JP7532090B2 - Water-based ink, ink cartridge, and ink-jet recording method - Google Patents

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 color gamut that can be expressed. 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, inkjet recording devices that use special color inks other than the basic colors of cyan, magenta, and yellow, as well as high-brightness special color inks, have come to be used in order to expand the color gamut.

Another need in the printing industry is the production of records with eye-catching, vivid colors. For example, notices such as posters and POPs, and packaging for food and beverage products, are required to be printed in vivid colors to attract customers' attention. Fluorescent colors are effective in meeting such needs. Fluorescent materials suitable for paints and inks have been proposed so far (Patent Document 1). However, fluorescent materials with sufficient inkjet suitability have not yet been established.

JP 2009-161688 A

Currently, offset printing is the mainstream method for recording fluorescent images. However, when recording fluorescent images with a single offset print, it is difficult to achieve vivid color development, so it has been common to perform two or more overprints. For this reason, the method of recording fluorescent images with excellent color development by overprinting has presented problems in terms of productivity and cost.

In the case of digital recording using electrophotography, it is possible to record highly colored fluorescent images using liquid toner. However, electrophotography is limited in the recording media that can be used, making it difficult to apply it to textile recording, large formats, or thick materials, for example.

In contrast, digital recording using the inkjet method can be applied to various recording media, taking advantage of the fact that the recording head that ejects the ink does not come into contact with the recording medium (non-contact). However, since mechanical or thermal energy is used to eject ink from tiny nozzles on the order of microns, it is easily restricted by the physical properties of the ink, such as viscosity. In particular, many of the materials that determine the performance of ink, such as colorants and resins, are solids, and in order to add these materials to ink, they must be dissolved or dispersed in a liquid medium such as water or organic solvents, which places restrictions on the amount that can be added to the ink. The same is true for fluorescent colorants such as fluorescent dyes, and even if a sufficient amount of fluorescent colorant is added to the ink to record an image with excellent color development, restrictions arise in terms of the physical properties of the ink.

Therefore, an object of the present invention is to provide an aqueous ink that has excellent ejection stability and adhesion recovery properties and is capable of recording fluorescent color images with excellent color development. Another object of the present invention is to provide an ink cartridge and an inkjet recording method that use this aqueous ink.

That is, according to the present invention, there is provided an aqueous inkjet ink containing resin particles dyed with a fluorescent dye and a water-soluble resin, wherein the fluorescent dye contains a dye exhibiting fluorescence selected from the group consisting of basic dyes, disperse dyes, and oil-soluble dyes, the resin particles are resin particles formed of an acrylic resin having a core portion containing an aromatic group-containing unit and a cyano group-containing unit, and a shell portion containing an aromatic group-containing unit, an anionic group-containing unit, and a unit derived from a crosslinking agent but not containing a cyano group-containing unit , the proportion (mass %) of the units derived from the crosslinking agent in the shell portion is 30 mass % or more and 80 mass % or less, the water-soluble resin is an acrylic resin having an aromatic group-containing unit and an anionic group-containing unit, and the acid value of the water-soluble resin is 10 the aromatic group-containing unit is a unit derived from a monomer having one ethylenically unsaturated bond that is a polymerizable functional group in its molecule and having no anionic group or cyano group, the cyano group-containing unit is a unit derived from a monomer having one ethylenically unsaturated bond that is a polymerizable functional group in its molecule and having no anionic group or aromatic group, the anionic group-containing unit is a unit derived from a monomer having one ethylenically unsaturated bond that is a polymerizable functional group in its molecule and having no aromatic group or cyano group, and the crosslinking agent is a compound having two or more ethylenically unsaturated bonds that are polymerizable functional groups in its molecule or having two or more glycidyl groups that are polymerizable functional groups in its molecule .

According to the present invention, it is possible to provide an aqueous ink that has excellent ejection stability and adhesion recovery properties and is capable of recording fluorescent color images with excellent color development. In addition, according to the present invention, it is possible to provide an ink cartridge and an inkjet recording method that use this aqueous ink.

FIG. 1 is a cross-sectional view illustrating an embodiment of an ink cartridge of the present invention. 1A and 1B are diagrams illustrating an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, in which FIG. 1A is a perspective view of a main portion of the inkjet recording apparatus, and FIG. 1B is a perspective view of a head cartridge.

The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt." In addition, water-based ink for inkjet printing may be simply referred to as "ink." Physical property values are values at room temperature (25°C) unless otherwise specified. In the present invention, the "unit" constituting the resin means a repeating unit derived from one monomer.

The inventors have investigated the composition of inks that have excellent inkjet suitability (ejection stability and adhesion recovery that easily resolves clogging of ejection ports) and that can record fluorescent color images with excellent color development. In particular, in order to improve the color development of images, the inventors have focused on expanding the color gamut in high-brightness areas that are difficult to express with basic colors. To expand the color gamut in high-brightness areas, it is preferable to use fluorescent dyes as color materials.

The inventors attempted to add the fluorescent dye itself to the ink. However, when the amount of fluorescent dye added was increased to achieve the desired level of color development, it was found that the saturation of the image improved but the brightness significantly decreased. This is thought to be due to the concentration quenching characteristic of fluorescent materials. Naturally, the water resistance of the image was not achieved. From the above, it was found that it was essential to dye the fluorescent dye into the resin particles. When the fluorescent dye is dyed into the resin particles, the fluorescent dye is fixed to the resin particles, so that it is possible to suppress the decrease in brightness of the image and improve the water resistance of the image.

Common methods for dyeing resin particles with fluorescent dyes include (i) a method called the addition condensation bulk resin crushing method, in which a lump of resin is condensed and dyed, and then crushed to obtain particles; and (ii) a method in which resin particles are produced by emulsion polymerization in a water-based system and then dyed. The resin particles obtained by method (i) are difficult to use in inks used in inkjet recording methods because they are micron-order in size and have low water dispersibility. On the other hand, the resin particles obtained by method (ii) are applicable to water-based systems and their size can be controlled to the nano-order, so they are excellent in inkjet suitability. However, when the color development and reliability were examined using ink containing conventional resin particles produced by method (ii), several problems were found to arise.

The inventors therefore investigated the color development of images recorded with ink containing resin particles dyed with a fluorescent dye. To improve the color development of an image, it is important to dye the resin with the fluorescent dye through strong interactions. For this reason, the inventors investigated the composition of resin particles that will efficiently dye the fluorescent dye, depending on the characteristics of the fluorescent dye.

First, the inventors investigated dyeing a resin with a fluorescent dye by using a fluorescent dye having a positively polarized portion and a resin containing an anionic group-containing unit, utilizing the electrostatic action generated between cations and anions. For example, it is considered preferable to use a basic dye having a cationic site and resin particles formed of a resin containing an anionic group-containing unit or a cyano group-containing unit. However, if there are many anionic group-containing units, the hydrophilicity of the resin increases excessively, which may inhibit the formation of resin particles. On the other hand, cyano group-containing units do not cause such problems, and are therefore suitable units for forming resin particles.

Next, the inventors have investigated dyeing resin with fluorescent dyes by utilizing hydrophobic interactions and dipole interactions. Specifically, they have investigated the combined use of substantially water-insoluble fluorescent dyes having hydrophobic parts such as aromatic groups, such as disperse dyes and oil-soluble dyes, with resin particles containing aromatic group-containing units and units containing cyano groups, which are polar groups. In addition to the hydrophobic interaction between the fluorescent dye and the hydrophobic groups of the resin particles, the fluorescent dye is stably dyed to the resin particles due to the dipole interaction between the highly polar parts, such as nitrogen atoms, sulfur atoms, and oxygen atoms, in the fluorescent dye molecule and the cyano groups in the resin particles. When the disperse dye or oil-soluble dye has an aromatic group, in addition to these effects, π-π interactions with the aromatic groups of the resin particles also occur.

