Ink composition and inkjet recording method

Abstract

Provided is an ink composition containing a colorant, a specific solvent component composed of at least one organic solvent having a ClogP value greater than 0.504 and less than 2.635, and water, the weighted average value obtained by weighting the ClogP value of each organic solvent that constitutes the specific solvent component by using the mass-based content value for each organic solvent being greater than 0.67 and less than 1.26. Also provided are an ink composition set comprising the ink composition, and an inkjet recording method in which the ink composition is used.

Description

[Technical Field]

[0001] The present invention relates to an ink composition and an ink jet recording method using the ink composition. [Background technology]

[0002] A recording method using an inkjet printer (inkjet recording method) involves ejecting small droplets of ink from the printer and depositing them onto a print medium such as paper to perform printing. This recording method has been rapidly gaining popularity in recent years due to its advantages of being easily miniaturized and high-speed. Recently, its application in industrial applications has also been expanding, with methods of printing on packaging materials and advertising media being considered. Examples of packaging materials include corrugated cardboard sheets or boxes made by gluing two sheets of paperboard together with a corrugated cardboard sandwiched between them, and coated cardboard with a surface coating for enhanced aesthetic appeal. Examples of advertising media include printing media with poor ink absorption, such as coated paper whose surface is coated with a white pigment or the like to impart gloss and whiteness.

[0003] When printing on the surface of a print medium using an inkjet recording method, it is often necessary to ensure a print gap of 1 mm or more, preferably 2 mm or more, and more preferably 3 mm or more, between the surface of the print medium and the inkjet head to prevent contact between the surface of the print medium and the inkjet head due to warping of the print medium, etc.

[0004] However, as the print gap increases, the distance that ink droplets ejected from the ink ejection ports of the inkjet head have to travel before landing on the surface of the print media increases, making the ink droplets more likely to deviate or produce excessive satellites. In particular, when using print media with a coated surface that is poorly ink-absorbent, such as coated cardboard or coated paper, the ink droplets may not spread sufficiently on the surface of the print media (in other words, the dot diameter may become small), resulting in problems such as streaks in the print. For this reason, there is strong market demand for inks that can print dots with large diameters regardless of the size of the print gap.

[0005] Patent Document 1 discloses an ink composition containing a specific alkali-soluble resin, a polyolefin resin emulsion, and an acetylene diol surfactant. Patent Document 2 discloses an ink composition containing a binder resin, a compound having a urea bond, a colorant, and water and an organic solvent as an aqueous medium. Patent Document 3 discloses a method for producing a printed matter in which the substrate temperature when ink droplets land is in the range of 40 to 80°C. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6640951 [Patent Document 2] Patent No. 6504423 [Patent Document 3] International Publication No. 2020 / 054567 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide an ink composition that can produce good prints with large dot diameters regardless of the size of the print gap, and an inkjet recording method that uses the ink composition. [Means for solving the problem]

[0008] Specific means for solving the above problems include the following embodiments. 1) The ink contains a colorant, a specific solvent component consisting of at least one organic solvent having a ClogP value of more than 0.504 and less than 2.635, and water, an ink composition in which the weighted average value of the ClogP values ​​of the organic solvents constituting the specific solvent component, weighted by the mass-based content of each organic solvent, is greater than 0.67 and less than 1.26; 2) 1) The ink composition according to 1), wherein the colorant comprises a pigment. 3) The ink composition according to 1) or 2), wherein the content of the colorant is 0.5 to 30.0% by mass with respect to the total mass of the ink composition. 4) An ink composition set comprising the ink composition according to any one of items 1) to 3) and another ink composition different from the ink composition. 5) An inkjet recording method comprising a step of ejecting droplets of the ink composition according to any one of 1) to 3) above and depositing them onto a printing medium to form an image. 6) 5) The inkjet recording method according to 5), wherein the printing medium comprises at least one selected from the group consisting of cardboard, liner paper, coated board, and coated paper. 7) 5) The inkjet recording method according to 5), wherein the printing medium is a printing medium that is poorly ink-absorbent or non-ink-absorbent. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an ink composition that can produce good printed matter with large dot diameters regardless of the size of the printing gap, and an inkjet recording method that uses the ink composition. DETAILED DESCRIPTION OF THE INVENTION

[0010] Specific embodiments to which the present invention is applied will be described in detail below. In this specification, when a unit is written for only one of the upper and lower limits of a range, such as "X to Y mass %, " it means that the units for the upper and lower limits of the range are the same, i.e., "X mass % to Y mass %". In this specification, "CI" stands for "Color Index." In addition, in this specification, the term "(meth)acrylic acid" means both "acrylic acid" and "methacrylic acid." Similarly, the term "(meth)acrylate" means both "acrylate" and "methacrylate."

[0011] <Ink composition> The ink composition according to this embodiment contains a colorant, a specific solvent component comprising at least one organic solvent having a ClogP value greater than 0.504 and less than 2.635, and water, and the weighted average ClogP value of each organic solvent constituting the specific solvent component, weighted by the mass-based content of each organic solvent, is greater than 0.67 and less than 1.26. Each component contained in the ink composition according to this embodiment will be described below. Each of the components described below may be used alone, or two or more may be used in combination.

[0012] [Coloring agent] Examples of the colorant that can be used include pigments, disperse dyes, solvent dyes, etc. Examples of the pigments that can be used include inorganic pigments, organic pigments, and extender pigments.

[0013] Examples of inorganic pigments include carbon black, titanium oxide, metal oxides, metal hydroxides, metal sulfides, metal ferrocyanides, and metal chlorides.

