Radiation-curable inkjet ink composition and recording device

Abstract

This invention provides a radiation-curable inkjet ink composition with good curability, blocking resistance of recorded materials, and odorless recorded materials. [Solution] A radiation-curable inkjet ink composition comprising a hydroxyl group-containing polymerizable compound (A), a monofunctional polymerizable compound (B) other than the hydroxyl group-containing polymerizable compound (A) having a glass transition temperature of 10°C or more and 90°C or less, and a polymer thioxanthone polymerization initiator (C).

Description

[Technical Field]

[0001] The present invention relates to a radiation-curable inkjet ink composition and a recording device. [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-curable inkjet inks have a distinctive odor, so reducing the odor is required to expand their applications further. In addition, good curability and blocking resistance 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: Radiation-curable inkjet ink composition, A hydroxyl group-containing polymerizable compound (A), A monofunctional polymerizable compound (B) other than the hydroxyl group-containing polymerizable compound (A) has a glass transition temperature of 10°C or higher and 90°C or lower, Polymer thioxanthone polymerization initiator (C), including

[0006] One aspect of the recording apparatus according to the present invention is the above-described radiation-curable inkjet ink composition, and a head for discharging the radiation-curable inkjet ink composition, and is provided.

Brief Description of the Drawings

[0007] [Figure 1] Perspective view of an example of a recording apparatus. [Figure 2] Front view of the ultraviolet irradiation apparatus shown in FIG. 1. [Figure 3] View taken along the line A-A of FIG. 2. [Figure 4] Schematic view of an example of a recording apparatus. [Figure 5] Table 1 showing the composition, etc. of the examples. [Figure 6] Table 2 showing the composition, etc. of the examples. [Figure 7] Table 3 showing the composition, etc. of the examples. [Figure 8] Table 4 showing the composition, etc. of the examples and comparative examples. [Figure 9] Table 5 showing the evaluation results of the examples and comparative examples.

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 for explanation. The present invention is not limited to the following embodiments, and also includes various modified forms implemented within the scope of not changing the gist of the present invention. Note that not all of the configurations described below are essential configurations of the present invention.

[0009] 1. Radiation-curable inkjet ink composition The radiation-curable inkjet ink composition according to this embodiment contains a hydroxyl group-containing polymerizable compound (A), a monofunctional polymerizable compound (B) having a glass transition temperature of 10°C or higher and 90°C or lower other than the hydroxyl group-containing polymerizable compound (A), and a polymer thioxanthone polymerization initiator (C).

[0010] 1.1. Hydroxyl group-containing polymerizable compound (A) The radiation-curable inkjet ink composition according to this embodiment contains a hydroxyl group-containing polymerizable compound (A). Examples of the hydroxyl group-containing polymerizable compound (A) include monofunctional polymerizable compounds and polyfunctional polymerizable compounds containing a hydroxyl group among polymerizable compounds. More specifically, examples of the hydroxyl group-containing polymerizable compound (A) include hydroxyalkyl (meth)acrylates, hydroxy (meth)acrylates having an alicyclic structure, and hydroxyl group-containing epoxy (meth)acrylates, etc., among polymerizable compounds having a hydroxyl group in the molecule.

[0011] In this specification, when "(meth)acrylate" is described, it means acrylate or methacrylate, and when "(meth)acrylic" is described, it means acrylic or methacrylic. The weight average molecular weight in this specification is the value obtained by measurement by mass spectrometry.

[0012] Examples of hydroxy (meth)acrylate include 2-hydroxyethyl acrylate (HEA), 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate (HPA), 2-hydroxypropyl methacrylate, 2-hydroxy-3-phenoxypropyl acrylate (HPPA), 2-hydroxy-3-phenoxypropyl methacrylate, 4-hydroxybutyl acrylate (4HBA), 4-hydroxybutyl methacrylate, etc.

[0013] Examples of hydroxy (meth)acrylate having an alicyclic structure include 1,4-cyclohexanedimethanol monoacrylate (CHDMMA), 1,4-cyclohexanedimethanol monomethacrylate, etc.

[0014] Examples of hydroxyl group-containing epoxy (meth)acrylates include epoxy acrylates obtained by adding (meth)acrylic acid to a diepoxy or polyepoxy compound. Such epoxy (meth)acrylates can be obtained commercially, and examples include DA-111, DA-141, DA-212, DA-250, DA-314, DA-721, DA-722, DA-911M, DA-920, DA-931, DM-201, DM-811, DM-832, and DM-851 (all manufactured by Nagase ChemteX Corporation).

[0015] The hydroxyl group-containing polymerizable compound (A) contained in the radiation-curable inkjet ink composition is preferably a monofunctional polymerizable compound containing a hydroxyl group among the compounds exemplified above, and it is more preferable to select one or more from 2-hydroxyethyl acrylate (HEA), 2-hydroxypropyl acrylate (HPA), 2-hydroxypropyl methacrylate (HPA), 2-hydroxy-3-phenoxypropyl acrylic acid (HPPA), and 4-hydroxybutyl acrylate (4HBA).

[0016] When a hydroxyl group-containing polymerizable compound (A) is selected as described above, radiation-curable inkjet This makes it easier to adjust the viscosity of the inkjet composition to a more suitable viscosity for inkjet applications, and it also improves the adhesion of the cured coating film of the composition to the recording medium. The reason for the improved adhesion is thought to be that the presence of hydroxyl groups increases the bulkiness of the molecules compared to polymerizable compounds that do not contain hydroxyl groups, resulting in less shrinkage during polymerization and thus less residual stress in the ink coating film. Furthermore, monofunctional polymerizable compounds contain more hydroxyl groups per polymerizable functional group, making it easier to obtain the above effect.

[0017] Furthermore, the hydroxyl group-containing polymerizable compound (A) may be used alone or in combination of two or more types.

[0018] The content of the hydroxyl group-containing polymerizable compound (A) 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 the hydroxyl group-containing polymerizable compound (A) within the above range further improves the flexibility of the cured product of the ink composition, further improves the adhesion of the ink composition to the recording medium, and further improves the blocking resistance of the coating film. Furthermore, the above content is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less.

[0019] 1.2. Monofunctional polymerizable compounds (B) The radiation-curable inkjet ink composition according to this embodiment includes a monofunctional polymerizable compound (B) other than the hydroxyl group-containing polymerizable compound (A) described above, wherein the monofunctional polymerizable compound has a glass transition temperature of 10°C or higher and 90°C or lower.

[0020] In this specification, the glass transition temperature (Tg) of a polymerizable compound refers to the glass transition temperature (Tg) of the polymer when the polymerizable compound forms a homopolymer. The glass transition temperature can be determined, for example, by differential scanning calorimetry (DSC) or viscoelasticity measurement, and is more preferably determined by differential scanning calorimetry (DSC).

