Radiation-curable inkjet ink composition

Abstract

The present invention provides a radiation-curable inkjet ink that has low odor and suitable viscosity and curability for use as an inkjet ink. [Solution] A radiation-curable inkjet ink composition comprising a polymerizable compound, a polymer thioxanthone polymerization initiator, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, wherein the polymerizable compound does not contain an amine-modified oligomer, or the polymerizable compound contains an amine-modified oligomer, and the content of the amine-modified oligomer is less than 5% by mass 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 enable high-resolution recording with relatively small-scale equipment, and many related technologies have been developed. For example, radiation-curable inks for packaging applications are being developed, and Patent Document 1 discloses a photocurable inkjet ink composition containing a thioxanthone polymerization initiator and an amine-modified oligomer that reduces migration and can be used for food packaging applications. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-33318 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, radiation-curing inkjet inks have a distinctive odor, so reducing the odor is required to expand their applications further. In addition, appropriate viscosity and curing properties are required for inkjet inks. [Means for solving the problem]

[0005] One embodiment of the radiation-curable inkjet ink composition according to the present invention is: Polymerizable compounds and Polymer thioxanthone polymerization initiator, Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide and Includes, The polymerizable compound does not contain an amine-modified oligomer, or The polymerizable compound contains an amine-modified oligomer, and the content of the amine-modified oligomer is less than 5% by mass of the total amount of the ink composition. [Brief explanation of the drawing]

[0006] [Figure 1] Table 1 shows the compositions of the radiation-curable inkjet ink compositions of Examples 1 to 19. [Figure 2] Table 2 shows the compositions of the radiation-curable inkjet ink compositions of Comparative Examples 1 to 4. [Figure 3] Table 3 shows the evaluation results for Examples 1 to 19. [Figure 4] Table 4 shows the evaluation results for Comparative Examples 1-4. [Modes for carrying out the invention]

[0007] 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.

[0008] In this specification, "(meth)acrylate" means either acrylate or methacrylate or both, and "(meth)acrylic" means either acrylic or methacrylic or both.

[0009] In this specification, "oligomer" refers to a polymer with a low molecular weight, consisting of dimers or more obtained by polymerization of monomers, and having a weight-average molecular weight of 10,000 or less. In this specification, the weight-average molecular weight is determined by mass spectrometry.

[0010] In this specification, "polymer" means a substance with a molecular weight of 500 or more.

[0011] 1. Radiation-curable inkjet ink composition The radiation-curable inkjet ink composition according to this embodiment contains a polymerizable compound, a polymeric thioxanthone polymerization initiator, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, wherein the polymerizable compound does not contain an amine-modified oligomer, or the polymerizable compound contains an amine-modified oligomer and the content of the amine-modified oligomer is less than 5% by mass based on the total amount of the ink composition. Hereinafter, the components that can be included in the radiation-curable inkjet ink composition according to this embodiment will be described in detail.

[0012] 1.1. Polymerization initiator The polymerization initiator has the function of generating active species upon irradiation with radiation such as ultraviolet rays and visible light, initiating polymerization, and curing the ink composition. By using ultraviolet rays (UV), it has excellent safety and can reduce the cost of the light source lamp.

[0013] The radiation-curable inkjet ink composition according to this embodiment (also referred to as "ink composition" in this specification) contains a polymeric thioxanthone polymerization initiator and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide as polymerization initiators.

[0014] The molecular weight of the polymeric thioxanthone polymerization initiator is preferably 500 or more and 2500 or less, more preferably 600 or more and 2300 or less, and even more preferably 650 or more and 2000 or less. When the molecular weight is within the above range, it is excellent in reducing the viscosity and odor of the ink composition.

[0015] The molecular weight of the polymeric thioxanthone polymerization initiator is preferably the weight average molecular weight.

[0016] The content of the polymeric thioxanthone polymerization initiator is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 5% by mass or less, and still more preferably 1.0% or more and 3.5% by mass or less, based on the total amount of the ink composition. When the content of the polymeric thioxanthone polymerization initiator is within the above range, the volatilization of unreacted polymerizable compounds and decomposition products of the polymerization initiator is suppressed, and the odor can be reduced.

[0017] The content of bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 8% by mass or less, and still more preferably 1.0% or more and 6% by mass or less, based on the total amount of the ink composition. When the content of bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide is within the above range, the curability of the ink composition is improved, the volatilization of unreacted polymerizable compounds and the polymerization initiator is suppressed, and the odor can be reduced.

[0018] By using a polymeric thioxanthone polymerization initiator and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide in combination as the polymerization initiator, the curability of the ink composition can be further improved, and an ink composition with low odor and high curability can be obtained.

