Aqueous ink for inkjet recording

Abstract

To provide an aqueous ink for inkjet recording, which has excellent intermittent dichargeability and provides recorded images with suppressed image bleeding.SOLUTION: An aqueous ink for inkjet recording comprises a pigment, resin particles A having a core-shell structure, a water-soluble organic solvent, and water. The core part resin A1 which constitutes the core part of the resin particles A has a crosslinked structure derived from a compound (R1) that has a plurality of reactive groups in the molecule and has a glass transition temperature of 25°C or more as calculated by Fox's equation from a mass ratio of a monomer component other than the compound (R1) which constitutes the core part resin A1. The shell part resin A2 which constitutes the shell part of the resin particles A comprises a structural unit derived from a carboxylic acid monomer (a2-1) and has an acid value of 90 mgKOH / g to 350 mgKOH / g.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-based ink for ink-jet printing. [Background technology]

[0002] Inkjet recording is a recording method in which ink droplets are directly ejected from fine nozzles and deposited on a recording medium to obtain a recorded matter on which characters or images are recorded. Inkjet recording is characterized by not requiring plate-making and easy operation of the printing device, and is used in offices and homes, and in recent years, the demand for inkjet recording has been increasing in industrial applications as well. In particular, from the viewpoint of reducing environmental load, there is a high demand for water-based inks for inkjet recording that mainly use water as a solvent, and from the viewpoint of water resistance and weather resistance of recorded matter, water-based inks that use pigments as colorants have been proposed, and water-based inks that use pigments and core-shell type resin particles have been studied.

[0003] For example, Patent Document 1 discloses a water-based ink for ink-jet printing that uses a water dispersion for ink-jet printing containing water-insoluble crosslinked polymer particles and core-shell polymer particles containing a pigment as a colorant, for the purpose of providing a water-based ink for ink-jet printing that is excellent in gloss and suppression of bronzing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-063500 A Summary of the Invention [Problem to be solved by the invention]

[0005] Conventionally, plain paper has been the main recording medium, but in recent years, there has been an increasing demand for printing on low-liquid-absorbent recording media such as coated paper and resin film. However, it may be difficult to form good images on such low-liquid-absorbent recording media with conventional water-based inks. In addition, in inkjet recording on a low-absorbency recording medium, a drying operation is generally performed after applying the water-based ink to the recording medium. However, in this drying operation, the vicinity of the recording head is also heated, so when the ink ejection is temporarily stopped and the ink around the hole of the ejection nozzle of the recording head dries, the resin component in the ink is concentrated and thickened or forms a film around the hole of the ejection nozzle, and a coagulated thickened substance is generated, which is likely to cause nozzle clogging and reduce the ejection property. In order to prevent the ink from drying around the hole of the ejection nozzle, a solvent with a high boiling point is generally used, but on the other hand, the drying property of the water-based ink after applying the water-based ink to the recording medium is reduced, and the image is likely to bleed. In particular, water, which is the main solvent of the water-based ink, has a high surface tension and is therefore difficult to wet and spread on the low-absorbency recording medium, and is also difficult to penetrate into the low-absorbency recording medium, so there is a problem that boundary bleeding occurs due to the coalescence of undried ink droplets of different colors, which is likely to lead to a decrease in image quality. Therefore, there is a demand for a water-based ink for ink-jet printing that has excellent ejection properties when ejection of the ink is temporarily stopped and then ejected again, i.e., so-called intermittent ejection properties, and that can provide printed matter with little image bleeding. An object of the present invention is to provide a water-based ink for ink-jet printing which has excellent intermittent ejection properties and can provide recorded matter with suppressed image bleeding. [Means for solving the problem]

[0006] The present inventors have found that the above-mentioned problems can be solved by a resin particle that contains a pigment, resin particles having a core-shell structure, a water-soluble organic solvent, and water, wherein the core resin that constitutes the core of the resin particle has a crosslinked structure derived from a compound having multiple reactive groups in the molecule, and has a glass transition temperature calculated by Fox's formula from the mass ratio of monomer components other than the compound that constitutes the core resin of a predetermined value or higher, and wherein the shell resin that constitutes the shell of the resin particle contains a structural unit derived from a carboxylic acid monomer and has an acid value within a predetermined range. That is, the present invention provides a pigment-based ink composition comprising a pigment, resin particles A having a core-shell structure, a water-soluble organic solvent, and water, a core resin A1 constituting a core of the resin particle A has a crosslinked structure derived from a compound (R1) having a plurality of reactive groups in the molecule, and has a glass transition temperature of 25° C. or higher calculated by Fox's formula from the mass ratio of monomer components other than the compound (R1) constituting the core resin A1; The present invention provides a water-based ink for ink-jet printing, in which a shell resin A2 constituting the shell of the resin particles A contains a structural unit derived from a carboxylic acid monomer (a2-1) and has an acid value of 90 mgKOH / g or more and 350 mgKOH / g or less. Effect of the Invention

[0007] According to the present invention, it is possible to provide a water-based ink for ink-jet printing which has excellent intermittent ejection properties and is capable of producing recorded matter with suppressed image bleeding. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Water-based ink for inkjet printing] The water-based ink for ink-jet printing of the present invention (hereinafter also simply referred to as "water-based ink") contains a pigment, resin particles A having a core-shell structure (hereinafter also referred to as "core-shell type resin particles A" or "resin particles A"), a water-soluble organic solvent, and water, in which a core resin A1 constituting the core of the resin particles A has a crosslinked structure derived from a compound (R1) having multiple reactive groups in the molecule, and has a glass transition temperature of 25°C or higher calculated by Fox's formula from the mass ratio of monomer components other than the compound (R1) constituting the core resin A1, and a shell resin A2 constituting the shell of the resin particles A contains a constituent unit derived from a carboxylic acid monomer (a2-1), and has an acid value of 90 mgKOH / g or more and 350 mgKOH / g or less. In the present invention, the term "water-based" means that water accounts for the largest proportion by mass of the ink medium. In the present invention, whether a recording medium is low absorbent or high absorbent is determined by the amount of water absorbed by the recording medium when the recording medium is in contact with pure water for 100 ms. The amount of water absorbed can be measured as the amount of transfer when the recording medium is in contact with pure water for 100 ms under conditions of 23°C and 50% relative humidity using an automatic scanning liquid absorption meter (for example, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.). "Low liquid absorption" is a concept that includes low liquid absorption and non-liquid absorption, and the water absorption of 0 g / m 2 More than 7g / m 2 "Highly absorbent" means that the water absorption is 7 g / m or less. 2 It means to be super.

[0009] The present invention has the special effect of being able to obtain a recorded matter having excellent intermittent ejection properties and suppressed image bleeding. Although the reason for this is not clear, it is believed to be as follows. The water-based ink of the present invention contains resin particles having a core-shell structure, and the core resin constituting the core of the resin particle has a crosslinked structure derived from a compound having multiple reactive groups in the molecule, and has a glass transition temperature calculated by Fox's formula from the mass ratio of monomer components other than the compound constituting the core resin of 25° C. or higher. Therefore, even if ink ejection is temporarily stopped and the ink around the holes of the ejection nozzles of the recording head dries, the core resin is unlikely to swell with the water-soluble organic solvent, film formation is suppressed even around the holes of the ejection nozzles, nozzle clogging is unlikely to occur, and it is believed that this improves intermittent ejection properties. On the other hand, since the shell resin constituting the shell of the resin particles having a core-shell structure contains a structural unit derived from a carboxylic acid monomer and has an acid value of 90 mgKOH / g or more and 350 mgKOH / g or less, when the ink droplets applied to the recording medium dry, the ink becomes concentrated and the shell resin swells due to the water-soluble organic solvent, causing the viscosity of the ink to increase and the fluidity of the ink to decrease, thereby preventing the ink droplets from coalescing, and as a result, it is believed that a recorded material can be obtained in which image bleeding is suppressed.

[0010] <Resin particles A having a core-shell structure> The water-based ink of the present invention contains resin particles A having a core-shell structure (core-shell type resin particles A). In the present invention, "resin particles A having a core-shell structure" refers to resin particles in which the core and shell of a single particle are made of different resin components. The resin present in the core of the core-shell type resin particles A is referred to as "core part resin A1", and the resin present in the outermost shell of the resin particles is referred to as "shell part resin A2". Even if the resin particles can be classified into three or more different resin components, the resin present in the outermost shell is referred to as "shell part resin A2", and the resins other than the resin present in the outermost shell are referred to as "core part resin A1". In the present invention, the term "different resin components" means that the types of monomers constituting the resin components are different from each other, that is, when comparing the type of monomer (a1) constituting the core resin A1 with the type of monomer (a2) constituting the shell resin A2, different types of monomer components are present. In addition, when determining whether the resin components are different types, a compound (R1) having multiple reactive groups in the molecule constituting the core resin A1, and a compound (R2) having multiple reactive groups in the molecule that may constitute the shell resin A2 are also determined to be monomer components. In the present invention, the core-shell type resin particles A are resin particles that do not contain a pigment and function as a fixing agent for a recording medium.

[0011] (Core resin A1) The core resin A1 has a crosslinked structure derived from a compound (R1) having multiple reactive groups in the molecule, and has a glass transition temperature of 25°C or higher, calculated by Fox's formula from the mass ratio of monomer components other than the compound (R1) that constitute the core resin A1. Specific examples of the core resin A1 include vinyl resins, polyester resins, and polyurethane resins. Among these, the core resin A1 is preferably a vinyl resin obtained by addition polymerization of a vinyl monomer (vinyl compound, vinylidene compound, vinylene compound), and more preferably a vinyl resin containing a structural unit derived from an ester (a1-1) of a monohydric alcohol having 1 to 22 carbon atoms and (meth)acrylic acid (hereinafter also referred to as "(meth)acrylic acid ester (a1-1)"). In this specification, the term "(meth)acrylic acid ester" refers to an acrylic acid ester and / or a methacrylic acid ester.

