Ink, ink cartridge, inkjet recording device, and recording method

Abstract

To provide an ink that achieves improvements in storage stability, and image density and chroma on plain paper and coated paper, which are both insufficient in the conventional ink.SOLUTION: An ink includes a pigment, a polymer compound, and water, the polymer compound being a copolymer represented by the general formula (1) (where, R1 represents a hydrogen atom or a methyl group, R2 represents a C1-18 alkyl group with an ester bond, and k: l: m=20-30: 10-20: 55-65 in molar ratio).SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Inkjet printers have become extremely popular due to their advantages such as low noise and low running costs, and color printers that can print on plain paper have also been introduced to the market in large numbers. However, it is extremely difficult to satisfy all of the required characteristics, such as image color reproducibility, abrasion resistance, durability, light fastness, image drying speed, character feathering, color boundary bleeding, double-sided printability, and ejection stability, and therefore inks are selected based on the characteristics that take priority depending on the application.

[0003] Inks used in inkjet recording are generally composed primarily of water, with a colorant and a water-soluble solvent such as glycerin added to prevent clogging. Dyes have been used as colorants due to their excellent color development and stability, but the lightfastness and waterfastness of the images produced are not sufficient. Waterfastness has been improved to some extent through improvements in inkjet recording paper with an ink-absorbing layer, but is not satisfactory for use on plain paper.

[0004] To compensate for these drawbacks, inks using pigments as colorants have begun to be used. Although the lightfastness and waterfastness of the image are greatly improved, the color development is poor, and it is generally said that the color development of pigments is inferior to that of dyes.

[0005] To compensate for the reduced color development when using such pigments, a method of improving color development by coating the pigment particles with a resin is used. With this method, the fixability and gas resistance are further improved by the resin, but the storage stability and color development of the ink are inferior to those of dyes.

[0006] Patent Document 1 discloses a pigment water dispersion in which a pigment (A) is dispersed in a water-insoluble polymer (B), the polymer (B) containing a constituent unit derived from itaconic acid (b-1) and a constituent unit derived from a hydrophobic monomer (b-2), and further in which at least a portion of the acid groups have been neutralized. The patent document provides a pigment water dispersion that is excellent in fixability to resin printing media and image density, and an ink containing the pigment water dispersion.

[0007] Patent Document 2 provides an ink that has good storage stability and can achieve high image density on both smooth and non-smooth paper, using an inkjet pigment dispersion that is a salt of a copolymer using A) a monomer having an aromatic ring, B) a monomer having two or three carboxyl groups, and C) acrylamide and / or methacrylamide. Summary of the Invention [Problem to be solved by the invention]

[0008] Conventional inks have not been satisfactory in terms of image density and storage stability on plain paper and coated paper, and saturation of color inks. An object of the present invention is to provide an ink that has improved storage stability, image density and saturation on plain paper and coated paper, which have been insufficient in conventional pigment inks. [Means for solving the problem]

[0009] The above-mentioned problems are solved by an ink containing a pigment, a polymer compound, and water, wherein the polymer compound is a copolymer represented by the following general formula (1). [ka] (wherein R1 is a hydrogen atom or a methyl group, R2 is an alkyl group having 1 to 18 carbon atoms and an ester bond, and the molar ratio of k:l:m is 20-30:10-20:55-65) [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an ink that has improved storage stability, and image density and saturation on plain paper and coated paper.

[0011] As will be understood from the detailed and specific description below, the present invention has the extremely excellent effect of improving the color development that was insufficient in conventional pigment inks, providing an inkjet ink that can realize highly colored images regardless of the type of paper, and providing an image forming technology using the same. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an example of an inkjet recording apparatus according to the present invention. [Figure 2] FIG. 2 is a perspective view showing an example of the cartridge according to the present invention. [Figure 3] FIG. 3 is a front cross-sectional view of an example of a cartridge according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below. The ink of the present invention is an ink containing a pigment, a polymer compound, and water, and the polymer compound is a copolymer represented by the following general formula (1). [ka] (wherein R1 is a hydrogen atom or a methyl group, R2 is an alkyl group having 1 to 18 carbon atoms and an ester bond, and the molar ratio of k:l:m is 20-30:10-20:55-65)

[0014] (Copolymer represented by general formula (1)) The copolymer represented by general formula (1) is a salt of a copolymer having the structure of general formula (1) in which R1 is a hydrogen atom or a methyl group, and R2 is an ester having a carbon chain containing 1 to 18 carbon atoms. Examples of the copolymer represented by general formula (1) include styrene, itaconic acid, methyl methacrylate, and isobutyl acrylate.

[0015] The reason why the copolymer represented by the above general formula (1) improves the storage stability of the ink and results in excellent image density and saturation on plain paper and coated paper when printed is not clear, but it is thought to be as follows.

[0016] The reason why the storage stability is improved is presumed to be as follows. For example, using a monomer with two carboxyl groups, such as itaconic acid, creates hydrophilic areas with a high acid group density locally, enhancing the polymer's pigment dispersibility. Furthermore, the absence of amide bonds reduces the energy of hydrogen bonds, further improving water solubility. Furthermore, using a monomer with an aromatic ring, such as styrene, facilitates localization on the pigment surface, reducing contact between compound molecules and improving hydrogen bond storage stability.

[0017] The reason why the image density and saturation are improved is presumed to be as follows. When a monomer with two carboxyl groups is used, when the ink comes into contact with paper during image formation, the calcium ions of the calcium carbonate contained in most papers form a complex with the monomer with two carboxyl groups, making it insoluble and increasing its coagulation properties. The ester bond of methyl methacrylate or isobutyl acrylate also prevents the ink from being absorbed into the paper, improving its coagulation properties.

[0018] The monomer having R1 and R2 in the above general formula (1) is not particularly limited as long as R1 is a hydrogen group or a methyl group and R2 is an ester bond having a carbon chain with 1 to 18 carbon atoms, but examples thereof include methyl methacrylate and isobutyl acrylate, and two or more types may be used as long as they are polymerizable. Furthermore, the carboxyl group is preferably in the form of a salt, and examples thereof include alkali metal salts such as Li, Na, and K; ammonium salts; organic amine salts of mono-, di-, or trimethylamine, mono-, di-, or triethylamine, monoethanolamine, diethanolamine, triethanolamine, methylethanolamine, methyldiethanolamine, dimethylethanolamine, choline, aminoethanepropanediol, monopropanolamine, dipropanolamine, tripropanolamine, isopropanolamine, trishydroxymethylaminomethane, and aminoethylpropanediol; and organic amine salts of cyclic amines such as monophorine, N-methylmonophorine, N-methyl-2-pyrrolidone, and 2-pyrrolidone. However, from the viewpoint of the effect of improving image density, Li salts and Na salts are preferred, and Na salts are particularly preferred. These may be used as monomer salts, or may be used in the form of compound salts obtained by polymerizing each monomer and then neutralizing it.

[0019] (pigment) The pigment may be either an inorganic pigment or an organic pigment. Examples of inorganic pigments include carbon black and metal oxides, and carbon black is particularly preferred for black inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black. Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. The hue is not particularly limited, and any chromatic pigment such as yellow, magenta, cyan, blue, red, orange, or green can be used. Specific examples of preferred organic pigments include one or more products selected from CI Pigment Yellow 74, CI Pigment Red 122, CI Pigment Violet 19, CI Pigment Blue 15:3, and CI Pigment Blue 15:4. The pigments may be used alone or in combination of two or more kinds in any ratio.

