Aqueous ink for inkjet recording

Abstract

To provide a new aqueous ink for inkjet recording which has good wettability to a hydrophobic recording medium, spreads ink droplets thereon, and can bury a predetermined area with a small amount.SOLUTION: A new aqueous ink for inkjet recording contains a surface active agent, a water-soluble organic solvent and water, in which the surface active agent has solubility to water at 20°C of 0.05 mass% to 0.2 mass%, and a content of the surface active agent in the total amount is 1 mass% or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous ink for inkjet recording.

Background Art

[0002] As an aqueous ink for inkjet recording having excellent fixability to coated paper or the like, an aqueous ink containing a vinyl chloride-acrylic copolymer has been proposed (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, there is a need for a new aqueous ink for inkjet recording that has good wettability to hydrophobic recording media such as coated paper, plastic, and film, spreads ink droplets on the surface thereof, and can fill a predetermined area with a small amount.

[0005] Therefore, an object of the present invention is to provide a new aqueous ink for inkjet recording that has good wettability to hydrophobic recording media, spreads ink droplets on the surface thereof, and can fill a predetermined area with a small amount.

Means for Solving the Problems

[0006] To achieve the above object, the aqueous ink for inkjet recording of the present invention contains a surfactant, a water-soluble organic solvent, and water, wherein the surfactant has a solubility in water at 20°C of 0.05 mass% to 0.2 mass%, and the content of the surfactant in the total amount is 1 mass% or more. This is the gist of the present invention.

Advantages of the Invention

[0007] The aqueous ink for inkjet recording of the present invention contains 1% by mass or more of a hydrophobic surfactant that is hardly soluble in water and has a solubility in water at 20°C of 0.05% by mass to 0.2% by mass. As a result, the wettability to a hydrophobic recording medium is good, ink droplets spread on the surface, and it is possible to fill a predetermined area with a small amount.

Brief Description of the Drawings

[0008]

Figure 1

Embodiments for Carrying Out the Invention

[0009] In the present invention, the “surfactant having a solubility in water at 20°C of X% by mass” means a surfactant in which X g dissolves in (100 - X) g of water at 20°C. For example, the “surfactant having a solubility in water at 20°C of 0.2% by mass” means a surfactant in which 0.2 g dissolves in 99.8 g of water at 20°C.

[0010] The aqueous ink for inkjet recording of the present invention (hereinafter sometimes referred to as “aqueous ink” or “ink”) can be suitably used for inkjet recording on hydrophobic recording media such as coated paper, plastic, film, and OHP sheets, but is not limited thereto. For example, it can also be used for inkjet recording on recording media other than hydrophobic recording media such as plain paper, glossy paper, and matte paper. In the present invention, the “coated paper” means, for example, plain paper mainly composed of pulp such as high-grade printing paper and medium-grade printing paper, to which a coating agent is applied for the purpose of improving smoothness, whiteness, glossiness, etc. Specifically, high-grade coated paper, medium-grade coated paper, etc. can be mentioned.

[0011] The aqueous ink of the present invention will be described. The aqueous ink of the present invention contains a surfactant, a water-soluble organic solvent, and water.

[0012] The surfactant is a hydrophobic one that is hardly soluble in water and has a solubility in water at 20°C of 0.05% by mass to 0.2% by mass. The surfactant may contain, for example, at least one of an acetylene glycol-based surfactant and a polyoxyethylene-based surfactant, and a commercially available product may be used. Examples of the commercially available products include "Orfin (registered trademark) E1004" (acetylene glycol-based) and "Surfynol (registered trademark) 440" (acetylene glycol-based) manufactured by Nissin Chemical Industry Co., Ltd.; "Emulgen (registered trademark) 106" (polyoxyethylene lauryl ether) and "Emulgen (registered trademark) 705" (polyoxyethylene alkyl ether) manufactured by Kao Corporation; "Nonion P-210" (polyoxyethylene cetyl ether) manufactured by NOF Corporation; "Acetylenol (registered trademark) E40" (acetylene glycol-based) manufactured by Kawaken Fine Chemicals Co., Ltd.; and the like. The surfactant may have, for example, a solubility in water at 20°C of 0.05% by mass to 0.1% by mass.

[0013] The content of the hydrophobic surfactant in the total amount of the aqueous ink is 1% by mass or more. By containing 1% by mass or more of the hydrophobic surfactant, the aqueous ink has good wettability to a hydrophobic recording medium, the ink droplets spread on its surface, and it is possible to fill a predetermined area with a small amount. The upper limit value of the content of the hydrophobic surfactant is not particularly limited. For example, since it needs to be dissolved in the aqueous ink, it depends on the blending amount of other components such as the water-soluble organic solvent, but is about 4% by mass to 5% by mass.

[0014] The surfactant contained in the aqueous ink may be only the hydrophobic surfactant. Further, the aqueous ink may contain, in addition to the hydrophobic surfactant, another surfactant other than the hydrophobic surfactant.

