper, and cast paper, which are commonly used in offset printing and have relatively low ink permeability.

[0094] Non-absorbent recording media are not particularly limited, but examples include films and plates of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane; plates of metals such as iron, silver, copper, and aluminum; or metal plates or plastic films in which these various metals are deposited by vapor deposition, or alloy plates such as stainless steel and brass; and recording media in which films of plastics such as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyurethane are bonded (coated) to a paper substrate.

[0095] 4. Inkjet recording method The inkjet recording method of this embodiment (hereinafter also simply referred to as the "recording method") includes an ink attachment step of ejecting the ink composition of this embodiment from an inkjet head and adhering it to a recording medium, and an irradiation step of irradiating the ink composition adhering to the recording medium with radiation. The recording method may optionally include other steps such as a transport step for transporting the recording medium.

[0096] 4.1. Ink application process In the ink application process, the ink composition of this embodiment is ejected from the inkjet head and applied to the recording medium. More specifically, a pressure generating means provided in the inkjet head is driven to eject the ink composition filled in the pressure generating chamber of the inkjet head from the nozzle.

[0097] Inkjet heads used in the ink application process include line heads that record using a line method and serial heads that record using a serial method.

[0098] In a line-type system using a line head, for example, an inkjet head having a width greater than the recording width of the recording medium is fixed to the recording device. The recording medium and the inkjet head are then moved relative to each other in the sub-scanning direction (the direction in which the recording medium is transported, i.e., the direction perpendicular to the width direction of the recording medium), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement, thereby recording an image on the recording medium.

[0099] In a serial method using a serial head, for example, an inkjet head is mounted on a carriage that can move in the width direction of the recording medium. The carriage is then moved along the main scanning direction (the width direction of the recording medium), and ink droplets are ejected from the nozzles of the inkjet head in conjunction with this movement, thereby recording an image on the recording medium.

[0100] 4.2.Irradiation process In the irradiation process, the ink composition attached to the recording medium is irradiated with radiation. When irradiated with radiation, the polymerization reaction of the polymerizable compounds begins, causing the composition to harden and a coating film to form. At this time, if a polymerization initiator is present, it generates active species (initiators) such as radicals, acids, and bases, and the polymerization reaction of the polymerizable compounds is promoted by the function of these initiators.

[0101] Here, examples of radiation include ultraviolet rays, infrared rays, visible light, and X-rays. The radiation source is installed downstream of the inkjet head and irradiates the ink composition. There are no particular limitations on the radiation source, but examples include UV-LEDs (ultraviolet light-emitting diodes). By using such a radiation source, it is possible to miniaturize the device and reduce costs. Since UV-LEDs as ultraviolet sources are small, they can be installed inside the inkjet recording device.

[0102] 4.3. Conveying Process The recording method of this embodiment may include a transport step. In the transport step, the recording medium is transported in a predetermined direction within the recording device. More specifically, the recording medium is transported from the paper feed section to the paper discharge section of the recording device using transport rollers or a transport belt provided within the recording device. During this transport process, the ink composition ejected from the inkjet head adheres to the recording medium, forming a recorded material. The order and timing of the ink adhesion step, the irradiation step, and the transport step are not particularly limited; for example, the three steps may be performed simultaneously or alternately. Alternatively, two of the three steps may be performed simultaneously, and the remaining step may be performed separately.

[0103] 5. Recording device As an example of a recording device used in the method for recording the ink composition of this embodiment, Figure 1 shows a schematic diagram of a serial printer. As shown in Figure 1, the serial printer 70 comprises a transport unit 720 and a recording unit 730. The transport unit 720 transports the recording medium F supplied to the serial printer 70 to the recording unit 730 and discharges the recording medium F after recording to the outside of the serial printer 70. Specifically, the transport unit 720 has feed rollers (not shown) and transports the recording medium F in the sub-scanning direction T2. ​​A serial printer is a printer that employs the serial inkjet head arrangement described above.

[0104] The recording unit 730 includes an inkjet head 731, a carriage 734 on which the inkjet head 731 is mounted, and a carriage movement mechanism 735 for moving the carriage 734. Although not shown in the figures, the inkjet head 731 has a plurality of nozzles for ejecting an ink composition onto the recording medium F sent from the transport unit 720.

[0105] Since the serial printer 70 uses a serial method, the width of the inkjet head 731 is shorter than the width of the recording medium F. The carriage 734 moves back and forth in the main scanning directions S1 and S2 together with the inkjet head 731 by the carriage movement mechanism 735. As the inkjet head 731 moves back and forth in the main scanning directions S1 and S2, ink compositions are ejected from the multiple nozzles and adhered to the recording medium F. Although not particularly limited, recording by the inkjet head 731 is performed in multiple passes, two or more passes. A pass is also called a main scan. Between passes, a sub-scan is performed to transport the recording medium F in the sub-scan direction T2. ​​In other words, main scans and sub-scans are performed alternately.