[0021] The monofunctional polymerizable compound (B) (hereinafter sometimes simply referred to as "monofunctional polymerizable compound (B)") other than the hydroxyl group-containing polymerizable compound (A), which has a glass transition temperature of 10°C or more and 90°C or less, is not particularly limited, but those having a cyclic skeleton are preferred. Examples of monofunctional polymerizable compounds having a cyclic skeleton include nitrogen-containing heterocyclic polymerizable compounds, hydrocarbon ring-containing polymerizable compounds, and cyclic ether-containing polymerizable compounds. In this specification, nitrogen-containing heterocyclic polymerizable compounds, hydrocarbon ring-containing polymerizable compounds, and cyclic ether-containing polymerizable compounds may be referred to as nitrogen-containing heterocyclic polymerizable compounds, hydrocarbon ring polymerizable compounds, and cyclic ether polymerizable compounds, respectively.

[0022] By using a monofunctional polymerizable compound having a cyclic skeleton, the curability and the abrasion resistance of the cured ink composition can be improved.

[0023] Examples of nitrogen-containing heterocyclic polymerizable compounds include N,N-diethylacrylamide (DEAA).

[0024] Examples of hydrocarbon ring polymerizable compounds include 4-tert-butylcyclohexyl acrylate (TBCHA), 3,3,5-trimethylcyclohexyl acrylate (TMCHA), isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate.

[0025] Examples of cyclic ether polymerizable compounds include cyclic trimethylolpropane formal acrylate (CTFA), cyclic trimethylolpropane formal methacrylate, Examples include tetrahydrofurfuryl methacrylate.

[0026] The monofunctional polymerizable compound (B) is selected from the examples above, with a glass transition temperature of 10°C or higher and 90°C or lower.

[0027] As the monofunctional polymerizable compound (B), it is preferable to use one or more selected from among these: cyclic trimethylolpropane formal acrylate (CTFA), 3,3,5-trimethylcyclohexyl acrylate (TMCHA), 4-tert-butylcyclohexyl acrylate (TBCHA), and N,N-diethylacrylamide (DEAA).

[0028] Furthermore, it is preferable to select one or more monofunctional polymerizable compounds (B) from the above-mentioned cyclic ether polymerizable compounds and hydrocarbon ring polymerizable compounds. In this case, the curability of the radiation-curable inkjet ink composition may be improved.

[0029] Furthermore, when selecting a cyclic ether polymerizable compound as the monofunctional polymerizable compound (B), it is even more preferable to select one that includes cyclic trimethylolpropane formal acrylate. Moreover, when selecting a hydrocarbon ring polymerizable compound as the monofunctional polymerizable compound (B), it is even more preferable to select one that includes 4-tert-butylcyclohexyl acrylate or 3,3,5-trimethylcyclohexyl acrylate. By making such selections, it may be possible to further improve the curability of the radiation-curable inkjet ink composition and the blocking resistance of its coating film.

[0030] Furthermore, the monofunctional polymerizable compound (B) may be used alone or in combination of two or more types.

[0031] The content of monofunctional polymerizable compound (B) is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, based on the total amount of the radiation-curable inkjet ink composition. Having the monofunctional polymerizable compound (B) content within the above range further improves the curability of the ink composition. Furthermore, the above content is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. Having the monofunctional polymerizable compound (B) content at this level further improves the curability of the composition and the blocking resistance of the coating film.

[0032] 1.3. Polymer thioxanthone polymerization initiator (C) The radiation-curable inkjet ink composition according to this embodiment contains a polymer thioxanthone polymerization initiator (C). In this specification, "polymer" means a polymer with a molecular weight of 500 or more.

[0033] The polymer thioxanthone polymerization initiator (C) generates active species upon irradiation with radiation such as ultraviolet light or visible light, initiating polymerization and curing the radiation-curable ink composition. Using ultraviolet (UV) light as the radiation source provides excellent safety and reduces the cost of the light source lamp.

[0034] The molecular weight of the polymer thioxanthone polymerization initiator (C) is preferably 500 to 2500, more preferably 600 to 2000, and even more preferably 1000 to 2000.

[0035] Furthermore, the molecular weight of the polymer thioxanthone polymerization initiator (C) is when it is a pure substance. This refers to the molecular weight, and if a molecular weight distribution exists, it refers to the weight-average molecular weight measured by GPC or similar methods.

[0036] The content of the polymer thioxanthone polymerization initiator (C) is preferably 0.1% to 10% by mass, more preferably 0.5% to 5% by mass, and even more preferably 1.0% to 3.5% by mass, based on the total amount of the radiation-curable inkjet ink composition. When the content of the polymer thioxanthone polymerization initiator is within the above range, the volatilization of unreacted polymerizable compounds and decomposition products of the polymerization initiator is suppressed, and odor can be reduced.

[0037] Examples of polymer thioxanthone polymerization initiators (C) 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: 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: 813452-37-8).

[0038] Examples of commercially available polymer thioxanthone polymerization initiators (C) 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).

[0039] The polymer thioxanthone polymerization initiator (C) preferably contains at least one of the above-mentioned commercially available products: Omnipol® TX and Speed ​​Cure® 7010.

[0040] In other words, it is more preferable that the polymer thioxanthone polymerization initiator (C) contains 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). In this way, the volatilization of unreacted polymerizable compounds and decomposition products of the polymerization initiator is suppressed, and odor is further reduced.

[0041] Furthermore, while polymer thioxanthone polymerization initiator (C) is involved in the odor and curability of radiation-curable inkjet ink compositions, it does not necessarily have an effect on its own. The odor and curability of radiation-curable inkjet ink compositions also change depending on the combination with polymerizable compounds, polymerization inhibitors, polymerization accelerators, etc.

[0042] 1.4. Other ingredients The radiation-curable inkjet ink composition according to this embodiment is as described below. It may also contain ingredients other than those described above.

[0043] 1.4.1. Polymerizable compounds other than those listed above The polymerizable compounds that may be included in the radiation-curable inkjet ink composition are not particularly limited as long as they are compounds that polymerize with a polymerization initiator, and include polymerizable compounds other than the hydroxyl group-containing polymerizable compound (A) or monofunctional polymerizable compound (B) described above. Examples of such polymerizable compounds include various monomers and oligomers, including monofunctional and bifunctional compounds.

[0044] Examples of such polymerizable compounds include unsaturated carboxylic acids such as (meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, and maleic acid, as well as their salts or esters, urethanes, amides and their anhydrides, acrylonitrile, styrene, various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes.

[0045] Furthermore, examples of oligomers include oligomers formed from the above monomers such as linear (meth)acrylic oligomers, epoxy (meth)acrylate, oxetane (meth)acrylate, aliphatic urethane (meth)acrylate, aromatic urethane (meth)acrylate, and polyester (meth)acrylate.

[0046] 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.

[0047] Radiation-curable inkjet ink compositions may contain N-vinyl compounds as monofunctional or polyfunctional monomers. Examples of N-vinyl compounds include N-vinylcarbazole, N-vinylcaprolactam, vinylmethyloxazolidinone (VMOX), dimethylacrylamide, dimethylaminopropylacrylamide, and their derivatives.

