Radiation-curable ink jet ink composition and recording apparatus

Abstract

To provide a radiation-curable inkjet ink composition which reduces odor after ink storage.SOLUTION: A radiation-curable ink jet ink composition according to an embodiment of the present invention contains a polymerizable compound and an imidazoline compound, and the polymerizable compound contains at least one of a vinyl ether group-containing polymerizable compound and an N-vinyl group-containing polymerizable compound.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] The inkjet recording method is capable of recording high-resolution images using a relatively simple device, and has been rapidly developing in various fields. In the process, various studies have been conducted on inkjet ink compositions that are cured by irradiation with radiation, such as reducing the odor.

[0003] For example, Patent Document 1 discloses a low-odor radiation-curable inkjet coloring composition containing a vinyl ether group-containing polymerizable compound such as 2-(2-vinyloxyethoxy)ethyl acrylate or an N-vinyl group-containing polymerizable compound such as N-vinylcaprolactam. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-78133 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the odor of the ink after storage could not be sufficiently reduced. [Means for solving the problem]

[0006] One embodiment of the radiation-curable inkjet ink composition according to the present invention comprises: a polymerizable compound; an imidazoline compound, The polymerizable compound contains at least one of a vinyl ether group-containing polymerizable compound and an N-vinyl group-containing polymerizable compound.

[0007] One aspect of the recording device according to the present invention is The present invention is provided with an inkjet head that ejects the radiation-curable inkjet ink composition according to the above embodiment. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing an example of a recording apparatus according to an embodiment of the present invention. [Figure 2] Table 1 showing the composition of the base ink. [Figure 3] Table 2 shows the compositions and evaluation results of radiation-curable inkjet ink compositions according to the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described. The embodiments described below are examples of the present invention. The present invention is not limited to the following embodiments, and includes various modified forms that are implemented within the scope of the present invention. Note that not all of the configurations described below are necessarily essential configurations of the present invention.

[0010] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, "(meth)acrylic" refers to acrylic or methacrylic, and "(meth)acrylate" refers to acrylate or methacrylate.

[0011] 1. Radiation-curable inkjet ink composition A radiation-curable inkjet ink composition according to one embodiment of the present invention comprises a polymerizable compound and an imidazoline compound, and the polymerizable compound comprises at least one of a vinyl ether group-containing polymerizable compound and an N-vinyl group-containing polymerizable compound.

[0012] Recently, research by the present inventors has revealed a new problem in that inks containing vinyl ether group-containing polymerizable compounds or N-vinyl group-containing polymerizable compounds generate acetaldehyde, an odorous component, during storage.

[0013] It is believed that the cause of acetaldehyde generation is due to the decomposition of vinyl ether groups and N-vinyl groups in polymerizable compounds through hydrolysis during ink storage. Acetaldehyde has a particularly strong odor among various odor-causing substances, and even a small amount can easily worsen the odor.

[0014] In order to address these new challenges, the present inventors conducted extensive research and found that adding an imidazoline compound to ink can reduce the odor of ink after storage. The mechanism of odor reduction is presumed to be as follows: Imidazoline compounds are basic compounds that tend to shift the pH of the entire ink composition toward alkaline. This is presumed to be because decomposition reactions such as hydrolysis of vinyl ether groups and N-vinyl groups in polymerizable compounds are suppressed.

[0015] Hereinafter, each component contained in the radiation-curable inkjet ink composition (hereinafter also referred to as "ink composition" or "ink") according to this embodiment will be described.

[0016] 1.1 Polymerizable compounds The radiation-curable inkjet ink composition according to this embodiment contains a polymerizable compound, and the polymerizable compound contains at least one of a vinyl ether group-containing polymerizable compound and an N-vinyl group-containing polymerizable compound. That is, the polymerizable compound may contain a vinyl ether group-containing polymerizable compound, an N-vinyl group-containing polymerizable compound, or both a vinyl ether group-containing polymerizable compound and an N-vinyl group-containing polymerizable compound.

[0017] The term "polymerizable compound" is a general term for compounds that are cured by irradiation with radiation. Polymerizable compounds include monofunctional monomers having one polymerizable functional group and polyfunctional monomers having multiple polymerizable functional groups, and may also include oligomers having one or more polymerizable functional groups as needed. Each polymerizable compound may be used alone or in combination of two or more.

[0018] The total content of the polymerizable compounds is not particularly limited, but is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more, relative to the total amount of the ink composition. The upper limit of this content is also not particularly limited, but is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less, relative to the total amount of the ink composition.

[0019] 1.1.1 Vinyl ether group-containing polymerizable compounds The vinyl ether group-containing polymerizable compound contains at least one vinyl ether group, and may contain two or more vinyl ether groups, or may contain a polymerizable functional group other than a vinyl ether group. The vinyl ether group is a group consisting of an optionally substituted vinyl group and an oxygen atom, and preferably refers to a group represented by "R-CH=CH2-O- (R is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms)." R, which is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms, is preferably a linear, branched, or cyclic alkyl group having 1 to 11 carbon atoms, which may be substituted, or an aromatic group having 6 to 11 carbon atoms, which may be substituted. More preferred are alkyl groups having 1 to 2 carbon atoms, such as methyl or ethyl, and aromatic groups having 6 to 8 carbon atoms, such as phenyl and benzyl.

[0020] Examples of the vinyl ether group-containing polymerizable compound include vinyl ether group-containing monofunctional monomers such as ethylene glycol monovinyl ether and diethylene glycol monovinyl ether; and vinyl ether group-containing polyfunctional monomers represented by the following formula (2). CH2=CR 1 -COOR2 -O-CH=CH-R 3 ···(2) (In the formula, R 1 is a hydrogen atom or a methyl group, and 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.

[0021] The polymerizable compound preferably contains a compound represented by the above formula (2) as a vinyl ether group-containing polymerizable compound. The compound represented by the above formula (2) (vinyl ether group-containing (meth)acrylate) is a polyfunctional monomer, but has a relatively low viscosity and excellent curability. Therefore, by including such a polymerizable compound, it is possible to further improve the abrasion resistance and curability while suppressing an increase in the viscosity of the ink composition. However, since the ink contains a vinyl ether group, there is a problem in that the ink generates an odor during storage. In contrast, the radiation-curable inkjet ink composition according to this embodiment can enjoy the benefits of including the compound represented by the above formula (2) while also reducing the odor.

[0022] In the above formula (2), R 2 Examples of the divalent organic residue having 2 to 20 carbon atoms represented by the formula (I) include a linear, branched, or cyclic alkylene group having 2 to 20 carbon atoms, which may be substituted; an alkylene group having 2 to 20 carbon atoms and having an oxygen atom via an ether bond and / or an ester bond in its structure, which may be substituted; and a divalent aromatic group 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 and having an oxygen atom via an ether bond in its structure, such as an oxyethylene group, an oxy-n-propylene group, an oxyisopropylene group, and an oxybutylene group, are preferred. Furthermore, from the viewpoint of further reducing the viscosity of the ink composition and further improving the abrasion resistance and curability of the ink composition, R 2is an alkylene group having 2 to 9 carbon atoms and having an oxygen atom by an ether bond in the structure, such as an oxyethylene group, an oxy-n-propylene group, an oxyisopropylene group, or an oxybutylene group, and more preferred are compounds having a glycol ether chain.

