Energy ray-curable inkjet ink composition

Abstract

To solve the problems that despite means for increasing a ratio of a monofunctional monomer having generally low viscosity in order to obtain a low-viscosity and solventless energy ray-curable inkjet ink: as the ratio of the monofunctional monomer is increased, there are concerns that the reactivity and curability are lowered when ink is cured; and furthermore, when stretchability and curability of an ink layer are insufficient, in the case where Roll to Roll or the like are used in a recording step, a non-recording medium causes cracks at the time of winding, and the non-recording media are stuck to each other.SOLUTION: An energy ray-curable inkjet ink composition substantially containing no solvent has a monofunctional monomer, a first polyfunctional monomer having an acrylic equivalent of larger than 150, and a second polyfunctional monomer having an acrylic equivalent of 150 or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an ink-jet ink composition, and more particularly to an energy beam-curable ink-jet ink composition. [Background technology]

[0002] The inkjet recording method is a method in which liquid ink is ejected from an ink head nozzle to record on a recording medium. One of the inks used in the inkjet recording method is an energy beam curable inkjet ink. In this method, after the ink is ejected, the polymerizable compound in the ink is crosslinked by irradiation with energy rays (e.g., ultraviolet rays, etc.), and the energy beam curable inkjet ink is cured to form an ink layer. The energy beam curable inkjet inks are roughly classified into solvent-based inks containing an organic solvent or water, and solventless inks that are substantially free of organic solvents, etc.

[0003] Energy beam curable inkjet inks are usually required to have a viscosity that allows them to be discharged from ink head nozzles. Furthermore, in order to obtain high-definition printed matter, it is required to have a lower viscosity so that the droplet size of the ink to be discharged can be made small and the ink can be discharged stably. As an example for obtaining an energy beam curable inkjet ink having a low viscosity, Patent Document 1 describes an energy beam curable ink composition in which "the polymerizable compound is composed only of a monofunctional monomer having an acrylic equivalent of 300 or less and having one ethylenic double bond in one molecule, and a polyfunctional monomer having an acrylic equivalent of 150 or less and having two or more ethylenic double bonds in one molecule, and the photopolymerization initiator contains an α-aminoalkylphenone compound and a thioxanthone compound." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-275175 A Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, Patent Document 1 discloses an energy beam-curable ink composition having a low viscosity, but does not disclose a composition of an energy beam-curable inkjet ink having an even lower viscosity (viscosity of about 10 mPa s (25°C) or less).

[0006] In order to obtain a solvent-free energy beam curable inkjet ink with a lower viscosity, it is generally considered to increase the ratio of monofunctional monomers, which have a low viscosity. However, if the ratio of monofunctional monomers is increased, the reactivity of the ink when cured decreases, resulting in a decrease in curability. In order to prevent the decrease in curability, an energy beam curable inkjet ink composition as described in Patent Document 1 is considered, but the use of a polyfunctional monomer increases the curability, but it is also considered that the viscosity of the ink increases.

[0007] Furthermore, in the process of recording onto a non-recording medium, when the non-recording medium requires winding such as roll to roll, the ink layer of the non-recording medium needs to have extensibility and hardening properties in order to prevent cracks from occurring during winding after recording onto the non-recording medium and to prevent the non-recording medium from sticking to each other. Patent Document 1 does not take these points into consideration.

[0008] An object of the present invention is to provide an energy beam-curable inkjet ink that has low viscosity and excellent curability and stretchability. [Means for solving the problem]

[0009] According to one embodiment of the present invention, an ink-jet ink composition includes a polymerizable compound and a photopolymerization initiator, and the polymerizable compound is configured to include a monofunctional monomer, a first polyfunctional monomer having an acrylic equivalent of more than 150 and having two or more ethylenic double bonds in one molecule, and a second polyfunctional monomer having an acrylic equivalent of 150 or less and having two or more ethylenic double bonds in one molecule. Effect of the Invention

[0010] According to the present invention, it is possible to provide an energy ray-curable inkjet ink composition that has low viscosity and excellent curability and stretchability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present embodiment will be described below.

[0012] The energy beam-curable inkjet ink (hereinafter also referred to as ink) of this embodiment contains at least a monofunctional monomer and a polyfunctional monomer, which are polymerizable compounds, and a photopolymerization initiator, as well as a colorant, additives, and the like.

[0013] A polymerizable compound is a compound that undergoes a polymerization reaction and hardens when irradiated with energy rays (ultraviolet rays, electron beams, etc.). Among the polymerizable compounds, a monofunctional monomer has one ethylenic double bond in one molecule, and a polyfunctional monomer has two or more ethylenic double bonds in one molecule.

[0014] In addition, the energy beam curable ink of the present embodiment is a solvent-free ink, and does not substantially contain a solvent. Here, "does not substantially contain a solvent" means that although it is not necessary to contain a dilution solvent, for example, when an industrial product is used, a dilution solvent may inevitably be mixed into the ink, and the content of the solvent contained in the total mass of the ink is 3 mass% or less. The solvent means various known solvents such as ether, ketone, aromatic, xylene, etc.

[0015] Since the energy beam curable ink is solvent-free, no volatile solvent remains in the ink layer, which is preferable from the viewpoint of being free of volatile organic compounds.