[0015] The water-soluble organic solvent contains at least one selected from the group consisting of propylene glycol, 1,3-butanediol, tripropylene glycol (hereinafter sometimes referred to as "TPG"), and diethylene glycol (hereinafter sometimes referred to as "DEG"). These water-soluble organic solvents can function, for example, as wetting agents that prevent the drying of the aqueous ink at the nozzle tip of the inkjet head. The content of the water-soluble organic solvent in the total amount of the aqueous ink is, for example, 10% by mass or more. The upper limit value of the content is not particularly limited, and is, for example, 50% by mass or less, and from the viewpoint of dissolving the hydrophobic surfactant, it is 20% to 40% by mass.

[0016] The water-soluble organic solvent may further contain wetting agents other than propylene glycol, 1,3-butanediol, TPG, and DEG. The wetting agents other than propylene glycol, 1,3-butanediol, TPG, and DEG are not particularly limited, and examples thereof include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol; amides such as dimethylformamide and dimethylacetamide; ketones such as acetone; ketoalcohols such as diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyethers such as polyalkylene glycol; alkylene glycols other than propylene glycol, 1,3-butanediol, TPG, and DEG, polyhydric alcohols such as glycerin, trimethylolpropane, and trimethylolethane; 2-pyrrolidone; N-methyl-2-pyrrolidone; 1,3-dimethyl-2-imidazolidinone; and the like. Examples of the polyalkylene glycol include polyethylene glycol and polypropylene glycol. Examples of the alkylene glycol other than propylene glycol, 1,3-butanediol, TPG, and DEG include ethylene glycol, triethylene glycol, dipropylene glycol, thiodiglycol, and hexylene glycol. These wetting agents may be used alone or in combination of two or more.

[0017] The water-soluble organic solvent may further contain a penetrant. The penetrant adjusts, for example, the drying rate on the recording medium.

[0018] Examples of the penetrant include glycol ethers. Examples of the glycol ethers include ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol-n-propyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol-n-propyl ether, diethylene glycol-n-butyl ether, diethylene glycol-n-hexyl ether, triethylene glycol methyl ether, triethylene glycol ethyl ether, triethylene glycol-n-propyl ether, triethylene glycol-n-butyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol-n-propyl ether, propylene glycol-n-butyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol-n-propyl ether, dipropylene glycol-n-butyl ether, tripropylene glycol methyl ether, tripropylene glycol ethyl ether, tripropylene glycol-n-propyl ether, and tripropylene glycol-n-butyl ether. Further, as the penetrant, lower alcohols such as ethyl alcohol, n-propyl alcohol, and isopropyl alcohol exemplified as the wetting agent, and a small amount of acetone can also be used, and these can function as both the wetting agent and the penetrant. The penetrant may be used alone or in combination of two or more.

[0019] The content of the penetrant in the total amount of the aqueous ink is, for example, 0% by mass to 20% by mass, 0% by mass to 15% by mass, or 1% by mass to 6% by mass.

[0020] The water is preferably ion-exchanged water or pure water. The content of the water in the total amount of the aqueous ink is, for example, 10% by mass to 90% by mass, or 20% by mass to 80% by mass. The content of the water may be, for example, the balance of the other components.

[0021] The aqueous ink may further contain resin fine particles. The glass transition temperature (Tg) of the resin fine particles is, for example, -60°C to 150°C, 20°C to 100°C, or 75°C or lower. The resin fine particles may be, for example, those contained in a resin emulsion. The resin emulsion is composed of, for example, the resin fine particles and a dispersion medium (such as water, etc.), and the resin fine particles are not in a dissolved state in the dispersion medium but are dispersed with a specific particle size. Examples of the resin fine particles include acrylic resins, maleic acid ester resins, vinyl acetate resins, carbonate resins, polycarbonate resins, styrene resins, ethylene resins, polyethylene resins, propylene resins, polypropylene resins, urethane resins, polyurethane resins, and copolymer resins thereof. The resin fine particles may be used alone or in combination of two or more. Among these, acrylic resins are preferred.

[0022] As the resin emulsion, for example, commercially available products may be used. Examples of the commercially available products include "Movinyl (registered trademark) 6969D" (Tg: 71°C), "Movinyl (registered trademark) 5450" (Tg: 53°C), "Movinyl (registered trademark) DM772" (Tg: 22°C) manufactured by Nippon Coating Resin Co., Ltd.; "Polyzol (registered trademark) AP-3770" manufactured by Showa Denko K.K.; "Superflex (registered trademark) 150" (Tg: 40°C) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., etc.

[0023] The average particle size of the resin fine particles is, for example, 5 nm to 500 nm, 20 nm to 300 nm, or 30 nm to 200 nm. The average particle size can be measured as the arithmetic mean diameter using, for example, a dynamic light scattering type particle size distribution measuring device "LB-550" manufactured by Horiba, Ltd.

