Ink set and inkjet recording method

Abstract

To provide: an ink set which enables offering of printed images having exceedingly good blurring characteristics; an inkjet recording method using the ink set; a printing medium; and a printing medium set.SOLUTION: Provided is an ink set for single pass inkjet printing, comprising a black ink and at least one color ink, where the color ink contains at least a pigment and a silicone-based surfactant, and the black ink contains at least a pigment and may contain a silicone-based surfactant. When the black ink contains a silicone-based surfactant, a content of the silicone-based surfactant in the black ink is 0.24 mass% or less, a difference in contents of the silicone-based surfactant in the black ink and the color ink is 0.2 mass% or more, and a content of the silicone-based surfactant in the black ink is less than a content of the silicone-based surfactant in the color ink.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an ink set and an inkjet recording method using the ink set.

Background Art

[0002] Among various color printing methods, the printing method using an inkjet printer, which is one of the representative methods, generates small droplets of ink and adheres them to a printing medium such as paper to perform printing. In recent years, the demand for industrial use has increased, and inks that can print on various printing media have been demanded.

[0003] Among printing media, for ink non-absorbent media and ink poorly absorbent media (hereinafter sometimes referred to as "ink non- / poorly absorbent media"), inks with good wet spreading on the media are desired. When the wet spreading on the media is good, the area that can be colored increases (in other words, the dot diameter of the ink becomes larger) when the same amount of ink droplets are used, so the consumption of ink can be suppressed. However, ink non- / poorly absorbent media are media with poor ink absorbency. Therefore, it is difficult for the ink to penetrate into the media, and compared with ink absorbent media, the wet spreading of the ink is poor, so generally the dot diameter of the ink becomes smaller. For this reason, its improvement has been desired.

[0004] Furthermore, in terms of print quality, it is required that the granularity be kept to a minimum. Inks containing water-insoluble colorants are in a non-uniform state (not a solution, but a dispersion). When solid printing is performed on a printing medium with such a non-uniform ink, the printed image may appear to have scattered "granules" of varying shades, and may not appear to be a uniform image. Such printed images are evaluated as having "granularity" and are one of the factors that significantly deteriorate print quality. For this reason, there is a strong demand for inks that can produce printed images with as little granularity as possible. For example, as disclosed in Patent Documents 1, 2, and 3, ink compositions combining specific organic solvents and surfactants have been disclosed, and inks with good wetting spread for non-ink-absorbing and poorly absorbing media have been disclosed.

[0005] Furthermore, when performing color printing, an ink set consisting of multiple colors is used. When performing color printing using such an ink set, it is known that bleeding can occur between the first and second colors when the landing positions of the first and second color inks are adjacent on the printing medium. This "bleeding between colors" is one of the factors that significantly degrades print quality. For this reason, there is a need to eliminate this bleeding between colors, and ink sets that solve this problem have been proposed.

[0006] According to Patent Document 4, an ink containing a polyalkoxylate of an acetylene glycol-based surfactant is disclosed to eliminate these color bleeding issues, and an ink is proposed that can produce high-quality images with less color unevenness and color bleeding for non-ink-absorbing and poor-absorbing media. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2016-044188 [Patent Document 2] Japanese Patent Publication No. 2014-139004 [Patent Document 3] International Publication No. 2011 / 136000 [Patent Document 4] Japanese Patent Publication No. 2012-136573 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] While the above method has led to the development of an ink that produces high-quality images with minimal bleeding, there is a need for an ink that produces even higher-quality images with even less bleeding.

[0009] This invention has been made in view of the above circumstances, and aims to provide an ink set that enables the provision of printed images with extremely good color bleeding, an inkjet recording method using the ink set, a printing medium, and a printing medium set. [Means for solving the problem]

[0010] The inventors of this invention conducted extensive research to solve the above-mentioned problems and, as a result, discovered that a specific ink set can solve the above-mentioned problems, thus completing the present invention.

[0011] In other words, the present invention relates to the following [1] to [5]. [1] An ink set consisting of black ink and at least one color ink, Each of the aforementioned color inks contains at least a pigment and a silicone-based surfactant. The black ink contains at least a pigment and may also contain a silicone-based surfactant. If the black ink contains a silicone-based surfactant, the content of the silicone-based surfactant in the black ink is 0.24% by mass or less. The difference in the content of silicone-based surfactants between the black ink and the colored ink is 0.2% by mass or more. A single-pass inkjet printer ink set in which the amount of silicone-based surfactant in the black ink is lower than the amount of silicone-based surfactant in the color inks. [2] The ink set described in [1], consisting of black, cyan, magenta, and yellow. [3] An ink media set including the ink set described in either [1] or [2] and printing media. [4] The ink media set described in [3], wherein the printing media is an ink-poorly absorbent or ink-non-absorbent printing media. [5] An inkjet recording method, Recording is done using an ink set consisting of black ink and at least one color ink. Each of the aforementioned color inks contains at least a pigment and a silicone-based surfactant. The black ink contains at least a pigment and may also contain a silicone-based surfactant. If the black ink contains a silicone-based surfactant, the content of the silicone-based surfactant in the black ink is 0.24% by mass or less. The difference in the content of silicone-based surfactants between the black ink and the colored ink is 0.2% by mass or more. An inkjet recording method that uses a single-pass inkjet printing ink set in which the amount of silicone-based surfactant in the black ink is less than the amount of silicone-based surfactant in the color ink. [Effects of the Invention]

[0012] The present invention provides an ink set, an inkjet printing method, a printing medium, and a printing medium set that enable the provision of printed images with extremely good color bleeding. [Modes for carrying out the invention]

[0013] The present invention will be described in detail below.

[0014] [Black Ink] The black ink contains water, a colorant (1), and optionally a silicone surfactant, and may further contain other components as required. Examples of other components include a dispersant, a penetrant, a viscosity modifier, and an ink preparation agent.

