Active energy radiation-hardenable inkjet ink and image forming method

Abstract

To provide an active energy radiation-hardenable inkjet ink which has excellent internal curability of the ink and which can be suppressed in yellowing during image formation, and to provide an image forming method.SOLUTION: Active energy radiation-hardenable inkjet ink is provided, containing a polymerizable compound, a polymerization initiator, and a gelling agent. The active energy radiation-hardenable inkjet ink includes at least one trifunctional monomer as the polymerizable compound, the content of the trifunctional monomer is more than 20 mass% relative to the active energy radiation-hardenable inkjet ink, and the active energy radiation-hardenable inkjet ink includes at least a thioxanthone-modified acrylate as the polymerization initiator.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an actinic ray-curable inkjet ink and an image forming method, and more particularly to an actinic ray-curable inkjet ink and an image forming method that have excellent internal curing properties and can suppress yellowing during image formation. [Background technology]

[0002] In recent years, there has been a demand for further improvements in quality in printing technology, and there has also been a demand for higher performance in the actinic energy ray-curable inkjet inks used during printing.

[0003] The technology disclosed in Patent Document 1 uses an actinic ray-curable inkjet ink in which the types and ratios of polymerizable compounds, polymerization initiators, etc. are controlled.

[0004] Here, deep section curing is one of the particularly valuable properties of printing inks, and attention has been drawn to actinic radiation-curable inkjet inks containing thioxanthone-based compounds, which are polymerization initiators with excellent deep section curing properties.

[0005] Patent Document 1 also discloses an example in which a thioxanthone compound is contained as a polymerization initiator in an actinic radiation-curable inkjet ink, but there is room for improvement in order to make better use of the properties of the thioxanthone compound.

[0006] An example of the use of ink that utilizes the properties of a thioxanthone-based compound is the technology disclosed in Patent Document 2. The ink used in the technology disclosed in Patent Document 2 contains a compound obtained by modifying a thioxanthone-based compound as a polymerization initiator, but the quality of the printed matter after the ink is cured is not satisfactory. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-165984 [Patent Document 2] International Publication No. 2023 / 154961 Summary of the Invention [Problem to be solved by the invention]

[0008] In the technology disclosed in the aforementioned Patent Document 1, the balance between the type, amount, and number of functional groups of the polymerizable compound contained in the ink is controlled, and a thioxanthone-based compound is contained as a polymerization initiator. However, because the balance between the type, amount, and number of functional groups of the polymerizable compound is not controlled in accordance with the thioxanthone-based compound, there remains room for improvement in terms of improving the internal curing properties of the ink and suppressing yellowing during image formation.

[0009] In the technology disclosed in Patent Document 2, a compound obtained by modifying a thioxanthone-based compound is contained in an ink as a polymerization initiator. Furthermore, a thioxanthone-modified acrylate is used as the compound obtained by modifying the thioxanthone-based compound. Thioxanthone-based compounds and thioxanthone-modified acrylates tend to migrate during ink curing, causing yellowing.

[0010] Furthermore, in the technology disclosed in Patent Document 2, the content of trifunctional monomers among the multiple polymerizable compounds contained in the ink is 20 mass % or less relative to the ink. If the content of trifunctional monomers is not large, the internal curing properties of the ink will not improve, and therefore there is still room for improvement in the performance of actinic energy ray-curable inkjet inks.

[0011] The present invention has been made in consideration of the above problems and circumstances, and an object of the present invention is to provide an actinic ray-curable inkjet ink that has excellent internal curing properties and can suppress yellowing during image formation. [Means for solving the problem]

[0012] The present inventors have investigated the causes of the above problems in order to solve the above problems, and as a result have found that the above problems can be solved by adding a polymerizable compound containing a trifunctional monomer, a thioxanthone-modified acrylate, and a polymerization initiator containing a gelling agent to an actinic energy ray-curable inkjet ink, and increasing the content of the trifunctional monomer to more than 20 mass %, thereby arriving at the present invention. That is, the above-mentioned problems of the present invention are solved by the following means.

[0013] 1. An actinic ray-curable inkjet ink containing a polymerizable compound, a polymerization initiator, and a gelling agent, The polymerizable compound contains at least one trifunctional monomer, The content of the trifunctional monomer is more than 20% by mass, The polymerization initiator contains at least a thioxanthone-modified acrylate. 1. An actinic ray-curable inkjet ink comprising:

[0014] 2. The polymerizable compound contains at least one monofunctional monomer. 2. The actinic ray-curable inkjet ink according to claim 1,

[0015] 3. The content of the monofunctional monomer is 10.0% by mass or more. 3. The actinic ray-curable inkjet ink according to claim 2.

[0016] 4. The content of the polymerization initiator is within the range of 0.1 to 15.0% by mass. 2. The actinic ray-curable inkjet ink according to claim 1,

[0017] 5. The molecular weight of the thioxanthone-modified acrylate is 360 or more. 2. The actinic ray-curable inkjet ink according to claim 1,

[0018] 6. The thioxanthone-modified acrylate is a thioxanthone-modified triacrylate. 2. The actinic ray-curable inkjet ink according to claim 1,

[0019] 7. The content of the thioxanthone-modified triacrylate is within the range of 0.1 to 5.0 mass%. 7. The actinic ray-curable inkjet ink according to claim 6.

[0020] 8. An image forming method using the actinic ray-curable inkjet ink according to item 1, a first step of ejecting the actinic energy ray-curable inkjet ink from an inkjet head and causing it to land on a recording medium; and a second step of curing the actinic energy ray-curable inkjet ink by irradiating the actinic energy ray. An image forming method comprising: [Effects of the Invention]

[0021] The above-described means of the present invention can provide an actinic ray-curable ink-jet ink and an image forming method that are excellent in internal curing properties and can suppress yellowing during image formation. The mechanism by which the effects of the present invention are manifested or the mechanism of action is not clear, but is speculated as follows.

[0022] The actinic energy ray-curable inkjet ink of the present invention is an actinic energy ray-curable inkjet ink containing a polymerizable compound, a polymerization initiator, and a gelling agent, and is characterized in that the polymerizable compound contains at least one trifunctional monomer, the content of the trifunctional monomer is more than 20 mass %, and the polymerization initiator contains at least a thioxanthone-modified acrylate. Hereinafter, "the actinic energy ray-curable inkjet ink of the present invention" may also be simply referred to as "the ink of the present invention."

[0023] As described above, in the prior art, inks containing a thioxanthone-based compound or a thioxanthone-modified acrylate as a polymerization initiator have room for improvement in terms of improving internal curing properties and suppressing yellowing during image formation.

[0024] The polymerization initiator, when contained in the ink together with the polymerizable compound, can initiate polymerization and crosslinking of the polymerizable compound upon irradiation with active energy rays.

[0025] High internal curing is important for printing inks, and many thioxanthone compounds have two absorption peaks in the region of strong ultraviolet radiation from medium-pressure mercury lamps, providing excellent deep curing for printing inks. Note that the above-mentioned thioxanthone compounds also include derivatives of these thioxanthone compounds.

[0026] Furthermore, thioxanthone-modified acrylates obtained by modifying the thioxanthone-based compounds also have excellent deep curing properties, and therefore inks containing the thioxanthone-modified acrylates as a polymerization initiator have high internal curing properties. However, the thioxanthone-modified acrylates tend to migrate during ink curing, which can cause yellowing.

[0027] When an image is formed using the printing ink, the compound should have a low tendency to migrate or be extracted during curing of the ink.

[0028] When the thioxanthone-modified acrylate is added as a polymerization initiator to an ink containing a trifunctional monomer as a polymerizable compound, if the content of the trifunctional monomer is greater than 20% by mass of the ink, the internal curing property of the ink is improved to a desired level and the tendency of the thioxanthone-modified acrylate to migrate during curing of the ink can be suppressed, which is presumably to suppress yellowing after image formation.

[0029] Furthermore, the polymerization initiator and polymerizable compound are compatible with a gelling agent, and the inclusion of the gelling agent improves the pinning ability of the ink on a recording medium and also improves the curing ability inside the ink coating film, thereby enhancing the effects of the present invention.

[0030] When the ink is pinned to the recording medium in a gel state, the ink is prevented from spreading on the recording medium, making it difficult for adjacent dots to be identical, allowing for the formation of higher-resolution images.

[0031] Furthermore, when the ink is in a gel state, oxygen from the environment is prevented from entering the ink droplets, making it less likely that oxygen will inhibit curing, allowing high-resolution images to be formed at higher speeds.

[0032] From the above, it is presumed that the ink of the present invention contains more than 20% by mass of a trifunctional monomer relative to the ink, contains a thioxanthone-modified acrylate, and also contains a gelling agent, and therefore the ink has excellent internal curing properties and can suppress yellowing during image formation. [Brief explanation of the drawings]

[0033] [Figure 1] An example of the configuration of an image forming apparatus DETAILED DESCRIPTION OF THE INVENTION

[0034] The actinic ray-curable inkjet ink of the present invention is an actinic ray-curable inkjet ink containing a polymerizable compound, a polymerization initiator, and a gelling agent, characterized in that the polymerizable compound contains at least one or more trifunctional monomers, the content of the trifunctional monomers is more than 20 mass %, and the polymerization initiator contains at least a thioxanthone-modified acrylate. This feature is a technical feature common to or corresponding to each of the following embodiments (modes).

[0035] In an embodiment of the present invention, it is preferable that the polymerizable compound contains at least one monofunctional monomer, from the viewpoint of imparting flexibility to the cured film obtained by curing the ink and improving scratch resistance.

[0036] It is preferable that the content of the monofunctional monomer is 10.0% by mass or more, from the viewpoints of increasing the flexibility of the cured film and further improving the scratch resistance.

[0037] The content of the polymerization initiator is preferably within a range of 0.1 to 15.0% by mass from the viewpoint of enhancing the reactivity of the polymerizable compound.

[0038] The molecular weight of the thioxanthone-modified acrylate is preferably 360 or more from the viewpoint of improving the internal curing property of the ink and suppressing yellowing during image formation.

