JP2022165911A - Aqueous inks, ink cartridges, and inkjet recording method - Google Patents

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

The present invention relates to an aqueous ink, an ink cartridge, and an inkjet recording method.

In the inkjet recording method, from the viewpoint of image fastness, a pigment ink containing a pigment as a coloring material has been used. However, an image recorded using a pigment ink has a problem of low scratch resistance because the coloring material is particles. The recording medium on which an image is recorded by the inkjet recording method is not limited to recording media with good ink absorption properties, such as conventional general-purpose plain paper and inkjet paper, but also ink-absorbing paper such as coated paper for printing. A recording medium with poor performance has also come to be used. In a recording medium having poor ink absorbency, the scratch resistance of an image tends to be low. Therefore, it is desired to improve the scratch resistance regardless of the ink absorbency of the recording medium.

So far, studies have been made to improve the fixability 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). Further, an ink has been proposed in which the coloring material of an image formed on a recording medium can be covered with the urethane resin to some extent by containing the coloring material and the urethane resin in a predetermined ratio (Patent Document 2).

JP 2008-183843 A JP 2018-058972 A

When using the coating liquid proposed in Patent Document 1 or the like, it is necessary to provide means for applying the coating liquid to the recording medium. In addition, although the ink proposed in Patent Document 2 can achieve a certain degree of scratch resistance of an image, when recording a large-sized image or when recording images continuously, Ejection stability is likely to be impaired. Accordingly, the present inventors have studied how to stably record an image having a higher level of scratch resistance than ever before by devising an ink composition without using a coating liquid or the like.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a water-based ink which is excellent in ejection stability and capable of recording an image with excellent abrasion resistance. Another object of the present invention is to provide an ink cartridge and an ink jet recording method using this water-based ink.

That is, according to the present invention, there is provided a water-based inkjet ink containing a pigment, resin particles, and an organic solvent, wherein the resin particles are first resin particles formed of a polyester resin, and the organic solvent is , 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). There is provided an aqueous ink characterized by:

（前記一般式（１）中、Ｒ_１及びＲ_２は、それぞれ独立に、炭素数１乃至６の直鎖又は分岐鎖のアルキル基を表す。前記一般式（２）中、Ｒ_３は、エチレン基又はプロピレン基を表し、Ｒ_４は、メチル基又はエチル基を表し、ｎは０又は１を表し、Ｒ_３がエチレン基である場合、ｎは１である。前記一般式（３）中、Ｒ_５及びＲ_６は、それぞれ独立に、炭素数１乃至４の直鎖又は分岐鎖のアルキル基を表し、Ｒ_７は、炭素数１乃至４のアルキレン基を表す）

(In general formula (1), R ₁ and R ₂ each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms. In general formula (2), R ₃ is ethylene or a propylene group, _R4 represents a methyl group or an ethyl group, n represents 0 or 1, and n is ₁ when R3 is an ethylene group. R ₅ and R ₆ each independently represent a linear or branched alkyl group having 1 to 4 carbon atoms, and R ₇ represents an alkylene group having 1 to 4 carbon atoms)

Further, according to the present invention, there is provided a water-based inkjet ink containing a pigment, resin particles, and an organic solvent, wherein the resin particles are second resin particles formed of a urethane resin, and the organic solvent is , a compound represented by the following general formula (1), and a compound represented by the following general formula (2).

（前記一般式（１）中、Ｒ_１及びＲ_２は、それぞれ独立に、炭素数１乃至６の直鎖又は分岐鎖のアルキル基を表す。前記一般式（２）中、Ｒ_３は、エチレン基又はプロピレン基を表し、Ｒ_４は、メチル基又はエチル基を表し、ｎは０又は１を表し、Ｒ_３がエチレン基である場合、ｎは１である）

(In general formula (1), R ₁ and R ₂ each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms. In general formula (2), R ₃ is ethylene or a propylene group, _R4 represents a methyl group or an ethyl group, n represents 0 or 1, and n is ₁ when R3 is an ethylene group)

According to the present invention, it is possible to provide a water-based ink which is capable of recording an image with excellent abrasion resistance and which has excellent ejection stability. Further, according to the present invention, it is possible to provide an ink cartridge and an inkjet recording method using this water-based ink.

1 is a cross-sectional view schematically showing one embodiment of an ink cartridge of the present invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically 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 main parts of the inkjet recording apparatus and (b) is a perspective view of a head cartridge;

The present invention will be further described in detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but for convenience, it is expressed as "containing the salt." In addition, water-based ink for inkjet is sometimes simply referred to as "ink". Unless otherwise specified, physical property values are values at normal temperature (25° C.), normal pressure (1 atm=101,325 Pa), and normal humidity (50% relative humidity). A "unit" means a unit structure corresponding to one monomer unless otherwise specified. "(Meth)acrylic acid" and "(meth)acrylate" mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate", respectively.

The inventors of the present invention have studied the composition of an ink that achieves a high level of compatibility between the abrasion resistance of an image recorded with a pigment ink and the ejection stability of the ink. As a result, the inventors have found that these properties can be achieved by combining the specific resin particles and the organic solvent described below, and have completed the present invention.
- From the group consisting of the first resin particles formed of a polyester resin, the compound represented by the general formula (1), the compound represented by the general formula (2), and the compound represented by the general formula (3) at least one selected organic solvent (first embodiment)
- second resin particles formed of urethane resin particles, and at least one organic solvent (second 2 embodiment)

（一般式（１）中、Ｒ_１及びＲ_２は、それぞれ独立に、炭素数１乃至６の直鎖又は分岐鎖のアルキル基を表す。一般式（２）中、Ｒ_３は、エチレン基又はプロピレン基を表し、Ｒ_４は、メチル基又はエチル基を表し、ｎは０又は１を表し、Ｒ_３がエチレン基である場合、ｎは１である。一般式（３）中、Ｒ_５及びＲ_６は、それぞれ独立に、炭素数１乃至４の直鎖又は分岐鎖のアルキル基を表し、Ｒ_７は、炭素数１乃至４のアルキレン基を表す）

