JP2022187337A - Aqueous ink, ink cartridge and inkjet recording method - Google Patents

Abstract

To provide an aqueous ink having excellent discharge stability and sticking-restoration property which can record a fluorescent color image having excellent color development regardless of a type of recording media.SOLUTION: There is provided an aqueous ink for inkjet which contains resin particles dyed with a fluorescent dye, a compound represented by a general formula (1) and a water-soluble resin. The fluorescent dye contains a coumarin dye exhibiting fluorescence, the resin particles have a core part containing an aromatic group-containing unit and a cyano group-containing unit and a shell part containing an aromatic group-containing unit, an anionic group-containing unit and a unit derived from a crosslinking agent and containing no cyano group-containing unit. (R1 represents an alkylamino group, R2 represents an aromatic group or a heteroaromatic group, M represents a hydrogen atom, an alkali metal, ammonium or an organic ammonium.)SELECTED DRAWING: None

Description

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

In the printing industry, there is a demand for an expansion of the expressible color gamut. Examples of color gamut standards include PANTONE certification (X-rite), Japan Color certification (Japan Printing Machinery Manufacturers Association), DIC color guide certification (DIC), and Kaleido certification (Toyo Ink). In recent years, in order to expand the color gamut, ink jet recording apparatuses using special color inks other than the basic colors of cyan, magenta, and yellow, and high-brightness special color inks have come to be used.

Another need in the printing industry is the production of eye-catching, brightly colored recordings. For example, notices such as posters and POPs, packaging of food and beverage products, etc. are required to be recorded in vivid colors to attract the customer's line of sight. It can be said that fluorescent colors are effective in satisfying such needs. Fluorescent materials suitable for paints, inks, etc. have been proposed so far (Patent Document 1). However, the current situation is that a fluorescent material having sufficient inkjet suitability has not yet been established.

JP 2009-161688 A

Currently, offset printing is the mainstream method for recording fluorescent color images. However, when a fluorescent color image is recorded by one-time offset printing, it is difficult to obtain vivid color development, so it has been common practice to carry out overprinting of two or more times. For this reason, the method of recording fluorescent images with excellent color development by overprinting has problems in terms of productivity and cost.

Further, in the case of digital recording using an electrophotographic method, it is possible to record a highly colored fluorescent color image using a liquid toner. However, since the electrophotographic method has restrictions on the recording medium, it is difficult to apply it to, for example, textile recording, development to large format, and application to thick materials.

On the other hand, digital recording using an inkjet method can be applied to various recording media by taking advantage of the fact that the recording head that ejects ink does not contact the recording medium. However, since the ink is ejected from minute nozzles on the order of microns by applying mechanical energy or thermal energy, the physical properties of the ink, such as viscosity, are likely to be restricted. In particular, many of the materials that affect ink performance, such as colorants and resins, are solid. There are restrictions on the amount added to the ink. The same is true for fluorescent coloring materials such as fluorescent dyes, and even if a sufficient amount of fluorescent coloring material is added to the ink in order to record an image with excellent color development, the physical properties of the ink are limited.

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 fixation recovery, and which is capable of recording a fluorescent color image with excellent color development regardless of the type of recording medium. be. 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, an aqueous ink for inkjet containing resin particles dyed with a fluorescent dye, a compound represented by the following general formula (1), and a water-soluble resin, wherein the fluorescent dye is , a fluorescent coumarin dye, and the resin particles comprise a core portion containing an aromatic group-containing unit and a cyano group-containing unit, an aromatic group-containing unit, an anionic group-containing unit, and a unit derived from a cross-linking agent. and a shell portion that does not contain a cyano group-containing unit, and the proportion (% by mass) of units derived from the crosslinking agent in the shell portion is 30% by mass or more and 80% by mass or less, and Provided is an aqueous ink, wherein the water-soluble resin has an aromatic group-containing unit and an anionic group-containing unit, and the water-soluble resin has an acid value of 100 mgKOH/g or more and 180 mgKOH/g or less. .

（前記一般式（１）中、Ｒ_１は、アルキルアミノ基を表し、Ｒ_２は、芳香族基又は複素芳香族基を表し、Ｍは、水素原子、アルカリ金属、アンモニウム、又は有機アンモニウムを表す）

(In the general formula (1), R ₁ represents an alkylamino group, R ₂ represents an aromatic group or a heteroaromatic group, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. )

According to the present invention, it is possible to provide a water-based ink that is excellent in ejection stability and fixation recovery, and that can record a fluorescent color image with excellent color development regardless of the type of recording medium. 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". Physical properties are values at room temperature (25° C.) unless otherwise specified. In the present invention, a "unit" constituting a resin means a repeating unit derived from one monomer.

The present inventors have found that ink jet suitability (ejection stability and fixation recovery property that easily eliminates clogging of ejection ports) that can record fluorescent images with excellent color development regardless of the type of recording medium ), the composition of the ink excellent in In particular, in order to improve the color development of images, we focused on expanding the color gamut in high-brightness areas that are difficult to express with basic colors. In order to expand the color gamut in a high-brightness region, it is preferable to use a fluorescent dye as a coloring material.

Fluorescent coumarin dyes are effective dyes for expanding color reproduction in high brightness regions. However, it has been found that an image recorded on some recording media such as plain paper with an ink containing a coumarin dye that exhibits fluorescence as a coloring material has high brightness and is therefore less visible. Therefore, the present inventors have studied a combination of colorants that can suppress the deterioration of visibility while enlarging the brightness range. As a result, they have found that a compound represented by the following general formula (1) is used together with a coumarin dye that exhibits fluorescence.

（前記一般式（１）中、Ｒ_１は、アルキルアミノ基を表し、Ｒ_２は、芳香族基又は複素芳香族基を表し、Ｍは、水素原子、アルカリ金属、アンモニウム、又は有機アンモニウムを表す）

(In the general formula (1), R ₁ represents an alkylamino group, R ₂ represents an aromatic group or a heteroaromatic group, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. )

It has been found that the use of the compound represented by formula (1) improves the ejection stability of ink containing resin particles dyed with a fluorescent dye, which will be described later. The aromatic ring in the structure of the compound represented by the general formula (1) adsorbs to the aromatic group-containing units constituting the resin particles through hydrophobic interactions. Since the carboxylic acid group and the hydroxy group in the structure of the compound represented by the general formula (1) are hydrophilic groups, these hydrophilic groups improve the dispersion stability of the resin particles in the water-based ink. play a supporting role. Therefore, it is considered that the use of the compound represented by the general formula (1) improves the ejection stability of ink containing resin particles dyed with a fluorescent dye. Furthermore, it has been found that it is essential to include resin particles dyed with a fluorescent dye.

The inventors have attempted to add the fluorescent dye itself to the ink. However, it was found that when the amount of fluorescent dye added was increased to obtain the desired level of color development, the chroma of the image was improved, but the brightness was significantly reduced. This is considered to be due to concentration quenching peculiar to the fluorescent material. From the above, it was found that it is essential to dye the resin particles with a fluorescent dye. When the resin particles are dyed with the fluorescent dye, the fluorescent dye is fixed to the resin particles, so that the decrease in brightness of the image can be suppressed.

Common methods for dyeing resin particles with a fluorescent dye include (i) a method called an addition-condensation bulk resin pulverization method, in which a bulk resin is condensed, dyed, and then pulverized to obtain particles; and (ii) ) A method in which resin particles are prepared by emulsion polymerization in an aqueous system and dyed. The resin particles obtained by the method (i) are micron-order in size and low in water dispersibility, making it difficult to apply them to the ink used in the ink jet recording method. On the other hand, the resin particles obtained by the method (ii) have applicability to aqueous systems and are excellent in inkjet suitability because the size thereof can be controlled to nano-order. However, when the conventional ink containing resin particles produced by the method (ii) was used to examine the color developability and reliability, it was found that several problems would arise.

Accordingly, the present inventors have investigated the color developability of an image recorded with an ink containing resin particles dyed with a fluorescent dye. In order to enhance the color development of images, it is important to dye the resin with a fluorescent dye through strong interaction. The inventors have found to exploit hydrophobic interactions and dipole interactions. Specifically, a fluorescent coumarin dye having a hydrophobic portion typified by an aromatic group and the like, and a resin particle containing an aromatic group-containing unit and a unit containing a cyano group, which is a polar group, are used in combination. I found out. As a result, in addition to the hydrophobic interaction between the fluorescent dye and the hydrophobic groups of the resin particles, highly polar portions such as nitrogen atoms, sulfur atoms, and oxygen atoms in the molecule of the fluorescent dye and the cyano groups in the resin particles The fluorescent dye is stably dyed to the resin particles by the dipole interaction of . If the fluorescent dye has an aromatic group, in addition to these effects, π-π interactions with the aromatic groups of the resin particles also occur. Thus, by using resin particles that are dyed by a plurality of strong interactions, it is possible to enhance the color developability of the image.