[0016] <1.Polymerizable compound> <1-1. Monofunctional monomers> Specific examples of monofunctional monomers include amyl (meth)acrylate, isoamyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, isomyristyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, tridecyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, neopentyl glycol (meth)acrylic acid benzoate, butoxyethyl (meth)acrylate, ethoxy-diethylene glycol (meth)acrylate, methoxy-triethylene glycol (meth)acrylate, methoxy-polyethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, fluoro- ... Phenoxyethyl (meth)acrylate, phenoxy-polyethylene glycol (meth)acrylate, 3,5,5-trimethylcyclohexyl acrylate 2-(2-ethoxyethoxyethyl acrylate) nonylphenol ethylene oxide adduct (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl-succinic acid, 2-(meth)acryloyloxyethyl-phthalic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalic acid, 1,4-cyclohexanedimethanol monoacrylate, ethoxylated nonylphenyl acrylate, etc. These may be used alone or in combination. The above monomers may also be substituted with functional groups such as phosphorus or fluorine.

[0017] Among these, tetrahydrofurfuryl (meth)acrylate, 3,5,5-trimethylcyclohexyl acrylate, 2-(2-ethoxyethoxyethyl acrylate), and 2-ethylhexyl (meth)acrylate are more preferable because they have low viscosity. Furthermore, it is particularly preferable to use 2-hydroxy-3-phenoxypropyl (meth)acrylate in combination. By using 2-hydroxy-3-phenoxypropyl (meth)acrylate containing a functional group such as a hydroxyl group in combination, it is possible to maintain low viscosity while providing adhesion to non-recording media (substrates).

[0018] As mentioned above, two or more types of monofunctional monomers can be used in combination, one of which has a viscosity of 10 mPa·s or less (25°C) and the other of which has a viscosity of 80 mPa·s or more (25°C). This allows the energy beam curable ink to have a low viscosity and improves adhesion to non-recording media.

[0019] Specific examples of monofunctional monomers with a viscosity of 10 mPa·s or less (25°C) include tetrahydrofurfuryl (meth)acrylate, 3,5,5-trimethylcyclohexyl acrylate, 2-(2-ethoxyethoxyethyl acrylate), and 2-ethylhexyl (meth)acrylate. Specific examples of monofunctional monomers with a viscosity of 80 mPa·s or more (25°C) include 2-hydroxy-3-phenoxypropyl (meth)acrylate, 1,4-cyclohexanedimethanol monoacrylate, and ethoxylated nonylphenyl acrylate. Even when using a monofunctional monomer with a viscosity of 80 mPa·s or more (25°C), the ink viscosity can be kept low while improving the adhesion of the ink to non-recording media by using a monofunctional monomer with a viscosity of 10 mPa·s or less (25°C) in combination.

[0020] Furthermore, the monofunctional monomer preferably has a functional group, specifically, a hydroxyl group, a carboxyl group, a phosphate group, etc. By having such a functional group, the adhesion to the non-recording medium can be improved. Among these, a hydroxyl group is particularly preferable, and the adhesion can be further improved.

[0021] The glass transition temperature of the monofunctional monomer is preferably −70° C. or higher and 30° C. or lower, which can impart appropriate hardness to the coating film and extensibility to the ink layer (ink coating film).

[0022] <1-2. Polyfunctional Monomers> The polyfunctional monomer includes a first polyfunctional monomer having an acrylic equivalent of more than 150 and having two or more ethylenic double bonds in one molecule, and a second polyfunctional monomer having an acrylic equivalent of 150 or less and having two or more ethylenic double bonds in one molecule. The polymerizable compound includes at least one each of the first polyfunctional monomer and the second polyfunctional monomer.

[0023] By using the first and second multifunctional monomers as the multifunctional monomers, it is possible to achieve both the extensibility and hardness (coating strength) of the ink layer. Furthermore, by using the multifunctional monomers, it is possible to improve the curability of the ink layer.

[0024] The acrylic equivalent is calculated by (acrylic equivalent)=(molecular weight of monomer / number of functional groups of monomer).

[0025] <1-2-1. First polyfunctional monomer> Specific examples of the first polyfunctional monomer having an acrylic equivalent of more than 150 and two ethylenic double bonds in one molecule include polyethylene glycol (200) diacrylate, tetraethylene glycol diacrylate, polyethylene glycol (400) diacrylate, ethoxylated (3) bisphenol A diacrylate, tricyclodecane dimethanol diacrylate, propoxylated (2) neopentyl glycol diacrylate, etc. These may be used alone or in combination.

[0026] Specific examples of polyfunctional monomers having three or more ethylenic double bonds in one molecule include ethoxylated (20) trimethylolpropane triacrylate, propoxylated (3) trimethylolpropane triacrylate, etc. These may be used alone or in combination.

[0027] Among the above polyfunctional monomers, tricyclodecane dimethanol diacrylate, polyethylene glycol (400) diacrylate, and propoxylated (2) neopentyl glycol diacrylate are preferred. By using these polyfunctional monomers, it is possible to maintain the viscosity of the ink at a low level and increase the coating strength of the ink layer.

[0028] The glass transition temperature of the first polyfunctional monomer is preferably -25°C or higher and 180°C or lower.

