Inkjet ink composition and recording method

Abstract

To provide an inkjet ink composition having excellent storage stability and curability under conditions of both low and high temperature, while odor is reduced.SOLUTION: An inkjet ink composition includes phenyl(2,4,6-trimethylbenzoyl)phosphine oxide ethyl and a hydroxyl group-containing monomer, wherein the composition does not contain an aromatic group-containing polymerizable compound, or, when an aromatic group-containing polymerizable compound is contained, the content of the aromatic group-containing polymerizable compound is 5.0 mass% or less with respect to the total amount of the inkjet ink composition, and wherein the composition does not contain water, or, when water is contained, the content of water is less than 2 mass% with respect to the total amount of the inkjet ink composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ink-jet ink composition and a recording method. [Background technology]

[0002] The inkjet recording method is capable of recording high-resolution images using a relatively simple device, and has been rapidly developing in various fields. In the process, various studies have been conducted on storage stability, etc. For example, a printing ink containing 20.0 to 70.0 mass% of a water-soluble acrylamide monomer, 5.0 to 60.0 mass% of a water-soluble hydroxyl group-containing monofunctional monomer, and 8.0 to 35.0 mass% of a water-insoluble polymerizable compound relative to the total mass of all polymerizable components, and further containing 3.0 to 10.0 mass parts of a photopolymerization initiator and / or sensitizer relative to 100 mass parts of the total mass of all polymerizable components, a pigment, and water, a mass ratio of the water-soluble acrylamide monomer to the water-soluble hydroxyl group-containing monofunctional monomer (acrylamide monomer / hydroxyl group-containing monofunctional monomer) of 0.3 to 10.0, and a UV-LED having a peak wavelength of 365 to 405 nm, with an integrated light intensity of 100 mJ / cm is used. 2 It is known that a UV-curable aqueous ink jet printing ink composition having excellent storage stability can be obtained by including the following step of provisionally curing the ink by irradiation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2022 / 180962 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the ink composition disclosed in Patent Document 1 does not have sufficient curability when formed into a coating film, and there are also problems with the odor of the coating film. Furthermore, the present inventors have conducted extensive research to enable storage of ink compositions while suppressing deterioration in quality even in various environments, and as a result have discovered new problems, such as the generation of foreign matter in the ink composition during long-term storage under low-temperature or high-temperature conditions. For example, these problems have revealed issues with the storage stability of ink compositions, such as the problem that the polymerization initiator in the ink composition precipitates and generates foreign matter during long-term storage under low-temperature conditions, and the problem that foreign matter is generated due to the influence of moisture in the inkjet ink composition during long-term storage under high-temperature conditions. [Means for solving the problem]

[0005] The inkjet ink composition of the present invention contains ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate and a hydroxyl group-containing monomer, and does not contain an aromatic group-containing polymerizable compound, or if it contains an aromatic group-containing polymerizable compound, the content of the aromatic group-containing polymerizable compound is 5.0 mass % or less relative to the total amount of the inkjet ink composition; and does not contain water, or if it contains water, the content of the water is less than 2 mass % relative to the total amount of the inkjet ink composition.

[0006] The recording method of the present invention includes a discharge step of discharging the inkjet ink composition from an inkjet head to adhere it to a recording medium. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a table showing the results of examples. [Figure 2] 1 is a table showing the results of examples. [Figure 3] 10 is a table showing the results of comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail. However, the embodiment described here is an example for explaining the present invention, and the present invention is not limited thereto. That is, the technical scope of the present invention should be defined based on the description of the claims, and the present invention can be practiced by arbitrarily modifying the following embodiment within the scope of the gist thereof. In this specification, for example, the expression of a numerical range such as "1 to 100" includes both the lower limit "1" and the upper limit "100". The same applies to the expression of other numerical ranges.

[0009] In this specification, "(meth)acryloyl" means at least one of acryloyl and its corresponding methacryloyl, "(meth)acrylate" means at least one of acrylate and its corresponding methacrylate, and "(meth)acrylic" means at least one of acrylic and its corresponding methacrylic.

[0010] 1. Inkjet ink composition The inkjet ink composition according to this embodiment (hereinafter also simply referred to as the "ink composition") contains ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate and a hydroxyl group-containing monomer, and does not contain an aromatic group-containing polymerizable compound, or if it contains an aromatic group-containing polymerizable compound, the content of the aromatic group-containing polymerizable compound is 5.0 mass% or less relative to the total amount of the inkjet ink composition; and does not contain water, or if it contains water, the content of water is less than 2 mass% relative to the total amount of the inkjet ink composition.

[0011] It has been found that conventional inkjet ink compositions containing 2,4,6-trimethylbenzoyldiphenylphosphine oxide or the like as an initiator precipitate and form foreign matter when stored for a long period of time in a low-temperature storage environment. Furthermore, moisture in the inkjet ink composition also forms foreign matter when stored in a high-temperature storage environment. Furthermore, when the inkjet ink composition is formed into a coating, it has no odor and exhibits insufficient curability.

[0012] To address these issues, the inkjet ink composition according to this embodiment contains ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate as a polymerization initiator, thereby suppressing precipitation of the polymerization initiator even when stored at low temperatures for long periods of time. Furthermore, the inclusion of a hydroxyl group-containing monomer that has good compatibility with the polymerization initiator can improve the curability of the inkjet ink composition. Furthermore, by adjusting the content of the aromatic group-containing polymerizable compound within the above range, the odor of the inkjet ink composition can be suppressed. Furthermore, by adjusting the content of water within the above range, the generation of foreign matter due to moisture can be suppressed even when stored at high temperatures for long periods of time.

[0013] The ink composition according to this embodiment is an ink composition that is ejected from an inkjet head by an inkjet method, and the ink composition may be a radiation-curable inkjet ink composition that is cured by exposure to radiation. Hereinafter, a radiation-curable ink composition will be described as one embodiment of the ink composition, but the composition according to this embodiment may also be a composition other than an ink composition, for example, a composition used for 3D modeling.

[0014] The radiation-curable inkjet composition is cured by irradiation with radiation. Examples of radiation include ultraviolet light, electron beams, infrared light, visible light, and X-rays. As the radiation, ultraviolet light is preferred because radiation sources are readily available and widely used, and materials suitable for curing by ultraviolet radiation are readily available and widely used.

[0015] 1.1. Photopolymerization initiator The ink composition of this embodiment contains ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate as a photopolymerization initiator, and may contain other photopolymerization initiators as needed.

