Aqueous inks, ink cartridges, and inkjet recording method

Abstract

To provide aqueous inks with excellent ejection stability which enable recording of images excellent in abrasion resistance, and also to provide ink cartridges and an inkjet recording method that use the aqueous inks.SOLUTION: Provided are aqueous inks for inkjet recording containing pigments, resin particles formed of polyester resin or urethane resin, and an organic solvent. The organic solvent includes carbonate compounds and the like. Also provided are the ink cartridges including ink containers for containing the aqueous inks, and the inkjet recording method recording images on a recording medium by ejecting the aqueous inks from an inkjet recording head.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In inkjet recording methods, pigment inks containing pigments as colorants are increasingly being used from the perspective of image robustness. However, images recorded using pigment inks have the problem of low scratch resistance because the colorants are particles. As for the recording media on which images are recorded using inkjet recording methods, in addition to conventional recording media with good ink absorption such as general-purpose plain paper and inkjet paper, recording media with poor ink absorption such as coated paper for printing are also being used. Recording media with poor ink absorption tend to have low image scratch resistance, so there is a need to improve scratch resistance regardless of the ink absorption of the recording media.

[0003] Studies have been conducted to improve the fixation and scratch resistance of images recorded with pigment inks. For example, an image forming method has been proposed in which an image recorded with an ink containing a resin component is coated with a liquid containing a solvent that dissolves or softens the resin component (Patent Document 1). In addition, an ink has been proposed that contains a colorant and a urethane resin in a predetermined ratio, thereby allowing the colorant of an image formed on a recording medium to be covered to some extent with the urethane resin (Patent Document 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2008-183843 [Patent Document 2] Japanese Patent Publication No. 2018-058972 [Overview of the project] [Problems that the invention aims to solve]

[0005] When using coating liquids proposed in Patent Document 1, etc., it is necessary to provide a means for applying the coating liquid to the recording medium. Furthermore, while the ink proposed in Patent Document 2 can achieve a certain degree of image scratch resistance, ejection stability tends to be impaired when recording large-sized images or recording images continuously. Therefore, the present inventors investigated how to stably record images with an even higher level of scratch resistance by devising the ink composition without using coating liquids or the like.

[0006] Therefore, an object of the present invention is to provide an aqueous ink with excellent ejection stability that can record images with excellent scratch resistance. Another object of the present invention is to provide an ink cartridge using this aqueous ink and an inkjet recording method. [Means for solving the problem]

[0007] In other words, the present invention provides an aqueous ink for inkjet use containing a pigment, resin particles, and an organic solvent, wherein the resin particles are first resin particles formed of polyester resin, and the organic solvent is at least one selected from the group consisting of a compound represented by the following general formula (1), a compound represented by the following general formula (2), and a compound represented by the following general formula (3).

[0008] TIFF2022165911000001.tif33170(In general formula (1), R1 and R2 each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms. In general formula (2), R3 represents an ethylene group or a propylene group, R4 represents a methyl group or an ethyl group, n represents 0 or 1, and when R3 is an ethylene group, n is 1. In general formula (3), R5 and R6 each independently represent a linear or branched alkyl group having 1 to 4 carbon atoms, and R7 represents an alkylene group having 1 to 4 carbon atoms)

[0009] Furthermore, the present invention provides an aqueous ink for inkjet use containing a pigment, resin particles, and an organic solvent, wherein the resin particles are second resin particles formed of urethane resin, and the organic solvent is at least one selected from the group consisting of compounds represented by the following general formula (1) and compounds represented by the following general formula (2).

[0010] TIFF2022165911000002.tif32170(In the above general formula (1), R1 and R2 each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms. In the above general formula (2), R3 represents an ethylene group or a propylene group, R4 represents a methyl group or an ethyl group, n represents 0 or 1, and when R3 is an ethylene group, n is 1) [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an aqueous ink with excellent ejection stability that can record images with excellent scratch resistance. Furthermore, according to the present invention, it is possible to provide an ink cartridge using this aqueous ink and an inkjet recording method. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. [Figure 2] This figure schematically shows an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. [Modes for carrying out the invention]

[0013] Hereinafter, the present invention will be described in more detail by giving preferred embodiments. In the present invention, when the compound is a salt, although the salt dissociates into ions in the ink, for convenience, it is expressed as "containing a salt". Also, the aqueous ink for inkjet may be simply described as "ink". Physical property values are values at normal temperature (25 °C), normal pressure (1 atm = 101,325 Pa), and normal humidity (relative humidity 50%) unless otherwise specified. "Unit" means a unit structure corresponding to one monomer unless otherwise specified. When "(meth)acrylic acid" and "(meth)acrylate" are described, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate", respectively.

[0014] The present inventors have studied the composition of an ink for achieving high-level compatibility between the rub resistance of an image recorded with a pigment ink and the ejection stability of the ink. As a result, it has been found that these properties can be made compatible by a combination of specific resin particles and an organic solvent shown below, leading to the present invention. · First resin particles formed of a polyester resin and at least one organic solvent selected from the group consisting of a compound represented by general formula (1), a compound represented by general formula (2), and a compound represented by general formula (3) (First Embodiment) · Second resin particles formed of urethane resin particles and at least one organic solvent selected from the group consisting of a compound represented by general formula (1) and a compound represented by general formula (2) (Second Embodiment)

[0015] TIFF2022165911000003.tif33170 (In general formula (1), R1 and R2 each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms. In general formula (2), R3 represents an ethylene group or a propylene group, R4 represents a methyl group or an ethyl group, n represents 0 or 1, and when R3 is an ethylene group, n is 1. In general formula (3), R5 and R6 each independently represent a linear or branched alkyl group having 1 to 4 carbon atoms, and R7 represents an alkylene group having 1 to 4 carbon atoms)

[0016] The compound represented by the general formula (1) is a chain carbonate compound. The compound represented by the general formula (2) is a cyclic carbonate compound. Further, the compound represented by the general formula (3) is a dioxolane compound. All of these compounds have a relatively high hydrophobicity among the organic solvents used in aqueous inks for inkjet, and in addition, there are a plurality of oxygen atoms in their skeletons. Therefore, these organic solvents are likely to specifically interact with the ester bond (-COO-) of the polyester resin forming the resin particles and the urethane bond (-NH-COO-) of the urethane resin forming the resin particles.

