Aqueous ink, ink cartridge, and inkjet recording method

Abstract

To provide aqueous ink for inkjet which enables recording of an image excellent in image clarity, suppresses discharge deflection, and is excellent in storage stability, an ink cartridge using the aqueous ink, and an inkjet recording method.SOLUTION: Aqueous ink for inkjet contains a pigment and resin particles in which the pigment is dispersed. A cumulative 50% particle diameter of volume-based particle size distribution of the resin particles is 10 nm or less, the resin particles have a crosslinking structure, a ratio of the cumulative 50% particle diameter of the volume-based particle size distribution of the pigment to the cumulative 50% particle diameter of the volume-based particle size distribution of the resin particles is 3.0 times or more and 8.0 times or less. There are also provided an ink cartridge using the aqueous ink, and an inkjet recording method.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, inkjet recording devices have made it possible to record high-definition, high-gloss images, similar to those achieved with silver halide photography and offset printing, relatively easily and inexpensively at home.

[0003] One type of ink capable of recording images with excellent gloss is dye-based ink, which contains dyes as colorants. Using dye-based ink allows for the recording of high-quality images with reduced granularity. However, images recorded with dye-based ink have drawbacks, such as poor durability in terms of lightfastness, water resistance, and gas resistance. For this reason, pigment-based inks, which contain pigments as colorants, have come into use in recent years.

[0004] Using pigment inks improves the robustness of recorded images, but there is a trade-off: graininess and gloss are inferior to images recorded with dye inks. To improve the gloss of images recorded with pigment inks, it is important to suppress light scattering at the surface of the pigment particles, and thus finer pigments must be used.

[0005] To disperse pigments in ink, dispersants such as surfactants and water-soluble resins are typically used. However, inks containing surfactants as dispersants tend to foam easily, and the dispersion of pigments can be unstable, potentially resulting in poor water resistance of the recorded image. Furthermore, when using water-soluble resins as dispersants, a large amount of water-soluble resin is required as the pigment becomes finer, i.e., its specific surface area increases. This can lead to an increase in ink viscosity and a decrease in inkjet suitability, such as ejection stability.

[0006] To address these challenges, for example, an aqueous pigment dispersion has been proposed, obtained by dispersing pigments with a surfactant and then reacting a water-soluble resin or a self-emulsifying resin with a crosslinking agent (Patent Document 1). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2002-294133 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The present inventors investigated an aqueous ink using an aqueous pigment dispersion proposed in Patent Document 1 and found that its viscosity tends to increase over time, resulting in insufficient storage stability. Furthermore, they confirmed that when ink ejection is stopped for a certain period and then restarted without recovery, a phenomenon called "ejection distortion" occurs, where the direction of ink ejection is bent. In addition, they found that the image quality of images recorded with the above aqueous ink is not always good, indicating room for improvement.

[0009] Therefore, an object of the present invention is to provide an aqueous inkjet ink that can record images with excellent image quality, suppresses ejection distortion, and has excellent storage stability. Another object of the present invention is to provide an ink cartridge using this aqueous ink and an inkjet recording method. [Means for solving the problem]

[0010] In other words, the present invention provides an aqueous inkjet ink containing a pigment and resin particles for dispersing the pigment, characterized in that the cumulative 50% particle diameter of the volume-based particle size distribution of the resin particles is 10 nm or less, the resin particles have a crosslinked structure, and the cumulative 50% particle diameter of the volume-based particle size distribution of the pigment is 3.0 times or more and 8.0 times or less in ratio to the cumulative 50% particle diameter of the volume-based particle size distribution of the resin particles. [Effects of the Invention]

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

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

[0013] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when a compound is a salt, the salt exists in the ink dissociated into ions, but for convenience, it will be expressed as "contains a salt." Also, water-based ink for inkjet printers may be simply referred to as "ink." Unless otherwise specified, physical properties are given at room temperature (25°C), normal pressure (1 atmosphere = 101,325 Pa), and normal humidity (50% relative humidity). Also, unless otherwise specified, "unit" refers to the unit structure corresponding to one monomer. When "(meth)acrylic acid" or "(meth)acrylate" is written, it refers to "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

[0014] The inventors investigated resin particles used to disperse pigments in order to stably maintain the dispersion state of pigments in aqueous inks. When pigments are made finer, the specific surface area increases inversely proportional to the particle size, and the inter-surface distance between pigment particles decreases. If the mass fraction of pigment in the ink is "c", the density of the pigment is "ρ", and the particle size of the pigment is "D", the average distance "h" between pigment particles is expressed by the following formula (1). h = D(((ρ(1-c)+c) / 3πc+5 / 6) 0.5 -1) ···(1) (See Hidehiro Kamiya and Shiyuki Iijima, "Crushing" (2012), Vol. 55, pp. 12-18)

[0015] Substituting the density of commonly used organic pigments and the pigment content (mass fraction) in the ink into equation (1) above, it can be seen that the average distance between pigment particles tends to be less than or equal to the particle size of the pigment. To stably disperse pigments, electrostatic repulsion due to electric charge and steric repulsion due to dispersants are utilized. However, water-soluble organic solvents are usually added to inks to improve ejection characteristics, etc. As a result, the dielectric constant of the ink is significantly lower than that of water, and the contribution of electrostatic repulsion becomes limited. Therefore, to stably disperse pigments in ink, it is necessary to effectively utilize steric repulsion due to dispersants.

[0016] The inventors have studied the use of resin particles as a dispersant for dispersing pigments. As a result, it has been found that by satisfying the following requirements (i) and (ii), the dispersion state of the pigment can be stably maintained without degrading the imageability, and the storage stability of the ink can be improved. (i) The cumulative 50% particle diameter of the volume-based particle size distribution of the resin particles is 10 nm or less. (ii) The cumulative 50% particle diameter of the volume-based particle size distribution of the pigment is 3.0 times or more and 8.0 times or less the ratio to the cumulative 50% particle diameter of the volume-based particle size distribution of the resin particles.

[0017] When the cumulative 50% particle diameter D of the volume-based particle size distribution of the resin particles 50 exceeds 10 nm, it becomes difficult for the resin particles to adsorb to the pigment, and it becomes difficult to stably maintain the dispersion state of the pigment, resulting in a decrease in the storage stability of the ink. The cumulative 50% particle diameter D of the volume-based particle size distribution of the pigment 50 is less than 3.0 times the ratio to the cumulative 50% particle diameter of the volume-based particle size distribution of the resin particles, the number of resin particles contributing to the dispersion of the pigment is, for example, 10 or less when the average coverage rate is 30%. Therefore, a sufficient steric repulsion effect cannot be obtained, and it becomes difficult to stably maintain the dispersion state of the pigment, resulting in a decrease in the storage stability of the ink. On the other hand, when the above ratio exceeds 8.0 times, the particle diameter of the pigment also increases, so the imageability of the recorded image deteriorates. The average coverage rate is a value obtained by dividing the total cross-sectional area of the resin particles adsorbed on the particle surface of the pigment by the total surface area of the pigment particles.