However, since the cyano group has a high polarity, it has been found that the cyano group tends to interact with many components in the ink including water, which tends to reduce the fixation recoverability of the ink. Water-based ink for inkjet is maintained so that it can be ejected normally by recovery processing such as pre-ejection and suction or pressurization using a cap, even when it is concentrated due to moisture evaporation from the ejection port. However, if the solid content such as resin particles aggregates and becomes difficult to redisperse, the original state may not be restored even by the recovery process, and as a result, the ink may not be ejected normally.

Even if an aqueous medium is added after an ink containing resin particles containing a cyano group-containing unit is evaporated to dryness, the resin particles can hardly be redispersed. In the ink that has been concentrated by water evaporation, the cyano groups in the resin particles interact strongly with highly polar components (water, water-soluble organic solvents, etc.), so re-dispersion is considered to be difficult. The present inventors have investigated the composition of an ink that is excellent in fixation recoverability while containing resin particles containing a cyano group-containing unit. As a result, the present inventors have found that by using resin particles having a core-shell structure and providing a cyano group-containing unit only in the core portion, it is possible to improve the color development of images and the recovery of ink fixation. Furthermore, they have found that it is important to have aromatic group-containing units in both the core portion and the shell portion. It is believed that the core and the shell are in strong contact with each other due to the hydrophobic interaction and π-π interaction of the aromatic groups, so that the deterioration of fixation recovery can be suppressed.

However, it has been found that ink ejection stability is insufficient even when the resin particles having the core-shell structure described above are used. In order to adapt the resin particles to the aqueous medium in the ink, it is necessary to incorporate the anionic group-containing unit into the shell portion. As a result of investigation, it has been found that it is difficult to improve the ejection stability of the ink by adjusting the amount of the anionic group-containing unit in the resin particles. That is, when the anionic group-containing unit is incorporated in the shell in an amount that can ensure the ejection stability of the ink, the hydrophilicity of the shell becomes too high, and the core cannot be sufficiently coated. The cyano group will be exposed. As a result, the exposed cyano group and the highly polar component strongly interact with each other, which is thought to reduce the ejection stability of the ink.

The anionic group in the shell easily interacts with the cyano group in the core. Therefore, the anionic group in the shell preferably exists in the surface layer of the shell in order to contribute to stabilizing the dispersion of the resin particles. However, in practice, the anionic groups in the shell are likely to be attracted to the cyano groups in the core and drawn into the shell. Therefore, compared with conventional resin particles having a core-shell structure, in the case of resin particles having a cyano group in the core portion, the amount of the anionic group-containing unit in the shell portion required to ensure the ejection stability of the ink is increases. As a result, the hydrophilicity of the shell portion becomes excessively high, making it difficult to sufficiently cover the core portion. As described above, it is difficult to improve ink ejection stability only by devising the composition of resin particles having a core-shell structure.

As a result of further studies, the present inventors have found that adding a water-soluble resin having an aromatic group-containing unit and an anionic group-containing unit to the ink can improve the ejection stability of the ink. The aromatic groups of the water-soluble resin and the aromatic groups of the resin particles undergo hydrophobic interaction and π-π interaction, and the water-soluble resin is adsorbed to the resin particles. As a result, it is considered that the water-soluble resin assists the dispersion of the resin particles.

Furthermore, it has been found that the addition of a water-soluble resin to the ink improves the color developability of the image. The resin particles are dyed with the fluorescent dye through interaction between the highly polar portion in the molecule of the fluorescent dye and the cyano group contained in the core portion constituting the resin particles. The present inventors have confirmed that the state in which the resin particles are dyed with the fluorescent dye is maintained even in the ink. However, when a water-soluble resin having an aromatic group and resin particles dyed with a fluorescent dye are used in combination, after the ink is stored for a long period of time, a part of the fluorescent dye is separated from the anionic groups of the water-soluble resin. It was found that they interacted with each other, separated from the resin particles, and moved to the vicinity of the water-soluble resin.

The present inventors verified the difference in behavior of the fluorescent dye depending on the presence or absence of the water-soluble resin. As a method for easily separating ink components, a centrifugal separation method using a density gradient was used to verify inks containing and not containing a water-soluble resin. As a result, in the case of the ink containing the water-soluble resin, in addition to the colored layer of the resin particles, a colored layer derived from the dye was also confirmed in the layer of the water-soluble resin. In contrast, in the case of ink containing no water-soluble resin, only a colored layer of resin particles was observed. From the above, it was found that part of the fluorescent dye migrated to the vicinity of the water-soluble resin.

As a part of the fluorescent dye moves from the resin particles to the vicinity of the water-soluble resin, the content of the fluorescent dye in the dyed resin particles decreases. The present inventors prepared a plurality of dyed resin particles with different fluorescent dye contents, and prepared an ink using these prepared resin particles. When the color developability of the image recorded using the prepared ink was evaluated, it was found that the brightness of the image recorded with the ink prepared using resin particles with a low content of fluorescent dye tended to be high. . It is believed that the phenomenon of "concentration quenching" peculiar to fluorescent dyes is responsible for the increase in brightness of images recorded with inks prepared using resin particles containing a small amount of fluorescent dye. If the density of the fluorescent dye in the system is too high, the excitation light and fluorescence of the dye molecules interfere with each other, which tends to cancel out the original vivid color development. On the other hand, when the density of the fluorescent dye in the system is low, interference is less likely to occur, and the original color development is maintained. That is, part of the fluorescent dye dyeing the resin particles moves to the vicinity of the water-soluble resin, and the content of the fluorescent dye in the resin particles is reduced, so that concentration quenching is suppressed and the brightness of the image is improved. did. Furthermore, since the amount of the fluorescent dye in the ink was kept constant, the chroma of the image did not fluctuate, and it is thought that the color developability was improved.

Further, it has been found that the addition of a water-soluble resin to an ink containing resin particles improves the ejection stability and the color development of an image, but reduces the fixation recoverability. Ions derived from the anionic groups of the water-soluble resin neutralize the anionic groups in the shell portion of the resin particles, increasing the hydrophilicity of the shell portion. As a result, the state of covering the core portion with the shell portion is loosened, and the cyano groups of the core portion are likely to be exposed. Furthermore, when a water-soluble resin is added to an ink containing resin particles, the fluorescent dye that has been released from the dyeing state and is separated from the resin particles tends to precipitate due to its low hydrophilicity, and the storage stability of the ink is improved. was also found to contribute to the decrease in It was also found that the degree of storage stability depends on the acid value of the water-soluble resin, and that the higher the acid value of the water-soluble resin, the lower the fixation recoverability and storage stability.

As a result of investigation, it was found that the water-soluble resin should have an acid value of 100 mgKOH/g or more in order to improve the ejection stability. On the other hand, when the acid value of the water-soluble resin is 100 mgKOH/g or more, as described above, the fixation recoverability tends to decrease. Therefore, the present inventors have studied the requirements for more firmly covering the core portion with the shell portion. As a result, they found that the unit derived from the cross-linking agent should be incorporated into the shell portion, and that the ratio (% by mass) of the unit derived from the cross-linking agent in the shell portion should be 30% by mass or more. This makes it difficult for the cyano group in the core portion to be exposed, thereby suppressing deterioration of fixation recoverability and storage stability. On the other hand, if the ratio (% by mass) of the units derived from the cross-linking agent is more than 80% by mass, the ejection stability is lowered. Further, regardless of the ratio of the units derived from the cross-linking agent, if the water-soluble resin has an acid value of more than 180 mgKOH/g, the hydration of the anionic groups in the shell is remarkably promoted. For this reason, the covering state of the core portion with the shell portion is likely to be loosened, making it impossible to suppress deterioration of fixation recoverability and storage stability. Note that when adding another resin particle having an aromatic group-containing unit and an anionic group-containing unit instead of a water-soluble resin to an ink containing resin particles, although the color development can be improved, the ejection stability of the ink can be improved. The effect of improving the properties is not obtained.

<Aqueous ink>
The ink of the present invention is a water-based ink for inkjet containing resin particles dyed with a fluorescent dye, a compound represented by the following general formula (1), and a water-soluble resin. Fluorescent dyes include coumarin dyes that exhibit fluorescence. The resin particle contains a core portion containing an aromatic group-containing unit and a cyano group-containing unit, and a shell containing an aromatic group-containing unit, an anionic group-containing unit, and a unit derived from a cross-linking agent, but not containing a cyano group-containing unit. and The ratio (% by mass) of units derived from the cross-linking agent in the shell portion is 30% by mass or more and 80% by mass or less. Moreover, the water-soluble resin has an aromatic group-containing unit and an anionic group-containing unit. The acid value of the water-soluble resin is 100 mgKOH/g or more and 180 mgKOH/g or less. Each component constituting the ink will be described below. The present invention is not limited by the following description as long as the gist thereof is not exceeded. Hereinafter, "(meth)acrylic acid", "(meth)acrylate", and "(meth)acryloyl" refer to "acrylic acid, methacrylic acid", "acrylate, methacrylate", and "acryloyl, methacryloyl", respectively. shall be Since the ink of the present invention does not need to be active energy ray-curable, it does not need to contain a monomer having a polymerizable group.

