JP5949031B2 - Ink jet ink composition and ink jet recording method - Google Patents

Description

  The present invention relates to an inkjet ink composition and an inkjet recording method.

Ink-jet printing is a method in which small droplets of ink are ejected from nozzles and attached to a surface to be printed such as paper, and then the solvent is dried from the attached ink to fix the color material to the surface to be printed. How to do it. According to this method, a high-resolution and high-quality image can be printed at high speed.
Water-based inks used in ink-jet printing do not contain volatile components in the ink and are excellent from the viewpoint of safety and environmental issues. However, bleeding is likely to occur when printing on high-quality paper or plain paper. Insufficient drying when printing on this paper, making high-speed printing difficult, and the problem that the printed ink cannot be fixed on a recording medium that does not absorb ink, such as polymer resin film, earthenware, or glass substrate Occurs. In order to solve such problems, various water-based ultraviolet curable inks have been disclosed.

  For example, Patent Document 1 discloses a water-based ultraviolet curable inkjet ink having a particle size and a zeta potential within a predetermined range. It is also disclosed that this ink-jet ink contains 20% by mass or more of a photocurable monomer or oligomer having three or more photofunctional groups and contains an emulsion type photopolymerizable compound.

  For example, Patent Document 2 discloses an ink for an ink jet printer in which a specific ultraviolet curable resin is emulsified and dispersed in water to lower the viscosity.

  For example, in Patent Document 3, in a photopolymerization-type aqueous ink containing a photopolymerizable resin and a photoradical polymerization initiator, the photopolymerizable resin is present in an emulsion state and the oligomer particles. An aqueous ink composed of a monomer present in particles and a photopolymerization initiator is disclosed.

  For example, Patent Document 4 discloses that in a photopolymerization type water-based ink containing a photopolymerizable resin and a photopolymerization initiator, a water-soluble organic solvent and a surfactant are used, whereby 10 mPa · s or more and 60 mPa · s are used. An inkjet ink adjusted to a viscosity of s or less is disclosed.

Japanese Patent No. 4411852 Japanese Patent No. 3659658 International Publication No. 01/057145 Pamphlet JP 2010-229179 A

  As described above, in the prior art ink, a surfactant is sometimes used to emulsify and disperse the photocurable resin in water, or a monomer and a photopolymerization initiator are present in the oligomer particles in the emulsion state. Or let me.

  However, in the prior art ink as described above, in order to be cured by low-energy ultraviolet irradiation, the amount of resin emulsion having a radical polymerizable group (hereinafter also referred to as resin emulsion) must be increased. For this reason, the solid content concentration of the resin emulsion in the ink increases, and the ink viscosity in the vicinity of the nozzle increases accordingly, which causes a problem in terms of ejection stability.

  Accordingly, an object of the present invention is to provide an ink-jet ink composition having excellent ejection stability while maintaining curability.

The inventors of the present application have made extensive studies to solve the above problems. As a result, it has been found that the above-mentioned problems can be solved by an ink composition for inkjet including water, a colorant, a resin emulsion having a radical polymerizable group, an inorganic particle dispersion, and a radical photopolymerization initiator, The present invention has been completed.
That is, the present invention is as follows.

  [Application Example 1] An ink-jet ink composition comprising water, a coloring material, a resin emulsion made of a compound having a radical polymerizable group, an inorganic particle dispersion, and a photo radical polymerization initiator.

  Application Example 2 The inkjet ink composition according to the application example, wherein the concentration of the compound having a radical polymerizable group in the ink composition is 6% by mass or more and 20% by mass or less.

  Application Example 3 The inkjet ink composition according to any one of the above application examples, wherein the inorganic particle dispersion is at least one of alumina, zinc oxide, cerium oxide, and colloidal silica.

  Application Example 4 The inkjet ink composition according to any one of the above application examples, wherein the inorganic particle dispersion has a solid content concentration in the ink of 0.5% by mass or more and 3% by mass or less. object.

  Application Example 5 The inkjet ink composition according to any one of the above application examples, wherein the inorganic particle dispersion has an average particle diameter (D50) of 40 nm to 500 nm.

  [Application Example 6] According to any one of the above-mentioned periodic examples, the compound having a radical polymerizable group is a compound having self-emulsifying ability, and the resin emulsion is a self-emulsifying resin emulsion. Ink-jet ink composition.

  [Application Example 7] In addition to the above-mentioned compound, the composition further includes another compound having a radical polymerizable group, and the other compound is a compound having three or more polymerizable functional groups in the molecule. The inkjet ink composition according to Application Example 6.

  [Application Example 8] In any one of the above application examples, the compound having a radical polymerizable group is at least one of a (meth) acryloyl group, a vinyl group, a vinyl ether group, and a mercapto group. Ink-jet ink composition.

  [Application Example 9] Any one of the above application examples, further including a water-soluble organic solvent, wherein the water-soluble organic solvent is an organic solvent containing at least one of a polar solvent and a permeable solvent. 2. An ink composition for inkjet according to the above.

  [Application Example 10] The ink-jet ink composition according to any one of the above application examples, wherein the photoradical polymerization initiator is a hydrophobic photopolymerization initiator.

  [Application Example 11] In addition to the above compound, the compound contains another compound having a radical polymerizable group, and the compound and the photo radical polymerizable initiator are encapsulated in the resin emulsion. The inkjet ink composition according to any one of Application Examples 6 to 10.

  [Application Example 12] The inkjet ink composition according to any one of the above application examples, in which recording is performed by a recording method including a heating step of heating a recording medium that discharges the ink composition. Ink-jet ink composition.

  Application Example 13 An ink jet recording method using the ink composition for ink jet recording according to any one of the application examples 1 to 12.

The schematic diagram which demonstrates macroscopically an example of the ultraviolet curable aqueous emulsion of a photocurable aqueous emulsion. The schematic diagram which demonstrates microscopically an example of the ultraviolet curable aqueous emulsion of a photocurable aqueous emulsion. FIG. 2 is a conceptual diagram showing the periphery of a head of an example of an ink jet recording apparatus according to an embodiment of the invention.

  Hereinafter, preferred embodiments of the present invention will be described. The embodiment described below describes an example of the present invention. In addition, the present invention is not limited to the following embodiments, and includes various modifications that are implemented within a range that does not change the gist of the present invention.

  In this specification, “curability” refers to a property of curing in response to light. “Ejection stability” refers to the property of constantly ejecting stable ink droplets from the nozzles without missing dots or flying bends. “Storage stability” refers to the property that the viscosity is difficult to change before and after storage.

  In the present specification, “recorded material” refers to a material in which ink is recorded on a recording medium to form a cured product. In addition, the hardened | cured material in this specification means the hardened | cured substance containing a cured film and a coating film.

  In the present specification, “(meth) acrylate” means at least one of acrylate and methacrylate corresponding thereto, and “(meth) acryl” means at least one of acrylic and methacryl corresponding thereto. To do.

[Inkjet ink composition]
One embodiment of the present invention relates to an inkjet ink composition (hereinafter also simply referred to as “ink composition”). The ink composition contains water, a coloring material, a resin emulsion having a radical polymerizable group, an inorganic particle dispersion, and a photo radical polymerization initiator.

  Hereinafter, the components contained in or capable of being contained in the inkjet ink composition will be described in detail.

[water]
As water used in the ink composition of the present embodiment, that is, water as a main solvent, pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, distilled water, or ultrapure water can be used. .

[Color material]
The ink composition of the present embodiment includes a color material. As the color material, at least one of a pigment and a dye can be used.

(Pigment)
In this embodiment, the light resistance of the ink composition can be improved by using a pigment as the color material. Any pigment can be used without particular limitation as long as it is commonly used in inkjet water-based pigment inks.

  Examples of the pigment include azo pigments (for example, azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc.), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, Organic pigments such as dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments), nitro pigments, nitroso pigments, aniline black; carbon blacks (eg furnace black, thermal lamp black, acetylene black, channel black), metals Inorganic pigments such as oxides, metal sulfides, and metal chlorides; extender pigments such as silica, calcium carbonate, and talc can be used.

  Specific examples of the pigment include C.I. I. Pigment Yellow 64, 74, 93, 109, 110, 128, 138, 139, 150, 151, 154, 155, 180, 185, C.I. I. Pigment red 122, 202, 209, C.I. I. Pigment violet 19, C.I. I. Pigment Blue 15: 3, 15: 4, 60, C.I. I. Pigment green 7 (phthalocyanine green), 10 (green gold), 36, 37, C.I. I. Pigment brown 3, 5, 25, 26, C.I. I. Pigment orange 1, 2, 5, 7, 13, 14, 15, 16, 34, 36, 38, 64, 71 and the like.

  The pigment may be obtained by dispersing a pigment dispersion obtained by dispersing in water with a dispersant, or by dispersing a self-dispersed surface-treated pigment into which hydrophilic groups are introduced by utilizing a chemical reaction on the surface of pigment particles in water. It is preferably added to the ink as a pigment dispersion obtained by dispersing a pigment coated with a polymer in water.

  The former, that is, a dispersant used for preparing a pigment dispersion obtained by dispersing in water with a dispersant is not particularly limited. For example, a polymer dispersant (such as glue, gelatin, casein, albumin, etc.) Natural rubbers such as gum arabic and tragacanth, glucosides such as saponin, alginic acid and propylene glycol esters, alginic acid triethanolamine, alginate fermented products such as ammonium alginate, cellulose derivatives such as methylcellulose, carboxymethylcellulose, ethylhydroxycellulose, polyvinyl Alcohols, polypyrrolidones, polyacrylic acid, acrylic acid-acrylonitrile copolymer, potassium acrylate-acrylonitrile copolymer, vinyl acetate-acrylic ester copolymer Acrylic resins such as acrylic acid-acrylic acid ester copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid ester copolymer, styrene-m-methylstyrene- Acrylic acid copolymer, styrene-acrylic resin, styrene-maleic acid copolymer, styrene-maleic anhydride copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl acetate-ethylene copolymer, vinyl acetate- Fatty acid vinyl ethylene copolymers, vinyl acetate-maleic acid ester copolymers, vinyl acetate-croton copolymers, vinyl acetate copolymers such as vinyl acetate-acrylic acid copolymers and their salts) and surface activity Agents (various anionic surfactants, nonionic surfactants, amphoteric surfactants, etc.) It is possible.