[0039] It is more preferable that the thioxanthone-modified acrylate is a thioxanthone-modified triacrylate from the viewpoints of improving the internal curing properties of the ink and suppressing yellowing during image formation.

[0040] The content of the thioxanthone-modified triacrylate is preferably within a range of 0.1 to 5.0% by mass from the viewpoints of improving the internal curing properties of the ink and suppressing yellowing during image formation.

[0041] The image forming method of the present invention is suitable for use with the actinic energy ray-curable inkjet ink of the present invention, and is characterized by comprising: a first step of ejecting the actinic energy ray-curable inkjet ink from an inkjet head and causing it to land on a recording medium; and a second step of irradiating the actinic energy ray-curable inkjet ink with actinic energy rays to cure it.

[0042] The present invention, its components, and embodiments for carrying out the present invention will be described in detail below. In this application, the symbol "to" is used to mean that the numerical values ​​before and after it are included as lower and upper limits.

[0043] However, advantages and features provided by one or more embodiments of the present invention will be more fully understood from the following detailed description and the accompanying drawings, which are for illustrative purposes only and are not intended to define the limits of the invention.

[0044] 1. Active energy ray curable inkjet ink The actinic ray-curable inkjet ink of the present invention is an actinic ray-curable inkjet ink containing a polymerizable compound, a polymerization initiator, and a gelling agent, characterized in that the polymerizable compound contains at least one or more trifunctional monomers, the content of the trifunctional monomers is more than 20 mass %, and the polymerization initiator contains at least a thioxanthone-modified acrylate.

[0045] (1.1) Polymerizable compounds The ink of the present invention contains a polymerizable compound. As the polymerizable compound, a photopolymerizable compound, a thermally polymerizable compound, a photo- and thermo-reactive compound, etc. are used. Hereinafter, a "photopolymerizable compound" will also be referred to as a "photocurable compound," and a "thermopolymerizable compound" will also be referred to as a "thermosetting compound."

[0046] (1.1.1) Photopolymerizable compound The term "photopolymerizable compound" refers to a compound having a polymerizable functional group, and is a compound that crosslinks or polymerizes (cures) when irradiated with active energy rays such as ultraviolet rays or electron beams. When the ink B according to the present invention, which will be described later, contains a photopolymerizable compound with a lower viscosity than the other photopolymerizable compounds, the viscosity of the ink is reduced.

[0047] The photopolymerizable compound may be any one of a monomer, a polymerizable oligomer, a prepolymer, or a mixture thereof. The inkjet ink may contain only one type of photopolymerizable compound, or two or more types of photopolymerizable compounds.

[0048] Examples of active energy rays include ultraviolet rays, electron beams, α rays, γ rays, and X-rays. From the viewpoint of safety and the ability to crosslink or polymerize (cure) with a low amount of energy, the active energy rays are preferably ultraviolet rays or electron beams.

[0049] The photopolymerizable compound used as the polymerizable compound according to the present invention may be a monofunctional monomer or a bifunctional monomer, but a plurality of monomers including at least one trifunctional monomer are used as the photopolymerizable compound.

[0050] (Type of photopolymerizable compound) Examples of the photopolymerizable compound contained in the ink of the present invention include radically polymerizable compounds and cationic photopolymerizable compounds, and the photopolymerizable compound is preferably a radically polymerizable compound.

[0051] The radical polymerizable compound preferably contains a (meth)acrylate modified with ethylene oxide or propylene oxide. Hereinafter, "a (meth)acrylate modified with ethylene oxide or propylene oxide" may also be simply referred to as "modified (meth)acrylate."

[0052] Modified (meth)acrylates have higher photosensitivity. Furthermore, modified (meth)acrylates are more likely to be encapsulated in the house-of-card structure when the ink gels at low temperatures, and are more compatible with other ink components even at high temperatures. Furthermore, modified (meth)acrylates have less shrinkage upon curing, making printed materials less likely to curl during image formation.

[0053] Examples of the photopolymerizable compound include a polymerizable compound having a (meth)acryloyl group, a polymerizable compound having a vinyl group, and a polymerizable compound having a maleimide group.

[0054] In this specification, a polymerizable compound having a (meth)acryloyl group means a compound having at least one of a methacryloyl group and an acryloyl group. The term "(meth)acrylate" refers to acrylate or methacrylate. The term "(meth)acrylic" refers to acrylic or methacrylic.

[0055] From the viewpoint of forming a cured composition layer with higher precision, the polymerizable compound preferably has a (meth)acryloyl group. The polymerizable compound may be used alone or in combination of two or more.

[0056] The photopolymerizable compound contained in the ink of the present invention may be an epoxy compound in addition to an acrylic compound. Also, a cationic photopolymerizable compound such as an oxetane compound may be used.

[0057] From the viewpoint of accelerating curing, the epoxy compound is preferably an aromatic epoxide or an alicyclic epoxide, and more preferably an alicyclic epoxide.

[0058] From the viewpoint of suppressing shrinkage of the recording medium when the ink is cured, it is preferable that the photopolymerizable compound contains at least one oxetane compound and at least one compound selected from an epoxy compound and a vinyl ether compound.

[0059] 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)acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, and methoxypolyethylene glycol. Examples of the 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, and 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalate and t-butylcyclohexyl (meth)acrylate.

[0060] Examples of bifunctional (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, bisphenol A PO adduct di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, and tripropylene glycol diacrylate.

[0061] Examples of trifunctional or higher (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate. Other examples include dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and glycerin propoxy tri(meth)acrylate. Other examples include pentaerythritol ethoxy tetra(meth)acrylate.

[0062] Commercially available monofunctional (meth)acrylates include, for example, "Miramer M144" (4EO-modified phenol acrylate) and "Miramer M166" (8EO-modified nonylphenol acrylate) manufactured by Toyo Chemicals Co., Ltd. Other examples include "M1602" (2PO-modified nonylphenol acrylate) manufactured by the same company, and lauryl acrylate manufactured by Osaka Organic Chemical Industry Ltd.

[0063] Commercially available bifunctional (meth)acrylates include, for example, "CN2270" (polyester acrylate oligomer: polyether) manufactured by Sartomer Co., Ltd., "EM223" (tripropylene glycol diacrylate) manufactured by Changxing Co., Ltd., and "A400" (polyethylene glycol diacrylate (#400)) manufactured by Daicel Corporation.

[0064] Commercially available tri- or higher functional (meth)acrylates include, for example, "Miramer M3130" (ethoxylated trimethylolpropane triacrylate (3EO)) manufactured by Toyo Chemicals Co., Ltd., "Miramer M3160" (ethoxylated trimethylolpropane triacrylate (6EO)) manufactured by the same company, "SR9020" (glycerol propoxy triacrylate) manufactured by Sartomer, and "ETERCURE6361-100" (hyperbranched polyester acrylate) manufactured by Choko Materials Industry Co., Ltd.

[0065] Commercially available bifunctional or higher modified (meth)acrylates include, for example, Sartomer's "CD561," "SR454," "SR499," and "SR494." Other examples include Shin-Nakamura Chemical's "NK Ester A-400," "NK Ester A-600," "NK Ester 9G," and "NK Ester 14G." Other examples include Shin-Nakamura Chemical's "NK Ester DOD-N," "NK Ester A-DCP," and "NK Ester DCP."

[0066] Examples of aromatic epoxides include di- or polyglycidyl ethers produced by reacting a polyhydric phenol having at least one aromatic nucleus or its alkylene oxide adduct with epichlorohydrin.

[0067] Examples of such aromatic epoxides include 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.

[0068] Examples of the alkylene oxide include ethylene oxide and propylene oxide.

[0069] Alicyclic epoxides include, for example, cyclohexene oxide- or cyclopentene oxide-containing compounds obtained by epoxidizing a compound having at least one cycloalkane ring, such as a cyclohexene or cyclopentene ring, with a suitable oxidizing agent, such as hydrogen peroxide or a peracid.

[0070] Examples of the aliphatic epoxide include di- or polyglycidyl ethers of aliphatic polyhydric alcohols or their alkylene oxide adducts.

[0071] Examples of such aliphatic epoxides include diglycidyl ethers of alkylene glycols, polyglycidyl ethers of polyhydric alcohols, and diglycidyl ethers of polyalkylene glycols.

[0072] Examples of the alkylene glycol include diglycidyl ether of ethylene glycol, diglycidyl ether of propylene glycol, and diglycidyl ether of 1,6-hexanediol.

[0073] Examples of polyhydric alcohols include glycerin and its alkylene oxide adducts.

[0074] Examples of polyalkylene glycols include polyethylene glycol and its alkylene oxide adducts, and polypropylene glycol and its alkylene oxide adducts.

[0075] Examples of the alkylene oxide include ethylene oxide and propylene oxide.

[0076] Examples of the vinyl ether compound include a monovinyl ether compound, a divinyl ether compound, and a trivinyl ether compound.

[0077] Examples of monovinyl ether compounds include 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.

[0078] Examples of divinyl ether compounds include 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, and cyclohexanedimethanol divinyl ether.

[0079] Examples of trivinyl ether compounds include trimethylolpropane trivinyl ether.

[0080] Of these vinyl ether compounds, divinyl ether compounds and trivinyl ether compounds are preferred from the viewpoints of curability, adhesion, and surface hardness, and from the above viewpoints, divinyl ether compounds are more preferred.

[0081] The oxetane compound is a compound having an oxetane ring. Examples of the oxetane compound include compounds having an oxetane ring described in JP-A Nos. 2001-220526 and 2001-310937.

[0082] From the viewpoint of not increasing the viscosity of the ink of the present invention more than necessary and appropriately adjusting the glass transition temperature of the ink to impart sufficient adhesiveness to the resulting cured product, it is preferable that the oxetane compound have 1 to 4 oxetane rings.

[0083] Examples of compounds having 1 to 4 oxetane rings include compounds represented by general formula (1) described in paragraph 0089 of JP-A No. 2005-255821. Other examples include compounds represented by general formula (2) described in paragraph 0092 of the same publication, general formula (7) described in paragraph 0107, general formula (8) described in paragraph 0109, and general formula (9) described in paragraph 0116.