[0017] In both the first and second embodiments, it is considered that the following phenomena occur in the recording medium by combining the above organic solvents with a resin having a particle form (resin particles). When the ink is ejected from the recording head and applied to the recording medium, water decreases due to evaporation or penetration into the recording medium, and the concentration of a specific organic solvent becomes relatively high. Then, the above organic solvent approaches and interacts with the resin particles, softening the resin particles. The resin chains of the softened resin particles are in a state where the pigments are entangled and held, so that the pigments are fixed on the recording medium, and the scratch resistance of the image can be enhanced.

[0018] In a state where water has not decreased, the interaction between the resin particles and the organic solvent is weakly suppressed due to the presence of water. Therefore, even in a situation where ink is continuously ejected, the ejection stability can be improved. However, in the case of the second resin particles formed of a urethane resin, the interaction with the hydroxy group of the compound represented by the general formula (3) strongly occurs even in the ink, so the degree of ejection stability is inferior. Therefore, as the organic solvent to be combined with the second resin particles, at least one of the compound represented by the general formula (1) and the compound represented by the general formula (2) needs to be used.

[0019] <Aqueous ink> The ink of the present invention is an aqueous inkjet ink containing a pigment, resin particles, and an organic solvent. The ink of the first embodiment contains a pigment, first resin particles formed of polyester resin, and at least one organic solvent selected from the group consisting of compounds represented by general formula (1), compounds represented by general formula (2), and compounds represented by general formula (3). The ink of the second embodiment contains a pigment, second resin particles formed of urethane resin, and at least one organic solvent selected from the group consisting of compounds represented by general formula (1) and compounds represented by general formula (2). The ink of the present invention does not need to be used in applications where another liquid such as a coating liquid or clear ink is applied after it has been applied to a recording medium, or in applications where it is subjected to processing such as active energy rays or heating after it has been applied to a recording medium. The components constituting the ink will be described below.

[0020] (Pigment) Ink contains pigments. Examples of pigment dispersion methods include resin-dispersed pigments dispersed with a resin dispersant, pigments dispersed with a surfactant, and microcapsule pigments in which at least a portion of the surface of the pigment particles is coated with a resin or the like. Furthermore, self-dispersing pigments, in which functional groups including hydrophilic groups such as anionic groups are bonded to the surface of the pigment particles, and pigments in which organic groups containing polymers are chemically bonded to the surface of the pigment particles (resin-bonded self-dispersing pigments) can also be used. In addition, pigments with different dispersion methods may be used in combination.

[0021] Inorganic pigments and organic pigments can be used as pigments. Specific examples of pigments include inorganic pigments such as carbon black and titanium dioxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolon, diketopyrrolopyrrole, and dioxazine. The pigment content (mass%) in the ink is preferably 0.1% to 15.0% by mass, and more preferably 1.0% to 10.0% by mass, based on the total mass of the ink.

[0022] (Resin particles) The ink contains first resin particles formed from polyester resin, or second resin particles formed from urethane resin. The ink may also contain both the first and second resin particles. However, when using both the first and second resin particles, it is preferable to use at least one of the compounds represented by general formula (1) and general formula (2) as the organic solvent, rather than the compound represented by general formula (3). In this specification, the first and second resin particles may be collectively referred to as "resin particles" below. The resin particles exist in the ink in a dispersed state, i.e., in the form of a resin emulsion. Furthermore, it is preferable that the resin particles do not contain colorants. It is also not very preferable to use active energy ray curable resin particles, i.e., resin particles having polymerizable groups.

[0023] In this specification, "resin particles" means a resin present in a liquid medium in a state in which particles whose particle size can be measured are formed when the resin is neutralized with a base at a molar ratio of 1.0 times or more relative to its acid value. The particle size of the resin is measured by dynamic light scattering. On the other hand, in this specification, "water-soluble resin" means a resin present in a liquid medium in a state in which particles whose particle size cannot be measured are not formed when the resin is neutralized with a base at a molar ratio of 1.0 times or more relative to its acid value.

[0024] Whether a resin is a water-soluble resin or resin particles (water-dispersible resin) can be determined according to the following method. First, a liquid containing the resin (resin content: approximately 10% by mass) is prepared, neutralized with a base (such as sodium hydroxide or potassium hydroxide) in an amount equivalent to or greater than the acid value. Next, the prepared liquid is diluted with pure water to prepare a sample with a resin content of approximately 1% by mass. Then, the particle size of the resin in the sample is measured by dynamic light scattering. If no particles with a particle size are measured, the resin is determined to be a water-soluble resin; if particles with a particle size are measured, the resin is determined to be resin particles. The measurement conditions can be set, for example, as follows: SetZero: 30 seconds, Number of measurements: 3, Measurement time: 180 seconds. A particle size analyzer using dynamic light scattering (for example, UPA-EX150, manufactured by Nikkiso) can be used as the particle size distribution analyzer. Of course, the particle size distribution analyzer and measurement conditions used are not limited to those described above.

[0025] [Resin particle content] The resin particle content (mass%) in the ink is preferably 0.1% by mass or more and 20.0% by mass or less, based on the total mass of the ink. More preferably, it is 0.5% by mass or more and 10.0% by mass or less, and particularly preferably 0.5% by mass or more and 5.0% by mass or less. If the resin particle content in the ink is less than 0.5% by mass, there are few resin particles, and the effect of improving the scratch resistance of the image may not be sufficiently obtained. Also, if the resin particle content is too high, interaction with organic solvents is likely to occur even in the ink, and the effect of improving the ink discharge stability may not be sufficiently obtained. For this reason, the resin particle content is preferably 10.0% by mass or less, and more preferably 5.0% by mass or less.

[0026] [Particle size of resin particles] The cumulative 50% particle size (D) of resin particles based on volume. 50 ) is preferably 30 nm to 300 nm. D of resin particles 50If the diameter of the resin particles is less than 30 nm, the resin particles are more likely to get stuck in the gaps between the pigment particles in the ink-coated recording medium, which may reduce the effect of improving scratch resistance. On the other hand, if the diameter of the resin particles is less than 30 nm, 50 When the particle diameter exceeds 300 nm, the number of particles becomes relatively small when considering a certain amount of resin particles, and an uneven distribution of resin particles tends to occur in the ink-coated recording medium. For this reason, it may be difficult to uniformly improve scratch resistance across the entire image. The cumulative 50% particle diameter (D) is based on the volume of resin particles. 50 This can be measured by dynamic light scattering under the same conditions as the method for determining whether the resin is made up of resin particles, as described above.

