Inkjet ink, ink set, and inkjet recording method

Abstract

To provide inks for various types of recording, especially inkjet recording, an ink set, and a recording method, that exhibit superior color neutrality, lightness, and redispersibility.SOLUTION: An inkjet ink contains carbon black as a water-insoluble pigment, pigment A, pigment B, and water, wherein pigment A has at least one absorption maximum wavelength at 450 nm or more and less than 600 nm among absorption wavelengths in ultraviolet-visible spectrophotometry, pigment B has at least one absorption maximum wavelength at 600 nm or more and less than 800 nm among absorption wavelengths in ultraviolet-visible spectrophotometry, the carbon black content is from 0.10 mass% or more to 1.00 mass% or less with respect to the total mass of the ink, and the combined amount of carbon black, pigment A, and pigment B is from 0.12 mass% or more to less than 1.80 mass% with respect to the total mass of the ink.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inkjet ink, an ink set, and an inkjet recording method. [Background technology]

[0002] Among various color recording methods, the recording method using an inkjet printer (inkjet recording method), which is one of the most representative methods, generates small droplets of ink and deposits them on a printing medium such as paper to perform recording. This recording method has the advantage of being easily miniaturized and made to operate at high speed, so in recent years demand for it has been increasing for commercial and industrial purposes, and significant growth is expected in the future.

[0003] In inkjet recording, dots are formed on a printing medium using small ink droplets, and the desired image is expressed by varying the arrangement and density of these dots. To achieve low-density gradations, the dots must be spaced apart. However, these dots often cause minute variations in density, resulting in a grainy appearance in the image. One way to address this issue is to use light-colored inks with lower concentrations of colorant in the same ink, thereby reducing the minute variations in density and allowing for smoother gradations. For example, using light-black inks in combination with black ink allows for smoother gray gradations.

[0004] The pale black ink can also be expected to have an auxiliary effect in improving the density of other colors. For example, to express a high density red, it is usually necessary to apply large amounts of magenta ink and yellow ink, but this requires a large amount of energy to dry and harden the ink, and magenta and yellow pigments are often expensive, which is a significant cost burden. Therefore, by applying a neutral pale black ink in an amount that does not significantly affect the brightness, saturation, and hue of the desired color, a high density red can be expressed with a smaller total amount of ink, which offers advantages in terms of energy and cost.

[0005] Pigments are widely used as colorants for inkjet recording inks. Among these pigments, carbon black is widely used for black inks and pale black inks. In order to achieve smooth gradation and improve density, it is desirable for the pale black ink to be an achromatic, neutral color with a certain range of brightness.

[0006] However, inks containing carbon black tend to produce printed images with a yellow or brown tinge due to the pigment's characteristic visible light absorption wavelength. To address this issue, a technology is known that adjusts the visible light absorption wavelength by incorporating other pigments along with carbon black, thereby producing a neutral color.

[0007] On the other hand, inks containing more than a certain amount of multiple pigments as described above have the problem of reduced redispersibility. Even if the ink dries near the nozzles of an inkjet head, the dried ink is redispersed by the ink itself being newly supplied from the head to the nozzles, making clogging less likely to occur and improving ejection stability, so redispersibility can be said to be an important ink performance feature. It is thought that the inclusion of multiple pigments makes the dispersion state in the ink unstable, and that containing more than a certain amount makes the ink more susceptible to clogging due to drying, resulting in reduced redispersibility.

[0008] Patent Document 1 reports that a neutral color image can be obtained by specifying the ratio of cyan pigment and magenta pigment to the amount of carbon black contained in the black ink, as well as the total amount of pigments. However, the ink in Patent Document 1 had low brightness and insufficient redispersibility.

[0009] As described above, a pale black ink that satisfies all of the requirements of moderate color and brightness and effective redispersibility has not yet been proposed. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-72270 Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide an inkjet ink that exhibits moderate color and brightness that can achieve smooth gray gradation expression and improved density of other colors, and also has excellent redispersibility, an ink set including the inkjet ink, and an inkjet recording method using the inkjet ink. [Means for solving the problem]

[0012] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by an inkjet ink containing carbon black as a water-insoluble pigment, Pigment A, Pigment B, and water, wherein the Pigment A has one or more absorption maximum wavelengths in the range of 450 nm to less than 600 nm within its absorption wavelengths in ultraviolet-visible spectroscopy, and the Pigment B has one or more absorption maximum wavelengths in the range of 600 nm to less than 800 nm within its absorption wavelengths in ultraviolet-visible spectroscopy, and the content of the carbon black is 0.10% by mass to 1.00% by mass, both inclusive, with respect to the total mass of the ink, and the total amount of the carbon black, Pigment A, and Pigment B is 0.12% by mass to less than 1.80% by mass, both inclusive, with respect to the total mass of the ink, and have completed the present invention.