[0084] (Photopolymerizable compound content) The content of the photopolymerizable compound is not particularly limited as long as the effects of the present invention are obtained, but it can be, for example, in the range of 1 to 97% by mass relative to the ink of the present invention. From the viewpoint of imparting flexibility to the cured film and improving scratch resistance, the content of the photopolymerizable compound is preferably in the range of 30 to 95% by mass relative to the ink.

[0085] [Content balance by number of functional groups] The ink of the present invention contains at least one trifunctional monomer as a polymerizable compound.

[0086] Photopolymerizable compounds of trifunctional monomers have a higher crosslink density upon irradiation with active energy rays than photopolymerizable compounds of monofunctional or bifunctional monomers, and are more likely to form polymers with a network structure. Furthermore, they are preferred from the standpoint of printing accuracy because they can increase the UV curing speed.

[0087] This network-like polymer restricts the movement of each component during curing of the actinic energy ray-curable inkjet ink, thereby providing the effect of making it difficult for the polymerization initiator, gelling agent, and uncured photopolymerizable compound to precipitate on the surface of the image.

[0088] Therefore, it is believed that by including a photopolymerizable trifunctional monomer compound in an amount of more than 20% by mass, it is possible to suppress a decrease in the gloss of the image surface and a decrease in the surface hardening property.

[0089] The ink of the present invention may optionally contain a monofunctional monomer within the range in which the effects of the present invention are exhibited.

[0090] It is preferable that the ink of the present invention contains at least one monofunctional monomer as a polymerizable compound, from the viewpoint of imparting flexibility to the cured film obtained by curing the ink and improving scratch resistance.

[0091] The trifunctional monomer according to the present invention is contained in an amount of more than 20 mass % relative to the ink of the present invention. However, if the trifunctional monomer is the only polymerizable compound contained in the ink of the present invention, the crosslink density will be too high, and the physical properties of the cured film will be too hard, making it brittle.

[0092] Therefore, by ensuring that the content of the monofunctional monomer is 10.0% by mass or more relative to the ink of the present invention, the flexibility of the cured film increases, and scratch resistance is further improved.

[0093] The ink of the present invention may optionally contain a bifunctional monomer within the range in which the effects of the present invention are achieved. The influence of the bifunctional monomer on the degree of crosslinking is intermediate between that of the trifunctional monomer and the monofunctional monomer, and therefore the content of the trifunctional monomer and the content of the monofunctional monomer may be appropriately adjusted depending on the desired physical properties of the cured film.

[0094] (1.1.2) Thermosetting compounds The term "thermosetting compound" refers to a compound having a curable functional group, which is a compound that polymerizes (cures) when heat is applied.

[0095] As the thermosetting compound, an epoxy resin is preferably used. Among them, an epoxy resin having an aromatic ring, such as a bisphenol A type epoxy resin, a phenol novolac type epoxy resin, or a cresol novolac type epoxy resin, is more preferable from the viewpoints of insulating properties and film strength. Also, it is more preferable from the viewpoints of coefficient of thermal expansion (CTE), glass transition temperature (Tg), etc.

[0096] In particular, when the above-mentioned epoxy resin is used in combination with a photopolymerizable compound such as (meth)acrylate, the epoxy resin is preferably a novolac type or a bisphenol type.

[0097] Examples of novolac epoxy compounds include phenol novolac epoxy compounds, cresol novolac epoxy compounds, biphenyl novolac epoxy compounds, and trisphenol novolac epoxy compounds. Also included are dicyclopentadiene novolac epoxy compounds.

[0098] Examples of bisphenol-type epoxy compounds include bisphenol A-type epoxy compounds, bisphenol F-type epoxy compounds, and 2,2'-diallyl bisphenol A-type epoxy compounds. Other examples include hydrogenated bisphenol-type epoxy compounds and polyoxypropylene bisphenol A-type epoxy compounds.

[0099] Examples of commercially available monofunctional thermosetting compounds include "Epogose 2EH" (2-ethylhexyl glycidyl ether) and "Epogose OCR" (glycidyl (2-methylphenyl) ether), both manufactured by Yokkaichi Chemical Co., Ltd. These can also be used as reactive diluents.

[0100] (1.1.3) Photothermally reactive compounds It is preferable that the ink according to the present invention contains a photo- and thermo-reactive compound from the viewpoints of film toughness after curing of the ink composition, crack resistance, drill resistance, adhesion, and durability in a heat cycle test. The reason for improved film toughness is that having a photopolymerizable functional group and a thermosetting functional group in the same molecule allows the photopolymerizable compound and the thermosetting compound to be bonded together.

[0101] In this specification, the term "photothermally reactive compound" refers to a compound having at least one photopolymerizable functional group and at least one thermosetting functional group.

[0102] The photothermally reactive compound preferably has one or more (meth)acryloyl groups and one or more epoxy groups. The photothermally reactive compound may be used singly or in combination of two or more.

[0103] The photopolymerizable compound and the thermosetting compound according to the present invention are preferably contained as components different from the photo- and thermo-reactive compound.

[0104] Examples of the photothermally reactive compound include a compound having a (meth)acryloyl group and an epoxy group, a partially (meth)acrylated epoxy compound, and a urethane-modified (meth)acrylic epoxy compound.

[0105] Examples of the compound having a (meth)acryloyl group and an epoxy group include glycidyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate glycidyl ether.

[0106] Examples of epoxy compounds that can be used for the partially (meth)acrylated epoxy compound include novolac-type epoxy compounds and bisphenol-type epoxy compounds. The partially (meth)acrylated epoxy compound can be obtained, for example, by reacting an epoxy compound with (meth)acrylic acid in the presence of a catalyst according to a conventional method.

[0107] The urethane-modified (meth)acrylic epoxy compound can be obtained, for example, by the following method.

[0108] A polyol is reacted with a difunctional or higher functional isocyanate, and then the remaining isocyanate groups are reacted with a (meth)acrylic monomer having an acid group and glycidol. Alternatively, without using a polyol, a difunctional or higher functional isocyanate may be reacted with a (meth)acrylic monomer having a hydroxyl group and glycidol. Alternatively, the urethane-modified (meth)acrylic epoxy compound can also be obtained by reacting a (meth)acrylate monomer having an isocyanate group with glycidol.

[0109] Specifically, for example, 1 mole of trimethylolpropane and 3 moles of isophorone diisocyanate are reacted in the presence of a tin catalyst. The remaining isocyanate group in the resulting compound is reacted with hydroxyethyl acrylate, an acrylic monomer having a hydroxyl group, and glycidol, an epoxy having a hydroxyl group. This produces the above-mentioned urethane-modified (meth)acrylic epoxy compound.

[0110] The polyol is not particularly limited, and examples thereof include ethylene glycol, glycerin, sorbitol, trimethylolpropane, and (poly)propylene glycol.

[0111] The isocyanate is not particularly limited as long as it is bifunctional or higher, and examples thereof include isophorone diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, diphenylmethane-4,4′-diisocyanate (MDI), hydrogenated MDI, polymeric MDI, 1,5-naphthalene diisocyanate, norbornane diisocyanate, tolidine diisocyanate, xylylene diisocyanate (XDI), hydrogenated XDI, lysine diisocyanate, triphenylmethane triisocyanate, tris(isocyanatephenyl)thiophosphate, tetramethylxylene diisocyanate, and 1,6,10-undecane triisocyanate.

[0112] The content of the photothermally reactive compound is preferably 0.5% by mass or more, and more preferably in the range of 1 to 30% by mass, of the ink of the present invention, from the viewpoint of further improving the physical properties of the cured film, particularly film toughness and crack resistance.

[0113] Commercially available photothermally reactive compounds include "4HBAGE" (4-hydroxybutyl acrylate glycidyl ether) manufactured by Mitsubishi Chemical Corporation, "G0497" (glycidyl acrylate) manufactured by TCI Corporation, "M0590" (glycidyl methacrylate) manufactured by the same company, and "EA-1010LC" (bisphenol A glycidyl ether-containing epoxy acrylate) manufactured by Shin-Nakamura Chemical Co., Ltd. Other examples include "EBECRYL 3605" (epoxy resin half acrylate) manufactured by Daicel-Allnex Corporation.

[0114] (1.2) Polymerization initiator The ink of the present invention contains a polymerization initiator. The polymerization initiator includes at least a thioxanthone-modified acrylate. Note that a polymerization initiator other than the thioxanthone-modified acrylate may be used in combination, and the polymerization initiator to be used in combination is preferably a photopolymerization initiator.

[0115] The polymerization initiator, when contained in the ink together with the photopolymerizable compound described above, can initiate polymerization and crosslinking of the photopolymerizable compound upon irradiation with actinic energy rays. The inkjet ink may contain only one type of polymerization initiator, or two or more types of polymerization initiators.

[0116] High internal curing is important for printing inks, and many thioxanthone compounds have two absorption peaks in the region of strong ultraviolet radiation from medium-pressure mercury lamps, providing excellent deep curing for printing inks. Note that the above-mentioned thioxanthone compounds also include derivatives of these thioxanthone compounds.

[0117] Furthermore, thioxanthone-modified acrylates obtained by modifying the thioxanthone-based compounds also have excellent deep curing properties, and therefore inks containing the thioxanthone-modified acrylates as a polymerization initiator have high internal curing properties. However, the thioxanthone-modified acrylates tend to migrate during ink curing, which can cause yellowing.

[0118] When an image is formed using the printing ink, the compound should have a low tendency to migrate or be extracted during curing of the ink.

[0119] When the thioxanthone-modified acrylate is added as a polymerization initiator to an ink containing a trifunctional monomer as a polymerizable compound, if the content of the trifunctional monomer is greater than 20% by mass of the ink, the internal curing property of the ink is improved to a desired level and the tendency of the thioxanthone-modified acrylate to migrate during curing of the ink can be suppressed, thereby suppressing yellowing after image formation.

