Active ray curable inkjet ink

Abstract

To provide an active ray curable inkjet ink that can inhibit gloss unevenness caused by precipitation of a gelling agent on the surface of an image after the ink lands on a base material.SOLUTION: An active ray curable inkjet ink includes an active ray polymerizable compound, a photopolymerization initiator, and a polymer compound, the active ray curable inkjet ink further including a gelling agent, where the polymer compound has a tolylene diisocyanate structure.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an actinic ray-curable inkjet ink, and more particularly to an actinic ray-curable inkjet ink that can suppress the occurrence of uneven gloss caused by precipitation of a gelling agent on the surface of an image after the ink has landed on a substrate, and that has excellent image definition. [Background technology]

[0002] Inkjet image forming methods are used in various printing fields because they can form images easily and inexpensively. One of the inkjet image forming methods is an actinic ray curable inkjet image forming method in which droplets of an actinic ray curable inkjet ink are deposited on a recording medium, and then the droplets are irradiated with actinic rays to cure the droplets, thereby forming an image. An actinic ray curable ink jet image forming method has been attracting attention in recent years because it is capable of forming images having high abrasion resistance and adhesion even on a recording medium that does not absorb ink. As an actinic ray curable ink used in such an image forming method, a technique described in Patent Document 1 is disclosed.

[0003] However, the ink described in Patent Document 1 does not contain a gelling agent, and therefore when the ink lands on a substrate, the ink dots wet and spread, resulting in a problem of poor image definition. Therefore, actinic radiation curable inks containing a gelling agent are generally used, however, images formed using actinic radiation curable inkjet inks containing a gelling agent may suffer from uneven gloss (blooming) due to precipitation of the gelling agent on the image surface. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-181163 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in consideration of the above problems and circumstances. An object of the present invention is to provide an actinic radiation-curable inkjet ink that can suppress the occurrence of uneven gloss caused by precipitation of a gelling agent on the surface of an image after the ink has landed on a substrate, and that has excellent image definition. [Means for solving the problem]

[0006] In order to solve the above problems, the present inventors have investigated the causes of the above problems. As a result, they have found that by incorporating a gelling agent and a polymeric compound having a tolylene diisocyanate structure into an actinic radiation curable inkjet ink, it is possible to prevent the gelling agent from precipitating on the image surface. Furthermore, by incorporating a gelling agent, the image definition is also excellent. That is, the above-mentioned problems of the present invention are solved by the following means.

[0007] 1. An actinic radiation curable inkjet ink containing an actinic radiation polymerizable compound, a photopolymerization initiator, and a polymer compound, Further comprising a gelling agent, The polymer compound has a tolylene diisocyanate structure. 1. An actinic ray curable inkjet ink comprising:

[0008] 2. The polymer compound has an ε-caprolactam structure. 2. The actinic ray curable ink-jet ink according to claim 1,

[0009] 3. The content of the polymer compound is more than 0% by mass and 5% by mass or less. 2. The actinic ray curable ink-jet ink according to claim 1,

[0010] 4. The weight average molecular weight Mw of the polymer compound is within the range of 5,000 to 15,000. 2. The actinic ray curable ink-jet ink according to claim 1,

[0011] 5. The number average molecular weight Mn of the polymer compound is within the range of 5,000 to 10,000. 2. The actinic ray curable ink-jet ink according to claim 1,

[0012] 6. Contains pigments 2. The actinic ray curable ink-jet ink according to claim 1,

[0013] 7. The gelling agent contains an aliphatic ketone compound or an aliphatic ester compound. 2. The actinic ray curable ink-jet ink according to claim 1, Effect of the Invention

[0014]

[0023] The above-described means of the present invention can provide an actinic ray-curable inkjet ink that can suppress the occurrence of uneven gloss caused by precipitation of a gelling agent on the surface of an image after the ink has landed on a substrate, and that has excellent image definition. Although the mechanism by which the effects of the present invention are manifested or the mechanism by which the effects of the present invention are acted upon has not been clearly understood, it is speculated as follows. In the following description, the "actinic radiation curable inkjet ink" will also be referred to simply as "ink." The ink of the present invention contains a gelling agent in addition to an actinic radiation polymerizable compound, a photopolymerization initiator, and a polymer compound, and the polymer compound has a tolylene diisocyanate structure. This increases the compatibility between the polymer compound having a tolylene diisocyanate structure and the gelling agent. Therefore, after the ink lands on the substrate, the gelling agent can be prevented from precipitating on the image surface. As a result, gloss unevenness (blooming) can be reduced, and an image with excellent quality can be obtained. Furthermore, since the ink contains a gelling agent, when the ink lands on a substrate, the ink dots do not wet and spread, resulting in excellent image definition. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a main part of an inkjet recording device using a line recording method. [Diagram 2] FIG. 1 is a diagram showing an example of the configuration of a main part of an inkjet printing apparatus using a serial printing method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The actinic ray curable inkjet ink of the present invention is an actinic ray curable inkjet ink containing an actinic ray polymerizable compound, a photopolymerization initiator, and a polymer compound, and is characterized in that it further contains a gelling agent, and the polymer compound has a tolylene diisocyanate structure. This feature is a technical feature common to or corresponding to each of the following embodiments.

[0017] In one embodiment of the present invention, the polymer compound is preferably a polymer compound having an ε-caprolactam structure, in that it has excellent compatibility with the gelling agent.

[0018] The content of the polymer compound is preferably more than 0% by mass and 5% by mass or less in terms of excellent compatibility with the gelling agent.

[0019] It is preferable that the weight average molecular weight Mw of the polymer compound is within the range of 5,000 to 15,000, in order to improve the dispersion of the polymer dispersant when preparing the ink.

[0020] It is preferable that the number average molecular weight Mn of the polymer compound is within the range of 5,000 to 10,000, in order to improve the dispersion of the polymer dispersant when preparing the ink.

[0021] It is preferable for the ink to contain a pigment in order to stabilize the storage stability of the ink.

[0022] It is preferable that the gelling agent contains an aliphatic ketone compound or an aliphatic ester compound in that high-definition images can be obtained.

[0023] The present invention, its components, and embodiments for carrying out the present invention will be described below. In this application, the symbol "to" is used to mean that the numerical values ​​before and after the symbol "to" are included as lower and upper limits.

[0024] [Outline of the actinic radiation curable inkjet ink of the present invention] The actinic ray curable inkjet ink of the present invention is an actinic ray curable inkjet ink containing an actinic ray polymerizable compound, a photopolymerization initiator, and a polymer compound, and is characterized in that it further contains a gelling agent, and the polymer compound has a tolylene diisocyanate structure.

[0025] The ink of the present invention is an ink that can be cured by actinic radiation. To be precise, "active rays" are also called "active energy rays." Moreover, active rays are light rays that can impart energy to generate reaction initiating species in ink by irradiation, and include X-rays, ultraviolet rays, and the like. Among them, ultraviolet rays are more preferable from the viewpoints of curing sensitivity and ease of availability of equipment.

[0026] [Ink composition] <Gelling agent> The ink of the present invention contains a gelling agent. The gelling agent imparts a function of causing the ink to undergo a reversible sol-gel phase transition depending on temperature. Such a gelling agent must at least 1) dissolve in the actinic radiation polymerizable compound at a temperature higher than the gelling temperature, and 2) crystallize in the ink at a temperature equal to or lower than the gelling temperature.

