JP7736713B2 - Inks, ink sets, ink media sets, and print media - Google Patents

Description

The present invention relates to an ink, an ink set comprising the ink, an ink media set comprising the ink or ink set and a printing media, and a printing media to which each ink comprised in the ink or ink set is adhered.

Among the various color printing methods, printing using an inkjet printer (inkjet printing) is one of the most representative methods. This method generates small droplets of ink and deposits them on a printing medium such as paper to print. Advances in inkjet printing technology have led to inkjet printing being used in the field of high-resolution printing, which was previously achieved using silver halide photography and offset printing. In such fields, printing media that has low ink absorption, such as coated paper, is often used.

In addition, in recent years, demand for industrial inkjet printing has increased, requiring different properties from those used in the past. One such property is the strong demand for improved abrasion resistance of ink adhered to print media.

For example, if an inkjet printer prints on coated paper and the resulting print is rubbed with a fingernail or similar, the ink coating is pressed against the rubbed area, smoothing the surface and resulting in stronger specular reflection of light and glare. The glare only in the rubbed area detracts from the overall appearance of the print and reduces print quality. For this reason, there is a strong demand for inks that minimize changes in the glare of the ink coating, even when scratched with a fingernail or similar.

Possible methods for reducing glare in ink coatings include applying a pretreatment agent to coated paper before printing, or applying an overcoat agent to coated paper after printing. However, considering the need to reduce printing costs, increase printing speed, and reduce the size of equipment due to additional processes, it is desirable to achieve the aforementioned abrasion resistance without using a pretreatment agent or overcoat agent.

Patent No. 5273434 Patent No. 4679322 International Publication No. 2016/035787

The objective of the present invention is to provide an ink that causes little change in the glare of the ink coating even when the print obtained by printing on printing media that has poor ink absorption, particularly offset coated paper, is scratched by a fingernail or the like; an ink set containing the ink; an ink media set containing the ink or ink set and printing media; and printing media to which the ink or each ink contained in the ink set is attached.

Specific means for solving the above problems include the following embodiments.
1)
The ink contains a water-insoluble colorant selected from the group consisting of pigments, disperse dyes, and solvent dyes, a resin dispersant having a weight-average molecular weight of less than 50,000, a resin emulsion having a solid content of 10 g or less dissolved in 100 g of methyl ethyl ketone at 25°C, a sol having an average particle size of 3 nm or more but less than 22 nm, and water,
The ink has a content of the sol of 1.0 to 5.0% by mass.

2)
1) The ink according to 1), wherein the sol contains at least one of a silica sol and a zirconium oxide sol.

3)
2) The ink according to 2), wherein the sol contains silica sol.

4)
3) The ink according to 3), wherein the sol contains at least one of a colloidal silica sol and an organosilica sol.

5)
5. The ink according to any one of 1) to 4), wherein the resin emulsion contains at least one of an acrylic resin emulsion and an oxidized polyethylene wax emulsion.

6)
6. The ink according to 5), wherein the resin emulsion comprises an acrylic resin emulsion and an oxidized polyethylene wax emulsion.

7)
7. The ink according to any one of 1) to 6), wherein the content of the resin emulsion is 0.6 to 6.0% by mass in terms of solid content.

8)
8) The ink according to any one of items 1) to 7), wherein the water-insoluble colorant comprises carbon black having a BET specific surface area of 180 m ² /g or more.

9)
An ink set comprising the ink according to any one of items 1) to 8) and another ink different from the ink.

10)
An ink-media set comprising the ink according to any one of items 1) to 8) or the ink set according to item 9) and a printing medium.

11)
A printing medium to which the ink according to any one of items 1) to 8) or each ink included in the ink set according to item 9) is adhered.

According to the present invention, it is possible to provide an ink that causes little change in the glare of the ink coating even when the print obtained by printing on printing media that has poor ink absorption, particularly offset coated paper, is scratched by a fingernail or the like; an ink set containing the ink; an ink media set containing the ink or ink set and printing media; and printing media to which each ink contained in the ink or ink set is attached.

Specific embodiments to which the present invention is applied will be described in detail below.
As used herein, "C.I." stands for "Color Index."
In addition, in this specification, the terms "alkylene,""propylene," and "alkyl" are used to mean both straight-chain and branched-chain structures unless otherwise specified.
In addition, in this specification, when a value in mass % is stated as a decimal point, the value is rounded to two decimal places and stated to one decimal place.

<Ink>
The ink according to this embodiment contains a water-insoluble colorant selected from the group consisting of pigments, disperse dyes, and solvent dyes; a resin dispersant having a weight-average molecular weight of less than 50,000; a resin emulsion having a sol content of 10 g or less in 100 g of methyl ethyl ketone at 25°C; a sol having an average particle size of 3 nm or more but less than 22 nm; and water, wherein the content of the sol is 1.0 to 5.0 mass %.

The components contained in the ink according to this embodiment are described in detail below. Note that each of the components described below may be used alone or in combination of two or more types.

[Water-insoluble colorant]
The water-insoluble colorant refers to a colorant whose solubility in water at 25° C. is usually 5 g/L or less, preferably 3 g/L or less, more preferably 1 g/L or less, and even more preferably 0.5 g/L or less. The lower limit of the solubility includes 0 g/L.

The water-insoluble colorant is selected from the group consisting of pigments, disperse dyes, and solvent dyes, and can be appropriately selected from known pigments, disperse dyes, and solvent dyes. Among these, pigments are preferred. Examples of pigments include inorganic pigments and organic pigments.