[0019] Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide is preferably contained more than the polymeric thioxanthone polymerization initiator. The ratio (w1 / w2) of the content (w2) of bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide to the content (w1) of the polymeric thioxanthone polymerization initiator is preferably 1 / 5 or more and less than 1 / 1, more preferably 1 / 4 or more and less than 1 / 1, and still more preferably 1 / 3 or more and less than 1 / 1. When w1 / w2 is within the above range, it is easier to achieve both excellent odor reduction and high curability. 合開始剤の含有量(w1)に対するビス(2,4,6-トリメチルベンゾイル)-フェニルホスフィンオキシドの含有量(w2)の比(w1 / w2)は、好ましくは1 / 5以上1 / 1未満であり、より好ましくは1 / 4以上1 / 1未満であり、さらに好ましくは1 / 3以上1 / 1未満である。w1 / w2が上記範囲内であると、臭気の低減と高い硬化性をより優れた状態で両立しやすい。

[0020] Examples of polymer thioxanthone polymerization initiators include 1,3-di({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxy)-2,2-bis({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxymethyl)propane (CAS No. 1003567-83-6) and α-[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]-ω-[[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]oxy]poly(oxy-1,4-butanediyl) (CAS No. 813452-37-8).

[0021] Examples of commercially available polymer thioxanthone polymerization initiators include Speed ​​Cure® 7010 (1,3-di({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxy)-2,2-bis({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxymethyl)propane) (product name of Sartomer), Omnipol® TX (α-[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]-ω-[[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]oxy]poly(oxy-1,4-butanediyl)) (product name of IGM RESINS), and Genopol Examples include the TX-2 (a product name manufactured by RAHN Corporation).

[0022] Among the commercially available products mentioned above, it is preferable to include one or more selected from Omnipol® TX and Speed ​​Cure® 7010.

[0023] The total content of polymerization initiators is preferably 1% by mass or more and 20% by mass or less of the total amount of the ink composition, in order to avoid undissolved polymerization initiators and discoloration caused by polymerization initiators.

[0024] Furthermore, while polymerization initiators contribute to the odor and curability of radiation-curable inkjet ink compositions, they do not necessarily contribute alone. The curability of radiation-curable inkjet ink compositions also changes depending on the combination with polymerizable compounds, polymerization inhibitors, polymerization accelerators, etc.

[0025] 1.2. Polymerizable compounds The radiation-curable inkjet ink composition according to this embodiment contains a polymerizable compound. Examples of polymerizable compounds include monofunctional monomers, polyfunctional monomers, and oligomers. In this specification, monofunctional monomers and polyfunctional monomers are collectively referred to simply as "monomers."

[0026] The monomer content in the polymerizable compound is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more, based on the total amount of polymerizable compound. When the monomer content is within the above range, the viscosity of the ink ejected during inkjet recording can be adjusted to an appropriate range.

[0027] In this embodiment, among polymerizable compounds, polymerizable compounds with a glass transition temperature of 15°C or lower are used. It is preferable that the compound is included.

[0028] The glass transition temperature (Tg) of polymerizable compounds with a glass transition temperature of 15°C or lower is preferably 15°C or lower, more preferably 5°C or lower, and even more preferably 0°C or lower. Including polymerizable compounds with a glass transition temperature of 15°C or lower improves the flexibility of the cured product of the ink composition and its adhesion to the recording medium.

[0029] Here, "glass transition temperature of a polymerizable compound" refers to the value obtained from differential scanning calorimetry (DSC) of a homopolymer when the polymerizable compound forms a homopolymer.

[0030] Polymerizable compounds with a glass transition temperature of 15°C or lower preferably include hydroxyl group-containing polymerizable compounds. The hydroxyl group-containing polymerizable compounds may be used individually or in combination of two or more. By using hydroxyl group-containing polymerizable compounds, the cured product of the ink composition can achieve higher adhesion to the recording medium.

[0031] Examples of such hydroxyl group-containing polymerizable compounds include 2-hydroxybutyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 4-hydroxybutyl acrylate, and 2-hydroxy-3-phenoxypropyl acrylate. Among these, it is preferable to include any one of 4-hydroxybutyl acrylate, hydroxypropyl acrylate, and hydroxyethyl acrylate.

[0032] The polymerizable compound with a glass transition temperature of 15°C or lower may be a monofunctional monomer, a polyfunctional monomer, or an oligomer, but a monofunctional monomer is preferred.

[0033] The content of polymerizable compounds with a glass transition temperature of 15°C or lower is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more, based on the total amount of the radiation-curable inkjet ink composition. Having the content of polymerizable compounds with a glass transition temperature of 15°C or lower within the above range further improves the flexibility of the cured product of the ink composition and further improves the adhesion of the ink composition to the recording medium. Furthermore, the above content is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less.

[0034] When a polymerizable compound contains two or more monomers, the glass transition temperature (Tg) of the monomers in the polymerizable compound is determined by a weighted average. The weighted average of the glass transition temperatures of the monomers is preferably 30°C or higher, more preferably 35°C or higher, and even more preferably 40°C or higher. When the glass transition temperature of the monomers is within the above range, the viscosity and curability of the ink composition can be stabilized. Furthermore, the weighted average of the glass transition temperatures of the monomers is preferably 70°C or lower, more preferably 65°C or lower, and even more preferably 60°C or lower.

[0035] 1.2.1. Monofunctional monomers The radiation-curable inkjet ink composition according to this embodiment may contain monofunctional monomers. The content of monofunctional monomers is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on the total amount of polymerizable compounds. When the content of monofunctional monomers is within the above range, the viscosity of the ink composition and the flexibility of the cured ink can be adjusted to an appropriate range.