[0027] [First resin particles formed from polyester resin] The ink of the first embodiment contains first resin particles formed of polyester resin. The proportion (by mass) of polyester resin in the resin forming the first resin particles is preferably 90.0% by mass or more, and may also be 100.0% by mass, based on the total mass of the resin particles. In other words, it is preferable that the first resin particles are substantially formed of polyester resin only. A commercially available resin may be used as the polyester resin (polyester resin particles).

[0028] Polyester resins typically contain units derived from polyhydric alcohols and units derived from polyhydric carboxylic acids. A structure containing an ester bond (-COO-) composed of units derived from polyhydric alcohols and units derived from polyhydric carboxylic acids is also referred to as an "ester unit."

[0029] [Polyhydric alcohols] Examples of polyhydric alcohols include dihydric to tetrahydric polyhydric alcohols. Examples of polyhydric alcohols include polyhydric alcohols having aliphatic groups, polyhydric alcohols having aromatic groups, and sugar alcohols. Examples of polyhydric alcohols include dihydric alcohols such as ethylene glycol [1,2-ethanediol], neopentyl glycol [2,2-dimethyl-1,3-propanediol], 1,3-propanediol, 1,4-butanediol, benzenediol, and 2,2-bis(4-hydroxyphenyl)propane [bisphenol A]; trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane; and tetrahydric alcohols such as pentaerythritol. Oligomers (low molecular weight polymers with a molecular weight of 1,000 or less) can also be used as polyhydric alcohols. The proportion (mass%) of units derived from polyhydric alcohols in the polyester resin forming the first resin particles is preferably 40.0% by mass or more and 60.0% by mass or less.

[0030] As the polyhydric alcohol, it is preferable to use a polyhydric alcohol having an aromatic group. Among these, bisphenol A is preferred. Alternatively, polyhydric alcohols having an aromatic group and polyhydric alcohols having an aliphatic group may be used in combination. As the polyhydric alcohol having an aliphatic group, polyhydric alcohols having a linear or branched aliphatic group having 1 to 6 carbon atoms are preferred. Among these, ethylene glycol and neopentyl glycol are preferred.

[0031] [Polyhydric carboxylic acid] Examples of polycarboxylic acids that constitute the units derived from polycarboxylic acids include divalent to tetravalent polycarboxylic acids. Examples of polycarboxylic acids include polycarboxylic acids having aliphatic groups; polycarboxylic acids having aromatic groups; nitrogen-containing polycarboxylic acids; and so on. Examples of polycarboxylic acids include divalent carboxylic acids such as glutaric acid, adipic acid, terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid; trivalent carboxylic acids such as trimellitic acid; and tetravalent carboxylic acids such as ethylenediaminetetraacetic acid. Oligomers (low molecular weight polymers with a molecular weight of 1,000 or less) can also be used as polycarboxylic acids. The proportion (mass%) of units derived from polycarboxylic acids in the polyester resin forming the first resin particles is preferably 40.0% by mass or more and 60.0% by mass or less.

[0032] As the polycarboxylic acid, it is preferable to use a polycarboxylic acid having an aromatic group. Among these, adipic acid, terephthalic acid, isophthalic acid, and trimellitic acid are preferred. Furthermore, it is preferable to use multiple types of other carboxylic acids. Specifically, it is preferable to use multiple types of dicarboxylic acids. Among these, terephthalic acid and isophthalic acid are preferred.

[0033] [Glass transition temperature of the first resin particle] The glass transition temperature of the first resin particles is preferably 50°C or higher, and more preferably 80°C or higher. The glass transition temperature is the temperature at which the resin particles begin to change from a glassy state to a viscous state, and is a physical property value that serves as an indicator of how easily the resin particles soften. The lower the glass transition temperature of the resin particles, the softer they tend to be at room temperature (around 25°C), and the softer they are, the easier they are to deform by external forces. If the glass transition temperature of the first resin particles is less than 50°C, the resin film formed by the first resin particles in a recording medium to which ink is applied is prone to softening, making it difficult to stably retain the pigment, and the effect of improving the scratch resistance of the image may not be sufficiently obtained. The glass transition temperature of the first resin particles is preferably 100°C or lower. The glass transition temperature of the resin particles can be measured using a thermal analyzer such as a differential scanning calorimeter (DSC).

[0034] [Method for manufacturing the first resin particles] The first resin particles can be produced, for example, by synthesizing a polyester resin and then atomizing it. The polyester resin can be obtained, for example, by reacting a polyhydric alcohol with a polyhydric carboxylic acid (esterification reaction). If necessary, a so-called transesterification reaction may be carried out by adding either the polyhydric alcohol or the polyhydric carboxylic acid to cleave part of the ester bond. It is preferable to carry out the transesterification reaction by adding a polyhydric carboxylic acid of 3 valency or higher (trimellitic acid is preferred among them). The synthesized polyester resin is preferably made into an appropriate form by pressurization, pulverization, etc., and then atomized by dispersion, phase inversion (emulsification), etc.

[0035] [Analysis of the first resin particle] The composition of the polyester resin constituting the first resin particles can be analyzed, for example, by the following method. First, a sample is prepared by dissolving the resin particles in an organic solvent such as tetrahydrofuran. By analyzing the prepared sample using analytical methods such as nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS), the types and proportions of units (monomers) constituting the polyester resin can be determined. In addition, the units (monomers) constituting the polyester resin can also be detected by analyzing the first resin particles with pyrolysis gas chromatography.

[0036] [Second resin particles formed from urethane resin] The ink of the second embodiment contains second resin particles formed of urethane resin. The proportion (by mass) of urethane resin in the resin forming the second resin particles is preferably 90.0% by mass or more, and may also be 100.0% by mass, based on the total mass of the resin particles. In other words, it is preferable that the second resin particles are substantially formed of urethane resin alone. A commercially available resin may be used as the urethane resin (urethane resin particles).

[0037] The urethane resins commonly used in water-based inkjet inks are synthesized using at least polyisocyanate and components that react with it (such as polyols and polyamines), with crosslinking agents and chain extenders used as needed.

