Active ray-curable inkjet ink and method for producing printed matter using the same

Abstract

To provide an active ray-curable inkjet ink containing a gelling agent, the ink having superior dispersion stability of a pigment and achieving high weather resistance in printed matter obtained therewith.SOLUTION: The active ray-curable inkjet ink comprises a photopolymerizable compound, a photoinitiator, a gelling agent, a pigment, a dispersing assistant, and a pigment dispersant, wherein the dispersing assistant contains a compound having a specific structure and the pigment contains a compound having a specific structure.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an actinic radiation-curable inkjet ink and a method for producing a printed matter using the same. [Background technology]

[0002] Image formation by the inkjet method is used in various printing fields because it allows for easy and inexpensive image formation. One such image formation method involves depositing droplets of actinic radiation-curable inkjet ink on a recording medium and then curing the ink by irradiating it with actinic radiation to form an image. This method allows for the formation of images with high abrasion resistance and adhesion, even on recording media that do not absorb ink.

[0003] Here, in the image forming method using the actinic radiation-curable inkjet ink, high-speed recording has been investigated, for example, by a single-pass image forming method or a high-speed serial image forming method using a few passes. However, when forming an image using a few passes, it is necessary to drop the actinic radiation-curable inkjet ink more densely than when forming an image using multiple passes. This reduces the distance between adjacent ink droplets (dots), which leads to a problem that adjacent dots tend to coalesce, resulting in a deterioration in image quality. In order to prevent such coalescence of adjacent dots, it has been investigated to improve the pinning ability of the actinic radiation-curable inkjet ink.

[0004] As a method for improving the pinning ability of actinic radiation-curable inkjet inks, for example, adding a gelling agent to the ink to induce a sol-gel phase transition depending on the temperature has been investigated. That is, it has been investigated to eject ink droplets in a liquid state at a high temperature, and at the same time impact the ink droplets on a recording medium, by cooling the ink droplets and gelling them, thereby suppressing the coalescence of the droplets (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2007 / 0058020 Summary of the Invention [Problem to be solved by the invention]

[0006] However, among various inks containing the gelling agent, yellow inks tend to have low stability. Typically, inks contain pigment dispersants to stabilize the pigment. However, yellow pigments (especially azo pigments) often lack groups that form stable bonds with pigment dispersants, making it difficult to improve the stability of yellow inks. To improve the affinity between the pigment and the pigment dispersant, a dispersing aid is sometimes used. However, yellow pigments have a high affinity with gelling agents. Therefore, the pigment tends to interact with the gelling agent without interacting with the dispersing aid. When the pigment and gelling agent interact, the dispersing aid is less likely to interact with the pigment. As a result, the pigment dispersant is less likely to function properly, making it difficult to improve the dispersion stability of the pigment. Furthermore, the function of the gelling agent itself is reduced, making it easier for image formation to be poor, and the weather resistance of the resulting images tends to be poor.

[0007] The present invention has been made in view of the above circumstances. An object of one aspect of the present invention is to provide an actinic radiation-curable inkjet ink containing a gelling agent, which has good pigment dispersion stability and produces printed matter with high weather resistance. Another object of one aspect of the present invention is to provide a method for producing printed matter using the actinic radiation-curable inkjet ink. [Means for solving the problem]

[0008] In order to achieve the above object, one aspect of the present invention provides an actinic radiation-curable inkjet ink containing a photopolymerizable compound, a photoinitiator, a gelling agent, a pigment, a dispersing aid, and a pigment dispersant, wherein the dispersing aid contains a compound represented by the following general formula (S), and the pigment contains a compound represented by the following general formula (P) or the following general formula (Q). [ka] (In the general formula (S), R 7 represents an atom or a monovalent group selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, and a carboxy group; R 1 represents a monovalent or divalent group selected from the group consisting of a substituted or unsubstituted saturated aliphatic hydrocarbon group, a substituted or unsubstituted unsaturated aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, a carboxy group, an ether bond, and combinations thereof; Z represents an a-valent atom or group selected from the group consisting of a single bond, a hydrogen atom, a halogen atom, a hydroxy group, an amino group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted saturated aliphatic hydrocarbon group, a substituted or unsubstituted unsaturated aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, and combinations thereof; W represents an acidic group selected from a phosphate group, a sulfonate group, a sulfonate group, and a nitrate group; a represents 1 or 2; b represents 0 or 1; when a is 1, b is 1; and when a=2, at least one b is 1. [ka] (In the general formula (P) and the general formula (Q), R 2 , R 3 , and R 5each independently represents an atom or a monovalent group selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy group, a nitro group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a carbonyl group, a carboxy group, and combinations thereof; R 6 represents a monovalent group selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, and combinations thereof; Y 1 represents a c-valent group selected from the group consisting of substituted or unsubstituted saturated aliphatic hydrocarbon groups, substituted or unsubstituted unsaturated aliphatic hydrocarbon groups, substituted or unsubstituted aromatic hydrocarbon groups, substituted or unsubstituted heterocyclic groups, ether bonds, and combinations thereof; Y 2 represents a d-valent group selected from the group consisting of a single bond, a substituted or unsubstituted saturated aliphatic hydrocarbon group, a substituted or unsubstituted unsaturated aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, an ether bond, and combinations thereof, and c and d each independently represent 1 or 2.

[0009] Furthermore, in order to achieve the above-mentioned object, one aspect of the present invention provides a method for producing a printed matter, including the steps of: ejecting ink droplets of an actinic radiation-curable inkjet ink from an inkjet recording head and causing them to land on a recording medium; and irradiating the ink droplets that have landed on the recording medium with actinic radiation, thereby curing the ink droplets. [Effects of the Invention]

[0010] According to one aspect of the present invention, there is provided an actinic radiation-curable inkjet ink that has good pigment dispersion stability and produces printed matter that is highly weather-resistant. Also, according to another aspect of the present invention, there is provided a method for producing high-quality printed matter that is highly weather-resistant. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0012] 1. Actinic light curable inkjet ink The actinic radiation-curable inkjet ink of this embodiment contains a photopolymerizable compound, a photoinitiator, a gelling agent, a pigment, a dispersing aid, and a pigment dispersant. In this specification, "actinic radiation-curable inkjet ink" (hereinafter also referred to as "ink") refers to ink that can be cured by actinic radiation. Furthermore, "actinic radiation" refers to radiation that can activate the photoinitiator in the ink and cure the ink. Examples of actinic radiation include α-rays, γ-rays, X-rays, ultraviolet rays, and electron beams. Note that, from the viewpoints of the availability of irradiation equipment and the curability of the ink, ultraviolet rays and electron beams are preferred as actinic radiation for curing the ink of this embodiment, with ultraviolet rays being more preferred.

[0013] In this embodiment, as described below, the dispersing aid contains a compound having a structure represented by the following general formula (S), and the pigment contains a compound represented by the following general formula (P) or a compound represented by the following general formula (Q). [ka] [ka]

[0014] That is, the dispersing aid and the pigment have the following common structure: [ka]

[0015] When the pigment and dispersing aid have the above-described common structure, they are less likely to sterically buffer and are more likely to stack. As a result, the pigment and dispersing aid are more likely to preferentially coordinate, and the dispersing aid is more likely to coordinate around the pigment. The dispersing aid coordinated around the pigment then interacts with the pigment dispersant, causing the pigment dispersant to be positioned around the pigment via the dispersing aid. This improves the dispersion stability of the pigment in the ink, making it less likely for the pigment to aggregate, even at high temperatures, for example. Furthermore, the dispersing aid or pigment dispersant positioned around the pigment also reduces the interaction between the pigment and the gelling agent. This allows the gelling agent to enhance the pinning ability of the ink, making it easier to obtain high-resolution, high-quality printed matter. Furthermore, the dispersing aid or pigment dispersant positioned around the pigment makes the pigment less susceptible to degradation by water, ultraviolet light, etc. in printed matter (cured ink). This improves the weather resistance of the resulting image. Each component is described below.