[0014] When a black ink composition is prepared, the inorganic pigment is preferably carbon black such as furnace black, lamp black, acetylene black, or channel black. Commercially available carbon black products include, for example, Raven 760 ULTRA, Raven 780 ULTRA, Raven 790 ULTRA, Raven 1060 ULTRA, Raven 1080 ULTRA, Raven 1170, Raven 1190 ULTRA II, Raven 1200, Raven 1250, Raven 1255, Raven 1500, Raven 2000, Raven 2500ULTRA, Raven 3500, Raven 5000 ULTRA II, Raven 5250, Raven 5750, and Raven 7000 (all manufactured by Columbia Carbon); Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, and Monarch 1400 (all manufactured by Columbia Carbon). 1400, Regal 1330R, Regal 1400R, Regal 1660R, Mogul L (manufactured by Cabot); Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Printex 140V, SpecIal Black 4, SpecIal Black 4A, SpecIal Black 5, Special Black No. 6, Nerox 305, Nerox 505, Nerox 510, Nerox 600, Nerox 605, NIPex 180IQ, NIPex 170IQ, NIPex 160IQ, NIPex 150IQ (all manufactured by Orion Engineered Carbons); MA7, MA8, MA100, MA600, MCF-88, No. 25, No. 33, No. 40, No. 47, No. 52, No. 900, No. 2300 (all manufactured by Mitsubishi Chemical Corporation); and the like.

[0015] Examples of organic pigments include various pigments such as azo, disazo, phthalocyanine, quinacridone, isoindolinone, dioxazine, perylene, perinone, thioindigo, anthraquinone, and quinophthalone. Specific examples of organic pigments include yellow pigments such as CI Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 24, 55, 73, 74, 75, 83, 93, 94, 95, 97, 98, 108, 114, 128, 129, 138, 139, 150, 151, 154, 155, 180, 185, 193, 199, 202, and 213; and CI Pigment Red. Red pigments such as 5, 7, 12, 48, 48:1, 57, 88, 112, 122, 123, 146, 149, 150, 166, 168, 177, 178, 179, 184, 185, 202, 206, 207, 254, 255, 257, 260, 264, and 272; blue pigments such as CI Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 25, 60, 66, and 80; violet pigments such as CI Pigment Violet 19, 23, 29, 37, 38, and 50; orange pigments such as CI Pigment Orange 13, 16, 68, 69, 71, and 73; and CI Pigment Green green pigments such as CI Pigment Black 1; and the like.

[0016] Examples of extender pigments include silica, calcium carbonate, talc, clay, barium sulfate, and white carbon.

[0017] Specific examples of disperse dyes include CI Dispers Yellow 3, 4, 5, 7, 9, 13, 24, 30, 33, 34, 42, 44, 49, 50, 51, 54, 56, 58, 60, 63, 64, 66, 68, 71, 74, 76, 79, 82, 83, 85, 86, 88, 90, 91, 93, 98, 99, 100, 104, 114, 116, 118, 119, 122, 124, 126, Yellow dyes such as 135, 140, 141, 149, 160, 162, 163, 164, 165, 179, 180, 184:1, 182, 183, 184, 186, 192, 198, 199, 201, 202, 204, 210, 211, 215, 216, 218, 224, 231, 232, and 241; CI Dispers Orange dyes such as Orange 1, 3, 5, 7, 11, 13, 17, 20, 21, 25, 26, 29, 30, 31, 32, 33, 37, 38, 42, 43, 44, 45, 47, 48, 50, 53, 54, 55, 56, 57, 58, 59, 61, 66, 76, 78, 80, 89, 90, 91, 93, 96, 97, 119, 127, 130, 139, and 142; CI Dispers Red 1, 4, 5, 7, 11, 12, 13, 15, 17, 27, 43, 44, 50, 52, 53, 54, 55, 56, 58, 59, 60, 65, 72, 73, 74, 75, 76, 78, 81, 82, 86, 88, 90, 91, 93, 96, 103, 105, 106, 107, 108, 110, 111, 113, 117, 118, 121, 122, 126, 127, 128, 131, 132, 134, 135, 137, 143, 145, 146, 151, 152, 153, 154, 157, 159, 164, 167, 169, 177, 179, 181, 183, 184, 185, 188, 189, 190, 191, 192, 200, 201, 202, 203, 205, 206, 207, 210, 221, 224, 225, 227, 229, 239, 240, 257, 258, 277, 278, 279, 281, 288, 289, 298, 302, 303, 310, 311, 312, 320, 324, 328, 343, 362, 364, etc.; CI red dyesViolet dyes such as Dispers Violet 1, 4, 8, 17, 23, 26, 27, 28, 31, 33, 35, 36, 38, 40, 43, 46, 48, 50, 51, 52, 56, 57, 59, 61, 63, 69, and 77; green dyes such as CI Dispers Green 6:1 and 9; brown dyes such as CI Dispers Brown 1, 2, 4, 9, 13, 19, 26, and 27; and CI Dispers Blue. 3, 7, 9, 14, 16, 19, 20, 26, 27, 35, 43, 44, 54, 55, 56, 58, 60, 62, 64, 71, 72, 73, 75, 79, 81, 82, 83, 87, 91, 93, 94, 95, 96, 102, 106, 108, 112, 113, 115, 118, 120, 122, 125, 128, 130, 139, 141, 142, 143, 146, 148, 149, 153, 154, 158, 165, Examples include blue dyes such as 167, 171, 173, 174, 176, 181, 183, 185, 186, 187, 189, 197, 198, 200, 201, 205, 207, 211, 214, 224, 225, 257, 259, 267, 268, 270, 284, 285, 287, 288, 291, 293, 295, 297, 301, 315, 330, 332, 333, 334, 343, 359, and 360; and black dyes such as CI Disperses Black 1, 3, 10, and 24.