[0038] [Polyisocyanate] In this invention, "polyisocyanate" means a compound having two or more isocyanate groups in its molecule. Examples of polyisocyanates include aliphatic and aromatic polyisocyanates. Examples of aliphatic polyisocyanates include polyisocyanates having a chain structure such as tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, and 2,2,4-trimethylhexamethylene diisocyanate; and polyisocyanates having a cyclic structure such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, and 1,4-cyclohexane diisocyanate. Examples of aromatic polyisocyanates include tolylene diisocyanate and xylylene diisocyanate. Among these, aliphatic polyisocyanates are preferred. The proportion (mol%) of units derived from polyisocyanate in the urethane resin forming the second resin particles is preferably 10.0 mol% or more and 80.0 mol% or less.

[0039] [Polyols, polyamines] Polyols and polyamines can be used as components that form units constituting the urethane resin through the reaction with the polyisocyanate described above. In this invention, "polyol" means a compound having two or more hydroxyl groups in its molecule. Examples of polyols include polyether polyols, polyester polyols, polycarbonate polyols, and other polyols without acid groups; polyols with acid groups; and so on. In this invention, "polyamine" means a compound having two or more "amino groups or imino groups" in its molecule. Preferably, the proportion (mol%) of units derived from polyols and polyamines in the urethane resin forming the second resin particles is 10.0 mol% or more and 80.0 mol% or less.

[0040] Examples of polyols without acid groups include the following: Polyether polyols include addition polymers of alkylene oxides and polyols; glycols such as (poly)alkylene glycols; etc. Polyester polyols include acid esters, etc. Polycarbonate polyols include alkanediol-based polycarbonate diols, etc. The number average molecular weight of polyols without acid groups is preferably 400 or more and 4,000 or less. Polyether polyols and polycarbonate polyols are preferred as polyols without acid groups, and polyether polyols are even more preferred. In addition, examples of polyols having acid groups include polyols having carboxylic acid groups such as dimethylolacetic acid, dimethylolpropionic acid, and dimethylolbutanoic acid.

[0041] Examples of polyamines include monoamines with multiple hydroxyl groups, such as dimethylolethylamine; bifunctional polyamines, such as ethylenediamine, isophoronediamine, and xylylenediamine; and polyamines with three or more functions, such as diethylenetriamine, triethylenetetramine, and tetraethylenepentamine. For convenience, compounds with multiple hydroxyl groups and one amino or imino group are also listed as "polyamines."

[0042] [Crosslinking agents, chain extenders] The urethane resin may contain units derived from crosslinking agents and chain extenders. Crosslinking agents are typically used when synthesizing prepolymers. Chain extenders are typically used when extending the chains of pre-synthesized prepolymers. Depending on the application, such as crosslinking or chain extension, water, the aforementioned polyisocyanates, polyols, and polyamines can be appropriately selected and used as crosslinking agents and chain extenders.

[0043] [Glass transition temperature of the second resin particle] The glass transition temperature of the second resin particles is preferably -40°C or higher, and more preferably -35°C or higher. If the glass transition temperature of the second resin particles is below -40°C, the resin film formed by the second resin particles in the ink-coated recording medium tends to soften, making it difficult to stably retain the pigment, and the effect of improving the scratch resistance of the image may not be sufficiently obtained. The glass transition temperature of the second resin particles is preferably 100°C or lower, and more preferably 80°C or lower.

[0044] [Method for manufacturing the second resin particle] The second resin particles can be produced, for example, by synthesizing a urethane resin and then atomizing it. The urethane resin can be obtained, for example, by reacting a polyisocyanate with a compound that reacts with it (polyol, polyamine) in the presence of an organic solvent. The synthesized urethane resin is preferably atomized by a dispersion method, phase inversion (emulsification) method, etc., in the presence of a base or the like, as needed.

[0045] [Analysis of the second resin particle] The composition of the urethane resin constituting the second resin particles can be analyzed, for example, by the following method. First, a sample is prepared by dissolving the resin particles in an organic solvent such as deuterated dimethyl sulfoxide. The prepared sample is then analyzed by proton nuclear magnetic resonance ( 1 By analyzing the peak positions obtained by 1H-NMR and the ratio of the integrated values ​​of the chemical shift peaks of each component, the types and proportions of units (monomers) constituting the urethane resin can be determined. Furthermore, by analyzing the second resin particles by pyrolysis gas chromatography, the units (monomers) constituting the urethane resin can also be detected.

[0046] (Organic solvents) The ink of the first embodiment contains at least one organic solvent selected from the group consisting of compounds represented by general formula (1), compounds represented by general formula (2), and compounds represented by general formula (3). The ink of the second embodiment also contains at least one organic solvent selected from the group consisting of compounds represented by general formula (1) and compounds represented by general formula (2). The content (mass%) of the above organic solvent in the ink is preferably 0.1% by mass or more and 25.0% by mass or less, and more preferably 0.2% by mass or more and 15.0% by mass or less, based on the total mass of the ink.

[0047] [Compounds represented by general formula (1)] The compound represented by general formula (1) is a chain-like carbonate compound. The compound represented by general formula (1) is characterized by a large proportion of structures similar to the ester bond (-COO-) of polyester resin and the urethane bond (-NH-COO-) of urethane resin within its molecule. For this reason, the compound represented by general formula (1) can specifically soften the first and second resin particles, improve the scratch resistance of the image, and does not impair the discharge stability.

[0048] TIFF2022165911000004.tif31170 (In the above general formula (1), R1 and R2 each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms.)

[0049] In general formula (1), R1 and R2 each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms. In general formula (1), if the alkyl groups represented by R1 and R2 have 7 or more carbon atoms, the viscosity of the ink tends to increase and the discharge stability decreases, which is undesirable. Examples of linear or branched alkyl groups having 1 to 6 carbon atoms for R1 and R2 include methyl group, ethyl group, n-propyl group, n-hexyl group, i-propyl group, and t-butyl group. Preferred compounds represented by general formula (1) include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0050] [Compounds represented by general formula (2)] The compound represented by general formula (2) is a cyclic carbonate compound. The compound represented by general formula (2) is characterized by a large proportion of structures similar to the ester bond (-COO-) of polyester resin and the urethane bond (-NH-COO-) of urethane resin within its molecule. For this reason, the compound represented by general formula (2) can specifically soften the first and second resin particles, improve the abrasion resistance of the image, and does not impair the discharge stability.