[0036] The radiation-curable inkjet ink composition according to this embodiment contains monofunctional monomers other than the monofunctional monomers with a glass transition temperature of 15°C or lower (hereinafter referred to as "other monofunctional monomers"). It is also called ". ) may include this.

[0037] Other monofunctional monomers are not particularly limited, but those having a cyclic skeleton are preferred. Examples of monofunctional monomers having a cyclic skeleton include nitrogen-containing heterocyclic compounds, hydrocarbon ring compounds, and cyclic ether compounds. Using monofunctional monomers having a cyclic skeleton improves curability and the abrasion resistance of the cured product of the ink composition.

[0038] Examples of nitrogen-containing heterocyclic compounds include N-vinylcaprolactam (n-VC), N-vinylcarbazole, N-vinylpyrrolidone, acryloylmorpholine (ACMO), and 5-methyl-3-vinyloxazolidine-2-one.

[0039] Examples of hydrocarbon ring compounds include tert-butylcyclohexyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate.

[0040] Examples of cyclic ether compounds include cyclic trimethylolpropane formal acrylate (CTFA), cyclic trimethylolpropane formal methacrylate, tetrahydrofurfuryl acrylate (THFA), and tetrahydrofurfuryl methacrylate.

[0041] Among these, it is preferable to include one or more selected from acryloylmorpholine, tert-butylcyclohexyl acrylate, and cyclic trimethylolpropane formal acrylate.

[0042] Monofunctional monomers may be used individually or in combination of two or more.

[0043] 1.2.2. Polyfunctional Monomers The radiation-curable inkjet ink composition according to this embodiment may contain polyfunctional monomers. The polyfunctional monomer content is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, based on the total amount of polymerizable compounds. When the polyfunctional monomer content is within the above range, the curability of the ink composition tends to improve.

[0044] The polyfunctional monomer preferably contains one or more selected from vinyl ether group-containing (meth)acrylate and propylene glycol diacrylate. Including vinyl ether group-containing (meth)acrylate and / or propylene glycol diacrylate improves the curability of the radiation-curable inkjet ink composition and also improves the abrasion resistance of the cured ink product.

[0045] Examples of vinyl ether group-containing (meth)acrylates include 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, and (meth) 1,1-dimethyl-2-vinyloxyethyl 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 Examples include xylmethyl, p-vinyloxymethylphenylmethyl (meth)acrylate, m-vinyloxymethylphenylmethyl (meth)acrylate, o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(2-vinyloxyethoxy)ethyl methacrylate, and 2-(2-vinyloxyethoxy)ethyl acrylate (VEEA).

[0046] Examples of propylene glycol diacrylates include tripropylene glycol diacrylate (TPGDA) and dipropylene glycol diacrylate (DPGDA).

[0047] 1.2.3. Oligomers 1.2.3.1. Amine-modified oligomers 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 either does not contain amine-modified oligomers, or the content of amine-modified oligomers relative to the total amount of the ink composition is greater than 0% by mass but less than 5% by mass.

[0048] Amine-modified oligomers improve the curability of radiation-curable inkjet ink compositions, but when present in amounts of 5% by mass or more, they tend to increase viscosity and worsen ejection stability during inkjet recording.

[0049] 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.

[0050] Examples of amine-modified oligomers include amine-modified (meth)acrylate oligomers.

[0051] 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 less than 0.5% by mass, and especially preferably 0% by mass, relative to 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.

[0052] 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.

[0053] 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).

[0054] While amine-modified oligomers strongly contribute to the curability and viscosity of radiation-curable inkjet ink compositions, this contribution is not solely due to their interaction with other polymerizable compounds. The properties of radiation-curable inkjet ink compositions and their cured products also change depending on the combination of oligomers used with them.

[0055] 1.2.3.2. Urethane Oligomers The radiation-curable inkjet ink composition according to this embodiment may contain urethane oligomers, but from the viewpoint of improving ejection stability without increasing the viscosity of the radiation-curable inkjet ink composition, it is preferable that the content of urethane oligomers in the total amount of the ink composition be less than 10% by mass.

[0056] Urethane oligomers tend to increase the viscosity of the ink composition and are used to maintain a good balance of physical properties. The urethane oligomer content is preferably less than 10% by mass, more preferably less than 5% by mass, and even more preferably less than 3% by mass, relative to the total amount of polymerizable compounds.

[0057] Examples of urethane oligomers include urethane (meth)acrylate oligomers.

[0058] Examples of commercially available urethane oligomers include CN991 NS, CN996 NS, CN9002, CN9010 NS, CN9013 NS (all product names from Sartomer Co., Ltd.), New Frontier R-1235, R-1220, R-1304, R-1214, R-1302XT, R-1603 (all product names from Daiichi Kogyo Seiyaku Co., Ltd.), and Quick Cure (registered trademark) (manufactured by KJ Chemicals Co., Ltd.).