[0012] [(Meth)acrylic acid ester (a1-1)] Examples of the monohydric alcohol constituting the (meth)acrylic acid ester (a1-1) include aliphatic monohydric alcohols and aromatic group-containing monohydric alcohols. The aliphatic monohydric alcohol has 1 or more carbon atoms and preferably 16 or less, more preferably 12 or less, even more preferably 8 or less, and still more preferably 6 or less. The aliphatic monohydric alcohol may be either a saturated aliphatic monohydric alcohol or an unsaturated aliphatic monohydric alcohol. Examples of the aliphatic monohydric alcohols include linear, branched, or alicyclic aliphatic monohydric alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, n-pentyl alcohol, isopentyl alcohol, neopentyl alcohol, n-hexanol, n-heptanol, n-octanol, 2-ethylhexyl alcohol, n-nonanol, isononyl alcohol, n-decanol, isodecyl alcohol, lauryl alcohol, tridecyl alcohol, myristyl alcohol, pentadecyl alcohol, cetyl alcohol, stearyl alcohol, isostearyl alcohol, oleyl alcohol, cyclohexanol, and cyclohexanemethanol. An example of the aromatic group-containing monohydric alcohol is benzyl alcohol. The (meth)acrylic acid ester (a1-1) may be used alone or in combination of two or more kinds.

[0013] Among these, from the viewpoint of improving intermittent ejection properties, the (meth)acrylic acid ester (a1-1) is preferably at least one selected from the group consisting of esters of (meth)acrylic acid and linear, branched, or alicyclic aliphatic monohydric alcohols having from 1 to 22 carbon atoms, and esters of (meth)acrylic acid and aromatic group-containing monohydric alcohols, more preferably at least one selected from the group consisting of esters of (meth)acrylic acid and linear, branched, or alicyclic aliphatic monohydric alcohols having from 1 to 6 carbon atoms, and esters of (meth)acrylic acid and aromatic monohydric alcohols, and even more preferably is at least one selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, and benzyl (meth)acrylate, more preferably at least one selected from the group consisting of methyl (meth)acrylate and n-butyl (meth)acrylate, and even more preferably a combination of methyl methacrylate and n-butyl acrylate. In this specification, "(meth)acrylate" refers to acrylate and / or methacrylate.

[0014] The core resin A1 may contain a structural unit derived from a monomer other than the (meth)acrylic acid ester (a1-1), such as a styrene-based monomer or an ionic group-containing vinyl monomer. Examples of styrene-based monomers include styrene, α-methylstyrene, vinyltoluene, and vinylnaphthalene. Among them, styrene and α-methylstyrene are preferred, and styrene is more preferred. The styrene-based monomers may be used alone or in combination of two or more. Examples of the ionic group-containing vinyl monomer include anionic group-containing vinyl monomers and cationic group-containing vinyl monomers. In the present specification, the term "anionic group" refers to a group that dissociates to release a hydrogen ion, such as a carboxyl group (-COOM), a sulfonic acid group (-SO3M), or a phosphoric acid group (-OPO3M2), or a dissociated ionic form thereof (-COO - , -SO3 - , -OPO3 2- , -OPO3 - In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. In this specification, the term "cationic group" refers to a proton acid salt of ammonia, a primary amine, or a monovalent functional group (-NH2, -NHR, -NRR') obtained by removing one hydrogen atom from a secondary amine, or a quaternary ammonium group, where R and R' represent a hydrocarbon group. Among these, anionic group-containing vinyl monomers are preferred. Examples of the anionic group-containing vinyl monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethylsuccinic acid. Among these, the anionic group-containing vinyl monomer is preferably at least one selected from the group consisting of acrylic acid and methacrylic acid. The ionic group-containing vinyl monomers may be used alone or in combination of two or more.

[0015] [Reactive group-containing compound (R1)] The core resin A1 is a resin having a crosslinked structure derived from a compound (R1) having a plurality of reactive groups in the molecule (hereinafter also referred to as "reactive group-containing compound (R1)"). In the present invention, the reactive group of the reactive group-containing compound (R1) is preferably a functional group that easily undergoes a chemical reaction with a radical, an anion, or a cation. The chemical reaction means an addition reaction or a ring-opening reaction, and does not include a neutralization reaction as a reaction with an anion or a cation. A preferred example of the reactive group having high reactivity with radicals is a vinyl group. Preferred examples of the reactive group having high reactivity with anions or cations include one or more groups selected from the group consisting of an epoxy group, an aziridine group, an oxazoline group, an isocyanate group, and a carbodiimide group. In the present invention, the term "vinyl group" refers to a concept including vinyl groups, vinylene groups, and vinylidene groups. In addition, in the present invention, hydroxyl groups, amino groups, carboxy groups, ester groups, amide groups, ketone groups, aldehyde groups, and saturated hydrocarbon groups are not classified as reactive groups. From the viewpoints of improving intermittent ejection properties and suppressing image bleeding, the molecular weight of the reactive group-containing compound (R1) is preferably 100 or more, more preferably 120 or more, even more preferably 140 or more, still more preferably 160 or more, and even more preferably 180 or more, and from the same viewpoints as above, it is preferably 600 or less, more preferably 400 or less, and even more preferably 300 or less.

[0016] When the core resin A1 is a vinyl resin, the reactive group of the reactive group-containing compound (R1) is preferably a vinyl group. In this case, the reactive group-containing compound (R1) is preferably a compound (R1V) having a plurality of vinyl groups in the molecule (hereinafter also referred to as "vinyl group-containing compound (R1V)"). In this case, the reactive group-containing compound (R1V) is preferably a compound that can be introduced into the polymer skeleton of the core resin A1 to form a crosslinked structure by being contained in the monomer (a1) constituting the core resin A1. Specific examples of the vinyl group-containing compound (R1V) include one or more selected from the group consisting of esters of polyhydric alcohols and (meth)acrylic acid and divinylbenzene. Among these, the vinyl group-containing compound (R1V) is more preferably an ester of polyhydric alcohols and (meth)acrylic acid, more preferably one or more selected from the group consisting of ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate, even more preferably 1,6-hexanediol di(meth)acrylate, and even more preferably 1,6-hexanediol diacrylate.

[0017] The content of structural units derived from the (meth)acrylic acid ester (a1-1) in the core resin A1 is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more from the viewpoint of suppressing image bleeding, and is preferably 98% by mass or less, more preferably 96% by mass or less, and even more preferably 90% by mass or less from the viewpoint of improving intermittent ejection properties. The content of structural units derived from the reactive group-containing compound (R1) in the core resin A1 is preferably 2% by mass or more, more preferably 4% by mass or more, and even more preferably 10% by mass or more from the viewpoint of improving intermittent ejection properties, and is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less from the viewpoint of suppressing image bleeding. The core resin A1 may contain other structural units than the above-mentioned structural units, provided that the effects of the present invention are not impaired.

[0018] The glass transition temperature (Tg) of the core resin A1 is, from the viewpoint of improving intermittent ejection properties, 25°C or higher, preferably 30°C or higher, and more preferably 40°C or higher, and, from the viewpoint of suppressing image bleeding, is preferably 110°C or lower, more preferably 100°C or lower, even more preferably 90°C or lower, still more preferably 80°C or lower, still more preferably 70°C or lower, and still more preferably 60°C or lower. In the present invention, the glass transition temperature (Tg) of the core resin A1 is calculated by Fox's formula from the mass ratio of the monomer components other than the reactive group-containing compound (R1) constituting the core resin A1, without taking into account the structural unit derived from the reactive group-containing compound (R1). The Fox's formula for determining the glass transition temperature is as follows: 1 / Tg=(W1 / Tg1)+(W2 / Tg2)+···+(W m / Tg m ) W1+W2+...W m =1 In the Fox formula, Tg is the glass transition temperature of the copolymer, and Tg1, Tg2, . . . , Tg m are the glass transition temperatures of the homopolymers of the monomer components constituting the copolymer, and the unit of temperature is K. In addition, W1, W2, ..., W m represents the mass ratio of each monomer component. As the glass transition temperature of the homopolymer of each monomer component in the Fox formula, for example, the value described in Polymer Handbook Third Edition (Wiley-Interscience 1989) can be used.

[0019] The crosslink density (q1) of the core resin is defined as the molar number of reactive groups of the reactive group-containing compound (R1) in the core resin A1 divided by the mass of the core resin A1, and is calculated by the following formula: Crosslink density (q1) (mmol / g)=[[(number of moles of structural units derived from the compound (R1) in the core resin A1)×(number of reactive groups possessed by the compound (R1)] / (mass of the core resin A1 in the resin particle A)]×1000 From the viewpoint of improving intermittent ejection performance, the crosslink density (q1) of the core resin A1 is preferably 0.2 mmol / g or more, more preferably 0.4 mmol / g or more, even more preferably 0.6 mmol / g or more, even more preferably 0.8 mmol / g or more, and even more preferably 1.0 mmol / g or more, and from the viewpoint of suppressing image bleeding, it is preferably 3.0 mmol / g or less, more preferably 2.5 mmol / g or less, even more preferably 2.0 mmol / g or less, and even more preferably 1.5 mmol / g or less.

[0020] (Shell resin A2) The shell resin A2 contains a structural unit derived from a carboxylic acid monomer (a2-1), and has an acid value of 90 mgKOH / g or more and 350 mgKOH / g or less. Specific examples of the shell resin A2 include vinyl resins, polyester resins, and polyurethane resins. Among these, vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, and vinylene compounds) are preferred.

[0021] [Carboxylic acid monomer (a2-1)] From the viewpoint of improving intermittent ejection property and suppressing image bleeding, the carboxylic acid monomer (a2-1) is preferably at least one selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, crotonic acid, and itaconic acid. Among these, from the viewpoint of the same as above, the carboxylic acid monomer (a2-1) is more preferably at least one selected from the group consisting of acrylic acid and methacrylic acid. The carboxylic acid monomer (a2-1) may be used alone or in combination of two or more kinds.