[0029] <1-2-2. Second polyfunctional monomer> Specific examples of the second polyfunctional monomer having an acrylic equivalent of 150 or less and two ethylenic double bonds in one molecule include 1,3-butylene glycol di(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol diacrylate, cyclohexanedimethanol di(meth)acrylate, dipropylene glycol di(meth)acrylate, etc. These may be used alone or in combination.

[0030] Specific examples of polyfunctional monomers having three or more ethylenic double bonds in one molecule include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, glyceryl tri(meth)acrylate, and ethylene oxide-modified, propylene oxide-modified, and caprolactone-modified versions of these. These may be used alone or in combination.

[0031] Among the above polyfunctional monomers, 1,6-hexanediol di(meth)acrylate, 1,4-butanediol diacrylate, and trimethylolpropane tri(meth)acrylate are preferred. By using these polyfunctional monomers, the viscosity of the ink can be kept low and the curing property of the ink layer can be improved.

[0032] The glass transition temperature of the second polyfunctional monomer is preferably 43° C. or higher and 100° C. or lower, which can increase the coating strength of the ink layer.

[0033] Among the above-mentioned first and second polyfunctional monomers, a combination of tricyclodecane dimethanol diacrylate and 1,6-hexanediol di(meth)acrylate is preferable, which can reduce the viscosity of the ink and increase the coating strength of the ink layer.

[0034] <1-3. Content of each polymerizable compound> The content of the polymerizable compound in the ink composition is preferably 70% by mass or more and 90% by mass or less, and more preferably 78% by mass or more and 88% by mass or less, based on the total mass of the ink composition. If the content of the polymerizable compound is within the above range, it is possible to obtain an ink that has high curability and adhesion while maintaining a low viscosity.

[0035] The content of the monofunctional monomer is preferably 50% by mass or more and 80% by mass or less, and more preferably 55% by mass or more and 75% by mass or less, based on the total amount of the ink composition. If the content of the monofunctional monomer is 50% by mass or more, it is possible to obtain an ink composition with low viscosity. On the other hand, if the content of the monofunctional monomer is 80% by mass or less, it is possible to contain a corresponding amount of a highly reactive polyfunctional monomer, thereby improving the curability and adhesion.

[0036] If the content of the monofunctional monomer is less than 50% by mass, the amount of the polyfunctional monomer increases, making it impossible to maintain the ink at a low viscosity.

[0037] The content of the first multifunctional monomer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 8% by mass or less, based on the total mass of the ink composition. By adjusting the content of the first multifunctional monomer to the above range, the strength of the ink coating film (coating film strength) can be imparted.

[0038] The content of the second polyfunctional monomer is preferably 5% by mass or more and 35% by mass or less, and more preferably 6% by mass or more and 30% by mass or less, based on the total mass of the ink composition. By setting the content of the second polyfunctional monomer to the above range, the curing speed of the ink layer can be improved.

[0039] In the prior art, it has been shown that when a polyfunctional monomer has an acrylic equivalent of more than 150, curability and adhesion decrease with low energy irradiation, even when used in combination with a polyfunctional monomer having an acrylic equivalent of 300 or less. On the other hand, in the present embodiment, even when a polyfunctional monomer having an acrylic equivalent of more than 150 is used, by using a monofunctional monomer in combination with a polyfunctional monomer having an acrylic equivalent of 150 or less, it is possible to obtain an energy beam curable ink that has low viscosity and excellent curability and stretchability even with low energy irradiation.

[0040] In addition, by setting the content of the polymerizable compounds (monofunctional monomer, first multifunctional monomer, second multifunctional monomer) within the above range, an energy beam-curable ink having low viscosity and excellent curability and stretchability is provided.

[0041] In the polymerizable compound of this embodiment, the ratio of the monofunctional monomer content to the entire ink composition is 50 mass % or more, and therefore it is possible to obtain an ink composition with low viscosity even when the polymerizable compound contains a polyfunctional monomer having three or more ethylenic double bonds in one molecule as described above.

[0042] The proportion of the monofunctional monomer in the polymerizable compound is preferably 60% or more and 95% or less, and more preferably 62% or more and 91% or less, based on the entire polymerizable compound.

[0043] The ratio of the first multifunctional monomer in the polymerizable compound is preferably 1% or more and 10% or less based on the entire polymerizable compound, and the ratio of the second multifunctional monomer in the polymerizable compound is preferably 5% or more and 35% or less.

[0044] The ratio of the monofunctional monomer to the polyfunctional monomer in the polymerizable compound is preferably 1 to 10 in terms of the mass ratio of the content of the monofunctional monomer to the content of the polyfunctional monomer (monofunctional monomer / polyfunctional monomer).

[0045] The ratio of the first polyfunctional monomer having an acrylic equivalent of more than 150 to the second polyfunctional monomer having an acrylic equivalent of 150 or less in the polyfunctional monomer is preferably 2 to 15 in terms of the mass ratio (second polyfunctional monomer / first polyfunctional monomer) of the content of the first polyfunctional monomer to the content of the second polyfunctional monomer.