[0013] That is, the present invention relates to the following 1) to 9). 1) An inkjet ink comprising carbon black as a water-insoluble pigment, Pigment A, Pigment B, and water, wherein Pigment A has one or more absorption maximum wavelengths in the range of 450 nm or more to less than 600 nm within its absorption wavelengths in ultraviolet-visible spectroscopy, and Pigment B has one or more absorption maximum wavelengths in the range of 600 nm or more to less than 800 nm within its absorption wavelengths in ultraviolet-visible spectroscopy, the content of the carbon black being 0.10% by mass or more and 1.00% by mass or less with respect to the total mass of the ink, and the total amount of the carbon black, Pigment A, and Pigment B being 0.12% by mass or more to less than 1.80% by mass with respect to the total mass of the ink. 2) The ink-jet ink according to 1), wherein the pigment A comprises at least one pigment selected from the group consisting of Pigment Red 48:3, Pigment Red 57:1, Pigment Red 150, Pigment Red 122, Pigment Red 146, Pigment Red 150, Pigment Red 184, Pigment Red 185, Pigment Red 269, Pigment Orange 34, Pigment Orange 43, Pigment Orange 64, Pigment Violet 23, and Pigment Violet 19. 3) The ink-jet ink according to 1) or 2), wherein the pigment B comprises at least one selected from the group consisting of Pigment Blue 15:3, Pigment Blue 15:4, Pigment Blue 60, Pigment Green 7, and Pigment Green 36. 4) The ink-jet ink according to 1) or 2), wherein the carbon black content is 0.40% by mass or more and 0.80% by mass or less relative to the total mass of the ink. 5) The ink-jet ink according to 1) or 2), wherein the total amount of carbon black, pigment A, and pigment B is 0.60% by mass or more and 1.40% by mass or less, based on the total mass of the ink. 6) An ink set comprising the water-based ink composition according to 1). 7) An inkjet recording method in which droplets of the inkjet ink according to 1) or 2) are ejected from an inkjet head to record on a printing medium. 8) The inkjet recording method according to 7), wherein the printing medium is a poorly absorbent or non-absorbent medium. 9) The inkjet recording method according to 7), wherein the inkjet head includes a circulation mechanism. [Effects of the Invention]

[0014] The present invention provides an inkjet ink having moderate color and brightness and excellent redispersibility. DETAILED DESCRIPTION OF THE INVENTION

[0015] Specific embodiments to which the present invention is applied will be described in detail below. As used herein, "CI" means "Color Index." Additionally, as used herein, the terms "alkylene," "propylene," and "alkyl" are used to encompass both linear and branched chain structures unless otherwise specified.

[0016] <Inkjet ink> The inkjet ink (hereinafter simply referred to as "ink") according to this embodiment contains carbon black as a water-insoluble pigment, pigment A, pigment B, and water. The components contained in the ink according to this embodiment will be described in detail below.

[0017] <Water-insoluble pigment> The pigment used in the present invention is not particularly limited as long as it is a water-insoluble pigment. For example, known pigments can be used. If necessary, these can also be used in combination. In this specification, a water-insoluble pigment means a pigment whose solubility in 1 liter of water at 25°C is usually 5 g or less, preferably 3 g or less, more preferably 1 g or less, and even more preferably 0.5 g or less. The lower limit of the solubility includes 0 g. Unless otherwise specified, a "water-insoluble pigment" will hereinafter be referred to as a "pigment."

[0018] <Pigments> Pigments are mainly classified into inorganic pigments, organic pigments, and extender pigments, and any of these pigments can be used in the present invention. It is also possible to combine these pigments; for example, an extender pigment can be added to an organic pigment to prepare a dispersion for inkjet printing. Examples of inorganic pigments include carbon black, titanium oxide, metal oxides, hydroxides, sulfides, ferrocyanides, and metal chlorides. Carbon black is particularly preferred for black inks and pale black inks.

[0019] <Carbon black> Preferred carbon blacks include thermal black, acetylene black, oil furnace black, gas furnace black, lamp black, gas black, channel black, etc. Specific examples of carbon black include the Raven series manufactured by Columbia Carbon Corporation, the Monarch series, Regal series, and Mogul series manufactured by Cabot Corporation, the HiBlack series, ColorBlack series, Printex series, SpecialBlack series, and Nerox series manufactured by Orion Engineered Carbons, and the MA series, MCF series, No. 25, No. 33, No. 40, No. 47, No. 52, No. 900, and No. 2300 manufactured by Mitsubishi Chemical Corporation.

[0020] The content of the carbon black in the total mass of the ink is preferably 0.10% by mass or more and 1.00% by mass or less, more preferably 0.40% by mass or more and 0.80% by mass or less, and even more preferably 0.50% by mass or more and 0.70% by mass or less.

[0021] <Pigment A> Pigment A refers to a pigment that has one or more absorption maximum wavelengths between 450 nm and 600 nm in ultraviolet-visible spectroscopy. Examples of pigment A include Pigment Red 48:3, Pigment Red 57:1, Pigment Red 150, Pigment Red 122, Pigment Red 146, Pigment Red 150, Pigment Red 184, Pigment Red 185, Pigment Red 269, Pigment Orange 34, Pigment Orange 43, Pigment Orange 64, Pigment Violet 23, and Pigment Violet 19. These pigments A can be used alone or in combination. They can also be used in combination with the inorganic pigments listed above. For example, an organic pigment can be used in combination with an extender pigment to improve the fluidity of the solid.