[0022] [Hydrophobic monomer (a2-2)] From the viewpoint of improving intermittent ejection properties and suppressing image bleeding, the shell resin A2 is preferably a vinyl resin that further contains a structural unit derived from a hydrophobic monomer (a2-2) in addition to a structural unit derived from a carboxylic acid monomer (a2-1). In this specification, the term "hydrophobic monomer" refers to a monomer that, when dissolved in 100 g of ion-exchanged water at 25° C. until saturated, dissolves in an amount of less than 10 g. The hydrophobic monomer (a2-2) may be used alone or in combination of two or more kinds.

[0023] As the hydrophobic monomer (a2-2), from the viewpoint of improving intermittent ejection properties and suppressing image bleeding, one or more types selected from the group consisting of esters of monohydric alcohols having 1 to 22 carbon atoms and (meth)acrylic acid, and aromatic group-containing monomers are preferably used. Examples of the ester of (meth)acrylic acid and a monohydric alcohol having 1 to 22 carbon atoms include those exemplified in the above-mentioned ester (a1-1) of a monohydric alcohol having 1 to 22 carbon atoms and (meth)acrylic acid. The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group with 6 to 22 carbon atoms, which may have a substituent containing a hetero atom, and more preferably at least one selected from a styrene-based monomer and an aromatic group-containing (meth)acrylate. The molecular weight of the aromatic group-containing monomer is preferably less than 500. Examples of styrene-based monomers include styrene, α-methylstyrene, vinyltoluene, and vinylnaphthalene. Among them, styrene and α-methylstyrene are preferred, and styrene is more preferred. Examples of the aromatic group-containing (meth)acrylate include phenyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate. Among these, from the viewpoint of improving intermittent ejection properties and suppressing image bleeding, the hydrophobic monomer (a2-2) is preferably an aromatic group-containing monomer, more preferably a styrene-based monomer, even more preferably one or more selected from the group consisting of styrene and α-methylstyrene, and even more preferably styrene.

[0024] [Reactive group-containing compound (R2)] From the viewpoint of intermittent ejection, the shell resin A2 is a resin that may have a crosslinked structure derived from a compound (R2) having multiple reactive groups in the molecule (hereinafter also referred to as "reactive group-containing compound (R2)"). In the present invention, the reactive group of the reactive group-containing compound (R2) is preferably a carboxy group or a functional group that easily undergoes a chemical reaction with a radical. Note that the chemical reaction with a carboxy group does not include a neutralization reaction. Preferred examples of the reactive group having high reactivity with a carboxy group include one or more groups selected from the group consisting of an epoxy group, an aziridine group, an oxazoline group, an isocyanate group, and a carbodiimide group. A preferred example of the reactive group having high reactivity with radicals is a vinyl group.

[0025] From the viewpoint of intermittent ejection property, the reactive group-containing compound (R2) is preferably a compound (R2E) (hereinafter also referred to as "reactive group-containing compound (R2E)") having multiple functional groups in the molecule that can react with the carboxy groups of the structural units derived from the carboxylic acid monomer (a2-1) that constitute the shell resin A2. When the shell resin A2 is a vinyl resin and the reactive group-containing compound (R2) is a reactive group-containing compound (R2E), the shell resin A2 is preferably a vinyl resin containing a structural unit derived from a carboxylic acid monomer (a2-1) and a structural unit derived from a reactive group-containing compound (R2E), more preferably a vinyl resin containing a structural unit derived from a carboxylic acid monomer (a2-1), a structural unit derived from a hydrophobic monomer (a2-2), and a structural unit derived from a reactive group-containing compound (R2E). In this case, the shell resin A2 is preferably a resin obtained by crosslinking a carboxyl group-containing polymer A2p containing a structural unit derived from a carboxylic acid monomer (a2-1) with a reactive group-containing compound (R2E), more preferably a resin obtained by crosslinking a carboxyl group-containing polymer A2p containing a structural unit derived from a carboxylic acid monomer (a2-1) and a structural unit derived from a hydrophobic monomer (a2-2) with a reactive group-containing compound (R2E). The carboxyl group-containing polymer A2p is a polymer used to disperse the crosslinked polymer particles constituting the core portion described below, and examples of the monomers constituting the carboxyl group-containing polymer A2p include the same as those exemplified for the shell portion resin A2 described above, and preferred examples are also similar.

[0026] Specific examples of the functional group capable of reacting with a carboxyl group contained in the reactive group-containing compound (R2E) include one or more selected from the group consisting of an epoxy group, an aziridine group, an oxazoline group, an isocyanate group, and a carbodiimide group. Among these, one or more selected from the group consisting of an epoxy group, an isocyanate group, and a carbodiimide group is more preferred, and an epoxy group is even more preferred. Examples of the reactive group-containing compound (R2E) include polyglycidyl ethers of polyhydric alcohols, polyisocyanates, polycarbodiimides, etc. The polyisocyanates may be blocked with a blocking agent in order to control the reactivity.

[0027] From the viewpoint of intermittent ejection properties, the reactive group-containing compound (R2E) is preferably a compound having multiple epoxy groups in the molecule (hereinafter, also referred to as an "epoxy group-containing compound"). From the same viewpoint as above, the epoxy group-containing compound is preferably a polyglycidyl ether of a polyhydric alcohol, more preferably at least one selected from the group consisting of a polyglycidyl ether of an aliphatic polyhydric alcohol and a polyglycidyl ether of a polyalkylene glycol. Among these, from the same viewpoint as above, more preferably at least one selected from the group consisting of cyclohexanedimethanol diglycidyl ether, trimethylolpropane polyglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, resorcinol diglycidyl ether, pentaerythritol polyglycidyl ether, triethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, hydrogenated bisphenol A type diglycidyl ether, and glycerin diglycidyl ether, and even more preferably 1,4-butanediol diglycidyl ether. The glycidyl ether is preferably one or more selected from the group consisting of 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, more preferably one or more selected from the group consisting of 1,6-hexanediol diglycidyl ether and cyclohexanedimethanol diglycidyl ether, even more preferably one or more selected from the group consisting of 1,6-hexanediol diglycidyl ether and cyclohexanedimethanol diglycidyl ether, and even more preferably 1,6-hexanediol diglycidyl ether. From the viewpoint of crosslinking with a carboxy group, the epoxy equivalent of the epoxy group-containing compound is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and is preferably 300 or less, more preferably 200 or less, even more preferably 170 or less.

[0028] When the shell resin A2 is a vinyl resin, the reactive group-containing compound (R2) may be a compound (R2V) having multiple vinyl groups in the molecule (hereinafter also referred to as "vinyl group-containing compound (R2V)"). In this case, the reactive group-containing compound (R2V) is preferably a compound that can be incorporated into the polymer skeleton of the shell resin A2 to form a crosslinked structure by being contained in the monomer (a2) constituting the shell resin A2. When the shell resin A2 is a vinyl resin and the reactive group-containing compound (R2) is a vinyl group-containing compound (R2V), the shell resin A2 is preferably a vinyl resin containing a structural unit derived from a carboxylic acid monomer (a2-1) and a structural unit derived from a vinyl group-containing compound (R2V), and more preferably a vinyl resin containing a structural unit derived from a carboxylic acid monomer (a2-1), a structural unit derived from a hydrophobic monomer (a2-2), and a structural unit derived from a vinyl group-containing compound (R2V). Specific examples of the vinyl group-containing compound (R2V) include esters of polyhydric alcohols and (meth)acrylic acid, and divinylbenzene. Among these, the vinyl group-containing compound (R2V) is preferably an ester of polyhydric alcohols and (meth)acrylic acid, and more preferably one or more selected from the group consisting of ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate.

[0029] From the viewpoint of improving intermittent ejection, the acid value of the shell resin A2 is 90 mgKOH / g or more, preferably 100 mgKOH / g or more, more preferably 150 mgKOH / g or more, even more preferably 170 mgKOH / g or more, and even more preferably 200 mgKOH / g or more, and from the viewpoint of suppressing image bleeding, it is 350 mgKOH / g or less, preferably 300 mgKOH / g or less, and more preferably 270 mgKOH / g or less. The acid value of the shell resin A2 can be calculated from the mass ratio of the constituent components. When the shell resin A2 is a resin obtained by crosslinking a carboxy group-containing polymer A2p with a reactive group-containing compound (R2E), the acid value of the shell resin A2 is derived from the carboxy groups of the carboxy group-containing polymer A2p constituting the resin A2, and can be obtained by calculating the carboxy groups of the carboxy group-containing polymer A2p that have not reacted with the reactive group-containing compound (R2E) using the following formula. Acid value (mg KOH / g) of shell resin A2=[Acid value (mg KOH / g) of carboxy group-containing polymer A2p×[(100−crosslinking rate (mol%)) / 100]×mass (g) of carboxy group-containing polymer A2p] / (mass (g) of carboxy group-containing polymer A2p+mass (g) of reactive group-containing compound (R2E)) Here, the crosslinking rate (mol %) can be calculated by the following formula. Crosslinking rate (mol %)=[(number of moles of reactive groups in reactive group-containing compound (R2E)) / (number of moles of carboxy groups in carboxy group-containing polymer A2p)]×100

[0030] From the viewpoint of suppressing image bleeding, the crosslink density (q2) of the shell resin A2 is preferably 2.0 mmol / g or less, more preferably 1.0 mmol / g or less, even more preferably 0.7 mmol / g or less, and even more preferably 0.3 mmol / g or less, and from the viewpoint of improving intermittent ejection properties, it is preferably 0 mmol / g or more, and even more preferably 0 mmol / g. The crosslink density (q2) of the shell resin A2 is calculated by the following formula (2). Crosslink density (q2) (mmol / g)=[[(number of moles of structural units derived from reactive group-containing compound (R2) in shell resin A2)×(number of reactive groups possessed by reactive group-containing compound (R2)] / (mass of shell resin A2 in resin particle A)]×1000

[0031] When the shell resin A2 is a resin having no crosslinked structure, the weight average molecular weight of the shell resin A2 is preferably 5,000 or more, more preferably 7,000 or more, and even more preferably 10,000 or more from the viewpoint of improving intermittent dischargeability, and is preferably 150,000 or less, more preferably 100,000 or less, even more preferably 50,000 or less, still more preferably 30,000 or less, and even more preferably 20,000 or less from the same viewpoint as above. The weight average molecular weight of the shell resin A2 can be measured by the method described in the Examples.