[0018] Specific examples of solvent dyes include yellow dyes such as CI Solvent Yellow 2, 6, 14, 16, 21, 25, 29, 30, 33, 51, 56, 77, 80, 82, 88, 89, 93, 116, 150, 160:1, 163, and 179; orange dyes such as CI Solvent Orange 1, 2, 14, 45, and 60; red dyes such as CI Solvent Red 1, 3, 7, 8, 9, 18, 19, 23, 24, 25, 27, 49, 100, 109, 121, 122, 125, 127, 130, 132, 135, 218, 225, and 230; violet dyes such as CI Solvent Violet 13 and 31; green dyes such as CI Solvent Green 3; brown dyes such as CI Solvent Brown 3 and 5; and CI Solvent Blue. blue dyes such as CI Solvent Black 2, 11, 14, 24, 25, 35, 36, 38, 48, 55, 59, 63, 67, 68, 70, 73, 83, 105, 111, and 132; and black dyes such as CI Solvent Black 3, 5, 7, 23, 27, 28, 29, and 34.

[0019] From the viewpoint of image fastness such as lightfastness and waterfastness of the recorded image, the colorant preferably contains a pigment, and more preferably consists of a pigment. As the pigment, it is preferable to use at least one selected from the group consisting of carbon black, CI Pigment Blue 15:3, 15:4, CI Pigment Yellow 74, 155, CI Pigment Red 122, 150, and CI Pigment Violet 19, and it is more preferable to use at least one selected from the group consisting of carbon black, CI Pigment Blue 15:4, CI Pigment Yellow 74, CI Pigment Red 122, and CI Pigment Violet 19.

[0020] The content of the colorant relative to the total mass of the ink composition is preferably 0.5 to 30.0 mass%, more preferably 1.0 to 10.0 mass%, even more preferably 2.0 to 7.0 mass%, and particularly preferably 2.0 to 4.8 mass%.

[0021] [Specific solvent components] The specific solvent component is composed of at least one organic solvent having a ClogP value of more than 0.504 and less than 2.635, and the weighted average ClogP value of each organic solvent constituting the specific solvent component, weighted by the mass content of each organic solvent, is more than 0.67 and less than 1.26.

[0022] Here, the ClogP value refers to a calculated logP value (1-octanol / water partition coefficient). The ClogP value can be calculated by the fragment method, the atomic approach method, or the like. More specifically, the ClogP value can be calculated using the fragment method described in the literature (C. Hansch and A. Leo, "Substituent Constants for Correlation Analysis in Chemistry and Biology" (John Wiley & Sons, New York, 1969)) or a commercially available software package. The ClogP values ​​described herein were calculated using the commercially available software package ChemDraw Ultra (CambridgeSoft Corporation, USA). Note that in this specification, the ClogP values ​​and their weighted average values ​​are reported to two or three decimal places, and the lowest decimal place is rounded off to one decimal place.

[0023] Examples of organic solvents constituting the specific solvent component include diethylene glycol diethyl ether (0.52), 1,2-hexanediol (0.53), diethylene glycol monoisobutyl ether (0.54), propyl propylene glycol (0.62), diethylene glycol monobutyl ether (0.67), dipropylene glycol monopropyl ether (0.75), 2,2-diethyl-1,3-propanediol (0.82), propylene glycol monobutyl ether (1.15), diethylene glycol monophenyl ether (1.25), 2-ethyl-1,3-hexanediol (1.26), 1,2-octanediol (1.59), diethylene glycol hexyl ether (1.72), and propylene glycol monohexyl ether (2.21). The values ​​in parentheses indicate the ClogP values ​​of each organic solvent.

[0024] The specific solvent component preferably contains an organic solvent having a ClogP value of greater than 0.505 and less than 2.635, more preferably contains an organic solvent having a ClogP value of greater than 0.520 and less than 2.215, and even more preferably contains an organic solvent having a ClogP value of greater than 0.530 and less than 1.755.

[0025] The weighted average value obtained by weighting the ClogP value of each organic solvent constituting the specific solvent component by the mass-based content of each organic solvent is preferably 0.68 or more and less than 1.26, more preferably 0.70 or more and less than 1.10, and even more preferably 0.74 or more and less than 1.00.

[0026] The weighted average ClogP value can be determined by multiplying the ClogP value of each organic solvent constituting the specific solvent component by the content (parts by mass) of each organic solvent, adding up the values ​​for all organic solvents constituting the specific solvent component, and dividing the total value by the content (parts by mass) of the specific solvent component.

[0027] For example, when the organic solvents constituting the specific solvent component are two types, solvent A and solvent B, the weighted average value Q1 can be calculated according to the following formulas (A) to (C). Content of solvent A (parts by mass) × ClogP value of solvent A = X Formula (A) Content of solvent B (parts by mass) × ClogP value of solvent B = Y Equation (B) (X + Y) / (content of solvent A + content of solvent B) = Q1 Equation (C)

[0028] Furthermore, when the organic solvents constituting the specific solvent component are three types, solvent A, solvent B, and solvent C, the weighted average value Q2 can be calculated according to the following formulas (A), (B), (D), and (E). Content of solvent A (parts by mass) × ClogP value of solvent A = X Formula (A) Content of solvent B (parts by mass) × ClogP value of solvent B = Y Equation (B) Content of solvent C (parts by mass) × ClogP value of solvent C = Z Formula (D) (X + Y + Z) / (content of solvent A + content of solvent B + content of solvent C) = Q2 Equation (E)

[0029] When the specific solvent component is composed of only one organic solvent, the ClogP value of that organic solvent is used as the weighted average value.

[0030] The organic solvent constituting the specific solvent component is preferably two or more types, more preferably three or more types. The specific solvent component preferably contains at least one type, more preferably at least two types, even more preferably three types, and particularly preferably consisting of these three types, selected from the group consisting of 1,2-octanediol, diethylene glycol phenyl ether, and 1,2-hexanediol.

[0031] The content rate of the specific solvent component is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, and even more preferably 5 to 10% by mass with respect to the total mass of the ink composition. When there are two or more organic solvents constituting the specific solvent component, it is preferable that the content of each of any two solvents satisfies the relationship of "content of the solvent with a high ClogP value < content of the solvent with a low ClogP value" in the ink composition.

