Actinic radiation curable ink, image forming method and printed matter

Abstract

To provide an active ray-curable ink that can suppress blooming even when a gelling agent is contained and is excellent in curability of an image, an image formation method and a printed matter formed therewith.SOLUTION: An active ray curable ink contains an active ray polymerizing compound, a gelling agent, and a compound represented by a general formula (1). In general formula (1), Ar1 to Ar7 each represents a substituted or unsubstituted aromatic ring, and at least one of Ar1 to Ar3 is a benzene ring. A to C represent an integer of 0 or larger. However, when C≠0, Ar2 is a benzene ring.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an actinic radiation curable ink, an image forming method, and a printed matter. [Background technology]

[0002] Inkjet recording methods are used in various printing fields because they can form images easily and inexpensively. As inks used in inkjet recording methods, actinic radiation curable inks containing actinic radiation polymerizable compounds as liquid components are known. When actinic radiation is irradiated, actinic radiation curable inks are cured by polymerization of the actinic radiation polymerizable compounds, and the coloring material is firmly attached to the recording medium. Image forming methods using actinic radiation curable inks have been attracting attention in recent years because they can form images with high resistance to printing and adhesion even on recording media that do not absorb ink.

[0003] As a type of actinic radiation curable ink, ink that undergoes a phase change depending on temperature by blending a gelling agent is known.

[0004] For example, Patent Document 1 describes an ink composition containing at least one curable monomer, at least one gelling agent, an optional photoinitiator, and an optional colorant. According to Patent Document 1, the concentration of the gelling agent is adjusted to 10 at a temperature of about 20° C. to about 40° C. 6 By adjusting the viscosity to less than centipoise, the ink composition is said to be jettable and pinnable at temperatures of about 20°C to about 40°C. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-104905 A Summary of the Invention [Problem to be solved by the invention]

[0006] As disclosed in Patent Document 1, inks containing a gelling agent are known.

[0007] However, according to the findings of the present inventors, in actinic radiation curable inks containing a gelling agent as in Patent Document 1, after the ink is cured, blooming occurs in which the gelling agent precipitates on the image surface, resulting in a problem of reduced curability of the ink cured film. When blooming occurs, the ink coating surface becomes powdery, not only impairing the appearance of the printed matter, but also causing a decrease in image density and gloss fluctuations.

[0008] The present invention has been made in view of the above circumstances, and has an object to provide an actinic ray-curable ink that can suppress blooming even when it contains a gelling agent and has good image curing properties, an image forming method, and a printed matter formed by the ink and the image forming method. [Means for solving the problem]

[0009] An actinic ray-curable ink according to one embodiment of the present invention for solving the above problems is an actinic ray-curable ink containing an actinic ray-polymerizable compound, a gelling agent, and a compound represented by general formula (1).

[0010] [ka]

[0011] In the general formula (1), Ar 1 ~Ar 6 represents a substituted or unsubstituted aromatic ring, Ar 1 ~Ar 3 At least one of a to c represents an integer of 0 or more. However, when c ≠ 0, Ar 2 is a benzene ring.

[0012] Further, an image forming method according to one embodiment for solving the above problem is an image forming method including the steps of applying the actinic ray curable ink to a recording medium, and irradiating the applied actinic ray curable ink with actinic rays.

[0013] A printed matter according to one embodiment for solving the above problem is a printed matter having a printed layer formed using the above actinic ray curable ink. Effect of the Invention

[0014] The present invention provides an actinic radiation curable ink and an image forming method that can suppress blooming even when a gelling agent is contained and have good image curing properties. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a side view showing the concept of an inkjet image forming apparatus according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] [Actinic radiation curable ink] An actinic ray curable ink according to one embodiment of the present invention is an actinic ray curable ink containing an actinic ray polymerizable compound, a gelling agent, and a compound represented by general formula (1).

[0017] [ka]

[0018] In the general formula (1), Ar 1 ~Ar 6 represents a substituted or unsubstituted aromatic ring, Ar 1 ~Ar 3 At least one of a to c represents an integer of 0 or more. However, when c ≠ 0, Ar 2 is a benzene ring.

[0019] As described above, in the case of actinic radiation curable ink containing a gelling agent, after the ink droplets land, the gelling agent in the ink quickly crystallizes and precipitates on the ink surface. When actinic radiation such as ultraviolet rays or electron beams is applied in this state, the ink hardens, and the gelling agent precipitated on the surface of the cured film causes blooming.

[0020] As a result of intensive research by the present inventors, it was found that when a hydrophobic aromatic compound with low hydrogen bonding and dipole interaction properties is added to an ink, the aromatic compound is present in the vicinity of a gelling agent. Although the details of this are not clear, it is believed that CH / π interaction occurs between the CH portion of the carbon chain of the gelling agent and the π electrons of the aromatic compound, causing the aromatic compound to be present in the vicinity of the gelling agent, and the aromatic compound prevents the crystal growth of the gelling agent, thereby stabilizing the gelling agent in a state in which the crystal size is small. When the crystal size becomes small, the crystal arrangement becomes dense, and the movement of the gelling agent toward the surface of the cured film is suppressed, and blooming is suppressed. In addition, it is believed that the dense crystal arrangement of the gelling agent makes it less susceptible to the effects of oxygen inhibition, thereby improving the curability of the ink cured film.

[0021] Furthermore, according to the present inventors, the problem of blooming occurring in actinic radiation curable inks containing a gelling agent is prominent when the ink contains a white pigment.

[0022] According to the findings of the present inventors, in inks for forming white images, compounds having hydrophilic properties such as titanium oxide are usually used as white pigments. These white pigments have low affinity with gelling agents having hydrophobic properties, and the gelling agents tend to precipitate on the surface of the ink cured film. For this reason, it is believed that blooming is likely to occur in actinic radiation curable inks containing a white pigment and a gelling agent.

[0023] Since the actinic ray-curable ink of the present invention contains the compound represented by the above general formula (1), it is believed that blooming is suppressed even if a white pigment is contained as a colorant.

[0024] (Compounds that form CH / π interactions) The actinic ray curable ink of the present invention contains the compound represented by the above general formula (1), and thereby forms a CH / π interaction with the gelling agent.

[0025] CH / π interaction is a weak affinity force acting between hydrogen of a CH group (such as CH of an alkyl group) and a double bond (C=C, C=O, C=N) or between π electrons of an aromatic ring. Although the energy per unit of CH / π interaction is small, since an alkyl group generally has multiple CHs and an aromatic ring also has multiple π electron clouds, multiple CH / π interactions can act simultaneously. Since the compound represented by the above general formula (1) has multiple aromatic rings, multiple CH / π interactions are formed with the gelling agent, and it is considered that the binding strength is sufficiently high when these are combined.

[0026] In the above general formula (1), Ar 1 ~Ar 6 represents an aromatic ring. The aromatic ring is not particularly limited, but specific examples thereof include a benzene ring, an aromatic heterocycle, and an aromatic condensed ring.

[0027] Specific examples of the aromatic heterocycle include a pyridine ring, a thiazole ring, an isothiazole ring, a thiophene ring, a tetrahydrothiophene ring, a furan ring, a tetrahydrofuran ring, an oxazole ring, an oxadiazole ring, a pyrrole ring, an imidazole ring, a pyridine ring, a pyrazine ring, a pyrimidine ring, a triazine ring, a pyrazole ring, a triazole ring, a benzoxazole ring, a benzimidazole ring, a dibenzothiophene ring, a benzothiazole ring, a dibenzofuran ring, and a carbazole ring.