[0018] As a result of further studies, the inventors have found that by using resin particles having a crosslinked structure, it becomes possible to reduce the viscosity of the ink and suppress ink bleeding. By having a crosslinked structure, entanglement of dissolved resin chains between the resin particles is suppressed, and it becomes difficult for the viscosity of the ink to increase. Therefore, it is considered that the ejection accuracy of the ink is maintained and bleeding is suppressed.

[0019] <Ink> The ink of the present invention is an aqueous ink for inkjet, containing a pigment and resin particles for dispersing the pigment. Hereinafter, the components constituting the ink of the present invention and the physical properties of the ink will be described in detail.

[0020] (Pigment) As the coloring material, a pigment that can be dispersed in the ink in a particulate state is used. The content (mass %) of the pigment in the ink is preferably 0.10 mass % or more and 15.00 mass % or less, more preferably 1.00 mass % or more and 10.00 mass % or less, based on the total mass of the ink.

[0021] Specific examples of the pigment include inorganic pigments such as carbon black and titanium oxide; organic pigments such as azo pigments, phthalocyanine pigments, perylene pigments, perinone pigments, quinacridone pigments, dioxazine pigments, diketopyrrolopyrrole pigments, quinophthalone pigments, isoindolinone pigments, and imidazolone pigments.

[0022] The pigment is preferably at least one of an organic pigment and carbon black. And the organic pigment is preferably at least one selected from the group consisting of azo pigments, phthalocyanine pigments, perylene pigments, perinone pigments, quinacridone pigments, dioxazine pigments, diketopyrrolopyrrole pigments, and quinophthalone pigments.

[0023] Whether or not pigments are dispersed by resin particles can be determined by the following method. Here, we will describe a method for extracting and analyzing resin particles from ink, but pigments and resin particles extracted from pigment dispersions can be analyzed in the same way. First, ultrafiltration is performed from the ink to separate the pigment and dispersant (resin particles, etc.) from other components that do not contribute to dispersion (water-soluble components) until a sufficient amount of permeate is obtained, and the components containing the pigment are separated as a liquid. The obtained liquid is subjected to ultracentrifugation, and the resin particles are separated from the pigment that was integrated with the dispersant (resin particles, etc.) by density gradient centrifugation. In the density gradient sedimentation velocity method, resin particles can be separated and extracted based on the difference in the sedimentation coefficient of the components, and in the density gradient sedimentation equilibrium method, they can be separated based on the difference in the density of the components. If resin particles are separated by such methods, it can be determined that the resin particles were a dispersant for dispersing the pigment.

[0024] [Physical properties of pigment particles] [Mass ratio of pigment to resin particles] The content of resin particles in the ink (mass%) is preferably 0.06 to 1.00 times the mass ratio of the pigment content (mass%). If the above mass ratio is less than 0.06 times, the resin particle content is low compared to the pigment, which may reduce the effect of improving storage stability. On the other hand, if the above mass ratio is greater than 1.00 times, the resin particle content is high compared to the pigment, which may increase the viscosity of the ink and reduce the effect of suppressing ink ejection unevenness. The above mass ratio is more preferably 0.06 to 0.50 times, and particularly preferably 0.10 to 0.20 times.

[0025] [Cumulative 50% particle size of the particle size distribution based on the volume of the pigment] The cumulative 50% particle diameter of the volume-based particle size distribution of the pigment is preferably 1 nm to 80 nm, and more preferably 10 nm to 70 nm. The volume-based cumulative 50% particle diameter refers to the diameter of the particle that reaches 50% when the total volume of the measured particles is accumulated from the smallest particle diameter side in the particle diameter integration curve. The volume-based cumulative 50% particle size distribution can be measured by dynamic light scattering, and the conditions for this can be the same as the method for determining whether or not a particle is a resin particle for resins, as described later.

[0026] (Resin particles) The resin particle content (mass%) in the ink is preferably 0.01% to 10.00% by mass, and more preferably 0.02% to 5.00% by mass, based on the total mass of the ink. The resin particles are dispersed in the ink, i.e., they exist in the ink in the form of a resin emulsion. The resin particles do not need to contain colorants.

[0027] In this invention, "resin particles" refers to resins that exist in an insoluble state in the aqueous medium constituting the ink. More specifically, it refers to resins that can exist in the aqueous medium in a state in which particles whose particle size can be measured by dynamic light scattering are formed. On the other hand, "water-soluble resin" refers to resins that exist in a dissolved state in the aqueous medium constituting the ink. More specifically, it refers to resins that can exist in the aqueous medium in a state in which particles whose particle size can not be measured by dynamic light scattering are not formed. If resin particles are expressed in contrast to "water-soluble resin," they become "water-dispersible resin (water-insoluble resin)."

[0028] Whether a resin qualifies as "resin particles" can be determined according to the following method. First, prepare a liquid containing the resin to be judged (resin content: 10% by mass). Next, prepare a sample by diluting this liquid with pure water to a resin content of approximately 1.0%. Then, measure the particle size of the resin in the sample using dynamic light scattering. If particles with a particle size are measured, the resin is determined to be "resin particles" (i.e., a "water-dispersible resin"). On the other hand, if no particles with a particle size are measured, the resin is determined not to be "resin particles" (i.e., a "water-soluble resin"). The measurement conditions in this case can be, for example, SetZero: 30 seconds, Number of measurements: 10 times, Measurement time: 120 seconds, Shape: Spherical, Refractive index: 1.5, Density: 1.0.

[0029] As a particle size distribution analyzer, a particle size analyzer using dynamic light scattering (for example, product name "NanoTrac WAVE II-Q," manufactured by MicroTrac-Bell) can be used. Of course, the particle size distribution analyzer and measurement conditions used are not limited to those mentioned above.

[0030] For other resins, such as resin dispersants, that can be used in addition to resin particles, the definition of whether or not they are resin particles is the same as described above. For other resins, it is possible to determine whether they are resin particles or water-soluble resins using the same method as described above. However, for the sake of simplicity, for other resins, it may be possible to determine this using a liquid containing the resin (resin content: 10% by mass) that has been neutralized with an alkali (such as sodium hydroxide or potassium hydroxide) with an acid value equivalent to that of the resin.