[0059] 1.3. Other ingredients The radiation-curable inkjet ink composition according to this embodiment may further contain additives such as colorants, dispersants, polymerization inhibitors, slip agents, and photosensitizers, as needed.

[0060] 1.3.1. Colorants The radiation-curable inkjet ink composition according to this embodiment may further contain a colorant. By including a colorant, the radiation-curable inkjet ink composition according to this embodiment can be used as a colored ink composition.

[0061] The total amount of 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 be a clear ink that contains no colorants or contains colorants in an amount not intended for coloring. An example of an amount not intended for coloring is 0.1% by mass or less relative to the total amount of the ink composition.

[0062] It is preferable to use pigments as colorants. When using pigments, a pigment dispersion may be prepared in advance and used in the ink composition. The pigment dispersion may contain polymerizable compounds and dispersants, as described later, to disperse the pigments. Both inorganic and organic pigments can be used.

[0063] Examples of inorganic pigments include carbon blacks (CI Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, as well as iron oxide and titanium dioxide.

[0064] Examples of organic pigments include azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and chelated azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; and dye chelates (e.g., basic dye type chelates, acidic dyes). Examples include dye-type chelates, dye lakes (basic dye-type lakes, acid dye-type lakes), nitro pigments, nitroso pigments, carbon black, aniline black, and daylight fluorescent pigments.

[0065] Black pigments include No.2300, No.900, MCF88, No.33, No.40, No.45, No.52, MA7, MA8, MA100, No.2200B, etc. (all product names manufactured by Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc. (all manufactured by Carbon Columbia), Rega1 400R, Rega1 330R, Rega1 660R, Mogul® L, Monarch® 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch Examples include the 1400 (product names from Cabot JAPAN KK), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex® 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black 4A, Special Black 4, etc. (product names from Degussa).

[0066] Examples of white pigments include CI Pigment White 6, 18, 21, metal oxides, barium sulfate, calcium carbonate, and other metal compounds. Examples of metal oxides include titanium dioxide, zinc oxide, silica, alumina, and magnesium oxide.

[0067] Examples of yellow pigments include CI Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172, and 180.

[0068] The magenta pigments include CI Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48(Ca), 48(Mn), 57(Ca), 57:1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, and CI Pigment Violet. Numbers 19, 23, 32, 33, 36, 38, 43, and 50 can be cited.

[0069] Examples of cyan pigments include CI Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, 66, and CI Bat Blue 4 and 60.

[0070] In addition, other color pigments besides magenta, cyan, and yellow include, for example, CI Pigment Green 7, 10, CI Pigment Brown 3, 5, 25, 26, and CI Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, and 63.

[0071] The above pigments may be used individually or in combination of two or more.

[0072] 1.3.2. Dispersant If the radiation-curable inkjet ink composition according to this embodiment 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.

[0073] The dispersant is not particularly limited, but examples include dispersants commonly used to prepare pigment dispersions, such as polymer dispersants. Specific examples of dispersants 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.

[0074] Commercially available polymer dispersants include the Azisper series from Ajinomoto Fine Techno Co., Ltd., the Solsperse series (Solsperse 36000, etc.) available from Avecia and Noveon, the Disparbic series from BYK Additives & Instruments, and the Disparon series from Kusumoto Chemicals Co., Ltd.

[0075] The dispersant content is preferably 0.01% by mass or more and 1.0% by mass or less, and more preferably 0.1% by mass or more and 0.5% by mass or less, relative to the total amount of the ink composition.

[0076] 1.3.3. Polymerization Inhibitors The radiation-curable inkjet ink composition according to this embodiment may further contain a polymerization inhibitor. The polymerization inhibitor may be used alone or in combination of two or more types.

[0077] Polymerization inhibitors include, but are not limited to, p-methoxyphenol, hydroquinone monomethyl ether (MEHQ), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, hydroquinone, cresol, tert-butylcatechol, 3,5-di-tert-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-butylphenol), and 4,4'-thiobis(3-methyl-6-tert-butylphenol), hindered amine compounds, and the like.

[0078] 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 ADEKA product names), 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 Examples include 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 brand names), FA-711HM, FA-712HM (2,2,6,6-tetramethylpiperidinyl methacrylate, Hitachi Chemical Co., Ltd. brand name), etc.

[0079] The polymerization inhibitor content is preferably 0.01% by mass or more and 1.0% by mass or less, and more preferably 0.1% by mass or more and 0.5% by mass or less, relative to the total amount of the ink composition.

[0080] 1.3.4. Slip agent The radiation-curable inkjet ink composition according to this embodiment may further contain a slip agent. The slip agent may be used alone or in combination of two or more types.

[0081] As a slip agent, a silicone-based surfactant is preferred, and a polyester-modified silicone or a polyether-modified silicone is more preferred. Examples of polyether-modified silicones include BYK-378, 3455, BYK-UV3500, 3510, and 3530 (all manufactured by BYK Additives & Instruments), and an example of a polyester-modified silicone is BYK-3570 (manufactured by BYK Additives & Instruments).

[0082] The slip agent content is preferably 0.1% by mass or more and 1.0% by mass or less, and more preferably 0.3% by mass or more and 0.8% by mass or less, relative to the total amount of the ink composition.