[0022] <Pigment B> Pigment B refers to a pigment that has one or more absorption maximum wavelengths in the range of 600 nm or more to less than 800 nm in ultraviolet-visible spectroscopy. Examples of pigment B include Pigment Blue 15:3, Pigment Blue 15:4, Pigment Blue 60, Pigment Green 7, and Pigment Green 36. These pigments B can be used alone or in combination of two or more. They can also be used in combination with the inorganic pigments listed above. One example of this is the use of an organic pigment in combination with an extender pigment to improve the fluidity of the solid.

[0023] The total amount of carbon black, pigment A, and pigment B is preferably 0.12% by mass or more and 1.80% by mass or less, more preferably 0.60% by mass or more and 1.40% by mass or less, and even more preferably 0.70% by mass or more and 1.30% by mass or less, of the total mass of the ink. By using this total amount, the pale black ink can exhibit a brightness suitable for the auxiliary effect of improving the density of other colors, and the ink also has excellent redispersibility, storage stability, and ejection stability.

[0024] The combination of the carbon black and pigment A contents in the total mass of the ink is preferably 0.10 to 1.00 mass% of carbon black and 0.01 to 0.40 mass% of pigment A, more preferably 0.40 to 0.80 mass% of carbon black and 0.04 to 0.32 mass% of pigment A, and even more preferably 0.50 to 0.70 mass% of carbon black and 0.05 to 0.28 mass% of pigment A. By using the above contents, saturation is suppressed and achromatic colors with excellent neutrality can be achieved. Furthermore, the combination of the carbon black and pigment B contents in the total mass of the ink is preferably 0.10% by mass to 1.00% by mass of carbon black and 0.01% by mass to 0.40% by mass of pigment B, more preferably 0.40% by mass to 0.80% by mass of carbon black and 0.04% by mass to 0.32% by mass of pigment B, and even more preferably 0.50% by mass to 0.70% by mass of carbon black and 0.05% by mass to 0.28% by mass of pigment B. By using the above contents, saturation is suppressed and achromatic colors with excellent neutrality can be achieved. Furthermore, the combination of the content ratios of pigment A and pigment B in the total mass of the ink is preferably from 0.01 to 0.40% by mass of pigment A and from 0.01 to 0.40% by mass of pigment B, more preferably from 0.04 to 0.32% by mass of pigment A and from 0.04 to 0.32% by mass of pigment B, and even more preferably from 0.05 to 0.28% by mass of pigment A and from 0.05 to 0.28% by mass of pigment B. By using the above content ratios, it is possible to suppress saturation and achieve achromatic colors with excellent neutrality.

[0025] Examples of extender pigments include silica, calcium carbonate, talc, clay, barium sulfate, white carbon, etc. Extender pigments are often used in combination with other pigments.

[0026] The average particle size of the pigment is preferably 30 to 300 nm, more preferably 50 to 250 nm. In this specification, the average particle size refers to the average particle size of particles measured using a laser light scattering method.

[0027] <Water> The water is preferably water with a low content of impurities such as metal ions, i.e., ion-exchanged water, distilled water, etc. The water content is preferably 60 to 90 mass % of the total mass of the ink according to this embodiment, and more preferably 70 to 90 mass %. By achieving this content, the ink has excellent storage stability, ejection stability, and drying properties on the printing medium.

[0028] The ink according to this embodiment may contain, as necessary, ink preparation agents such as dispersants, organic solvents, surfactants, antifungal agents, preservatives, pH adjusters, chelating agents, rust inhibitors, antifoaming agents, water-soluble UV absorbers, antioxidants, resin emulsions, etc. The content of each ink preparation agent can be set as desired depending on the intended use of the ink, etc.

[0029] Examples of dispersants include copolymers composed of at least two monomers (preferably at least one of which is a hydrophilic monomer) selected from the following monomers: 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; faric acid and its derivatives; vinyl acetate, vinyl alcohol, vinylpyrrolidone, acrylamide, and their derivatives. Examples of hydrophilic monomers include monomers that leave a carboxyl group after polymerization, such as acrylic acid and methacrylic acid.

[0030] 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, (meth)acrylic acid ester-(meth)acrylic acid copolymers being even more preferred, and methacrylic acid ester-methacrylic acid copolymers being particularly preferred. Examples of types of copolymers include block copolymers, random copolymers, and graft copolymers. These copolymers may be in the form of a salt. In this specification, the term "(meth)acrylic" is used to mean both "acrylic" and "methacrylic." The same applies to "(meth)acrylate" and the like.

[0031] Dispersants can be synthesized or commercially available. Examples of synthetic dispersants 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.

[0032] Examples of commercially available dispersants include Joncyrl 62, 67, 68, 678, and 687 (styrene-acrylic copolymers manufactured by BASF); Aron AC-10SL (polyacrylic acid manufactured by Toa Gosei Co., Ltd.); and BYKJET 9151, 9152, 9170, and 9171 (wetting dispersants manufactured by BYK).