Examples of inorganic pigments include carbon black, metal oxides, metal hydroxides, metal sulfides, metal ferrocyanides, and metal chlorides.

Examples of organic pigments include various pigments such as azo, disazo, phthalocyanine, quinacridone, isoindolinone, dioxazine, perylene, perinone, thioindigo, anthraquinone, and quinophthalone.

Specific examples of organic pigments include yellow pigments such as 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, and 213; C.I. red pigments 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, 269, 272; blue pigments 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; violet pigments such as C.I. Pigment Violet 19, 23, 29, 37, 38, 50; Examples of suitable pigments include orange pigments such as C.I. Pigment Orange 13, 16, 43, 68, 69, 71, and 73; green pigments such as C.I. Pigment Green 7, 36, and 54; and black pigments such as C.I. Pigment Black 1.

Preferred disperse dyes are, for example, dyes selected from C.I. Disperses. Specific examples include yellow dyes such as C.I. Dispers 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, and 237; C.I. Red dyes such as C.I. Dispers Red 60, 73, 88, 91, 92, 111, 127, 131, 143, 145, 146, 152, 153, 154, 167, 179, 191, 192, 206, 221, 258, 283; orange dyes such as C.I. Dispers Orange 9, 25, 29, 30, 31, 32, 37, 38, 42, 44, 45, 53, 54, 55, 56, 61, 71, 73, 76, 80, 96, 97; violet dyes such as C.I. Dispers Violet 25, 27, 28, 54, 57, 60, 73, 77, 79, 79:1; Blue dyes such as Dispers 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, and 368;

As a solvent dye, for example, a dye selected from C.I. Solvent is preferred.

To adjust the color tone, it is possible to blend two or more water-insoluble colorants. For example, in the case of black ink, it is preferable to use three to five types of water-insoluble colorants in combination, and in the case of color inks other than black ink, it is preferable to use two or more types of water-insoluble colorants in combination. However, when black ink contains carbon black as a water-insoluble colorant, it is preferable to use two or one type of water-insoluble colorant. In this specification, color ink refers to colored inks other than black ink (e.g., inks of colors such as yellow, magenta, cyan, red, orange, brown, violet, blue, and green).

Preferred water-insoluble colorants contained in the black ink include carbon blacks such as thermal black, acetylene black, oil furnace black, gas furnace black, lamp black, gas black, and channel black. Specific examples of carbon black include the Raven series manufactured by Columbia Carbon; the Monarch series, Regal series, and Mogul series manufactured by Cabot Corporation; the Printex series, Colour Black series, Special Black series, HIBLACK series, NIPex 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.

Among these carbon blacks, from the viewpoint of improving print density on coated paper and plain paper, those having a BET specific surface area of 180 m ² /g or more are preferred, those having a BET specific surface area of 220 m ² /g or more are more preferred, and those having a BET specific surface area of 260 m ² /g or more are even more preferred. Specific examples include Raven 2000, 2350 ULTRA, 2500 ULTRA, 2800 ULTRA, 2900 ULTRA, 3000 ULTRA, 3500, and 5000 ULTRA (all manufactured by Columbia Carbon); Monarch 700, 880, 900, 1000, and 1300 (all manufactured by Cabot Corporation); Printex 75, 80, 85, 95, and L6, Colour Black S160S, S170, FW18, FW182, FW1, FW2, FW171, FW200, FW285, and Special Black. 5, 6, HIBLACK 50L, 600L, 890, 930L, 970LB, NIPex 90, 160IQ, 170IQ, 180IQ (all manufactured by Orion Engineered Carbons). The BET specific surface area of carbon black can be measured, for example, in accordance with ASTM D 6556.

The DBP oil absorption of carbon black is preferably, for example, 40 to 150 mL/100 g, and from the viewpoint of improving color development on plain paper, is preferably 70 mL/100 g or more, and more preferably 90 mL/100 g or more. The DBP oil absorption indicates the amount of DBP (dibutyl phthalate) absorbed by 100 g of carbon black in ^cm3 , and can be measured, for example, in accordance with JIS K 6221.

The average particle size of the water-insoluble colorant is typically 50 to 250 nm, preferably 60 to 200 nm. In this specification, the average particle size refers to the average particle size of particles measured using a laser light scattering method.

The content of the water-insoluble colorant is typically 1 to 30% by mass, preferably 1 to 10% by mass, and more preferably 2 to 7% by mass, relative to the total mass of the ink in this embodiment.

[Resin dispersant]
Examples of the resin dispersant include copolymers composed of at least two types of 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; phalic 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, with styrene-(meth)acrylic acid copolymer, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer, and (meth)acrylic acid ester-(meth)acrylic acid copolymer being more preferred, with (meth)acrylic acid ester-(meth)acrylic acid copolymer being even more preferred, and methacrylic acid ester-methacrylic acid copolymer being particularly preferred. Examples of copolymer types 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 include both "acrylic" and "methacrylic." The same applies to "(meth)acrylate," etc.

Resin dispersants can be synthesized or obtained commercially.

Examples of resin dispersants obtained by synthesis include the A-B block polymer disclosed in WO 2013/115071. The monomer constituting the A block of the A-B 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, with at least one monomer selected from methacrylic acid and n-butyl methacrylate being preferred, and a combination of these two monomers being even more preferred. Furthermore, the monomer constituting the B block of the A-B block polymer disclosed in WO 2013/115071 is at least one monomer selected from benzyl methacrylate and benzyl acrylate, with benzyl methacrylate being preferred. Specific examples of A-B block polymers include the block copolymers disclosed in Synthesis Examples 3 to 8 of WO 2013/115071.