[0028] Specific examples of the aromatic condensed ring include a naphthalene ring, an anthracene ring, a phenanthrene ring, a fluorene ring, and an indene ring.

[0029] In the above general formula (1), a to c each independently represent an integer of 0 or more, and are usually 0 to 10. a to c each independently are preferably 0 to 5, more preferably 0 to 3, and even more preferably 1 to 2. If a to c are 10 or more, various interaction forms may be obtained if the molecular weight becomes too large, but by being within the above range, the interaction between the gelling agent and the compound represented by the above general formula (1) functions effectively.

[0030] In the above general formula (1), Ar 1 ~Ar 3 At least one of the groups is a benzene ring. This makes it easier to form CH / π interactions with the CH groups of the gelling agent, and since it is possible to form multiple CH / π interactions simultaneously, it is believed that the binding strength due to the above interactions is greater. This means that the compound represented by the above general formula (1) is present in the vicinity of the gelling agent, making it difficult for the gelling agent crystals to aggregate together, and therefore the gelling agent crystals are less likely to grow. This is believed to make it possible to stabilize the gelling agent crystals in a small state in the actinic radiation-curable ink.

[0031] The compound represented by the above general formula (1) is Ar 2 When the structure has a branched structure at c ≠ 0, Ar 2 is a benzene ring. When c ≠ 0, Ar 2 Since it is a benzene ring, it can function as a π acceptor (π electron acceptor).

[0032] The compound of the above general formula (1) is Ar 1 ~Ar 3At least one of the rings is a benzene ring. Since the benzene ring easily forms a CH / π interaction with a gelling agent, it is considered that the compound represented by the above general formula (1) having a benzene ring can increase the binding strength due to the CH / π interaction. Therefore, the compound represented by the above general formula (1) preferably has at least two benzene rings, more preferably has 2 to 7 benzene rings, and even more preferably has 2 to 4 benzene rings. When the compound has a benzene ring in the above range, the binding strength due to the CH / π interaction can be further increased.

[0033] For the same reasons as above, the compound represented by the general formula (1) preferably has a 5-membered heterocycle, preferably has at least two 5-membered heterocycles, more preferably has 2 to 5 5-membered heterocycles, and even more preferably has 2 to 4 5-membered heterocycles. The 5-membered heterocycle may contain a sulfur atom, an oxygen atom, or a nitrogen atom as a heteroatom, and among these, it is preferable that the 5-membered heterocycle contains a nitrogen atom. When the 5-membered heterocycle contains a nitrogen atom, the π-acceptor property (π-electron accepting property) is enhanced. It is preferable that the 5-membered heterocycle contains 1 to 3 nitrogen atoms.

[0034] In the general formula (1), Ar 1 ~Ar 6 may have a substituent. From the viewpoint of enhancing the π-acceptor property, the substituent may be an aromatic hydrocarbon ring (e.g., a benzene ring, a naphthalene ring, a coronene ring, a triphenylene ring, an anthracene ring, etc.), an aromatic heterocycle (e.g., an Ar 1 ~Ar 6 The substituent may be any one of halogen, alkyl group, alkoxy group, and acyl group. The alkyl group may contain an ether bond, an amide bond, a urethane bond, or the like in the structure. The alkyl group preferably has 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms. When the alkyl group has a carbon number within the above range, steric hindrance is small, and intermolecular interaction can be promoted.

[0035] The compound represented by the above general formula (1) may be contained in the actinic ray-curable ink alone or in two or more types.

[0036] The compound represented by the general formula (1) may be present in an amount of 1% by mass to 20% by mass, preferably 1% by mass to 10% by mass, more preferably 3% by mass to 10% by mass, and even more preferably 3% by mass to 8% by mass, based on the total mass of the actinic radiation curable ink. By being present in the above range, blooming can be suppressed by CH / π interaction with the gelling agent.

[0037] Examples of the compound represented by the above general formula (1) include the following compounds.

[0038] [ka]

[0039] [ka]

[0040] [ka]

[0041] [ka]

[0042] [ka]

[0043] Among the above-exemplified compounds (1) to (33), compounds having at least two benzene rings and at least two five-membered heterocycles, such as compounds (8) to (14), (18), (20), (24), (25), and (30) to (32), are preferred.

[0044] (Active radiation polymerizable compound) The actinic ray polymerizable compound is a compound that polymerizes and crosslinks when irradiated with actinic rays. Examples of the actinic ray polymerizable compound include radical polymerizable compounds and cationic polymerizable compounds. Of these, the actinic ray polymerizable compound is preferably a radical polymerizable compound.

[0045] Examples of the actinic radiation include electron beams, ultraviolet rays, α rays, γ rays, and X-rays, etc. Among these, ultraviolet rays and electron beams are preferred, and ultraviolet rays are more preferred.

[0046] The radical polymerizable compound is a compound (monomer, oligomer, polymer, or a mixture thereof) having an ethylenically unsaturated bond capable of radical polymerization. The radical polymerizable compound may be used alone or in combination of two or more kinds.

[0047] Examples of compounds 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.

[0048] The radical polymerizable compound is preferably an unsaturated carboxylic acid ester compound, more preferably a (meth)acrylate. In this specification, "(meth)acrylate" means acrylate or methacrylate, and "(meth)acrylic" means acrylic or methacrylic.

[0049] Examples of monofunctional (meth)acrylates 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)acryloyloxyethylhexahydrophthalic acid, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypoly ... Examples of suitable acrylates include 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.

[0050] Examples of polyfunctional (meth)acrylates include 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, PO adduct di(meth)acrylate of bisphenol A, and neopentyl glycol di(meth)acrylate of hydroxypivalic acid. Examples of the acrylates include difunctional (meth)acrylates, such as polytetramethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, and tripropylene glycol diacrylate, as well as trifunctional or higher (meth)acrylates, 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, and pentaerythritol ethoxy tetra(meth)acrylate.

[0051] The radical polymerizable compound preferably contains a (meth)acrylate modified with ethylene oxide or propylene oxide (hereinafter, simply referred to as "modified (meth)acrylate"). The modified (meth)acrylate has higher photosensitivity. In addition, the modified (meth)acrylate is more compatible with other components even at high temperatures. Furthermore, the modified (meth)acrylate has less shrinkage on curing, and therefore is less likely to curl the printed matter when exposed to actinic rays.

[0052] Examples of the cationically polymerizable compound include an epoxy compound, a vinyl ether compound, and an oxetane compound.

[0053] Examples of the epoxy compounds include cycloaliphatic epoxy resins such as 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, vinylcyclohexene monoepoxide, ε-caprolactone-modified 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexanecarboxylate, 1-methyl-4-(2-methyloxiranyl)-7-oxabicyclo[4,1,0]heptane, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexanone-meta-dioxane and bis(2,3-epoxycyclopentyl)ether, diglycidyl ether of 1,4-butanediol, diglycidyl ether of 1,6-hexanediol, triglyceride of glycerin, and the like. Examples of the epoxy compounds include aliphatic epoxy compounds including polyglycidyl ethers of polyether polyols obtained by adding one or more alkylene oxides (such as ethylene oxide and propylene oxide) to aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin, as well as di- or polyglycidyl ethers of bisphenol A or its alkylene oxide adducts, di- or polyglycidyl ethers of hydrogenated bisphenol A or its alkylene oxide adducts, and novolac-type epoxy resins.

[0054] Examples of the vinyl ether compound include monovinyl ether compounds including 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, as well as di- or trivinyl ether compounds including 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.

