JP7765334B2 - Aqueous pigment dispersion and aqueous pigment ink for inkjet recording - Google Patents

Description

The objective is to provide a method for producing an aqueous pigment dispersion with excellent storage stability, and an aqueous inkjet recording ink.

Among various color recording methods, the recording method using an inkjet printer, which is one of the most representative methods, generates small droplets of ink and deposits them on various recording materials (paper, film, fabric, etc.) This method is quiet because there is no direct contact between the recording head and the recording material, and it is also easy to make the printer smaller and faster, so it has been rapidly expanding as a commercial printing method in recent years.
In recent years, pigment inks have replaced dye inks in aqueous inks to improve lightfastness, water resistance, and other properties. Furthermore, as the trend toward expanding the range of media applications for environmentally friendly aqueous inkjet printers accelerates, low-surface-tension solvents have been added in large amounts to inks to accommodate media that are difficult to wet. Low-surface-tension solvents destabilize the dispersion state of pigment dispersions, causing aggregation, sedimentation, and increased viscosity in storage stability evaluations. Given this background, pigment inks are required to have higher levels of storage stability in addition to conventional performance such as gloss, abrasion resistance, and stable ejection. One proposed method for producing pigment inks involves kneading and dispersing a pigment with a resin neutralized with a basic substance, adding acid to precipitate the resin on the pigment surface, and then neutralizing the resin again with a basic substance to maintain a fine particle size, thereby redispersing the pigment in an aqueous medium (see Patent Document 1). However, this method requires complex processes such as kneading with the pigment and re-neutralization, as well as cumbersome cleaning procedures. Furthermore, methods have been reported for obtaining pigment dispersions with higher dispersion stability, such as a method of encapsulating a pigment in a polymer having a crosslinked structure (Patent Documents 2 and 3). However, crosslinking reactions and polymerization reactions have the drawback of being cumbersome operations, such as requiring a high-temperature, high-pressure device for the pigment encapsulation process, and also have insufficient storage stability evaluation.

Japanese Patent Application Publication No. 9-31360 Japanese Patent Application Publication No. 11-140343 Japanese Patent Application Laid-Open No. 2002-338859

The present invention was made in light of this current situation, and aims to provide an ink that can be dispersed using a simple process and has high storage stability.

As a result of extensive research aimed at solving the above-mentioned problems, the inventors discovered that the above-mentioned problems could be solved by an aqueous ink containing a dispersion (DS) that includes a pigment, a water-insoluble resin, an organic solvent (B) having a boiling point below 120°C and a ClogP value of 1.0 to 5.0, and water, and in which the content of the organic solvent (B) is greater than 250 ppm and not more than 5,000 ppm, thereby completing the present invention.

That is, the present invention relates to the following 1) to 7).
1)
The aqueous ink comprises a dispersion (DS) that contains a pigment, a water-insoluble resin, an organic solvent (B) that has a boiling point of less than 120°C and a ClogP value of 1.0 to 5.0, and water, and the content of the organic solvent (B) is more than 250 ppm and not more than 5,000 ppm.
2)
1) The water-based ink according to 1), wherein the organic solvent (B) includes at least one selected from the group consisting of hexane, heptane, cyclohexane, and 3-methylpentane.
3)
1) The water-based ink according to 1) or 2), wherein the pigment comprises carbon black.
4)
3) The water-based ink according to any one of 1) to 3), wherein the water-insoluble resin is a block polymer.
5)
an emulsion composition preparation step of preparing an emulsion composition containing the water-insoluble resin, an organic solvent (A) having a solubility of 5 to 40 parts by mass in 100 parts by mass of water at 20°C, the organic solvent (B) having a boiling point of less than 120°C and a ClogP value of 1.0 to 5.0, a neutralizing agent, and water;
a dispersion treatment step of dispersing a mixture obtained by mixing the emulsion composition and the pigment;
a step of distilling off a part or all of the organic solvent (A) and the organic solvent (B) from the mixture after the dispersion treatment;
A method for producing a dispersion comprising:
6)
6. The method for producing a dispersion according to 5), wherein in the emulsion composition preparation step, the total amount b of the organic solvent (B) and the total amount p of the pigment satisfy the relationship 0.03≦b/p≦0.7.
7)
5) or 6) The method for producing a dispersion according to 5) or 6), wherein the organic solvent (A) contains methyl ethyl ketone.

The present invention provides an aqueous ink composition for inkjet printing that has high storage stability over long periods of time.

In this specification, "C.I." means "Color Index." Furthermore, in this specification, including the examples, "%,""parts," and "amounts" are all written on a mass basis unless otherwise specified.
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, when a mass% value is stated as a decimal point, the value is rounded to two decimal places and stated to one decimal place.