[0027] When the gelling agent crystallizes in the ink, it is preferable that the plate-like crystals, which are the crystallized product of the gelling agent, form a space surrounded three-dimensionally and encapsulate the actinic radiation curable compound in the space. Such a structure in which the actinic radiation curable compound is encapsulated in a space surrounded three-dimensionally by the plate-like crystals is sometimes called a "house of cards structure." When the house of cards structure is formed, the liquid actinic radiation curable compound can be held and the ink droplets can be pinned, thereby preventing the droplets from coalescing. In order to form the house of cards structure, it is preferable that the actinic radiation polymerizable compound and the gelling agent dissolved in the ink are compatible. On the other hand, if the actinic radiation polymerizable compound and the gelling agent dissolved in the ink are phase-separated, it may be difficult to form the house of cards structure.

[0028] In order to stably eject ink droplets from an inkjet recording device, it is necessary that the compatibility between the actinic radiation polymerizable compound and the gelling agent is good in the sol-like ink (at high temperature). Furthermore, in order to stably prevent droplets from coalescing even during high-speed printing, it is necessary that the gelling agent crystallizes quickly after the ink droplets land on the recording medium and form a strong house-of-cards structure.

[0029] As such a gelling agent, an aliphatic ketone compound or an aliphatic ester compound is preferably contained. The gelling agent, which is an aliphatic ketone compound, is a compound represented by the following general formula (G1). General formula (G1): R1-CO-R2

[0030] In general formula (G1), R1 and R2 each independently represent an alkyl group containing a straight chain portion having 9 to 25 carbon atoms. The alkyl group may be an alkyl group having an unsaturated group as a substituent, but from the viewpoint of increasing the gelation temperature, it is preferably an alkyl group having no unsaturated group. When the numbers of carbon atoms in the alkyl groups of R1 and R2 are approximately the same, the melting point of a compound in which R1 and R2 are saturated alkyl groups is often higher than the melting point of a compound in which R1 and R2 are alkyl groups having unsaturated groups, and the gelation temperature is also likely to be higher. The alkyl group may be a straight-chain alkyl group, a branched alkyl group, or a cyclic alkyl group, but in order to obtain high crystallinity, a straight-chain alkyl group is preferred.

[0031] When the number of carbon atoms in the linear portion of the alkyl group is 9 to 25, the above-mentioned house of cards structure can be formed while having the crystallinity required for a gelling agent. In addition, the melting point is not too high, and the alkyl ketone compound dissolves in the ink without raising the ink ejection temperature. The number of carbon atoms in the linear portion of the alkyl group of R1 and R2 is preferably 11 or more and less than 23. Therefore, it is particularly preferable that R1 and R2 are linear alkyl groups having 11 or more and less than 23 carbon atoms.

[0032] Examples of alkyl groups containing a straight-chain portion having 9 to 25 carbon atoms include docosanyl group (C22), henicosanyl group (C21), icosanyl group (C20), and octadecanyl group (stearyl group). Examples of alkyl groups containing a straight-chain portion having 9 to 25 carbon atoms include C18), heptadecanyl group (C17), hexadecanyl group (palmityl group, C16), and pentadecanyl group (C15). Examples of alkyl groups containing a straight-chain portion having 9 to 25 carbon atoms include tetradecanyl group (myristyl group, C14), tridecanyl group (C13), dodecanyl group (lauryl group, C12), undecanyl group (C11), and decanyl group (C10).

[0033] Examples of the compound represented by the general formula (G1) include dibehenyl ketone (C22-C22), distearyl ketone (19-heptatriacontanone, C18-C18), dipalmityl ketone (C16-C16), dilauryl ketone (C12-C12), 25-nonatetracontanone (C24-C24), dihenicosanyl ketone (22-tritetracontanone, C25-C25-C25), and 25-triphenylphosphine ketone (C25-C25). Contanone, C21-C21, melting point 88°C), diheptadecyl ketone (18-pentatriacontanone, C17-C17, melting point 84°C), 21-hentriacontanone (C20-C20), dipentadecyl ketone (16-hentriacontanone, C15-C15, melting point 80°C), 14-heptacosanone (C13-C13), diundecyl ketone 12-tricosanone (C11-C11, melting point 68°C), 11-hencosanone (C10-C10), 13-heptacosanone (C12-C14), 13-nonacosanone (C12-C16), 13-hentriacontanone (C12-C18), 13-pentatriacontanone (C12-C22), 15-hentriacontanone (C14-C1 6), 15-propatriacontanone (C14-C18), 15-heptatriacontanone (C14-C22), 17-heptatriacontanone (C16-C18), 17-nonatriacontanone (C16-C22), 19-hentetracontanone (C18-C22), preferably diheptadecyl ketone (C17-C17).

[0034] Examples of commercially available products of the compound represented by general formula (G1) include 18-Pentatriacontanone (manufactured by Alfa Aeser), Hentriacontan-16-one (manufactured by Alfa Aeser), Kaowax T1 (manufactured by Kao Corporation), etc. Since these commercially available products are often mixtures of two or more types, they may be separated and purified before use, if necessary.

[0035] The aliphatic ketone compound may be one type of compound represented by general formula (G1), or may be a mixture of two or more types of compounds represented by general formula (G1).

[0036] The gelling agent, which is an aliphatic ester compound, is a compound represented by the following general formula (G2). General formula (G2): R3-COO-R4

[0037] In general formula (G2), R3 and R4 are each independently an alkyl group containing a straight chain portion having a carbon number of 9 to 26. The alkyl group may be a saturated or unsaturated alkyl group, but is preferably a saturated alkyl group. The alkyl group may be a linear alkyl group, a branched alkyl group, or a cyclic alkyl group, but in order to obtain high crystallinity, a linear alkyl group is preferable.

[0038] When the linear portion contained in the alkyl groups of R3 and R4 has 9 to 26 carbon atoms, like the compound represented by general formula (G1), the above-mentioned house-of-cards structure can be formed while having the crystallinity required for a gelling agent, and the melting point is not too high. In order to enhance the crystallinity of the compound represented by general formula (G2), it is preferable that the number of carbon atoms in the linear portion contained in the alkyl group of R3 is 11 or more and less than 23, and the number of carbon atoms in the linear portion contained in the alkyl group of R4 is 12 or more and less than 24. Therefore, it is particularly preferable that R3 is a linear alkyl group having 11 or more and less than 23 carbon atoms, and R4 is a linear alkyl group having 12 or more and less than 24 carbon atoms.

[0039] Examples of the alkyl group containing a straight-chain portion having 9 to 26 carbon atoms include the same alkyl groups as those in the above general formula (G1) containing a straight-chain portion having 9 to 25 carbon atoms.

[0040] Examples of the compound represented by the general formula (G2) include behenyl behenate (C21-C22, melting point 70°C), icosanoic acid icosyl (C19-C20), stearyl stearate (C17-C18, melting point 60°C), palmityl stearate (C17-C16), lauryl stearate (C17-C12), palmityl palmitate (cetyl palmitate C15-C16, melting point 54°C), stearyl palmitate (C15-C18), myristyl myristate ( C13-C14, melting point 43°C), cetyl myristate (C13-C16, melting point 50°C), octyldodecyl myristate (C13-C20), lauryl laurate (C11-C12, melting point 30°C), cetyl caprate (C9-C16, melting point 30°C), stearyl oleate (C17-C18), stearyl erucate (C21-C18), stearyl linoleate (C17-C18), isostearyl palmitate (C15-C18), etc.

[0041] Examples of commercially available products of the compound represented by general formula (G2) include Unistar M-2222SL (manufactured by NOF Corporation), Exepar SS (manufactured by Kao Corporation, melting point 60°C), and EMALEX CC-18 (manufactured by Nippon Emulsion Co., Ltd.). Examples of the commercially available products include Amureps PC (manufactured by Kokyu Alcohol Kogyo Co., Ltd.), Exepar MY-M (manufactured by Kao Corporation), Sperm Acetate (manufactured by NOF Corporation), and EMALEX CC-10 (manufactured by Nippon Emulsion Co., Ltd.). These commercially available products are often mixtures of two or more types, and may be separated and purified before use, if necessary.