[0031] The cumulative 50% particle diameter of the volume-based particle size distribution of resin particles must be 10 nm or less, preferably 1 nm or more, and more preferably 4 nm or more. The cumulative 50% particle diameter of the volume-based particle size distribution of resin particles can be measured under the same conditions as the method for determining whether or not a particle is a resin particle as described above. The cumulative 50% particle diameter of the volume-based particle size distribution of pigments must be 3.0 to 8.0 times, and preferably 4.0 to 7.0 times, relative to the cumulative 50% particle diameter of the volume-based particle size distribution of resin particles.

[0032] Examples of resins that form resin particles include acrylic resins, polyester resins, urethane resins, and polystyrene resins. Among these, acrylic resins, polyester resins, and urethane resins are preferred. These resins readily adsorb pigments stably, thus improving the storage stability of the ink. In particular, if the resin has carboxylic acid groups, the storage stability of the ink is further improved. This is because ionic repulsion occurs due to ionically dissociated carboxylic acid groups, and the shape of the resin particles is stably maintained by hydrogen bonding between multiple resin particles, making it easier for the resin particles to stably adsorb onto the surface of the pigment particles. Furthermore, resin particles formed from acrylic resin are particularly preferred because they do not easily adhere to the ink flow path of the recording head and effectively suppress ejection distortion. The resin particles may be formed from one or more types of resins, but resin particles formed from one type of resin are preferred.

[0033] [Material composition of resin particles: Acrylic resin] The acrylic resin forming the resin particles may be a random copolymer, a block copolymer, or a graft copolymer. The acrylic resin is preferably one having hydrophilic units and hydrophobic units as constituent units. Among these, an acrylic resin having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from monomers having aliphatic or aromatic groups is preferred.

[0034] Hydrophilic units are units that have hydrophilic groups such as anionic groups, hydroxyl groups, and ethylene oxide groups. Hydrophilic units can be formed, for example, by polymerizing monomers that have hydrophilic groups. Specific examples of monomers that have hydrophilic groups include acidic monomers having carboxylic acid groups such as (meth)acrylic acid; anionic monomers such as anhydrides and salts of these acidic monomers; monomers having hydroxyl groups such as 2-hydroxyethyl (meth)acrylate; and monomers having ethylene oxide groups such as methoxypolyethylene glycol (meth)acrylate. Cationic ions that constitute salts of acidic monomers include lithium, sodium, potassium, ammonium, and organic ammonium ions.

[0035] A hydrophobic unit is a unit that does not have hydrophilic groups such as anionic groups, hydroxyl groups, or ethylene oxide groups. Hydrophobic units can be formed, for example, by polymerizing hydrophobic monomers that do not have hydrophilic groups. Specific examples of hydrophobic monomers include monomers having aromatic groups such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and monomers having aliphatic groups such as ethyl (meth)acrylate, methyl (meth)acrylate, (iso-)propyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0036] [Material composition of resin particles: polyester resin] The polyester resin that forms the resin particles preferably has carboxylic acid groups. Typically, unreacted hydroxyl groups or carboxylic acid groups are present at the ends of the polyester resin. If carboxylic acid groups are not present at the ends of the polyester resin, they are present in other parts of the resin. Polyester resins are typically composed of units derived from polyhydric alcohols and units derived from polyhydric carboxylic acids. A structure containing an ester bond (-COO-) composed of a unit derived from a polyhydric alcohol and a unit derived from a polyhydric carboxylic acid is also referred to as an "ester unit."

[0037] [Polyhydric alcohols] Polyhydric alcohols that form units derived from polyhydric alcohols that constitute the polyester resin through reaction include dihydric to tetrahydric polyhydric alcohols. Examples of polyhydric alcohols include polyhydric alcohols having aliphatic groups, polyhydric alcohols having aromatic groups, and sugar alcohols. It is preferable to use dihydric or trihydric polyhydric alcohols because it is easy to adjust the weight-average molecular weight of the polyester resin. In particular, it is preferable to use polyhydric alcohols having linear aliphatic groups because it improves the crystallinity of the polyester resin and allows for the recording of images with excellent chemical resistance.

[0038] [Polyhydric carboxylic acids] Polycarboxylic acids that form units constituting polyester resins through reactions include divalent to tetravalent polycarboxylic acids. Examples of polycarboxylic acid structures include polycarboxylic acids having aliphatic groups, polycarboxylic acids having aromatic groups, and nitrogen-containing polycarboxylic acids. It is preferable to use divalent or trivalent polycarboxylic acids because it is easy to adjust the weight-average molecular weight and acid value of the polyester resin. In particular, it is preferable to use polycarboxylic acids having linear aliphatic groups because it improves the crystallinity of the polyester resin and allows for the recording of images with excellent chemical resistance.

[0039] [Materials of resin particles: Urethane resin] The urethane resin forming the resin particles preferably has carboxylic acid groups. The urethane resin has units derived from polyisocyanate, units derived from polyols without acid groups, and units derived from polyols with acid groups.

[0040] [Polyisocyanate] Polyisocyanates are compounds having two or more isocyanate groups in their molecule. Examples of polyisocyanates include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, and aromatic aliphatic polyisocyanates.

[0041] [Polyol] Examples of polyols include polyester polyols, polycarbonate polyols, polyether polyols, and other polyols without acidic groups; and polyols with acidic groups. For polycarbonate polyols, in addition to those having 1,6-hexanediol as a basic skeleton, polycarbonate diols produced by known methods can be used. Examples of polyether polyols include addition polymers of alkylene oxides and polyhydric alcohols, and (poly)alkylene glycols. Examples of polyamines include polyhydric amines such as ethylenediamine, diethylenetriamine, hydrazine, and polyethylenepolyimine. For polyols with acidic groups, those in which the acidic group is a carboxylic acid group are preferred. Examples of polyols with carboxylic acid groups include dimethylolacetic acid, dimethylolpropionic acid, and dimethylolbutanoic acid.

[0042] [Neutralizing agents, chain extenders] Examples of neutralizing agents used in the production of urethane resins include organic bases such as triethanolamine, trimethylamine, and triethylamine; and inorganic bases such as potassium hydroxide, sodium hydroxide, lithium hydroxide, and ammonia. Among these, the use of monovalent inorganic bases is preferred, and the use of at least one of potassium hydroxide, sodium hydroxide, and lithium hydroxide is particularly desirable. Furthermore, examples of chain extenders that can be used in the production of polyurethane resins include compounds having two or more hydroxyl groups or amino groups in their molecules.