（前記一般式（１）中、Ｒ_１は、アルキルアミノ基を表し、Ｒ_２は、芳香族基又は複素芳香族基を表し、Ｍは、水素原子、アルカリ金属、アンモニウム、又は有機アンモニウムを表す）

(In the general formula (1), R ₁ represents an alkylamino group, R ₂ represents an aromatic group or a heteroaromatic group, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. )

(fluorescent dye)
As used herein, the term "fluorescent dye" refers to a dye that emits fluorescence when exposed to ultraviolet or visible excitation light. Whether a given dye is a “fluorescent dye” that exhibits fluorescence can be determined, for example, according to the method described below. A sample obtained by dissolving a dye in a liquid capable of dissolving the dye is irradiated with ultraviolet light (ultraviolet light) having a slightly visible long wavelength (about 315 to 400 nm) using a black light or the like. Then, if light of a color different from the ultraviolet light emitted by the black light can be visually observed, it can be determined that the dye is a "fluorescent dye" that exhibits fluorescence. As the black light, commercially available products (eg, product name “SLUV-4” (manufactured by AS ONE), etc.) can be used.

The fluorescent dye in the resin particles dyed with the fluorescent dye can be analyzed, for example, according to the procedure shown below. A sample is prepared by dissolving the resin particles taken out from the ink according to a conventional method in an organic solvent such as chloroform. Fluorescent dyes are isolated from prepared samples using HPLC (high performance liquid chromatograph). The isolated dyes are analyzed by common structural analysis techniques such as nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS).

Fluorescent dyes include coumarin dyes that exhibit fluorescence. Among fluorescent dyes, coumarin dyes are excellent in color development in a high-brightness region, and are effective dyes for expanding the color reproduction region. As the coumarin dye, it is preferable to use a compound having low water solubility or substantially no water solubility, such as an oil-soluble dye or a disperse dye. Disperse dyes are compounds exhibiting fluorescence that are poorly soluble or insoluble in water. Examples of "disperse dyes" include "dyes whose names include 'disperse' in the color index". Also, the oil-soluble dye is a compound exhibiting fluorescence that has low water solubility or does not dissolve in water. Examples of oil-soluble dyes include "dyes whose names include 'solvent' in the Color Index".

A specific example of a fluorescent coumarin dye is C.I. I. Indicated by number, C.I. I. Solvent Yellow 160:1, 172, 196; C.I. I. Disperse Yellow 82; C.I. I. Basic Yellow 40 and the like can be mentioned. Among them, C.I. I. Solvent Yellow 160:1, 196; C.I. I. Disperse Yellow 82 and the like are preferred.

The content (% by mass) of the fluorescent dye in the ink is preferably 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink. The ratio (% by mass) of the fluorescent dye in the resin particles is preferably 1.0% by mass or more and 15.0% by mass or less, and more preferably 3.0% by mass or more and 8.0% by mass or less. preferable. If the proportion of the fluorescent dye in the resin particles is too low, the color development (chroma) of the image may be slightly lowered. On the other hand, if the proportion of the fluorescent dye in the resin particles is too high, the color development (brightness) of the image may slightly decrease due to concentration quenching.

(resin particles)
The term "resin particles" as used herein means a resin that can exist in an aqueous medium in a state of being dispersed in the aqueous medium and having a particle size. Therefore, the resin particles exist in a state of being dispersed in the ink, that is, in a state of a resin emulsion.

Whether or not a certain resin is a "resin particle" can be determined according to the method described below. First, a liquid (resin solid content: 10% by mass) containing a resin neutralized with an acid value equivalent alkali (sodium hydroxide, potassium hydroxide, etc.) is prepared. Next, the prepared liquid is diluted 10-fold (by volume) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by the dynamic light scattering method, if particles having a particle size are measured, the resin can be determined to be "resin particles". A particle size analyzer (for example, trade name “UPA-EX150” manufactured by Nikkiso Co., Ltd.) can be used as a particle size distribution measuring device using the dynamic light scattering method. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: spherical, refractive index: 1.59. Of course, the particle size distribution measuring device and measurement conditions to be used are not limited to those described above. The reason why the particle size is measured using the neutralized resin is to confirm that particles are formed even when the resin is sufficiently neutralized to make it more difficult to form particles. Even under such conditions, the resin having the shape of particles exists in the form of particles even in the water-based ink.

As the resin particles, resin particles having a so-called core-shell structure, which has a core portion and a shell portion covering the core portion, are used. The core portion includes an aromatic group-containing unit and a cyano group-containing unit. By including the aromatic group-containing unit and the cyano group-containing unit in the core portion, the various interactions described above between the fluorescent dye and the resin particles are increased. For this reason, the resin particles are efficiently dyed with the fluorescent dye, and the original color development property of the fluorescent dye is efficiently exhibited, so that the color development property of the image can be improved. It is preferable to use resin particles made of an acrylic resin.

The shell portion includes an aromatic group-containing unit, an anionic group-containing unit, and a unit derived from a cross-linking agent. Moreover, the shell part does not substantially contain a cyano group-containing unit. Since the shell portion does not contain a cyano group-containing unit, substantially no cyano group exists on the surface of the resin particles, and the recovery from fixation of the ink can be improved. If a highly polar cyano group is exposed on the surface of the resin particles, the cyano group interacts with water in the ink or a water-soluble organic solvent. When the cyano group interacts with water and the like to form a film of the resin particles, it becomes difficult to redisperse the resin particles, resulting in a decrease in ink fixation recoverability.

Also, when the shell portion contains the aromatic group-containing unit, hydrophobic interaction and π-π interaction occur with the aromatic group in the core portion. As a result, the shell portion is less likely to separate from the core portion, and the cyano groups in the core portion are less likely to be exposed on the surface of the resin particles, thereby improving the recovery from the fixation of the ink. It is preferable that the aromatic group-containing unit contained in the core portion and the aromatic group-containing unit contained in the shell portion are of the same type. “Homogeneous units” means units derived from the same monomer. When the aromatic group-containing unit contained in the core portion and the aromatic group-containing unit contained in the shell portion are of the same type, the interaction between the core and shell is further enhanced, thereby further improving the fixation recovery of the ink. can be improved.

As a monomer that becomes an aromatic group-containing unit by polymerization, a monomer having one polymerizable functional group such as an ethylenically unsaturated bond in the molecule is preferable. Specifically, styrene, vinyltoluene, p-fluorostyrene, p-chlorostyrene, α-methylstyrene, 2-vinylnaphthalene, 9-vinylanthracene, 9-vinylcarbazole, phenyl (meth)acrylate, benzyl (meth) Acrylates, 2-phenoxyethyl (meth)acrylate, 2,4-diamino-6-((meth)acryloyloxy)ethyl-1,3,5-triazine, 2-naphthyl (meth)acrylate, 9-anthryl (meth) Acrylate, (1-pyrenyl)methyl (meth)acrylate and the like can be mentioned. As a monomer that becomes an aromatic group-containing unit by polymerization, a monomer that does not have an anionic group or a cyano group, or has a molecular weight of 300 or less is preferable, and a molecular weight of 200 or less is more preferable. Among these, styrene and its derivatives are more preferable, and styrene and vinyltoluene are particularly preferable, because the reactivity during polymerization is good and the stability of the resulting resin particles is excellent.

As a monomer that becomes a cyano group-containing unit by polymerization, a monomer having one polymerizable functional group such as an ethylenically unsaturated bond in the molecule is preferable. Specific examples include acrylonitrile, methacrylonitrile, chloroacrylonitrile, 2-cyanoethyl (meth)acrylate and the like. As a monomer that becomes a cyano group-containing unit by polymerization, a monomer having no anionic group or aromatic group or having a molecular weight of 300 or less is preferable, and a molecular weight of 200 or less is more preferable. Among these, acrylonitrile and methacrylonitrile are particularly preferred because they have good reactivity during polymerization and excellent stability of the resulting resin particles.