[0024] The content of the resin fine particles in the total amount of the aqueous ink is, for example, 0.1% by mass to 30% by mass, 0.5% by mass to 20% by mass, or 1% by mass to 10% by mass. The resin fine particles may be used alone or in combination of two or more kinds.

[0025] The aqueous ink may be a colored ink containing a colorant or a colorless ink not containing a colorant. In the colored ink, the colorant may be either a pigment or a dye. Further, the colorant may be used as a mixture of a pigment and a dye.

[0026] The pigment is not particularly limited, and examples thereof include carbon black, inorganic pigments, and organic pigments. Examples of the carbon black include furnace black, lamp black, acetylene black, channel black, and the like. Examples of the inorganic pigments include titanium oxide, iron oxide-based inorganic pigments, and carbon black-based inorganic pigments. Examples of the organic pigments include azo pigments such as azo lake, insoluble azo pigments, condensed azo pigments, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye lake pigments such as basic dye type lake pigments and acid dye type lake pigments; nitro pigments; nitroso pigments; aniline black daylight fluorescent pigments; and the like. In addition, other pigments that can be dispersed in the aqueous phase can also be used. Specific examples of these pigments include, for example, C.I. Pigment Black 1, 6, and 7; C.I. Pigment Yellow 1, 2, 3, 12, 13, 14, 15, 16, 17, 55, 74, 78, 150, 151, 154, 180, 185, and 194; C.I. Pigment Orange 31 and 43; C.I. Pigment Red 2, 3, 5, 6, 7, 12, 15, 16, 48, 48:1, 53:1, 57, 57:1, 112, 122, 123, 139, 144, 146, 149, 150, 166, 168, 175, 176, 177, 178, 184, 185, 190, 202, 209, 221, 222, 224, and 238; C.I. Pigment Violet 19 and 196; C.I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 16, 22, and 60; C.I. Pigment Green 7 and 36; and solid solutions of these pigments. The aqueous ink of the present invention may be one in which the pigment is dispersed in water with a dispersant. As the dispersant, for example, general polymer dispersants (resins for pigment dispersion, resin dispersants) and the like may be used, or it may be prepared in-house. Further, in the aqueous ink of the present invention, the pigment may be encapsulated with a polymer.

[0027] The pigment may be a self-dispersing pigment. The self-dispersing pigment is, for example, a pigment particle to which at least one of hydrophilic functional groups such as a carbonyl group, a hydroxyl group, a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and salts thereof is introduced by chemical bonding directly or via another group, so that it can be dispersed in water without using a dispersant. As the self-dispersing pigment, for example, those obtained by treating pigments by the methods described in JP-A-8-3498, JP-T-2000-513396, JP-T-2008-524400, JP-T-2009-515007, JP-T-2011-515535, etc. can be used. As the raw material of the self-dispersing pigment, either an inorganic pigment or an organic pigment can be used. Further, examples of the pigment suitable for performing the treatment include carbon black such as "MA8" and "MA100" manufactured by Mitsubishi Chemical Corporation. The self-dispersing pigment may be, for example, a commercially available product. Examples of the commercially available product include "CAB-O-JET (registered trademark) 200", "CAB-O-JET (registered trademark) 250C", "CAB-O-JET (registered trademark) 260M", "CAB-O-JET (registered trademark) 270Y", "CAB-O-JET (registered trademark) 300", "CAB-O-JET (registered trademark) 400", "CAB-O-JET (registered trademark) 450C", "CAB-O-JET (registered trademark) 465M", and "CAB-O-JET (registered trademark) 470Y" manufactured by Cabot Corporation; "BONJET (registered trademark) BLACK CW-2" and "BONJET (registered trademark) BLACK CW-3" manufactured by Orient Chemical Industries, Ltd.; "LIOJET (registered trademark) WD BLACK 002C" manufactured by Toyo Ink Manufacturing Co., Ltd., etc.

[0028] The solid content of the pigment (pigment solid content) in the total amount of the aqueous ink is not particularly limited and can be appropriately determined, for example, according to a desired optical density, chroma, etc. The pigment solid content is, for example, 0.1% by mass to 20% by mass, 1% by mass to 15% by mass, 2% by mass to 10% by mass.