[0023] In the above formula (2), R 3 Suitable monovalent organic residues having 1 to 11 carbon atoms and represented by the formula (I) are linear, branched, or cyclic alkyl groups having 1 to 11 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.

[0024] When each of the above organic residues is a group that may be substituted, the substituent is divided into a group containing carbon atoms and a group not containing carbon atoms. First, when the above substituent is a group containing carbon atoms, the carbon atom is counted in the number of carbon atoms of the organic residue. Examples of the group containing carbon atoms include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing carbon atoms include, but are not limited to, a hydroxyl group and a halo group.

[0025] Specific examples of the compound represented by the above formula (2) include, but are not limited to, 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, acrylate, 3-vinyloxybutyl (meth)acrylate, 1-methyl-2-vinyloxypropyl (meth)acrylate, 2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl (meth)acrylate, 6-vinyloxyhexyl (meth)acrylate, 4-vinyloxymethylcyclohexylmethyl (meth)acrylate, 3-vinyloxymethylcyclohexylmethyl (meth)acrylate, 2-vinyloxymethylcyclohexylmethyl (meth)acrylate, p-vinyloxymethylphenylmethyl (meth)acrylate, m-vinyloxymethyl (meth)acrylate Phenylmethyl, 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-(vinyloxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxy)ethyl (meth)acrylate (meth)acrylate 2-(vinyloxyethoxyisopropoxy)ethyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)ethyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)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-(vinyloxyisopropoxyisopropoxy)propyl2-(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)ethyl (meth)acrylate ethyl, 2-(isopropenoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate, polyethylene glycol monovinyl ether (meth)acrylate, and polypropylene glycol monovinyl ether (meth)acrylate. Of these specific examples, 2-(2-vinyloxyethoxy)ethyl acrylate is particularly preferred in that it is easy to balance the curability, abrasion resistance, and viscosity of the composition. In this embodiment, 2-(2-vinyloxyethoxy)ethyl acrylate is also referred to as VEEA.

[0026] The content of the vinyl ether group-containing polymerizable compound is preferably 5 to 90% by mass, more preferably 10 to 70% by mass, even more preferably 10 to 50% by mass, and particularly preferably 12 to 30% by mass, relative to the total amount of the ink composition. Even when the content of the vinyl ether group-containing polymerizable compound is within the above range, there is a tendency for the curability and abrasion resistance to be further improved while reducing odor. It is also preferable for the content of the compound represented by formula (2) to be within the above range.

[0027] 1.1.2 N-vinyl group-containing polymerizable compounds The N-vinyl group-containing polymerizable compound contains at least one N-vinyl group, and may contain two or more N-vinyl groups, or may contain a polymerizable functional group other than the N-vinyl group. The N-vinyl group refers to a vinyl group (CH=CH-) bonded to a nitrogen atom.

[0028] Examples of N-vinyl group-containing polymerizable compounds include 5-methyl-3-vinyloxazolidin-2-one (VMOX), N-vinylcaprolactam (NVC), N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, and N-vinylpyrrolidone.

[0029] The polymerizable compound preferably contains a polymerizable compound having a nitrogen-containing heterocyclic structure as an N-vinyl group-containing polymerizable compound. When a polymerizable compound having a nitrogen-containing heterocyclic structure is contained, the adhesion and abrasion resistance of the coating film tend to be further improved, but since the ink contains an N-vinyl group, there is a problem of odor generation during storage. In contrast, the radiation-curable inkjet ink composition according to this embodiment can enjoy the benefits of containing a polymerizable compound having a nitrogen-containing heterocyclic structure while also reducing odor.

[0030] The term "nitrogen-containing heterocyclic structure" refers to a structure containing at least one nitrogen atom as a hetero atom contained in a heterocycle.

[0031] Examples of polymerizable compounds having a nitrogen-containing heterocyclic structure in the N-vinyl group-containing polymerizable compounds include 5-methyl-3-vinyloxazolidin-2-one (VMOX), N-vinylcaprolactam (NVC), N-vinylcarbazole, and N-vinylpyrrolidone.

[0032] Among polymerizable compounds having a nitrogen-containing heterocyclic structure, those having an oxazolidinone group are more preferred. Polymerizable compounds having such a structure tend to further improve the abrasion resistance of the coating film, but because they contain an N-vinyl group, they have the problem of generating an odor during ink storage. In contrast, the radiation-curable inkjet ink composition according to this embodiment can enjoy the benefits of containing a polymerizable compound having an oxazolidinone group while also reducing the odor.

[0033] Examples of the polymerizable compound having an oxazolidinone group in the N-vinyl group-containing polymerizable compound include 5-methyl-3-vinyloxazolidin-2-one (VMOX).

[0034] The content of the N-vinyl group-containing polymerizable compound is preferably 5 to 50 mass %, more preferably 5 to 40 mass %, even more preferably 8 to 30 mass %, and particularly preferably 8 to 25 mass %, relative to the total amount of the ink composition. Even when the content of the N-vinyl group-containing polymerizable compound is within the above range, there is a tendency for the abrasion resistance to be further improved while reducing odor. It is also preferable that the content of the polymerizable compound having a nitrogen-containing heterocyclic structure or the polymerizable compound having an oxazolidinone group in the N-vinyl group-containing polymerizable compound be within the above range.

[0035] 1.1.3 Other polymerizable compounds The polymerizable compound contained in the radiation-curable inkjet ink composition according to this embodiment may also contain polymerizable compounds other than those mentioned above.

[0036] 1.1.3.1 Monofunctional Monomers The polymerizable compound may contain a monofunctional monomer other than those described above. The monofunctional monomer is not particularly limited, but examples thereof include aromatic group-containing monofunctional monomers, nitrogen-containing monofunctional monomers, alicyclic group-containing monofunctional monomers, monofunctional monomers containing a cyclic ether structure, urethane acrylates, aliphatic group-containing monofunctional monomers, and hydroxy group-containing monofunctional monomers. Furthermore, other monofunctional monomers may be contained as necessary. The other monofunctional monomers are not particularly limited, but conventionally known monofunctional monomers having a polymerizable functional group, particularly a polymerizable functional group having a carbon-carbon unsaturated double bond, can be used.

[0037] The content of the monofunctional monomer relative to the total amount of the ink composition is preferably 20 to 90 mass %, more preferably 30 to 80 mass %, even more preferably 35 to 70 mass %, and particularly preferably 40 to 60 mass %. When the monofunctional monomer is in this range, the abrasion resistance of the coating film tends to be further improved.

[0038] The aromatic group-containing monofunctional monomer is not particularly limited as long as it has an aromatic group, and examples thereof 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.

[0039] Among these, phenoxyethyl (meth)acrylate and benzyl (meth)acrylate are preferred, phenoxyethyl (meth)acrylate is more preferred, and phenoxyethyl acrylate (PEA) is even more preferred. The use of such aromatic group-containing monomers tends to further improve the solubility of polymerization initiators that are solid at room temperature, thereby improving the curability of the ink composition. In particular, when using acylphosphine oxide-based polymerization initiators or thioxanthone-based polymerization initiators that are solid at room temperature, the solubility tends to be improved. Furthermore, the use of phenoxyethyl (meth)acrylate tends to further reduce odor.