[0032] In the core-shell type resin particles A, the ratio of the mass of the core resin A1 to the total mass of the core resin A1 and the shell resin A2 [core resin A1 / (core resin A1+shell resin A2)] (hereinafter also referred to as "mass ratio [core resin A1 / (core resin A1+shell resin A2)]") is preferably 0.30 or more, more preferably 0.40 or more, even more preferably 0.50 or more, and even more preferably 0.60 or more from the viewpoint of improving intermittent ejection properties, and is preferably 0.90 or less, more preferably 0.80 or less, and even more preferably 0.70 or less from the viewpoint of suppressing image bleeding.

[0033] (Production of resin particles A having a core-shell structure) There is no limitation on the method for producing resin particles A having a core-shell structure (core-shell type resin particles A). However, it is preferable that the core-shell type resin particles A are (i) those obtained by dispersing crosslinked polymer particles with a carboxy group-containing polymer A2p containing a structural unit derived from a carboxylic acid monomer (a2-1), or (ii) those formed by multi-stage emulsion polymerization.

[0034] In the case of (i), when the shell resin A2 is a resin obtained by crosslinking a carboxy group-containing polymer A2p with a reactive group-containing compound (R2E), it is preferable that the crosslinked polymer particles are dispersed in the carboxy group-containing polymer A2p, and then the carboxy group-containing polymer A2p is crosslinked with the reactive group-containing compound (R2E). That is, in the case of method (i), the crosslinked polymer particles constitute the core portion, and the carboxy group-containing polymer A2p or a resin obtained by crosslinking the carboxy group-containing polymer A2p with the reactive group-containing compound (R2E) constitutes the shell portion.

[0035] As the method (i), a method including a step (i-1) of emulsion-polymerizing the monomer (a1) constituting the core resin A1 in the presence of the carboxyl group-containing polymer A2p to obtain the core-shell type resin particles A is preferable. Specifically, the step (i-1) is preferably a step of mixing and emulsifying an aqueous dispersion of the monomer (a1) and the carboxyl group-containing polymer A2p to obtain a monomer emulsion, and then adding a polymerization initiator to the monomer emulsion to perform emulsion polymerization to obtain an aqueous dispersion of the core-shell type resin particles A including a core part made of the core resin A1 and a shell part made of the carboxyl group-containing polymer A2p (shell part resin A2). When the shell resin A2 is a resin obtained by crosslinking a carboxy group-containing polymer A2p with a reactive group-containing compound (R2E), it is preferable that the method includes, after step (i-1), step (i-2) of reacting the carboxy group-containing polymer A2p constituting the shell resin A2 of the core-shell type resin particle A with the reactive group-containing compound (R2E) to obtain a core-shell type resin particle A having a crosslinked structure introduced into the shell resin A2. Specifically, step (i-2) is preferably a step of adding a reactive group-containing compound (R2) to the aqueous dispersion of the core-shell resin particles A obtained in step (i-1) and reacting the carboxy group-containing polymer A2p constituting the shell resin A2 of the core-shell resin particles A with the reactive group-containing compound (R2) to obtain an aqueous dispersion of the core-shell resin particles A in which a crosslinked structure has been introduced into the shell resin A2.

[0036] The monomers constituting the carboxyl group-containing polymer A2p used in the method (i) include the same as those exemplified for the shell resin A2 described above, and the preferred examples are also the same. From the viewpoint of improving intermittent ejection properties and suppressing image bleeding, the carboxyl group-containing polymer A2p is a vinyl resin that contains a structural unit derived from a carboxylic acid monomer (a2-1), preferably a structural unit derived from a carboxylic acid monomer (a2-1) and a structural unit derived from a hydrophobic monomer (a2-2), more preferably a structural unit derived from a carboxylic acid monomer (a2-1) and a structural unit derived from a hydrophobic monomer (a2-2), as described above. From the viewpoint of improving intermittent ejection properties and suppressing image bleeding, the content of structural units derived from the carboxylic acid monomer (a2-1) in the carboxy group-containing polymer A2p is preferably 5 mass% or more, more preferably 10 mass% or more, even more preferably 20 mass% or more, still more preferably 25 mass% or more, and is preferably 50 mass% or less, more preferably 45 mass% or less, even more preferably 40 mass% or less, and still more preferably 35 mass% or less. From the viewpoint of improving intermittent ejection properties and suppressing image bleeding, the content of the structural unit derived from the hydrophobic monomer (a2-2) in the carboxy group-containing polymer A2p is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, still more preferably 65% ​​by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and still more preferably 75% by mass or less. The carboxy group-containing polymer A2p may contain other structural units than the above-mentioned structural units, provided that the effects of the present invention are not impaired.

[0037] The acid value of the carboxyl group-containing polymer A2p is preferably 90 mgKOH / g or more, more preferably 100 mgKOH / g or more, even more preferably 150 mgKOH / g or more, and even more preferably 200 mgKOH / g or more from the viewpoint of improving intermittent ejection, and is preferably 350 mgKOH / g or less, more preferably 300 mgKOH / g or less, and even more preferably 250 mgKOH / g or less from the viewpoint of suppressing image bleeding. The acid value of the carboxyl group-containing polymer A2p can be measured by the method described in the examples. It can also be calculated from the mass ratio of the monomer components constituting the polymer. The weight average molecular weight of the carboxyl group-containing polymer A2p is preferably 5,000 or more, more preferably 7,000 or more, and even more preferably 10,000 or more from the viewpoint of improving intermittent dischargeability, and is preferably 150,000 or less, more preferably 100,000 or less, even more preferably 50,000 or less, still more preferably 30,000 or less, and even more preferably 20,000 or less from the same viewpoint as above. The weight average molecular weight of the carboxyl group-containing polymer A2p can be measured by the method described in the Examples.

[0038] Method (ii) is a method including a step (ii-1) of forming a core resin A1 by polymerizing a monomer (a1) constituting the core resin A1, and then further polymerizing a monomer (a2) constituting a shell resin A2 in the presence of the core resin A1 to form a shell resin A2 on the surface of the core resin A1, thereby obtaining a core-shell type resin particle A. In the method (ii), the core resin A1 and the shell resin A2 may be formed continuously, or the core resin A1 may be isolated and purified, and then the shell resin A2 may be formed on the surface of the core resin A1. Specifically, step (ii-1) preferably includes a step of mixing a monomer (a1) constituting the core resin A1 with an aqueous medium, and heating the mixture with stirring in the presence of a polymerization initiator to form the core resin A1, and then mixing a monomer (a2) constituting the shell resin A2 with an aqueous medium in the presence of the core resin A1, and heating the mixture with stirring in the presence of a polymerization initiator to form the shell resin A2 on the surface of the core resin A1, thereby obtaining the core-shell type resin particles A. Both the monomer (a1) forming the core resin A1 and the monomer (a2) forming the shell resin A2 may be dropped directly into the reaction vessel or may be added dropwise after being emulsified in an aqueous medium in advance, and may also contain a polymerization initiator. In the method (ii), when the shell resin A2 is a resin having a crosslinked structure derived from a reactive group-containing compound (R2), the method may be such that the monomer (a2) constituting the shell resin A2 used in step (ii-1) contains the reactive group-containing compound (R2), thereby forming a structural unit derived from the carboxylic acid monomer (a2-1) constituting the shell resin A2 and a crosslinked structure derived from the reactive group-containing compound (R2). Similarly to step (i-2) in the method (i), the method may include a step (ii-2) of reacting the core-shell type resin particle A with the reactive group-containing compound (R2) after step (ii-1) to obtain a core-shell type resin particle A having a crosslinked structure introduced into the shell resin A2.

[0039] The polymerization initiator used in the production of the core-shell type resin particles A is preferably a water-soluble polymerization initiator that is soluble in an aqueous medium. Here, the term "aqueous medium" refers to a medium in which water accounts for the largest proportion by mass. As the polymerization initiator, known initiators such as inorganic peroxides such as potassium persulfate, sodium persulfate, and ammonium persulfate; azo initiators such as 4,4'-azobis(4-cyanovaleric acid); and redox initiators in which a peroxide is combined with a reducing agent such as sodium sulfite can be used. In addition, a surfactant may be used as an emulsifier during polymerization. Examples of such surfactants include nonionic surfactants, anionic surfactants, and cationic surfactants. In the case of method (ii), it is preferable to use an anionic surfactant. Examples of anionic surfactants include fatty acid salts, alkyl sulfate ester salts, alkylbenzene sulfonate salts, polyoxyethylene alkylphenyl ether sulfate ester salts, polyoxyethylene aralkyl aryl ether sulfate ester salts, and polyoxyethylene alkyl ether sulfate ester salts, and polyoxyethylene alkyl ether sulfate ester salts are more preferable. The polymerization conditions can be appropriately adjusted depending on the type of polymerization initiator, etc., but the polymerization temperature is preferably 50° C. to 90° C., and the polymerization time is preferably 1 hour to 20 hours. The polymerization atmosphere is preferably a nitrogen gas atmosphere, an inert gas atmosphere such as argon, etc.

[0040] As the method for producing the core-shell type resin particles A, among the above-mentioned methods (i) and (ii), the method (i) is preferred from the viewpoint of improving intermittent ejection property and suppressing image bleeding. That is, the core-shell type resin particles A are preferably prepared by dispersing crosslinked polymer particles with a carboxyl group-containing polymer A2p or a resin obtained by crosslinking a carboxyl group-containing polymer A2p with a reactive group-containing compound (R2E). In the case of the method (i), the core-shell type resin particles A can be obtained without using an anionic surfactant, so that the water-based ink of the present invention can be substantially free of anionic surfactant, and image bleeding can be further suppressed.