[0083] 1.3.5. Photosensitizers The radiation-curable inkjet ink composition according to this embodiment may further contain a photosensitizer. Examples of photosensitizers include amine compounds (aliphatic amines, amines containing aromatic groups, piperidines, reaction products of epoxy resins and amines, triethanolamine triacrylate, etc.), urea compounds (allylthiourea, o-tolylthiourea, etc.), sulfur compounds (sodium diethyldithiophosphate, soluble salts of aromatic sulfinic acid, etc.), nitrile compounds (N,N-diethyl-p-aminobenzonitrile, etc.), phosphorus compounds (tri-n-butylphosphine, sodium diethyldithiophospide, etc.), nitrogen compounds (Michler ketone, N-nitrisohydroxylamine derivatives, oxazolidine compounds, tetrahydro-1,3-oxazine compounds, condensates of formaldehyde or acetaldehyde and diamine, etc.), and chlorine compounds (carbon tetrachloride, hexachloroethane, etc.).

[0084] 1.4. Physical Properties The viscosity of the radiation-curable inkjet ink composition according to this embodiment at 20°C is preferably less than 25 mPa·s, more preferably 15 mPa·s or more and less than 20 mPa·s, and even more preferably less than 15 mPa·s. When 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, making it suitable for use in an inkjet recording device. The viscosity was measured using a viscoelasticity tester MCR-301 (manufactured by Anton Paar) at 20°C with a shear rate of 10 [s]. -1 ] to 1000[s -1 The viscosity can be measured by increasing the setting and reading the viscosity at a Shear Rate of 200.

[0085] 2. Inkjet recording method Next, an inkjet recording method using the above-described radiation-curable inkjet ink composition will be described. Such an inkjet recording method includes an ejection step of ejecting the above-described radiation-curable inkjet ink composition from an inkjet head and adhering it to a recording medium, and an irradiation step of irradiating the radiation-curable inkjet ink composition adhering to the recording medium with radiation. The following describes each of the inkjet recording methods. The process and recording media used in the inkjet recording method will be described.

[0086] 2.1.Discharge process In the ejection process, the ink composition is ejected from the inkjet head onto the recording medium in the form of tiny droplets.

[0087] Inkjet heads used in the ejection process include line heads used in line systems and serial heads used in serial systems.

[0088] In the line method, an inkjet head (line head) having a width greater than the recording width of the recording medium is mounted on the recording device, and an image is recorded on the recording medium by ejecting an ink composition while relatively moving the line head and the recording medium in a scanning direction (the vertical direction of the recording medium, the transport direction) that intersects the width direction of the recording medium.

[0089] In the serial method, an inkjet head (serial head) is mounted on a carriage that can move in the width direction of the recording medium, and an image is recorded on the recording medium by ejecting an ink composition while moving the carriage along the main scanning direction (lateral direction, width direction of the recording medium).

[0090] 2.2.Irradiation process In the irradiation process, radiation is applied to the radiation-curable inkjet ink composition attached to the recording medium. Irradiation with radiation initiates a polymerization reaction in the polymerizable compounds within the ink composition, causing it to harden and form a coating film.

[0091] If an ink composition contains a polymerization initiator, irradiation with radiation will excite and cleave the polymerization initiator, generating radicals and acids. These generated radicals and acids will accelerate the polymerization reaction of monomers.

[0092] Examples of radiation include ultraviolet rays, infrared rays, visible light, and X-rays. When using ultraviolet rays as the radiation source, light sources such as UV-LEDs (Light Emitting Diodes), LDs (Laser Diodes), high-pressure mercury lamps, and metal halide lamps can be used. When using UV-LEDs or LDs, the wavelength of the emitted radiation is preferably between 350.0 nm and 430.0 nm.

[0093] In the irradiation process, the irradiation energy of the radiation irradiated in a single pass is preferably 150 mJ / cm². 2 More than 250mJ / cm 2 Less than 150 mJ / cm² 2 It is less than the above range. If the radiation irradiation energy is within the above range, the surface and overall effects of the ink composition can be achieved more efficiently.

[0094] 2.3. Recording media The form of the recording medium used in the inkjet recording method is not particularly limited, but examples include film-like and boat-like forms.

[0095] The material of the recording medium is not particularly limited, but examples include resins such as polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, polyurethane, polyethylene, polypropylene, polyvinyl acetal, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, and cellulose nitrate, as well as metals such as iron, silver, copper, and aluminum, and glass.

[0096] 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.

[0097] 3.1. Preparation of Ink Composition First, the pigment, dispersant, and a portion of the polymerizable compound were placed in a container and stirred to obtain a pigment dispersion in which the pigment was dispersed in the polymerizable compound. Next, the above pigment dispersion and the remaining components were placed in a container to obtain the compositions shown in Table 1 (Figure 1) and Table 2 (Figure 2) (unit: mass%), mixed and stirred with a magnetic stirrer for 2 hours, and then filtered through a membrane filter with a pore size of 5 μm to obtain the ink compositions for each example and comparative example.

