Active light-curable inkjet ink and method for manufacturing printed materials using the same

Abstract

The present invention provides an active light-curing inkjet ink that is less likely to generate satellites or mist during printing and can form a coating film with good post-processing properties. [Solution] The active light-curable inkjet ink contains a photopolymerizable compound, a photoinitiator, a gelling agent, a pigment, and a pigment dispersant. It also further contains a compound represented by a specific structural formula, and the amount of the photopolymerizable compound is 70% by mass or more of the total mass of the active light-curable inkjet ink.

Description

[Technical Field]

[0001] This invention relates to an active light-curable inkjet ink and a method for manufacturing printed materials using the same. [Background technology]

[0002] Inkjet printing is used in various printing fields because it allows for easy and inexpensive image formation. One such image formation method involves depositing droplets of active light-curable inkjet ink onto a recording medium and then curing it by irradiating it with active light. This method makes it possible to form images even on recording media that do not absorb ink. Active light-curable inkjet inks generally contain a photopolymerizable compound, a polymerization initiator, and a colorant such as a pigment (for example, Patent Document 1).

[0003] When ink droplets are ejected from the inkjet nozzle of an inkjet device, pressure is applied to the ink droplets, or the ink droplets become electrically charged. As a result, some of the ink droplets split, causing phenomena such as satellites and mist. Satellites are unintended ink droplets that have split from the main ink droplet, and when these satellites land on the recording medium, printing defects occur. Mist, on the other hand, refers to ink droplets that are significantly smaller in diameter than satellites, and this mist can lead to contamination of the inkjet nozzle and surrounding equipment. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2014-156506 [Overview of the project] [Problems that the invention aims to solve]

[0005] Attempts have been made to reduce the aforementioned satellites and mist by lowering the viscosity of the ink or reducing its surface tension. However, these adjustment methods present challenges, such as making it difficult for the inkjet ink to droplet, resulting in difficulties in printing and making it difficult to obtain images of the desired quality.

[0006] On the other hand, there is a demand for various post-processing treatments, such as applying varnish, to printed materials obtained by printing with light-curing ink. However, as mentioned above, when the viscosity of the ink is reduced or the surface tension is adjusted, the surface of the cured material tends to repel varnish and other post-processing materials, resulting in the problem that conventional printed materials have poor post-processing properties.

[0007] The present invention has been made in view of the above circumstances. One aspect of the present invention aims to provide an active light-curable inkjet ink that is less likely to generate satellites or mist during printing and can form a coating film with good post-processing properties, and a method for manufacturing printed materials using the same. [Means for solving the problem]

[0008] To achieve the above objective, one aspect of the present invention provides an active light-curable inkjet ink containing a photopolymerizable compound, a photoinitiator, a pigment, and a pigment dispersant, further containing a compound represented by the following general formula (1), wherein the amount of the photopolymerizable compound is 70% by mass or more of the total mass of the active light-curable inkjet ink. [ka] (In general formula (1), R 1 and R 2 Each of these independently represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alkylthio group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, or a combination thereof. 3represents an alkylene group having 2 to 6 carbon atoms, which may be substituted or unsubstituted, and n represents an integer of 50 or more and 300 or less)

[0009] Further, one aspect of the present invention for achieving the above object is a method for manufacturing a printed matter, including a step of ejecting ink droplets of an active energy ray curable inkjet ink from an inkjet recording head and landing them on a recording medium, and a step of irradiating the ink droplets landed on the recording medium with active energy rays to cure the ink droplets.

Advantages of the Invention

[0010] According to one aspect of the present invention, there is provided an active energy ray curable inkjet ink that is less likely to generate satellites and mist during printing and can form a coating film with good post-processing properties. Further, according to one aspect of the present invention, there is provided a method for manufacturing a high-quality printed matter with good post-processing properties.

Embodiments for Carrying Out the Invention

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

[0012] 1. Active Energy Ray Curable Inkjet Ink The active energy ray curable inkjet ink of the present embodiment contains a photopolymerizable compound, a photoinitiator, a pigment, a pigment dispersant, and a compound represented by the following general formula (1). In the present specification, "active energy ray curable inkjet ink" (hereinafter also referred to as "ink") means an ink that can be cured by active energy rays. Further, "active energy rays" means rays that can activate the photoinitiator in the ink and cure the ink. Examples of active energy rays include α-rays, γ-rays, X-rays, ultraviolet rays, visible rays, electron beams, etc. Note that, as the active energy rays for curing the ink of the present embodiment, ultraviolet rays, visible rays, and electron beams are preferable, and ultraviolet rays or visible rays are more preferable, from the viewpoints of the availability of irradiation devices and the curability of the ink.

[0013] As mentioned above, conventional inks have the problem of easily splitting when extruded from the inkjet head, resulting in the generation of satellites and mist. Furthermore, when the viscosity or surface tension of the ink is adjusted to suppress the above-mentioned satellites and mist, the printed materials obtained from that ink have the problem of poor post-processing properties. In contrast, the ink of the present invention contains a compound represented by the following general formula (1) (hereinafter also referred to as the "droplet adjusting agent"), so that satellites and mist are less likely to occur, and the resulting printed materials have good post-processing properties. [ka] (In general formula (1), R 1 and R 2 Each of these independently represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alkylthio group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, or a combination thereof. 3 (where n represents a substituted or unsubstituted alkylene group with 2 to 6 carbon atoms, and n represents an integer between 50 and 300.)