The anionic group in the anionic group-containing unit preferably has one polymerizable functional group such as an ethylenically unsaturated bond in the molecule. Specific examples include a carboxylic acid group, a phenolic hydroxy group, and a phosphate ester group. Among them, a carboxylic acid group is preferable because the stability of the resin particles in the ink is good. Monomers that become anionic group-containing units by polymerization include (meth)acrylic acid, p-vinylbenzoic acid, 4-vinylphenol, β-carboxyethyl (meth)acrylate, and phosphoric acid (2-hydroxyethyl methacrylate). Esters, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate and the like can be mentioned. As a monomer that becomes an anionic group-containing unit by polymerization, a monomer having no aromatic group or cyano group, or having a molecular weight of 300 or less is preferable, and a molecular weight of 200 or less is more preferable. Among them, (meth)acrylic acid is particularly preferred. Moreover, the anionic group in the anionic group-containing unit is preferably only a carboxylic acid group. The anionic group may be in either an acid form or a salt form, and in the case of a salt form, it may be in a partially dissociated state or in a completely dissociated state. When the anionic group is in the salt form, cations that serve as counter ions include alkali metal cations, ammonium and organic ammonium.

At least one cross-linking agent constituting a unit derived from a cross-linking agent may be used, and two or more cross-linking agents are preferably used. When the cross-linking agent contains two or more cross-linking agents, at least one cross-linking agent is preferably a cross-linking agent having a glycidyl group. A cross-linking agent having a glycidyl group reacts with an anionic group such as a carboxylic acid group present in the shell to cross-link. As a result, it is possible to suppress an excessive increase in the hydrophilicity of the shell portion, and to further improve the fixation recoverability of the ink. Furthermore, by using two or more kinds of cross-linking agents, it is possible to form a dense cross-linked structure that can more efficiently suppress an excessive increase in the hydrophilicity of the shell portion. In addition, by forming such a dense crosslinked structure, it is possible to suppress leakage of the dye that dyes the resin particles to the outside of the resin particles.

Examples of the cross-linking agent that becomes a unit derived from the cross-linking agent by polymerization include compounds having two or more polymerizable functional groups such as ethylenically unsaturated bonds in the molecule. Such crosslinking agents include diene compounds such as butadiene and isoprene; 1,4-butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, (mono-, di-, tri-, Poly-) ethylene glycol di(meth)acrylate, (mono-, di-, tri-, poly-) propylene glycol di(meth)acrylate, (mono-, di-, tri-, poly-) tetramethylene glycol di( meth)acrylate, ethylene oxide-modified bisphenol A di(meth)acrylate, 2-hydroxy-3-(meth)acryloyloxypropyl methacrylate, propoxylated ethoxylated bisphenol A di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate , 9,9-bis(4-(2-(meth)acryloyloxyethoxy)phenyl)fluorene, tricyclodecanedimethanol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,6- Bifunctional (meth)acrylates such as hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, ethoxylated polypropylene glycol di(meth)acrylate, glycerin di(meth)acrylate, etc. meth)acrylate; tris(2-(meth)acryloyloxyethyl)isocyanurate, trimethylolpropane tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth) ) acrylate, pentaerythritol tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, propoxylated glyceryl tri(meth)acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, ε-caprolactone-modified tris-(2- (Meth)acryloyloxyethyl)isocyanurate, trifunctional (meth)acrylates such as ethylene oxide-modified trimethylolpropane tri(meth)acrylate; ditrimethylolpropane tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, tetrafunctional (meth)acrylates such as pentaerythritol tetra(meth)acrylate; divinylbenzene and the like.

The cross-linking agent preferably has a molecular weight of more than 200, more preferably has a molecular weight of more than 300, and particularly preferably has a molecular weight of 400 or more. Moreover, as the cross-linking agent, a compound having two ethylenically unsaturated bonds in the molecule is preferable. By using a compound having two ethylenically unsaturated bonds in the molecule as a cross-linking agent, aggregation of resin particles caused by excessive cross-linking is suppressed, and resin particles having a more uniform particle size can be obtained. Among the compounds having two ethylenically unsaturated bonds in the molecule, divinylbenzene and ethylene glycol di(meth)acrylate are more preferable.

Cross-linking agents having a glycidyl group include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, sorbitol polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and pentaerythritol polyglycidyl ether. , propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, trimethylolpropane polyglycidyl ether, neopentyl glycol diglycidyl ether, and the like. Among them, ethylene glycol diglycidyl ether can form a high-density crosslinked structure, suppresses excessive increase in the hydrophilicity of the shell, and has a large effect of suppressing leakage of the dye from the resin particles. is preferred.

A surfactant can be used when producing the resin particles. It is preferable to produce resin particles in the presence of a surfactant because the particle size and shape of the obtained resin particles tend to be stable. However, the non-reactive surfactant may easily peel off from the resin particles. If the surfactant is peeled off in the ink, it may affect the physical properties of the ink and tend to lower the ejection stability. For this reason, reactive surfactants are preferred as surfactants used when producing resin particles.

Reactive surfactants are compounds in which polymerizable functional groups such as (meth)acryloyl groups, maleyl groups, vinyl groups, and allyl groups are bound to the inside or end of a molecule composed of a hydrophilic portion and a hydrophobic portion. is preferably used. Examples of hydrophilic moieties include polyoxyalkylene chains such as ethylene oxide chains and propylene oxide chains. Hydrophobic moieties can also include structures such as alkyl, aryl, and combinations thereof. The hydrophilic portion and the hydrophobic portion may be bonded via a linking group such as an ether group. As the reactive surfactant, those having a molecular weight of more than 200 are preferable, those having a molecular weight of more than 300 are more preferable, and those having a molecular weight of 400 or more are particularly preferable.

Specific examples of reactive surfactants include polyoxyethylene nonylpropenylphenyl ether, polyoxyethylene nonylpropenylphenyl ether ammonium sulfate, polyoxyethylene-1-(allyloxymethyl)alkyl ether ammonium sulfate, α-hydro-ω -(1-alkoxymethyl-2-(2-propenyloxy)ethoxy)-poly(oxy-1,2-ethanediyl)), α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl] -ω-hydroxypolyoxyethylene, α-sulfo-ω-(1-alkoxymethyl-2-(2-propenyloxy)ethoxy)-poly(oxy-1,2-ethanediyl)ammonium salt, 2-sodiumsulfoethyl Methacrylate, bis(polyoxyethylene polycyclic phenyl ether) methacrylate sulfate, alkoxypolyethylene glycol methacrylate, alkoxypolyethylene glycol maleate, polyoxyalkylene alkenyl ether, polyoxyalkylene alkenyl ether ammonium sulfate, vinyl ether alkoxylate, alkylallyl sulfosuccinate salts, polyoxyalkylene methacrylate sulfate ester salts, unsaturated phosphate esters, and the like. Among them, α-sulfo-ω-(1-alkoxymethyl-2-(2-propenyloxy)ethoxy)-poly(oxy-1,2-ethanediyl)ammonium salt (manufactured by Adeka under the trade name “Adekari Soap” SR -10S, SR-10, SR-20, SR-3025, SE-10N, SE-20N, etc.) are preferred.

The core portion and the shell portion of the resin particles may each contain units other than the above units as long as the effects of the present invention are not impaired. Units other than the above units preferably have one polymerizable functional group in the molecule, and specific examples thereof include units derived from ethylenically unsaturated monomers.

Ethylenically unsaturated monomers include alkenes such as ethylene and propylene; alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, lauryl (meth)acrylate and hexadecyl (meth)acrylate Acrylates; monocyclic (meth)acrylates such as cyclopropyl (meth)acrylate, cyclohexyl (meth)acrylate, cyclooctyl (meth)acrylate, cyclodecyl (meth)acrylate; isobornyl (meth)acrylate, norbornyl (meth)acrylate, etc. Bicyclic (meth) acrylates; adamantyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate and other tricyclic (meth) acrylates; methoxy (mono, di nonionic hydrophilic group-containing (meth)acrylates such as , tri, and poly)ethylene glycol (meth)acrylates; As the ethylenically unsaturated monomer, those having no anionic group, cyano group, or aromatic group and those having a molecular weight of 300 or less are preferable, and those having a molecular weight of 200 or less are more preferable. Among them, alkenes having 1 to 22 carbon atoms; alkyl (meth)acrylates having an alkyl group having 1 to 22 carbon atoms are preferable. Further, since the physical properties of the resin particles can be easily adjusted and resin particles having excellent polymerization stability can be obtained, an alkyl (meth)acrylate having an alkyl group having 1 or more and 12 or less carbon atoms is more preferable, and methyl (meth) Acrylates, ethyl (meth)acrylate are particularly preferred.