[0051] TIFF2022165911000005.tif31170 (In the above general formula (2), R3 represents an ethylene group or a propylene group, R4 represents a methyl group or an ethyl group, n represents 0 or 1, and when R3 is an ethylene group, n is 1)

[0052] In general formula (2), R3 represents an ethylene group or a propylene group. Also, in general formula (2), R4 represents a methyl group or an ethyl group, and n represents 0 or 1. When R3 is an ethylene group, n is 1. In general formula (2), when R3 is an alkylene group having 4 or more carbon atoms, when R4 is an alkyl group having 3 or more carbon atoms, and when R3 is an ethylene group and R4 is absent (n=0), the viscosity of the ink tends to increase and the discharge stability decreases, which is undesirable. As compounds represented by general formula (2), propylene carbonate and butylene carbonate are preferred, and propylene carbonate is preferred among them.

[0053] [Compounds represented by general formula (3)] The compound represented by general formula (3) is a dioxolane compound. The compound represented by general formula (3) is characterized by a large proportion of its molecule having a structure similar to the ester bond (-COO-) of polyester resin. For this reason, the compound represented by general formula (3) can specifically soften the first resin particles, improving the scratch resistance of the image without impairing the ejection stability. However, in the case of the second resin particles formed from urethane resin, the ejection stability is poor because they strongly interact with the hydroxyl group of the compound represented by general formula (3) even in the ink.

[0054] TIFF2022165911000006.tif35170 (In the above general formula (3), R5 and R6 each independently represent a linear or branched alkyl group having 1 to 4 carbon atoms, and R7 represents an alkylene group having 1 to 4 carbon atoms)

[0055] In general formula (3), R5 and R6 each independently represent a linear or branched alkyl group having 1 to 4 carbon atoms. Also, in general formula (3), R7 represents an alkylene group having 1 to 4 carbon atoms. In general formula (3), if the alkyl groups represented by R5 and R6 have 5 or more carbon atoms, and if the alkylene group represented by R7 has 5 or more carbon atoms, the viscosity of the ink tends to increase and the discharge stability decreases, which is undesirable. Examples of linear or branched alkyl groups having 1 to 4 carbon atoms represented by R5 and R6 include methyl group, ethyl group, n-propyl group, n-butyl group, i-propyl group, etc. Examples of alkylene groups having 1 to 4 carbon atoms represented by R7 include methylene group, ethylene group, n-propylene group, n-butylene group, etc. Preferred compounds represented by general formula (3) include 2,2-dimethyl-1,3-dioxolane-4-methanol, 2,2-diethyl-1,3-dioxolane-4-methanol, and 2,2-dimethyl-1,3-dioxolane-4-ethanol.

[0056] Compared to compounds represented by general formula (1) (chain carbonate compounds), compounds represented by general formula (2) and general formula (3) (cyclic carbonate compounds, dioxolane compounds) have a greater effect in improving the scratch resistance of images. This is thought to be because compounds represented by general formula (2) and general formula (3) tend to have a higher dielectric constant, making them more likely to soften resin particles.

[0057] The content of resin particles in the ink (mass%) is preferably 0.1 to 10.0 times the content of organic solvent (mass%), and more preferably 0.1 to 5.0 times. When the above mass ratio is 0.1 times or more, the resin particles can be efficiently softened by the organic solvent, which tends to improve the scratch resistance of the image. On the other hand, when the above mass ratio is 10.0 times or less, preferably 5.0 times or less, excessive softening of the resin particles by the organic solvent is suppressed, which suppresses an excessive increase in the viscosity of the ink and further improves the discharge stability. When the above mass ratio is 1.0 times or more, it is more preferable.

[0058] (aqueous medium) The ink is an aqueous ink containing at least water as an aqueous medium. Deionized water or ion-exchanged water is preferred as the water. The water content (mass%) in the ink is preferably 40.0% by mass or more, more preferably 45.0% by mass or more, and particularly preferably 50.0% by mass or more, based on the total mass of the ink. The water content (mass%) in the ink is preferably 95.0% by mass or less, and more preferably 90.0% by mass or less, based on the total mass of the ink. Any water-soluble organic solvent commonly used in inks can be used. Examples include alcohols, (poly)alkylene glycols, nitrogen-containing compounds, and sulfur-containing compounds. However, it is preferable not to use water-soluble organic solvents such as glycol ethers, or if used, to use only a small amount (approximately 0.1% by mass or less). The water-soluble organic solvent content (mass%) in the ink is preferably 3.0% by mass or more and 50.0% by mass or less, based on the total mass of the ink. This water-soluble organic solvent content includes the content of the aforementioned organic solvents.

[0059] (Other additives) In addition to the components mentioned above, the ink may also contain, as necessary, water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols like trimethylolpropane and trimethylolethane, and urea derivatives like urea and ethylene urea. Furthermore, the ink may also contain, as necessary, various additives such as surfactants, pH adjusters, rust inhibitors, preservatives, fungicides, antioxidants, reduction inhibitors, evaporation accelerators, chelating agents, and other resins.

[0060] <Ink Cartridge> The ink cartridge of the present invention comprises ink and an ink storage section for storing this ink. The ink stored in this ink storage section is the aqueous ink of the present invention as described above. Figure 1 is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. As shown in Figure 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage section for storing ink. The ink storage section consists of an ink storage chamber 14 and an absorbent storage chamber 16, which are in communication with each other via a communication port 18. The absorbent storage chamber 16 is also in communication with the ink supply port 12. Liquid ink 20 is stored in the ink storage chamber 14, and absorbent materials 22 and 24 that hold the ink in an impregnated state are stored in the absorbent storage chamber 16. The ink storage section may not have an ink storage chamber for storing liquid ink, and the entire amount of ink to be stored may be held by an absorbent. Alternatively, the ink storage section may not have an absorbent, and the entire amount of ink may be stored in a liquid state. Furthermore, the ink cartridge may be configured to include an ink storage section and a recording head.

[0061] <Inkjet recording method> The inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting the aqueous ink of the present invention described above from an inkjet recording head. Methods for ejecting the ink include methods that impart mechanical energy to the ink and methods that impart thermal energy to the ink. In the present invention, it is particularly preferable to employ a method that imparts thermal energy to the ink to eject it. Aside from using the ink of the present invention, the steps of the inkjet recording method may be those of known origin.

