Radiation-curable inkjet ink composition

Abstract

To provide a radiation-curable inkjet ink composition that achieves both excellent abrasion resistance and excellent storage stability of the ink composition in high and low temperature environments. [Solution] A radiation-curable inkjet ink composition according to one embodiment of the present invention comprises a polymerizable compound and a photopolymerization initiator, wherein the polymerizable compound comprises a polyfunctional polymerizable compound, the photopolymerization initiator comprises (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide, the content of (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is 3% by mass or more of the total amount of the ink composition, and the content of the polyfunctional polymerizable compound is 20% by mass or more of the total amount of the ink composition.

Description

[Technical Field]

[0001] This invention relates to a radiation-curable inkjet ink composition. [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. Within this context, various studies are being conducted on inkjet ink compositions that harden when exposed to radiation.

[0003] For example, Patent Document 1 describes a radiation-curable inkjet composition containing a relatively large number of polyfunctional monomers and ethyl 2,4,6-trimethylbenzoylphenylphosphinate as a photopolymerization initiator. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-163470 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, there are challenges in achieving both excellent abrasion resistance and excellent storage stability of the ink composition under high and low temperature conditions. [Means for solving the problem]

[0006] One embodiment of the radiation-curable inkjet ink composition according to the present invention is: It contains a polymerizable compound and a photopolymerization initiator, The polymerizable compound includes a polyfunctional polymerizable compound, The photopolymerization initiator comprises (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide, The content of the (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is 3% by mass or more relative to the total amount of the ink composition. The content of the polyfunctional polymerizable compound is 20% by mass or more relative to the total amount of the ink composition. [Brief explanation of the drawing]

[0007] [Figure 1] A perspective view showing an example of a recording device. [Figure 2] Table 1 shows the composition and evaluation results of the radiation-curable inkjet ink compositions for each example. [Figure 3] Table 2 shows the composition and evaluation results of the radiation-curable inkjet ink compositions for each example and comparative example. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below. The embodiments described below are examples of the present invention. The present invention is not limited in any way to the embodiments described below, and includes various modifications that can be implemented without changing the gist of the present invention. Not all of the configurations described below are necessarily essential to the present invention.

[0009] In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. In this specification, "(meth)acrylic" means acrylic or methacrylic, and "(meth)acrylate" means acrylate or methacrylate.

[0010] 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 a photopolymerization initiator, wherein the polymerizable compound comprises a polyfunctional polymerizable compound, the photopolymerization initiator comprises (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide, the content of the (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is 3% by mass or more based on the total amount of the ink composition, and the content of the polyfunctional polymerizable compound is 20% by mass or more based on the total amount of the ink composition.

[0011] In a recorded matter obtained using a radiation-curable inkjet ink composition (hereinafter sometimes simply referred to as "ink composition" or "ink"), it is desirable that the cured coating film formed from the ink is excellent in abrasion resistance.

[0012] Further, as photopolymerization initiators used in radiation-curable inkjet ink compositions, acylphosphine oxide-based photopolymerization initiators are known, such as ethyl 2,4,6-trimethylbenzoylphenylphosphinate (TPO-L, also known as ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate) and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (819). It has now been found that inks containing ethyl 2,4,6-trimethylbenzoylphenylphosphinate have degraded storage stability when left to stand in high-temperature environments, and inks containing bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide have degraded storage stability when left to stand in low-temperature environments. It is presumed that this is because 2,4,6-trimethylbenzoylphenylphosphinic acid ethyl ester (TPO-L) is a liquid-type photopolymerization initiator, which contains more impurities than the powder-type, so its stability tends to deteriorate in high-temperature environments. In addition, it is presumed that bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (819) has a relatively large molecular weight and low solubility in ink, so it precipitates in low-temperature environments and its stability tends to deteriorate.

[0013] In contrast, the radiation-curable inkjet ink composition according to this embodiment contains a predetermined amount or more of (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide as a photopolymerization initiator, and also contains a predetermined amount or more of a polyfunctional polymerizable compound, thereby achieving both excellent abrasion resistance and excellent storage stability of the ink composition under high and low temperature environments.

[0014] The "radiation-curable inkjet ink composition" according to this embodiment is an ink composition that is ejected from an inkjet head by an inkjet method. Hereinafter, a radiation-curable ink composition will be described as one embodiment of the radiation-curable inkjet ink composition, but the composition according to this embodiment may be a composition other than an ink composition, for example, a composition used for 3D printing.

[0015] Furthermore, the radiation-curable inkjet ink composition according to this embodiment hardens when irradiated with radiation. Examples of radiation include ultraviolet rays, electron beams, infrared rays, visible light, X-rays, and active energy rays. As for the radiation, ultraviolet rays are preferred because radiation sources are readily available and widely used, and materials suitable for curing by ultraviolet radiation are readily available and widely used.

[0016] The following describes each component included in the radiation-curable inkjet ink composition according to this embodiment.

[0017] 1.1 Polymerizable compounds The radiation-curable inkjet ink composition according to this embodiment contains a polymerizable compound, the polymerizable compound contains a polyfunctional polymerizable compound, and the content of the polyfunctional polymerizable compound is 20% by mass or more of the total amount of the ink composition.

[0018] A "polymerizable compound" refers to a compound that contains polymerizable functional groups, and may be a monomer or a polymer. A "polymerizable functional group" refers to a group that participates in polymerization reactions.

[0019] Examples of polymerizable compounds include polyfunctional polymerizable compounds having multiple polymerizable functional groups and monofunctional polymerizable compounds having one polymerizable functional group. Each polymerizable compound may be used individually or in combination of two or more.

[0020] From the viewpoint of superior scratch resistance, the content of polymerizable compounds is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more, based on the total amount of the ink composition. Furthermore, there is no particular upper limit to the content of polymerizable compounds, but it is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less, based on the total amount of the ink composition.

[0021] 1.1.1 Polyfunctional polymerizable compounds Polymerizable compounds include polyfunctional polymerizable compounds. Examples of polyfunctional polymerizable compounds include bifunctional polymerizable compounds containing two polymerizable functional groups, and trifunctional or higher polymerizable compounds containing three or more polymerizable functional groups.

[0022] In the radiation-curable inkjet ink composition according to this embodiment, the content of the polyfunctional polymerizable compound is 20% by mass or more relative to the total amount of the ink composition, but is preferably 25% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, and particularly preferably 40% by mass or more. When the content of the polyfunctional polymerizable compound is within the above range, the curability and abrasion resistance of the ink tend to be superior. From the viewpoint of achieving superior flexibility in the cured ink, the upper limit of the polyfunctional polymerizable compound content is preferably 90% by mass or less, more preferably 70% by mass or less, even more preferably 60% by mass or less, and particularly preferably 50% by mass or less, relative to the total amount of the ink composition.

[0023] From a similar viewpoint, the content of the polyfunctional polymerizable compound is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and particularly preferably 30% by mass or more, based on the total amount of polymerizable compounds. The content of the polyfunctional polymerizable compound is preferably 90% by mass or less, more preferably 90% by mass or less, even more preferably 70% by mass or less, and particularly preferably 50% by mass or less, based on the total amount of polymerizable compounds.

[0024] 1.1.1.1 Bifunctional polymerizable compounds It is preferable that the polyfunctional polymerizable compound contains a difunctional polymerizable compound. When the polyfunctional polymerizable compound contains a difunctional polymerizable compound, the flexibility of the cured ink tends to be superior.

[0025] The bifunctional polymerizable compounds are not particularly limited, but examples include vinyl ether group-containing (meth)acrylates and bifunctional (meth)acrylates other than vinyl ether group-containing (meth)acrylates.

[0026] From the viewpoint of having superior curability and abrasion resistance of the ink, the content of the bifunctional polymerizable compound is preferably 20% by mass or more, and preferably 25% by mass or less, relative to the total amount of the ink composition. It is more preferable that the amount be above, even more preferable that it be 30% by mass or more, even more preferable that it be 35% by mass or more, and particularly preferable that it be 40% by mass or more. From the viewpoint of achieving superior flexibility in the cured ink, the upper limit of the content of the bifunctional polymerizable compound is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less, relative to the total amount of the ink composition. Since this tends to improve both the curability and abrasion resistance of the ink, as well as the flexibility of the cured ink, the content of the bifunctional polymerizable compound is preferably 20% by mass or more and 70% by mass or less of the total amount of the ink composition.