[0020] The above-mentioned CI Pigment Yellow 74, CI Pigment Blue 15:3, CI Pigment Blue 15:4, CI Pigment Red 122, and CI Pigment Violet 19 are pigments represented by the following structural formulas, respectively. Structural formula (1): CI Pigment Yellow 74 Structural formula (2): CI Pigment Blue 15:3, 15:4 Structural formula (3): CI Pigment Red 122 Structural formula (4): CI Pigment Violet 19

[0021] [ka] [ka] [ka] [ka]

[0022] Ink can be obtained by mixing a pigment with materials such as water or an organic solvent. Alternatively, ink can be produced by mixing a pigment with other ingredients such as water or a dispersant to form a pigment dispersion, and then mixing the pigment with materials such as water or an organic solvent. The pigment dispersion is obtained by mixing and dispersing water, a pigment, a pigment dispersant, and optionally other components, and adjusting the particle size. Dispersion is preferably performed using a disperser. The pigment concentration in the pigment dispersion is preferably from 0.1% to 50% by mass, particularly preferably from 0.1% to 30% by mass. Furthermore, as the pigment according to the present invention, it is possible to use one that has been coated with a surfactant such as a dispersant or a resin, or that has been subjected to a grafting treatment or an encapsulation treatment. However, it is more preferable to use the copolymer represented by the above general formula (1) as the dispersant. The amount of dispersant must be appropriately selected depending on the type of pigment, but in general, the mass ratio of pigment to compound is preferably 90 / 10 to 70 / 30, more preferably 83 / 17 to 72 / 28.

[0023] The diameter of the pigment particles dispersed in the ink of the present invention is preferably from 30 to 120 nm, more preferably from 60 to 100 nm. Methods for adjusting the pigment particle diameter to this range can include a kneading disperser using balls such as a bead mill or a ball mill, a kneading disperser using shear force such as a roll mill, and an ultrasonic disperser. Among these, a bead mill disperser is particularly effective in the present invention. If the pigment particle size is greater than 30 nm, the light resistance is good, and color change is small, thereby providing the advantage of using a pigment. When the pigment particle diameter is smaller than 100 nm, glossiness is obtained in the image, and therefore, a good image with high saturation and brightness can be obtained.

[0024] The pigment concentration in the ink is preferably 1% by mass to 15% by mass, more preferably 2% by mass to 12% by mass, and even more preferably 3% by mass to 9% by mass. If the pigment concentration is greater than 1% by mass, sufficient coloring power can be obtained, resulting in high saturation and image density. A pigment concentration of 15% by mass or less improves ink stability, allowing for ink that is stable for a long period of time. However, after this dispersion process, the ink often contains coarse particles that can clog inkjet nozzles and supply channels, so particles with a diameter of 1 μm or larger must be removed using a filter or centrifuge.

[0025] Furthermore, the copolymer represented by the above general formula (1) can be used in combination with other dispersants as long as the effects of the present invention are not impaired. Other dispersants include various surfactants such as anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants, as well as polymeric dispersants. Examples of anionic surfactants include alkyl sulfocarboxylates, α-olefin sulfonates, polyoxyethylene alkyl ether acetates, N-acylamino acids and salts thereof, N-acylmethyl taurines, alkyl sulfates, polyoxyalkyl ether sulfates, polyoxyethylene alkyl ether phosphates, rosin acid soap, castor oil sulfates, lauryl alcohol sulfates, alkylphenol phosphates, naphthalene sulfonate formalin condensates, alkyl phosphates, alkyl allyl sulfonates, diethyl sulfosuccinate, diethylhexyl sulfosuccinate, and dioctyl sulfosuccinate. Examples of cationic surfactants include 2-vinylpyridine derivatives and poly-4-vinylpyridine derivatives. Examples of amphoteric surfactants include lauryl dimethylamino acetic acid betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine, coconut oil fatty acid-amidopropyl dimethylamino-acetic acid betaine, polyoctyl polyaminoethyl glycine, and imidazoline derivatives.

[0026] Examples of nonionic surfactants include the following: Ether-based compounds such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, polyoxyethylene alkyl ether, and polyoxyarylalkyl alkyl ether; Esters such as polyoxyethylene oleic acid, polyoxyethylene oleate, polyoxyethylene distearate, sorbitan laurate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate, polyoxyethylene monooleate, and polyoxyethylene stearate; Acetylenic glycols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, and 3,5-dimethyl-1-hexyn-3-ol.

[0027] The dispersion medium for the pigment dispersion preferably contains water, but various organic solvents may be used in combination as needed. Examples of water-soluble organic solvents include alcohols such as methanol, ethanol, 1-propanol, and 2-propanol, polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and glycerin, pyrrolidone derivatives such as N-methylpyrrolidone and 2-pyrrolidone, ketones such as acetone and methyl ethyl ketone, and alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine.

[0028] The pigment dispersion and ink may contain various additives, such as resins, wetting agents, surfactants, penetrants, pH adjusters, antiseptics and antifungals, chelating agents, rust inhibitors, antioxidants, ultraviolet absorbers, oxygen absorbers, and light stabilizers, as needed. As the resin, at least one of a water-soluble resin and a water-dispersible resin is preferably used. The water-soluble resin is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include polyvinyl alcohol, modified polyvinyl alcohols such as anion-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, and acetal-modified polyvinyl alcohol; polyurethane; modified polyvinylpyrrolidone such as polyvinylpyrrolidone and a copolymer of polyvinylpyrrolidone and vinyl acetate, a copolymer of vinylpyrrolidone and dimethylaminoethyl methacrylic acid, a copolymer of quaternized vinylpyrrolidone and dimethylaminoethyl methacrylic acid, and a copolymer of vinylpyrrolidone and methacrylamidopropyl trimethylammonium chloride; celluloses such as carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose; modified celluloses such as cationized hydroxyethyl cellulose; synthetic resins such as polyesters, polyacrylic acid (esters), melamine resins, or modified products thereof, and copolymers of polyesters and polyurethane; poly(meth)acrylic acid, poly(meth)acrylamide, oxidized starch, phosphate-esterified starch, self-modified starch, cationized starch, various modified starches, polyethylene oxide, sodium polyacrylate, and sodium alginate. These may be used alone or in combination of two or more. Among these, polyvinyl alcohol, cation-modified polyvinyl alcohol, acetal-modified polyvinyl alcohol, polyester, polyurethane, copolymer of polyester and polyurethane, and the like are particularly preferred from the viewpoint of ink absorbency.

[0029] The water-dispersible resin is not particularly limited and can be appropriately selected depending on the purpose. Water-dispersible resins have excellent film-forming properties (image-forming properties) and are also highly water-repellent, water-resistant, and weather-resistant, making them useful for recording images with high water resistance and high image density (high color development). Specific examples include polyurethane, polyvinyl acetate, ethylene-vinyl acetate copolymer, polystyrene, styrene-(meth)acrylic acid ester copolymer, (meth)acrylic acid ester polymer, vinyl acetate-(meth)acrylic acid (ester) copolymer, styrene-butadiene copolymer, ethylene-propylene copolymer, polyvinyl ether, silicone-acrylic copolymer, and the like. Furthermore, it may contain a crosslinking agent such as methylolated melamine, methylolated urea, methylolated hydroxypropylene urea, isocyanate, or may be a copolymer containing units such as N-methylolacrylamide, which has self-crosslinking properties. Among these, polyurethane resin particles, acrylic-silicone resin particles, and fluorine-based resin particles are particularly preferred. It is also possible to use a plurality of these water-dispersible resins at the same time.