[0040] When an aromatic group-containing monofunctional monomer is contained, its content is preferably 5 to 50 mass % relative to the total amount of the ink composition, more preferably 10 to 45 mass %, even more preferably 15 to 40 mass %, and particularly preferably 20 to 35 mass %. When the content of the aromatic group-containing monofunctional monomer relative to the total amount of the ink composition is within the above range, the viscosity of the ink composition tends to be further reduced, and the abrasion resistance of the coating film tends to be further improved.

[0041] The nitrogen-containing monofunctional monomer is not particularly limited, and examples thereof include nitrogen-containing monofunctional acrylate monomers such as acryloylmorpholine; and nitrogen-containing monofunctional acrylamide monomers such as (meth)acrylamide, N-hydroxymethyl(meth)acrylamide, diacetone acrylamide, N,N-dimethyl(meth)acrylamide, and dimethylaminoethyl acrylate benzyl chloride quaternary salt.

[0042] When a nitrogen-containing monofunctional monomer is contained, its content is preferably 5 to 45 mass %, more preferably 10 to 40 mass %, and more preferably 15 to 30 mass %, relative to the total amount of the ink composition. When the content of the nitrogen-containing monofunctional monomer is within the above range, the abrasion resistance of the coating film may be further improved.

[0043] The alicyclic group-containing monofunctional monomer is not particularly limited as long as it is a monomer having one or more saturated or unsaturated carbon rings that do not have aromaticity, but examples thereof include monomers having monocyclic hydrocarbon groups such as tertbutylcyclohexanol acrylate and 2-(meth)acrylic acid-1,4-dioxaspiro[4,5]dec-2-ylmethyl; monomers having unsaturated polycyclic hydrocarbon groups such as dicyclopentenyl acrylate and dicyclopentenyloxyethyl acrylate; and monomers having saturated polycyclic hydrocarbon groups such as dicyclopentanyl acrylate and isobornyl acrylate (IBXA). Monomers having saturated polycyclic hydrocarbon groups are preferred, and isobornyl acrylate (IBXA) is particularly preferred. By using such alicyclic group-containing monofunctional monomers, it is easy to adjust the glass transition temperature of the coating film low, and the stretchability of the coating film tends to be improved, thereby improving adhesion and abrasion resistance.

[0044] The content of the alicyclic group-containing monofunctional monomer is preferably 5 to 50 mass %, more preferably 5 to 30 mass %, and even more preferably 10 to 20 mass %, relative to the total amount of the ink composition. When the content of the alicyclic group-containing monofunctional monomer is within the above range, the abrasion resistance and other properties of the coating film tend to be further improved.

[0045] The monofunctional monomer containing a cyclic ether structure is not particularly limited as long as it is a monomer containing a cyclic ether skeleton such as tetrahydrofuran or tetrahydropyran, and examples thereof include cyclic trimethylolpropane formal acrylate (CTFA), cyclic trimethylolpropane formal methacrylate, tetrahydrofurfuryl acrylate (THFA), and tetrahydrofurfuryl methacrylate, and among these, cyclic trimethylolpropane formal acrylate (CTFA) and tetrahydrofurfuryl acrylate (THFA) are preferred. When such a monofunctional monomer containing a cyclic ether structure is used, the glass transition temperature of the coating film is easily adjusted to a low level, and the stretchability of the coating film tends to be increased, thereby improving adhesion and abrasion resistance.

[0046] When a monofunctional monomer having a cyclic ether structure is contained, the content thereof is preferably 5 to 30% by mass, and more preferably 10 to 25% by mass, relative to the total amount of the ink composition. When the content of the monofunctional monomer having a cyclic ether structure is within the above range, the adhesion of the coating film may be further improved.

[0047] The urethane acrylate is not particularly limited as long as it is a (meth)acrylic acid ester having a urethane bond, and examples thereof include (methylcarbamoyloxy)ethyl (meth)acrylate, (ethylcarbamoyloxy)ethyl (meth)acrylate, (propylcarbamoyloxy)ethyl (meth)acrylate, (butylcarbamoyloxy)ethyl (meth)acrylate, (methylcarbamoyloxy)ethoxyethyl (meth)acrylate, (ethylcarbamoyloxy)ethoxyethyl (meth)acrylate, (propylcarbamoyloxy)ethoxyethyl (meth)acrylate, and (butylcarbamoyloxy)ethoxyethyl (meth)acrylate. By using such a urethane acrylate, the viscosity of the ink composition tends to be further reduced, and the abrasion resistance of the resulting coating film tends to be further improved.

[0048] When a urethane acrylate is contained, its content is preferably 0.5 to 7.5% by mass, more preferably 1.0 to 5.0% by mass, and even more preferably 2.0 to 4.0% by mass, relative to the total amount of the ink composition. When the content of the urethane acrylate relative to the composition is within the above range, the viscosity of the ink composition tends to be further reduced, and the abrasion resistance of the resulting coating film tends to be further improved.

[0049] The aliphatic group-containing monofunctional monomer is not particularly limited, but examples thereof include monomers represented by the following general formula (3). H2C=CR 4 -CO-OR 5 ···(3) (In formula (3), R 4 represents a hydrogen atom or a methyl group, and R 5 represents a straight-chain or branched-chain aliphatic group having 4 to 20 carbon atoms.

[0050] Such aliphatic group-containing monofunctional monomer is not particularly limited as long as it is a saturated or unsaturated, straight-chain or branched-chain monomer that does not have a carbon ring, and examples thereof include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, isononyl (meth)acrylate, isomyristyl (meth)acrylate, isostearyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, butoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, etc. Among these, aliphatic group-containing monofunctional monomers having a saturated straight-chain or branched chain are preferred, and lauryl (meth)acrylate and isononyl (meth)acrylate are more preferred. By using such an aliphatic group-containing monofunctional monomer, the viscosity of the ink composition tends to be further reduced and the adhesion of the coating film tends to be further improved.

[0051] When an aliphatic group-containing monofunctional monomer is contained, its content is preferably 1.0 to 17% by mass, more preferably 3.0 to 15% by mass, and even more preferably 5.0 to 12% by mass, relative to the total amount of the ink composition. When the content of the aliphatic group-containing monofunctional monomer in the ink composition is within the above range, the viscosity of the ink composition tends to be further reduced, and the adhesion of the coating film tends to be further improved.

[0052] The hydroxy group-containing monofunctional monomer is not particularly limited, and examples thereof include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, ethylene glycol monovinyl ether, diethylene glycol monovinyl ether, 2-(meth)acryloyloxy-2-hydroxypropyl phthalate, etc. Use of such a hydroxy group-containing monofunctional monomer tends to further reduce the viscosity of the ink composition and further improve the adhesion of the coating film.

[0053] When a hydroxyl group-containing monofunctional monomer is contained, its content is preferably 1.0 to 35 mass %, more preferably 3.0 to 25 mass %, and even more preferably 5.0 to 15 mass %, relative to the total amount of the ink composition. When the content of the hydroxyl group-containing monofunctional monomer in the ink composition is within the above range, the viscosity tends to be further reduced, and the adhesion of the resulting coating film tends to be further improved.