[0015] (colorant (1)) The colorant is not particularly limited as long as it is a water-insoluble colorant. In the specification and claims of the present application, a water-insoluble colorant means a colorant having a solubility of 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 in 1 liter of water at 25°C. The lower limit of the solubility includes 0 g. Hereinafter, unless otherwise specified, the "water-insoluble colorant" is also simply referred to as "colorant". As the colorant, for example, known pigments, disperse dyes, solvent dyes, and water-insoluble resins colored with colorants such as dyes and pigments can be used. The colorant is preferably a pigment.

[0016] Examples of the colorant contained in the black ink include carbon black. As the carbon black to be contained in the black ink, thermal black, acetylene black, oil furnace black, gas furnace black, lamp black, gas black, and channel black are preferable. Specific examples of carbon black include, for example, the Raven series manufactured by Columbian Carbon; the Monarch series, Regal series, and Mogul series manufactured by Cabot; the ColorBlack series, Printex series, SPECIALBLACK series, and Nerox series manufactured by Orion Engineered Carbons; 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, etc.

[0017] The above black ink may contain a colorant other than carbon black. Examples of the colorant other than carbon black include organic pigments, extender pigments, and disperse dyes.

[0018] Examples of organic pigments include various pigments such as azo, diazo, phthalocyanine, quinacridone, isoindolinone, dioxazine, perylene, perinone, thioindigo, anthraquinone, and quinophthalone. Specific examples of organic pigments include, for example, yellows such as C.I.Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 24, 55, 73, 74, 75, 83, 93, 94, 95, 97, 98, 108, 114, 128, 129, 138, 139, 150, 151, 154, 180, 185, 193, 199, 202, 213; reds such as C.I.Pigment Red 5, 7, 12, 48, 48:1, 57, 88, 112, 122, 123, 146, 149, 150, 166, 168, 177, 178, 179, 184, 185, 202, 206, 207, 254, 255, 257, 260, 264, 272; blues such as C.I.Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 25, 60, 66, 80; violets such as C.I.Pigment Violet 19, 23, 29, 37, 38, 50; oranges such as C.I.Pigment Orange 13, 16, 68, 69, 71, 73; greens such as C.I.Pigment Green7, 36, 54; blacks such as C.I.Pigment Black 1.

[0019] Examples of extender pigments include, for example, silica, calcium carbonate, talc, clay, barium sulfate, and white carbon. Extender pigments are often used in combination with other colorants.

[0020] Examples of disperse dyes include well-known disperse dyes. Among these, dyes selected from CIDispers are preferred. Specific examples include, for instance, CIDispers Yellow 9, 23, 33, 42, 49, 54, 58, 60, 64, 66, 71, 76, 79, 83, 86, 90, 93, 99, 114, 116, 119, 122, 126, 149, 160, 163, 165, 180, 183, 186, 198, 200, 211, 224, 226, 227, 231, 237, etc.; CIDispers Red 60, 73, 88, 91, 92, 111, 127, 131, 143, 145, 146, 152, 153, 154, 167, 179, 191, 192, 206, 221, 258, 283, etc.; CIDispers Orange Disperse dyes in various colors include orange (9, 25, 29, 30, 31, 32, 37, 38, 42, 44, 45, 53, 54, 55, 56, 61, 71, 73, 76, 80, 96, 97, etc.), violet (CIDisperse Violet 25, 27, 28, 54, 57, 60, 73, 77, 79, 79:1, etc.), and blue (CIDisperse Blue 27, 56, 60, 79:1, 87, 143, 165, 165:1, 165:2, 181, 185, 197, 202, 225, 257, 266, 267, 281, 341, 353, 354, 358, 364, 365, 368, etc.).

[0021] The content of the colorant relative to the total mass of the black ink is typically 1 to 30%, preferably 1 to 10%, and more preferably 2 to 7%. Herein, in the specification and claims of this application, unless otherwise specified, "%" and "parts" are expressed on a mass basis. Furthermore, the average particle size of the colorant is typically 50 nm to 250 nm, preferably 60 nm to 200 nm. In the specification and claims of this application, the average particle size refers to the particle size at 50% of the integrated value in the particle size distribution determined by laser diffraction and scattering.

[0022] To disperse water-insoluble colorants in the ink, it is preferable to use a dispersant. The dispersant is not particularly limited, and known dispersants can be used. Generally, polymeric dispersants such as resins are used as dispersants. Examples of such resins include polymers derived from polyvinyl alcohol, cellulose derivatives, polyethylene oxide, polypropylene oxide, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester, fumaric acid, fumaric acid monoester, vinylsulfonic acid, sulfoethyl methacrylate, sulfopropyl methacrylate, ionic monomers such as α,β-unsaturated monomers of sulfonated vinylnaphthalene, styrene, styrene derivatives, vinylnaphthalene, vinylnaphthalene derivatives, aliphatic alcohol esters of α,β-ethylenically unsaturated carboxylic acids, acrylonitrile, vinylidene chloride, vinyl acetate, vinyl chloride, acrylamide, methacrylamide, hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycidyl methacrylate, N-butoxymethylacrylamide, etc.