[0032] In addition, it is preferable that the ink composition according to the present embodiment does not substantially contain an organic solvent having a ClogP value of 2.635 or more. By not substantially containing an organic solvent having a ClogP value of 2.635 or more, separation of the organic solvent in the ink composition is prevented, and the stability of the ink composition tends to be improved. The content rate of the organic solvent having a ClogP value of 2.635 or more is preferably less than 1.0% by mass, more preferably less than 0.8% by mass, even more preferably less than 0.5% by mass, and particularly preferably less than 0.2% by mass with respect to the total mass of the ink composition.

[0033] [Water] As the water, those with few impurities (such as metal ions) such as ion-exchanged water and distilled water are preferable.

[0034] The content rate of water is usually 1 to 90% by mass, preferably 5 to 85% by mass, more preferably 10 to 80% by mass, even more preferably 20 to 80% by mass, particularly preferably 30 to 80% by mass, and extremely preferably 50 to 80% by mass with respect to the total mass of the ink composition.

[0035] [Ink preparation agent] The ink composition according to the present embodiment may further contain an ink preparation agent in addition to the above components. Examples of the ink preparation agent include surfactants, viscosity modifiers, defoamers, preservatives, fungicides, pH adjusters, chelating reagents, rust inhibitors, water-soluble ultraviolet absorbers, water-soluble polymer compounds, dispersants, resin emulsions, wax agents, antioxidants, and the like.

[0036] (surfactant) Examples of surfactants include known surfactants such as anionic, cationic, nonionic, amphoteric, silicone-based and fluorine-based surfactants, with anionic, nonionic, silicone-based and fluorine-based surfactants being preferred.

[0037] Examples of anionic surfactants include alkyl sulfocarboxylates, α-olefin sulfonates, polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl ether sulfates, N-acylamino acids or salts thereof, N-acylmethyltaurines, alkyl sulfates, polyoxyalkyl ether sulfates, alkyl sulfates, polyoxyethylene alkyl ether phosphates, rosin acid soaps, castor oil sulfates, lauryl alcohol sulfates, alkylphenol phosphates, alkyl phosphates, alkylaryl sulfonates, diethyl sulfosuccinates, diethylhexyl sulfosuccinates, dioctyl sulfosuccinates, etc. Examples of commercially available products include Hitenol LA-10, LA-12, LA-16, Neo Hitenol ECL-30S, and ECL-45 (all manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[0038] Examples of cationic surfactants include 2-vinylpyridine derivatives and poly(4-vinylpyridine) derivatives.

[0039] Examples of nonionic surfactants include ether-based surfactants such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, and polyoxyethylene alkyl ether; ester-based surfactants such as polyoxyethylene oleate, polyoxyethylene distearate, sorbitan laurate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate, polyoxyethylene monooleate, and polyoxyethylene stearate; acetylene glycol (alcohol)-based surfactants such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, and 3,5-dimethyl-1-hexyn-3-ol; Surfynol 104, 104PG50, 105PG50, 82, 420, 440, 465, 485, and Olfine. Examples include STG (both manufactured by Nissin Chemical Industry Co., Ltd.); polyglycol ether-based (for example, TergItol 15-S-7 manufactured by SIGMA-ALDRICH); and the like.

[0040] Examples of amphoteric surfactants include lauryl dimethylaminoacetic acid betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine, coconut oil fatty acid amidopropyl dimethylaminoacetic acid betaine, polyoctyl polyaminoethyl glycine, and imidazoline derivatives.

[0041] Examples of silicone surfactants include polyether-modified siloxanes and polyether-modified polydimethylsiloxanes. Examples of commercially available products include BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, and BYK-3455 (all manufactured by BYK-Chemie); KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, and KF-6017 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0042] Examples of fluorine-based surfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide compounds, polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chains, etc. Commercially available products include Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300 (all manufactured by DuPont); FS-30, FS-31, FS-3100 (all manufactured by Chemours); PF-151N, PF-154N (all manufactured by Omnova); F-114, F-410, F-444, EXP.TF-2066, EXP.TF-2148, EXP.TF-2149, F-430, F-477, F-552, F-553, F-554, F-555, F-556, F- 557, F-558, F-559, F-561, F-562, R-40, R-41, RS-72-K, RS-75, RS-76-E, RS-76-NS, RS-77, EXP.TF-1540, EXP.TF-1760 (all manufactured by DIC Corporation); BYK-340, BYK-3440, BYK-3441 (all manufactured by BYK-Chemie); and the like.

[0043] When the ink composition according to this embodiment contains a surfactant, the surfactant content is typically 0.1 to 3 mass %, and preferably 0.3 to 1 mass %, relative to the total mass of the ink composition. By setting the surfactant content to 0.1 to 3 mass %, the dispersion stability of the colorant in the ink composition tends to be improved.

[0044] (Viscosity modifier) Industrial inkjet printers usually have a set viscosity range for the ink they can eject, based on the specifications of the printer head (the head that ejects the ink). For this reason, it is sometimes important to add a viscosity modifier to the ink composition to adjust its viscosity to an appropriate range.

[0045] The viscosity adjuster is not particularly limited as long as it can adjust the viscosity of the ink composition, and known substances can be used. Specific examples include organic solvents and sugars with a ClogP value of 0.504 or less. Examples of organic solvents include glycerin (-1.54), triethylene glycol (-1.48), ethylene glycol (-1.37), diethylene glycol (-1.30), propylene glycol (-1.06), 1,2-pentanediol (-0.00), ethylene glycol monoallyl ether (0.03), isopropyl alcohol (0.07), isopropyl glycol (0.09), diethylene glycol ethyl methyl ether (0.13), dipropylene glycol dimethyl ether (0.36), 3-methoxy-3-methyl-1-butanol (0.42), and butyl triglycol (0.49). The numbers in parentheses indicate the ClogP value of each organic solvent. Examples of sugars include carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.