As described above, the core portion includes an aromatic group-containing unit and a cyano group-containing unit. The ratio (% by mass) of the aromatic group-containing unit in the core portion is preferably 25% by mass or more and 90% by mass or less, and preferably 35% by mass or more and 90% by mass or less. The ratio (% by mass) of the cyano group-containing unit in the core portion is preferably 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 55% by mass or less. If the proportion of the cyano group-containing unit in the core portion is less than 10% by mass, the color developability of the image may slightly deteriorate. On the other hand, if the proportion of the cyano group-containing unit in the core portion is more than 60% by mass, part of the cyano group in the core portion is likely to be exposed on the surface of the resin particles, and the recovery from the fixation of the ink may slightly decrease. There is The proportion (% by mass) of other units in the core portion is preferably 15% by mass or less. "Other units" in the core portion are units other than the aromatic group-containing unit and the cyano group-containing unit. The "other unit" of the core portion preferably includes a unit derived from a reactive surfactant. Moreover, it is preferable that the core part is not crosslinked. That is, it is preferable that the "other units" of the core portion do not include units derived from the cross-linking agent.

In addition, as described above, the shell part contains an aromatic group-containing unit, an anionic group-containing unit, and a unit derived from a cross-linking agent, and does not substantially contain a cyano group-containing unit. The ratio (% by mass) of the aromatic group-containing unit in the shell portion is preferably 1% by mass or more and 60% by mass or less, more preferably 10% by mass or more and 50% by mass or less.

The proportion (% by mass) of the anionic group-containing unit in the shell portion is preferably 5% by mass or more and 30% by mass or less, more preferably 10% by mass or more and 20% by mass or less. If the ratio of the anionic group-containing unit in the shell portion is less than 5% by mass, the ejection stability of the ink may slightly decrease. On the other hand, if the proportion of the anionic group-containing unit in the shell portion exceeds 30% by mass, the hydrophilicity of the shell portion may become too high. For this reason, the shell part may be easily peeled off from the core part, and the cyano group of the core part is likely to be exposed on the surface of the resin particles, which may slightly reduce the recovery from fixation of the ink.

The ratio (% by mass) of units derived from the crosslinking agent in the shell portion is 30% by mass or more and 80% by mass or less, preferably 40% by mass or more and 70% by mass or less. If the ratio of units derived from the cross-linking agent in the shell portion is less than 30% by mass, the cyano group in the core portion will be exposed under conditions where the hydrophilicity of the shell portion is excessively increased by combined use with the water-soluble resin. It becomes easy, and fixation recoverability of ink becomes insufficient. On the other hand, if the proportion of units derived from the crosslinking agent in the shell portion exceeds 80% by mass, the ejection stability of the ink will be insufficient.

The proportion (% by mass) of other units in the shell portion is preferably 10% by mass or less, more preferably 5% by mass or less. "Other units" in the shell portion are units other than the aromatic group-containing unit, the anionic group-containing unit, and the unit derived from the cross-linking agent. The "other unit" of the shell portion preferably includes a unit derived from a reactive surfactant.

The mass ratio of the core part and the shell part of the resin particles is a mass ratio with the total being 100, and the core part: shell part is preferably 50:50 to 95:5, and 60:40 to 90:10. It is even more preferable to have

The volume-based cumulative 50% particle diameter (D50) of the resin particles is preferably 120 nm or less. When the volume-based cumulative 50% particle diameter (D50) of the resin particles is more than 120 nm, the resin particles tend to scatter light, and the color developability of the image may slightly deteriorate. The volume-based cumulative 50% particle diameter (D50) of the resin particles is preferably 50 nm or more. The volume-based cumulative 50% particle diameter (D50) of the resin particles can be measured by the same method as the above-described method for determining whether or not the particles are resin particles.

The content (% by mass) of the resin particles in the ink is preferably 1.0% by mass or more and 10.0% by mass or less based on the total mass of the ink. If the content of the resin particles is less than 1.0% by mass, the color developability of the image may slightly deteriorate. On the other hand, if the content of the resin particles exceeds 10.0% by mass, the ejection stability of the ink may slightly decrease.

[Method for producing dyed resin particles]
Resin particles can be produced, for example, according to conventionally known methods such as emulsion polymerization, mini-emulsion polymerization, seed polymerization, and phase inversion emulsification. Examples of the method for dyeing the resin particles include a method of polymerizing a monomer mixed solution in which a fluorescent dye is dissolved to form resin particles; a method of adding a fluorescent dye to the resin particles and heating; and the like. Among them, the method of adding the fluorescent dye to the resin particles and heating the resin particles is preferable because it can be applied to a wider variety of fluorescent dyes. It is preferable not to add a dyeing aid (water-soluble resin, surfactant, etc.) during heating. When a water-soluble resin is used as a dyeing adjuvant, the water-soluble resin may form a film and hinder the redispersion of the resin particles, which may result in a slight decrease in the fixation recoverability of the ink. Further, when a surfactant is used as a dyeing aid, the physical properties of the ink may be affected, and the ejection stability of the ink may be slightly lowered.

[Verification method of resin particles]
The composition of the resin particles can be verified according to the methods shown in (i) to (iii) below. A method of extracting, analyzing, and verifying resin particles from ink will be described below, but resin particles extracted from an aqueous dispersion or the like can also be analyzed and verified in the same manner.

(i) Extraction of Resin Particles Resin particles can be separated and extracted from ink containing resin particles by a density gradient centrifugation method. Among the density gradient centrifugation methods, the density gradient sedimentation velocity method separates and extracts resin particles based on the difference in the sedimentation coefficients of components. Among the density gradient centrifugation methods, the density gradient sedimentation equilibrium method separates and extracts resin particles based on the difference in component density.

(ii) Confirmation and Separation of Layer Structure First, the resin particles are dyed and fixed with ruthenium tetroxide, and then embedded in an epoxy resin and held stably. The resin particles embedded in the epoxy resin are then cut with an ultramicrotome, and the cross section is observed using a scanning transmission electron microscope (STEM). By observing a cross section cut through the center of gravity of the resin particles, the layer structure of the resin particles can be confirmed. Quantitative analysis of the elements contained in the layers (core part, shell part) constituting the resin particles by STEM-EDX with energy dispersive X-ray spectroscopy (EDX) using resin particles embedded in epoxy resin as an analysis sample. can do.

(iii) Analysis of Units (Monomers) Constituting Resin of Each Layer The resin particles used as a sample for separating the resin of each layer may be in the form of a dispersion. Alternatively, a film obtained by drying the resin particles may be used as the sample. After dissolving the sample resin particles in an organic solvent, each layer is separated by gel permeation chromatography (GPC), and the resin constituting each layer is collected. Then, the fractionated resin is subjected to elemental analysis by a combustion method. Separately from this, after pretreating the resin fractionated by the acid decomposition (hydrofluoric acid addition) method or alkali fusion method, the inorganic components are quantitatively analyzed by the inductively coupled plasma atomic emission spectrometry method. By comparing the results of the elemental analysis and the quantitative analysis of the inorganic components with the results of the quantitative analysis of the elements by STEM-EDX obtained in (ii) above, the layer of the resin particles constituted by the separated resin was determined. can know.

The aliquots of resin are also analyzed by nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). This makes it possible to know the types and proportions of units (monomers) and crosslinkable components that constitute the resin. Further, the monomers generated by depolymerization can be directly detected by analyzing the separated resin by pyrolysis gas chromatography.

(Compound represented by general formula (1))
The ink contains a compound represented by the following general formula (1). The compound represented by the general formula (1) has a structure similar to that of a coumarin dye that exhibits fluorescence, and is a component that contributes to the improvement of image visibility by developing high-brightness colors and improving the optical density of images. be. In addition, a hydrophobic portion and a hydrophilic portion are present in the molecular structure of the compound represented by general formula (1). For this reason, the hydrophobic portion is adsorbed to the resin particles, thereby stabilizing the dispersed state of the resin particles and improving the ejection stability of the ink.

（前記一般式（１）中、Ｒ_１は、アルキルアミノ基を表し、Ｒ_２は、芳香族基又は複素芳香族基を表し、Ｍは、水素原子、アルカリ金属、アンモニウム、又は有機アンモニウムを表す）

(In the general formula (1), R ₁ represents an alkylamino group, R ₂ represents an aromatic group or a heteroaromatic group, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. )

In general formula (1), the alkylamino group represented by R ₁ may be any of a monoalkylamino group, a dialkylamino group, and a trialkylamino group, and the alkyl group has 1 to 5 carbon atoms. Preferably. Examples of alkylamino groups include ethylamino, dimethylamino, diethylamino and trimethylamino groups.

In general formula (1), the aromatic group or heteroaromatic group represented by R ₂ may be substituted with a halogen atom such as a fluorine atom, a chlorine atom, or a bromine atom. The aromatic group preferably has 6 to 10 carbon atoms. A phenyl group, a naphthyl group, etc. can be mentioned as an aromatic group. The heteroaromatic group is an aromatic ring containing heteroatoms such as a nitrogen atom, an oxygen atom and a sulfur atom, and preferably has 6 to 10 atoms constituting the ring. Examples of heteroaromatic groups include pyrrole, furan, thiophene, imidazole, pyrazole, oxazole, and thiazole groups. The group represented by R ₂ may have a structure in which an aromatic ring and a heterocyclic ring are condensed, and examples thereof include a benzofuran group, an indole group, a benzimidazole group, a benzoxazole group, and a benzothiazole group. .