[0043] [Crosslinking agent] The resin particles have a crosslinked structure. Resin particles having a crosslinked structure can be manufactured by using a crosslinking agent. Preferably, the crosslinking agent is a compound having two or more polymerizable functional groups in its molecule. Specifically, compounds having two or more ethylenically unsaturated bonds, compounds having two or more glycidyl groups, etc., can be used. Furthermore, as a crosslinking agent that reacts with carboxylic acid groups, carbodiimide, aziridine, oxazoline, hydrazide, etc., can be used.

[0044] Examples of crosslinking agents that become units derived from the crosslinking agent through polymerization include compounds having two or more ethylenically unsaturated bonds.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, and 2-hydroxy-3-(meth)acryloy Oxypropyl 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-decanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, ethoxylated polypropylene Difunctional (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) Examples 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.Among compounds having two ethylenically unsaturated bonds in their molecule, divinylbenzene and (mono-, di-, tri-, poly-)ethylene glycol di(meth)acrylate are even more preferred. Compounds having two or more ethylenically unsaturated bonds are particularly suitable as crosslinking agents for acrylic resins.

[0045] Examples of compounds having two or more glycidyl groups 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 can form a high-density crosslinked structure. Compounds having two or more glycidyl groups can be used as crosslinking agents regardless of the type of resin.

[0046] The crosslinking agent that becomes a unit derived from the crosslinking agent through polymerization is preferably one with a molecular weight of 200 or more, more preferably one with a molecular weight of 300 or more, and particularly preferably one with a molecular weight of 400 or more. Furthermore, a compound having two ethylenically unsaturated bonds is preferred as the crosslinking agent. By using a compound having two ethylenically unsaturated bonds as the crosslinking agent, aggregation of resin particles that may occur due to excessive crosslinking is effectively suppressed, and resin particles with a more uniform particle size can be obtained.

[0047] Resin particles formed from a resin having a crosslinked structure containing alkylene oxide groups are preferred. Examples of alkylene oxide groups include ethylene oxide groups and propylene oxide groups, with ethylene oxide groups being preferred. Resin particles formed from a resin containing alkylene oxide groups in its crosslinked structure are less prone to changes in particle size even if the resin dissolves or liquid components penetrate the resin particles due to changes in the environment in which the ink is placed. Therefore, the resin particles are more likely to remain stably adsorbed on the surface of the pigment particles, improving the storage stability of the ink. Furthermore, it is preferable that the number of repeating alkylene oxide groups in a single crosslinked structure is 9 or less. In this case, the crosslinked structure in the resin forming the resin particles is small, and the network structure formed by the crosslinking becomes dense. Therefore, even if the resin dissolves due to changes in the environment in which the ink is placed, the degree of dissolution is kept low, making it less likely to adhere to the ink flow path of the recording head and effectively suppressing ejection distortion, which is preferable. It is preferable that the number of repeating alkylene oxide groups in a single crosslinked structure is 1 or more.

[0048] [Acid value of resins] The acid value of the resin forming the resin particles is preferably between 10 mg KOH / g and 150 mg KOH / g. If the acid value of the resin is less than 10 mg KOH / g, the resin particles tend to aggregate due to the small amount of carboxylic acid groups, making it difficult to control the particle size. On the other hand, if the acid value of the resin is greater than 150 mg KOH / g, the hydrophilicity of the resin particles may become too high due to the large amount of carboxylic acid groups, making it difficult to control the particle size. The acid value of the resin is more preferably between 10 mg KOH / g and 130 mg KOH / g. The acid value of the resin can be measured by neutralization titration using a potential difference.

[0049] [Weight-average molecular weight of resins] The weight-average molecular weight of the resin forming the resin particles is preferably between 5,000 and 70,000. The weight-average molecular weight of the resin is a polystyrene equivalent value measured by gel permeation chromatography.

[0050] [Method of manufacturing resin] Acrylic resins can be synthesized as follows. Any of the industrially used polymerization methods—solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization—may be used. In the case of solution polymerization, for example, acrylic resins can be synthesized as follows: A polymerization vessel equipped with a stirrer, thermometer, inert gas inlet tube, condenser, and monomer dropper is charged with a polymerization solvent such as toluene and monomers, and the temperature is raised to a predetermined polymerization temperature. Once the predetermined polymerization temperature is reached, a solution of polymerization initiator equivalent to 0.02 to 1.00 moles relative to the number of moles of monomer is dropped into the polymerization vessel over a predetermined time. After the droppering is complete, the polymerization reaction is carried out until the desired polymerization rate is reached, thereby producing an acrylic resin. Examples of polymerization initiators include organic peroxides such as benzoyl peroxide; and azo polymerization initiators such as 2,2'-azobis(isobutyronitrile).

[0051] Polyester resins can be synthesized by reacting polyhydric alcohols and polyhydric carboxylic acids (esterification reaction). It is preferable to use an esterification catalyst during the esterification reaction. If necessary, the molecular weight of the resulting polyester resin can be adjusted by adding either a polyhydric alcohol or a polyhydric carboxylic acid to the reaction system and performing a transesterification reaction to partially cleave the ester bond. By adjusting the amount of raw materials used during the esterification reaction so that the number of moles of carboxylic acid groups from the polyhydric carboxylic acid exceeds the number of moles of hydroxyl groups from the polyhydric alcohol, a polyester resin containing carboxylic acid groups can be obtained. Alternatively, a polyester resin containing carboxylic acid groups can also be obtained by using a polyhydric carboxylic acid during the transesterification reaction.

[0052] Urethane resins can be synthesized as follows: Polyisocyanate and polyol are placed in a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, and reflux tube, and the mixture is heated and reacted under a nitrogen gas atmosphere. Then, a chain extender, a diol having an acid group, and a solvent are added, and the remaining percentage of isocyanate groups is confirmed by FT-IR. The reaction is continued until the desired percentage of isocyanate groups is reached, thereby producing a urethane resin.

[0053] [Method for manufacturing resin particles] The synthesized resin is preferably used in the next step of particle formation after being processed into an appropriate form by pressurization and pulverization. Since the resin particles formed from the resin are used as components of aqueous ink, it is preferable that they be in the form of a dispersion in an aqueous liquid medium. The aqueous liquid medium mainly consists of water, such as deionized water, ion-exchanged water, and distilled water, and may contain a water-soluble organic solvent as needed. The water content (mass%) in the aqueous liquid medium is preferably 50% by mass or more, and it is also preferable to use a liquid medium that substantially does not contain a water-soluble organic solvent (i.e., water).

[0054] Methods for atomizing resin to form resin particles include, for example, dispersion methods and phase inversion (emulsification) methods. Dispersion methods include the methods shown in (1) and (2) below. (1) A method of dispersing a resin by adding a solution obtained by dissolving the resin in an organic solvent to an aqueous liquid medium. (2) A method of adding a resin to an organic solvent, then adding an aqueous liquid medium and mixing to disperse the resin.