[0055] Examples of the oxetane compound include 3-hydroxymethyl-3-methyloxetane, 3-hydroxymethyl-3-ethyloxetane, 3-hydroxymethyl-3-propyloxetane, 3-hydroxymethyl-3-n-butyloxetane, 3-hydroxymethyl-3-phenyloxetane, 3-hydroxymethyl-3-benzyloxetane, 3-hydroxyethyl-3-methyloxetane, 3-hydroxyethyl-3-ethyloxetane, 3-hydroxyethyl-3-propyloxetane, 3-hydroxyethyl -3-phenyloxetane, 3-hydroxypropyl-3-methyloxetane, 3-hydroxypropyl-3-ethyloxetane, 3-hydroxypropyl-3-propyloxetane, 3-hydroxypropyl-3-phenyloxetane, 3-hydroxybutyl-3-methyloxetane, 1,4 bis{[(3-ethyl-3-oxetanyl)methoxy]methyl}benzene, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane and di[1-ethyl(3-oxetanyl)]methyl ether.

[0056] The content of the actinic ray polymerizable compound can be, for example, from 1% by mass to 97% by mass with respect to the total mass of the actinic ray curable ink.

[0057] (Activin Radiation Polymerization Initiator) The actinic ray curable ink may contain an actinic ray polymerization initiator.

[0058] The actinic radiation polymerization initiator is a compound that initiates polymerization and crosslinking of the actinic radiation polymerizable compound by irradiation with actinic radiation. When the polymerization and crosslinking of the actinic radiation polymerizable compound can be initiated without the actinic radiation polymerization initiator, for example, when an image is formed by irradiation with an electron beam, the actinic radiation curable ink does not need to contain an actinic radiation polymerization initiator.

[0059] The actinic radiation polymerization initiator can be a radical initiator when the actinic radiation curable ink contains a radically polymerizable compound, and can be a cationic initiator (photoacid generator) when the actinic radiation curable ink contains a cationic polymerizable compound.

[0060] The radical polymerization initiator includes an intramolecular bond cleavage type radical polymerization initiator and an intramolecular hydrogen abstraction type radical polymerization initiator.

[0061] Examples of the intramolecular bond cleavage type radical polymerization initiator include acetophenone-based initiators including 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-methylthiophenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone, benzoins including benzoin methyl ether, and benzoin isopropyl ether, acylphosphine oxide-based initiators including 2,4,6-trimethylbenzoin diphenylphosphine oxide, and benzyl and methylphenyl glyoxyesters.

[0062] Examples of the intramolecular hydrogen abstraction type radical polymerization initiator include benzophenone-based initiators including 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 including 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone; aminobenzophenone-based initiators including Michler's ketone and 4,4'-diethylaminobenzophenone; 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, and camphorquinone.

[0063] Examples of cationic polymerization initiators include photoacid generators. Examples of photoacid generators include aromatic onium compounds such as diazonium, ammonium, iodonium, sulfonium, and phosphonium, such as B(C6F5)4.- , PF6 - , AsF6 - , SbF6 - , CF3SO3 - These include salts, sulfonates which generate sulfonic acids, halides which photogenerate hydrogen halides, and iron-allene complexes.

[0064] The content of the actinic radiation polymerization initiator can be set arbitrarily within a range in which the actinic radiation curable ink is sufficiently cured by irradiation with actinic radiation and the ejection properties of the actinic radiation curable ink are not significantly reduced. For example, the actinic radiation curable ink preferably contains 0.1% by mass to 10% by mass of the actinic radiation polymerization initiator relative to the total mass of the ink, more preferably 4% by mass to 8% by mass of the actinic radiation polymerization initiator, and even more preferably 4% by mass to 5% by mass of the actinic radiation polymerization initiator.

[0065] (Gelling agent) The gelling agent may be any compound capable of gelling and temporarily fixing (pinning) the ink droplets that have landed on the recording medium. The gelling agent causes the actinic ray curable ink to become a sol when heated and to become a gel at about room temperature. This allows the actinic ray curable ink that has been heated and turned into a sol to be ejected from an inkjet head, and the actinic ray curable ink that has landed on the recording medium and cooled and gelled to be temporarily solidified, thereby improving the pinning ability of the ink. When the ink that has landed on the recording medium is gelled and pinned, the ink is prevented from spreading and adjacent dots are less likely to become identical, so that a higher-definition image can be formed.

[0066] The gelling agent is preferably a compound that dissolves in the actinic radiation polymerizable compound contained in the ink at a temperature higher than the gelling temperature of the actinic radiation curable ink and crystallizes in the ink at a temperature equal to or lower than the gelling temperature of the ink. The gelling temperature means the temperature at which the ink undergoes a phase transition from sol to gel and the viscosity of the ink suddenly changes when the actinic radiation curable ink that has been solated or liquefied by heating is cooled. Specifically, the solated or liquefied ink is cooled while the viscosity is measured with a rheometer (e.g., MCR300 manufactured by Anton Paar), and the temperature at which the viscosity suddenly increases can be determined as the gelling temperature of the ink.

[0067] The gelling agent crystallizes in the ink at a temperature below the gelling temperature of the ink and crystallizes into plates. The structure in which the radical polymerizable compound is encapsulated in the three-dimensional space formed by the gelling agent was It is preferable to form a house-of-cards structure (such a structure will be referred to hereinafter as a "house-of-cards structure"). When a house-of-cards structure is formed, the liquid actinic radiation polymerizable compound is retained within the space, so that dots formed by the ink adhering to the recording medium are less likely to wet and spread, and the pinning ability of the ink is further enhanced. When the pinning ability of the ink is enhanced, dots formed by the ink adhering to the recording medium are less likely to coalesce with each other.

[0068] From the viewpoint of making it easier to form a house-of-cards structure, it is preferable that the radical polymerizable compound and the gelling agent dissolved in the ink are compatible with each other.

[0069] Examples of gelling agents suitable for forming a house of cards structure by crystallization include ketone waxes, ester waxes, petroleum-based waxes, vegetable waxes, animal waxes, mineral waxes, hydrogenated castor oil, modified waxes, higher fatty acids, higher alcohols, hydroxystearic acid, fatty acid amides including N-substituted fatty acid amides and special fatty acid amides, higher amines, esters of sucrose fatty acids, synthetic waxes, dibenzylidene sorbitol, dimer acid and dimer diol.

[0070] Examples of the ketone waxes include dilignoceryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristyl palmityl ketone and palmityl stearyl ketone.

[0071] Examples of the ester wax include behenyl behenate, icosanoic acid icosyl, stearyl stearate, palmityl stearate, cetyl palmitate, myristyl myristate, cetyl myristate, myricyl cerotenate, stearyl stearate, oleyl palmitate, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, ethylene glycol fatty acid ester, and polyoxyethylene fatty acid ester. Examples of commercially available products of the ester wax include the EMALEX series, manufactured by Nihon Emulsion Co., Ltd. ("EMALEX" is a registered trademark of the company), the Rikemal series, and the Poem series, manufactured by Riken Vitamin Co., Ltd. ("Rikemal" and "Poem" are both registered trademarks of the company).

[0072] Examples of the petroleum-based waxes include paraffin wax, microcrystalline wax and petroleum-based waxes including petroleum lactam.

[0073] Examples of the vegetable waxes include candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax and jojoba esters.

[0074] Examples of such animal-based waxes include beeswax, lanolin and spermaceti.

[0075] Examples of the mineral wax include montan wax and hydrogenated wax.