Commercially available resin dispersants include, for example, Joncyrl 62, 67, 68, 678, and 687 (styrene-acrylic copolymers manufactured by BASF); Movinyl S-100A (modified vinyl acetate copolymer manufactured by Japan Coating Resins Co., Ltd.); and Jurymer AT-210 (polyacrylic ester copolymer manufactured by Toa Gosei Co., Ltd.).

The weight-average molecular weight (MW) of the resin dispersant is less than 50,000, preferably between 3,000 and 50,000, and more preferably between 7,000 and 25,000. The weight-average molecular weight of the resin dispersant can be measured by gel permeation chromatography (GPC). Specifically, the GPC system is an HLC-8320GPC (manufactured by Tosoh Corporation), two TSK gel Super Multipore HZ-H columns (manufactured by Tosoh Corporation, inner diameter 4.6 mm x 15 cm) are used, tetrahydrofuran is used as the eluent, and TSK Standard (manufactured by Tosoh Corporation) is used as the standard sample.

The acid value of the resin dispersant is, for example, preferably 50 to 300 mgKOH/g, more preferably 80 to 275 mgKOH/g, and even more preferably 80 to 250 mgKOH/g.

Resin dispersants can be used in a mixed state with a water-insoluble colorant. They can also be used with the water-insoluble colorant partially or entirely coated on its surface. Alternatively, both of these states can be used in combination.

The ratio of the total mass of the resin dispersant to the total mass of the water-insoluble colorant is typically 0.1 to 1.0, preferably 0.1 to 0.6, and more preferably 0.2 to 0.5.

[Resin emulsion]
The resin emulsion contains a solid content (resin) that dissolves in an amount of 10 g or less in 100 g of methyl ethyl ketone at 25° C. The dissolution amount is preferably 8 g or less, more preferably 5 g or less, and even more preferably 2 g or less. A solid content (resin) that dissolves in an amount of 10 g or less in 100 g of methyl ethyl ketone at 25° C. typically has a weight average molecular weight of 50,000 or more.

In this specification, the dissolution amount is measured as follows: The resin emulsion is completely dried in an environment of 35°C to obtain a solid content. The obtained solid content is then gradually added to 100 g of methyl ethyl ketone, and the upper limit at which complete dissolution can be confirmed visually is defined as the "dissolution amount."

The resin emulsion preferably contains at least one of a polymer emulsion and a wax emulsion.

Examples of polymer emulsions include emulsions in which urethane-based, polyester-based, acrylic-based, vinyl acetate-based, vinyl chloride-based, styrene-acrylic-based, acrylic-silicone-based, and styrene-butadiene-based polymers are dispersed in water or a water-soluble organic solvent. Among these, emulsions of polymers selected from urethane-based, acrylic-based, and styrene-butadiene-based polymers are preferred, with emulsions of acrylic polymers being more preferred.

Polymer emulsions can be synthesized or purchased commercially.

An example of a polymer emulsion obtained by synthesis is the polymer emulsion disclosed in WO 2015/147192. Among the polymers contained in the polymer emulsion disclosed in WO 2015/147192, a preferred polymer is one obtained by polymerizing 0.5 to 3.5 parts by mass (preferably 1 to 3 parts by mass) of methacrylic acid, 41 to 59 parts by mass (preferably 42 to 58 parts by mass) of methyl methacrylate, 41 to 59 parts by mass (preferably 42 to 58 parts by mass) of 2-ethylhexyl acrylate, and 0.2 to 3 parts by mass (preferably 0.5 to 2 parts by mass) of methacrylic acid, without the addition of other monomers.

Commercially available polymer emulsions include, for example, Superflex 126, 130, 150, 170, 210, 420, 470, 820, 830, and 890 (urethane resin emulsions manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.); Hydran HW-350, HW-178, HW-163, HW-171, AP-20, AP-30, WLS-201, and WLS-210 (urethane resin emulsions manufactured by DIC Corporation); 0569, 0850Z, and 2108 (styrene-butadiene resin emulsions manufactured by JSR Corporation); AE980, AE981A, AE982, AE986B, and AE104 (acrylic resin emulsions manufactured by E-Tech Co., Ltd.); and NeoCryl A-1105, A-1125, A-1127 (all acrylic resin emulsions manufactured by Kusumoto Chemicals Co., Ltd.); and the like.

As a wax emulsion, an emulsion in which natural wax or synthetic wax is dispersed in water or a water-soluble organic solvent can be used.

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-based waxes such as carnauba wax and candelilla wax; and animal and vegetable-based waxes such as beeswax and lanolin.

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 waxes selected from polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and paraffin wax are preferred, with oxidized polyethylene wax emulsions being more preferred.

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, and MINERPOL 221 (all manufactured by BYK); Mitsui Hiwax NL100, NL200, NL500, 4202E, 1105A, 2203A, NP550, NP055, and NP505 (all manufactured by Mitsui Chemicals, Inc.); KUE-100 and 11 (all manufactured by Sanyo Chemical Industries, Ltd.); and HYTEC E-6500, 9015, 6400 (all manufactured by Toho Chemical Industry Co., Ltd.);

Of the above resin emulsions, it is preferable to include at least one of an acrylic resin emulsion and an oxidized polyethylene wax emulsion, and it is even more preferable to include both.