[0046] As described above, by using a monofunctional monomer, a first polyfunctional monomer having an acrylic equivalent of more than 150, and a second polyfunctional monomer having an acrylic equivalent of 150 or less as the polymerizable compound, it is possible to provide an energy beam-curable inkjet ink that is substantially free of solvent, and that has low viscosity and excellent curability and stretchability.

[0047] <2. Photopolymerization initiator> The ink composition contains at least one of an alkylphenone compound and a thioxanthone compound as a photopolymerization initiator, which allows polymerization of the ink composition to be initiated by energy irradiation.

[0048] Examples of alkylphenone compounds include α-amino alkylphenone compounds or benzyl methyl ketal compounds, specifically 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1, 2-methyl-1-[4-(methoxythio)-phenyl]-2-morpholinopropan-2-one, 2,2-dimethoxy-1,2-diphenylethan-1-one, etc. These compounds may be used alone or in combination. Examples of commercially available alkylphenone compounds include Irgacure 369, Irgacure 907, Irgacure 651, etc., manufactured by Ciba.

[0049] Specific examples of thioxanthone compounds include thioxanthone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, and 1-chloro-4-propoxythioxanthone. These compounds may be used alone or in combination. Commercially available thioxanthone compounds include KAYACURE DETX-S manufactured by Nippon Kayaku Co., Ltd. and Chivacure ITX manufactured by Double Bond Chemical Co., Ltd.

[0050] The content of the photopolymerization initiator in the ink composition is preferably 8% by mass or more and 15% by mass or less with respect to the entire composition.

[0051] In addition to the above, the ink composition may further contain a conventionally known photopolymerization initiator such as an acylphosphine oxide compound, an aryl alkyl ketone, an oxime ketone, an acylphosphine oxide, an acylphosphonate, S-phenyl thiobenzoate, titanocene, an aromatic ketone, benzyl, a quinone derivative, or a ketocoumarin.

[0052] Specific examples of these photopolymerization initiators include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 1-hydroxy-cyclohexyl-phenyl-ketone-1,2-octanedione-[4-(phenylthio)-2-(o-benzoyloxime)], bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, and 2,4,6-trimethylbenzoyl-phosphine oxide.

[0053] <3. Coloring agents> As the coloring material, various dyes known in the art may be used, but from the viewpoint of weather resistance, it is preferable to use either an inorganic pigment or an organic pigment, or both.

[0054] Specific examples of inorganic pigments include titanium oxide, zinc oxide, zinc oxide, tripon, iron oxide, aluminum oxide, silicon dioxide, kaolinite, montmorillonite, talc, barium sulfate, calcium carbonate, silica, alumina, cadmium red, red iron oxide, molybdenum red, chrome vermilion, molybdate orange, yellow lead, chrome yellow, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, pyridian, cobalt green, titanium cobalt green, cobalt chrome green, ultramarine blue, Prussian blue, cobalt blue, cerulean blue, manganese violet, cobalt violet, and mica.

[0055] Specific examples of organic pigments include azo, azomethine, polyazo, phthalocyanine, quinacridone, anthraquinone, indigo, thioindigo, quinophthalone, benzimidazolone, and isoindoline organic pigments. Carbon black made of acidic, neutral, or basic carbon may also be used. Hollow particles of crosslinked acrylic resin may also be used as the organic pigment.

[0056] Specific examples of pigments having a cyan color include CI Pigment Blue 1, CI Pigment Blue 2, CI Pigment Blue 3, CI Pigment Blue 15:3, CI Pigment Blue 15:4, CI Pigment Blue 16, CI Pigment Blue 22, and CI Pigment Blue 60. Among these, in terms of weather resistance, coloring power, etc., either or both of CI Pigment Blue 15:3 and CI Pigment Blue 15:4 are preferred.

[0057] Specific examples of pigments having a magenta color include CI Pigment Red 5, CI Pigment Red 7, CI Pigment Red 12, CI Pigment Red 48 (Ca), CI Pigment Red 48 (Mn), CI Pigment Red 57 (Ca), CI Pigment Red 57:1, CI Pigment Red 112, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 168, CI Pigment Red 184, CI Pigment Red 202, CI Pigment Red 209, CI Pigment Red 254, and CI Pigment Violet 19. Among these, from the viewpoints of weather resistance, coloring power, and the like, at least one selected from the group consisting of CI Pigment Red 122, CI Pigment Red 202, CI Pigment Red 209, CI Pigment Red 254, and CI Pigment Violet 19 is preferred.

[0058] Specific examples of pigments having a yellow color include CI Pigment Yellow 1, CI Pigment Yellow 2, CI Pigment Yellow 3, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14C, CI Pigment Yellow 16, CI Pigment Yellow 17, CI Pigment Yellow 73, CI Pigment Yellow 74, CI Pigment Yellow 75, CI Pigment Yellow 83, CI Pigment Yellow 93, CI Pigment Yellow 95, CI Pigment Yellow 97, CI Pigment Yellow 98, CI Pigment Yellow 109, CI Pigment Yellow 110, CI Pigment Yellow 114, CI Pigment Yellow 120, CI Pigment Yellow 128, CI Pigment Yellow 129, CI Pigment Yellow 130, CI Pigment Yellow 138, CI Pigment Yellow 139, CI Pigment Yellow 147, CI Pigment Yellow 150, CI Pigment Yellow 151, CI Pigment Yellow 154, CI Pigment Yellow 155, CI Pigment Yellow 180, CI Pigment Yellow 185, CI Pigment Yellow 213, CI Pigment Yellow 214, and the like. Among these, from the viewpoint of weather resistance and the like, at least one selected from the group consisting of CI Pigment Yellow 74, CI Pigment Yellow 83, CI Pigment Yellow 109, CI Pigment Yellow 110, CI Pigment Yellow 120, CI Pigment Yellow 128, CI Pigment Yellow 138, CI Pigment Yellow 139, CI Pigment Yellow 150, CI Pigment Yellow 151, CI Pigment Yellow 154, CI Pigment Yellow 155, CI Pigment Yellow 213, and CI Pigment Yellow 214 is preferred.