  On the other hand, among the latter, self-dispersed surface-treated pigments having the above hydrophilic groups introduced are dispersed or dissolved in water without a dispersant by surface treatment in which carboxyl groups and salts thereof are directly bonded to the surface of the pigment. Is possible. Specifically, by grafting functional groups or molecules containing functional groups onto the pigment surface by physical treatment such as vacuum plasma or chemical treatment using an oxidizing agent such as sodium hypochlorite or ozone. Can be obtained. The functional group grafted on one pigment particle may be single or plural kinds. The type and degree of the functional group to be grafted may be appropriately determined in consideration of the dispersion stability in the ink, the color density, the drying property on the front surface of the inkjet head, and the like.

  Among the latter, the pigment coated with the above polymer is not particularly limited. For example, after dispersing the pigment using a dispersant having a polymerizable group, the monomer (copolymer) that can be copolymerized with the dispersant is used. It can be obtained by carrying out emulsion polymerization in water using a polymerizable monomer) and a radical photopolymerization initiator. Among these polymers, monomers and oligomers having at least one of acryloyl group, methacryloyl group, vinyl group, and allyl group as double bonds are polymerized according to a known polymerization method using a photoradical polymerization initiator However, it can be preferably used. A general method can be used for the above emulsion polymerization, and the polymerization proceeds by free radicals generated by thermal decomposition of a water-soluble photoradical polymerization initiator in the presence of an emulsifier.

  The pigment and the dispersant constituting the pigment dispersion may be used alone or in combination of two or more.

  Since the pigment dispersion has an advantageous effect of forming a clear image on various types of media, it is 0.05 to 25% by mass with respect to the total amount (100% by mass) of the ink composition in terms of solid content. %, Preferably 0.1 to 20% by mass.

[Inorganic particle dispersion]
The ink composition of the present embodiment includes an inorganic particle dispersion. This inorganic particle dispersion has a specific particle size and refers to that dispersed in water. In the ink composition, the dispersibility of the ink composition disperses the micelles formed by the resin emulsion contained in the ink, thereby preventing thickening due to a local concentration increase of the micelles formed by the resin emulsion. ing. By preventing this thickening, the inkjet ink composition can be stably ejected.

  The thickening due to the local concentration increase of the resin emulsion described above occurs for the following reason.

  In particular, the particle size of the self-emulsifying resin emulsion varies depending on the concentration. This is due to the fact that the micelles formed by the resin emulsion form a larger aggregate when the concentration is high, and at this time, the viscosity increases significantly.

  Remarkable thickening accompanying the increase in the particle size of the micelle formed by the resin emulsion at the high concentration described above easily occurs in the vicinity of the ink jet discharge port, thereby destabilizing the discharge.

  At this time, the addition of the inorganic particle dispersion can prevent the thickening accompanying the increase of the micelle particle size formed by the resin emulsion. This is because the inorganic particle dispersion prevents the increase in particle size by entering into the micelle gap when the micelle formed by the resin emulsion is at a high concentration. Thereby, ejection instability is unlikely to occur.

  The dispersion method of the inorganic particle dispersion is not particularly limited, but includes, for example, self-emulsification type and emulsification with a dispersant.

  The inorganic particle dispersion is composed of an inorganic compound and can be stably dispersed in water. The material is not particularly limited, and examples thereof include zinc oxide, cerium oxide, alumina, and colloidal silica. Among them, it is most preferable to use colloidal silica because of excellent dispersibility.

  The inorganic particle dispersion preferably has a particle size of 10 to 500 nm, more preferably 40 to 500 nm. Also, from the functional property of preventing the resin emulsions from aggregating into the gaps between the micelles formed by the resin emulsion, the particle size of the micelles formed by the resin emulsion is preferably equal to or greater than that. More preferably. When the particle size of the micelle formed by the resin emulsion is 250 nm, it is particularly preferable to use one having a particle size of 200 to 450 nm.

  The concentration of the inorganic particle dispersion in the inkjet ink composition is not particularly limited, but is preferably 0.5% to 3%, more preferably 0.5 to 2%, More preferably, it is contained in an amount of 1% to 1%.

[Photo radical polymerization initiator]
The ink composition of this embodiment contains a radical photopolymerization initiator. This photo-radical polymerization initiator generates radicals (initiator radicals) by photo-cleavage or hydrogen abstraction caused by irradiation with active energy rays such as ultraviolet rays, and attacks radical-polymerizable compounds to cause radical polymerization. cause.

  Specific examples of the photo radical polymerization initiator are not particularly limited, but include acetophenone, 2,2-diethoxyacetophenone, p-dimethylaminoacetophenone, benzophenone, 2-chlorobenzophenone, p, p′-dichlorobenzophenone, p, p. '-Bisdiethylaminobenzophenone, Michler's ketone, benzyl, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-propyl ether, benzoin isobutyl ether, benzoin-n-butyl ether, benzylmethyl ketal, 2,2-dimethoxy -1,2-diphenylethane-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-1- {4- [4- (2-hydroxy-2-methylpro Onyl) benzyl] phenyl} 2-methylpropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) butanone-1,2-dimethylamino-2- (4-methylbenzyl) -1- (4-morpholin-4-yl-phenyl) butan-1-one, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide, Bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide, 2-methyl-1- [4- (methylthio) phenyl] 2-morpholinopropan-1-one, thioxanthone, 2- Chlorothioxanthone, 2-hydroxy-2-methyl-1-phenyl-1-one, 1- (4- Isopropyl phenyl) -2-hydroxy-2-methylpropan-1-one, methyl benzo fill formate, azo-bis-isobutyronitrile Lilo nitrile, benzoyl peroxide, and di -tert- butyl peroxide.

  Examples of commercially available photo radical polymerization initiators include IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethane-1-one), IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173. (2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959 (1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propane- 1-one), IRGACURE 127 (2-hydroxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] phenyl} -2-methyl-propan-1-one}, IRGACURE 907 (2-Methyl-1- (4-methylthiophenyl) -2-morphol Linopropan-1-one), IRGACURE 369 (2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1), IRGACURE 379 (2- (dimethylamino) -2-[(4- Methylphenyl) methyl] -1- [4- (4-morpholinyl) phenyl] -1-butanone), DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), Speedcure TPO (2,4,4) 6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE 819 (bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide), IRGACURE 784 (bis (η5-2,4-cyclopentadien-1-yl) ) -Bis (2,6 Difluoro-3- (1H-pyrrol-1-yl) -phenyl) titanium), IRGACURE OXE 01 (1.2-octanedione, 1- [4- (phenylthio)-, 2- (O-benzoyloxime)]) IRGACURE OXE 02 (ethanone, 1- [9-ethyl-6- (2-methylbenzoyl) -9H-carbazol-3-yl]-, 1- (O-acetyloxime)), IRGACURE 754 (oxyphenylacetic acid, 2- [2-oxo-2-phenylacetoxyethoxy] ethyl ester and oxyphenylacetic acid, 2- (2-hydroxyethoxy) ethyl ester mixture (above, manufactured by BASF), DETX-S (2,4-diethyl) Thioxanthone) (Nippon Kayaku Co. , Ltd. )), Lucirin TPO, LR8883, LR8970 (above, manufactured by BASF), Ubekrill P36 (manufactured by UCB), and the like.

  When the photocurable composition according to the present embodiment is cured by an ultraviolet LED, it is preferable to use a photopolymerization initiator having a maximum absorption wavelength in a wavelength region of 350 nm or more and 430 nm or less. Specifically, 2,4,6-trimethylbenzoyl-diphenyl-oxide (DAROCUR TPO, manufactured by BASF), Speedcure TPO (produced by Lambson Group Ltd), and bis (2,4,6-trimethylbenzoyl) -phenyl oxide (IRGACURE 819, manufactured by BASF).

A radical photopolymerization initiator may be used individually by 1 type, and may be used in combination of 2 or more type. The radical photopolymerization initiator is preferably contained in an amount of 0.1 to 10% by mass, more preferably 0.5 to 8% by mass, based on the total amount (100% by mass) of the ink composition. When it is within the above range, the curability is good.
The radical photopolymerization initiator is preferably included in the resin emulsion from the viewpoint of radical polymerization initiation efficiency. In addition, it is preferable that the radical photopolymerization initiator is hydrophobic because it is easily included in the resin emulsion.

[Resin emulsion]
In the ink composition of the present embodiment, the resin emulsion is composed of a compound having a radical polymerizable group. The compound having the radical polymerizable group has a predetermined structure and a weight average molecular weight. This compound may be any compound having a radical polymerizable group and forming an emulsion, and may be a compound having an emulsifying ability or a compound constituting an emulsion together with a compound having an emulsifying ability. By using a resin emulsion comprising a compound having a radical polymerizable group, an ink composition having excellent curability can be obtained, and a photo radical initiator can be easily included. In particular, the self-emulsifying emulsion having self-emulsifying ability and emulsifying property is preferable in that the curability is particularly excellent. The ink composition of the present embodiment is particularly effective in a self-emulsifying resin emulsion using a compound having a radical polymerizable group having self-emulsifying ability and emulsifying ability.

  In the self-emulsifying resin emulsion, the compound is an amphiphilic compound having a hydrophilic part and a hydrophobic part in the molecule, and refers to a compound that forms micelles and is stably dispersed in the solvent. The particle size (average particle size D50) of the micelle formed by the resin emulsion is preferably 100 to 350 nm, and more preferably 200 to 300 nm. The average particle diameter of the micelle of the resin emulsion and the inorganic particle dispersion described above means a cumulative 50% particle diameter based on the volume, and is measured by a dynamic light scattering method. The average particle diameter can be measured using, for example, Microtrac UPA150 (trade name, manufactured by Microtrac Inc.). In each Example mentioned later, the average particle diameter of an inorganic particle dispersion and a resin emulsion was measured by the said method.

  Examples of the radical polymerizable group of the compound having a radical polymerizable group include a (meth) acryloyl group, a vinyl group, a vinyl ether group, and a mercapto group.

  As a structural feature of the compound having a radical polymerizable group, it is preferable to include any of a urethane bond, an ester bond, an amide bond, and an ether bond.

[Compound having a radical polymerizable group]
In the ink composition of the present embodiment, the resin emulsion is preferably a photocurable aqueous emulsion. The resin emulsion is composed of at least a compound having a radical polymerizable group, and further composed of another compound having the radical polymerizable group (hereinafter also referred to as another compound) and a photo radical polymerization initiator. Can be done. In this case, it is excellent in curability by ultraviolet irradiation in the presence of water or a solvent, and the odor can be effectively suppressed.