The average particle size of the wax is preferably 50 nm to 5 μm, and more preferably 100 nm to 1 μm, to prevent clogging of the inkjet head.

The solid content of the resin emulsion is typically 0.6 to 6.0% by mass, and preferably 1.0 to 5.0% by mass, relative to the total mass of the ink in this embodiment, from the viewpoints of the ink's fixation to paper, ink ejection properties, and ink storage stability.

[Zol]
The sol is a liquid in which colloidal particles are dispersed. From the viewpoint of storage stability of the ink, the sol preferably contains at least one of silica sol and zirconium oxide sol. From the viewpoint of improving print density on coated paper and plain paper, the sol preferably contains silica sol, and more preferably contains at least one of colloidal silica sol and organosilica sol. In particular, in order to improve print density on coated paper and plain paper when used as a black ink, it is preferable to combine carbon black having a BET specific surface area of 180 m ² /g or more with colloidal silica sol.

Sols are commercially available. Commercially available colloidal silica sols include the Snowtex series manufactured by Nissan Chemical Industries, Ltd., the SI series manufactured by JGC Catalysts and Chemicals Co., Ltd., the Silicadol series manufactured by Nippon Chemical Industry Co., Ltd., and the PL series manufactured by Fuso Chemical Co., Ltd. Commercially available organosilica sols include methanol silica sol, IPA-ST, EG-ST, NPC-ST-30, PGM-ST, and NMP-ST manufactured by Nissan Chemical Industries, Ltd. Commercially available zirconium oxide sols include the SZR series manufactured by Sakai Chemical Industry Co., Ltd.

The average particle diameter of the sol is 3 nm or more and less than 22 nm, preferably 5 to 20 nm, in order to prevent scratches from being too shiny.

The content of the sol is from 1.0 to 5.0% by mass, preferably from 1.0 to 3.5% by mass, from the viewpoint of preventing scratches from becoming shiny and from the viewpoint of storage stability of the ink.
[water]
As the water, ion-exchanged water, distilled water, or the like having a small amount of impurities (metal ions, etc.) is preferred.

[Ink preparation agents]
In addition to the components described above, the ink according to this embodiment may further contain ink preparation agents, such as organic solvents, surfactants, antifungal agents, preservatives, pH adjusters, rust inhibitors, and antifoaming agents.

(organic solvent)
Examples of organic solvents include C1-C6 alkanols such as methanol, ethanol, propanol, Texanol, isopropanol, butanol, isobutanol, secondary butanol, and tertiary 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, and carbonates such as acetone, 2-methyl-2-hydroxypentan-4-one, and ethylene carbonate. cyclic ethers such as tetrahydrofuran and dioxane; mono-, oligo-, or polyalkylene glycols or thioglycols having a C2-C6 alkylene unit, such as ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butylene glycol, 1,4-butylene glycol, diethylene glycol, 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; glycerin, diglycerin, C3-C9 polyols (triols) such as hexane-1,2,6-triol and trimethylolpropane; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoallyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether (butyl carbitol), triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol Examples of suitable alkoxides include glycol ethers such as diethanolamine monobutyl ether and dipropylene glycol monomethyl ether (preferably selected from C3-C10 mono-, di-, or triethylene glycol ethers and C4-C13 mono-, di-, or tripropylene glycol ethers); C5-C9 alkanediols such as 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, 2-ethyl-1,3-hexanediol, and 2,4-diethyl-1,5-pentanediol; γ-butyrolactone, and dimethyl sulfoxide. Of these, 1,2-hexanediol and Texanol are preferred.

(Surfactant)
Examples of surfactants include anionic, nonionic, silicone-based, and fluorine-based surfactants. Among these, surfactants selected from silicone-based and fluorine-based surfactants are preferred, and silicone-based surfactants are more preferred from the viewpoint of safety to living organisms and the environment.

Examples of anionic surfactants include alkyl sulfocarboxylates, α-olefin sulfonates, polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl ether sulfates, N-acylamino acids or their salts, N-acylmethyltaurines, alkyl sulfates, polyoxyalkyl ether sulfates, alkyl sulfates, polyoxyethylene alkyl ether phosphates, rosin acid soap, castor oil sulfates, lauryl alcohol sulfates, alkylphenol phosphates, alkyl phosphates, alkylaryl sulfonates, diethyl sulfosuccinates, diethylhexyl sulfosuccinates, and dioctyl sulfosuccinates.

Examples of nonionic surfactants include ether-based surfactants such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene alkyl ether, and polyoxyethylene distyrenated phenyl ether; ester-based surfactants such as polyoxyethylene oleate, polyoxyethylene distearate, sorbitan laurate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate, polyoxyethylene monooleate, and polyoxyethylene stearate; acetylene glycol (alcohol)-based surfactants such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, and 3,5-dimethyl-1-hexyne-3-ol; and polyglycol ether-based surfactants. Examples of commercially available products include Surfynol 104, 104PG50, 82, 420, 440, 465, 485, and Olfine STG manufactured by Nissin Chemical Industry Co., Ltd.; and Emulgen A-60, A-90, and A-500 manufactured by Kao Corporation.

Examples of silicone surfactants include polyether-modified siloxanes and polyether-modified polydimethylsiloxanes. Examples of commercially available products include Dynol 960 and 980 manufactured by Air Products Co., Ltd.; Silface SAG001, SAG002, SAG003, SAG005, SAG503A, SAG008, SAG009, and SAG010 manufactured by Nissin Chemical Co., Ltd.; BYK-345, 347, 348, 349, 3455, LP-X23288, LP-X23289, and LP-X23347 manufactured by BYK; and TEGO Twin 4000, TEGO Wet KL 245, 250, 260, 265, 270, and 280 manufactured by Evonik Tego Chemie.