[0106] In addition to the serial method described above, a line-type printer may also be used to record the ink composition of this embodiment. A line-type printer has a line head, which is an inkjet head with a length greater than or equal to the recording width of the recording medium, and a moving mechanism that moves the recording medium and the inkjet head relative to each other in a direction perpendicular to the width direction of the recording medium, and is a printer that records on the recording medium in a single scan. [Examples]

[0107] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited in any way by the following examples. Unless otherwise specified, the following operations were performed at room temperature (25°C) and 1 atmosphere.

[0108] 1. Preparation of the ink composition The ink compositions of the examples and comparative examples were obtained by placing each component into a stainless steel container, a mixing tank, to obtain the compositions shown in Figures 2 and 3, mixing and stirring, and then filtering through a 5 μm membrane filter. Unless otherwise specified, the numerical values ​​of each component shown in the examples in the figures represent mass percent.

[0109] The abbreviations and product ingredients used in Figures 2 and 3 are as follows. Note that in each column of Figures 2 and 3, the "-" indicates that the ingredient was not used. • 4-HBA (manufactured by Osaka Organic Chemical Industry Co., Ltd., 4-hydroxybutyl acrylate) • CHDMM (product name "CHDMMA", manufactured by Mitsubishi Chemical Corporation, 1,4-cyclohexanedimethanol monoacrylate) • M-600A (product name "Epoxy Ester M-600A", manufactured by Kyoeisha Chemical Co., Ltd., 2-hydroxy-3-phenoxypropyl (meth)acrylate) • LA (Lauryl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.) • DPGDA (product name "MIRAMER M222", manufactured by MIWON, dipropylene glycol diacrylate) • VEEA (manufactured by Nippon Shokubai Co., Ltd., 2-(2-vinyloxyethoxy)ethyl acrylate) • 1,6-HDDA (manufactured by Osaka Organic Chemical Industry Co., Ltd., 1,6-hexanediol diacrylate) • A-DPH (manufactured by Shin-Nakamura Chemical Industry Co., Ltd., dipentaerythritol hexaacrylate) • CN9893 (manufactured by Sartomer, a bifunctional urethane acrylate oligomer) • Omnirad 819 (manufactured by IGM Resins BV, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide) • PEA (product name "Viscote #192", manufactured by Osaka Organic Chemical Industry Co., Ltd., phenoxyethyl acrylate) • Omnirad TPO-L (manufactured by IGM Resins BV, ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate) • Speedcure DETX (manufactured by Sartomer, 2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propane) • Omnipol TX (manufactured by IGM Resins BV, alpha-[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]omega-[[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]oxy]poly(oxy-1,4-butanediyl) (CAS: 813452-37-8)) • Speed ​​cure 7010 (Manufactured by Sartomer, 1,3-di({a-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxy)-2,2-bis({a-[1-methylethylene]}oxymethyl)propane (CAS: 1003567-83-6)) • BYK-UV3500 (Manufactured by BYK Additives & Instruments, a polyether-modified polydimethylsiloxane containing acryloyl groups) • MEHQ (product name "p-methoxyphenol", manufactured by Kanto Chemical Co., Ltd., hydroquinone monomethyl ether)

[0110] 2. Evaluation Method 2.1.Initial viscosity Using a rotational viscometer (product name "Rheometer MCR-301," manufactured by Anton Paar), the initial viscosity of the ink compositions of the examples and comparative examples immediately after preparation was measured at room temperature (25°C) in accordance with JIS Z 8803. The initial viscosity was evaluated according to the following evaluation criteria, and the results are shown in Figures 2 and 3. [Evaluation Criteria] A: The viscosity is between 20 mPa·s and 22 mPa·s. B: Viscosity is greater than 19 mPa·s and less than 20 mPa·s, or greater than 22 mPa·s and less than 23 mPa·s. C: Viscosity is 19 mPa·s or less, or 23 mPa·s or more.

[0111] 2.2.Low molecular weight residual As one indicator of migration risk, the amount of low-molecular-weight residue in the cured coating film of the ink composition was investigated. Specifically, each ink composition was applied to a polyester film using a bar coater to a coating thickness of 10 μm, and the concentration was measured at 1000 mJ / cm². 2 The samples were irradiated with ultraviolet light. A UV-LED with a peak wavelength of 395 nm was used as the ultraviolet source. Each polyester film level was then immersed in THF (tetrahydrofuran) for one week. The extract in the THF was analyzed by LC / MS (liquid chromatography-mass spectrometry) to quantify the residual sensitizer with a molecular weight of 300 or less, and the extraction rate relative to the total coating film was calculated. The extraction rate was evaluated according to the following evaluation criteria, and the results are shown in Figures 2 and 3. A lower extraction rate indicates a reduced migration risk. [Evaluation Criteria] A: Extraction rate: Less than 1%. B: Extraction rate: 1% or more but less than 2%. C: Extraction rate: 2% or higher.