[0076] Examples of the modified wax include montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives, 12-hydroxystearic acid derivatives and polyethylene wax derivatives.

[0077] Examples of such higher fatty acids include behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid.

[0078] Examples of the higher alcohols include stearyl alcohol and behenyl alcohol.

[0079] Examples of the hydroxystearic acids include 12-hydroxystearic acid.

[0080] Examples of the fatty acid amides include lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, and 12-hydroxystearic acid amide. Examples of commercially available fatty acid amides include the Nikkaamide series manufactured by Nippon Kasei Kasei Co., Ltd. ("Nikkaamide" is a registered trademark of the company), the ITOWAX series manufactured by Ito Oil Mills Co., Ltd., and the FATTYAMID series manufactured by Kao Corporation.

[0081] Examples of the N-substituted fatty acid amides include N-stearyl stearic acid amide and N-oleyl palmitic acid amide.

[0082] Examples of the special fatty acid amides include N,N'-ethylenebisstearylamide, N,N'-ethylenebis-12-hydroxystearylamide and N,N'-xylylenebisstearylamide.

[0083] Examples of the higher amines include dodecylamine, tetradecylamine and octadecylamine.

[0084] Examples of the esters of the above sucrose fatty acids include sucrose stearate and sucrose palmitate.

[0085] Examples of commercially available sucrose fatty acid esters include the Ryoto Sugar Ester series manufactured by Mitsubishi Chemical Foods Corporation (Ryoto is a registered trademark of the company).

[0086] Examples of the synthetic waxes include polyethylene wax and α-olefin maleic anhydride copolymer wax.

[0087] Commercially available examples of the synthetic waxes include the UNILIN series manufactured by Baker-Petrolite ("UNILIN" is a registered trademark of the company).

[0088] Examples of the dibenzylidene sorbitol include 1,3:2,4-bis-O-benzylidene-D-glucitol.

[0089] An example of a commercially available product of the above dibenzylidene sorbitol is Gelall D, manufactured by New Japan Chemical Co., Ltd. ("Gelall" is a registered trademark of the company).

[0090] Examples of commercially available dimer diols include the PRIPOR series manufactured by CRODA ("PRIPOR" is a registered trademark of the company).

[0091] From the viewpoint of enhancing pinning property and facilitating the formation of CH / π interaction between the gelling agent and the compound represented by the general formula (1), the gelling agent is preferably any one of ketone wax, ester wax, petroleum wax, and fatty acid amide, more preferably any one of ketone wax, ester wax, and fatty acid amide, and even more preferably ketone wax and ester wax. This allows the CH donor property (electron donor property) of the gelling agent to function effectively, and from the viewpoint of facilitating the formation of CH / π interaction with the compound represented by the general formula (1), the gelling agent preferably has an alkyl chain having a straight chain portion with a carbon number of 10 to 30. Furthermore, when the straight chain portion has a carbon number of 10 or more, a sufficient space is generated in the card house structure, and the radical polymerizable compound is easily encapsulated in the space. When the carbon number is 30 or less, the temperature at which the ink is sol-formed is not excessively high, so that there is no need to heat the ink excessively when ejecting the ink.

[0092] From the viewpoint of not having a polar group at the end of the alkyl chain and improving the stability of the gelling agent in the ink, the gelling agent is preferably a compound represented by the following general formulas (G1) and (G2).

[0093] Formula (G1):R 1 -CO-R 2 (In formula (G1), R 1 and R 2 are linear hydrocarbon groups each having 10 to 30 carbon atoms, which may have a branched chain.

[0094] Formula (G2):R 3 -COO-R 4 (In formula (G2), R 3 and R 4 are linear hydrocarbon groups each having 10 to 30 carbon atoms, which may have a branched chain.

[0095] Examples of ketone waxes represented by the above formula (G1) include dilignoceryl ketone (carbon number: 23-24), dibehenyl ketone (carbon number: 21-22), distearyl ketone (carbon number: 17-18), dieicosyl ketone (carbon number: 19-20), dipalmityl ketone (carbon number: 15-16), dimyristyl ketone (carbon number: 13-14), dilauryl ketone (carbon number: 11-12), lauric acid wax (carbon number: 13-14 ... Myristyl myristyl ketone (carbon number: 11-14), lauryl palmityl ketone (11-16), myristyl palmityl ketone (13-16), myristyl stearyl ketone (13-18), myristyl behenyl ketone (13-22), palmityl stearyl ketone (15-18), palmityl behenyl ketone (15-22) and stearyl behenyl ketone (17-22). The number of carbons in the parentheses above indicates the number of carbons in each of the two hydrocarbon groups separated by the carbonyl group.

[0096] Commercially available examples of ketone waxes represented by formula (G1) include 18-Pentatriacontanone, manufactured by Alfa Aeser, Hentriacontan-16-one, manufactured by Alfa Aeser, and Kaowax T1, manufactured by Kao Corporation ("Kaowax" is a registered trademark of the company).

[0097] Examples of fatty acids or ester waxes represented by formula (G2) include behenyl behenate (carbon number: 21-22), icosanoic acid icosyl (carbon number: 19-20), stearyl stearate (carbon number: 17-18), palmityl stearate (carbon number: 17-16), lauryl stearate (carbon number: 17-12), cetyl palmitate (carbon number: 15-16), stearyl palmitate (carbon number: 15-18), and myristyl stearate (carbon number: 15-18). These include myristyl myristate (carbon number: 13-14), cetyl myristate (carbon number: 13-16), octyldodecyl myristate (carbon number: 13-20), stearyl oleate (carbon number: 17-18), stearyl erucate (carbon number: 21-18), stearyl linoleate (carbon number: 17-18), behenyl oleate (carbon number: 18-22), and arachidyl linoleate (carbon number: 17-20). The number of carbons in the parentheses above indicates the number of carbons in each of the two hydrocarbon groups separated by the ester group.

[0098] Commercially available examples of the ester wax represented by formula (G2) include Unistar M-2222SL and Sperm Acetate, manufactured by NOF Corp. ("Unistar" is a registered trademark of the company), Exepar SS and Exepar MY-M, manufactured by Kao Corp. ("Exepar" is a registered trademark of the company), EMALEXCC-18 and EMALEXCC-10, manufactured by Nippon Emulsion Co., Ltd., and Amureps PC, manufactured by Kokyu Alcohol Kogyo Co., Ltd. ("Amureps" is a registered trademark of the company). These commercially available products are often mixtures of two or more types, so they may be separated and purified as necessary before being added to the ink.

[0099] The content of the gelling agent is preferably 1.0% by mass or more and 10.0% by mass or less, more preferably 2.0% by mass or more and 7.5% by mass or less, and even more preferably 2.0% by mass or more and 3.5% by mass or less, based on the total mass of the ink. By making the content of the gelling agent 1.0% by mass or more, the pinning property of the ink can be sufficiently improved, and a higher resolution image can be formed. By making the content of the gelling agent 10.0% by mass or less, the gelling agent is less likely to precipitate on the surface of the formed image, blooming can be suppressed, and the amount of wax near the surface of the ink cured film can be more appropriately controlled, thereby further improving the curability of the actinic radiation curable ink.

[0100] (Coloring agent) The actinic radiation curable ink of the present invention may contain a colorant, if necessary.

[0101] The colorant may be a dye or a pigment, with pigments being preferred because they have good dispersibility in the ink components and are weather resistant. The pigment may be selected from, for example, yellow pigments, red or magenta pigments, blue or cyan pigments, black pigments, and white pigments, depending on the color of the image to be formed.