[0054] Other monofunctional monomers that may be used include, in addition to the above, unsaturated carboxylic acids such as (meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, and maleic acid; salts of the unsaturated carboxylic acids; esters, urethanes, amides, and anhydrides of unsaturated carboxylic acids; acrylonitrile, styrene, various unsaturated polyesters, unsaturated polyethers, and unsaturated polyamides.

[0055] 1.1.3.2 Multifunctional Monomers The polymerizable compound may contain a polyfunctional monomer other than those mentioned above. The polyfunctional monomer is not particularly limited, but examples thereof include bifunctional (meth)acrylates and trifunctional or higher polyfunctional (meth)acrylates.

[0056] The bifunctional (meth)acrylate is not particularly limited, and examples thereof include dipropylene glycol diacrylate (DPGDA), diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol dimethacrylate, tripropylene glycol diacrylate (TPGDA), tripropylene glycol dimethacrylate, polypropylene glycol di(meth)acrylate, and 1,4-butanediol. Examples of the di(meth)acrylate include bisphenol A di(meth)acrylate, 1,6-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 hydroxypivalate di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate. Note that "acrylate" is sometimes referred to as "acrylate."

[0057] When a bifunctional (meth)acrylate is contained, the content thereof is preferably 5 to 80 mass % relative to the total amount of the ink composition, more preferably 10 to 70 mass %, more preferably 15 to 40 mass %, and even more preferably 20 to 30 mass %.

[0058] The tri- or higher functional polyfunctional (meth)acrylate is not particularly limited, and examples thereof include trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexaacrylate (DPHA), dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxy tri(meth)acrylate, caprolactone-modified trimethylolpropane tri(meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, and caprolactam-modified dipentaerythritol hexa(meth)acrylate.

[0059] When a tri- or higher functional (meth)acrylate is contained, the content thereof is preferably 1 to 20% by mass, and more preferably 3 to 10% by mass, relative to the total amount of the ink composition.

[0060] 1.1.3.3 Oligomers An oligomer is a polymer containing a polymerizable compound as a constituent component and refers to a compound having one or more polymerizable functional groups. Note that the polymerizable compound referred to here is not limited to the above-mentioned monomer. In this embodiment, a compound having a molecular weight of 1000 or more is defined as an oligomer, and a compound having a molecular weight of less than 1000 is defined as a monomer.

[0061] Such oligomers are not particularly limited, but examples thereof include urethane acrylate oligomers in which the repeating unit is a urethane, polyester acrylate oligomers in which the repeating unit is an ester, and epoxy acrylate oligomers in which the repeating unit is an epoxy.

[0062] Among these, urethane acrylate oligomers are preferred, aliphatic urethane acrylate oligomers and aromatic urethane acrylate oligomers are more preferred, and aliphatic urethane acrylate oligomers are even more preferred. Furthermore, the urethane acrylate oligomer is preferably a tetrafunctional or less urethane acrylate oligomer, and more preferably a bifunctional urethane acrylate oligomer. By using such an oligomer, the viscosity tends to be further reduced and the abrasion resistance and the like tend to be further improved.

[0063] Commercially available oligomers include, for example, CN9893 (difunctional aliphatic urethane oligomer, manufactured by Sartomer Corporation).

[0064] When an oligomer is used, the content of the oligomer is preferably 0.5 to 10% by mass, more preferably 0.5 to 5% by mass, and even more preferably 1 to 3% by mass, relative to the total amount of the ink composition. When the content is within the above range, the viscosity tends to be further reduced, and the abrasion resistance and the like tend to be further improved.

[0065] Among these, it is preferable that the polymerizable compound contained in the radiation-curable inkjet ink composition according to this embodiment further contains dipropylene glycol diacrylate or tripropylene glycol diacrylate, as this tends to result in an ink coating with better curability and adhesion.

[0066] When dipropylene glycol diacrylate or tripropylene glycol diacrylate is contained, the content thereof is preferably 5 to 50 mass %, more preferably 10 to 40 mass %, and even more preferably 20 to 30 mass %, relative to the total amount of the ink composition.

[0067] Furthermore, the polymerizable compound contained in the radiation-curable inkjet ink composition according to this embodiment preferably does not contain an acrylate group-containing polymerizable compound, or contains an acrylate group-containing polymerizable compound in an amount of more than 0% by mass but not more than 90% by mass relative to the total amount of the inkjet ink composition. An acrylate group-containing polymerizable compound (acrylate group-based polymerizable compound) refers to a compound in which the only polymerizable functional group possessed by the polymerizable compound is acrylate. Because acrylate groups do not decompose into acetaldehyde, they are less likely to produce odor-causing substances. Therefore, the odor problem becomes more pronounced as the content of the acrylate group-containing polymerizable compound decreases; however, with the radiation-curable inkjet ink composition according to this embodiment, odor can be reduced even when the content of the acrylate group-containing polymerizable compound is as described above. When the polymerizable compound includes an acrylate group-containing polymerizable compound, the content thereof is more preferably greater than 0% by mass and not greater than 85% by mass, even more preferably greater than 15% by mass and not greater than 80% by mass, particularly preferably greater than 30% by mass and not greater than 75% by mass, and more preferably greater than 45% by mass and not greater than 70% by mass, relative to the total amount of the inkjet ink composition.

[0068] 1.2 Imidazoline compounds The radiation-curable inkjet ink composition according to this embodiment contains an imidazoline compound. The inclusion of an imidazoline compound inhibits decomposition reactions, such as hydrolysis, of vinyl ether groups and N-vinyl groups in the polymerizable compound, thereby suppressing the generation of acetaldehyde. This is presumably because imidazoline compounds are basic compounds that tend to shift the pH of the entire ink composition toward the alkaline side, thereby inhibiting decomposition reactions, such as hydrolysis, of vinyl ether groups and N-vinyl groups in the polymerizable compound.

[0069] The imidazoline compound refers to a compound having an imidazoline ring in the molecule, and may be in the form of a salt. Specific examples of the imidazoline compound include 2-methyl-2-imidazoline, 2-ethyl-2-imidazoline, 2-heptadecyl-2-imidazoline-1-ethanol, 2-[2-(8-heptadecenyl)-2-imidazolin-1-yl]ethanol, 2-undecyl-2-imidazoline-1-ethanol, 2-tridecyl-2-imidazoline-1-ethanol, 2-dodecyl-2-imidazoline-1-ethanol, 2-(1-heptadecenyl)-2-imidazoline. Examples of imidazoline-1-ethanol include 2-pentadecyl-2-imidazoline-1-ethanol, 2-[(Z)-8-heptadecenyl]-2-imidazoline-1-ethanol, 2-octyl-2-imidazoline-1-ethanol, 2-heptadecenyl-2-imidazoline-1-ethanol, 2-nonyl-2-imidazoline-1-ethanol, 2-henicosyl-2-imidazoline-1-ethanol, and 2-isooctadecyl-2-imidazoline-1-ethanol.

[0070] As the imidazoline compound, commercially available products may be used, such as DISPERBYK-109 (trade name, manufactured by BYK, 1-hydroxyethyl-2-alkenylimidazoline) and AMINE-O (trade name, manufactured by BASF, 2-[2-(8-heptadecenyl)-2-imidazolin-1-yl]ethanol).