[0055] Phase inversion (emulsification) methods include adding an aqueous liquid medium to a solution obtained by dissolving the resin in an organic solvent, thereby inverting the resin from a solvent system to an aqueous system and precipitating it in the form of particles. In any of these methods, it is preferable to use a known disperser and adjust the particle size of the resulting resin particles by atomizing them while applying appropriate shear force.

[0056] Since the particle size of the resulting resin particles can be precisely controlled, it is preferable to manufacture resin particles by the phase inversion (emulsification) method. The method for manufacturing resin particles by the phase inversion (emulsification) method will be described below.

[0057] First, the resin is dissolved in an organic solvent to obtain a resin solution. Examples of organic solvents include ethers such as tetrahydrofuran and dibutyl ether; ketones such as acetone and methyl ethyl ketone; and alcohols such as isopropanol. If only organic solvents with low water solubility and poor miscibility with water in any proportion (such as methyl ethyl ketone) are used, it may be difficult to precisely adjust the particle size. For this reason, it is preferable to use ethers such as tetrahydrofuran, which can be miscible with water in any proportion, as the organic solvent. Ethers such as tetrahydrofuran are also preferable because they have excellent resin solubility.

[0058] To ensure uniform dissolution of the resin, it is preferable to dissolve the resin in an organic solvent while heating it. However, it is preferable to heat the solution to a temperature lower than the boiling point of the organic solvent. If the concentration of resin in the resin solution is dilute, it may be difficult to control the particle size distribution. For this reason, the resin content (mass%) in the resin solution is preferably 10.0% by mass or more and 60.0% by mass or less, and more preferably 20.0% by mass or more and 40.0% by mass or less.

[0059] Next, an aqueous liquid medium is gradually added to the obtained resin solution to precipitate resin particles. It is preferable to add a base before or during the addition of the aqueous liquid medium in order to maintain a stable dispersion state of the resin particles. As the base, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, or ammonia can be used, and it is preferable to add them in the form of an aqueous solution. The amount of base to be added can be controlled by the neutralization rate (mol%) based on the acid value of the resin. The neutralization rate is preferably 70 mol% or more and 100 mol% or less. As the amount of aqueous liquid medium added increases, the resin solution, which was initially transparent, becomes cloudy and emulsifies, and resin particles are formed. By adjusting the resin content in the resin solution, the neutralization rate, and the shear force applied during dispersion, the particle size and particle size distribution of the obtained resin particles can be controlled.

[0060] The resulting emulsion is subjected to reduced pressure to remove the organic solvent by distillation, and if necessary, it is filtered using a filter of appropriate pore size (stainless steel mesh) to remove coarse particles. Next, water is added to adjust the resin particle content, thereby preparing a liquid containing resin particles (aqueous dispersion of resin particles). The water used to adjust the content is preferably deionized water, ion-exchanged water, or distilled water. From the viewpoint of ink productivity, the resin particle content (mass%) in the liquid containing resin particles is preferably 5.0% by mass or more and 30.0% by mass or less, and more preferably 15.0% by mass or more and 30.0% by mass or less.

[0061] Furthermore, by adding a crosslinking agent to the obtained resin particles and reacting them, resin particles having a crosslinked structure can be obtained. The amount of crosslinking agent is preferably such that the number of crosslinking groups is between 0.1 and 0.5 molar times the amount of carboxylic acid groups in the resin. If the amount of crosslinking agent is too small, the degree of crosslinking may not increase sufficiently, the viscosity of the ink may increase, and the effect of suppressing dispensing distortion may be slightly reduced. On the other hand, if the amount of crosslinking agent is too large, the amount of remaining carboxylic acid groups will be small, making it difficult to maintain a stable dispersion state of the resin particles, and the storage stability may be slightly reduced. During crosslinking, it is preferable to heat the mixture to promote the reaction. It is preferable to track the remaining amount of crosslinking agent using FT-IR or similar methods and continue the reaction until the desired remaining percentage is reached. Here, a method of crosslinking after the formation of resin particles has been described as an example, but the crosslinking agent may also be used when synthesizing the resin.

[0062] [Compositional analysis of resin particles] The type and composition of resin particles can be analyzed, for example, by the following methods. First, a sample is prepared by dissolving the resin particles in an organic solvent capable of dissolving them, such as tetrahydrofuran. The resin particles may be in an aqueous dispersion or a dry state. The prepared sample is analyzed by nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS), etc. This allows for the determination of the types and proportions of the units (monomers) that make up the resin. Alternatively, the resin particles themselves can be analyzed by pyrolysis gas chromatography to detect the units (monomers) that make up the resin. If insoluble matter that does not dissolve in the organic solvent is generated during sample preparation, the resulting insoluble matter can be analyzed by pyrolysis gas chromatography to detect the units (monomers) that make up the resin.

[0063] The cross-linked structure of resin particles (the cross-linked structure of the resin that forms the resin particles) can be analyzed, for example, by the following method. First, the units (monomers) that make up the resin are analyzed according to the compositional analysis procedure described above. The cross-linked structure is insoluble matter that does not dissolve in organic solvents. Regarding the insoluble matter, 13By using the C-CP / MAS solid-state NMR measurement method, the NMR spectrum can be analyzed by waveform separation, and the amount of functional groups can be quantified to analyze the cross-linking structure.

[0064] (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 water content (mass%) in the ink is preferably 50.00% by mass or more and 95.00% by mass or less, based on the total mass of the ink. As the water-soluble organic solvent, any solvent usable for inkjet inks, such as alcohols, glycols, (poly)alkylene glycols, nitrogen-containing compounds, and sulfur-containing compounds, can be used. The water-soluble organic solvent content (mass%) in the ink is preferably 3.00% by mass or more and 50.00% by mass or less, based on the total mass of the ink. If the water-soluble organic solvent content is outside the above range, the reliability of the inkjet aqueous ink, such as its adhesion resistance, may be slightly reduced.

[0065] (Other ingredients) In addition to the components mentioned above, the ink may also contain, as necessary, water-soluble organic compounds that are solid at 25°C, such as polyhydric alcohols like trimethylolpropane and trimethylolethane, and urea derivatives like urea and ethyleneurea. Furthermore, the ink may contain, as necessary, various additives such as surfactants, pH adjusters, defoamers, rust inhibitors, preservatives, fungicides, antioxidants, reduction inhibitors, and chelating agents. When surfactants are used, the surfactant content (mass%) in the ink is preferably 0.10% by mass or more and 5.00% by mass or less, and more preferably 0.10% by mass or more and 2.00% by mass or less, based on the total mass of the ink.