[0102] Examples of yellow pigments include CI Pigment Yellow (hereinafter, also simply referred to as "PY") 1, PY3, PY12, PY13, PY14, PY17, PY34, PY35, PY37, PY55, PY74, PY81, PY83, PY93, PY94, PY95, PY97, PY108, PY109, PY110, PY137, PY138, PY139, PY153, PY154, PY155, PY157, PY166, PY167, PY168, PY180, PY185, and PY193.

[0103] Examples of red or magenta pigments include CI Pigment Red (hereinafter referred to simply as "PR") 3, PR5, PR19, PR22, PR31, PR38, PR43, PR48:1, PR48:2, PR48:3, PR48:4, PR48:5, PR49:1, PR53:1, PR57:1, PR57:2, PR58:4, PR63:1, PR81, PR81:1, PR81:2, PR81:3, PR81:4, PR88, PR104, PR108, PR112, PR122, PR123, PR144, PR146, PR149, PR166, PR168, PR169, PR170, PR177, PR178, PR179, PR184, PR185, PR208, PR216, PR226, and PR257, CI Pigment These include CI Pigment Orange (hereinafter referred to simply as "PO") 13, PO16, PO20, and PO36, as well as CI Pigment Violet (hereinafter referred to simply as "PV") 3, PV19, PV23, PV29, PV30, PV37, PV50, and PV88, as well as CI Pigment Orange (hereinafter referred to simply as "PO") 13, PO16, PO20, and PO36.

[0104] Examples of blue or cyan pigments include CI Pigment Blue (hereinafter also simply referred to as "PB") 1, PB15, PB15:1, PB15:2, PB15:3, PB15:4, PB15:6, PB16, PB17-1, PB22, PB27, PB28, PB29, PB36, and PB60.

[0105] Examples of green pigments include CI Pigment Green (hereinafter also simply referred to as "PG") 7, PG26, PG36, and PG50.

[0106] An example of a black pigment is CI Pigment Black (hereinafter, simply referred to as "PBk"). )7, PBk26, and PBk28.

[0107] The white pigment may be any pigment that imparts a white color to the cured film formed by curing the white ink. Examples of the white pigment include inorganic pigments such as titanium oxide, zinc oxide, calcium carbonate, barium sulfate, and aluminum hydroxide. Among these, titanium oxide is preferred.

[0108] The crystal form of the titanium oxide may be any of rutile, anatase, and brookite types. From the viewpoint of making it easier to reduce the particle size of the white pigment, the anatase type, which has a small specific gravity, is preferred, and from the viewpoint of further improving the hiding power of the image formed, the rutile type, which has a large refractive index in the visible light region, is preferred.

[0109] The content of the colorant is preferably 0.1% to 10% by mass, and more preferably 1% to 5% by mass, based on the total amount of the ink. The content of the white pigment is preferably 3% to 8% by mass.

[0110] [Pigment dispersant] The actinic radiation curable inkjet ink of the present invention may contain a pigment dispersant. By including a pigment dispersant in the ink, the dispersibility of the pigment can be improved. It is more preferable that the pigment dispersant contains a comb block copolymer having a tertiary amine (hereinafter, also simply referred to as a copolymer). In the present invention, the comb block copolymer refers to a copolymer in which a different type of polymer is graft-polymerized as a side chain for each unit of the monomer constituting the main chain to a linear polymer forming the main chain.

[0111] The content of the pigment dispersant is not limited, but is preferably from 0.1% by mass to 10.0% by mass, and more preferably from 0.5% by mass to 5.0% by mass.

[0112] In addition to the copolymer, the pigment dispersant may contain, for example, a pigment dispersant such as a hydroxyl group-containing carboxylate ester, a salt of a long-chain polyaminoamide and a high molecular weight acid ester, a salt of a high molecular weight polycarboxylate, a salt of a long-chain polyaminoamide and a polar acid ester, a high molecular weight unsaturated acid ester, a polymer copolymer, a modified polyurethane, a modified polyacrylate, a polyether ester-type anionic surfactant, a naphthalene sulfonate-formaldehyde condensate salt, an aromatic sulfonate-formaldehyde condensate salt, a polyoxyethylene alkyl phosphate ester, a polyoxyethylene nonylphenyl ether, and a stearylamine acetate. Examples of commercially available pigment dispersants include the Solsperse series manufactured by Avecia and the PB series manufactured by Ajinomoto Fine-Techno Co., Ltd.

[0113] The copolymer has a tertiary amine, which increases the electron density of the amine, a functional group that has an adsorptivity to the pigment, and exerts strong basicity, allowing it to be firmly adsorbed to the acidic groups on the pigment surface. Therefore, the copolymer according to the present invention is unlikely to dissociate from the pigment even at temperatures around 85°C at which the inkjet ink is discharged. In addition, when a copolymer having a tertiary amine in the main chain is used as the copolymer according to the present invention, the side chain is compatible with the photopolymerizable compound, and the pigment dispersant itself is easily dispersed, so that the dispersibility of the pigment adsorbed by the pigment dispersant can be improved.

[0114] The substituent of the amine is not particularly limited, but an alkyl group having 1 or 2 carbon atoms is preferable.

[0115] The copolymer is not particularly limited in type as long as it is a pigment dispersant that satisfies the above conditions.Preferred examples of such pigment dispersants include BYK-2164, BYK-168, BYK N-22024 manufactured by BYK-Chemie, BYK JET-9150, BYK JET-9151 manufactured by Altana, Efka 4310, Efka 4320, Efka 4401 manufactured by BASF, SOLSPERSE 39000 manufactured by Avecia, and Ajisper PB-824 manufactured by Ajinomoto Fine-Techno Co., Ltd.

[0116] The hydrogen of the amine of the comb block copolymer having a secondary or primary amine may be replaced with another substituent by a known method to tertiaryize the amine. For example, the secondary or primary amine of the comb block copolymer can be reacted with an alcohol such as decyl alcohol in the presence of a reduction catalyst to form a tertiary amine substituted with an alkyl group.

[0117] The actinic radiation curable inkjet ink of the present invention may further contain a dispersing agent, if necessary. The dispersing agent may be selected depending on the pigment.

[0118] The total amount of the pigment dispersant and the dispersion aid is preferably from 1% by mass to 60% by mass based on the pigment.

[0119] The actinic radiation curable inkjet ink of the present invention may further contain a dispersion medium for dispersing the pigment, if necessary. A solvent may be contained in the ink as the dispersion medium, but in order to suppress the solvent from remaining in the formed image, it is preferable to use the above-mentioned photopolymerizable compound (particularly a monomer having a low viscosity) as the dispersion medium.

[0120] The pigment can be dispersed, for example, by a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker, etc. The pigment is preferably dispersed so that the volume average particle size of the pigment particles is preferably 0.08 μm or more and 0.5 μm or less, and the maximum particle size is preferably 0.3 μm or more and 10 μm or less, more preferably 0.3 μm or more and 3 μm or less. The pigment dispersion is adjusted by the selection of the pigment, dispersant, and dispersion medium, the dispersion conditions, the filtration conditions, etc.

[0121] (Other Ingredients) The actinic ray curable ink of the present invention may further contain other components such as a surfactant, a polymerization inhibitor, and a moisturizer, as long as the effects of the present invention are achieved.