The compound having a radically polymerizable group constituting the resin emulsion in the ink composition of the present embodiment is such that the amphiphilic compound has a self-emulsifying ability, constitutes a self-emulsifying resin emulsion, and has excellent curability. preferable. An amphiphilic compound is a compound having a parent part and a hydrophobic part. The hydrophilic part is preferably a polyalkylene glycol residue, more preferably a polyalkylene glycol monoalkyl ether residue, and the hydrophobic part is a diisocyanate residue used to form a urethane bond or an acyclic carbonization. Hydrogen or cyclic hydrocarbon residues are preferred. The amphiphilic compound is, for example, a crosslinked urethane in which any one of the following general formulas (1), (4), (5) and general formulas (1), (4), and (5) is crosslinked with a (meth) acrylate residue A ¹ Any one of the compounds. In each general formula, the hydrophilic part is D ¹ , D ² , D ³ , and the hydrophobic part is B ¹ , C ¹ .
Although it does not specifically limit as a compound which has a radically polymerizable group, For example, urethane (meth) acrylate which is demonstrated below can be used, and amphiphilic urethane (meth) acrylate is used especially. Is preferred.

  Among them, it is preferable to use an amphiphilic straight-chain urethane (meth) acrylate, and a radical polymerizable (meth) acrylic compound is included as a radical photopolymerization initiator and another compound having a radical polymerizable group. Therefore, the curability is excellent and preferable. Since the urethane (meth) acrylate is an amphiphilic substance, it is a photo-curing that has the advantageous effect of being stable, excellent in dispersibility, and having low viscosity by making its molecular structure a linear structure. A mold-type aqueous emulsion can be obtained.

  The above-mentioned effects resulting from the photocurable aqueous emulsion are considered to have been brought about for the following reasons.

  FIG. 1 is a schematic diagram illustrating a macroscopic example of an ultraviolet curable aqueous emulsion of a photocurable aqueous emulsion, and FIG. 2 is a microscopic example of an ultraviolet curable aqueous emulsion of a photocurable aqueous emulsion. FIG. As shown in FIG. 1 and FIG. 2, the amphiphilic urethane (meth) acrylate, which is an example of a compound having a radical polymerizable group, is a shell layer in water with the hydrophobic portion facing the core and the hydrophilic portion facing the aqueous phase. To form a micelle, and in water, a radical polymerizable compound (preferably radical polymerizable (preferably a compound having a radical polymerizable group in the figure)). It is believed that micelles encapsulating (meth) acrylate) and a radical photopolymerization initiator can be formed.

  This is considered due to the molecular structure of the urethane (meth) acrylate. In other words, at the time of micelle formation, the molecular structure of urethane (meth) acrylate is bent with less steric hindrance than when the main chain is branched or when it has a hydrophobic portion at both ends of the main chain. It is thought that there is no conformation. Therefore, it is considered that the hydrophilic portion can be regularly and densely oriented toward the aqueous phase. Therefore, if the micelles are closely oriented, hydrogen bonds between urethane bonds work effectively, and the micelle formation strength (packing property) increases, which is considered to contribute to the stability and dispersibility of the micelles.

  Therefore, the photocurable aqueous emulsion has excellent stability and good photopolymerization property even when the radical polymerizable compound (preferably radical polymerizable (meth) acrylate) and the photo radical polymerization initiator are contained in the micelle. Can be obtained.

  In addition, the photocurable aqueous emulsion can be selected by a person skilled in the art in the present technical field by appropriately improving and changing the method performed in the Examples section described below. A known method such as a combination method, a high pressure emulsification method, a phase inversion emulsification method, or the like may be employed. Moreover, you may use various well-known emulsifiers and a dispersing agent as needed in the range which does not impair the effect of this invention.

  The emulsion polymerization method is a method in which an amphiphilic substance such as a surfactant is added to an aqueous phase and an oil phase is added thereto. The high-pressure emulsification method is a method in which an amphiphilic substance such as an aqueous phase, an oil phase and a surfactant is premixed and emulsified with a high-pressure emulsifier such as a homogenizer to obtain an aqueous emulsion. The phase inversion emulsification method is a method in which an amphiphilic substance such as a surfactant is dissolved and dispersed in an oil phase, and an aqueous phase is added thereto to obtain an O / W type emulsion. This is called phase inversion emulsification because the continuous phase changes from water to oil during the emulsification (phase inversion).

Thus, the ink composition containing a photocurable aqueous emulsion using urethane (meth) acrylate in particular has a low viscosity, excellent curability, can be photocured even in the presence of water, and is resistant to hydrolysis. Excellent in properties. In particular, in the form in which the micelle formed by the urethane (meth) acrylate includes a compound having a radical polymerizable group and a photo radical polymerization initiator, excellent curability and light in the presence of a predetermined concentration of water are also obtained. Performance that is not found in conventional photocurable aqueous emulsions that harden can be obtained. In addition, urethane (meth) acrylates that form micelles of photocurable aqueous emulsions can be closely oriented from the structure, and further have urethane bonds (urethane groups) in the hydrophobic part of the structure, so the urethanes arranged It is considered that a strong bonding force due to hydrogen bonding works between (meth) acrylates. Therefore, it is considered that a stable emulsion in which the inclusions of micelles are difficult to leak out and hardly hydrolyze is obtained.
This inference is made to explain the curability of the photocurable aqueous emulsion, and does not limit the photocurable aqueous emulsion in the present embodiment.

  Hereinafter, details of urethane (meth) acrylate, which is an example of a compound having a radical polymerizable group constituting the resin emulsion, will be described.

<Configuration of urethane (meth) acrylate>
The urethane (meth) acrylate has a weight average molecular weight of 1,000 to 10,000 and a structure represented by the following general formula (1).
^{A 1 -O- (CONH-B 1} -NHCOO-C 1 -O) n -CONH-B 1 -NH-COO-D 1 ... (1)
(In formula (1), n represents a natural number of 1 to 30, A ¹ represents a hydroxyl group-containing (meth) acrylate residue, B ¹ represents a diisocyanate residue, and C ¹ represents an acyclic carbonization. And represents a residue of a hydrogen or cyclic hydrocarbon diol, and D ¹ represents a residue of a polyoxyalkylene glycol monoalkyl ether.)

Here, the residue is a portion of the raw material structure of the urethane (meth) acrylate represented by the general formula (1) excluding the functional group that forms a urethane bond. In the group-containing (meth) acrylate, the portion excluding the hydroxyl group (represented by A ¹ ), in the diisocyanate the portion excluding the isocyanate group (B ¹ ), in the acyclic hydrocarbon or cyclic hydrocarbon diol, the hydroxyl A portion excluding a group (C ¹ ), and a polyoxyalkylene glycol monoalkyl ether is a portion excluding a hydroxyl group (D ¹ ).

The weight average molecular weight of the urethane (meth) acrylate represented by the general formula (1) can be calculated by measuring a molecular weight distribution by gel permeation chromatography (GPC). The weight average molecular weight in the present specification is a weight average molecular weight in terms of standard polystyrene molecular weight, and GPC (HLC-8220 [trade name], manufactured by TOSOH CORPORATION) has a column: TSK-gel SuperHZM- M (exclusion limit molecular weight: 4 × 10 ⁶ , molecular weight fractionation range: 266 to 4 × 10 ⁶ , theoretical plate number: 16,000 plates / piece, filler material: styrene copolymer, filler particle size: 3 μm) Is measured by using three in series.

  The weight average molecular weight of the urethane (meth) acrylate represented by the general formula (1) is 1,000 to 10,000, preferably 2,000 to 8,000. When the weight average molecular weight is within the above range, micelles can be easily formed and excellent self-emulsifying properties can be obtained, and an advantageous effect that a hydrophobic substance can be easily encapsulated in the micelles can be obtained. This is presumably because a good balance between hydrophilicity and hydrophobicity was obtained by using the urethane (meth) acrylate represented by the general formula (1).

  In the general formula (1), n represents a natural number of 1 to 30. In addition, the specific numerical value of n is determined by adjusting said weight average molecular weight.

(Hydroxyl group-containing (meth) acrylate)
Hydroxyl group-containing (meth) acrylates described above is a compound which gives structure of A ¹ in the general formula (1). The hydroxyl group-containing (meth) acrylate is used for introducing a polymerizable group into the general formula (1). Specifically, the hydroxyl group-containing (meth) acrylate is a compound having one or more (meth) acryloyl groups and one hydroxyl group, wherein the hydroxyl group is one of diisocyanates. By urethanation with an isocyanate group, a (meth) acryloyl group is introduced into one end of the main chain of urethane (meth) acrylate. The introduction of at least one (meth) acryloyl group enables photopolymerization (photocuring), and the introduction of two or more (meth) acryloyl groups increases the photopolymerization rate and increases the hardness of the cured product. An advantageous effect is obtained.

  Although it does not specifically limit as monohydroxy mono (meth) acrylate which is monofunctional, For example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (Meth) acrylate and polycaprolactone mono (meth) acrylate may be mentioned.

  Although it does not specifically limit as monohydroxy di (meth) acrylate which is bifunctional, For example, glycerol di (meth) acrylate is mentioned.

  Although it does not specifically limit as monohydroxy poly (meth) acrylate which is trifunctional or more, For example, pentaerythritol tri (meth) acrylate and dipentaerythritol penta (meth) acrylate are mentioned.

  Among these, polypropylene glycol mono (meth) acrylate is preferable and polypropylene glycol monoacrylate is more preferable because an emulsion having a low viscosity can be obtained. On the other hand, since an emulsion having particularly excellent curability can be obtained, at least one of pentaerythritol tri (meth) acrylate and dipentaerythritol penta (meth) acrylate is preferable as the hydroxyl group-containing (meth) acrylate.

  Said hydroxyl group containing (meth) acrylate may be used individually by 1 type, and may be used in combination of 2 or more type.

(Diisocyanate)
Additional diisocyanates are compounds which provide the structure of B ¹ in the general formula (1). The diisocyanate refers to an organic diisocyanate having two reactive isocyanate groups in one molecule.

  Urethane (meth) acrylate synthesized using an organic polyisocyanate having 3 or more isocyanate groups in the molecule tends to have a high molecular weight and tends to have a high viscosity. A molecular chain having at least one hydrophilic group and a molecular chain having at least two (meth) acryloyl groups having a polyisocyanate having three or more isocyanate groups as a main skeleton in these urethane (meth) acrylates. An emulsion (aqueous emulsion) obtained by emulsifying water having a hydrophilic portion in a branched structure molecule also tends to increase in viscosity.

  In contrast, urethane (meth) acrylate synthesized using diisocyanate having two isocyanate groups in one molecule has a linear structure in which the structure derived from diisocyanate and the structure derived from diol are arranged in a straight line. As shown in the general formula (1), there is a hydrophilic part derived from polyoxyalkylene glycol monoalkyl ether at one end, and at least one (meth) acryloyl group and one hydroxyl group at the other end. Hydrophobic part in which a structure derived from acyclic hydrocarbon or cyclic hydrocarbon diol having two hydroxyl groups in the molecule is bonded to the structure derived from (meth) acrylate having a urethane bond via a diisocyanate Because of this structure, the emulsifiability in water is particularly excellent, and the viscosity of the emulsion (aqueous emulsion) Can be drastically reduced compared with the emulsion of the prior art urethane (meth) acrylates described above.