However, because the cyano group is highly polar, it is prone to interact with many components in the ink, including water, and it has been found that this can easily reduce the ink's ability to recover from adhesion. Even when water-based inkjet ink is concentrated due to evaporation of water from the nozzle, it can be maintained so that it can be ejected normally by a recovery process such as preliminary ejection or suction or pressure application using a cap. However, when solids such as resin particles aggregate and become difficult to redisperse, they may not be able to return to their original state even with the recovery process, and as a result, the ink may not be ejected normally.

Even if an aqueous medium is added after evaporating and drying an ink containing resin particles containing a cyano group-containing unit, the resin particles can hardly be redispersed. In an ink concentrated by evaporation of water, the cyano group in the resin particles strongly interacts with highly polar components (such as water and water-soluble organic solvents), making it difficult to redisperse. The present inventors have investigated the composition of an ink that has excellent adhesion recovery properties while containing resin particles containing a cyano group-containing unit. As a result, they have found that by using resin particles having a core-shell structure and having a cyano group-containing unit only in the core, it is possible to improve the adhesion recovery properties of the ink while increasing the color development of the image. Furthermore, they have found that it is important to have an aromatic group-containing unit in both the core and shell. It is believed that the core and shell parts come into strong contact with each other due to the hydrophobic interaction and π-π interaction of the aromatic group, which can suppress the decrease in adhesion recovery properties.

However, it was found that even when resin particles having the above-mentioned core-shell structure were used, the ejection stability of the ink was insufficient. In order to make the resin particles compatible with the aqueous medium in the ink, it is necessary to incorporate an anionic group-containing unit into the shell portion. As a result of the investigation, it was 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. In other words, if an amount of anionic group-containing unit that can ensure the ejection stability of the ink is incorporated into the shell portion, the shell portion becomes too hydrophilic and is unable to sufficiently cover the core portion, resulting in the exposure of the cyano group in the core portion. As a result, it is believed that the exposed cyano group and the highly polar component strongly interact with each other, resulting in a decrease in the ejection stability of the ink.

The anionic group in the shell part easily interacts with the cyano group in the core part. For this reason, it is preferable that the anionic group in the shell part is present in the surface layer of the shell part to contribute to the dispersion stabilization of the resin particles. However, in reality, the anionic group in the shell part is easily attracted to the cyano group in the core part and drawn into the inside of the shell part. For this reason, compared with conventional resin particles having a core-shell structure, in the case of resin particles having a cyano group in the core part, the amount of anionic group-containing units in the shell part required to ensure the ejection stability of the ink increases. As a result, it is considered that the hydrophilicity of the shell part becomes excessively high, making it difficult to sufficiently cover the core part. As described above, it is difficult to improve the ejection stability of the ink by only devising the composition of the resin particles having a core-shell structure.

After further investigation, the inventors discovered that the ejection stability of the ink can be improved by adding a water-soluble resin having an aromatic group-containing unit and an anionic group-containing unit to 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, causing the water-soluble resin to adsorb to the resin particles. As a result, it is believed that the water-soluble resin assists in the dispersion of the resin particles.

Furthermore, it was found that the color development of the image is improved by adding a water-soluble resin to the ink. The basic dye dyes the resin particles by interacting with the cyano group in the core part. In addition, the highly polar part in the dye molecule interacts with the cyano group in the core part of the resin particles, and the disperse dyes and oil-soluble dyes dye the resin particles. The inventors confirmed that if resin particles having a cyano group are used, the state in which the fluorescent dye (basic dye, disperse dye, oil-soluble dye) dyes the resin particles can be maintained even in the ink. However, it was found that if a water-soluble resin having an anionic group is used in combination with dyed resin particles, after the ink is stored for a long period of time, a part of the fluorescent dye electrostatically interacts with the anionic group of the water-soluble resin, detaches from the resin particles, and moves to the vicinity of the water-soluble resin.

The inventors have investigated the difference in the behavior of the fluorescent dye depending on whether or not the water-soluble resin is present. As a simple method for separating the constituent components of the ink, a centrifugal separation method using a density gradient was used to investigate inks containing water-soluble resin and inks not containing water-soluble resin. As a result, in the case of inks containing water-soluble resin, in addition to a colored layer of the resin particles, a colored layer derived from the dye was confirmed in the water-soluble resin layer. In contrast, in the case of inks not containing water-soluble resin, only a colored layer of the resin particles was confirmed. From the above, it was found that a part of the fluorescent dye migrates to the vicinity of the water-soluble resin.

The fluorescent dye content in the dyed resin particles decreases as a result of a portion of the fluorescent dye moving from the resin particles to the vicinity of the water-soluble resin. The inventors prepared a number of dyed resin particles with different fluorescent dye contents, and prepared ink using these prepared resin particles. When the color development of images recorded using the prepared ink was evaluated, it was found that the brightness of images recorded with ink prepared using resin particles with a low fluorescent dye content tended to be higher. It is believed that the brightness of images recorded with ink prepared using resin particles with a low fluorescent dye content increased due to the phenomenon of "concentration quenching" that is unique to fluorescent dyes. 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, and the original vivid coloring is easily offset. On the other hand, if the density of the fluorescent dye in the system is low, interference is less likely to occur, and the original coloring is maintained. In other words, a portion of the fluorescent dye that had dyed the resin particles moved to the vicinity of the water-soluble resin, and the content of the fluorescent dye in the resin particles decreased, suppressing concentration quenching and improving the brightness of the image. Furthermore, because the amount of fluorescent dye in the ink is kept constant, the saturation of the image does not fluctuate, which is thought to have improved color development.

It was also found that adding a water-soluble resin to an ink containing resin particles improves the ejection stability and color development of the image, but reduces the adhesion recovery. The anionic groups in the shell of the resin particles are neutralized by ions derived from the anionic groups of the water-soluble resin, increasing the hydrophilicity of the shell. This loosens the coverage of the core by the shell, making the cyano groups in the core more easily exposed, which is thought to reduce the adhesion recovery. It was found that the degree of adhesion recovery 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 adhesion recovery.

As a result of the study, it was found that in order to improve the ejection stability, the acid value of the water-soluble resin needs to be 100 mgKOH/g or more. On the other hand, if the acid value of the water-soluble resin is 100 mgKOH/g or more, as described above, the adhesion recovery property is likely to decrease. Therefore, the present inventors have studied the requirements for more firmly covering the core part with the shell part. As a result, it was found that the unit derived from the crosslinking agent is incorporated into the shell part, and the proportion (mass%) of the unit derived from the crosslinking agent in the shell part is 30 mass% or more. This makes it difficult for the cyano group of the core part to be exposed, and the decrease in the adhesion recovery property can be suppressed. On the other hand, if the proportion (mass%) of the unit derived from the crosslinking agent is more than 80 mass%, the ejection stability is decreased. In addition, regardless of the proportion of the unit derived from the crosslinking agent, if the acid value of the water-soluble resin is more than 180 mgKOH/g, the hydration of the anionic group of the shell part is significantly promoted. For this reason, the covering state of the core part by the shell part is easily loosened, and it becomes impossible to suppress the decrease in the adhesion recovery property. Furthermore, when resin particles having aromatic group-containing units and anionic group-containing units, rather than a water-soluble resin, are added to an ink containing resin particles, the color development can be improved, but the effect of improving the ejection stability of the ink cannot be obtained.

<Water-based ink>
The ink of the present invention is an aqueous ink for inkjet printing, which contains resin particles dyed with a fluorescent dye and a water-soluble resin. The fluorescent dye includes a dye exhibiting fluorescence selected from the group consisting of basic dyes, disperse dyes, and oil-soluble dyes. The resin particles have a core portion including an aromatic group-containing unit and a cyano group-containing unit, and a shell portion including an aromatic group-containing unit, an anionic group-containing unit, and a unit derived from a crosslinking agent, and not including a cyano group-containing unit. The proportion (mass%) of the units derived from the crosslinking agent in the shell portion is 30 mass% or more and 80 mass% or less. 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, unless it exceeds the gist of the present invention. Hereinafter, the terms "(meth)acrylic acid", "(meth)acrylate", and "(meth)acryloyl" refer to "acrylic acid, methacrylic acid", "acrylate, methacrylate", and "acryloyl, methacryloyl", respectively. The ink of the present invention does not need to be of the active energy ray curing type, and therefore does not need to contain a monomer having a polymerizable group.