[0033] The mass average molecular weight (MW) of the dispersant is preferably 3,000 to 50,000, and more preferably 7,000 to 25,000. The mass average molecular weight of the dispersant can be measured by gel permeation chromatography (GPC). Specifically, the measurement can be performed using an HLC-8320GPC (manufactured by Tosoh Corporation) as the GPC device, two TSK gel Super Multipore HZ-H columns (manufactured by Tosoh Corporation, inner diameter 4.6 mm × 15 cm), tetrahydrofuran as the eluent, and TSK Standard (manufactured by Tosoh Corporation) as the standard sample.

[0034] The acid value of the dispersant is preferably from 50 to 300 mgKOH / g, more preferably from 80 to 275 mgKOH / g, and even more preferably from 80 to 250 mgKOH / g.

[0035] The dispersant can be used in a state where it is mixed with the pigment, or in a state where the pigment surface is partially or entirely coated with the dispersant, or both of these states can be used in combination.

[0036] When the ink according to this embodiment contains a dispersant, the ratio of the total mass of the dispersant to the total mass of the pigment is preferably 0.01 to 1.0, more preferably 0.05 to 0.6, and even more preferably 0.1 to 0.5.

[0037] Examples of organic solvents include C1-C6 alkanols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, and tert-butanol; carboxylic acid amides such as N,N-dimethylformamide and N,N-dimethylacetamide; lactams such as 2-pyrrolidone, N-methyl-2-pyrrolidone, and N-methylpyrrolidin-2-one; cyclic ureas such as 1,3-dimethylimidazolidin-2-one and 1,3-dimethylhexahydropyrimid-2-one; ketones, ketoalcohols, or carbonates such as acetone, 2-methyl-2-hydroxypentan-4-one, and ethylene carbonate; and cyclic ethers such as tetrahydrofuran and dioxane.Ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-heptanediol, 1,2-octanediol, 1,2-nonanediol, 1,2-decanediol, 1,2-undecanediol, 1,2-dodecanediol, diethylene glycol monohexyl ether, diethylene glycol monoheptyl ether, ethylene glycol monohexyl ether, ethylene glycol monoheptyl ether, 1,7-heptanediol, 1,8-octanediol hexanediol, 2-ethyl-1,3-hexanediol, 1,9-nonanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monophenyl ether, diethylene glycol monobenzyl ether, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol mono-, oligo-, or polyalkylene glycols or thioglycols having C2-C6 alkylene units, such as ethanol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 3-methoxy-3-methyl-1-butanol, 3-methoxy-1-butanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol (preferably those having a molecular weight of 400, 800, 1540, or more), polypropylene glycol, thiodiglycol, and dithiodiglycol; C3-C9 polyols (triols), such as glycerin, diglycerin, hexane-1,2,6-triol, and trimethylolpropane;Examples of suitable alkyl ethers include glycol ethers such as ethylene glycol monoallyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol monomethyl ether (preferably C7-C10 triethylene glycol ether, or C4-C13 mono-, di-, or tripropylene glycol ether); C6-C9 alkanediols such as 1,2-hexanediol, 1,6-hexanediol, and 2-methyl-2,4-pentanediol; γ-butyrolactone; and dimethyl sulfoxide.

[0038] Examples of the surfactant include anionic, nonionic, silicone, and fluorine-based surfactants. Among these, surfactants selected from nonionic and silicone surfactants are preferred, and nonionic surfactants are more preferred from the viewpoints of storage stability of the ink and wettability to poorly absorbent media and non-absorbent media.

[0039] 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-acylmethyl taurines, 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, and dioctyl sulfosuccinates.

[0040] Examples of nonionic surfactants include ether surfactants such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene alkyl ether, and polyoxyethylene distyrenated phenyl ether (for example, Emulgen A-60, A-90, and A-500 manufactured by Kao Corporation); polyoxyethylene oleate, polyoxyethylene distearate, sorbitan laurate, and sorbitan monostearate. ester-based surfactants such as sorbitan monooleate, sorbitan sesquioleate, polyoxyethylene monooleate, and polyoxyethylene stearate; acetylene glycol (or acetylene 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 (for example, Surfynol 104, 104PG50, 82, 420, 440, 465, and 485; Olfine STG; and the like, manufactured by Evonik Japan Co., Ltd.); and polyglycol ether-based surfactants.

[0041] Examples of silicone surfactants include polyether-modified siloxanes and polyether-modified polydimethylsiloxanes. Examples of such products include Dynol 960 and 980 manufactured by Air Products; Silface SAG001, SAG002, SAG003, SAG005, SAG503A, SAG008, SAG009, and SAG010 manufactured by Nissin Chemical Industry Co., Ltd.; BYK-345, 347, 348, 349, 3450 (also known as BYKLPX 23289), 3451 (also known as BYKLPX 23347), 3455, LP-X23288, and LP G20726 manufactured by BYK; and TEGO Twin 4000, TEGOWet KL 245, 250, 260, 265, 270, and 280 manufactured by Evonic Tego Chemie.