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 on the side chains.

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

(preservatives)
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, and inorganic salt compounds. Specific examples of organic halogen compounds include sodium pentachlorophenol. Specific examples of pyridine oxide compounds include sodium 2-pyridinethiol-1-oxide. Specific examples of isothiazoline compounds include 1,2-benzisothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one magnesium chloride, 5-chloro-2-methyl-4-isothiazolin-3-one calcium chloride, 2-methyl-4-isothiazolin-3-one calcium chloride, etc. Specific examples of other antiseptics and antifungals include anhydrous sodium acetate, sodium sorbate, sodium benzoate, and Proxel GXL(S), LV, and XL-2(S) manufactured by Lonza.

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

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

(Antifoaming agent)
Examples of the defoaming agent include silicone-based, silica mineral oil-based, olefin-based, and acetylene-based compounds. Commercially available products include Surfynol DF37, DF58, DF110D, DF220, MD-20, and Olefin SK-14 manufactured by Shin-Etsu Chemical Co., Ltd.

[Ink preparation method, etc.]
The ink according to this embodiment can be prepared by preparing an aqueous dispersion containing a water-insoluble colorant and a resin dispersant, and then adding and mixing a resin emulsion, a sol, and, if necessary, ink preparation agents to this aqueous dispersion.

Methods for preparing aqueous dispersions include, for example, phase inversion emulsification, acid precipitation, interfacial polymerization, in-situ polymerization, submerged hardening coating, coacervation (phase separation), submerged drying, melt-dispersion cooling, air suspension coating, and spray drying. Of these, phase inversion emulsification, acid precipitation, and interfacial polymerization are preferred, with phase inversion emulsification being more preferred.

When preparing an aqueous dispersion using the phase inversion emulsification method, for example, a resin 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. A water-insoluble colorant is added to the resulting emulsion, and a dispersion process is then carried out. The organic solvent and a portion of the water are then distilled off under reduced pressure from the resulting liquid to obtain the desired aqueous dispersion.

Dispersion 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 size of approximately 0.01 to 1 mm can be used, and the bead packing rate can be appropriately set to carry out dispersion. The particle size of the particles contained in the aqueous dispersion can be made uniform by subjecting the aqueous dispersion obtained as described above to filtration, centrifugation, etc. If foaming occurs during preparation of the aqueous dispersion, a trace amount of a known silicone-based, acetylene glycol-based, or other antifoaming agent can be added.

The average particle size (D50) of the water-insoluble colorant in the aqueous dispersion is typically 300 nm or less, preferably 30 to 280 nm, more preferably 40 to 270 nm, and even more preferably 50 to 250 nm. Similarly, D90 is typically 400 nm or less, preferably 350 nm or less, and more preferably 300 nm or less. The lower limit of D90 is preferably 100 nm or more. Similarly, D10 is typically 10 nm or more, preferably 20 nm or more, and more preferably 30 nm or more. The upper limit of D10 is preferably 100 nm or less. The average particle size of the water-insoluble colorant can be measured using laser light scattering.

When the ink according to this embodiment is used as an inkjet ink, it is preferable that the content of inorganic impurities, such as chlorides of metal cations (e.g., sodium chloride) and sulfates of metal cations (e.g., sodium sulfate), be low. Such inorganic impurities are often contained in commercially available water-insoluble colorants. The inorganic impurity content should be approximately 1% by mass or less of the total amount of the water-insoluble colorant, with the lower limit being below the detection limit of analytical equipment, i.e., 0%, being ideal. Methods for obtaining water-insoluble colorants with low inorganic impurities include, for example, a method using a reverse osmosis membrane; a method in which a solid water-insoluble colorant is suspended and stirred in a mixed solvent of water and a C1-C4 alcohol, such as methanol, followed by filtration and drying of the water-insoluble colorant; and a method in which inorganic impurities are exchanged and adsorbed using an ion exchange resin.

When the ink according to this embodiment is used as an inkjet ink, it is preferable to microfilter the ink. For microfiltration, a membrane filter, glass filter paper, or the like can be used. The pore size of the filter used for microfiltration is typically 0.5 to 20 μm, and preferably 0.5 to 10 μm.

The ink of this embodiment can be used in various printing fields such as writing, printing, information printing, and textile printing, and is particularly preferred for use in inkjet printing.

<Ink set, ink media set>
The ink set according to this embodiment comprises the ink according to this embodiment described above and another ink different from the ink according to this embodiment. The other ink is not particularly limited as long as it has a different constitution 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.

Furthermore, the ink set of this embodiment comprises the ink or ink set of this embodiment described above and printing media.

Examples of printing media include paper, film, fibers and cloth (cellulose, nylon, wool, etc.), leather, and color filter substrates. These recording media can be broadly divided into those with and without an ink-receiving layer.

Examples of recording media with ink-receiving layers include those with a substrate such as paper, synthetic paper, or film to which an ink-receiving layer is applied. The ink-receiving layer can be formed, for example, by impregnating or coating the substrate with a cationic polymer; or by coating the substrate surface with inorganic fine particles such as porous silica, alumina sol, or special ceramics together with a hydrophilic polymer such as polyvinyl alcohol or polyvinylpyrrolidone. Such recording media are commonly referred to as inkjet paper, inkjet film, or glossy paper. Specific examples of commercially available products include Canon Inc.'s Professional Photo Paper, Super Photo Paper, Glossy Gold, and Matte Photo Paper; Seiko Epson Corporation's Crispia Photo Paper (High Gloss), Photo Paper (Glossy), and Photo Matte Paper; Hewlett-Packard Japan, Ltd.'s Advanced Photo Paper (Glossy); and Fujifilm Corporation's Gasai Photo Finishing Pro.