[0066] The ink may further contain other resins in addition to the aforementioned resin particles. It is preferable to use water-soluble resins as the other resins. Examples of water-soluble resins include acrylic resins, urethane resins, and olefin resins. Among these, acrylic resins and urethane resins are preferred.

[0067] (Ink properties) The ink of the present invention is an aqueous ink for use in inkjet systems. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. The viscosity of the ink at 25°C is preferably 1.0 mPa·s to 10.0 mPa·s, more preferably 1.0 mPa·s to 5.0 mPa·s, and particularly preferably 1.0 mPa·s to 3.0 mPa·s. The surface tension of the ink at 25°C is preferably 10 mN / m to 60 mN / m, more preferably 20 mN / m to 60 mN / m, and particularly preferably 30 mN / m to 50 mN / m. The pH of the ink at 25°C is preferably 5.0 to 10.0, and more preferably 7.0 to 9.5.

[0068] <Ink Cartridge> The ink cartridge of the present invention comprises ink and an ink storage section for storing this ink. The ink stored in this ink storage section is the aqueous ink of the present invention as described above. Figure 1 is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. As shown in Figure 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage section for storing ink. The ink storage section consists of an ink storage chamber 14 and an absorbent storage chamber 16, which are in communication with each other via a communication port 18. The absorbent storage chamber 16 is also in communication with the ink supply port 12. Liquid ink 20 is stored in the ink storage chamber 14, and absorbent materials 22 and 24 that hold the ink in an impregnated state are stored in the absorbent storage chamber 16. The ink storage section may not have an ink storage chamber for storing liquid ink, and the entire amount of ink to be stored may be held by an absorbent. Alternatively, the ink storage section may not have an absorbent, and the entire amount of ink may be stored in a liquid state. Furthermore, the ink cartridge may be configured to include an ink storage section and a recording head.

[0069] <Inkjet recording method> The inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting the aqueous ink of the present invention described above from an inkjet recording head. Methods for ejecting the ink include methods that impart mechanical energy to the ink and methods that impart thermal energy to the ink. In the present invention, it is particularly preferable to employ a method that imparts thermal energy to the ink to eject it. Aside from using the ink of the present invention, the steps of the inkjet recording method may be those of known origin.

[0070] Figure 2 is a schematic diagram showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. The inkjet recording apparatus is provided with a transport means (not shown) for transporting the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 comprises recording heads 38 and 40 and is configured to hold an ink cartridge 42. While the head cartridge 36 is transported along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is transported in the sub-scanning direction by the transport means (not shown), and an image is recorded on the recording medium 32. [Examples]

[0071] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components indicated in "parts" and "%" are based on mass.

[0072] <Method for measuring physical properties> (Acid value of resin) Resin particles were precipitated using a 1.0 mol / L hydrochloric acid aqueous solution, thoroughly washed with water, and then dried at 60°C. The resulting dried material was added to 50 mL of tetrahydrofuran at 50°C and dissolved, then 5 mL of water was added and the mixture was cooled to room temperature to obtain the measurement sample. The acid value of the resin was measured by neutralization titration of the obtained measurement sample. For neutralization titration, a potentiometric automatic titrator (product name "AT510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a composite glass electrode (product name "C-171", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) was used. A 0.5 mol / L potassium hydroxide ethanol solution was used as the titration reagent.

[0073] (Weight-average molecular weight of resin) Resin particles were added to tetrahydrofuran and dissolved at 25°C for 24 hours. The mixture was then filtered through a membrane filter to prepare the sample. The resin content in the sample was adjusted to approximately 0.3%. Gel permeation chromatography was performed on the prepared sample under the conditions described below. The weight-average molecular weight of the resin was then calculated from a molecular weight calibration curve created using standard polystyrene resins. The standard polystyrene resins used were "TSK Standard Polystyrene" F-850, F-450, F-288, F-128, F-80, F-40, F-20, F-10, F-4, F-2, F-1, A-5000, A-2500, A-1000, and A-500 (manufactured by Tosoh). HPLC system: Product name "2695 Separations Module" (manufactured by Waters) Differential refractive index (RI) detector: Product name "2414 detector" (manufactured by Waters) Column: Four-compartment column of product name "GPC KF-806M" (manufactured by Showa Denko). Eluent: Tetrahydrofuran Flow rate: 1.0mL / min Oven temperature: 40℃ Sample injection volume: 100 μL

[0074] (Determination of whether the sample is a particle or not, particle size) The liquid containing the sample was diluted with pure water to obtain a measurement sample with a sample content of approximately 1.0%. Then, the particle size (D) of the particles in the measurement sample was measured using a particle size analyzer. 50 The particle size was measured. The measurement conditions are as follows. A particle size analyzer using the dynamic light scattering method (product name "NanoTrac WAVE II-Q", manufactured by MicroTrac-Bel) was used as the particle size analyzer. If particles with a particle size were measured using the above method, the sample was judged to be "particles" ("aqueous dispersion"), and if particles with a particle size were not measured, the sample was judged not to be "particles" ("aqueous solution"). Cumulative 50% particle size D of the volume-based particle size distribution of resin particles R (nm) and cumulative 50% particle size D of pigment volume-based particle size distribution P(nm) was measured using the same method. [Measurement conditions] SetZero: 30 seconds Number of measurements: 10 Measurement time: 120 seconds Shape: true spherical Refractive index: 1.5 Density: 1.0

[0075] <Synthesis of resins> (Acrylic resin) A reaction vessel equipped with a stirrer, nitrogen gas inlet tube, condenser, and thermometer was prepared. 100 parts of monomer (66 parts styrene, 18 parts n-butyl acrylate, and 16 parts acrylic acid) and 100 parts of toluene were added to this vessel. Three parts of benzoyl peroxide were then added, and the reaction was carried out at 100°C for 2 hours under a nitrogen gas atmosphere. After removing the solvent at 140°C and 26 Pa, the mixture was returned to 25°C and atmospheric pressure. The product was crushed to obtain acrylic resin 1. The acid value of the obtained acrylic resin was 120 mg KOH / g, and the weight-average molecular weight was 10,000.

[0076] (Polyester resin) A reaction vessel equipped with a stirrer, condenser, and thermometer was prepared. A mixture of 80 parts ethylene glycol, 10 parts bisphenol A, 50 parts terephthalic acid, 50 parts isophthalic acid, and 10 parts trimellitic acid, along with tetra-n-butyl titanate, was added to this reaction vessel, and the temperature was raised to 240°C over 4 hours to carry out the esterification reaction. The amount of tetra-n-butyl titanate was set to 200 ppm based on the amount of the above mixture. After reducing the pressure to 26 Pa over 20 minutes, the reduced pressure of 240°C and 26 Pa was maintained for 90 minutes. After returning to 25°C and atmospheric pressure, the product was crushed with a crusher to obtain a polyester resin. The acid value of the obtained polyester resin was 30 mg KOH / g, and the weight-average molecular weight was 10,000.