[0098] The components listed in Tables 1 and 2 are as follows:

[0099] <Monofunctional monomer (without hydroxyl group)> ACMO: Product name, manufactured by KJ Chemicals Co., Ltd., acryloylmorpholin TBCHA: tert-butylcyclohexyl acrylate CTFA: Cyclic trimethylolpropane formal acrylate <Monofunctional monomer (containing hydroxyl group)> 4HBA: 4-Hydroxybutyl acrylate HPA: Hydroxypropyl acrylate HEA: Hydroxyethyl acrylate 620-100: Product name, manufactured by KJ Chemicals Co., Ltd., 2-hydroxy-3-phenoxypropyl acrylate <Polyfunctional monomers> VEEA: 2-(2-vinyloxyethoxy)ethyl acrylate TPGDA: Tripropylene glycol diacrylate DPGDA: Dipropylene glycol diacrylate <Oligomer> CN371 NS: Product name, manufactured by Sartomer, amine-modified (meth)acrylate CN991 NS: Product name, manufactured by Sartmar, urethane diacrylate <Polymerization inhibitor> MEHQ: Hydroquinone monomethyl ether LA-7RD: Product name "ADEKA Stub LA-7RD", manufactured by ADEKA Corporation. <Polymerization initiator> 819: Product name "Omnirad 819", manufactured by IGM RESINS, acylphosphine oxide polymerization initiator. 7010: Product name "SpeedCure 7010", manufactured by Sartomer, polymer thioxanthone polymerization initiator. TX: Product name "Omnipol TX", manufactured by IGM RESINS, polymer thioxanthone polymerization initiator. <Slip agent> BYK UV3500: Manufactured by BYK Additives & Instruments. <Dispersant> Solsperse36000: Product name, manufactured by Lubrizol. <Pigments> Carbon Black: CI Pigment Black 7 3.2. Evaluation of inkjet ink compositions and cured products 3.2.1. Glass transition temperature (Tg) of monomers The glass transition temperature (Tg) of the monomers in the ink composition was calculated by weighting the mass ratio of each monomer to the total monomers in the ink composition.

[0100] 3.2.2. Viscosity The viscosity (mPa·s) of each radiation-curable inkjet ink was measured using a rotational viscometer, "Rheometer (MCR-301, manufactured by Anton Paar)." The evaluation criteria were as follows, and the evaluation results are shown in Table 3 (Figure 3) and Table 4 (Figure 4). (Evaluation Criteria) A: Less than 15 mPa·s B: 15 mPa·s or more, less than 20 mPa·s C: 20 mPa·s or higher, less than 25 mPa·s D:25mPa·s or more

[0101] 3.2.3. Curability A radiation-curable inkjet ink composition was applied onto a PET film using a bar coater. Next, irradiation was performed under the conditions described in Tables 3 and 4 using a UV-LED, and the irradiation energy until it became tack-free was determined.

[0102] Note that the tack-free state was judged by rubbing the surface of the cured product after curing 10 times with a 100 g weight using a cotton swab to check whether the ink adhered to the cotton swab or whether the cured product on the recording medium was scratched.

[0103] Irradiation energy [mJ / cm 2 was determined from the product of the irradiation intensity [mW / cm 2 measured on the irradiated surface irradiated from the light source and the irradiation duration [sec]. The irradiation intensity was measured using an ultraviolet intensity meter UM-10 and a light receiving unit UM-400 (both manufactured by KONICA MINOLTA SENSING, INC.). The evaluation criteria were as follows, and the evaluation results are shown in Tables 3 and 4. (Evaluation criteria) A: Less than 150 mJ / cm 2 B: 150 mJ / cm 2 or more and less than 250 mJ / cm 2 C: 250 mJ / cm 2 or more and less than 350 mJ / cm 2 D: 350 mJ / cm 2 or more

[0104] 3.2.4. Adhesion The adhesion of the cured film obtained in the above evaluation of curability was evaluated by a cross-cut test according to JIS K5600-5-6.

[0105] ​​​Specifically, a cutter blade was applied perpendicular to the cured film, and a grid of 6x6 squares was made using a grid with a 1mm distance between cuts. A transparent adhesive tape approximately 75mm long was attached to the grid, and the tape was rubbed thoroughly with a finger so that the cured film could be seen through it. Next, within 5 minutes of attaching the tape, the tape was peeled off the cured film at an angle close to 60° for 0.5 to 1.0 seconds, and the condition of the grid was observed visually. The evaluation criteria were as follows, and the evaluation results are shown in Tables 3 and 4. (Evaluation Criteria) A: Peeling of the hardened film was observed in less than 20% of the grid. B: Peeling of the hardened film was observed in 20% to less than 25% of the grid. C: Peeling of the cured film was observed in 25% to less than 30% of the lattice. D: Peeling of the hardened film was observed in more than 30% of the grid.

[0106] 3.2.5. Odor Each example of radiation-curable inkjet ink composition was applied to a recording medium and cured using a UV-LED. The odor of the resulting cured product was evaluated. The evaluation criteria were as follows: The evaluation results are shown in Tables 3 and 4. (Evaluation Criteria) A: No odor, or a slight odor. B: It has an odor. C: Has a strong odor.