[0016] [Photopolymerizable compound] The actinic radiation-curable inkjet ink of this embodiment contains a photopolymerizable compound. The photopolymerizable compound may be any compound that polymerizes when irradiated with actinic radiation, and the photopolymerizable compound may be a radically polymerizable compound or a cationically polymerizable compound. From the viewpoint of curability, the photopolymerizable compound is preferably a radically polymerizable compound.

[0017] The radical polymerizable compound may be a compound (monomer, oligomer, polymer, or a mixture thereof) having a radically polymerizable ethylenically unsaturated bond. The ink may contain only one type of radical polymerizable compound as the photopolymerizable compound, or may contain two or more types.

[0018] Examples of the compound having a radically polymerizable ethylenically unsaturated bond include unsaturated carboxylic acids and their salts, unsaturated carboxylic acid ester compounds, unsaturated carboxylic acid urethane compounds, unsaturated carboxylic acid amide compounds and their anhydrides, acrylonitrile, styrene, unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, unsaturated urethanes, etc. Examples of unsaturated carboxylic acids include (meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, etc.

[0019] Among the above, the radical polymerizable compound is preferably an unsaturated carboxylic acid ester compound, and more preferably a (meth)acrylate compound. In this specification, the term "(meth)acrylate" includes acrylate, methacrylate, and a mixture thereof.

[0020] Examples of the (meth)acrylate compound include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomylstyryl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene monofunctional monomers such as ethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalate, and t-butylcyclohexyl (meth)acrylate; Bifunctional monomers such as triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, 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, bisphenol A PO adduct di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, and tricyclodecane dimethanol diacrylate; Included are trifunctional or higher polyfunctional monomers such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxy tri(meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, ethylene oxide-modified pentaerythritol tetraacrylate, caprolactone-modified trimethylolpropane tri(meth)acrylate, and caprolactam-modified dipentaerythritol hexa(meth)acrylate; polymers (oligomers) of the above monomers; mixtures of the above monomers and oligomers; and modified products thereof.

[0021] Furthermore, when the (meth)acrylate compound is a modified product of the above-mentioned monomer, the modified product may contain a polymerizable functional group other than an unsaturated double bond in its structure. Examples of the (meth)acrylate compound having such a polymerizable functional group include amine-modified (meth)acrylate oligomers, epoxy (meth)acrylate oligomers, aliphatic urethane (meth)acrylate oligomers, aromatic urethane (meth)acrylate oligomers, polyester (meth)acrylate oligomers, and linear (meth)acrylic oligomers.

[0022] Among (meth)acrylate compounds, from the viewpoint of photosensitivity and the like, stearyl (meth)acrylate, lauryl (meth)acrylate, isostearyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, isobornyl (meth)acrylate, tetraethylene glycol di(meth)acrylate, glycerin propoxy tri(meth)acrylate, tripropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, (propylene oxide-modified) trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and amine-modified (meth)acrylate oligomers are preferred.

[0023] On the other hand, examples of cationically polymerizable compounds that can be photopolymerizable compounds include epoxy compounds, vinyl ether compounds, oxetane compounds, etc. The ink may contain only one type of cationically polymerizable compound as the photopolymerizable compound, or may contain two or more types.

[0024] The epoxy compound may be an aromatic epoxide, an alicyclic epoxide, an aliphatic epoxide, etc. Among these, aromatic epoxides and alicyclic epoxides are preferred from the viewpoint of enhancing the curability of the ink.

[0025] The aromatic epoxide may be a di- or polyglycidyl ether obtained by reacting a polyhydric phenol or its alkylene oxide adduct with epichlorohydrin. Examples of the polyhydric phenol or its alkylene oxide adduct to be reacted include bisphenol A or its alkylene oxide adduct. The alkylene oxide in the alkylene oxide adduct may be ethylene oxide, propylene oxide, or the like.

[0026] The alicyclic epoxide may be a cycloalkane oxide-containing compound obtained by epoxidizing a cycloalkane-containing compound with an oxidizing agent such as hydrogen peroxide or a peracid. The cycloalkane in the cycloalkane oxide-containing compound may be cyclohexene or cyclopentene.

[0027] The aliphatic epoxide may be a di- or polyglycidyl ether obtained by reacting an aliphatic polyhydric alcohol or its alkylene oxide adduct with epichlorohydrin. Examples of the aliphatic polyhydric alcohol include alkylene glycols such as ethylene glycol, propylene glycol, and 1,6-hexanediol. The alkylene oxide in the alkylene oxide adduct may be ethylene oxide, propylene oxide, or the like.

[0028] Examples of vinyl ether compounds include monovinyl ether compounds such as ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, isopropenyl ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether; Examples of suitable vinyl ether compounds include di- and trivinyl ether compounds such as ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, and trimethylolpropane trivinyl ether. Among these vinyl ether compounds, di- and trivinyl ether compounds are preferred in consideration of curability, adhesion, and the like.

[0029] The oxetane compound is a compound having an oxetane ring. Examples include the oxetane compounds described in JP-A-2001-220526, JP-A-2001-310937, and JP-A-2005-255821. Compounds represented by general formula (1) described in paragraph 0089 of JP-A-2005-255821, general formula (2) described in paragraph 0092, general formula (7) described in paragraph 0107, general formula (8) described in paragraph 0109, and general formula (9) described in paragraph 0116 are preferred. The general formulae (1), (2), (7), (8), and (9) described in JP-A-2005-255821 are shown below.

[0030] [ka]

[0031] Here, the content of the photopolymerizable compound in the ink is preferably 1% by mass or more and 97% by mass or less, and more preferably 30 to 95% by mass, based on the total mass of the ink.

[0032] [Photoinitiator] The photoinitiator may be any compound that can be activated by irradiation with actinic rays and initiate polymerization of the photopolymerizable compound. The photoinitiator may be an intramolecular bond cleavage type or an intramolecular hydrogen abstraction type.

[0033] Examples of intramolecular bond cleavage photoinitiators include acetophenone-based initiators such as diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone; benzoin-based initiators such as benzoin, benzoin methyl ether, and benzoin isopropyl ether; acylphosphine oxide-based initiators such as 2,4,6-trimethylbenzoindiphenylphosphine oxide; benzyl glyoxyester-based initiators; and methylphenyl glyoxyester-based initiators.

[0034] Examples of intramolecular hydrogen abstraction photoinitiators include benzophenone-based initiators such as benzophenone, o-benzoylmethylbenzoate-4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acrylated benzophenone, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone; thioxanthone-based initiators such as 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone; aminobenzophenone-based initiators such as Michler's ketone and 4,4'-diethylaminobenzophenone; 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, and camphorquinone.

[0035] When the photoinitiator is an acylphosphine oxide or an acylphosphonate, the sensitivity to actinic rays is improved and the ink curing properties are improved. The photoinitiator is more preferably bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide or bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide.

[0036] The photoinitiator may be a photoacid generator. Examples of photoacid generators include compounds used in chemically amplified photoresists and photocationic polymerization (see Organic Electronics Materials Research Group, "Imaging Organic Materials," Bunshin Publishing (1993), pp. 187-192).

[0037] The content of the photoinitiator in the ink is appropriately selected depending on the actinic rays irradiated during ink curing, the type of photopolymerizable compound, etc. The content of the photoinitiator is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 8% by mass or less, of the total mass of the ink.

[0038] [Gelling agent] In this specification, the gelling agent is defined as "an organic substance that is solid at room temperature and becomes liquid when heated, and that has the function of causing a reversible sol-gel phase transition in an actinic radiation-curable inkjet ink depending on the temperature."

[0039] The gelling agent is preferably a compound that crystallizes at or below the gelling temperature of the ink. The gelling temperature of the ink refers to the temperature at which the gelling agent undergoes a phase transition from sol to gel when the ink, which has been solated or liquefied by heating, is cooled, causing a sudden change in the viscosity of the ink. Specifically, the solated or liquefied ink is cooled while its viscosity is measured using a viscoelasticity measuring device (e.g., MCR300, manufactured by Physica), and the temperature at which the viscosity suddenly increases is taken as the gelling temperature of the ink.