(In general formula (1), R ₁ and R ₂ each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms. In general formula (2), R ₃ is an ethylene group or represents a propylene group, R ₄ represents a methyl group or an ethyl group, n represents 0 or 1, and when R ₃ is an ethylene group, n is 1. In general formula (3), R ₅ and R ₆ each independently represents a linear or branched alkyl group having 1 to 4 carbon atoms, and R ₇ represents an alkylene group having 1 to 4 carbon atoms)

The compound represented by general formula (1) is a chain carbonate compound. The compound represented by general formula (2) is a cyclic carbonate compound. Moreover, the compound represented by the general formula (3) is a dioxolane compound. All of these compounds have relatively high hydrophobicity among organic solvents used in water-based inks for inkjet, and also have a plurality of oxygen atoms in their skeletons. Therefore, these organic solvents are specific to 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. Easy to interact with.

In both the first and second embodiments, it is considered that the following phenomenon occurs in the recording medium by combining the above organic solvent with the resin in the form of particles (resin particles). When the ink is ejected from the print head and applied to the print medium, water decreases due to evaporation and permeation into the print medium, and the concentration of the specific organic solvent becomes relatively high. Then, the organic solvent approaches and interacts with the resin particles to soften the resin particles. Since the pigment is entangled and held by the resin chains of the softened resin particles, the pigment is fixed on the recording medium, so that the abrasion resistance of the image can be improved.

When the amount of water is not reduced, the presence of water weakens the interaction between the resin particles and the organic solvent. can be improved. However, in the case of the second resin particles formed of a urethane resin, the ejection stability is inferior because of the strong interaction with the hydroxy groups of the compound represented by the general formula (3) even in the ink. Therefore, it is necessary to use at least one of the compound represented by the general formula (1) and the compound represented by the general formula (2) as the organic solvent to be combined with the second resin particles.

<Aqueous ink>
The ink of the present invention is a water-based inkjet ink containing a pigment, resin particles, and an organic solvent. The ink of the first embodiment comprises a pigment, first resin particles formed of a polyester resin, a compound represented by general formula (1), a compound represented by general formula (2), and a compound represented by general formula (3) ) containing at least one organic solvent selected from the group consisting of compounds represented by The ink of the second embodiment is selected from the group consisting of pigments, second resin particles made of urethane resin, and compounds represented by general formula (1) and compounds represented by general formula (2). contains at least one organic solvent. The ink of the present invention is used in applications in which another liquid such as a coating liquid or clear ink is applied after being applied to a recording medium, or in applications in which processing such as active energy rays or heating is performed after being applied to a recording medium. No need. Each component constituting the ink will be described below.

(pigment)
The ink contains pigments. Examples of the pigment dispersion method 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 pigment particle surface is coated with a resin or the like. can. In addition, there are self-dispersing pigments in which functional groups including hydrophilic groups such as anionic groups are bonded to the surface of pigment particles, and pigments in which organic groups including macromolecules are chemically bonded to the surface of pigment particles (resin bonding). type self-dispersing pigment) can also be used. Also, pigments with different dispersion methods may be used in combination.

As the pigment, an inorganic pigment, an organic pigment, or the like can be used. Specific examples of pigments include inorganic pigments such as carbon black and titanium oxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole and dioxazine. The content (% by mass) of the pigment in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, and 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. is more preferable.

(resin particles)
The ink contains first resin particles made of polyester resin or second resin particles made of urethane resin. The ink can also use the first resin particles and the second resin particles in combination. However, when the first resin particles and the second resin particles are used together, the compound represented by the general formula (1) and the compound represented by the general formula (2) are used as the organic solvent instead of the compound represented by the general formula (3). ) is preferably used at least one of the compounds represented by In this specification, hereinafter, the first resin particles and the second resin particles may be collectively referred to as "resin particles". The resin particles are present in the ink in a dispersed state, that is, in the form of a resin emulsion. Moreover, it is preferable that the resin particles do not contain a coloring material. In addition, it is not so preferable to use active energy ray-curable resin particles, that is, resin particles having a polymerizable group.

The term "resin particles" as used herein means that when the resin is neutralized with a base having an acid value of 1.0 times (molar ratio) or more, a liquid is formed in a state in which particles whose particle diameter can be measured are formed. means the resin present in the medium. The particle size of the resin is measured by a dynamic light scattering method. On the other hand, the "water-soluble resin" in this specification does not form particles whose particle size can be measured when the resin is neutralized with a base having an acid value of 1.0 times (molar ratio) or more. It means a resin that exists in a liquid medium in a state.

Whether a certain resin is a water-soluble resin or a resin particle (water-dispersible resin) can be determined according to the method shown below. First, a liquid (resin content: about 10% by mass) containing a resin neutralized with a base (sodium hydroxide, potassium hydroxide, etc.) in an amount equal to or greater than the acid value is prepared. Next, the prepared liquid is diluted with pure water to prepare a sample having a resin content of about 1% by mass. Then, the particle size of the resin in the sample is measured by the dynamic light scattering method. If particles with a particle size are not measured, the resin is determined to be a water-soluble resin, and if particles with a particle size are measured, the resin is determined to be resin particles. The measurement conditions at this time can be set to, for example, SetZero: 30 seconds, the number of measurements: 3, and the measurement time: 180 seconds. As a particle size distribution analyzer, a particle size analyzer using dynamic light scattering (for example, UPA-EX150, manufactured by Nikkiso Co., Ltd.) can be used. Of course, the particle size distribution measuring device and measurement conditions to be used are not limited to those described above.