[0046] When the ink composition according to this embodiment contains a viscosity modifier, the content thereof is typically 1 to 20 mass %, preferably 3 to 20 mass %, more preferably 8 to 18 mass %, even more preferably 10 to 18 mass %, and particularly preferably 12 to 18 mass %, relative to the total mass of the ink composition.

[0047] (Antifoaming agent) Examples of antifoaming agents include silicone-based, silica mineral oil-based, olefin-based, and acetylene-based compounds. Commercially available products include Surfynol DF37, DF58, DF110D, DF220, MD-20, and Olfine SK-14 (all manufactured by Nissin Chemical Industry Co., Ltd.).

[0048] (Anti-mold agent) Examples of antifungal agents include sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, p-hydroxybenzoic acid ethyl ester, 1,2-benzisothiazolin-3-one and salts thereof.

[0049] (preservatives) Examples of preservatives include organic sulfur compounds, organic nitrogen sulfur compounds, organic halogen compounds, haloaryl sulfone compounds, iodopropargyl compounds, haloalkylthio compounds, nitrile compounds, pyridine compounds, 8-oxyquinolines, benzothiazole compounds, isothiazolinone compounds, dithiols, pyridine oxide compounds, nitropropane compounds, organic tin compounds, phenol compounds, quaternary ammonium salt compounds, triazine compounds, thiazine compounds, anilides, adamantane compounds, dithiocarbamates, brominated indanone compounds, benzyl bromoacetate compounds, and inorganic salt compounds. Specific examples of organic halogen compounds include sodium pentachlorophenol. Specific examples of pyridine oxide compounds include sodium 2-pyridinethiol-1-oxide. Specific examples of isothiazoline compounds include 1,2-benzisothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one magnesium chloride, 5-chloro-2-methyl-4-isothiazolin-3-one calcium chloride, 2-methyl-4-isothiazolin-3-one calcium chloride, etc. Specific examples of other antiseptics and antifungals include anhydrous sodium acetate, sodium sorbate, sodium benzoate; Proxel GXL(S), Proxel XL-2(S) (all manufactured by Arch Chemical Co.); etc.

[0050] (pH adjuster) Examples of pH adjusters include alkanolamines such as diethanolamine, triethanolamine, and N-methyldiethanolamine; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; ammonium hydroxide (aqueous ammonia); alkali metal carbonates such as lithium carbonate, sodium carbonate, and potassium carbonate; alkali metal salts of organic acids such as potassium acetate; and inorganic bases such as disodium phosphate.

[0051] (chelating agent) Examples of chelating agents include disodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, and sodium uracildiacetate.

[0052] (rust inhibitor) Examples of the rust inhibitor include acid sulfite, sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

[0053] (Water-soluble UV absorber) Examples of the water-soluble ultraviolet absorber include sulfonated benzophenone compounds, benzotriazole compounds, salicylic acid compounds, cinnamic acid compounds, and triazine compounds.

[0054] (Water-soluble polymer compound) Examples of the water-soluble polymer compound include polyethylene glycol, polyvinyl alcohol, cellulose derivatives, polyamines, and polyimines.

[0055] (dispersant) Examples of dispersants include copolymers composed of at least two monomers (preferably at least one of which is a hydrophilic monomer) selected from the group consisting of styrene and its derivatives, vinylnaphthalene and its derivatives, aliphatic alcohol esters of α,β-ethylenically unsaturated carboxylic acids, (meth)acrylic acid and its derivatives, maleic acid and its derivatives, itaconic acid and its derivatives, fumaric acid and its derivatives, vinyl acetate, vinyl alcohol, vinylpyrrolidone, acrylamide, and their derivatives. Examples of hydrophilic monomers include monomers that leave a carboxy group after polymerization, such as (meth)acrylic acid.

[0056] Examples of such copolymers include styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymers, (meth)acrylic acid ester-(meth)acrylic acid copolymers, polyethylene glycol (meth)acrylate-(meth)acrylic acid copolymers, and styrene-maleic acid copolymers. Among these, styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymers, (meth)acrylic acid ester-(meth)acrylic acid copolymers, and polyethylene glycol (meth)acrylate-(meth)acrylic acid copolymers are preferred, with styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymers, and (meth)acrylic acid ester-(meth)acrylic acid copolymers being more preferred, with (meth)acrylic acid ester-(meth)acrylic acid copolymers being even more preferred, and methacrylic acid ester-methacrylic acid copolymers being particularly preferred. Examples of copolymers include block copolymers, random copolymers, and graft copolymers, with block copolymers being preferred. These copolymers may be in the form of a salt.

[0057] Dispersants can be synthesized or commercially available.

[0058] Examples of commercially available dispersants include JONCRYL 62, 67, 68, 678, and 687 (styrene-acrylic copolymers manufactured by BASF); MOVINYL S-100A (modified vinyl acetate copolymer manufactured by Japan Coating Resins Co., Ltd.); and JURYMER AT-210 (polyacrylic acid ester copolymer manufactured by Nihon Junyaku Co., Ltd.).

[0059] Examples of dispersants obtained by synthesis include the AB block polymer disclosed in WO 2013 / 115071. The monomer constituting the A block of the AB block polymer disclosed in WO 2013 / 115071 is at least one monomer selected from (meth)acrylic acid and linear or branched C4 alkyl (meth)acrylates, preferably at least one monomer selected from methacrylic acid and n-butyl methacrylate, and more preferably a combination of these two monomers. Furthermore, the monomer constituting the B block of the AB block polymer disclosed in WO 2013 / 115071 is at least one monomer selected from benzyl methacrylate and benzyl acrylate, preferably benzyl methacrylate. Specific examples of AB block polymers include the block copolymers disclosed in Synthesis Examples 3 to 8 of WO 2013 / 115071.