[0027] From a similar viewpoint, it is also preferable that the content of the bifunctional polymerizable compound relative to the total amount of polymerizable compounds be the same as the content of the polyfunctional polymerizable compound relative to the total amount of polymerizable compounds.

[0028] 1.1.1.1.1 Vinyl ether group-containing (meth)acrylates The bifunctional polymerizable compound preferably contains a polymerizable compound represented by the following formula (1) (vinyl ether group-containing (meth)acrylate). The inclusion of such a vinyl ether group-containing (meth)acrylate in the bifunctional polymerizable compound tends to reduce the viscosity of the ink composition and further improve ejection stability. Furthermore, the curability of the ink composition is improved, and this improvement in curability allows for faster recording speeds. Additionally, scratch resistance tends to be further improved. H2C=CR 1 -CO-OR 2 -O-CH=CH-R 3 ... (1) (In the formula, R 1 R is a hydrogen atom or a methyl group, 2 R is a divalent organic residue with 2 to 20 carbon atoms. 3 (This refers to a hydrogen atom or a monovalent organic residue with 1 to 11 carbon atoms.)

[0029] In the above equation (1), R 2 Examples of divalent organic residues having 2 to 20 carbon atoms represented by include linear, branched, or cyclic alkylene groups having 2 to 20 carbon atoms, optionally substituted alkylene groups having 2 to 20 carbon atoms, optionally substituted alkylene groups having oxygen atoms in the structure via ether and / or ester bonds, and optionally substituted divalent aromatic groups having 6 to 11 carbon atoms. Among these, alkylene groups having 2 to 6 carbon atoms such as ethylene, n-propylene, isopropylene, and butylene groups, and alkylene groups having 2 to 9 carbon atoms having oxygen atoms in the structure via ether bonds such as oxyethylene, oxy-n-propylene, oxyisopropylene, and oxybutylene groups are preferred. Furthermore, from the viewpoint of further reducing the viscosity of the composition and further improving the curability of the composition, R 2, a compound having a glycol ether chain in which the alkylene group is an alkylene group having 2 to 9 carbon atoms having an oxygen atom derived from an ether bond in a structure such as oxyethylene group, oxy n-propylene group, oxyisopropylene group, and oxybutylene group, is more preferred.

[0030] In the above formula (1), R 3 As the monovalent organic residue having 1 to 11 carbon atoms represented by , a linear, branched or cyclic optionally substituted alkyl group having 1 to 10 carbon atoms, and an optionally substituted aromatic group having 6 to 11 carbon atoms are preferred. Among these, alkyl groups having 1 to 2 carbon atoms which are methyl group or ethyl group, and aromatic groups having 6 to 8 carbon atoms such as phenyl group and benzyl group are suitably used.

[0031] When each of the above organic residues is an optionally substituted group, the substituents are classified into groups containing a carbon atom and groups not containing a carbon atom. First, when the substituent is a group containing a carbon atom, the carbon atom is counted in the number of carbon atoms of the organic residue. Examples of the group containing a carbon atom include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing a carbon atom include, but are not limited to, a hydroxyl group and a halo group.

[0032] Specific examples of the compound of formula (1) include, but are not particularly limited to, (meth)acrylic 2-vinyloxyethyl acid, 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, 3-vinyloxybutyl (meth)acrylate, 1-methyl-2-vinyl Xyxypropyl, 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-vinyloxymethylphenylmethyl (meth)acrylate, o-vinyloxymethylphenylmethyl (meth)acrylate, methacrylate 2-(2-vinyloxyethoxy)ethyl lylate, 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-(vinyloxyethoxyethoxy)ethyl meth)acrylate, 2-(vinyloxyisopropyl) (Poxy)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,Examples include 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, 2-(isopropenoxyethoxy)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. Of these specific examples, 2-(2-vinyloxyethoxy)ethyl acrylate is particularly preferred because it allows for an easy balance between the curability and viscosity of the composition. In this embodiment, 2-(2-vinyloxyethoxy)ethyl acrylate may also be referred to as VEEA.

[0033] The content of the polymerizable compound represented by formula (1) above is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, particularly preferably 25% by mass or more, and most particularly preferably 30% by mass or more, based on the total amount of the ink composition. When the content of the polymerizable compound represented by formula (1) above is within the above range, and especially when it is 10% by mass or more based on the total amount of the ink composition, the ink tends to have better scratch resistance, as well as curability and viscosity.

[0034] Furthermore, the content of the polymerizable compound represented by formula (1) above is preferably 70% by mass or less, more preferably 50% by mass or less, even more preferably 30% by mass or less, particularly preferably 20% by mass or less, and most particularly preferably 15% by mass or less, based on the total amount of the ink composition. When the content of the polymerizable compound represented by formula (1) above is within the above range, the cured ink They tend to have better flexibility in that regard.

[0035] 1.1.1.1.2 Difunctional (meth)acrylates The difunctional (meth)acrylate is not particularly limited as long as it is a difunctional (meth)acrylate other than the one in formula (1) above, but for example, 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 Examples include di(meth)acrylate, 1,4-butanediol 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 di(meth)acrylate of hydroxypivalate, and polytetramethylene glycol di(meth)acrylate.

[0036] Among these difunctional (meth)acrylates, it is preferable that the difunctional polymerizable compound contains one or more selected from 1,6-hexanediol diacrylate (1,6HDDA), dipropylene glycol diacrylate (DPGDA), and tripropylene glycol diacrylate (TPGDA). When the difunctional polymerizable compound contains these compounds, it tends to have superior abrasion resistance and ink curability.

[0037] From the viewpoint of having superior scratch resistance and ink curing properties, the content of the bifunctional (meth)acrylate is preferably 5% by mass or more, and more preferably 10% by mass or more, relative to the total amount of the ink composition. Furthermore, the content of the bifunctional (meth)acrylate is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and particularly preferably 15% by mass or less, based on the total amount of the ink composition.

[0038] 1.1.1.2 Polymerizable compounds with three or more functions It is preferable that the polyfunctional polymerizable compound contains three or more polymerizable compounds. When the polyfunctional polymerizable compound contains three or more polymerizable compounds, the ink tends to have superior curability.

[0039] Examples of polymerizable compounds with three or more functionalities include trimethylolpropane tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexaacrylate, 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.

[0040] Among these, it is preferable that the polymerizable compound with three or more functions contains one or more selected from trimethylolpropane triacrylate (TMPTA), ethylene oxide-modified trimethylolpropane triacrylate (EO-modified TMPTA), and dipentaerythritol hexaacrylate (DPHA). When this compound is included, the ink tends to have superior curability.

[0041] From the viewpoint of having superior curability of the ink, the content of a polymerizable compound with three or more functions is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on the total amount of the ink composition. Furthermore, the content of the trifunctional or higher polymerizable compound is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass or less, relative to the total amount of the ink composition.

[0042] 1.1.2 Monofunctional Polymerizable Compounds The polymerizable compound may contain monofunctional polymerizable compounds. While not particularly limited, examples of monofunctional polymerizable compounds include aromatic group-containing polymerizable compounds, nitrogen-containing monofunctional polymerizable compounds, hydroxyl group-containing monofunctional polymerizable compounds, hydrocarbon ring-containing monofunctional polymerizable compounds, ether ring-containing monofunctional polymerizable compounds, aliphatic group-containing polymerizable compounds, and urethane acrylates. Other monofunctional monomers may also be included as needed. While not particularly limited, other monofunctional monomers with polymerizable functional groups, particularly those having unsaturated double bonds between carbon atoms, are conventionally known and can be used.

[0043] The content of the monofunctional polymerizable compound is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less, based on the total amount of the ink composition. When the content of the monofunctional polymerizable compound is within the above range, it tends to suppress the increase in viscosity of the ink composition and result in excellent abrasion resistance. Furthermore, there is no particular lower limit to the content of the monofunctional polymerizable compound, but it is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and even more preferably 30% by mass or more, based on the total amount of the ink composition.

[0044] From a similar viewpoint, the content of monofunctional polymerizable compounds is preferably 80% by mass or less, preferably 60% by mass or less, and more preferably 50% by mass or less, relative to the total amount of polymerizable compounds. There is no particular lower limit to the content of monofunctional polymerizable compounds, but it is preferably 10% by mass or more, preferably 20% by mass or more, and more preferably 30% by mass or more, relative to the total amount of polymerizable compounds.