  The diisocyanate is not particularly limited. For example, diisocyanates having an alicyclic hydrocarbon skeleton such as isophorone diisocyanate, diisocyanates having an aliphatic hydrocarbon skeleton such as hexamethylene diisocyanate, xylylene diisocyanate, tolylene diisocyanate, and diphenylmethane diisocyanate. And diisocyanates having a hydrogenated aromatic hydrocarbon skeleton such as diisocyanates having an aromatic hydrocarbon skeleton such as hydrogenated xylylene diisocyanate and hydrogenated diphenylmethane diisocyanate.

  Among these, an advantageous effect that a cured product of urethane (meth) acrylate is hardly yellowed by sunlight (ultraviolet rays) is obtained, so that isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated xylylene diisocyanate, and hydrogenated diphenylmethane diisocyanate One or more selected from the group consisting of

  Said diisocyanate may be used individually by 1 type in a molecule | numerator and between molecules, and may be used in combination of 2 or more type.

(Acyclic hydrocarbon or cyclic hydrocarbon diol)
The acyclic hydrocarbon or the diol of the cyclic hydrocarbon is a compound that gives the structure of C ¹ in the general formula (1). The diol is introduced to adjust the degree of hydrophobicity of the hydrophobic portion of the urethane (meth) acrylate represented by the general formula (1). The diol is selected so as to obtain good hydrophobicity. As a specific example, one or more diols selected from the group consisting of aliphatic, alicyclic, and aromatic diols having two hydroxyl groups in one molecule are preferably used. The diol shown is more preferred. Specifically, since the hydrophobicity is particularly excellent, the carbon number of the acyclic hydrocarbon or the diol of the cyclic hydrocarbon is preferably 6-20.

  In addition, the diol may be selected to be suitable for controlling the rigidity or flexibility of the urethane (meth) acrylate and exhibiting good hydrophobicity depending on the purpose of use and intended use. it can.

  As said aliphatic diol, if it is a diol which does not have an aromatic structure and an alicyclic structure in a molecule | numerator, it will not specifically limit and a well-known thing can be used. Specific examples include 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14. -Tetradecanediol, 1,15-pentadecanediol, 1,18-octadecanediol, 1,19-nonadecanediol, 1,20-eicosanediol, polypropylene glycol (eg, dipropylene glycol, tripropylene glycol), aliphatic Examples include polycarbonate polyol, aliphatic polyester polyol, and aliphatic polycaprolactone diol.

  As said aromatic diol, if it has an aromatic structure in a molecule | numerator, it will not specifically limit and a well-known thing can be used. Specific examples include biphenyl-4,4'-diol, 1,4-benzenediol, bisphenol A, ethylene oxide modified bisphenol A, propylene oxide modified bisphenol A, aromatic polycarbonate polyol, and aromatic polyester polyol.

  As said alicyclic diol, if it has an alicyclic structure in a molecule | numerator, it will not specifically limit and a well-known thing can be used. Specific examples include hydrogenated bisphenol A, ethylene oxide-modified hydrogenated bisphenol A, propylene oxide-modified hydrogenated bisphenol A, 1,4-cyclohexanediol, tricyclodecane dimethanol, alicyclic polycarbonate polyol, alicyclic polyester polyol, etc. Is mentioned.

  Among these, aliphatic diols and alicyclic diols are preferable because emulsification in water becomes favorable and a cured product of urethane (meth) acrylate is hardly yellowed by sunlight (ultraviolet rays). Among the aliphatic diols, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,15-pentadecanediol, 1,18-octadecanediol, 1,19-nonadecanediol, 1,20-eicosanediol, polypropylene glycol, aliphatic polycarbonate polyol, aliphatic polyester polyol, And at least one selected from the group consisting of aliphatic polycaprolactone diols is more preferred. Further, among the alicyclic diols, selected from the group consisting of hydrogenated bisphenol A, ethylene oxide-modified hydrogenated bisphenol A, propylene oxide-modified hydrogenated bisphenol A, 1,4-cyclohexanediol, and tricyclodecane dimethanol. One or more are more preferable.

  The above diols may be used alone or in combination of two or more in one molecule and between molecules.

(Polyoxyalkylene glycol monoalkyl ether)
Polyoxyalkylene glycol monoalkyl ethers described above is a compound which gives structure of D ¹ in the general formula (1). The polyoxyalkylene glycol monoalkyl ether is a compound in which one hydroxyl group of the polyoxyalkylene glycol is blocked with an alkyl group, and is represented by the following general formula (2).
HO— (CH ₂ CH ₂ O) _m —R (2)
(In formula (2), R represents an alkyl group, and m represents a natural number of 9 to 90.)

  This hydroxyl group is introduced into one end of the main chain of urethane (meth) acrylate by urethanation reaction with one isocyanate group of diisocyanate. As a result, urethane (meth) acrylate has a hydrophilic portion at one end of the linear main chain and at least one polymerizable group (meth) acryloyl group and hydrophobic group at the other end. Since the structure of the amphipathic substance arranged by the constituted hydrophobic portion is obtained, the emulsifiability in water is particularly excellent.

  Moreover, since the polyoxyalkylene glycol monoalkyl ether has the advantageous effect that the hydrophilicity can be freely adjusted, it is preferable that the molecule contains a polyoxyethylene structure.

  The polyoxyethylene structure is a repeating structure of oxyethylene groups. The average number of repeating oxyethylene groups, that is, m in the general formula (2), is determined by adjusting the balance between hydrophilicity and hydrophobicity so that emulsification of urethane (meth) acrylate in water is good, and 9 to 90 The natural number of 9 to 60 is preferable, the natural number of 9 to 60 is more preferable, and the natural number of 9 to 30 is more preferable.

  The polyoxyalkylene glycol monoalkyl ether is not particularly limited, and examples thereof include polyethylene glycol monoalkyl ethers such as polyethylene glycol monomethoxy ether and polyethylene glycol monoethoxy ether.

  In addition to the polyoxyethylene structure, polyoxyalkylene glycol monoalkyl ethers containing other polyoxyalkylene structures in the molecule can also be used. In that case, it is preferable for emulsification that the polyoxyethylene structure is located on the terminal alkyl group side. In this case, examples of the polyoxyalkylene structure that can be used together with the polyoxyethylene structure include a polyoxypropylene structure and a polyoxytetramethylene structure. The number of repeating oxyalkylene groups of the polyoxyalkylene structure used together with the polyoxyethylene structure is appropriately determined in consideration of the hydrophilicity / hydrophobicity balance of the urethane (meth) acrylate.

  As the terminal alkyl group of the polyoxyalkylene glycol monoalkyl ether, that is, R in the general formula (2), an alkyl group having a smaller number of carbon atoms is more hydrophobic and more emulsifying, so that a methyl group, an ethyl group, Or a propyl group is preferable and a methyl group is more preferable.

  Said polyoxyalkylene glycol monoalkyl ether may be used individually by 1 type, and may be used in combination of 2 or more type.

  Moreover, urethane (meth) acrylate may be used individually by 1 type, and may be used in combination of 2 or more type.

  When used as an ink composition, the content of urethane (meth) acrylate is such that the total amount of ink composition (100% by mass) can form a coating film and obtain coating film performance such as good film strength and adhesion. %) To 5 to 50% by mass, and more preferably 10 to 40% by mass.

[Crosslinked urethane (meth) acrylate]
The ink composition of the present embodiment may contain a crosslinked urethane (meth) acrylate having a structural unit containing the urethane (meth) acrylate together with or instead of the above-described urethane (meth) acrylate. The crosslinked urethane (meth) acrylate having the urethane (meth) acrylate represented by the general formula (1) as a structural unit is excellent in curability and further excellent in storage stability of the emulsion.

(Crosslinking agent)
Said crosslinked urethane (meth) acrylate can be obtained by making the above-mentioned urethane (meth) acrylate and a bifunctional or more functional crosslinking agent react.

  By using a crosslinking agent, urethane (meth) acrylate can be made high molecular weight. Thereby, it is possible to obtain a crosslinked urethane (meth) acrylate having further excellent curability and further excellent storage stability of the emulsion.

  In addition, gelation can be prevented by carrying out the reaction in an oil system (oil phase) in an O / W emulsion instead of a solvent system or a solvent-free system (solvent-free system).

  The above bifunctional or higher functional crosslinking agent is preferably hydrophobic because it undergoes an addition reaction with a (meth) acryloyl group. In other words, the bifunctional or higher functional crosslinking agent is Michael-added to the (meth) acryloyl group in the urethane (meth) acrylate represented by the general formula (1) in the oil phase in the emulsion. Crosslink urethane (meth) acrylate.

  Examples of the crosslinking agent that reacts with such a (meth) acryloyl group include those having a thiol group or an amino group in the molecule. Especially, since reaction can be advanced rapidly, at least any one among a polyfunctional thiol compound and a polyfunctional amine compound is preferable, and a polyfunctional thiol compound is more preferable.

  Specific examples of the bifunctional or higher functional crosslinking agent include, but are not particularly limited to, mercapto group-containing compounds and amino group-containing compounds. Among them, a mercapto group-containing compound is preferable because of its low solubility in water and easy incorporation into the oil phase when dispersed in water.

  The mercapto group-containing compound is not particularly limited. For example, pentaerythritol tetrakis (3-mercaptopropionate) (hereinafter also referred to as “PEMP”), trimethylolpropane tris (3-mercaptopropionate), Tris-[(3-mercaptopropionyloxy) -ethyl] -isocyanurate, tetraethylene glycol bis (3-mercaptopropionate), dipentaerythritol hexakis (3-mercaptopropionate), pentaerythritol tetrakis (3- Mercaptobutyrate) and trimethylolpropane tris (3-mercaptobutyrate).

  The content of the bifunctional or higher functional crosslinking agent is preferably 3 to 10% by mass, and 5 to 8% by mass with respect to the total mass (100% by mass) of the (meth) acryloyl group-containing resin. Is more preferable.

  In addition, the “(meth) acryloyl group-containing resin” in the present specification means all resins containing a (meth) acryloyl group that is crosslinked by the crosslinking agent. Therefore, the (meth) acryloyl group-containing resin includes both the urethane (meth) acrylate represented by the general formula (1) and a compound having three or more (meth) acryloyl groups in the molecule described later. included.