[0029] The dye is not particularly limited, and examples thereof include direct dyes, acid dyes, basic dyes, reactive dyes, food dyes, etc. Specific examples of the dye include C.I. Direct Black, C.I. Direct Blue, C.I. Direct Red, C.I. Direct Yellow, C.I. Direct Orange, C.I. Direct Violet, C.I. Direct Brown, C.I. Direct Green, C.I. Acid Black, C.I. Acid Blue, C.I. Acid Red, C.I. Acid Yellow, C.I. Acid Orange, C.I. Acid Violet, C.I. Basic Black, C.I. Basic Blue, C.I. Basic Red, C.I. Basic Violet, C.I. Reactive Blue, C.I. Reactive Red, C.I. Reactive Yellow, C.I. Food Black, C.I. Food Red, C.I. Food Yellow, etc. Examples of the C.I. Direct Black include C.I. Direct Black 17, 19, 22, 31, 32, 51, 62, 71, 74, 108, 112, 113, 146, 154, 168, and 195, etc. Examples of the C.I. Direct Blue include C.I. Direct Blue 1, 6, 15, 22, 25, 41, 71, 76, 77, 80, 86, 90, 98, 106, 108, 120, 158, 163, 168, 199, and 226, etc. Examples of the C.I. Direct Red include C.I. Direct Red 1, 2, 4, 9, 11, 17, 20, 23, 24, 28, 31, 39, 46, 62, 75, 79, 80, 83, 89, 95, 197, 201, 218, 220, 224, 225, 226, 227, 228, 229, and 230, etc. Examples of the C.I. Direct Yellow include C.I. Direct Yellow 8, 11, 12, 24, 26, 27, 28, 33, 39, 44, 50, 58, 85, 86, 87, 88, 89, 98, 100, 110, 132, 142, and 173, etc. Examples of the C.I. Direct Orange include C.I. Direct Orange 34, 39, 44, 46, and 60, etc. Examples of the C.I. Direct Violet include C.I. Direct Violet 47 and 48, etc.Examples of the C.I. Direct Brown include C.I. Direct Brown 109 and the like. Examples of the C.I. Direct Green include C.I. Direct Green 59 and the like. Examples of the C.I. Acid Black include C.I. Acid Black 2, 7, 24, 26, 31, 48, 51, 52, 63, 110, 112, 115, 118, and 156 and the like. Examples of the C.I. Acid Blue include C.I. Acid Blue 1, 7, 9, 15, 22, 23, 25, 29, 40, 43, 59, 62, 74, 78, 80, 90, 93, 100, 102, 104, 117, 120, 127, 138, 158, 161, 167, 220, and 234 and the like. Examples of the C.I. Acid Red include C.I. Acid Red 1, 6, 8, 9, 13, 14, 18, 26, 27, 32, 35, 37, 42, 51, 52, 80, 83, 85, 87, 89, 92, 94, 106, 114, 115, 133, 134, 145, 158, 180, 198, 249, 256, 265, 289, 315, and 317 and the like. Examples of the C.I. Acid Yellow include C.I. Acid Yellow 1, 3, 7, 11, 17, 23, 25, 29, 36, 38, 40, 42, 44, 61, 71, 76, 98, and 99 and the like. Examples of the C.I. Acid Orange include C.I. Acid Orange 7 and 19 and the like. Examples of the C.I. Acid Violet include C.I. Acid Violet 49 and the like. Examples of the C.I. Basic Black include C.I. Basic Black 2 and the like. Examples of the C.I. Basic Blue include C.I. Basic Blue 1, 3, 5, 7, 9, 24, 25, 26, 28, and 29 and the like. Examples of the C.I. Basic Red include C.I. Basic Red 1, 2, 9, 12, 13, 14, and 37 and the like. Examples of the C.I. Basic Violet include C.I. Basic Violet 7, 14, and 27 and the like.Examples of the C.I. Reactive Blue include C.I. Reactive Blue 4, 5, 7, 13, 14, 15, 18, 19, 21, 26, 27, 29, 32, 38, 40, 44, and 100. Examples of the C.I. Reactive Red include C.I. Reactive Red 7, 12, 13, 15, 17, 20, 23, 24, 31, 42, 45, 46, and 59. Examples of the C.I. Reactive Yellow include C.I. Reactive Yellow 2, 3, 17, 25, 37, and 42. Examples of the C.I. Food Black include C.I. Food Black 1 and 2. Examples of the C.I. Food Red include C.I. Food Red 87, 92, and 94. Examples of the C.I. Food Yellow include C.I. Food Yellow 3.

[0030] The dye may be used alone or in combination of two or more. The content of the dye in the total amount of the aqueous ink is, for example, 0.1% by mass to 20% by mass, 1% by mass to 15% by mass, or 2% by mass to 10% by mass.

[0031] The aqueous ink may further contain a conventionally known additive as necessary. Examples of the additive include a pH adjuster, a viscosity adjuster, a surface tension adjuster, and a fungicide. Examples of the viscosity adjuster include polyvinyl alcohol, cellulose, and water-soluble resins.

[0032] The aqueous ink can be prepared, for example, by uniformly mixing the surfactant, the water-soluble organic solvent, the water, and other additive components as necessary by a conventionally known method, and removing insoluble matters with a filter or the like.

[0033] Next, the inkjet recording apparatus and the inkjet recording method of the present invention will be described.

[0034] The inkjet recording apparatus of the present invention includes an ink storage unit and an ink ejection means, and is an inkjet recording apparatus that ejects the ink stored in the ink storage unit by the ink ejection means, wherein the ink storage unit stores the aqueous ink for inkjet recording of the present invention. As will be described later, the inkjet recording apparatus of the present invention may further include a drying means for drying the recording portion with the ink.