[0042] The aliphatic ester compound may be one type of compound represented by general formula (G2), or may be a mixture of two types of compounds represented by general formula (G2).

[0043] The melting points of all the compounds in the aliphatic ketone compound group contained in the ink are preferably equal to or lower than 100° C. In order to improve the pinning properties of the ink, the melting points are more preferably within the range of 60 to 100° C. On the other hand, it is preferable that the melting points of all the compounds in the aliphatic ester compound group contained in the ink are not higher than 100° C. In order to improve the ejection properties of the ink, the melting points are preferably within the range of 30 to 75° C.

[0044] As the gelling agent contained in the actinic ray-curable inkjet ink, the aliphatic ketone compound or the aliphatic ester compound may be used alone or in combination of two or more kinds.

[0045] The total amount of the aliphatic ketone compound represented by general formula (G1) and the aliphatic ester compound represented by general formula (G2) is preferably 0.5% by mass or more and less than 10% by mass with respect to the total mass of the ink, and more preferably 1% by mass or more and less than 7% by mass. When the total amount is 0.5% by mass or more, the ink is easily gelled (sol-gel phase transition due to temperature), whereas when the total amount is less than 10% by mass, the aliphatic ketone compound and the aliphatic ester compound can be sufficiently dissolved in the ink, improving the ejection properties of the ink.

[0046] The ink of the present invention may further contain other gelling agents as necessary. Examples of other gelling agents include polymeric compounds and low molecular weight compounds, and low molecular weight compounds are preferred in order to improve the ejection properties of the ink.

[0047] Examples of polymeric compound gelling agents include fatty acid inulins such as inulin stearate; fatty acid dextrins such as dextrin palmitate and dextrin myristate (e.g., the Leopearl series manufactured by Chiba Flour Milling Co., Ltd.); glyceryl docosanoate eicosandioate, eicosane polyglyceryl docosanoate, etc. (e.g., the Nomcoat series manufactured by Nisshin Oillio Co., Ltd.).

[0048] Examples of low molecular weight gelling agents include: an aliphatic ketone compound other than the compound represented by the above general formula (G1); Aliphatic ester compounds other than the compounds represented by the above general formula (G2); Low molecular weight oil gelling agents described in JP2005-126507A, JP2005-255821A, and JP2010-111790A; Amide compounds such as N-lauroyl-L-glutamic acid dibutylamide and N-(2-ethylhexanoyl)-L-glutamic acid dibutylamide (available from Ajinomoto Fine-Techno); Dibenzylidene sorbitols such as 1,3:2,4-bis-O-benzylidene-D-glucitol (Gelol D available from Shin Nippon Rika); Petroleum-based waxes such as paraffin wax, microcrystalline wax, and petrolactam; vegetable waxes such as candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax, and jojoba ester; animal waxes such as beeswax, lanolin, and spermaceti; mineral waxes such as montan wax and hydrogenated wax; hydrogenated castor oil or hydrogenated castor oil derivatives; modified waxes such as montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives, and polyethylene wax derivatives; higher fatty acids such as docosanoic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid; higher alcohols such as stearyl alcohol and behenyl alcohol; Hydroxystearic acids, such as 12-hydroxystearic acid; 12-Hydroxystearic acid derivatives; Fatty acid amides such as lauric acid amide, stearic acid amide, docosanoic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, and 12-hydroxystearic acid amide (for example, the Nikkaamide series manufactured by Nippon Kasei Co., Ltd., the ITOWAX series manufactured by Ito Oil Mills Co., Ltd., and the FATTYAMID series manufactured by Kao Corporation); N-substituted fatty acid amides such as N-stearyl stearic acid amide and N-oleyl palmitic acid amide; Special fatty acid amides such as N,N'-ethylenebisstearylamide, N,N'-ethylenebis12-hydroxystearylamide, and N,N'-xylylenebisstearylamide; Higher amines such as dodecylamine, tetradecylamine or octadecylamine; Fatty acid ester compounds such as stearyl stearic acid, oleyl palmitic acid, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, ethylene glycol fatty acid ester, polyoxyethylene fatty acid ester (for example, the EMALLEX series manufactured by Nippon Emulsion Co., Ltd., the Rikemal series manufactured by Riken Vitamin Co., Ltd., the Poem series manufactured by Riken Vitamin Co., Ltd., etc.); Sucrose fatty acid esters such as sucrose stearate and sucrose palmitate (e.g., Ryoto Sugar Ester Series, manufactured by Mitsubishi Chemical Foods Corporation); Synthetic waxes such as polyethylene wax and α-olefin maleic anhydride copolymer wax; polymerizable waxes (Baker-Petrolite's UNILIN series, etc.); Dimer acids; dimer diols (CRODA PRIPOR series, etc.); and the like. These gelling agents may be used alone or in combination of two or more kinds.

[0049] <Polymer compounds> The polymer compound according to the present invention has a tolylene diisocyanate structure. When the polymer compound has a tolylene diisocyanate structure, the structure acts as a steric hindrance, making it possible to suppress shrinkage during polymerization. In addition, the tolylene diisocyanate structure has high compatibility with gelling agents, so that the gelling agent can be prevented from precipitating on the image surface after the ink lands on the substrate, resulting in reduced gloss unevenness (blooming) and high-quality images. The tolylene diisocyanate structure is, for example, the structure of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate shown below.

[0050] [ka]

[0051] Moreover, the polymer compound preferably further has the following ε-caprolactam structure.

[0052] [ka]

[0053] The weight average molecular weight (Mw) of the polymer compound is preferably within the range of 5,000 to 15,000. The number average molecular weight (Mn) of the polymer compound is preferably within the range of 5,000 to 10,000.

[0054] The weight average molecular weight and number average molecular weight of the polymer compound can be measured in terms of polystyrene by gel permeation chromatography (GPC). Specifically, a GPC device HLC-8120GPC (manufactured by Tosoh Corporation) and a column TSKguardcolumn+TSKgelSuperHZ-m triple column (manufactured by Tosoh Corporation) are used. Then, tetrahydrofuran is run as a carrier solvent at a flow rate of 0.2 mL / min while the column temperature is maintained at 40°C. Then, 10 μL of the prepared sample solution is injected into the GPC device together with the carrier solvent. The sample is detected using a refractive index detector (RI detector), and the molecular weight distribution of the sample is calculated using a calibration curve measured using monodisperse polystyrene standard particles.

[0055] Preferred examples of the polymer compound according to the present invention include the following polymer compounds A to E. In the structures of the following polymer compounds A to E, n is preferably an integer of 10 to 50.

[0056] [ka]

[0057] A preferred commercially available product of the polymer compound is, for example, DISPERBYK-168 (manufactured by BYK Japan KK).

[0058] The content of the polymer compound in the ink is preferably more than 0% by mass and 5% by mass or less based on the total mass of the ink of the present invention. The polymer compound is preferably used as a dispersant for improving the dispersibility of the pigment, which will be described later, when preparing a pigment dispersion liquid.

[0059] <Active radiation polymerizable compound> The actinic radiation polymerizable compound is a polymerizable compound that is crosslinked or polymerized by irradiation with actinic radiation. As described above, the actinic radiation is preferably ultraviolet light. The photopolymerizable compound is a radically polymerizable compound or a cationic polymerizable compound, and is preferably a radically polymerizable compound.