[0059] Specific examples of black pigments include HCF, MCF, RCF, LFF, and SCF manufactured by Mitsubishi Chemical Corporation, Monarch and Regal manufactured by Cabot Corporation, Color Black, Special Black, and Printex manufactured by Degussa-Huls Co., Ltd., Toka Black manufactured by Tokai Carbon Co., Ltd., and Raven manufactured by Columbia Chemical Co., Ltd. Among these, at least one selected from the group consisting of HCF#2650, HCF#2600, HCF#2350, HCF#2300, MCF#1000, MCF#980, MCF#970, MCF#960, MCF88, LFFMA7, MA8, MA11, MA77, and MA100 manufactured by Mitsubishi Chemical Corporation, and Printex 95, Printex 85, Printex 75, Printex 55, and Printex 45 manufactured by Degussa-Huls Co., Ltd. is preferred.

[0060] Specific examples of white pigments include Pigment White 6, 18, and 21. Basic lead carbonate (2PbCO 3 Pb(OH) 2 , also known as silver white), zinc oxide (ZnO, also known as zinc white), titanium oxide (TiO 2 , so-called titanium white), strontium titanate (SrTiO 3 , so-called titanium strontium white). Among these, titanium oxide has a smaller specific gravity, a larger refractive index, and is chemically and physically stable compared to other white pigments, and therefore has a large hiding power and coloring power as a pigment, and is also excellent in durability against acids, alkalis, and other environments. Therefore, it is more preferable to use titanium oxide as a white pigment.

[0061] The content of the colorant in the ink composition is preferably from 1 to 10% by mass, and more preferably from 1 to 9% by weight, based on the total weight of the ink composition.

[0062] When a pigment is used as the colorant, a pigment derivative or a pigment dispersant may be further used to improve the dispersibility of the pigment.

[0063] Specific examples of the pigment derivative include pigment derivatives having a dialkylaminoalkyl group, and pigment derivatives having a dialkylaminoalkylsulfonic acid amide group.

[0064] Specific examples of pigment dispersants include ionic or nonionic surfactants, and anionic, cationic or nonionic polymer compounds. Among these, polymer compounds containing cationic or anionic groups are preferred from the viewpoint of dispersion stability. Commercially available pigment dispersants include SOLSPERSE manufactured by Lubrizol Corporation, DISPERBYK manufactured by BYK-Chemie, and EFKA manufactured by EFKA Additives.

[0065] The content of the pigment derivative and the content of the pigment dispersant in the ink composition are each preferably 0.05 to 5% by mass relative to the total amount of the ink composition.

[0066] <4. Additives> <4-1. Surface conditioners> The surface conditioner may contain a silicone-based compound having a polydimethylsiloxane structure. By using the silicone-based compound as a surface conditioner together with the polymerizable compound, the liquid properties such as the surface tension of the ink can be adjusted to a range suitable for the inkjet recording method.

[0067] Specific examples of the silicone-based compound include BYK-UV3500, BYK-UV3510, and BYK-UV3570 manufactured by BYK-Chemie, Tego-Rad2100, Tego-Rad2200N, Tego-Rad2250, Tego-Rad2300, Tego-Rad2500, Tego-Rad2600, and Tego-Rad2700 manufactured by Degussa, and UCR-L72 and UCR-L93 manufactured by Kyoeisha Chemical Co., Ltd. These compounds contain a polydimethylsiloxane structure having an ethylenic double bond in the molecule, and therefore can further improve adhesion.

[0068] The content of the silicone compound in the ink composition is preferably 0.005% by mass or more and 1% by mass or less with respect to the entire ink composition.

[0069] <4-2. Anti-gelling agents> It is preferable that the anti-gelling agent further contains a hindered amine compound having a 2,2,6,6-tetramethylpiperidinyl group. By using the hindered amine compound as an anti-gelling agent together with a highly reactive polymerizable compound and a photopolymerization initiator, it is possible to obtain an ink having excellent storage stability without decreasing the reactivity of the ink. Specific examples of the anti-gelling agent include bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)sebacate, 2,2,6,6-tetramethylpiperidinoxy, and decanedioic acid bis(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl)ester. These may be used alone or in combination. Examples of commercially available anti-gelling agents include IRGASTAB UV-10 and TINUVIN 123 manufactured by Ciba, and HYDROXY-TEMPO manufactured by Evonik Degussa Japan.