(Fluorescent dye)
In this specification, the term "fluorescent dye" refers to a dye that emits fluorescence when exposed to ultraviolet or visible excitation light. Whether or not a certain dye is a "fluorescent dye" that exhibits fluorescence can be determined, for example, according to the method shown below. A sample obtained by dissolving a dye in a liquid that can dissolve the dye is irradiated with ultraviolet light (ultraviolet light) of a long wavelength (approximately 315 to 400 nm) that is barely visible to the naked eye using a black light or the like. If light of a color different from the ultraviolet light irradiated by the black light can be visually observed, the dye can be determined to be a "fluorescent dye" that exhibits fluorescence. As the black light, a commercially available product (for example, the product name "SLUV-4" (manufactured by AS ONE)) 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. Resin particles extracted from the ink in a conventional manner are dissolved in an organic solvent such as chloroform to prepare a sample. The fluorescent dye is isolated from the prepared sample using HPLC (high performance liquid chromatography). The isolated dye is analyzed by common structural analysis techniques such as nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS).

Basic dyes are fluorescent compounds that have an amino group or an imino group (which may form a salt) in their molecular structure. Examples of compounds that have an amino group or an imino group in their molecular structure include "dyes whose names in the Colour Index include 'basic'". The Colour Index is a database of colouring materials compiled by the British Society of Dyes and Colourants and others. Examples of dye skeletons include xanthene, azine, azole, thiazole, azo, diarylmethane, triarylmethane, acridine, coumarin and methine. Of these, compounds with skeletons such as xanthene and coumarin are preferred, and compounds with xanthene skeletons are even more preferred.

Specific examples of fluorescent basic dyes, listed by C.I. number or general name, include C.I. Basic Red 1, 1:1, 2, 4, 8, 11, 12, 13; C.I. Basic Violet 1, 3, 10, 11, 11:1, 14; Rhodamine 19, 575; C.I. Basic Yellow 1, 2, 9, 13, 24, 37, 40, 96; C.I. Basic Blue 7; C.I. Basic Green 1; C.I. Fluorescent Brightener 363, etc. Among these, C.I. Basic Red 1, 1:1; C.I. Basic Violet 11, 11:1; C.I. Basic Yellow 40, etc. are preferred due to their excellent color development.

Disperse dyes are compounds that are poorly soluble or insoluble in water and exhibit fluorescence. Examples of "disperse dyes" include "dyes whose names in the Color Index include 'disperse'". Examples of dye skeletons include azo, coumarin, and anthraquinone. Of these, compounds with a skeleton such as coumarin or anthraquinone are preferred, and compounds with a coumarin skeleton are even more preferred.

Specific examples of fluorescent disperse dyes, expressed by C.I. number, include C.I. Disperse Yellow 82 and 186; C.I. Disperse Red 58 and 60; and C.I. Disperse Orange 11. Among these, C.I. Disperse Yellow 82 is preferred due to its excellent color development.

An oil-soluble dye is a compound that is poorly soluble or insoluble in water and exhibits fluorescence. Examples of oil-soluble dyes include "dyes whose names in the Color Index include 'solvent'". Examples of dye skeletons include coumarin, xanthene, azo, aminoketone, anthraquinone, etc. Among these, compounds with a skeleton such as coumarin or xanthene are preferred, and compounds with a coumarin skeleton are even more preferred.

Specific examples of fluorescent oil-soluble dyes, expressed by C.I. numbers, include C.I. Solvent Yellow 7, 43, 44, 85, 98, 131, 160:1, 172, 196; C.I. Solvent Red 43, 44, 45, 49, 149; C.I. Solvent Orange 5, 45, 63, 115, etc. Among these, C.I. Solvent Yellow 160:1, 196, etc. are preferred due to their excellent color development.

It is preferable that the fluorescent dye contains two or more types of fluorescent dye. The presence of multiple fluorescent dyes in the resin particles inhibits the crystallization of the fluorescent dye, allowing the fluorescent dye to efficiently interact with the resin particles at the molecular level and achieve a stable dyeing state.

The content (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 proportion (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. If the proportion of the fluorescent dye in the resin particles is too low, the color development (saturation) of the image may be slightly reduced. 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 be slightly reduced due to concentration quenching.

(Resin particles)
In this specification, the term "resin particles" refers to a resin that can be dispersed in an aqueous medium and exists in the aqueous medium in a state of having a particle size. Therefore, the resin particles exist in a dispersed state 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 following method. First, prepare a liquid (resin solid content: 10% by mass) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value. Next, dilute the prepared liquid 10 times (volume basis) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by dynamic light scattering, if particles having a particle size are measured, the resin can be determined to be a "resin particle". A particle size analyzer (for example, product name "UPA-EX150", manufactured by Nikkiso) can be used as a particle size distribution measurement device using the dynamic light scattering method. The measurement conditions at this time can be, for example, Set Zero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: spherical, refractive index: 1.59. Of course, the particle size distribution measurement device and measurement conditions used are not limited to those mentioned above. The particle size is measured using neutralized resin in order to confirm that particles are formed even when the resin is sufficiently neutralized to make it more difficult to form particles. Even under these conditions, resins that have a particulate shape will remain in particulate form in the water-based ink.

The resin particles used have a core and a shell that covers the core, that is, resin particles having a so-called core-shell structure. The core contains an aromatic group-containing unit and a cyano group-containing unit. When the core contains an aromatic group-containing unit and a cyano group-containing unit, the above-mentioned various interactions that occur between the fluorescent dye and the resin particles are increased. Therefore, the resin particles are efficiently dyed with the fluorescent dye, and the inherent color development of the fluorescent dye is efficiently exhibited, thereby improving the color development of the image. It is preferable to use resin particles formed of an acrylic resin.

The shell portion contains an aromatic group-containing unit, an anionic group-containing unit, and a unit derived from a crosslinking agent. The shell portion also does not substantially contain a cyano group-containing unit. Because the shell portion does not contain a cyano group-containing unit, there are substantially no cyano groups on the surface of the resin particles, which can improve the adhesion recovery of the ink. When highly polar cyano groups are exposed on the surface of the resin particles, these cyano groups interact with the water and water-soluble organic solvents in the ink. When the cyano groups interact with water, etc., and the resin particles form a film, the resin particles become difficult to redisperse, which reduces the adhesion recovery of the ink.

Furthermore, when the shell portion contains an aromatic group-containing unit, hydrophobic interactions and π-π interactions occur between the aromatic group of the core portion. This makes it difficult for the shell portion to peel off from the core portion, and the cyano group of the core portion is less likely to be exposed on the surface of the resin particle, improving the fixation recovery 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 the same type of unit. "The same type of unit" means that the unit is 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 the same type of unit, the interaction between the core and shell is further strengthened, and the fixation recovery of the ink can be further improved.

As the monomer that becomes an aromatic group-containing unit by polymerization, one 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)acrylate, 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, etc. can be mentioned. As the monomer that becomes an aromatic group-containing unit by polymerization, one that does not have an anionic group or a cyano group, or one with a molecular weight of 300 or less is preferable, and one with a molecular weight of 200 or less is even more preferable. Among these, styrene and its derivatives are more preferred because they have good reactivity during polymerization and the resulting resin particles have excellent stability, with styrene and vinyltoluene being particularly preferred.

As a monomer that becomes a cyano group-containing unit by polymerization, one having one polymerizable functional group such as an ethylenically unsaturated bond in the molecule is preferred. Specific examples include acrylonitrile, methacrylonitrile, chloroacrylonitrile, and 2-cyanoethyl (meth)acrylate. As a monomer that becomes a cyano group-containing unit by polymerization, one that does not have an anionic group or an aromatic group and one that has a molecular weight of 300 or less is preferred, and one that has a molecular weight of 200 or less is even more preferred. Among these, acrylonitrile and methacrylonitrile are particularly preferred because they have good reactivity during polymerization and the stability of the resulting resin particles is excellent.