[0077] (urethane resin) A reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, and reflux tube was prepared. 35 parts of isophorone diisocyanate and 50 parts of polyethylene glycol with a number-average molecular weight of 1000 were added to this vessel and reacted at 100°C for 2 hours under a nitrogen atmosphere. 14 parts of dimethylolpropionic acid, 1 part of ethylenediamine, and 100 parts of methyl ethyl ketone were added, and the mixture was reacted at 78°C until the desired percentage of isocyanate groups was reached, while monitoring the remaining percentage by FT-IR, to obtain a reaction solution. After cooling the resulting reaction solution to 40°C, the methyl ethyl ketone was removed under reduced pressure to obtain a paste. Tetrahydrofuran was added to dissolve the paste, obtaining a liquid containing urethane resin. The acid value of the obtained urethane resin was 30 mgKOH / g, and the weight-average molecular weight was 10,000.

[0078] (Polystyrene resin) A polystyrene resin was obtained in the same manner as described above for the acrylic resin, except that 45 parts of styrene, 50 parts of sodium styrenesulfonate, and 5 parts of divinylbenzene were used as monomers totaling 100 parts. The acid value of the obtained polystyrene resin was 120 mgKOH / g, and the weight-average molecular weight was 10,000.

[0079] <Manufacturing of resin particles> A 2 L beaker equipped with a stirrer (trade name: "Tornado Stirrer Standard SM-104", manufactured by AS ONE) was prepared. Resins of the types shown in Table 1 were dissolved in tetrahydrofuran heated to 45 °C, and 300 parts of a resin solution adjusted to a desired concentration was placed in the beaker. A 5% aqueous potassium hydroxide solution containing the amount of potassium hydroxide corresponding to the neutralization rate (mol%) based on the acid value of the resin shown in Table 1 was added, and the mixture was stirred for 30 minutes to neutralize the acid groups of the resin. However, the polystyrene resin was not neutralized. Then, in order to adjust the particle size, 300 parts of deionized water was dropped at a rate of 20 mL / min while stirring at a predetermined rotation speed at 45 °C. After reducing the pressure to distill off the organic solvent and part of the water, the contents of the beaker were filtered using a 150-mesh wire mesh (a filter in which 150 stainless steel wires are woven vertically and horizontally per 1 inch square). Next, a crosslinking agent of the type shown in Table 1 was added, and a crosslinking reaction was carried out at 80 °C for 6 hours. After cooling to room temperature, an appropriate amount of deionized water was added to adjust the resin particle content, and a liquid containing each resin particle with a resin particle content of 20.0% was obtained. In the liquid containing the obtained resin particles, the cumulative 50% particle diameter (D 50 ) D R (nm) and the presence or absence of a crosslinked structure are shown in Table 1. The meanings of each component in Table 1 are shown below. · EX-810: Ethylene glycol diglycidyl ether (trade name: "Denacol EX-810", manufactured by Nagase ChemteX) · WS-300: Oxazoline group-containing polymer (trade name: "Epocros WS-300", manufactured by Nippon Shokubai) · EX-830: Polyethylene glycol diglycidyl ether (trade name: "Denacol EX-830", manufactured by Nagase ChemteX) · EX-841: Polyethylene glycol diglycidyl ether (trade name: "Denacol EX-841", manufactured by Nagase ChemteX)

[0080] TIFF2023087649000001.tif104170

[0081] <Preparation of Pigment> The pigments listed below were prepared, and the finely milled pigments were prepared by the solvent-salt milling method. Specifically, the prepared pigments were ground using a kneader in the presence of sodium chloride and diethylene glycol as grinding agents under predetermined temperature conditions for a predetermined time to obtain a mixture of finely milled pigments. After thoroughly washing the resulting mixture, it was filtered and dried to obtain finely milled pigments. Commercially available carbon black and titanium dioxide were used as is. CI Pigment Red 122 CI Pigment Yellow 74 CI Pigment Blue 15:3 CI Pigment Green 36 CI Pigment Red 149 CI Pigment Violet 23 CI Pigment Red 254

[0082] <Manufacturing of Pigment Dispersion> (Pigment dispersions 1-23, 25-28) A batch-type vertical sand mill (manufactured by AIMEX) filled with 200 zirconia beads with a diameter of 0.3 mm was filled with a mixture of pigments, resin particles, and pure water in the types and quantities shown in Table 2, and dispersed for a predetermined time. After removing coarse particles by centrifugation, each pigment dispersion was obtained by pressure filtration through a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm.

[0083] (Pigment dispersion 24) Pigment dispersion 24 was obtained in the same manner as in the cases of pigment dispersions 1-23 and 25-28 described above, except that instead of using a liquid containing resin particles, an aqueous solution with a resin content of 16.0% was used, which was prepared by dissolving a water-soluble resin in an aqueous solution containing potassium hydroxide equimolar to its acid value. As the water-soluble resin, a styrene-ethyl acrylate-acrylic acid copolymer with an acid value of 125 mgKOH / g and a weight-average molecular weight of 10,000 was used.

[0084] The properties of each obtained pigment dispersion are shown in Table 2.

[0085] TIFF2023087649000002.tif200170

[0086] <Ink preparation> (Examples 1-23, Comparative Examples 1, 2, 4-6) The following components were mixed and thoroughly stirred, then pressure filtered through a 2.5 μm pore size microfilter to prepare the ink. Of the components listed below, "Acetylenel E100" is a trade name for a nonionic surfactant (manufactured by Kawaken Fine Chemicals). The properties of the ink are shown in Table 3. • Pigment dispersions of the types shown in Table 3: 30.00% Glycerin: 10.00% Triethylene glycol: 10.00% • Acetyleneol E100: 0.10% • Ion-exchanged water: 49.00%

[0087] TIFF2023087649000003.tif225170

[0088] (Comparative Example 3) The following components were mixed and thoroughly stirred, then pressure filtered through a 2.5 μm pore size microfilter to prepare the ink. Of the components listed below, "Acetylenel E100" is a trade name for a nonionic surfactant (manufactured by Kawaken Fine Chemicals). • Pigment dispersion 24:30.00% Glycerin: 10.00% Triethylene glycol: 10.00% • Acetyleneol E100: 0.10% • Liquid containing resin particles 1: 2.40% • Ion-exchanged water: 46.60%

[0089] <Rating> In this invention, "A" and "B" were defined as acceptable levels, and "C" as an unacceptable level, according to the evaluation criteria for each item shown below. The evaluation results are shown in Table 4.