[0030] The ink of the present invention uses water as a liquid medium, but the following water-soluble solvents are used to prevent the ink from drying, improve dispersion stability, and prevent curling on plain paper. These water-soluble solvents may be used in combination. Specific examples of the water-soluble solvent include the following: Polyhydric alcohols such as glycerin, ethylene glycol, diethylene glycol, isopropylideneglycerol, 1,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, propylene glycol, dipropylene glycol, trimethylolpropane, trimethylolethane, ethylene glycol, diethylene glycol, dipropylene glycol, tripropylene glycol, tetraethylene glycol, hexylene glycol, polyethylene glycol, polypropylene glycol, 1,5-pentanediol, 1,6-hexanediol, glycerol, 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, and petriol.

[0031] Polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether.

[0032] Polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether. Nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethylimidazolidinone, ε-caprolactam, and γ-butyrolactone. Amides such as formamide, N-methylformamide, N,N-dimethylformamide, N,N-dimethyl-β-methoxypropionamide, and N,N-dimethyl-β-butoxypropionamide.

[0033] Amines such as monoethanolamine, diethanolamine, triethanolamine, monoethylamine, diethylamine, and triethylamine. Sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol. Examples include 3-ethyl-3-hydroxymethyloxetane, propylene carbonate, and ethylene carbonate. Among these water-soluble solvents, 3-ethyl-3-hydroxymethyloxetane, isopropylideneglycerol, N,N-dimethyl-β-methoxypropionamide, and N,N-dimethyl-β-butoxypropionamide are particularly preferred, as they are highly effective in preventing curling of plain paper.

[0034] In addition, in the present invention, sugars can be contained as the water-soluble solvent. Examples of sugars include monosaccharides, disaccharides, oligosaccharides (including trisaccharides and tetrasaccharides), and polysaccharides, and preferred examples include glucose, mannose, fructose, ribose, xylose, arabinose, galactose, maltose, cellobiose, lactose, sucrose, trehalose, and maltotriose. Here, the term "polysaccharides" refers to sugars in a broad sense, and is used to include substances widely found in nature, such as α-cyclodextrin and cellulose. Derivatives of these sugars include the aforementioned reduced sugars, oxidized sugars, amino acids, thioacids, etc. Sugar alcohols are particularly preferred, and specific examples include maltitol and sorbitol.

[0035] The ratio of pigment to water-soluble solvent has a significant impact on the stability of ink ejection from the head. If the amount of water-soluble solvent is low despite the high pigment solids content, evaporation of water near the ink meniscus in the nozzle will occur, resulting in ejection problems. The amount of water-soluble solvent is preferably 10 to 70% by mass, more preferably 20 to 50% by mass, of the total ink. Inks within this range exhibit excellent drying properties and perform well in storage tests and reliability tests.

[0036] Adding a penetrant to ink reduces surface tension, improves ink filling in nozzles, and improves ejection stability. In addition, it speeds up ink penetration into the recording medium after ink droplets land on the recording medium, thereby reducing feathering and color bleeding. Penetrants include surfactants and penetrating solvents. Surfactants can be broadly classified into anionic surfactants, nonionic surfactants, and amphoteric surfactants based on the hydrophilic group, and into fluorine-based surfactants, acetylene-based surfactants, etc. based on the hydrophobic group.

[0037] Examples of anionic surfactants include polyoxyethylene alkyl ether acetates, dodecylbenzenesulfonates, laurates, and salts of polyoxyethylene alkyl ether sulfates.

[0038] Examples of nonionic surfactants include polyols, glycol ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkylamines, polyoxyethylene alkylamides, and acetylene glycol.

[0039] Examples of fluorine-based surfactants include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphates, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, perfluoroalkyl amine oxides, and perfluoroalkyl ether compounds, and fluorine-containing compounds represented by structural formula (3) or structural formula (4) can be particularly useful.

[0040] As the acetylene glycol surfactant, acetylene glycol surfactants such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, and 3,5-dimethyl-1-hexyn-3-ol (for example, Surfynol 104, 82, 465, 485, or TG from Air Products Inc. (USA)) can be used, with Surfynol 465, 104, and TG in particular demonstrating good print quality.

[0041] As the penetrating solvent, polyols having 8 or more carbon atoms, such as 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol, or glycol ethers can be used.

[0042] The surfactants can be used alone or in combination. According to a preferred embodiment of the present invention, the amount of penetrant added to the ink is preferably 0.01% by mass to 5% by mass, more preferably 0.03% by mass to 2% by mass. If the amount of surfactant is more than 0.01% by mass, the printed dots spread sufficiently and can fill in solid images completely, maintaining high image density and saturation. If the amount of surfactant is kept below 5% by mass, foaming is suppressed and bubbles do not clog the flow paths in the nozzles, allowing for good ink droplet ejection.

[0043] If necessary, conventionally known additives such as pH adjusters, antiseptics and antifungals, rust inhibitors, antioxidants, ultraviolet absorbers, oxygen absorbers, light stabilizers, and kogation inhibitors can be appropriately selected and added to the ink of the present invention.

[0044] Adding the pH adjuster to maintain an alkaline state stabilizes the dispersion state and thus the ejection. Furthermore, at a pH of 11 or higher, the inkjet head and ink supply unit dissolve to a large extent, resulting in problems such as ink deterioration, leakage, and ejection failure. It is preferable to add the pH adjuster when kneading and dispersing the pigment in water together with the dispersant, rather than adding it after the kneading and dispersion together with additives such as a water-soluble solvent or penetrant. This is because the addition of some pH adjusters can destroy the dispersion. The pH adjuster preferably contains one or more of alcohol amines, alkali metal hydroxides, ammonium hydroxides, phosphonium hydroxides, and alkali metal carbonates. Examples of alcohol amines include diethanolamine, triethanolamine, and 2-amino-2-ethyl-1,3-propanediol. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of ammonium hydroxides include ammonium hydroxide, quaternary ammonium hydroxides, and quaternary phosphonium hydroxides. Examples of alkali metal carbonates include lithium carbonate, sodium carbonate, and potassium carbonate.

[0045] As the antiseptic and antifungal agent, sodium dehydroacetate, sodium sorbate, sodium 2-pyridinethiol-1-oxide, sodium benzoate, sodium pentachlorophenol, etc. can be used in the present invention.

[0046] Examples of the rust inhibitor include acid sulfite, sodium thiosulfate, ammonium thiodiglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

[0047] Examples of the antioxidant include phenol-based antioxidants (including hindered phenol-based antioxidants), amine-based antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants.

[0048] Examples of the ultraviolet absorber include benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, and nickel complex salt-based ultraviolet absorbers.