The anionic group in the anionic group-containing unit is preferably one having one polymerizable functional group such as an ethylenically unsaturated bond in the molecule. Specific examples include carboxylic acid groups, phenolic hydroxy groups, and phosphate groups. Among these, carboxylic acid groups are preferred because the stability of the resin particles in the ink is good. Examples of monomers that become anionic group-containing units by polymerization include (meth)acrylic acid, p-vinylbenzoic acid, 4-vinylphenol, β-carboxyethyl (meth)acrylate, and (methacrylic acid-2-hydroxyethyl) phosphate . Examples of monomers that become anionic group-containing units by polymerization include those that do not have aromatic groups or cyano groups, and those that have a molecular weight of 300 or less, and more preferably those that have a molecular weight of 200 or less. Among these, (meth)acrylic acid is particularly preferred. In addition, the anionic group in the anionic group-containing unit is preferably only a carboxylic acid group. The anionic group may be either an acid type or a salt type, and when it is a salt type, it may be either a partially dissociated state or a completely dissociated state. When the anionic group is in the salt form, examples of the cation that serves as the counter ion include an alkali metal cation, ammonium, and organic ammonium.

At least one type of crosslinking agent may be used as a crosslinking agent constituting a unit derived from the crosslinking agent, and it is preferable to use two or more types of crosslinking agents. When the crosslinking agent contains two or more types of crosslinking agents, it is preferable that at least one type of crosslinking agent is a crosslinking agent having a glycidyl group. The crosslinking agent having a glycidyl group reacts with anionic groups such as carboxylic acid groups present in the shell portion to form crosslinks. This makes it possible to suppress excessive increase in hydrophilicity of the shell portion and further improve the fixation recovery properties of the ink. Furthermore, by using two or more types of crosslinking agents, it is possible to form a dense crosslinked structure that can more efficiently suppress excessive increase in hydrophilicity of the shell portion.

Examples of crosslinking agents that become units derived from the crosslinking agent through polymerization include compounds having two or more polymerizable functional groups, such as ethylenically unsaturated bonds, in the molecule. Examples of 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)acryloyl propyloxypropyl methacrylate, propoxylated ethoxylated bisphenol A di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, 9,9-bis(4-(2-(meth)acryloyloxyethoxy)phenyl)fluorene, tricyclodecane dimethanol di(meth)acrylate, 1,10-decane diol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, ethoxylated polypropylene Bifunctional (meth)acrylates such as pyrene glycol di(meth)acrylate and glycerin di(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 Examples of such compounds include trifunctional (meth)acrylates such as acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, ε-caprolactone modified tris-(2-(meth)acryloyloxyethyl)isocyanurate, and ethylene oxide modified trimethylolpropane tri(meth)acrylate; tetrafunctional (meth)acrylates such as ditrimethylolpropane tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, and pentaerythritol tetra(meth)acrylate; and divinylbenzene.

As the crosslinking agent, one having a molecular weight of more than 200 is preferred, one having a molecular weight of more than 300 is more preferred, and one having a molecular weight of 400 or more is particularly preferred. As the crosslinking agent, a compound having two ethylenically unsaturated bonds in the molecule is preferred. By using a compound having two ethylenically unsaturated bonds in the molecule as the crosslinking agent, the aggregation of resin particles caused by excessive crosslinking is suppressed, and resin particles with 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 preferred.

Examples of crosslinking 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, pentaerythritol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, trimethylolpropane polyglycidyl ether, and neopentyl glycol diglycidyl ether. Among these, ethylene glycol diglycidyl ether is preferred because it is capable of forming a high-density crosslinked structure and is highly effective in suppressing excessive hydrophilicity of the shell portion.

A surfactant can be used when producing resin particles. It is preferable to produce resin particles in the presence of a surfactant, since the particle size and shape of the resulting resin particles tend to be stable. However, non-reactive surfactants may be prone to peeling off from the resin particles. If the surfactant peels off in the ink, it may affect the physical properties of the ink, making it more likely that the ejection stability will decrease. For this reason, reactive surfactants are preferred as surfactants for use when producing resin particles.

As the reactive surfactant, it is preferable to use a compound in which a polymerizable functional group such as a (meth)acryloyl group, a maleyl group, a vinyl group, or an allyl group is bonded to the inside or end of a molecule composed of a hydrophilic part and a hydrophobic part. Examples of the hydrophilic part include polyoxyalkylene chains such as an ethylene oxide chain and a propylene oxide chain. Examples of the hydrophobic part include structures such as alkyl, aryl, and combinations thereof. The hydrophilic part and the hydrophobic part 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 nonylpropenyl phenyl ether, polyoxyethylene nonylpropenyl phenyl 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) Examples of suitable α-sulfo-ω-(1-alkoxymethyl-2-(2-propenyloxy)ethoxy)-poly(oxy-1,2-ethanediyl)ammonium salts include 2-sodium sulfoethyl methacrylate, bis(polyoxyethylene polycyclic phenyl ether) methacrylate sulfate salts, alkoxypolyethylene glycol methacrylates, alkoxypolyethylene glycol maleates, polyoxyalkylene alkenyl ethers, polyoxyalkylene alkenyl ether ammonium sulfates, vinyl ether alkoxylates, alkylaryl sulfosuccinates, polyoxyalkylene methacrylate sulfate salts, and unsaturated phosphate esters. Among these, α-sulfo-ω-(1-alkoxymethyl-2-(2-propenyloxy)ethoxy)-poly(oxy-1,2-ethanediyl)ammonium salts (product names "ADEKA REASOAP" manufactured by ADEKA, SR-10S, SR-10, SR-20, SR-3025, SE-10N, SE-20N, etc.) are preferred.

The core and shell of the resin particles may each contain units other than the above units, so long as the effects of the present invention are not impaired. As units other than the above units, those having one polymerizable functional group in the molecule are preferred, and specific examples include units derived from ethylenically unsaturated monomers.

Examples of 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; monocyclic (meth)acrylates such as cyclopropyl (meth)acrylate, cyclohexyl (meth)acrylate, cyclooctyl (meth)acrylate, and cyclodecyl (meth)acrylate; bicyclic (meth)acrylates such as isobornyl (meth)acrylate and norbornyl (meth)acrylate; tricyclic (meth)acrylates such as adamantyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate; and nonionic hydrophilic group-containing (meth)acrylates such as methoxy (mono-, di-, tri-, and poly)ethylene glycol (meth)acrylate. 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 preferred, and those having a molecular weight of 200 or less are even more preferred. Among them, alkenes having 1 to 22 carbon atoms; alkyl (meth)acrylates having an alkyl group with 1 to 22 carbon atoms, and the like are preferred. In addition, alkyl (meth)acrylates having an alkyl group with 1 to 12 carbon atoms are even more preferred, and methyl (meth)acrylate and ethyl (meth)acrylate are particularly preferred, since the physical properties of the resin particles can be easily adjusted and resin particles having excellent polymerization stability can be obtained.

As described above, the core portion includes an aromatic group-containing unit and a cyano group-containing unit. The ratio (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 more preferably 35% by mass or more and 90% by mass or less. The ratio (mass%) of the cyano group-containing unit in the core portion is preferably 10% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 55% by mass or less. If the ratio of the cyano group-containing unit in the core portion is less than 10% by mass, the color development of the image may be slightly reduced. On the other hand, if the ratio of the cyano group-containing unit in the core portion is more than 60% by mass, some of the cyano groups in the core portion may be easily exposed to the surface of the resin particles, and the fixation recovery of the ink may be slightly reduced. The ratio (mass%) of the other units in the core portion is preferably 15% by mass or less. The "other units" in the core portion are units other than the aromatic group-containing unit and the cyano group-containing unit. The "other units" of the core part are preferably composed of units derived from a reactive surfactant. In addition, the core part is preferably not crosslinked. In other words, the "other units" of the core part preferably do not include units derived from a crosslinking agent.

As described above, the shell portion contains aromatic group-containing units, anionic group-containing units, and units derived from a crosslinking agent, and is substantially free of cyano group-containing units. The proportion (mass%) of aromatic group-containing units in the shell portion is preferably 1 mass% or more and 60 mass% or less, and more preferably 10 mass% or more and 50 mass% or less.