[0120] Because thioxanthone compounds themselves are poorly soluble in printing inks and most common organic solvents, they are generally used in combination with other photoinitiators to provide the right balance of properties, cost, and ease of use.

[0121] (1.2.1) Thioxanthone-modified acrylate By including a thioxanthone-modified acrylate obtained by modifying the above-mentioned thioxanthone-based compound in the polymerization initiator contained in the ink of the present invention, it is possible to suppress the tendency of the ink to migrate after curing while retaining the advantages of the thioxanthone-based compound.

[0122] Thioxanthone (C 13 The structural formula of H8OS (molecular weight 212.27) and thioxanthone acrylate is as follows:

[0123] [ka]

[0124] Thioxanthone acrylate having the above structural formula has polymerizable groups, and by modifying these to increase the number of polymerizable groups, it is possible to increase the number of reactive sites. Furthermore, modification increases not only the number of polymerizable groups but also the molecular weight. This reduces the mobility of the polymerization initiator within the ink cured film, and this mobility is further restricted by the network structure formed by polymerization and crosslinking of the photopolymerizable compound, thereby improving the internal curing properties of the ink. Furthermore, because the polymerization initiator is less likely to precipitate on the image surface, yellowing during image formation is suppressed.

[0125] The thioxanthone-modified acrylate according to the present invention is not particularly limited as long as it is a compound obtained by modifying the above-mentioned thioxanthone acrylate so as to increase the number of polymerizable groups and the molecular weight.

[0126] (molecular weight) The molecular weight of the thioxanthone-modified acrylate according to the present invention is preferably 360 or more from the viewpoints of improving the internal curing properties of the ink and suppressing yellowing during image formation.

[0127] When the molecular weight of the thioxanthone-modified acrylate is 360 or more, the polymerization initiator is less likely to move within the cured ink film, and this movement is further restricted by the network structure formed by polymerization and crosslinking of the photopolymerizable compound, thereby improving the internal curing properties of the ink. In addition, the thioxanthone-modified acrylate is less likely to precipitate on the image surface, thereby suppressing yellowing during image formation.

[0128] Examples of the thioxanthone-modified acrylate include 2-carboxymethoxythioxanthone described in paragraph 0044 of JP-A 2005-512973. The chemical structural formula of 2-carboxymethoxythioxanthone is shown below. The thioxanthone-modified acrylate may also be a thioxanthone-modified triacrylate.

[0129] [ka]

[0130] The molecular weight of the polymerization initiator other than the thioxanthone-modified acrylate according to the present invention is not particularly limited.

[0131] (1.2.2) Thioxanthone-modified triacrylate It is more preferable that the thioxanthone-modified acrylate according to the present invention is a thioxanthone-modified triacrylate from the viewpoints of improving the internal curing properties of the ink and suppressing yellowing during image formation.

[0132] The thioxanthone-modified triacrylate is a compound obtained by modifying the above-mentioned thioxanthone acrylate, and has three polymerizable groups, so it is believed to have a molecular weight of at least 460 or more.

[0133] Thioxanthone-modified triacrylate has a higher molecular weight (460 or more) than conventional thioxanthone, and because it has three polymerizable groups, it also has many reactive sites. This increases the crosslinking density with the polymerizable compound, and the resulting network structure restricts migration. This makes it less likely for the ink to precipitate on the surface of the recording medium after being applied to the recording medium during image formation. This results in excellent internal curing of the ink and suppresses yellowing during image formation.

[0134] (Content) It is preferable that the content of the thioxanthone-modified triacrylate according to the present invention is within the range of 0.1 to 5.0% by mass from the viewpoints of improving the internal curing properties of the ink and suppressing yellowing during image formation.

[0135] The content of the polymerization initiator other than the thioxanthone-modified triacrylate according to the present invention is preferably 7.0% by mass or less.

[0136] When the molecular weight of the polymerization initiator other than the thioxanthone-modified triacrylate is less than 360, the content of the polymerization initiator is preferably 7.0% by mass or less relative to the ink.

[0137] When the molecular weight of the polymerization initiator other than the thioxanthone-modified acrylate is 360 or more, the content of the polymerization initiator is preferably 7.0% by mass or less relative to the ink.

[0138] (Commercially available) An example of a commercially available thioxanthone-modified triacrylate is the photopolymerization initiator "PRO22669" manufactured by Sartomer.

[0139] (1.2.3) Other polymerization initiators The ink of the present invention may contain a polymerization initiator other than the thioxanthone-modified acrylate. It is also possible to use a polymerization initiator having an unmodified thioxanthone structure in combination with the thioxanthone-modified acrylate.

[0140] The polymerization initiator other than the thioxanthone-modified acrylate is not particularly limited, and various known polymerization initiators can be contained.

[0141] Examples of various known polymerization initiators include radical polymerization initiators and cationic polymerization initiators.

[0142] Examples of the radical polymerization initiator include a polymerization initiator having a thioxanthone structure, a polymerization initiator having a bisacylphosphine structure, a polymerization initiator having an alkylphenone structure, a polymerization initiator having an acylphosphine structure, and a polymerization initiator having a benzophenone structure. Note that the "polymerization initiator having a thioxanthone structure" includes the aforementioned thioxanthone-modified acrylate.

[0143] Of the above polymerization initiators, from the viewpoint of further enhancing the effects of the present invention, polymerization initiators having a thioxanthone structure other than thioxanthone-modified acrylates, polymerization initiators having a bisacylphosphine structure, and polymerization initiators having an alkylphenone structure are preferred.

[0144] When the polymerization initiator contains a radical polymerization initiator having a bisacylphosphine structure, the decrease in gloss of the image surface and the decrease in surface hardening properties are lessened. This is thought to be because the radical polymerization initiator having a bisacylphosphine structure is highly reactive and polymerization and crosslinking are likely to develop around this radical polymerization initiator, thereby further restricting the movement of the polymerization initiator.

[0145] (1.2.4) Polymerization initiator content in ink From the viewpoint of enhancing the reactivity of the polymerizable compound, it is preferable that the content of the polymerization initiator according to the present invention is within the range of 0.1 to 15.0% by mass based on the ink of the present invention. The term "performance of the thioxanthone-modified acrylate" refers to the function of improving curability and the function of suppressing yellowing during image formation, which are attributable to the thioxanthone-modified acrylate.

[0146] The content of the radical polymerization initiator having a bisacylphosphine structure is preferably within a range of 2 to 8% by mass, and more preferably within a range of 3 to 5% by mass, relative to the total mass of the ink.

[0147] The content of the polymerization initiator in the ink includes the content of the thioxanthone-modified acrylate, the content of polymerization initiators other than the thioxanthone-modified acrylate, and the content of the radical polymerization initiator having a bisacylphosphine structure.

[0148] (1.2.5) Other (Radical polymerization initiator) Commercially available radical polymerization initiators having a molecular weight of 360 or more include, for example, the following commercially available products (1) to (6).

[0149] (1) Radical polymerization initiators with thioxanthone structures (2) Radical polymerization initiators with bisacylphosphine structures (3) Radical polymerization initiators with bisacylphosphine structures (4) Radical polymerization initiators having an alkylphenone structure (5) Radical polymerization initiators having an acylphosphine structure (6) Radical polymerization initiators having a benzophenone structure

[0150] Examples of the above-mentioned (1) polymerization initiator having a molecular weight of 360 or more include "GENOPOL TX-1" manufactured by Rahn and "SPEEDCURE 7010" manufactured by Lambson.

[0151] Examples of the polymerization initiator (2) having a molecular weight of 360 or more include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,6-dimethylbenzoyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2-methoxyphenylphosphine oxide, bis(2,6-dimethylbenzoyl)-2-methoxyphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-dimethoxyphenylphosphine oxide, bis(2,6-dimethylbenzoyl)-2,4-dimethoxyphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-dipentyloxyphenylphosphine oxide, and bis(2,6-dimethylbenzoyl)-2,4-dipentyloxyphenylphosphine oxide.

[0152] An example of the polymerization initiator (3) having a molecular weight of 360 or more is "IRGACURE 819" manufactured by BASF ("IRGACURE" is a registered trademark of the company).

[0153] Examples of the polymerization initiator (4) having a molecular weight of 360 or more include "IRGACURE 369" and "IRGACURE 379" manufactured by BASF ("IRGACURE" is a registered trademark of the company).

[0154] Other examples include "ESACURE 1001M" and "ESACURE KIP150" manufactured by Lamberti ("ESACURE" is a registered trademark of the company).

[0155] Examples of the polymerization initiator (5) having a molecular weight of 360 or more include 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide, 2,6-dimethylbenzoylethoxyphenylphosphine oxide, 2,4,6-trimethylbenzoylmethoxyphenylphosphine oxide, 2,6-dimethylbenzoylmethoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyl(4-pentyloxyphenyl)phenylphosphine oxide, and 2,6-dimethylbenzoyl(4-pentyloxyphenyl)phenylphosphine oxide.

[0156] Examples of the polymerization initiator (6) having a molecular weight of 360 or more include "SPEEDCURE 7005" manufactured by Lambson and "Omnipol BP" manufactured by Rahn AG.

[0157] Commercially available radical polymerization initiators having a molecular weight of less than 360 include, for example, radical polymerization initiators having a thioxanthone structure, radical polymerization initiators having a bisacylphosphine structure, and radical polymerization initiators having an alkylphenone structure.

[0158] Commercially available radical polymerization initiators having a thioxanthone structure and a molecular weight of less than 360 include, for example, "SPEEDCURE ITX" manufactured by BASF.

[0159] Commercially available radical polymerization initiators having a bisacylphosphine structure and a molecular weight of less than 360 include, for example, "LUCIRIN TPO" manufactured by BASF ("LUCIRIN" is a registered trademark of the company).

[0160] Commercially available radical polymerization initiators having an alkylphenone structure and a molecular weight of less than 360 include, for example, "IRGACURE 184" manufactured by BASF and "IRGACURE 907" manufactured by the same company.

[0161] (cationic polymerization initiator) Examples of the cationic polymerization initiator include salts of aromatic onium compounds, sulfonates that generate sulfonic acid, halides that photogenerate hydrogen halide, and iron-allene complexes.