[0035] The inkjet recording method of the present invention includes a recording step of ejecting an aqueous ink onto a recording medium by an inkjet method for recording, and in the recording step, the aqueous ink for inkjet recording of the present invention is used as the aqueous ink. The inkjet recording method of the present invention may further include a fixing step of fixing the aqueous ink to the recording medium using a drying means for drying the recording portion of the recording medium.

[0036] The inkjet recording method of the present invention can be implemented using, for example, the inkjet recording apparatus of the present invention. The recording includes printing, printing pictures, printing, etc.

[0037] The schematic diagram of FIG. 1 shows the configuration of an example of the inkjet recording apparatus of the present invention. As shown in FIG. 1, this inkjet recording apparatus <100> includes a paper feed tray <101>, a conveyance mechanism (not shown) such as rollers, recording mechanisms <102A> and <102B>, a platen <103>, a drying means <104>, a paper discharge tray <105>, and an ink storage unit (not shown) such as an ink cartridge or an ink tank. The paper feed tray <101> can support a plurality of stacked recording media (for example, coated paper) .

[0038] The recording mechanism includes a carriage 102A and an inkjet head (ink ejection means) 102B. The carriage 102A is supported by two guide rails (not shown) extending perpendicular to the conveyance direction of the recording medium P. The two guide rails are supported by a housing (not shown) of the inkjet recording apparatus 100. The carriage 102B is connected to a known belt mechanism (not shown) provided on the two guide rails. This belt mechanism is driven by a carriage motor (not shown). The carriage 102A connected to the belt mechanism reciprocates in a direction perpendicular to the conveyance direction of the recording medium P by the drive of the carriage motor.

[0039] Further, four ink tubes (not shown) connecting the ink storage section and the inkjet head 102B, and a flexible flat cable (not shown) electrically connecting the control board (not shown) and the inkjet head 102B extend from the carriage 102A. The four ink tubes supply four colors of aqueous ink, namely yellow, magenta, cyan, and black, stored in the ink storage section to the inkjet head 102B. At least one of the four colors of aqueous ink is the aqueous ink for inkjet recording of the present invention. The flexible flat cable transmits a control signal output from the control board to the inkjet head 102B.

[0040] As shown in FIG. 1, the inkjet head 102B is mounted on the carriage 102A. A plurality of nozzles 102C are formed on the lower surface of the inkjet head 102B. The tips of the plurality of nozzles 102C are exposed from the lower surfaces of the carriage 102A and the inkjet head 102B. The inkjet head 102B has an actuator (not shown) for applying a force to discharge the aqueous ink supplied from the ink storage section to the inkjet head 102B via the ink tube. The actuator may be of any type, such as a piezoelectric element type, a thermal ink type, an electrostatic attraction type, etc. In the process of the carriage 102A reciprocating in the direction perpendicular to the conveyance direction of the recording medium P, the inkjet head 102B discharges the aqueous ink as minute ink droplets from the plurality of nozzles 102C. Thereby, an image is recorded on the recording medium P. The platen 103 is arranged to face the recording mechanism and supports the recording medium P conveyed from the paper feed tray 101.

[0041] The drying means 104 heats and dries the recording portion of the recording medium P. The temperature during this drying can be appropriately adjusted by changing the setting of the drying means 104. Specifically, for example, it is 20°C to 200°C, 50°C to 100°C. Also, the drying time can be appropriately adjusted by changing the setting of the drying means 104. For example, it exceeds 0 seconds and is 300 seconds or less, 0.1 seconds to 60 seconds, 1 second to 60 seconds. The drying means 104 may be any means as long as it can dry the recording portion. Examples of the drying means 104 include commercially available dryers, infrared heaters, ovens, belt conveyor ovens, irons, hot press machines, etc. Non-contact drying means that dries the recording portion of the recording medium P without contacting the recording portion, such as dryers, infrared heaters, ovens, belt conveyor ovens, etc., is preferable.

[0042] The recording medium P after recording and drying is conveyed to the paper discharge tray 105.

Example

[0043] Next, examples of the present invention will be described together with comparative examples. Note that the present invention is not limited or restricted by the following examples and comparative examples.

