Aqueous ink, ink cartridge, and inkjet recording method

Abstract

To provide aqueous ink for inkjet which can record an image having high optical concentration, and is excellent in storage stability.SOLUTION: Aqueous ink for inkjet contains a pigment and resin particles. The resin particles are formed of a copolymer having a carboxylic acid group and a sulfonic acid group, and the resin particles include at least one kind selected from the group consisting of polyolefin which has a carboxylic acid group and weight average molecular weight of 2,000 or more, a fluorine-based surface active agent, and a silicone-based surface active agent.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Conventionally, inkjet recording devices have been widely used as small home printers. In recent years, inkjet recording devices have also been deployed for use in offices and commercial printing. For inkjet recording devices used in fields such as offices and commercial printing, it is required to record higher-quality images, such as being able to record images with high optical density. On the other hand, inks capable of recording images with high optical density may have poor storage stability because they have high cohesiveness after landing on the recording medium.

[0003] For example, in order to achieve both the storage stability of the ink and the optical density of the image, inks using resin particles prepared using surface-treated carbon black and an emulsifier have been proposed (Patent Document 1). In addition, inks using a dispersible pigment and resin particles having a specific functional group have been proposed (Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The inventors of the present invention examined the inks proposed in Patent Documents 1 and 2. As a result, it was found that it is difficult for the inks proposed in Patent Documents 1 and 2 to achieve both high-level storage stability and image optical density required in recent years. When a resin with a low acid dissociation constant (pKa) is added to the ink, the hydrophilicity is improved, so that there is a certain effect on the storage stability of the ink. However, due to the improved hydrophilicity, aggregation on the recording medium is likely to be inhibited, and it is difficult to increase the optical density of the image.

[0006] Therefore, an object of the present invention is to provide an aqueous ink for inkjet that has excellent storage stability and can record an image with high optical density. Another object of the present invention is to provide an ink cartridge using this aqueous ink and an inkjet recording method.

Means for Solving the Problems

[0007] That is, according to the present invention, there is provided an aqueous ink for inkjet containing a pigment and resin particles, wherein the resin particles are formed of a copolymer having a carboxylic acid group and a sulfonic acid group, and the resin particles contain at least one selected from the group consisting of a polyolefin having a carboxylic acid group and a weight average molecular weight of 2,000 or more, a fluorosurfactant, and a silicone surfactant.

Effects of the Invention

[0008] According to the present invention, it is possible to provide an aqueous ink for inkjet that has excellent storage stability and can record an image with high optical density. Further, according to the present invention, it is possible to provide an ink cartridge using this aqueous ink and an inkjet recording method.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in more detail by giving preferred embodiments. In the present invention, when the compound is a salt, the salt dissociates into ions and exists in the aqueous ink, but for convenience, it is expressed as "containing a salt". In addition, the aqueous ink for inkjet may be simply referred to as "ink". Physical property values are values at normal temperature (25 ° C), normal pressure (1 atmospheric pressure = 101,325 Pa), and normal humidity (relative humidity 50%) unless otherwise specified.

[0011] "Unit" means a unit structure corresponding to one monomer unless otherwise specified. When "(meth) acrylic acid" and "(meth) acrylate" are described, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate", respectively. Resin particles mean the whole including all components other than the resin such as the initiator used in the production of the resin particles and resins used other than the main component resin (the resin having the largest proportion).

[0012] The present inventors have studied an ink containing a pigment and resin particles in order to record an image with a high optical density while improving the storage stability of the ink. Resin particles having a carboxylic acid group on their particle surfaces have the carboxylic acid group functioning as an aggregative functional group. Therefore, when an ink containing resin particles having a carboxylic acid group on their particle surfaces is used, the resin particles aggregate with the pigment to form aggregates on the recording medium, and the optical density of the image is improved. However, when the amount of carboxylic acid groups in the resin forming the resin particles is increased, the carboxylic acid groups also increase inside the resin particles. For this reason, water molecules also easily enter inside the resin particles, making it difficult to maintain the particle interface. As a result, the dispersion state of the resin particles becomes unstable, aggregation between the resins is likely to be caused, and the storage stability of the ink is likely to decrease.

[0013] The present inventors have studied incorporating a sulfonic acid group into resin particles in order to maintain the dispersion state of resin particles having a carboxylic acid group on their particle surfaces and improve the storage stability of the ink. The acid dissociation constant of the sulfonic acid group is smaller than that of the carboxylic acid group. Therefore, the present inventors predicted that an ink containing resin particles having a carboxylic acid group and a sulfonic acid group would have improved storage stability compared to an ink containing resin particles having only a carboxylic acid group. However, when resin particles having a carboxylic acid group and a sulfonic acid group were used, it was found that although the storage stability of the ink was improved, it became difficult to aggregate the pigment on the recording medium, and the optical density of the image was likely to decrease.

[0014] The present inventors have studied encapsulating at least one component selected from the group consisting of the following (i) to (iii) in resin particles formed of a copolymer (resin) having a carboxylic acid group and a sulfonic acid group. And, by using such resin particles, it has been found that the optical density of the image and the storage stability of the ink are improved, leading to the present invention. (i) A polyolefin having a carboxylic acid group and a weight average molecular weight of 2,000 or more (ii) A fluorine-based surfactant (iii) A silicone-based surfactant

[0015] By encapsulating the above components in resin particles, it is considered that the carboxylic acid groups in the resin particles can be oriented outside the particles, enhancing the aggregability of the pigment. Furthermore, when a polyolefin with a weight average molecular weight of 2,000 or more is encapsulated in the resin particles, the hydrophobicity of the polyolefin exerts an effect of suppressing the penetration of water molecules into the resin particles, improving the storage stability of the ink. Note that when a polyolefin with a weight average molecular weight of less than 2,000 is used, the carboxylic acid groups cannot be oriented and retained outside the resin particles, resulting in a decrease in the aggregability of the pigment and an inability to improve the optical density of the image.