[0122] Examples of surfactants include dialkyl sulfosuccinates, alkyl naphthalene sulfonates, etc. Anionic surfactants such as salts and fatty acid salts, polyoxyethylene alkyl ethers polyoxyethylene alkyl aryl ethers, acetylene glycols and poly Nonionic surfactants such as polyoxyethylene-polyoxypropylene block copolymers cationic surfactants such as alkylamine salts and quaternary ammonium salts; As well as silicone-based and fluorine-based surfactants.

[0123] Examples of polymerization inhibitors 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, dibutylcresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraldoxime, methyl ethyl ketoxime, and cyclohexanone oxime.

[0124] (Physical Properties) From the viewpoint of improving ejection properties from an inkjet head, the viscosity of the inkjet ink at 80° C. is preferably 3 mPa s or more and 20 mPa s or less. Furthermore, from the viewpoint of sufficiently gelling the ink when it lands and is cooled to room temperature, the viscosity of the inkjet ink at 25° C. is preferably 1000 mPa s or more.

[0125] The gelling temperature of the inkjet ink is preferably 40° C. or higher and 70° C. or lower. When the gelling temperature of the ink is 40° C. or higher, the ink quickly gels after landing on a recording medium, resulting in higher pinning properties. When the gelling temperature of the ink is 70° C. or lower, the ink is less likely to gel when ejected from an inkjet head, where the ink temperature is usually around 80° C., and the ink can be ejected more stably.

[0126] The viscosity at 80°C, the viscosity at 25°C, and the gelling temperature of the inkjet ink can be determined by measuring the temperature change of the dynamic viscoelasticity of the ink using a rheometer. Specifically, the ink is heated to 100°C and cooled to 25°C under conditions of a shear rate of 11.7 (1 / s) and a temperature drop rate of 0.1°C / s, and a viscosity temperature change curve is obtained. The viscosities at 80°C and 25°C can be determined by reading the viscosities at 80°C and 25°C, respectively, on the viscosity temperature change curve. The gelling temperature can be determined as the temperature at which the viscosity becomes 200 mPas on the viscosity temperature change curve.

[0127] The rheometer used may be a stress-controlled rheometer from the Physica MCR series manufactured by Anton Paar. The diameter of the cone plate may be 75 mm, and the cone angle may be 1.0°.

[0128] (Method of preparing actinic radiation curable ink) The actinic radiation curable ink can be prepared by mixing the above-mentioned components. At this time, it is preferable to mix the components while heating in order to increase the solubility of each component.

[0129] Alternatively, a pigment dispersion containing the pigment and the pigment dispersant may be prepared in advance, and the remaining components may be added and mixed thereto. In this case, it is also preferable to prepare the pigment dispersion by mixing the pigment and the dispersant while heating in order to increase the solubility of the pigment dispersant and the like.

[0130] [Image forming method] An image forming method according to one embodiment of the present invention relates to a method for forming an image using the actinic ray curable ink described above. The image forming method can be carried out in the same manner as a conventionally known image forming method, except that the actinic ray curable ink described above is used.

[0131] Specifically, the image forming method includes: (1) a step of applying the above-mentioned actinic ray curable ink to a recording medium; and (2) a step of irradiating the applied actinic ray curable ink with actinic rays.

[0132] (Adding step) In this process, the actinic ray curable ink is applied to a recording medium at a position corresponding to an image to be formed.

[0133] The method of applying the ink to the recording medium is not particularly limited, and the actinic radiation curable ink may be applied to the surface of the substrate using a roll coater or a spin coater, or may be applied to the surface of the substrate by a method such as spray application, immersion, screen printing, gravure printing, offset printing, or may be deposited on the surface of the substrate by an inkjet method. Of these, the inkjet method is preferred from the viewpoint of forming a finer recorded matter.

[0134] The ejection method from the inkjet head may be either an on-demand method or a continuous method. The on-demand inkjet head may be any of electro-mechanical conversion methods such as single cavity type, double cavity type, bender type, piston type, shear mode type, and shared wall type, and electro-thermal conversion methods such as thermal inkjet type and bubble jet type ("Bubble Jet" is a registered trademark of Canon Inc.).

[0135] The inkjet head may be either a scanning type or a line type inkjet head, but the line type is preferable.

[0136] The droplets of the actinic ray curable ink are heated and solubilized before being ejected from the inkjet head. From the viewpoint of improving the ejection properties of the ink from the inkjet head, it is preferable to set the temperature of the ink when filled into the inkjet head to be the gelation temperature of the ink +10°C or higher and the gelation temperature +30°C or lower. When the temperature of the actinic ray curable ink in the inkjet head is the gelation temperature +10°C or higher, the ink is unlikely to gel inside the inkjet head or on the nozzle surface, resulting in a decrease in ejection properties. On the other hand, when the temperature of the ink in the inkjet head is the gelation temperature +30°C or lower, the components are unlikely to deteriorate due to high temperatures. In addition, the viscosity of the actinic ray curable ink when ejected is preferably 7 mPa·s or higher and 15 mPa·s or lower, more preferably 8 mPa·s or higher and 13 mPa·s or lower.

[0137] The method for heating the actinic radiation-curable ink is not particularly limited. For example, at least one of an ink supply system such as an ink tank constituting the head carriage, a supply pipe, and an anterior ink tank immediately before the head, a pipe with a filter, and a piezo head can be heated by a panel heater, a ribbon heater, or warm water.

[0138] The amount of droplets of the actinic ray curable ink when ejected is preferably 2 pL or more and 20 pL or less, from the viewpoint of further increasing the recording speed and image quality.

[0139] The deposition onto the recording medium may be performed by directly landing the discharged actinic ray curable ink on the recording medium, or the discharged actinic ray curable ink may be caused to land on an intermediate transfer body to form an intermediate image, and the intermediate image may be transferred from the intermediate transfer body to the recording medium and deposited thereon.

[0140] (Irradiation step) In this process, the droplets of the actinic ray-curable ink deposited on the recording medium in the first process are irradiated with actinic rays to cure the droplets, thereby forming an image made of a cured film of the actinic ray-curable ink.

[0141] The actinic radiation can be selected from, for example, electron beams, ultraviolet rays, α rays, γ rays, and X-rays, but is preferably ultraviolet rays or electron beams. The ultraviolet rays are preferably light having a peak wavelength of 360 nm or more and 410 nm or less. The ultraviolet rays are preferably irradiated from an LED light source. LEDs emit less radiant heat than conventional light sources (e.g., metal halide lamps, etc.). Therefore, when irradiated with actinic radiation, LEDs are less likely to melt the ink and less likely to cause uneven gloss.

[0142] [Printed material] A printed matter according to one embodiment of the present invention is a printed matter having a printed layer formed using the actinic ray curable ink described above.

[0143] The printed matter is not particularly limited as long as it has a printed layer formed using the actinic radiation-curable ink. The method for forming the printed layer may be the image forming method described above or any other known method.

[0144] The recording medium is not particularly limited, and in addition to ordinary uncoated paper and coated paper, synthetic paper Yupo ("Yupo" is a registered trademark of Yupo Corporation), various plastics used in soft packaging, and their films can be used. Examples of various plastic films include PP film, PET film, OPS film, OPP film, ONy film, PVC film, PE film, and TAC film. Other plastics that can be used include polycarbonate, (meth)acrylic resin, ABS, polyacetal, PVA, and rubbers. The recording medium may also be metals, glass, and the like.

[0145] [Image forming device] An image forming apparatus according to still another embodiment of the present invention is an image forming apparatus capable of carrying out the above-mentioned method.