[0162] The onium includes, for example, diazonium, ammonium, iodonium, sulfonium, and phosphonium.

[0163] Counter ions that form salts of aromatic onium compounds include, for example, B(C6F5) 4- , P.F. 6- , AsF 6- , SbF 6- , and CF3SO 3- etc.

[0164] Examples of aromatic onium compounds include the compounds described in paragraph 0134 of JP-A No. 2005-255821.

[0165] Examples of sulfonated compounds that generate sulfonic acid include the compounds described in paragraph 0136 of JP-A No. 2005-255821, the compounds described in claim 1 of JP-A No. 2004-91698, and the compounds described in claim 1 of JP-A No. 2006-518332.

[0166] Examples of halides that photogenerate hydrogen halide include the compounds described in paragraph 0138 of JP-A No. 2005-255821.

[0167] Examples of iron allene complexes include the compounds described in paragraph 0140 of JP-A No. 2005-255821.

[0168] Commercially available cationic polymerization initiators having a molecular weight of 360 or more include, for example, "CPI-100P" manufactured by San-Apro Co., Ltd. and "IRGACURE 250" manufactured by BASF.

[0169] An example of a cationic polymerization initiator having a molecular weight of less than 360 is triphenylsulfonium bromide.

[0170] (1.3) Gelling agent The ink according to the present invention contains a gelling agent, which improves the pinning ability of the ink on a recording medium, improves the curing property inside the ink coating, and further enhances the effects of the present invention. The ink according to the present invention may contain only one type of gelling agent, or two or more types of gelling agents.

[0171] By including a gelling agent in the ink of the present invention, droplets of ink that have landed on a recording medium can be put into a gel state and temporarily fixed (pinned).

[0172] When the ink is pinned to the recording medium in a gel state, the ink is prevented from spreading on the recording medium, making it difficult for adjacent dots to be identical, allowing for the formation of higher-resolution images.

[0173] Furthermore, when the ink is in a gel state, oxygen from the environment is prevented from entering the ink droplets, making it less likely that oxygen will inhibit curing, allowing high-resolution images to be formed at higher speeds.

[0174] The gelling agent is preferably substantially free of photopolymerizable functional groups, where "substantially free" means that the amount of photopolymerizable functional groups per mole of gelling agent is 0.1 molar equivalents or less.

[0175] By substantially not containing the photopolymerizable functional groups possessed by the gelling agent, it is thought that the functional groups possessed by the gelling agent are less likely to inhibit the polymerization and crosslinking of the photopolymerizable compound, thereby making it possible to sufficiently increase the crosslink density.

[0176] Furthermore, from the following viewpoint, it is preferable that the gelling agent crystallizes in the ink at a temperature equal to or lower than the gelling temperature of the ink: "Gelation temperature" refers to the temperature at which, when ink that has been converted into a sol or liquid by heating is cooled, the gelling agent undergoes a phase transition from sol to gel, causing a sudden change in the viscosity of the ink.

[0177] For example, the viscosity of the solated or liquefied ink can be measured using a viscoelasticity measuring device "MCR300" manufactured by Physica while the ink is cooled, and the temperature at which the viscosity of the ink suddenly increases can be determined as the gelation temperature of the ink.

[0178] When the gelling agent crystallizes in the ink, a structure may be formed in which the photopolymerizable compound is encapsulated in the three-dimensional space formed by the gelling agent crystallized into plates. Hereinafter, such a structure will be referred to as a "house of cards structure."

[0179] When the gelling agent forms a house-of-cards structure, the liquid photopolymerizable compound is retained within the space, making it more difficult for the ink droplets to wet and spread, and improving the ink pinning ability. When the ink pinning ability is improved, ink droplets that land on the recording medium are less likely to coalesce, making it possible to form higher-resolution images.

[0180] To form a house-of-cards structure, it is preferable that the photopolymerizable compound and gelling agent dissolved in the ink are compatible with each other. On the other hand, if the photopolymerizable compound and gelling agent dissolved in the ink are phase-separated, it may be difficult to form a house-of-cards structure.

[0181] Gelling agents suitable for forming a house-of-cards structure by crystallization include, for example, (1) ketone wax, (2) ester wax, (3) petroleum-based wax, (4) vegetable wax, (5) animal wax, (6) mineral wax, (7) modified wax, (8) higher fatty acid, (9) higher alcohol, (10) hydroxystearic acid, (11) fatty acid amide including N-substituted fatty acid amide and special fatty acid amide, (12) higher amine, (13) ester of sucrose fatty acid, (14) synthetic wax, (15) dibenzylidene sorbitol, (16) dimer diol, and other examples include hydrogenated castor oil and dimer acid.

[0182] (1) Examples of ketone waxes include dilignoceryl ketone, dibehenyl ketone, distearyl ketone, and dieicosyl ketone. Further examples include dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristyl palmityl ketone, and palmityl stearyl ketone.

[0183] (2) Examples of ester waxes include behenyl behenate, icosanoic acid ethyl ester, stearyl stearate, palmityl stearate, cetyl palmitate, myristyl myristate, cetyl myristate, and myricyl cerotate. Other examples include stearyl stearate, oleyl palmitate, glycerin fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters, and polyoxyethylene fatty acid esters. Commercially available ester waxes include the EMALEX series manufactured by Nippon Emulsion Co., Ltd. ("EMALEX" is a registered trademark of the company). Other examples include the Rikemal series and Poem series manufactured by Riken Vitamin Co., Ltd. ("Rikemal" and "Poem" are both registered trademarks of the company).

[0184] (3) Examples of petroleum waxes include paraffin wax, microcrystalline wax, and petrolactam.

[0185] (4) Examples of vegetable waxes include candelilla wax, carnauba wax, rice wax, Japan wax, jojoba oil, jojoba solid wax, and jojoba ester.

[0186] (5) Examples of animal waxes include beeswax, lanolin, and whale wax.

[0187] (6) Examples of mineral waxes include montan wax and hydrogenated wax.

[0188] (7) Examples of modified waxes include montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives, 12-hydroxystearic acid derivatives, and polyethylene wax derivatives.

[0189] (8) Examples of higher fatty acids include behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid.

[0190] (9) Examples of higher alcohols include stearyl alcohol and behenyl alcohol.

[0191] (10) Examples of hydroxystearic acids include 12-hydroxystearic acid.

[0192] (11) Examples of 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. Commercially available fatty acid amides include the Nikkaamide series manufactured by Nippon Kasei Chemical Co., Ltd. ("Nikkaamide" is a registered trademark of the company). Other examples include the ITOWAX series manufactured by Ito Oil Mills, and the FATTYAMID series manufactured by Kao Corporation.

[0193] Examples of N-substituted fatty acid amides include N-stearyl stearic acid amide and N-oleyl palmitic acid amide.

[0194] Examples of the special fatty acid amides include N,N'-ethylenebisstearylamide, N,N'-ethylenebis-12-hydroxystearylamide, and N,N'-xylylenebisstearylamide.

[0195] (12) Examples of higher amines include dodecylamine, tetradecylamine, and octadecylamine.

[0196] (13) Examples of sucrose fatty acid esters include sucrose stearic acid, sucrose palmitic acid, etc. 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).

[0197] (14) Examples of synthetic waxes include polyethylene wax and α-olefin maleic anhydride copolymer wax. Examples of commercially available synthetic waxes include the UNILIN series manufactured by Baker-Petrolite (UNILIN is a registered trademark of the company).

[0198] (15) Examples of dibenzylidene sorbitol include 1,3:2,4-bis-O-benzylidene-D-glucitol, etc. Commercially available dibenzylidene sorbitol products include Gelall D manufactured by New Japan Chemical Co., Ltd. ("Gelall" is a registered trademark of the company).

[0199] (16) Commercially available dimer diols include, for example, the PRIPOR series manufactured by CRODA (PRIPOR is a registered trademark of the company).

[0200] Among the gelling agents (1) to (16) above, from the viewpoint of further enhancing the pinning ability, ketone waxes, ester waxes, higher fatty acids, higher alcohols, and fatty acid amides are preferred, and from the viewpoint of enhancing the pinning ability, ketone waxes represented by the following general formula (G1) are more preferred.

[0201] General formula (G1): R1-CO-R2 In general formula (G1), R1 and R2 are both linear or branched hydrocarbon groups having 9 or more and 25 or less carbon atoms.

[0202] From the viewpoint of enhancing pinning properties, ester waxes represented by the following general formula (G2) are also preferred.

[0203] General formula (G2): R3-COO-R4 In general formula (G2), R3 and R4 are both linear or branched hydrocarbon groups having 9 or more and 25 or less carbon atoms.

[0204] The ink may contain only one kind of the ketone wax represented by general formula (G1) and the ester wax represented by general formula (G2), or may contain two or more kinds of them. Furthermore, the ink may contain only one kind of the ketone wax represented by general formula (G1) and the ester wax represented by general formula (G2), or may contain both kinds.

[0205] The ketone wax represented by general formula (G1) and the ester wax represented by general formula (G2) each have a linear or branched hydrocarbon group with 9 or more carbon atoms, which increases the crystallinity of the gelling agent and creates more space in the house-of-card structure. This makes it easier for the photopolymerizable compound to be fully encapsulated in the space, improving the ink's pinning ability. Furthermore, because the linear or branched hydrocarbon group has 25 or fewer carbon atoms, the melting point of the gelling agent does not increase excessively, eliminating the need to excessively heat the ink when ejecting it.

[0206] From the viewpoint of further enhancing the pinning properties of the ink and eliminating the need to excessively heat the ink, it is particularly preferable that R1 and R2 in general formula (G1) are linear hydrocarbon groups having 11 or more but less than 23 carbon atoms.

[0207] Furthermore, from the viewpoint of increasing the gelling temperature of the ink and causing the ink to gel more rapidly after landing, it is preferable that either R1 or R2 in general formula (G1) is a saturated hydrocarbon group having 11 or more but less than 23 carbon atoms.