[0016] Also, when a fluorine-based surfactant or a silicone-based surfactant is encapsulated in the resin particles, it is considered that the hydrogen bonding of the carboxylic acid groups within the resin particles is inhibited, and the carboxylic acid groups are oriented outside the particles, enhancing the aggregability of the pigment. Furthermore, since fluorine and silicone in the surfactant are hydrophobic, the hydrophilic-hydrophobic interface inside and outside the resin particles becomes clear, and it is considered that the resin particles are stabilized and the storage stability of the ink is improved. Even if only a surfactant other than a fluorine-based surfactant or a silicone-based surfactant (such as a hydrocarbon-based surfactant) is encapsulated in the resin particles, the carboxylic acid groups cannot be oriented outside the particles. As a result, the storage stability of the ink cannot be improved.

[0017] <Ink> The ink of the present invention is an aqueous ink for inkjet containing a pigment and resin particles, and the resin particles are formed of a copolymer having a carboxylic acid group and a sulfonic acid group. And these resin particles encapsulate at least one selected from the group consisting of a polyolefin having a carboxylic acid group and a weight average molecular weight of 2,000 or more, a fluorine-based surfactant, and a silicone-based surfactant. Hereinafter, each component constituting the ink and the physical properties of the ink will be described.

[0018] (Pigment) The ink contains a pigment as a coloring material. The content (mass %) of the pigment in the ink is preferably 0.1 mass % or more and 15.0 mass % or less, more preferably 1.0 mass % or more and 10.0 mass % or less, based on the total mass of the ink.

[0019] Examples of the pigment include inorganic pigments such as carbon black and titanium oxide; organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, dioxazine, and perinone.

[0020] Examples of the pigment dispersion method include resin-dispersed pigments using a resin as a dispersant, self-dispersed pigments in which a hydrophilic group is bonded to the particle surface of the pigment, etc. Also, resin-bonded pigments in which an organic group containing a resin is chemically bonded to the particle surface of the pigment, microcapsule pigments in which the surface of the pigment particles is coated or encapsulated with a resin, etc. can be used. It is also possible to use pigments with different dispersion methods in combination. Among them, resin-dispersed pigments using a resin as a dispersant are preferred.

[0021] As the resin dispersant, it is preferable to use a resin capable of dispersing the pigment in an aqueous medium by the action of an anionic group. Examples of the resin dispersant include acrylic resins and urethane resins. Among them, acrylic resins composed of hydrophilic units and hydrophobic units are more preferred.

[0022] The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of the hydrophilic monomer having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of the cation constituting the salt of the acidic monomer include ions such as lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit having no hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer having no hydrophilic group such as an anionic group. Specific examples of the hydrophobic monomer include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; (meth)acrylate-based monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, and the like.

[0023] The urethane resin can be obtained, for example, by reacting a polyisocyanate and a polyol. Further, it may be a product obtained by further reacting a chain extender. Examples of the olefin resin include polyethylene, polypropylene, and the like.

[0024] Examples of the self-dispersing pigment include those in which an anionic group is directly bonded to the particle surface of the pigment or bonded via another atomic group. Examples of the anionic group include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. Examples of the counter ion of the anionic group include cations such as a hydrogen atom, an alkali metal, ammonium, and an organic ammonium. The other atomic group is a group having a function as a spacer between the particle surface of the pigment and the anionic group, and preferably has a molecular weight of 1,000 or less. Examples of the other atomic group include an alkylene group having 1 to 6 carbon atoms, an arylene group such as a phenylene group and a naphthylene group, an ester group, an imino group, an amide group, a sulfonyl group, and an ether group.

[0025] (Resin particles) The resin particles are present in the ink in a dispersed state, that is, in the form of a resin emulsion. The content (mass %) of the resin particles in the ink is preferably 1.0 mass % or more and 20.0 mass % or less, more preferably 3.0 mass % or more and 15.0 mass % or less, based on the total mass of the ink. The resin particles do not necessarily need to encapsulate a coloring material. The "resin particles" in this specification means a resin that exists in a state that is not dissolved in the aqueous medium constituting the ink. More specifically, it means a resin that can exist in the aqueous medium in a state where particles having a particle diameter measurable by the dynamic light scattering method are formed. On the other hand, the "water-soluble resin" means a resin that exists in a state dissolved in the aqueous medium constituting the ink. More specifically, it means a resin that can exist in the aqueous medium in a state where particles having a particle diameter measurable by the dynamic light scattering method are not formed. When expressing the resin particles as a pair with the "water-soluble resin", it becomes "water-dispersible resin (water-insoluble resin)".

[0026] Whether a certain resin is "resin particles" can be determined according to the method shown below. First, prepare a liquid containing a resin neutralized with an alkali equivalent to the acid value (such as sodium hydroxide, potassium hydroxide, etc.) (resin solid content: 10% by mass). Next, dilute the prepared liquid 10 times (volume basis) with pure water to prepare a sample solution. Then, when measuring the particle size of the resin in the sample solution by the dynamic light scattering method, if particles having a particle size are measured, it can be determined that the resin is "resin particles". As a particle size distribution measuring device by the dynamic light scattering method, a particle size analyzer (for example, trade name "UPA-EX150", manufactured by Nikkiso Co., Ltd.) etc. can be used. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: true sphere, refractive index: 1.59. Of course, the particle size distribution measuring device to be used, the measurement conditions, etc. are not limited to the above. Measuring the particle size using the neutralized resin is to confirm that particles are formed even when it is sufficiently neutralized and it becomes difficult to form particles. Even under such conditions, a resin having the shape of particles exists in the form of particles in the aqueous ink.

[0027] The weight average molecular weight of the copolymer (resin) forming the resin particles is preferably 10,000 or more and 200,000 or less, and more preferably 100,000 or more and 200,000 or less. When the weight average molecular weight of the copolymer is less than 10,000, the amount of carboxylic acid groups present on the surface of the resin particles may be small, the aggregability of the pigment may be weakened, and the effect of improving the optical density may not be sufficiently obtained in some cases. On the other hand, when the weight average molecular weight of the copolymer exceeds 200,000, the hydrophobicity of the resin particles becomes too high, and it may become difficult to manufacture the resin particles in an aqueous system in some cases.