[0045] 1.1.2.1 Polymerizable compounds containing aromatic groups Monofunctional polymerizable compounds may contain aromatic group-containing polymerizable compounds. The aromatic group-containing polymerizable compounds are not particularly limited as long as they have aromatic groups, 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.

[0046] 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. By using such aromatic group-containing polymerizable compounds, the solubility of photopolymerization initiators that are solid at room temperature tends to be further improved, and the curability of the ink composition can be improved. In particular, the solubility tends to be good when using acyl phosphine oxide-based polymerization initiators or thioxanthone-based polymerization initiators that are solid at room temperature. Furthermore, by using phenoxyethyl (meth)acrylate, odor tends to be further reduced.

[0047] The content of the aromatic group-containing polymerizable compound is preferably 0 to 100% of the total amount of the ink composition. The content of the aromatic group-containing polymerizable compound is 50% by mass, more preferably 5 to 30% by mass, even more preferably 5 to 20% by mass, and particularly preferably 5 to 15% by mass. When the content of the aromatic group-containing polymerizable compound is within the above range, the viscosity of the ink composition tends to decrease further, and the abrasion resistance of the coating film tends to improve further.

[0048] 1.1.2.2 Nitrogen-containing monofunctional polymerizable compounds The monofunctional polymerizable compound may contain a nitrogen-containing monofunctional polymerizable compound. The nitrogen-containing monofunctional polymerizable compound is not particularly limited, but examples include nitrogen-containing monofunctional vinyl monomers such as 5-methyl-3-vinyloxazolidine-2-one (VMOX, also known as 3-vinyl-5-methyl-2-oxazolidinone), N-vinylcaprolactam, N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, and N-vinylpyrrolidone; nitrogen-containing monofunctional acrylate monomers such as acryloylmorpholin; and nitrogen-containing monofunctional acrylamide monomers such as (meth)acrylamide, N-hydroxymethyl(meth)acrylamide, diacetoneacrylamide, N,N-dimethyl(meth)acrylamide, and dimethylaminoethyl acrylate benzyl chloride quaternary salt. Nitrogen-containing monofunctional vinyl monomers are preferred, and 5-methyl-3-vinyloxazolidine-2-one (VMOX) is particularly preferred. Using such nitrogen-containing monofunctional polymerizable compounds tends to improve the adhesion and curing properties of printed materials. Furthermore, the use of 5-methyl-3-vinyloxazolidine-2-one (VMOX) is particularly preferable because, in addition to improving adhesion and curing properties, it also significantly reduces the viscosity of the ink.

[0049] When a nitrogen-containing monofunctional polymerizable compound is included, its content is preferably 5 to 30% by mass, and more preferably 10 to 20% by mass, relative to the total amount of the ink composition. When the nitrogen-containing monofunctional polymerizable compound content is within the above range, the adhesion and curing properties of the printed material tend to improve.

[0050] 1.1.2.3 Hydroxyl group-containing monofunctional polymerizable compounds The monofunctional polymerizable compound may include a hydroxyl group-containing monofunctional polymerizable compound. The hydroxyl group-containing monofunctional polymerizable compound is not particularly limited, but examples 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, and 2-(meth)acryloyloxy-2-hydroxypropyl phthalate, with 4-hydroxybutyl acrylate (4HBA) being particularly preferred. Using such a hydroxyl group-containing monofunctional polymerizable compound tends to improve the adhesion and curability of printed materials.

[0051] The content of the hydroxyl group-containing monofunctional polymerizable compound is preferably 0 to 40% by mass, more preferably 5 to 30% by mass, and even more preferably 10 to 20% by mass, based on the total amount of the ink composition. When the content of the hydroxyl group-containing monofunctional polymerizable compound is within the above range, the adhesion and curability of the printed material tend to improve.

[0052] 1.1.2.4 Hydrocarbon ring-containing monofunctional polymerizable compounds The monofunctional polymerizable compound may contain a hydrocarbon ring-containing monofunctional polymerizable compound, and more preferably contains a saturated hydrocarbon ring-containing monofunctional polymerizable compound. The hydrocarbon ring-containing monofunctional polymerizable compound is not particularly limited as long as it is a monomer having one or more saturated or unsaturated hydrocarbon rings that do not possess aromaticity. Examples include monomers having monocyclic hydrocarbon groups such as tert-butylcyclohexanol acrylate and 2-(meth)acrylic acid-1,4-dioxaspiro[4,5]decy-2-ylmethyl; and monomers having unsaturated polycyclic hydrocarbon groups such as dicyclopentenyl acrylate and dicyclopentenyloxyethyl acrylate. Examples include monomers having saturated polycyclic hydrocarbon groups, such as dicyclopentanyl acrylate and isobornyl acrylate (IBXA). Among these, monofunctional polymerizable compounds containing saturated hydrocarbon rings are preferred, and isobornyl acrylate (IBXA) is particularly preferred. By using such monofunctional polymerizable compounds containing hydrocarbon rings, especially monofunctional polymerizable compounds containing saturated hydrocarbon rings, the shrinkage rate during polymerization is reduced, and the adhesion of printed materials tends to improve.

[0053] When a hydrocarbon ring-containing monofunctional polymerizable compound is included, its content is preferably 5 to 30% by mass, and more preferably 10 to 20% by mass, relative to the total amount of the ink composition. When the content of the hydrocarbon ring-containing monofunctional polymerizable compound, particularly the content of saturated hydrocarbon ring-containing monofunctional polymerizable compound, is within the above range, the shrinkage rate during polymerization is further reduced, and the adhesion of printed materials tends to improve further.

[0054] 1.1.2.5 Monofunctional polymerizable compounds containing ether rings The monofunctional polymerizable compound may include an ether ring-containing monofunctional polymerizable compound. The ether ring-containing monofunctional polymerizable compound is not particularly limited as long as it contains a cyclic ether skeleton such as tetrahydrofuran or tetrahydropyran, but examples include cyclic trimethylolpropane formal acrylate (CTFA), cyclic trimethylolpropane formal methacrylate, tetrahydrofurfuryl acrylate (THFA), and tetrahydrofurfuryl methacrylate, among which cyclic trimethylolpropane formal acrylate (CTFA) and tetrahydrofurfuryl acrylate (THFA) are preferred. When such an ether ring-containing monofunctional polymerizable compound is used, odor tends to be reduced and the adhesion of printed materials tends to be improved.

[0055] When an ether ring-containing monofunctional polymerizable compound is included, its content is preferably 5 to 30% by mass, and more preferably 10 to 20% by mass, relative to the total amount of the ink composition. When the content of the ether ring-containing monofunctional polymerizable compound is within the above range, odor is further reduced, and the adhesion of printed materials tends to be further improved.

[0056] 1.1.2.6 Polymerizable compounds containing aliphatic groups Monofunctional polymerizable compounds may contain aliphatic group-containing polymerizable compounds. While there are no particular limitations on the aliphatic group-containing polymerizable compounds, examples include polymerizable compounds represented by the following formula (2). H2C=CR 4 -CO-OR 5 ... (2) (In formula (2), R 4 R represents a hydrogen atom or a methyl group. 5 (This represents a linear or branched aliphatic group with 4 to 20 carbon atoms.)

[0057] Such aliphatic group-containing polymerizable compounds are not particularly limited as long as they are saturated or unsaturated, linear or branched, and do not have a carbon ring. Examples include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, isononyl (meth)acrylate, isomiristyl (meth)acrylate, isostearyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, butoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate. Among these, saturated linear or branched aliphatic group-containing polymerizable compounds are preferred, and lauryl (meth)acrylate and isononyl (meth)acrylate are more preferred. Using such aliphatic group-containing polymerizable compounds tends to improve the adhesion of printed materials.

[0058] If an aliphatic group-containing polymerizable compound is included, its content is relative to the total amount of the ink composition. The content is preferably 5 to 30% by mass, and more preferably 10 to 20% by mass. When the content of the aliphatic group-containing polymerizable compound is within the above range, the adhesion of the printed material tends to improve.

[0059] 1.1.2.7 Urethane acrylate The monofunctional polymerizable compound may contain urethane acrylate. The urethane acrylate is not particularly limited as long as it is a (meth)acrylic acid ester having a urethane bond, and examples include (methyl carbamoyloxy)ethyl (meth)acrylate, (ethyl carbamoyloxy)ethyl (meth)acrylate, (propyl carbamoyloxy)ethyl (meth)acrylate, (butyl carbamoyloxy)ethyl (meth)acrylate, (methyl carbamoyloxy)ethoxyethyl (meth)acrylate, (ethyl carbamoyloxy)ethoxyethyl (meth)acrylate, (propyl carbamoyloxy)ethoxyethyl (meth)acrylate, and (butyl carbamoyloxy)ethoxyethyl (meth)acrylate. Using urethane acrylate tends to improve the adhesion of printed materials.