[0048] The radiation-curable inkjet ink composition of this embodiment may contain vinyl ether group-containing (meth)acrylic acid esters represented by the following general formula (I) as polyfunctional monomers. CH2=CR 1 -COOR 2 -O-CH=CH-R 3 ...(I) (In formula (I), 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.)

[0049] Specific examples of such compounds include (meth)acrylate 2-vinyloxyethyl, (meth)acrylate 3-vinyloxypropyl, (meth)acrylate 1-methyl-2-vinyloxyethyl, acrylate 2-(2-vinyloxyethoxy)ethyl (VEEA), methacrylate 2-(2-vinyloxyethoxy)ethyl, (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, 3-vinyloxybutyl (meth)acrylate, 1-methyl-2-vinyloxypropyl (meth)acrylate, 2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl (meth)acrylate, 6-vinyloxyhexyl (meth)acrylate, 4-vinyloxymethylcyclohexylmethyl (meth)acrylate, 3-vinyloxymethylcyclohexylmethyl (meth)acrylate, 2-vinyloxymethylcyclohexylmethyl (meth)acrylate, p-vinyloxymethylphenylmethyl (meth)acrylate, m-vinyloxymethylphenylmethyl (meth)acrylate, o-vinyloxy methylphenylmethyl, 2-(vinyloxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxy)propyl (meth)acrylate, 2-(2-vinyloxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate, 2-(vinyloxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxyethoxy)ethyl (meth)acrylate ) 2-(vinyloxyethoxyisopropoxy)ethyl acrylate, 2-(vinyloxyisopropoxyethoxy)ethyl meth)acrylate, 2-(vinyloxyisopropoxyisopropoxy)ethyl meth)acrylate, 2-(vinyloxyethoxyethoxy)propyl meth)acrylate, 2-(vinyloxyethoxyisopropoxy)propyl meth)acrylate, 2-(vinyloxyisopropoxy)propyl meth)acrylate, 2-(vinyloxyisopropoxy)propyl meth)acrylate (Xyisopropoxy)propyl, (meth)acrylate 2-(vinyloxyethoxyethoxy)isopropyl, (meth)acrylate 2-(vinyloxyethoxyisopropoxy)isopropyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)isopropyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)isopropyl, (meth)acrylate 2-(vinyloxyethoxyethoxyethoxy)ethyl, (meth)acrylate 2-(vinyloxyethoxyethoxy) Examples include xyethoxy)ethyl, 2-(isopropenoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate, polyethylene glycol monovinyl ether (meth)acrylate, and polypropylene glycol monovinyl ether (meth)acrylate.

[0050] Furthermore, radiation-curable inkjet ink compositions may contain compounds belonging to the glycol di(meth)acrylate group. Examples of such compounds include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol diacrylate (DPGDA), dipropylene glycol dimethacrylate, tripropylene glycol diacrylate (TPGDA), tripropylene glycol dimethacrylate, 1,4-butanediol di(meth)acrylate, and 1,3-butanediol di(meth)acrylate. Examples include dibutylene glycol di(meth)acrylate, tributylene glycol di(meth)acrylate, tetrabutylene glycol di(meth)acrylate, 1,5-pentanediol di(meth)acrylate, 1,4-pentanediol di(meth)acrylate, 1,3-pentanediol di(meth)acrylate, dipentylene glycol di(meth)acrylate, tripentylene glycol di(meth)acrylate, cyclopentanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, etc.

[0051] Furthermore, radiation-curable inkjet ink compositions may also contain (meth)acrylates having an aromatic ring skeleton. Examples of (meth)acrylate compounds having an aromatic ring skeleton include phenoxyethyl acrylate (PEA), phenoxyethyl methacrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, benzyl (meth)acrylate, and phenoxydiethylene glycol (meth)acrylate, nonylphenoxyethyl (meth)acrylate, and alkoxylated phenoxyethyl (meth)acrylate.

[0052] Furthermore, radiation-curable inkjet ink composition, N-methacryloylmorpholin, 1-acryloylpyrrolidine-2-one, 1-methacryloylpyrrolidine-2-one, 1-acryloylpiperidine-2-one, 1-methacryloylpiperidine-2-one, It may also contain 2-hydroxy-3-phenoxypropyl (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate (MEDOL-10 (trade name)), hydroxyethyl acrylamide (HEAA), hydroxyethyl methacrylamide, dimethylaminopropyl acrylamide (DMAPAA), dimethylaminopropyl methacrylamide, or derivatives thereof.

[0053] The radiation-curable inkjet ink composition according to this embodiment may contain an amine-modified oligomer as a polymerizable compound. However, from the viewpoint of improving ejection stability without increasing the viscosity of the radiation-curable inkjet ink composition, it is preferable that the amine-modified oligomer is either not included or not included in an amount exceeding 5% by mass. If it is included, it is preferable that the amount of amine-modified oligomer relative to the total amount of the ink composition be greater than 0% by mass and less than 5% by mass.

[0054] Amine-modified oligomers improve the curability of radiation-curable inkjet ink compositions, but when included in amounts exceeding 5% by mass, they tend to increase viscosity and worsen ejection stability during inkjet recording.

[0055] 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.

[0056] Examples of amine-modified oligomers include amine-modified (meth)acrylate oligomers.

[0057] 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.

[0058] 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).

[0059] 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.

[0060] The radiation-curable inkjet ink composition according to this embodiment may contain a urethane oligomer as a polymerizable compound. However, from the viewpoint of improving ejection stability without increasing the viscosity of the radiation-curable inkjet ink composition, it is preferable that the amount of urethane oligomer in the total amount of the ink composition does not exceed 5% by mass.

[0061] 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 5% by mass or less, more preferably less than 5% by mass, and even more preferably less than 3% by mass, relative to the total amount of polymerizable compounds.

[0062] Examples of urethane oligomers include urethane (meth)acrylate oligomers.

[0063] 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.).

[0064] The polymerizable compounds (monomers and / or oligomers) described herein may be used individually or in combination of two or more. The lower limit of the total content of all polymerizable compounds contained in the radiation-curable inkjet ink composition is not limited to 30.0% by mass or more, preferably 50.0% by mass or more, more preferably 60.0% by mass or more, and even more preferably 70.0% by mass or more, relative to the total mass (100% by mass) of the ink composition. The upper limit of the total content of polymerizable compounds is not limited to 95.0% by mass or less, preferably 90.0% by mass or less, more preferably 85.0% by mass or less, and even more preferably 80.0% by mass or less, relative to the total mass (100% by mass) of the ink composition.

[0065] 1.4.2. Formulation of polymerizable compounds The radiation-curable inkjet ink composition of this embodiment may contain polymerizable compounds other than the hydroxyl group-containing polymerizable compound (A) and the monofunctional polymerizable compound (B) as described in "1.4.1. Polymerizable Compounds Other Than Those Listed Above," but there is a preferred range for their formulation as follows.

[0066] The radiation-curable inkjet ink composition of this embodiment more preferably has a weighted average of the glass transition temperatures of the polymerizable compounds contained therein of 30°C to 70°C, and even more preferably 35°C to 65°C.