[0090] (Mapping property) Each prepared ink was filled into an ink cartridge and mounted on an inkjet recording device (product name "PIXUS iP3100", manufactured by Canon) that ejects ink from the recording head using thermal energy. In this embodiment, a recording duty cycle of 100% is defined as a solid image recorded under the condition that one drop of ink with a volume of 5 pL per drop is applied to a unit area of ​​1 / 1,200 inch x 1 / 1,200 inch. Using this inkjet recording device, a 2 cm x 2 cm solid image with a recording duty cycle of 100% was recorded on a recording medium (product name "Canon Photo Paper Gloss Gold GL-101", manufactured by Canon). After drying the recorded image at 25°C for 24 hours, the image was illuminated at a 45-degree angle from a distance of 2 m using two fluorescent lamps placed in parallel at a distance of 10 cm apart (illumination angle 45 degrees). The shape of the fluorescent lamp projected onto the image was visually confirmed from a 45-degree angle (observation angle 45 degrees), and the image quality was evaluated according to the evaluation criteria shown below. A: The boundary between the two projected fluorescent lights was clear, and no blurring was observed at the edges. B: The boundary between the two projected fluorescent lights was discernible, but blurring was observed at the edges. C: I couldn't see the boundary between the two projected fluorescent lights.

[0091] (Discharge misaligned) Using the inkjet recording device described above, a preliminary ejection was performed to ensure that ink was ejected normally from each ejection port of the recording head. After the preliminary ejection was completed, ejection was paused for 2 seconds, and lines with a width of 3 ink droplets were recorded. The recorded lines were visually inspected, and the ink ejection irregularity was evaluated according to the evaluation criteria shown below. A: There was no misalignment in the placement of the dots that make up the grid lines, and continuous grid lines were recorded. B: There was a slight misalignment of about one dot in the placement of the dots that make up the grid lines, but continuous grid lines were recorded. C: There were areas in the ruled lines that were not extended or were discontinuous.

[0092] (Storage stability) The viscosity of each prepared ink was measured (viscosity before storage). The inks were then placed in sealed containers and stored in a 70°C constant temperature bath for two weeks. The inks were then allowed to return to 25°C, and their viscosity was measured again (viscosity after storage). Viscosity was measured using an E-type viscometer (RE-80L, manufactured by Toki Sangyo). The ratio of viscosity after storage to viscosity before storage was calculated, and the storage stability of the inks was evaluated according to the evaluation criteria shown below. A: The ratio of "viscosity after storage / viscosity before storage" was 1.2 times or less. B: The ratio of "viscosity after storage / viscosity before storage" was greater than 1.2 times and less than or equal to 1.3 times. C: The ratio of "viscosity after storage / viscosity before storage" was more than 1.3 times.

[0093] TIFF2023087649000004.tif218170

[0094] Furthermore, the disclosure of this embodiment includes the following configurations and methods. (Configuration 1) An aqueous inkjet ink containing a pigment and resin particles that disperse the pigment, The cumulative 50% particle size of the volume-based particle size distribution of the aforementioned resin particles is 10 nm or less. The resin particles have a crosslinked structure, An aqueous ink characterized in that the cumulative 50% particle size of the volume-based particle size distribution of the pigment is 3.0 times or more and 8.0 times or less than the cumulative 50% particle size of the volume-based particle size distribution of the resin particles. (Configuration 2) The aqueous ink according to Configuration 1, wherein the content (mass%) of the resin particles is 0.06 times or more and 1.00 times or less in mass ratio to the content (mass%) of the pigment. (Configuration 3) The aqueous ink according to Configuration 1 or 2, wherein the resin particles are formed of a resin having at least one carboxylic acid group selected from the group consisting of acrylic resins, polyester resins, and urethane resins. (Configuration 4) The aqueous ink according to any one of Configurations 1 to 3, wherein the resin particles are formed of an acrylic resin. (Configuration 5) The aqueous ink according to any one of Configurations 1 to 4, wherein the crosslinked structure includes an alkylene oxide group. (Configuration 6) The aqueous ink according to Configuration 5, wherein the number of repeating alkylene oxide groups in the crosslinked structure is 9 or less. (Configuration 7) An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge characterized in that the ink is an aqueous ink according to any one of the items 1 to 6 of the configuration. (Method 1) An inkjet recording method in which ink is ejected from an inkjet recording head to record an image on a recording medium, An inkjet recording method characterized in that the ink is an aqueous ink according to any one of the items 1 to 6.

Claims

1. A water-based inkjet ink containing a pigment and resin particles for dispersing the pigment, the resin particles have a cumulative 50% particle size of a volume-based particle size distribution of 10 nm or less; the resin particles have a crosslinked structure, the ratio of a cumulative 50% particle diameter of the volume-based particle size distribution of the pigment to a cumulative 50% particle diameter of the volume-based particle size distribution of the resin particles is 3.0 times or more and 8.0 times or less; The water-based ink is characterized in that the resin particles are adsorbed to the pigment.

2. 2. The aqueous ink according to claim 1, wherein the resin particles have a cumulative 50% particle diameter of 1 nm or more in a volume-based particle size distribution.

3. 2. The aqueous ink according to claim 1, wherein the content (mass %) of the resin particles is 0.06 to 1.00 times the content (mass %) of the pigment in terms of mass ratio.

4. 2. The aqueous ink according to claim 1, wherein the resin particles are formed from at least one resin having a carboxylic acid group selected from the group consisting of acrylic resins, polyester resins, and urethane resins.

5. 2. The water-based ink according to claim 1, wherein the resin particles are formed from an acrylic resin.

6. The aqueous ink according to claim 1 , wherein the crosslinked structure contains an alkylene oxide group.

7. The water-based ink according to claim 6 , wherein the number of repeating alkylene oxide groups in the crosslinked structure is 9 or less.

8. 2. The aqueous ink according to claim 1, wherein the content (mass %) of the pigment is 0.10 mass % or more and 15.00 mass % or less based on the total mass of the ink.

9. The aqueous ink according to claim 1 , wherein the content (% by mass) of the resin particles is 0.01% by mass or more and 10.00% by mass or less.

10. 2. The aqueous ink according to claim 1, wherein the particle diameter at 50% of the cumulative volume of the particle size distribution of the pigment is 1 nm or more and 80 nm or less.

11. An ink cartridge comprising ink and an ink storage section for storing the ink, 11. An ink cartridge, wherein the ink is the aqueous ink according to claim 1.

12. An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, An ink-jet recording method, wherein the ink is the aqueous ink according to any one of claims 1 to 10.

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