[0071] The imidazoline compound preferably has a hydroxy group, more preferably a hydroxyethyl group. Imidazoline compounds having a hydroxy(ethyl) group are weaker in basicity than imidazoline compounds not having a hydroxy(ethyl) group, and therefore tend to be able to further reduce the viscosity increase of the ink during storage.

[0072] It is more preferable that the imidazoline compound contains a compound represented by the following formula (1): In this case, there is a tendency that the increase in viscosity of the ink during storage can be further reduced. [ka] (In the formula, R represents an alkyl group or alkenyl group having 7 to 23 carbon atoms. The number of carbon atoms in R is preferably 10 to 23, and more preferably 15 to 20.)

[0073] The content of the imidazoline compound is preferably 0.1% by mass to 10% by mass, more preferably 0.1% by mass to 5% by mass, even more preferably 0.1% by mass to 2% by mass, particularly preferably 0.5% by mass to 2% by mass, and even more particularly preferably 0.7% by mass to 1.5% by mass. When the content of the imidazoline compound is within the above range, the ink tends to have excellent odor properties and also tends to be less prone to thickening during storage.

[0074] 1.3 Colorants The radiation-curable inkjet ink composition according to this embodiment may contain a coloring material, which may be at least one of a pigment and a dye.

[0075] The total content of coloring materials is preferably 0.1% by mass to 10.0% by mass, more preferably 0.5% by mass to 8.0% by mass, and even more preferably 1.5% by mass to 6% by mass, relative to the total amount of the ink composition. The radiation-curable inkjet ink composition according to this embodiment may be a clear ink that does not contain any coloring materials or that contains coloring materials to an extent that coloring is not intended (for example, 0.1% by mass or less).

[0076] When a pigment is used, a pigment dispersion may be prepared in advance and used in the radiation-curable inkjet ink composition. The pigment dispersion may contain a polymerizable compound, a dispersant (described below) for dispersing the pigment, and the like.

[0077] 1.3.1 Pigments When a pigment is used as the coloring material, the storage stability of the ink composition can be improved in some cases. Either an inorganic pigment or an organic pigment can be used as the pigment.

[0078] Examples of inorganic pigments that can be used include carbon blacks such as CI Pigment Black 6 (lamp black, vegetable black), CI Pigment Black 7 (furnace black, channel black, thermal black, acetylene black), CI Pigment Black 8 (charcoal black), and CI Pigment Black 10 (graphite), iron oxide, titanium oxide, zinc oxide, and silica.

[0079] Examples of carbon black include No. 2300, 900, MCF88, No. 20B, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, and No. 2200B manufactured by Mitsubishi Chemical Corporation. Examples of carbon black include Color Black FW1, FW2, FW2V, FW18, FW200, S150, S160, and S170, Pretex 35, U, V, and 140U, and Special Black 6, 5, 4A, 4, and 250 manufactured by Degussa. Examples of carbon black include Conductex SC, Raven 1255, 5750, 5250, 5000, 3500, 1255, and 700 manufactured by Columbia Carbon Corporation. Examples include Cabot Corporation's Regal 400R, 330R, 660R, Mogul L, Monarch 700, 800, 880, 900, 1000, 1100, 1300, 1400, and Elftex 12.

[0080] Examples of organic pigments include quinacridone pigments, quinacridonequinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, anthanthrone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimidazolone pigments, isoindolinone pigments, azomethine pigments, and azo pigments.

[0081] Specific examples of organic pigments include the following:

[0082] Examples of cyan pigments include CI Pigment Blue 1, 2, 3, 15:3, 15:4, 15:34, 16, 22, 60, etc.; CI Vat Blue 4, 60, etc., and preferably, one or a mixture of two or more selected from the group consisting of CI Pigment Blue 15:3, 15:4, and 60 can be exemplified.

[0083] Examples of magenta pigments include CI Pigment Red 5, 7, 12, 48, 48, 57, 57:1, 112, 122, 123, 168, 184, 202, and CI Pigment Violet 19, and preferably include one or a mixture of two or more pigments selected from the group consisting of CI Pigment Red 122, 202, and 209, and CI Pigment Violet 19. Solid solutions of the above pigments are also acceptable.

[0084] Examples of yellow pigments include CI Pigment Yellow 1, 2, 3, 12, 13, 14C, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 119, 110, 114, 128, 129, 138, 150, 151, 154, 155, 180, and 185. Of these, preferred examples include one or a mixture of two or more selected from the group consisting of CI Pigment Yellow 74, 109, 110, 128, 138, 155, and 180.

[0085] Examples of orange pigments include CI Pigment Orange 36 or 43, or a mixture thereof. Examples of green pigments include CI Pigment Green 7 or 36, or a mixture thereof.

[0086] Luster pigments may also be used, and are not particularly limited as long as they can exhibit luster when attached to a medium. Examples include metal particles of one or more alloys (also called metal pigments) selected from the group consisting of aluminum, silver, gold, platinum, nickel, chromium, tin, zinc, indium, titanium, and copper, and pearl pigments with pearly luster. Representative examples of pearl pigments include pigments with pearly luster or interference luster, such as titanium dioxide-coated mica, fish scale foil, and bismuth oxychloride. The luster pigment may also be surface-treated to suppress reaction with water.

[0087] White pigments may also be used, including, for example, metal oxides, barium sulfate, calcium carbonate, and other metal compounds. Examples of metal oxides include titanium dioxide, zinc oxide, silica, alumina, magnesium oxide, and the like. The white pigment may also be particles having a hollow structure.

[0088] The pigments may be used alone or in combination of two or more. From the viewpoint of storage stability such as light resistance, weather resistance, and gas resistance, the pigment is preferably an organic pigment.

[0089] The volume average particle diameter (D50) of the pigment, as measured by dynamic light scattering, is 20 nm or more and 300 nm or less, more preferably 30 nm or more and 200 nm or less, and even more preferably 40 nm or more and 100 nm or less.

[0090] The volume average particle size may be measured, for example, using a Nanotrac Series particle distribution analyzer manufactured by Microtrac Bell Co., Ltd. Methods for adjusting the volume average particle size include, for example, adjusting the degree of pulverization of the pigment before dispersion, adjusting the stirring conditions during dispersion (e.g., stirring speed, stirring temperature, etc.), and adjusting by filtration using a filter after dispersion.

[0091] When the radiation-curable inkjet ink composition contains a pigment, it may further contain a dispersant to improve the pigment dispersibility. The dispersant may be used alone or in combination of two or more types.

[0092] The dispersant is not particularly limited, but examples thereof include dispersants commonly used in preparing pigment dispersions, such as polymer dispersants, and specific examples thereof include those containing one or more of polyoxyalkylene, polyalkylene polyamine, vinyl polymers and copolymers, acrylic polymers and copolymers, polyester, polyamide, polyimide, polyurethane, amino polymer, silicon-containing polymer, sulfur-containing polymer, fluorine-containing polymer, and epoxy resin as a main component.

[0093] Commercially available polymer dispersants include the Ajisper series manufactured by Ajinomoto Fine-Techno Co., Ltd., the Solsperse series (Solsperse 36000, etc.) available from Avecia and Noveon, the Disperbic series manufactured by BYK Additives & Instruments, and the Disparlon series manufactured by Kusumoto Chemicals Co., Ltd.