[0014] The reason why the above effect is obtained by adding a droplet modifier is not clear, but it is thought to be as follows. The above droplet modifier is R 1 and R 2It has a relatively hydrophobic portion represented by (hereinafter also referred to as the "hydrophobic portion") and a highly hydrophilic portion sandwiched therebetween (hereinafter also referred to as the "hydrophilic portion"). When the ink of this embodiment is extruded from an inkjet head, the hydrophobic portion of the droplet regulator moves to the surface (gas-liquid interface) side of the droplet and is likely to align, and the droplet regulator is likely to cover the surface of the droplet. Further, the droplet regulator has a large value of n in the general formula (1) and a relatively large molecular weight. Therefore, the entire surface of the ink droplet is likely to be covered with the droplet regulator having a large molecular weight. As a result, even when pressure or the like is applied to the droplet, the droplet is difficult to split, and satellites and mists are less likely to occur. Also, in the above droplet regulator, the chain constituting the hydrophilic portion is long and the hydrophilic portion is large. Therefore, the hydrophilic portion of the droplet regulator is likely to be present on the surface of the coating film (cured product of the ink), and a hydrophilic region is formed. Therefore, the affinity between the coating film and the hydrophilic liquid for post-processing becomes good, and the post-processability becomes good. Hereinafter, each component will be described.

[0015] [Droplet Regulator] As described above, the droplet regulator is a compound represented by the following general formula (1). The ink may contain only one kind of the droplet regulator or two or more kinds. [Chemical Formula] In general formula (1), R 1 and R 2 each independently represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alkylthio group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, or a combination thereof.

[0016] The above R 1 and R 2Possible alkyl groups include linear or branched alkyl groups having 1 to 30 carbon atoms, preferably 12 to 22. Examples of alkoxy groups include linear or branched alkoxy groups having 1 to 30 carbon atoms, preferably 12 to 22. Examples of alkylthio groups include linear or branched alkylthio groups having 1 to 30 carbon atoms, preferably 12 to 22. Examples of aryl groups include phenyl and naphthyl groups, with phenyl being preferred. Examples of heterocyclic groups include groups derived from five-membered rings such as furan, tetrahydrofuran, pyrrole, pyrrolidine, thiophene, and imidazole; groups derived from six-membered rings such as pyridine and pyrrolidine; and groups derived from fused rings such as quinoline and indole, with furan being preferred. Among these, alkyl groups having 12 to 22 carbon atoms are preferred, and unsubstituted alkyl groups are particularly preferred.

[0017] Furthermore, examples of substituents that may be bonded to the alkyl, alkoxy, or alkylthio groups include halogen atoms and hydroxyl groups. Also, examples of substituents that may be bonded to aryl or heterocyclic groups include alkyl groups having 1 to 12 carbon atoms, alkoxy groups having 1 to 12 carbon atoms, and alkylthio groups having 1 to 12 carbon atoms. The above R 1 and R 2 Among the above, from the viewpoint of high hydrophobicity, it is preferable that the alkyl group is unsubstituted or substituted with 12 to 22 carbon atoms, and in particular, an unsubstituted alkyl group with 12 to 22 carbon atoms is preferred.

[0018] On the other hand, R in the above general formula (1) 3 This represents a substituted or unsubstituted alkylene group having 2 to 6 carbon atoms, and examples include the ethylene group (-CH2CH2-), propylene group (-CH2CH(CH3)-), trimethylene group (-CH2CH2CH2-), tetramethylene group (-CH2CH2CH2CH2-), hexamethylene group (-CH2CH2CH2CH2CH2CH2-), etc. Examples of substituents that may be attached to the alkylene group include halogen atoms, hydroxyl atoms, etc.

[0019] Furthermore, in the above general formula (1), n ​​may be any integer between 50 and 300, preferably between 100 and 250. If n is less than 50, the length of the hydrophilic portion of the droplet adjusting agent becomes shorter, reducing post-processing performance. On the other hand, if n exceeds 300, an increase in viscosity occurs due to the increase in molecular weight, reducing the ejection performance from the inkjet nozzle.

[0020] The compound represented by the above general formula (1) is preferably the compound represented by the following general formula (2). [ka] In the above general formula (2), R 4 x represents a substituted or unsubstituted ethylene group, propylene group, trimethylene group, or tetramethylene group. Also, x and y independently represent integers between 1 and 30, and n represents an integer between 50 and 300.

[0021] Furthermore, the compound represented by the above general formula (1) is more preferably the compound represented by the following general formula (3). [ka] In general formula (3), x1 and y1 independently represent integers between 15 and 19, and n represents an integer between 170 and 210.

[0022] Here, the amount of droplet modifier in the ink is preferably 0.1% by mass or more and 4.0% by mass or less, and more preferably 0.4% by mass or more and 2.0% by mass or less, relative to the total mass of the ink. When the amount of droplet modifier is 0.1% by mass or more, the droplet modifier is more likely to cover the surface of the droplets when the ink is ejected from the inkjet nozzle, and satellites and mist are less likely to occur. In addition, the post-processing properties of the resulting image (cured ink) tend to be good. On the other hand, when the amount of droplet modifier is 4.0% by mass or less, it is less likely to affect the ejection performance from the inkjet nozzle, and it is easier to obtain higher quality printed materials.