[0107] 3.3. Evaluation Results The following was found from the examples and comparative examples.

[0108] Each example relating to a radiation-curable inkjet ink composition containing a polymer thioxanthone polymerization initiator and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, with an amine-modified oligomer content of less than 5% by mass, showed good results in all evaluation items of curability, odor, and viscosity.

[0109] In contrast, none of the comparative examples that did not meet the above conditions yielded satisfactory results in terms of curability, odor, or viscosity.

[0110] A comparison of Example 1 with Comparative Examples 1 and 2 showed that when a polymer thioxanthone polymerization initiator and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide were used in combination as polymerization initiators, the ink composition exhibited appropriate viscosity, good curability and adhesion, and reduced odor.

[0111] A comparison of Examples 1-3 with Comparative Examples 3 and 4 showed that when the amine-modified oligomer content in the ink composition was less than 5% by mass, the ink composition exhibited an appropriate viscosity.

[0112] The results from Examples 1, 2, and 3 showed that when the amine-modified oligomer content was within a predetermined range, the curability and viscosity of the ink composition improved, and the odor was also reduced.

[0113] The results from Examples 1, 4, and 5 showed that the inclusion of one or more monofunctional monomers having a cyclic structure tended to improve curability.

[0114] The results from Examples 1, 6, and 7 showed that when the polymerization initiator content was within a predetermined range, the curability of the ink composition improved and the odor tended to be reduced.

[0115] The results from Examples 1 and 8 show that using a specific polymer thioxanthone polymerization initiator improved the curability of the ink composition and reduced its odor.

[0116] The results from Examples 1 and 9 showed that when the content of polymerizable compounds with a glass transition temperature of 15°C or lower was within a predetermined range, the adhesion of the ink composition to the recording medium tended to be good.

[0117] The results from Examples 1, 10, 11, 12, 13, and 14 showed that even when various hydroxyl group-containing polymerizable compounds were used, the curability of the ink composition improved and the odor tended to be reduced. Furthermore, the ink composition exhibited an appropriate viscosity.

[0118] The results from Examples 1, 15, and 16 showed that even when various polyfunctional monomers were used, the curability of the ink composition improved and the odor tended to be reduced.

[0119] The results from Examples 1 and 17 show that various combinations of monofunctional monomers and polyfunctional monomers are possible. As a result, the curing properties of the ink composition improved, and the odor tended to be reduced.

[0120] The results from Examples 1 and 18 showed that even when other monofunctional monomers were used without containing hydroxyl group-containing polymerizable compounds, good curability and appropriate viscosity were observed.

[0121] The results from Examples 1 and 19 showed that the ink composition exhibited appropriate viscosity when it contained a urethane oligomer.

[0122] 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.

[0123] The following can be derived from the embodiments and modifications described above.

[0124] Radiation-curable inkjet ink composition, Polymerizable compounds and Polymer thioxanthone polymerization initiator, Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide and Includes, The polymerizable compound does not contain an amine-modified oligomer, or The polymerizable compound contains an amine-modified oligomer, and the content of the amine-modified oligomer is less than 5% by mass of the total amount of the ink composition.

[0125] This radiation-curable inkjet ink composition contains a polymer thioxanthone polymerization initiator and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide as polymerization initiators. This suppresses the volatilization of unreacted polymerizable compounds and decomposition products of the polymerization initiator, reducing the odor of the ink composition and improving curability.

[0126] Furthermore, while a high content of amine-modified oligomers improves curability, it also increases viscosity. By not including amine-modified oligomers, or by including them in amounts of less than 5% by mass of the total amount of the ink composition, it is possible to achieve appropriate viscosity and good curability for inkjet inks.

[0127] In the above radiation-curable inkjet ink composition, The polymerizable compound may include a polymerizable compound having a glass transition temperature of 15°C or lower.

[0128] This radiation-curable inkjet ink composition, by containing polymerizable compounds with a glass transition temperature of 15°C or lower, exhibits appropriate viscosity for inkjet inks, and enhances the flexibility of the cured ink composition and its adhesion to recording media.

[0129] In the above radiation-curable inkjet ink composition, The content of the polymerizable compound having a glass transition temperature of 15°C or lower may be 5% by mass or more and 35% by mass or less relative to the total amount of the radiation-curable inkjet ink composition.

[0130] According to this radiation-curable inkjet ink composition, by adjusting the content of polymerizable compounds with a glass transition temperature of 15°C or lower, the adhesion of the ink composition to the recording medium can be improved. It can be improved further. Also, In the above radiation-curable inkjet ink composition, The polymerizable compound having a glass transition temperature of 15°C or lower may include a polymerizable compound containing a hydroxyl group.

[0131] This radiation-curable inkjet ink composition, by containing a hydroxyl group-containing polymerizable compound, exhibits an appropriate viscosity for inkjet inks, and the cured product of the ink composition can achieve high adhesion to the recording medium.

[0132] In the above radiation-curable inkjet ink composition, The hydroxyl group-containing polymerizable compound may contain one or more selected from 4-hydroxybutyl acrylate, hydroxypropyl acrylate, and hydroxyethyl acrylate.