[0016] The total content of the photopolymerization initiators is preferably 4 to 17 mass %, 8 to 16 mass %, or 12 to 15 mass %, relative to the total amount of the ink composition.

[0017] 1.1.1. Ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate Ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate is a photopolymerization initiator, and is a reactant that, when irradiated with radiation, absorbs the radiation to generate radicals, thereby promoting polymerization of the ink composition.

[0018] By including ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate, the ink composition not only functions as a polymerization initiator, but also suppresses precipitation of the polymerization initiator even when the ink composition is stored at low temperatures for an extended period of time, thereby providing the ink composition with excellent storage stability.

[0019] The content of ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate is preferably 1 to 14 mass%, 2 to 12 mass%, 3 to 10 mass%, or 4 to 10 mass%, relative to the total amount of the ink composition. When the content of ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate is within the above range, storage stability under low temperature conditions tends to be further improved.

[0020] The content of ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate is preferably 10 to 100 mass%, 20 to 90 mass%, or 30 to 80 mass%, relative to the total amount of the polymerization initiator. When the content of ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate is within the above range, storage stability and curability under low temperature conditions tend to be further improved.

[0021] Commercially available products of ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate include IRGACURETPO-L (manufactured by BASF).

[0022] 1.1.2. Other photoinitiators The ink composition according to this embodiment may further contain a photopolymerization initiator other than ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate. The other photopolymerization initiators may be used alone or in combination of two or more. By including the other photopolymerization initiator, the curability is further improved.

[0023] The other photopolymerization initiator is not particularly limited as long as it generates an active species upon irradiation with radiation. Examples include known photopolymerization initiators such as acylphosphine oxide-based photopolymerization initiators other than ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate, alkylphenone-based photopolymerization initiators, titanocene-based photopolymerization initiators, and thioxanthone-based photopolymerization initiators. Among these, acylphosphine oxide-based photopolymerization initiators are preferred. Using such a photopolymerization initiator in combination with ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate further improves the curability of the ink composition, particularly the curability in a curing process using UV-LED light. Therefore, both storage stability and curability at low temperature conditions can be improved.

[0024] The acylphosphine oxide photopolymerization initiator is not particularly limited, but examples thereof include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0025] Commercially available examples of such acylphosphine oxide photopolymerization initiators include IRGACURE 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide), IRGACURE 1800 (a mixture of bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide and 1-hydroxycyclohexylphenyl ketone in a mass ratio of 25:75), and IRGACURE TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide) (all manufactured by BASF).

[0026] The content of the acylphosphine oxide photopolymerization initiator is preferably 0.5 to 10.0 mass %, 2.0 to 8.5 mass %, or 4.0 to 7.0 mass %, relative to the total amount of the ink composition.

[0027] The thioxanthone-based photopolymerization initiator is not particularly limited, but examples thereof include thioxanthone, 2-methylthioxanthone, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, and 2,4-diethylthioxanthone.

[0028] Commercially available thioxanthone-based photopolymerization initiators include, for example, KAYACURE DETX-S (2,4-diethylthioxanthone, trade name of Nippon Kayaku Co., Ltd.), Speedcure DETX (2,4-diethylthioxanthone, trade name of Lambson Co., Ltd.), and KAYACURE ITX (2- / 4-isopropylthioxanthone, trade name of Nippon Kayaku Co., Ltd.).

[0029] The content of the thioxanthone-based photopolymerization initiator is preferably 0.5 to 5.0 mass %, 1.0 to 4.0 mass %, or 2.0 to 3.0 mass %, relative to the total amount of the ink composition.

[0030] 1.2. Polymerizable compounds The ink composition of this embodiment contains a hydroxyl group-containing monomer as a polymerizable compound, but does not contain an aromatic group-containing polymerizable compound, or if it contains an aromatic group-containing polymerizable compound, the amount of the aromatic group-containing polymerizable compound is 5.0 mass% or less relative to the total amount of the inkjet ink composition. Furthermore, the ink composition of this embodiment may optionally contain an alicyclic ring-containing monofunctional monomer, an oxygen-containing cyclic monofunctional monomer, or a nitrogen-containing cyclic monofunctional monomer as a monofunctional monomer not containing a hydroxyl group, and may also contain a polyfunctional monomer not containing a hydroxyl group.

[0031] The content of the monofunctional monomer is preferably 10 to 80 mass %, 15 to 70 mass %, or 20 to 50 mass % relative to the total amount of the ink composition.

[0032] The content of the polyfunctional monomer is preferably 20 to 80 mass %, 30 to 70 mass %, or 40 to 60 mass % relative to the total amount of the ink composition.

[0033] 1.2.1. Hydroxyl-containing monomers The hydroxyl group-containing monomer of this embodiment is not particularly limited and may be a hydroxyl group-containing monofunctional monomer having one polymerizable functional group or a hydroxyl group-containing polyfunctional monomer having multiple polymerizable functional groups. The hydroxyl group-containing monomer may be used alone or in combination of two or more.

[0034] The hydroxyl group-containing monomer is not particularly limited, and examples of hydroxyl group-containing monofunctional monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; hydroxycycloalkyl methacrylates such as 1,4-cyclohexanedimethanol monoacrylate; acrylamides such as N-hydroxymethyl (meth)acrylamide; and polyfunctional monomers such as pentaerythritol triacrylate.

[0035] Among these, hydroxyl group-containing monofunctional monomers such as 4-hydroxybutyl(meth)acrylate and 1,4-cyclohexanedimethanol monoacrylate (CHDMMA) are preferred, and 4-hydroxybutyl acrylate (4-HBA) is particularly preferred. Use of such hydroxyl group-containing monomers tends to improve the adhesion and curability of the coating film.

[0036] The content of the hydroxyl group-containing monomer relative to the total amount of the ink composition is preferably 5 to 50 mass %, 10 to 45 mass %, or 20 to 40 mass %. When the content of the hydroxyl group-containing monomer is within the above range, the adhesion and curability of the coating film tend to be further improved.

[0037] 1.2.2. Polymerizable compounds containing aromatic groups It is preferable that the composition does not contain an aromatic group-containing polymerizable compound, but if an aromatic group-containing polymerizable compound is contained, its content is preferably small. The aromatic group-containing polymerizable compound is not particularly limited as long as it has an aromatic group and one or more polymerizable functional groups, but for example, it may contain an aromatic group-containing monofunctional monomer having one polymerizable functional group, an aromatic group-containing polyfunctional monomer having multiple polymerizable functional groups, or an oligomer having one or more polymerizable functional groups as needed. The aromatic group-containing polymerizable compound may be used alone or in combination of two or more.