[Content of resin particles]
The content (% by mass) of the resin particles 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. Above all, it is more preferably 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 content of the resin particles in the ink is less than 0.5% by mass, the amount of the resin particles is so small that the effect of improving the scratch resistance of the image may not be sufficiently obtained. Also, if the content of the resin particles is too large, interaction with the organic solvent tends to occur even in the ink, and the effect of improving the ejection stability of the ink may not be sufficiently obtained. Therefore, the content of the resin particles is preferably 10.0% by mass or less, more preferably 5.0% by mass or less.

[Particle size of resin particles]
The volume-based cumulative 50% particle diameter ( _D50 ) of the resin particles is preferably 30 nm or more and 300 nm or less. If the _D50 of the resin particles is less than 30 nm, the resin particles tend to enter the gaps between the pigment particles in the ink-applied recording medium, which may reduce the effect of improving the scratch resistance. On the other hand, when the _D50 of the resin particles is more than 300 nm, the number of particles is relatively small when considering a fixed amount of resin particles, and the distribution of the resin particles tends to be uneven on the recording medium to which the ink is applied. . Therefore, it may be difficult to uniformly improve the abrasion resistance over the entire image. The volume-based cumulative 50% particle diameter (D ₅₀ ) of the resin particles can be measured by a dynamic light scattering method under the same conditions as the method for determining whether or not the resin is a resin particle. .

[First Resin Particles Made of Polyester Resin]
The ink of the first embodiment contains first resin particles made of a polyester resin. The ratio (% by mass) of the polyester resin in the resin forming the first resin particles is preferably 90.0% by mass or more, and 100.0% by mass, based on the total mass of the resin particles. may That is, it is preferable that the first resin particles are substantially formed only of the polyester resin. A commercially available resin may be used as the polyester resin (polyester resin particles).

A polyester resin usually contains a unit derived from a polyhydric alcohol and a unit derived from a polycarboxylic acid. A structure containing an ester bond (--COO--) composed of a unit derived from a polyhydric alcohol and a unit derived from a polycarboxylic acid is also referred to as an "ester unit."

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

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

[Polyvalent carboxylic acid]
Divalent to tetravalent polycarboxylic acids can be mentioned as the polyvalent carboxylic acid that constitutes the unit derived from the polyvalent carboxylic acid. Examples of polyvalent carboxylic acids include polyvalent carboxylic acids having an aliphatic group; polyvalent carboxylic acids having an aromatic group; nitrogen-containing polyvalent carboxylic acids; and the like. Examples of polyvalent carboxylic 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; tetravalent carboxylic acids; and the like. Oligomers (low-molecular-weight polymers having a molecular weight of 1,000 or less) can also be used as polyvalent carboxylic acids. The ratio (% by mass) of units derived from polycarboxylic acid in the polyester resin forming the first resin particles is preferably 40.0% by mass or more and 60.0% by mass or less.

As polyvalent carboxylic acid, it is preferable to use polyvalent carboxylic acid having an aromatic group. Among them, it is preferable to use adipic acid, terephthalic acid, isophthalic acid and trimellitic acid. Also, it is preferable to use a plurality of other carboxylic acids. Specifically, it is preferable to use a plurality of types of divalent carboxylic acids. Among them, it is preferable to use terephthalic acid and isophthalic acid.

[Glass transition temperature of first resin particles]
The glass transition temperature of the first resin particles is preferably 50°C or higher, 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 ease of softening of the resin particles. Resin particles tend to exist in a softer state near room temperature (25° C.) as the glass transition temperature is lower, and the softer the resin particles, the more easily they are deformed by an external force. If the glass transition temperature of the first resin particles is less than 50°C, the resin film formed by the first resin particles tends to soften on the recording medium to which the ink is applied, making it difficult to stably retain the pigment. In some cases, the effect of improving the scratch resistance of the image cannot be sufficiently obtained. The glass transition temperature of the first resin particles is preferably 100° C. or less. The glass transition temperature of resin particles can be measured using a thermal analysis device such as a differential scanning calorimeter (DSC).

[Method for producing first resin particles]
The first resin particles can be produced, for example, by synthesizing a polyester resin and then granulating it. A polyester resin can be obtained, for example, by reacting a polyhydric alcohol and a polycarboxylic acid (esterification reaction). If necessary, a so-called transesterification reaction, in which either a polyhydric alcohol or a polycarboxylic acid is added to cleave a portion of the ester bond, may be performed. It is preferable to add a polyvalent carboxylic acid having a valence of 3 or more (among them, trimellitic acid is preferable) to carry out the transesterification reaction. The synthesized polyester resin is preferably formed into particles by a dispersion method, a phase inversion (emulsification) method, or the like after being brought into an appropriate form by pressurization, pulverization, or the like.

[Analysis of first resin particles]
The composition of the polyester resin that constitutes the first resin particles can be analyzed, for example, by the method shown below. First, a sample is prepared by dissolving resin particles in an organic solvent such as tetrahydrofuran. The prepared sample is analyzed by analysis methods such as nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) to determine the unit (monomer) constituting the polyester resin. Know the types and proportions. Further, by analyzing the first resin particles by pyrolysis gas chromatography, it is also possible to detect units (monomers) constituting the polyester resin.

[Second Resin Particles Made of Urethane Resin]
The ink of the second embodiment contains second resin particles made of urethane resin. The ratio (% by mass) of the urethane resin in the resin forming the second resin particles is preferably 90.0% by mass or more based on the total mass of the resin particles, and is preferably 100.0% by mass. may That is, it is preferable that the second resin particles are substantially formed only of urethane resin. A commercially available resin may be used as the urethane resin (urethane resin particles).

Urethane resins commonly used in water-based inks for inkjets are synthesized using at least polyisocyanate and components (polyols and polyamines) that react with it, and if necessary, cross-linking agents and chain extenders are also used.