[0028] The copolymer forming the resin particles has a carboxylic acid group and a sulfonic acid group. By using a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as copolymerization monomers, a carboxylic acid group and a sulfonic acid group can be introduced into the copolymer.

[0029] Examples of the monomer having a carboxylic acid group include unsaturated carboxylic acids. Examples of the unsaturated carboxylic acid include benzyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, acrylonitrile, (meth)acrylic acid, and methoxypolyethylene glycol (meth)acrylate.

[0030] Examples of the monomer having a sulfonic acid group include unsaturated sulfonic acids and their salts. As the monomer having a sulfonic acid group, either synthesized or commercially available ones may be used.

[0031] As the copolymerization monomer for forming the copolymer, other monomers other than the above monomers having a carboxylic acid group and monomers having a sulfonic acid group may be used. From the viewpoint of improving storage stability without attracting water molecules into the resin particles, hydrophobic monomers are preferred. Examples of the hydrophobic monomer include monomers having an aromatic group such as styrene, α-methylstyrene, and benzyl (meth)acrylate; monomers having an aliphatic group such as ethyl (meth)acrylate, methyl (meth)acrylate, (iso-)propyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and the like. Further, maleic anhydride, citraconic anhydride, and the like may be used as the copolymerization monomer constituting the copolymer.

[0032] The ratio (b / a) of the anionic group b (μmol / g) present on the particle surface of the resin particles to the anionic group a (μmol / g) present in the resin particles is preferably 0.50 times or more and 0.80 times or less, and more preferably 0.60 times or more and 0.75 times or less. By setting the ratio within the above range, the optical density of the recorded image can be further increased, and the storage stability of the ink can be further improved. Here, the value of the anionic group a present in the resin particles represents the density of the anionic groups (in micromoles) present in the resin particles per unit mass of the resin particles. The value of the anionic group b present on the particle surface of the resin particles represents the density of the anionic groups (in micromoles) present on the particle surface of the resin particles per unit mass of the resin particles. If the above ratio is less than 0.50 times, the amount of anionic groups such as carboxylic acid groups present on the particle surface of the resin particles is relatively small, so the effect of improving the optical density may not be sufficiently obtained. On the other hand, if the above ratio exceeds 0.80 times, the amount of anionic groups such as carboxylic acid groups present on the particle surface of the resin particles is relatively large, so the effect of improving the storage stability of the ink may not be sufficiently obtained.

[0033] The ratio (c / a) of the sulfonic acid group c (μmol / g) present in the resin particles to the anionic acid group a (μmol / g) present in the resin particles is preferably 0.20 times or more and 0.30 times or less. By setting the ratio within the above range, the optical density of the recorded image can be further increased, and the storage stability of the ink can be further improved. Here, the value of the sulfonic acid group c present in the resin particles represents the density of the sulfonic acid groups (in micromoles) present in the resin particles per unit mass of the resin particles. If the above ratio is less than 0.20 times, the amount of anionic groups such as carboxylic acid groups present in the resin particles is relatively large, so the effect of improving the storage stability of the ink may not be sufficiently obtained. On the other hand, if the above ratio exceeds 0.30 times, the amount of anionic groups such as carboxylic acid groups present in the resin particles is relatively small, so the effect of improving the optical density may not be sufficiently obtained.

[0034] The anionic group b present on the particle surface of the resin particles can be adjusted by, for example, the methods shown below. That is, when the amount of the unit having an anionic group is fixed, it can be adjusted by adjusting the polymerization temperature or by adjusting the addition amounts of (i), (ii), and (iii). Specifically, b can be increased by increasing the addition amounts of (i), (ii), and (iii).

[0035] The anionic group a present in the resin particles, the anionic group b present on the particle surface of the resin particles, and the sulfonic acid group c present in the resin particles can be verified by measuring the titration amount using a potentiometric titration apparatus. As the potentiometric titration apparatus, for example, the product named "Automatic Potentiometric Titrator AT-510" (manufactured by Kyoto Electronics Industry Co., Ltd.) can be used. The conditions (titration parameters, control parameters) when using the above potentiometric titration apparatus can be as follows.

[0036] · Titration mode: Automatic intermittent · Titration style: Total amount · Detection method: Detector No2 / mV · Maximum titration amount: 20 mL · Waiting time before titration: 30 sec · Endpoint detection direction: Positive direction

[0037] · Endpoint judgment mode: Automatic · Setting of endpoint detection range: Not set · Gain: 1 · Data acquisition potential: 1 mV · Data acquisition titration amount: 0.5 mV · Control speed mode: Standard

[0038] As a sample for measuring the anionic group a present in the resin particles, pure water is added to the resin particles, and the pH is adjusted to 12 with an alkaline component such as potassium hydroxide, and the concentration of the resin particles is adjusted to 0.2 mass%. As the titrant, 1 mol / L hydrochloric acid is used.

[0039] ​​ When measuring the anionic group b present on the particle surface of the resin particles, as a sample, pure water is added to the resin particles, and the pH is adjusted to 12 with an alkaline component such as potassium hydroxide, and the concentration of the resin particles is adjusted to 0.2 mass%. As the titrant, an N / 200 methyl glycol chitosan aqueous solution (manufactured by Fujifilm) is used.

[0040] For the sulfonic acid group c present in the resin particles, pure water is added to the resin particles, and the pH is adjusted to 4 with an acid component such as sulfuric acid, and the concentration of the resin particles is adjusted to 0.2 mass%. As the titrant, 1 mol / L hydrochloric acid is used.

[0041] The acid value of the copolymer forming the resin particles is preferably 100 mgKOH / g or more and 300 mgKOH / g or less. When the acid value of the copolymer is less than 100 mgKOH / g, the pigment may aggregate violently, large aggregates may be formed, and the effect of improving the optical density may not be sufficiently obtained. On the other hand, when the acid value of the copolymer exceeds 300 mgKOH / g, the hydrophilicity may be too high, the hydrophilic-hydrophobic interface inside / outside the resin particles may become unstable, and the effect of improving the storage stability of the ink may not be sufficiently obtained.