[0094] When a dispersant is used, the content thereof is preferably 0.01% by mass or more and 5.0% by mass or less, more preferably 0.1% by mass or more and 3.0% by mass or less, and even more preferably 0.4% by mass or more and 1.5% by mass or less, relative to the total amount of the ink composition.

[0095] 1.3.2 Dyes A dye may be used as a coloring material. The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. The dyes may be used alone or in combination of two or more.

[0096] The dye is not particularly limited, and examples thereof include CI 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, 14 2, 144, 173, 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, CI Reactive Black 3, 4, 35.

[0097] 1.4 Polymerization initiator The radiation-curable inkjet ink composition according to this embodiment may contain a polymerization initiator that generates an active species upon irradiation with radiation.

[0098] The polymerization initiator is not particularly limited as long as it generates active species upon irradiation with radiation, and examples thereof include known polymerization initiators such as acylphosphine oxide-based polymerization initiators, thioxanthone-based polymerization initiators, alkylphenone-based polymerization initiators, and benzophenone-based polymerization initiators. Among these, acylphosphine oxide-based polymerization initiators and thioxanthone-based polymerization initiators are preferred, and acylphosphine oxide-based polymerization initiators are more preferred. Use of such polymerization initiators tends to further improve the curability and abrasion resistance of the ink composition. The polymerization initiators may be used alone or in combination of two or more.

[0099] The acylphosphine oxide polymerization initiator is not particularly limited, and examples thereof include ethyl 2,4,6-trimethylbenzoylphenylphosphineate (another name: ethylphenyl(2,4,6-trimethylbenzoyl)phosphineate), 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (another name: phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide), bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and the like.

[0100] Commercially available examples of such acylphosphine oxide polymerization initiators include Omnirad TPO-L (manufactured by IGM Resins BV), Omnirad 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide), IRGACURE 1800 (a mixture of bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide and 1-hydroxy-cyclohexyl-phenyl ketone in a mass ratio of 25:75), and Omnirad TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide).

[0101] The content of the acylphosphine oxide polymerization initiator is preferably 2% by mass or more and 20% by mass or less, more preferably 5% by mass or more and 15% by mass or less, and even more preferably 7% by mass or more and 13% by mass or less, relative to the total amount of the ink composition. When the content of the acylphosphine oxide polymerization initiator is within the above range, the curability and abrasion resistance of the ink composition tend to be further improved.

[0102] The thioxanthone polymerization initiator is not particularly limited, but examples thereof include thioxanthone, 2-methylthioxanthone, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, and 2,4-diethylthioxanthone, 2,4-diethylthioxanthone, 2,4-diethylthioxanthone-9-one (also known as 2,4-diethyl-9H-thioxanthen-9-one), a diester of carboxymethoxythioxanthone and polytetramethylene glycol, and 1,3-di({α-[1-chloro-9-oxo-9H-thioxanthen-4-yl]oxy}acetylpoly[oxy(1-methylethylene)])oxy)-2,2-bis({α-[1-chloro-9-oxo-9H-thioxanthen-4-yl]oxy}acetylpoly[oxy(1-methylethylene)])oxymethylpropane.

[0103] A thioxanthone-based polymerization initiator may be used in combination with the polymerization initiator as a sensitizer. The content of the sensitizer is preferably 0.1% by mass or more, more preferably 0.5 to 10% by mass, and even more preferably 1.0 to 5.0% by mass, relative to the total amount of the ink composition. An example of a commercially available sensitizer is Speedcure DETX (manufactured by LAMBSON, 2,4-diethylthioxanthen-9-one).

[0104] The alkylphenone polymerization initiator is not particularly limited, but examples thereof include 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, and 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one.

[0105] The benzophenone-based polymerization initiator is not particularly limited, but examples thereof include 4,4'-bis(diethylamino)benzophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, and 4,4'-diaminobenzophenone.

[0106] 1.5 Polymerization inhibitors The radiation-curable inkjet ink composition according to this embodiment may contain a polymerization inhibitor, from the viewpoint of further improving the storage stability of the ink composition. The polymerization inhibitor may be used alone, or two or more types may be used in combination.

[0107] Examples of the polymerization inhibitor include, but are not limited to, p-methoxyphenol, hydroquinone monomethyl ether (MEHQ, also known as 4-methoxyphenol), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, hydroquinone, cresol, t-butylcatechol, 3,5-di-t-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-butylphenol), and 4,4'-thiobis(3-methyl-6-t-butylphenol), and hindered amine compounds.

[0108] Commercially available polymerization inhibitors include ADK STAB LA-7RD (2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, also known as 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl), LA-52, LA-57, LA-62, LA-63P, LA-68LD, LA-77Y, LA-77G, LA-81, LA-82 (1,2,2,6,6-pentamethyl-4-piperidyl methacrylate), and LA-87 (all trade names manufactured by ADEKA Corporation), IRGASTAB UV 10 (4,4'-[1,10-dioxo-1,10-decanediyl)bis(oxy)]bis[2,2,6,6-tetramethyl]-1-piperidinyloxy) (CAS. 2516-92-9), and TINUVIN 123 (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl), TINUVIN 111FDL, TINUVIN 144, TINUVIN 152, TINUVIN 292, TINUVIN 765, TINUVIN 770DF, TINUVIN 5100, SANOL LS-2626, CHIMASSORB 119FL, CHIMASSORB 2020 FDL, CHIMASSORB 944 FDL, TINUVIN 622 LD (all trade names manufactured by BASF), FA-711HM, FA-712HM (2,2,6,6-tetramethylpiperidinyl methacrylate, trade names manufactured by Hitachi Chemical Co., Ltd.), and the like.

[0109] When a polymerization inhibitor is used, the content thereof is preferably 0.01% by mass or more and 1.0% by mass or less, more preferably 0.1% by mass or more and 0.5% by mass or less, and even more preferably 0.1% by mass or more and 0.2% by mass or less, relative to the total amount of the ink composition.

[0110] 1.6 Surfactants The radiation-curable inkjet ink composition according to this embodiment may contain a surfactant. The surfactant is not particularly limited, but examples thereof include acetylene glycol-based surfactants, fluorine-based surfactants, and silicone-based surfactants.

[0111] The acetylene glycol surfactant is not particularly limited, but examples thereof include alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and alkylene oxide adducts of 2,4-dimethyl-5-decyne-4-ol and 2,4-dimethyl-5-decyne-4-ol. Examples include:

[0112] The fluorine-based surfactant is not particularly limited, but examples thereof include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphates, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, and perfluoroalkyl amine oxide compounds.

[0113] Examples of silicone surfactants include polysiloxane compounds, polyester-modified silicones, and polyether-modified organosiloxanes. Examples of polyester-modified silicones include BYK-347, 348, 3510, and 3530 (all manufactured by BYK Additives & Instruments). Examples of polyether-modified silicones include BYK-3570 and BYK-UV3500 (manufactured by BYK Additives & Instruments).

[0114] The content of the surfactant is preferably 0.1 to 1% by mass, and more preferably 0.2 to 0.8% by mass, relative to the total mass of the ink composition. When the content of the surfactant is within the above range, the wettability of the ink composition tends to be further improved.

[0115] 1.7 Other ingredients The radiation-curable inkjet ink composition according to this embodiment may further contain various additives, such as a fluorescent brightening agent, a chain transfer agent, a crosslinking agent, an antioxidant, a preservative, a flame retardant, an antistatic agent, and an organic or inorganic filler, as needed.