[Polyisocyanate]
"Polyisocyanate" in the present invention means a compound having two or more isocyanate groups in the 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; isophorone diisocyanate, hydrogenated xylylene diisocyanate, 1, polyisocyanates having a cyclic structure such as 4-cyclohexanediisocyanate; and the like. Examples of aromatic polyisocyanates include tolylene diisocyanate and xylylene diisocyanate. Among them, 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.

[Polyol, polyamine]
A polyol or a polyamine can be used as a component that becomes a unit constituting the urethane resin by reaction with the above polyisocyanate. "Polyol" in the present invention means a compound having two or more hydroxy groups in the molecule. Examples of polyols include polyols having no acid groups such as polyether polyols, polyester polyols and polycarbonate polyols; polyols having acid groups; and the like. Further, the "polyamine" in the present invention means a compound having two or more "amino groups, imino groups" in the molecule. The proportion (mol %) of units derived from polyols and polyamines in the urethane resin forming the second resin particles is preferably 10.0 mol % or more and 80.0 mol % or less.

Examples of polyols having no acid groups include the following. Polyether polyols include addition polymers of alkylene oxides and polyols; glycols such as (poly)alkylene glycol; and the like. Examples of polyester polyols include acid esters. Examples of polycarbonate polyols include alkanediol-based polycarbonate diols. The number average molecular weight of the polyol having no acid group is preferably 400 or more and 4,000 or less. Polyether polyols and polycarbonate polyols are preferable as polyols having no acid group, and polyether polyols are more preferable. Examples of polyols having acid groups include polyols having carboxylic acid groups such as dimethylolacetic acid, dimethylolpropionic acid and dimethylolbutanoic acid.

Examples of polyamines include monoamines having multiple hydroxyl groups such as dimethylolethylamine; bifunctional polyamines such as ethylenediamine, isophoronediamine and xylylenediamine; trifunctional or higher polyamines such as diethylenetriamine, triethylenetetramine and tetraethylenepentamine; can be mentioned. For convenience, compounds having multiple hydroxy groups and one "amino group, imino group" are also listed as "polyamines".

[Crosslinking agent, chain extender]
The urethane resin may have units derived from a cross-linking agent or a chain extender. A cross-linking agent is usually used when synthesizing the prepolymer. A chain extender is generally used when chain-extending a pre-synthesized prepolymer. The cross-linking agent and chain extender can be appropriately selected from water, the above-described polyisocyanate, polyol, polyamine, and the like, depending on the purpose of cross-linking and chain extension.

[Glass transition temperature of second resin particles]
The glass transition temperature of the second resin particles is preferably −40° C. or higher, more preferably −35° C. or higher. If the glass transition temperature of the second resin particles is less than −40° C., the resin film formed by the second resin particles tends to soften on the ink-applied recording medium, making it difficult to stably retain the pigment. , 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, more preferably 80° C. or lower.

[Method for producing second resin particles]
The second resin particles can be produced, for example, by synthesizing a urethane resin and then granulating it. A urethane resin can be obtained, for example, by reacting a polyisocyanate with a compound (polyol, polyamine) that reacts with it in the presence of an organic solvent. The synthesized urethane resin is preferably granulated by a dispersion method, a phase inversion (emulsification) method, or the like in the presence of a base, if necessary.

[Analysis of second resin particles]
The composition of the urethane resin that constitutes the second resin particles can be analyzed, for example, by the method shown below. First, a sample is prepared by dissolving resin particles in an organic solvent such as deuterated dimethylsulfoxide. The prepared sample was analyzed by proton nuclear magnetic resonance ( ¹ H-NMR), and from the position of the peak obtained and the ratio of the integrated value of the chemical shift peak of each component, the unit constituting the urethane resin (unit It is possible to know the types and proportions of Also, by analyzing the second resin particles by pyrolysis gas chromatography, it is possible to detect the units (monomers) that constitute the urethane resin.

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

[Compound represented by general formula (1)]
The compound represented by general formula (1) is a chain carbonate compound. The compound represented by the general formula (1) is characterized in that a structure similar to the ester bond (-COO-) of the polyester resin and the urethane bond (-NH-COO-) of the urethane resin occupies a large proportion in the molecule. have. Therefore, the compound represented by the general formula (1) tends to specifically soften the first resin particles and the second resin particles, can improve the scratch resistance of the image, and impairs the ejection stability. Not at all.

（前記一般式（１）中、Ｒ_１及びＲ_２は、それぞれ独立に、炭素数１乃至６の直鎖又は分岐鎖のアルキル基を表す）

(In general formula (1), R ₁ and R ₂ each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms)

In general formula (1), R ₁ and R ₂ each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms. If the number of carbon atoms in the alkyl group represented by R ₁ and R ₂ in general formula (1) is 7 or more, the viscosity of the ink tends to increase and the ejection stability decreases, which is not preferable. The linear or branched alkyl group having 1 to 6 carbon atoms for R ₁ and R ₂ includes methyl group, ethyl group, n-propyl group, n-hexyl group, i-propyl group, t-butyl group and the like. can be mentioned. As the compound represented by the general formula (1), dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like are preferable.

[Compound represented by general formula (2)]
The compound represented by general formula (2) is a cyclic carbonate compound. The compound represented by the general formula (2) is characterized in that a structure similar to the ester bond (-COO-) of the polyester resin and the urethane bond (-NH-COO-) of the urethane resin occupies a large proportion in the molecule. have. Therefore, the compound represented by the general formula (2) tends to specifically soften the first resin particles and the second resin particles, can improve the scratch resistance of the image, and impairs the ejection stability. Not at all.