On the other hand, examples of recording media that do not have an ink-receiving layer include various types of paper, such as coated paper and art paper, used in applications such as gravure printing and offset printing; cast-coated paper, used for label printing; etc. Specific examples of commercially available products include OK Top Coat+, a product name manufactured by Oji Paper Co., Ltd.

<Inkjet printing method>
The inkjet printing method according to this embodiment is a method of printing by ejecting droplets of the ink according to this embodiment or each ink included in the ink set according to this embodiment in response to a print signal and depositing them onto 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.

The inkjet printing method according to this embodiment also includes a method for improving image quality by ejecting a large number of small volumes of inks each having a low content of water-insoluble colorant; a method for improving image quality by using multiple inks having substantially the same hue but different contents of water-insoluble colorant; and a method for improving the adhesion of water-insoluble colorant to printing media by using a colorless, transparent ink in combination with an ink containing a water-insoluble colorant.

Known inkjet printing methods can be used, including charge control, drop-on-demand (pressure pulse), acoustic inkjet, and thermal inkjet.

When printing on print media, for example, a container containing ink (ink tank) is loaded into a predetermined position in an inkjet printer, and printing is performed on the print media using the printing method described above. It is also possible to achieve full-color printing by loading containers containing ink of each color into a predetermined position in an inkjet printer and printing on the print media using the printing method described above.

For all of the above, 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, etc.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples.

In the examples, unless otherwise specified, "parts" means parts by mass, and "%" means % by mass. All synthesis, preparation, and other operations in the examples were carried out under stirring unless otherwise specified. Furthermore, when quantitative determination of the solid content of the colorant in the aqueous dispersion was required, it was calculated using an MS-70 manufactured by A&D Co., Ltd. by the dry weight method, converting it into a value equivalent to the colorant alone.

Preparation Example 1: Preparation of Dispersion DP1
The block copolymer of Synthesis Example 3 was prepared by following up on Synthesis Example 3 of WO 2013/115071. The acid value of the resulting block copolymer was 105 mg KOH/g and the weight average molecular weight was 25,000. The resulting block copolymer (6.6 parts) was dissolved in 2-butanone (20 parts), and a solution of sodium hydroxide (0.36 parts) dissolved in ion-exchanged water (50 parts) was added thereto and stirred for 30 minutes to form an emulsion. Nerox 605 (carbon black manufactured by Orion Engineered Carbons) (20 parts) was added to the resulting emulsion, and the mixture was dispersed in a sand grinder at 1,500 rpm for 15 hours to obtain a liquid. Ion-exchanged water (120 parts) was added to the resulting liquid, and the dispersion beads were separated by filtration to obtain a filtrate. 2-Butanone and a portion of the water were distilled off from the resulting filtrate under reduced pressure using an evaporator to obtain a dispersion DP1 having a colorant solids content of 12%.

Preparation Example 2: Preparation of Dispersion DP2
A dispersion DP2 having a colorant solids content of 12% was obtained in the same manner as in Preparation Example 1, except that C.I. Pigment Yellow 74 (manufactured by Clariant, HANSA YELLOW 5GX01-JP) was used instead of Nerox 605.

Preparation Example 3: Preparation of Resin Emulsion A
Water (100 parts), ammonium persulfate (0.3 parts), and a reactive emulsifier (1 part) were added to a glass reaction vessel (volume 3 L) to obtain a liquid. After the air inside the reaction vessel was replaced with nitrogen, the temperature of the liquid was raised to 70 ° C. A liquid consisting of water (120 parts), a reactive emulsifier (0.9 parts), methacrylic acid (2 parts), methyl methacrylate (37 parts), 2-ethylhexyl acrylate (59 parts), and allyl methacrylate (2 parts) was added dropwise to this liquid over 3 hours. During the dropwise addition of the liquid, the reaction was carried out by maintaining the liquid temperature at 70 ° C. while introducing nitrogen. After the dropwise addition of the liquid was completed, the reaction was further carried out at 70 ° C. for 2 hours and then cooled to 40 ° C. Triethanolamine (3.1 parts) was added to the obtained liquid to obtain Resin Emulsion A as a white suspension with a solids content of 25%. The amount of solids (resin) contained in Resin Emulsion A that dissolved in 100 g of methyl ethyl ketone at 25°C was 5 g or less, the acid value was 13 mg KOH/g, and the glass transition temperature (Tg) was -10°C.

Examples 1 to 15: Preparation of inks
The components shown in Tables 1 and 2 below were mixed and then filtered through a membrane filter with a pore size of 3 μm to obtain inks of Examples 1 to 15, respectively.

Comparative Examples 1 to 6: Preparation of Comparative Inks
The components shown in Table 3 below were mixed and then filtered through a membrane filter with a pore size of 3 μm to obtain inks of Comparative Examples 1 to 6. The ink of Comparative Example 5 had extremely poor storage stability, and could not be evaluated for rub resistance and other properties, which will be described later.