[0040] When the gelling agent crystallizes in the ink, a structure may be formed in which the photopolymerizable compound is encapsulated in a three-dimensional space formed by the gelling agent crystallized into plates. In this specification, this structure is also referred to as a "house of card structure." When a house of card structure is formed in the ink, the photopolymerizable compound is retained within the space. Therefore, ink droplets are less likely to wet and spread, and the pinning ability of the ink is enhanced. When the pinning ability of the ink is enhanced, ink droplets that land on a recording medium are less likely to coalesce, allowing for the formation of higher-resolution images.

[0041] In order to retain the photopolymerizable compound within the card house structure, it is preferable that the photopolymerizable compound and the gelling agent are compatible with each other within the ink. Also, from the viewpoint of stably ejecting ink droplets from an inkjet recording device, it is preferable that the compatibility between the photopolymerizable compound and the gelling agent is good.

[0042] Examples of gelling agents include aliphatic ketone compounds; aliphatic ester compounds; petroleum waxes such as paraffin wax, microcrystalline wax, and petrolactam; vegetable waxes such as candelilla wax, carnauba wax, rice wax, Japan wax, jojoba oil, jojoba solid wax, and jojoba ester; animal waxes such as beeswax, lanolin, and spermaceti; mineral waxes such as montan wax and hydrogenated wax; hydrogenated castor oil or hydrogenated castor oil derivatives; montan wax derivatives, paraffin wax derivatives, microcrystalline wax modified waxes such as wax derivatives or polyethylene wax derivatives; higher fatty acids such as behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid; higher alcohols such as stearyl alcohol and behenyl alcohol; hydroxystearic acids such as 12-hydroxystearic acid; 12-hydroxystearic acid derivatives; fatty acid amides such as lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, and 12-hydroxystearic acid amide (e.g., manufactured by Nippon Kasei Chemical Co., Ltd.); N-substituted fatty acid amides such as N-stearylstearamide and N-oleylpalmitamide; special fatty acid amides such as N,N'-ethylenebisstearylamide, N,N'-ethylenebis-12-hydroxystearylamide, and N,N'-xylylenebisstearylamide; higher amines such as dodecylamine, tetradecylamine, and octadecylamine; fatty acid ester compounds such as stearylstearic acid, oleylpalmitic acid, glycerin fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters, and polyoxyethylene fatty acid esters (e.g., the EMALLEX series manufactured by Nippon Emulsion Co., Ltd., the Rikemal series manufactured by Riken Vitamin Co., Ltd., and the Poem series manufactured by Riken Vitamin Co., Ltd.); sucrose fatty acid esters such as sucrose stearic acid and sucrose palmitic acid (e.g., the Ryoto Sugar Ester series manufactured by Mitsubishi Chemical Foods Corporation);Synthetic waxes such as polyethylene wax and α-olefin maleic anhydride copolymer wax (e.g., Baker-Petrolite's UNILIN series); dimer acid; dimer diol (e.g., Croda's PRIPOR series); fatty acid inulins such as inulin stearate; fatty acid dextrins such as dextrin palmitate and dextrin myristate (e.g., Chiba Flour Milling's Leopearl series); glyceryl behenate eicosandioate; eicosane polyglyceryl behenate (e.g., Nisshin Oillio's Nomcoat series); amide compounds such as N-lauroyl-L-glutamic acid dibutylamide and N-(2-ethylhexanoyl)-L-glutamic acid dibutylamide (available from Ajinomoto Fine-Techno); 1,3:2,4-bis-O-benzylidene-D-glucitol (Gelol D dibenzylidene sorbitols such as those available from New Japan Chemical Co., Ltd.; low molecular weight oil gelling agents described in JP-A Nos. 2005-126507, 2005-255821, and 2010-111790; and the like.

[0043] The gelling agent preferably contains a linear or branched alkyl group having 12 to 26 carbon atoms in its molecular structure. When the gelling agent contains such an alkyl group, the aforementioned "house of cards structure" is more likely to be formed. When the gelling agent contains a linear alkyl group having 12 to 26 carbon atoms in its molecular structure, the aforementioned house of cards structure is more likely to be formed.

[0044] Specific examples of gelling agents containing a linear or branched alkyl group having 12 to 26 carbon atoms include aliphatic ketone compounds, aliphatic ester compounds, higher fatty acids, higher alcohols, fatty acid amides, etc., each having the above alkyl group.

[0045] The gelling agent is more preferably an aliphatic ketone compound or an aliphatic ester compound, and is preferably a compound represented by the following general formula (G1) or (G2). General formula (G1): R1-CO-R2 General formula (G2): R3-COO-R4

[0046] In general formulas (G1) and (G2), R1 to R4 each independently represent a linear or branched alkyl group having from 12 to 26 carbon atoms. Each of R1 to R4 may partially contain a branched moiety.

[0047] In general formula (G1), the alkyl groups represented by R1 and R2 are not particularly limited, but are preferably alkyl groups having 12 to 26 carbon atoms and no branched chains.

[0048] Examples of the aliphatic ketone compound represented by the general formula (G1) include 18-pentatriacontanone (C17-C17), dilignoceryl ketone (C24-C24), dibehenyl ketone (C22-C22), distearyl ketone (C18-C18), dieicosyl ketone (C20-C20), dipalmityl ketone (C16-C16), dimyristyl ketone (C14-C14), dilauryl ketone (C12-C12), These include lauryl myristyl ketone (C12-C14), lauryl palmityl ketone (C12-C16), myristyl palmityl ketone (C14-C16), myristyl stearyl ketone (C14-C18), myristyl behenyl ketone (C14-C22), palmityl stearyl ketone (C16-C18), palmityl behenyl ketone (C16-C22), and stearyl behenyl ketone (C18-C22).

[0049] Commercially available examples of the compound represented by general formula (G1) include 18-Pentatriacontanone (manufactured by Alfa Aeser), Hentriacontan-16-one (manufactured by Alfa Aeser), Kaowax T1 (manufactured by Kao Corporation), etc. The ink may contain only one type of aliphatic ketone compound as a gelling agent, or may contain two or more types.

[0050] On the other hand, in general formula (G2), the alkyl groups represented by R3 and R4 are not particularly limited, but are preferably alkyl groups having 12 to 26 carbon atoms and no branched chains.

[0051] Examples of the aliphatic ester compound represented by general formula (G2) include behenyl behenate (C21-C22), icosanoic acid icosyl (C19-C20), stearyl stearate (C17-C18), palmityl stearate (C17-C16), lauryl stearate (C17-C12), behenyl stearate (C17-C22), cetyl palmitate (C15-C16), stearyl palmitate (C15-C18), myristyl myristate (C13-C14), cetyl myristate ( C13-C16), octyldodecyl myristate (C13-C20), stearyl oleate (C17-C18), stearyl erucate (C21-C18), stearyl linoleate (C17-C18), behenyl oleate (C18-C22), myricyl ceramide (C25-C16), stearyl montanate (C27-C18), behenyl montanate (C27-C22), arachidyl linoleate (C17-C20), palmityl triacontanoate (C29-C16), etc.

[0052] Commercially available examples of aliphatic ester compounds represented by general formula (G2) include Unistar M-2222SL (manufactured by NOF Corporation), Exeparl SS (manufactured by Kao Corporation), EMALEX CC-18 (manufactured by Nippon Emulsion Co., Ltd.), Amreps PC (manufactured by Kokyu Alcohol Kogyo Co., Ltd.), Exeparl MY-M (manufactured by Kao Corporation), Sperm Acetate (manufactured by NOF Corporation), EMALEX CC-10 (manufactured by Nippon Emulsion Co., Ltd.), and WE (manufactured by NOF Corporation). These commercially available products are often mixtures of two or more types, and therefore may be separated and purified as necessary. Furthermore, the ink may contain only one type of aliphatic ester compound as a gelling agent, or two or more types.