（前記一般式（２）中、Ｒ_３は、エチレン基又はプロピレン基を表し、Ｒ_４は、メチル基又はエチル基を表し、ｎは０又は１を表し、Ｒ_３がエチレン基である場合、ｎは１である）

(In the general formula (2), R ₃ represents an ethylene group or a propylene group, R ₄ represents a methyl group or an ethyl group, n represents 0 or 1, and R ₃ is an ethylene group, n is 1)

In general formula ( ₂ ), R3 represents an ethylene group or a propylene group. In general formula (2), _R4 represents a methyl group or an ethyl group, n represents 0 or 1, and n is ₁ when R3 is an ethylene group. In general formula (2), when R ₃ is an alkylene group having 4 or more carbon atoms, when R ₄ is an alkyl group having 3 or more carbon atoms, or when R ₃ is an ethylene group and R ₄ does not exist (n = 0), the viscosity of the ink tends to increase, and the ejection stability decreases, which is not preferable. As the compound represented by the general formula (2), propylene carbonate, butylene carbonate and the like are preferable, and propylene carbonate is particularly preferable.

[Compound represented by general formula (3)]
The compound represented by general formula (3) is a dioxolane compound. The compound represented by the general formula (3) is characterized in that a structure similar to the ester bond (--COO--) of the polyester resin occupies a large proportion of its molecule. Therefore, the compound represented by the general formula (3) tends to specifically soften the first resin particles, can improve the scratch resistance of the image, and does not impair the ejection stability. However, in the case of the second resin particles formed of a urethane resin, they strongly interact with the hydroxy groups of the compound represented by the general formula (3) even in the ink, resulting in poor ejection stability.

（前記一般式（３）中、Ｒ_５及びＲ_６は、それぞれ独立に、炭素数１乃至４の直鎖又は分岐鎖のアルキル基を表し、Ｒ_７は、炭素数１乃至４のアルキレン基を表す）

(In general formula (3), R ₅ and R ₆ each independently represent a linear or branched alkyl group having 1 to 4 carbon atoms, and R ₇ represents an alkylene group having 1 to 4 carbon atoms. show)

In general formula (3), R ₅ and R ₆ each independently represent a linear or branched alkyl group having 1 to 4 carbon atoms. In general formula (3), _R7 represents an alkylene group having 1 to 4 carbon atoms. In general formula (3), when the number of carbon atoms in the alkyl group represented by R ₅ and R ₆ is 5 or more, and when the number of carbon atoms in the alkylene group represented by R ₇ is 5 or more, the viscosity of the ink is likely to increase, and the ejection stability is lowered, which is not preferable. Linear or branched alkyl groups having 1 to 4 carbon atoms represented by R ₅ and R ₆ include methyl group, ethyl group, n-propyl group, n-butyl group and i-propyl group. can be done. Examples of the alkylene group having 1 to 4 carbon atoms for R ₇ include methylene group, ethylene group, n-propylene group and n-butylene group. Compounds represented by the general formula (3) include 2,2-dimethyl-1,3-dioxolane-4-methanol, 2,2-diethyl-1,3-dioxolane-4-methanol, 2,2-dimethyl -1,3-dioxolane-4-ethanol and the like are preferred.

Compared with the compound represented by the general formula (1) (chain carbonate compound), the compound represented by the general formula (2) and the compound represented by the general formula (3) (cyclic carbonate compound, dioxolane compound) The effect of improving the scratch resistance of the image is greater. It is considered that this is because the compound represented by the general formula (2) and the compound represented by the general formula (3) tend to have a higher relative dielectric constant and soften the resin particles more easily.

The content (mass%) of the resin particles in the ink is preferably 0.1 times or more and 10.0 times or less, and preferably 0.1 times or more and 5 times the organic solvent content (mass%). 0 times or less is more preferable. When the above mass ratio is 0.1 times or more, the resin particles can be softened efficiently by the organic solvent, so the effect of improving the scratch resistance of the image tends to increase. 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, so that excessive viscosity increase of the ink is suppressed and discharge is possible. Stability can be further improved. More preferably, the above mass ratio is 1.0 times or more.

(aqueous medium)
The ink is an aqueous ink containing at least water as an aqueous medium. As water, it is preferable to use deionized water or ion-exchanged water. The water content (% by mass) in the ink is preferably 40.0% by mass or more, more preferably 45.0% by mass or more, and more preferably 50.0% by mass, based on the total mass of the ink. It is particularly preferable that it is above. The water content (% by mass) in the ink is preferably 95.0% by mass or less, more preferably 90.0% by mass or less, based on the total mass of the ink. As the water-soluble organic solvent, any one commonly used for ink can be used. Examples include alcohols, (poly)alkylene glycols, nitrogen-containing compounds, and sulfur-containing compounds. However, it is preferable not to use a water-soluble organic solvent such as glycol ethers, or to use a small amount (approximately 0.1% by mass or less) when using. The content (% by mass) of the water-soluble organic solvent 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. The content of the water-soluble organic solvent includes the content of the organic solvent described above.

(Other additives)
In addition to the above components, the ink optionally contains water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethyleneurea. You may Further, the ink may contain surfactants, pH adjusters, rust inhibitors, preservatives, anti-mold agents, antioxidants, anti-reducing agents, evaporation accelerators, chelating agents, and other resins, etc., as necessary. may contain various additives.

<Ink cartridge>
The ink cartridge of the present invention includes ink and an ink containing portion that contains the ink. The ink contained in this ink container is the water-based ink of the present invention described above. FIG. 1 is a cross-sectional view schematically showing one embodiment of the ink cartridge of the present invention. As shown in FIG. 1, the bottom surface of the ink cartridge is provided with an ink supply port 12 for supplying ink to the recording head. The interior of the ink cartridge serves as an ink containing portion for containing ink. The ink storage section is composed of an ink storage chamber 14 and an absorber storage chamber 16 which communicate with each other through a communication port 18 . Also, the absorber storage chamber 16 communicates with the ink supply port 12 . The ink containing chamber 14 contains liquid ink 20 , and the absorber containing chamber 16 contains absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage section may have a configuration in which the absorber retains the total amount of the stored ink without having an ink storage chamber for storing liquid ink. Further, the ink containing portion may have a form in which the ink is contained in a liquid state without having an absorber. Further, the ink cartridge may be configured to have an ink containing portion and a recording head.