The above-mentioned water-based ink contains a pigment, a water-insoluble resin, an organic solvent (B) having a boiling point below 120°C and a ClogP value of 1.0 to 5.0, and water, and includes a dispersion (DS) in which the content of the organic solvent (B) is greater than 250 ppm and not more than 5,000 ppm. Note that throughout this specification, water-based ink may be abbreviated to "ink."

[Dispersion liquid (DS)]
The ink contains the dispersion (DS).

[Pigment]
Examples of the pigment include inorganic pigments, organic pigments, and extender pigments. These pigments can be used alone or in combination of two or more. Examples of inorganic pigments include carbon black, titanium oxide, metal oxides, hydroxides, sulfides, ferrocyanides, and metal chlorides. The pigment preferably contains carbon black, and more preferably consists of carbon black.
The carbon black is not particularly limited, but preferably has a BET specific surface area of 100 m ² /g or more, and from the viewpoint of color development on plain paper and coated paper, more preferably 150 m ² /g or more, and particularly preferably 180 m ² /g or more. Specific examples of the carbon black that can be used include thermal black, acetylene black, oil furnace black, gas furnace black, lamp black, gas black, and channel black. More specifically, 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, and FW285, and Special Black. Examples of such carbon fiber include HIBLACK 50L, 600L, 890, 930L, 970LB, NIPex 90, 160IQ, 170IQ, and 180IQ (all manufactured by Orion Engineered Carbons).

The DBP oil absorption of the carbon black is not particularly limited, but is preferably 40 to 150 mL/100 g, and from the viewpoint of color development on plain paper, is more preferably 70 mL/100 g or more, and particularly preferably 90 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 determined by measurement with reference to JIS K 6221, for example.

Examples of the 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 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, and 213; C.I. 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; Examples of pigments include orange pigments such as C.I. Pigment Orange 13, 16, 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.

Examples of the extender pigment include silica, calcium carbonate, talc, clay, barium sulfate, and white carbon. It is preferable to use extender pigments in combination with other pigments.

[Water-insoluble resin]
The dispersion (DS) contains a water-insoluble resin. The water-insoluble resin refers to a polymer that, when dried at 70° C. for 24 hours and dissolved in 100 g of water at 25° C., dissolves in an amount of 10 g or less. The amount of dissolution is preferably 5 g or less, and more preferably 1 g or less.
Examples of the water-insoluble resin include copolymers composed of at least two monomers (preferably at least one of which is a hydrophilic monomer) selected from the group consisting of styrene and its derivatives, vinylnaphthalene and its derivatives, aliphatic alcohol esters of α,β-ethylenically unsaturated carboxylic acids, acrylic acid and its derivatives, maleic acid and its derivatives, itaconic acid and its derivatives, faric acid and its derivatives, vinyl acetate, vinyl alcohol, vinylpyrrolidone, acrylamide, and derivatives thereof. 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, styrene-maleic acid copolymer, etc.
Among these, 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 are preferred; styrene-(meth)acrylic acid copolymer, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer, (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 this specification, the term "(meth)acrylic" is used to mean both "acrylic" and "methacrylic." The same applies to "(meth)acrylate" and the like.
Examples of the copolymer include block copolymers, random copolymers, graft copolymers, and/or salts thereof, and block copolymers are preferred. In this specification, block copolymers may also be referred to as block polymers.
The water-insoluble resin can be synthesized or obtained as a commercially available product. Specific examples of commercially available products include styrene-acrylic copolymers such as JONCRYL 62, 67, 68, 678, 611, 687, 690, and 819, all manufactured by Johnson Polymer Co.; Movinyl S-100A (a modified vinyl acetate copolymer manufactured by Hoechst Chemical Co., Ltd.); and JURIMER AT-210 (a polyacrylic acid ester copolymer manufactured by Nippon Junyaku Co., Ltd.).
Preferred examples of copolymers obtained by synthesis include the AB block polymers disclosed in WO 2013/115071 Gazette.

From the viewpoints of improving the storage stability and jetting ability of the aqueous pigment dispersion and the durability of the printed matter after printing, the weight-average molecular weight of the water-insoluble resin is less than 50,000, preferably from 3,000 to less than 50,000, and more preferably from 7,000 to less than 25,000. Furthermore, the acid value of the resin used as the dispersant is preferably from 50 to 300 KOHmg/g, more preferably from 60 to 275 KOHmg/g, and particularly preferably from 70 to 250 KOHmg/g.

The above-mentioned water-insoluble resins can be used either in a mixed state with the pigment, or in a state in which part or all of the pigment surface is coated with the resin as a dispersant. Both of these states can also be used in combination.

The water-insoluble resin has a salt-forming group. Salt-forming groups include carboxyl, hydroxyl, sulfo, phosphate, and amino groups. Salt-forming groups can be introduced into the water-insoluble resin by polymerizing a monomer mixture containing a salt-forming group-containing monomer.