[0062] Figure 2 is a schematic diagram showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. The inkjet recording apparatus is provided with a transport means (not shown) for transporting the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 comprises recording heads 38 and 40 and is configured to hold an ink cartridge 42. While the head cartridge 36 is transported along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is transported in the sub-scanning direction by the transport means (not shown), and an image is recorded on the recording medium 32. Examples of recording heads 38 include serial recording heads and line recording heads. Among these, it is preferable to use a serial recording head.

[0063] The recording medium used for recording with ink is not particularly limited. For example, both recording media without a coating layer and recording media with a coating layer can be used. Examples of recording media without a coating layer include plain paper. Examples of recording media with a coating layer include ink-absorbing recording media such as glossy paper and matte paper for inkjet printers. In addition, recording media with low or no ink absorption (hereinafter also referred to as "non-absorbent recording media") such as printing paper or resin materials can also be used. Among these, the use of non-absorbent recording media is preferred. A non-absorbent recording media is defined as the Bristow method described in JAPAN TAPPI Paper Pulp Test Method No. 51, "Test Method for Liquid Absorption of Paper and Paperboard," from the start of contact for 30 msec 1 / 2 Up to 10 mL / m² of water absorption capacity 2The following refers to the recording medium. In this invention, a recording medium that satisfies the above water absorption requirements is defined as a "non-absorbent recording medium". Examples of substrates for recording media having a coating layer include paper and resin, and among these, paper-based substrates are preferred. [Examples]

[0064] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components indicated in "parts" and "%" are based on mass.

[0065] <Preparation of Pigment Dispersion> (Pigment dispersion 1) A mixture was obtained by mixing 15.0 parts of pigment (CI pigment blue 15:3), 50.0 parts of an aqueous solution (resin content 20.0%) obtained by dissolving styrene-acrylic acid copolymer in water containing equimolar sodium hydroxide with an acid value equal to its own, and 35.0 parts of deionized water. The styrene-acrylic acid copolymer was a water-soluble acrylic resin with an acid value of 100 mg KOH / g and a weight-average molecular weight of 10,000. The mixture obtained using a batch-type vertical sand mill was dispersed for 2 hours, and then centrifuged to remove coarse particles. Pigment dispersion 1 was obtained by pressure filtration through a 3.0 μm pore size microfilter (manufactured by Fujifilm). The pigment content in pigment dispersion 1 was 15.0%, and the resin (solids) content was 10.0%.

[0066] (Pigment dispersion 2) Pigment dispersion 2 was obtained using the same procedure as described above for pigment dispersion 1, except that CI Pigment Red 122 was used as the pigment. The pigment content in pigment dispersion 2 was 15.0%, and the resin content was 10.0%.

[0067] (Pigment dispersion 3) Pigment dispersion 3 was obtained using the same procedure as described above for pigment dispersion 1, except that CI Pigment Yellow 74 was used as the pigment. The pigment content in pigment dispersion 3 was 15.0%, and the resin content was 10.0%.

[0068] (Pigment dispersion 4) Pigment dispersion 4 was obtained using the same procedure as described above for pigment dispersion 1, except that carbon black (product name "NIPex 170IQ", manufactured by Orion Engineered Carbons) was used as the pigment. The pigment content in pigment dispersion 4 was 15.0%, and the resin content was 10.0%.

[0069] (Pigment dispersion 5) 5.0g of concentrated hydrochloric acid was dissolved in 5.5g of water, and the solution was cooled to 5°C. 1.6g of 4-aminophthalic acid was then added. The container of this solution was placed in an ice bath and stirred to maintain the solution temperature below 10°C. A solution obtained by dissolving 1.8g of sodium nitrite in 9.0g of ion-exchanged water at 5°C was added. After stirring for 15 minutes, 6.0g of carbon black (product name "NIPex 170IQ", manufactured by Orion Engineered Carbons) was added under stirring, and the mixture was stirred for another 15 minutes to obtain a slurry. The obtained slurry was filtered through filter paper (product name "Standard Filter Paper No. 2", manufactured by Advantec), the particles were thoroughly washed with water, and the mixture was dried in an oven at 110°C. Subsequently, the counterions were replaced from sodium ions to potassium ions by ion exchange to obtain a self-dispersing pigment in which two -C6H3-(COOK) groups were bonded to the surface of the carbon black particles. An appropriate amount of deionized water was added to adjust the pigment content, and a pigment dispersion 5 with a pigment content of 15.0% was obtained.

[0070] <Analysis conditions for resins> (Determination of whether the resin is resin particles or not, particle size) A sample containing approximately 1.0% resin was prepared by diluting a resin-containing liquid with deionized water. The particle size of the resin particles (cumulative 50% particle size by volume) was measured using a dynamic light scattering particle size analyzer according to the following measurement conditions. 50It was measured. As the particle size distribution meter, the product name "NanoTrack WAVEII-Q" (manufactured by Microtrac Bell) was used. When particles having a particle diameter were measured by this measurement method, the resin was judged to be "resin particles" (it is a "water-dispersible resin"). On the other hand, when particles having a particle diameter were not measured by this measurement method, the resin was judged not to be "resin particles" (it is a "water-soluble resin"). [Measurement conditions]: ·SetZero: 30 seconds ·Number of measurements: 3 times ·Measurement time: 180 seconds ·Shape: True sphere ·Refractive index: 1.6 ·Density: 1.0 g / cm 3

[0071] (Glass transition temperature of resin particles) 2 mg of resin particles obtained by drying the liquid containing resin particles at 60 °C was put into an aluminum container and sealed to prepare a sample for measurement. For the prepared sample, a differential scanning calorimeter (product name "Q1000", manufactured by TA instruments) was used, and thermal analysis was performed according to the temperature program shown below to create a heating curve. The temperature at the intersection of the straight line extended to the high temperature side through two points in the low temperature side curve and the tangent line drawn at the point where the gradient of the stepped change part in the curve becomes maximum in the created heating curve (horizontal axis: temperature, vertical axis: heat quantity) was defined as the "glass transition temperature of resin particles". [Temperature program]: (1) Heat up to 200 °C at 10 °C / min (2) Cool down from 200 °C to -50 °C at 5 °C / min (3) Heat up from -50 °C to 200 °C at 10 °C / min