[0023] Examples of resins used as dispersants include copolymers composed of at least two monomers (preferably at least one of which is hydrophilic) selected from monomers in the group consisting of styrene and its derivatives; vinylnaphthalene and its derivatives; aliphatic alcohol esters of α,β-ethylenically unsaturated carboxylic acids; acrylic acid and its derivatives; maleic acid and its derivatives; itaconic acid and its derivatives; fahric acid and its derivatives; vinyl acetate, vinyl alcohol, vinylpyrrolidone, acrylamide, and their derivatives. Examples of such copolymers include styrene-(meth)acrylic acid copolymer, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer, (meth)acrylic acid ester-(meth)acrylic acid copolymer, polyethylene glycol (meth)acrylate-(meth)acrylic acid copolymer, and styrene-maleic acid copolymer. Among these, styrene-(meth)acrylic acid copolymer, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer, (meth)acrylic acid ester-(meth)acrylic acid copolymer, and polyethylene glycol (meth)acrylate-(meth)acrylic acid copolymer are preferred; styrene-(meth)acrylic acid copolymer, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer, and (meth)acrylic acid ester-(meth)acrylic acid copolymer are more preferred; (meth)acrylic acid ester-(meth)acrylic acid copolymer is even more preferred; and methacrylic acid ester-methacrylic acid copolymer is particularly preferred. In the specification and claims of this application, the term "(meth)acrylic acid" is used to mean both "acrylic acid" and "methacrylic acid." Similarly, "(meth)acrylate" means both methacrylate and acrylate. Examples of copolymer types include block copolymers, random copolymers, graft copolymers, and / or salts thereof.

[0024] The resins used as dispersants can be synthesized or obtained commercially. Specific examples of commercially available products include styrene-acrylic copolymers such as Joncryl 62, 67, 68, 678, and 687 (manufactured by BASF); Movinyl S-100A (modified vinyl acetate copolymer manufactured by Japan Coating Resin Co., Ltd.); and Julimar AT-210 (polyacrylic acid ester copolymer manufactured by Toagosei Co., Ltd.). As copolymers obtained by synthesis, the AB block polymer disclosed in International Publication No. 2013 / 115071 is a preferred example.

[0025] The acid value of the above dispersant is typically 90-200 mgKOH / g, preferably 100-150 mgKOH / g, and more preferably 100-120 mgKOH / g. The mass-average molecular weight of the dispersant is typically 10,000 to 60,000, preferably 10,000 to 40,000, more preferably 15,000 to 30,000, and even more preferably 20,000 to 25,000. The PDI (mass-average molecular weight / number-average molecular weight) of the dispersant is approximately 1.29 to 1.49. By keeping it within this range, the dispersibility and storage stability of the ink can be improved.

[0026] Examples of neutralizing agents used to dissolve the dispersion of the colorant prepared using the block copolymer in water include ammonia, alkali metal hydroxides, alkaline earth metal hydroxides, aliphatic amine compounds, and alkanolamine compounds. Ammonia and alkali metal hydroxides are preferred, and ammonia is particularly preferred. The amount of neutralizing agent used is not particularly limited. As a guideline, the degree of neutralization is usually 30-300%, more preferably 50-200%, with 100% neutralization being defined as neutralization with a theoretical equivalent amount of the acid value of the dispersant.

[0027] The resin used as a dispersant can be used either mixed with the colorant, or with part or all of the surface of the colorant coated with the resin as a dispersant. Both of these conditions can also be used in combination. The aforementioned black ink is preferably prepared by first preparing a dispersion containing a water-insoluble colorant and a resin as a dispersant, and then mixing it with other components. Known methods can be used to prepare the dispersion. One example is the phase inversion emulsification method. That is, the resin as a dispersant is dissolved in an organic solvent such as 2-butanone, and an aqueous solution of a neutralizing agent is added to prepare an emulsion. The colorant is added to the obtained emulsion and dispersed. The desired dispersion can be obtained by removing the organic solvent and some of the water from the liquid obtained in this way under reduced pressure. Dispersion processing can be carried out using, for example, 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 size of about 0.01 mm to 1 mm can be used, and the dispersion processing can be carried out by appropriately setting the bead packing ratio. The dispersion obtained as described above can be subjected to operations such as filtration and / or centrifugation. This operation can standardize the particle size of the particles contained in the dispersion. If foaming occurs during the preparation of the dispersion, a very small amount of a known defoaming agent, such as a silicone-based or acetylene glycol-based agent, can be added. Other methods for preparing dispersions include acid precipitation, interfacial polymerization, in-situ polymerization, liquid curing coating, coacervation (phase separation), liquid drying, melt-dispersion-cooling, air suspension coating, and spray drying. Among these, acid precipitation and interfacial polymerization are preferred.

[0028] The average particle size (D50) of the colorant dispersion in the dispersion is usually 300 nm or less, preferably 30 to 280 nm, more preferably 40 to 270 nm, and even more preferably 50 to 250 nm. D90 is usually 400 nm or less, preferably 350 nm or less, and more preferably 300 nm or less. The lower limit is preferably 100 nm. D10 is usually 10 nm or more, preferably 20 nm or more, more preferably 30 nm or more, and the upper limit is 100 nm. By having the particle size of the colorant in the dispersion within the above range, it is possible to ensure ink storage stability while stably ejecting ink without clogging the inkjet head nozzles. Here, the average particle size (D50) is the particle size at which the cumulative particle size distribution from the small particle size side accounts for 50% of the particle size distribution determined by the laser diffraction-scattering method, D10 is the particle size at which the cumulative particle size distribution from the small particle size side accounts for 10%, and D90 is the particle size at which the cumulative particle size distribution from the small particle size side accounts for 90%.

[0029] (Silicone-based surfactants) It is important that the aforementioned black ink has sufficient wettability on non-ink-absorbing or poorly absorbing media, and surfactants are commonly used to impart wettability. Various surfactants are widely known for imparting wettability, including silicone-based, fluorine-based, and acetylene-based surfactants, depending on the application. Among these, silicone-based surfactants are particularly excellent in their ability to impart wettability.