[0208] Alternatively, either R3 or R4 in general formula (G2) is preferably a saturated hydrocarbon group having 11 or more but less than 23 carbon atoms.

[0209] In view of the above, from the viewpoint of increasing the gelling temperature of the ink and causing the ink to gel more rapidly after landing, it is more preferable that both R1 and R2 in general formula (G1), or both R3 and R4 in general formula (G2), are saturated hydrocarbon groups having 11 or more but less than 23 carbon atoms.

[0210] Examples of the ketone wax represented by general formula (G1) include the following ketone waxes: The number of carbon atoms in the parentheses below indicates the number of carbon atoms in each of the two hydrocarbon groups separated by the carbonyl group.

[0211] 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), lauryl myristyl ketone (carbon number: 11-14), lauryl These include palmityl ketone (carbon number: 11-16), myristyl palmityl ketone (carbon number: 13-16), myristyl stearyl ketone (carbon number: 13-18), myristyl behenyl ketone (carbon number: 13-22), palmityl stearyl ketone (carbon number: 15-18), palmityl behenyl ketone (carbon number: 15-22), and stearyl behenyl ketone (carbon number: 17-22).

[0212] Commercially available ketone waxes represented by general formula (G1) include, for example, "18-Pentatriacontanone" manufactured by Alfa Aeser and "Hentriacontan-16-one" manufactured by Alfa Aeser, as well as "Kaowax T1" manufactured by Kao Corporation.

[0213] Examples of fatty acid or ester waxes represented by general formula (G2) include the following waxes: The number of carbon atoms in the following parentheses indicates the number of carbon atoms in each of the two hydrocarbon groups separated by the ester group.

[0214] Behenyl behenate (carbon number: 21-22), eicosanoic 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), 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).

[0215] Commercially available ester waxes represented by general formula (G2) include, for example, Unistar M-2222SL, Sperm Acetate, and Nissan Elector WEP3 manufactured by NOF Corporation. Other examples include Nissan Elector WEP2 manufactured by NOF Corporation (both "Unistar" and "Nissan Elector" are registered trademarks of the company). Other examples include Exepar SS and Exepar MY-M manufactured by Kao Corporation ("Exepar" is a registered trademark of the company). Other examples include EMALEX CC-18 and EMALEX CC-10 manufactured by Nippon Emulsion Co., Ltd. ("EMALEX" is a registered trademark of the company). Other examples include Amuleps PC manufactured by Kokyu Alcohol Kogyo Co., Ltd. ("Amuleps" is a registered trademark of the company). These commercially available products are often mixtures of two or more types, and may be separated and purified before being incorporated into the ink, as necessary.

[0216] The gelling agent content is preferably within the range of 1.0 to 5.0% by mass relative to the ink. By setting the gelling agent content to 1.0% by mass or more relative to the ink, it is possible to control the wetting and spreading of each ink droplet on the recording medium to the same extent, thereby reducing the occurrence of gloss differences within the image. Furthermore, by setting the gelling agent content to 5.0% by mass or less relative to the ink, it is possible to reduce the occurrence of precipitation of the gelling agent on the surface of the formed image, reducing the occurrence of gloss differences within the image, and also to increase the strength of the cured film and improve scratch resistance.

[0217] From the viewpoint of preventing gloss variations within an image and of eliminating gloss variations within an image and increasing the strength of the cured film and scratch resistance, the content of the gelling agent relative to the ink is more preferably within the range of 2.5 to 5.0% by mass, and even more preferably within the range of 2.5 to 4.0% by mass.

[0218] (1.4) Other ingredients The actinic ray-curable inkjet ink of the present invention may further contain other components including a colorant, a dispersant, a polymerization initiator aid, a polymerization inhibitor, a sensitizer, and a surfactant, as long as the effects of the present invention are obtained. Only one of these components may be contained in the ink, or two or more types may be contained.

[0219] (colorant) Examples of the coloring material include dyes and pigments. From the viewpoint of obtaining an image with good weather resistance, the coloring material is preferably a pigment. The pigment can be selected from, for example, a yellow pigment, a red or magenta pigment, a blue or cyan pigment, a black pigment, etc., depending on the color of the image to be formed.

[0220] Examples of yellow pigments include CI Pigment Yellow (hereinafter, "CI Pigment Yellow" may be 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.

[0221] An example of a red or magenta pigment is CI Pigment Red 3. Hereinafter, "CI Pigment Red" will also be referred to simply as "PR," and for example, "CI Pigment Red 3" will be referred to simply as "PR3." Other examples include 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.

[0222] Other examples include CI Pigment Violet 3. Hereinafter, "CI Pigment Violet" will be simply referred to as "PV", for example, "CI Pigment Violet 3" will be simply referred to as "PV3". Other examples include PV19, PV23, PV29, PV30, PV37, PV50, and PV88.

[0223] Other examples include CI Pigment Orange 13. Hereinafter, "CI Pigment Orange" will be simply referred to as "PO," for example, "CI Pigment Orange 13" will be simply written as "PO13." Other examples include PO16, PO20, and PO36.

[0224] An example of a blue or cyan pigment is CI Pigment Blue 1. Hereinafter, "CI Pigment Blue" will be referred to simply as "PB," and for example, "CI Pigment Blue 1" will be referred to simply as "PB1." Other examples include PB15, PB15:1, PB15:2, PB15:3, PB15:4, PB15:6, PB16, PB17-1, PB22, PB27, PB28, PB29, PB36, and PB60.

[0225] An example of a black pigment is CI Pigment Black 7. Hereinafter, "CI Pigment Black" will be simply referred to as "PBk," and "CI Pigment Black 7" will be simply referred to as "PBk7." Other examples include PBk28 and PBk26.

[0226] From the viewpoint of further improving the storage stability and ejection stability of the ink, the volume average particle size of the pigment is preferably within the range of 0.08 to 0.5 μm. The maximum particle size of the pigment is preferably within the range of 0.3 to 10 μm, and from the viewpoint of further improving the storage stability and ejection stability of the ink, the maximum particle size of the pigment is more preferably within the range of 0.3 to 3 μm.

[0227] The average particle size of pigment particles refers to the value determined by dynamic light scattering using Malvern's Datasizer Nano ZSP. Note that inks containing colorants are highly concentrated, and light does not pass through this measuring device, so the ink is diluted 200 times before measurement. Measurement temperature is room temperature (25°C).

[0228] The pigment content is preferably in the range of 0.1 to 20.0% by mass, more preferably 0.4 to 10.0% by mass, based on the ink. By setting the pigment content to 0.1% by mass or more, the formed image can have sufficient color development. By setting the pigment content to 20.0% by mass or more, the ejection stability of the ink can be further improved.

[0229] (dispersant) Examples of 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, naphthalenesulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate.

[0230] Commercially available dispersants include, for example, BYK-2164, BYK-168, BYK N-22024, BYK JET-9150, and BYK JET-9151 manufactured by BYK-Chemie ("BYK" is a registered trademark of the company). Other examples include EFKA 7701, EFKA 4310, EFKA 4320, and EFKA 4401 manufactured by BASF. Other examples include SOLSPERSE 24000GR and SOLSPERSE 39000 manufactured by Lubrizol ("SOLSPERSE" is a registered trademark of the company). Other examples include Ajisper PB821 and Ajisper PB824 manufactured by Ajinomoto Fine-Techno Co., Ltd. ("Ajisper" is a registered trademark of Ajinomoto Co., Ltd.).

[0231] The content of the dispersant can be, for example, within a range of 20 to 70% by mass relative to the total mass of the pigment. By making the content of the dispersant 20% by mass or more relative to the pigment, the dispersant covers the pigment surface, making it possible to further prevent aggregation of the pigments during storage of the ink. By making the content of the dispersant 70% by mass or less relative to the pigment, association between the dispersant and the gelling agent is further prevented, allowing the ink that has landed on the recording medium to be more fully gelled and pinned.

[0232] (Polymerization initiator aid) Examples of the polymerization initiator aid include tertiary amine compounds including aromatic tertiary amine compounds.

[0233] Examples of aromatic tertiary amine compounds include N,N-dimethylaniline, N,N-diethylaniline, N,N-dimethyl-p-toluidine, N,N-dimethylamino-p-benzoic acid ethyl ester, N,N-dimethylamino-p-benzoic acid isoamyl ethyl ester, N,N-dihydroxyethylaniline, triethylamine, and N,N-dimethylhexylamine.

[0234] (polymerization inhibitor) 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, dibutyl cresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraldoxime, methyl ethyl ketoxime, and cyclohexanone oxime.

[0235] (sensitizer) Examples of the sensitizer include polycyclic aromatic compounds, carbazole derivatives, thioxanthone derivatives, and anthracene derivatives, each having at least one hydroxyl group, an optionally substituted aralkyloxy group, or an alkoxy group as a substituent.

[0236] From the viewpoint of increasing the curing rate, it is preferred that the sensitizer has an ultraviolet spectrum absorption at wavelengths longer than 300 nm.

[0237] (surfactant) Examples of surfactants include anionic surfactants such as dialkyl sulfosuccinates, alkyl naphthalene sulfonates, and fatty acid salts. Other examples include nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, and polyoxyethylene-polyoxypropylene block copolymers. Other examples include cationic surfactants such as alkylamine salts and quaternary ammonium salts. Other examples include silicone-based surfactants and fluorine-based surfactants.

[0238] Commercially available silicone surfactants include, for example, Shin-Etsu Chemical Co., Ltd.'s KF-351A, KF-352A, KF-642, and X-22-4272. Other examples include Big-Chemie's BYK307, BYK345, BYK347, and BYK348 ("BYK" is a registered trademark of the company). Other examples include Toshiba Silicone's TSF4452.

[0239] The content of the surfactant is preferably within the range of 0.001 to 10% by mass.

[0240] (1.5) Ink properties From the viewpoint of improving ejection properties from an inkjet head, the viscosity of the ink of the present invention at 80°C is preferably in the range of 3 mPa·s to 20 mPa·s. Furthermore, from the viewpoint of ensuring that the ink is sufficiently gelled when it lands and is cooled to room temperature, the viscosity of the ink at 25°C is preferably 1000 mPa·s or more.