[0044] [Preparation of Resin Dispersant] In a flask equipped with a dropping funnel, a condenser, and a stirrer, under a nitrogen atmosphere, 135 g of Terathane (registered trademark) 650 (a polyether diol manufactured by Invista (Wichita, KS)), 54 g of 2,2'-dimethylolpropanoic acid (DMPA), 132 g of sulfolane, and 0.06 g of dibutyltin dilaurate (DBTDL) were added. The mixture was heated to 60 °C while mixing and further mixed thoroughly. To this mixture, 164 g of m-tetramethylenexylylene diisocyanate (TMXDI) was added by a dropping funnel, and the remaining TMXDI in the dropping funnel was rinsed into the flask with 15 g of sulfolane. The temperature was raised to 100 °C and maintained at 100 °C until the isocyanate content reached 1.3% by mass or less. Next, the temperature was lowered to 60 °C, and 12.9 g of diethanolamine (DEA) was added by a dropping funnel over 5 minutes and maintained at 60 °C until the remaining DEA in the dropping funnel was rinsed into the flask with 5 g of sulfolane. Further, after maintaining the temperature at 60 °C for 1 hour, 376 g of a 3% by mass aqueous potassium hydroxide solution was added by a dropping funnel over 10 minutes, and then 570 g of deionized water was added. Thereafter, it was maintained at 60 °C for 1 hour and cooled to room temperature to obtain a resin dispersant having a solid content of 24% by mass.

[0045] [Preparation of Pigment Dispersion A] The resin dispersant was neutralized with either potassium hydroxide or an amine to increase its solubility in water and facilitate dissolution in water. Next, using a high-pressure compressed air type Microfluidizer (Model M-110Y, manufactured by Microfluidics of Newton, Massachusetts), a mixture was produced in which the carbon black content was approximately 27% by mass and the mass ratio of the carbon black content (P) to the resin dispersant content (D) was P / D = 3. Thereafter, for optimal media mill grinding conditions, the carbon black content was adjusted to approximately 24% by mass by adding deionized water, and the mixture was ground for 4 hours. After grinding, deionized water was added and thoroughly mixed. Next, after filtering and removing impurities, the carbon black content was adjusted to 15% by mass by dilution with deionized water, thereby obtaining Pigment Dispersion A.

[0046] [Preparation of Pigment Dispersion B] Pigment Dispersion B was obtained in the same manner as the preparation of Pigment Dispersion A, except that an Eiger Minimill (Model M250, VSE EXP, manufactured by Eiger Machinery Inc., Chicago, Illinois) was used instead of the high-pressure compressed air type Microfluidizer, and a phthalocyanine pigment was used instead of carbon black.

[0047] [Examples 1 to 6, 8 to 11 and Comparative Examples 1 to 6] In the aqueous ink composition (Table 1 or Table 2), the components excluding the resin fine particles (resin emulsion) and Pigment Dispersions A and B were uniformly mixed to obtain an ink solvent. Next, the resin emulsion was added to the ink solvent and uniformly mixed. Thereafter, Pigment Dispersion A or B was added to the ink solvent in which the resin emulsion was mixed and uniformly mixed. Then, the resulting mixture was filtered through a cellulose acetate type membrane filter (pore size 3.00 μm) manufactured by Toyo Roshi Kaisha, Ltd., thereby obtaining the aqueous ink for inkjet recording of Examples 1 to 6, 8 to 11 shown in Table 1 and the aqueous ink for inkjet recording of Comparative Examples 1 to 6 shown in Table 2.

[0048] [Example 7] In the aqueous ink composition (Table 1), the components excluding resin fine particles (resin emulsion) and C.I. Acid Red 52 (azo dye) were uniformly mixed to obtain an ink solvent. Next, the resin emulsion was added to the ink solvent and uniformly mixed. Then, C.I. Acid Red 52 was added to the ink solvent mixed with the resin emulsion and uniformly mixed. Thereafter, the obtained mixture was filtered through a cellulose acetate type membrane filter (pore size: 3.00 μm) manufactured by Toyo Roshi Kaisha, Ltd. to obtain the aqueous ink for inkjet recording of Example 7 shown in Table 1. The aqueous ink of Example 7 uses a dye as a colorant.

[0049] [Example 12] In the aqueous ink composition (Table 1), the components excluding resin fine particles (resin emulsion) were uniformly mixed to obtain an ink solvent. Next, the resin emulsion was added to the ink solvent and uniformly mixed. Thereafter, the obtained mixture was filtered through a cellulose acetate type membrane filter (pore size: 3.00 μm) manufactured by Toyo Roshi Kaisha, Ltd. to obtain the aqueous ink for inkjet recording of Example 12 shown in Table 1. The aqueous ink of Example 12 is a colorless ink (clear ink) containing no colorant.

[0050] Regarding the aqueous inks of Examples 1 to 12 and Comparative Examples 1 to 6, (a) evaluation of surfactant solubility, (b) evaluation of ink droplet spread, (c) evaluation of fixing property on paper, and (d) evaluation of fixing property on film were carried out by the following methods.

[0051] (a) Evaluation of surfactant solubility The filtration filter after preparing the aqueous ink was visually observed and evaluated according to the following evaluation criteria.

[0052] Evaluation Criteria for Surfactant Solubility G: There was no residue or aggregate on the filter. NG: There was residue or aggregate on the filter.

[0053] (b) Evaluation of ink droplet spread Using an inkjet printer MFC-J4225N manufactured by Brother Industries, Ltd., aqueous inks of the examples and comparative examples were used to record images on coated paper ("OK Top Coat +" manufactured by Oji Paper Co., Ltd.) at 600 dpi while changing the ink amount per dot (8 to 10 pL / dot and 12 to 14 pL / dot). The images were visually observed and evaluated according to the following evaluation criteria.