[0030] Examples of the above-mentioned silicone-based surfactants include polyether-modified polysiloxane and polyether-modified polydimethylsiloxane. Specific examples of polyether-modified siloxanes include BYK-345, BYK-346, BYK-347, BYK-348, and BYK-349 (manufactured by Bic Chemie). Specific examples of polyether-modified polydimethylsiloxanes include BYK-306, BYK-307, BYK-333, BYK-342, BYK-3420, BYK-3455 (manufactured by Bic Chemie), KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, and KF-6017 (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0031] When the above black ink contains a silicone-based surfactant, the total surfactant content is usually 0.24% by mass or less, preferably 0.1% to 0.24% by mass, and more preferably 0.1% to 0.2% by mass, relative to the total mass of the black ink.

[0032] The black ink described above may also contain an ink preparation agent. (Ink preparation agent) Examples of ink preparation agents include binders, penetrants, viscosity modifiers, surfactants other than silicone-based surfactants, preservatives, fungicides, pH adjusters, chelating agents, rust inhibitors, water-soluble UV absorbers, and antioxidants. The total content of ink preparations, excluding binders, penetrants, and viscosity modifiers, is typically 0-30%, preferably 0.1-20%, and more preferably 0.5-10%, relative to the total mass of black ink.

[0033] (a) Binder The binder is preferably at least one selected from wax and (meth)acrylic acid polymers. Incorporating the binder into the ink can improve the scratch resistance of the printed image. The binder is preferably included in emulsion form, with aqueous emulsions being more preferred. The average particle size of the binder is preferably 50 nm to 5 μm, and more preferably 100 nm to 1 μm, in order to prevent clogging of the inkjet head. When black ink contains a binder, the binder content relative to the total mass of the ink is typically 0.1 to 14%, preferably 0.5 to 12%, more preferably 2 to 10%, and even more preferably 3 to 8%, in terms of solid content. Such a content can improve the scratch resistance of the printed image.

[0034] Natural waxes and synthetic waxes can be used as the wax. Examples of natural waxes include petroleum-based waxes such as paraffin wax and microcrystalline wax; lignite-based waxes such as montane wax; plant-based waxes such as carnauba wax and candelilla wax; and emulsions in which waxes such as beeswax and lanolin are dispersed in an aqueous medium. Examples of synthetic waxes include polyalkylene wax (preferably poly C2-C4 alkylene wax), oxidized polyalkylene wax (preferably oxidized poly C2-C4 alkylene wax), and paraffin wax. Of these, one or more waxes selected from polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and paraffin wax are preferred, with oxidized polyethylene wax being more preferred. Examples of commercially available wax emulsions include CERAFLOUR 925, 929, 950, 991; AQUACER 498, 515, 526, 531, 537, 539, 552, 1547; AQUAMAT 208, 263, 272; MINERPOL 221, etc. from BIC Chemie; Mitsui High Wax NL100, NL200, NL500, 4202E, 1105A, 2203A, NP550, NP055, NP505, etc. from Mitsui Chemicals, Inc.; and KUE-100, 11, etc. from Sanyo Chemical Co., Ltd. Among these, AQUACER 515, 531, 537, 539, and 1547 are preferred, and AQUACER 515, 531, 537, and 1547 are more preferred.

[0035] The (meth)acrylic acid polymer used as a binder is a different polymer from the dispersant described above. Preferably, the (meth)acrylic acid polymer is a polymer composed of four types of monomers: C1-C4 alkyl methacrylate, C6-C10 alkyl acrylate, methacrylic acid, and allyl methacrylate. For C1-C4 alkyl methacrylate, the alkyl portion is preferably linear or branched, with linear being more preferred. The C1-C4 alkyl methacrylate is preferably a C1-C3 alkyl methacrylate, more preferably a C1-C2 alkyl methacrylate, and even more preferably a methyl methacrylate. The C6-C10 alkyl acrylate is preferably a linear or branched alkyl group, with a branched group being more preferred. The C6-C10 alkyl acrylate is preferably a C7-C9 alkyl acrylate, more preferably a C8 alkyl acrylate, and even more preferably a 2-ethylhexyl acrylate. The content of the four monomers in (meth)acrylic acid polymers—C1-C4 alkyl methacrylate, C6-C10 alkyl acrylate, methacrylic acid, and allyl methacrylate—is typically 40-60%, 38-58%, 1-10%, and 1-5% by mass, respectively, and preferably 45-55%, 52-42%, 2-4%, and 1-3%. It is preferable that the total content of these monomers be within this range and reach 100%. The acid value (in mgKOH / g) of (meth)acrylic acid polymers is typically -10 to 35, preferably -5 to 30, and more preferably 0 to 25. The glass transition temperature (Tg) of (meth)acrylic acid polymers is typically -20 to 30°C, preferably -15 to 25°C, and more preferably -10 to 20°C.

[0036] (b) Penetrating agent The black ink may further contain, as a penetrating agent, at least one organic solvent selected from glycol ethers and C4-C9 alkanediols, having a water-octanol partition coefficient of 0.00 or more and less than 2.00. This tends to improve the wetting and drying of the ink on non- or poorly absorbing media. Penetrating agents having a Clog P within the above numerical range include, for example, 1,2-pentanediol (-0.00), ethylene glycol monoallyl ether (0.03), isopropyl alcohol (0.07), isopropyl glycol (0.09), diethylene glycol ethyl methyl ether (0.13), dipropylene glycol dimethyl ether (0.36), 3-methoxy-3-methyl-1-butanol (0.42), butyl triglycol (0.49), diethylene glycol diethyl ether (0.52), 1,2-hexanediol (0.53), diethylene glycol monoisobutyl ether (0.54), propylpropylene glycol (0.62), butyl diglycol (0.67), and dipropylene glycol. Examples include n-propyl ether (0.75), 2,2-diethyl-1,3-propanediol (0.82), 2,2,4-trimethyl-1,3-pentanediol (1.00), 2-ethyl-1,3-hexanediol (1.26), 1,2-octanediol (1.58), and hexyl diclycol (1.72). If the above ink contains a penetrating agent, the total content of these in the total mass of the ink is usually 0.1 to 30%, preferably 0.2 to 20%, more preferably 0.5 to 10%, even more preferably 2 to 8%, and particularly preferably 4 to 6%.