[0241] The gelling temperature of the inkjet ink is preferably within the range of 40 to 70°C. 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, allowing for more stable ink ejection.

[0242] The viscosity of the ink at 80° C. or 20° C. and the gelling temperature of the ink can be determined by measuring the temperature change in the dynamic viscoelasticity of the ink using a rheometer.

[0243] The ink viscosity and gelation temperature are values ​​obtained by the following method. The inkjet ink is heated to 100°C. While measuring the ink viscosity using a stress-controlled rheometer "Physica MCR301" manufactured by Anton Paar, the ink is cooled to 20°C at a shear rate of 11.7 (1 / s) and a temperature drop rate of 0.1°C / s. This gives a temperature change curve of the ink viscosity. At this time, the diameter of the cone plate of the stress-controlled rheometer "Physica MCR301" is set to 75 mm, and the cone angle is set to 1.0°.

[0244] The ink viscosity at 80°C and the ink viscosity at 25°C are determined by reading the viscosity at 80°C and 25°C on the ink viscosity temperature change curve. The ink gelling temperature is determined as the temperature at which the ink viscosity reaches 200 mPa s on the ink viscosity temperature change curve.

[0245] (1.6) Ink preparation method The actinic energy ray-curable inkjet ink of the present invention can be a mixed liquid obtained by mixing, for example, the above-mentioned polymerization initiator, photopolymerizable compound, and gelling agent with any optional components under heating.

[0246] The mixed liquid obtained as described above is preferably filtered through a predetermined filter. When the ink of the present invention contains a pigment and a dispersant, a pigment dispersion in which the pigment and the dispersant are dispersed in a solvent may be prepared in advance, and the remaining components may be added to this and mixed while heating.

[0247] The pigment and dispersant can be dispersed using, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paint shaker, or the like.

[0248] 2. Image forming method The image forming method of the present invention is an image forming method using the actinic energy ray-curable inkjet ink of the present invention, and is characterized by comprising: a first step of ejecting the actinic energy ray-curable inkjet ink from an inkjet head and causing it to land on a recording medium; and a second step of irradiating the actinic energy ray-curable inkjet ink with actinic energy rays to cure it.

[0249] (2.1) First step In the first step, droplets of the ink of the present invention are ejected from an inkjet head and landed at desired positions on a recording medium.

[0250] Examples of methods for ejecting ink from an inkjet head include an on-demand method and a continuous method.

[0251] Examples of inkjet heads compatible with the on-demand ejection method include the following inkjet heads.

[0252] Electro-mechanical inkjet heads including single cavity type, double cavity type, bender type, piston type, shear mode type, and shared wall type, and thermal inkjet type.

[0253] Other examples include inkjet heads of electrothermal conversion type including bubble jet type (Bubble Jet is a registered trademark of Canon Inc.).

[0254] From the viewpoint of further improving the ejection stability of the ink, it is preferable that the ink droplets are ejected from the inkjet head in a heated state.

[0255] From the above viewpoint, the temperature of the ink when ejected is preferably within the range of 35 to 100°C, and more preferably within the range of 35 to 80°C.

[0256] Furthermore, from the viewpoint of improving ejection stability, it is preferable to perform ejection at an ink temperature that gives an ink viscosity in the range of 7 to 15 mPa·s, more preferably in the range of 8 to 13 mPa·s.

[0257] From the viewpoint of improving the ejection properties of the ink from the inkjet head, it is preferable that the ink of the present invention is heated so that the temperature when filled into the inkjet head is within the range of (gelation temperature + 10) to (gelation temperature + 30)°C of the ink.

[0258] When the temperature of the ink inside the inkjet head is (gelation temperature + 10)°C or higher, the ink is less likely to gel inside the inkjet head or on the nozzle surface, thereby improving ejection stability.When the temperature of the ink inside the inkjet head is (gelation temperature + 30)°C or lower, the ink components are less likely to deteriorate during image formation.

[0259] The method for heating the ink is not particularly limited. For example, it can be a method of heating at least one of the ink supply system including the ink tank, supply pipe, and front chamber ink tank immediately before the head, the piping with filter, the piezo head, etc., to a predetermined temperature. As the heating means, any of a panel heater, a ribbon heater, and warm water can be used.

[0260] From the viewpoint of facilitating faster image formation and further improving image quality, the volume of ink droplets ejected is preferably within the range of 2 to 20 pL.

[0261] (2.2) Second step In the second step, the ink that has landed in the first step is irradiated with active energy rays, and the inkjet ink is cured to form an image.

[0262] The active energy rays are preferably irradiated within a range of 0.001 to 1.0 seconds after the ink lands, and more preferably within a range of 0.001 to 0.5 seconds in order to form a high-definition image.

[0263] Examples of active energy rays include electron beams, ultraviolet rays, α rays, γ rays, and X-rays.

[0264] From the viewpoint of safety and the ability to cure the inkjet ink with a lower amount of energy, the active energy rays are preferably ultraviolet rays or electron beams, and more preferably ultraviolet rays.

[0265] The light source is preferably a light emitting diode (LED). By using an LED as the light source, poor curing of the ink due to melting of the ink caused by radiant heat from the light source is less likely to occur.

[0266] An example of an LED light source that emits ultraviolet light is the "395nm water-cooled LED" manufactured by Phoseon Technology.

[0267] From the viewpoint of sufficiently curing the ink, the LED light source is required to have a peak irradiance of 0.5 to 10 W / cm on the image surface of ultraviolet light having a wavelength in the range of 370 to 410 nm. 2 within the range of 1 to 5 W / cm 2 It is preferable to set it so that it is within the range of

[0268] To prevent radiant heat from reaching the ink, the amount of light irradiated onto the image is set to 350 mJ / cm 2 It is preferable that it is less than 10 ...

[0269] The irradiation of active energy rays may be divided into two stages. First, the ink is pre-cured by irradiating it with active energy rays by the method described above within a range of 0.001 to 2.0 seconds after the ink has landed, and then the ink is fully cured by further irradiating it with active energy rays after all printing has been completed.

[0270] By dividing the irradiation of active energy rays into two stages, shrinkage of the recording material that occurs when the ink hardens is less likely to occur.

[0271] From the viewpoint of more suitably achieving the effects of the present invention, it is preferable to control the surface temperature of the recording medium on the side where the inkjet ink lands to within a range of 20 to 40°C before or simultaneously with the second step.

[0272] In the image forming method using the ink of the present invention, if the total ink film thickness after the ink deposited on a recording medium is irradiated with actinic energy rays and cured is within the range of 2 to 20 μm, the occurrence of curling and wrinkling of the recording medium can be more efficiently suppressed, and changes in the texture of the recording medium can also be more efficiently prevented.

[0273] The term "total ink film thickness" refers to the sum of the film thicknesses of all inks applied or printed on a recording medium. The total ink film thickness can be, for example, the average of the film thicknesses measured at multiple points where a large amount of ink is expected to land.

[0274] (2.3) Recording Media Examples of recording media that can be used in an image forming method using the ink of the present invention include non-absorbent recording media (plastic substrates) made of plastics such as polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, and polybutadiene terephthalate; non-absorbent inorganic recording media such as metal-laminated paper, metal-vapor-deposited paper, metal-laminated plastic film, metal-vapor-deposited plastic film, metals, and glass; and absorbent papers such as coated paper for printing and coated paper for printing.

[0275] When the ink of the present invention is used for package printing, it is preferable to use a recording medium with a relatively thin film thickness, preferably 150 μm or less, more preferably 120 μm or less, even more preferably 90 μm or less, and particularly preferably 50 μm or less. [Example]

[0276] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the examples, the terms "parts" and "%" are used, but unless otherwise specified, they represent "parts by mass" or "% by mass."

[0277] A. Preparation of pigment dispersions to be contained in each ink (A.1) Preparation of Yellow Pigment Dispersion [Y] A mixture of yellow pigment, pigment dispersant, solvent, antifungal agent, and ion-exchanged water in the amounts shown below was premixed. Pigment Yellow 150 (yellow pigment) 40% by mass Joncryl 819 (pigment dispersant) 4% by weight Disperbyk-2019 (pigment dispersant) 4% by weight Propylene glycol (solvent) 20% by mass ·Proxel GXL(S) (antifungal agent) 0.1% by mass Ion-exchanged water (balance: amount that makes the total amount 100% by mass)

[0278] Pigment Yellow 150 is manufactured by LANXESS AG. "Joncryl 819" is an anionic polymer dispersant manufactured by BASF, an acrylic dispersant with carboxyl groups neutralized with dimethylaminoethanol, with an acid value of 75 mg KOH / g and a solids content of 20% by mass. "Disperbyk-2019" is a solvent-free wetting dispersant manufactured by BYK-Chemie. "Proxel GXL(S)" is 1,2-benzisothiazolin-3-one.

[0279] Thereafter, the mixture was dispersed using a bead mill filled with 0.3 mm zirconia beads at a volumetric rate of 50%, to prepare a yellow pigment dispersion [Y] with a pigment content of 20 mass %.

[0280] The average particle size of the pigment particles contained in this pigment dispersion was 250 nm, and the average particle size was measured using a Zetasizer Nano S-90 manufactured by Marballoon Co., Ltd.

[0281] (A.2) Preparation of magenta pigment dispersion [M], cyan pigment dispersion [C], and black pigment dispersion [K] Magenta pigment dispersion [M], cyan pigment dispersion [C], and black pigment dispersion [K], each with a pigment content of 20 mass %, were prepared in the same manner as in the preparation of yellow pigment dispersion [Y], except that the yellow pigment was changed to the pigments listed below. Magenta pigment: Mixed crystal of Pigment Red 122 and Pigment Violet 19 Cyan pigment: Pigment Blue 15 (Tokyo Chemical Industry Co., Ltd.) Black pigment: Pigment Black 7 (Mitsubishi Chemical Corporation)

[0282] The average particle size of the pigment particles contained in these pigment dispersions was 250 nm, and the average particle size was measured using a Zetasizer Nano S-90 manufactured by Marballoon Co., Ltd.