[0060] The radical polymerizable compound is a compound (monomer, oligomer, polymer, or a mixture thereof) having an ethylenically unsaturated bond capable of radical polymerization. The radical polymerizable compound may be used alone or in combination of two or more kinds.

[0061] Examples of the compound having a radically polymerizable ethylenically unsaturated bond include unsaturated carboxylic acids and their salts, unsaturated carboxylic acid ester compounds, unsaturated carboxylic acid urethane compounds, unsaturated carboxylic acid amide compounds and their anhydrides. Examples of the compound having an ethylenically unsaturated bond include acrylonitrile, styrene, unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, unsaturated urethanes, etc. Examples of the unsaturated carboxylic acids include (meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, etc.

[0062] In particular, the radical polymerizable compound is preferably an unsaturated carboxylic acid ester compound, more preferably a (meth)acrylate compound. The (meth)acrylate compound may be not only a monomer described below, but also an oligomer, a mixture of a monomer and an oligomer, a modified product, an oligomer having a polymerizable functional group, or the like.

[0063] Examples of (meth)acrylate compounds include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomylstyryl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene monofunctional monomers such as ethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalate, and t-butylcyclohexyl (meth)acrylate; Bifunctional monomers such as triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, PO adduct di(meth)acrylate of bisphenol A, hydroxypivalic acid neopentyl glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate; Examples of polyfunctional monomers having three or more functional groups include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxy tri(meth)acrylate, and pentaerythritol ethoxy tetra(meth)acrylate.

[0064] The (meth)acrylate compound may be a modified product, and examples thereof include ethylene oxide-modified (meth)acrylate compounds such as ethylene oxide-modified trimethylolpropane tri(meth)acrylate and ethylene oxide-modified pentaerythritol tetraacrylate; caprolactone-modified (meth)acrylate compounds such as caprolactone-modified trimethylolpropane tri(meth)acrylate; and caprolactam-modified (meth)acrylate compounds such as caprolactam-modified dipentaerythritol hexa(meth)acrylate. Among these, ethylene oxide-modified (meth)acrylate compounds are preferred from the viewpoints of high photosensitivity, ease of formation of a card house structure described below when gelling at low temperatures, etc. Furthermore, ethylene oxide-modified (meth)acrylate compounds are easily soluble in other ink components at high temperatures and suffer little shrinkage upon curing, so that curling of printed matter is unlikely to occur.

[0065] Examples of ethylene oxide modified (meth)acrylate compounds include 4EO modified hexanediol diacrylate CD561 (molecular weight 358), 3EO modified trimethylolpropane triacrylate SR454 (molecular weight 429), 6EO modified trimethylolpropane triacrylate SR499 (molecular weight 560), and 4EO modified pentaerythritol tetraacrylate SR494 (molecular weight 528), all manufactured by Sartomer; polyethylene glycol diacrylate NK ester A-400 (molecular weight 508), polyethylene glycol diacrylate NK ester A-600 (molecular weight 742), polyethylene glycol dimethacrylate NK ester 9G (molecular weight 536), and polyethylene glycol dimethacrylate NK ester 14G (molecular weight 770), all manufactured by Shin-Nakamura Chemical; tetraethylene glycol diacrylate V#335HP (molecular weight 302), all manufactured by Osaka Organic Chemical; and 3PO modified trimethylolpropane triacrylate Photomer (molecular weight 302), all manufactured by Cognis. 4072 (molecular weight 471, ClogP 4.90); 1,10-decanediol dimethacrylate NK ester DOD-N (molecular weight 310, ClogP 5.75), tricyclodecane dimethanol diacrylate NK ester A-DCP (molecular weight 304, ClogP 4.69) and tricyclodecane dimethanol dimethacrylate NK ester DCP (molecular weight 332, ClogP 5.12) manufactured by Shin-Nakamura Chemical Co., Ltd.; trimethylolpropane PO modified triacrylate Miramer M360 (molecular weight 471, ClogP 4.90) manufactured by Miwon Co., Ltd.

[0066] The (meth)acrylate compound may be a polymerizable oligomer. Examples of the polymerizable oligomer include epoxy (meth)acrylate oligomer, aliphatic urethane (meth)acrylate oligomer, and aromatic urethane (meth)acrylate oligomer. Examples of the polymerizable oligomer include polyester (meth)acrylate oligomer, and linear (meth)acrylic oligomer.

[0067] The cationically polymerizable compound may be an epoxy compound, a vinyl ether compound, an oxetane compound, etc. The cationically polymerizable compound may be used alone or in combination of two or more kinds.

[0068] The epoxy compound may be an aromatic epoxide, an alicyclic epoxide, or an aliphatic epoxide, and in order to enhance curability, aromatic epoxides and alicyclic epoxides are preferred.

[0069] The aromatic epoxide may be a di- or polyglycidyl ether obtained by reacting a polyhydric phenol or its alkylene oxide adduct with epichlorohydrin. Examples of polyhydric phenols or their alkylene oxide adducts to be reacted include bisphenol A or its alkylene oxide adducts, etc. The alkylene oxide in the alkylene oxide adduct may be ethylene oxide, propylene oxide, etc.

[0070] The alicyclic epoxide may be a cycloalkane oxide-containing compound obtained by epoxidizing a cycloalkane-containing compound with an oxidizing agent such as hydrogen peroxide or a peracid, etc. The cycloalkane in the cycloalkane oxide-containing compound may be cyclohexene or cyclopentene.

[0071] The aliphatic epoxide may be a di- or polyglycidyl ether obtained by reacting an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof with epichlorohydrin. Examples of the aliphatic polyhydric alcohol include alkylene glycols such as ethylene glycol, propylene glycol, 1,6-hexanediol, etc. The alkylene oxide in the alkylene oxide adduct may be ethylene oxide, propylene oxide, etc.

[0072] Examples of vinyl ether compounds include monovinyl ether compounds such as ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, isopropenyl ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether; Examples of the vinyl ether compounds include di- or trivinyl ether compounds such as ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, and trimethylolpropane trivinyl ether. Among these vinyl ether compounds, di- or trivinyl ether compounds are preferred in consideration of curability, adhesion, and the like.

[0073] The oxetane compound is a compound having an oxetane ring. Examples of the oxetane compound include the oxetane compounds described in JP-A-2001-220526, JP-A-2001-310937, and JP-A-2005-255821. Among these, there may be mentioned a compound represented by general formula (1) described in paragraph number 0089 of JP-A No. 2005-255821, and a compound represented by general formula (2) described in paragraph number 0092 of the same publication. Further examples include a compound represented by general formula (7) in paragraph number 0107 of JP-A No. 2005-255821, a compound represented by general formula (8) in paragraph number 0109, and a compound represented by general formula (9) in paragraph number 0116. General formulae (1), (2), and (7) to (9) described in JP-A-2005-255821 are shown below.

[0074] [ka]

[0075] The content of the actinic radiation polymerizable compound contained in the ink of the present invention is preferably within a range from 1 to 97% by mass, and more preferably within a range from 30 to 95% by mass, based on the total mass of the ink.

[0076] <Photopolymerization initiator> The ink of the present invention contains a photopolymerization initiator. Photopolymerization initiators include intramolecular bond cleavage type initiators and intramolecular hydrogen abstraction type initiators. Examples of the intramolecular bond cleavage type photopolymerization initiator include acetophenones such as diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone; benzoins such as benzoin, benzoin methyl ether, and benzoin isopropyl ether; acylphosphine oxides such as 2,4,6-trimethylbenzoin diphenylphosphine oxide; and benzyl and methylphenyl glyoxyesters.