[0070] The content of the antigelling agent in the ink composition is preferably 0.1% by mass or more and 4% by mass or less based on the total mass of the ink composition. If the content of the antigelling agent is less than 0.1% by mass, the radicals generated during storage cannot be sufficiently captured, and storage stability tends to decrease. On the other hand, if the content of the antigelling agent is more than 4% by mass, the radical capturing effect becomes saturated and the polymerization reaction during energy ray irradiation tends to be inhibited.

[0071] The gelation inhibitor may further contain other hindered amine compounds, phenolic antioxidants, phosphorus antioxidants, hydroquinone monoalkyl ethers, etc. Specific examples of such gelation inhibitors include hydroquinone monomethyl ether, hydroquinone, t-butylcatechol, pyrogallol, and TINUVIN 111 FDL, TINUVIN 144, TINUVIN 292, TINUVIN XP40, TINUVIN XP60, and TINUVIN 400 manufactured by Ciba Corporation.

[0072] <4-3. Other additives> If necessary, the ink composition of the present embodiment may further contain, as optional components, known general additives such as a surfactant, a leveling agent, an antifoaming agent, an antioxidant, a pH adjuster, a charge imparting agent, a bactericide, a preservative, a deodorant, a charge adjuster, a wetting agent, an antiskinning agent, and a fragrance.

[0073] <5. Adjustment Method> As a method for preparing the ink, a conventionally known preparation method can be used. When a pigment is used as the colorant, the following preparation method is preferred.

[0074] First, a mixture of a colorant, a part of a polymerizable compound, and, if necessary, a pigment dispersant is premixed to prepare a mixture, and the mixture is dispersed by a dispersing machine to prepare a primary dispersion. Specific examples of the dispersing machine include a disperser; a container-driven media mill such as a ball mill, a centrifugal mill, or a planetary ball mill; a high-speed rotating mill such as a sand mill; and a media stirring mill such as a stirring tank type mill.

[0075] Next, the remaining polymerizable compound, the photopolymerization initiator, the surface conditioner, and other additives such as an antigelling agent, if necessary, are added to the primary dispersion, and mixed uniformly using a stirrer. Specific examples of the stirrer include a three-one motor, a magnetic stirrer, a disperser, and a homogenizer. The ink composition may also be mixed using a mixer such as a line mixer. Furthermore, the ink composition may also be mixed using a disperser such as a bead mill or a high-pressure jet mill for the purpose of further miniaturizing the particles in the ink composition.

[0076] When a pigment is used as the colorant, the dispersed average particle size of the pigment particles in the ink composition is preferably 20 to 250 nm, and more preferably 50 to 230 nm.

[0077] According to this embodiment, since the polymerizable compound is composed of a monofunctional monomer, a first polyfunctional monomer having an acrylic equivalent of more than 150 and having two or more ethylenic double bonds in one molecule, and a second polyfunctional monomer having an acrylic equivalent of 150 or less and having two or more ethylenic double bonds in one molecule, it is possible to prepare an ink composition having a low viscosity of 6 to 8 mPa s at 25°C.

[0078] In addition, the ink composition of the present embodiment does not need to be diluted with a dilution solvent, has low viscosity even without heating, and further has good pigment dispersibility when the colorant is a pigment, and has good dispersion stability that does not cause problems such as an increase in viscosity or pigment sedimentation during storage or use. Therefore, in the inkjet recording method, stable ejection can be obtained at room temperature without heating the ink.

[0079] <6.Others> Inkjet recording methods include, but are not limited to, a charge control method that uses electrostatic attraction to eject ink, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element, an acoustic inkjet recording method that uses radiation pressure to convert an electric signal into an acoustic beam and irradiate the ink, and a thermal inkjet recording method that heats the ink to form bubbles and uses the resulting pressure, etc. The above inkjet recording methods include a method of ejecting a large number of low-concentration inks called photo inks in a small volume, a method of improving image quality by using multiple inks of substantially the same hue but different densities, and a method of using colorless and transparent ink.

[0080] In the present embodiment, examples of the irradiation means include ultraviolet ray irradiation means such as a mercury lamp or a metal halide lamp. In the case of the ink composition of the present embodiment, the integrated amount of ultraviolet ray is 200 mJ / cm. 2 The following low energy can also be used. The ink composition is preferably irradiated with the energy beam within 1 to 1,000 ms after the ink composition is ejected onto the recording medium. If the elapsed time is less than 1 ms, the distance between the head and the light source is too short, and the head may be irradiated with the energy beam, leading to an unexpected event. On the other hand, if the elapsed time exceeds 1,000 ms, the image quality tends to deteriorate due to ink bleeding when multiple colors are used.

[0081] The present invention will be described in more detail below with reference to examples, but is not limited to these examples. In the following, "parts" refers to "parts by mass." EXAMPLES

[0082] The components of the ink compositions used in each of the Examples and Comparative Examples are shown in Table 1 below.

[0083] [Table 1]

[0084] [Preparation of Ink Composition] Examples (Example) 1 to 9 and Comparative Examples (Comparative) 1 to 6 were prepared according to the blending amounts of the ink composition shown in Table 2. The indications in Table 2 correspond to those in Table 1.