[0049] An anti-kogation agent can be added to the ink that can be used in the present invention. Kogation is a problem that occurs in thermal heads, which eject ink by using the force of ink bubbles generated by passing an electric current through a heater to instantly heat the ink. When the ink is heated, the ink components change in quality, and the changed material adheres to the heater. If kogation occurs, the heater will not heat properly, the ejection force will be weakened, and in the worst case, the ink will not be ejected at all. Therefore, in order to prevent kogation, an anti-kogation agent can be added to the ink that can be used in the present invention. Examples of anti-kogation agents include polyphosphoric acid, polyaminocarboxylic acid, aldonic acid, hydroxycarboxylic acid, polyol phosphate ester, and salts thereof, acids having an amino group and / or their salts, and ammonium salts of acids having a methyl group or a methylene group and a carboxyl group.

[0050] The water used in the present invention may be pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, or ultrapure water. The water content is preferably 20% by mass or more and 80% by mass or less of the total amount of ink.

[0051] The ink of the present invention can be suitably used in various recording devices using the ink jet recording method, such as ink jet recording printers, facsimile machines, copying machines, and printer / fax / copier combination machines.

[0052] An example of the inkjet recording apparatus of the present invention will be described with reference to the drawings. 1 is equipped with cartridges 20 containing pretreatment liquid and ink, and the pretreatment liquid and ink are supplied to the recording head 18a from the cartridges 20. Here, the cartridges 20 are attached in a state where they are separated into cartridges 20 for the pretreatment liquid and cartridges 20 for the inks of each color. The recording head 18a is mounted on a carriage 18 and moves while being guided by guide shafts 21 and 22 via a timing belt 23 driven by a main scanning motor 24. Meanwhile, the recording material is placed by a platen 19 in a position facing the recording head 18a. In the figure, 2 is a main body housing, 7 is a common cartridge for processing liquid and ink, 16 is a gear mechanism, 17 is a sub-scanning motor, 25 is a gear mechanism, 26 is a main scanning motor, and 27 is a gear mechanism.

[0053] 2 and 3 show a cartridge capable of storing both the pretreatment liquid and the ink. This cartridge can store both the pretreatment liquid and the ink. The cartridge housing 41 contains a liquid absorber 42, which absorbs ink or pretreatment liquid, thereby retaining the ink within the cartridge. A top cover member 44 is provided on top of the cartridge. The ink or pretreatment liquid can be filled into the cartridge through an air-vent 47 provided in the top cover member 44. After filling, the air-vent 47 is sealed with a seal member 55. The ink or pretreatment liquid is supplied to the recording head through a liquid supply port 45. The cartridge positioning portion 71 has a protruding shape and can be aligned with a recess in the cartridge storage compartment of the printer body to maintain a consistent cartridge position. The cartridge attachment / detachment protrusion 81, cartridge attachment / detachment finger hook 81a, and cartridge attachment / detachment recess 82 are designed to be secured by the concave and convex portions of the cartridge storage compartment of the printer body when the cartridge is tried on. Reference numeral 43 denotes a case, 46 denotes a seal ring, 48 denotes a groove, 50 denotes a cap member, 51 denotes a protrusion for preventing liquid leakage, 53 denotes a cap member, and A denotes the space between the cartridge housing 41 and the liquid absorber 42. It is most preferable that the ink and the pretreatment liquid are ejected from the recording head in an overlapping manner onto the same location. However, in the present invention, a sufficient effect can be obtained, for example, by thinning out the pretreatment liquid and then overlapping the ink on top of the pretreatment liquid that has expanded due to bleeding or the like, or by applying the pretreatment liquid only to the outline of the image and then overlapping part of the ink on top of that.

[0054] (Recorded matter and method of manufacturing recorded matter) The method for producing a recorded matter of the present invention is a method for producing a recorded matter, which comprises a step of ejecting ink from an inkjet head to perform recording on a recording medium, and the ink is the ink of the present invention. Furthermore, the recorded matter of the present invention is a recorded matter in which information or an image is recorded on a recording medium using ink, and the ink is the ink of the present invention. That is, the recorded matter of the present invention has information or an image recorded on a recording medium using the ink of the present invention. The recorded matter of the present invention can be produced by a process of ejecting the ink from an inkjet head to record on the recording medium.

[0055] The recording medium is not particularly limited and can be appropriately selected depending on the purpose. Examples include plain paper, coated printing paper, glossy paper, specialty paper, cloth, film, and OHP sheets. These may be used alone or in combination of two or more. Among these, at least one of plain paper and coated printing paper is preferred. Plain paper is advantageous in that it is inexpensive. Furthermore, coated printing paper is advantageous in that it is relatively inexpensive compared to glossy paper and provides a smooth, glossy image. Plain paper and coated printing paper generally have poor drying properties and are difficult to use for inkjet printing, but the ink of the present invention improves drying properties, making them usable. The recorded matter of the present invention has high image quality, is free from bleeding, and has excellent stability over time, and can be suitably used for various purposes such as documents on which various prints or images are recorded. [Example]

[0056] The present invention will be described in more detail and specifically below with reference to examples. However, these examples are intended to facilitate understanding of the present invention and are not intended to limit the present invention. In each example, "parts" and "%" mean "parts by mass" and "% by mass" unless otherwise specified.

[0057] (Synthesis example of copolymer represented by general formula (1)) <Preparation of compound α-1> A four-neck flask was equipped with a thermometer, a stirrer, and a reflux condenser. To a solution containing 500 g of water and 15 g of ammonium persulfate, 100 g of styrene, 40 g of itaconic acid, 158 g of methyl methacrylate, and 41 g of isobutyl acrylate were slowly added dropwise as monomers under heating conditions of 80 to 90°C while stirring. The mixture was then allowed to react for 4 hours, cooled, and neutralized with NaOH. Further, distilled water was added to adjust the solid content to 20%, to obtain an aqueous solution of the Na salt of styrene-itaconic acid-methyl methacrylate-isobutyl acrylate copolymer (compound α-1).

[0058] <Preparation of Compounds α-2 to α-3, and β-1 to β-2> Compound α-1 was synthesized in the same manner as compound α-1 so as to have the monomer ratio and carbon number shown in Table 1 below, and an aqueous solution of the Na salt of the compound was obtained.

[0059] <Synthesis of compound β-3> A reaction vessel equipped with a stirrer, thermometer, and reflux condenser was charged with 500 g of propylene glycol monomethyl ether acetate, and the internal temperature was raised to 135°C while stirring. 120 g of acrylic acid as an unsaturated carboxylic acid, 480 g of styrene as a monomer copolymerizable with unsaturated carboxylic acids, and 8 g of di-t-butyl peroxide were then charged over 4 hours. After charging was completed, the internal temperature was maintained at 145°C for 1 hour, after which the unreacted unsaturated carboxylic acids, unsaturated carboxylic acid copolymerizable monomers, and solvent were removed from the system to obtain copolymer S-1. Next, 50 g of acrylic acid, 350 g of methyl methacrylate instead of styrene, and 225 g of n-butyl acrylate were added in the same manner as in the copolymer S-1, to obtain copolymer S-2. Next, copolymers S-1 and S-2 were mixed in a mass ratio of 2:1 and neutralized with 2-dimethylaminoethanol. Distilled water was added to adjust the solid content to 20%, and an aqueous solution of a styrene-acrylic acid copolymer and a salt of an acrylic acid-methyl methacrylate-n-butyl acrylate copolymer with dimethylethanolamine (compound β-3) was obtained.