[0038] The aromatic group-containing polymerizable compound is not particularly limited, but examples thereof include phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, alkoxylated 2-phenoxyethyl (meth)acrylate, ethoxylated nonylphenyl (meth)acrylate, alkoxylated nonylphenyl (meth)acrylate, p-cumylphenol EO-modified (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate.

[0039] When an aromatic group-containing polymerizable compound is contained, the content of the aromatic group-containing polymerizable compound is 5% by mass or less, preferably 1% by mass or less, and 0.1% by mass or less, relative to the total amount of the ink composition. The lower limit of the content of the aromatic group-containing polymerizable compound is not particularly limited, and the lower the content, the better, and it may not be contained at all (0% by mass. 0% by mass includes 0% by mass obtained by rounding down to one decimal place). By containing an aromatic group-containing polymerizable compound in an amount of 5% by mass or less, the odor of the cured product of the ink composition tends to be suppressed. When an aromatic group-containing polymerizable compound is not contained, the odor can be further suppressed.

[0040] 1.2.3. Other polymerizable compounds The ink composition of this embodiment may contain other polymerizable compounds. Examples of other polymerizable compounds include monofunctional monomers having one polymerizable functional group and no hydroxyl group, polyfunctional monomers having multiple polymerizable functional groups, and, as needed, oligomers having one or more polymerizable functional groups. Each of these polymerizable compounds may be used alone, or two or more may be used in combination.

[0041] 1.2.3.1. Monofunctional monomers that do not contain hydroxyl groups The monofunctional monomer not containing a hydroxyl group is not particularly limited, but examples thereof include an alicyclic monofunctional monomer, a nitrogen-containing cyclic monofunctional monomer, an oxygen-containing cyclic monofunctional monomer, a monofunctional (meth)acrylate having a crosslinked condensed ring structure, and a saturated aliphatic group-containing monofunctional monomer. Alternatively or in addition to these, other monofunctional monomers may be included as needed. The other monofunctional monomers are not particularly limited, but conventionally known monofunctional monomers having a polymerizable functional group, particularly a polymerizable functional group having a carbon-carbon unsaturated double bond, can be used. Among these, it is preferable to include one or more selected from the group consisting of an alicyclic monomer, an oxygen-containing cyclic monomer, and a nitrogen-containing cyclic monomer.

[0042] The alicyclic ring-containing monofunctional monomer is not particularly limited, but examples thereof include isobornyl(meth)acrylate (IBXA), tert-butylcyclohexanol acrylate (TBCHA), and 2-(meth)acrylate-1,4-dioxaspiro[4,5]dec-2-ylmethyl.

[0043] The content of the alicyclic monofunctional monomer relative to the total amount of the ink composition is preferably 1 to 30 mass%, 3 to 25 mass%, or 5 to 20 mass%. When the content of the alicyclic monofunctional monomer is within the above range, the adhesion and curability of the coating film tend to be further improved.

[0044] The oxygen-containing cyclic monofunctional monomer is not particularly limited, but examples thereof include ether cyclic monofunctional monomers, such as cyclic trimethylolpropane formal acrylate (CTFA), cyclic trimethylolpropane formal methacrylate, tetrahydrofurfuryl acrylate (THFA), (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl acrylate (MEDOL-10), and tetrahydrofurfuryl methacrylate.

[0045] The content of the oxygen-containing cyclic monofunctional monomer is preferably 1 to 40 mass%, 2 to 35 mass%, 3 to 30 mass%, or 5 to 30 mass%, relative to the total amount of the ink composition. When the content of the oxygen-containing cyclic monofunctional monomer is within the above range, the adhesion and curability of the coating film tend to be further improved.

[0046] The nitrogen-containing monofunctional monomer is not particularly limited, but examples thereof include nitrogen-containing vinyl monomers such as vinylmethyloxazolidinone (VMOX), N-vinylcaprolactam, N-vinylcarbazole, and N-vinylpyrrolidone; nitrogen-containing acrylate monomers such as acryloylmorpholine; and nitrogen-containing acrylamide monomers such as (meth)acrylamide, diacetoneacrylamide, N,N-dimethyl(meth)acrylamide, and dimethylaminoethyl acrylate benzyl chloride quaternary salt. Among these, nitrogen-containing vinyl monomers are preferred from the viewpoint of the adhesion and curability of the coating film, and among nitrogen-containing vinyl monomers, oxazolidine group-containing monofunctional monomers having an oxazolidine group are more preferred, with vinylmethyloxazolidinone (VMOX) being particularly preferred.

[0047] The content of the nitrogen-containing monofunctional monomer is preferably 3 to 30 mass %, 4 to 25 mass %, or 5 to 20 mass %, relative to the total amount of the ink composition. When the content of the nitrogen-containing monofunctional monomer is within the above range, the adhesion and curability of the coating film tend to be further improved.

[0048] Among the above-mentioned monofunctional monomers not containing a hydroxyl group, it is preferable to include one or more selected from the group consisting of isobornyl (meth)acrylate, cyclic trimethylolpropane formal acrylate, tert-butylcyclohexanol acrylate, and vinylmethyloxazolidinone. By using such monofunctional monomers not containing a hydroxyl group, the adhesion and curability of the coating film tend to be further improved.

[0049] The content of the monofunctional monomer not containing a hydroxyl group is preferably 0 to 70 mass%, 0 to 60 mass%, 0 to 55 mass%, or 0 to 50 mass%, relative to the total amount of the ink composition. When the content of the monofunctional monomer not containing a hydroxyl group is within the above range, the adhesion and curability of the coating film tend to be further improved.

[0050] 1.2.3.2. Polyfunctional Monomers The ink composition of this embodiment may further contain a polyfunctional monomer. Examples of polyfunctional monomers include, but are not limited to, vinyl ether group-containing (meth)acrylates and polyfunctional (meth)acrylates.

[0051] 1.2.3.2.1. (Meth)acrylates containing vinyl ether groups The vinyl ether group-containing (meth)acrylate is not particularly limited, and examples thereof include compounds represented by the following formula (1): By including such a vinyl ether group-containing (meth)acrylate, the viscosity of the composition tends to decrease, and the ejection stability tends to be improved. Furthermore, the curability of the composition is improved, and the improved curability also allows for faster recording speeds. CH2=CR 1 -COOR 2 -O-CH=CH-R 3 ··· (1) (In the formula, R 1 is a hydrogen atom or a methyl group, and R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.