[0053] The content of the gelling agent in the ink is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less, based on the total mass of the ink.

[0054] [Pigment] The pigment contains at least a compound having a structure represented by the following general formula (P) or (Q). However, compounds having structures other than these may also be contained within a range that does not impair the object and effect of this embodiment. Compounds having a structure represented by the following general formula (P) or (Q) exhibit a yellow color. The ink may contain only one type of pigment, or may contain two or more types.

[0055] The general formula (P) is shown below. [ka] R 2 and R 3 each independently represents an atom or a monovalent group selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy group, a nitro group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a carbonyl group, a carboxy group, and combinations thereof. Examples of the halogen atom include a chlorine atom and a fluorine atom.

[0056] The alkyl group preferably has 1 to 12 carbon atoms, and examples thereof include methyl, ethyl, propyl, hexyl, and nonyl groups. The alkyl group more preferably has 1 to 6 carbon atoms, and a methyl group is particularly preferred.

[0057] The alkoxy group preferably has 1 to 12 carbon atoms, and examples thereof include a methoxy group, an ethoxy group, a propoxy group, a hexyloxy group, and a nonyloxy group. The alkoxy group more preferably has 1 to 6 carbon atoms, and a methoxy group is more preferred.

[0058] Examples of the substituent bonded to the alkyl group or alkoxy group include a halogen atom, a hydroxy group, a substituted or unsubstituted aryl group, and the like.

[0059] Among the above, R 2 and R 3are each preferably independently a hydrogen atom, a methyl group, a methoxy group, or CH3-OC(=O)-.

[0060] R 5 represents an atom or monovalent group selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy group, a nitro group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a carbonyl group, a carboxy group, and combinations thereof. Specific examples of the halogen atom, alkyl group, alkoxy group, and substituent are those listed above for R 2 and R 3 This is the same as the specific example explained in R 5 Among the above, is preferably a hydrogen atom, a nitro group, or a substituted or unsubstituted alkyl group.

[0061] Y 1 represents a c-valent group selected from the group consisting of substituted or unsubstituted saturated aliphatic hydrocarbon groups, substituted or unsubstituted unsaturated aliphatic hydrocarbon groups, substituted or unsubstituted aromatic hydrocarbon groups, substituted or unsubstituted heterocyclic groups, ether bonds, and combinations thereof. The aliphatic group here includes not only linear or branched hydrocarbon groups but also alicyclic hydrocarbon groups. c represents an integer of 1 or 2. That is, when c is 1, Y 1 is a monovalent group, and when c is 2, Y 1 is a divalent group. When c is 2, Y 1 The two structures that bind to may be the same or different.

[0062] Above Y 1Examples of saturated aliphatic hydrocarbon groups that may be present include linear saturated hydrocarbons having 1 to 18 carbon atoms, branched saturated hydrocarbons having 3 to 18 carbon atoms, and alicyclic saturated hydrocarbons having 3 to 14 carbon atoms. Examples of unsaturated aliphatic hydrocarbon groups include linear unsaturated hydrocarbons having 1 to 18 carbon atoms, branched unsaturated hydrocarbons having 3 to 18 carbon atoms, and alicyclic unsaturated hydrocarbons having 3 to 14 carbon atoms. These aliphatic hydrocarbon groups may be bonded to an ether bond (-O-). Y containing an aliphatic hydrocarbon group 1 Specific examples of include a nonyl group, a methoxy group, etc. Examples of the substituents which may be bonded to these include a halogen atom, a hydroxy group, an alkoxy group, etc.

[0063] On the other hand, the above Y 1 Examples of aromatic hydrocarbons that can be used include phenyl, phenylene, biphenyl, biphenylene, naphthalene, and azulene. Examples of heterocyclic groups include furan, thiophene, and pyrrole. Examples of substituents that can be bonded to these groups include halogen atoms (e.g., chlorine and fluorine atoms), hydroxy groups, alkyl groups having 1 to 12 carbon atoms (e.g., methyl groups), alkoxy groups having 1 to 12 carbon atoms (e.g., methoxy groups), and hexyloxy groups.

[0064] Y 1 Among these, a substituted or unsubstituted phenyl group, phenylene group, or biphenylene group is preferred.

[0065] The compound represented by the above general formula (P) is more preferably a compound represented by the following general formula (P1). [ka] R 21 , R 22 , R 31 , and R 32Each of R independently represents an atom or group selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a carbonyl group, a carboxy group, and combinations thereof. 1 and R 2 is the same as:

[0066] Y 11 represents a substituted or unsubstituted alkylene group, or a substituted or unsubstituted arylene group. Specific examples of alkylene groups, arylene groups, and substituents bonded thereto are listed below. 1 The groups are the same as those described above.

[0067] General formula (Q) is shown below. [ka] R 2 and R 3 Each independently represents an atom or a monovalent group selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy group, a nitro group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a carbonyl group, a carboxy group, and combinations thereof. Specific examples of the halogen atom, alkyl group, alkoxy group, and substituent are R 2 and R 3 The specific examples are similar to those of R. 2 and R 3 are each preferably independently a hydrogen atom, a chlorine atom, a methyl group, a methoxy group, or CH3-OC(=O)-.

[0068] R 6 R represents a monovalent group selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, and combinations thereof. 6 When R is an alkyl group, the number of carbon atoms therein is preferably 1 or more and 18 or less, and more preferably 1 or more and 6 or less. 6is particularly preferably an aryl group. Examples of substituents that can be bonded to these include halogen atoms (e.g., chlorine atoms, fluorine atoms, etc.), hydroxy groups, alkyl groups having 1 to 12 carbon atoms (e.g., methyl groups), substituted or unsubstituted alkoxy groups, carbonyl groups, carboxy groups, etc.

[0069] Y 2 represents a d-valent group selected from the group consisting of substituted or unsubstituted saturated aliphatic hydrocarbon groups, substituted or unsubstituted unsaturated aliphatic hydrocarbon groups, substituted or unsubstituted aromatic hydrocarbon groups, substituted or unsubstituted heterocyclic groups, ether bonds, and combinations thereof. d represents an integer of 1 or 2. That is, when d is 1, Y 2 is a monovalent group, and when d is 2, Y 2 is a divalent group. When d is 2, Y 2 The two structures bound to Y may be the same or different. 2 Specific examples of the saturated aliphatic hydrocarbon group, unsaturated aliphatic hydrocarbon group, aromatic hydrocarbon group, heterocyclic group, and substituents that can be bonded to these groups are Y in the above general formula (P). 1 The same as the specific example of Y 2 Among these, a substituted or unsubstituted phenyl group, phenylene group, or biphenylene group is preferred.

[0070] Specific examples of the compounds represented by the above general formula (P) or (Q) include, but are not limited to, the following compounds. Note that stereoisomers of the following compounds are also preferred. [ka]

[0071] Among the above, the compounds represented by the following formula are particularly preferred. [ka]

[0072] The average particle size of the pigment in the ink is preferably 0.08 μm or more and 0.5 μm or less, and the maximum particle size of the pigment is preferably 0.3 μm or more and 10 μm or less, and more preferably 0.3 μm or more and 3 μm or less. By adjusting the particle size of the pigment, clogging of the nozzles of the inkjet recording head can be suppressed, and the storage stability, ink transparency, and curing sensitivity of the ink can be maintained. The average particle size of the pigment is measured by dynamic light scattering (for example, Zetasizer Nano S (manufactured by Malvern Instruments)).

[0073] The content of the pigment is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 0.4% by mass or more and 10% by mass or less, based on the total mass of the ink.