[0042] The content (mass%) of the pigment in the ink is preferably 0.03 times or more and 0.70 times or less, more preferably 0.10 times or more and 0.30 times or less, as a mass ratio to the content (mass%) of the resin particles. When the above mass ratio is less than 0.03 times, the amount of resin particles relative to the pigment increases, and the pigment disposed on the surface of the image is likely to be biased, and the effect of improving the optical density may not be sufficiently obtained. On the other hand, when the above mass ratio exceeds 0.70 times, the amount of resin particles relative to the pigment decreases, the dispersion state of the pigment in the ink becomes unstable, and the aggregation of the pigment may be promoted. For this reason, the effect of improving the storage stability of the ink may not be sufficiently obtained.

[0043] [Method for Producing Resin Particles] The resin particles can be produced according to known methods. Specifically, the resin particles can be produced by methods such as the emulsion polymerization method, the pre-emulsion polymerization method, the seed polymerization method, and the phase inversion emulsification method. Further, by polymerizing a monomer in the presence of at least one component selected from the group consisting of a predetermined polyolefin, a fluorosurfactant, and a silicone surfactant, resin particles encapsulating these components can be produced.

[0044] [Method for Analyzing Resin Particles] Regarding the composition of the resin (copolymer) constituting the resin particles, etc., it can be verified and analyzed according to, for example, the methods shown below. First, a sample is prepared by dissolving the resin particles in an organic solvent capable of dissolving the resin particles, such as tetrahydrofuran. The resin particles used in this case may be in the state of an aqueous dispersion or in a dry state. The prepared sample is analyzed by an analytical method such as nuclear magnetic resonance (NMR) spectroscopy or matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). Thereby, the types and ratios of the units (monomers) constituting the resin can be known. Further, the resin particles themselves can be analyzed by pyrolysis gas chromatography to detect the units (monomers) constituting the resin. Furthermore, when an insoluble component that does not dissolve in the organic solvent is generated when preparing the above sample, this insoluble component can also be analyzed by pyrolysis gas chromatography to detect the units (monomers) constituting the resin. Also, for the dried sample, differential scanning calorimetry (DSC) can be used to estimate the presence of multiple types of resins by the presence of multiple glass transition points.

[0045] [Polyolefin] The polyolefin has a carboxylic acid group in its molecular structure. The carboxylic acid group can be introduced into the polyolefin by polymerizing using a monomer having a carboxylic acid group or by chemically reacting directly or indirectly with an unsaturated olefin.

[0046] Examples of monomers having a carboxylic acid group include maleic acid, fumaric acid, itaconic acid, acrylic acid, methacrylic acid, etc. There is no particular limitation on monomers having no carboxylic acid group, and they can be appropriately selected according to the purpose. For example, acrylic acid ester monomers such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-methoxyethyl acrylate, acryloylmorpholine, N,N'-dimethylaminoethyl acrylate; methacrylic acid ester monomers such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, 2-methoxyethyl methacrylate, N,N'-dimethylaminoethyl methacrylate; amide-based acrylates such as N-methylolacrylamide, methoxymethylacrylamide, etc. can be mentioned. In addition, other polymerizable monomers can be used as necessary. Examples of other polymerizable monomers include aromatic vinyl monomers such as styrene, unsaturated nitriles such as acrylonitrile, vinyl esters such as vinyl acetate, etc.

[0047] The polyolefin may have units derived from unsaturated olefins such as ethylene and α-olefins having 10 or fewer carbon atoms. Examples of α-olefins having 10 or fewer carbon atoms include propylene, 1-butene, 1-pentene, 1-heptene, 1-hexene, 1-octene, and 1-nonene.

[0048] The weight average molecular weight of the polyolefin is 2,000 or more, preferably 50,000 or less, more preferably 40,000 or less. When the weight average molecular weight of the polyolefin exceeds 50,000, the movement of molecules in the resin particles may be excessively suppressed, and it may easily aggregate with other resin particles, and the effect of improving storage stability may not be sufficiently obtained.

[0049] The content (mass %) of the polyolefin in the resin particles is preferably a mass ratio to the content (mass %) of the resin particles in the ink, and is preferably 0.02 times or more and 0.10 times or less, and more preferably 0.05 times or more and 0.08 times or less. When the above mass ratio is less than 0.02 times, the carboxylic acid groups in the resin particles may be less likely to be unevenly distributed on the surface of the resin particles, and the effect of improving the optical density may not be sufficiently obtained. On the other hand, when the above mass ratio exceeds 0.10 times, the carboxylic acid groups inside the resin particles are likely to increase, and the effect of improving the storage stability may not be sufficiently obtained.

[0050] [Fluorine-based surfactant] As the fluorine-based surfactant, those having a structure represented by the following general formula (1) can be used. Also, as the fluorine-based surfactant, a synthesized one or a commercially available product may be used. CF3CF2-(CF2CF2) m -(CH2) n -O-(CH2CH2) o -OH ···(1) (In the general formula (1), m represents an integer of 0 or more and 10 or less, n represents an integer of 1 or more and 4 or less, and o represents an integer of 0 or more and 40 or less)

[0051] In the general formula (1), m is preferably 2 or more and 4 or less, and o is preferably 6 or more and 10 or less. When m is less than 2 or o exceeds 10, the hydrophobic effect may become small and it may be difficult to orient inside the resin particles. As a result, the effect of unevenly distributing the carboxylic acid groups on the surface of the resin particles is slightly reduced, and the effect of improving the optical density may not be sufficiently obtained. On the other hand, when m exceeds 4 or o is less than 6, the hydrophobicity is slightly strong, and the carboxylic acid groups are likely to be unevenly distributed on the surface of the resin particles more than the required amount, and the effect of improving the storage stability of the ink may not be sufficiently obtained.