[0060] (resin emulsion) The resin emulsion is not particularly limited as long as it is different from the above-mentioned dispersant, and examples thereof include emulsions containing urethane-based, polyester-based, acrylic-based, vinyl acetate-based, vinyl chloride-based, acrylic-styrene-based, and acrylic-silicone-based resins. Commercially available products include, for example, Superflex 126, 150, 170, 210, 420, 470, 820, 830, 860, and 890 (urethane resin emulsions manufactured by Daiichi Kogyo Seiyaku Co., Ltd.); Hydran HW-350, HW-178, HW-163, HW-171, AP-20, AP-30, AP-40F, WLS-201, and WLS-210 (urethane resin emulsions manufactured by DIC Corporation); 0569, 0850Z, and 2108 (styrene-butadiene resin emulsions manufactured by JSR Corporation); AE980, AE981A, AE982, AE986B, and AE104 (acrylic resin emulsions manufactured by E-Tech Co., Ltd.); Saivinol SK-200 (acrylic resin emulsion manufactured by Saiden Chemical Co., Ltd.); and Boncoat. 4001, 5454 (acrylic resin emulsions manufactured by DIC Corporation);

[0061] When the ink composition according to this embodiment contains a resin emulsion, the solid content thereof is preferably 0.1 to 10 mass %, more preferably 0.3 to 7 mass %, even more preferably 0.5 to 5 mass %, particularly preferably 0.5 to 3 mass %, and extremely preferably 0.5 to 1.5 mass %, relative to the total mass of the ink composition.

[0062] (wax agent) The wax agent is preferably a wax emulsion, and more preferably an aqueous wax emulsion. Natural waxes and synthetic waxes can be used as the wax agent. Examples of natural waxes include petroleum-based waxes such as paraffin wax and microcrystalline wax; lignite-based waxes such as montan wax; vegetable waxes such as carnauba wax and candelilla wax; and animal and vegetable waxes such as beeswax and lanolin. Examples of synthetic waxes include polyalkylene waxes (preferably poly C2-C4 alkylene wax), oxidized polyalkylene waxes (preferably poly C2-C4 alkylene wax), and paraffin wax. Among these, at least one selected from the group consisting of polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and paraffin wax is preferred, with oxidized polyethylene wax being more preferred. The average particle size of the wax agent is preferably 50 nm to 5 μm, more preferably 100 nm to 1 μm, to prevent clogging of the inkjet head. Examples of commercially available wax emulsions include AQUACER 515 (acid value: 5 mg KOH / g) manufactured by BYK Japan and HYTEC E-6500 (acid value: 10 to 20 mg KOH / g) manufactured by Toho Chemical Industry Co., Ltd.

[0063] When the ink composition according to this embodiment contains a wax agent, the solid content thereof is preferably 0.1 to 5 mass %, more preferably 0.2 to 3 mass %, even more preferably 0.5 to 3 mass %, particularly preferably 0.5 to 2 mass %, and extremely preferably 0.5 to 1.5 mass %, relative to the total mass of the ink composition.

[0064] (antioxidant) As the antioxidant, for example, various organic and metal complex anti-fading agents can be used. Examples of organic anti-fading agents include hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, and heterocycles.

[0065] [Ink preparation method, etc.] The method for preparing the ink composition according to this embodiment is not particularly limited, and any known preparation method can be used. One example of such a method is to prepare an aqueous dispersion containing a colorant and a dispersant, and then add a specific solvent component, water, and, if necessary, an ink preparation agent to this aqueous dispersion, and mix them.

[0066] When the ink composition according to this embodiment is used for inkjet recording, it is preferable to filter the ink composition to remove aggregates and the like. As a filtration method, a known method can be appropriately adopted. For example, suction filtration using filter paper such as glass filter paper GC-50 (retention particle diameter: 0.5 μm, manufactured by Advantec Co., Ltd.) or glass filter paper GA-100 (retention particle diameter: 1.0 μm, manufactured by Advantec Co., Ltd.) can be used.

[0067] The ink composition according to this embodiment exhibits good wet spread on poorly ink-absorbent or non-ink-absorbent printing media, making it possible to obtain good-quality printed matter with large dot diameters regardless of the size of the printing gap. Furthermore, the ink composition according to this embodiment exhibits excellent storage stability, redispersibility, various abrasion resistance, color development, and saturation, and also exhibits little coating unevenness during image formation, resulting in excellent image formability. Furthermore, printed images recorded using the ink composition according to this embodiment exhibit excellent fastness properties, such as water resistance, light resistance, heat resistance, and oxidizing gas resistance (e.g., ozone gas resistance).

[0068] <Ink composition set> The ink composition set according to this embodiment includes the ink composition according to this embodiment described above and another ink composition that is different from the ink composition according to this embodiment. The other ink composition is not particularly limited as long as it has a different constitution from the ink composition according to this embodiment, but it is preferable that the other ink composition has a different hue from the ink composition according to this embodiment.

[0069] <Inkjet recording method> The inkjet recording method according to this embodiment includes a step of ejecting droplets of the ink composition according to this embodiment described above, or each of the ink compositions included in the ink composition set according to this embodiment described above, onto a printing medium, thereby forming an image.

[0070] Print media refers to media onto which the ink composition can be applied, and can be broadly divided into ink-absorbent print media and ink-poorly absorbent or non-ink-absorbent print media.

[0071] Examples of ink-absorbent printing media include inkjet paper, inkjet film, glossy paper, corrugated board, and liner paper included in corrugated board, etc. Specific examples of liner paper include K-liner, C-liner, lightweight liner, etc., commercially available from Oji Materia Co., Ltd., Nippon Paper Industries Co., Ltd., etc.