[0067] Here, the "weighted average of the glass transition temperatures of the contained polymerizable compounds" is calculated as follows: The glass transition temperature of each polymerizable compound contained in the radiation-curable inkjet ink composition is the glass transition temperature of the respective homopolymer of each polymerizable compound. The temperature obtained by apportioning the glass transition temperature of each polymerizable compound according to the mass ratio in which it is contained is defined as the "weighted average of the glass transition temperatures of the contained polymerizable compounds." In other words, the "weighted average of the glass transition temperatures of the contained polymerizable compounds" is calculated by setting the total mass of all polymerizable compounds contained in the radiation-curable inkjet ink composition to 100% by mass, and weighting the glass transition temperature of each polymerizable compound according to the proportion (mass%) that each polymerizable compound occupies.

[0068] If the weighted average of the glass transition temperatures of the polymerizable compounds contained is between 30°C and 70°C, it is easier to obtain recording materials with even better blocking and shrinking properties. The higher the glass transition temperature, the less the coating film and recording medium stick together, resulting in superior blocking properties. The lower the glass transition temperature, the greater the flexibility of the coating film, resulting in superior shrinking properties.

[0069] Furthermore, the radiation-curable inkjet ink composition of this embodiment preferably contains 50% by mass or more of monofunctional polymerizable compounds, more preferably 55% by mass or more, and even more preferably 60% by mass or more, based on the total mass of polymerizable compounds contained. This is preferable. In this way, the curability of the composition and the blocking resistance of the coating film can be further improved.

[0070] Furthermore, it is more preferable that the radiation-curable inkjet ink composition contains a nitrogen-containing heterocyclic compound as a polymerizable compound with a glass transition temperature of over 90°C. Examples of nitrogen-containing heterocyclic compounds with a glass transition temperature of over 90°C include acryloylmorpholine (ACMO) and vinylmethyloxazolidinone (VMOX). This further improves the blocking resistance of the coating film. Including a polymerizable compound with a glass transition temperature of over 90°C increases the weighted average of the glass transition temperatures of the contained polymerizable compounds, resulting in excellent blocking properties. Furthermore, including a nitrogen-containing heterocyclic compound also improves the curability of the coating film.

[0071] Furthermore, if the radiation-curable inkjet ink composition contains a polymerizable compound with a glass transition temperature exceeding 90°C, it is preferable that the content of such compound be 5% to 55% by mass, more preferably 10% to 50% by mass, even more preferably 15% to 45% by mass, and still more preferably 20% to 40% by mass, based on the total amount of the composition. This further improves the blocking resistance of the coating film.

[0072] 1.4.3. Colorants The radiation-curable inkjet ink composition according to this embodiment may contain a colorant. By containing a colorant, the radiation-curable inkjet ink composition according to this embodiment can be used as a colored ink composition.

[0073] The colorant content 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 colorant or contains a colorant in an amount not intended for coloring. An example of a colorant content not intended for coloring is 0.1% by mass or less, relative to the total amount of the ink composition.

[0074] 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.

[0075] 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.

[0076] Examples of organic pigments include azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye chelates (e.g., basic dye type chelates, acid dye type chelates, etc.); dye lakes (basic dye type lakes, acid dye type lakes); nitro pigments; nitroso pigments; carbon black; aniline black; and daylight fluorescent pigments.

[0077] Examples of black pigments include No.2300, No.900, MCF88, No.33, No.40, No.45, No.52, MA7, MA8, MA100, No.2200B, etc. (all are product names manufactured by Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5 000, Raven 3500, Raven 1255, Raven 700, etc. (manufactured by Carbon Columbia), Rega1 400R, Rega1 330R, Rega1 660R, Mogul (registered trademark) L, Monarch (registered trademark) 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc. (product names manufactured by Cabot JAPAN KK), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color B1ackS150, Color Black S160, Color Black S170, Printex(R) 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5. Special Examples include the Black 4A and Special Black 4 (all product names from Degussa).

[0078] 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.

[0079] 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, 180, and 185.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] The above pigments may be used individually or in combination of two or more.

[0084] 1.4.4. 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.

[0085] 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.

[0086] Commercially available polymer dispersants include the Azisper series from Ajinomoto Fine Techno Co., Ltd., the Solsperse series (Solsperse 36000, etc.) available from Avecia, Noveon, Lubrizol, etc., the Disparbic series from BYK Additives & Instruments, and the Disparon series from Kusumoto Chemicals, Ltd.

[0087] 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.

[0088] 1.4.5. Polymerization Inhibitors The radiation-curable inkjet ink composition according to this embodiment may contain a polymerization inhibitor. The polymerization inhibitor may be used alone or in combination of two or more types.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 1.4.6. Slip agents (surfactants) The radiation-curable inkjet ink composition according to this embodiment further comprises a slip agent That's fine. The slip agent may be used alone or in combination of two or more types.

[0093] 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).

[0094] 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.

[0095] 1.4.7. 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.).

[0096] 1.5. 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.

[0097] 1.6. Effects and Effects The radiation-curable inkjet ink composition of this embodiment contains a hydroxyl group-containing polymerizable compound (A) and a polymer thioxanthone polymerization initiator (C) as a polymerization initiator, thereby reducing the odor of the composition and improving its curability. Furthermore, the radiation-curable inkjet ink composition of this embodiment contains a monofunctional polymerizable compound (B) with a glass transition temperature of 10°C to 90°C, thereby suppressing the decrease in the blocking properties (and / or adhesion to the recording medium) of the coating film caused by the inclusion of a hydroxyl group-containing polymerizable compound (A) with a relatively low glass transition temperature.

[0098] 2. Inkjet recording method Next, an inkjet recording method using the above-described radiation-curable inkjet ink composition will be explained. This inkjet recording method includes an ejection step in which the above-described radiation-curable inkjet ink composition is ejected from the inkjet head and attached to a recording medium, and a radiation-curing step in which radiation is emitted onto the radiation-curable inkjet ink composition attached to the recording medium. One example is a method that includes an irradiation step of irradiating lines. The following describes each step of the inkjet recording method and the recording medium used in the inkjet recording method.

[0099] 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.

[0100] Inkjet heads used in the ejection process include line heads used in line systems and serial heads used in serial systems.

[0101] 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.

[0102] 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).

[0103] 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.

[0104] Since the ink composition contains a polymerization initiator, when irradiated with radiation, the polymerization initiator is excited, cleaved, and generates radicals and acids. These generated radicals and acids then accelerate the polymerization reaction of the monomers.

[0105] Examples of radiation include ultraviolet rays, infrared rays, visible light, X-rays, etc. When using ultraviolet rays as the radiation, examples of the light source include UV-LED (Light Emitting Diode), LD (Laser Diode), high-pressure mercury lamp, metal halide lamp, etc. When using a UV-LED or LD, the wavelength of the emitted radiation is preferably 200.0 nm or more and 430.0 nm or less.