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

The proportion (mass %) of the units derived from the crosslinking agent in the shell portion is 30% by mass or more and 80% by mass or less, and preferably 40% by mass or more and 70% by mass or less. If the proportion of the units derived from the crosslinking agent in the shell portion is less than 30% by mass, the cyano groups in the core portion are easily exposed under circumstances in which the hydrophilicity of the shell portion is excessively increased by combined use with a water-soluble resin, resulting in insufficient ink fixation recovery. On the other hand, if the proportion of the units derived from the crosslinking agent in the shell portion exceeds 80% by mass, the ink ejection stability becomes insufficient.

The proportion (mass %) of other units in the shell portion is preferably 10 mass % or less, and more preferably 5 mass % or less. The "other units" in the shell portion are units other than aromatic group-containing units, anionic group-containing units, and units derived from crosslinking agents. The "other units" in the shell portion are preferably composed of units derived from reactive surfactants.

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

The volume-based cumulative 50% particle diameter (D50) of the resin particles is preferably 120 nm or less. If the volume-based cumulative 50% particle diameter (D50) of the resin particles exceeds 120 nm, the resin particles are more likely to scatter light, and the color development of the image may be slightly reduced. 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 using the same method as the method for determining whether or not the resin particles are resin particles described above.

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

[Method of manufacturing dyed resin particles]
The resin particles can be produced according to a conventional method such as emulsion polymerization, mini-emulsion polymerization, seed polymerization, and phase inversion emulsification. Examples of the dyeing method of the resin particles include a method of polymerizing a monomer mixture in which a fluorescent dye is dissolved to form resin particles; a method of adding a fluorescent dye to resin particles and heating the particles; and the like. Among them, the method of adding a fluorescent dye to resin particles and heating the particles is preferred because it can be applied to a wider variety of fluorescent dyes. It is preferable not to add a dyeing assistant (water-soluble resin, surfactant, etc.) during heating. If a water-soluble resin is used as a dyeing assistant, the water-soluble resin may form a film and inhibit the redispersion of the resin particles, which may slightly reduce the fixation recovery of the ink. In addition, if a surfactant is used as a dyeing assistant, the physical properties of the ink may be affected, and the ejection stability of the ink may slightly decrease.

[Method for verifying resin particles]
The composition of the resin particles can be verified according to the following methods (i) to (iii). Below, a method for extracting resin particles from ink and analyzing and verifying them will be described, 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 By density gradient centrifugation, resin particles can be separated and extracted from ink containing resin particles. Among density gradient centrifugation methods, density gradient sedimentation velocity method separates and extracts resin particles based on the difference in sedimentation coefficient of components. Also, among density gradient centrifugation methods, density gradient sedimentation equilibrium method separates and extracts resin particles based on the difference in density of components.

(ii) Confirmation and Separation of Layer Structure First, the resin particles are stained and fixed with ruthenium tetroxide, and then embedded in epoxy resin to hold them in a stable state. Next, the resin particles embedded in the epoxy resin are cut with an ultramicrotome, and the cross section is observed using a scanning transmission electron microscope (STEM). By observing the cross section cut through the center of gravity of the resin particles, the layer structure of the resin particles can be confirmed. The resin particles embedded in the epoxy resin are used as an analysis sample, and the elements contained in the layers (core and shell) constituting the resin particles can be quantitatively analyzed by STEM-EDX, which is equipped with an energy dispersive X-ray spectroscopy (EDX).

(iii) Analysis of units (monomers) constituting the resin of each layer The resin particles to be used as a sample for separating the resin of each layer may be in the form of a dispersion liquid. Alternatively, the resin particles may be dried to form a film as a sample. After dissolving the resin particles to be used as a sample in an organic solvent, the layers are separated by gel permeation chromatography (GPC) and the resins constituting each layer are separated. Then, the separated resin is subjected to elemental analysis by a combustion method. Separately, the separated resin is pretreated by an acid decomposition (addition of hydrofluoric acid) method or an alkali fusion method, and then the inorganic components are quantitatively analyzed by an inductively coupled plasma optical 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 that constituted the separated resin can be known.

The separated resin is then analyzed using nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). This makes it possible to determine the types and proportions of the units (monomers) and crosslinking components that make up the resin. Furthermore, the separated resin can be analyzed using pyrolysis gas chromatography to directly detect the monomers produced by depolymerization.

(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 an acrylic resin or a urethane resin, and more preferably an acrylic resin. When a water-soluble resin having an aromatic group-containing unit is present, hydrophobic interactions and π-π interactions occur 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 aids in the dispersion of the resin particles, improving the ejection stability of the ink.

In addition, when the ink is stored for a long period of time, some of the fluorescent dye adsorbed to the resin particles transfers to the water-soluble resin due to various interactions (electrostatic interaction, hydrophobic interaction, dipole interaction) with the water-soluble resin. When this phenomenon occurs, the amount of dye adsorbed to the resin particles decreases while the dye content in the ink remains constant. This reduces the concentration quenching that occurs between the dyes in the resin particles, improving the color development of the image.

The transfer of dye to the water-soluble resin can be easily confirmed by the density gradient centrifugation method described above. In the case of ink that does not contain water-soluble resin, there is only one band of resin particles as a coloring component. In contrast, in the case of ink that contains 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. Examples of monomers constituting the other units, including those having a substituent such as an alkoxy group or a hydroxy group, include 2-hydroxyethyl (meth)acrylate; 3-hydroxypropyl (meth)acrylate; methoxy (mono-, di-, tri-, poly)ethylene glycol (meth)acrylate; 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. acrylate; monocyclic (meth)acrylates such as cyclopropyl (meth)acrylate, cyclohexyl (meth)acrylate, cyclooctyl (meth)acrylate, and cyclodecyl (meth)acrylate; bicyclic (meth)acrylates such as isobornyl (meth)acrylate and norbornyl (meth)acrylate; tricyclic (meth)acrylates such as adamantyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate; and the like. The water-soluble acrylic resin may be any of a random copolymer, a block copolymer, and a graft copolymer.

As the water-soluble urethane resin, a resin obtained by reacting polyisocyanate with a component that reacts with it (such as a polyol having an acid group, a polyol not having an acid group, or a polyamine) can be used. It may also be a resin obtained by further reacting a chain extender or a crosslinking agent. 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 becomes insufficient. On the other hand, if the acid value of the water-soluble resin is more than 180 mgKOH/g, the anionic groups in the shell of the resin particles are neutralized by ions derived from the anionic groups of the water-soluble resin, promoting water solubility and loosening the inclusion state in the core. This makes the core having cyano groups more likely to be exposed, reducing the fixation recovery of the ink.

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 ejection stability of the ink may be slightly reduced. On the other hand, if the weight average molecular weight of the water-soluble resin is more than 20,000, the viscosity of the ink is likely to increase, and the effect of improving the ejection stability of the ink may be slightly reduced.

The content (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 (mass%) of the water-soluble resin is preferably 0.1 times or more and 2.0 times or less in mass ratio to the content (mass%) of the resin particles. If the mass ratio is less than 0.1 times, the effect of improving the ejection stability of the ink may be slightly reduced. On the other hand, if the mass ratio is more than 2.0 times, the anionic groups of the shell part of the resin particles are neutralized by ions derived from the anionic groups of the water-soluble resin, and the core part having a cyano group is easily exposed. This may slightly reduce the effect of improving the fixation recovery of the ink.

The composition, weight average molecular weight, acid value, and other physical properties of the water-soluble resin can be measured according to conventional methods. Specifically, the ink is centrifuged and the sediment and supernatant liquid obtained are analyzed to measure the physical properties of the water-soluble resin. Although the water-soluble resin can be analyzed in the ink state, it is preferable to analyze the water-soluble resin extracted from the ink, since this improves the measurement accuracy. Specifically, it is preferable to add an excess of acid (such as hydrochloric acid) to the supernatant liquid obtained by centrifuging the ink at 75,000 rpm, and then dry the precipitated resin and analyze it.