The abbreviations in Tables 1 to 3 have the following meanings.
12HD: 1,2-hexanediol PG: 1,2-propanediol TEX: Texanol TEA: Triethanolamine BYK349: BYK-349 manufactured by BYK Corporation
Resin emulsion B: AQUACER 515 manufactured by BYK (solid content: 35%, amount of solid content dissolved in 100 g of methyl ethyl ketone at 25°C: 1 g or less)
ST30: Snowtex 30 (colloidal silica sol, solid content: 30%), manufactured by Nissan Chemical Industries, Ltd.
STXS: Snowtex XS (colloidal silica sol, solid content: 20%), manufactured by Nissan Chemical Industries, Ltd.
STC: Snowtex C (colloidal silica sol, solid content: 20%), manufactured by Nissan Chemical Industries, Ltd.
SD40: Silicadol 40 (colloidal silica sol, solid content: 40%), manufactured by Nippon Chemical Industry Co., Ltd.
SZRCW: SZR-CW (zirconium oxide sol, solid content: 30%), manufactured by Sakai Chemical Industry Co., Ltd.
SZRGCW: SZR-GCW (zirconium oxide sol, solid content: 30%), manufactured by Sakai Chemical Industry Co., Ltd.
PGMST: PGM-ST (organosilica sol, solid content: 30%), manufactured by Nissan Chemical Industries, Ltd.
ST50T: Snowtex 50T (colloidal silica sol, solid content: 50%), manufactured by Nissan Chemical Industries, Ltd.
ST30L: Snowtex 30L (colloidal silica sol, solid content: 30%), manufactured by Nissan Chemical Industries, Ltd.
GXL(S): Proxel GXL(S), manufactured by Lonza Pharmaceuticals

<Evaluation>
[Evaluation of abrasion resistance]
Using each of the inks of Examples 1 to 15 and Comparative Examples 1 to 4 and 6, inkjet printing was performed on printing media using a single pass (1 pass) method, resulting in a 100% duty printed image. The printing media used was offset coated paper "OK Topcoat+" manufactured by Oji Paper Co., Ltd. The inkjet head used was a 600 dpi head manufactured by Kyocera Corporation, and the head temperature was set to 32°C. The amount of ink droplets ejected was 12 pL. After inkjet printing, the resulting printed image was dried.

The dried printed image was scratched with a fingernail, and the printed image was held up to a fluorescent lamp to observe the difference in glare between the scratched area and other areas, and the scratch resistance was evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 4 and 5 below.
-Evaluation criteria-
A: All 10 out of 10 observers judged that there was no glare or change in gloss in the rubbed area.
B: All 10 out of 10 observers judged that there was a glitter or change in gloss in the rubbed area.
C: When the line was rubbed, the ink in the rubbed area peeled off from the paper, and no difference in glare could be observed.

As shown in Tables 4 and 5, the prints obtained using each of the inks in the examples had excellent abrasion resistance, with little change in the glare of the ink coating, even when scratched with a fingernail on offset coated paper.

[Evaluation of Print Density]
Using each of the inks of Examples 1 to 6, 13 to 15, and Comparative Examples 1 to 4 and 6, inkjet printing was performed on printing media using a single pass (1 pass) method, resulting in a 100% duty printed image. The printing media used were offset coated paper "OK Topcoat+" manufactured by Oji Paper Co., Ltd. and plain paper "Npi Form 70NEXT-IL" manufactured by Nippon Paper Industries Co., Ltd. The inkjet head used was a 600 dpi head manufactured by Kyocera Corporation, and the head temperature was set to 32°C. The amount of ink droplets ejected was 12 pL. After inkjet printing, the resulting printed image was dried.

The printed image after drying was measured using a spectrophotometer (eXact, manufactured by X-Rite). Colorimetry was performed under the following conditions: density standard: ANSI T, light source: D65, viewing angle: 2°. The print density was then evaluated according to the evaluation criteria shown in Table 6 below. The results are shown in Table 7 below.

As shown in Table 7, each of the inks in the examples was able to achieve good print density when printed on both offset coated paper and plain paper.

Preparation Example 4: Preparation of Dispersion DP3
The block copolymer of Synthesis Example 3 was prepared by reproducing Synthesis Example 3 of WO 2013/115071. The acid value of the obtained block copolymer was 105 mg KOH/g and the weight average molecular weight was 25,000. The obtained block copolymer (6.6 parts) was dissolved in 2-butanone (20 parts), and a solution of sodium hydroxide (0.36 parts) dissolved in ion-exchanged water (50 parts) was added thereto and stirred for 30 minutes to obtain an emulsion. HIBLACK890 (carbon black manufactured by Orion Engineered Carbons) (20 parts) was added to the obtained emulsion, and the mixture was dispersed in a sand grinder at 1,500 rpm for 15 hours to obtain a liquid. Ion-exchanged water (120 parts) was added to the obtained liquid, and the dispersion beads were separated by filtration to obtain a filtrate. The 2-butanone and a portion of the water were removed from the resulting filtrate under reduced pressure using an evaporator, to obtain a dispersion DP3 having a colorant solids content of 12%.

Preparation Example 5: Preparation of Dispersion DP4
A dispersion DP4 having a colorant solids content of 12% was obtained in the same manner as in Preparation Example 4, except that NIPex 90 (carbon black manufactured by Orion Engineered Carbons) was used instead of HIBLACK 890.

Preparation Example 6: Preparation of Dispersion DP5
A dispersion DP5 having a colorant solids content of 12% was obtained in the same manner as in Preparation Example 4, except that Printex 80 (carbon black manufactured by Orion Engineered Carbons) was used instead of HIBLACK 890.