<Method for producing urethane (meth) acrylate>
Hereinafter, the manufacturing method of the said urethane (meth) acrylate is demonstrated. The urethane (meth) acrylate is obtained by reacting the hydroxyl group-containing (meth) acrylate, the diisocyanate, the acyclic hydrocarbon or the diol of the cyclic hydrocarbon, and the polyoxyalkylene glycol monoalkyl ether. It is obtained with. More specifically, the method for producing urethane (meth) acrylate includes a first step, a second step, and a third step.

In the first step, a urethane bond represented by the following general formula (1a) is obtained by reacting the diisocyanate with a diol of an acyclic hydrocarbon or a cyclic hydrocarbon, preferably having 6 to 20 carbon atoms. A first reactant having is obtained.
^{OCN- (B 1 -NHCOO-C 1} -O) n -CONH-B 1 -NCO ... (1a)
In the first step, the molar ratio between the diisocyanate and the acyclic hydrocarbon having 6 to 20 carbon atoms or the diol of the cyclic hydrocarbon is preferably 5: 1 to 5: 4, More preferably, it is 5: 2 to 5: 3.

In the second step, the first reactant is reacted with the polyoxyalkylene glycol monoalkyl ether to obtain a second reactant represented by the following general formula (1b).
^{OCN- (B 1 -NHCOO-C 1} -O) n -CONH-B 1 -NH-COO-D 1 ... (1b)
In this second step, the molar ratio of the first reactant to the polyoxyalkylene glycol is preferably 1: 0.5 to 1: 1 because emulsification in water becomes good. .

  In the third step, the second reactant is reacted with the hydroxyl group-containing (meth) acrylate. In the third step, the molar ratio of the second reactant to the hydroxyl group-containing (meth) acrylate is preferably 1: 1.5 to 1: 1, more preferably 1: 1. .4 to 1: 1.2.

<Method for producing crosslinked urethane (meth) acrylate>
The manufacturing method of crosslinked urethane (meth) acrylate is a method of manufacturing said crosslinked urethane (meth) acrylate. The said manufacturing method reacts the urethane (meth) acrylate represented by General formula (1) obtained through said 1st process-3rd process, and the above-mentioned bifunctional or more cross-linking agent. The fourth step of crosslinking the urethane (meth) acrylate is included.

  In the fourth step, in addition to the urethane (meth) acrylate represented by the general formula (1), other compounds having the radical polymerizable group described above are reacted with the bifunctional or higher functional crosslinking agent. In particular, compounds having three or more (meth) acryloyl groups in the molecule are preferred.

In the fourth step, the aforementioned fixing urethane (meth) acrylate may be further added. In particular, when the substrate is made of polyvinyl chloride (hereinafter also simply referred to as “PVC”), it is preferable to further add fixing urethane (meth) acrylate. Specifically, when a PVC base material is used, the coating film (described later) requires adhesion to the PVC base material. Therefore, it can be said that the use of the fixing urethane (meth) acrylate is preferable because the adhesion to the substrate becomes better by adding the fixing urethane (meth) acrylate.
In addition, when using a base material made of polyethylene terephthalate (PET) other than PVC, because the particles are fragmented, the curability is further improved and the storage stability of the emulsion is further improved. The content (addition amount) of the urethane (meth) acrylate is preferably low, and the content of the compound having 3 or more (meth) acryloyl groups in the molecule is preferably as much as that.

  In the fourth step, the content of the urethane (meth) acrylate represented by the general formula (1) and a compound having three or more (meth) acryloyl groups in the molecule (when present), and the above The content of the bifunctional or higher functional crosslinking agent is preferably 100: 1 to 100: 10, more preferably 100: 5 to 100: 8, in terms of mass. When the content ratio is not less than the lower limit of the above range, the curability and the storage stability are further improved. In addition, when the content ratio is less than or equal to the upper limit of the above range, it is possible to prevent the generation of insoluble matter, and to prevent the disappearance of the (meth) acryloyl group in the system and to maintain the curability better. it can.

  As described above, the fourth step includes a bifunctional or higher functional crosslinker such as urethane (meth) acrylate represented by the general formula (1) and a polyfunctional thiol monomer, and 3 in the molecule as an optional component. One or more compounds selected from the group consisting of a compound having one or more (meth) acryloyl groups, a urethane (meth) acrylate for fixing, preferably a radical photopolymerization initiator containing a thioxanthone group, and a fluorescent brightening agent Then, water is dropped and emulsified (dispersed in water). The obtained emulsion is heated, for example, at 80 ° C. for 6 hours, whereby the Michael addition reaction is promoted and a crosslinked urethane (meth) acrylate is obtained.

  At this time, the compound having a (meth) acryloyl group reacts with the crosslinking agent to crosslink the compound having a (meth) acryloyl group. In other words, the crosslinking agent does not react only with urethane (meth) acrylate but reacts with a compound having a (meth) acryloyl group. Therefore, the structure of the crosslinked urethane (meth) acrylate is a compound obtained by crosslinking the urethane (meth) acrylate represented by the general formula (1), the urethane (meth) acrylate represented by the general formula (1) and the inclusion. Various cross-linked products such as a compound formed by cross-linking with a (meth) acryloyl group-containing compound that is a product and a compound formed by cross-linking (meth) acryloyl group-containing compounds that are inclusions can coexist. Here, the inclusion means an object existing inside the micelle when an emulsion is formed to obtain a micelle structure.

  As mentioned above, when the compound having a (meth) acryloyl group reacts with the crosslinking agent, all of the compounds having a (meth) acryloyl group are crosslinked and some are crosslinked and the rest are crosslinked. May remain. Further, a catalyst may be used to further promote the Michael addition reaction.

[Compounds having other radical polymerizable groups]
The compound having a radical polymerizable group constituting the resin emulsion of the ink composition of the present embodiment may be a compound having other radical polymerizable properties other than the compound having the self-emulsifying ability described above. May be a compound having no self-emulsifying ability. When the compound does not have self-emulsifying ability, it is preferable to form an emulsion together with an emulsifier such as a surfactant. In particular, a compound having a radical polymerizable group that does not have self-emulsifying ability may be included together with the above-mentioned compound having radical polymerizable ability having self-emulsifying ability. Among the other compounds having a radical polymerizable group, those used together with the compound having a radical polymerizable group having the self-emulsifying ability are particularly referred to as other compounds having a radical polymerizable group.
It is preferable that other compounds having a radical polymerizable property are encapsulated in the resin emulsion. Other compounds having a radical polymerizable group react in a chain reaction under the attack of an initiator radical described later generated by irradiation with ultraviolet rays having a specific wavelength (range). At the same time, the radical polymerizable groups of the compound having the radical polymerizable group contained in the resin emulsion, which are present in the same uniform field, also react in a chain manner. Thus, the ink composition forms a cured film on the recording medium.

  Examples of the radical polymerizable group in the compound having another radical polymerizable group include a (meth) acryloyl group, a vinyl group, a vinyl ether group, and a mercapto group.

  Among the other compounds having the radical polymerizable group contained in the ink composition, those having at least one (meth) acryloyl group in the structure are particularly preferable, and those having an acryloyl group in the structure are further included. preferable. The radically polymerizable compound includes a monomer having a molecular weight of about several hundreds, an oligomer having a molecular weight of about several thousands, and a polymer having a molecular weight of tens of thousands or less.

  Although it does not specifically limit as a radically polymerizable compound which has one (meth) acryloyl group in a molecule | numerator, For example, isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, Decyl (meth) acrylate, isomyristyl (meth) acrylate, isostearyl (meth) acrylate, butoxyethyl (meth) acrylate, phenoxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2- Hydroxy-3-phenoxypropyl (meth) acrylate, lactone-modified flexible (meth) acrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentenyl (meth) acrylate, di Black pentenyl oxyethyl (meth) acrylate, glycidyl (meth) acrylate and isobornyl (meth) acrylate.

  The compound having a radically polymerizable group having two (meth) acryloyl groups in the molecule is not particularly limited. For example, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meta ) Acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol-tricyclodecane di (meth) acrylate.

  Among these, as a compound having another radical polymerizable group, a compound having three or more (meth) acryloyl groups in the molecule is more preferable because of excellent photopolymerizability.

  The compound having a radically polymerizable group having three or more (meth) acryloyl groups in the molecule is not particularly limited. For example, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (Meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, caprolactone-modified trimethylolpropane tri (meth) acrylate, pentaerythritol ethoxytetra (meth) Acrylate, epichlorohydrin modified trimethylolpropane tri (meth) acrylate, tripentaerythritol octa (meth) acrylate, tetrapenta Suritorudeka (meth) acrylate, poly pentaerythritol poly (meth) acrylate, and caprolactone-modified dipentaerythritol hexa (meth) acrylate and the like.

  In addition, the compound having three or more (meth) acryloyl groups in the molecule is not particularly limited. For example, polyester (meth) acrylate, polyurethane (meth) acrylate (however, the above urethane (meth) acrylate) ), Epoxy (meth) acrylate, polyether (meth) acrylate, oligo (meth) acrylate, alkyd (meth) acrylate, and polyol (meth) acrylate and other oligomers having molecular weights of up to several thousand (meth) Examples include those having 3 or more acryloyl groups, oligomers having 3 or more acryloyl groups in the molecule, polymers having molecular weights of up to several thousand, polymers having molecular weights of up to several tens of thousands, and dendrimer type (meth) acrylates.

As another compound having a radical polymerizable group, urethane (meth) acrylate may be used. Thereby, when forming the coating film containing an emulsion on a PVC base material, the fixability (adhesiveness) of the said coating film becomes more excellent. Therefore, hereinafter, it is also referred to as fixing urethane (meth) acrylate. As described above, since the other compound having a radical polymerizable group preferably includes a compound having excellent photopolymerizability (curability), the fixing urethane (meta) that improves the adhesion in combination with the compound. It is more preferable to use acrylate.
The fixing urethane (meth) acrylate is different from the urethane (meth) acrylate represented by the general formula (1).

  The fixing urethane (meth) acrylate is composed of diisocyanate, a diol component having an aromatic skeleton, and a hydroxyl group-containing (meth) acrylate, as will be described later.

  The weight average molecular weight of the fixing urethane (meth) acrylate is preferably 1,000 to 10,000, and more preferably 3,000 to 8,000. When the weight average molecular weight is within the above range, the adhesion of the coating film to the PVC substrate is excellent and the stability of the emulsion is also good.