[Organic solvent B]
The organic solvent B refers to a solvent having a boiling point of less than 120°C and a ClogP value of 1.0 to 5.0. The organic solvent B is not particularly limited as long as it satisfies the conditions of a boiling point of less than 120°C and a ClogP value of 1.0 to 5.0, and examples thereof include aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and halogenated aliphatic hydrocarbon solvents that satisfy these conditions. Examples of the aromatic hydrocarbon solvent include o-xylene, toluene, and benzene. Examples of the aliphatic hydrocarbon solvent include heptane, hexane, 3-methylpentane, and cyclohexane. Examples of the halogenated aliphatic hydrocarbon solvent include chloroform and dichloromethane. The organic solvent B can be used alone or in combination of two or more. Preferred organic solvents B are hexane, heptane, 3-methylpentane, and cyclohexane. Hexane is more preferred in terms of safety and operability when distilling off the solvent in post-treatment.

From the perspective of dispersion stability, the ClogP value of the organic solvent B is preferably 2.0 to 4.0. The ClogP value of organic solvent B is calculated using ChemBioDrawUltra 13.0 (CambridgeSoft).

The content of the organic solvent B contained in the dispersant (DS) is 500 ppm or more and 5000 ppm or less, preferably in the range of 251 to 5000 ppm, more preferably in the range of 255 to 4000 ppm, and even more preferably in the range of 260 to 3000 ppm or less from the standpoint of odor and safety. By setting the content of the organic solvent B contained in the dispersant (DS) to 500 ppm or more and 5000 ppm or less, it is possible to improve the storage stability of the dispersant (DS).

[water]
The dispersion liquid (DS) contains water. The water is preferably water with a low content of impurities such as metal ions, i.e., ion-exchanged water, distilled water, etc. Such water can be prepared by a known method.

The dispersion (DS) can be prepared by any known method. One example is the phase inversion emulsification method. Specifically, a resin serving as a dispersant is dissolved in an organic solvent such as methyl ethyl ketone, and an aqueous solution of a neutralizing agent (described below) is added to prepare an emulsion. A pigment is then added to the resulting emulsion, followed by a dispersion treatment. The desired dispersion can be obtained by distilling off the organic solvent and a portion of the water from the resulting solution under reduced pressure.

The above emulsion can be prepared by mixing the components in any order, but it is preferable to dissolve or disperse the water-insoluble resin in organic solvent A (described below) and then mix it with water and a neutralizing agent, as this will result in a uniform emulsion composition. Furthermore, since organic solvent B has low solubility in water, it is preferable to add organic solvent A, the water-insoluble resin, and the neutralizing agent to prepare the emulsion and then add organic solvent B, as this will prevent precipitation of the water-insoluble resin.

The dispersion treatment can be carried out using, for example, a sand mill (bead mill), a roll mill, a ball mill, a paint shaker, an ultrasonic disperser, a microfluidizer, etc. When using a sand mill, for example, beads having a particle diameter of about 0.01 mm to 1 mm are used, and the dispersion treatment can be carried out by appropriately setting the bead packing rate.
The dispersion obtained as described above can be subjected to filtration and/or centrifugation, etc. This operation can make the particle diameter of the particles contained in the dispersion uniform.
If foaming occurs during the preparation of the dispersion, a very small amount of a known antifoaming agent such as a silicone-based or acetylene glycol-based agent can be added.
Other methods for preparing the dispersion liquid include acid precipitation, interfacial polymerization, in-situ polymerization, submerged hardening coating, coacervation (phase separation), submerged drying, melt-dispersion cooling, air suspension coating, spray drying, etc. Among these, phase inversion emulsification, acid precipitation, and interfacial polymerization are preferred.

The average particle size (D50) of the pigment 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.
Similarly, D90 is usually 400 nm or less, preferably 350 nm or less, more preferably 300 nm or less. The lower limit is preferably 100 nm or more.
Similarly, D10 is usually 10 nm or more, preferably 20 nm or more, more preferably 30 nm or more, with an upper limit of 100 nm or less. Particle size can be measured using laser light scattering.

[Neutralizing agent]
It is preferable that some or all of the salt-forming groups of the water-insoluble resin are neutralized with a neutralizing agent. An acid or a base can be used as the neutralizing agent depending on the type of salt-forming group. Examples of acids include inorganic salts such as hydrochloric acid and sulfuric acid, and organic acids such as acetic acid, propionic acid, lactic acid, succinic acid, glycolic acid, gluconic acid, glyceric acid, and polyethylene glycolic acid. Examples of bases include tertiary amines such as trimethylamine and triethylamine, ammonia, sodium hydroxide, and potassium hydroxide. There are no particular limitations on the degree of neutralization, but it is preferable to adjust the pH of the dispersion (DS) to a neutral value, for example, a pH of 4.5 to 10.

[Organic solvent A]
The organic solvent A is an organic solvent other than the organic solvent B and has a solubility of 5 to 40 parts by weight in 100 parts by weight of water at 20°C, and preferably has a solubility of 10 to 30 parts by weight at 20°C.