[0041] In preparing the aqueous dispersion of the carboxyl group-containing polymer A2p used in the method (i), a neutralizing agent may be used. When using a neutralizing agent, it is preferable to neutralize the aqueous dispersion to a pH of 7 or more and 11 or less. The neutralizing agent includes alkali metal hydroxides, organic amines, ammonia, and the like. The alkali metal hydroxide includes lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide. Examples of the organic amine include trimethylamine, ethylamine, diethylamine, triethylamine, triethanolamine, diethanolamine, n-methyldiethanolamine, and n-methylethanolamine. The neutralizing agent is preferably one or more selected from the group consisting of alkali metal hydroxides and organic amines, more preferably an organic amine, even more preferably one or more selected from the group consisting of triethanolamine and n-methylethanolamine, and even more preferably triethanolamine. The amount of the neutralizing agent used is preferably 20 mol% or more, more preferably 30 mol% or more, even more preferably 40 mol% or more, and preferably 200 mol% or less, more preferably 100 mol% or less, even more preferably 80 mol% or less. Here, the equivalent of the neutralizing agent used can be calculated by the following formula: When the equivalent of the neutralizing agent used is 100 mol % or less, it is synonymous with the degree of neutralization, and when the equivalent of the neutralizing agent used in the following formula exceeds 100 mol %, it means that the neutralizing agent is in excess relative to the carboxy groups of the carboxy group-containing polymer A2p, and the degree of neutralization of the carboxy group-containing polymer A2p in this case is considered to be 100 mol %. Equivalent amount of neutralizing agent used (mol %)=[(mass of neutralizing agent added (g) / equivalent amount of neutralizing agent (g / mol)) / [(acid value of carboxyl group-containing polymer A2p (mg KOH / g)×mass of carboxyl group-containing polymer A2p (g)) / (56.1×1,000)]]×100

[0042] The carboxyl group-containing polymer A2p used in the method (i) may be an appropriately synthesized polymer or a commercially available product. Commercially available products of the carboxy group-containing polymer A2p include, for example, acrylic acid / styrene copolymers such as "JONCRYL 61", "JONCRYL 67", "JONCRYL 611", "JONCRYL 678", "JONCRYL 680", "JONCRYL 690" and "JONCRYL 819" (all manufactured by BASF Japan Ltd.); and polyacrylic acids such as "ARON AC-10SL" (manufactured by Toagosei Co., Ltd.).

[0043] The average particle size of the core-shell type resin particles A in the aqueous dispersion is preferably 20 nm or more, more preferably 30 nm or more, even more preferably 40 nm or more, and is preferably 150 nm or less, more preferably 100 nm or less, even more preferably 80 nm or less, and still more preferably 60 nm or less. The average particle size of the core-shell resin particles A in the water-based ink of the present invention is preferably the same as the average particle size in the water-based dispersion, and a preferred embodiment of the average particle size of the core-shell resin particles A in the water-based ink of the present invention is the same as the preferred embodiment of the average particle size in the water-based dispersion. The average particle size of the core-shell type resin particles A in the aqueous dispersion is measured by the method described in the Examples.

[0044] <Pigments> The water-based ink of the present invention contains a pigment. Examples of the pigment include white pigments such as titanium oxide; black pigments such as carbon black; and chromatic pigments such as azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. The form of the pigment in the water-based ink of the present invention may be a form dispersed with a polymer dispersant or a surfactant, or a form of a self-dispersing pigment in which a hydrophilic functional group is chemically or physically introduced onto the pigment surface and dispersed without using a polymer dispersant or a surfactant. Among these, the form of the pigment in the water-based ink of the present invention is preferably a form dispersed with a polymer dispersant (hereinafter also referred to as "polymer dispersant B") from the viewpoint of improving intermittent ejection properties and suppressing image bleeding. The form in which the pigment is dispersed by the polymer dispersant B is preferably in the form of polymer particles containing the pigment (hereinafter, also referred to as "pigment-containing polymer particles").

[0045] (Polymer Dispersant B) It is preferable that the polymer dispersant B has a function as a pigment dispersant that exhibits a pigment dispersion effect, and also has a function of assisting the fixation of the polymer dispersant to the recording medium. The polymeric dispersant is preferably a water-insoluble polymer having anionic groups. The anionic group may be a group that dissociates to release a hydrogen ion, such as a carboxyl group (-COOM), a sulfonic acid group (-SO3M), or a phosphoric acid group (-OPO3M2), or a group in the form of a dissociated ion (-COO - , -SO3 - , -OPO3 2- , -OPO3 - In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. Moreover, the term "water-insoluble polymer" means that when a polymer that has been dried at 105°C for 2 hours and has reached a constant weight is dissolved in 100 g of water at 25°C until saturation is reached, the amount of dissolution is 10 g or less. The amount of dissolution is preferably 5 g or less, more preferably 1 g or less. When the anionic group is neutralized with a neutralizing agent, the amount of dissolution is determined by the amount of dissolution measured in the presence of the neutralizing agent under conditions where the mass ratio of the polymer to the neutralizing agent is the same as that in the water-based ink for inkjet printing.

[0046] Specific examples of the polymer dispersant B include vinyl resins, polyester resins, and polyurethane resins. Among these, from the viewpoint of improving intermittent ejection properties and suppressing image bleeding, vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds) are preferred. From the viewpoint of improving intermittent ejection property and suppressing image bleeding, the polymer dispersant is preferably a vinyl resin containing a structural unit derived from a carboxylic acid monomer (b-1), more preferably a vinyl resin containing a structural unit derived from a carboxylic acid monomer (b-1) and a structural unit derived from a hydrophobic monomer (b-2). The polymer dispersant may further contain a structural unit derived from a nonionic monomer (b-3) in addition to the structural unit derived from the carboxylic acid monomer (b-1) and the structural unit derived from the hydrophobic monomer (b-2). The polymer dispersant B may have the same monomer composition and weight average molecular weight as the carboxy group-containing polymer A2p.

[0047] [Carboxylic acid monomer (b-1)] As the carboxylic acid monomer (b-1), from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, one or more selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, crotonic acid, and itaconic acid are preferred. Among these, from the same viewpoint as above, the carboxylic acid monomer (a2-1) is more preferably one or more selected from the group consisting of acrylic acid and methacrylic acid. The carboxylic acid monomer (b-1) may be used alone or in combination of two or more kinds.

[0048] [Hydrophobic monomer (b-2)] The "hydrophobicity" of the hydrophobic monomer (b-2) is the same as that of the above-mentioned hydrophobic monomer (a2-2). As the hydrophobic monomer (b-2), from the viewpoint of improving intermittent ejection properties and suppressing image bleeding, one or more types selected from the group consisting of esters of monohydric alcohols having 1 to 22 carbon atoms and (meth)acrylic acid, and aromatic group-containing monomers are preferably used. Examples of the ester of (meth)acrylic acid and a monohydric alcohol having 1 to 22 carbon atoms include those exemplified in the above-mentioned ester (a1-1) of a monohydric alcohol having 1 to 22 carbon atoms and (meth)acrylic acid. The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group with 6 to 22 carbon atoms, which may have a substituent containing a hetero atom, and more preferably at least one selected from a styrene-based monomer and an aromatic group-containing (meth)acrylate. The molecular weight of the aromatic group-containing monomer is preferably less than 500. As the styrene-based monomer and the aromatic group-containing (meth)acrylate, those exemplified in the hydrophobic monomer (a2-2) can be mentioned. Among these, from the viewpoint of improving intermittent ejection properties and suppressing image bleeding, the hydrophobic monomer (b-2) is preferably an aromatic group-containing monomer, more preferably a styrene-based monomer, even more preferably one or more selected from the group consisting of styrene and α-methylstyrene, and even more preferably styrene. The hydrophobic monomer (b-2) may be used alone or in combination of two or more kinds.

[0049] [Nonionic monomer (b-3)] The nonionic monomer (b-3) is a monomer that has a high affinity for water or a water-soluble organic solvent, and is, for example, a monomer that contains a hydroxyl group or a polyalkylene glycol chain. Specific examples of the nonionic monomer (b-3) include those described in paragraph

[0018] of JP 2018-83938 A. Among them, one or more selected from the group consisting of polyalkylene glycol (meth)acrylate and alkoxy polyalkylene glycol (meth)acrylate are preferred, alkoxy polyalkylene glycol (meth)acrylate is more preferred, and methoxy polyethylene glycol (n = 1 to 30) (meth)acrylate is even more preferred. Here, n represents the average number of moles of oxyethylene groups added. The nonionic monomer (b-3) component can be used alone or in combination of two or more kinds.

[0050] From the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, the content of the structural unit derived from the carboxylic acid monomer (b-1) in the polymer dispersant B is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, still more preferably 25% by mass or more, and is preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, and still more preferably 35% by mass or less. From the viewpoint of improving intermittent ejection properties and suppressing image bleeding, the content of the structural unit derived from the hydrophobic monomer (b-2) in the polymer dispersant B is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, still more preferably 65% ​​by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and still more preferably 75% by mass or less. When the polymer dispersant B contains a structural unit derived from the nonionic monomer (b-3), the content of the structural unit derived from the nonionic monomer (b-3) in the polymer dispersant B is preferably 30 mass% or less, more preferably 20 mass% or less, even more preferably 10 mass% or less, and still more preferably 5 mass% or less.

[0051] The polymer dispersant B is produced by copolymerizing the monomer (b) containing the carboxylic acid monomer (b-1), the hydrophobic monomer (b-2), and, if necessary, the nonionic monomer (b-3) by a known polymerization method such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc. Among these polymerization methods, the solution polymerization method is preferred. There is no limitation on the solvent used in the solution polymerization method, but polar solvents such as water, lower aliphatic alcohols, ketones such as methyl ethyl ketone, ethers, and esters are preferred. In the polymerization, a polymerization initiator such as an azo compound or a persulfate, or a polymerization chain transfer agent such as a mercaptan can be used. The polymerization temperature varies depending on the types of polymerization initiator, monomer, solvent, etc. used, but is preferably 30° C. or higher, more preferably 50° C. or higher, and is preferably 100° C. or lower, more preferably 90° C. or lower. The polymeric dispersant is preferably neutralized with a neutralizing agent as described below.