[0072] Examples of poorly ink-absorbent or non-ink-absorbent printing media include various types of paper, such as coated paper, lightweight coated paper, lightly coated paper, coated cardboard, and art paper, used in applications such as gravure printing and offset printing; cast-coated paper, used in label printing; etc. These printing media are formed by applying a coating agent to untreated high-quality paper or the like to provide a coating layer to impart whiteness, etc. Specific examples include OK Top Coat+ and Mirror Coat Platinum (both manufactured by Oji Paper Co., Ltd.); Aurora Coat (manufactured by Nippon Paper Industries Co., Ltd.); Pearl Coat (manufactured by Mitsubishi Paper Mills Co., Ltd.); Mari Coat (manufactured by Hokuetsu Corporation Co., Ltd.); and Raicho Coat (manufactured by Chuetsu Pulp Industries Co., Ltd.).

[0073] The inkjet recording method according to this embodiment is preferably a recording method using a printing medium containing at least one selected from the group consisting of cardboard, liner paper, coated board, and coated paper. Also preferred is a recording method using a printing medium that is poorly ink-absorbent or non-ink-absorbent.

[0074] When using printing media that are poorly ink-absorbent or non-ink-absorbent, it is also preferable to subject the printing media to a surface modification treatment in order to improve the fixation of the colorant.

[0075] The surface modification treatment is preferably at least one treatment selected from the group consisting of corona discharge treatment, plasma treatment, and flame treatment. The surface modification of the printing medium can be carried out by appropriately adjusting the number of treatments, treatment time, applied voltage, etc., so as to obtain the desired effect. The state of the surface modification can be confirmed by measuring the contact angle using a known method. It is generally known that the effect of the surface modification treatment weakens over time. Therefore, after the surface modification treatment has been carried out on the printing medium, it is preferable to carry out inkjet recording promptly.

[0076] There are no particular limitations on the ink nozzles of the inkjet printer used in the inkjet recording method according to this embodiment, and they can be selected appropriately depending on the purpose.

[0077] Known printing methods can be used for inkjet printers. Examples include a charge control method that uses electrostatic attraction to eject ink; a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element; an acoustic inkjet method that converts an electric signal into an acoustic beam and irradiates the ink with the resulting radiation pressure to eject the ink; and a thermal inkjet method that uses the pressure generated by heating the ink to form bubbles. The above printing methods also include a method that improves the fixation of colorants by using colorless, transparent ink. For industrial inkjet printers, single-pass printing using a linehead inkjet printer is also preferred for the purpose of increasing printing speed. The ink composition according to this embodiment can produce printed matter with large dot diameters even under such printing conditions, regardless of the size of the printing gap.

[0078] When printing on the surface of a print medium using an inkjet recording method, it is preferable to ensure a print gap of typically 0.5 to 10 mm, preferably 0.75 to 7 mm, more preferably 1 to 5 mm, and even more preferably 1 to 3 mm, to prevent contact between the print medium surface and the inkjet head due to warping of the print medium, etc.

[0079] For all of the above items, combinations of preferred items are more preferred, and combinations of more preferred items are even more preferred. The same applies to combinations of preferred items and more preferred items, and combinations of more preferred items and even more preferred items. [Example]

[0080] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0081] In the examples, unless otherwise specified, "parts" means parts by mass, and "%" means % by mass. In the examples, all synthesis and other operations were carried out under stirring unless otherwise specified. Furthermore, when quantitative determination of the pigment solid content in the dispersion was required, it was determined by the dry weight method using an MS-70 manufactured by A&D Co., Ltd. The pigment solid content is a converted value calculated from the total amount of solids, taking only the pigment solid content.

[0082] <Preparation Example 1: Preparation of Black Dispersion Liquid 1> A block copolymer (dispersant) was obtained by reproducing Synthesis Example 3 of WO 2013 / 115071. The obtained block copolymer (6 parts) was dissolved in methyl ethyl ketone (20 parts) to obtain a homogeneous solution. A mixed solution of sodium hydroxide (0.45 parts) dissolved in water (53.55 parts) was added to this solution, followed by carbon black (Nerox 605, manufactured by Orion Engineered Carbons) (20 parts). The mixture was dispersed in a sand grinder at 1500 rpm for 15 hours to obtain a liquid. Water (100 parts) was added to the obtained liquid, and the mixture was filtered using glass filter paper GA-100 to remove aggregates and other particles, obtaining a filtrate. The methyl ethyl ketone and a portion of the water in the filtrate were distilled under reduced pressure using an evaporator to obtain Black Dispersion 1 (Kdp1) with a pigment solids content of 12.0%.

[0083] <Preparation Example 2: Preparation of cyan dispersion> A cyan dispersion (Cdp) with a pigment solids content of 12.0% was obtained in the same manner as in Preparation Example 1, except that CI Pigment Blue 15:4 (manufactured by Dainichiseika Color & Chemicals Co., Ltd., Chromofine blue 4851) was used instead of the carbon black used in Preparation Example 1.

[0084] <Preparation Example 3: Preparation of Yellow Dispersion> A yellow dispersion (Ydp) having a pigment solids content of 12.0% was obtained in the same manner as in Preparation Example 1, except that CI Pigment Yellow 74 (manufactured by Clariant, HANSA Yellow 5GX01) was used instead of the carbon black used in Preparation Example 1.

[0085] <Preparation Example 4: Preparation of magenta dispersion> A magenta dispersion (Mdp) having a pigment solids content of 12.0% was obtained in the same manner as in Preparation Example 1, except that CI Pigment Red 122 (Clariant, Inkjet Magenta E02VP2621) was used instead of the carbon black used in Preparation Example 1.

[0086] <Preparation Example 5: Preparation of Joncryl aqueous solution> Joncryl 68 (25 parts), triethanolamine (13.3 parts), and ion-exchanged water (61.7 parts) were placed in a three-necked flask equipped with a condenser, and the mixture was heated to 90°C while stirring at 150 rpm to form a solution, yielding an aqueous Joncryl solution containing 25% Joncryl 68.