[0077] Examples of the intramolecular hydrogen abstraction type photopolymerization initiator include benzophenone-based initiators such as benzophenone, o-benzoylmethylbenzoate-4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acrylated benzophenone, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone; thioxanthone-based initiators such as 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone; aminobenzophenone-based initiators such as Michler's ketone and 4,4'-diethylaminobenzophenone; 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, and camphorquinone.

[0078] When the photopolymerization initiator is an acylphosphine oxide or an acylphosphonate, the sensitivity is improved. Specifically, the photopolymerization initiator is preferably bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, or the like.

[0079] The content of the photopolymerization initiator in the ink of the present invention depends on the type of light irradiated during ink curing and the type of photopolymerizable compound, but is preferably within the range of 0.1 to 10% by mass.

[0080] The photopolymerization initiator in the ink of the present invention may contain a photoacid generator. Examples of photoacid generators include compounds used in chemically amplified photoresists and photocationic polymerization. For such compounds, it is preferable to refer to, for example, Organic Electronics Materials Research Group (ed.), "Organic Materials for Imaging," Bunshin Shuppan (1993), pp. 187-192.

[0081] The ink of the present invention may further contain a photopolymerization initiator assistant, a polymerization inhibitor, and the like, if necessary. The photoinitiator coagent may be a tertiary amine compound, preferably an aromatic tertiary amine compound. Examples of the aromatic tertiary amine compound 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, and among these, examples of the aromatic tertiary amine compound preferably include N,N-dimethylamino-p-benzoic acid ethyl ester and N,N-dimethylamino-p-benzoic acid isoamyl ethyl ester. The ink of the present invention may contain only one of these compounds, or two or more of them.

[0082] Examples of polymerization inhibitors include (alkyl)phenols, hydroquinone, catechol, resorcin, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone, nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cupferron, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N-(3-oxyanilino-1,3-dimethylbutylidene)aniline oxide, dibutylcresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraldoxime, methyl ethyl ketoxime, cyclohexanone oxime, and the like.

[0083] <Coloring material> The ink of the present invention may further contain a colorant. The coloring material may be a dye or a pigment, with pigments being more preferred since they have good dispersibility in the components of the ink and excellent weather resistance.

[0084] The dye may be an oil-soluble dye, etc. Examples of the oil-soluble dye include the following various dyes. Examples of magenta dyes include MS Magenta VP, MS Magenta HM-1450, MS Magenta HSo-147 (all manufactured by Mitsui Toatsu Corporation), AIZENSOT Red-1, AIZEN SOT Red-2, AIZEN SOTRed-3, AIZEN SOT Pink-1, SPIRON Red GEH SPECIAL (all manufactured by Hodogaya Chemical Co., Ltd.), RESOLIN Red FB 200%, MACROLEX Red Violet R, MACROLEX ROT5B (all manufactured by Bayer Japan KK), KAYASET Red B, KAYASET Red 130, KAYASET Red 802 (all manufactured by Nippon Kayaku Co., Ltd.), PHLOXIN, ROSE BENGAL, ACID Red (all manufactured by Daiwa Kasei Co., Ltd.), HSR-31, DIARESIN Red K (all manufactured by Mitsubishi Kasei Corporation), and Oil Red (manufactured by BASF Japan Ltd.).

[0085] Examples of cyan dyes include MS Cyan HM-1238, MS Cyan HSo-16, Cyan HSo-144, and MS Cyan VPG (all manufactured by Mitsui Toatsu Corporation), AIZEN SOT Blue-4 (manufactured by Hodogaya Chemical Co., Ltd.), RESOLIN BR.Blue BGLN 200%, MACROLEX Blue RR, CERES Blue GN, SIRIUS SUPRATURQ.Blue Z-BGL, and SIRIUS SUPRA TURQ.Blue FB-LL 330% (all manufactured by Bayer Japan Co., Ltd.), KAYASET Blue FR, KAYASET Blue N, KAYASET Blue 814, Turq.Blue GL-5 200, and Light Blue BGL-5 200 (all manufactured by Nippon Kayaku Co., Ltd.), DAIWA Blue 7000, Oleosol Fast Blue GL (all manufactured by Daiwa Kasei Co., Ltd.), DIARESIN Blue P (manufactured by Mitsubishi Kasei Co., Ltd.), and SUDAN Blue. 670, NEOPEN Blue 808, ZAPON Blue 806 (all manufactured by BASF Japan Ltd.), etc.

[0086] Examples of yellow dyes include MS Yellow HSm-41, Yellow KX-7, Yellow EX-27 (Mitsui Toatsu), AIZEN SOT Yellow-1, AIZEN SOT Yellow W-3, AIZEN SOT Yellow-6 (all manufactured by Hodogaya Chemical Co., Ltd.), MACROLEX Yellow 6G, MACROLEX FLUOR.Yellow 10GN (all manufactured by Bayer Japan Ltd.), KAYASET Yellow SF-G, KAYASET Yellow 2G, KAYASET Yellow AG, KAYASET Yellow EG (all manufactured by Nippon Kayaku Co., Ltd.), DAIWA Yellow 330HB (manufactured by Daiwa Kasei Co., Ltd.), HSY-68 (manufactured by Mitsubishi Kasei Corporation), SUDAN Yellow 146, NEOPEN Yellow 075 (all manufactured by BASF Japan Ltd.), and the like.

[0087] Examples of black dyes include MS Black VPC (manufactured by Mitsui Toatsu Co., Ltd.), AIZEN SOT Black-1, and AIZEN SOT Black-5 (all manufactured by Hodogaya Chemical Co., Ltd.). These include RESORIN Black GSN 200%, RESOLIN Black BS (all manufactured by Bayer Japan), KAYASET Black AN (manufactured by Nippon Kayaku Co., Ltd.), DAIWA Black MSC (manufactured by Daiwa Kasei Co., Ltd.), HSB-202 (manufactured by Mitsubishi Kasei Co., Ltd.), NEPTUNE Black X60, NEOPEN Black X58 (all manufactured by BASF Japan Co., Ltd.), etc.

[0088] The pigment is not particularly limited, but may be, for example, an organic or inorganic pigment having the following numbers as described in the Color Index:

[0089] Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment Orange Includes 13, 16, 20, 36, etc.

[0090] Examples of blue or cyan pigments include Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17-1, 22, 27, 28, 29, 36, 60, and the like. Examples of green pigments include Pigment Green 7, 26, 36, and 50. Examples of yellow pigments include Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137, 138, 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193, and the like. Examples of black pigments include Pigment Black 7, 28, 26, and the like.