[0112] 2.3. Curability As an indicator of the curability of the ink compositions, we evaluated the tackiness under load using a cotton swab. Specifically, each ink composition was applied to a polyvinyl chloride recording medium with a coating thickness of 10 μm using a bar coater, and the coating film was irradiated with ultraviolet light at a speed of 0.04 cm / sec. A UV-LED with a peak wavelength of 395 nm was used as the ultraviolet source. The irradiation energy of the ultraviolet light was increased in steps, and the surface of the coating film was rubbed with a cotton swab. The irradiation energy at which the cotton swab stopped being colored was recorded. The curability was then evaluated according to the following evaluation criteria, and the results are shown in Figures 2 and 3. [Evaluation Criteria] A: The irradiation energy required for the cotton swab to stop discoloring is 500 mJ / cm². 2 It is less than. B: The irradiation energy at which the cotton swab stops discoloring is 500 mJ / cm². 2 More than 700mJ / cm 2 It is less than. C: The irradiation energy at which the cotton swab no longer becomes discolored is 700 mJ / cm². 2 That's all.

[0113] 2.4.Abrasion resistance The abrasion resistance of each ink composition was evaluated. Specifically, first, an 8 μm thick coating film was prepared by curing it to a tack-free state (where the cotton swab did not stain) in the same manner as the cotton swab load tack evaluation described above. Next, the abrasion resistance test of each coating film was performed using a JSPS-type friction fastness tester (manufactured by TESTER SANGYO CO., LTD.) in accordance with JIS K 5701 (ISO 11628) (which specifies methods for testing inks, color samples, and printed materials used in lithographic printing). In detail, high-quality paper was placed on the surface of the coating film, which had been cut into strips of a predetermined size, and rubbed with a load of 500 g. The staining of the high-quality paper after rubbing and the condition of the coating film were visually observed and evaluated according to the following evaluation criteria. The results are shown in Figures 2 and 3. [Evaluation Criteria] A: The high-quality paper is clean and free of stains, and the recording surface is free of peeling and scratches. B: The high-quality paper has some stains, but the recording surface is free from peeling or scratches. C: The high-quality paper has stains, and there is peeling and scratches on the recording surface.

[0114] 2.5. High temperature storage stability As an indicator of storage stability, the viscosity of each ink composition, whose initial viscosity was measured, was measured after storage at 70°C for 8 days. Each ink composition was stored in a resealable glass bottle. The viscosity increase ratio from the initial viscosity to the post-storage viscosity was calculated and evaluated according to the following evaluation criteria, and the results are shown in Figures 2 and 3. [Evaluation Criteria] A: The viscosity is less than 5%. B: The thickening rate is 5% or more but less than 10%. C: The viscosity is 10% or more.

[0115] 3. Summary of evaluation results As shown in Figures 2 and 3, the ink compositions of Examples 1 to 13 demonstrated excellent curability and abrasion resistance of the coating film while reducing migration risk. In contrast, the ink compositions of Comparative Examples 1 to 4 showed little improvement in migration risk, curability, or abrasion resistance. [Explanation of Symbols]

[0116] 70...Serial printer, 720...Transport unit, 730...Recording unit, 731...Inkjet head, 734...Carriage, 735...Carriage movement mechanism, F...Recording medium, S1, S2...Main scanning direction, T2...Sub-scanning direction.

Claims

1. Polymerizable compounds and Polymerization initiator and A thioxanthone sensitizer having a molecular weight of 300 or more is included, The polymerizable compound includes a monofunctional polymerizable compound and a difunctional polymerizable compound. The polymerization initiator comprises phenylbis(2,4,6,-trimethylbenzoyl)phosphine oxide, The monofunctional polymerizable compound includes a hydroxyl group-containing monofunctional polymerizable compound, A radiation-curable inkjet ink composition wherein the content of the aforementioned bifunctional polymerizable compound is 30% by mass or more of the total amount.

2. The radiation-curable inkjet ink composition according to claim 1, wherein the content of the hydroxyl group-containing monofunctional polymerizable compound is 5% by mass or more and 40% by mass or less based on the total amount.

3. The radiation-curable inkjet ink composition according to claim 1, wherein the hydroxyl group-containing monofunctional polymerizable compound comprises one or more selected from 4-hydroxybutyl acrylate, 1,4-cyclohexanedimethanol monoacrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate.

4. It does not contain the oligomer, or it contains the oligomer, The radiation-curable inkjet ink composition according to claim 1, wherein, if the oligomer is included, the content of the oligomer is 9% by mass or less of the total amount.

5. The radiation-curable inkjet ink composition according to claim 1, wherein the content of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide is 1% by mass or more based on the total amount of the inkjet composition.

6. The radiation-curable inkjet ink composition according to claim 1, wherein the thioxanthone sensitizer comprises one or more selected from 1,3-di({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxy)-2,2-bis({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxymethyl)propane and alpha-[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]omega-[[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]oxy]poly(oxy-1,4-butanediyl).

7. The radiation-curable inkjet ink composition according to claim 1, comprising one or more selected from dipropylene glycol diacrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, or 1,6-hexanediol diacrylate.

8. The radiation-curable inkjet ink composition according to claim 1, wherein the content of the monofunctional polymerizable compound is 10% by mass or more and 50% by mass or less based on the total amount.

9. An inkjet recording method comprising a dispensing step of dispensing the radiation-curable inkjet ink composition described in claim 1.

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