[0052] In the above formula (1), R 2Examples of the divalent organic residue having 2 to 20 carbon atoms and represented by the formula (I) include a linear, branched, or cyclic alkylene group having 2 to 20 carbon atoms, which may be substituted, an alkylene group having 2 to 20 carbon atoms and having an oxygen atom via an ether bond and / or an ester bond in its structure, and a divalent aromatic group having 6 to 11 carbon atoms, which may be substituted. Among these, alkylene groups having 2 to 6 carbon atoms, such as an ethylene group, an n-propylene group, an isopropylene group, and a butylene group, and alkylene groups having 2 to 9 carbon atoms and having an oxygen atom via an ether bond in its structure, such as an oxyethylene group, an oxy-n-propylene group, an oxyisopropylene group, and an oxybutylene group, are preferred. Furthermore, from the viewpoint of further reducing the viscosity of the composition and further improving the curability of the composition, a compound having a glycol ether chain in which R2 is an alkylene group having 2 to 9 carbon atoms and having an oxygen atom via an ether bond in the structure, such as an oxyethylene group, an oxy-n-propylene group, an oxyisopropylene group, or an oxybutylene group, is more preferred.

[0053] In the above formula (1), R 3 Suitable examples of the monovalent organic residue having 1 to 11 carbon atoms and represented by the formula (I) are linear, branched, or cyclic alkyl groups having 1 to 10 carbon atoms, which may be substituted, and aromatic groups having 6 to 11 carbon atoms, which may be substituted. Among these, alkyl groups having 1 to 2 carbon atoms, such as methyl or ethyl groups, and aromatic groups having 6 to 8 carbon atoms, such as phenyl and benzyl groups, are preferably used.

[0054] When each of the above organic residues is a group that may be substituted, the substituent is divided into a group containing carbon atoms and a group not containing carbon atoms. First, when the above substituent is a group containing carbon atoms, the carbon atom is counted in the number of carbon atoms of the organic residue. Examples of the group containing carbon atoms include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing carbon atoms include, but are not limited to, a hydroxyl group and a halo group.

[0055] Specific examples of the compound of formula (1) include, but are not limited to, 2-vinyloxyethyl (meth)acrylate, 3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl (meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl (meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate, 1-vinyloxymethylpropyl (meth)acrylate, 2-methyl-3-vinyloxypropyl (meth)acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth)acrylate, ) 3-vinyloxybutyl 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-vinyloxymethylphenyl (meth)acrylate Methyl, o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxy)propyl (meth)acrylate, 2-(vinyloxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate, 2-(vinyloxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxy)ethyl (meth)acrylate (meth)acrylate 2-(vinyloxyethoxyisopropoxy)ethyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)ethyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)ethyl, (meth)acrylate 2-(vinyloxyethoxyethoxy)propyl, (meth)acrylate 2-(vinyloxyethoxyisopropoxy)propyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)propyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)propyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)propyl,2-(vinyloxyethoxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxyethoxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate Examples of suitable acrylates include ethyl (meth)acrylate, 2-(isopropenoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate, polyethylene glycol monovinyl ether (meth)acrylate, and polypropylene glycol monovinyl ether (meth)acrylate. Among these specific examples, 2-(2-vinyloxyethoxy)ethyl acrylate is particularly preferred in that it is easy to balance the curability and viscosity of the composition. In this embodiment, 2-(2-vinyloxyethoxy)ethyl acrylate is also referred to as VEEA.

[0056] The content of the vinyl ether group-containing (meth)acrylate relative to the total amount of the ink composition is preferably 0.1 to 50 mass%, 1 to 40 mass%, or 10 to 30 mass%. When the content of the vinyl ether group-containing (meth)acrylate relative to the total amount of the ink composition is within the above range, the storage stability of the ink composition tends to be excellent, the viscosity of the composition tends to be reduced, and the ejection stability tends to be further improved. 1.2.3.2.2. Multifunctional (meth)acrylates The polyfunctional (meth)acrylate is not particularly limited, and examples thereof include dipropylene glycol diacrylate (DPGDA), diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol dimethacrylate, tripropylene glycol di(meth)acrylate (TPGDA), polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, EO (ethylene oxide) adduct di(meth)acrylate of bisphenol A, and PO (propylene oxide) adduct di(meth)acrylate of bisphenol A. bifunctional (meth)acrylates such as hydroxypivalic acid neopentyl glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate; and trifunctional or higher polyfunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate (ADPH), ditrimethylolpropane tetra(meth)acrylate, glycerin propoxy tri(meth)acrylate, caprolactone-modified trimethylolpropane tri(meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, and caprolactam-modified dipentaerythritol hexa(meth)acrylate (ADPH).

[0057] The content of the polyfunctional (meth)acrylate relative to the total amount of the ink composition is preferably 1 to 50 mass%, 10 to 45 mass%, 15 to 40 mass%, or 20 to 35 mass%. When the content of the polyfunctional (meth)acrylate relative to the total amount of the composition is within the above range, the adhesion of the coating film tends to be improved.

[0058] 1.3.Water It is desirable that the ink-jet ink composition does not contain water, but if it does contain water, the content is preferably small, less than 2% by mass of the total amount of the ink-jet ink composition.

[0059] Water functions as a dispersion medium for the ink composition. As the water, for example, pure water such as RO water, distilled water, or ion-exchanged water may be used.

[0060] When water is contained, the water content is less than 2% by mass, preferably 1% by mass or less, and 0.1% by mass or less, relative to the total amount of the ink composition. There are no particular restrictions on the lower limit of the water content, and the lower the content, the better, and the ink composition may not contain water at all (0% by mass; 0% by mass includes 0% by mass obtained by rounding down to the first decimal place). By containing less than 2% by mass of water, the generation of foreign matter tends to be suppressed when the ink composition is stored under high-temperature conditions. When water is not contained, the generation of foreign matter can be further suppressed.

[0061] 1.4.Other Ingredients The ink composition according to this embodiment may further contain additives such as a dispersant, a polymerization inhibitor, a slip agent, and a fluorescent brightening agent, as needed.

[0062] 1.4.1. Polymerization inhibitors The 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.