[0106] In the irradiation step, the irradiation energy of the radiation irradiated at one time is preferably 150 mJ / cm 2 or more and 250 mJ / cm 2 less, and more preferably less than 150 mJ / cm 2 less. If the irradiation energy of the radiation is within the above range, the effects on the surface and the whole of the ink composition can be carried out more efficiently.

[0107] 2.3. Recording medium The form of the recording medium used in the inkjet recording method is not particularly limited, and examples include a film form, a boat form, etc.

[0108] The material of the recording medium is not particularly limited, and 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, cellulose nitrate, etc., metals such as iron, silver, copper, aluminum, etc., and glass.

[0109] 3. Recording device The recording device according to this embodiment includes the above-described radiation-curable inkjet ink composition and a head that discharges the radiation-curable inkjet ink composition.

[0110] The recording device of this embodiment can record with less odor and form images with good curability by including a hydroxyl group-containing polymerizable compound (A) and a polymer thioxanthone polymerization initiator (C) in the radiation-curable inkjet ink composition described above. Furthermore, with this recording device, by including a monofunctional polymerizable compound (B) with a glass transition temperature of 10°C to 90°C in the radiation-curable inkjet ink composition described above, images with good blocking properties (and / or adhesion to the recording medium) of the coating film that forms the resulting image can be formed.

[0111] The recording method of this embodiment can be performed using the inkjet recording apparatus of this embodiment. An example of an inkjet recording apparatus capable of performing the recording method of this embodiment is described below.

[0112] The inkjet recording apparatus of this embodiment includes a recording head for depositing a radiation-curable inkjet ink composition onto a film-like recording medium, an ultraviolet irradiation means for curing the coating by irradiating it with ultraviolet light to form a cured film, and a heating means for heating the cured film to a temperature above its glass transition temperature and below the thermal distortion temperature of the polymer contained in the recording medium.

[0113] As an inkjet recording apparatus used in the recording method according to this embodiment, for example, the one shown in Figure 1 can be used. Figure 1 is a perspective view of an inkjet recording apparatus that can be used in the recording method according to this embodiment. Figure 2 is a front view of the ultraviolet irradiation apparatus 90A (corresponding to 190A in Figure 2) and 90B (corresponding to 190B in Figure 2) shown in Figure 1. Figure 3 is a view taken along arrow AA in Figure 2.

[0114] The inkjet recording apparatus 20 shown in Figure 1 comprises a motor 30 that moves the recording medium P in the sub-scanning direction SS, a platen 40, a recording head 52 that ejects a radiation-curable inkjet ink composition as fine droplets from a head nozzle onto the recording medium P, a carriage 50 on which the recording head 52 is mounted, a carriage motor 60 that moves the carriage 50 in the main scanning direction MS, and a pair of ultraviolet irradiation devices 90A and 90B that eject droplets of the radiation-curable inkjet ink composition from the recording head 52 and irradiate the droplets that have adhered to the recording medium P with ultraviolet light.

[0115] The carriage 50 is towed by a traction belt 62 driven by a carriage motor 60 and moves along a guide rail 64.

[0116] The recording head 52 is mounted on the carriage 50 and moves in the main scanning direction MS as the carriage 50 moves in the direction of movement MS (hereinafter also referred to as the "main scanning direction").

[0117] Furthermore, the recording head 52 is capable of ejecting radiation-curable inkjet ink compositions. In the example shown in Figure 1, the recording head 52 is a serial head for full-color printing that ejects four colors of ink, and is equipped with numerous head nozzles for each color. In addition to the recording head 52, the carriage 50 on which the recording head 52 is mounted also includes a black cartridge 54, which serves as a black ink container for the black ink supplied to the recording head 52, and a color ink cartridge 56, which serves as color ink for the color ink supplied to the recording head 52. At least one of each cartridge 54, 56 contains the radiation-curable inkjet ink composition described above.

[0118] In the coating film formation process of this embodiment, the amount of liquid droplets ejected from the recording head 52 is preferably 1 pl or more and 20 pl or less. By keeping the liquid amount within this range, ejection stability is good and high-quality images can be obtained.

[0119] The carriage 50 is equipped with a capping device 80 at its home position (right-hand position in Figure 1) for sealing the nozzle surface of the recording head 52 when stopped. When the print job is finished and the carriage 50 reaches above this capping device 80, the capping device 80 automatically rises by a mechanism (not shown) to seal the nozzle surface of the recording head 52. This capping prevents the ink inside the nozzles from drying out or deteriorating. Positioning control of the carriage 50 is performed, for example, to precisely position the carriage 50 at the position of this capping device 80.

[0120] By using such an inkjet recording device 20, droplets of radiation-curable inkjet ink composition can be ejected onto a recording medium and adhered to the recording medium to form a coating film. Furthermore, with the inkjet recording device 20, the coating film formation process and the curing process can be performed continuously in a single device, without having to perform the coating film formation process and the curing process in separate devices.

[0121] Examples of irradiation means capable of emitting ultraviolet light include the ultraviolet irradiation devices shown in Figures 1 and 2.

[0122] As shown in Figures 1 to 3, the ultraviolet irradiation devices 190A and 190B are mounted on both ends of the carriage 50 along the direction of movement.

[0123] As shown in Figure 2, the ultraviolet irradiation device 190A, mounted on the left side of the recording head 52, irradiates droplets ejected onto the recording medium P with ultraviolet light when the carriage 50 moves to the right (in the direction of arrow B in Figure 2) during a right scan. On the other hand, the ultraviolet irradiation device 190B, mounted on the right side of the recording head 52, irradiates droplets ejected onto the recording medium P with ultraviolet light when the carriage 50 moves to the left (in the direction of arrow C in Figure 2) during a left scan.

[0124] Each ultraviolet irradiation device 190A and 190B is mounted on a carriage 50 and comprises a housing 194 that supports one ultraviolet light source 192 in alignment, and a light source control circuit (not shown) that controls the illumination and extinguishing of the ultraviolet light sources 192. As shown in Figures 2 and 3, each ultraviolet irradiation device 190A and 190B is provided with one ultraviolet light source 192, but two or more may be provided. It is preferable to use either an LED (Light Emitting Diode) or an LD (Laser Diode) as the ultraviolet light source 192. This avoids the need to enlarge the ultraviolet light source due to the installation of filters, etc., compared to cases where mercury lamps, metal halide lamps, or other lamps are used as the ultraviolet light source. Furthermore, the intensity of emitted ultraviolet light is not reduced by absorption by the filter, and radiation-curable inkjet ink compositions can be cured efficiently.

[0125] Furthermore, each ultraviolet light source 192 may emit the same wavelength or different wavelengths. When using an LED or LD as the ultraviolet light source 192, the wavelength of the emitted ultraviolet light should be within the range of approximately 350.0 nm to 430.0 nm.

[0126] According to the ultraviolet irradiation devices 190A and 190B, as shown in Figure 2, ultraviolet light 192a is irradiated onto droplets attached to the recording medium P by ejection from the recording head 52 by an ultraviolet light source 192 that irradiates the recording medium P near the recording head 52, and at least the surface of the droplets is irradiated. The material can be hardened to form an image on a recording medium.