[0023] [Photopolymerizable compound] The ink of this embodiment contains a photopolymerizable compound. The photopolymerizable compound may be any compound that polymerizes upon irradiation with active light, and may be a radical polymerizable compound or a cationic polymerizable compound. From the viewpoint of curability, the photopolymerizable compound is preferably a radical polymerizable compound.

[0024] Radical polymerizable compounds may be compounds (monomers, oligomers, polymers, or mixtures thereof) having ethylenically unsaturated bonds that are capable of radical polymerization. The ink may contain only one radical polymerizable compound as a photopolymerizable compound, or it may contain two or more.

[0025] Examples of compounds having ethylenically unsaturated bonds that can be radically polymerized 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, and unsaturated urethanes. Examples of unsaturated carboxylic acids include (meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, and maleic acid.

[0026] 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 mixtures thereof.

[0027] Examples of (meth)acrylate compounds include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomirsutyl (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, and methoxypolyethyl 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 succinic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalic acid, t-butylcyclohexyl (meth)acrylate, etc. Difunctional 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, hydroxypivalate neopentyl glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, tricyclodecanedimethanol diacrylate, etc. This includes polyfunctional monomers with three or more functions, such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxytri(meth)acrylate, pentaerythritol ethoxytetra(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.

[0028] Furthermore, if the (meth)acrylate compound is a modified product of the above monomer, the modified product may contain polymerizable functional groups other than unsaturated double bonds in its structure. Examples of (meth)acrylate compounds having such polymerizable functional groups 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.

[0029] Among (meth)acrylate compounds, 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 from the viewpoint of photosensitivity and other factors.

[0030] On the other hand, examples of cationic polymerizable compounds that can be photopolymerizable include epoxy compounds, vinyl ether compounds, and oxetane compounds. The ink may contain only one cationic polymerizable compound as the photopolymerizable compound, or it may contain two or more types.

[0031] Epoxy compounds can include aromatic epoxides, alicyclic epoxides, and aliphatic epoxides. Among these, aromatic epoxides and alicyclic epoxides are preferred from the viewpoint of improving the curability of the ink.

[0032] Aromatic epoxides can be di or polyglycidyl ethers obtained by reacting a polyhydric phenol or its alkylene oxide adduct with epichlorohydrin. Examples of polyhydric phenols or their alkylene oxide adducts to be reacted include bisphenol A or its alkylene oxide adduct. The alkylene oxide in the alkylene oxide adduct may be ethylene oxide or propylene oxide.

[0033] Alicyclic epoxides can be cycloalkane oxide-containing compounds obtained by epoxidizing cycloalkane-containing compounds with an oxidizing agent such as hydrogen peroxide or a peracid. The cycloalkane in the cycloalkane oxide-containing compound may be cyclohexene or cyclopentene.

[0034] Aliphatic epoxides can be di or polyglycidyl ethers obtained by reacting an aliphatic polyhydric alcohol or its alkylene oxide adduct with epichlorohydrin. Examples of aliphatic polyhydric alcohols include ethylene glycol, propylene glycol, and alkylene glycols such as 1,6-hexanediol. The alkylene oxide in the alkylene oxide adduct may be ethylene oxide or propylene oxide.

[0035] 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; This includes di- or tri-vinyl 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. Of these vinyl ether compounds, di- or tri-vinyl ether compounds are preferred when considering curability and adhesion.

[0036] Oxetane compounds are compounds having an oxetane ring. Examples include the oxetane compounds described in Japanese Patent Publication No. 2001-220526, Japanese Patent Publication No. 2001-310937, and Japanese Patent Publication No. 2005-255821. Compounds represented by general formula (1) described in paragraph 0089, general formula (2) described in paragraph 0092, general formula (7) in paragraph 0107, general formula (8) in paragraph 0109, and general formula (9) in paragraph 0116 of Japanese Patent Publication No. 2005-255821 are preferred. General formulas (1), (2), (7), (8), and (9) described in Japanese Patent Publication No. 2005-255821 are shown below.

[0037] [ka]

[0038] Here, the content of the photopolymerizable compound in the ink should be 70% by mass or more relative to the total mass of the ink, but from the viewpoint of the curability of the ink, it is preferable to be 75% by mass or more and 98% by mass or less, and more preferably 80% by mass or more and 96% by mass or less.

[0039] [Photoinitiator] The photoinitiator can be any compound that is activated by irradiation with an active light and capable of initiating the polymerization of the photopolymerizable compound. The ink may contain only one type of photoinitiator or two or more types. The photoinitiator may be of the intramolecular bond cleavage type or the intramolecular hydrogen abstraction type.

[0040] Examples of intramolecular bond cleavage type photoinitiators include acetophenone-based initiators such as diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexylphenyl 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; benzylglyoxyester-based initiators, and methylphenylglyoxyester-based initiators.

[0041] Examples of intramolecular hydrogen abstraction type photoinitiators include benzophenone-based initiators such as benzophenone, o-benzoylmethyl-4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acrylic 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; and 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, and camphorquinone.

[0042] When the photoinitiator is an acylphosphine oxide or acylphosphonate, sensitivity to active light is improved, and the curability of the ink is improved. It is more preferable that the photoinitiator be bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide or bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide.

[0043] The photoinitiator may also be a photoacid generator. Examples of photoacid generators include compounds used in chemically amplified photoresists and photocationic polymerization (see Organic Electronic Materials Research Group, ed., "Organic Materials for Imaging," Bunshin Publishing (1993), pp. 187-192).