Examples of organic solvent A include alcohol solvents, ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and halogenated aliphatic hydrocarbon solvents. Examples of alcohol solvents include 1-butanol and 2-butanol. Examples of ketone solvents include methyl ethyl ketone. Examples of ester solvents include ethyl acetate. Examples of ether solvents include diethyl ether. These organic solvents can be used alone or in combination. Among organic solvents A, methyl ethyl ketone is preferred, considering its safety and the ease of removing the solvent in post-treatment.

The ink may contain other additives in addition to the dispersant (DS). It is preferable to prepare the ink by first preparing the dispersion (DS) containing the pigment and water-insoluble resin, and then mixing it with other components.

The other components mentioned above include binder resins, water-soluble organic solvents, surfactants, antifungal agents, antibacterial agents, pH adjusters, rust inhibitors, and antifoaming agents. These may be used alone or in combination of two or more.

[Binder resin]
The binder resin preferably contains one or more selected from polymers and waxes.
Examples of the polymer include urethane-based, polyester-based, acrylic-based, vinyl acetate-based, vinyl chloride-based, styrene-acrylic-based, acrylic-silicone-based, and styrene-butadiene-based polymers, and emulsions containing the same. Among these, urethane-based, acrylic-based, and styrene-butadiene-based polymers are preferred, and acrylic polymers are more preferred.
The polymer can be synthesized or purchased commercially. When synthesizing a polymer, for example, the polymer disclosed in WO 2015/147192 Gazette is preferred.
Commercially available products include, for example, Superflex 126, 130, 150, 170, 210, 420, 470, 820, 830, and 890 (urethane resin emulsions manufactured by Daiichi Kogyo Seiyaku Co., Ltd.); Hydran HW-350, HW-178, HW-163, HW-171, AP-20, AP-30, 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 (acrylic resin emulsions manufactured by Kusumoto Chemical Co., Ltd.) and the like.

The wax is preferably a wax emulsion, more preferably a water-based wax emulsion. The wax may be a natural wax or a synthetic wax.
Examples of natural waxes include petroleum-based waxes such as paraffin wax and microcrystalline wax; lignite-based waxes such as montan wax; plant-based waxes such as carnauba wax and candelilla wax; and emulsions of animal and plant-based waxes such as beeswax and lanolin dispersed in an aqueous medium.

Examples of synthetic waxes include polyalkylene waxes (preferably poly C2-C4 alkylene waxes), oxidized polyalkylene waxes (preferably poly C2-C4 alkylene waxes), and paraffin waxes. Among these, one or more waxes selected from polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and paraffin wax are preferred, and oxidized polyethylene wax is more preferred.
The average particle size of the wax is preferably 50 nm to 5 μm, more preferably 100 nm to 1 μm, in order to prevent clogging of the inkjet head.

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

The total content of the binder resin relative to the total mass of the ink is preferably 0.6% to 6.0%, and more preferably 1.0% to 5%, from the viewpoints of ink fixation to paper, ink ejection properties, and ink storage stability.

[Water-soluble organic solvent]
The water-soluble organic solvent is not particularly limited, and examples thereof include C1-C6 alkanols such as methanol, ethanol, propanol, 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. esters; 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 with a molecular weight of 400, 800, 1540 or more), polypropylene glycol, thiodiglycol or dithiodiglycol; glycerin, diglycerin, hexane C3-C9 polyols (triols) such as 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 monobutyl ether glycol ethers such as diethyl ether and dipropylene glycol monomethyl ether (preferably glycol ethers selected from the group consisting of 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 or dimethyl sulfoxide; and the like.

[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.

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 sulfosuccinate, diethylhexyl sulfosuccinate, and dioctyl sulfosuccinate.

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 (e.g., Emulgen A-60, A-90, and A-500 manufactured by Kao Corporation); 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. Commercially available products include, for example, Surfynol 104, 104PG50, 82, 420, 440, 465, 485, and Olfin STG manufactured by Nissin Chemical 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 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 Additives &Instruments; and TEGO Twin 4000, TEGO Wet KL 245, 250, 260, 265, 270, and 280 manufactured by Evonic 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]
Specific examples of antifungal agents include sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, p-hydroxybenzoic acid ethyl ester, 1,2-benzisothiazolin-3-one and salts thereof.

[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.
A specific example of the organic halogen compound is sodium pentachlorophenol.
A specific example of the pyridine oxide compound is sodium 2-pyridinethiol-1-oxide.
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, and 2-methyl-4-isothiazolin-3-one calcium chloride.
Other specific examples of antiseptic and antifungal agents include anhydrous sodium acetate, sodium sorbate, sodium benzoate, and trade names Proxel GXL(S), Proxel LV, and Proxel XL-2(S), manufactured by Lonza.