[0133] This radiation-curable inkjet ink composition exhibits a viscosity more suitable for inkjet applications, and the cured product of the ink composition can achieve even higher adhesion to the recording medium.

[0134] In the above radiation-curable inkjet ink composition, The polymer thioxanthone polymerization initiator may contain one or more selected from 1,3-di({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxy)-2,2-bis({α-[1-chloro-9-oxo-9H-thioxanthene-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxymethyl)propane and α-[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]-ω-[[2-[(9-oxo-9H-thioxanthenyl)oxy]acetyl]oxy]poly(oxy-1,4-butanediyl).

[0135] This radiation-curable inkjet ink composition, by including a polymer thioxanthone polymerization initiator, suppresses the volatilization of unreacted polymerizable compounds and decomposition products of the polymerization initiator, thereby reducing odor.

[0136] In the above radiation-curable inkjet ink composition, The monomer of the polymerizable compound may have a weighted average glass transition temperature of 30°C or higher and 70°C or lower.

[0137] This radiation-curable inkjet ink composition allows for stable viscosity and curability.

[0138] In the above radiation-curable inkjet ink composition, The polymerizable compound may contain 50% by mass or more of monofunctional monomers relative to its total amount.

[0139] This radiation-curable inkjet ink composition allows for adjustment of the viscosity of the ink composition and the flexibility of the cured product to an appropriate range.

[0140] In the above radiation-curable inkjet ink composition, The polymerizable compound comprises a polyfunctional monomer, The polyfunctional monomer may contain one or more selected from vinyl ether group-containing (meth)acrylates and propylene glycol diacrylates.

[0141] This radiation-curable inkjet ink composition provides good curability, and also, The abrasion resistance of the cured ink composition is also improved.

[0142] In the above radiation-curable inkjet ink composition, The polymerizable compound may include one or more selected from acryloylmorpholine, tert-butylcyclohexyl acrylate, and cyclic trimethylolpropaneformal acrylate.

[0143] This radiation-curable inkjet ink composition offers improved curability and further enhances the abrasion resistance of the cured ink product.

[0144] In the above radiation-curable inkjet ink composition, The polymerizable compound may contain 90% by mass or more of monomers relative to its total amount.

[0145] This radiation-curable inkjet ink composition allows the viscosity of the ink ejected during inkjet recording to be adjusted to a range suitable for inkjet ink.

[0146] In the above radiation-curable inkjet ink composition, The urethane oligomer may be contained in an amount of 10% by mass or less relative to the total amount of the polymerizable compound.

[0147] This radiation-curable inkjet ink composition improves the viscosity of the ink composition with the addition of urethane oligomers, making it possible to achieve a viscosity suitable for inkjet ink.

Claims

1. Polymerizable compounds and Polymer thioxanthone polymerization initiator, Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and Includes, The polymerizable compound does not contain an amine-modified oligomer, or A radiation-curable inkjet ink composition comprising an amine-modified oligomer, wherein the polymerizable compound comprises an amine-modified oligomer, and the content of the amine-modified oligomer is less than 5% by mass of the total amount of the ink composition.

2. The radiation-curable inkjet ink composition according to claim 1, wherein the polymerizable compound comprises a polymerizable compound having a glass transition temperature of 15°C or less.

3. The radiation-curable inkjet ink composition according to claim 2, wherein the content of the polymerizable compound with a glass transition temperature of 15°C or less is 5% by mass or more and 35% by mass or less based on the total amount of the radiation-curable inkjet ink composition.

4. The radiation-curable inkjet ink composition according to claim 2, wherein the polymerizable compound having a glass transition temperature of 15°C or less includes a hydroxyl group-containing polymerizable compound.

5. The radiation-curable inkjet ink composition according to claim 4, wherein the hydroxyl group-containing polymerizable compound comprises one or more selected from 4-hydroxybutyl acrylate, hydroxypropyl acrylate, and hydroxyethyl acrylate.

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

7. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein the monomer of the polymerizable compound has a weighted average glass transition temperature of 30°C or more and 70°C or less.

8. The radiation-curable inkjet ink composition according to claim 1 or 2, comprising 50% by mass or more of a monofunctional monomer based on the total amount of the polymerizable compound.

9. The polymerizable compound comprises a polyfunctional monomer, The radiation-curable inkjet ink composition according to claim 1 or 2, wherein the polyfunctional monomer comprises one or more selected from vinyl ether group-containing (meth)acrylate and propylene glycol diacrylate.

10. The radiation-curable inkjet ink composition according to claim 1 or 2, wherein the polymerizable compound comprises one or more selected from acryloylmorpholine, tert-butylcyclohexyl acrylate, and cyclic trimethylolpropaneformal acrylate.

11. The polymerizable compound contains 90% by mass or more of the monomer relative to the total amount, as described in claim 1 or 2. A radiation-curable inkjet ink composition.

12. The radiation-curable inkjet ink composition according to claim 1 or 2, comprising 10% by mass or less of a urethane oligomer based on the total amount of the polymerizable compound.

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