[0063] Examples of the polymerization inhibitor include, but are not limited to, p-methoxyphenol, hydroquinone monomethyl ether (MEHQ), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, hydroquinone, cresol, t-butylcatechol, 3,5-di-t-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-butylphenol), and 4,4'-thiobis(3-methyl-6-t-butylphenol); hindered amine compounds, etc. Among these, hindered amine compounds are preferred.

[0064] The hindered amine compound is not particularly limited, but is preferably a hindered amine compound represented by the following formula (2) or (3). [ka] (In formula (2), R 4 is H-, O=, HO-, or R 5 -COO-, where R 5 represents an alkyl group having 1 to 6 carbon atoms or a substituted or unsubstituted aromatic group. [ka] (In formula (3), R 6 -OOC-R 7 -COO-, where R 7 represents an alkyl group having 1 to 12 carbon atoms.

[0065] R 5 The alkyl group having 1 to 6 carbon atoms represented by the formula (I) is not particularly limited, but examples thereof include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group. 5 Examples of the substituted or unsubstituted aromatic group represented by the formula (I) include a phenyl group.

[0066] R 7The alkyl group having 1 to 12 carbon atoms represented by the formula (I) is not particularly limited, but examples thereof include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, an ethylhexyl group, a nonyl group, and a decyl group.

[0067] Such hindered amine compounds are not particularly limited, but examples thereof include compounds having a 2,2,6,6-tetramethylpiperidine-N-oxyl skeleton, compounds having a 2,2,6,6-tetramethylpiperidine skeleton, compounds having a 2,2,6,6-tetramethylpiperidine-N-alkyl skeleton, and compounds having a 2,2,6,6-tetramethylpiperidine-N-acyl skeleton. Among these, bis(2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) sebacate is preferred.

[0068] The content of the hindered amine compound is preferably 0.01 to 0.0.50% by mass, 0.01 to 0.10% by mass, or 0.01 to 0.05% by mass relative to the total amount of the ink composition.

[0069] The content of the polymerization inhibitor is preferably 0.05 to 1% by mass, and more preferably 0.05 to 0.5% by mass, relative to the total amount of the ink composition.

[0070] 1.4.2.Slip agents The 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.

[0071] The slip agent is preferably a silicone surfactant, more preferably a polyester-modified silicone or a polyether-modified silicone. Examples of polyester-modified silicones include BYK-347, 348, BYK-UV3500, 3510, and 3530 (all manufactured by BYK Additives & Instruments). Examples of polyether-modified silicones include BYK-3570 (manufactured by BYK Additives & Instruments).

[0072] The content of the slip agent is preferably 0.01 to 2% by mass, and more preferably 0.05 to 1% by mass, based on the total amount of the ink composition.

[0073] Dispersants The ink composition of this embodiment may further contain a dispersant to improve the dispersibility of the colorant, etc. The dispersant may be used alone or in combination of two or more types.

[0074] The dispersant is not particularly limited, but examples thereof include dispersants commonly used in preparing pigment dispersions, such as polymer dispersants, etc. Specific examples thereof include those containing one or more of polyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxy resins as the main component.

[0075] Commercially available polymer dispersants include the Ajisper series manufactured by Ajinomoto Fine-Techno Co., Ltd., the Solsperse series (Solsperse 36000, etc.) available from Avecia and Noveon, the Disperbic series manufactured by BYK Additives & Instruments, and the Disparlon series manufactured by Kusumoto Chemicals Co., Ltd.

[0076] The content of the dispersant is preferably 0.1 to 2 mass %, 0.1 to 1.5 mass %, or 0.1 to 1.0 mass %, relative to the total amount of the ink composition.

[0077] Colorants The ink composition of this embodiment may further contain a coloring material. The coloring material may be used alone or in combination of two or more types.

[0078] The coloring material is not particularly limited, but examples thereof include pigments and dyes. One type of coloring material may be used alone, or two or more types may be used in combination.

[0079] The content of the colorant relative to the total amount of the ink composition is preferably 0.5 to 15% by mass, more preferably 1.0 to 10% by mass, and even more preferably 2.0 to 7% by mass. When the content of the colorant is within the above range, color development tends to be further improved.

[0080] The ink composition of this embodiment may contain a pigment as a colorant. The pigment is not particularly limited, but examples thereof include organic pigments such as azo pigments (including, for example, azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments), polycyclic pigments (such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments), nitro pigments, nitroso pigments, and aniline black; inorganic pigments such as carbon black (such as furnace black, thermal lamp black, acetylene black, and channel black), metal oxides, metal sulfides, and metal chlorides; and extender pigments such as calcium carbonate and talc.

[0081] The pigment may be added to the ink composition as a pigment dispersion obtained by dispersing the pigment in water with a dispersant, or as a pigment dispersion obtained by dispersing a self-dispersing surface-treated pigment in which hydrophilic groups have been introduced to the pigment particle surface using a chemical reaction (hereinafter also referred to as a "self-dispersing pigment") in water, or as a pigment dispersion obtained by dispersing a polymer-coated pigment (hereinafter also referred to as a "resin-dispersed pigment") in water. Among these, it is preferable to include a self-dispersing pigment. The use of a self-dispersing pigment tends to further improve the water repellency of the nozzle plate and the intermittent printing stability.

[0082] The pigment and dispersant constituting the pigment dispersion may each be used alone or in combination of two or more.

[0083] The ink composition of this embodiment may contain a dye as a colorant. The dye is not particularly limited, but examples include acid dyes such as CI Acid Yellow, CI Acid Red, CI Acid Blue, CI Acid Orange, CI Acid Violet, and CI Acid Black; basic dyes such as CI Basic Yellow, CI Basic Red, CI Basic Blue, CI Basic Orange, CI Basic Violet, and CI Basic Black; direct dyes such as CI Direct Yellow, CI Direct Red, CI Direct Blue, CI Direct Orange, CI Direct Violet, and CI Direct Black; reactive dyes such as CI Reactive Yellow, CI Reactive Red, CI Reactive Blue, CI Reactive Orange, CI Reactive Violet, and CI Reactive Black; and disperse dyes such as CI Disperse Yellow, CI Disperse Red, CI Disperse Blue, CI Disperse Orange, CI Disperse Violet, and CI Disperse Black. The dyes may be used alone or in combination.

[0084] 1.4.5. Optical brighteners The ink composition of this embodiment may further contain a fluorescent brightening agent. The fluorescent brightening agent may be used alone or in combination of two or more.