[pH adjuster]
Specific 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]
Specific examples of the rust inhibitor include acid sulfite, sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

[Antifoaming agent]
Examples of antifoaming agents include silicone-based, silica mineral oil-based, olefin-based, acetylene-based, etc. Examples of commercially available antifoaming agents include Surfynol DF37, DF58, DF110D, DF220, MD-20, and Olefin SK-14, all manufactured by Shin-Etsu Chemical Co., Ltd.

The total amount of the pigments relative to the total amount of the ink is usually 1 to 20%, preferably 1.5 to 10%, and more preferably 2 to 8%. Herein, in the specification and claims of the present application, "%" and "parts" are written on a mass basis unless otherwise specified.
The average particle size of the pigment is usually 50 nm to 250 nm, and 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 a laser diffraction/scattering method.

The content of the organic solvent B contained in the ink containing the dispersion liquid (DS), which will be described later, is preferably 30 ppm or more and 3,500 ppm or less, and from the standpoint of odor and safety, it is more preferably 50 ppm or more and 1,500 ppm or less.

an emulsion composition preparation step of preparing an emulsion composition containing the water-insoluble resin, an organic solvent (A) having a solubility of 5 to 40 parts by mass in 100 parts by mass of water at 20°C, the organic solvent (B) having a boiling point of less than 120°C and a ClogP value of 1.0 to 5.0, a neutralizing agent, and water;
a dispersion treatment step of dispersing a mixture obtained by mixing the emulsion composition and the pigment;
and a step of distilling off a part or all of the organic solvent (A) and the organic solvent (B) from the mixture after the dispersion treatment.

In the emulsion composition preparation process, where b is the total amount of the organic solvent (B) and p is the total amount of the pigment, and b/p is the total amount of the pigment, from the viewpoint of improving storage stability, it is preferable that b/p satisfy the relationship of 0.03≦b/p≦0.7, and it is even more preferable that b/p satisfy the relationship of 0.04≦b/p≦0.6. Furthermore, in consideration of improving the dissolution stability of the water-insoluble resin, the ease of preparing the emulsion, and the operability when distilling off the solvent in post-processing, it is particularly preferable that b/p satisfy the relationship of 0.06≦b/p≦0.5.

The present invention also includes an ink set containing two or more of the above inks, and an ink set containing an ink other than the above inks.
The other ink is not particularly limited as long as it has a different constitution from the ink described above, but it is preferable that the other ink has a different hue from the ink described above.

When the ink is used as an inkjet ink, it is preferable that the ink contains a small amount of inorganic impurities, such as chlorides of metal cations (e.g., sodium chloride) and sulfates (e.g., sodium sulfate). Such inorganic impurities are often contained in commercially available carbon black. The inorganic impurity content is approximately 1% or less of the total amount of carbon black, and the lower limit is ideally below the detection limit of analytical equipment, i.e., 0%.
Examples of methods for obtaining carbon black with reduced inorganic impurities include desalination treatments such as a method using a reverse osmosis membrane; a method in which carbon black solids are suspended and stirred in a mixed solvent of water and a C1-C4 alcohol such as methanol, followed by filtration to separate the colored product and drying; and a method in which inorganic impurities are exchanged and adsorbed by an ion exchange resin.
Furthermore, when the ink is used as an inkjet ink, it is preferable to microfilter the ink. When microfiltering, a membrane filter and/or glass filter paper can be used. The pore size of the filter used for microfiltration is usually 0.5 μm to 20 μm, preferably 0.5 μm to 10 μm.

The above ink can be used in a variety of printing fields. For example, it is suitable for applications such as writing, printing, information printing, and textile printing. It is particularly preferable for use in inkjet printing.

The present invention also includes print media printed using the above ink or ink set, ink-media sets of the above ink or ink set and print media, and methods for improving print density using the above ink or ink set.

The inkjet printing method involves ejecting droplets of the ink in response to a printing signal and depositing them on a printing medium, and there are no particular limitations on the ink nozzles of the inkjet printer that eject the ink, and they can be selected appropriately depending on the purpose.
Inkjet printing methods include a method of improving image quality by ejecting a large number of inks with a low carbon black content in a small volume, a method of improving image quality by using multiple inks of substantially the same hue but with different carbon black contents, and a method of improving the fixation of carbon black to printing media by using a colorless, transparent ink in combination with an ink containing carbon black. The above inks can also be used as inks containing carbon black in these methods.

Any known inkjet printing method can be used. Examples include charge control, drop-on-demand (also known as pressure pulse), acoustic inkjet, and thermal inkjet.

The recording medium is not particularly limited as long as it is a material that can be colored by the ink, and examples of the recording medium include paper, film, fiber or cloth (cellulose, nylon, wool, etc.), leather, and a substrate for a color filter.
These recording media can be broadly divided into those with an ink-receiving layer and those without an ink-receiving layer.