[0127] The following describes a method for forming an image in a desired area by repeating the coating film formation process and curing process multiple times in this embodiment.

[0128] First, the carriage 50 is moved to the right (in the direction of arrow B in Figure 2) while droplets of one or more colors of radiation-curable inkjet ink composition are ejected onto the recording medium P, and ultraviolet light is irradiated onto the coating film by the ultraviolet irradiation device 190A. Next, a sub-scan is performed in which the recording medium P is moved in the sub-scanning direction SS. In this specification, one main scan in which droplets are ejected while the carriage 50 is moved in one direction of the main scanning direction MS and ultraviolet light is irradiated onto the droplets is referred to as one pass.

[0129] Subsequently, while moving the carriage 50 to the left (in the direction of arrow C in Figure 2), droplets of one or more colors are ejected onto the recording medium P using the method shown in the coating film formation step, and one main scan (1 pass) is performed in which ultraviolet light is irradiated onto the coating film by the ultraviolet irradiation device 190B. At this time, the coating film on the recording medium is irradiated with ultraviolet light by the ultraviolet irradiation device 190A and the ultraviolet irradiation device 190B. Next, a sub-scan is performed in which the recording medium P is moved in the sub-scan direction SS.

[0130] Through the above process, the coating formed in the first pass is irradiated with ultraviolet light in two passes, resulting in a total of three ultraviolet irradiations: once in the first pass and twice in the second pass. The coating formed in the second pass is irradiated with ultraviolet light in one pass, resulting in one ultraviolet irradiation.

[0131] By repeating this process, an image consisting of a collection of coatings can be formed in a predetermined area.

[0132] Furthermore, the inkjet recording apparatus 20 used in the recording method of this embodiment may also be equipped with a separate ultraviolet irradiation means (not shown) downstream of the sub-scanning direction SS, which is the direction in which the recording medium P moves. This allows the coating film on the recording medium P to be sufficiently cured to the interior after all passes have been completed and the image has been formed on the recording medium.

[0133] For example, if the integrated irradiation energy irradiated by the ultraviolet irradiation device 190A or 190B is insufficient and the droplet on the recording medium P is not cured to the inside, the ultraviolet irradiation means in the sub-scanning direction SS can be used to reliably cure the droplet to the inside.

[0134] The ultraviolet irradiation means for the sub-scanning direction SS only needs to be positioned so as to irradiate droplets on the recording medium P that have been sent in the sub-scanning direction SS with ultraviolet light. For example, it can be installed on the carriage 50 and downstream of the recording head 52 (in the sub-scanning direction SS, which is the direction in which the recording medium P moves). Furthermore, the same device as the ultraviolet irradiation device 190A (190B) can be used as the ultraviolet irradiation means for the sub-scanning direction SS.

[0135] Figure 4 is a schematic cross-sectional view illustrating the inkjet recording device 20. As shown in Figure 4, the inkjet recording device 20 includes a recording head 52, a heating element 5, a cooling fan 6, and a platen 40. The operation of the entire inkjet recording device 20 is controlled by a control unit (not shown).

[0136] The heating element 5 is a heater that can be used to heat the cured film attached to the recording medium P, that is, in a heating step after the curing process. The heating element 5 can relieve stress in the film by heating the recording medium P on which the cured film is recorded. This improves the adhesion between the cured film and the recording medium.

[0137] The heating element 5 may be an IR heater or the like, and the cured film may be heated by radiation using infrared radiation. Although not shown in the figures, the cured film may also be heated by blowing hot air onto the recording medium P. Furthermore, the heating element 5 may be of the conductive (contact) type.

[0138] Furthermore, the inkjet recording device 20 may also have a cooling fan 6. By heating the cured film onto the recording medium P and then cooling it with the cooling fan 6, it may be possible to form a cured film on the recording medium P with even better adhesion.

[0139] The lower limit of the surface temperature of the recording medium P heated by the heating element 5 is 30.0°C or higher, preferably 40.0°C or higher, and more preferably 50.0°C or higher. The upper limit of the surface temperature of the recording medium reached by the heating process is 150.0°C or lower, preferably 120.0°C or lower, and more preferably 100.0°C or lower. This allows the cured film to be heated to a similar temperature.

[0140] 4. Examples and Comparative Examples The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Hereinafter, "parts" and "%" refer to mass unless otherwise specified. Unless otherwise specified, evaluations were performed in an environment of 25°C and 40.0% relative humidity.

[0141] 4.1. Preparation of each composition For each example of the radiation-curable inkjet ink composition listed in Tables 1 to 4, the colorant, dispersant, and a portion of each monomer were weighed and placed in a pigment dispersion tank. A ceramic bead mill with a diameter of 1 mm was placed in the tank and stirred to obtain a pigment dispersion in which the colorant was dispersed in a polymerizable compound. Next, the remaining monomer, polymerization initiator, and other listed components were placed in a stainless steel mixing tank to obtain the composition shown in Tables 1 to 4. After mixing and stirring until completely dissolved, the pigment dispersion was added and the mixture was stirred at room temperature for 1 hour. Finally, the mixture was filtered through a 5 μm membrane filter to obtain the radiation-curable inkjet ink compositions shown in Tables 1 to 4. The numerical values ​​for each component in the tables represent mass percent.

[0142] Tables 1 to 4 show the glass transition temperature (Tg) and molecular weight of each polymerizable compound. Tables 1 to 4 also show, for each example composition, the percentage (mass%) of monofunctional monomers relative to the total composition, the percentage (mass%) of monofunctional monomers relative to the total amount of polymerizable compounds in the composition, the percentage (mass%) of polyfunctional monomers relative to the total amount of polymerizable compounds in the composition, and the weighted average value (°C) of the glass transition temperatures of the polymerizable compounds in the composition.

[0143] The ingredients used in each table are as follows: • CN991: Product name, manufactured by Sartomer, urethane diacrylate oligomer • CN9893: Product name, manufactured by Sartomer, urethane diacrylate oligomer • MEHQ: Hydroquinone monomethyl ether • LA-7RD: Product name "ADEKA Stab LA-7RD" (2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl), manufactured by ADEKA Corporation. • Omnirad 819: Trade name, manufactured by IGM Resins, acylphosphine-based photoinitiator, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide • TPO-L: Product name "Omnirad TPO-L", manufactured by IGM RESINS, acylphosphine-based photoinitiator, ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate • Speedcure 7010: Product name, manufactured by Sartomer, high molecular weight thioxanthone polymerization initiator (thioxanthone polymer type) • Omnipol TX: Product name, manufactured by IGM Resins, high molecular weight thioxanthone polymerization initiator (thioxanthone polymer type) • Speedcure DETX: Brand name, manufactured by IGM RESINS, low molecular weight thioxanthone polymerization initiator (thioxanthone type), 2,4-diethylthioxanthone • BYK UV3500: Manufactured by BYK Additives & Instruments (surfactant, slip agent) • Solsperse 36000: Product name, manufactured by Lubrizol (polymer dispersant) • Carbon Black: CI Pigment Black 7

[0144] 4.2. Evaluation Method 4.2.1. Curability Each example of radiation-curable ink composition was applied to a PET film using a bar coater to a film thickness of 5 μm (as the thickness of the cured film). UV-LED (peak wavelength 395 nm, irradiation intensity 1000 mW / cm²) was used. 2 The irradiation was performed using [mJ / cm²], and the irradiation energy used until the tack-free state was achieved was determined. Irradiation energy [mJ / cm²] 2 ] is the irradiation intensity [mW / cm²] on the irradiated surface from the light source. 2 [ ] was measured and the result was obtained from the product of this value and the irradiation duration [sec].