[0085] For example, fluorescent brighteners absorb light with wavelengths of approximately 300 to 450 nm and emit fluorescence with wavelengths of approximately 400 to 500 nm. That is, when ultraviolet light is used as radiation, fluorescent brighteners increase the long-wavelength range of ultraviolet light irradiated onto the ink, thereby improving curing properties. Combining a fluorescent brightener with a photoinitiator exhibits a sensitizing effect, so containing a fluorescent brightener tends to result in better curing properties than when only a photoinitiator is included.

[0086] Examples of fluorescent brightening agents include naphthalene benzoxazolyl derivatives, thiophene benzoxazolyl derivatives, stilbene benzoxazolyl derivatives, coumarin derivatives, styrene biphenyl derivatives, pyrazolone derivatives, stilbene derivatives, styryl derivatives of benzene and biphenyl, bis(benzazol-2-yl) derivatives, carbostyril, naphthalimide, dibenzothiophene-5,5'-dioxide derivatives, pyrene derivatives, and pyridotriazole.

[0087] Commercially available fluorescent brightening agents may be used, such as TELALUX (registered trademark) OB (2,5-bis(5-tert-butyl-2-benzoxazolyl)thiophene) and KCB (1,4-bis(2-benzoxazolyl)naphthalene) from Clariant Japan.

[0088] The content of the fluorescent brightening agent in the ink composition is preferably 0.07 to 0.70% by mass or less, and more preferably 0.10 to 0.50% by mass or less, based on the total amount of the ink composition. When the content of the fluorescent brightening agent is within the above range, the curability of the ink composition tends to be improved.

[0089] 1.5. Recording Media The ink composition according to this embodiment can be suitably used as an ink composition for ejection onto a recording medium in the recording method described below. The recording medium is not particularly limited, but examples thereof include absorbent recording media and non-absorbent recording media.

[0090] Examples of absorbent recording media include plain paper such as electrophotographic paper, inkjet paper, art paper used in general offset printing, coated paper, and cast paper.

[0091] Examples of non-absorbent recording media include plastics such as polyvinyl chloride (PVC), polystyrene (PS), polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), polycarbonate, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, and polyvinyl acetal, as well as plastics with treated surfaces, glass, metal, and wood.

[0092] The form of the recording medium is not particularly limited, and examples thereof include film, board, and cloth.

[0093] 1.6. Method for producing inkjet ink composition The production (preparation) of the ink composition is carried out by mixing the components contained in the ink composition and stirring the mixture to ensure a sufficiently uniform mixture. In this embodiment, the preparation of the ink composition preferably includes a step of subjecting a mixture of a photopolymerization initiator and at least a portion of the monomers to at least one of ultrasonic treatment and heating treatment during the preparation process. This reduces the amount of dissolved oxygen in the prepared ink composition, resulting in an ink composition with excellent ejection stability and storage stability. The mixture may contain at least the above components, and may further contain other components contained in the ink composition, or may contain all of the components contained in the ink composition. The monomer contained in the mixture may be at least a portion of the monomers contained in the ink composition.

[0094] 2. Recording method The recording method according to this embodiment includes a discharge step of discharging the ink composition according to this embodiment using a predetermined inkjet head to adhere it to a recording medium.

[0095] 2.1.Discharge process In the ejection step, the heated ink composition is ejected from a liquid ejection head and deposited on a recording medium. More specifically, a pressure generating means is driven to eject the ink composition filled in the pressure generating chamber of the liquid ejection head from the nozzle. This ejection method is also called an ink jet method. The ejection conditions in the ejection step may be adjusted as appropriate depending on the physical properties of the ink composition.

[0096] The recording medium can be any of the above-mentioned recording media, and is not particularly limited, and absorbent recording media, non-absorbent recording media, etc. can be used.

[0097] 2.2.Curing process In the curing process, the ink composition attached to the recording medium is irradiated with radiation. When irradiated with radiation, a polymerization reaction of the monomers is initiated, curing the composition and forming a coating film. If a photopolymerization initiator is present, it generates active species (initiation species) such as radicals, acids, and bases, and the polymerization reaction of the monomers is accelerated by the function of these initiation species. If a photosensitizer is present, it absorbs radiation and becomes excited, and upon contact with the photopolymerization initiator, it accelerates the decomposition of the photopolymerization initiator, thereby achieving a more rapid curing reaction.

[0098] Examples of the radiation include ultraviolet light, infrared light, visible light, and X-rays. The radiation source is provided downstream of the liquid jet head and irradiates the composition with the radiation. The radiation source is not particularly limited, but examples thereof include ultraviolet light-emitting diodes. Use of such a radiation source can reduce the size and cost of the device. Because ultraviolet light-emitting diodes as an ultraviolet light source are small, they can be installed inside the inkjet device.

[0099] For example, ultraviolet light-emitting diodes can be attached to a carriage (both ends along the medium width direction and / or the medium transport direction side) on which a liquid jet head that ejects the ink composition is mounted. Furthermore, due to the composition of the inkjet composition described above, curing can be achieved at low energy and high speed. The irradiation energy is calculated by multiplying the irradiation time by the irradiation intensity. Therefore, the irradiation time can be shortened, and the printing speed can be increased. On the other hand, the irradiation intensity can also be reduced. This reduces the temperature rise of the printed material, which also leads to a reduced odor of the cured film. [Example]

[0100] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples.

[0101] 1. Preparation of Inkjet Ink Composition First, the colorant, dispersant, and a portion of each monomer were weighed and placed in a pigment dispersion tank. A 1 mm diameter ceramic bead mill was then placed in the tank and stirred to obtain a pigment dispersion in which the colorant was dispersed in the monomer. Next, the remaining monomer, resin, photopolymerization initiator, polymerization inhibitor, and slip agent were placed in a stainless steel mixing tank and mixed and stirred to completely dissolve the components, as shown in Figures 1, 2, and 3. The resulting pigment dispersion was then added, and the mixture was further mixed and stirred at room temperature for an hour. The resulting mixture was then filtered through a 5 μm membrane filter to obtain the ink composition shown in each example. Note that the numerical values ​​for each component shown in each example in the figures represent mass % unless otherwise specified.