[0116] The radiation-curable inkjet ink composition according to this embodiment may contain water, preferably in an amount of 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, particularly preferably 0.1% by mass or less, and even more preferably 0.01% by mass or less, based on the total amount of the ink composition. Preferably, the ink composition contains no water (0% by mass). With this water content, the vinyl ether groups and N-vinyl groups in the polymerizable compound are less likely to be decomposed by hydrolysis during storage of the ink, which tends to further reduce odor.

[0117] 1.8 Physical Properties The viscosity of the radiation-curable inkjet ink composition according to this embodiment at 20° C. is preferably 15 mPa s or less, more preferably 10 mPa s or less, and even more preferably less than 6 mPa s. When the viscosity of the ink composition at 20° C. is within this range, an appropriate amount of the ink composition is ejected from the nozzle, and deflection and scattering of the ink composition can be further reduced, making the ink composition suitable for use in inkjet recording devices.

[0118] The viscosity can be measured, for example, using a viscoelasticity tester MCR-300 (manufactured by Pysica) in an environment of 20°C, by increasing the shear rate from 10 to 1000 and reading the viscosity at a shear rate of 200.

[0119] The surface tension of the radiation-curable inkjet ink composition according to this embodiment at 20°C is preferably 20 mN / m or more and 40 mN / m or less. When the surface tension of the radiation-curable inkjet ink composition at 20°C is within this range, the ink composition is less likely to wet a nozzle surface that has been treated with a liquid repellent coating. This allows the ink composition to be ejected normally and in an appropriate amount from the nozzle, and further reduces deflection and scattering of the ink composition, making the composition suitable for use in inkjet recording devices.

[0120] The surface tension can be measured, for example, by using an automatic surface tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) to check the surface tension when a platinum plate is wetted with the radiation-curable inkjet ink composition in an environment of 20°C.

[0121] 1.9 Manufacturing method The production (preparation) of a radiation-curable inkjet ink composition can be carried out, for example, by mixing the components contained in the ink composition and stirring the mixture to achieve a sufficiently uniform mixture. In this embodiment, the preparation of a radiation-curable inkjet ink composition preferably includes a step of subjecting a mixture of a polymerization initiator and at least a portion of a polymerizable compound to at least one of ultrasonic treatment and heating treatment during the preparation process. This reduces the amount of dissolved oxygen in the prepared ink composition, and tends to result in a radiation-curable inkjet ink composition with excellent ejection stability and storage stability. The mixture may contain at least the above components, and may further contain other components contained in a radiation-curable inkjet ink composition, or may contain all of the components contained in a radiation-curable inkjet ink composition. The polymerizable compound contained in the mixture may be at least a portion of the polymerizable compound contained in the radiation-curable inkjet ink composition.

[0122] 2. Recording device A recording apparatus according to one embodiment of the present invention includes an inkjet head that ejects the radiation-curable inkjet ink composition described above.

[0123] The recording apparatus according to this embodiment is equipped with an inkjet head that ejects the radiation-curable inkjet ink composition described above, and therefore can reduce odors that may occur after storage of the ink.

[0124] The recording apparatus according to this embodiment may include the radiation-curable inkjet ink composition described above. The recording apparatus according to this embodiment may also include a radiation source that irradiates the ink composition with radiation.

[0125] As an example of an inkjet device, a perspective view of a serial printer is shown in Fig. 1. As shown in Fig. 1, the serial printer 20 includes a conveying unit 220 and a recording unit 230. The conveying unit 220 conveys the recording medium F fed to the serial printer to the recording unit 230, and ejects the recording medium after recording outside the serial printer. Specifically, the conveying unit 220 has feed rollers and conveys the fed recording medium F in the sub-scanning direction T2.

[0126] The recording unit 230 also includes an inkjet head 231 that ejects the above-mentioned radiation-curable inkjet ink composition onto the recording medium F sent from the conveying unit 220, a radiation source 232 that irradiates the deposited ink composition with radiation, a carriage 234 that carries these elements, and a carriage movement mechanism 235 that moves the carriage 234 in the main scanning directions S1 and S2 of the recording medium F.

[0127] In the case of a serial printer, an inkjet head 231 having a length smaller than the width of the recording medium is provided, and the head moves to perform recording in multiple passes (multi-pass). In a serial printer, the head 231 and radiation source 232 are mounted on a carriage 234 that moves in a predetermined direction, and the head moves in conjunction with the movement of the carriage, thereby ejecting the ink composition onto the recording medium. In this way, recording is performed in two or more passes (multi-pass). A pass is also called a main scan. A sub-scan is performed to transport the recording medium between passes. In other words, main scans and sub-scans are performed alternately.

[0128] Although FIG. 1 shows an embodiment in which the radiation source is mounted on a carriage, the present invention is not limited to this, and the radiation source may be one that is not mounted on a carriage.

[0129] Furthermore, the inkjet device of this embodiment is not limited to the serial printer, but may be the line printer described above.

[0130] 3. Working Example The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "%" below is based on mass.

[0131] 3.1 Preparation of radiation-curable inkjet ink composition First, the pigment, dispersant, and a portion of each polymerizable compound were weighed and placed in a pigment dispersion tank. A 1 mm diameter ceramic bead mill was then placed in the tank and stirred to obtain a pigment dispersion in which the pigment was dispersed in the monomer. Next, the remaining polymerizable compound, polymerization initiator, surfactant, and polymerization inhibitor were placed in a stainless steel mixing tank, and mixed and stirred to completely dissolve the components, according to the composition shown in Table 1 (shown in Figure 2). The pigment dispersion obtained above was then added, and the mixture was further mixed and stirred at room temperature for an hour. The resulting mixture was then filtered through a 5 μm membrane filter to obtain the base inks (Inks 1 to 10). The numerical values ​​for each component shown in each example in the table represent mass %.

[0132] Using the base inks (inks 1 to 10) obtained above, imidazoline compounds were added so as to obtain the compositions shown in Table 2 (shown in FIG. 3), thereby obtaining radiation-curable inkjet ink compositions according to the respective Examples and Comparative Examples.

[0133] The following provides additional explanations for the descriptions in Tables 1 and 2. [Polymerizable compound] VEEA: 2-(2-vinyloxyethoxy)ethyl acrylate, CAS number 86273-46-3 VMOX: 5-methyl-3-vinyloxazolidin-2-one, CAS number 3395-98-0 NVC: N-vinylcaprolactam, CAS number 2235-00-9 TPGDA: Tripropylene glycol diacrylate, CAS number 42978-66-5 DPGDA: Dipropylene glycol diacrylate, CAS number 57472-68-1 PEA: Phenoxyethyl acrylate, CAS number 48145-04-6 DPHA: Dipentaerythritol hexaacrylate, CAS number 29570-58-9 [Polymerization initiator] Omnirad TPO-L: Trade name, manufactured by IGM, Ethyl phenyl (2,4,6-trimethylbenzoyl) phosphinate, CAS number 84434-11-7 Omnirad 819: Trade name, manufactured by IGM, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, CAS number 162881-26-7 Speedcure DETX: Trade name, manufactured by LAMBSON, 2,4-diethyl-9H-thioxanthen-9-one, CAS number 82799-44-8 [Surfactant] BYK-UV3500: Product name, manufactured by BYK Additives & Instruments, polyether-modified polydimethylsiloxane with acrylic groups [Polymerization inhibitor] LA-7RD: Trade name "ADEKA STAB LA-7RD", manufactured by ADEKA Corporation, 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl, CAS number 2226-96-2 MEHQ: Trade name "p-Methoxyphenol", manufactured by Kanto Chemical Co., Ltd., 4-Methoxyphenol, CAS number 150-76-5 [Imidazoline compounds] DISPERBYK-109: BYK brand name, 1-hydroxyethyl-2-alkenylimidazoline AMINE-O: BASF brand name, 2-[2-(8-heptadecenyl)-2-imidazolin-1-yl]ethanol, CAS number 95-38-5