[0072] <Preparation of resin> (Resins 1 - 7) A mixture of the components (in parts) listed under "Esterification Reaction" in Table 1 was placed in a reaction vessel set up in an autoclave, and the esterification reaction was carried out by heating at 220°C for 4 hours. Next, the temperature was raised to 240°C and the pressure was reduced to 13 Pa over 90 minutes. The esterification (dehydration condensation) reaction was continued by maintaining the reduced pressure of 240°C and 13 Pa for 5 hours, after which nitrogen gas was introduced to return to atmospheric pressure. After lowering the temperature to 220°C, the catalyst (tetra-n-butyl titanate) and the components (in parts) listed under "Transesterification Reaction" in Table 1 were added, and the transesterification reaction was carried out by heating at 220°C for 2 hours. The amount of catalyst used was 3 × 10⁻⁶. -4 The total amount of polycarboxylic acid used (moles) was specified. Then, nitrogen gas was introduced to create a pressurized state, and the sheet-like resin was extracted. After cooling the extracted resin to 25°C, it was crushed using a crusher to obtain polyester resin. The properties of the obtained polyester resin are shown in Table 1. The meanings of the abbreviations for each component in Table 1 are explained below. • EG: Ethylene glycol • NPG: Neopentyl glycol • BPA: 2,2-bis(4-hydroxyphenyl)propane tPA: Terephthalic acid iPA: Isophthalic acid • HAD: Adipic acid BTA: Trimellitus

[0073] TIFF2022165911000007.tif58170

[0074] A stirrer (product name "Tornado Stirrer Standard SM-104", manufactured by AS ONE) was set up in a 2L beaker. 210g of the type of polyester resin shown in Table 2 and the amount of tetrahydrofuran used (g) shown in Table 2 were added to this beaker, and the mixture was stirred at 25°C to dissolve the components. Next, a 5.0% sodium hydroxide aqueous solution was added in an amount corresponding to the neutralization rate (mol%) based on the acid value of the polyester resin, and the mixture was stirred for 30 minutes. Furthermore, while stirring at 25°C at the stirring speed shown in Table 2, 900g of deionized water was added dropwise at a rate of 20mL / min. The temperature was then raised to 60°C, and the tetrahydrofuran and some of the water were removed by distillation under reduced pressure. The beaker was placed in a water bath and heated at 85°C for 1 hour. After filtering the contents through a 150-mesh (150 gaps per inch) wire mesh, the resin particle content was adjusted. In this way, a liquid containing resins 1 to 7, each being a polyester resin particle, was obtained, with a resin content of 40.0%. The properties of the obtained resins are shown in Table 2.

[0075] TIFF2022165911000008.tif77170

[0076] (Liquid containing resins 8-16) The commercially available resin-containing liquids shown in Table 3 were prepared as resins 8-16.

[0077] TIFF2022165911000009.tif183170

[0078] (Liquid containing resin 17) In a four-necked flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and reflux tube, 32.8 parts of isophorone diisocyanate and 52.0 parts of polypropylene glycol with a number average molecular weight of 2,000 were added and reacted at 100°C for 2 hours under a nitrogen gas atmosphere. Next, 14.3 parts of dimethylolpropionic acid, 0.9 parts of ethylenediamine, and 150 parts of methyl ethyl ketone were added and reacted at 78°C to obtain a reaction solution. After cooling the obtained reaction solution to 40°C, deionized water was added, and potassium hydroxide equivalent to the acid value of the resin was added while stirring at high speed with a homomixer to obtain a resin-containing liquid. Methyl ethyl ketone was removed from the obtained liquid by heating and reducing pressure. This yielded a resin-containing liquid containing resin 17, a water-soluble urethane resin, with a resin content of 40.0%.

[0079] (Liquid containing resin 18) 55.0 parts methyl methacrylate, 30.0 parts butyl acrylate, and 15.0 parts acrylic acid were mixed to prepare 100.0 parts monomer mixture. Half of the monomer mixture (50.0 parts), 2.0 parts sodium dodecylbenzenesulfonate (emulsifier), and 150.0 parts deionized water were charged into a four-necked flask equipped with a thermometer, stirrer, nitrogen inlet tube, and reflux condenser. Nitrogen was then introduced to maintain a nitrogen atmosphere inside the flask, and the mixture was stirred with a homogenizer (product name "T50D Ultra-Turrax", manufactured by IKA) and heated to 90°C. Next, the remaining monomer mixture (50.0 parts) and a solution of 1.0 part potassium persulfate dissolved in 20.0 parts deionized water were added dropwise to the flask over 2 hours. After stirring at 90°C for another 2 hours, the mixture was returned to 25°C. Next, the pH of the liquid was adjusted to 8.5 using an appropriate amount of potassium hydroxide, and an appropriate amount of deionized water was added to obtain a liquid containing resin 18, which is acrylic resin particles, with a resin content of 40.0%. The glass transition temperature of resin 18 is 37°C, and D 50 It was 120 nm.

[0080] (Liquid containing resin 19) Except for replacing butyl acrylate with styrene, the procedure was the same as for preparing the liquid containing resin 18, and a liquid containing resin 19, which is acrylic resin particles, was obtained with a resin content of 40.0%. The glass transition temperature of resin 19 was 104°C, and D 50 It was 120 nm.

[0081] <Ink preparation> Each ink was prepared by mixing the components (in %) shown in the upper section of Tables 4-1 to 4-7, stirring thoroughly, and then pressure filtering through a 3.0 μm pore size microfilter (manufactured by Fujifilm). The properties of the inks are shown in the lower section of Tables 4-1 to 4-7. For inks containing the first resin particles, "Content S of specific organic solvents" is the content of compounds represented by general formulas (1) to (3). For inks containing the second resin particles, "Content S of specific organic solvents" is the content of compounds represented by general formulas (1) and (2). Furthermore, for inks containing resins other than the first and second resin particles, "Content S of specific organic solvents" is the content of compounds represented by general formulas (1) to (3).

[0082] TIFF2022165911000010.tif183170

[0083] TIFF2022165911000011.tif183170

[0084] TIFF2022165911000012.tif183170

[0085] TIFF2022165911000013.tif184170

[0086] TIFF2022165911000014.tif182170

[0087] TIFF2022165911000015.tif209170

[0088] TIFF2022165911000016.tif210170

[0089] <Rating> The following evaluations were performed using the inks obtained above. In this invention, "A" and "B" were defined as acceptable levels, and "C" as an unacceptable level in the evaluation criteria for each item below. The evaluation results are shown in Table 5.