[0060] The synthesis recipe for the copolymer represented by the above general formula (1) is shown in Table 1 below. In Table 1, k, l, and m represent the monomer ratios of the respective structural units of general formula (1), and m1 and m2 represent the breakdown ratios of the monomers corresponding to m in general formula (1). In the "Structure" column, "St-It" indicates that the copolymer is a styrene-itaconic acid copolymer, and "St-Ac" indicates that the copolymer is a styrene-acrylic copolymer.

[0061] [Table 1]

[0062] Example 1 <Preparation of Pigment Dispersion 1> The materials in the following formulation were premixed and then dispersed in a centrifugal separator type bead mill (MSC100 circulation type manufactured by Nippon Coke Engineering Co., Ltd.) using 0.05 mm zirconia beads at a peripheral speed of 15 m / s, a liquid temperature of 7°C, and a residence time of 4 minutes to obtain Pigment Dispersion 1. This formulation was set so that the mass ratio of the pigment to the solid content of Compound α-1 was 80 / 20. (Prescription) Carbon black: 16.84 parts (Asahi Carbon Co., Ltd.: SunBlack805) Aqueous solution of compound α-1 (solid content 20%): 21.05 parts 2-Ethyl-1,3-hexanediol: 2.0 parts Distilled water: 60.06 parts Antifungal agent 0.05 parts

[0063] <Preparation of Ink 1> The materials in the following formulation were stirred for 15 minutes and filtered through a 1.2 μm filter to obtain [Ink 1] for inkjet recording. (Prescription) Pigment Dispersion 1: 35.84 parts Propylene glycol: 23.80 parts 1,3-butanediol: 4.76 parts 2-Ethyl-1,3-hexanediol: 1.28 parts Glycerin: 9.11 parts Fluorosurfactant: 0.02 parts Antifoaming agent: 0.08 parts Rust inhibitor: 0.05 parts pH adjuster: 0.40 parts Antifungal agent: 0.05 parts Distilled water: 24.61 parts

[0064] Example 2 <Preparation of Pigment Dispersion 2> The materials in the following formulation were premixed and then dispersed in a centrifugal bead mill (Nippon Coke Engineering Co., Ltd., MSC100 circulation type) using 0.05 mm zirconia beads at a peripheral speed of 15 m / s, a liquid temperature of 7°C, and a residence time of 4 minutes to obtain pigment dispersion 2. This formulation was set so that the mass ratio of the pigment to the solid content of compound α-2 was 90 / 10. (Prescription) Carbon black: 16.84 parts (Asahi Carbon Co., Ltd.: SB805) Aqueous solution of compound α-2 (solid content 20%): 9.36 parts 2-Ethyl-1,3-hexanediol: 2.0 parts Antifungal agent: 0.05 parts Distilled water: 71.75 parts

[0065] An inkjet recording ink 2 was obtained using the same formulation and method as in Example 1, except that Pigment Dispersion 1 in Example 1 was changed to Pigment Dispersion 2.

[0066] Example 3 <Preparation of Pigment Dispersion 3> The materials in the following formulation were premixed and then dispersed in a disk-type bead mill (HFM02 batch type, manufactured by Ashizawa Finetech Co., Ltd.) using 0.05 mm zirconia beads at a peripheral speed of 12 m / s and a liquid temperature of 10°C for 5 minutes to obtain pigment dispersion 3. This formulation was set so that the mass ratio of the pigment to the solid content of compound α-1 was 77 / 23. (Prescription) Yellow pigment: 15.00 parts (Synthesia 5GXS (Pigment Yellow 74)) Aqueous solution of compound α-1 (solid content 20%): 22.50 parts 1,3-butanediol: 2.0 parts Distilled water: 60.45 parts Antifungal agent: 0.05 parts

[0067] <Ink preparation> The materials in the following formulation were stirred for 15 minutes and filtered through a 1.2 μm filter to obtain [Ink 3] for inkjet recording. (Prescription) Pigment Dispersion 3: 36.52 parts Propylene glycol: 33.75 parts 1,3-butanediol: 6.02 parts 2-Ethyl-1,3-hexanediol: 2.00 parts Glycerin: 3.57 parts Fluorosurfactant: 0.04 parts Antifoaming agent: 0.16 parts pH adjuster: 0.10 parts Antifungal agent: 0.05 parts 17.79 parts distilled water

[0068] Example 4 <Preparation of Pigment Dispersion 4> The materials in the following formulation were premixed and then dispersed in a disk-type bead mill (HFM02 batch type, manufactured by Ashizawa Finetech Co., Ltd.) using 0.05 mm zirconia beads at a peripheral speed of 12 m / s and a liquid temperature of 10°C for 5 minutes to obtain pigment dispersion 4. This formulation was set so that the mass ratio of pigment to compound α-1 was 70 / 30. (Prescription) Yellow pigment: 15.00 parts (Synthesia 5GXS (Pigment Yellow 74)) Aqueous solution of compound α-1 (solid content 20%): 32.14 parts 1,3-butanediol: 2.00 parts Antifungal agent: 0.05 parts Distilled water: 50.81 parts

[0069] <Ink preparation> Ink 4 for inkjet recording was obtained using the same formulation and method as in Example 3, except that Pigment Dispersion 3 in the formulation of the ink in Example 3 was changed to Pigment Dispersion 4.

[0070] Example 5 <Preparation of Pigment Dispersion 5> The materials in the following formulation were premixed and then dispersed in a centrifugal bead mill (Nippon Coke Engineering Co., Ltd., MSC100 circulation type) using 0.1 mm zirconia beads at a peripheral speed of 13 m / s, a liquid temperature of 7°C, and a residence time of 6 minutes to obtain Pigment Dispersion 5. This formulation was set so that the mass ratio of the pigment to the solid content of Compound α-2 was 72 / 28. (Prescription) Cyan pigment: 18.00 parts (DIC Corporation TGR-SD (Pigment Blue 15:3)) Aqueous solution of compound α-2 (solid content 20%): 33.75 parts 1,3-butanediol: 19.2 parts Antifungal agent: 0.05 parts Distilled water: 29.00 parts

[0071] <Ink preparation> The materials in the following formulation were stirred for 15 minutes and filtered through a 1.2 μm filter to obtain [Ink 5] for inkjet recording. (Prescription) Pigment Dispersion 5: 27.78 parts Propylene glycol: 27.92 parts 1,3-butanediol: 0.25 parts 2-Ethyl-1,3-hexanediol: 2.00 parts Glycerin: 4.17 parts Fluorosurfactant: 0.03 parts Antifoaming agent: 0.12 parts pH adjuster: 0.50 parts Antifungal agent: 0.05 parts Distilled water: 37.18 parts

[0072] Example 6 <Preparation of Pigment Dispersion 6> The materials in the following formulation were premixed and then dispersed in a disk-type bead mill (HFM02 batch type, manufactured by Ashizawa Finetech Co., Ltd.) using 0.05 mm zirconia beads at a peripheral speed of 8 m / s and a liquid temperature of 10°C for 15 minutes to obtain pigment dispersion 6. This formulation was set so that the mass ratio of pigment to compound α-1 was 70 / 30. Cyan pigment: 15.00 parts (DIC Corporation 5452K (Pigment Blue 15:4)) Aqueous solution of compound α-1 (solid content 20%): 33.75 parts 1,3-butanediol: 8.00 parts Antifungal agent: 0.05 parts Distilled water: 43.20 parts