[0044] The amount of photoinitiator in the ink is appropriately selected depending on the type of active light and photopolymerizable compound used during ink curing. The amount of photoinitiator is preferably 0.1% to 10% by mass, and more preferably 2% to 8% by mass, relative to the total mass of the ink.

[0045] [Pigments] The pigments contained in the ink of this embodiment are appropriately selected according to the application of the ink. The ink may contain only one type of pigment, or it may contain two or more types. The type of pigment is not particularly limited and can be any known pigment. For example, organic or inorganic pigments with the following numbers listed in the color index can be selected.

[0046] Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257; Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88; and Pigment Orange. This includes 13, 16, 20, 36, etc., and any two or more solid solutions of these magenta pigments.

[0047] Examples of blue or cyan pigments include Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17-1, 22, 27, 28, 29, 36, 60, etc.

[0048] Examples of green pigments include Pigment Green 7, 26, 36, and 50. Examples of yellow pigments include Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137, 138, 139, 150, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193, etc.

[0049] Examples of black pigments include Pigment Black 7, 28, and 26. Titanium dioxide (especially rutile-type titanium dioxide) can also be used as a white pigment.

[0050] The volume-average particle diameter of the pigment, as measured by dynamic scattering or laser diffraction, is preferably between 0.08 μm and 0.5 μm. The maximum particle diameter of the pigment is preferably between 0.3 μm and 10 μm, and more preferably between 0.3 μm and 3 μm. When the pigment particle diameter is within this range, the ink is more easily ejected from the inkjet nozzle. In addition, the storage stability of the ink tends to be better.

[0051] The amount of pigment in the ink 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. When the amount of pigment is within this range, it becomes easier to obtain images of the desired color. On the other hand, the viscosity of the ink does not become excessively high, making it easier to eject the ink from the inkjet nozzle.

[0052] [Pigment dispersant] The pigment dispersant is appropriately selected according to the type of pigment. The ink may contain only one type of pigment dispersant, or it may contain two or more types.

[0053] Examples of pigment dispersants 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, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalene sulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate. Examples of commercially available pigment dispersants include Avecia's Solsperse series and Ajinomoto Fine Techno's PB series.

[0054] The ink may further contain known dispersing agents as needed. The dispersing agent is appropriately selected depending on the type of pigment. One example is Solspers 22000 (manufactured by Lubrizol, a disazo yellow intermediate), which is commonly used for dispersing yellow pigments. The total amount of the pigment dispersant and dispersing agent is preferably 1% by mass or more and 50% by mass or less relative to the pigment.

[0055] [Gelling agent] The ink may further contain a gelling agent as needed. In this specification, a gelling agent is defined as "an organic substance that is solid at room temperature and becomes liquid when heated, and is a compound that has the function of reversibly causing a sol-gel phase transition of an active light-curable inkjet ink depending on the temperature."

[0056] The gelling agent is preferably a compound that crystallizes at or below the gelling temperature of the ink. The gelling temperature of the ink is the temperature at which, when ink that has been sol-like or liquefied by heating is cooled, the gelling agent undergoes a phase transition from sol to gel, and the viscosity of the ink changes abruptly. Specifically, the sol-like or liquefied ink is cooled while its viscosity is measured using a viscoelasticity measuring device (for example, MCR300, manufactured by Physica), and the temperature at which the viscosity rapidly increases is defined as the gelling temperature of the ink.

[0057] When a gelling agent crystallizes in the ink, a structure may be formed in which a photopolymerizable compound is encapsulated in a three-dimensional space created by the plate-like crystallized gelling agent. In this specification, such a structure is also referred to as a "cardhouse structure." When a cardhouse structure is formed in the ink, the photopolymerizable compound is retained within the space. Therefore, ink droplets become less likely to spread and the pinning properties of the ink are improved. When the pinning properties of the ink are improved, ink droplets that have landed on the recording medium are less likely to coalesce, and a higher-resolution image can be formed.

[0058] For the photopolymerizable compound to be retained within the cardhouse structure, it is preferable that the photopolymerizable compound and the gelling agent are compatible within the ink. Furthermore, from the viewpoint of stably ejecting ink droplets from the inkjet nozzle, good compatibility between the photopolymerizable compound and the gelling agent is also preferable.

[0059] Examples of gelling agents include: aliphatic ketone compounds; aliphatic ester compounds; petroleum waxes such as paraffin wax, microcrystalline wax, and petrolactam; plant waxes such as candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax, and jojoba esters; animal waxes such as beeswax, lanolin, and whale wax; mineral waxes such as montan wax and hydrogenated wax; hydrogenated castor oil or hydrogenated castor oil derivatives; montan wax derivatives, paraffin wax derivatives, and microcrystalline wax. Modified waxes such as sulfate 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 acid 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 (for example, manufactured by Nippon Chemical Corporation) Nikka Amid series, ITOWAX series manufactured by Ito Oil Co., Ltd., FATTYAMID series manufactured by Kao Corporation, etc.; N-substituted fatty acid amides such as N-stearyl stearate amide and N-oleyl palmitate amide; special fatty acid amides such as N,N'-ethylenebisstearylamide, N,N'-ethylenebis-12-hydroxystearylamide, and N,N'-xylylenebisstearylamide; higher amines such as dodecylamine, tetradecylamine, or octadecylamine; fatty acid ester compounds such as stearyl stearate, oleyl palmitic acid, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, ethylene glycol fatty acid ester, and polyoxyethylene fatty acid ester (e.g., EMALLEX series manufactured by Nippon Emulsion Co., Ltd., Rikemar series manufactured by Riken Vitamin Co., Ltd., Poem series manufactured by Riken Vitamin Co., Ltd.); esters of sucrose fatty acids such as sucrose stearic acid and sucrose palmitic acid (e.g., Ryoto Sugar Ester series manufactured by Mitsubishi Chemical Foods Co., Ltd.);Synthetic waxes such as polyethylene wax and α-olefin maleic anhydride copolymer wax (e.g., Baker-Petrolite's UNILIN series); dimer acids; dimer diols (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 Co., Ltd.'s Leopal series); glyceryl eicosanedioate behenate; polyglyceryl eicosanedioate 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 This includes dibenzylidenesorbitol derivatives (available from Shin Nippon Rika), low molecular weight oil gelling agents described in Japanese Patent Publication No. 2005-126507, Japanese Patent Publication No. 2005-255821, and Japanese Patent Publication No. 2010-111790, etc.