<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 above-described water-based ink of the present invention from an inkjet recording head. Methods for ejecting ink include a method in which mechanical energy is applied to ink and a method in which thermal energy is applied to ink. In the present invention, it is particularly preferable to adopt a method of applying thermal energy to the ink to eject the ink. Other than using the ink of the present invention, the steps of the ink jet recording method may be known.

FIG. 2 is a diagram schematically showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, (a) is a perspective view of the main part of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge. is. The inkjet recording apparatus is provided with 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 has recording heads 38 and 40, and is constructed so that an ink cartridge 42 is set therein. While the head cartridge 36 is conveyed 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 . An image is recorded on the recording medium 32 by conveying the recording medium 32 in the sub-scanning direction by conveying means (not shown). Examples of the printhead 38 include a serial printhead and a line printhead. Among them, it is preferable to use a serial print head.

There is no particular limitation on the recording medium to be recorded with ink. For example, both a recording medium having no coat layer and a recording medium having a coat layer can be used. Examples of the recording medium having no coat layer include plain paper. Examples of recording media having a coat layer include ink-absorbing recording media such as inkjet glossy paper and matte paper. In addition, a recording medium having low or no ink absorbency (hereinafter also referred to as “non-absorbent recording medium”) such as printing paper or resin material can be used. Among them, it is preferable to use a non-absorbent recording medium. The non-absorbent recording medium refers to JAPAN TAPPI Paper Pulp Test Method No. 51, "Liquid absorption test method for paper and paperboard", a recording medium having a water absorption of 10 mL/m ² or less from the start of contact to 30 msec ^1/2 in the Bristow method. In the present invention, a recording medium that satisfies the condition of water absorption is defined as a "non-absorbent recording medium". Examples of the base material of the recording medium having a coat layer include paper and resin, among which paper-based base materials are preferred.

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited by the following examples as long as the gist thereof is not exceeded. "Parts" and "%" regarding component amounts are based on mass unless otherwise specified.

<Preparation of pigment dispersion>
(Pigment dispersion liquid 1)
Pigment (C.I. Pigment Blue 15:3) 15.0 parts, aqueous solution obtained by dissolving styrene-acrylic acid copolymer in water containing sodium hydroxide equivalent to its acid value (resin content 20.0%) and 35.0 parts of ion-exchanged water were mixed to obtain a mixture. The styrene-acrylic acid copolymer was a water-soluble acrylic resin having an acid value of 100 mgKOH/g and a weight average molecular weight of 10,000. After dispersing the obtained mixture for 2 hours using a batch-type vertical sand mill, it was centrifuged to remove coarse particles. A pigment dispersion liquid 1 was obtained by pressure filtration through a microfilter having a pore size of 3.0 μm (manufactured by FUJIFILM Corporation). The pigment content in the pigment dispersion liquid 1 was 15.0%, and the resin (solid content) content was 10.0%.

(Pigment dispersion liquid 2)
C. I. Pigment Dispersion Liquid 2 was obtained in the same manner as Pigment Dispersion Liquid 1 described above, except that Pigment Red 122 was used as the pigment. The content of the pigment in the pigment dispersion liquid 2 was 15.0%, and the content of the resin was 10.0%.

(Pigment dispersion liquid 3)
C. I. Pigment Dispersion 3 was obtained in the same manner as Pigment Dispersion 1 described above, except that Pigment Yellow 74 was used as the pigment. The content of the pigment in the pigment dispersion 3 was 15.0%, and the content of the resin was 10.0%.

(Pigment dispersion liquid 4)
Pigment Dispersion 4 was obtained in the same manner as Pigment Dispersion 1 above, except that carbon black (trade name “NIPex 170IQ”, manufactured by Orion Engineered Carbons) was used as the pigment. The content of the pigment in the pigment dispersion liquid 4 was 15.0%, and the content of the resin was 10.0%.

(Pigment dispersion liquid 5)
5.0 g of concentrated hydrochloric acid was dissolved in 5.5 g of water, the solution was cooled to 5° C., and 1.6 g of 4-aminophthalic acid was added in this state. The container containing this solution was placed in an ice bath, and while stirring to keep the temperature of the solution below 10°C, a solution obtained by dissolving 1.8 g of sodium nitrite in 9.0 g of deionized water at 5°C was prepared. added. After stirring for 15 minutes, 6.0 g of carbon black (trade name “NIPex 170IQ”, manufactured by Orion Engineered Carbons) was added with stirring, and the mixture was further stirred for 15 minutes to obtain a slurry. The resulting slurry was filtered through a filter paper (trade name “Standard Filter Paper No. 2”, manufactured by Advantech), and the particles were thoroughly washed with water and dried in an oven at 110°C. Thereafter, sodium ions were replaced with potassium ions as counter ions by an ion exchange method to obtain a self-dispersing pigment in which —C ₆ H ₃ —(COOK) ₂ groups were bonded to the surface of carbon black particles. An appropriate amount of ion-exchanged water was added to adjust the pigment content, and a pigment dispersion liquid 5 having a pigment content of 15.0% was obtained.