[0085] In a 100cc plastic bottle, the colorant, pigment dispersant, and monofunctional monomer were weighed out in the amounts shown in Table 2, 100 parts of zirconia beads were added thereto, and the mixture was dispersed for 2 hours using a paint conditioner (manufactured by Toyo Seiki Co., Ltd.) to obtain a primary dispersion. Next, the remaining components were added to the obtained primary dispersion in the amounts shown in Table 2, and the mixture was stirred for 30 minutes using a magnetic stirrer. After stirring, the mixture was suction filtered using a glass filter (manufactured by Kiriyama Seisakusho Co., Ltd.) to prepare an ink composition. In Comparative Examples 4 and 5, the ink compositions were prepared in the same manner as above, except that the primary dispersion was prepared using tricyclodecane dimethanol diacrylate and 1,6 hexanediol diacrylate, respectively, instead of the monofunctional monomer.

[0086] [Table 2]

[0087] [evaluation] The viscosity of each of the ink compositions of the Examples and Comparative Examples prepared as described above was measured.

[0088] Furthermore, the ink layers (printed films) recorded on non-recording media using the ink compositions of the Examples and Comparative Examples were evaluated for adhesion, coating strength, stretchability, and curability. The evaluation results for the Examples and Comparative Examples shown in Table 2 are shown in Table 3. 〔viscosity〕 The viscosity was measured using an R100 type viscometer (manufactured by Toki Sangyo Co., Ltd.) at 25° C. and a cone rotation speed of 20 rpm. [Curability] The ink composition was printed on a non-recording medium made of a film made of polyethylene terephthalate (PET) to form a printed film having a thickness of 2 μm. A metal halide lamp was used as an irradiation means to irradiate the printed film with a total irradiation amount of 200 mJ / cm. 2The resin was cured by irradiating it with ultraviolet light so that the resin became hard.

[0089] The thus cured printed film was touched with a finger or a nail, and the presence or absence of ink adhesion to the finger or nail was visually examined and evaluated according to the following criteria.

[0090] ○: Ink does not adhere to fingers or nails, and the surface of the print film is not scratched even when rubbed with a nail. ×: Ink gets on your fingers

[0091] [Adhesion] The ink composition was printed on the non-recording medium of each film made of polyvinyl chloride (PVC) to form a printed film having a thickness of 2 μm. A metal halide lamp was used as an irradiation means for this printed film, and the total amount of irradiation light was 200 mJ / cm. 2 The resin was cured by irradiating it with ultraviolet light so that the resin became

[0092] The thus-cured printed film was subjected to a cross-cut test (100 pieces, 1 mm square) using Scotch tape (registered trademark) in accordance with JIS-K-5400 to check the peeling state. The number of peeled pieces out of the 100 pieces was counted and evaluated according to the following criteria.

[0093] ○: 10 or less peeled pieces in cross-cut test ×: 21 or more peeled pieces in the cross-cut test

[0094] [Coating film strength] The ink composition was printed on an acrylic plate as a non-recording medium to form a printed film having a thickness of 2 μm. A metal halide lamp was used as an irradiation means to irradiate the printed film with a total irradiation amount of 200 mJ / cm. 2 The resin was cured by irradiating it with ultraviolet light so that the resin became hard.

[0095] The pencil hardness of the thus cured printed film was measured and evaluated according to the following criteria. The measurements were performed using a surface property tester "HEIDON-14DR" manufactured by Shinto Scientific Co., Ltd., based on the pencil hardness measurement method specified in Japanese Industrial Standards (JIS) K5400.

[0096] 〇: Pencil hardness 4H or higher ×: Pencil hardness less than 4H

[0097] [Stretchability] The ink composition was printed on the non-recording medium of the stretching test medium to form a printed film. A metal halide lamp was used as an irradiation means to irradiate the printed film with a total irradiation amount of 200 mJ / cm. 2 The resin was cured by irradiating it with ultraviolet light so that the resin became hard.

[0098] The printed film thus obtained was cut into a 10 mm x 70 mm rectangular shape to prepare a test piece. The test piece was fixed to a sample stage at 10 mm positions on both sides, and evaluated at a pulling speed of 50 mm / min using a tensile tester (Autograph AGS-H 100N manufactured by SIMADZU). When cracks appeared in the printed part of the test piece, pulling was stopped, and the elongation was calculated and evaluated according to the following criteria.

[0099] 〇: Growth rate 160% or more ×: Elongation rate less than 160%

[0100] [Table 3]

[0101] As shown in Table 3 above, the ink composition of the example containing a monofunctional monomer as a polymerizable compound, a first polyfunctional monomer having an acrylic equivalent of more than 150 and having two or more ethylenic double bonds in one molecule, a second polyfunctional monomer having an acrylic equivalent of 150 or less and having two or more ethylenic double bonds in one molecule, at least one of an alkylphenone compound and a thioxanthone compound as a photopolymerization initiator, and a silicone compound having a polydimethylsiloxane structure as a surface conditioner, has a viscosity of 6 mPa s or more and 8 mPa s or less at 25°C, which is low.

[0102] As shown in Examples 1 to 9 in Tables 2 and 3, this embodiment can provide an energy beam-curable inkjet ink composition that is substantially free of a solvent, has low viscosity, and is excellent in curability and stretchability. Therefore, the ink compositions of the examples have excellent ejection stability and can provide high-definition printed matter.