[0091] Commercially available examples of pigments include: Chromofine Yellow 2080, 5900, 5930, AF-1300, 2700L, Chromofine Orange 3700L, 6730, Chromofine Scarlet 6750, Chromofine Magenta 6880, 6886, 6891N, 6790, 6887, Chromofine Violet RE, Chromofine Red 6820, 6830, Chromofine Blue HS-3, 5187, 5108, 5197, 5085N, SR-5020, 5026, 5050, 4920, 4927, 4937, 4824, 4933GN-EP, 4940, 4973, 5205, 5208, 5214, 5221, 5000P , Chrome Fine Green 2GN, 2GO, 2G-550D, 5310, 5370, 6830, Chrome Fine Black A-1103, Seika Fast Yellow 10GH, A-3, 2035, 2054, 2200, 2270, 2300, 2400(B), 2500, 2600, ZAY-260, 2700(B), 2770 , Seika Fast Red 8040, C405(F), CA120, LR-116, 1531B, 8060R, 1547, ZAW-262, 1537B, GY, 4R-4016, 3820, 3891, ZA-215, Seika Fast Carmine 6B1476T-7, 1483LT, 3840, 3870, Seika Fast Bordeaux 10B-430, Seika Light Rose R40, Seika Light Violet B800, 7805, Seika Fast Maroon 460N, Seika Fast Orange 900, 2900, Seika Light Blue C718, A612, Cyanine Blue 4933M, 4933GN-EP, 4940, 4973 (Dainichi Seika Chemicals); KET Yellow 401, 402, 403, 404, 405, 406, 416, 424, KET Orange 501, KET Red 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 336, 337, 338, 346, KET Blue 101, 102, 103, 104, 105, 106, 111, 118, 124, KET Green 201 (manufactured by Dainippon Ink & Chemicals); Colortex Yellow 301, 314, 315, 316, P-624, 314, U10GN, U3GN, UNN, UA-414, U263, Finecol Yellow T-13, T-05, Pigment Yellow1705, Colortex Orange 202, Colortex Red101, 103, 115, 116, D3B, P-625, 102, H-1024, 105C, UFN, UCN, UBN, U3BN, URN, UGN, UG276, U456, U457, 105C, USN, Colortex Maroon601, Colortex BrownB610N, Colortex Violet600, Pigment Red 122, Colortex Blue516, 517, 518, 519, A818, P-908, 510, Colortex Green 402, 403, Colortex Black 702, U905 (manufactured by Sanyo Pigment); Lionol Yellow1405G, Lionol Blue FG7330, FG7350, FG7400G, FG7405G, ES, ESP-S (manufactured by Toyo Ink), Toner Magenta E02, Permanent RubinF6B, Toner Yellow HG, Permanent Yellow GG-02, Hostapeam BlueB2G (manufactured by Hoechst Industry); Novoperm P-HG, Hostaperm Pink E, Hostaperm Blue B2G (manufactured by Clariant); Carbon black #2600, #2400, #2350, #2200, #1000, #990, #980, #970, #960, #950, #850, MCF88, #750, #650, MA600, MA7, MA8, MA11, MA100, MA100R, MA77, #52, #50, #47, #45, #45L, #40, #33, #32, #30, #25, #20, #10, #5, #44, and CF9 (manufactured by Mitsubishi Chemical) are examples.

[0092] The average particle size of the pigment is preferably 0.08 to 0.5 μm. The maximum particle size of the pigment is preferably 0.3 to 10 μm, and more preferably 0.3 to 3 μm. Adjusting the particle size of the pigment is preferable in terms of suppressing clogging of the nozzles of the inkjet recording head and maintaining the storage stability, ink transparency, and curing sensitivity of the ink.

[0093] The content of the pigment or dye in the actinic radiation-curable inkjet ink is preferably 0.1 to 20% by mass, and more preferably 0.4 to 10% by mass, because if the content of the pigment or dye is too low, the color development of the resulting image is insufficient, whereas if the content is too high, the viscosity of the ink increases, decreasing the ejection properties.

[0094] The pigment can be dispersed by using, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker, or the like. The pigment is preferably dispersed so that the average particle size of the pigment particles is preferably 0.08 to 0.5 μm, and the maximum particle size is preferably 0.3 to 10 μm, more preferably 0.3 to 3 μm. The pigment dispersion is adjusted by selecting the pigment, dispersant, and dispersion medium, dispersing conditions, filtration conditions, etc.

[0095] Since the ink of the present invention contains the above-mentioned polymer compound, the dispersibility of the pigment can be improved, but it may further contain other dispersants. Examples of dispersants include hydroxyl-containing carboxylates, salts of long-chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylates, salts of long-chain polyaminoamides and polar acid esters, high molecular weight unsaturated acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalene sulfonate-formaldehyde condensate salts, aromatic sulfonate-formaldehyde condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate, etc. Examples of commercially available dispersants include the Solsperse series from Avecia and the PB series from Ajinomoto Fine-Techno Co., Ltd.

[0096] The actinic radiation curable inkjet ink may further contain a dispersion aid as necessary. The dispersion aid may be selected depending on the pigment.

[0097] The total amount of the dispersant and the dispersion aid is preferably within the range of 1 to 50% by mass relative to the pigment.

[0098] The ink of the present invention may further contain a dispersion medium for dispersing the pigment, if necessary. A solvent may be contained in the ink as a dispersion medium, but in order to suppress the solvent from remaining in the formed image, it is preferable that the dispersion medium is a photopolymerizable compound (particularly a monomer with low viscosity) as described above.

[0099] <Other ingredients> The ink of the present invention may further contain other components as required. The other components may be various additives, other resins, and the like. Examples of the additives include surfactants, leveling additives, matting agents, ultraviolet absorbing agents, infrared absorbing agents, antibacterial agents, and basic compounds for enhancing the storage stability of the ink. Examples of the basic compound include basic alkali metal compounds, basic alkaline earth metal compounds, and basic organic compounds such as amines. Examples of other resins include resins for adjusting the physical properties of the cured film. Examples of such resins include polyester resins, polyurethane resins, vinyl resins, acrylic resins, rubber resins, and waxes.

[0100] <Sol-gel phase transition type inkjet ink> Since the actinic ray curable inkjet ink of the present invention contains a gelling agent as described above, it undergoes a reversible sol-gel phase transition depending on the temperature. The actinic ray curable ink that undergoes a sol-gel phase transition is a liquid (sol) at high temperatures (for example, about 80° C.), and can be ejected in a sol state from an inkjet recording head. When the ink is ejected at high temperatures, the ink droplets (dots) land on a recording medium, and then naturally cool and gel. This makes it possible to suppress the coalescence of adjacent dots, thereby improving image quality.

[0101] In order to improve the ejection properties of ink droplets, it is preferable that the viscosity of the ink at high temperatures is below a certain level. Specifically, it is preferable that the viscosity of the ink at 80°C is within the range of 3 to 20 mPa·s. On the other hand, in order to prevent adjacent dots from merging, it is preferable that the viscosity of the ink at room temperature after landing is above a certain level. Specifically, it is preferable that the viscosity of the ink at 25°C is 1000 mPa·s or more.

[0102] The gelling temperature of the ink is preferably within a range of 40 to 70° C. in terms of good ejection properties, and more preferably within a range of 50 to 65° C. The gelling temperature is the temperature at which ink in a sol state gels and its fluidity decreases in the process of cooling.

[0103] The viscosity of the ink at 80°C, the viscosity at 25°C, and the gelling temperature can be determined by measuring the temperature change of the dynamic viscoelasticity of the ink with a rheometer. Specifically, the ink is heated to 100°C and cooled to 20°C under conditions of a shear rate of 11.7 ( / s) and a cooling rate of 0.1°C / s, and a viscosity temperature change curve is obtained. The viscosities at 80°C and 25°C can then be determined by reading the viscosities at 80°C and 25°C, respectively, on the viscosity temperature change curve. The gelling temperature can be determined as the temperature at which the viscosity becomes 200 mPa·s on the viscosity temperature change curve.

[0104] The rheometer used may be a stress-controlled rheometer from the Physica MCR series manufactured by Anton Paar. The diameter of the cone plate may be 75 mm, and the cone angle may be 1.0°.

[0105] [Ink manufacturing method] The ink of the present invention is obtained by mixing the actinic radiation polymerizable compound, photopolymerization initiator, polymer compound, gelling agent, and other components as necessary under heating. Preferably, a pigment dispersant in which a coloring material (particularly a pigment) is dispersed in a portion of the actinic radiation polymerizable compound is prepared, and the pigment dispersant is mixed with other ink components. The obtained ink is preferably filtered through a predetermined filter.