<Resin analysis conditions>
(Determination of whether resin is resin particles, particle size)
A resin-containing liquid was diluted with deionized water to prepare a sample having a resin content of about 1.0%. With respect to this sample, the particle size of the resin particles (volume-based cumulative 50% particle size D ₅₀ ) was measured using a particle size distribution analyzer based on the dynamic light scattering method under the following measurement conditions. As the particle size distribution analyzer, a trade name "Nanotrack WAVE II-Q" (manufactured by Microtrack Bell) was used. When particles having a particle size were measured by this measurement method, the resin was determined to be "resin particles"("water-dispersibleresin"). On the other hand, when particles having a particle size were not measured by this measurement method, it was determined that the resin was not a "resin particle" (a "water-soluble resin").
[Measurement condition]:
・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

(Glass transition temperature of resin particles)
2 mg of resin particles obtained by drying a liquid containing resin particles at 60° C. was placed in an aluminum container and sealed to prepare a sample for measurement. Using a differential scanning calorimeter (trade name “Q1000”, manufactured by TA Instruments), the prepared sample was thermally analyzed according to the temperature program shown below to create a temperature rise curve. In the created temperature rise curve (horizontal axis: temperature, vertical axis: heat quantity), the straight line extending to the high temperature side through two points in the curve on the low temperature side and the gradient of the stepped change part in the curve are maximized. The temperature at the point of intersection with the tangent line drawn at the point was taken as the "glass transition temperature of the resin particles".
[Temperature program]:
(1) Raise the temperature to 200°C at a rate of 10°C/min (2) Decrease the temperature from 200°C to -50°C at a rate of 5°C/min (3) Raise the temperature from -50°C to 200°C at a rate of 10°C/min

<Resin preparation>
(Resin 1-7)
A mixture of the components (unit: part) shown in the item "Esterification reaction" in Table 1 was placed in a reaction vessel installed in an autoclave, and the mixture was heated at 220°C for 4 hours to carry out an esterification reaction. Then, the temperature was raised to 240° C. and the pressure was reduced to 13 Pa over 90 minutes. After the esterification (dehydration condensation) reaction was continued while maintaining the pressure of 240° C. and the reduced pressure of 13 Pa for 5 hours, the pressure was returned to normal pressure by introducing nitrogen gas. After lowering the temperature to 220° C., the catalyst (tetra-n-butyl titanate) and the components (unit: parts) shown in the item “Transesterification reaction” in Table 1 are added and heated at 220° C. for 2 hours. A transesterification reaction was carried out. The amount of catalyst used was defined as “3×10 ⁻⁴ ×total amount of polycarboxylic acid used (mol)”. After that, nitrogen gas was introduced to pressurize, and the sheet-like resin was taken out. After cooling the removed resin to 25° C., it was pulverized using a crusher to obtain a polyester resin. Table 1 shows the properties of the obtained polyester resin. The meaning of the abbreviation of each component in Table 1 is shown below.
・EG: ethylene glycol ・NPG: neopentyl glycol ・BPA: 2,2-bis(4-hydroxyphenyl)propane ・tPA: terephthalic acid ・iPA: isophthalic acid ・HAD: adipic acid ・BTA: trimellitic acid

A stirrer (trade name “Tornado Stirrer Standard SM-104” manufactured by AS ONE) was set in a 2 L beaker. Into this beaker, 210 g of the polyester resin of the type shown in Table 2 and tetrahydrofuran in the amount (g) shown in Table 2 were added and 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. Further, 900 g of ion-exchanged water was added dropwise at a rate of 20 mL/min while stirring at 25° C. and a stirring rate shown in Table 2. After that, the temperature was raised to 60° C., and tetrahydrofuran and part of water were distilled off under reduced pressure. The beaker was placed in a water bath and stirred at 85°C for 1 hour for heat treatment. After the content was filtered through a 150-mesh (150 gaps per inch) wire mesh, the resin particle content was adjusted. In this way, liquids containing resins 1 to 7, which are polyester resin particles and have a resin content of 40.0%, were obtained. Table 2 shows the properties of the obtained resin.

(liquid containing resins 8 to 16)
Liquids containing commercially available resins shown in Table 3 were prepared as resins 8-16.

(liquid containing resin 17)
32.8 parts of isophorone diisocyanate and 52.0 parts of polypropylene glycol having a number average molecular weight of 2,000 were placed in a four-necked flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and reflux tube, and the mixture was stirred under a nitrogen gas atmosphere. , and 100° C. for 2 hours. Then, 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., ion-exchanged water is added, and while stirring at high speed with a homomixer, potassium hydroxide is added in an amount equimolar to the acid value of the resin to obtain a liquid containing the resin. rice field. Methyl ethyl ketone was distilled off from the resulting liquid by heating under reduced pressure. As a result, a liquid containing resin 17, which is a water-soluble urethane resin and has a resin content of 40.0%, was obtained.

(liquid containing resin 18)
55.0 parts of methyl methacrylate, 30.0 parts of butyl acrylate, and 15.0 parts of acrylic acid were mixed to prepare a mixture of 100.0 parts of monomers. In a four-necked flask equipped with a thermometer, stirrer, nitrogen inlet, and reflux condenser, half the above monomer mixture (50.0 parts), sodium dodecylbenzenesulfonate (emulsifier) 2.0 parts, and 150.0 parts of ion-exchanged water were charged. Then, nitrogen was introduced to keep the inside of the flask under a nitrogen atmosphere, and the mixture was stirred with a homogenizer (trade name “T50D Ultra Turrax”, manufactured by IKA) and heated to 90°C. Next, the remaining amount (50.0 parts) of the above monomer mixture and a solution of 1.0 part of potassium persulfate dissolved in 20.0 parts of ion-exchanged water were added dropwise to the flask over 2 hours. . After that, the mixture was stirred at 90°C for another 2 hours and then returned to 25°C. Next, the pH of the liquid is adjusted to 8.5 using an appropriate amount of potassium hydroxide, and an appropriate amount of ion-exchanged water is added to contain the resin 18, which is an acrylic resin particle, and the resin content is 40.0. % of resin 18 was obtained. Resin 18 had a glass transition temperature of 37° C. and a _D50 of 120 nm.

(Liquid containing resin 19)
Contains resin 19, which is acrylic resin particles and has a resin content of 40.0%, in the same procedure as the preparation of liquid containing resin 18, except that butyl acrylate is changed to styrene got the liquid. Resin 19 had a glass transition temperature of 104° C. and a _D50 of 120 nm.