[0052] The acid value of the polymer dispersant B is preferably 90 mgKOH / g or more, more preferably 100 mgKOH / g or more, even more preferably 150 mgKOH / g or more, and even more preferably 200 mgKOH / g or more from the viewpoint of improving intermittent ejection, and is preferably 350 mgKOH / g or less, more preferably 300 mgKOH / g or less, and even more preferably 250 mgKOH / g or less from the viewpoint of suppressing image bleeding. The acid value of the polymer dispersant B can be measured by the method described in the examples. It can also be calculated from the mass ratio of the constituent monomer components. From the viewpoint of improving intermittent dischargeability, the weight average molecular weight of the polymer dispersant B is preferably 5,000 or more, more preferably 7,000 or more, and even more preferably 10,000 or more, and from the same viewpoint as above, it is preferably 150,000 or less, more preferably 100,000 or less, even more preferably 50,000 or less, still more preferably 30,000 or less, and even more preferably 20,000 or less. The weight average molecular weight of the polymer dispersant B can be measured by the method described in the Examples.

[0053] The polymer dispersant B preferably has a crosslinked structure obtained by crosslinking using a crosslinking agent. That is, in the present invention, the form of the pigment-containing polymer particles is preferably a crosslinked polymer particle containing a pigment (hereinafter also referred to as "pigment-containing crosslinked polymer particle"). In this case, the polymer constituting the pigment-containing crosslinked polymer particles is preferably the above-mentioned vinyl resin crosslinked by a crosslinking agent. By crosslinking, the vinyl resin having a two-dimensional structure becomes a crosslinked polymer having a three-dimensional structure by the crosslinking agent, and the crosslinked polymer is firmly adsorbed or fixed on the pigment surface, suppressing the aggregation of the pigment in the ink and further suppressing the swelling of the polymer, which is considered to improve the intermittent ejection property.

[0054] From the viewpoint of improving the intermittent ejection property, the crosslinking agent is preferably a compound having a plurality of epoxy groups in the molecule (an epoxy group-containing compound). The epoxy group-containing compound is preferably a compound having a plurality of glycidyl ether groups in the molecule, and more preferably a polyglycidyl ether of a polyhydric alcohol having a hydrocarbon group having 3 to 8 carbon atoms. The epoxy group-containing compounds can be used alone or in combination of two or more.

[0055] Specific examples of the epoxy group-containing compound include polyglycidyl ethers such as polypropylene glycol diglycidyl ether, glycerin polyglycidyl ether, polyglycerin polyglycidyl ether, trimethylolpropane polyglycidyl ether, 1,6-hexanediol diglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether. Among these, at least one selected from the group consisting of 1,6-hexanediol diglycidyl ether, trimethylolpropane polyglycidyl ether, and pentaerythritol polyglycidyl ether is preferred. From the viewpoint of more efficiently crosslinking with the carboxyl group of the vinyl resin in an aqueous medium mainly composed of water, the epoxy equivalent of the epoxy group-containing compound is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and is preferably 300 or less, more preferably 200 or less, even more preferably 170 or less.

[0056] It is preferable that at least a portion of the anionic groups of the polymer dispersant B is neutralized with a neutralizing agent, which is believed to increase the charge repulsive force exhibited after neutralization, suppress the aggregation of pigment particles in the water-based ink, improve the dispersion stability of the pigment, and improve the intermittent ejection properties. In the case of neutralization, it is preferable to neutralize so that the pH is 7 or more and 11 or less. Examples of the neutralizing agent include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonia, and organic amines, and preferably organic amines. Examples of the organic amines include those exemplified in the neutralizing agent used in the preparation of the aqueous dispersion of the carboxyl group-containing polymer A2p described above. Also, the polymer dispersant B may be neutralized in advance.

[0057] The pigment-containing polymer particles are preferably blended in the water-based ink of the present invention as an aqueous dispersion. The aqueous dispersion of the pigment-containing polymer particles is preferably produced by a method including the following steps I and II. Step I: A step of dispersing a pigment mixture containing a pigment, a polymer dispersant B, an organic solvent, water, and, if necessary, a neutralizing agent to obtain a dispersion. Step II: A step of removing the organic solvent from the dispersion obtained in step I to obtain an aqueous dispersion of pigment-containing polymer particles. When the pigment-containing polymer particles are in the form of pigment-containing crosslinked polymer particles, they can be produced more efficiently by a method further including the following step III. Step III: A step of adding a crosslinking agent to the aqueous dispersion of pigment-containing polymer particles obtained in step II to perform crosslinking treatment to obtain an aqueous dispersion of pigment-containing crosslinked polymer particles.

[0058] The dispersion treatment in step I can be carried out by a known method using a kneading machine such as a roll mill or a kneader, a high-pressure homogenizer such as a Microfluidizer (manufactured by Microfluidics), a paint shaker, a media-type dispersing machine such as a bead mill, or the like. The organic solvent in step II can be removed by a known method. The temperature of the crosslinking treatment in step III is, from the viewpoints of completion of the crosslinking reaction and economic efficiency, preferably 50° C. or higher, more preferably 70° C. or higher, and preferably 95° C. or lower, more preferably 92° C. or lower. From the same viewpoints as above, the time of the crosslinking treatment is, from the same viewpoints as above, preferably 0.5 hours or higher, more preferably 1 hour or higher, and preferably 10 hours or lower, more preferably 6 hours or lower.

[0059] From the viewpoint of improving intermittent ejection properties, the average particle size of the pigment-containing polymer particles or pigment-containing crosslinked polymer particles in the aqueous dispersion is preferably 60 nm or more, more preferably 70 nm or more, even more preferably 80 nm or more, still more preferably 100 nm or more, and is preferably 200 nm or less, more preferably 160 nm or less, and even more preferably 155 nm or less. The average particle size of the pigment-containing polymer particles or pigment-containing crosslinked polymer particles in the aqueous dispersion is measured by the method described in the Examples. It is preferable that the pigment-containing polymer particles and the pigment-containing crosslinked polymer particles do not swell or shrink, and do not aggregate with each other. The average particle size of the pigment-containing polymer particles or the pigment-containing crosslinked polymer particles in the water-based ink of the present invention is preferably the same as the average particle size in the water-based dispersion, and preferred aspects of the average particle size of the pigment-containing polymer particles or the pigment-containing crosslinked polymer particles in the water-based ink of the present invention are the same as the preferred aspects of the average particle size in the water-based dispersion.

[0060] <Water-soluble organic solvent> The water-based ink of the present invention contains a water-soluble organic solvent. The water-soluble organic solvent is preferably one that can be mixed with water in any ratio. The water-soluble organic solvent may be used alone or in combination of two or more kinds. The boiling point of the water-soluble organic solvent is preferably 90° C. or higher, more preferably 150° C. or higher, even more preferably 180° C. or higher, and is preferably 250° C. or lower, more preferably 240° C. or lower, even more preferably 230° C. or lower. When two or more water-soluble organic solvents are used, the boiling point value is a weighted average value weighted by the content (mass%) of each water-soluble organic solvent. Examples of the water-soluble organic solvent include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, etc. Among these, the water-soluble organic solvent is preferably at least one selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers, from the viewpoint of improving intermittent ejection properties and suppressing image bleeding.

[0061] Examples of the polyhydric alcohol include polyalkylene glycols such as ethylene glycol, propylene glycol, 1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol, diethylene glycol, dipropylene glycol, and triethylene glycol, glycerin, and trimethylolpropane. Among these, one or more selected from the group consisting of propylene glycol, 1,2-hexanediol, dipropylene glycol, triethylene glycol, and glycerin are preferred.

[0062] Examples of polyhydric alcohol alkyl ethers include diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, triethylene glycol monoisobutyl ether, etc. Among these, at least one selected from the group consisting of diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, and diethylene glycol monoisobutyl ether is preferred. As the water-soluble organic solvent, it is preferable to use propylene glycol as the polyhydric alcohol and diethylene glycol monoisobutyl ether as the polyhydric alcohol alkyl ether in combination.

[0063] <Water> The water-based ink of the present invention contains water. The water used in the water-based ink of the present invention is preferably pure water or ion-exchanged water from the viewpoint of preventing the inclusion of unintended substances.

[0064] The water-based ink of the present invention may contain various additives, such as surfactants, humectants, wetting agents, wetting / penetrating agents, viscosity adjusters, defoamers, preservatives, antifungals, and rust inhibitors, as necessary. Examples of the surfactant include nonionic surfactants, anionic surfactants, amphoteric surfactants, etc. Among these, nonionic surfactants are preferred. Examples of nonionic surfactants include polyoxyalkylene alkyl ether surfactants, acetylene glycol surfactants, polyhydric alcohol surfactants, fatty acid alkanolamides, silicone surfactants, and fluorine-based surfactants.

[0065] (Production of Water-Based Inks for Ink-Jet Printing) The water-based ink of the present invention can be produced by mixing an aqueous dispersion of core-shell type resin particles A, an aqueous dispersion of pigment-containing polymer particles or pigment-containing crosslinked polymer particles, a water-soluble organic solvent, and, if necessary, various additives such as water and a surfactant. There is no particular limitation on the method of mixing each component. Among these, the aqueous dispersion of core-shell type resin particles A is preferably obtained by either the above-mentioned method (i) or method (ii), and more preferably by the above-mentioned method (i). That is, the method of producing the water-based ink of the present invention preferably includes a step of obtaining core-shell type resin particles A by emulsion polymerization of the monomer (a1) constituting the core part resin A1 in the presence of a carboxyl group-containing polymer A2p.