Preparation Example 7: Preparation of Dispersion DP6
A dispersion DP6 having a colorant solids content of 12% was obtained in the same manner as in Preparation Example 4, except that HIBLACK 50L (carbon black manufactured by Orion Engineered Carbons) was used instead of HIBLACK 890.

The physical properties of the carbon black used in Preparation Examples 4 to 7 above are listed in Table 8 below.

Examples 16 to 25: Preparation of inks
The components shown in Tables 9 and 10 below were mixed and then filtered through a membrane filter with a pore size of 3 μm to obtain inks of Examples 16 to 25, respectively.

Comparative Examples 7 to 11: Preparation of Comparative Inks
The components shown in Table 11 below were mixed and then filtered through a membrane filter with a pore size of 3 μm to obtain inks of Comparative Examples 7 to 11, respectively.

The abbreviations in Tables 9 to 11 have the following meanings.
12HD: 1,2-hexanediol PG: 1,2-propanediol TEX: Texanol TEA: Triethanolamine BYK349: BYK-349 manufactured by BYK Corporation
Resin emulsion C: NeoCryl A-1127 manufactured by Kusumoto Chemicals Co., Ltd. (solid content: 44%, amount of solid content dissolved in 100 g of methyl ethyl ketone at 25°C: 1 g or less)
Resin emulsion D: AQUACER 531 manufactured by BYK (solid content: 45%, amount of solid content dissolved in 100 g of methyl ethyl ketone at 25°C: 5 g or less)
ST30: Snowtex 30 (colloidal silica sol, solid content: 30%), manufactured by Nissan Chemical Industries, Ltd.
STXS: Snowtex XS (colloidal silica sol, solid content: 20%), manufactured by Nissan Chemical Industries, Ltd.
SD40: Silicadol 40 (colloidal silica sol, solid content: 40%), manufactured by Nippon Chemical Industry Co., Ltd.
ST50T: Snowtex 50T (colloidal silica sol, solid content: 50%), manufactured by Nissan Chemical Industries, Ltd.
ST30L: Snowtex 30L (colloidal silica sol, solid content: 30%), manufactured by Nissan Chemical Industries, Ltd.
SZRCW: SZR-CW (zirconium oxide sol, solid content: 30%), manufactured by Sakai Chemical Industry Co., Ltd.
SZRGCW: SZR-GCW (zirconium oxide sol, solid content: 30%), manufactured by Sakai Chemical Industry Co., Ltd.
PGMST: PGM-ST (organosilica sol, solid content: 30%), manufactured by Nissan Chemical Industries, Ltd.
GXL(S): Proxel GXL(S), manufactured by Lonza Pharmaceuticals

<Evaluation>
[Evaluation of Print Density]
Using a bar coater No. 3 (Yasuda Machinery Works, Ltd.), each of the inks of Examples 11 to 25 and Comparative Examples 7 to 11 was applied to a print medium. The print media used were offset coated paper "OK Top Coat +" manufactured by Oji Paper Co., Ltd. and plain paper "Npi Form 70NEXT-IL" manufactured by Nippon Paper Industries Co., Ltd. The obtained image was dried at 70°C for 2 minutes to obtain a test specimen.

The optical density (OD value) of the obtained test piece was measured at five points using a spectrophotometer (eXact, manufactured by X-Rite), and the average value was used as the OD value of the test piece. Colorimetry was performed under the following conditions: density standard: ANSI T, light source: D65, and viewing angle: 2°. The print density was then evaluated according to the following evaluation criteria. The results are shown in Table 12 below.
-Evaluation criteria (OK top coat +)-
A: OD value is 2.3 or more B: OD value is 2.0 or more but less than 2.3 C: OD value is 1.7 or more but less than 2.0 D: OD value is less than 1.7 - Evaluation criteria (Npi Form 70 NEXT-IJ) -
A: OD value is 1.30 or more B: OD value is 1.25 or more but less than 1.30 C: OD value is 1.20 or more but less than 1.25 D: OD value is less than 1.20

As shown in Table 12, each of the inks in the examples was able to achieve good print density when printed on both offset coated paper and plain paper.

Claims (9)

a water-insoluble colorant selected from the group consisting of pigments, disperse dyes, and solvent dyes; a resin dispersant having a weight-average molecular weight of less than 50,000; a resin emulsion having a solubility of 10 g or less of solid content in 100 g of methyl ethyl ketone at 25°C; a sol having an average particle size of 3 nm or more and less than 22 nm; and water, wherein the resin emulsion contains an acrylic resin emulsion and an oxidized polyethylene wax emulsion;
The ink has a content of the sol of 1.0 to 5.0% by mass. The ink according to claim 1, wherein the sol comprises at least one of silica sol and zirconium oxide sol. The ink described in claim 2, wherein the sol comprises silica sol. The ink described in claim 3, wherein the sol includes at least one of a colloidal silica sol and an organosilica sol. The ink according to any one of claims 1 to 4, wherein the resin emulsion content is 0.6 to 6.0% by mass in terms of solids. 6. The ink according to claim 1, wherein the water-insoluble colorant comprises carbon black having a BET specific surface area of 180 m ² /g or more. An ink set comprising the ink according to any one of claims 1 to 6 and another ink different from said ink. An ink-media set comprising the ink according to any one of claims 1 to 6 or the ink set according to claim 7 , and a printing medium. A printing medium to which the ink according to any one of claims 1 to 6 or each of the inks included in the ink set according to claim 7 is adhered.