The resin separated from the ink can be analyzed using a high-temperature gas chromatography/mass spectrometer (high-temperature GC/MS) to confirm the types of units that make up the water-soluble resin. In addition, the molecular weight and type of monomers that make up each unit can be confirmed by quantitatively analyzing the resin using nuclear magnetic resonance ( ¹³ C-NMR) or a Fourier transform infrared spectrometer (FT-IR).

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

The weight average molecular weight of the water-soluble resin can be measured by gel permeation chromatography (GPC). The measurement conditions for GPC can be as follows: Apparatus: Alliance GPC 2695 (manufactured by Waters)
Column: Shodex KF-806M 4-column (Showa Denko)
・Mobile phase: THF (special grade)
・Flow rate: 1.0mL/min
Oven temperature: 40.0°C
Amount of sample solution injected: 0.1 mL
Detector: RI (refractive index)
Polystyrene standard samples: PS-1 and PS-2 (manufactured by Polymer Laboratories, molecular weights: 17 types: 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 the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the ink is preferably 50.0 mass% or more and 95.0 mass% or less based on the total mass of the ink. In addition, as the water-soluble organic solvent, any of those generally used in inks can be used. Examples include alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.0 mass% or more and 50.0 mass% or less based on the total mass of the ink.

(Light fastener)
The resin particles preferably further encapsulate a light-resistant agent. The state in which the resin particles encapsulate a light-resistant agent means a state in which the light-resistant agent is present inside the three-dimensional structure formed by the entanglement of the resins forming the resin particles. The decomposition of the fluorescent dye by light is considered to occur when the fluorescent dye is exposed to light (ultraviolet light) and the radicals or peroxides generated react with the fluorescent dye. Therefore, as the light-resistant agent, a compound that can suppress the deterioration of components due to light by absorbing ultraviolet light or capturing radicals or peroxides can be used. As the light-resistant agent, at least one of an antioxidant, a light stabilizer, and an ultraviolet absorber can be used.

Antioxidants are components that suppress the deterioration of fluorescent dyes by decomposing peroxides. Specific examples of antioxidants include sulfides, hindered phenols, and phosphites. Light stabilizers are components that suppress the deterioration of fluorescent dyes by capturing radicals. Specific examples of light stabilizers include hindered amines. UV absorbers are components that absorb UV rays and convert them into thermal energy, suppressing the generation of radicals and peroxides, thereby suppressing the deterioration of fluorescent dyes. Specific examples of UV absorbers include benzotriazoles and triazines. The deterioration of fluorescent dyes can be effectively suppressed by decomposing peroxides, so it is preferable to use antioxidants, and it is even more preferable to use sulfides. On the other hand, UV absorbers may absorb part of the UV light when the fluorescent dye emits light, and the color development of the fluorescent dye may be slightly reduced compared to other light fasteners.

The content (mass %) of the lightfast agent 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 proportion (mass %) of the lightfast agent in the resin particles is preferably 0.1% by mass or more and 10.0% by mass or less. If the proportion of the lightfast agent in the resin particles is too low, the effect of improving the lightfastness of the image may be slightly reduced. On the other hand, if the proportion of the lightfast agent in the resin particles is too high, the ejection characteristics may be slightly reduced.

Whether or not the resin particles contain a lightfast agent can be determined, for example, according to the method shown below. The method for analyzing resin particles extracted from ink will be described, but resin particles extracted from an aqueous dispersion can also be analyzed in the same way. First, the resin particles are separated from the ink by density gradient centrifugation. In density gradient sedimentation velocity analysis, resin particles can be separated and extracted based on the difference in sedimentation coefficient of the components. In density gradient sedimentation equilibrium analysis, resin particles can be separated and extracted based on the difference in density of the components. After drying the obtained dispersion of resin particles, the sample solution is prepared by dissolving it in an organic solvent that can dissolve both the lightfast agent and the resin. Then, the lightfast agent and the resin are separated by gel permeation chromatography (GPC), high performance liquid chromatography (HPLC), column chromatography, or the like. The separated lightfast agent and the resin are analyzed by nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), or the like. This allows us to know the type and proportion of light stabilizers, as well as the type and proportion of units (monomers) that make up the resin.

(Other additives)
In addition to the above-mentioned components, the ink may contain, as necessary, 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. Furthermore, the ink may contain, as necessary, various additives such as surfactants, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, reduction inhibitors, evaporation promoters, chelating agents, and other resins. The ink may contain coloring materials such as pigments and dyes (including dyes that do not exhibit fluorescence, basic dyes, disperse dyes, and dyes that exhibit fluorescence other than oil-soluble dyes), but usually does not need to contain such coloring materials.

(Physical properties of ink)
Since the ink is a water-based ink applied to the inkjet method, 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, and 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, and more preferably 1.0 mPa·s or more and 5.0 mPa·s or less. 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 storage section that stores the ink. The ink stored in the ink storage section is the water-based ink of the present invention described above. FIG. 1 is a cross-sectional view that shows a schematic diagram of an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to a recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage section for storing ink. The ink storage section is composed of an ink storage chamber 14 and an absorber storage chamber 16, which are communicated with each other via a communication port 18. The absorber storage chamber 16 is also communicated with the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 stores absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage section may not have an ink storage chamber that stores liquid ink, and may be in a form in which the entire amount of ink stored is held by the absorber. The ink storage section may also be in a form in which the entire amount of ink stored is stored in a liquid state, without having an absorber. Furthermore, the ink cartridge may be configured to have an ink container and a recording head.

<Inkjet recording method>
The inkjet recording method of the present invention is a method of ejecting the above-described aqueous ink of the present invention from an inkjet recording head to record an image on a recording medium. Methods for ejecting the ink include a method of imparting mechanical energy to the ink and a method of imparting thermal energy to the ink. In the present invention, it is particularly preferable to adopt a method of ejecting the ink by imparting thermal energy to the ink. Other than using the ink of the present invention, the steps of the inkjet recording method may be known.

2 is a diagram showing an example of an inkjet recording device used in the inkjet recording method of the present invention, in which (a) is a perspective view of the main part of the inkjet recording device, and (b) is a perspective view of the head cartridge. The inkjet recording device is provided with a conveying means (not shown) for conveying the recording medium 32, and a carriage shaft 34. The carriage shaft 34 is capable of mounting a head cartridge 36. The head cartridge 36 is equipped with recording heads 38 and 40, and is configured so that an ink cartridge 42 is set thereon. While the head cartridge 36 is conveyed in the main scanning direction along the carriage shaft 34, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, an image is recorded on the recording medium 32 by conveying the recording medium 32 in the sub-scanning direction by a conveying means (not shown). There are no particular limitations on the recording medium 32, but it is preferable to use a recording medium based on paper, such as a recording medium without a coating layer such as plain paper, or a recording medium with a coating layer such as glossy paper or matte paper. This recording medium does not need to be used for transfer purposes.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way to the following examples as long as it does not deviate from the gist of the invention. The terms "parts" and "%" used to describe the amounts of components are by weight 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 placed in the reaction vessel, and the internal temperature was maintained at 70°C. A monomer to be the aromatic group-containing unit, a monomer to be the cyano group-containing unit (including a monomer as a control example), and a reactive surfactant to be the reactive surfactant unit were mixed in the amounts (parts) and breakdown (%) shown in Tables 1-1 and 1-2. This prepared a monomer mixture for the core portion. As the reactive surfactant, a product name "ADEKA REASOAP SR-10" (manufactured by ADEKA) was used. In addition, 1.9 parts of potassium persulfate and 659 parts of water were mixed to prepare an aqueous solution of polymerization initiator 1. The monomer mixture for the core portion and the aqueous solution of polymerization initiator 1 were dropped into the reaction vessel in parallel over 60 minutes. After the dropwise addition, stirring was continued to react for another 30 minutes to synthesize particles to be the core portion of the resin particles. However, the core portion was not synthesized for resin particle 47.