[0066] (Composition of Water-Based Ink for Ink-Jet Printing) The content of the core-shell resin particles A in the water-based ink of the present invention is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more, from the viewpoints of improving intermittent ejection properties and suppressing image bleeding, and from the same viewpoints as above, is preferably 20% by mass or less, more preferably 16% by mass or less, even more preferably 12% by mass or less, and even more preferably 10% by mass or less.

[0067] The pigment content in the water-based ink of the present invention is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more from the viewpoint of image density, and is preferably 18% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of intermittent ejection property.

[0068] The mass ratio of the pigment content to the core-shell type resin particles (A) in the water-based ink of the present invention [pigment / core-shell type resin particles (A)] is preferably 0.5 or more, more preferably 0.7 or more, and even more preferably 1.0 or more from the viewpoint of image density, and is preferably 3.0 or less, more preferably 2.5 or less, even more preferably 2.0 or less, and even more preferably 1.7 or less, from the viewpoint of improving intermittent ejection properties and suppressing image bleeding.

[0069] When the pigment is dispersed with polymer dispersant B, the mass ratio of the pigment content to the total content of the pigment and polymer dispersant B in the water-based ink of the present invention [pigment / (pigment+polymer dispersant B)] is preferably 0.6 or more, more preferably 0.7 or more, and even more preferably 0.8 or more from the viewpoint of image density, and is preferably 0.99 or less, more preferably 0.95 or less, and even more preferably 0.9 or less from the viewpoint of improving intermittent ejection properties. When the polymer dispersant is crosslinked with a crosslinking agent, the content of polymer dispersant B in the water-based ink of the present invention is the total content of polymer dispersant B and the crosslinking agent before crosslinking. When the pigment is dispersed with the polymer dispersant B, the mass ratio of the pigment content to the total content of the core-shell type resin particles A and the polymer dispersant B in the water-based ink of the present invention [pigment / (core-shell type resin particles A+polymer dispersant B)] is preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.4 or more, still more preferably 0.5 or more, still more preferably 0.7 or more, and still more preferably 1.0 or more from the viewpoint of image density, and is preferably 4.5 or less, more preferably 4.0 or less, even more preferably 3.5 or less, still more preferably 3.0 or less, still more preferably 2.5 or less, and still more preferably 2.0 or less from the viewpoint of improving intermittent ejection property and suppressing image bleeding. When the polymer dispersant B is crosslinked with a crosslinking agent, the content of the polymer dispersant B in the water-based ink of the present invention is the total content of the polymer dispersant B and the crosslinking agent before crosslinking. When the pigment is dispersed in polymer dispersant B, the mass ratio of the core-shell resin particles A to the total content of the core-shell resin particles A and polymer dispersant B in the water-based ink of the present invention [core-shell resin particles A / (core-shell resin particles A+polymer dispersant B)] is, from the viewpoint of improving intermittent ejection properties and from the viewpoint of suppressing image bleeding, preferably 0.4 or more, more preferably 0.5 or more, even more preferably 0.6 or more, still more preferably 0.7 or more, still more preferably 0.8 or more, and from the same viewpoints as above, is preferably 0.98 or less, more preferably 0.97 or less, even more preferably 0.96 or less, and still more preferably 0.95 or less.

[0070] The content of the water-soluble organic solvent in the water-based ink of the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less. From the viewpoint of reducing the environmental impact, the water content in the water-based ink of the present invention is preferably 40% by mass or more, more preferably 45% by mass or more, even more preferably 50% by mass or more, still more preferably 55% by mass or more, still more preferably 60% by mass or more, and is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0071] From the viewpoint of suppressing bleeding of images, it is preferable that the water-based ink of the present invention contains substantially no anionic surfactant. Here, "substantially free of anionic surfactant" means that the content of anionic surfactant in the water-based ink of the present invention is preferably 1% by mass or less, more preferably 0.5% by mass or less, even more preferably 0.3% by mass or less, and even more preferably 0% by mass. Examples of anionic surfactants include fatty acid salts, alkyl sulfate salts, alkylbenzene sulfonates, polyoxyethylene alkylphenyl ether sulfate salts, polyoxyethylene aralkyl aryl ether sulfate salts, polyoxyethylene alkyl ether sulfate salts, etc.

[0072] The viscosity of the water-based ink of the present invention at 32°C is preferably 2 mPa s or more, more preferably 3 mPa s or more, even more preferably 5 mPa s or more, and preferably 12 mPa s or less, more preferably 9 mPa s or less, even more preferably 7 mPa s or less. The viscosity of the water-based ink can be measured using an E-type viscometer. From the viewpoint of improving intermittent ejection, the pH of the water-based ink of the present invention is preferably 7.0 or more, more preferably 7.2 or more, and even more preferably 7.5 or more. From the viewpoint of member resistance and skin irritation, the pH is preferably 11 or less, more preferably 10 or less, and even more preferably 9.5 or less. The pH of the water-based ink can be measured by a conventional method.

[0073] The recording medium to which the water-based ink of the present invention is applied includes high-absorbency plain paper, low-absorbency coated paper, and resin film. The coated paper includes general-purpose glossy paper and multicolor foam gloss paper, and the resin film includes polyester film, polyvinyl chloride film, polypropylene film, polyethylene film, and the like. The resin film may be a biaxially stretched film, a uniaxially stretched film, or a non-stretched film. EXAMPLES

[0074] In the following Preparation Examples, Production Examples, Examples and Comparative Examples, "parts" refers to "parts by mass" unless otherwise specified. Measurements of various physical properties were carried out by the following methods.

[0075] (1) Acid value of carboxyl group-containing polymer A2p or polymer dispersant B The measurement was performed according to the neutralization titration method described in JIS K0070-1992, except that the measurement solvent was changed from a mixed solvent of ethanol and ether to a mixed solvent of acetone and toluene [acetone:toluene=1:1 (volume ratio)].

[0076] (2) Weight average molecular weight of carboxyl group-containing polymer A2p (shell resin A2) or polymer dispersant B The measurement was performed by gel permeation chromatography under the following conditions. GPC equipment: Tosoh Corporation "HLC-8320GPC" Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolum Super AW-H" manufactured by Tosoh Corporation Eluent: N,N-dimethylformamide with phosphoric acid and lithium bromide dissolved at concentrations of 60mmol / L and 50mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kits with known molecular weights "PStQuick B (F-550, F-80, F-10, F-1, A-1000)" and "PStQuick C (F-288, F-40, F-4, A-5000, A-500)" (both manufactured by Tosoh Corporation) Measurement sample: 0.1 g of anionic polymer P was mixed with 10 mL of the eluent in a glass vial, stirred with a magnetic stirrer at 25° C. for 10 hours, and filtered with a syringe filter “DISMIC-13HP” (PTFE 0.2 μm, manufactured by Advantec Co., Ltd.) to obtain a liquid.

[0077] (3) Average particle size of core-shell type resin particles A in the aqueous dispersion, and average particle size of pigment-containing polymer particles or pigment-containing crosslinked polymer particles in the aqueous dispersion Measurement was performed by cumulant analysis using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.) The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent, and the obtained cumulant average particle size was taken as the average particle size of the core-shell type resin particles A, or the average particle size of the pigment-containing polymer particles or the pigment-containing crosslinked polymer particles. The measurement sample used to measure the average particle size of the core-shell type resin particles A has a concentration of the core-shell type resin particles A of about 5 × 10 -3 A dispersion diluted with water to a mass % was used. The measurement sample used to measure the average particle size of the pigment-containing polymer particles or the pigment-containing crosslinked polymer particles has a concentration of the pigment-containing polymer particles or the pigment-containing crosslinked polymer particles of about 2 × 10 -4 A dispersion diluted with water to a mass % was used.

[0078] (4) Solid content concentration 10.0 g of sodium sulfate, which had been kept constant in a desiccator, was weighed out into a 30 mL polypropylene container (φ: 40 mm, height: 30 mm), and about 1.0 g of the sample was added thereto and mixed, then weighed, and maintained at 105°C for 2 hours to remove volatile matter, and left in the desiccator for another 15 minutes, and the mass was measured. The mass of the sample after removing the volatile matter was taken as the solid content, and was divided by the mass of the sample added to obtain the solid content concentration (mass%).

[0079] (Preparation of Carboxy Group-Containing Polymer) Preparation Example 1-1 A monomer mixture was prepared by mixing 31 parts of acrylic acid and 69 parts of styrene. 5 parts of methyl ethyl ketone (hereinafter referred to as "MEK"), 0.25 parts of 3-mercaptopropionic acid as a polymerization chain transfer agent, and 10 mass % of the monomer mixture were mixed in a reaction vessel, and the inside of the vessel was thoroughly replaced with nitrogen gas. Meanwhile, a mixture of the remainder of the monomer mixture (90% by mass of the monomer mixture), 2.25 parts of the polymerization chain transfer agent, 75 parts of MEK, and 1.5 parts of 4,4'-azobis(4-cyanovaleric acid) ("V-501" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as an azo-based radical polymerization initiator was placed in a dropping funnel, and the monomer mixture in the reaction vessel was heated to 77°C while stirring under a nitrogen atmosphere, and the mixture in the dropping funnel was dropped over 5 hours. After the dropping was completed, a solution in which 0.5 parts of the polymerization initiator was dissolved in 5 parts of MEK was added, and the mixture was further reacted at 77°C for 2 hours to obtain a solution of a carboxyl group-containing polymer P1. The acid value of the carboxyl group-containing polymer P1 was 240 mgKOH / g and the weight average molecular weight was 13,900.

[0080] Preparation Examples 1-2 to 1-11 Solutions of carboxyl group-containing polymers P2 to P11 were obtained in the same manner as in Preparation Example 1-1, except that the blending amounts of acrylic acid, styrene, and 3-mercaptopropionic acid were changed as shown in Table 1. The acid values ​​and weight average molecular weights of the carboxyl group-containing polymers P2 to P11 are shown in Table 1.