<Ink preparation>
Each component (unit: %) shown in the upper row of Tables 4-1 to 4-7 was mixed and thoroughly stirred, and then pressure-filtered through a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm. Inks were prepared. Ink properties are shown in the lower part of Tables 4-1 to 4-7. In the case of the ink containing the first resin particles, the “specific organic solvent content S” is the content of the compounds represented by the general formulas (1) to (3). In the case of the ink containing the second resin particles, the "specific organic solvent content S" is the content of the compounds represented by the general formulas (1) and (2). Furthermore, in the case of an ink containing a resin other than the first resin particles and the second resin particles, the "specific organic solvent content S" is the content of the compounds represented by the general formulas (1) to (3). is.

<Evaluation>
The following evaluation was performed using the ink obtained above. In the present invention, in the following evaluation criteria for each item, "A" and "B" were defined as acceptable levels, and "C" was defined as an unacceptable level. Table 5 shows the evaluation results.

(Scratch resistance)
Each of the prepared inks was filled in an ink cartridge, and set in an inkjet recording apparatus (trade name “PIXUS iP3100” manufactured by Canon Inc.) that ejects ink from a recording head by the action of thermal energy. In this embodiment, the printing duty of a solid image printed under the condition that one ink droplet of about 5 ng per droplet is applied to a unit area of 1/1,200 inch×1/1,200 inch is assumed to be 100%. Define. A solid image of 200 mm×200 mm (recording duty 100%) was recorded on a recording medium (coated paper, product name “LX Gloss Coat 157”, manufactured by Sakurai) using the inkjet recording apparatus described above. This recording medium is a low-absorbent recording medium having a water absorption of 10 mL/m ² or less from the start of contact to 30 msec ^1/2 in the Bristow method. After leaving the recorded solid image for one day, it was tested with a load of 500 g using a Gakushin-type testing machine (trade name: "Abrasion Resistance Tester", manufactured by Imoto Seisakusho Co., Ltd.) capable of performing measurements according to JIS L 0849. A friction test was conducted under the condition of 10 reciprocations. The images after the friction test were visually observed, and the abrasion resistance of the images was evaluated according to the evaluation criteria shown below.
A: There was no scratch mark on the image.
B: The image had scratches, but the recording medium was not visible.
C: The image had scratches and the recording medium was visible.

(Ejection stability)
An ink cartridge was filled with each of the prepared inks, and set in an inkjet recording apparatus (trade name: "iB4030", manufactured by Canon Inc.) that ejects ink from a recording head by the action of thermal energy. In this embodiment, the print duty of a solid image printed under the condition that one ink droplet of approximately 22 ng per droplet is applied to a unit area of 1/600 inch×1/600 inch is defined as 100%. After recording one solid image with a recording duty of 5% on the entire surface of an A4 size recording medium (plain paper, product name “PB PAPER”, manufactured by Canon) in an environment with a temperature of 30° C. and a relative humidity of 10%, A cycle of pausing recording for 240 seconds was repeated. This cycle was repeated until the total number of printed sheets reached 800 and 1,000. After recording solid images on 800 sheets and 1,000 sheets, vertical ruled lines were recorded on the recording medium. The recorded vertical ruled lines were visually observed, and the ejection stability of the ink was evaluated according to the evaluation criteria shown below.
AA: There was no disorder in the vertical ruled lines on the 1,000th sheet.
A: The vertical ruled lines on the 800th sheet were not disturbed, and the vertical ruled lines on the 1,000th sheet were disturbed, but the ruled lines were not broken.
B: On both the 800th sheet and the 1,000th sheet, the vertical ruled lines were disturbed, but the ruled lines were not interrupted.
C: The vertical ruled line on the 1,000th sheet was disturbed and part of the ruled line was missing.

Claims (11)

A water-based inkjet ink containing a pigment, resin particles, and an organic solvent,
The resin particles are first resin particles made 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) A water-based ink characterized by being a seed.

(In general formula (1), R ₁ and R ₂ each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms. In general formula (2), R ₃ is ethylene or a propylene group, _R4 represents a methyl group or an ethyl group, n represents 0 or 1, and n is ₁ when R3 is an ethylene group. R ₅ and R ₆ each independently represent a linear or branched alkyl group having 1 to 4 carbon atoms, and R ₇ represents an alkylene group having 1 to 4 carbon atoms) The water-based ink according to claim 1, wherein the first resin particles have a glass transition temperature of 50°C or higher. A water-based inkjet ink containing a pigment, resin particles, and an organic solvent,
The resin particles are second resin particles made of urethane resin,
A water-based ink, wherein the organic solvent is at least one selected from the group consisting of a compound represented by the following general formula (1) and a compound represented by the following general formula (2).

(In general formula (1), R ₁ and R ₂ each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms. In general formula (2), R ₃ is ethylene or a propylene group, _R4 represents a methyl group or an ethyl group, n represents 0 or 1, and n is ₁ when R3 is an ethylene group) 4. The water-based ink according to claim 3, wherein the glass transition temperature of the second resin particles is -40°C or higher. 5. 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. 6. The water-based ink according to any one of claims 1 to 5, wherein the content (% by 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. 6. The water-based ink according to any one of claims 1 to 5, wherein the content (% by 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. 8. The content (% by mass) of the organic solvent is 0.1 times or more and 10.0 times or less as a mass ratio with respect to the content (% by mass) of the resin particles, according to any one of claims 1 to 7 Aqueous ink as described. 8. The content (% by mass) of the organic solvent is 0.1 times or more and 5.0 times or less as a mass ratio with respect to the content (% by mass) of the resin particles, according to any one of claims 1 to 7 Aqueous ink as described. An ink cartridge comprising ink and an ink containing portion containing the ink,
An ink cartridge, wherein the ink is the water-based ink according to any one of claims 1 to 9. An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head,
An inkjet recording method, wherein the ink is the water-based ink according to any one of claims 1 to 9.

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