[0102] The abbreviations and product components used in Figures 1, 2 and 3 are as follows:

[0103] <Hydroxyl group-containing monomer> 4HBA (Mitsubishi Chemical Corporation, 4-hydroxybutyl acrylate) CHDMMA (Mitsubishi Chemical Corporation, 1,4-cyclohexanedimethanol monoacrylate) Pentaerythritol triacrylate (trade name "Viscoat #802", manufactured by Osaka Organic Chemical Industry Co., Ltd.) <Aromatic group-containing polymerizable compound> BZA (product name "Viscoat #160, manufactured by Osaka Organic Chemical Industry Ltd., benzyl acrylate") <Monofunctional monomers that do not contain hydroxyl groups> IBXA (Osaka Organic Chemical Industry, Ltd., isobornyl acrylate) CTFA (product name: Viscoat #200, manufactured by Osaka Organic Chemical Industry Co., Ltd., cyclic trimethylolpropane formal acrylate) TBCHA (product name "SR217", manufactured by Sartomer Corporation, tert-butyl cyclohexanol acrylate) VMOX (BASF, vinylmethyloxazolidinone) <Polyfunctional Monomer> VEEA (2-(2-vinyloxyethoxy)ethyl acrylate, manufactured by Nippon Shokubai Co., Ltd.) DPGDA (product name "SR508", manufactured by Sartomer Corporation, dipropylene glycol diacrylate) ADPH (Shin-Nakamura Chemical Co., Ltd., Pentaerythritol Hexaacrylate) <Photopolymerization initiator> Irg.819 (trade name "IRGACURE 819" manufactured by BASF, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) TPO (trade name "IRGACURE TPO", manufactured by BASF, 2,4,6-trimethylbenzoyldiphenylphosphine oxide) TPO-L (trade name "IRGACURE TPO-L", manufactured by BASF, ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate) DETX (trade name "Speedcure DETX", Lambson, 2,4-diethylthioxanthen-9-one) <Polymerization inhibitor> MEHQ (product name "p-methoxyphenol", manufactured by Kanto Chemical Co., Ltd., hydroquinone monomethyl ether) Sebacic acid BisTEMPO (UV10) (Seiko Chemical Co., Ltd., bis(2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) sebacic acid) LA-7RD (Adeka Corporation, 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl) <Slip agent> BYK-UV3500 (BYK Additives & Instruments, polyether-modified polydimethylsiloxane with acryloyl groups) <Fluorescent whitening agents> TELALUX KCB (Clariant Japan, 1,4-bis(2-benzoxazolyl)naphthalene) <Dispersant> Solsperse 36000 (Lubrizol polymer dispersant) <Colorant> Black pigment (product name "Microlith Black CK", manufactured by Ciba Japan Co., Ltd.)

[0104] 2. Evaluation Method 2.1. Evaluation of low-temperature long-term storage stability Each ink composition obtained was filled into a glass bottle and stored in an environment of -20°C for 7 days. After storage, 10 ml of each ink composition was filtered through a 10 μm filter. The low-temperature long-term storage stability was evaluated based on the number of foreign particles after filtration. The evaluation criteria are as follows: A (excellent), B (good), C (fair) were considered to be pass, and D (poor) was considered to be fail. A: The number of foreign objects is less than 10. B: The number of foreign objects is 10 or more but less than 30. C: The number of foreign objects is 30 or more but less than 50. D: There are 50 or more foreign bodies.

[0105] 2.2. Odor evaluation The resulting ink compositions were each smelled and evaluated for odor. To reduce individual differences in olfaction, 10 people tested the same sample and assigned a score for odor as follows. The average score of the 10 people was calculated, and the odor was evaluated on a four-level scale from A to D based on this average score. A rating of A (excellent), B (good), or C (fair) was considered a pass, and D (poor) was considered a fail. 0: No odor or barely noticeable odor. 1 point: Slight odor is detected. 2 points: The odor is easily detected. 3 points: A strong odor is felt. A: The average score is between 0 and 0.5 points. B: Average score is 0.5 or more and less than 1.5 points C: Average score is 1.5 or more and less than 2.5 points D: Average score is 2.5 or more and less than 3.0 points

[0106] 2.3. Evaluation of curability The tackiness under cotton swab load was evaluated. Specifically, each inkjet composition was applied to a polyvinyl chloride medium using a bar coater to a coating thickness of 10 μm to form a coating film, and the coating film was irradiated with ultraviolet light at a predetermined irradiation intensity and a speed of 0.04 sec / cm. An LED with a peak wavelength of 395 nm was used as the light source. The surface of the coating film was then rubbed with a cotton swab, and the irradiation energy at which the cotton swab no longer became colored was measured to evaluate curability. The evaluation criteria are as follows: A (excellent), B (good), or C (fair) was considered pass, and D (poor) was considered fail. A: The irradiation energy at which the cotton swab becomes uncolored is 300mJ / cm 2 less than B: The irradiation energy at which the cotton swab becomes uncolored is 300 mJ / cm 2 More than 500mJ / cm 2 less than C: The irradiation energy at which the cotton swab becomes uncolored is 500 mJ / cm 2 More than 700mJ / cm 2 less than D: The irradiation energy at which the cotton swab becomes uncolored is 700 mJ / cm 2 End

[0107] 2.4. Evaluation of long-term storage stability at high temperatures Each ink composition obtained was filled into a glass bottle and stored in an environment of 70°C for 8 days. After storage, 10 ml of each ink composition was filtered through a 10 μm filter. The high-temperature long-term storage stability was evaluated based on the number of foreign particles after filtration. The evaluation criteria are as follows: A (excellent), B (good), or C (fair) was considered pass, and D (poor) was considered fail. A: The number of foreign objects is less than 10. B: The number of foreign objects is 10 or more but less than 30. C: The number of foreign objects is 30 or more but less than 50. D: There are 50 or more foreign bodies.

[0108] 2.5. Evaluation of viscosity change rate during long-term storage at high temperatures The ink composition was stored in an environment at 70°C for 8 days, and the viscosity of the ink composition was measured before and after storage in an environment at 25°C using a rotational viscometer (product name "Rheometer MCR-301", manufactured by Anton Paar) in accordance with JIS Z 8803. The evaluation criteria are as follows: A: The viscosity change rate is less than 5%. B: The viscosity change rate is 5% or more and less than 10%. C: The viscosity change rate is 10% or more and less than 15%. D: The viscosity change rate is 15% or more.

[0109] 2.6. Viscosity evaluation Immediately after preparation, the viscosity of each ink composition was measured using a rotational viscometer (product name "Rheometer MCR-301", manufactured by Anton Paar) at 20°C in accordance with JIS Z 8803. The evaluation criteria were as follows: A: Viscosity is less than ±5% of 20 mPa·s. B: Viscosity is ±5% or more and less than ±10% of 20 mPa·s. C: Viscosity is ±10% or more but less than ±15% of 20 mPa·s. D: Viscosity is ±15% or more of 20 mPa·s.