Examples of recording media having an ink-receiving layer include those having an ink-receiving layer formed on a substrate such as paper, synthetic paper, film, etc. The ink-receiving layer can be formed, for example, by impregnating or coating the substrate with a cationic polymer, or by coating the surface of the substrate 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 usually called inkjet paper, inkjet film, glossy paper, etc. Typical examples of commercially available products include those manufactured by Canon Inc. under the trade names of Professional Photo Paper, Super Photo Paper, Glossy Gold, and Matte Photo Paper; those manufactured by Seiko Epson Corporation under the trade names of Photo Paper Crispia (high gloss), Photo Paper (gloss), and Photo Matte Paper; those manufactured by Hewlett-Packard Japan, Ltd. under the trade name of Advanced Photo Paper (gloss); and those manufactured by Fujifilm Corporation under the trade name of Gasai Photo Finishing Pro.

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.

When printing on a print medium using the inkjet printing method, for example, a container containing the ink (referred to as an ink tank or the like) is loaded into a predetermined position of an inkjet printer, and printing is performed on the print medium using the printing method.
The inkjet printing method can be used to print full color using an ink set of multiple inks selected from the color inks described above. In this case, containers containing inks of each color are loaded into the inkjet printer in predetermined positions in the same manner as described above, and printing is performed on a print medium using the printing method described above.

All of the above-mentioned components can be used alone, or multiple components can be used in combination as needed.
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.

The ink of the present invention has excellent viscosity stability, storage stability (such as inhibition of aggregation and sedimentation), redispersibility, various abrasion resistance, color development, and saturation. Furthermore, images recorded with the ink of the present invention have excellent fastness properties, including water resistance, light resistance, heat resistance, and resistance to oxidizing gases (e.g., ozone gas). Furthermore, there is little coating unevenness during image formation, resulting in excellent image formation properties.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Furthermore, all operations such as synthesis reactions were carried out under stirring unless otherwise specified.
In the examples, when quantitative determination of the pigment solid content in the dispersion was required, it was determined by the dry weight method using MS-70 manufactured by A&D Co., Ltd. The pigment solid content is a converted value calculated from the total amount of solids, i.e., the pigment solid content alone.