[0074] The method for dispersing the pigment among the other components in the ink is not particularly limited, and can be carried out using, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paint shaker, etc. The pigment is preferably dispersed so that the average particle size of the pigment particles is preferably 0.08 μm to 0.5 μm, and the maximum particle size is preferably 0.3 μm to 10 μm, more preferably 0.3 μm to 3 μm. The pigment dispersion method is adjusted depending on the types of pigment, pigment dispersant, and dispersing aid, the dispersion conditions, the filtration conditions, etc.

[0075] When dispersing the pigment in other components, a dispersion medium may be used. A solvent may be used as the dispersion medium. However, in order to prevent the solvent from remaining in the resulting image, it is preferable to use the above-mentioned photopolymerizable compound (particularly a low-viscosity monomer, such as tripropylene glycol diacrylate) as the dispersion medium.

[0076] [Dispersion aid] In this specification, a dispersing aid refers to a compound having a moiety that adsorbs to the surface of the pigment (in this embodiment, the common structure described above) and a moiety that adsorbs to the pigment dispersant (in this embodiment, an acidic group). In the ink, the dispersing aid can increase the affinity between the pigment and the pigment dispersant and suppress dissociation between the pigment and the pigment dispersant. The ink may contain only one type of dispersing aid, or two or more types.

[0077] The dispersing aid includes a compound represented by the following general formula (S): [ka] R 7 represents an atom or group selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, and a carboxy group. Examples of the halogen atom include a chlorine atom and a fluorine atom.

[0078] The alkyl group preferably has 1 to 18 carbon atoms, and examples thereof include a methyl group, an ethyl group, a propyl group, a hexyl group, and a nonyl group. The alkyl group more preferably has 1 to 9 carbon atoms, and a methyl group is particularly preferred.

[0079] The alkoxy group preferably has 1 to 18 carbon atoms, and examples thereof include a methoxy group, an ethoxy group, a propoxy group, a hexyloxy group, and a nonyloxy group. The alkoxy group more preferably has 1 to 9 carbon atoms, and a methoxy group is more preferred.

[0080] Examples of the substituent that can be bonded to the alkyl group or the alkoxy group include a halogen atom, a hydroxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, etc. 7 is preferably a hydrogen atom or an alkyl group having 1 to 18 carbon atoms (methyl group).

[0081] R 1represents a monovalent or divalent group selected from the group consisting of substituted or unsubstituted saturated aliphatic hydrocarbon groups, substituted or unsubstituted unsaturated aliphatic hydrocarbon groups, substituted or unsubstituted aromatic hydrocarbon groups, substituted or unsubstituted heterocyclic groups, carboxy groups, ether bonds, and combinations thereof. Here, aliphatic includes not only linear or branched hydrocarbon groups but also alicyclic hydrocarbon groups. b is 0 or 1, and when b is 0, R 1 is a monovalent group, and when b is 1, R 1 is a divalent group.

[0082] Above R 1 Examples of saturated aliphatic hydrocarbon groups that may be present include linear saturated hydrocarbons having 1 to 18 carbon atoms, branched saturated hydrocarbons having 3 to 18 carbon atoms, and alicyclic saturated hydrocarbons having 3 to 14 carbon atoms. Examples of unsaturated aliphatic hydrocarbon groups include linear unsaturated hydrocarbons having 1 to 18 carbon atoms, branched unsaturated hydrocarbons having 3 to 18 carbon atoms, and alicyclic unsaturated hydrocarbons having 3 to 14 carbon atoms. These aliphatic hydrocarbon groups may also be bonded to an ether bond (-O-). R containing an aliphatic hydrocarbon group 1 Examples of the substituent include a nonyl group, a methoxy group, etc. Examples of the substituent that may be bonded to these groups include a halogen atom, a hydroxy group, an alkoxy group, etc.

[0083] Above R 1 Examples of unsaturated aromatic hydrocarbons that can be heterocyclic include phenyl, phenylene, biphenyl, biphenylene, and naphthalene rings. Examples of heterocyclic rings include furan, thiophene, and pyrrole groups. Examples of substituents that can be bonded to these include halogen atoms (e.g., chlorine, fluorine), hydroxy groups, alkyl groups having 1 to 12 carbon atoms (e.g., methyl), alkoxy groups having 1 to 12 carbon atoms (e.g., methoxy), and hexyloxy groups.

[0084] R 1 When is single-valued, R 1is preferably a substituted or unsubstituted phenyl group or naphthyl group. 1 When is bivalent, R 1 is preferably a substituted or unsubstituted phenylene group or naphthylene group.

[0085] W represents an acidic group selected from a phosphate group, a sulfonic acid group, a sulfonate group (-SO3M), and a nitrate group. a represents 1 or 2, and when a is 1, b is 1, and when a=2, at least one b is 1. In the case of a sulfonate group, a sulfonate ion (-SO3 - ) and counter ions (M + ) constitutes a salt. The counter ion of the sulfonate ion (M + ) Examples include Li ions, Na ions, K ions, ammonium ions, N + H(CH3)3, N + (CH3)2{(CH2) n CH3}2 (n is an integer of 1 or more and 20 or less), etc.

[0086] Z represents an a-valent atom or group selected from the group consisting of a single bond, a hydrogen atom, a halogen atom, a hydroxy group, an amino group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted saturated aliphatic hydrocarbon group, a substituted or unsubstituted unsaturated aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, and combinations thereof. That is, when a is 1, Z is a monovalent group, and when a is 2, Z is a divalent group. Examples of halogen atoms, alkoxy groups, saturated aliphatic hydrocarbon groups, unsaturated aliphatic hydrocarbon groups, aromatic hydrocarbon groups, heterocyclic groups, and substituents bonded to these that can be Z include those listed above for R. 7 or R 1 This includes those described as.

[0087] When Z is a monovalent group, it is preferably a hydrogen atom, an alkyl group having 1 to 18 carbon atoms (e.g., a methyl group), an alkoxy group having 1 to 18 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group. When Z is a divalent group, it is preferably a single bond or a phenylene group.

[0088] The compound represented by the above general formula (S) is more preferably a compound represented by the following general formula (S1). [ka] R 71 and R 72 each independently represents an atom or group selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, and a carboxy group. 1 This is similar to what has been described above.

[0089] R 11 and R 12 each independently represents a group selected from the group consisting of a substituted or unsubstituted saturated aliphatic hydrocarbon group, a substituted or unsubstituted unsaturated aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, a carboxy group, and combinations thereof, and each represents the same as R 1 The formula is the same as that described above. W represents an acidic group selected from a phosphate group, a sulfonic acid group, a sulfonate group, and a nitrate group. A represents a hydrogen atom, an acidic group selected from a phosphate group, a sulfonic acid group, a sulfonate group, and a nitrate group.

[0090] Specific examples of the dispersing aid represented by the above general formula (S) include compounds represented by the following chemical formulas: Note that stereoisomers of the following compounds are also included as preferred compounds. [ka]

[0091] The content of the dispersion aid in the ink is preferably 0.01% by mass or more and 2% by mass or less, and more preferably 0.02% by mass or more and 1% by mass or less, based on the total mass of the ink.

[0092] [Pigment dispersant] The pigment dispersant is a component for improving the dispersibility of the pigment and the ejection stability of the ink, and preferably has a site that can bond to the above-mentioned dispersion aid (acidic group).

[0093] Examples of the pigment dispersant include hydroxyl group-containing carboxylic acid esters, salts of long-chain polyaminoamides and high-molecular-weight acid esters, salts of high-molecular-weight polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, high-molecular-weight unsaturated acid esters, polymeric copolymers such as acrylic block copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalenesulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate.

[0094] A preferred pigment dispersant is selected depending on the type of the dispersing aid described above, and may be an acidic pigment dispersant (acidic pigment dispersant) or a basic pigment dispersant (basic pigment dispersant). Among these, a basic pigment dispersant is preferred.