[0283] B. Ink Preparation The product names, properties, and company names of the polymerizable compounds and polymerization initiators used in preparing each ink are shown in Tables I and II below.

[0284] [Table 1]

[0285] [Table 2]

[0286] (B.1) Preparation of Ink [1] (Preparation of Ink [1Y]) The following polymerizable compound, polymerization initiator, gelling agent, pigment dispersion, polymerization inhibitor, and surfactant were mixed in the amounts shown below to prepare ink [1Y]. <Polymerizable compound> Miramer M144 (monofunctional) 12.0% by mass ·EM223 (bifunctional) 17.8% by mass ·Miramer M3130 (trifunctional) 13.8% by mass ·Miramer M3160 (trifunctional) 8.0% by mass ·SR9020 (trifunctional) 23.0% by mass ·ETERCURE6361-100 (trifunctional) 8.0% by mass <Polymerization initiator> Omnirad819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) 3.0% by mass PRO22669 (Thioxanthone-modified triacrylate) 0.5% by mass <Gelling agent> Stearyl stearate 3.5% by mass Behenyl behenate 0.2% by mass <Pigment dispersion> Yellow pigment dispersion [Y] 10.0% by mass <Polymerization inhibitor> ·Irgastab UV-10 0.1% by mass <Surfactant> ·KF352 0.1% by mass

[0287] (Preparation of Inks [1M], [1C], and [1K]) Ink [1M], Ink [1C], and Ink [1K] were prepared in the same manner as Ink [1Y], except that magenta pigment dispersion [M], cyan pigment dispersion [C], and black pigment dispersion [K] were used, respectively, instead of Yellow pigment dispersion [Y]. Hereinafter, Ink [1Y], Ink [1M], Ink [1C], and Ink [1K] will be collectively referred to as Ink [1].

[0288] (B.2) Preparation of inks [2] to

[15] The yellow pigment dispersion [Y], magenta pigment dispersion [M], cyan pigment dispersion [C], and black pigment dispersion [K] were the same as those used in the preparation of ink [1]. Inks [2Y] to [15Y], inks [2M] to [15M], inks [2C] to [15C], and inks [2K] to [15K] were prepared in the same manner as ink [1], except that the polymerizable compound and polymerization initiator were changed as shown in Tables III and IV. Hereinafter, these are collectively referred to as inks [2] to

[15] . For example, ink [2] collectively refers to inks [2Y], [2M], [2C], and [2K]. The values ​​in Tables III, IV, and V represent mass % (the total amount of ink is 100 mass %).

[0289] In Table IV, "Thioxanthone-modified acrylate α" marked with "*1" is a compound synthesized using 2-carboxymethoxythioxanthone, as described in paragraph 0044 of JP-A-2005-512973, and the synthesis method is described below. The product can be analyzed by high-performance liquid chromatography. In addition, "Thioxanthone-modified triacrylate" marked with "*2" is the photopolymerization initiator "PRO22669" manufactured by Sartomer.

[0290] 8.58 g (0.03 mol) of 2-carboxymethoxythioxanthone and 4.82 g of ethoxylated trimethylolpropane (TP70 manufactured by Perstorp) were azeotropically distilled with 200 ml of toluene together with 0.15 g of p-toluenesulfonic acid monohydrate catalyst.

[0291] After 2.5 hours, the cooled solution was filtered and all the solvent was removed by rotary evaporation to obtain thioxanthone-modified acrylate α.

[0292] [Table 3]

[0293] [Table 4]

[0294] [Table 5]

[0295] C. Evaluation (Image formation preparation) Image formation was performed using an image forming apparatus configured as shown in Figure 1. The conveying direction of the recording medium F was direction D in Figure 1, the conveying speed was set to 300 mm / sec, and the recording medium F was made of a PP substrate ("#20 FOR" manufactured by Futamura Chemical Co., Ltd.).

[0296] In FIG. 1, "1" is a take-up roller for taking up the recording medium F. "2" is a delivery roller for delivering the recording medium F. "3" is an active energy ray irradiation device. Y is an inkjet head for filling yellow ink. M is an inkjet head for filling magenta ink. C is an inkjet head for filling cyan ink. Kis an inkjet head for filling black ink.

[0297] For example, ink [1] is composed of ink [1Y], ink [1M], ink [1C], and ink [1K]. In this case, when ink [1] is filled into the inkjet head, H Y is filled with ink [1Y]. M is filled with ink [1M]. C is filled with ink [1C]. K is filled with ink [1K].

[0298] Four independently driven inkjet heads (360 npi, discharge volume 6 pL or 14 pL, 1024 nozzles) manufactured by Konica Minolta, Inc. (JP 2018-202768 A) Y , H M , H C , H K We prepared a scanning printer equipped with

[0299] The inkjet head was filled with inks [1] to

[15] .

[0300] (Formation of evaluation image) An image was formed using an image forming apparatus 10 having the configuration shown in FIG. 1. A PP substrate ("#20 FOR" manufactured by Futamura Chemical Co., Ltd.) was used as the recording medium F, i.e., the substrate. Inks [1] to

[15] were applied from each inkjet head at a coating amount of 13 g / m. 2 A solid image was printed to prepare an image for evaluation.

[0301] Thereafter, each ink was cured by irradiating it with active rays in the active energy ray irradiation device 3, and an image for evaluation corresponding to each ink [1] to

[15] was formed. The active energy ray irradiation conditions were as follows: <Activated energy ray irradiation conditions> ·Wavelength 395nm Accumulated light output: 400mJ / m 2

[0302] (C.1) Internal hardening evaluation (Evaluation method) Glass artificial nails were prepared in advance, and a rubbing test was performed on each evaluation image using the artificial nails. The rubbing test was performed by applying a load of approximately 250 g to the evaluation image, and rubbing the surface of the evaluation image 20 times. The allowable range for the load was ±50 g. The evaluation criteria were as follows:

[0303] (Evaluation criteria) A: No peeling occurs on the surface of the evaluation image. B: The number of times that peeling first occurred on the surface of the evaluation image was 15 or more. C: The number of times that peeling first occurred on the surface of the evaluation image was within the range of 10 to 14 times. D: The number of times that peeling first occurred on the surface of the evaluation image was 9 or less.

[0304] (C.2) Color density (yellowing) evaluation (Evaluation method) For each evaluation image, the image quality of the printed solid image was evaluated using the color difference ΔE as follows: * The evaluation was carried out by determining the change in ab between the initial printing and after the durability test.

[0305] The solid image was measured using a spectrophotometer. * a * b * Expressed in the color system, and ΔE * ab was calculated. * a * b * A "color system" is a useful means of expressing color numerically. * The axis direction indicates brightness, and a * The axis indicates the red-green hue, and b * The axis indicates the hue in the yellow-blue direction. * ab is the L immediately after forming the evaluation image * a * b *The values ​​are (L1, a1, b1), and the L * a * b * When the values ​​are (L2, a2, b2), the value was calculated by substituting each value into the following formula.

[0306] ΔE = [(L1 - L2) 2 +(a1-a2) 2 +(b1-b2) 2 〕 0.5

[0307] L * , a * , and b * The measurements were performed using a spectrophotometer "Gretag Macbeth Spectrolino" (manufactured by Gretag Macbeth). A D65 light source was used, a Φ4mm aperture was used for the reflectance measurement, and the measurement wavelength range was 380-730nm at 10nm intervals, with a viewing angle of 2°. Measurements were performed using a dedicated white tile for reference alignment.

[0308] The evaluation criteria for density unevenness were as follows: In the evaluation criteria below, A and B were considered to be acceptable for practical use and were rated as passing, and C was considered to be failing.

[0309] (Evaluation criteria) A: The color difference (ΔE) is less than 0.2. B: The color difference (ΔE) is within the range of 0.2 to 0.5. C: The color difference (ΔE) is within the range of 0.5 to 1.0. D: Color difference (ΔE) is greater than 1.0.

[0310] [Table 6]

[0311] (C.3) Overall evaluation As is clear from Table V, the Examples are superior to the Comparative Examples.

[0312] While embodiments of the present invention have been described and illustrated in detail above, the disclosed embodiments are made for purposes of illustration and example only, and not limitation, and the scope of the invention should be construed in terms of the appended claims. [Explanation of symbols]

[0313] 1 Winding roller 2 Feed roller 3. Active energy ray irradiation equipment 10 Image forming device D Recording medium transport direction F. Recording Media H Y , H M , H C , H K Inkjet head

Claims

1. An actinic ray-curable inkjet ink containing a polymerizable compound, a polymerization initiator, and a gelling agent, The polymerizable compound contains at least one trifunctional monomer, The content of the trifunctional monomer is more than 20% by mass, The polymerization initiator contains at least a thioxanthone-modified acrylate.

1. An actinic ray-curable inkjet ink comprising:

2. The polymerizable compound contains at least one monofunctional monomer.

2. The actinic ray-curable inkjet ink according to claim 1.

3. The content of the monofunctional monomer is 10.0% by mass or more.

3. The actinic ray-curable ink-jet ink according to claim 2.

4. The content of the polymerization initiator is in the range of 0.1 to 15.0% by mass.

2. The actinic ray-curable inkjet ink according to claim 1.

5. The molecular weight of the thioxanthone-modified acrylate is 360 or more.

2. The actinic ray-curable inkjet ink according to claim 1.

6. The thioxanthone-modified acrylate is a thioxanthone-modified triacrylate.

2. The actinic ray-curable ink-jet ink according to claim 1.

7. The content of the thioxanthone-modified triacrylate is within the range of 0.1 to 5.0% by mass.

7. The actinic ray-curable ink-jet ink according to claim 6.

8. 10. An image forming method using the actinic ray-curable inkjet ink according to claim 1, The method includes a first step of ejecting the actinic energy ray-curable inkjet ink from an inkjet head and causing it to land on a recording medium, and a second step of curing the actinic energy ray-curable inkjet ink by irradiating it with actinic energy rays. An image forming method comprising:

Images