Preferred examples of the compound represented by the general formula (1) can be represented by the free acid form, and exemplary compounds 1 to 6 shown below can be mentioned. Of course, the compounds are not limited to the exemplary compounds shown below as long as they are included in the structure of general formula (1) and its definition. Among the exemplary compounds shown below, exemplary compound 1 is preferable.

(Method for verifying compound represented by general formula (1))
In order to verify whether the compound represented by the general formula (1) is contained in the ink, the following methods (1) to (3) using high performance liquid chromatography (HPLC) are applied. can be done.
(1) Retention time of peak (2) Maximum absorption wavelength for peak (1) (3) M/Z (posi), M/Z (nega) of mass spectrum for peak (1)

HPLC analysis conditions are as shown below. A sample for measurement is prepared by diluting a dried solid precipitate obtained by ultracentrifugation (8,000 rpm×5 hr, 25° C.) of the ink with a methanol solution 50 times (by mass). Then, it is analyzed by HPLC according to the conditions shown below, and the peak retention time and peak maximum absorption wavelength are measured.
・ Column: SunFire C18 (manufactured by Nippon Waters) 2.1 mm × 150 mm
・Column temperature: 40°C
・Flow rate: 0.2 mL/min
・PDA: 200 to 700 nm
・ Mobile phase and gradient conditions: Table 1

Moreover, the analysis conditions of the mass spectrum are as shown below. For the peaks obtained by HPLC, a mass spectrum is measured according to the conditions shown below, and the most strongly detected MZ is measured for each of posi and nega.
・Ionization method: ESI
・Capillary voltage: 3.5 kV
・Desolvation gas: 300°C
・Ion source temperature: 120°C
·Detector:
posi; 40V 200-1500amu/0.9sec
40V 200-1500amu/0.9sec

Exemplified compound 1, which is a specific example of the compound represented by general formula (1), was analyzed according to the above method and conditions. Table 2 shows the measured retention time, maximum absorption wavelength, M/Z (posi), and M/Z (nega) values. An unknown ink is analyzed according to the above method and conditions, and if the obtained measurement values correspond to the values shown in Table 2, the ink is considered to contain the compound represented by the general formula (1). can judge.

The content (% by mass) of the compound represented by formula (1) is preferably 0.010 to 0.100 times the content (% by mass) of the coumarin dye as a mass ratio. If the above mass ratio is less than 0.010 times or more than 0.100 times, the color development of the image may be slightly reduced.

The content (% by mass) of the compound represented by formula (1) is preferably 0.01% by mass or more and 1.00% by mass or less based on the total mass of the resin particles. If the content (% by mass) of the compound represented by formula (1) is less than 0.01% by mass based on the total mass of the resin particles, the ejection stability of the ink may slightly deteriorate. On the other hand, if it exceeds 1.00% by mass, the recovery from fixation of the ink may be slightly lowered.

(Water-soluble resin)
The water-soluble resin has an aromatic group-containing unit and an anionic group-containing unit. The water-soluble resin is preferably acrylic resin or urethane resin, more preferably acrylic resin. The presence of a water-soluble resin having aromatic group-containing units causes hydrophobic interactions and π-π interactions between the aromatic groups of the water-soluble resin and the aromatic groups of the resin particles. As a result, the water-soluble resin is adsorbed to the resin particles, and the water-soluble resin assists the dispersion of the resin particles, thereby improving the ejection stability of the ink.

In addition, when the ink is stored for a long period of time, some of the fluorescent dyes dyed to the resin particles cause various interactions (electrostatic interaction, hydrophobic interaction, dipole interaction) with the water-soluble resin. By doing so, it shifts to a water-soluble resin. When such a phenomenon occurs, the amount of dye attached to the resin particles decreases while the amount of dye in the ink is kept constant. As a result, concentration quenching occurring between dyes in the resin particles is alleviated, thereby improving the color developability of the image.

Transfer of the dye to the water-soluble resin can be easily confirmed by the density gradient centrifugation method described above. For inks that do not contain water-soluble resins, there is only one band of resin particles as the coloring component. On the other hand, in the case of an ink containing a water-soluble resin, there are two bands, a band of resin particles and a band of colored resin particles.

As the aromatic group-containing unit and the anionic group-containing unit in the water-soluble acrylic resin, the aromatic group-containing unit and the anionic group-containing unit described above can be used. The water-soluble acrylic resin may further have units (other units) other than the aromatic group-containing unit and the anionic group-containing unit. Monomers constituting other units, including those having substituents such as alkoxy groups and hydroxy groups, include 2-hydroxyethyl (meth)acrylate; 3-hydroxypropyl (meth)acrylate; methoxy (mono, di, tri, poly)ethylene glycol (meth)acrylate; alkenes such as ethylene and propylene; alkyls such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, lauryl (meth)acrylate and hexadecyl (meth)acrylate (Meth) acrylate; monocyclic (meth) acrylates such as cyclopropyl (meth) acrylate, cyclohexyl (meth) acrylate, cyclooctyl (meth) acrylate, cyclodecyl (meth) acrylate; isobornyl (meth) acrylate, norbornyl (meth) ) Bicyclic (meth)acrylates such as acrylate; Tricyclic (meth)acrylates such as adamantyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate; can be mentioned. The water-soluble acrylic resin may be any of random copolymers, block copolymers, and graft copolymers.

As the water-soluble urethane resin, those obtained by reacting a polyisocyanate with a component that reacts therewith (polyol having an acid group, polyol having no acid group, polyamine, etc.) can be used. Moreover, what made the chain extension agent and the crosslinking agent further react may be used. At least one of these components has an aromatic group.

The acid value of the water-soluble resin is 100 mgKOH/g or more and 180 mgKOH/g or less. If the acid value of the water-soluble resin is less than 100 mgKOH/g, the ejection stability of the ink will be insufficient. On the other hand, when the acid value of the water-soluble resin is more than 180 mgKOH/g, the anionic groups in the shell portion of the resin particles are neutralized by ions derived from the anionic groups of the water-soluble resin, promoting water solubility. The state of inclusion in the core is loosened. As a result, the core portion having the cyano group is likely to be exposed, and the recovery from fixation of the ink is lowered.

The weight average molecular weight of the water-soluble resin is preferably 5,000 or more and 20,000 or less. If the weight-average molecular weight of the water-soluble resin is less than 5,000, the effect of improving the ink ejection stability may be somewhat reduced. On the other hand, if the weight-average molecular weight of the water-soluble resin exceeds 20,000, the viscosity of the ink tends to increase, and the effect of improving the ejection stability of the ink may slightly decrease.

The content (% by mass) of the water-soluble resin in the ink is preferably 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink. The content (% by mass) of the water-soluble resin is preferably 0.1 times or more and 2.0 times or less as a mass ratio to the content (% by mass) of the resin particles. If the above mass ratio is less than 0.1 times, the effect of improving the ejection stability of the ink may slightly decrease. On the other hand, when the mass ratio is more than 2.0 times, the anionic groups in the shell portion of the resin particles are neutralized by the ions derived from the anionic groups of the water-soluble resin, and the core portion having a cyano group is formed. Easier to expose. As a result, the effect of improving the fixation recoverability of the ink may be slightly reduced.

Physical properties such as the composition, weight average molecular weight, and acid value of the water-soluble resin can be measured by conventionally known methods. Specifically, the physical properties of the water-soluble resin can be measured by analyzing the sediment and supernatant obtained by centrifuging the ink. Although the water-soluble resin can be analyzed even in the state of the ink, it is preferable to analyze the water-soluble resin extracted from the ink because the measurement accuracy can be improved. Specifically, it is preferable to add excess acid (hydrochloric acid, etc.) to the supernatant obtained by centrifuging the ink at 75,000 rpm, and then dry the precipitated resin for analysis.

By analyzing the resin separated from the ink using a high-temperature gas chromatography/mass spectrometer (high-temperature GC/MS), it is possible to confirm the type of units constituting the water-soluble resin. In addition, quantitative analysis by nuclear magnetic resonance ( ¹³ C-NMR) or Fourier transform infrared spectrophotometer (FT-IR) confirms the molecular weight and type of the monomers that make up each unit. can be done.

The acid value of the water-soluble resin can be measured by a titration method. Specifically, a water-soluble resin is dissolved in tetrahydrofuran (THF) to prepare a measurement sample. Then, the acid value of the water-soluble resin can be measured by subjecting the prepared measurement sample to potentiometric titration using a potassium hydroxide ethanol titrant using an automatic potentiometric titrator. As the potentiometric automatic titrator, for example, the product name "AT510" (manufactured by Kyoto Electronics Industry Co., Ltd.) can be used.