[0106] [Inkjet recording apparatus and image recording method using the same] An ink jet recording apparatus of the actinic ray curing type ink jet method used in the present invention will be described. Inkjet recording apparatuses using the actinic ray curing inkjet method include those using a line recording method (single pass recording method) and those using a serial recording method. The method may be selected according to the required image resolution and recording speed, but from the viewpoint of high speed recording, it is preferable that the inkjet recording apparatus is a line recording method (single pass recording method).

[0107] Fig. 1 is a diagram showing an example of the configuration of the main part of a line-recording type inkjet recording device, in which Fig. 1(a) is a side view and Fig. 1(b) is a top view. As shown in FIG. 1, the inkjet recording apparatus 10 includes a head carriage 16, an ink flow path 30, an ink tank 31, an actinic ray irradiation unit 18, and a temperature control unit 19. The head carriage 16 accommodates a plurality of inkjet recording heads 14 . The ink tank 31 stores ink to be supplied through an ink flow path 30 connected to the head carriage 16 . The active ray irradiation unit 18 covers the entire width of the recording medium 12, and is disposed downstream of the head carriage 16 (in the conveying direction of the recording medium). The temperature control section 19 is disposed on the lower surface of the recording medium 12. A detailed description will be given below.

[0108] The head carriage 16 is fixedly disposed so as to cover the entire width of the recording medium 12, and houses a plurality of inkjet recording heads 14 provided for each color. Ink is supplied to the inkjet recording heads 14. For example, ink may be supplied directly from an ink cartridge (not shown) removably mounted on the inkjet recording device 10, or by ink supply means (not shown).

[0109] A plurality of inkjet recording heads 14 are arranged for each color in the transport direction of the recording medium 12 . The number of inkjet recording heads 14 arranged in the transport direction of the recording medium 12 is set according to the nozzle density of the inkjet recording heads 14 and the resolution of the printed image. For example, when forming an image with a resolution of 1440 dpi using inkjet recording heads 14 with a droplet volume of 2 pl and a nozzle density of 360 dpi, it is preferable that the four inkjet recording heads 14 are arranged with a staggered arrangement in the transport direction of the recording medium 12. Furthermore, when forming an image with a resolution of 720 x 720 dpi using inkjet recording heads 14 with a droplet volume of 6 pl and a nozzle density of 360 dpi, it is preferable to displace the two inkjet recording heads 14. dpi represents the number of ink droplets (dots) per 2.54 cm.

[0110] The ink tank 31 is connected to the head carriage 16 via an ink flow path 30. The ink flow path 30 is a path that supplies the ink in the ink tank 31 to the head carriage 16. In order to stably eject ink droplets, the ink in the ink tank 31, the ink flow path 30, the head carriage 16, and the inkjet recording head 14 is heated to a predetermined temperature and maintained in a gel state.

[0111] The active ray irradiation unit 18 covers the entire width of the recording medium 12, and is disposed downstream of the head carriage 16 in the transport direction of the recording medium. The active ray irradiation unit 18 irradiates droplets that have been discharged by the inkjet recording head 14 and landed on the recording medium with active rays, thereby curing the droplets.

[0112] When the actinic ray is ultraviolet ray, examples of the actinic ray irradiation unit 18 (ultraviolet ray irradiation means) include fluorescent tubes (low pressure mercury lamps, germicidal lamps), cold cathode fluorescent tubes, ultraviolet lasers, low pressure, medium pressure, and high pressure mercury lamps having operating pressures of several hundreds of Pa to 1 MPa, metal halide lamps, and LEDs. 2 The ultraviolet ray irradiation means for irradiating the above ultraviolet rays is preferably a high pressure mercury lamp, a metal halide lamp, an LED, etc. LED is more preferable from the viewpoint of low power consumption. Specifically, a 395 nm water-cooled LED manufactured by Phoseon Technology can be used.

[0113] When the actinic radiation is an electron beam, examples of the actinic radiation irradiation unit 18 (electron beam irradiation means) include electron beam irradiation means of a scanning type, a curtain beam type, a broad beam type, etc. From the viewpoint of processing capacity, a curtain beam type electron beam irradiation means is preferable. Examples of the electron beam irradiation means include "Curetron EBC-200-20-30" manufactured by Nissin High Voltage Co., Ltd., "Min-EB" manufactured by AIT Co., Ltd., etc.

[0114] The temperature control unit 19 is disposed below the recording medium 12 and maintains the recording medium 12 at a predetermined temperature. The temperature control unit 19 can be, for example, any of various heaters.

[0115] An image recording method using the line recording type inkjet recording apparatus 10 will be described below. The recording medium 12 is transported between a head carriage 16 of the inkjet recording apparatus 10 and a temperature control unit 19. Meanwhile, the recording medium 12 is adjusted to a predetermined temperature by the temperature control unit 19. Next, high-temperature ink is ejected from the ink jet recording head 14 of the head carriage 16 and adheres (lands) on the recording medium 12. Then, the active ray irradiation unit 18 irradiates the ink droplets adhered to the recording medium 12 with active rays to harden them.

[0116] When ejecting ink from the inkjet recording head, the temperature of the ink inside the inkjet recording head 14 is preferably set to a temperature 10 to 30° C. higher than the gelling temperature of the ink. By setting the temperature within this range, the ejection properties of the ink can be improved, and the ink components are not deteriorated.

[0117] The amount of each droplet ejected from each nozzle of the ink jet recording head 14 depends on the image resolution, but is preferably 1 to 10 pl, and more preferably 0.5 to 4.0 pl. By setting the amount of each droplet within this range, a high resolution image can be formed.

[0118] In order to prevent adjacent ink droplets from coalescing, the actinic radiation is preferably applied within 10 seconds after the ink droplets are deposited on the recording medium, and the irradiation is preferably performed within 0.001 to 5 seconds, more preferably within 0.01 to 2 seconds. It is preferable that the irradiation with actinic rays is carried out after all of the ink jet recording heads 14 housed in the head carriage 16 have ejected ink.

[0119] The conveying speed of the recording medium is preferably 500 to 2000 mm / s. A faster conveying speed is preferable because the image formation speed increases as the conveying speed increases, but if the conveying speed is too fast, the image quality may decrease or the ink droplets may not be cured sufficiently.

[0120] When the actinic radiation is an electron beam, the acceleration voltage of the electron beam irradiation is preferably 30 to 250 kV, more preferably 30 to 100 kV, in order to achieve sufficient curing. When the acceleration voltage is 100 to 250 kV, the electron beam irradiation dose is preferably 30 to 100 kGy, more preferably 30 to 60 kGy.

[0121] The total ink film thickness after curing is preferably 2 to 25 μm. The "total ink film thickness" is the maximum thickness of the ink film drawn on the recording medium.

[0122] FIG. 2 is a diagram showing an example of the configuration of the main parts of an inkjet recording apparatus 20 using a serial recording method. As shown in FIG. 2, an inkjet recording device 20 can be configured in the same manner as in FIG. 1, except that instead of the head carriage 16 fixedly arranged to cover the entire width of the recording medium, a head carriage 26 is used as described below, and a guide section 27 is different. The head carriage 26 has a width less than the overall width of the recording medium and houses a plurality of ink jet recording heads 24 . The guide portion 27 moves the head carriage 26 in the width direction of the recording medium 12 .

[0123] In the serial recording type recording device 20 , while a head carriage 26 moves in the width direction of the recording medium 12 along a guide portion 27 , ink droplets are ejected from an inkjet recording head 24 housed in the head carriage 26 . After the head carriage 26 has completely moved in the width direction of the recording medium 12 (for each pass), the recording medium 12 is fed in the transport direction. Then, the actinic ray irradiation unit 28 irradiates light onto the ink droplets attached to the recording medium 12. Apart from these operations, an image is recorded in almost the same manner as in the inkjet recording device 10 of the line recording type described above. EXAMPLES

[0124] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. In the following examples, unless otherwise specified, the operations were performed at room temperature (25°C). Furthermore, unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass", respectively.