[0095] The basic pigment dispersant is, for example, a polymeric pigment dispersant containing one or more primary amines and secondary amines. Examples of the basic pigment dispersant include Solsperse 11200, Solsperse 13240, Solsperse 13650, Solsperse 13940, Solsperse 16000, Solsperse 17000, Solsperse 18000, Solsperse 20000, Solsperse 24000SG, Solsperse 24000GR, Solsperse 28000, Solsperse 31845, Solsperse 32000, Solsperse 32500, and Solsperse 31845, all manufactured by Lubrizol. 2550, Solspers 32600, Solspers 33000, Solspers 34750, Solspers 35100, Solspers 35200, Solspers 37500, Solspers 38500, Solspers 39000, Solspers 56000, Solspers 71000, Solspers 76500, Solspers 88000, Solspers X300, Solspers 9000; DISPERBYK-108 and DISPERBY by BYK-Chemie K-109, DISPERBYK-112, DISPERBYK-116, DISPERBYK-130, DISPERBYK-161, DISPERBYK-162, DISPERBYK-163, DISPERBYK-1 64, DISPERBYK-166, DISPERBYK-167, DISPERBYK-168, DISPERBYK-182, DISPERBYK-183, DISPERBYK-184, DISPERBYK-185, Examples of suitable dyes include DISPERBYK-2000, DISPERBYK-2008, DISPERBYK-2009, DISPERBYK-2022, DISPERBYK-2050, DISPERBYK-2150, DISPERBYK-2155, DISPERBYK-2163, DISPERBYK-2164, and BYK-9077; Ajinomoto Fine-Techno Co., Ltd.'s Ajisper PB821, PB822, PB823, PB824, and PB827; and BASF's EFKA 4300, EFKA 4330, EFKA 4340, EFKA 4400, EFKA PX 4701, EFKA 4585, EFKA 5207, EFKA 6230, and EFKA 7731.

[0096] Among the basic pigment dispersants listed above, polyester-based basic dispersants are particularly preferred from the viewpoint of ink ejection stability. Examples of polyester-based basic dispersants include Solsperse 13940, 17000, 24000, and 32000 manufactured by Lubrizol Corporation, and Ajisper PB821, PB822, PB823, PB824, and PB827 manufactured by Ajinomoto Fine-Techno Co., Ltd. Also preferred are acrylic block copolymer-based basic pigment dispersants such as EFKA PX 4701 manufactured by BASF.

[0097] Examples of the acidic pigment dispersant include Solsperse 3000, Solsperse 21000, Solsperse 26000, Solsperse 36600, Solsperse 41000, Solsperse 41090, Solsperse 43000, Solsperse 44000, Solsperse 46000, Solsperse 47000, and Solsperse 55000, manufactured by The Lubrizol Corporation; and DISPERBYK-102, DISPERBYK-111, DISPERBYK-170, DISPERBYK-171, DISPERBYK-174, DISPERBYK-2096, BYK-P104, BYK-P104S, BYK-P105, and BYK-220S, manufactured by BYK-Chemie.

[0098] The ink may contain only one type of pigment dispersant, or may contain two or more types. The amount of pigment dispersant in the ink is preferably 0.1% by mass or more and 10% by mass or less relative to the total mass of the ink.

[0099] [Other ingredients] In addition to the above components, the ink may further contain a photoinitiator aid, a polymerization inhibitor, etc., as necessary. Examples of photoinitiator aids include tertiary amine compounds. Among these, aromatic tertiary amine compounds are preferred. Examples of aromatic tertiary amine compounds include N,N-dimethylaniline, N,N-diethylaniline, N,N-dimethyl-p-toluidine, N,N-dimethylamino-p-benzoic acid ethyl ester, N,N-dimethylamino-p-benzoic acid isoamyl ethyl ester, N,N-dihydroxyethylaniline, triethylamine, and N,N-dimethylhexylamine. Among these, N,N-dimethylamino-p-benzoic acid ethyl ester and N,N-dimethylamino-p-benzoic acid isoamyl ethyl ester are preferred. The ink may contain only one photoinitiator aid, or two or more.

[0100] Examples of the polymerization inhibitor include (alkyl)phenols, hydroquinone, catechol, resorcinol, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone, nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cupferron, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N-(3-oxyanilino-1,3-dimethylbutylidene)aniline oxide, dibutyl cresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraldoxime, methyl ethyl ketoxime, cyclohexanone oxime, and the like.

[0101] The ink may further contain other components as necessary. The other components may be various additives, other resins, etc. Examples of additives include surfactants, leveling additives, matting agents, ultraviolet absorbers, infrared absorbers, antibacterial agents, and basic compounds for improving the storage stability of the ink. Examples of basic compounds include basic alkali metal compounds, basic alkaline earth metal compounds, and basic organic compounds such as amines. Examples of other resins include resins for adjusting the physical properties of the cured product, such as polyester-based resins, polyurethane-based resins, vinyl-based resins, acrylic-based resins, and rubber-based resins.

[0102] [Physical properties of inkjet ink] As mentioned above, the ink contains a gelling agent, and therefore undergoes a reversible sol-gel phase transition depending on the temperature. Actinic radiation-curable ink that undergoes a sol-gel phase transition is a liquid (sol) at high temperatures (for example, about 80°C), and can be ejected in a sol state from an inkjet recording head. When actinic radiation-curable inkjet ink is ejected at high temperatures, the ink droplets (dots) land on the recording medium, then naturally cool and gel. This prevents adjacent dots from coalescing, improving image quality.

[0103] To improve the ejection properties of ink droplets, the ink preferably has a viscosity of a certain level or less at high temperatures. Specifically, the ink preferably has a viscosity of 3 mPa·s or more and 20 mPa·s or less at 80°C. On the other hand, to prevent adjacent dots from coalescing, the ink preferably has a viscosity of a certain level or more at room temperature after landing. Specifically, the ink has a viscosity of 1000 mPa·s or more at 25°C.

[0104] The gelling temperature of the ink is preferably 30°C or higher but lower than 100°C, and more preferably 50°C or higher but lower than 65°C. If the gelling temperature of the ink is too high, gelation is likely to occur during ejection, resulting in poor ejectability. On the other hand, if the gelling temperature of the ink is too low, it is difficult for the ink to gel quickly after landing on a recording medium. The gelling temperature is the temperature at which ink in a sol state gels and its fluidity decreases during the process of cooling.

[0105] The viscosity of inkjet ink at 80°C, viscosity at 25°C, and gel temperature are determined by measuring the temperature change of the ink's dynamic viscoelasticity using a rheometer. Specifically, the ink is heated to 100°C and cooled to 20°C at a shear rate of 11.7 ( / s) and a cooling rate of 0.1°C / s, and a viscosity temperature change curve is obtained. The viscosities at 80°C and 25°C are then taken as the viscosities at 80°C and 25°C on the temperature change curve. The gel temperature is the temperature at which the viscosity reaches 200 mPa·s on the viscosity temperature change curve.

[0106] The rheometer used can be a stress-controlled rheometer from the Physica MCR series manufactured by Anton Paar. The diameter of the cone plate can be set to 75 mm and the cone angle to 1.0°.

[0107] The sol-gel phase transition ink ejects liquid ink droplets at high temperatures and lands on a recording medium. At the same time, the ink droplets are cooled and gelled, preventing the droplets from coalescing. This allows for the formation of high-resolution images even during high-speed recording.

[0108] [Inkjet ink preparation method] The ink is obtained by mixing the photopolymerizable compound, pigment, pigment dispersant, gelling agent, photoinitiator, and dispersing aid under heating. The mixing method is not particularly limited, but it is preferable to prepare a composition in which a pigment, pigment dispersant, dispersing aid, etc. are dispersed in a portion of the photopolymerizable compound, and then mix this composition with other components. The obtained ink is preferably filtered through a predetermined filter.

[0109] 2. Manufacturing method of printed matter The method for producing a printed matter of this embodiment includes at least the following two steps. (1) A step of ejecting ink droplets of the ink from an inkjet recording head and landing them on a recording medium. (2) A process of irradiating the ink droplets that have landed on the recording medium with actinic rays to harden the ink droplets.