[0042] Examples of fluorine-based surfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chains, etc. Commercially available products include Capstone FS-30 and FS-31 manufactured by Chemours.

[0043] 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.

[0044] Examples of preservatives include organic sulfur compounds, organic nitrogen sulfur compounds, organic halogen compounds, haloarylsulfone 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, inorganic salt compounds, etc. Specific examples of organic halogen compounds include pentachlorophenol, Sodium, etc. Specific examples of pyridine oxide compounds include 2-pyridinethiol-1-oxide sodium, etc. 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 antiseptic and antifungal agents include anhydrous sodium acetate, sodium sorbate, sodium benzoate, and Arch Chemical's trade names Proxel GXL(S), Proxel LV, and Proxel XL-2(S).

[0045] 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, sodium bicarbonate, and potassium carbonate; alkali metal salts of organic acids such as sodium silicate and potassium acetate; and inorganic bases such as disodium phosphate.

[0046] Examples of chelating agents include disodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, and sodium uracildiacetate.

[0047] Examples of the rust inhibitor include acid sulfite, sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

[0048] Examples of the defoaming agent include silicone-based, silica mineral oil-based, olefin-based, acetylene-based compounds, etc. Examples of commercially available defoaming agents include Surfynol DF37, DF58, DF110D, DF220, MD-20, and Olfine SK-14, all of which are manufactured by Shin-Etsu Chemical Co., Ltd.

[0049] Examples of the water-soluble ultraviolet absorber include sulfonated benzophenone compounds, benzotriazole compounds, salicylic acid compounds, cinnamic acid compounds, and triazine compounds.

[0050] 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.

[0051] The ink according to this embodiment may contain a resin emulsion for the purpose of improving the fixation of the ink to the printing medium. When the ink according to this embodiment contains a resin emulsion, the image fastness, such as water resistance, abrasion resistance, and alcohol resistance, of the image printed on the printing medium tends to be improved. The resin emulsion is preferably at least one selected from a polymer emulsion and a wax emulsion.

[0052] Examples of polymer emulsions include emulsions containing urethane-based, polyester-based, acrylic-based, vinyl acetate-based, vinyl chloride-based, styrene-acrylic-based, acrylic-silicone-based, and styrene-butadiene-based polymers. Among these, emulsions of polymers selected from urethane-based, acrylic-based, and styrene-butadiene-based are preferred.

[0053] Commercially available polymer emulsions include Superflex 420, 470, and 890 (urethane-based resin emulsions manufactured by Daiichi Kogyo Seiyaku Co., Ltd.); Hydran HW-350, HW-178, HW-163, HW-171, AP-20, AP-30, WLS-201, and WLS-210 (urethane-based resin emulsions manufactured by DIC Corporation); 0569, 0850Z, and 2108 (styrene-butadiene-based resin emulsions manufactured by JSR Corporation); AE980, AE981A, AE982, AE986B, and AE104 (acrylic resin emulsions manufactured by E-Tech Co., Ltd.); NeoCryl A-1105, A-1125, and A-1127 (acrylic resin emulsions manufactured by DSM Coating Resin); and NeoCryl A-655 (DSM Coating Resin). styrene-acrylic resin emulsion manufactured by Resin Co., Ltd.);

[0054] The wax emulsion may be an emulsion in which a natural wax or a synthetic wax is dispersed in an aqueous medium.

[0055] Examples of natural wax emulsions include emulsions of various waxes, such as 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.

[0056] Examples of synthetic wax emulsions include emulsions of polyalkylene wax (preferably poly C2-C4 alkylene wax), oxidized polyalkylene wax (preferably poly C2-C4 alkylene wax), paraffin wax, etc. Among these, emulsions of wax selected from polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and paraffin wax are preferred.

[0057] The average particle size of the wax is preferably 50 nm to 5 μm, more preferably 100 nm to 1 μm, in order to prevent clogging of the inkjet head.

[0058] Commercially available wax emulsions include, for example, CERAFLOUR 925, 929, 950, 991, AQUACER 498, 515, 526, 531, 537, 539, 552, 1547, AQUAMAT 208, 263, 272; MINERPOL 221 (all manufactured by BYK); Mitsui Hiwax NL100, NL200, NL500, 4202E, 1105A, 2203A, NP550, NP055, NP505 (all manufactured by Mitsui Chemicals, Inc.); KUE-100, 11 (all manufactured by Sanyo Chemical Industry Co., Ltd.); and HYTEC P-5300, E-6500, 9015, 6400 (all manufactured by Toho Chemical Industry Co., Ltd.).

[0059] When the ink according to this embodiment contains a resin emulsion, the solid content is preferably 1 to 20% by mass, and more preferably 3 to 15% by mass. By setting the solid content of the resin emulsion to 1% by mass or more, the ink tends to exhibit good fixability to the printing medium. Furthermore, by setting the solid content of the resin emulsion to 20% by mass or less, the ink tends to have good jetting properties and storage stability.