[0090] (Abrasion resistance) Each prepared ink was filled into an ink cartridge and set in an inkjet recording device (product name "PIXUS iP3100", manufactured by Canon) that ejects ink from the recording head using thermal energy. In this embodiment, a recording duty cycle of 100% is defined as a solid image recorded under the condition that one drop of ink containing approximately 5 ng per drop is applied to a unit area of ​​1 / 1,200 inch x 1 / 1,200 inch. Using the above inkjet recording device, a 200 mm x 200 mm solid image (recording duty cycle 100%) was recorded on a recording medium (coated paper, product name "LX Gloss Coat 157", manufactured by Sakurai). This recording medium was recorded using the Bristow method from the start of contact for 30 msec. 1 / 2 Up to 10 mL / m² of water absorption capacity 2 The following is a low-absorption recording medium. After leaving the recorded solid image for one day, a friction test was performed using a JSPS-type testing machine (product name "Abrasion Resistance Tester", manufactured by Imoto Seisakusho) capable of performing measurements in accordance with JIS L 0849, under the condition of 10 reciprocating motions with a load of 500g. The image after the friction test was visually inspected, and the abrasion resistance of the image was evaluated according to the evaluation criteria shown below. A: There were no scratches on the image. B: The image had scratches, but the recording medium was not visible. C: The image had scratches on it, and the recording medium was visible.

[0091] (Discharge stability) Each prepared ink was filled into an ink cartridge and set in an inkjet recording device (product name "iB4030", manufactured by Canon) that ejects ink from the recording head using thermal energy. In this embodiment, a recording duty cycle of 100% is defined as recording a solid image under the condition that one drop of ink with approximately 22 ng per drop is applied to a unit area of ​​1 / 600 inch x 1 / 600 inch. In an environment of 30°C and 10% relative humidity, one solid image with a recording duty cycle of 5% was recorded on the entire surface of an A4 size recording medium (plain paper, product name "PB PAPER", manufactured by Canon), and then recording was paused for 240 seconds. This cycle was repeated until the total number of recorded sheets reached 800 and 1,000. After recording 800 and 1,000 solid images, vertical lines were recorded on the recording medium. The recorded vertical lines were visually inspected, and the ink ejection stability was evaluated according to the evaluation criteria shown below. AA: There were no irregularities in the vertical lines on the 1,000th sheet. A: The vertical lines on the 800th sheet were undisturbed, and there were some irregularities in the vertical lines on the 1,000th sheet, but the lines were not broken. B: In both the 800th and 1,000th sheets, there were irregularities in the vertical lines, but the lines were not broken. C: The vertical ruled lines on the 1,000th sheet were distorted, with part of the ruled line missing.

[0092] TIFF2022165911000017.tif225170

Claims

1. A water-based inkjet ink containing a pigment, resin particles, and an organic solvent, the resin particles are first resin particles formed of a polyester resin, The organic solvent is at least one selected from the group consisting of a compound represented by the following general formula (1), a compound represented by the following general formula (2), and a compound represented by the following general formula (3). (In the general formula (1), R １ and R ２ Each of R independently represents a linear or branched alkyl group having 1 to 6 carbon atoms. ３ represents an ethylene group or a propylene group; R ４ represents a methyl group or an ethyl group, n represents 0 or 1, R ３ When R is an ethylene group, n is 1. ５ and R ６ each independently represents a linear or branched alkyl group having 1 to 4 carbon atoms; R ７ represents an alkylene group having 1 to 4 carbon atoms.

2. The water-based ink according to claim 1 , wherein the first resin particles have a glass transition temperature of 50° C. or higher.

3. An aqueous ink described in claim 1 or 2, wherein the organic solvent comprises at least one selected from the group consisting of ethyl methyl carbonate, butylene carbonate, 2,2-dimethyl-1,3-dioxolane-4-methanol, 2,2-diethyl-1,3-dioxolane-4-methanol, and 2,2-dimethyl-1,3-dioxolane-4-ethanol.

4. A water-based inkjet ink containing a pigment, resin particles, and an organic solvent, the resin particles are second resin particles formed of a urethane resin, The aqueous ink is characterized in that the organic solvent is at least one selected from the group consisting of compounds represented by the following general formula (1) and compounds represented by the following general formula (2): (In the general formula (1), R １ and R ２ Each of R independently represents a linear or branched alkyl group having 1 to 6 carbon atoms. ３ represents an ethylene group or a propylene group; R ４ represents a methyl group or an ethyl group, n represents 0 or 1, R ３ is an ethylene group, n is 1.

5. 5. The water-based ink according to claim 4, wherein the second resin particles have a glass transition temperature of -40° C. or higher.

6. An aqueous ink described in claim 4 or 5, wherein the organic solvent includes at least one selected from the group consisting of ethyl methyl carbonate and butylene carbonate.

7. The water-based ink according to claim 1 , wherein the resin particles have a volume-based cumulative 50% particle diameter of 30 nm or more and 300 nm or less.

8. The aqueous ink according to claim 1 , wherein the content (mass %) of the resin particles is 0.5% by mass or more and 10.0% by mass or less based on the total mass of the ink.

9. The aqueous ink according to claim 1 , wherein the content (mass %) of the resin particles is 0.5% by mass or more and 5.0% by mass or less based on the total mass of the ink.

10. 10. The aqueous ink according to claim 1, wherein the content (mass %) of the organic solvent is 0.1 to 10.0 times, in mass ratio, the content (mass %) of the resin particles.

11. An aqueous ink described in any one of claims 1 to 9, wherein the content (mass %) of the organic solvent is 2.0 times or more and 10.0 times or less in mass ratio to the content (mass %) of the resin particles.

12. The aqueous ink according to claim 1 , wherein the content (mass %) of the organic solvent is 0.1 to 5.0 times, in mass ratio, relative to the content (mass %) of the resin particles.

13. An ink cartridge including an ink and an ink storage section for storing the ink, 13. An ink cartridge, wherein the ink is a water-based ink according to claim 1.

14. An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, comprising: An ink-jet recording method, wherein the ink is a water-based ink according to claim 1 .

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