[0110] [Regarding step (1)] In this process, ink droplets of the ink described above are ejected from an inkjet recording head and landed on a recording medium at positions corresponding to the image to be formed.

[0111] The ejection method from the inkjet recording head may be either an on-demand method or a continuous method. On-demand inkjet heads may be any of electromechanical conversion types such as single cavity type, double cavity type, bender type, piston type, shear mode type, and shared wall type, and electrothermal conversion types such as thermal inkjet type and bubble jet type (Bubble Jet is a registered trademark of Canon Inc.).

[0112] The ejection stability of ink droplets can be improved by ejecting them from the inkjet head in a heated state. The ink temperature during ejection is preferably 35°C or higher and 100°C or lower, and more preferably 35°C or higher and 80°C or lower to further improve ejection stability. In particular, it is preferable to eject the ink at a temperature that results in a viscosity of 7 mPa·s or higher and 15 mPa·s or lower, more preferably 8 mPa·s or higher and 13 mPa·s or lower.

[0113] The ink is heated in the inkjet recording head of the inkjet recording device, in an ink flow path connected to the inkjet recording head, or in an ink tank connected to the ink flow path.

[0114] The amount of liquid ejected per droplet from each nozzle of the inkjet recording head depends on the image resolution, but is preferably 0.5 pL to 10 pL, and more preferably 0.5 pL to 2.5 pL to form a high-resolution image.

[0115] It is preferable that ink droplets that have landed on a recording medium undergo a sol-gel phase transition by cooling and quickly gel. This allows the ink droplets to be pinned without spreading. Furthermore, oxygen is less likely to enter the ink droplets, which makes it less likely that oxygen will inhibit the curing of the photopolymerizable compound.

[0116] The recording medium may be paper or a resin film. Examples of paper include printing coated paper and printing coated paper B. Examples of resin films include polyethylene terephthalate film, polypropylene film, and vinyl chloride film.

[0117] The conveying speed of the recording medium is preferably 30 to 120 m / min.

[0118] [Regarding step (2)] By irradiating the ink droplets that have landed on the recording medium with actinic rays, the photopolymerizable compound contained in the ink droplets is polymerized, thereby hardening the ink droplets.

[0119] The actinic rays can be selected from, for example, electron beams, ultraviolet rays, α rays, γ rays, and X-rays. Among these, ultraviolet rays are preferred, and an LED light source that emits light having a peak wavelength of 360 nm or more and 410 nm or less is more preferred. An example of an LED light source is a water-cooled LED (peak wavelength 395 nm) manufactured by Phoseon Technology. LEDs emit less radiant heat than conventional light sources (e.g., metal halide lamps). Therefore, when exposed to actinic rays, the ink is less likely to melt and uneven gloss is less likely to occur.

[0120] When irradiating light having a peak wavelength of 360 nm or more and 410 nm or less, the peak illuminance on the recording medium surface or ink droplet surface is 0.5 W / cm 2 More than 10.0W / cm 2 It is preferable that the peak irradiance is 1.0 W / cm or less. 2 More than 5.0W / cm 2 It is more preferable to set the following:

[0121] The actinic ray irradiation is preferably carried out between 0.001 and 1.0 seconds after the ink lands on the recording medium, and more preferably between 0.001 and 0.5 seconds in order to form a high-definition image.

[0122] Alternatively, the actinic ray irradiation may be performed in two stages. In this case, the ink is pre-cured by irradiating it with actinic ray between 0.001 and 2.0 seconds after the ink lands on the recording medium, and then after all printing is completed, the ink is fully cured by irradiating it with actinic ray again. By irradiating it with actinic ray in two stages, the ink is less likely to shrink during curing. [Example]

[0123] The present invention will be specifically described below with reference to examples, but the embodiments of the present invention are not limited to these examples.

[0124] (1) Preparation of pigment dispersion 1 (1-1) Preparation of materials As materials for the pigment dispersion, the following photopolymerizable compound, pigment dispersant, pigment, and dispersing aid were prepared.

[0125] [Photopolymerizable compound] Tripropylene glycol diacrylate (M220, manufactured by Toagosei Co., Ltd.)

[0126] [Pigment dispersant] Acrylic block copolymer (EFKA PX 4701, manufactured by BASF)

[0127] [Pigment] Pigment 1 [ka] Pigment 2 [ka] Pigment 3 [ka] Pigment 4 [ka] Pigment 5 [ka]

[0128] [Dispersion aid] Dispersing agent 1 [ka] Dispersing agent 2 [ka] Dispersing agent 3 [ka] Dispersing agent 4 [ka] Dispersing agent 5 [ka] Dispersing agent 6 [ka]

[0129] (1-2) Preparation of pigment dispersion Preparation of pigment dispersion 1 3.0 parts by mass of the pigment dispersant, 35.7 parts by mass of the photopolymerizable compound, and 0.3 parts by mass of a dispersing aid (dispersing aid 1) were placed in a stainless steel beaker. The mixture was then heated and stirred on a hot plate at 65°C for 1 hour. After the resulting solution was cooled to room temperature, 6.0 parts by mass of a pigment (pigment 1) was added, and the mixture was placed in a glass bottle together with 200 g of zirconia beads with a diameter of 0.5 mm, sealed, and dispersed for 8 hours using a paint shaker. The zirconia beads were then removed to prepare pigment dispersion 1.

[0130] Preparation of pigment dispersions 2 to 23 Pigment dispersions were prepared in the same manner as in Pigment Dispersion 1, except that the combinations of dispersing aid and pigment were changed as shown in Table 1.

[0131] [Table 1]

[0132] (2) Preparation of inkjet ink (2-1) Preparation of materials The following photopolymerizable compound, the above photoinitiator, gelling agent, and polymerization inhibitor were prepared.

[0133] [Photopolymerizable compound] Tripropylene glycol diacrylate (M220, manufactured by Toagosei Co., Ltd.) Polyethylene glycol #600 diacrylate (EBECRYL11, manufactured by Daicel-Cytec Co., Ltd.) 3PO-modified trimethylolpropane triacrylate (M360, manufactured by Miwon) 6EO-modified trimethylolpropane triacrylate (M3160, manufactured by SARTOMER) Ditrimethylolpropane tetraacrylate (SR355, manufactured by SARTOMER) Amine-modified acrylate (CN371, manufactured by SARTOMER)

[0134] [Photoinitiator] Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (IRGACURE819, manufactured by BASF) 1,3-Di({α-[1-chloro-9-oxo-9H-thioxanthen-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxy)-2,2-bis({α-[1-chloro-9-oxo-9H-thioxanthen-4-yl)oxy]acetylpoly[oxy(1-methylethylene)]}oxymethyl)propane (Speedcure 7010, manufactured by LAMBSON)

[0135] [Gelling agent] Hentriacontan-16-one (dipalmityl ketone, manufactured by Arfa Aeser, gelling agent represented by general formula (G1)) Behenyl stearate (WE11, manufactured by NOF Corporation, a gelling agent having the structure represented by the above general formula (G2))

[0136] [Surfactants] Polyether-modified polydimethylsiloxane (BYK-307, manufactured by BASF)

[0137] [Polymerization inhibitor] 4,4'-[(1,10-dioxo-1,10-decanediyl)bis(oxy)]bis[2,2,6,6-tetramethyl]-1-piperidinyloxy (UV-10, manufactured by BASF)

[0138] (2-2) Preparation of inkjet ink The components shown in Table 2 below were mixed with the pigment dispersion liquid described above, heated to 80°C, and stirred. While heated, the resulting solution was filtered through a 3 μm Teflon (registered trademark) membrane filter manufactured by Advantec, to obtain inkjet inks 1 to 23. The units of components shown in Table 2 are parts by mass.