[0060] 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 alkyl group, the aforementioned "card house structure" is easily formed. When the gelling agent contains a linear alkyl group having 12 to 26 carbon atoms in its molecular structure, the above-mentioned card house structure is further easily formed.

[0061] Specific examples of gelling agents containing linear or branched alkyl groups having 12 to 26 carbon atoms include aliphatic ketone compounds, aliphatic ester compounds, higher fatty acids, higher alcohols, fatty acid amides, etc., that have the above alkyl groups.

[0062] The gelling agent is more preferably an aliphatic ketone compound or an aliphatic ester compound, and more preferably a compound represented by the following general formula (G1) or (G2). General formula (G1):R 5 -CO-R 6 General formula (G2):R 7-COO-R 8 In general formulas (G1) and (G2), R 5 ~R 8 Each of these independently represents a linear or branched alkyl group having 12 to 26 carbon atoms. 5 ~R 8 Each of these may include a branched chain portion.

[0063] In the general formula (G1), R 5 and R 6 The alkyl group represented by is not particularly limited, but it is preferably an alkyl group that does not contain branched chains and has 12 to 26 carbon atoms.

[0064] Examples of aliphatic ketone compounds represented by the above general formula (G1) include 18-pentatriacontanone (C17-C17), dilignoseryl ketone (C24-C24), dibehenyl ketone (C22-C22), distearyl ketone (C18-C18), dieicosyl ketone (C20-C20), dipalmityl ketone (C16-C16), dimyristyl ketone (C14-C14), and dilauryl ketone (C12-C12). This includes 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), stearyl behenyl ketone (C18-C22), etc.

[0065] Examples of commercially available compounds represented by general formula (G1) include 18-Pentatriacontanon (manufactured by Alfa Aeser), Hentriacontan-16-one (manufactured by Alfa Aeser), and Kao Wax T1 (manufactured by Kao Corporation). The ink may contain only one aliphatic ketone compound as a gelling agent, or it may contain two or more.

[0066] On the other hand, in the general formula (G2), R 7 and R 8The alkyl group represented by is not particularly limited, but it is preferably an alkyl group that does not contain branched chains and has 12 to 26 carbon atoms.

[0067] Examples of aliphatic ester compounds represented by general formula (G2) include behenyl behenate (C21-C22), eicosyl eicosanoate (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 ( This includes C13-C16, octyldodecyl myristate (C13-C20), stearyl oleate (C17-C18), stearyl erucate (C21-C18), stearyl linoleate (C17-C18), behenyl oleate (C18-C22), myricyl cerotate (C25-C16), stearyl montanate (C27-C18), behenyl montanate (C27-C22), arachidyl linoleate (C17-C20), palmityl triacontanoate (C29-C16), etc.

[0068] Examples of commercially available aliphatic ester compounds represented by general formula (G2) include Unistar M-2222SL (manufactured by NOF Corporation), Exepearl SS (manufactured by Kao Corporation), EMALEX CC-18 (manufactured by Nippon Emulsion Co., Ltd.), Amlepus PC (manufactured by Higher Alcohol Industry Co., Ltd.), Exepearl MY-M (manufactured by Kao Corporation), Sperm Acetate (manufactured by NOF Corporation), EMALEX CC-10 (manufactured by Nippon Emulsion Co., Ltd.), WE (manufactured by NOF Corporation), etc. Since these commercially available products are often mixtures of two or more types, they may be separated and purified as needed. In addition, the ink may contain only one aliphatic ester compound as a gelling agent, or it may contain two or more types.

[0069] The gelling agent content in the ink is preferably 0.5% by mass or more and 10% by mass or less, relative to the total mass of the ink, and more preferably 1% by mass or more and 7% by mass or less.

[0070] [Other ingredients] In addition to the components listed above, the ink may further contain photoinitiator auxiliaries, polymerization inhibitors, etc., as needed. Examples of photoinitiator auxiliaries 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-benzoate ethyl ester, N,N-dimethylamino-p-benzoate isoamyl ethyl ester, N,N-dihydroxyethylaniline, triethylamine, and N,N-dimethylhexylamine. Among these, N,N-dimethylamino-p-benzoate ethyl ester and N,N-dimethylamino-p-benzoate isoamyl ethyl ester are preferred. The ink may contain only one photoinitiator auxiliary, or two or more.

[0071] Examples of polymerization inhibitors include (alkyl)phenol, 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, cuperone, 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.