[0037] (c) Viscosity modifier The aforementioned black ink may further contain a viscosity modifier. Industrial inkjet printers typically have a defined viscosity range for the ink they can eject, based on the specifications of the printer head (the head that ejects the ink). Therefore, a viscosity modifier can be added to the ink to adjust its viscosity to an appropriate range. The viscosity modifier is not particularly limited as long as it is a substance that can adjust the viscosity of the ink, and known substances can be used. Specific examples include, for example, water-soluble organic solvents (this does not include the "organic solvents" mentioned above as penetrating agents), sugars, etc. Among these, water-soluble organic solvents with a ClogP value of usually less than 0.00, preferably -0.05 or less, and more preferably -0.08 or less are mentioned. The lower limit of the Clog P value of the water-soluble organic solvent is not particularly limited, but is usually -4.00 or more, preferably -3.00 or more, more preferably -2.00 or more, and even more preferably -1.50 or more. Examples of such water-soluble organic solvents include 2-methyl-2,4-pentanediol (-0.02), tripropylene glycol monomethyl ether (-0.03), isopropyl diglycol (-0.08), dipropylene glycol monomethyl ether (-0.16), ethanol (-0.24), 3-methyl-1,5-pentanediol (-0.24), diethylene glycol dimethyl ether (-0.26), propylene glycol monomethyl ether (-0.30), 3-methyl-1,3-butanediol (-0.33), trimethylolpropane (-0.39), N-methyl-2-pyrrolidone (-0.40), 1,2-butanediol (-0.53), and 3-ethyl-3-hydroxymethyl Examples include thioxetane (-0.58), 1,5-pentanediol (-0.64), 2-methyl-1,3-propanediol (-0.64), dipropylene glycol (-0.69), 1,3-butanediol (-0.73), methyl diglycol (-0.78), methyl triglycol (-0.96), 2-pyrrolidone (-0.97), propylene glycol (-1.06), 1,4-butanediol (-1.16), diethylene glycol (-1.30), ethylene glycol (-1.37), triethylene glycol (-1.48), glycerin (-1.54), diglycerin (-2.96), glycereth-3 (-3.49) and glycereth-20 (-5.42) manufactured by Aoki Oil & Fat Industry Co., Ltd. When the above black ink contains a water-soluble organic solvent, the total content of the water-soluble organic solvent is usually 0% to 55%, preferably 5% to 40%, and more preferably 10% to 30%.

[0038] (d) Surfactants other than silicone-based surfactants Other surfactants besides the silicone-based surfactants mentioned above include anionic, cationic, amphoteric, and fluorine-based surfactants.

[0039] Examples of anionic surfactants include alkyl sulfocarboxylates, α-olefin sulfonates, polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl ether sulfates, N-acyl amino acids or their salts, N-acyl methyl taurates, alkyl sulfates, polyoxyalkyl ether sulfates, alkyl sulfates, polyoxyethylene alkyl ether phosphates, rosinic acid soaps, castor oil sulfates, lauryl alcohol sulfates, alkylphenol-type phosphates, alkyl-type phosphates, alkylaryl sulfonates, diethyl sulfosaturates, diethylhexyl sulfosaturates, and dioctyl sulfosaturates.

[0040] Examples of cationic surfactants include 2-vinylpyridine derivatives and poly-4-vinylpyridine derivatives.

[0041] Examples of amphoteric surfactants include lauryldimethylaminoacetic acid betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, coconut oil fatty acid amidopropyl dimethylaminoacetic acid betaine, polyoctyl polyaminoethylglycine, and imidazoline derivatives.

[0042] Examples of fluorine-based surfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in their side chains. If the above black ink contains surfactants other than silicone-based surfactants, the content of surfactants other than silicone-based surfactants in the ink is preferably 0.1 to 2.0%.

[0043] (e) Preservatives Examples of preservatives include compounds such as organosulfur, organonitrogen-sulfur, organohalogen, haloarylsulfone, iodopropagyl, haloalkylthio, nitrile, pyridine, 8-oxyquinoline, benzothiazole, isothiazolin, dithiol, pyridine oxide, nitropropane, organotin, phenol, quaternary ammonium salt, triazine, thiazine, anilide, adamantane, dithiocarbamate, brominated indanone, benzylbromacetate, and inorganic salts. Specific examples of commercially available preservatives include Proxel GXL(S) and XL-2(S) manufactured by Arch Chemical.

[0044] (f) Antifungal agents Examples of fungicides include sodium dehydroacetate, sodium benzoate, sodium pyridinethion-1-oxide, p-hydroxybenzoate ethyl ester, and 1,2-benzisothiazolin-3-one, as well as salts thereof.

[0045] (g) pH adjuster Any substance can be used as a pH adjuster, as long as it can adjust the pH of the prepared ink to 5-11 without adversely affecting it. Specific examples include alkanolamines such as diethanolamine, triethanolamine, and N-methyldiethanolamine; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; ammonium hydroxide (ammonia water); or 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] (h) Chelating agents Examples of chelating agents include disodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, and sodium uracildiacetate.

[0047] (i) Rust inhibitors Examples of rust inhibitors include acidic sulfites, sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitride, pentaerythritol tetranitrate, and dicyclohexylammonium nitride.

[0048] (j) Water-soluble UV absorber Examples of water-soluble ultraviolet absorbers include sulfonated benzophenone compounds, benzotriazol compounds, salicylic acid compounds, cinnamic acid compounds, and triazine compounds.