[0060] The method for preparing the ink 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 a dispersion containing a pigment and a dispersant, and then add water and, if necessary, an ink preparation agent to this dispersion and mix them.

[0061] Examples of methods for preparing the dispersion include phase inversion emulsification, acid precipitation, interfacial polymerization, in-situ polymerization, submerged hardening coating, coacervation (phase separation), submerged drying, melt-dispersion cooling, air suspension coating, spray drying, etc. Among these, phase inversion emulsification, acid precipitation, and interfacial polymerization are preferred, and phase inversion emulsification is more preferred.

[0062] When preparing a dispersion by phase inversion emulsification, for example, a dispersant is dissolved in an organic solvent such as 2-butanone, and an aqueous solution of a neutralizer is added to prepare an emulsion. A pigment is added to the obtained emulsion, and a dispersion treatment is performed. The organic solvent and a portion of the water are distilled off under reduced pressure from the obtained liquid to obtain the desired dispersion.

[0063] Dispersion treatment can be carried out using a sand mill (bead mill), roll mill, ball mill, paint shaker, ultrasonic disperser, microfluidizer, etc. For example, when using a sand mill, beads with a particle diameter of about 0.01 to 1 mm can be used, and the bead packing rate can be appropriately set to carry out dispersion treatment. The particle diameter of the particles contained in the dispersion can be made uniform by subjecting the dispersion obtained as described above to operations such as filtration and centrifugation. If foaming occurs during preparation of the dispersion, a trace amount of a known silicone-based, acetylene glycol-based, or other antifoaming agent can be added.

[0064] The ink according to this embodiment preferably contains a low content of inorganic impurities such as chlorides of metal cations (e.g., sodium chloride) and metal sulfates (e.g., sodium sulfate). Such inorganic impurities are often contained in commercially available pigments. The inorganic impurity content should be approximately 1% by mass or less relative to the total mass of the pigment, with the lower limit being below the detection limit of analytical instruments, i.e., 0% by mass, being ideal. Methods for obtaining pigments with low inorganic impurities include, for example, a method using a reverse osmosis membrane; a method in which a solid pigment is suspended and stirred in a mixed solvent of C1-C4 alcohol, such as methanol, and water, followed by filtering and separating the colored body and drying; and a method in which inorganic impurities are exchanged and adsorbed using an ion exchange resin.

[0065] The ink according to this embodiment is preferably microfiltered in advance. For microfiltration, a membrane filter, glass filter paper, or the like can be used. The pore size of the filter used for microfiltration is usually 0.5 to 20 μm, and preferably 0.5 to 10 μm.

[0066] The ink according to this embodiment is also excellent in storage stability, redispersibility, color development, and color neutrality. Furthermore, printed images recorded using the ink according to this embodiment are also excellent in various fastness properties, such as light resistance, heat resistance, and oxidizing gas resistance (e.g., ozone gas resistance). Furthermore, the ink according to this embodiment has little coating unevenness during image formation, and is also excellent in image forming properties.

[0067] Examples of ink sets according to this embodiment include a set of the inks according to this embodiment described above, or a set including the ink according to this embodiment described above and another ink different from the ink. The other ink is not particularly limited as long as it has a different structure from the ink according to this embodiment, but it is preferable that the other ink has a different hue from the ink according to this embodiment.

[0068] Furthermore, the print medium according to this embodiment has at least one selected from the group consisting of the inks or inkjet inks included in the ink set according to this embodiment adhered thereto.

[0069] The ink media set according to this embodiment includes the ink or ink set according to this embodiment described above and a print medium.

[0070] The printing medium is not particularly limited, but is preferably a printing medium that is poorly ink-absorbent or non-ink-absorbent, and more preferably a non-ink-absorbent printing medium. Examples of poorly ink-absorbent printing media include plain paper without an ink-receiving layer, media used in gravure printing or offset printing, art paper, coated paper, matte paper, and cast paper. Examples of non-ink-absorbent printing media include PET (polyethylene terephthalate) film, PP (polypropylene) film, vinyl chloride sheet, glass, and rubber.

[0071] The inkjet recording method according to this embodiment involves ejecting droplets of the ink according to this embodiment from an inkjet head to record on a print medium. There are no particular restrictions on the ink nozzles of the inkjet printer that eject the ink, and they can be selected appropriately depending on the purpose.

[0072] The inkjet recording method according to this embodiment also includes a method of improving image quality by ejecting a large number of inks in a small volume, each ink having a low pigment content; a method of improving image quality by using a plurality of inks having substantially the same hue but different pigment contents; and a method of improving the fixation of pigment to printing media by using a colorless, transparent ink in combination with an ink containing a pigment.

[0073] Known inkjet recording methods can be used. Examples include charge control, drop-on-demand (also known as pressure pulse), acoustic inkjet, and thermal inkjet. The inkjet recording method may be either a multi-pass or single-pass (one-pass printing) method. For industrial inkjet printers, single-pass printing using a linehead inkjet printer is also preferred for the purpose of increasing printing speed. Recently, circulation heads have been actively developed, each equipped with a mechanism (i.e., a circulation mechanism) that prevents ink from drying near the nozzles by circulating the ink to the vicinity of the nozzles. The ink according to this embodiment can also be suitably used in such circulation heads.