[0103] In addition, in an energy beam curable ink that does not substantially contain a solvent, it is possible to include an oligomer as a polymerizable compound, but in this case, the viscosity of the ink becomes high and the ejection stability becomes insufficient, resulting in poor continuous ejection properties and insufficient curability and adhesion.

[0104] It is clear that the ink composition containing only a monofunctional monomer as the polymerizable compound has poor coating strength due to the absence of a polyfunctional monomer component, and has poor adhesion and curability due to the small amount of crosslinking components (Comparative Example 1).

[0105] It is found that an ink composition containing a monofunctional monomer and a first polyfunctional monomer having an acrylic equivalent of more than 150 as a polymerizable compound has poor coating strength due to an extremely small amount of the polyfunctional monomer component of the crosslinking component, and has poor stretchability and adhesion due to the lack of coating strength sufficient to withstand tensile strength (Comparative Example 2).

[0106] It is understood that an ink composition containing a monofunctional monomer and a second polyfunctional monomer having an acrylic equivalent of 150 or less as a polymerizable compound has poor coating strength due to a decrease in the polyfunctional monomer component of the crosslinking component (Comparative Example 3).

[0107] Ink compositions containing only a first polyfunctional monomer having an acrylic equivalent of more than 150 as a polymerizable compound, and ink compositions containing only a second polyfunctional monomer having an acrylic equivalent of 150 or less, have high viscosity and poor adhesion because they lack the monofunctional monomer component that serves as a diluting and adhesive component. It can be seen that the coating film becomes hard because it is made up of only polyfunctional monomers, and therefore stretchability is poor (Comparative Examples 4 and 5).

[0108] Even in an ink composition containing a monofunctional monomer, a first polyfunctional monomer having an acrylic equivalent greater than 150, and a second polyfunctional monomer having an acrylic equivalent of 150 or less as polymerizable compounds, if the content of the monofunctional monomer is 45% by mass or less relative to the total ink composition, the monofunctional monomer component, which is a diluting and adhesive component, disappears, resulting in high viscosity and poor adhesion, and the ratio of the polyfunctional monomer in the crosslinking component increases, resulting in a hard coating film and poor stretchability (Comparative Example 6). Preferred aspects of the present invention include the following. [1] An ink-jet ink composition comprising a polymerizable compound and a photopolymerization initiator, The polymerizable compound is A monofunctional monomer, a first polyfunctional monomer having an acrylic equivalent of more than 150 and having two or more ethylenic double bonds in one molecule; and a second polyfunctional monomer having an acrylic equivalent of 150 or less and two or more ethylenic double bonds in one molecule. [2] The inkjet ink composition according to [1], wherein the content of the monofunctional monomer is 50 to 80% by mass, the content of the first polyfunctional monomer is 1 to 10% by mass, and the content of the second polyfunctional monomer is 5 to 35% by mass, based on the total mass of the inkjet ink composition. [3] The ink-jet ink composition according to [1], wherein the polymerization initiator comprises at least one of an alkylphenone compound and a thioxanthone compound. [4] In [1], The glass transition temperature of the monofunctional monomer is −70° C. or more and 29° C. or less, The glass transition temperature of the first polyfunctional monomer is −25° C. or more and 180° C. or less; The ink-jet ink composition, wherein the second polyfunctional monomer has a glass transition temperature of 43° C. or higher and 100° C. or lower. [5] The ink-jet ink composition according to [1], further comprising a surface conditioner and a colorant. [6] The ink-jet ink composition according to [1], wherein the ink-jet ink composition has a viscosity of 6.5 to 8.0 mPa·s at 25° C.

Claims

1. An inkjet ink composition comprising a polymerizable compound, a photopolymerization initiator, a colorant, and a surface conditioner, The polymerizable compound is Contains a monofunctional monomer and a polyfunctional monomer, the monofunctional monomer includes a monofunctional monomer having a viscosity of 10 mPa·s or less at 25°C and a monofunctional monomer having a viscosity of 80 mPa·s or more at 25°C; The polyfunctional monomer is a first polyfunctional monomer having an acrylic equivalent of more than 150 and having two or more ethylenic double bonds in one molecule; a second polyfunctional monomer having an acrylic equivalent of 150 or less and two or more ethylenic double bonds in one molecule, the content of the first polyfunctional monomer is 1 to 8% by mass based on the total mass of the inkjet ink composition; the content of the second polyfunctional monomer is 5 to 35% by mass based on the total mass of the inkjet ink composition; the surface conditioner contains a silicone compound having a polydimethylsiloxane structure in an amount of 0.005 to 1% by mass based on the total mass of the inkjet ink composition; Inkjet ink composition.

2. The inkjet ink composition described in claim 1, wherein the photopolymerization initiator includes at least one of an alkylphenone-based compound and a thioxanthone-based compound.

3. An inkjet ink composition described in claim 1 or 2, wherein the mass ratio of the content of the first polyfunctional monomer to the content of the second polyfunctional monomer (second polyfunctional monomer / first polyfunctional monomer) is 2 to 15.

4. An inkjet ink composition described in any of claims 1 to 3, wherein the inkjet ink composition has a viscosity of 6 to 8 mPa·s measured under conditions of 25°C and a cone rotation speed of 20 rpm.