[0049] (k) Antioxidant Examples of antioxidants include various organic and metal complex-based colorfastness inhibitors. Examples of the above-mentioned organic colorfastness inhibitors include hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, and heterocyclic compounds.

[0050] [water] The ink composition contains each of the above components, and optionally an ink preparation agent, with the remainder being water. The water used for the ink is preferably deionized water or distilled water, which contains few impurities such as metal ions.

[0051] The pH of the above black ink is typically 7 to 11, preferably 8 to 10. The surface tension of the ink composition is typically 10 to 50 mN / m, preferably 20 to 40 mN / m. The viscosity of the ink composition is typically 2 to 30 mPa·s, preferably 3 to 20 mPa·s. The pH and surface tension of the ink composition can be adjusted by using pH adjusters, surfactants, and water-soluble organic solvents.

[0052] The above-mentioned black ink can be used in various printing applications. For example, it is suitable for writing instruments, various types of printing, information printing, and textile printing, and is particularly preferred for use in inkjet printing.

[0053] [Color Ink] The above color ink contains water, a colorant (2), and a silicone-based surfactant, and may optionally further contain other components. Examples of other components include dispersants, penetrating agents, viscosity modifiers, and ink preparations. The same silicone-based surfactant and other components as those used in the black ink can be used, and the content of each component in the color ink, excluding the silicone-based surfactant, can be within the preferred range described for the black ink. The color ink is preferably selected from the group including cyan, magenta, yellow, green, orange, red, and violet. Among these, cyan, magenta, and yellow are particularly preferred.

[0054] (Coloring agent (2)) The colorant (2) contained in the color ink is not particularly limited as long as it is a water-insoluble colorant. In the specification and claims of this application, a water-insoluble colorant means a colorant 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 solubility includes 0 g. Hereinafter, unless otherwise specified, "water-insoluble colorant" will also be simply referred to as "colorant". Examples of colorants that can be used include known pigments, disperse dyes, solvent dyes, and water-insoluble resins colored with colorants such as dyes and pigments. The coloring agent is preferably a pigment. Examples of pigments include inorganic pigments, organic pigments, and extender pigments.

[0055] Examples of inorganic pigments include titanium dioxide, metal oxides, hydroxides, sulfides, ferrocyanides, and metal chlorides.

[0056] Examples of organic pigments include various pigments such as azo, diazo, phthalocyanine, quinacridone, isoindolinone, dioxazine, perylene, perinone, thioindigo, antholaquinone, and quinophthalone. Specific examples of organic pigments include, for example, CIPigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 24, 55, 73, 74, 75, 83, 93, 94, 95, 97, 98, 108, 114, 128, 129, 138, 139, 150, 151, 154, 180, 185, 193, 199, 202, 213, etc.; CIPigment Red Red 5, 7, 12, 48, 48:1, 57, 88, 112, 122, 123, 146, 149, 150, 166, 168, 177, 178, 179, 184, 185, 202, 206, 207, 254, 255, 257, 260, 264, 272, etc.; CIPigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 25, 60, 66, 80, etc.; CIPigment Violet 19, 23, 29, 37, 38, 50, etc.; CIPigment Orange 13, 16, 68, 69, 71, 73, etc.; CIPigment Green 7, 36, 54, etc.; CIPigment Examples of black pigments include those for Black 1st grade.

[0057] Examples of extender pigments include silica, calcium carbonate, talc, clay, barium sulfate, and white carbon. Extender pigments are often used in combination with other colorants.

[0058] Examples of disperse dyes include well-known disperse dyes. Among these, dyes selected from CIDispers are preferred. Specific examples include, for instance, CIDispers Yellow 9, 23, 33, 42, 49, 54, 58, 60, 64, 66, 71, 76, 79, 83, 86, 90, 93, 99, 114, 116, 119, 122, 126, 149, 160, 163, 165, 180, 183, 186, 198, 200, 211, 224, 226, 227, 231, 237, etc.; CIDispers Red 60, 73, 88, 91, 92, 111, 127, 131, 143, 145, 146, 152, 153, 154, 167, 179, 191, 192, 206, 221, 258, 283, etc.; CIDispers Orange Disperse dyes in various colors include orange (9, 25, 29, 30, 31, 32, 37, 38, 42, 44, 45, 53, 54, 55, 56, 61, 71, 73, 76, 80, 96, 97, etc.), violet (CIDisperse Violet 25, 27, 28, 54, 57, 60, 73, 77, 79, 79:1, etc.), and blue (CIDisperse Blue 27, 56, 60, 79:1, 87, 143, 165, 165:1, 165:2, 181, 185, 197, 202, 225, 257, 266, 267, 281, 341, 353, 354, 358, 364, 365, 368, etc.).

[0059] (Silicone-based surfactants) It is important that the aforementioned color ink has sufficient wettability on ink-non-absorbent or poorly absorbent media, and surfactants are commonly used to impart wettability. Various surfactants are widely known for imparting wettability, including silicone-based, fluorine-based, and acetylene-based surfactants, depending on the application. Among these, silicone-based surfactants are particularly excellent in their ability to impart wettability.

[0060] Examples of the above-mentioned silicone-based surfactants include polyether-modified polysiloxane and polyether-modified polydimethylsiloxane. Specific examples of polyether-modified siloxanes include BYK-345, BYK-346, BYK-347, BYK-348, and BYK-349 (manufactured by Bic Chemie). Specific examples of polyether-modified polydimethylsiloxanes include BYK-306, BYK-307, BYK-333, BYK-342, BYK-3420, BYK-3455 (manufactured by Bic Chemie), KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, and KF-6017 (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0061] When the above color ink contains a silicone-based surfactant, the total surfactant content is usually 0.2% by mass or more, preferably 0.3% by mass or more, relative to the total mass of the ink. More preferably 0.3% to 1.5% by mass, even more preferably 0.3% to 1.2% by mass, and especially more preferably 0.3% to 0.9% by mass.