[0052] As the fluorosurfactant represented by the general formula (1), for example, the compound represented by the following formula (1)-1, the compound represented by the following formula (1)-2, and the compound represented by the following formula (1)-3 can be used. · Formula (1)-1: In the general formula (1), m = 3, n = 2, о = 8 · Formula (1)-2: In the general formula (1), m = 0, n = 2, о = 15 · Formula (1)-3: In the general formula (1), m = 5, n = 2, о = 4

[0053] The content (mass%) of the fluorosurfactant in the resin particles is preferably 0.02 times or more and 0.10 times or less, and more preferably 0.03 times or more and 0.08 times or less, as the mass ratio with respect to the content (mass%) of the resin particles in the ink. By setting the mass ratio within the above range, it is possible to achieve both a higher level of the optical density of the image and the storage stability of the ink. If the above mass ratio is less than 0.02 times, the effect of unevenly distributing the carboxylic acid groups on the surface of the resin particles may slightly decrease, and the effect of improving the optical density may not be sufficiently obtained. On the other hand, if the above mass ratio exceeds 0.10 times, the carboxylic acid groups tend to be unevenly distributed on the surface of the resin particles in an amount more than necessary, and the effect of improving the storage stability of the ink may not be sufficiently obtained.

[0054] [Silicone surfactant] As the silicone surfactant, those having a structure represented by the following general formula (2) can be used. Also, as the silicone surfactant, a synthesized one or a commercially available product may be used. The silicone surfactant can be synthesized, for example, with reference to the description in "Surfactants - From Basics to Applications - (Publisher: The Japan Oil Chemists' Society)". (CH3)3-SiO-(Si(CH3)2O) x -SiCH3O-Si(CH3)3-(CH2) w -O-(CH2CH2) y -O-(CH2CH2CH2) z -OH ···(2) (In the general formula (2), w represents an integer of 1 or more and 5 or less, x represents an integer of 1 or more and 3 or less, y represents an integer of 6 or more and 8 or less, and z represents an integer of 2 or more and 4 or less.)

[0055] In the general formula (2), x is preferably 2, y is preferably 6 or more and 8 or less, and z is preferably 2 or more and 4 or less. When x is less than 2, y exceeds 8, or z exceeds 4, the hydrophobic effect may become small and it may be difficult to orient within the resin particles. As a result, the effect of unevenly distributing the carboxylic acid groups on the surface of the resin particles is slightly reduced, so the effect of improving the optical density may not be sufficiently obtained in some cases.

[0056] As the silicone-based surfactant represented by the general formula (2), for example, a compound represented by the following formula (2)-1, a compound represented by the following formula (2)-2, and a compound represented by the following formula (2)-3 can be used. · Formula (2)-1: In the general formula (2), w = 3, x = 2, y = 7, z = 3 · Formula (2)-2: In the general formula (2), w = 3, x = 1, y = 9, z = 5 · Formula (2)-3: In the general formula (2), w = 2, x = 3, y = 5, z = 1

[0057] The content (% by mass) of the silicone-based surfactant in the resin particles is preferably 0.02 times or more and 0.10 times or less in terms of the mass ratio to the content (% by mass) of the resin particles in the ink. By setting the mass ratio within the above range, it is possible to achieve both a higher level of the optical density of the image and the storage stability of the ink. When the above mass ratio is less than 0.02 times, the effect of unevenly distributing the carboxylic acid groups on the surface of the resin particles is slightly reduced, and the effect of improving the optical density may not be sufficiently obtained in some cases. On the other hand, when the above mass ratio exceeds 0.10 times, the carboxylic acid groups tend to be unevenly distributed on the surface of the resin particles more than the required amount, and the effect of improving the storage stability of the ink may not be sufficiently obtained in some cases.

[0058] [Method for verifying whether a specific component is encapsulated in resin particles] Whether a specific component is encapsulated in resin particles can be determined, for example, by the following method. Add ion-exchanged water to 30 parts of the prepared resin particles, perform ultrafiltration using a 100 kDa ultrafiltration membrane, and remove water-soluble components other than the resin particles containing the water-soluble polymer in a free state rather than inside the resin particles. Next, confirm that there are no multiple types of resin particles by measuring the particle size distribution and specific gravity distribution of the obtained resin particles. After drying the above resin particles, confirm the presence of a predetermined resin (copolymer having a carboxylic acid group and a sulfonic acid group) constituting the resin particles by a general analysis method. General analysis methods for confirming the predetermined resin include gel permeation chromatography (GPC), matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), and the like. Then, confirm whether it is encapsulated by detecting a specific component (polyolefin, fluorosurfactant, silicone surfactant) encapsulated in the resin particles by nuclear magnetic resonance (NMR), pyrolysis gas chromatography, or the like.

[0059] (Other resins) The ink may further contain a resin other than the aforementioned resin particles (other resins). The other resin can be added to the ink (i) to stabilize the dispersion state of the pigment, that is, as a resin dispersant or its auxiliary. Also, (ii) it can be added to the ink to improve various properties of the recorded image. Examples of the form of the other resin include block copolymers, random copolymers, graft copolymers, and combinations thereof. The other resin is preferably a water-soluble resin that can be dissolved in an aqueous medium.

[0060] Examples of the water-soluble resin include acrylic resins different from the above resins (other acrylic resins), urethane resins, and the like. Among them, other acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylate are more preferable.

[0061] (Aqueous medium) The ink of the present invention is an aqueous ink containing an aqueous medium which is water or a mixed solvent of water and a water-soluble organic solvent. Deionized water (ion-exchanged water) is preferably used as the water. The content (% by mass) of water 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 of those that can be used in inks for inkjet, such as alcohols, glycols, (poly)alkylene glycols, nitrogen-containing compounds, and sulfur-containing compounds, can be used. 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.

[0062] (Other components) In addition to the above-described components, the ink may contain water-soluble organic compounds that are solid at 25°C, such as polyhydric alcohols like trimethylolpropane and trimethylolethane, and urea derivatives like urea and ethylene urea, as needed. Further, the ink may contain various additives such as surfactants, pH adjusters, antifoaming agents, rust preventives, preservatives, antifungal agents, antioxidants, anti-reduction agents, and chelating agents, as needed.