[0087] <Preparation Example 6: Preparation of Black Dispersion Liquid 2> The Joncryl aqueous solution obtained in Preparation Example 5 (15 parts), water (60 parts), and carbon black (NIPex 160IQ, manufactured by Orion Engineered Carbons) (25 parts) were mixed and dispersed in a sand grinder at 1500 rpm for 15 hours. The mixture was then filtered through glass filter paper GA-100 to remove aggregates and obtain a filtrate. Water was added to the filtrate to obtain Black Dispersion 2 (Kdp2) with a pigment solids content of 15.0%.

[0088] <Preparation Example 7: Preparation of resin emulsion> A resin emulsion with an acid value of 6 mg KOH / g and a solids content of 25% was prepared by following Preparation Example 4 of WO 2015 / 147192. This resin emulsion is designated "Resin 1."

[0089] <Examples 1 to 24 and Comparative Examples 1 to 3: Preparation of Ink Compositions> Each of the components shown in Tables 1 to 4 below was mixed and then filtered through a membrane filter with a pore size of 3 μm to obtain each of the ink compositions for evaluation tests.

[0090] The abbreviations in Tables 1 to 4 below represent the following: In addition, the numerical value in the column for each component in Tables 1 to 4 below indicates the amount (parts) of that component added, and a blank cell indicates that that component was not added. Kdp1: Black dispersion 1 obtained in Preparation Example 1 Cdp: Cyan dispersion obtained in Preparation Example 2 Ydp: Yellow dispersion obtained in Preparation Example 3 Mdp: Magenta dispersion obtained in Preparation Example 4 Kbp2: Black dispersion 2 obtained in Preparation Example 6 PG: Propylene glycol (ClogP value: -1.06) 1,2OD: 1,2-octanediol (ClogP value: 1.58) DEGHe: Diethylene glycol hexyl ether (ClogP value: 1.72) DEGPh: Diethylene glycol phenyl ether (ClogP value: 1.25) 1,2HD: 1,2-Hexanediol (ClogP value: 0.53) EHD: 2-ethyl-1,3-hexanediol (ClogP value: 1.26) TEA: Triethanolamine SF440: Surfynol 440 (manufactured by Nissin Chemical Industry Co., Ltd.) AQ515: AQUACER 515 (manufactured by BYK Japan; solid content 35%) Resin 1: Resin emulsion obtained in Preparation Example 7 Water: Ion-exchanged water

[0091] The weighted average ClogP values ​​in Tables 1 to 4 below are the values ​​of Q1 or Q2 calculated using the formulas (A) to (E) shown above.

[0092] [Table 1]

[0093] [Table 2]

[0094] [Table 3]

[0095] [Table 4]

[0096] <Evaluation> [Dot diameter evaluation test] Gradation printing was performed in 1% increments using the ink compositions of each Example and Comparative Example to obtain printed images. Printing was performed using a printing tool equipped with two KJ4B inkjet heads manufactured by Kyocera Corporation, with a frequency of 10 kHz, binary (medium droplets), and print gaps of 1 mm and 3 mm, using "OK Topcoat+" manufactured by Oji Paper Co., Ltd. as the printing medium. The obtained printed image was dried for 3 seconds under an IR heater set at 100°C to obtain a test piece.

[0097] The dot diameter of the 2% density portion of the obtained test piece was measured using a print image evaluation device PIAS-II manufactured by QEA, and the obtained value was rounded off to the nearest whole number and evaluated according to the following five-level evaluation criteria of S to D. The evaluation results are shown in Tables 5 to 7 below. -Evaluation criteria- S:80μm or more A:75μm or more and 79μm or less B:70μm or more and 74μm or less C:66μm or more and 69μm or less D: 65μm or less

[0098] [Table 5]

[0099] [Table 6]

[0100] [Table 7]

[0101] As shown in Tables 5 to 7 above, the ink compositions of Examples 1 to 24 had significantly larger dot diameters at a gap of at least 1 mm than the ink compositions of Comparative Examples 1 to 3. Furthermore, the ink compositions of Examples 1 to 14 and 16 to 24 had larger dot diameters at a gap of 3 mm than the ink compositions of Comparative Examples 1 to 3. These results demonstrate that the ink compositions of Examples 1 to 24 have excellent dot diameter performance in printed matter.

Claims

1. An ink composition comprising: a colorant; a specific solvent component consisting of at least one organic solvent having a ClogP value of more than 0.504 and less than 2.635; a surfactant; a viscosity modifier; and water; the content of the specific solvent component is 5 to 10% by mass relative to the total mass of the ink composition; the content of the surfactant is 0.3 to 1.0% by mass relative to the total mass of the ink composition; the content of the viscosity modifier is 10 to 18% by mass relative to the total mass of the ink composition; an ink composition in which a weighted average value, obtained by weighting the ClogP value of each organic solvent constituting the specific solvent component by the mass content of each organic solvent, is greater than 0.67 and less than 1.26;

2. The ink composition of claim 1 , wherein the colorant comprises a pigment.

3. 2. The ink composition according to claim 1, wherein the content of the colorant is 0.5 to 30.0% by mass with respect to the total mass of the ink composition.

4. An ink composition set comprising the ink composition according to any one of claims 1 to 3 and another ink composition different from the ink composition.

5. An inkjet recording method comprising a step of ejecting droplets of the ink composition according to any one of claims 1 to 3 onto a printing medium to form an image.

6. The inkjet recording method according to claim 5 , wherein the print medium comprises at least one selected from the group consisting of corrugated cardboard, liner paper, coated cardboard, and coated paper.

7. The inkjet recording method according to claim 5, wherein the printing medium is a printing medium that is poorly ink-absorbent or non-ink-absorbent.

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