[0062] The content of silicone-based surfactants in the black ink and the color ink are determined to have a specific relationship. Specifically, the black ink does not contain silicone-based surfactants, or if it does, the content is 0.24% by mass or less, the difference in content between the black ink and the color ink is 0.2% by mass or more, preferably 0.2% by mass or more and 0.9% by mass or less, and more preferably 0.2% by mass or more and 0.7% by mass or less, and it is preferable that the content of silicone-based surfactants in the black ink is less than the content of silicone-based surfactants in the color ink. When the black ink does not contain silicone-based surfactants, or if it does, the content is 0.24% by mass or less, and the difference in content between the black ink and the color ink is 0.2% by mass or more, high-quality images with less bleeding can be obtained even when printed at high speed. "High speed" here refers to a speed of, for example, 25.4 m / min.

[0063] <Ink Set> The above ink set consists of a black ink containing water, a colorant (1), and optionally a silicone-based surfactant, and a color ink containing water, a colorant (2), and a silicone-based surfactant. The number of color inks to be combined is not particularly limited. Preferably, the above ink set consists of black ink and cyan ink, magenta ink, and yellow ink as color inks.

[0064] The above ink set enables the creation of printed images with extremely good color bleeding. This ink set is extremely useful for various printing applications, especially inkjet printing.

[0065] In other words, in the above inkjet recording method, it is preferable that the color inks each contain at least a pigment and a silicone-based surfactant, the black ink contains at least a pigment and may also contain a silicone-based surfactant, and if the black ink contains a silicone-based surfactant, the content of the silicone-based surfactant in the black ink is 0.24% by mass or less, the difference in the content of the silicone-based surfactant between the black ink and the color inks is 0.2% by mass or more, and the content of the silicone-based surfactant in the black ink is less than the content of the silicone-based surfactant in the color inks, and that the inkjet recording method is performed using a single-pass inkjet printing ink set.

[0066] <Inkjet recording method> The inkjet recording method is an inkjet recording method using the above-mentioned ink set, and includes the steps of: ejecting droplets of a first ink composition and adhering them to a printing medium to form a first image; and ejecting droplets of a second ink composition and adhering them to the printing medium on which the first image has been formed to form a second image. The steps of forming the first image and forming the second image can be performed using an inkjet method. In the above inkjet recording method, it is preferable that the first ink composition is black ink and the second ink composition is color ink. Furthermore, in the case of an ink set containing two or more color inks, the process includes steps for forming a third image, a fourth image, and so on, after the step for forming the second image.

[0067] Any known inkjet method can be used. Specific examples of inkjet methods include, for example, charge control methods, drop-on-demand (pressure pulse) methods, acoustic inkjet methods, and thermal inkjet methods. Furthermore, inkjet methods also include methods that improve image quality by ejecting many small volumes of ink with a low colorant content, methods that improve image quality by using multiple inks with essentially the same hue but different concentrations of colorants, and methods that improve the fixation of colorants by using colorless and transparent ink.

[0068] <Print media> Printing media refers to materials to which the inks of the above-mentioned ink set can adhere. Examples of printing media include paper, film, fibers and cloth (cellulose, nylon, wool, etc.), leather, and substrates for color filters. Printing media can be broadly classified into those with an ink-receiving layer and those without. The above ink set can be applied to either type of printing media, but it is preferably used with printing media that do not have an ink-receiving layer. Printing media with an ink-receiving layer are commonly referred to as inkjet paper, inkjet film, glossy paper, etc. Representative examples of commercially available products include Canon's Professional Photo Paper, Super Photo Paper, Glossy Gold, and Matte Photo Paper; Seiko Epson Corporation's Photo Paper Crispia (High Gloss), Photo Paper (Glossy), and Photo Matte Paper; Hewlett-Packard Japan Ltd.'s Advanced Photo Paper (Glossy); and Fujifilm Corporation's Gakusai Photo Finish Pro, among others. Printing media without an ink-receiving layer include various types of paper such as coated paper and art paper used for gravure printing and offset printing, as well as cast-coated paper used for label printing. When using printing media without an ink-receiving layer, it is also preferable to perform surface modification treatment on the printing media in order to improve the fixation of colorants. Known methods for surface modification treatment include corona discharge treatment, plasma treatment, and flame treatment.

[0069] <Ink Media Set> The ink media set is a set that includes the above-mentioned ink set and the above-mentioned printing media.

[0070] For all of the above, a combination of desirable items is more desirable, and a combination of more desirable items is even more desirable. The same applies to combinations of desirable items and more desirable items, and combinations of more desirable items and even more desirable items, etc. Furthermore, unless otherwise specified, all of the above ingredients can be used individually or in combination of two or more. [Examples]

[0071] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples. In the examples, when it was necessary to measure the amount of colorant (solid content) contained in various liquids, the dry weight method was used with the MS-70 manufactured by A&D Co., Ltd., and the converted value of only the colorant was calculated.

[0072] [Preparation Example 1]: Preparation of Black dispersion A block copolymer described in Synthesis Example 3 of International Publication No. 2013 / 115071 was prepared, and the obtained block copolymer (6 parts) was dissolved in 20 parts methyl ethyl ketone to obtain a homogeneous solution. A mixture of sodium hydroxide (0.45 parts) dissolved in water (53.55 parts) was added to this solution, and then 20 parts carbon black (Nerox 605, manufactured by ORION ENGINEERED CARBONS) was added. The mixture was dispersed in a sand grinder at 1500 rpm for 15 hours to obtain a liquid. After adding water (100 parts) to the obtained liquid, aggregates and other impurities were removed by filtration using glass filter paper GA-100 to obtain a filtrate. The obtained filtrate was subjected to vacuum distillation of the methyl ethyl ketone and a portion of the water using an evaporator, so that the pigment content in the filtrate was 12.0%, thereby obtaining a black dispersion.