[0060] When urethane acrylate is included, its content is preferably 5 to 30% by mass, and more preferably 10 to 20% by mass, relative to the total amount of the ink composition. A urethane acrylate content within this range tends to improve the adhesion of printed materials.

[0061] 1.1.2.8 Other Monofunctional Polymerizable Compounds In addition to the above, monofunctional polymerizable compounds may also include, for example, 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.

[0062] The above monofunctional polymerizable compounds may be used individually or in combination of two or more.

[0063] Among these, the monofunctional polymerizable compound preferably contains at least one selected from phenoxyethyl acrylate (PEA), 5-methyl-3-vinyl oxazolidine-2-one (VMOX), 4-hydroxybutyl acrylate (4HBA), isobornyl acrylate (IBXA), and cyclic trimethylolpropane formal acrylate (CTFA). Including such a monofunctional polymerizable compound tends to further improve the adhesion and curability of printed materials.

[0064] 1.1.3 Oligomers Polymerizable compounds may or may not contain oligomers. An oligomer is a polymer composed of a polymerizable compound, and refers to a polymerizable compound having one or more polymerizable functional groups and a molecular weight exceeding 1000. Polymerizable compounds with a molecular weight of 1000 or less are considered monomers. When polymerizable compounds contain oligomers, viscosity may decrease further, and abrasion resistance and other properties may improve.

[0065] Such oligomers are not particularly limited, but examples include urethane acrylate oligomers with a repeating urethane structure, polyester acrylate oligomers with an ester repeating structure, epoxy acrylate oligomers with an epoxy repeating structure, and amine-modified oligomers.

[0066] Among these, urethane acrylate oligomers are preferred, and aliphatic urethane acrylate 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. Using such oligomers tends to further reduce viscosity and improve abrasion resistance, etc.

[0067] The radiation-curable inkjet ink composition according to this embodiment may contain amine-modified oligomers, but from the viewpoint of improving ejection stability without increasing the viscosity of the radiation-curable inkjet ink composition, it is preferable that it does not contain amine-modified oligomers or contains them in small amounts. If it does contain them, the content is preferably more than 0% by mass and 5% by mass or less, more preferably more than 0% by mass and less than 1% by mass, even more preferably more than 0% by mass and 0.9% or less, and especially preferably more than 0% by mass and 0.5% by mass or less, relative to the total amount of the ink composition.

[0068] An amine-modified oligomer is an oligomer having one or more amino groups in its molecule. An amine-modified oligomer may also contain one or more functional groups other than amino groups, and it is preferable that it contains two or more functional groups other than amino groups.

[0069] Examples of amine-modified oligomers include amine-modified (meth)acrylate oligomers.

[0070] The content of the amine-modified oligomer is preferably less than 5% by mass, more preferably less than 3% by mass, even more preferably less than 2% by mass, particularly preferably less than 1% by mass, even more preferably 0.9% by mass or less, especially preferably 0.5% by mass or less, and even more preferably 0% by mass or less, based on the total amount of the ink composition. By having an amine-modified oligomer content of less than 5% by mass, the curability of the radiation-curable inkjet ink composition can be improved without increasing its viscosity.

[0071] Furthermore, if an amine-modified oligomer is included, its content is greater than 0% by mass relative to the total amount of the ink composition, but may be 0.5% by mass or more, 1% by mass or more, or 2% by mass or more.

[0072] Examples of commercially available amine-modified oligomers include CN371 NS, CN373, CN374, CN383, CN386, CN550, CN551 (all product names from Sartomer), PHOTOMER® 4771, PHOTOMER 4250, PHOTOMER 4068 (all from IGM Resins), EBECRYL® 80, EBECRYL 7100, EBECRYL P115 (all from Daicel Ornex Co., Ltd.), and LAROMER® PO 77F, LAROMER PO 8996, LAROMER PO 94F (all from BASF).

[0073] Examples of commercially available oligomers include CN9893 (a bifunctional aliphatic urethane oligomer, manufactured by Sartomer).

[0074] When oligomers are used, their content 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. Having such a content within the above range may further reduce viscosity and improve abrasion resistance, etc.

[0075] When oligomers are used, their content is preferably 0.5 to 10% by mass, more preferably 0.9 to 5% by mass, and even more preferably 1 to 2% by mass, relative to the total amount of monomers in the ink composition. Having such a content within the above range results in a lower viscosity. This may further improve abrasion resistance and other properties.

[0076] 1.2 Photopolymerization Initiators The radiation-curable inkjet ink composition according to this embodiment contains a photopolymerization initiator, the photopolymerization initiator contains (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide, and the content of (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is 3% by mass or more with respect to the total amount of the ink composition.

[0077] Photopolymerization initiators are compounds that generate active species when irradiated with radiation.

[0078] In the radiation-curable inkjet ink composition according to this embodiment, the content of the photopolymerization initiator is 3% by mass or more relative to the total amount of the ink composition, but preferably 5% by mass or more, more preferably 7% by mass or more, even more preferably 9% by mass or more, and particularly preferably 10% by mass or more. The upper limit of the photopolymerization initiator content is not particularly limited, but it is preferably 20% by mass or less, more preferably 17% by mass or less, even more preferably 15% by mass or less, and particularly preferably 12% by mass or less, relative to the total amount of the ink composition.

[0079] 1.2.1 TMO The photopolymerization initiator contains (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide (TMO). (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is a compound represented by the following chemical formula (CAS 270586-78-2). By including a predetermined amount or more of (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide in the photopolymerization initiator, the storage stability of the ink composition in high and low temperature environments can be improved.

[0080] [ka]

[0081] In the radiation-curable inkjet ink composition according to this embodiment, the content of (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is 3% by mass or more relative to the total amount of the ink composition, but preferably 5% by mass or more, more preferably 7% by mass or more, even more preferably 9% by mass or more, and particularly preferably 10% by mass or more. When the content of (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is within the above range, the storage stability of the ink composition under high and low temperature environments tends to be superior. The upper limit of the content of (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is not particularly limited, but it is preferable to limit it to 20% by mass or less relative to the total amount of the ink composition. More preferably 17% by mass or less, even more preferably 15% by mass or less, and particularly preferably 12% by mass or less.

[0082] The content of (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is preferably 30% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more, relative to the total amount of photopolymerization initiator.

[0083] 1.2.2 Other Photopolymerization Initiators The photopolymerization initiator may contain other photopolymerization initiators besides (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide (TMO). Examples of other photopolymerization initiators include known polymerization initiators such as acylphosphine oxide-based polymerization initiators (excluding TMO), 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. The photopolymerization initiator may be used alone or in combination of two or more types.

[0084] Acylphosphine oxide polymerization initiators are not particularly limited, but examples include ethyl 2,4,6-trimethylbenzoylphenylphosphinate (TPO-L), 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (819), and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0085] Examples of commercially available acylphosphine oxide polymerization initiators include Omnirad TPO-L (2,4,6-trimethylbenzoylphenylphosphinate ethyl), Omnirad 819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide), Omnirad TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide) (all trade names of IGM Resins BV), and 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) (all trade names of Ciba Specialty Chemicals).

[0086] Thioxanthone-based polymerization initiators are not particularly limited, but examples include thioxanthone, 2-methylthioxanthone, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, and 2,4-diethylthioxanthone, 2,4-diethylthioxanthene-9-one (also known as 2,4-diethyl-9H-thioxanthene-9-one), diesters of carboxymethoxythioxanthone and polytetramethylene glycol, and 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)])oxymethylpropane).

[0087] Furthermore, a thioxanthone-based polymerization initiator may be used in combination with a photopolymerization initiator as a sensitizer. The sensitizer content 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, based on the total amount of the ink composition. Examples of commercially available sensitizers include Speedcure DETX (manufactured by Lambson, 2,4-diethylthioxanthene-9-one).

[0088] There are no particular limitations on alkylphenone polymerization initiators, but examples 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.

[0089] Benzophenone-based polymerization initiators are not particularly limited, but examples include 4,4'-bis(diethylamino)benzophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, and 4,4'-diaminobenzophenone.