[0145] Irradiation intensity was measured using a UV intensity meter UM-10 and a light receiving unit UM-400 (both manufactured by Konica Minolta Sensing, Inc.). The tack-free state was determined by the following conditions: whether or not ink adhered to the cotton swab, or whether or not scratches appeared on the ink-cured material on the recording medium. The cotton swabs used were Johnson & Johnson cotton swabs. The swabbing was performed 10 times back and forth, with a swabbing force of 100g.

[0146] Based on the irradiation energy at which the material became tack-free, the curing properties were evaluated according to the evaluation criteria below, and the results are shown in Table 5. A rating of "B" or higher was considered a good level. (Evaluation Criteria) AA: Tack-free energy 150 mJ / cm² 2 less than A: Tack-free energy 150 mJ / cm² 2 More than 250mJ / cm 2 less than B: Tack-free energy 250 mJ / cm² 2More than 350mJ / cm 2 less than C: Tack-free energy 350 mJ / cm² 2 That's all.

[0147] 4.2.2. Blocking Using an inkjet printer "PX-G5000" (product name, manufactured by Seiko Epson Corporation), a solid pattern image, i.e., 100% dot generation, was printed on the PET film "Bonset" (product name, manufactured by Takiron CI Co., Ltd.), the recording medium, at room temperature and atmospheric pressure, with a recording resolution of 600 dpi x 600 dpi and a droplet weight of 10 ng, to obtain a printed sample with a film thickness of 5 μm.

[0148] The solid pattern image is an image in which dots are recorded for all pixels of the pixel, which is the smallest recording unit area defined by the recording resolution. The above printing was performed, and ultraviolet light was irradiated from a UV-LED in an ultraviolet irradiation device mounted next to the carriage, to obtain a recording on which a cured film of the ink composition with a thickness of 5 μm was formed on the recording medium.

[0149] The recording obtained as described above was rolled up so that the hardened film was on the inside and processed into a cylindrical shape. This recording was placed around the container (glass bottle), which was the packaged object, that had been preheated in a constant temperature bath. The recording material was placed in a 90°C constant temperature bath and left undisturbed for 10 seconds to shrink and adhere tightly to the container.

[0150] In the packaging of the packaged material described above, the presence or absence of adhesion was evaluated by visually observing whether the hardened film had transferred to the container by shrinking and adhering the record to the packaged material. Blocking resistance was evaluated according to the following evaluation criteria, and the results are shown in Table 5. A rating of "B" or higher was considered a good level. (Evaluation Criteria) A: No adhesion of the hardened film to the container. B: The hardened film is slightly adhered to the container. C: The hardened film adheres to the container (and peels off).

[0151] 4.2.3. Odor of Records The recorded samples obtained in the same manner as described in "4.2.1. Curability" above were smelled and evaluated according to the following criteria, and the results are recorded in Table 5. A rating of "A" or higher was considered a good level. A: There is no odor, or there is a slight odor. B: It smells bad. C: It has a strong odor.

[0152] 4.2.4. Adhesion For the records obtained in the same manner as described in "4.2.1. Curability" above, adhesion was evaluated by a cross-cut test in accordance with JIS K5600-5-6. Specifically, an incision was made in the obtained cured coating, transparent adhesive tape was applied to the incision, and the tape was rubbed thoroughly with a finger until the cured coating was visible through it. Next, within 5 minutes of applying the tape, the tape was peeled off the cured coating at an angle close to 60° for 0.5 to 1.0 seconds. Based on whether or not the cured coating peeled off the film at this time, adhesion was evaluated according to the evaluation criteria below, and the results are shown in Table 5. (Evaluation Criteria) A: Peeling of the cured film was observed in less than 20% of the grid. B: Peeling of the cured film was observed in 10% to less than 30% of the grid. C: Peeling of the cured film was observed in more than 30% of the lattice.

[0153] 4.2.5. Shrinkage Characteristics In the evaluation of blocking resistance described in "4.2.2. Blocking" above, the wrinkle formation after shrinkage was visually observed in the packaging of the prepared material, and the shrinkage characteristics were evaluated according to the following evaluation criteria. The results are shown in Table 5. (Evaluation Criteria) A: No wrinkles in the hardened film. B: Wrinkles present in the hardened film.

[0154] 4.3. Evaluation Results As seen in each table, the radiation-curable inkjet ink compositions of each example, which included a hydroxyl group-containing polymerizable compound (A), a monofunctional polymerizable compound (B) other than the hydroxyl group-containing polymerizable compound (A) with a glass transition temperature of 10°C to 90°C, and a polymer thioxanthone polymerization initiator (C), all showed good results in terms of curability, blocking resistance, and odor of the recorded material. In contrast, the comparative examples, which did not include any of the hydroxyl group-containing polymerizable compound (A), the monofunctional polymerizable compound (B) other than the hydroxyl group-containing polymerizable compound (A) with a glass transition temperature of 10°C to 90°C, and the polymer thioxanthone polymerization initiator (C), all showed insufficient results in terms of curability, blocking resistance, and odor of the recorded material.

[0155] The present invention includes configurations substantially identical to those described in the embodiments, for example, configurations with the same function, method, and results, or configurations with the same purpose and effect. Furthermore, the present invention 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 those described in the embodiments. Finally, the present invention includes configurations that add known technology to the configurations described in the embodiments.

[0156] The following can be derived from the embodiments and modifications described above.

[0157] Radiation-curable inkjet ink composition, A hydroxyl group-containing polymerizable compound (A), A monofunctional polymerizable compound (B) other than the hydroxyl group-containing polymerizable compound (A) has a glass transition temperature of 10°C or more and 90°C or less, Polymer thioxanthone polymerization initiator (C), Includes.

[0158] This radiation-curable inkjet ink composition contains a hydroxyl group-containing polymerizable compound (A) and a polymer thioxanthone polymerization initiator (C) as a polymerization initiator, thereby reducing the odor of the composition and improving its curability. Furthermore, this radiation-curable inkjet ink composition contains a monofunctional polymerizable compound (B) with a glass transition temperature of 10°C to 90°C, which suppresses the decrease in the blocking properties (and / or adhesion to recording media) of the coating film caused by the inclusion of a hydroxyl group-containing polymerizable compound (A) with a relatively low glass transition temperature.