[0146] 1 is a side view showing the concept of an image forming apparatus 100 according to this embodiment. Note that the image forming apparatus 100 is an inkjet image forming apparatus, but the present invention is not limited to this.

[0147] As shown in Fig. 1, an image forming apparatus 100 has an inkjet head 110, a transport section 120, and an irradiation section 130. In Fig. 1, an arrow indicates the transport direction of a recording medium.

[0148] (Inkjet head 110) The inkjet head 110 has a nozzle surface 113 on which the nozzles 111 are provided, on a surface facing the transport unit 120 when forming an image, and ejects actinic ray curable ink onto the recording medium 200 transported by the transport unit 120. From the viewpoint of improving the ejection properties of the actinic ray curable ink, the inkjet head 110 may have a temperature adjustment means for adjusting the ink temperature to adjust the ink to a low viscosity. Examples of the temperature adjustment means include a panel heater, a ribbon heater, and a heating means using warm water.

[0149] The inkjet head 110 may be a scanning type inkjet head whose width in a direction perpendicular to the transport direction of the recording medium is smaller than that of the recording medium 200, or may be a line type inkjet head whose width in a direction perpendicular to the transport direction of the recording medium is larger than that of the recording medium 200.

[0150] The nozzles 111 have ejection openings in the nozzle surface 113. The number of nozzles 111 may be equal to or greater than the number of inks used in image formation (for example, four). When the inkjet head 110 has multiple nozzles 111, from the viewpoint of simplifying the configuration of the device and facilitating control, the multiple nozzles 111 are preferably arranged side by side at approximately equal intervals in the transport direction of the recording medium.

[0151] The inkjet head 110 is configured to be capable of changing the amount of ink that is ejected and lands on the recording medium 200. For example, the inkjet head 110 is configured to be controlled by a control unit to change the vibration amplitude of the piezoelectric element or to stop ink from being ejected from some nozzles.

[0152] (Transportation section 120) When forming an image, the conveying unit 120 conveys the recording medium 200 so that the recording medium 200 facing the inkjet head 110 moves directly below the inkjet head 110 in the vertical direction. For example, the conveying unit 120 has a driving roller 121, a driven roller 122, and a conveying belt 123.

[0153] The drive roller 121 and the driven roller 122 are disposed at a predetermined interval in the transport direction of the recording medium 200 and extend in a direction perpendicular to the transport direction of the recording medium 200. The drive roller 121 is rotated by a drive source (not shown).

[0154] The conveyor belt 123 is a belt for conveying the recording medium 200 placed thereon, and is stretched across a drive roller 121 and a driven roller 122. The conveyor belt 123 can be, for example, an endless belt formed to be wider than the recording medium 200. At this time, when the drive source rotates the drive roller 121, the conveyor belt 123 rotates following the drive roller 121, and the recording medium 200 on the conveyor belt 123 is conveyed.

[0155] (Irradiation unit 130) The irradiation unit 130 has a light source and irradiates the upper surface of the transport unit 120 with active rays from the light source. This allows the droplets of the active ray-curable ink that have landed on the transported recording medium 200 to be irradiated with active rays, thereby curing the droplets. The irradiation unit 130 can be disposed immediately above the transport unit 120, downstream of the inkjet head 110.

[0156] (Other configurations) In addition to the above configuration, the image forming apparatus 100 may have an ink tank (not shown) for storing actinic ray curable ink before ejection, an ink flow path (not shown) that connects the ink tank and the inkjet head 110 so that the ink can flow therethrough, and a control unit (not shown) that controls the operation of the inkjet head 110, the transport unit 120, and the irradiation unit 130.

[0157] The image forming apparatus 100 may also have an intermediate transfer body and a transfer unit (both not shown). At this time, the inkjet head 110 ejects actinic ray curable ink onto the intermediate transfer body, causing it to land on the surface of the intermediate transfer body, and forms an intermediate image on the surface of the intermediate transfer body, which is made up of droplets of actinic ray curable ink. Thereafter, the transfer unit transfers the intermediate image from the surface of the intermediate transfer body to the surface of the recording medium. Then, the irradiation unit 130 irradiates the intermediate image transferred to the surface of the recording medium with actinic rays, thereby curing the droplets of actinic ray curable ink. EXAMPLES

[0158] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these descriptions.

[0159] 1. Preparation of actinic radiation curable inkjet ink The following components (actinic radiation polymerizable compound, actinic radiation polymerization initiator, gelling agent, polymerization inhibitor, surfactant, pigment dispersion liquid) and any of the exemplary compounds represented by the above general formula (1) shown in the above [Actinic radiation curable ink] were used as the inkjet ink material.

[0160] 1-1.Active radiation polymerizable compounds Tripropylene glycol diacrylate (referred to as TPGDA in Table 1) Trimethylolpropane triacrylate (referred to as TMPTA in Table 1) Neopentyl glycol diacrylate (referred to as NPGDA in Table 1) 2PO-modified neopentyl glycol diacrylate (2PO-NPGDA in Table 1)

[0161] 1-2. Actinic polymerization initiator IRGACURE TPO (manufactured by BASF) (referred to as IRC TPO in Table 1) IRGACURE 819 (manufactured by BASF) (referred to as IRC 819 in Table 1)

[0162] 1-3. Gelling agents Paraffin (HNP-1, manufactured by Nippon Seiro Co., Ltd.) (referred to as HNP-1 in Table 1) Lauryl amide (Diamid Y, manufactured by Nippon Kasei Kasei Co., Ltd.) (referred to as Diamid Y in Table 1) Stearyl stearate (Excepar SS, manufactured by Kao Corporation) (referred to as Excepar SS in Table 1) Stearon (Kaowax T-1, manufactured by Kao Corporation) (referred to as T-1 in Table 1) Glyceryl behenate eicosanedioate (Nomcort HK-G, manufactured by Nisshin Oillio Group Co., Ltd.) (referred to as HK-G in Table 1)

[0163] 1-4. Polymerization inhibitors Irgastab UV10 (manufactured by BASF)

[0164] 1-5.Surfactants KF-352 (Shin-Etsu Chemical Co., Ltd.)

[0165] 1-6. Pigment dispersion (Preparation of Cyan Pigment Dispersion) 9.0% by mass of Efka4310 (manufactured by BASF) as a pigment dispersant and 71.0% by mass of trimethylolpropane triacrylate (EM232, manufactured by Eternal Chemical Co., Ltd.) as an actinic radiation polymerizable compound were placed in a stainless steel beaker, which was heated and stirred for 1 hour while being heated on a hot plate at 65°C. The mixture was cooled to room temperature, and 20.0% by mass of NX-053 Blue CI Pigment Blue-15:4 (manufactured by Dainichi Seika Chemicals Co., Ltd.) as a pigment was added. This solution was placed in a glass bottle together with 200g of zirconia beads with a diameter of 0.5 mm, sealed, and dispersed for 5 hours using a paint shaker (manufactured by Seiwa Giken Co., Ltd.). The zirconia beads were then removed to obtain a cyan pigment dispersion.

[0166] (Preparation of White Pigment Dispersion) 9.0% by mass of PB824 (manufactured by Ajinomoto Fine-Techno Co., Ltd.) as a pigment dispersant and 71.0% by mass of tripropylene glycol diacrylate (APG-200, manufactured by Shin-Nakamura Chemical Co., Ltd.) as an actinic radiation polymerizable compound were placed in a stainless steel beaker, and the mixture was heated and stirred for 1 hour while being heated on a hot plate at 65°C. The mixture was cooled to room temperature, and 20.0% by mass of titanium oxide (manufactured by Sakai Chemical Industry Co., Ltd., TCR-52) as a pigment was added, and the mixture was placed in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm, sealed, and dispersed for 5 hours using a paint shaker (manufactured by Seiwa Giken Co., Ltd.). The zirconia beads were then removed to obtain a white pigment dispersion.