(Hydroxyl group-containing (meth) acrylate)
Hydroxyl group-containing (meth) acrylates are used for the introduction of polymerizable groups. Specifically, the hydroxyl group-containing (meth) acrylate used in the present embodiment is a compound having at least one (meth) acryloyl group and one hydroxyl group, and having an isocyanate group and urethanization. By reacting, (meth) acryloyl groups are introduced into both ends of the main chain of the fixing urethane (meth) acrylate. Curing (photopolymerization) is possible by introducing at least one (meth) acryloyl group, and further, the curing rate can be increased by introducing two or more (meth) acryloyl groups, and the hardness of the cured product Can be increased.

  Although it does not specifically limit as monohydroxy mono (meth) acrylate, For example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, polyethyleneglycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate , Polycaprolactone mono (meth) acrylate, glycerol di (meth) acrylate, pentaerythritol tri (meth) acrylate, and dipentaerythritol penta (meth) acrylate.

  Said hydroxyl group containing (meth) acrylate may be used individually by 1 type, and may be used in combination of 2 or more type.

(Diisocyanate)
The diisocyanate is not particularly limited. For example, diisocyanate having an alicyclic hydrocarbon skeleton such as isophorone diisocyanate, diisocyanate having an aliphatic hydrocarbon skeleton such as hexamethylene diisocyanate, xylylene diisocyanate, tolylene diisocyanate, and diphenylmethane diisocyanate. And diisocyanates having a hydrogenated aromatic hydrocarbon skeleton such as hydrogenated xylylene diisocyanate and hydrogenated diphenylmethane diisocyanate.
Among these, the cured urethane (meth) acrylate for fixing is not easily yellowed by sunlight (ultraviolet rays), so it is selected from the group consisting of isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated xylylene diisocyanate, and hydrogenated diphenylmethane diisocyanate. One or more of these are preferred.
Said diisocyanate may be used individually by 1 type in a molecule | numerator and between molecules, and may be used in combination of 2 or more type.

(Diol component having an aromatic skeleton)
As the diol having an aromatic skeleton, any known diol can be used as long as it has an aromatic structure in the molecule. Specific examples include biphenyl-4,4′-diol, 1,4-benzenediol, bisphenol A, ethylene oxide modified bisphenol A, propylene oxide modified bisphenol A, aromatic polycarbonate polyol, and aromatic polyester polyol.
Among these, aromatic polyester polyol is preferable because adhesion to the PVC base material is further improved. Among the aromatic polyester polyols, isophthalate is more preferable.
The above diols may be used alone or in combination of two or more in one molecule and between molecules.
Since the content of the urethane (meth) acrylate is more excellent in adhesion to the PVC substrate and stability after water dispersion, the content of the urethane (meth) acrylate is 0. 0% with respect to the total mass (100% by mass) of the photocurable aqueous emulsion. 5-4 mass% is preferable and 1-3 mass% is more preferable.

  The above radical polymerizable compounds (other compounds having a radical polymerizable group) may be used alone or in combination of two or more.

  The compound having another radical polymerizable group is contained in an amount of 1 to 60% by mass with respect to the total amount (100% by mass) of the ink composition in order to impart excellent photopolymerizability (curability) to the ink composition. Is preferable, and it is more preferable that 2-30 mass% is contained.

[Water-soluble organic solvent]
The ink composition of this embodiment may contain a water-soluble organic solvent. When the ink composition contains a water-soluble organic solvent, an ink-jet ink that can maintain fluidity and redispersibility for a long time even when left in an open state (a state where the ink is in contact with air at room temperature) is obtained. be able to. Furthermore, since such an ink composition is less likely to be clogged with an ink jet nozzle during printing using an ink jet printer or upon restart after printing interruption, the ink composition has excellent ejection stability from the ink jet nozzle. Things are obtained.

  As this water-soluble organic solvent, those used in this kind of ink composition can be used without any particular limitation. In particular, in order to impart water retention and wettability to the ink composition, it is preferable to use a high boiling point wetting agent having a boiling point of 180 ° C. or higher, preferably 200 ° C. or higher. Specific examples of the high boiling point wetting agent are not particularly limited, but ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, pentamethylene glycol, trimethylene glycol, 2-butene-1,4-diol, 2-ethyl-1 , 3-hexanediol, triethylene glycol monobutyl ether, 2-methyl-2,4-pentanediol, tripropylene glycol, polyethylene glycol having a molecular weight of 2000 or less, 1,3-propylene glycol, isopropylene glycol, isobutylene glycol, glycerin, Examples include mesoerythritol, pentaerythritol, and 2-pyrrolidone.

  A water-soluble organic solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

  As described above, since these water-soluble organic solvents inhibit the ink curing reaction, in order to achieve both ink reliability and good curability, the total amount (100% by mass) of the ink composition is used. On the other hand, it is preferable that 1-30 mass% is contained, and 1-10 mass% is more preferable.

[Other additives]
The ink composition of the present embodiment may include additives other than the above-described additives. Other additives include, but are not particularly limited to, for example, penetrating solvents, antifungal agents, antiseptics, rust inhibitors, antioxidants, thickeners, pH adjusters, (fixing) resins, and surfactants. It is done.

  The ink composition may contain a penetrating solvent. By including an osmotic solvent, an advantageous effect of appropriate wetting and spreading on a wide range of media can be obtained. The osmotic solvent is not particularly limited, but includes 1,2-alkanediol, acetylene glycol, alkylene glycol, alkylene. Examples include glycol alkyl ethers and glycol ethers. Among these, by using 1,2-alkanediol, it is difficult to absorb ink such as printing paper and plastic film, or when printing on a recording medium that does not absorb it, than when using other permeable solvents. It is possible to reduce unevenness in the aggregation of recorded matter.

  Specific examples of 1,2-alkanediol include, but are not limited to, 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol, and 4-methyl-1,2-pentanediol. Can be mentioned.

  The ink composition may contain a surfactant. The surfactant is not particularly limited. For example, polyester-modified silicone or polyether-modified silicone can be used as the silicone-based surfactant, and polyether-modified polydimethylsiloxane or polyester-modified polydimethylsiloxane can be used. Is particularly preferred. As specific examples, BYK-331, BYK-333, BYK-375, BYK-347, BYK-348, BYK-349, BYK-UV3500, 3510, 3530, 3570 (above, BYK Japan KK) Manufactured).

  Surfactant may be used individually by 1 type and may be used in combination of 2 or more type.

[Method for producing ink-jet ink composition]
The ink composition of the present embodiment can be obtained by mixing water, a colorant, a resin emulsion having a radical polymerizable group, an inorganic particle dispersion, a radical photopolymerization initiator, and other necessary materials. it can.

  As described above, according to the present embodiment, the ink composition for inkjet is excellent in the curability by ultraviolet irradiation, the ejection stability such as missing dots and flying curves, the ability to recover from nozzle clogging after standing for a long time, and the storage stability of ink. Is obtained. Furthermore, this ink-jet ink composition achieves high-speed printing and low viscosity, and is excellent in safety and compatibility with recording media.

[Recordings]
One embodiment of the present invention relates to a recorded matter. The recorded matter is obtained by recording the ink composition of the above embodiment on a recording medium, and includes a recording medium and a cured product of the ink composition recorded on the recording medium. The recorded matter is characterized by excellent scratch resistance and gas resistance.

[Inkjet recording method]
One embodiment of the present invention relates to an inkjet recording method. The ink jet recording method includes a discharge step of discharging the ink composition of the above-described embodiment onto a recording medium, and irradiating the ink composition discharged by the discharge step with active energy rays to thereby apply the ink composition. And a curing step for curing. In this way, a cured film (coating film) is formed by the ink composition cured on the recording medium. Hereafter, each said process is demonstrated in detail.

[Discharge process]
In the ejection step, a conventionally known ink jet recording apparatus can be used. When discharging the ink composition, the viscosity of the ink composition is preferably 30 mPa · s or less, and more preferably 2 to 20 mPa · s. When the viscosity of the ink composition is within the above range, good ejection stability is realized.

[Curing process]
Next, in the curing step, the ink composition ejected on the recording medium is cured by irradiation with active energy rays.

  Specifically, the polymerization reaction of the polymerizable compound is started by irradiation with active energy rays. In addition, the radical photopolymerization initiator contained in the ink composition is decomposed by irradiation with active energy rays to generate initiation species such as radicals, acids, and bases, and the polymerization reaction of the polymerizable compound causes the initiation species. Promoted by function. At this time, if the sensitizing dye is present together with the photoradical polymerization initiator in the ink composition, the sensitizing dye in the system absorbs the active energy ray to be in an excited state, and is brought into contact with the photoradical polymerization initiator to form the photoradical. It is possible to accelerate the decomposition of the polymerization initiator and achieve a more sensitive curing reaction.

  Mercury lamps and gas / solid lasers are mainly used as light sources (active energy ray sources). Mercury lamps and metal halide lamps are used as light sources for curing photocurable ink jet ink compositions. Widely known. On the other hand, there is a strong demand for mercury-free from the viewpoint of environmental protection, and replacement with a GaN-based semiconductor ultraviolet light-emitting device is very useful industrially and environmentally. Furthermore, ultraviolet light emitting diodes (UV-LEDs) and ultraviolet laser diodes (UV-LDs) are small, have a long life, have high efficiency, and are low in cost, and are expected as light sources for photo-curable ink jets. Among these, UV-LED is preferable.

Here, the active energy ray can have an emission peak wavelength suitable for curing the first or second radical polymerizable compound. In the present embodiment, an ink composition that can be cured by irradiation with radiation having an emission peak wavelength preferably in the range of 360 to 420 nm is used. The irradiation energy is preferably 500 mJ / cm ² or less.

  In the above case, curing at low energy and high speed is possible due to the composition of the ink composition of the above embodiment. The irradiation energy is calculated by multiplying the irradiation time by the irradiation intensity. The irradiation time can be shortened by the composition of the ink composition of the above embodiment, and in this case, the recording speed is increased. On the other hand, the irradiation intensity can be reduced by the composition of the ink composition of the above embodiment, and in this case, the apparatus can be downsized and the cost can be reduced. In this case, UV-LED is preferably used for radiation irradiation. Such an ink composition can be obtained by including a radical photopolymerization initiator that decomposes upon irradiation with radiation in the above wavelength range and a polymerizable compound that initiates polymerization upon irradiation with radiation in the above wavelength range. The emission peak wavelength may be one or plural within the above wavelength range. Even in the case where there are a plurality, the irradiation energy of the whole radiation having the emission peak wavelength is set as the irradiation energy.

[Heating process]
In the present embodiment, the recording method may include a heating step of heating the recording medium. By the heating process, the temperature of the recording medium on which the ink composition is ejected in the ejection process can be increased, and the evaporation of water contained in the ink composition can be accelerated to complete the recording earlier. For the heating, the recording medium may be heated with a heater, or warm air may be applied to the recording medium. The heating process may be performed at least one of before, simultaneously with, and after the discharging process, and may be performed at least one of before, simultaneously with, and after the curing process. The temperature of the recording medium in the heating step is preferably 35 to 70 ° C., and more preferably 35 to 60 ° C., from the viewpoint of speeding up drying of the ink and reducing damage due to heat of the recording medium.