[0073] <Preparation of Ink 6> The materials in the following formulation were stirred for 15 minutes and filtered through a 1.2 μm filter to obtain [Ink 6] for inkjet recording. (Prescription) Pigment Dispersion 6: 33.78 parts Propylene glycol: 27.92 parts 1,3-butanediol: 2.88 parts 2-Ethyl-1,3-hexanediol: 2.00 parts Glycerin: 4.17 parts Fluorosurfactant: 0.03 parts Antifoaming agent: 0.12 parts pH adjuster: 0.50 parts Antifungal agent: 0.05 parts Distilled water: 28.55 parts

[0074] Example 7 <Preparation of Pigment Dispersion 7> The materials in the following formulation were premixed and then dispersed in a centrifugal separator type bead mill (MSC100 circulation type manufactured by Nippon Coke Engineering Co., Ltd.) using 0.05 mm zirconia beads at a peripheral speed of 13 m / s, a liquid temperature of 7°C, and a residence time of 10 minutes, to obtain Pigment Dispersion 7. This formulation was determined so that the mass ratio of the pigment to the solid content of compound α-3 was 83 / 17. (Prescription) Magenta pigment: 20.00 parts (Honor Chemical China HP RED 2574 (Pigment Red 122)) Aqueous solution of compound α-3 (solid content 20%): 20.00 parts 2-Ethyl-1,3-hexanediol: 2.00 parts Antifungal agent: 0.05 parts Distilled water: 57.95 parts

[0075] <Preparation of Ink 7> The materials in the following formulation were stirred for 15 minutes and filtered through a 1.2 μm filter to obtain [Ink 7] for inkjet recording. (Prescription) Pigment Dispersion 7: 35.00 parts Propylene glycol: 37.28 parts 2-Ethyl-1,3-hexanediol: 1.30 parts Glycerin: 4.67 parts Fluorosurfactant: 0.03 parts Antifoaming agent: 0.12 parts pH adjuster: 0.10 parts Antifungal agent: 0.05 parts Distilled water: 21.45 parts

[0076] Example 8 <Preparation of Pigment Dispersion 8> The materials in the following formulation were premixed and then dispersed in a disk-type bead mill (HFM02 batch type, manufactured by Ashizawa Finetech Co., Ltd.) using 0.05 mm zirconia beads at a peripheral speed of 6 m / s and a liquid temperature of 10°C for 7 minutes to obtain pigment dispersion 8. This formulation was determined so that the mass ratio of the pigment to compound α-1 was 87 / 13. Magenta pigment: 15.00 parts (Honor Chemical China HP RED 2574 (Pigment Red 122)) Aqueous solution of compound α-1 (solid content 20%): 11.25 parts Propylene glycol: 12.00 parts Antifungal agent 0.05 parts Distilled water: 61.70 parts

[0077] <Preparation of Ink 8> The materials in the following formulation were stirred for 15 minutes and filtered through a 1.2 μm filter to obtain [Ink 8] for inkjet recording. (Prescription) Pigment Dispersion 8: 46.67 parts Propylene glycol: 30.90 parts 2-Ethyl-1,3-hexanediol: 2.00 parts Glycerin: 4.67 parts Fluorosurfactant: 0.03 parts Antifoaming agent: 0.12 parts pH adjuster: 0.10 parts Antifungal agent: 0.05 parts Distilled water: 15.46 parts

[0078] Example 9 <Preparation of Pigment Dispersion 9> The materials in the following formulation were premixed and then dispersed in a centrifugal separator type bead mill (MSC100 circulation type manufactured by Nippon Coke Engineering Co., Ltd.) using 0.05 mm zirconia beads at a peripheral speed of 15 m / s, a liquid temperature of 7°C, and a residence time of 4 minutes, to obtain Pigment Dispersion 9. This formulation was determined so that the mass ratio of the pigment to the solid content of compound α-2 was 95 / 5. (Prescription) Carbon black: 16.84 parts (Asahi Carbon Co., Ltd.: SunBlack805) Aqueous solution of compound α-2 (solid content 20%): 21.05 parts 2-Ethyl-1,3-hexanediol: 2.0 parts Antifungal agent: 0.05 parts Distilled water: 60.06 parts

[0079] <Preparation of Ink 9> The materials in the following formulation were stirred for 15 minutes and filtered through a 1.2 μm filter to obtain [Ink 9] for inkjet recording. (Prescription) Pigment Dispersion 9: 35.84 parts Propylene glycol: 23.80 parts 1,3-butanediol: 4.76 parts 2-Ethyl-1,3-hexanediol: 1.28 parts Glycerin: 9.11 parts Fluorosurfactant: 0.02 parts Antifoaming agent: 0.08 parts Rust inhibitor: 0.05 parts pH adjuster: 0.40 parts Antifungal agent: 0.05 parts Distilled water: 24.61 parts

[0080] (Comparative Example 1) <Preparation of Pigment Dispersion 10> The materials in the following formulation were premixed and then dispersed in a disk-type bead mill (HFM02 batch type, manufactured by Ashizawa Finetech Co., Ltd.) using 0.05 mm zirconia beads at a peripheral speed of 15 m / s and a liquid temperature of 10°C for 4 minutes to obtain pigment dispersion 10. This formulation was determined so that the mass ratio of the pigment to the solid content of compound β-3 was 80 / 20. (Prescription) Carbon black: 16.84 parts (SunBlack805 manufactured by Asahi Carbon Co., Ltd.) Aqueous solution of compound β-3 (solid content 20%): 21.04 parts Antifungal agent: 0.05 parts Distilled water: 62.07 parts

[0081] <Preparation of Ink 10> The materials in the following formulation were stirred for 15 minutes and filtered through a 1.2 μm filter to obtain [Ink 10] for inkjet recording. (Prescription) Pigment Dispersion 10: 35.84 parts Propylene glycol: 23.80 parts 1,3-butanediol: 4.76 parts 2-Ethyl-1,3-hexanediol: 2.00 parts Glycerin: 9.11 parts Fluorosurfactant: 0.02 parts Antifoaming agent: 0.08 parts Rust inhibitor: 0.05 parts pH adjuster: 0.40 parts Antifungal agent: 0.05 parts Distilled water: 23.89 parts

[0082] (Comparative Example 2) <Preparation of Pigment Dispersion 11> The materials in the following formulation were premixed, and then dispersed in a disk-type bead mill (HFM02 batch type, manufactured by Ashizawa Finetech Co., Ltd.) using 0.05 mm zirconia beads at a peripheral speed of 12 m / s and a liquid temperature of 10°C for 3 minutes to obtain pigment dispersion 11. This formulation was determined so that the mass ratio of the pigment to the solid content of compound β-3 was 77 / 23. (Prescription) Yellow pigment: 15.00 parts (Clariant Hansa Yellow 5GX01 (Pigment Yellow 74)) Aqueous solution of compound β-3 (solid content 20%): 22.50 parts Antifungal agent: 0.05 parts Distilled water: 62.45 parts