Preparation Example 1: Preparation of water-insoluble resin C.
A block copolymer (water-insoluble resin C) of Synthesis Example 3 was prepared by reproducing Synthesis Example 3 of WO 2013/115071. The acid value of the resulting block copolymer was 105 mg KOH/g and Mw was 25,000.
[Example 1]
4.8 parts of the water-insoluble resin C obtained in Preparation Example 1 was dissolved in 15 parts of methyl ethyl ketone, and a solution prepared by dissolving 0.35 parts of sodium hydroxide in 50 parts of ion-exchanged water was added. 4.0 parts of hexane (normal hexane, manufactured by Junsei Chemical Co., Ltd.) was then added, and the mixture was stirred for 30 minutes to form an emulsion. NEROX 600 (16 parts, manufactured by Orion Engineered Carbons) was added to the resulting emulsion, and dispersion beads were added. The mixture was then dispersed in a sand grinder at 1500 rpm for 15 hours to obtain a liquid. 120 parts of ion-exchanged water was added to the resulting liquid, and the dispersion beads were filtered off to obtain a filtrate. The methyl ethyl ketone, hexane, and a portion of the water were distilled off under reduced pressure from the resulting filtrate in an evaporator at a bath temperature of 55°C until the pigment solids content reached 12%, thereby obtaining Dispersion 1. The hexane content in Dispersion 1 was 610 ppm.
To the dispersion 1 obtained above, 1,2-hexanediol (5 parts), 1,2-propanediol (15 parts), BYK-349 (0.5 parts, manufactured by BYK), Texanol (1.0 part), AQUACER 515 (1.0 part, manufactured by BYK: solids content 35%), triethanolamine (0.3 parts), Proxel GXL(s) (0.05 parts, manufactured by Lonza), and water were added to make a total volume of 100 parts. The solution was stirred for 1 hour and then filtered through a 3 μm membrane filter (product number A300A047A, manufactured by Advantec Co., Ltd.), to obtain ink of Example 1. The pigment content in the ink was 5.0%.
[Example 2]
Dispersion 2 having a pigment content of 12% was obtained in the same manner as in Example 1, except that NEROX 605 (manufactured by Orion Engineered Carbons) was used instead of NEROX 600. The hexane content in Dispersion 2 was 590 ppm. Furthermore, the ink of Example 2 was obtained in the same manner as in Example 1, except that Dispersion 1 was changed to Dispersion 2.
[Example 3]
Dispersion 3 having a pigment content of 12% was obtained in the same manner as in Example 1, except that #45L (manufactured by Mitsubishi Chemical Corporation) was used instead of NEROX 600. The hexane content in Dispersion 3 was 420 ppm. Furthermore, the ink of Example 3 was obtained in the same manner as in Example 1, except that Dispersion 1 was changed to Dispersion 3.
[Example 4]
Dispersion 4 having a pigment content of 12% was obtained in the same manner as in Example 1, except that MA600 (manufactured by Mitsubishi Chemical Corporation) was used instead of NEROX 600. The hexane content in Dispersion 4 was 850 ppm. Furthermore, the ink of Example 4 was obtained in the same manner as in Example 1, except that Dispersion 1 was changed to Dispersion 4.
[Example 5]
Dispersion 5 having a pigment content of 12% was obtained in the same manner as in Example 1, except that Printex 80 (manufactured by Orion Engineered Carbons) was used instead of NEROX 600. The hexane content in Dispersion 5 was 1,800 ppm. Furthermore, the ink of Example 5 was obtained in the same manner as in Example 1, except that Dispersion 1 was changed to Dispersion 5.
[Example 6]
Dispersion 6 having a pigment content of 12% was obtained in the same manner as in Example 1, except that Printex 80 (manufactured by Orion Engineered Carbons) was used instead of NEROX 600 and heptane was used instead of hexane. The heptane content in Dispersion 6 was 1,700 ppm. Furthermore, the ink of Example 6 was obtained in the same manner as in Example 1, except that Dispersion 1 was replaced with Dispersion 6.
[Example 7]
Dispersion 7 having a pigment content of 12% was obtained in the same manner as in Example 1, except that Printex 80 (manufactured by Orion Engineered Carbons) was used instead of NEROX 600 and 3-methylpentane was used instead of hexane. The 3-methylpentane content in Dispersion 7 was 580 ppm. Furthermore, the ink of Example 7 was obtained in the same manner as in Example 1, except that Dispersion 1 was replaced with Dispersion 7.
[Example 8]
Dispersion 8 having a pigment content of 12% was obtained in the same manner as in Example 1, except that Printex 80 (manufactured by Orion Engineered Carbons) was used instead of NEROX 600 and cyclohexane was used instead of hexane. The cyclohexane content in Dispersion 8 was 1600 ppm. Furthermore, the ink of Example 8 was obtained in the same manner as in Example 1, except that Dispersion 1 was replaced with Dispersion 8.
[Example 9]
Dispersion 9 having a pigment content of 12% was obtained in the same manner as in Example 1, except that Printex 80 (manufactured by Orion Engineered Carbons) was used instead of NEROX 600 and toluene was used instead of hexane.
The toluene content in Dispersion Liquid 9 was 4100 ppm. In addition, the ink of Example 9 was obtained in the same manner as in Example 1, except that Dispersion Liquid 1 was changed to Dispersion Liquid 9.
[Example 10]
Dispersion 10 having a pigment content of 12% was obtained in the same manner as in Example 1, except that Printex 80 (manufactured by Orion Engineered Carbons) was used instead of NEROX 600 and chloroform was used instead of hexane. The chloroform content in Dispersion 10 was 340 ppm. Furthermore, the ink of Example 10 was obtained in the same manner as in Example 1, except that Dispersion 1 was replaced with Dispersion 10.
[Example 11]
Dispersion 11 having a pigment content of 12% was obtained in the same manner as in Example 1, except that Printex 80 (manufactured by Orion Engineered Carbons) was used instead of NEROX 600 and dichloromethane was used instead of hexane. The dichloromethane content in Dispersion 11 was 260 ppm. Furthermore, the ink of Example 11 was obtained in the same manner as in Example 1, except that Dispersion 1 was replaced with Dispersion 11.
[Example 12]
4.8 parts of JONCRYL 819 (manufactured by Johnson Polymer: Mw 14500, acid value 75) (water-insoluble resin D) were dissolved in 15 parts of methyl ethyl ketone, to which was added a solution prepared by dissolving 0.26 parts of sodium hydroxide in 50 parts of ion-exchanged water. 4.0 parts of hexane were then added, and the mixture was stirred for 30 minutes to form an emulsion. Printex 80 (16 parts, manufactured by Orion Engineered Carbons) was added to the resulting emulsion, and dispersion beads were added. The mixture was then dispersed in a sand grinder at 1500 rpm for 15 hours to obtain a liquid. 120 parts of ion-exchanged water was added to the resulting liquid, and the dispersion beads were filtered off to obtain a filtrate. The methyl ethyl ketone, hexane, and a portion of the water were distilled off from the resulting filtrate under reduced pressure using an evaporator to obtain Dispersion 12, which had a pigment solids content of 12%. The hexane content in Dispersion 12 was 430 ppm. In addition, the ink of Example 12 was obtained in the same manner as in Example 1, except that Dispersion 1 was changed to Dispersion 12.

The physical properties of the various carbon blacks used in Examples 1 to 12 above are listed in Table 1 below.