Next, a monomer (including a monomer as a control example) that will become the aromatic group-containing unit, a monomer that will become the anionic group-containing unit, a crosslinking agent that will become the crosslinking agent unit, and a reactive surfactant that will become the reactive surfactant unit were prepared. These prepared monomers were mixed in the amounts (parts) and breakdown (%) shown in Tables 1-3 and 1-4 to prepare a monomer mixture for the shell portion. As the reactive surfactant, "ADEKA REASOAP SR-10" (manufactured by ADEKA) was used. In addition, 0.1 parts of potassium persulfate and 133 parts of water were mixed to prepare an aqueous solution of polymerization initiator 2. The monomer mixture for the shell portion and the aqueous solution of polymerization initiator 2 were dropped in parallel over 10 minutes into a reaction vessel containing particles that will become the core portion. After the dropping was completed, the mixture was stirred at 80°C for 10 minutes to continue the reaction to synthesize the shell portion, and resin particles having a core-shell structure in which the particles that will become the core portion are coated with the resin that will become the shell portion were synthesized. However, the shell portion was not synthesized for resin particle 46.

Then, an appropriate amount of 8 mol/L potassium hydroxide aqueous solution was added to the reaction vessel, and the pH of the liquid was adjusted to 8.5. Furthermore, a fluorescent dye powder was added in the amount (parts) and breakdown (%) shown in Tables 1-5 and 1-6, and the temperature was raised to 80°C. At this time, for resin particles 38 to 44, a light fastener was added together with the fluorescent dye in the amount (parts) and breakdown (%) shown in Tables 1-7 and 1-8. Then, the mixture was stirred for 2 hours to dye the resin particles with the fluorescent dye. For resin particles other than 45, no surfactant was used as a dyeing aid. On the other hand, for resin particle 45, an anionic surfactant (sodium lauryl sulfate) was used as a dyeing aid. Next, an appropriate amount of 8 mol/L potassium hydroxide aqueous solution was added to the reaction vessel, and the pH of the liquid was adjusted to 8.5. An appropriate amount of water was further added to obtain an aqueous dispersion of each resin particle with a resin particle content of 20%. Tables 1-7 and 1-8 show the particle diameters of the obtained resin particles (cumulative 50% particle diameter based on volume). The particle diameters of the resin particles were measured using a dynamic light scattering particle size analyzer (product name "UPA-EX150", manufactured by Nikkiso) under the following conditions: Set Zero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: spherical, refractive index: 1.59. However, resin particles 58 were not dyed with dye. Of the fluorescent dyes used, "C.I. Acid Red 52" and "C.I. Acid Yellow 73" do not belong to any of the basic dyes, disperse dyes, and oil-soluble dyes.

The meanings of the abbreviations in Tables 1-1 to 1-8 are as follows:
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 (product name "Denacol EX-810", manufactured by Nagase ChemteX)
EX-830: Polyethylene glycol diglycidyl ether (product name "Denacol EX-830", manufactured by Nagase ChemteX)
EX-521: Polyglycerol polyglycidyl ether (product name "Denacol EX-521", manufactured by Nagase ChemteX)
・BR1: C.I. Basic Red 1
・BR1:1: C.I. Basic Red 1:1
・BV11: C.I. Basic Violet 11
BV11:1: C.I. Basic Violet 11:1
・BY40: C.I. Basic Yellow 40
・FB363: Fluorescent Brightener 363
・AR52: C.I. Acid Red 52
DY82: C.I. Disperse Yellow 82
SY196: C.I. Solvent Yellow 196
SY160:1: C.I. Solvent Yellow 160:1
SR43: C.I. Solvent Red 43
SR45: C.I. Solvent Red 45
SO5: C.I. Solvent Orange 5
SO45: C.I. Solvent Orange 45
AY73: C.I. Acid Yellow 73
Light stabilizer 1: Light stabilizer having a sulfide structure (product name "IRGANOX1520L", manufactured by BASF)
Light stabilizer 2: Light stabilizer having a sulfide structure (product name "ADK STAB AO-412S", manufactured by ADEKA)
Light stabilizer 3: Light stabilizer having a hindered phenol structure (product name "ADK STAB AO-40", manufactured by ADEKA)
Light stabilizer 4: Light stabilizer having a phosphite structure (product name "ADK STAB TPP", manufactured by ADEKA)
Light stabilizer 5: a light stabilizer having a hindered amine structure (product name "ADK STAB LA-81", manufactured by ADEKA)
Light stabilizer 6: Light stabilizer having a benzotriazole structure (product name "ADEKA STAB LA-29", manufactured by ADEKA)
Light stabilizer 7: Light stabilizer having a triazine structure (product name "ADK STAB LA-46", manufactured by ADEKA)

<Synthesis of Water-Soluble Resin>
(Water-soluble resin 1 to 8)
Monomers were polymerized by a conventional method to synthesize a water-soluble acrylic resin, which is a random copolymer having the composition and properties shown in Table 2. Water containing potassium hydroxide in an amount equimolar to the acid value was added to neutralize the anionic group, and then an appropriate amount of water was further added to obtain an aqueous solution of the water-soluble resin with a resin content of 10.0%. The water-soluble resin was dissolved in tetrahydrofuran to prepare a measurement sample, and the acid value of the water-soluble resin was measured by potentiometric titration using an automatic potentiometric titrator (trade name "AT510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) with potassium hydroxide ethanol titrant. The weight average molecular weight of the water-soluble resin, measured in terms of polystyrene, measured by GPC was 10,000 in all cases.

The meanings of the abbreviations in Table 2 are as follows:
St: styrene; BzMA: benzyl methacrylate; BA: n-butyl acrylate; MAA: methacrylic acid; AA: acrylic acid

(Water-soluble resin 9)
A four-neck flask equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux tube was prepared. 80.0 parts of toluene diisocyanate, 68.5 parts of polypropylene glycol with a number average molecular weight of 2,000, 47.8 parts of dimethylolpropionic acid, and 300 parts of methyl ethyl ketone were placed in the flask, and reacted at 80° C. for 6 hours under a nitrogen gas atmosphere. Then, 3.8 parts of ethylenediamine were added and reacted at 80° C. Then, the mixture was cooled to 40° C., ion-exchanged water was added, and water containing potassium hydroxide equimolar to the acid value of the resin was added while stirring at high speed with a homomixer. After distilling off the methyl ethyl ketone under heating and reduced pressure, an appropriate amount of water was added to obtain an aqueous solution of water-soluble resin 9 with a resin content of 10.0%. The water-soluble resin 9 was a water-soluble urethane resin with an acid value of 100 mgKOH/g and a weight average molecular weight of 18,000.

<Ink Preparation>
Each ink was prepared by mixing the components (unit: %) shown in the upper part of Tables 3-1 to 3-6, thoroughly stirring, and then filtering under pressure with a microfilter (manufactured by Fujifilm) having a pore size of 3.0 μm. In Tables 3-1 to 3-6, "Acetylenol E100" is the trade name of a nonionic surfactant manufactured by Kawaken Fine Chemicals. The lower part of Tables 3-1 to 3-6 shows the properties of the ink. The pH of each of the prepared inks was within the range of 8.5 to 9.0.

<Evaluation>
Each prepared ink was filled into an ink cartridge, and the ink cartridge was set in an inkjet recording device (product name "PIXUS Pro-10", manufactured by Canon) equipped with a recording head that ejects ink by thermal energy. In this inkjet recording device, an image recorded under the condition that 8 droplets of 3.8 ng±10% ink are applied to a unit area of 1/600 inch×1/600 inch is defined as having a recording duty of 100%. The recording environment was a temperature of 25° C. and a relative humidity of 55%. In the present invention, in the evaluation criteria for each item below, "A" and "B" were defined as acceptable levels, and "C" was defined as an unacceptable level. The evaluation results are shown in Table 4.