[0054] Evaluation Criteria for Ink Drop Spread AA: In the image recorded at 8 to 10 pL / dot, there was no gap between dots. A: In the image recorded at 12 to 14 pL / dot, there was no gap between dots. B: In the image recorded at 12 to 14 pL / dot, there was a gap between dots.

[0055] (c) Evaluation of Fixing Property on Paper Using the inkjet printer MFC-J4225N, aqueous inks of the examples and comparative examples were used to record images on coated paper ("OK Top Coat +" manufactured by Oji Paper Co., Ltd.) at 600 dpi with an ink amount of 8 to 10 pL / dot. Thereafter, the recorded matter was dried in an atmosphere of 100°C for 1 minute and then cooled to room temperature (about 20°C). After cooling, a cotton swab with a pressure of 0.2 MPa or 0.1 MPa applied thereto was moved on the image surface at a speed of about 50 mm / second, and the fixing property of the aqueous ink on the paper was visually observed and evaluated according to the following evaluation criteria.

[0056] Evaluation Criteria for Fixing Property on Paper AA: Even at a pressure of 0.2 MPa, no aqueous ink adhered to the cotton swab and it was fixed on the paper. A: At a pressure of 0.1 MPa, no aqueous ink adhered to the cotton swab and it was fixed on the paper. B: A small amount of aqueous ink adhered to the cotton swab at a pressure of 0.1 MPa.

[0057] (d) Evaluation of Fixing Property on Film Instead of using coated paper (OK Top Coat + manufactured by Oji Paper Co., Ltd.), the fixability of the aqueous ink on the film was visually observed and evaluated according to the following evaluation criteria in the same manner as the evaluation of the fixability on the paper in (c) above, except that a commercially available PET (polyethylene terephthalate) film was used.

[0058] Evaluation Criteria for Fixing Property on Film AA: No aqueous ink adhered to the cotton swab even under a pressure of 0.2 MPa and was fixed on the paper. A: No aqueous ink adhered to the cotton swab under a pressure of 0.1 MPa and was fixed on the paper. B: A small amount of aqueous ink adhered to the cotton swab under a pressure of 0.1 MPa.

[0059] The aqueous ink compositions and evaluation results of Examples 1 to 12 and Comparative Examples 1 to 6 are shown in Tables 1 and 2.

[0060]

Table 1

[0061]

Table 2

[0062] As shown in Table 1, in Examples 1 to 12, the evaluation results of the solubility of the surfactant, the spread of the ink droplets, the fixability on the paper, and the fixability on the film were good.

[0063] On the other hand, in Comparative Examples 1 to 3 in which a surfactant having a solubility in water at 20 °C exceeding 0.2 mass% was used instead of the surfactant having a solubility in water at 20 °C of 0.05 mass% to 0.2 mass%, the evaluation results of any of the spreading of the ink droplets, the fixability on the paper, and the fixability on the film were poor. Further, in Comparative Example 4 in which a surfactant having a solubility in water at 20 °C of less than 0.05 mass% was used instead of the surfactant having a solubility in water at 20 °C of 0.05 mass% to 0.2 mass%, the evaluation result of the solubility of the surfactant was poor, recording could not be performed, and the evaluation of the spreading of the ink droplets, the fixability on the paper, and the fixability on the film could not be performed. Further, in Comparative Examples 5 and 6 in which the content of the surfactant having a solubility in water at 20 °C of 0.05 mass% to 0.2 mass% was less than 1 mass%, the evaluation results of the spreading of the ink droplets and the fixability on the film were poor.