[0072] The ink may contain other components as needed. These other components may be various additives or other resins. Examples of additives include surfactants, leveling additives, matting agents, UV absorbers, infrared absorbers, antibacterial agents, and basic compounds to improve 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 to adjust the physical properties of the cured product, such as polyester resins, polyurethane resins, vinyl resins, acrylic resins, and rubber resins.

[0073] [Ink properties] The viscosity of the ink described above differs depending on whether or not it contains the gelling agent. For example, in ink without a gelling agent, the viscosity at 25°C is preferably 1 mPa·s to 30 mPa·s, and more preferably 5 mPa·s to 20 mPa·s. This viscosity makes it easier to eject from the inkjet nozzle and facilitates the formation of ink droplets. This viscosity is measured using a rheometer. Anton Paar's PhysicaMCR series stress-controlled rheometer can be used. The diameter of the cone plate can be 75 mm, and the cone angle can be 1.0°. This viscosity can be adjusted, for example, by the type and amount of the photopolymerizable compound.

[0074] On the other hand, if the ink contains a gelling agent, the ink undergoes a reversible sol-gel phase transition depending on the temperature. Active light-curable inks that undergo a sol-gel phase transition are liquid (sol) at high temperatures (e.g., around 80°C), and can therefore be ejected from the inkjet recording head in a sol state. When active light-curable inkjet ink is ejected at high temperatures, the ink droplets (dots) land on the recording medium and then naturally cool and gel. This suppresses the coalescence of adjacent dots, thereby improving image quality.

[0075] In inks containing a gelling agent, it is preferable that the viscosity of the ink at high temperatures be below a certain level in order to improve the ejection properties of the ink droplets. Specifically, it is preferable that the viscosity of the ink at 80°C is between 3 mPa·s and 20 mPa·s. On the other hand, in order to suppress the coalescence of adjacent dots, it is preferable that the viscosity of the ink at room temperature after impact be above a certain level. Specifically, it is preferable that the viscosity of the ink at 25°C be 1000 mPa·s or higher.

[0076] The gelation temperature of the ink is preferably 30°C or higher and less than 100°C, and more preferably 50°C or higher and 65°C or lower. If the gelation temperature of the ink is too high, gelation is likely to occur during injection, which tends to reduce the ejectability. On the other hand, if the gelation temperature of the ink is too low, it will not gel quickly after landing on the recording medium. The gelation temperature is the temperature at which the ink, which is in a sol state, gels and its fluidity decreases during the cooling process.

[0077] The viscosity at 80°C, viscosity at 25°C, and gelation temperature of inkjet ink are determined by measuring the temperature dependence of the ink's dynamic viscoelasticity using a rheometer. Specifically, the ink is heated to 100°C and cooled to 20°C under conditions of a shear rate of 11.7°C / s and a cooling rate of 0.1°C / s to obtain a temperature dependence curve of viscosity. The viscosity at 80°C and 25°C are then defined as the viscosity at 80°C and 25°C on the obtained temperature dependence curve. The gelation temperature is defined as the temperature at which the viscosity on the temperature dependence curve becomes 200 mPa·s. The rheometer is the same as described above.

[0078] The sol-gel phase-transition ink described above ejects liquid ink droplets at high temperatures, which then land on the recording medium. Simultaneously, the ink droplets are cooled and gelled, suppressing droplet coalescence. This allows for the formation of high-resolution images even during high-speed recording.

[0079] [Method for preparing inkjet ink] The above ink is obtained by mixing the aforementioned droplet modifier, photopolymerizable compound, photoinitiator, pigment, and pigment dispersant, as well as a gelling agent if necessary. The mixing method is not particularly limited, but it is preferable to prepare a composition in which the pigment and pigment dispersant are dispersed in some of the photopolymerizable compounds, and then mix this composition with the other components. The obtained ink is preferably filtered using a predetermined filter.

[0080] 2. Method of manufacturing printed materials The method for manufacturing printed materials according to this embodiment includes at least the following two steps. (1) The process of ejecting ink droplets of the above ink from the inkjet recording head and landing them on the recording medium. (2) A process of curing ink droplets that have landed on a recording medium by irradiating them with active light.

[0081] [Regarding process (1)] In this process, ink droplets of the aforementioned ink are ejected from the inkjet recording head and landed on the recording medium at positions corresponding to the image to be formed.

[0082] The ejection method from the inkjet recording head may be either on-demand or continuous. The on-demand inkjet head may be any of the following: electromechanical conversion methods such as single-cavity type, double-cavity type, bender type, piston type, shear-mode type and shared-wall type, or electro-thermal conversion methods such as thermal inkjet type and bubble jet (bubble jet is a registered trademark of Canon Inc.).

[0083] Ink droplets without a gelling agent can be ejected from an inkjet head at room temperature, but the ejection stability of ink droplets containing a gelling agent can be improved by ejecting them from the inkjet head while heated. The temperature of the ink during ejection is not particularly limited, but when using ink containing a gelling agent, a temperature of 35°C to 100°C is preferred, and a temperature of 35°C to 80°C is more preferred to further improve ejection stability. In particular, it is preferable to perform ejection at an ink temperature such that the viscosity of the ink is 7 mPa·s to 15 mPa·s, more preferably 8 mPa·s to 13 mPa·s.

[0084] Ink heating can be performed in the inkjet recording head of an inkjet recording device, in the ink channel connected to the inkjet recording head, or in the ink tank connected to the ink channel.