The weight average molecular weight of the water-soluble resin can be measured by gel permeation chromatography (GPC). GPC measurement conditions can be as shown below.・Apparatus: Alliance GPC 2695 (manufactured by Waters)
・Column: Shodex KF-806M quadruple column (manufactured by Showa Denko)
・Mobile phase: THF (special grade)
・Flow rate: 1.0 mL/min
・Oven temperature: 40.0°C
・Injection amount of sample solution: 0.1 mL
・Detector: RI (refractive index)
- Polystyrene standard samples: PS-1 and PS-2 (manufactured by Polymer Laboratories, molecular weight: 7,500,000, 2,560,000, 841,700, 377,400, 320,000, 210,500, 148,000 , 96,000, 59,500, 50,400, 28,500, 20,650, 10,850, 5,460, 2,930, 1,300, 580).

(aqueous medium)
The ink is an aqueous ink containing at least water as an aqueous medium. The ink may further contain a water-soluble organic solvent 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 50.0% by mass or more and 95.0% 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, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds. 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.

(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. The ink can contain coloring materials such as pigments and dyes (including dyes that do not show fluorescence and dyes that show fluorescence other than coumarin dyes). may

(Physical properties of ink)
Since the ink is a water-based ink applied to the inkjet system, it is preferable to appropriately control its physical properties. Specifically, the surface tension of the ink at 25° C. measured by the plate method is preferably 20 mN/m or more and 60 mN/m or less, more preferably 25 mN/m or more and 45 mN/m or less. The viscosity of the ink at 25° C. is preferably 1.0 mPa·s or more and 10.0 mPa·s or less, more preferably 1.0 mPa·s or more and 5.0 mPa·s or less. Also, the pH of the ink at 25° C. is preferably 7.0 or more and 10.0 or less.

<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 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 aqueous dispersion of resin particles>
A reaction vessel equipped with a stirrer was set in a hot water bath. 1,178 parts of water was put into the reactor and the internal temperature was kept at 70°C. The amounts shown in Table 3-1 of the monomers to be aromatic group-containing units, the monomers to be cyano group-containing units (including monomers as control examples), and the reactive surfactants to be reactive surfactant units (parts) and breakdown (%). In this way, a monomer mixed solution for the core portion was prepared. As the reactive surfactant, the product name "Adekari Soap SR-10" (manufactured by ADEKA) was used. Further, 1.9 parts of potassium persulfate and 659 parts of water were mixed to prepare an aqueous solution 1 of a polymerization initiator. The monomer mixed solution for the core part and the aqueous solution 1 of the polymerization initiator were dropped in parallel into the reaction vessel over 60 minutes. After completion of the dropwise addition, stirring was continued and the mixture was allowed to react for an additional 30 minutes to synthesize particles that would become the core portion of the resin particles. However, for the resin particles 28, the core portion was not synthesized.

Next, a monomer to be an aromatic group-containing unit (including a monomer as a control example), a monomer to be an anionic group-containing unit, a cross-linking agent to be a cross-linking agent unit, and a reactive surfactant to be a reactive surfactant unit prepared the drug. These prepared monomers were mixed in amounts (parts) and breakdowns (%) shown in Table 3-2 to prepare a monomer mixed solution for the shell part. As the reactive surfactant, the product name "Adekari Soap SR-10" (manufactured by ADEKA) was used. Further, 0.1 part of potassium persulfate and 133 parts of water were mixed to prepare an aqueous solution 2 of a polymerization initiator. A mixture of monomers for the shell portion and an aqueous solution 2 of the polymerization initiator were added dropwise in parallel to the reactor containing the particles for the core portion over 10 minutes. After completion of dropping, the mixture was stirred at 80° C. for 10 minutes to continue the reaction to synthesize a shell portion, thereby synthesizing a resin particle having a core-shell structure in which a particle serving as a core portion was coated with a resin serving as a shell portion. However, for the resin particles 27, the shell portion was not synthesized.

After that, an appropriate amount of 8 mol/L potassium hydroxide aqueous solution was added into the reaction vessel to adjust the pH of the liquid to 8.5. Further, the amount (parts) and breakdown (%) of the fluorescent dye powder shown in Table 3-3 were added, and the temperature was raised to 80°C. After that, the mixture was stirred for 2 hours to dye the resin particles with the fluorescent dye. Next, an appropriate amount of 8 mol/L potassium hydroxide aqueous solution was added into the reaction vessel to adjust the pH of the liquid to 8.5. An appropriate amount of water was further added to obtain an aqueous dispersion of each resin particle having a resin particle content of 20%. Table 3-3 shows the particle diameters of the obtained resin particles (volume-based cumulative 50% particle diameter). The particle size of the resin particles is determined using a dynamic light scattering particle size analyzer (trade name “UPA-EX150” manufactured by Nikkiso), SetZero: 30 seconds, Number of measurements: 3, Measurement time: 180 seconds, Shape Measured under the conditions of: perfect sphere, refractive index: 1.59. However, the resin particles 38 were not dyed. Among the fluorescent dyes used, "CI Acid Yellow 73" does not belong to coumarin dyes.

The meanings of abbreviations in Tables 3-1 to 3-3 are shown below.
・St: Styrene ・Vt: Vinyl toluene ・AN: Acrylonitrile ・MAN: Methacrylonitrile ・EMA: Ethyl methacrylate ・MAA: Methacrylic acid ・AA: Acrylic acid ・EDMA: Ethylene glycol dimethacrylate ・DVB: Divinylbenzene ・EX-810 : Ethylene glycol diglycidyl ether (trade name “Denacol EX-810”, manufactured by Nagase ChemteX)
・EX-830: Polyethylene glycol diglycidyl ether (trade name “Denacol EX-830”, manufactured by Nagase ChemteX)
・EX-521: Polyglycerol polyglycidyl ether (trade name “Denacol EX-521”, manufactured by Nagase ChemteX)
- DY82: C.I. I. Disperse Yellow 82
- SY196: C.I. I. Solvent Yellow 196
- SY160:1: C.I. I. Solvent yellow 160:1
- BY40: C.I. I. basic yellow 40
- AY73: C.I. I. acid yellow 73

<Synthesis of compound represented by general formula (1)>
(Exemplary compound 1)
Exemplary compound 1 was synthesized according to the synthesis flow and procedure shown below.

19.3 g of compound A1 (4-(diethylamino)-2-hydroxybenzaldehyde, manufactured by Tokyo Chemical Industry Co., Ltd.) and 15.7 g of compound B1 (2-cyanomethylbenzimidazole, manufactured by Tokyo Chemical Industry Co., Ltd.) were added to 600 mL of ethanol, Dissolved. After adding 0.9 g of piperidine, the mixture was stirred at room temperature (25° C.) for 24 hours to react. After confirming the completion of the reaction by HPLC, the deposited precipitate was collected by filtration to obtain the intermediate compound C1. The compound C1 thus obtained was added to 500 mL of a 5% aqueous sodium hydroxide solution, dispersed, and stirred at 70° C. for reaction. After confirming the completion of the reaction by HPLC, the mixture was cooled to room temperature and concentrated hydrochloric acid was added. The deposited precipitate was separated by filtration and washed with water. As a result, Exemplified Compound 1 (acid form) was obtained. The resulting Exemplified Compound 1 was dissolved in pure water to obtain an aqueous solution of Exemplified Compound 1 (1.0% aqueous solution).

(Exemplary compound 2)
Exemplified Compound 2 was prepared in the same manner as Exemplified Compound 1 described above, except that 16.5 g of Compound A2 (4-(ethylamino)-2-hydroxybenzaldehyde, manufactured by Aldrich) was used instead of Compound A1. An aqueous solution (1.0% aqueous solution) was obtained.

(Exemplary compound 3)
Exemplified Compound 3 was prepared in the same manner as Exemplified Compound 1 described above, except that 16.5 g of Compound A3 (4-(dimethylamino)-2-hydroxybenzaldehyde, manufactured by Aldrich) was used instead of Compound A1. An aqueous solution (1.0% aqueous solution) was obtained.

(Exemplary compound 4)
Instead of compound A1, 18.0 g of compound A4 (4-formyl-3-hydroxy-phenyl)-trimethylammonium-bromide, manufactured by Chemieliva Pharmaceutical) was used. Except for this, an aqueous solution (1.0% aqueous solution) of Exemplified Compound 4 was obtained in the same manner as Exemplified Compound 1 described above.

(Exemplary compound 5)
An aqueous solution of Exemplified Compound 5 (1.0% aqueous solution) was obtained.