[0073] [Preparation Example 2]: Preparation of cyanide dispersion. A cyanide dispersion with a pigment content of 12.0% was obtained in the same manner as in Preparation Example 1, except that CIPigment Blue 15:4 (manufactured by Dainichi Seika Co., Ltd., Chromofine blue 4851) was used instead of the carbon black used in Preparation Example 1.

[0074] [Preparation Example 3]: Preparation of Yellow Dispersion A yellow dispersion with a pigment content of 12.0% was obtained in the same manner as in Preparation Example 1, except that CIPigment Yellow 74 (HANSA Yellow 5GX01, manufactured by Clariant) was used instead of the carbon black used in Preparation Example 1.

[0075] [Preparation Example 4]: Preparation of Magenta Dispersion A magenta dispersion with a pigment content of 12.0% was obtained in the same manner as in Preparation Example 1, except that CIPigment Red 122 (Inkjet Magenta E02VP2621, manufactured by Clariant) was used instead of the carbon black used in Preparation Example 1.

[0076] [Preparation Example 7]: Preparation of resin emulsion. By replicating Preparation Example 4 of International Publication No. 2015 / 147192, a resin emulsion with an acid value of 6 KOH mg / g and a solid content of 25% was prepared. This was designated as Resin 1.

[0077] [Examples 1-7 and Comparative Examples 1-4: Examples of Ink Composition Preparation] After mixing the components listed in Tables 1 and 2 below, each ink composition for evaluation testing was obtained by filtering the mixture through a 3 μm membrane filter.

[0078] The abbreviations in Tables 2 and 3 below represent the following: PG: Propylene glycol. 1,2HD: 1,2-Hexanediol. TEA: Triethanolamine. AQ515: AQUACER515. (Manufactured by Big Chemie Japan; solids content 35%) Resin 1: Resin emulsion obtained in Preparation Example 7. DW: Ion-exchanged water.

[0079] [Evaluation of color bleeding] (1) Preparation of test specimen 1 Using the ink sets of Examples 1-6 and Comparative Examples 1-6, a 100% solid image (black image) recorded with the black ink composition was superimposed perpendicularly on top of a 100% solid image (black image) recorded with the color ink composition, with a line width of 100%. 0.25mm A single linear image (color image) was printed using the specified settings to obtain the printed image. Printing was performed using a printing jig equipped with two Kyocera KJ4B inkjet heads, with the black ink composition followed by the color ink composition, at a frequency of 10 kHz and a tri-level setting (combination of microdroplets and medium droplets), using Oji Paper's "OK Topcoat+" as the printing medium. The two inkjet heads were mounted in the printing evaluation device in the order of black ink composition followed by color ink composition, from the upstream side in the feeding direction of the printing medium. At this time, the distance between the inkjet heads filled with the black ink composition and the color ink composition was set to 90 mm. The obtained printed image was left to stand in a constant temperature bath set to 70°C for 2 minutes to dry and obtain test piece 1. The line width of test piece 1 was measured, and the expansion rate was calculated according to the following expansion rate calculation formula. This expansion rate is called bleeding. A QEA PIAS-II printing image evaluation device was used to measure the line width. The printing speed was 25.4 m / min. (Expansion rate calculation formula) Expansion rate (%) = Line width of color image on black image ÷ Line width of color image not overlapping on black image × 100 (2) Evaluation The expansion rate was evaluated based on the evaluation criteria shown in the following evaluation criteria table. The evaluation was based on the ratio of the first line width. A lower ratio indicates better performance in preventing color bleeding.

[0080] [Table 1]

[0081] As is clear from Tables 2 and 3 below, the ink sets of Examples 1 to 7 showed no bleeding. Therefore, the ink sets of Examples 1 to 6 demonstrated excellent performance in suppressing color bleeding.

[0082] [Table 2]

[0083] [Table 3]

[0084] The present invention provides an ink set that enables the provision of printed images with extremely good color bleeding, an inkjet printing method using the same, a printing medium, and a printing medium set. The ink set of the present invention is extremely useful for various printing applications, particularly inkjet printing.

Claims

1. This is an ink set consisting of black ink and at least one colored ink. Each of the aforementioned color inks contains at least a pigment and a silicone-based surfactant. The black ink contains at least a pigment and a silicone-based surfactant, and the content of the silicone-based surfactant in the black ink is 0.1% to 0.24% by mass. The difference in the content of silicone-based surfactants between the black ink and the colored ink is 0.2% by mass or more and 0.7% by mass or less. A single-pass inkjet printer ink set in which the amount of silicone-based surfactant in the black ink is lower than the amount of silicone-based surfactant in the color inks.

2. The ink set according to claim 1, comprising black, cyan, magenta, and yellow.

3. An ink media set comprising the ink set according to claim 1 or 2 and a printing medium.

4. The ink media set according to claim 3, wherein the above-mentioned printing media is an ink-poorly absorbent or ink-non-absorbent printing media.

5. An inkjet recording method, Recording is done using an ink set consisting of black ink and at least one color ink. Each of the aforementioned color inks contains at least a pigment and a silicone-based surfactant. The black ink contains at least a pigment and a silicone-based surfactant, and the content of the silicone-based surfactant in the black ink is 0.1% to 0.24% by mass. The difference in the content of silicone-based surfactants between the black ink and the colored ink is 0.2% by mass or more and 0.7% by mass or less. An inkjet recording method that uses a single-pass inkjet printing ink set in which the amount of silicone-based surfactant in the black ink is less than the amount of silicone-based surfactant in the color ink.

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