[0083] <Preparation of Ink 11> The materials in the following formulation were stirred for 15 minutes and filtered through a 1.2 μm filter to obtain [Ink 11] for inkjet recording. (Prescription) Pigment Dispersion 11: 34.25 parts Propylene glycol: 33.75 parts 1,3-butanediol: 6.75 parts 2-Ethyl-1,3-hexanediol: 2.00 parts 3.57 parts glycerin Fluorosurfactant: 0.04 parts Antifoaming agent: 0.16 parts pH adjuster: 0.10 parts Antifungal agent: 0.05 parts Distilled water: 19.33 parts

[0084] (Comparative Example 3) <Preparation of Pigment Dispersion 12> The materials in the following formulation were premixed and then dispersed in a disk-type bead mill (HFM02 batch type, manufactured by Ashizawa Finetech Co., Ltd.) using 0.05 mm zirconia beads at a peripheral speed of 8 m / s and a liquid temperature of 10°C for 15 minutes to obtain pigment dispersion 12. This formulation was determined so that the mass ratio of pigment to compound β-3 was 72 / 28. Cyan pigment: 15.00 parts (DIC Corporation 5452K (Pigment Blue 15:4)) Aqueous solution of compound β-3 (solid content 20%): 33.75 parts 1,3-butanediol: 8.00 parts Antifungal agent: 0.05 parts Distilled water: 43.20 parts

[0085] <Preparation of Ink 12> The materials in the following formulation were stirred for 15 minutes and filtered through a 1.2 μm filter to obtain [Ink 12] for inkjet recording. (Prescription) Pigment Dispersion 12: 35.06 parts Propylene glycol: 27.92 parts 1,3-butanediol: 2.78 parts 2-Ethyl-1,3-hexanediol: 2.00 parts Glycerin: 4.17 parts Fluorosurfactant: 0.03 parts Antifoaming agent: 0.12 parts pH adjuster: 0.50 parts Antifungal agent: 0.05 parts Distilled water: 27.37 parts

[0086] Comparative Example 4 <Preparation of Pigment Dispersion 13> The materials in the following formulation were premixed and then dispersed in a centrifugal bead mill (MSC100 circulation type manufactured by Nippon Coke Engineering Co., Ltd.) using 0.05 mm zirconia beads at a peripheral speed of 8 m / s, a liquid temperature of 7°C, and a residence time of 13.5 minutes to obtain pigment dispersion 13. This formulation was determined so that the mass ratio of the pigment to the solid content of compound β-3 was 83 / 17. (Prescription) Magenta pigment: 15.00 parts (DIC Corporation JM04 (Pigment Red 122 / Pigment Violet 19)) Aqueous solution of compound β-3 (20% solids): 15.00 parts Propylene glycol: 12.00 parts Antifungal agent: 0.05 parts Distilled water: 57.95 parts

[0087] <Preparation of Ink 13> The materials in the following formulation were stirred for 15 minutes and filtered through a 1.2 μm filter to obtain [Ink 13] for inkjet recording. (Prescription) Pigment Dispersion 13: 46.67 parts Propylene glycol: 30.90 parts 2-Ethyl-1,3-hexanediol: 2.00 parts Glycerin: 4.67 parts Fluorosurfactant: 0.03 parts Antifoaming agent: 0.12 parts pH adjuster: 0.10 parts Antifungal agent: 0.05 parts Distilled water: 15.46 parts

[0088] (Comparative Example 5) <Preparation of Pigment Dispersion 14> The materials in the following formulation were premixed and then dispersed in a disk-type bead mill (HFM02 batch type manufactured by Ashizawa Finetech Co., Ltd.) using 0.05 mm zirconia beads at a peripheral speed of 15 m / s and a liquid temperature of 10°C for 4 minutes to obtain pigment dispersion 14. This formulation was determined so that the mass ratio of the pigment to the solid content of compound β-1 was 80 / 20. (Prescription) Carbon black: 16.84 parts (SunBlack805 manufactured by Asahi Carbon Co., Ltd.) Aqueous solution of compound β-1 (solid content 20%): 21.04 parts Antifungal agent: 0.05 parts Distilled water: 62.07 parts

[0089] <Preparation of Ink 14> The materials in the following formulation were stirred for 15 minutes and filtered through a 1.2 μm filter to obtain [Ink 14] for inkjet recording. (Prescription) Pigment Dispersion 14: 35.84 parts Propylene glycol: 23.80 parts 1,3-butanediol: 4.76 parts 2-Ethyl-1,3-hexanediol: 2.00 parts Glycerin: 9.11 parts Fluorosurfactant: 0.02 parts Antifoaming agent: 0.08 parts Rust inhibitor: 0.05 parts pH adjuster: 0.40 parts Antifungal agent: 0.05 parts Distilled water: 23.89 parts

[0090] (Comparative Example 6) <Preparation of Pigment Dispersion 15> The materials in the following formulation were premixed and then dispersed in a disk-type bead mill (HFM02 batch type, manufactured by Ashizawa Finetech Co., Ltd.) using 0.05 mm zirconia beads at a peripheral speed of 8 m / s and a liquid temperature of 10°C for 15 minutes to obtain Pigment Dispersion 15. This formulation was determined so that the mass ratio of pigment to compound β-2 was 72 / 28. Cyan pigment: 15.00 parts (DIC Corporation TGR-SD (Pigment Blue 15:3)) Aqueous solution of compound β-2 (solid content 20%): 33.75 parts 1,3-butanediol: 8.00 parts Antifungal agent: 0.05 parts Distilled water: 43.20 parts

[0091] <Preparation of Ink 15> The materials in the following formulation were stirred for 15 minutes and filtered through a 1.2 μm filter to obtain [Ink 15] for inkjet recording. (Prescription) Pigment Dispersion 15: 35.06 parts Propylene glycol: 27.92 parts 1,3-butanediol: 2.78 parts 2-Ethyl-1,3-hexanediol: 2.00 parts Glycerin: 4.17 parts Fluorosurfactant: 0.03 parts Antifoaming agent: 0.12 parts pH adjuster: 0.50 parts Antifungal agent: 0.05 parts Distilled water: 27.37 parts

[0092] Examples 1 to 9 and Comparative Examples 1 to 6 are summarized in Table 2 below. The abbreviations for pigments in Table 2 refer to the following pigments. CB: Carbon black PY-74: Pigment Yellow 74 PB15:3: Pigment Blue 15:3 PB15:4: Pigment Blue 15:4 PR122: Pigment Red 122 PV19: Pigment Violet 19

[0093] [Table 2]

[0094] (Evaluation method, evaluation results) The evaluation items and evaluation methods for the dispersions and recording inks prepared in the examples and comparative examples are described below.