[Comparative Examples 1 to 5]
Each dispersion liquid having a pigment content of 12% was obtained in the same manner as in Examples 1 to 5, except that the amount of hexane added was 0 parts. Each of the obtained dispersion liquids was subjected to the same ink-making procedure as in Example 1, to obtain each of the inks of Comparative Examples 1 to 5 having a pigment content of 5.0%.
[Comparative Example 6]
A dispersion liquid with a pigment content of 12% was obtained in the same manner as in Example 2, except that the amount of hexane added was 0 parts. The obtained dispersion liquid was subjected to the same ink-making procedure as in Example 1, to obtain an ink of Comparative Example 6 with a pigment content of 5.0%.
[Comparative Example 7]
A dispersion liquid with a pigment content of 12% was obtained in the same manner as in Example 1, except that Printex 80 (manufactured by Orion Engineered Carbons) was used instead of NEROX 600 and 1,2-hexanediol was used instead of hexane. The obtained dispersion liquid was subjected to the same ink-making procedure as in Example 1, to obtain an ink of Comparative Example 7 with a pigment content of 5.0%.

(Measurement of the amount of organic solvent B in the dispersion)
Quantitative analysis was performed by gas chromatography. An Agilent gas chromatograph "Agilent 7890B" was used, with an Agilent HP-FFAP column (length 50 m, inner diameter 0.32 mm, film thickness 0.5 μm). The amount of organic solvent B was determined in terms of butyl acetate as an internal standard. Specifically, 300 mg of sample was weighed into a sample bottle, and butyl acetate (equivalent to approximately 0.05 wt%) and 1 mL of ethanol were added as internal standard substances. After 20 minutes of ultrasonic irradiation, the sample was measured under gas chromatography measurement conditions, and the content of the solvent component was calculated using a factor previously determined from the obtained area value. The measurement conditions were an inlet temperature of 270 °C, helium as the carrier gas, a column linear velocity of 1.0 mL/min, and a split ratio of 50. The column oven temperature was maintained at 50°C for 2 minutes, then increased at 10°C per minute to 150°C and maintained at 150°C for 5 minutes. The detector temperature was set to 250°C.

(Viscosity Measurement)
The viscosity was measured using an E-type viscometer TV-35L (manufactured by Toki Sangyo Co., Ltd.).

[Storage stability test]
The rate of change in viscosity between the measured values immediately after ink preparation and after storage at 60°C for 7 days was calculated using the following formula.
The smaller the discrepancy between the measured values immediately after ink preparation and those after 7 days of storage, the better the stability, indicating excellent storage stability.
Viscosity change rate = (measured value after 7 days of storage - measured value immediately after preparation) / (measured value immediately after preparation) x 100%
In Table 3, a hyphen indicates that the dispersion does not contain organic solvent (B) or any solvent other than organic solvent (B). The hyphen in the "Amount of solvent B remaining in the dispersion (ppm)" of Comparative Example 7 indicates that no measurement was performed. In Table 3, the type of organic solvent B used in each example is indicated by "○."

(Storage stability evaluation)
A: Viscosity change rate is within ±4% B: Viscosity change rate is greater than ±4% but within ±7% C: Viscosity change rate is greater than ±7% but within ±10% D: Viscosity change rate is greater than ±10%

It can be seen that the inks of the examples have clearly superior storage stability compared to the inks of comparative examples 1 to 7. In particular, it can be seen that even in the case of example 5, which uses carbon with a relatively large specific surface area and high cohesive properties, a water-based ink with high storage stability can be obtained.

The aqueous dispersion of the present invention can be suitably used in water-based inks for inkjet printing.

Claims (5)

A water-based ink comprising a dispersion (DS) containing a pigment, a water-insoluble resin, an organic solvent (B) having a boiling point of less than 120°C and a ClogP value of 1.0 to 5.0, and water, wherein the content of the organic solvent (B) is more than 250 ppm and not more than 5000 ppm,
The organic solvent (B) includes at least one selected from the group consisting of hexane, heptane, cyclohexane, and 3-methylpentane. 10. The water-based ink of claim 1 , wherein the pigment comprises carbon black. 3. The water-based ink according to claim 1, wherein the water-insoluble resin is a block polymer. an emulsion composition preparation step of preparing an emulsion composition containing a water-insoluble resin, an organic solvent (A) having a solubility of 5 to 40 parts by mass in 100 parts by mass of water at 20°C, an organic solvent (B) having a boiling point of less than 120°C and a ClogP value of 1.0 to 5.0, a neutralizing agent, and water;
a dispersion treatment step of dispersing a mixture of the emulsion composition and the pigment;
a step of distilling off a part or all of the organic solvent (A) and the organic solvent (B) from the mixture after the dispersion treatment;
wherein in the emulsion composition preparation step, a total amount b of the organic solvent (B) and a total amount p of the pigment satisfy the relationship 0.03≦b/p≦0.7. The method for producing a dispersion according to claim 4 , wherein the organic solvent (A) comprises methyl ethyl ketone.