[0063] Examples of surfactants include anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants. Among them, it is preferable to use anionic surfactants. Examples of anionic surfactants include alkyl allyls, alkyl naphthalene sulfonates, alkyl phosphates, alkyl sulfates, alkyl sulfonates, alkyl ether sulfates, alkyl sulfosuccinates, alkyl ester sulfates, alkyl benzene sulfonates, alkyl diphenyl ether disulfonates, alkyl aryl ether phosphates, alkyl aryl ether sulfates, alkyl aryl ether ester sulfates, olefin sulfonates, alkane olefin sulfonates, polyoxyethylene alkyl ether phosphates, polyoxyethylene alkyl ether sulfate ester salts, ether carboxylates, sulfosuccinates, α-sulfo fatty acid esters, fatty acid salts, condensates of higher fatty acids and amino acids, and naphthenates. Among them, polyoxyethylene alkyl ether acetates and dialkyl sulfosuccinates are preferable.

[0064] Examples of nonionic surfactants include acetylene glycol-based surfactants, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan fatty acid esters.

[0065] The content (mass%) of the surfactant (excluding the aforementioned fluorine-based surfactant and silicone-based surfactant) in the ink is preferably 0.1 mass% or more and 5.0 mass% or less based on the total mass of the ink. More preferably, it is 0.1 mass% or more and 2.0 mass% or less.

[0066] (Physical properties of the ink) The ink of the present invention is an aqueous ink applicable to an inkjet system. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical property values. 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, and particularly preferably 1.0 mPa·s or more and 3.0 mPa·s or less. Further, the surface tension of the ink at 25°C is preferably 10 mN / m or more and 60 mN / m or less, more preferably 20 mN / m or more and 60 mN / m or less, and particularly preferably 30 mN / m or more and 50 mN / m or less. The pH of the ink at 25°C is preferably 5.0 or more and 10.0 or less, and more preferably 7.0 or more and 9.5 or less.

[0067] <Ink cartridge> The ink cartridge of the present invention includes ink and an ink storage section for storing the ink. And the ink stored in this ink storage section is the aqueous ink of the present invention described above. FIG. 1 is a cross-sectional view schematically showing an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage section for storing ink. The ink storage section is composed of an ink storage chamber 14 and an absorber storage chamber 16, which communicate with each other through a communication port 18. Further, the absorber storage chamber 16 communicates 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 for storing liquid ink, and may be in a form in which the entire amount of the stored ink is held by the absorber. Further, the ink storage section may not have an absorber and may be in a form in which the entire amount of the ink is stored in a liquid state. Furthermore, it may be an ink cartridge configured to have an ink storage section and a recording head.

[0068] <Inkjet recording method> The inkjet recording method of the present invention is a method of discharging the aqueous ink of the present invention described above from an inkjet recording head and recording an image on a recording medium. Examples of the method of discharging 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 imparting thermal energy to the ink to discharge the ink. Except for using the ink of the present invention, the steps of the inkjet recording method may be known ones.

[0069] Figure 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 the head cartridge. The inkjet recording apparatus is provided with a conveying means (not shown) for conveying 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 includes recording heads 38 and 40 and is configured such that an ink cartridge 42 can be set. While the head cartridge 36 is conveyed in the main scanning direction along the carriage shaft 34, ink (not shown) is discharged 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 the conveying means (not shown).

Examples

[0070] Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Regarding the amounts of components, “parts” and “%” are based on mass unless otherwise specified.

[0071] <Method for Measuring Physical Property Values> (Judgment as to Whether the Sample is Particles or Not, Particle Diameter) A liquid containing a sample was diluted with pure water to obtain a measurement sample with the sample content adjusted to approximately 1.0%. Then, the particle size of the particles in the measurement sample was measured using a particle size measuring device. The measurement conditions at this time are shown below. As the particle size measuring device, a particle size distribution meter based on the dynamic light scattering method (trade name "NanoTrack WAVEII-Q", manufactured by Microtrac Bell) was used. When particles having a particle size were measured by the above method, the sample was determined to be "particles" (a "water dispersion"), and when particles having a particle size were not measured, the sample was determined not to be "particles" (an "aqueous solution"). [Measurement Conditions] SetZero: 30 seconds Number of measurements: 10 times Measurement time: 120 seconds Shape: True sphere Refractive index: 1.5 Density: 1.0

[0072] <Synthesis of Polyolefin> (Polyolefin 1) 5.6 parts of 1-butene and 10.0 parts of toluene were placed in a flask, purged with nitrogen, and then heated to 90 °C and stirred while adding 7.5 parts of acrylic acid and 0.15 part of di-tert-butyl peroxide (DTBP). It was heated to 160 °C and reacted for 6 hours while evaporating and removing toluene. After completion of the reaction, the content was cooled and solidified to obtain a 1-butene-acrylic acid copolymer (Polyolefin 1).

[0073] The obtained 1-butene-acrylic acid copolymer, 3000 parts of tetrahydrofuran, and 10.2 parts of a 48% aqueous sodium hydroxide solution were added to a flask and stirred at 55 °C for 1 hour. While stirring, 3000 parts of ion-exchanged water were added dropwise over 30 minutes. After distilling off tetrahydrofuran under reduced pressure, water was further distilled off to obtain solid Polyolefin 1. The acid value of Polyolefin 1 was 130 mgKOH / g, and the weight average molecular weight (Mw) was 30,000.

[0074] (Polyolefins 2 - 5) Solid polyolefins 2 to 5 were obtained in the same manner as in the case of polyolefin 1 described above, except that DTBT in the amounts shown in Table 1 was used. The acid values and weight average molecular weights (Mw) of polyolefins 2 to 5 are shown in Table 1.

[0075] TIFF2025095571000001.tif58170

[0076] <Manufacture of Resin Particles> (Resins 1 to 27) Each component in the types and amounts (unit: part) shown in Tables 2-1 to 2-3, 10% potassium hydroxide aqueous solution in an amount such that the neutralization rate of the resin particles becomes 80%, and 150 parts of ion-exchanged water were mixed using a homogenizer (trade name "T50D Ultra Turrax", manufactured by IKA) to obtain a mixed solution. 50 parts of the obtained mixed solution was put into a flask equipped with a stirrer, a nitrogen inlet tube, a reflux condenser, and a thermometer and stirred, and the temperature was raised to 90 °C under a nitrogen atmosphere. Liquids prepared by dissolving the remaining portion of the mixed solution and 1.0 part of potassium persulfate in 20.0 parts of ion-exchanged water were each added dropwise over 2 hours. After stirring at 90 °C for 2 hours, ultrafiltration was performed by a diafiltration method using the ultrafiltration membrane shown below to remove polyolefins, fluorosurfactants, and silicone surfactant components not encapsulated in the resin particles. After adjusting the pH to 8.5, an appropriate amount of ion-exchanged water was added to obtain dispersions of resin particles 1 to 27 having a resin particle content of 25.0%. In the production of resin particles 22 to 25, the temperature (polymerization temperature) for raising the temperature was appropriately adjusted so as to be b described in the lower part of Tables 2-2 and 2-3. It was determined whether the resin particles encapsulated polyolefins or the like by the above method. The meanings of the abbreviations in Tables 2-1 to 2-3 are shown below.