[0095] (1) Storage stability After measuring the initial viscosity of the ink, 10 g of the ink was sealed in a 13.5 ml screw cap bottle manufactured by AS ONE Corporation and stored in an environment of 70°C for 2 weeks. After this storage, the viscosity of the ink was measured, and the rate of change was calculated and ranked according to the following formula. The viscometer used was a TV-25 manufactured by Toki Sangyo Co., Ltd. A and B are within the acceptable range. Change rate (%) = [(viscosity after 2 weeks at 70°C - initial viscosity) / initial viscosity] x 100 [Evaluation criteria] A: Change rate is less than 5% (good) B: Change rate is 5% or more and less than 10% (level that does not cause any problems in practical use) C: The rate of change is between 10% and 20% (problematic level). D: Change rate is 20% or more (problematic level)

[0096] (2) Image density evaluation The black inks for inkjet recording in the examples and comparative examples were filled into a Ricoh IPSiO GX e5500 inkjet printer with the structure shown in Figures 1 and 2, and a solid image was printed in one pass. Printing evaluation was performed using the following evaluation paper, and after printing and drying, the brightness was measured with a reflective color spectrodensitometer, X-Rite 939 (manufactured by X-Rite). A and B are within the acceptable range. [Evaluation paper] Plain paper (1): My Paper (A4, manufactured by NBS Ricoh Co., Ltd.) Plain paper (2): Fore Multi-Purpuse (HAMMERMILL) Coated paper: OKTC+127.9gsm A4 T-size (Oji Paper Co., Ltd.) [Evaluation criteria] -Plain paper (1), (2)- A: Image density 1.10 or more B: Image density 1.00 or more and less than 1.10 C: Image density less than 1.00 -Coated paper- A: Image density 2.20 or higher B: Image density 1.70 or more and less than 2.20 C: Image density less than 1.70

[0097] (3) Saturation evaluation Of the inkjet recording inks in the Examples and Comparative Examples, yellow, cyan, and magenta were filled into a Ricoh inkjet printer IPSiO GX e5500 having the structure shown in Figures 1 and 2, and a solid image was printed in one pass. For print evaluation, the following evaluation paper was used, and after printing and drying, the brightness was measured with a reflective color spectrodensitometer X-Rite 939 (manufactured by X-Rite). The obtained a * , b * From the value of saturation C * =((a * ) 2 +(b * ) 2 ) 1 / 2 was calculated and evaluated according to the following evaluation criteria. Ranks A and B are within the acceptable range. [Evaluation paper] Plain paper (1): My Paper (A4, manufactured by NBS Ricoh Co., Ltd.) Plain paper (2): Fore Multi-Purpuse (HAMMERMILL) Coated paper: OKTC+127.9gsm A4 T-size (Oji Paper Co., Ltd.)

[0098] [Evaluation criteria] <Yellow> -Plain paper (1)(2)- A:C * ≧80 B:80>C * ≧75 C:75>C * -Coated paper- A:C*≧95 B:95>C* ≧90 C:90>C * <cyan> -Plain paper (1)(2)- A:C * ≧45 B:45>C * ≧40 C:40>C * -Coated paper- A:C * ≧65 B:65>C * ≧60 C:60>C * <Magenta> -Plain paper (1)(2)- A:C * ≧70 B:70>C * ≧65 C:65>C * -Coated paper- A:C*≧80 B:80>C * ≧75 C:75>C *

[0099] The evaluation results of the inks of the examples and comparative examples are shown in Table 3 below.

[0100] [Table 3]

[0101] From Table 3, it can be seen that Examples 1 to 9 are superior to Comparative Examples 1 to 6. Use of the copolymer represented by the general formula (1) above improves the storage stability of the pigment ink, and provides a pigment dispersion that exhibits excellent image density and saturation when printed, as well as a water-based ink containing the pigment aqueous dispersion. Furthermore, depending on the mass ratio of the pigment to the compound, a pigment dispersion having superior storage stability, image density, and saturation, and a water-based ink containing the pigment water dispersion are provided.

[0102] The present invention relates to the ink of (1) below, but also includes the following (2) to (11) as embodiments. (1) An ink containing a pigment, a polymer compound, and water, wherein the polymer compound is a copolymer represented by the following general formula (1): [ka] (wherein R1 is a hydrogen atom or a methyl group, R2 is an alkyl group having 1 to 18 carbon atoms and an ester bond, and the molar ratio of k:l:m is 20-30:10-20:55-65) (2) The ink according to (1) above, wherein the mass ratio of the pigment to the copolymer represented by general formula (1) is 90 / 10 to 70 / 30. (3) The ink according to (1) or (2) above, wherein the mass ratio of the pigment to the copolymer represented by the general formula (1) is 83 / 17 to 72 / 28. (4) The ink according to any one of (1) to (3) above, wherein the pigment is carbon black. (5) The ink according to any one of (1) to (3) above, wherein the pigment is CI Pigment Yellow 74 represented by the following structural formula (1): [ka] (6) The ink according to any one of (1) to (3) above, wherein the pigment is CI Pigment Blue 15:3 or 15:4 represented by the following structural formula (2): [ka] (7) The ink according to any one of (1) to (3) above, wherein the pigment is CI Pigment Red 122 represented by the following structural formula (3): [ka] (8) The ink according to any one of (1) to (3) above, wherein the pigment is CI Pigment Violet 19 represented by the following structural formula (4): [ka] (9) An ink cartridge comprising a container containing the ink according to any one of (1) to (8) above. (10) An inkjet recording apparatus comprising the ink cartridge according to (9) above and a discharge means for discharging ink supplied from the ink cartridge. (11) A recording method comprising recording on a recording medium using the ink according to any one of (1) to (8) above. [Explanation of symbols]

[0103] 1. Inkjet recording device 2 Main unit housing 7 Treatment liquid and ink common cartridge 16 Gear mechanism 17 Sub-scanning motor 18 Carriage 18a Recording head 19 Platen 20 ink cartridges 21 Guide shaft 22 Guide shaft 23 Timing belt 24 Main scanning motor 25 Gear mechanism 26 Main scanning motor 27 Gear mechanism 41 Cartridge housing 42 Liquid absorber 43 cases 44 Top cover member 45 Liquid supply port 46 Seal ring 47 Atmospheric release port 48 Groove 50 Cap member 51 Leak prevention protrusion 53 Cap member 55 Sealing material 71 Cartridge positioning part 81 Cartridge attachment / detachment protrusion 81a Finger hook for cartridge installation / removal 82 Cartridge insertion / removal recess A Space [Prior art documents] [Patent documents]

[0104] [Patent Document 1] Japanese Patent Application Publication No. 2019-019293 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-241307

Claims

1. An ink comprising a pigment, a polymer compound, and water, wherein the polymer compound is a copolymer represented by the following general formula (1): 【Chemistry 1】 (wherein R1 is a hydrogen atom or a methyl group, R2 is an alkyl group having 1 to 18 carbon atoms and an ester bond, and the molar ratio of k:l:m is 20-30:10-20:55-65)

2. 2. The ink according to claim 1, wherein the mass ratio of the pigment to the copolymer represented by general formula (1) is 90 / 10 to 70 / 30.

3. 3. The ink according to claim 1, wherein the mass ratio of the pigment to the copolymer represented by general formula (1) is 83 / 17 to 72 / 28.

4. The ink according to any one of claims 1 to 3, wherein the pigment is carbon black.

5. The ink according to any one of claims 1 to 3, wherein the pigment is C. I. Pigment Yellow 74 represented by the following structural formula (1): 【Chemistry 2】

6. The ink according to any one of claims 1 to 3, wherein the pigment is C.I. Pigment Blue 15:3 or 15:4 represented by the following structural formula (2): 【Transformation 3】

7. The ink according to any one of claims 1 to 3, wherein the pigment is C. I. Pigment Red 122 represented by the following structural formula (3): 【Chemistry 4】

8. An ink cartridge comprising a container containing the ink according to any one of claims 1 to 7.

9. 9. An ink jet recording apparatus comprising: the ink cartridge according to claim 8; and a discharge means for discharging ink supplied from the ink cartridge.

10. A recording method comprising recording on a recording medium using the ink according to any one of claims 1 to 7.

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