[Inkjet recording device]
One embodiment of the present invention relates to an inkjet recording apparatus. The ink jet recording apparatus is a recording apparatus that performs recording by the above ink jet recording method. FIG. 3 is a conceptual diagram showing the periphery of the head of an example of the ink jet recording apparatus according to the embodiment of the present invention. The ink jet recording apparatus 1 includes a platen 2 that supports a recording medium P that is supplied from a medium roll Q, is guided by a guide roll 6 and is taken up by a take-up roll R, and heats the recording medium. The platen 2 is provided with a heater 3. The transport roller 4 and the pinch roller 5 sandwich the recording medium P, and the transport roller 4 is rotated by a motor (not shown) to transport the recording medium P in the transport direction Y. The carriage 8 is provided with a head 10 that ejects ink onto the recording medium P, an irradiation device 11 that irradiates the recording medium P, and an attachment member 9, and moves in the main scanning direction X along the carriage rail 7. The main scanning is performed. The position of the irradiation device 11 is not limited to that shown in FIG. 3, and may be downstream of the head 10 in the transport direction Y.

  As described above, according to the present embodiment, it is possible to provide an ink jet recording method that is excellent in curability by irradiation with active energy rays, ejection stability such as missing dots and flying bends, and nozzle clogging recovery properties.

  Hereinafter, the embodiments of the present invention will be described more specifically by way of examples. However, the embodiments of the present invention are not limited to these examples.

[Materials used]
[Synthetic material of urethane acrylate]
(A: hydroxyl group-containing acrylate)
Polypropylene glycol monoacrylate having a weight average molecular weight of 400 (Blemmer AP400 [trade name], manufactured by NOF Corporation) (hereinafter referred to as “PPG acrylate”)
Pentaerythritol triacrylate (Aronix M-305 [trade name], manufactured by Toagosei Co., Ltd.)
Dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate (Aronix M-403 [trade name], manufactured by Toagosei Co., Ltd., 50 to 60% by mass as dipentaerythritol pentaacrylate)

(B: diisocyanate)
Isophorone diisocyanate (hereinafter referred to as “IPDI”)

(C: acyclic hydrocarbon having 6 to 20 carbon atoms or diol of cyclic hydrocarbon)
-1,12-dodecanediol-Polypropylene glycol having a weight average molecular weight of 400 (Uniol D-400 [trade name], manufactured by NOF Corporation)

(D: polyoxyalkylene glycol monoalkyl ether)
Polyethylene glycol monomethyl ether having a weight average molecular weight of 400 (methoxy PEG 400 [trade name], manufactured by TOHO Chemical Industry Co., Ltd.) (hereinafter referred to as “methoxy PEG 400”)
Polyethylene glycol monomethyl ether having a weight average molecular weight of 1000 (methoxy PEG 1000 [trade name], manufactured by Toho Chemical Industry Co., Ltd.) (hereinafter referred to as “methoxy PEG 1000”)
Polyethylene glycol monomethyl ether having a weight average molecular weight of 2000 (Uniox M-2000 [trade name], manufactured by NOF Corporation) (hereinafter also referred to as “methoxy PEG2000”).

[Compound having a radical polymerizable group]
Dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate (Aronix M-403 [trade name], manufactured by Toagosei Co., Ltd .; 50 to 60% by mass as dipentaerythritol pentaacrylate)
・ Polypentaerythritol polyacrylate (Biscoat 802 [trade name], manufactured by OSAKA ORGANIC CHEMICAL IND., LTD.)
Dendrimer acrylate (Biscoat 1000 [trade name], manufactured by OSAKA ORGANIC CHEMICAL IND., LTD.)
・ 10-functional urethane acrylate (KU-DPU [trade name], manufactured by Arakawa Chemical Industries)
-Urethane acrylate for fixing (see Production Example 1 below for the production method)

[Photo radical polymerization initiator]
Acylphosphine oxide photopolymerization initiator (DAROCUR TPO [trade name], manufactured by BASF, hereinafter also referred to as “TPO”)
Thioxanthone photoradical polymerization initiator (Speedcure DETX [trade name], manufactured by LAMBSON) (hereinafter simply referred to as “DETX”)

[Fluorescent brightener]
1,4-bis (2-benzoxazolyl) naphthalene) (HOSTALUX KCB [trade name], manufactured by Clariant (Japan) K.K.) (hereinafter simply referred to as “KCB”)

[Waterborne urethane acrylate]
Aromatic urethane acrylate dispersion (LR 8983 [trade name] manufactured by BASF, solid content 40%)

(Pigment dispersion)
Cab-o-jet-260M (self-dispersing magenta pigment dispersion, solid content concentration 9.96% by mass, manufactured by Cabot Corporation)
Cab-o-jet-300 (self-dispersing black pigment dispersion, solid content concentration 15% by mass, manufactured by Cabot Corporation)

(Water-soluble organic solvent)
・ Propylene glycol ・ 1,2-hexanediol

[Surfactant]
・ Polyether-modified organosiloxane (BYK-348 [trade name], manufactured by BYK)
Polyether-modified polydimethylsiloxane (BYK-333 [trade name], manufactured by BYK)

[Inorganic particle dispersion]
・ Colloidal silica particle size 10-20nm (Snowtex C [trade name], manufactured by Nissan Chemical Industries, Ltd.)
・ Colloidal silica particle size 40-60nm (Snowtex XL [trade name], manufactured by Nissan Chemical Industries, Ltd.)
・ Colloidal silica particle size 70-100nm (Snowtex ZL [trade name], manufactured by Nissan Chemical Industries, Ltd.)
・ Colloidal silica particle size 200nm (MP-2040 [trade name], manufactured by Nissan Chemical Industries, Ltd.)
・ Colloidal silica particle size 450nm (MP4540M [trade name], manufactured by Nissan Chemical Industries, Ltd.)
・ Alumina particle size 40nm (NANOBYK-3600 [trade name], manufactured by BYK)
・ Cerium oxide particle size 10nm (NANOBYK-3810 [trade name], manufactured by BYK)
・ Zinc oxide particle size 20nm (NANOBYK-3820 [trade name], manufactured by BYK)

[Structure and synthesis of urethane acrylate]
[Structure of urethane acrylate]
The urethane acrylate is one of the above general formula (1) and the following general formulas (3), (4), (5), and a crosslinked urethane acrylate obtained by crosslinking any of them with an acrylate residue. Urethane acrylate is preferably usable. Any of them was used in the following Examples and Comparative Examples.
^{A 1 -O- (CONH-B 1} -NHCOO-C 1 -O) n -CONH-B 1 -NH-COO-A 1 ... (3)

Ａ¹−Ｏ−ＣＯＮＨ−Ｂ¹−ＮＨ−ＣＯＯ−Ｄ³ …（５）

^{A 1 -O-CONH-B 1} -NH-COO-D 3 ... (5)

Here, A ¹ represents a structure derived from a hydroxyl group-containing acrylate having one or more acryloyl groups, B ¹ represents a structure derived from diisocyanate, C ² represents a structure derived from diol, and D ² and D ³ represent Of those represented by the general formula (2), it represents a structure derived from one-terminally methyl-blocked poly (oxyethylene) glycol (hereinafter also referred to as “polyoxyethylene glycol monomethyl ether”).

(Synthesis Example 1: Synthesis of urethane acrylate (a))
Into a reaction vessel equipped with a stirrer, a cooling tube, a dropping funnel, and an air introduction tube, 444.6 parts by mass of IPDI and 202.3 parts by mass of 1,12-dodecanediol were charged and stirred while stirring. 26 parts by mass of tin octylate was added, and the temperature in the reaction vessel was raised to 90 ° C. and reacted for 1.5 hours. Thereafter, 700.0 parts by mass of methoxy PEG 1000 and 0.54 parts by mass of tin octylate were added and further reacted for 1.5 hours. Next, 1300.0 parts by mass of dipentaerythritol pentaacrylate, 1.32 parts by mass of methoquinone, and 1.06 parts by mass of tin octylate are charged into the reaction vessel, mixed, and the reaction vessel is subjected to bubbling of air. The temperature inside was raised to 85 ° C., reacted for 3 hours, and then cooled to obtain an amphiphilic urethane acrylate (a) represented by the above general formula (1). The urethane acrylate (a) had a weight average molecular weight of 5,600.

(Synthesis Example 2: Synthesis of urethane acrylate (b))
In a reaction vessel similar to Synthesis Example 1, 578.0 parts by mass of HMDI trimer (Coronate HXR, manufactured by Nippon Polyurethane Co., Ltd.), 200.0 parts by mass of methoxy PEG 400, and 200.0 parts by mass of methoxy PEG 1000 were added. While charging and stirring, 0.39 parts by mass of tin octylate was added, and the temperature in the reaction vessel was raised to 75 ° C. and reacted for 1.5 hours. Next, 1051.6 parts by mass of pentaerythritol triacrylate, 1.01 parts by mass of methoquinone, and 0.81 parts by mass of tin octylate are charged in the reaction vessel, mixed, and mixed in the reaction vessel under air bubbling. Was raised to 80 ° C., reacted for 2 hours, and then cooled to obtain urethane acrylate (b). In addition, this urethane acrylate (b) is a urethane acrylate in which one terminal is an acryloyl group and trifunctional isocyanate is used, and is represented by the general formula (4). The urethane acrylate (b) had a weight average molecular weight of 7,400.

(Synthesis Example 3 Synthesis Example 4: Synthesis of Urethane Acrylate (c))
In a reaction vessel similar to Synthesis Example 1, 444.6 parts by mass of IPDI (2 mol) and 400.0 parts by mass of polypropylene glycol having a weight average molecular weight of 400 were charged, and while stirring, 0.34 parts by mass of After adding tin octylate and raising the temperature in the reaction vessel to 90 ° C. and reacting for 1.5 hours, 1400.0 parts by mass of methoxy PEG 2000 and 0.90 parts by mass of tin octylate were added, and The reaction was allowed for 1.5 hours. Next, 1300 parts by mass of dipentaerythritol pentaacrylate, 1.77 parts by mass of methoquinone and 2.13 parts by mass of tin octylate are charged into the reaction vessel, mixed, and the temperature in the reaction vessel under air bubbling. Was heated to 85 ° C., reacted for 3 hours, and then cooled to obtain an amphiphilic urethane acrylate (c) represented by the general formula (1). The urethane acrylate (c) had a weight average molecular weight of 9,000.