[0077] [Ultrafiltration Membrane] · Type: Modified polyethersulfone hollow fiber module (trade name "MicroKross", manufactured by Spectrum Laboratories) · Fractional molecular weight: 70 kDa · Membrane area: 1,600 cm 2 · Inner diameter: 0.5 mm

[0078] · SR10K: Emulsifier, trade name "ADEKA Liasop SR-10", manufactured by ADEKA · AE100: Hydrocarbon-based nonionic surfactant, trade name "Acetylenol E100", manufactured by Kawaken Fine Chemicals

[0079] TIFF2025095571000002.tif212170

[0080] TIFF2025095571000003.tif225170

[0081] TIFF2025095571000004.tif226170

[0082] <Preparation of Pigment Dispersion Liquid> (Pigment Dispersion Liquid 1) A batch vertical sand mill (manufactured by Imex) filled with 200 parts of 0.3 mm diameter zirconia beads was charged with a mixture of 10.0 parts of carbon black, 20.0 parts of a liquid containing resin, and 70.0 parts of ion-exchanged water, and dispersed for 3 hours. As the liquid containing resin, an aqueous solution having a resin content of 30.0% was used, which was prepared by dissolving a water-soluble resin in an aqueous potassium hydroxide solution equimolar to its acid value. This water-soluble resin is a styrene-ethyl acrylate-acrylic acid copolymer having an acid value of 167 mgKOH / g and a weight average molecular weight of 10,000. After removing coarse particles by centrifugation, it was pressure-filtered through a microfilter (manufactured by Fuji Film) with a pore size of 3.0 μm. An appropriate amount of ion-exchanged water was added to adjust the concentration, and Pigment Dispersion Liquid 1 having a pigment content of 10.0% was obtained.

[0083] (Pigment Dispersion Liquid 2) Pigment Dispersion Liquid 2 having a pigment content of 10.0% was obtained in the same manner as in the case of Pigment Dispersion Liquid 1 described above, except that C.I. Pigment Blue 15:3 was used instead of carbon black.

[0084] <Preparation of Ink> The following components were mixed and stirred well, and then each ink was prepared by pressure filtration through a microfilter with a pore size of 2.5 μm (manufactured by Fujifilm). The characteristics of the obtained inks are shown in the lower rows of Tables 3-1 to 3-5. · Pigment dispersion: Amount (parts) shown in Tables 3-1 to 3-5 · Dispersion of resin particles: Amount (parts) shown in Tables 3-1 to 3-5 · Glycerin: 5.0 parts · Triethylene glycol: 10.0 parts · Acetylenol E100: 0.1 part · Ion-exchanged water: The remaining amount to make a total of 100 parts

[0085] TIFF2025095571000005.tif170170

[0086] TIFF2025095571000006.tif171170

[0087] TIFF2025095571000007.tif171170

[0088] TIFF2025095571000008.tif171170

[0089] TIFF2025095571000009.tif163170

[0090] <Evaluation> Each of the prepared inks was filled into an ink cartridge and mounted on an inkjet recording apparatus (trade name "PIXUS Pro9500", manufactured by Canon) that discharges ink from a recording head by the action of thermal energy. In this example, the recording duty of a solid image recorded under the condition of applying 8 drops of ink droplets of 3.5 ng per drop to a unit area of 1 / 600 inch × 1 / 600 inch was defined as 100%. Using this inkjet recording apparatus, a pattern including a 5 cm × 5 cm solid image with a recording duty of 100% was recorded on a recording medium (glossy paper, trade name "Canon Photo Paper · Fine Grain Glossy Raster", manufactured by Canon) to obtain a recorded product. In the present invention, according to the evaluation criteria of each evaluation item shown below, "A" was defined as an excellent level, "B" as an acceptable level, and "C" as an unacceptable level. The evaluation results are shown in Table 4.

[0091] (Optical density) One day after the recording, the optical density of the solid image was measured using a fluorescence spectrophotometer (trade name "FD-7", manufactured by Konica Minolta), and the optical density of the image was evaluated according to the evaluation criteria shown below. In Examples 2 and 14, since they were cyan inks, different from other examples and comparative examples (black ink), they were evaluated according to the evaluation criteria in parentheses. A: The optical density was 2.50 or more (2.10 or more). B: The optical density was 2.20 or more and less than 2.50 (1.90 or more and less than 2.10). C: The optical density was less than 2.20 (less than 1.90).

[0092] (Storage stability) The prepared ink was put into a sealed container and stored in an oven at 80 °C for 4 days. After returning to room temperature, the viscosity of the ink was measured. The viscosity of the ink was measured using an E-type viscometer (trade name "RE80-L", manufactured by Toki Sangyo Co., Ltd.) with a rotor (1°34’×R24) attached, through which antifreeze was circulated via a tube in a thermostatic bath set at 25 °C. The viscosity increase rate (%) of the ink was calculated according to the following formula (A), and the storage stability of the ink was evaluated according to the evaluation criteria shown below. Viscosity increase rate (%) ={(Viscosity after storage - Initial viscosity) / Initial viscosity} × 100 ···(A) A: The rate of increase in viscosity was 5% or less. B: The rate of increase in viscosity exceeded 5% and was 10% or less. C: The rate of increase in viscosity exceeded 10%.