[0159] In the above radiation-curable inkjet ink composition, The monofunctional polymerizable compound (B) may include one or more selected from cyclic ether polymerizable compounds and hydrocarbon ring polymerizable compounds.

[0160] This radiation-curable inkjet ink composition allows for better curability.

[0161] In the above radiation-curable inkjet ink composition, The cyclic ether polymerizable compound of the monofunctional polymerizable compound (B) may include cyclic trimethylolpropane formal acrylate. Or, The hydrocarbon ring polymerizable compound of the monofunctional polymerizable compound (B) may include 4-tert-butylcyclohexyl acrylate or 3,3,5-trimethylcyclohexyl acrylate.

[0162] This radiation-curable inkjet ink composition allows for further improvement in the curability of the composition and the blocking resistance of the coating film.

[0163] In the above radiation-curable inkjet ink composition, The content of the monofunctional polymerizable compound (B) may be 10% by mass or more and 50% by mass or less based on the total amount of the composition.

[0164] This radiation-curable inkjet ink composition allows for further improvement in the curability of the composition and the blocking resistance of the coating film.

[0165] In the above radiation-curable inkjet ink composition, The hydroxyl group-containing polymerizable compound (A) is 4-hydroxybutyl acrylate, hydroxy It may also contain one or more selected from cypropyl acrylate, hydroxyethyl acrylate, and 2-hydroxy-3-phenoxypropyl acrylate.

[0166] This radiation-curable inkjet ink composition exhibits a viscosity more suitable for inkjet applications, and the cured coating film of the composition can achieve even higher adhesion to the recording medium.

[0167] In the above radiation-curable inkjet ink composition, The content of the hydroxyl group-containing polymerizable compound (A) may be 5% by mass or more and 40% by mass or less based on the total amount of the composition.

[0168] This radiation-curable inkjet ink composition can further improve the blocking resistance of the coating film.

[0169] In the above radiation-curable inkjet ink composition, The polymer thioxanthone polymerization initiator (C) 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).

[0170] This radiation-curable inkjet ink composition suppresses the volatilization of unreacted polymerizable compounds and decomposition products of polymerization initiators, thereby further reducing odor.

[0171] In the above radiation-curable inkjet ink composition, The composition may also contain a polymerizable compound with a glass transition temperature exceeding 90°C in an amount of 10% to 50% by mass relative to the total amount of the composition.

[0172] This radiation-curable inkjet ink composition can further improve the blocking resistance of the coating film.

[0173] In the above radiation-curable inkjet ink composition, The polymerizable compound having a glass transition temperature of over 90°C may include a compound having a nitrogen-containing heterocyclic structure.

[0174] This radiation-curable inkjet ink composition can further improve the blocking resistance of the coating film.

[0175] In the above radiation-curable inkjet ink composition, The glass transition temperature of the polymerizable compound contained may be 30°C or higher and 70°C or lower on a weighted average basis.

[0176] This radiation-curable inkjet ink composition yields recordings with excellent blocking and shrinking properties.

[0177] In the above radiation-curable inkjet ink composition, The product contains 50% or more by mass of monofunctional polymerizable compounds relative to the total mass of polymerizable compounds. It may also be used.

[0178] This radiation-curable inkjet ink composition allows for further improvement in the curability of the composition and the blocking resistance of the coating film.

[0179] In the above radiation-curable inkjet ink composition, The oligomer does not need to be contained in more than 5% by mass relative to the total amount of the composition.

[0180] This radiation-curable inkjet ink composition suppresses the increase in viscosity of the ink composition due to oligomers, making it possible to achieve a viscosity more suitable for inkjet applications.

[0181] The recording device is The above-mentioned radiation-curable inkjet ink composition, A head for ejecting the radiation-curable inkjet ink composition, It is equipped with.

[0182] According to this recording device, the above-mentioned radiation-curable inkjet ink composition contains a hydroxyl group-containing polymerizable compound (A) and a polymer thioxanthone polymerization initiator (C) as a polymerization initiator, enabling recording with less odor and forming images with good curability. Furthermore, according to this recording device, the above-mentioned radiation-curable inkjet ink composition contains a monofunctional polymerizable compound (B) with a glass transition temperature of 10°C to 90°C, enabling the formation of images with good blocking properties (and / or adhesion to the recording medium) of the coating film that forms the resulting image. [Explanation of Symbols]

[0183] 5…Heating heater, 6…Cooling fan, 20…Inkjet recording device, 30…Motor, 40…Platen, 50…Carriage, 52…Recording head, 54…Black ink cartridge, 56…Color ink cartridge, 60…Carriage motor, 62…Tow belt, 64…Guide rail, 80…Capping device, 90A (190A), 90B (190B)…Active radiation irradiation device, 192, 193…Active radiation light source, 194…Housing, P…Recording medium

Claims

1. A hydroxyl group-containing polymerizable compound (A), A monofunctional polymerizable compound (B) other than the hydroxyl group-containing polymerizable compound (A) has a glass transition temperature of 10°C or more and 90°C or less, Polymer thioxanthone polymerization initiator (C), A radiation-curable inkjet ink composition containing the following:

2. The radiation-curable inkjet ink composition according to claim 1, wherein the monofunctional polymerizable compound (B) comprises one or more selected from cyclic ether polymerizable compounds and hydrocarbon ring polymerizable compounds.

3. The cyclic ether polymerizable compound of the monofunctional polymerizable compound (B) contains cyclic trimethylolpropaneformal acrylate, or The radiation-curable inkjet ink composition according to claim 2, wherein the hydrocarbon ring polymerizable compound of the monofunctional polymerizable compound (B) comprises 4-tert-butylcyclohexyl acrylate or 3,3,5-trimethylcyclohexyl acrylate.

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

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

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

7. The radiation-curable inkjet ink composition according to claim 1, wherein the polymer thioxanthone polymerization initiator (C) 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).

8. The radiation-curable inkjet ink composition according to claim 1, comprising 10% by mass or more and 50% by mass or less of a polymerizable compound having a glass transition temperature of over 90°C, based on the total amount of the composition.

9. The radiation-curable inkjet ink composition according to claim 1, wherein the polymerizable compound having a glass transition temperature of more than 90°C includes a compound having a nitrogen-containing heterocyclic structure.

10. The radiation-curable inkjet ink composition according to claim 1, wherein the weighted average glass transition temperature of the polymerizable compound contained is 30°C or higher and 70°C or lower.

11. The radiation-curable inkjet ink composition according to claim 1, wherein monofunctional polymerizable compounds are contained in an amount of 50% by mass or more based on the total mass of polymerizable compounds contained.

12. The radiation-curable inkjet ink composition according to claim 1, wherein the oligomer does not contain more than 5% by mass of the total amount of the composition.

13. A radiation-curable inkjet ink composition according to any one of claims 1 to 12, A head for ejecting the radiation-curable inkjet ink composition, A recording device equipped with this device.

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