[0090] If the photopolymerization initiator contains other photopolymerization initiators, the content of the other photopolymerization initiators is preferably 10% by mass or less, more preferably 7% by mass or less, even more preferably 5% by mass or less, and particularly preferably 3% by mass or less, based on the total amount of the ink composition. The lower limit is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1.0% by mass or more, based on the total amount of the ink composition. Even if the photopolymerization initiator contains something other than (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide (TMO), the above-mentioned content tends to result in excellent storage stability of the ink composition under high and low temperature environments.

[0091] 1.3 Polymerization inhibitors The radiation-curable inkjet ink composition according to this embodiment may contain a polymerization inhibitor to further improve the storage stability of the ink composition. The polymerization inhibitor may be used alone or in combination of two or more types.

[0092] Polymerization inhibitors include, but are not limited to, bis(2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) sebacate (BisTEMPO), 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl (OH-TEMPO), p-methoxyphenol, hydroquinone monomethyl ether (MEHQ), 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), hindered amine compounds, and others.

[0093] In addition, commercially available polymerization inhibitors include ADEKA LA-7RD (2,2,6,6-tetramethyl-4-hydroxypiperidine-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), LA-87 (all are trade names of ADEKA), 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), TINUVIN 123 (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl), and 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 BASF product names), FA- Examples include 711HM, FA-712HM (2,2,6,6-tetramethylpiperidinyl methacrylate, a product name manufactured by Hitachi Chemical Co., Ltd.), and UV-10 (all product names manufactured by Seiko Chemical Co., Ltd.).

[0094] The polymerization inhibitor preferably includes a TEMPO(2,2,6,6-tetramethylpiperidine-N-oxyl)-based polymerization inhibitor. Because TEMPO has free radicals that are stable at room temperature, it has high radical scavenging ability and tends to significantly improve the storage stability of the ink composition.

[0095] Examples of TEMPO-based polymerization inhibitors include 4-benzoyloxyTEMPO (4-benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl free radical), sebacate BisTEMPO (bis(2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) sebacate), 4-MCTEMPO (4-cyclohexylcarbonyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl free radical), and 4-AcTEMPO (4-acetyloxy-2,2,6,6- Examples include tetramethylpiperidine-1-oxyl free radical, EGG-TEMPO (a mixture of 4-[2-hydroxypropoxy-3-(2-hydroxyethoxy)]-TEMPO and 4-[3-hydroxypropoxy-2-(2-hydroxyethoxy)]-TEMPO), G-TEMPO (4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl free radical), OH-TEMPO (2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl), etc.

[0096] In particular, it is more preferable that the polymerization inhibitor contains one or more compounds selected from bis(2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) sebacate and 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl. When the polymerization inhibitor contains these compounds, the storage stability of the ink composition tends to be improved more effectively.

[0097] The polymerization inhibitor content 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, based on the total amount of the ink composition.

[0098] Furthermore, the content of the TEMPO-based polymerization inhibitor is preferably 0.001% by mass or more and 1.0% by mass or less, more preferably 0.01% by mass or more and 0.5% by mass or less, and even more preferably 0.02% by mass or more and 0.1% by mass or less, relative to the total amount of the ink composition.

[0099] 1.4 Fluorescent whitening agents The radiation-curable inkjet ink composition according to this embodiment may contain a fluorescent whitening agent. The inclusion of a fluorescent whitening agent may suppress yellowing of the cured product. Furthermore, the inclusion of a fluorescent whitening agent may improve curability and enhance the whiteness of the cured product. Yellowing of the cured product can be confirmed, for example, using a general-purpose colorimeter.

[0100] Fluorescent whitening agents include, but are not limited to, naphthalene-benzoxazoyl derivatives such as 1,4-bis-(2-benzoxazoyl)naphthalene, thiophene-benzoxazoyl derivatives such as 2,5-thiophene-diylbis(5-tert-butyl-1,3-benzoxazole), stilbene-benzoxazoyl derivatives, coumarin derivatives, styrene-biphenyl derivatives, pyrazolone derivatives, stilbene derivatives, styryl derivatives of benzene and biphenyl, bis(benzazole-2-yl) derivatives, carbostyryl, naphthalimide, dibenzothiophene-5,5'-dioxide derivatives, pyrene derivatives, and pyridotol Reazol is one example.

[0101] Examples of commercially available fluorescent whitening agents include Telalux OB, Telalux KCB, Telalux KS, Telalux KS-N (all manufactured by Clariant Japan), and Tinopal OB-CO and Tinopal NFW LIQ (both manufactured by BASF).

[0102] Furthermore, it is preferable to use fluorescent whitening agents in combination with acyl phosphine oxide polymerization initiators (including TMO). This tends to result in even better curability.

[0103] When a fluorescent whitening agent is used, its content is preferably 0.01% by mass or more and 1.0% by mass or less, and more preferably 0.10% by mass or more and 0.50% by mass or less, relative to the total amount of the ink composition.

[0104] 1.5 Colorants The radiation-curable inkjet ink composition according to this embodiment may further contain a colorant. The colorant can be at least one of a pigment and a dye.

[0105] The total content of the colorants is preferably 0.1% by mass or more and 10.0% by mass or less, and more preferably 0.5% by mass or more and 5.0% by mass or less, relative to the total amount of the ink composition. The radiation-curable inkjet ink composition according to this embodiment may also be a clear ink that does not contain colorants, or contains colorants to an extent not intended for coloring (e.g., 0.1% by mass or less).

[0106] When using pigments, a pigment dispersion may be prepared in advance and used in the radiation-curable inkjet ink composition. The pigment dispersion may contain polymerizable compounds, dispersants for dispersing the pigment (described later), etc.

[0107] 1.5.1 Pigments When pigments are used as colorants, the weather resistance of the ink composition can sometimes be improved. Examples of pigments include inorganic pigments and organic pigments.

[0108] 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), as well as iron oxide, titanium oxide, zinc oxide, silica, and the like.

[0109] Examples of carbon black include Mitsubishi Chemical Corporation's No. 2300, 900, MCF88, No. 20B, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, and No. 2200B. Examples of Degussa's Color Black FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Pritex 35, U, V, 140U, and Special Black 6, 5, 4A, 4, and 250. Examples of Columbia Carbon's Conductex SC, Raven 1255, 5750, 5250, 5000, 3500, 1255, and 700. Examples include Cabot's Regal 400R, 330R, 660R, Mogul L, Monarch 700, 800, 880, 900, 1000, 1100, 1300, 1400, and Elftex 12.

[0110] Organic pigments include quinacridone pigments, quinacridone quinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, anthanceron pigments, and Examples include danthron pigments, flavanthron pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimimidazolone pigments, isoindolinone pigments, azomethine pigments, or azo pigments.

[0111] Specific examples of organic pigments include the following:

[0112] Examples of cyan pigments include CI Pigment Blue 1, 2, 3, 15:3, 15:4, 15:34, 16, 22, 60, etc.; CI Bat Blue 4, 60, etc. Preferably, one or more mixtures selected from the group consisting of CI Pigment Blue 15:3, 15:4, and 60 can be exemplified.

[0113] Examples of magenta pigments include CI Pigment Red 5, 7, 12, 48, 48, 57, 57:1, 112, 122, 123, 168, 184, 202, CI Pigment Violet 19, and the like. Preferably, one or more mixtures selected from the group consisting of CI Pigment Red 122, 202, and 209, and CI Pigment Violet 19 can be used as examples. Solid solutions of the above pigments may also be used.

[0114] 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, 185, etc. Preferably, one or more mixtures selected from the group consisting of CI Pigment Yellow 74, 109, 110, 128, 138, 155, and 180 can be exemplified.

[0115] Examples of orange pigments include CI Pigment Orange 36 or 43, or mixtures thereof. Examples of green pigments include CI Pigment Green 7 or 36, or mixtures thereof.

[0116] Furthermore, lustrous pigments may be used, and are not particularly limited as long as they exhibit lustrous properties when attached to a medium. Examples include metal particles of one or more alloys (also called metallic pigments) selected from the group consisting of aluminum, silver, gold, platinum, nickel, chromium, tin, zinc, indium, titanium, and copper, or pearl pigments having a pearlescent luster. Typical examples of pearl pigments include titanium dioxide-coated mica, fish scale foil, and bismuth acid chloride, which are pigments that have a pearlescent or interference luster. In addition, lustrous pigments may be subjected to surface treatment to suppress their reaction with water.