[0125] [Ink preparation] Each actinic radiation curable inkjet ink was prepared using the following components.

[0126] <Preparation of Pigment Dispersion A> Polymer compound A and a polymerizable compound shown below were placed in a stainless steel beaker and heated on a hot plate at 65° C. for 1 hour while stirring and dissolving. Pigment dispersant: Polymer compound A 9 parts by weight Polymerizable compound: Tricyclodecane dimethacrylate 70 parts by mass After cooling to room temperature, 20 parts by mass of the pigment described below was added, and the mixture was placed in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm and sealed. This was dispersed in a paint shaker for 8 hours, after which the zirconia beads were removed. Pigment: Pigment Red 122 (Dainichi Seika, Chromofine Red 6112JC)

[0127] <Preparation of pigment dispersions B to I> Each pigment dispersion was prepared in the same manner as in the preparation of the pigment dispersion A, except that the polymer compound A was changed to the type and content of the polymer compound shown in Table I below. The polymer compounds used are as follows. The weight average molecular weight and number average molecular weight of each polymer compound are as shown in the table below. The weight average molecular weight and number average molecular weight were calculated as described above. [ka]

[0128] <Active radiation polymerizable compound> Tricyclodecane Dimethanol Diacrylate 6EO modified trimethylolpropane triacrylate 4EO modified pentaerythritol tetraacrylate PO modified neopentyl glycol diacrylate 3PO modified trimethylolpropane triacrylate 3-Methylpentanediol diacrylate 2-(2-vinyloxyethoxy)ethyl acrylate

[0129] <Photopolymerization initiator> DAROCURE TPO (Acylphosphine compound, manufactured by BASF)

[0130] <Gelling agent> Stearyl stearate (fatty ester compound, alkyl group carbon number: C17-C18) Distearyl ketone (aliphatic ketone compound, alkyl group carbon number: C18-C18) Eicosanoic acid icosyl (aliphatic ester compound, alkyl group carbon number: C19-C20) Dilauryl ketone (aliphatic ketone compound, alkyl group carbon number: C12-C12)

[0131] <Polymerization inhibitor> Irgastab UV10 (BASF)

[0132] <Surfactant> KF-352 (Shin-Etsu Chemical Co., Ltd.)

[0133] <Preparation of Inks 1 to 10> The ingredients were mixed according to the ink compositions shown in Tables I to III below, and then heated to 80° C. and stirred. While maintaining the temperature of the resulting solution, it was filtered through a 3 μm Teflon (registered trademark) membrane filter manufactured by ADVATEC Corporation to prepare each ink. This ink was evaluated as follows.

[0134] <Inkjet recording method> Four inkjet recording heads filled with Y, M, C, and K inks were prepared. Each inkjet recording head used a piezo head with a nozzle diameter of 20 μm and 512 nozzles (256 nozzles x 2 rows, staggered arrangement, nozzle pitch per row 360 dpi). The ejection conditions were such that the volume of one droplet was 2.5 pl, droplets were ejected at a droplet speed of approximately 6 m / s, and recording was performed at a resolution of 1440 dpi x 1440 dpi. Images were formed in an environment of 23°C and 55% RH. Note that dpi refers to the number of dots per 2.54 cm.

[0135] Using a line-recording type inkjet recording device, Y, M, C, and K images were formed. Specifically, printing coated paper A (OK topcoat, 128 g / m2) was used. 2 A recording medium (manufactured by Oji Paper Co., Ltd.) was prepared. The temperature of the recording medium was adjusted to 25° C. by a temperature control unit, and the conveying speed was set to 500 mm / s. Meanwhile, the obtained ink was filled into an inkjet recording head of an inkjet recording device and heated so that the ink temperature became 80° C. Then, ink droplets were ejected onto printing coated paper A to form a 5 cm×5 cm solid image.

[0136] After printing, light (395 nm, 8 W / cm) was emitted from an LED lamp manufactured by Phoseo Technology. 2The ink was cured by irradiating the ink with a UV integrating light meter C9536 and H9958 manufactured by Hamamatsu Photonics. The distance from the LED lamp to the recording medium surface was set to 20 mm.

[0137] <Blooming evaluation> The solid images thus formed were stored at 40° C. for 2 weeks, and blooming was evaluated by visual inspection according to the following criteria: “AA” and “A” in the following criteria were deemed to be acceptable for practical use. (standard) AA: In all images of Y, M, C, and K, there are zero deposits or uneven gloss on the image surface even when observed from a distance of 15 cm. A: In all images of Y, M, C, and K, when observed from a distance of 15 cm, the number of deposits or gloss unevenness on part of the image surface is between 1 and 10, but from a distance of 30 cm, the number of deposits or gloss unevenness on the image surface is 0. B: In all of the Y, M, C, and K images, the number of deposits or gloss unevenness on the image surface is 10 or more even when observed from a distance of 30 cm.

[0138] [Creating print samples] Using a piezo type head that ejects droplets of 14 pl, print samples were created by printing with colored inks on the following three types of paper at a resolution of 720 dpi (hereinafter, dpi refers to the number of dots per 2.54 cm). In addition, when recording with an ink set of colored ink and colorless ink, the colorless ink was applied to the entire recording area at a rate of 6 g / m2 prior to printing with the colored inks. 2 The printout contents for each evaluation are described in the explanation of each evaluation method. Paper A: Shiraoi [64g / m 2 ](Made by Nippon Paper Industries Co., Ltd.) Paper B: OK Prince Eco G100 [64g / m 2 ](Oji Paper Co., Ltd.) Paper C: Recycled high-quality [52g / m 2 ](Made by Nippon Paper Industries Co., Ltd.)

[0139] <Character quality evaluation> The characters "Excellent" were printed in 4-point, 5-point, 7-point, and 9-point sizes on Paper A, Paper B, and Paper C. The characters obtained were visually observed and evaluated according to the following criteria. "A" and "B" on the following criteria were deemed to be acceptable for practical use. (standard) A: Even 4-point text can be reproduced without any loss of detail. B: Details are lost in 4-point letters, but are reproduced without loss in 5-point letters. C: Details are lost in 5-point letters, but are reproduced without loss in 7-point letters. D: Details are lost in 7-point letters, but are reproduced without loss in 9-point letters. E: Even with 9 point text, details are lost.

[0140] [Table 1]

[0141] [Table 2]

[0142] [Table 3]

[0143] [Table 4]

[0144] As shown by the above results, it is apparent that the ink of the present invention is able to suppress the occurrence of blooming in comparison with the ink of the comparative example, and also provides good image definition. [Explanation of symbols]

[0145] 10, 20 Inkjet recording device 12 Recording media 14, 24 Inkjet recording head 16, 26 Head carriage 18, 28 Active radiation irradiation section 19 Temperature control unit 27 Guide section 30 Ink flow path 31 Ink tank

Claims

1. An actinic ray curable inkjet ink containing an actinic ray polymerizable compound, a photopolymerization initiator, and a polymer compound, Further comprising a gelling agent, The polymer compound has a tolylene diisocyanate structure.

1. An actinic ray curable inkjet ink comprising:

2. The polymer compound has an ε-caprolactam structure.

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

3. The content of the polymer compound is more than 0% by mass and 5% by mass or less.

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

4. The weight average molecular weight Mw of the polymer compound is within a range of 5,000 to 15,000.

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

5. The number average molecular weight Mn of the polymer compound is within a range of 5,000 to 10,000.

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

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

7. The gelling agent contains an aliphatic ketone compound or an aliphatic ester compound.

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

Images