[0134] 3.2 Evaluation method 3.2.1 Storage thickening Using a rotational viscometer (product name "Rheometer MCR-301", manufactured by Anton Paar), the initial viscosity of the radiation-curable inkjet ink composition according to each Example and Comparative Example was measured in an environment of 20°C. Thereafter, the radiation-curable inkjet ink composition according to each Example and Comparative Example was stored in a light-shielding PP bottle at 60°C for 14 days, and the viscosity was measured in the same manner. The rate of increase in viscosity after storage from the initial viscosity was determined, and the storage-related viscosity increase was evaluated based on the following evaluation criteria. (Evaluation criteria) A: Viscosity increase rate is less than 5% B: Viscosity increase rate is 5% or more but less than 10% C: Viscosity increase rate is 10% or more

[0135] 3.2.2 Ink odor after storage The radiation-curable inkjet ink compositions according to the respective Examples and Comparative Examples were stored in light-shielding PP bottles at 60° C. for 14 days, and the ink odor after storage was evaluated based on the odor intensity indication method and evaluation criteria below. (Odor Intensity Indication Method) Odorless: 0 Barely detectable smell: 1 Weak smell that I can identify: 2 Easily detectable odors: 3 Strong smell: 4 Strong smell: 5 (Evaluation criteria) A: Odor intensity less than 3 B: Odor intensity is 3 or more but less than 4 C: Odor intensity is 4 or higher

[0136] 3.3 Evaluation method Table 2 shows the evaluation results.

[0137] The evaluation results shown in Table 2 indicate that the radiation-curable inkjet ink compositions according to the examples, which contain a polymerizable compound and an imidazoline compound, and in which the polymerizable compound contains at least one of a vinyl ether group-containing polymerizable compound and an N-vinyl group-containing polymerizable compound, are able to effectively reduce odor after ink storage.

[0138] In contrast, the radiation-curable inkjet ink compositions according to the comparative examples, which do not satisfy the above requirements, are unable to reduce the odor of the ink after storage.

[0139] The following can be derived from the above-described embodiment.

[0140] One embodiment of the radiation-curable inkjet ink composition comprises: a polymerizable compound; an imidazoline compound, The polymerizable compound includes at least one of a vinyl ether group-containing polymerizable compound and an N-vinyl group-containing polymerizable compound.

[0141] In the above-described embodiment of the radiation-curable inkjet ink composition, The imidazoline compound may have a hydroxy group.

[0142] In any one of the above radiation-curable inkjet ink compositions, The imidazoline compound may include a compound represented by the following formula (1): [ka] (In the formula, R represents an alkyl group or alkenyl group having 7 to 23 carbon atoms.)

[0143] In any one of the above radiation-curable inkjet ink compositions, The imidazoline compound may be present in an amount of 0.1% by mass or more and 2% by mass or less relative to the total amount of the inkjet ink composition.

[0144] In any one of the above radiation-curable inkjet ink compositions, The polymerizable compound may include a compound represented by the following formula (2). CH2=CR 1 -COOR 2 -O-CH=CH-R 3 ···(2) (In the formula, R 1is a hydrogen atom or a methyl group, and 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.

[0145] In any one of the above radiation-curable inkjet ink compositions, The polymerizable compound may include a polymerizable compound having a nitrogen-containing heterocyclic structure.

[0146] In any one of the above radiation-curable inkjet ink compositions, The polymerizable compound having a nitrogen-containing heterocyclic structure may have an oxazolidinone group.

[0147] In any one of the above radiation-curable inkjet ink compositions, The polymerizable compound may further include dipropylene glycol diacrylate or tripropylene glycol diacrylate.

[0148] In any one of the above radiation-curable inkjet ink compositions, The polymerizable compound is does not contain an acrylate group-containing polymerizable compound, or The ink-jet ink composition may contain more than 0% by mass and up to 90% by mass of an acrylate group-containing polymerizable compound relative to the total amount of the ink-jet ink composition.

[0149] One aspect of the recording device is The present invention is provided with an inkjet head that ejects the radiation-curable inkjet ink composition according to any one of the above embodiments.

[0150] The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the present invention includes configurations that are substantially the same as the configurations described in the embodiments, such as configurations with the same functions, methods, and results, or configurations with the same purpose and effects. The present invention also includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. The present invention also includes configurations that achieve the same effects or purposes as the configurations described in the embodiments. The present invention also includes configurations in which publicly known technology is added to the configurations described in the embodiments. [Explanation of symbols]

[0151] 20... serial printer, 220... transport unit, 230... recording unit, 231... inkjet head, 232... radiation source, 234... carriage, 235... carriage moving mechanism, F... recording medium, S1, S2... main scanning direction, T2... sub-scanning direction

Claims

1. a polymerizable compound; an imidazoline compound, The polymerizable compound in the radiation-curable inkjet ink composition includes at least one of a vinyl ether group-containing polymerizable compound and an N-vinyl group-containing polymerizable compound.

2. The radiation-curable ink-jet ink composition according to claim 1 , wherein the imidazoline compound has a hydroxy group.

3. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein the imidazoline compound comprises a compound represented by the following formula (1): 【Chemistry 1】 (In the formula, R represents an alkyl group or alkenyl group having 7 to 23 carbon atoms.)

4. 3. The radiation-curable ink-jet ink composition according to claim 1, wherein the imidazoline compound is present in an amount of 0.1% by mass or more and 2% by mass or less relative to the total amount of the ink-jet ink composition.

5. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein the polymerizable compound comprises a compound represented by the following formula (2): CH ２ =CR １ -COOR ２ -O-CH=CH-R ３ ・・・(2) (In the formula, R １ is a hydrogen atom or a methyl group, and 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.

6. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein the polymerizable compound includes a polymerizable compound having a nitrogen-containing heterocyclic structure.

7. The radiation-curable inkjet ink composition according to claim 6 , wherein the polymerizable compound having a nitrogen-containing heterocyclic structure has an oxazolidinone group.

8. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein the polymerizable compound further comprises dipropylene glycol diacrylate or tripropylene glycol diacrylate.

9. The polymerizable compound is does not contain an acrylate group-containing polymerizable compound, or The radiation-curable inkjet ink composition according to claim 1 or claim 2, comprising more than 0% by mass and up to 90% by mass of the acrylate group-containing polymerizable compound relative to the total amount of the inkjet ink composition.

10. A recording apparatus comprising an inkjet head that ejects the radiation-curable inkjet ink composition according to claim 1 or 2.

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