(Production Example 1: Synthesis of fixing urethane acrylate)
In the same reaction vessel as in Synthesis Example 1, 444.6 parts by mass of IPDI (2 mol) and 900.0 parts by mass of aromatic polyester diol (weight average molecular weight 900, 1 mol, YG-108 [trade name], ADEKA Was added, 0.27 parts by mass of tin octylate was added, and the temperature in the reaction vessel was raised to 85 ° C. and reacted for 2 hours, and then 232. 3 parts by mass of 2-hydroxyethyl acrylate (2 mol), 0.79 parts by mass of methoquinone and 0.63 parts by mass of tin octylate were charged and mixed, and the temperature in the reaction vessel was 85 ° C. under air bubbling. The mixture was heated up to react for 2 hours and then cooled to obtain fixing urethane acrylate. The fixing urethane acrylate had a weight average molecular weight of 5,000.

(Synthesis Example 1: Preparation of photocurable aqueous emulsion (a-1))
In the same reaction vessel as in Synthesis Example 1, 27.5 parts by mass of the amphiphilic urethane acrylate (a) obtained above, 9.2 parts by mass of polypentaerythritol polyacrylate, and radical photopolymerization initiator (TPO) 3 .3 parts by mass was added, the temperature in the container was raised to 80 ° C. while stirring, and the temperature was kept for 2 hours. Next, after cooling the temperature in the container to 50 ° C., 60 parts by mass of deionized water was added with stirring, and the mixture was kept warm at 40 ° C. for 1 hour, whereby the non-volatile content (amphiphilic urethane acrylate (a), A photocurable aqueous emulsion (a-1) containing 40% of polypentaerythritol polyacrylate and photoradical polymerization initiator (TPO) was obtained. The composition table is shown in Table 1 below.

(Synthesis Example 2: Preparation of photocurable aqueous emulsion (b-1))
In the same reaction vessel as in Synthesis Example 1, 27.5 parts by mass of the urethane acrylate (b) obtained above, 9.2 parts by mass of polypentaerythritol polyacrylate, and 3.3 parts by mass of radical photopolymerization initiator (TPO). The temperature in the container was raised to 80 ° C. while stirring, and the temperature was kept for 2 hours. Next, after cooling the temperature in the container to 50 ° C., 60 parts by mass of deionized water was added with stirring, and the mixture was kept at 40 ° C. for 1 hour, whereby non-volatile components (amphiphilic urethane acrylate (b), A photocurable aqueous emulsion (b-1) containing 40% of polypentaerythritol polyacrylate and photoradical polymerization initiator (TPO) was obtained. The composition table is shown in Table 1 below.

(Synthesis Example 3: Preparation of photocurable aqueous emulsion (c-1))
In the same reaction vessel as in Synthesis Example 1, 23.3 parts by weight of the amphiphilic urethane acrylate (c) obtained above, 8.3 parts by weight of polypentaerythritol polyacrylate, 1.7 parts by weight of fixing urethane acrylate, A photo radical polymerization initiator (TPO) 5.0 parts by mass, a photo radical polymerization initiator (DETX) 1.7 parts by mass, and a fluorescent whitening agent (KCB) 0.07 parts by mass were charged and stirred. The temperature was raised to 80 ° C. and kept warm for 2 hours. Next, after cooling the temperature in the container to 50 ° C., 60 parts by mass of deionized water was added with stirring, and the mixture was kept at 50 ° C. for 1 hour, whereby non-volatile components (amphiphilic urethane acrylate (c), A photocurable aqueous emulsion (c-1) containing 40% of polypentaerythritol polyacrylate, fixing urethane acrylate, radical photopolymerization initiator (TPO, DETX), and optical brightener (KCB) was obtained. The composition table is shown in Table 1 below.

(Synthesis Example 4: Preparation of photocurable aqueous emulsion (c-2))
In the same reaction vessel as in Synthesis Example 1, 21.6 parts by mass of the amphiphilic urethane acrylate (c) obtained above, 7.7 parts by mass of polypentaerythritol polyacrylate, 1.5 parts by mass of fixing urethane acrylate, A photo radical polymerization initiator (TPO) 5.0 parts by mass and a photo radical polymerization initiator (DETX) 1.7 parts by mass were charged, the temperature in the container was raised to 80 ° C. while stirring, and the temperature was kept for 2 hours. . Next, after cooling the temperature in the container to 50 ° C., 2.5 parts by mass of a crosslinking agent (PEMP) was added while stirring, and stirring was continued for 15 minutes. Thereafter, 60 parts by mass of deionized water was added, and the mixture was kept at 50 ° C. for 1 hour, and then the temperature in the container was raised to 80 ° C. and kept for 6 hours, whereby non-volatile components (amphiphilic urethane acrylate (c ), Polypentaerythritol polyacrylate, fixing urethane acrylate, photoradical polymerization initiator (TPO, DETX), and crosslinker (PEMP)) 40% of a photocurable aqueous emulsion (c-2) was obtained. When this emulsion was measured by GPC, a crosslinked urethane (meth) acrylate having a weight average molecular weight of 18,000 was confirmed. The composition table is shown in Table 1 below.

[Examples 1-11 Comparative Examples 1-4]
Each ink composition was prepared according to the composition (parts by mass) shown in Tables 2 to 3 below using the above materials and the photocurable aqueous emulsions obtained in Synthesis Examples 1 to 4. Here, “%” in the table means mass%. The average particle diameter of the resin emulsion in the ink composition was 250 nm for all ink compositions.

[Measurement / Evaluation Items]
(Discharge stability)
Ink printed immediately after the non-ejection period causes missing dots and scattering, but if the amount of ink ejected thereafter increases, printing can be performed at a normal position. Necessary to print at a normal position when each ink is filled in an ink-jet ink printer PX-G930 (trade name, manufactured by Seiko Epson Corporation) and printed after a 60-second non-ejection period in a thermostatic chamber at 35 ° C. The number of dots was determined as ejection stability, and the smaller the number, the better the ejection stability. The evaluation criteria are shown below. The evaluation results are shown in Tables 4-5.
AA: Less than 10 dots required to print at a normal position.
A: The number of dots required to print at a normal position is 10 or more and less than 20.
B: The number of dots required to print at a normal position is 20 or more and less than 30.
C: The number of dots required for printing at a normal position is 30 or more.

[Ink storage stability]
The ink was allowed to stand at 60 ° C. for 1 week, and evaluated according to the following evaluation criteria according to the rate of change in viscosity. The evaluation results are shown in Tables 4-5.
AA: Viscosity change rate is within 5%.
A: The rate of change in viscosity is greater than 5% and 10% or less.
B: Viscosity change rate is greater than 10% and 20% or less.
C: The rate of change in viscosity is greater than 20%.

[Ink curability]
A swab weighted tackiness evaluation was performed. Specifically, each medium was coated with an ink prepared to have a coating thickness of 20.61 μm with a bar coater, dried at 50 ° C. for 3 minutes, and then irradiated with ultraviolet rays. At that time, LED was used for the ultraviolet lamp. Thereafter, the surface of the coating film was rubbed with a cotton swab, and irradiation energy without coloring was evaluated as curing energy. The evaluation criteria are as follows. The evaluation results are shown in Tables 4-5.
AA: Curing energy of Y, M, C, Bk ink is 100 mJ / cm ² or less for PET media and 300 mJ / cm ² or less for PVC media.
A: Y, M, C, curing energy of Bk ink is large 300 mJ / cm ² or less than 100 mJ / cm ² in PET media, more than 300 mJ / cm ² in PVC Media 1000 mJ / cm ² or less.
B: Y, M, C, large 500 mJ / cm ² or less than 300 mJ / cm ² curing energy of Bk ink in PET media, greater than 1000 mJ / cm ² in PVC media.
C: Curing energy of Y, M, C, Bk ink is greater than 500 mJ / cm ^{2 for} PET media and greater than 1000 mJ / cm ^{2 for} PVC media.
-: Not cured.

  As shown in Tables 4 to 5, it was found that the ink compositions of Examples 1 to 14 were all excellent in ink ejection stability as compared with the ink composition of Comparative Example 1. Moreover, it turned out that Examples 1-3, 6-9, and 11 are especially excellent in discharge stability, storage stability, and sclerosis | hardenability. In addition, although the comparative example 2 is an example which does not contain a resin emulsion, although it did not contain an inorganic particle dispersion, although discharge stability was good, it turned out that curability is inferior. Comparative Example 3 was also found to be inferior in curability. In Comparative Examples 2 and 3, in the stage of adjusting the ink composition, 1 part by weight of radical photopolymerization initiator (TPO) was added to 100 parts by weight of the ink composition. Since the agent did not dissolve, the radical photopolymerization initiator was not used. In addition, when the discharge stability test was performed in the same manner as in Comparative Example 1 except that the temperature in the thermostatic chamber in the discharge stability test was 20 ° C., the discharge stability was B. It was found that the higher the temperature, the worse the ejection stability.

  The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the present invention includes substantially the same configuration (for example, a configuration having the same function, method, and result, or a configuration having the same purpose and effect) as the configuration described in the embodiment. In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

Claims (6)

Ink jet ink comprising water as a main solvent, a colorant used for image formation of at least one of a pigment and a dye, a resin emulsion comprising a compound having a radical polymerizable group, and a photo radical polymerization initiator in the composition,
Furthermore, the inorganic particle dispersion for preventing thickening of the inkjet ink composition, wherein the average particle size (D50) is 40 nm or more and 500 nm or less in at least one of alumina, zinc oxide, cerium oxide, and colloidal silica. An ink-jet ink composition comprising 0.5% by mass or more and 3% by mass or less in a solid content concentration in the ink-jet ink composition .   The inkjet ink composition according to claim 1, wherein the concentration of the compound having a radical polymerizable group in the ink composition is 6% by mass or more and 20% by mass or less. The inkjet ink composition according to claim 1 or 2 , wherein the compound having a radical polymerizable group is a compound having a self-emulsifying ability, and the resin emulsion is a self-emulsifying resin emulsion. The inkjet according to any one of claims 1 to 3 , wherein the compound having a radical polymerizable group is at least one of a (meth) acryloyl group, a vinyl group, a vinyl ether group, and a mercapto group. Ink composition. The inkjet ink composition according to any one of claims 1 to 4 , wherein the photo radical polymerization initiator is a hydrophobic photo polymerization initiator. A step of discharging the inkjet ink composition according to any one of claims 1 to 5 onto a recording medium from a nozzle;
Irradiating the inkjet ink composition ejected onto the recording medium with active energy rays;
Heating the recording medium;
An ink jet recording method comprising:

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