[0064] Some or all of the above embodiments and examples may be described as follows in the appended claims, but are not limited thereto. (Appended Claim 1) A surfactant, a water-soluble organic solvent, and water, wherein the surfactant has a solubility in water at 20 °C of 0.05 mass% to 0.2 mass%, and the content of the surfactant in the total amount is 1 mass% or more, characterized in that it is an aqueous ink for inkjet recording. (Appended Claim 2) The aqueous ink for inkjet recording according to Appended Claim 1, wherein the surfactant contains at least one of an acetylene glycol-based surfactant and a polyoxyethylene-based surfactant. (Appended Claim 3) The aqueous ink for inkjet recording according to Appended Claim 1 or 2, wherein the water-soluble organic solvent contains at least one selected from the group consisting of propylene glycol, 1,3-butanediol, tripropylene glycol, and diethylene glycol. (Appended Claim 4) The aqueous ink for inkjet recording according to any one of Appended Claims 1 to 3, wherein the content of the water-soluble organic solvent in the total amount is 10 mass% or more. (Appended Claim 5) Furthermore, an aqueous ink for inkjet recording according to any one of Appendices 1 to 4, containing resin fine particles. (Appendix 6) Furthermore, an aqueous ink for inkjet recording according to any one of Appendices 1 to 5, containing a colorant. (Appendix 7) Containing a surfactant, a water-soluble organic solvent, water, and resin fine particles, the solubility of the surfactant in water at 20°C is 0.05 mass% to 0.2 mass%, the content of the surfactant in the total amount is 1 mass% or more, the surfactant contains an acetylene glycol-based surfactant, the water-soluble organic solvent contains propylene glycol, the content of the water-soluble organic solvent in the total amount is 20 mass% or more, An aqueous ink for inkjet recording, characterized by the above. (Appendix 8) Containing a surfactant, a water-soluble organic solvent, water, and resin fine particles, the solubility of the surfactant in water at 20°C is 0.05 mass% to 0.2 mass%, the content of the surfactant in the total amount is 1 mass% or more, the surfactant contains an acetylene glycol-based surfactant, the water-soluble organic solvent contains 1,3-butanediol, the content of the water-soluble organic solvent in the total amount is 20 mass% or more, An aqueous ink for inkjet recording, characterized by the above. (Appendix 9) Containing a surfactant, a water-soluble organic solvent, water, and resin fine particles, the solubility of the surfactant in water at 20°C is 0.05 mass% to 0.2 mass%, the content of the surfactant in the total amount is 1 mass% or more, the surfactant contains a polyoxyethylene-based surfactant, the water-soluble organic solvent contains propylene glycol, The content of the water-soluble organic solvent in the total amount is 20% by mass or more. An aqueous ink for inkjet recording, characterized by the above. (Appendix 10) Comprising a surfactant, a water-soluble organic solvent, water, and resin fine particles, The surfactant has a solubility in water at 20 °C of 0.05% by mass to 0.2% by mass, The content of the surfactant in the total amount is 1% by mass or more, [[ID=I2]]The surfactant includes a polyoxyethylene-based surfactant, The water-soluble organic solvent includes 1,3-butanediol, The content of the water-soluble organic solvent in the total amount is 20% by mass or more. An aqueous ink for inkjet recording, characterized by the above. (Appendix 11) An inkjet recording apparatus including an ink storage unit and an ink ejection means, for ejecting the ink stored in the ink storage unit by the ink ejection means, The ink storage unit stores the aqueous ink for inkjet recording according to any one of Appendices 1 to 10. An inkjet recording apparatus, characterized by the above. (Appendix 12) Furthermore, an inkjet recording apparatus according to Appendix 11, including a drying means for drying the recording portion by the ink. (Appendix 13) Including a recording step of ejecting an aqueous ink onto a recording medium by an inkjet method for recording, In the recording step, the aqueous ink for inkjet recording according to any one of Appendices 1 to 10 is used as the aqueous ink. An inkjet recording method, characterized by the above. (Appendix 14) Furthermore, including a fixing step of fixing the aqueous ink to the recording medium using a drying means for drying the recording portion of the recording medium, in the inkjet recording method according to Appendix 13.

Industrial Applicability

[0065] As described above, the aqueous ink of the present invention has good wettability to a hydrophobic recording medium, and ink droplets spread on its surface and can fill a predetermined area with a small amount. The use of the aqueous ink of the present invention is not limited to inkjet recording on hydrophobic recording media such as coated paper, and it can be widely applied to inkjet recording on various recording media such as plain paper, glossy paper, and matte paper.

Explanation of Reference Signs

[0066] 100 Inkjet recording apparatus 101 Paper feed tray 102A Carriage 102B Inkjet head (ink ejection means) 102C Nozzle 103 Platen 104 Drying means 105 Paper discharge tray

Claims

1. An aqueous ink for inkjet recording, comprising a surfactant (excluding surfactants containing at least one of silicone-based surfactants and fluorine-based surfactants), a water-soluble organic solvent, and water, wherein the surfactant contains at least a polyoxyethylene-based surfactant, the surfactant has a solubility in water at 20 °C of 0.05% by mass to 0.2% by mass, and the content of the surfactant in the total amount is 2% by mass to 2.7% by mass.

2. The aqueous ink for inkjet recording according to Claim 1, further comprising an acetylene glycol-based surfactant as the surfactant.

3. The aqueous ink for inkjet recording according to Claim 1 or 2, wherein the water-soluble organic solvent contains at least one selected from the group consisting of propylene glycol, 1,3-butanediol, tripropylene glycol, and diethylene glycol.

4. The aqueous ink for inkjet recording according to any one of Claims 1 to 3, wherein the content of the water-soluble organic solvent in the total amount is 10% by mass or more.

5. The aqueous ink for inkjet recording according to any one of Claims 1 to 4, further comprising resin fine particles.

6. The aqueous ink for inkjet recording according to any one of Claims 1 to 5, further comprising a colorant.

7. The aqueous ink for inkjet recording according to any one of Claims 1 to 6, for use in recording on a hydrophobic recording medium. ​

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