[0167] 2. Ink Preparation The ink components shown in Table 1 were mixed, heated to 80°C and stirred. The mixture was then filtered with a 3 μm Teflon (registered trademark of Chemours) membrane filter (manufactured by Advantec) while being heated, to obtain inks 1 to 29. In addition, the "No." in the "Additive Compound" column in Table 1 corresponds to the number given to the exemplified compound represented by the above general formula (1) shown in the above [Actinic Ray Curable Ink]. The comparative compounds 1 to 7 used in inks 23 to 29 are shown below.

[0168] [ka]

[0169] 3. Evaluation Using the obtained ink, an image was formed as described below, and the blooming, image quality (pinning property) and curing property were evaluated.

[0170] (Image forming method) A piezo head with a nozzle diameter of 20 μm and 512 nozzles (256 nozzles x 2 rows, staggered arrangement, nozzle pitch of 1 row 360 dpi) was used to print coated paper (OK top coat, US basis weight 128 g / m 2 An image was formed on a paper (manufactured by Oji Paper Co., Ltd.) by the method described below.

[0171] The temperature of the inkjet head was set to 80°C, and the droplets were ejected at a speed of about 6 m / s under the condition that the volume of one droplet was 2.5 pl, and recording was performed at a resolution of 1440 dpi x 1440 dpi. The recording speed was 500 mm / s. The image was formed in an environment of 23°C and 55% RH. After the image was formed, the image was irradiated with ultraviolet light from a 395 nm LED lamp (manufactured by Phoseon Technology) placed downstream of the recording device to cure the ink.

[0172] (Blooming) A 5 cm x 5 cm solid image formed on the printing coated paper, which is a recording medium, by the above method was stored for one month in an environment of 40° C. After storage, the image was visually observed and evaluated for blooming according to the following criteria. 7: No deposits were observed on the image surface. 6: A thin deposit is present on the image surface (less than 10% of the printed surface) and can be visually confirmed. 5: A thin deposit is present on the image surface (10% or more but less than 25% of the printed surface) and can be visually confirmed. 4: A thin deposit is present on the image surface (25% or more but less than 40% of the printed surface) and can be visually confirmed. 3: There are faint deposits on the image surface (more than 40% and less than 55% of the printed surface), which can be visually confirmed. 2: There are faint deposits on the image surface (more than 55% and less than 70% of the printed surface), which can be visually confirmed. 1: The image surface is covered with powdery substances (more than 70% of the printed surface), which can be clearly confirmed visually.

[0173] (Image quality (pinning property)) Using the above image forming method, the printed coated paper was printed with the cut-out characters of the Chinese characters "口, 四, 日, 回, 因, 困, 固, 国, 目, 図, 國". The cut-out characters were in MS Mincho font with a resolution of 1400 dpi × 1440 dpi, 3 points and 5 points. The printed character images were visually observed. The character quality was evaluated based on the following criteria. 3: All of the 3-point cut-out characters are clearly recorded in detail. 2: Only some of the 3-point cut-out characters can be read, but all of the 5-point cut-out characters are readable. 1: There are some 5-point cut-out characters that cannot be read.

[0174] (Hardening property) Using the above method, a solid image of 5 cm × 5 cm was formed on the printed coated paper as the recording medium. According to the method described in "JIS Standard K5701-1 6.2.3 Abrasion resistance test", the printed coated paper cut to a size of 4 cm 2 was placed on the image and rubbed together with a load of 500 g. After that, the degree of image density reduction was visually observed and evaluated according to the following criteria. 3: Even after rubbing 50 times or more, no change in the image is observed. 2: A reduction in image density is observed at the stage of rubbing 50 times, but it is within the acceptable range in practical use. 1: A clear reduction in image density is observed with less than 50 rubs, and the quality is not durable for practical use.

[0175] The evaluation results of blooming, pinning property, and hardening property of the above Ink No.1~29 are shown in Table 2.

[0176] [Table 1]

[0177] [Table 2]

[0178] Results and Discussion Blooming was suppressed in inks No. 1 to 20 because they contained the compound represented by formula (1). Furthermore, blooming was also suppressed in inks 6, 7, 11, 12, 15, 17, 18, and 20, which contain white pigments. This is believed to be because the compound represented by formula (1) is highly hydrophobic, and forms an interaction with the hydrophobic portion of the gelling agent, enabling control of a stable crystalline state.

[0179] Furthermore, Ink No. 2 had better blooming inhibition and curing properties than Ink No. 3. Furthermore, Ink No. 4 had better blooming inhibition and curing properties than Ink No. 3. This is thought to be because the compound represented by formula (1) contained in Ink No. 2 has two benzene rings, and the compound represented by formula (1) contained in Ink No. 4 has two benzene rings and two five-membered heterocycles, which increases the binding strength with the gelling agent through CH / π interactions.

[0180] On the other hand, the suppression of blooming was inferior in inks No. 21 and 22 that did not contain the compound represented by formula (1) and inks No. 23 to 29 that contained compounds other than the compound represented by formula (1). This is thought to be because they were unable to form an interaction with the gelling agent and were unable to control the crystal state. [Industrial Applicability]

[0181] The actinic radiation-curable ink of the present invention makes it possible to suppress blooming even when it contains a gelling agent. Therefore, the present invention makes it possible to produce printed matter that not only does not impair the appearance, but also suppresses a decrease in image density and gloss fluctuation, and is expected to contribute to the advancement and spread of technology in this field. [Explanation of symbols]

[0182] 100 Image forming device 110 Inkjet head 111 Nozzle 113 Nozzle surface 120 Conveyor 121 Drive roller 122 Driven roller 123 Conveyor Belt 130 Irradiation unit 200 Recording media

Claims

1. The composition contains an actinic radiation polymerizable compound, a gelling agent, and a compound represented by general formula (1), The gelling agent has an alkyl chain having a carbon number of 10 to 30 in a linear portion. Actinic radiation curing ink. 【Chemistry 1】 (In the general formula (1), Ar １ ~Ar ６ represents a substituted or unsubstituted aromatic ring; Ar １ ~Ar ３ At least one of a to c represents an integer of 0 or more. However, when c is not 0, Ar ２ is a benzene ring.)

2. The actinic ray curable ink according to claim 1 , wherein the compound has at least two benzene rings.

3. The actinic ray curable ink according to claim 1 , wherein the compound has at least two five-membered heterocycles.

4. The actinic ray curable ink according to claim 3 , wherein the five-membered heterocycle contains a nitrogen atom.

5. 5. The actinic ray curable ink according to claim 1, further comprising a colorant.

6. The actinic ray curable ink according to claim 5 , wherein the colorant contains a white pigment.

7. The actinic ray curable ink according to claim 6 , wherein the white pigment contains titanium oxide.

8. Inkjet ink, The actinic ray curable ink according to any one of claims 1 to 7.

9. A printed matter having a printed layer formed using the actinic ray curable ink according to any one of claims 1 to 8.

10. A step of applying the actinic radiation curable ink according to any one of claims 1 to 8 onto a recording medium; irradiating the applied actinic ray curable ink with actinic ray; An image forming method comprising:

11. The image forming method according to claim 10 , wherein the applying step is performed by an ink-jet method.

Images