[0117] White pigments may also be used, such as metal oxides, barium sulfate, and calcium carbonate. Examples of metal oxides include titanium dioxide, zinc oxide, silica, alumina, and magnesium oxide. Furthermore, particles with a hollow structure may be used as the white pigment.

[0118] The above pigments may be used individually or in combination of two or more. From the viewpoint of storage stability, such as lightfastness, weather resistance, and gas resistance, organic pigments are preferable.

[0119] The radiation-curable inkjet ink composition according to this embodiment is preferably a black ink or a yellow ink, from the viewpoint of making the present invention more effective. If the ink composition is a black ink, it is preferable to include carbon black as a colorant. If the ink composition is a yellow ink, it is preferable to include a yellow pigment as a colorant. Colorants used in black or yellow ink, especially carbon black and yellow Pigments are susceptible to the influence of functional groups on the surface of the colorant, making it more difficult to maintain dispersion stability compared to other colorants. Liquid photopolymerization initiators such as TPO-L contain many impurities, and these impurities react with the functional groups on the surface of the colorant, resulting in poor storage stability of the ink composition in high-temperature environments. In contrast, the radiation-curable inkjet ink composition according to this embodiment contains TMO, so even if it is a black or yellow ink, the storage stability of the ink composition in high-temperature environments can be improved.

[0120] The volume-average particle size (D50) of the pigment, as measured by dynamic light scattering, is 20 nm to 300 nm, more preferably 30 nm to 200 nm, and even more preferably 40 nm to 100 nm.

[0121] The volume-average particle size can be measured, for example, using a NanoTrac series particle distribution analyzer manufactured by MicroTracBel. Methods for adjusting the volume-average particle size include, for example, adjusting the degree of grinding 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.

[0122] If the radiation-curable inkjet ink composition contains a pigment, a dispersant may be further included to improve pigment dispersibility. The dispersant may be used alone or in combination of two or more types.

[0123] The dispersant is not particularly limited, but examples include dispersants commonly used to prepare pigment dispersions, such as polymer dispersants. Specific examples include those mainly composed of one or more of the following: 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.

[0124] Commercially available polymer dispersants include the Ajisper series from Ajinomoto Fine Techno, the Solspers series (Solsperse 36000, etc.) available from Avecia and Noveon, the Disparbic series from BYK Additives & Instruments, and the Disparon series from Kusumoto Chemical Co., Ltd.

[0125] When a dispersant is used, its content is preferably 0.01% by mass or more and 5.0% by mass or less, more preferably 0.1% by mass or more and 4.0% by mass or less, even more preferably 0.5% by mass or more and 3.0% by mass or less, and particularly preferably 1.0% by mass or more and 2.0% by mass or less, relative to the total amount of the ink composition.

[0126] 1.5.2 Dyes Dyes may be used as colorants. The dyes used are not particularly limited and include acid dyes, direct dyes, reactive dyes, and basic dyes. Dyes may be used individually or in combination of two or more.

[0127] There are no particular restrictions on the dyes used, but for example, 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, 142, 144, 173; CI Dye Examples include Rectred 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.

[0128] 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 include acetylene glycol-based surfactants, fluorine-based surfactants, and silicone-based surfactants.

[0129] The acetylene glycol-based surfactant is not particularly limited, but examples include 2,4,7,9-tetramethyl-5-decine-4,7-diol and alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decine-4,7-diol, as well as 2,4-dimethyl-5-decine-4-ol and alkylene oxide adducts of 2,4-dimethyl-5-decine-4-ol.

[0130] The fluorine-based surfactant is not particularly limited, but examples include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphate esters, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, and perfluoroalkylamine oxide compounds.

[0131] Examples of silicone-based surfactants include polysiloxane compounds, polyester-modified silicones, or polyether-modified organosiloxanes. Examples of polyester-modified silicones include BYK-347, 348, 3510, and 3530 (all manufactured by BYK Additives & Instruments), while examples of polyether-modified silicones include BYK-3570 and BYK-UV3500 (manufactured by BYK Additives & Instruments).

[0132] The surfactant content 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 surfactant content is within this range, the wettability of the ink composition tends to improve.

[0133] 1.7 Other Ingredients The radiation-curable inkjet ink composition according to this embodiment may further contain various additives as needed, such as chain transfer agents, crosslinking agents, antioxidants, preservatives, flame retardants, antistatic agents, and organic or inorganic fillers.

[0134] The content of such additives is not particularly limited, but is preferably 0.01% to 20% by mass, more preferably 0.1% to 15% by mass, even more preferably 1% to 10% by mass, and particularly preferably 2% to 5% by mass.

[0135] 1.8 Physical Properties The viscosity of the radiation-curable inkjet ink composition according to this embodiment at 20°C is preferably less than 30 mPa·s, more preferably less than 20 mPa·s, and even more preferably less than 10 mPa·s. Since the viscosity of the ink composition at 20°C is within the above range, an appropriate amount of the ink composition is ejected from the nozzle, further reducing the deviation and scattering of the ink composition, making it suitable for use in inkjet recording devices.

[0136] For viscosity measurement, for example, a viscoelasticity tester MCR-300 (manufactured by Pysica) is used. In a 20°C environment, the viscosity can be measured by increasing the shear rate from 10 to 1000 and reading the viscosity at a shear rate of 200.

[0137] The surface tension of the radiation-curable inkjet ink composition according to this embodiment at 20°C is preferably 20 mN / m to 40 mN / m. 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 the liquid-repellent treated nozzle surface. As a result, the ink composition is ejected normally and in the appropriate amount from the nozzle, and flight deviation and scattering of the ink composition can be further reduced, making it suitable for use in inkjet recording devices.

[0138] Surface tension can be measured, for example, by using an automatic surface tension meter CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) to check the surface tension when a platinum plate is wetted with a radiation-curable inkjet ink composition in an environment of 20°C.

[0139] 1.9 Manufacturing method The production (preparation) of a radiation-curable inkjet ink composition can be carried out, for example, by mixing each component contained in the ink composition and stirring so that the components are sufficiently and uniformly mixed. In this embodiment, it is preferable that the preparation of the radiation-curable inkjet ink composition includes a step of subjecting the mixture, which is a mixture of at least a portion of the polymerizable compound, to at least one of ultrasonic treatment and heating treatment during the preparation process. This can reduce the amount of dissolved oxygen in the prepared ink composition, and in some cases, a radiation-curable inkjet ink composition with excellent ejection stability and storage stability can be obtained. The above mixture only needs to contain at least the above components, and may further contain other components contained in the radiation-curable inkjet ink composition, or it may contain all the components contained in the radiation-curable inkjet ink composition. The polymerizable compound contained in the mixture only needs to be at least a portion of the polymerizable compound contained in the radiation-curable inkjet ink composition.

[0140] 2. Recording device A recording device that can preferably use the above-mentioned radiation-curable inkjet ink composition will be described.

[0141] The recording device according to this embodiment preferably includes an inkjet head that ejects the above-described radiation-curable inkjet ink composition and the above-described radiation-curable inkjet ink composition. Furthermore, the recording device according to this embodiment may also include a radiation source that irradiates the ink composition with radiation.

[0142] As an example of a recording device, Figure 1 shows a perspective view of a serial printer. As shown in Figure 1, the serial printer 20 comprises a transport unit 220 and a recording unit 230. The transport unit 220 transports the recording medium F supplied to the serial printer to the recording unit 230 and discharges the recorded recording medium outside the serial printer after recording. Specifically, the transport unit 220 has feed rollers and transports the fed recording medium F in the sub-scanning direction T2.

[0143] Furthermore, the recording unit 230 includes an inkjet head 231 that ejects the above-mentioned radiation-curable inkjet ink composition onto the recording medium F sent from the transport unit 220, a radiation source 232 that irradiates the attached ink composition with radiation, a carriage 234 on which these are mounted, and a carriage movement mechanism 235 that moves the carriage 234 in the main scanning directions S1 and S2 of the recording medium F.

[0144] In the case of a serial printer, the inkjet head 231 is equipped with a head that is shorter than the width of the recording medium, and the head moves and recording is performed in one or more passes. In a serial printer, a head 231 and a radiation source 232 are mounted on a carriage 234 that moves in a predetermined direction, and the head moves along with the movement of the carriage, ejecting the ink composition onto the recording medium. This allows recording to be performed in one or more passes. A pass is also called a main scan. A sub-scan to transport the recording medium may be performed between passes. In other words, main scans and sub-scans are performed alternately.