[0093] TIFF2025095571000010.tif190170

[0094] Note that the disclosure of this embodiment includes the following configurations and methods. (Configuration 1) An aqueous ink for inkjet containing a pigment and resin particles, wherein the resin particles are formed of a copolymer having a carboxylic acid group and a sulfonic acid group, and the resin particles encapsulate at least one selected from the group consisting of a polyolefin having a carboxylic acid group and a weight average molecular weight of 2,000 or more, a fluorosurfactant, and a silicone surfactant. The aqueous ink is characterized by this. (Configuration 2) The aqueous ink according to Configuration 1, wherein the weight average molecular weight of the polyolefin is 50,000 or less. (Configuration 3) The aqueous ink according to Configuration 1 or 2, wherein the content (% by mass) of the polyolefin in the resin particles is 0.02 times or more and 0.10 times or less in terms of the mass ratio to the content (% by mass) of the resin particles in the aqueous ink. (Configuration 4) The aqueous ink according to any one of Configurations 1 to 3, wherein the content (% by mass) of the fluorosurfactant in the resin particles is 0.02 times or more and 0.10 times or less in terms of the mass ratio to the content (% by mass) of the resin particles in the aqueous ink. (Configuration 5) The aqueous ink according to any one of Configurations 1 to 4, wherein the fluorosurfactant has a structure represented by the following general formula (1). CF3CF2-(CF2CF2) m -(CH2) n -O-(CH2CH2) o -OH ···(1) (In the general formula (1), m represents an integer of 2 or more and 4 or less, n represents an integer of 1 or more and 4 or less, and o represents an integer of 6 or more and 10 or less.) (Configuration 6) The aqueous ink according to any one of Configurations 1 to 5, wherein the silicone surfactant has a structure represented by the following general formula (2). (CH3)3-SiO-(Si(CH3)2O)2-SiCH3O-Si(CH3)3-(CH2) w -O-(CH2CH2) y -O-(CH2CH2CH2) z -OH ···(2) (In the general formula (2), w represents an integer of 1 or more and 5 or less, y represents an integer of 6 or more and 8 or less, and z represents an integer of 2 or more and 4.) (Configuration 7) The aqueous ink according to any one of Configurations 1 to 6, wherein the ratio of the anionic group b (μmol / g) present on the particle surface of the resin particles to the anionic group a (μmol / g) present in the resin particles is 0.50 times or more and 0.80 times or less. (Configuration 8) The aqueous ink according to any one of Configurations 1 to 7, wherein the ratio of the sulfonic acid group c (μmol / g) present in the resin particles to the anionic group a (μmol / g) present in the resin particles is 0.20 times or more and 0.30 times or less. (Configuration 9) The aqueous ink according to any one of Configurations 1 to 8, wherein the content (mass%) of the pigment is 0.03 times or more and 0.70 times or less in terms of the mass ratio to the content (mass%) of the resin particles. (Configuration 10) An ink cartridge including ink and an ink containing portion that contains the ink, wherein the ink is the aqueous ink according to any one of Configurations 1 to 9. (Method 1) An inkjet recording method of ejecting ink from an inkjet recording head and recording an image on a recording medium, wherein the ink is the aqueous ink according to any one of Configurations 1 to 9.

Claims

1. An aqueous ink for inkjet containing a pigment and resin particles, wherein the resin particles are formed of a copolymer having a carboxylic acid group and a sulfonic acid group, and the resin particles encapsulate at least one selected from the group consisting of a polyolefin having a carboxylic acid group and a weight average molecular weight of 2,000 or more, a fluorosurfactant, and a silicone surfactant, and the aqueous ink is characterized by this.

2. The aqueous ink according to Claim 1, wherein the weight average molecular weight of the polyolefin is 50,000 or less.

3. The aqueous ink according to Claim 1, wherein the content (% by mass) of the polyolefin in the resin particles is 0.02 times or more and 0.10 times or less in terms of the mass ratio to the content (% by mass) of the resin particles in the aqueous ink.

4. The aqueous ink according to Claim 1, wherein the content (% by mass) of the fluorosurfactant in the resin particles is 0.02 times or more and 0.10 times or less in terms of the mass ratio to the content (% by mass) of the resin particles in the aqueous ink.

5. The aqueous ink according to Claim 1, wherein the fluorosurfactant has a structure represented by the following general formula (1). CF ３ CF ２ -(CF ２ CF ２ ) ｍ -(CH ２ ) ｎ -O-(CH ２ CH ２ ) ｏ -OH ・・・（１） (In the general formula (1), m represents an integer of 2 or more and 4 or less, n represents an integer of 1 or more and 4 or less, and o represents an integer of 6 or more and 10 or less)

6. The aqueous ink according to Claim 1, wherein the silicone surfactant has a structure represented by the following general formula (2). (CH ３ ) ３ -SiO-(Si(CH ３ ) ２ O) ２ -SiCH ３ O-Si(CH ３ ) ３ -(CH ２ ) ｗ -O-(CH ２ CH ２ ) ｙ -O-(CH ２ CH ２ CH ２ ) ｚ -OH ・・・（２） (In the general formula (2), w represents an integer of 1 or more and 5 or less, y represents an integer of 6 or more and 8 or less, and z represents an integer of 2 or more and 4 or less)

7. The aqueous ink according to Claim 1, wherein the ratio of the anionic group b (μmol / g) present on the particle surface of the resin particles to the anionic group a (μmol / g) present in the resin particles is 0.50 times or more and 0.80 times or less.

8. The aqueous ink according to Claim 1, wherein the ratio of the sulfonic acid group c (μmol / g) present in the resin particles to the anionic group a (μmol / g) present in the resin particles is 0.20 times or more and 0.30 times or less.

9. The aqueous ink according to Claim 1, wherein the content (% by mass) of the pigment is 0.03 times or more and 0.70 times or less in terms of the mass ratio to the content (% by mass) of the resin particles.

10. An ink cartridge including an ink and an ink storage unit for storing the ink, An ink cartridge, characterized in that the ink is an aqueous ink according to any one of claims 1 to 9.

11. An inkjet recording method for ejecting ink from an inkjet recording head and recording an image on a recording medium, An inkjet recording method, characterized in that the ink is an aqueous ink according to any one of claims 1 to 9.

Images