[0139] 3. Production and evaluation of printed materials (1) Production of printed materials A monochrome image was formed using a line-recording inkjet recording device. The ink supply system of the inkjet recording device was composed of an ink tank, a supply pipe, a sub-ink tank immediately before the head, a pipe with a filter, and a piezo head (inkjet recording head), all connected in this order. The inkjet ink obtained above was supplied to the ink supply system of the inkjet recording device, and the entire ink supply system from the ink tank to the inkjet recording head was heated to 80°C.

[0140] The inkjet recording head used had 1,776 nozzles and a resolution of 600 dpi. Two inkjet heads manufactured by Konica Minolta were modularized to achieve a resolution of 1,200 dpi. The applied voltage was adjusted so that the droplet volume was 3.5 pL, and images were formed. dpi refers to the number of dots per 2.54 cm. Images were formed in an environment of 23°C and 55% RH.

[0141] The recording media used were microflute paper containers (F-stage, 0.7 mm thick, crown packaging), coated cardboard (Maricoat, 550 g / m 2 A recording medium (manufactured by Hokuetsu Paper Mills) was prepared. The temperature of the recording medium was adjusted to 30°C using a temperature control unit. The recording medium was conveyed at a speed of 1000 mm / s. Ink droplets were then ejected from the inkjet recording head onto the recording medium to form the following image.

[0142] After image formation, an LED lamp (Kyocera, 8 W / cm) placed downstream of the inkjet recording device was used. 2 , wavelength 450nm, irradiation width 68mm, distance from LED lamp to recording medium surface 50mm, illuminance on recording medium 2.0W / cm 2 ) so that the recording medium was irradiated with actinic rays in an integrated amount of 350 mJ. Then, the ink that had landed on the recording medium was cured.

[0143] (2) Evaluation The high-temperature stability of the inkjet ink and the weather resistance of the printed matter were evaluated according to the following criteria. The results are shown in Table 2.

[0144] High temperature stability of inkjet ink The high temperature stability of the inkjet ink was evaluated as follows. The particle size of the particles in the inkjet ink prepared above was measured using a Zetasizer Nano S (manufactured by Malvern Instruments). The ink was then stored in an environment at 90°C for two weeks. After that, the particle shape in the inkjet ink was measured in the same manner as above. The change in particle size before and after storage was evaluated according to the following criteria. ◎: Particle size change 0nm or more and less than 5nm ○: Particle size change is 5 nm or more and less than 10 nm △: Particle size change 10nm or more but less than 20nm ×: Particle size change of 20 nm or more

[0145] Weather resistance of printed matter The color space (L*, a*, b*) of the image obtained from the above-mentioned printed matter was evaluated. After that, a xenon weather meter was used to measure the color space at 120 W / m 2 The image was then subjected to accelerated degradation under conditions of spray water exposure at 25°C for 169 hours. The image color space (L1*, a1*, b1*) was then evaluated again. These changes ΔE (= [(L1*-L*) 2 +(a1*-a*) 2 +(b1*-b1) 2 〕 1 / 2 was calculated and evaluated according to the following criteria. ◎:ΔE≦5 ○:5<ΔE≦10 △:10<ΔE≦15 ×:15<ΔE

[0146] [Table 2]

[0147] As shown in Table 2 above, inkjet inks containing a dispersing aid having the structure represented by the above general formula (S) and a pigment having the structure represented by the above general formula (P) or (Q) exhibited good high-temperature stability. The resulting images also exhibited good weather resistance (Examples 1 to 20). In contrast, when dispersing aids with different structures were combined, or when pigments with different structures were combined, the high-temperature stability was poor, and the images also exhibited poor weather resistance (Comparative Examples 1 to 3). [Industrial Applicability]

[0148] According to the present invention, an actinic radiation-curable inkjet ink having good pigment dispersion stability is provided. Furthermore, according to a method for producing a printed matter using the actinic radiation-curable inkjet ink, the weather resistance of the resulting printed matter is good. Therefore, the inkjet ink is useful in various printing fields.

Claims

1. An actinic radiation-curable inkjet ink containing a photopolymerizable compound, a photoinitiator, a gelling agent, a pigment, a dispersing aid, and a pigment dispersant, The dispersing aid contains a compound represented by the following general formula (S): The pigment contains a compound represented by the following general formula (P) or the following general formula (Q): Actinic light curing inkjet ink. 【Chemistry 1】 (In the general formula (S), R ７ represents an atom or a monovalent group selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, and a carboxy group; R １ represents a monovalent or divalent group selected from the group consisting of a substituted or unsubstituted saturated aliphatic hydrocarbon group, a substituted or unsubstituted unsaturated aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, a carboxy group, an ether bond, and combinations thereof; Z represents an a-valent atom or group selected from the group consisting of a single bond, a hydrogen atom, a halogen atom, a hydroxy group, an amino group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted saturated aliphatic hydrocarbon group, a substituted or unsubstituted unsaturated aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, and combinations thereof; W represents an acidic group selected from a phosphate group, a sulfonic acid group, a sulfonate group, and a nitrate group; a represents 1 or 2, b represents 0 or 1, When a is 1, b is 1, and when a=2, at least one b is 1. 【Chemistry 2】 (In the general formula (P) and the general formula (Q), R ２ , R ３ , and R ５ each independently represents an atom or a monovalent group selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy group, a nitro group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a carbonyl group, a carboxy group, and combinations thereof; R ６ represents a monovalent group selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, and combinations thereof; Y １ represents a c-valent group selected from the group consisting of substituted or unsubstituted saturated aliphatic hydrocarbon groups, substituted or unsubstituted unsaturated aliphatic hydrocarbon groups, substituted or unsubstituted aromatic hydrocarbon groups, substituted or unsubstituted heterocyclic groups, ether bonds, and combinations thereof; Y ２ represents a d-valent group selected from the group consisting of a single bond, a substituted or unsubstituted saturated aliphatic hydrocarbon group, a substituted or unsubstituted unsaturated aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, an ether bond, and a combination thereof; c and d each independently represent 1 or 2.

2. The dispersing aid contains a compound represented by the following general formula (S1): The actinic radiation-curable ink-jet ink according to claim 1 . 【Transformation 3】 (In general formula (S1), R ７１ and R ７２ each independently represents an atom or group selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, and a carboxy group; R １１ and R １２ each independently represents a group selected from the group consisting of a substituted or unsubstituted saturated aliphatic hydrocarbon group, a substituted or unsubstituted unsaturated aliphatic hydrocarbon group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, a carboxy group, an ether bond, and combinations thereof; W represents an acidic group selected from a phosphate group, a sulfonic acid group, a sulfonate group, and a nitrate group; A represents a hydrogen atom, a phosphate group, a sulfonate group, and an acid group selected from the group consisting of a nitrate group and a phosphate group.

3. The pigment contains a compound represented by the following general formula (P1): The actinic radiation-curable ink-jet ink according to claim 1 . 【Chemistry 4】 (In general formula (P1), Y １１ represents a substituted or unsubstituted alkylene group or a substituted or unsubstituted arylene group; R ２１ , R ２２ , R ３１ , and R ３２ each independently represents an atom or a monovalent group selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a carbonyl group, a carboxy group, and combinations thereof.

4. The pigment contains a compound represented by the following general formula (P2): The actinic radiation curable inkjet ink according to claim 3. 【Transformation 5】

5. 5. The actinic radiation-curable inkjet ink according to claim 1, wherein the gelling agent contains at least one compound selected from compounds represented by the following general formulas (G1) and (G2): General formula (G1): R1-CO-R2 General formula (G2): R3-COO-R4 (In general formulas (G1) and (G2), R1 to R4 each independently represent a linear or branched alkyl group having 12 to 26 carbon atoms.)

6. a step of ejecting ink droplets of the actinic radiation curable inkjet ink according to any one of claims 1 to 4 from an inkjet recording head and causing the ink droplets to land on a recording medium; and irradiating the ink droplets that have landed on the recording medium with actinic light rays to cure the ink droplets. Methods for producing printed materials.

Images