[0145] Although Figure 1 shows a configuration in which the radiation source is mounted on a carriage, the system is not limited to this configuration, and the radiation source may be mounted on a carriage or not.

[0146] Furthermore, the recording device of this embodiment is not limited to the serial printer described above, but may also be the line printer described above.

[0147] 3. Examples 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 refers to mass.

[0148] 3.1 Preparation of radiation-curable inkjet ink composition First, the pigment, dispersant, and a portion of the polymerizable compound (base monomer) are weighed and placed in a tank for pigment dispersion. A ceramic bead mill with a diameter of 1 mm is then placed in the tank and stirred to obtain a pigment dispersion in which the pigment is dispersed in the base monomer. Next, the remaining polymerizable compound, photopolymerization initiator, sensitizer, fluorescent whitening agent, surfactant, and polymerization inhibitor are placed in a stainless steel container, a mixing tank, to obtain the composition shown in Table 1 (Figure 2) or Table 2 (Figure 3). After mixing and stirring until completely dissolved, the pigment dispersion obtained above is added, and the mixture is further mixed and stirred at room temperature for 1 hour. Finally, the mixture is filtered through a 5 μm membrane filter to obtain the radiation-curable inkjet ink composition for each example. The numerical values ​​of each component shown in each example in the table represent mass percent.

[0149] Further explanation is provided regarding the information in Tables 1 and 2. [Dispersion] PY155: CI Pigment Yellow 155 PB15:4 :CI Pigment Blue 15:4 Dispersant: Product name "Solsperse32000", manufactured by Lubrizol Japan, polymer dispersant, amine value 35 [Monofunctional polymerizable compounds] PEA: Phenoxyethyl acrylate, product name "Viscoat #192", manufactured by Osaka Organic Chemical Industry Co., Ltd. IBXA: Isobornyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. 4HBA: 4-Hydroxybutyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. VMOX: 5-methyl-3-vinyloxazolidine-2-one, manufactured by BASF Japan. ACMO: Acryloylmorpholin, manufactured by Tokyo Chemical Industry Co., Ltd. CTFA: Cyclic trimethylolpropane formal acrylate, trade name "Viscoat #200", manufactured by Osaka Organic Chemical Industry Co., Ltd. [Polyfunctional polymerizable compound] VEEA: 2-(2-vinyloxyethoxy)ethyl acrylate, manufactured by Nippon Shokubai Co., Ltd. DPGDA: Dipropylene glycol diacrylate, trade name "SR508NS", manufactured by Sartomer. 1,6HDDA: 1,6-Hexanediol diacrylate, trade name "SR238NS", manufactured by Sartomer Corporation. PETTA: Pentaerythritol triacrylate, trade name "EM235", manufactured by ETERNAL MATERIALS. DPHA: Dipentaerythritol hexaacrylate, trade name "A-DPH", manufactured by Shin-Nakamura Chemical Co., Ltd. CN9893:2-functional aliphatic urethane oligomer, trade name "CN9893 NS", manufactured by Sartomer. [Photopolymerization initiator] TMO: (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide, manufactured by Merck. Omnirad 819: IGM brand name, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide Omnirad TPO-L: IGM brand name, ethylphenyl (2,4,6-trimethylbenzoyl) phosphinate [Sensitizer] DETX: Product name "Speedcure DETX", manufactured by LAMBSON, 2,4-diethylthioxanthene-9-one [Fluorescent whitening agent] Telalux KCB: 1,4-bis-(2-benzoxazoyl)naphthalene, manufactured by Clariant Japan Co., Ltd. [Surfactants] BYK-UV3500: Product name manufactured by BYK Additives & Instruments. [Polymerization inhibitors] LA-7RD: Product name "ADEKA Stab LA-7RD", manufactured by ADEKA Corporation, 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl UV-10: BisTEMPO sebacate (bis(2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) sebacate, manufactured by Seiko Chemical Co., Ltd.) MEHQ: p-Methoxyphenol, manufactured by Kanto Chemical Co., Ltd.

[0150] 3.2 Evaluation Method 3.2.1 Viscosity The viscosity of each radiation-curable inkjet ink composition obtained above is measured using a rotational viscometer (product name "Rheometer MCR-301," manufactured by Anton Paar) at 20°C. The evaluation criteria are as follows. (Evaluation Criteria) AA: Viscosity less than 10 mPa·s A: Viscosity of 10 mPa·s or more, and less than 15 mPa·s. B: Viscosity of 15 mPa·s or more, and less than 20 mPa·s. C: Viscosity of 20 mPa·s or higher

[0151] 3.2.2 High temperature storage stability The radiation-curable inkjet ink compositions obtained from each example above are filled into glass bottles and stored at 60°C for 21 days. The viscosity at 20°C before and after storage is measured in the same manner as above to confirm the change in viscosity before and after storage. The evaluation criteria are shown below. (Evaluation Criteria) A: Thickening rate is less than 5% B: Thickening rate of 5% or more, but less than 10% C: Thickness of 10% or more

[0152] 3.2.3 Low temperature storage stability The radiation-curable inkjet ink compositions obtained from each example above were filled into glass bottles and stored at -20°C for 4 days. The ink compositions before and after storage were then filtered through a metal mesh filter. The sample is filtered, and the filter is visually inspected. The evaluation criteria are as follows. (Evaluation Criteria) A: No foreign matter was detected. B: The presence of foreign matter is observed.

[0153] 3.2.4 Curability A cotton swab-weighted tackiness evaluation will be performed. Specifically, the radiation-curable inkjet ink compositions obtained above will be applied to a polyvinyl chloride media using a bar coater to a coating thickness of 10 μm, and ultraviolet light will be irradiated at a predetermined irradiation intensity at a speed of 0.04 sec / cm. At that time, an LED with a peak wavelength of 395 nm will be used as the light source. The surface of the coating film will then be rubbed with a cotton swab, and the curability will be evaluated based on the irradiation energy at which the cotton swab does not become discolored. The evaluation criteria are as follows. (Evaluation Criteria) A: Irradiation energy is 200 mJ / cm 2 less than B: Irradiation energy is 200 mJ / cm 2 More than 350mJ / cm 2 less than C: Irradiation energy is 350 mJ / cm² 2 More than 500mJ / cm 2 less than

[0154] 3.2.5 Scratch resistance Using a bar coater, the radiation-curable inkjet ink compositions according to each example obtained above are applied to a polyvinyl chloride film (JT5829R, manufactured by MACtac) to a thickness of 10 μm. Then, a metal halide lamp (manufactured by I-Graphics) is used to apply 400 mJ / cm² of radiation. 2 The coating is hardened using energy to form a film. Then, in accordance with JIS K5701 (ISO 11628) (which specifies methods for testing inks, color samples, and printed materials used in lithographic printing), the abrasion resistance is evaluated using a JSPS-type friction fastness tester (manufactured by TESTER SANGYO CO., LTD.). Specifically, a metal cloth is placed on the surface of the coating, a load of 500g is applied, and it is rubbed 50 times. The peeling of the hardened surface of the recorded material after rubbing is then visually compared. The evaluation criteria are as follows. (Evaluation Criteria) A: No stains on the cloth, and no peeling or scratches on the image surface are visible. B: At least one of the following is visible: dirt on the cloth, or peeling or scratches on the image surface. (The underlying surface is not visible.) C: The image surface has significant scratches and peeling, and the underlying material is visible in some areas.

[0155] 3.2.6 Bending Test Using a bar coater, the radiation-curable inkjet ink compositions according to each example obtained above are applied to a polyvinyl chloride film (JT5829R, manufactured by MACtac) to a thickness of 10 μm. Then, a metal halide lamp (manufactured by I-Graphics) is used to apply 400 mJ / cm² of radiation. 2 The film is hardened using energy to form a coating. The release paper is peeled off the PVC film with the above coating, and test specimens are prepared by cutting them into strips 1 cm wide and 8 cm long. For each test specimen, the elongation as a measure of stretchability is measured using a tensile testing machine (TENSILON, manufactured by ORIENTEC). The elongation is defined as the value at which a crack occurs when pulled at 5 mm / min. This value is calculated using the formula {(length at crack - length before stretching) / length before stretching × 100}. The evaluation criteria are shown below. (Evaluation Criteria) A: No delamination is observed, or delamination of the cured film is observed in less than 10% of the grid. B: Peeling of the cured film is observed in 10% to less than 35% of the grid. C: Peeling of the hardened film is observed in more than 35% of the grid.