[0085] The amount of liquid ejected per drop from each nozzle of the inkjet recording head is preferably between 0.5 pl and 10 pl, depending on the image resolution, and more preferably between 0.5 pl and 2.5 pl to form a high-definition image.

[0086] Furthermore, if the ink contains a gelling agent, it is preferable to rapidly gel the ink droplets that have landed on the recording medium by cooling them to induce a sol-gel phase transition. This prevents the ink droplets from diffusing and allows for pinning. Moreover, because oxygen is less likely to penetrate the ink droplets, the curing of the photopolymerizable compound is less likely to be inhibited by oxygen.

[0087] The recording medium may be paper or a resin film. Examples of paper include coated paper for printing, coated paper B for printing, etc. Examples of resin films include polyethylene terephthalate film, polypropylene film, vinyl chloride film, etc.

[0088] The transport speed of the recording medium is preferably 30 to 120 m / min.

[0089] [Regarding process (2)] By irradiating ink droplets that have landed on a recording medium with active light, the photopolymerizable compounds contained in the ink droplets are polymerized, causing the ink droplets to harden.

[0090] The active light can be selected from, for example, electron beams, ultraviolet light, visible light, alpha rays, gamma rays, and X-rays. Among these, ultraviolet or visible light is preferred, and an LED light source with a peak wavelength of 360 nm to 500 nm is more preferred. Compared to conventional light sources (e.g., metal halide lamps), LEDs emit less radiant heat. Therefore, when irradiated with active light, the ink is less likely to dissolve, and uneven gloss is less likely to occur.

[0091] When irradiating with light having a peak wavelength between 360 nm and 410 nm, the peak illuminance on the recording medium surface or ink droplet surface should be 0.5 W / cm². 2 More than 10.0W / cm 2 The following is preferable: Peak illuminance is 1.0 W / cm². 2 More than 5.0W / cm 2 The following is more preferable.

[0092] Irradiation with active light is preferably performed between 0.001 seconds and 1.0 second after the ink lands on the recording medium. To form a high-resolution image, it is more preferable to perform the irradiation between 0.001 seconds and 0.5 seconds.

[0093] Alternatively, the irradiation with active light may be performed in two stages. In this case, the active light can be irradiated between 0.001 and 2.0 seconds after the ink lands on the recording medium to partially cure the ink, and then, after all printing is complete, the active light can be irradiated again to fully cure the ink. Dividing the irradiation of active light into two stages makes it less likely for the ink to shrink during curing. [Examples]

[0094] The present invention will be described in detail below with reference to examples, but the embodiments of the present invention are not limited to these examples.

[0095] 1. Preparation of materials The following materials were prepared.

[0096] <Pigments> • Yellow pigment: VERSAL YELLOW 4GM (Synthesia)

[0097] <Photopolymerizable compound> • Phenol EO-modified acrylate: Miramer® M144 (manufactured by MIWON Corporation) • Polyethylene glycol #400 diacrylate (PEGDA) • 4EO-modified pentaerythritol tetraacrylate (4EO-modified PETA) • 3PO-modified trimethylolpropane triacrylate (3PO-modified TMPTA)

[0098] <Photopolymerization initiator> • Photopolymerization initiator: IRGACURE® 819 (manufactured by BASF)

[0099] <Pigment dispersant> • Polymer-based pigment dispersant: Adisper PB821 (manufactured by Ajinomoto Fine Techno Co., Ltd.)

[0100] <Photopolymerization inhibitor> • Photopolymerization inhibitor: Irgastab (registered trademark) UV10 (manufactured by BASF)

[0101] <Droplet regulator (Droplet regulator represented by general formula (1))> [ka]

[0102] <Droplet modifiers (other compounds)> [ka]

[0103] <Gelling agent> • Gelling agent: "Amlepus PC" (cetyl palmitate, manufactured by Higher Alcohol Industry Co., Ltd.)

[0104] 2. Ink preparation (1) Preparation of pigment dispersion As the material for the pigment dispersion, each component was mixed in the composition ratio shown below. Then, this mixture and 0.3 mm zirconia beads (YTZ balls, manufactured by Nikkatoh) were placed in a 100 mL plastic container. After dispersing the above mixture in a paint shaker for 3 hours, the zirconia beads were removed to obtain pigment dispersion composition 1.

[0105] (Composition of pigment dispersion) • Polymer-based pigment dispersant: Adisper PB821 (manufactured by Ajinomoto Fine Techno Co., Ltd.) 6.5 parts by mass • Phenol EO-modified acrylate: Miramer® M144 (manufactured by MIWON) 73.2 parts by mass • Photopolymerization inhibitor: Irgastab® UV10 (manufactured by BASF) 0.3 parts by mass

[0106] (2) Preparation of inks 1-20 The components were mixed according to the composition ratios shown in Table 1 and stirred at 105°C for 45 minutes. The mixture was then filtered through a 3 μm membrane filter (Teflon® manufactured by ADVANTEC) to prepare inks 1 to 20.

[0107] 3. Evaluation Satellite mist evaluation and image gloss of the obtained prints were performed using the following method.

[0108] (1) Satellite mist evaluation The above ink was filled into an ink ejection evaluation device equipped with an inkjet recording head featuring a piezo-type inkjet nozzle. One drop of ink was then ejected from the device, and the state after ejection was observed using a JetXpert droplet observation device (ImageXpert). The satellite and mist were then evaluated according to the following criteria: ◎, ○, and △ indicate acceptable levels. ◎: No satellite or mist activity was detected. ○: The total number of satellites and mist particles per main droplet is between 1 and 2. △: The total number of satellites and mist particles per main droplet is between 3 and 5. ×: The total number of satellites and mist particles per main droplet is 6 or more.