[0110] 2.7.Evaluation of Adhesion The ink compositions of the Examples and Comparative Examples were applied to a PET film (PET50A PL Thin [product name], manufactured by Lintec Corporation) in an amount to give a film thickness of 10 μm (film thickness after curing), and the film was irradiated with radiation under the same conditions as those for the curing evaluation until the film was no longer scratched, thereby curing the ink compositions of the Examples and Comparative Examples to produce recorded matter. These recorded matter were evaluated using the cross-cut method in accordance with JIS K5600-5-6.

[0111] More specifically, a cutter was used to make a 10 x 10 grid by placing the blade of a cutting tool perpendicular to the cured film and creating squares with 1 mm spacing between cuts. A transparent adhesive tape (25 mm wide) approximately 75 mm long was attached to the grid, and the tape was rubbed thoroughly with a finger so that the cured film was visible through it. Next, within 5 minutes of applying the tape, the tape was firmly peeled off the cured film at an angle close to 60° in 0.5 to 1.0 seconds, and the state of the grid was visually observed. The evaluation criteria are as follows: A: No peeling of the cured film is observed, or peeling is observed in less than 1% of the lattices. B: Peeling of the cured film was observed in 1% or more but less than 10% of the lattice. C: Peeling of the cured film was observed in 10% or more but less than 35% of the lattice. D: Peeling of the cured film was observed in more than 35% of the lattice.

[0112] 3. Evaluation Results The compositions and evaluation results of the ink compositions used in each example are shown in Figures 1, 2, and 3. Figures 1 and 2 show that the ink compositions of Examples 1 to 21, which contained ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate and a hydroxyl group-containing monomer, and either did not contain an aromatic group-containing polymerizable compound, or, if an aromatic group-containing polymerizable compound was contained, the content of the aromatic group-containing polymerizable compound was 5.0 mass% or less relative to the total amount of the inkjet ink composition, and either did not contain water, or, if water was contained, the water content was less than 2 mass% relative to the total amount of the inkjet ink composition, were evaluated to have good levels of storage stability, odor, and curability at both low and high temperature conditions.

[0113] In detail, when comparing each Example with Comparative Examples 1 and 4, it is shown that the odor of each Example is suppressed more than that of Comparative Examples 1 and 4, in which the content of the aromatic group-containing polymerizable compound is more than 5.0 mass% relative to the total amount of the ink composition.

[0114] Furthermore, when each Example is compared with Comparative Example 2, it is shown that each Example has improved curability compared to Comparative Example 2, which does not contain a hydroxyl group-containing monomer.

[0115] Furthermore, when comparing each Example with Comparative Example 3, it is shown that each Example has improved storage stability under low temperature conditions compared to Comparative Example 3, which does not contain ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate.

[0116] Furthermore, when comparing each Example with Comparative Example 5, it is shown that each Example has improved storage stability under high temperature conditions compared to Comparative Example 5, in which the water content is 2.0 mass % or more relative to the total amount of the ink composition.

Claims

1. ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate, Contains a hydroxyl group-containing monomer, the ink-jet ink composition does not contain an aromatic group-containing polymerizable compound, or if it contains an aromatic group-containing polymerizable compound, the content of the aromatic group-containing polymerizable compound is 5.0% by mass or less relative to the total amount of the ink-jet ink composition; the ink-jet ink composition does not contain water, or if it contains water, the content of water is less than 2% by mass relative to the total amount of the ink-jet ink composition; Inkjet ink composition.

2. the content of the hydroxyl group-containing monomer is 5.0 to 50% by mass relative to the total amount of the inkjet ink composition; The ink-jet ink composition of claim 1 .

3. the hydroxyl group-containing monomer includes a hydroxyl group-containing monofunctional monomer; The ink-jet ink composition of claim 1 .

4. the ink-jet ink composition does not contain the aromatic group-containing polymerizable compound, or if it contains the aromatic group-containing polymerizable compound, the content of the aromatic group-containing polymerizable compound is 0.1% by mass or less relative to the total amount of the ink-jet ink composition; The ink-jet ink composition of claim 1 .

5. the ink-jet ink composition does not contain water, or if it contains water, the content of water is 0.1% by mass or less relative to the total amount of the ink-jet ink composition; The ink-jet ink composition of claim 1 .

6. The vinyl ether group-containing (meth)acrylate is represented by the following formula (1): The ink-jet ink composition of claim 1 . H ２ C=CR １ -CO-OR ２ -O-CH=CH-R ３ ・・・(1) (In formula (1), R １ is a hydrogen atom or a methyl group, and R ２ is a divalent organic residue having 2 to 20 carbon atoms, and R ３ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.

7. A hindered amine compound represented by the following formula (2) or the following formula (3): The ink-jet ink composition of claim 1 . 【Chemical 1】 (In formula (2), R ４ is H-, O=, HO- or R ５ represents —COO—, where R ５ represents an alkyl group having 1 to 6 carbon atoms or a substituted or unsubstituted aromatic group. 【Chemistry 2】 (In formula (3), R ６ is -OOC-R ７ represents —COO—, where R ７ represents an alkyl group having 1 to 12 carbon atoms.

8. Contains a monofunctional monomer that does not contain a hydroxyl group, the monofunctional monomer not containing a hydroxyl group includes one or more selected from the group consisting of an aliphatic ring-containing monomer, an oxygen-containing cyclic monomer, and a nitrogen-containing cyclic monomer; The ink-jet ink composition of claim 1 .

9. the monofunctional monomer not containing a hydroxyl group includes one or more selected from the group consisting of isobornyl (meth)acrylate, cyclic trimethylolpropane formal acrylate, tert-butyl cyclohexanol acrylate, and vinylmethyl oxazolidinone; The ink-jet ink composition of claim 8.

10. the content of the ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate is 2 to 10% by mass relative to the total amount of the inkjet ink composition; The ink-jet ink composition of claim 1 .

11. the content of the ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate is 15 to 100 mass% based on the total amount of the polymerization initiator; The ink-jet ink composition of claim 1 .

12. a discharge step of discharging the inkjet ink composition according to any one of claims 1 to 11 from an inkjet head and depositing the inkjet ink composition on a recording medium; Recording method.

Images