(Exemplary compound 6)
Exemplified Compound 6 was prepared in the same manner as Exemplified Compound 1 described above, except that 19.3 g of Compound A6 (5-chlorobenzo[d]oxazole-2-acetonitrile, manufactured by Alichem) was used instead of Compound A1. An aqueous solution (1.0% aqueous solution) was obtained.

<Synthesis of water-soluble resin>
A water-soluble acrylic resin, which is a random copolymer having the composition and properties shown in Table 4, was synthesized by polymerizing the monomers by a conventional method. After adding water containing potassium hydroxide in an equimolar amount to the acid value to neutralize the anionic groups, an appropriate amount of water is further added to obtain an aqueous solution of a water-soluble resin with a resin content of 10.0%. got A water-soluble resin is dissolved in tetrahydrofuran to prepare a sample for measurement, and an automatic potentiometric titrator (trade name "AT510", manufactured by Kyoto Electronics Industry) is used to perform potentiometric titration with a potassium hydroxide ethanol titrant. , the acid value of the water-soluble resin was measured. The polystyrene-equivalent weight-average molecular weight of the water-soluble resin measured by GPC was 10,000.

The meanings of the abbreviations in Table 4 are shown below.
・St: styrene ・BzMA: benzyl methacrylate ・BA: n-butyl acrylate ・MAA: methacrylic acid ・AA: acrylic acid

<Ink preparation>
Each component (unit: %) shown in the upper row of Tables 5-1 to 5-7 was mixed, thoroughly stirred, and filtered under pressure through a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm to obtain each ink. was prepared. In Tables 5-1 to 5-7, "acetylenol E100" is a trade name of a nonionic surfactant manufactured by Kawaken Fine Chemicals. Ink properties are shown in the lower part of Tables 5-1 to 5-7. All of the prepared inks had a pH within the range of 8.5 to 9.0.

<Evaluation>
Each prepared ink was filled in an ink cartridge, and set in an inkjet recording apparatus (trade name “PIXUS Pro-10” manufactured by Canon Inc.) equipped with a recording head that ejects ink by thermal energy. In this inkjet recording apparatus, an image recorded under the condition of applying 8 droplets of 3.8 ng±10% ink to a unit area of 1/600 inch×1/600 inch is defined as having a recording duty of 100%. The recording environment was set at a temperature of 25° C. and a relative humidity of 55%. 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 6 shows the evaluation results.

(chromogenic)
Using the inkjet recording apparatus described above, an image including the following gradation pattern was recorded on a recording medium (glossy paper, trade name "Canon Photo Paper/Fine Grain Surface Glossy Raster", manufactured by Canon). The gradation pattern is a 2 cm x 2 cm solid image in which a maximum of 6 droplets of ink is applied to a unit area of 1/600 inch x 1/600 inch, and the amount of ink applied is changed in stages. Configured. After drying the recorded image for one day, a spectrophotometer (trade name “X-RiteeXact” (M1 light source), manufactured by X-Rite) was used to measure hue angle (H) and saturation in the Lab color system. (C ^* ), and lightness (L ^* ) were measured. Then, the color developability of the image was evaluated according to the evaluation criteria shown below. Brightness was evaluated by the value at chroma 50. However, when the maximum saturation did not reach 50, the data obtained by colorimetrically measuring the gradation pattern was extrapolated, and the obtained calculated value of brightness was evaluated. The reason why the evaluation criteria are changed according to the hue angle is that the preferred color tones that can be perceived visually differ depending on the type of color.
A: The maximum saturation was 60 or more and the brightness was 80 or more, or the maximum saturation was 50 or more and the brightness was 85 or more.
B: The maximum saturation was 50 or more and less than 60, and the brightness was 80 or more and less than 85.
C: The maximum chroma was less than 50, or the brightness was less than 80.

(optical density)
Images containing the following gradation patterns were recorded on three types of recording media (plain paper) using the inkjet recording apparatus described above. The recording media used are the trade name "PB-Paper" (manufactured by Canon), the trade name "Oce Red Label Paper" (manufactured by Canon), and the trade name "Bright White Inkjet Paper" (manufactured by Hewlett-Packard). The gradation pattern is a 2 cm x 2 cm solid image in which a maximum of 4 droplets of ink are applied to a unit area of 1/600 inch x 1/600 inch, and the amount of ink applied is changed in stages. Configured. After the recorded image was dried for one day, the optical density was measured using a spectrophotometer (trade name “X-RiteeXact” (M1 light source), manufactured by X-Rite), and the optical densities of the three types of recording media were measured. The average value of was calculated. Then, the optical density of the image was evaluated according to the following evaluation criteria.
A: The average optical density was 0.6 or more.
B: The average optical density was 0.5 or more and less than 0.6.
C: The average optical density was less than 0.5.

(Ejection stability)
A 19 cm×26 cm solid image with a recording duty of 100% was recorded on 10 recording media (plain paper, product name “GF-500”, manufactured by Canon Inc.) using the inkjet recording apparatus described above. Solid images recorded on the fifth recording medium and the tenth recording medium were visually checked, and ejection stability was evaluated according to the evaluation criteria shown below.
A: There was no white streak or blur on the 5th sheet, but there was a slight white streak or blur on the 10th sheet.
B: There were no white streaks or fading on the 5th sheet, but there were white streaks or fading on the 10th sheet.
C: White streaks and blurring were observed on the 5th sheet.

(fixation recoverability)
The following operations were performed using the ink jet recording apparatus described above. After recovery processing (cleaning) was performed from the printer driver, a nozzle check pattern was printed with the inkjet printing apparatus. After that, while the carriage is moving (when the recording head is at a position other than the home position), the power cable is pulled out to set the recording head in an uncapped state. Then, in this state, the inkjet recording apparatus was left for 14 days in an environment with a temperature of 30° C. and a relative humidity of 10%. Next, after the inkjet recording apparatus was placed in an environment at a temperature of 25° C. for 6 hours, a nozzle check pattern was recorded while performing recovery processing (cleaning). The recorded nozzle check pattern was confirmed, and fixation recoverability was evaluated according to the evaluation criteria shown below.
A: Normal recording became possible after 3 to 5 recovery processes.
B: After 6 to 10 recovery processes, normal recording was achieved.
C: When the recovery process was performed 11 times, normal recording was not possible.

Claims (12)

A water-based inkjet ink containing resin particles dyed with a fluorescent dye, a compound represented by the following general formula (1), and a water-soluble resin,
wherein the fluorescent dye comprises a coumarin dye that exhibits fluorescence;
The resin particle contains a core portion containing an aromatic group-containing unit and a cyano group-containing unit, an aromatic group-containing unit, an anionic group-containing unit, and a unit derived from a cross-linking agent, and does not contain a cyano group-containing unit. a shell portion;
The ratio (% by mass) of units derived from the crosslinking agent in the shell portion is 30% by mass or more and 80% by mass or less,
The water-soluble resin has an aromatic group-containing unit and an anionic group-containing unit,
A water-based ink, wherein the water-soluble resin has an acid value of 100 mgKOH/g or more and 180 mgKOH/g or less.

(In the general formula (1), R ₁ represents an alkylamino group, R ₂ represents an aromatic group or a heteroaromatic group, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. ) 2. The aqueous ink according to claim 1, wherein the ratio (% by mass) of the cyano group-containing unit in the core portion is 10% by mass or more and 60% by mass or less. 3. The water-based ink according to claim 1, wherein the ratio (% by mass) of the anionic group-containing unit in the shell portion is 5% by mass or more and 30% by mass or less. 4. The aqueous ink according to any one of claims 1 to 3, wherein the aromatic group-containing unit contained in the core portion and the aromatic group-containing unit contained in the shell portion are of the same type. 5. The water-based ink according to any one of claims 1 to 4, wherein the ratio (% by mass) of the fluorescent dye in the resin particles is 3.0% by mass or more and 8.0% by mass or less. 2. The content (mass %) of the compound represented by the general formula (1) is 0.010 times or more and 0.100 times or less as a mass ratio with respect to the content (mass %) of the coumarin dye. 6. The water-based ink according to any one of items 1 to 5. 7. The content (% by mass) of the compound represented by the general formula (1) is 0.01% by mass or more and 1.00% by mass or less based on the total mass of the resin particles. The water-based ink according to any one of items 1 and 2. The water-based ink according to any one of claims 1 to 7, wherein the resin particles have a volume-based cumulative 50% particle diameter of 120 nm or less. 9. Any one of claims 1 to 8, wherein the content (mass%) of the water-soluble resin is 0.10 times or more and 2.00 times or less as a mass ratio with respect to the content (mass%) of the resin particles. The water-based ink described in . 10. The water-based ink according to any one of claims 1 to 9, wherein the content (% by mass) of the resin particles is 1.00% by mass or more and 10.00% by mass or less based on the total mass of the ink. 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 10. 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 10.

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