[0109] (2) Evaluation of post-processability A monochrome image was formed using a line-recording type inkjet recording device. The ink supply system of the inkjet recording device consists of an ink tank, a supply pipe, a sub-ink tank immediately before the print head, filtered piping, 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 printing was performed.

[0110] The inkjet recording head used consisted of two Konica Minolta inkjet heads with 1776 nozzles and a resolution of 600 dpi, which were modularized to achieve a resolution of 1200 dpi. The applied voltage was adjusted so that the droplet volume per sheet was 3.5 pl, and an image was formed. dpi represents the number of dots per 2.54 cm. Image formation was performed under conditions of 23°C and 55% RH.

[0111] A double-sided Yupo Super Yupo Double FRBW 130 μm was prepared as the recording medium. The recording medium was heated to 30°C using a temperature control unit. The transport speed of the recording medium was set to 1000 mm / s. Then, ink droplets were ejected from the inkjet recording head onto the recording medium to form a solid image.

[0112] After image formation, an LED lamp (Kyocera Corporation, 8W / cm²) is placed downstream of the inkjet recording device. 2 Wavelength 450nm, illumination width 68mm, distance from LED lamp to recording medium surface 50mm, illuminance on recording medium 2.0W / cm 2The recording medium was irradiated with active light so that the integrated light intensity was 350 mJ. Lines were drawn on the resulting image using a dyne pen. The upper limit of the value at which the drawn lines did not turn into droplets and remained unchanged for 2 to 4 seconds was calculated, and the image was evaluated according to the following evaluation criteria. ◎, ○, and △ are within the acceptable range. ◎:35mN / m or more ○: 30 mN / m or more and less than 35 mN / m △: 25 mN / m or more and less than 30 mN / m ×: Less than 25 mN / m

[0113] [Table 1]

[0114] As shown in Table 1 above, inks containing the droplet modifier represented by the general formula (1) and having a photopolymerizable compound amount of 70% by mass or more were less prone to generating satellite mist (Inks 1-18). This is because the inclusion of the droplet modifier represented by the general formula (1) causes the compound to orient itself on the surface of the inkjet ink droplets, covering the entire droplet. As a result, the droplets become less likely to split, reducing the likelihood of satellite and mist formation. Furthermore, the prints obtained from these inks exhibited good post-processing properties. The cured products of these inks had a large hydrophilic area, and the presence of hydrophilic regions on the surface of the cured products is thought to have contributed to the good post-processing properties.

[0115] On the other hand, when the droplet adjusting agent represented by the general formula (1) above was not included, especially when the hydrophilic portion was small, satellites and mist were generated, and post-processing properties were also poor (ink 19). Furthermore, when the hydrophilic portion was too large, the ejection performance from the inkjet nozzle tended to decrease, and satellites and mist were generated (ink 20). In this case, the droplets became unstable, and the post-processing properties of the cured product were also poor. [Industrial applicability]

[0116] The present invention provides an active light-curable inkjet ink that is less likely to generate satellites or mist during printing and can form a coating film with good post-processing properties. This ink is extremely useful in printing in various industrial fields.

Claims

1. This is an active light-curable inkjet ink containing a photopolymerizable compound, a photoinitiator, a pigment, and a pigment dispersant. It further contains a compound represented by the following general formula (1), and The amount of the photopolymerizable compound is 70% by mass or more relative to the total mass of the active light-curable inkjet ink. Light-curing inkjet ink. 【Chemistry 1】 (In general formula (1), R １ and R ２ Each of these independently represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alkylthio group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, or a combination thereof. R ３ This represents a substituted or unsubstituted alkylene group having 2 to 6 carbon atoms. (n represents an integer between 50 and 300, inclusive.)

2. The amount of the compound represented by the general formula (1) is 0.1% by mass or more and 4.0% by mass or less relative to the total mass of the active light-curable inkjet ink. The active light-curable inkjet ink according to claim 1.

3. The compound represented by the above general formula (1) is the compound represented by the following general formula (2). The active light-curable inkjet ink according to claim 1. 【Chemistry 2】 (In general formula (2), R ４ These represent ethylene group, propylene group, trimethylene group, and tetramethylene group. x and y each independently represent integers between 1 and 30, (n represents an integer between 50 and 300, inclusive.)

4. The compound represented by the above general formula (1) is the compound represented by the following general formula (3). The active light-curable inkjet ink according to claim 1. 【Transformation 3】 (In general formula (3), x1 and y1 each independently represent integers between 15 and 19, (n represents an integer between 170 and 210)

5. It further contains a gelling agent, The active light-curable inkjet ink according to claim 1.

6. The gelling agent contains at least one compound from among the compounds represented by the following general formulas (G1) and (G2). The active light-curable inkjet ink according to claim 5. General form (G1): R ５ -CO-R ６ General form (G2): R ７ -COO-R ８ (In general formulas (G1) and (G2), R ５ ~R ８ each independently represents a linear or branched alkyl group having 12 to 26 carbon atoms)

7. A step of ejecting ink droplets of the active light-curable inkjet ink described in any one of claims 1 to 6 from an inkjet recording head and depositing them on a recording medium, The process includes irradiating the ink droplets that have landed on the recording medium with an active light to cure the ink droplets, A method for manufacturing printed materials.

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