[0074] When recording on a print medium, for example, a container containing ink (ink tank) is loaded into a predetermined position of an inkjet printer, and recording is performed on the print medium using the above-mentioned printing method. Note that full-color printing can also be achieved by loading containers containing ink of each color into a predetermined position of the inkjet printer and recording on the print medium using the above-mentioned printing method.

[0075] When using a printing medium without an ink-receiving layer, it is also preferable to perform a surface modification treatment. Examples of surface modification treatments include corona discharge treatment, plasma treatment, and flame treatment. It is generally known that the effect of surface modification treatment decreases over time. For this reason, it is preferable to perform the surface modification treatment step and the inkjet recording step consecutively, and it is more preferable to perform the surface modification treatment step immediately before the inkjet recording step.

[0076] 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.

[0077] The ink of the present invention is excellent in color neutrality, brightness, and redispersibility, and also in storage stability, ejection stability, adhesion, abrasion resistance, weather resistance, ozone resistance, humidity resistance, and water resistance. [Example]

[0078] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the text, "parts" and "%" are by mass unless otherwise specified. In the examples, 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, i.e., the pigment solid content alone. The inks described in the examples are included in the above-mentioned inkjet inks.

[0079] [Preparation Example 1] Preparation of Carbon Black Dispersion 1 4.5 parts of BYKJET9151 (BYK Japan Co., Ltd.) were dissolved in 80.5 parts of ion-exchanged water and stirred for 1 hour. 15 parts of carbon black (Orion Engineered Carbons, NEROX600) were added to the resulting solution, and the mixture was dispersed in a sand grinder at 1500 rpm for 10 hours. 30 parts of ion-exchanged water were added dropwise to the resulting solution, and the dispersion beads were removed by filtration to obtain Carbon Black Dispersion 1 with a pigment solids content of 11.5%. [Preparation Example 2] Preparation of Carbon Black Dispersion 2 4.5 parts of Joncyrl 68 (BASF Japan Ltd., mass average molecular weight: 13,000) and 3 parts of triethanolamine were dissolved in 77.5 parts of ion-exchanged water and stirred for 1 hour. 15 parts of carbon black (Orion Engineered Carbons, Inc., NEROX 600) were added to the resulting solution, and the mixture was dispersed in a sand grinder at 1,500 rpm for 15 hours. 30 parts of ion-exchanged water was added dropwise to the resulting solution, and the dispersion beads were removed by filtration, yielding Carbon Black Dispersion 2 with a pigment solids content of 11.5%. [Preparation Example 3] Preparation of Carbon Black Dispersion 3 A block copolymer was prepared as described in Synthesis Example 3 of WO 2013 / 115071. 4.5 parts of the resulting polymeric dispersant was dissolved in 30 parts of 2-butanone to form a homogeneous solution. To this solution, a solution prepared by dissolving 0.68 parts of 28% aqueous ammonia in 53 parts of ion-exchanged water was added and stirred for 1 hour to prepare an emulsified solution containing the polymeric dispersant. 15 parts of carbon black (NEROX600, Orion Engineered Carbons Co., Ltd.) was added and dispersed in a sand grinder at 1500 rpm for 10 hours. 100 parts of ion-exchanged water was added dropwise to the resulting solution, which was then filtered to remove the dispersing beads. The 2-butanone and a portion of the water were then distilled off under reduced pressure using an evaporator to obtain Carbon Black Dispersion 3, with a pigment solids content of 12%. [Adjustment Examples 4-12] Pigment dispersions of Preparation Examples 4 to 12 were obtained in the same manner as Preparation Example 1, except that the types of pigments added were in the compositions shown in Table 1 below.

[0080] [Table 1]

[0081] [Example 1] The carbon black dispersion 1, pigment dispersion A-1, and pigment dispersion B-1 obtained above were mixed with the components shown in Table 2 below, and then filtered through a 3 μm membrane filter to obtain an ink for evaluation test of Example 1. The content of carbon black in the total mass of the ink was adjusted to 0.60%, and the total amount of carbon black, pigment A, and pigment B was adjusted to 1.00%. [Examples 2 to 14, Comparative Examples 1 to 4] The inks of Examples 2 to 14 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1, except that the types of carbon black dispersion liquid and pigment dispersion liquids A and B to be added were formulated as shown in Tables 2 and 3 below. The abbreviations in Tables 1 and 2 represent the following: SF440: Surfynol (registered trademark) 440 (acetylene glycol surfactant, manufactured by Air Products Co., Ltd.) A-1127: NeoCryl A-1127 (acrylic resin emulsion, manufactured by DSM Coating Resin Ltd., solid content 44.0%)

[0082] [Table 2]

[0083] [Table 3]