[0156] 3.3 Evaluation Results The evaluation results are shown in Tables 1 and 2.

[0157] Based on the evaluation results in Tables 1 and 2, radiation-curable inkjet ink compositions according to each example, comprising a polymerizable compound and a photopolymerization initiator, wherein the polymerizable compound comprises a polyfunctional polymerizable compound, the photopolymerization initiator comprises (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide, the content of (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is 3% by mass or more of the total amount of the ink composition, and the content of the polyfunctional polymerizable compound is 20% by mass or more of the total amount of the ink composition, can achieve both excellent abrasion resistance and excellent storage stability of the ink composition under high and low temperature environments.

[0158] In contrast, the radiation-curable inkjet ink compositions of each comparative example that do not satisfy the above configuration are inferior in at least one of the following: abrasion resistance, storage stability of the ink composition in high-temperature environments, and storage stability of the ink composition in low-temperature environments.

[0159] The following conclusions can be drawn from the embodiments described above.

[0160] One embodiment of a radiation-curable inkjet ink composition is: It contains a polymerizable compound and a photopolymerization initiator, The polymerizable compound includes a polyfunctional polymerizable compound, The photopolymerization initiator comprises (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide, The content of the (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is 3% by mass or more relative to the total amount of the ink composition. The content of the polyfunctional polymerizable compound is 20% by mass or more relative to the total amount of the ink composition.

[0161] In one embodiment of the above radiation-curable inkjet ink composition, The polyfunctional polymerizable compound may also contain a difunctional polymerizable compound.

[0162] In any embodiment of the above radiation-curable inkjet ink composition, The aforementioned bifunctional polymerizable compound includes a polymerizable compound represented by the following formula (1): The content of the polymerizable compound represented by formula (1) may be 10% by mass or more relative to the total amount of the ink composition. H2C=CR 1 -CO-OR 2 -O-CH=CH-R 3 ... (1) (In the formula, R 1 R is a hydrogen atom or a methyl group, 2 R is a divalent organic residue with 2 to 20 carbon atoms.3 (This refers to a hydrogen atom or a monovalent organic residue with 1 to 11 carbon atoms.)

[0163] In one embodiment of the above radiation-curable inkjet ink composition, The content of the polymerizable compound represented by formula (1) may be 70% by mass or less relative to the total amount of the ink composition.

[0164] In any embodiment of the above radiation-curable inkjet ink composition, The content of the aforementioned bifunctional polymerizable compound may be 20% by mass or more and 70% by mass or less based on the total amount of the ink composition.

[0165] In any embodiment of the above radiation-curable inkjet ink composition, The aforementioned bifunctional polymerizable compound may contain one or more selected from 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, and tripropylene glycol diacrylate.

[0166] In any embodiment of the above radiation-curable inkjet ink composition, The polyfunctional polymerizable compound comprises a polymerizable compound with three or more functions, The aforementioned three- or more-functional polymerizable compound may contain one or more selected from trimethylolpropane triacrylate, ethylene oxide-modified trimethylolpropane triacrylate, and dipentaerythritol hexaacrylate.

[0167] In any embodiment of the above radiation-curable inkjet ink composition, The polymerizable compound includes a monofunctional polymerizable compound, The monofunctional polymerizable compound may also contain a nitrogen-containing monofunctional polymerizable compound.

[0168] In any embodiment of the above radiation-curable inkjet ink composition, The polymerizable compound includes a monofunctional polymerizable compound, The monofunctional polymerizable compound may also contain a hydroxyl group-containing monofunctional polymerizable compound.

[0169] In any embodiment of the above radiation-curable inkjet ink composition, The polymerizable compound includes a monofunctional polymerizable compound, The monofunctional polymerizable compound may include a saturated hydrocarbon ring-containing monofunctional polymerizable compound.

[0170] In any embodiment of the above radiation-curable inkjet ink composition, The polymerizable compound includes a monofunctional polymerizable compound, The monofunctional polymerizable compound may also include an ether ring-containing monofunctional polymerizable compound.

[0171] In any embodiment of the above radiation-curable inkjet ink composition, Contains polymerization inhibitors, The polymerization inhibitor may contain one or more selected from bis(2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) sebacate and 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl.

[0172] In any embodiment of the above radiation-curable inkjet ink composition, It may contain a fluorescent whitening agent.

[0173] In any embodiment of the above radiation-curable inkjet ink composition, Black or yellow ink may be used.

[0174] The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the present invention includes configurations that are substantially identical to the configurations described in the embodiments, for example, configurations that have the same function, method and result, or configurations that have the same purpose and effect. The present invention also includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. Furthermore, the present invention includes configurations that produce the same effects or achieve the same purpose as the configurations described in the embodiments. Furthermore, the present invention includes configurations that add known technology to the configurations described in the embodiments. [Explanation of symbols]

[0175] 20...Serial printer, 220...Transport unit, 230...Recording unit, 231...Inkjet head, 232...Radiation source, 234...Carriage, 235...Carriage movement mechanism, F...Recording medium, S1, S2...Main scanning direction, T2...Sub-scanning direction.

Claims

1. It contains a polymerizable compound and a photopolymerization initiator, The polymerizable compound includes a polyfunctional polymerizable compound, The photopolymerization initiator comprises (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide, The content of the (2,4,6-trimethylbenzoyl)bis(p-tolyl)phosphine oxide is 3% by mass or more relative to the total amount of the ink composition. A radiation-curable inkjet ink composition in which the content of the polyfunctional polymerizable compound is 20% by mass or more relative to the total amount of the ink composition.

2. The radiation-curable inkjet ink composition according to claim 1, wherein the polyfunctional polymerizable compound comprises a bifunctional polymerizable compound.

3. The aforementioned bifunctional polymerizable compound includes a polymerizable compound represented by the following formula (1): The radiation-curable inkjet ink composition according to claim 2, wherein the content of the polymerizable compound represented by formula (1) is 10% by mass or more relative to the total amount of the ink composition. H ２ C=CR １ -CO-OR ２ -O-CH=CH-R ３ ・・・ (1) (In the formula, R １ R is a hydrogen atom or a methyl group, ２ R is a divalent organic residue having 2 to 20 carbon atoms. ３ (This is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.)

4. The radiation-curable inkjet ink composition according to claim 3, wherein the content of the polymerizable compound represented by formula (1) is 70% by mass or less with respect to the total amount of the ink composition.

5. The radiation-curable inkjet ink composition according to claim 3, wherein the content of the bifunctional polymerizable compound is 20% by mass or more and 70% by mass or less based on the total amount of the ink composition.

6. The radiation-curable inkjet ink composition according to claim 2, wherein the bifunctional polymerizable compound comprises one or more selected from 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, and tripylene glycol diacrylate.

7. The polyfunctional polymerizable compound comprises a polymerizable compound with three or more functions, The radiation-curable inkjet ink composition according to claim 1 or claim 2, wherein the three- or more polymerizable compounds include one or more selected from trimethylolpropane triacrylate, ethylene oxide-modified trimethylolpropane triacrylate, and dipentaerythritol hexaacrylate.

8. The polymerizable compound includes a monofunctional polymerizable compound, The radiation-curable inkjet ink composition according to claim 1 or claim 2, wherein the monofunctional polymerizable compound comprises a nitrogen-containing monofunctional polymerizable compound.

9. The polymerizable compound includes a monofunctional polymerizable compound, The radiation-curable inkjet ink composition according to claim 1 or claim 2, wherein the monofunctional polymerizable compound comprises a hydroxyl group-containing monofunctional polymerizable compound.

10. The polymerizable compound includes a monofunctional polymerizable compound, The radiation-curable inkjet ink composition according to claim 1 or claim 2, wherein the monofunctional polymerizable compound comprises a saturated hydrocarbon ring-containing monofunctional polymerizable compound.

11. The polymerizable compound includes a monofunctional polymerizable compound, The radiation-curable inkjet ink composition according to claim 1 or claim 2, wherein the monofunctional polymerizable compound includes an ether ring-containing monofunctional polymerizable compound.

12. Contains polymerization inhibitors, The radiation-curable inkjet ink composition according to claim 1 or claim 2, wherein the polymerization inhibitor comprises one or more selected from bis(2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) sebacate and 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl.

13. A radiation-curable inkjet ink composition according to claim 1 or claim 2, comprising a fluorescent whitening agent.

14. A radiation-curable inkjet ink composition according to claim 1 or claim 2, wherein the ink is black ink or yellow ink.

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