(Color development)
Using the above inkjet recording device, an image including the following gradation pattern was recorded on a recording medium (glossy paper, product name "Canon Photo Paper Fine Grain Gloss Luster", manufactured by Canon). The gradation pattern is composed of a 2 cm x 2 cm solid image in which the amount of ink applied is changed stepwise under the condition that a maximum of 6 drops of ink are applied to a unit area of 1/600 inch x 1/600 inch. After drying the recorded image for one day, the hue angle (H), chroma (C*), and lightness (L*) in the Lab color system were measured using a spectrophotometer (product name "X-RiteeXact" (M1 light ^source ), manufactured by X ^- Rite). Then, the color development of the image was evaluated according to the following evaluation criteria. The lightness was evaluated as a value at a chroma of 50. However, when the maximum chroma did not reach 50, the data obtained by measuring the color of the gradation pattern was extrapolated, and the calculated lightness value obtained was used for evaluation. The evaluation criteria were changed depending on the hue angle because the preferred color tone perceived visually differs depending on the type of color.

[When the hue angle is 0° or more and less than 180°]
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 saturation was less than 50, or the brightness was less than 80.

[When the hue angle is 180° or more and less than 360°]
A: The maximum saturation was 60 or more and the brightness was 70 or more, or the maximum saturation was 50 or more and the brightness was 75 or more.
B: The maximum saturation was 50 or more and less than 60, and the brightness was 70 or more and less than 75.
C: The maximum saturation was less than 50, or the brightness was less than 70.

(Discharge stability)
Using the above inkjet recording device, a 19 cm x 26 cm solid image was recorded on 10 sheets of recording medium (plain paper, product name "GF-500", manufactured by Canon) with a recording duty of 100%. The solid images recorded on the fifth and tenth recording media were visually confirmed, and the ejection stability was evaluated according to the following evaluation criteria.
A: There were no white streaks or smudges on the fifth sheet, but there were slight white streaks or smudges on the tenth sheet.
B: There were no white streaks or smudges on the fifth sheet, but there were white streaks or smudges on the tenth sheet.
C: There were white streaks and scratches on the fifth piece.

(Adhesion recovery)
The following operations were performed using the above inkjet recording device. After performing a recovery process (cleaning) from the printer driver, a nozzle check pattern of the inkjet recording device was recorded. Thereafter, the power cable was pulled out while the carriage was in operation (when the recording head was in a position other than the home position) to leave the recording head in an uncapped state. In this state, the inkjet recording device was left in an environment with a temperature of 30° C. and a relative humidity of 10% for 14 days. Next, the inkjet recording device was placed in an environment with a temperature of 25° C. for 6 hours, and then a nozzle check pattern was recorded while performing a recovery process (cleaning). The recorded nozzle check pattern was checked, and the adhesion recovery was evaluated according to the following evaluation criteria.
A: After performing the recovery process 3 to 5 times, the disc was able to record normally.
B: After performing the recovery process 6 to 10 times, normal recording was possible.
C: After the recovery process was performed 11 times, normal recording was not possible.

(Light resistance)
Using the above inkjet recording device, a 2 cm x 2 cm solid image with a recording duty of 100% was recorded on two sheets of recording medium (plain paper, product name "GF-500", manufactured by Canon). One of the recorded solid images was placed in a xenon test device (product name "Atlas Weather-O-Meter Ci4000", manufactured by Toyo Seiki Seisakusho), and the solid image was irradiated with xenon light for 3 hours under conditions of a temperature of 50°C, a relative humidity of 70%, and an irradiation intensity of 0.39 W/ ^m2 . Thereafter, the solid image irradiated with xenon light and the solid image not irradiated with xenon light were visually confirmed and compared. As a result, the images recorded with the inks of Examples 43 to 49 had less fading than the images recorded with the inks of the other Examples.

Claims (20)

A water-based inkjet ink containing resin particles dyed with a fluorescent dye and a water-soluble resin,
The fluorescent dye includes a dye exhibiting fluorescence selected from the group consisting of a basic dye, a disperse dye, and an oil-soluble dye;
the resin particles are formed of an acrylic resin and have a core portion including an aromatic group-containing unit and a cyano group-containing unit, and a shell portion including an aromatic group-containing unit, an anionic group-containing unit, and a unit derived from a crosslinking agent and not including a cyano group-containing unit;
a ratio (mass %) of units derived from the crosslinking agent in the shell portion is 30 mass % or more and 80 mass % or less,
the water-soluble resin is an acrylic resin having 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,
the aromatic group-containing unit is a unit derived from a monomer having one ethylenically unsaturated bond, which is a polymerizable functional group, in the molecule and having no anionic group or cyano group,
the cyano group-containing unit is a unit derived from a monomer having one ethylenically unsaturated bond, which is a polymerizable functional group, in the molecule and having no anionic group or aromatic group,
the anionic group-containing unit is a unit derived from a monomer having one ethylenically unsaturated bond, which is a polymerizable functional group, in the molecule and having neither an aromatic group nor a cyano group,
The water-based ink according to claim 1, wherein the crosslinking agent is a compound having, in its molecule, two or more ethylenically unsaturated bonds which are polymerizable functional groups, or having, in its molecule, two or more glycidyl groups which are polymerizable functional groups . the aromatic group-containing unit is a unit derived from at least one selected from the group consisting of styrene, vinyl toluene, and benzyl methacrylate;
the cyano group-containing unit is a unit derived from at least one selected from the group consisting of acrylonitrile and methacrylonitrile,
the anionic group-containing unit is a unit derived from at least one selected from the group consisting of methacrylic acid and acrylic acid,
2. The aqueous ink according to claim 1, wherein the crosslinking agent is at least one selected from the group consisting of ethylene glycol dimethacrylate, divinylbenzene, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether. The aqueous ink according to claim 1 or 2 , wherein a ratio (% by mass) of the cyano group-containing unit to the core portion is 10% by mass or more and 60% by mass or less. The aqueous ink according to claim 1 , wherein the proportion (mass %) of the anionic group-containing unit in the shell portion is 5 mass % or more and 30 mass % or less. The water-based ink according to claim 1 , wherein the aromatic group-containing unit contained in the core portion and the aromatic group-containing unit contained in the shell portion are the same type of unit. the crosslinking agent comprises two or more crosslinking agents,
6. The aqueous ink according to claim 1, wherein at least one crosslinking agent is a crosslinking agent having a glycidyl group. The aqueous ink according to claim 1 , wherein a ratio (% by mass) of the fluorescent dye to the resin particles is 1.0% by mass or more and 15.0% by mass or less . The aqueous ink according to claim 1 , wherein a ratio (% by mass) of the fluorescent dye to the resin particles is 3.0% by mass or more and 8.0% by mass or less. The aqueous ink according to claim 1 , wherein the fluorescent dye comprises two or more fluorescent dyes. 10. The aqueous ink according to claim 1, wherein the basic dye is at least one selected from the group consisting of compounds having a xanthene skeleton and compounds having a coumarin skeleton. 11. The aqueous ink according to claim 1, wherein the disperse dye is at least one selected from the group consisting of compounds having a coumarin skeleton and compounds having an anthraquinone skeleton. 12. The water-based ink according to claim 1, wherein the oil-soluble dye is at least one selected from the group consisting of compounds having a coumarin skeleton and compounds having a xanthene skeleton. The aqueous ink according to claim 1 , wherein the content (mass %) of the fluorescent dye is 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink. The water-based ink according to claim 1 , wherein the resin particles have a volume-based cumulative 50% particle diameter of 120 nm or less. The water-based ink according to claim 1 , wherein the resin particles have a volume-based cumulative 50% particle size of 50 nm or more. The aqueous ink according to any one of claims 1 to 15, wherein the content (mass%) of the water-soluble resin is 0.1 to 2.0 times the content (mass%) of the resin particles in terms of mass ratio. The aqueous ink according to any one of claims 1 to 16, wherein the content (mass %) of the water-soluble resin is 0.1 mass % or more and 5.0 mass % or less based on the total mass of the ink. The aqueous ink according to any one of claims 1 to 16, wherein the content (mass%) of the resin particles is 1.0 mass% or more and 10.0 mass% or less based on the total mass of the ink. An ink cartridge including an ink and an ink storage section for storing the ink,
19. An ink cartridge, wherein the ink is a water-based ink as claimed in claim 1. An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, comprising:
19. An ink-jet recording method, wherein the ink is a water-based ink according to claim 1.

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