[0084] [Print evaluation method] 20 μL of each of the inks from Examples 1 to 14 and Comparative Examples 1 to 4 was dropped onto a PET film (E5102, manufactured by Toyobo Co., Ltd.) and coated using a bar coater No. 6 (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) with an automatic coater (PI-1210, manufactured by Tester Sangyo Co., Ltd.). The coated PET film was then dried for 2 minutes in a thermo-hygrostat at 70°C. Five sheets of Seiko Epson glossy photographic paper were placed under the film, and the L* and C* values of the ink coating were measured using an X-Rite eXact portable spectral densitometer (measurement conditions: filterless M0, light source and viewing angle D50 / 2°, IsoStatus E). The obtained L* and C* values were evaluated for lightness and color neutrality according to the following criteria. A rating of B or higher is desirable for both lightness and color neutrality in practical use. (Brightness evaluation standard) A: L* value is 35 or more and 65 or less B:L* value is 25 or more but less than 35, or 65 or more but less than 80 C:L* value is 20 or more but less than 25, or 80 or more but less than 85 D:L* value less than 20 or greater than 85 (Color neutrality evaluation standard) A: C* value is less than 1.0 B: C* value is 1.0 or more and less than 3.0 C: C* value is 3.0 or more and less than 5.0 D: C* value is 5.0 or higher [Redispersibility evaluation method] Using a glass capillary with an inner diameter of 0.29 mm (manufactured by AS ONE, EM Meister Ring Caps, 5 μL, 1 / 5 scale), the inks of Examples 1 to 14 and Comparative Examples 1 to 4 were drawn up to 30 mm (two scale marks) from the bottom of the capillary by capillary action. The ink-filled capillary was then placed vertically in a thermo-hygrostat at 40°C for 10 minutes. The bottom of the capillary was then immersed in a screw capillary containing 10 g of the same ink as the ink drawn into the capillary. The time required for the ink to be drawn up to 75 mm (five scale marks) from the bottom was measured and evaluated according to the following criteria. In actual inkjet heads, nozzles with a diameter of approximately 20 μm tend to become clogged with dried ink, resulting in unstable ejection. Therefore, this evaluation is believed to simulate the phenomenon of ink drying and clogging in nozzles with a fairly small diameter. When new ink is supplied to this dried ink, the dried material immediately loosens and the clogging is eliminated, i.e., the shorter the time it takes for the ink to be sucked into the capillary, the better the redispersibility. A rating of B or higher is preferable for practical use. (Redispersibility evaluation criteria) A: Less than 2 minutes B: 2 minutes or more but less than 3 minutes C: 3 minutes or more but less than 5 minutes D: More than 5 minutes

[0085] [Table 3]

[0086] [Table 4]

[0087] The results in Tables 3 and 4 above show that the inks of the examples are superior to the inks of the comparative examples in color neutrality, brightness, and redispersibility. [Industrial Applicability]

[0088] The ink of the present invention is excellent in color neutrality, brightness, and redispersibility, and is therefore extremely useful as an ink for various recording applications, particularly as an ink for ink-jet recording.

Claims

1. an inkjet ink comprising carbon black as a water-insoluble pigment, Pigment A, and Pigment B, and water, wherein the Pigment A has one or more absorption maximum wavelengths in the range of 450 nm or more to less than 600 nm within its absorption wavelengths in ultraviolet-visible spectroscopy, and the Pigment B has one or more absorption maximum wavelengths in the range of 600 nm or more to less than 800 nm within its absorption wavelengths in ultraviolet-visible spectroscopy; the content of the carbon black is from 0.10% by mass to 1.00% by mass, both inclusive, with respect to the total mass of the ink; and the total amount of the carbon black, Pigment A, and Pigment B is from 0.12% by mass to less than 1.80% by mass, both inclusive, with respect to the total mass of the ink.

2. 2. The ink-jet ink according to claim 1, wherein the pigment A comprises at least one pigment selected from the group consisting of Pigment Red 48:3, Pigment Red 57:1, Pigment Red 150, Pigment Red 122, Pigment Red 146, Pigment Red 150, Pigment Red 184, Pigment Red 185, Pigment Red 269, Pigment Orange 34, Pigment Orange 43, Pigment Orange 64, Pigment Violet 23, and Pigment Violet 19.

3. 3. The ink-jet ink according to claim 1, wherein the pigment B comprises at least one pigment selected from the group consisting of Pigment Blue 15:3, Pigment Blue 15:4, Pigment Blue 60, Pigment Green 7, and Pigment Green 36.

4. 3. The ink-jet ink according to claim 1, wherein the carbon black content is 0.40% by mass or more and 0.80% by mass or less relative to the total mass of the ink.

5. 3. The ink-jet ink according to claim 1, wherein the total amount of carbon black, pigment A, and pigment B is 0.60% by mass or more and 1.40% by mass or less, based on the total mass of the ink.

6. An ink set comprising the water-based ink composition according to claim 1.

7. An inkjet recording method comprising ejecting droplets of the inkjet ink according to claim 1 or 2 from an inkjet head to record on a printing medium.

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

9. 8. The inkjet recording method according to claim 7, wherein the inkjet head includes a circulation mechanism.

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