[0081] [Table 1]

[0082] (Preparation of Water Dispersion of Carboxy Group-Containing Polymer) Preparation Example 2-1 The solution of the carboxyl group-containing polymer P1 obtained in Preparation Example 1-1 was dried under reduced pressure, and 80 parts of the solution was added with 300 parts of ion-exchanged water and 20.4 parts of triethanolamine (hereinafter referred to as "TEA") (Kishida Chemical Co., Ltd.) as an amine compound (neutralizing agent), and neutralized so that the ratio of the number of moles of triethanolamine to the number of moles of carboxyl groups in the carboxyl group-containing polymer P1 was 40 mol% (neutralizing agent usage equivalent: 40 mol%). The resulting aqueous solution was heated at 90°C for 5 hours while stirring at 150 rpm to obtain an aqueous dispersion of the carboxyl group-containing polymer P1 (solid content concentration: 20% by mass).

[0083] Preparation Examples 2-2 to 2-11 Aqueous dispersions of carboxyl group-containing polymers P2 to P11 were obtained in the same manner as in Preparation Example 2-1, except that the type of carboxyl group-containing polymer and the amounts of TEA and ion-exchanged water were changed as shown in Table 2.

[0084] [Table 2]

[0085] (Preparation of Water Dispersion of Pigment-Containing Crosslinked Polymer Particles) Manufacturing Example 1 To 68.2 parts of the aqueous dispersion of the carboxyl group-containing polymer P1 obtained in Preparation Example 2-1 (solid content concentration: 20% by mass) (effective content of the carboxyl group-containing polymer P1: 13.6 parts), which was used as the polymer dispersant B, were added 372 parts of ion-exchanged water, 28 parts of MEK, and 100 parts of a cyan pigment (CI Pigment Blue 15:3, manufactured by DIC Corporation), in that order, and the mixture was stirred for 60 minutes using a disper ("Ultra Disper" manufactured by Asada Iron Works Co., Ltd.) at 20°C with the disper blade rotating at 7,000 rpm, to obtain a pigment mixture. The resulting pigment mixture was subjected to a dispersion treatment with a Microfluidizer (trade name, manufactured by Microfluidics Corp.) at a pressure of 200 MPa for 10 passes to obtain a dispersion. From the obtained dispersion, MEK was removed at 60°C under reduced pressure, and then some of the water was removed. The mixture was then filtered through a filter with a pore size of 5 μm (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) to remove coarse particles, thereby obtaining an aqueous dispersion of pigment-containing polymer particles with a solid content of 22% by mass. 300 parts of the obtained aqueous dispersion of pigment-containing polymer particles was placed in a screw-capped glass bottle, and 1.83 parts of 1,6-hexanediol diglycidyl ether ("Denacol EX-212L" manufactured by Nagase ChemteX Corporation, epoxy equivalent: 135) was added as an epoxy group-containing compound so that 40 mol % of all carboxy groups of the polymer in the aqueous dispersion were crosslinked (crosslinking rate: 40 mol %). The bottle was then sealed and heated at 90°C for 5 hours while stirring with a stirrer. The temperature was then lowered to room temperature and the bottle was filtered through a filter with a pore size of 5 μm (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to remove coarse particles. Then, ion-exchanged water was added to adjust the solid concentration to 20 mass %, thereby obtaining an aqueous dispersion D1 of pigment-containing crosslinked polymer particles. The resulting aqueous dispersion D1 of pigment-containing crosslinked polymer particles had a pigment mass ratio to the total solids content [pigment / solids content] of 0.88 and an average particle size of 101 nm.

[0086] <Production of Water-Based Ink for Ink-Jet Printing> Example 1 (Preparation of Water Dispersion of Core-Shell Type Resin Particles A-1) In a plastic container, 20.2 parts of n-butyl acrylate and 65.7 parts of methyl methacrylate as monomer (a1), 14.1 parts of 1,6-hexanediol diacrylate as reactive group-containing compound (R1), 250 parts of the water dispersion of the carboxy group-containing polymer P1 obtained in Preparation Example 2-1 as the carboxy group-containing polymer A2p (solid content concentration: 20% by mass) (effective content of the carboxy group-containing polymer P1: 50.0 parts), and 250 parts of ion-exchanged water were mixed and shaken to obtain a monomer emulsion. Separately, 2.0 parts of 4,4'-azobis(4-cyanovaleric acid) as a radical polymerization initiator, 21.0 parts of ion-exchanged water, and 1.0 part of a 25% by mass aqueous ammonia solution were mixed and stirred in a glass container to obtain an aqueous radical polymerization initiator solution. The monomer emulsion obtained was put into a separable flask and stirred, and then nitrogen gas replacement was thoroughly performed. Next, 24.0 parts of the radical polymerization initiator aqueous solution was added to a dropping funnel, and the mixture in the separable flask was heated to 80°C while stirring under a nitrogen atmosphere, and the radical polymerization initiator aqueous solution in the dropping funnel was dropped over 3 hours to perform emulsion polymerization. After the drop of the radical polymerization initiator aqueous solution was completed, the mixture was aged at 80°C for 1 hour, and then cooled to 25°C to form core-shell type resin particles A-1. The mixture was filtered through a filter having a pore size of 5 μm (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and ion-exchanged water was added so that the solid content concentration became 20% by mass, to obtain an aqueous dispersion of core-shell type resin particles A-1 (average particle size: 43 nm, glass transition temperature (calculated value) of core resin A1: 50° C., acid value of core resin A1: 0 mg KOH / g, crosslink density of core resin A1: 1.25 mmol / g, acid value of shell resin A2: 240 mg KOH / g, weight average molecular weight of shell resin A2: 13,900, crosslink density of shell resin A2: 0.00 mmol / g, mass ratio [core resin A1 / (core resin A1+shell resin A2)]: 0.67) (=[100 parts / (100 parts+50.0 parts)]). (Preparation of Water-Based Ink) Next, in a 100 mL screw tube, 40.0 parts of the aqueous dispersion D1 of the pigment-containing crosslinked polymer particles obtained in Production Example 1 (content of pigment: 7.0 parts, content of polymer dispersant B (crosslinked carboxyl group-containing polymer P1): 1.0 parts), 25.0 parts of the aqueous dispersion of the core-shell type resin particles A-1 obtained above (content of core-shell type resin particles A-1: ​​5.0 parts), 5.0 parts of diethylene glycol monoisobutyl ether (iBDG) (reagent manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 20.0 parts of propylene glycol (reagent manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 0.7 parts of polyether-modified silicone surfactant (PEG-11 methyl ether dimethicone, Shin-Etsu Chemical Co., Ltd. "KF-6011"), and ion-exchanged water were added to prepare a total amount of 100 parts, and the mixture was stirred at room temperature for 15 minutes to obtain a mixed liquid. The mixture was then filtered through a filter with a pore size of 5 μm (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain water-based ink I-1 (pigment content: 7.0 mass%, mass ratio [pigment / (resin particle A + polymer dispersant B)]: 1.18, mass ratio [resin particle A / (resin particle A + polymer dispersant B)]: 0.84).

[0087] Examples 2 to 5 In Example 1, the aqueous dispersion of the carboxyl group-containing polymer P1 was replaced with aqueous dispersions of the carboxyl group-containing polymers P2 to P5, as shown in Table 3, respectively, and the same procedure as in Example 1 was repeated to obtain aqueous dispersions of the core-shell type resin particles A-2 to A-5, respectively. Next, water-based inks I-2 to I-5 were obtained, respectively, in the same manner as in Example 1, except that the water dispersion of the core-shell type resin particles A-1 was replaced with the water dispersion of the core-shell type resin particles A-2 to A-5.

[0088] Examples 6 to 10 Aqueous dispersions of core-shell type resin particles A-6 to A-10 were obtained in the same manner as in Example 1, except that the blending amount of monomer (a1) constituting the core resin A1 was changed as shown in Table 3. Next, water-based inks I-6 to I-10 were obtained in the same manner as in Example 1, except that the water dispersion of the core-shell type resin particles A-1 was replaced with the water dispersion of the core-shell type resin particles A-6 to A-10.

[0089] Examples 11 to 14 In the same manner as in Example 1, except that the crosslink density (q1) of the core resin A1 was changed as shown in Table 3, aqueous dispersions of the core-shell type resin particles A-11 to A-14 were obtained. Next, water-based inks I-11 to I-14 were obtained in the same manner as in Example 1, except that the water dispersion of the core-shell type resin particles A-11 to A-14 was used instead of the water dispersion of the core-shell type resin particles A-1.

[0090] Example 15 In Example 1, the reactive group-containing compound (R1) of the monomer (a1) constituting the core resin A1 was changed as shown in Table 3, and the same procedure was followed as in Example 1 to obtain an aqueous dispersion of core-shell type resin particles A-15. Next, a water-based ink I-15 was obtained in the same manner as in Example 1, except that the water dispersion of the core-shell type resin particles A-15 was used instead of the water dispersion of the core-shell type resin particles A-1.

[0091] Example 16 (Preparation of Water Dispersion of Core-Shell Type Resin Particles A-16) Core-shell type resin particles A-1 were formed in the same manner as in Example 1. Next, 4.8 parts of 1,6-hexanediol diglycidyl ether ("Denacol EX-212" manufactured by Nagase Chemtex Corporation, epoxy equivalent: 151) was added as a reactive group-containing compound (R2) (epoxy group-containing compound) to the core-shell type resin particles A-1 in the separable flask and mixed, and then heated at 90 ° C. for 5 hours while stirring with a stirrer. The temperature was lowered to 25 ° C., and the mixture was filtered with a filter (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) having a pore size of 5 μm, and ion-exchanged water was added so that the solid content concentration was 20 mass%, to obtain an aqueous dispersion of core-shell type resin particles A-16 in which a crosslinked structure was introduced into the shell resin A2. (Preparation of Water-Based Ink) A water-based ink I-16 was obtained in the same manner as in Example 1, except that the water dispersion of the core-shell type resin particles A-16 was used instead of the water dispersion of the core-shell type resin particles A-1.

[0092] Examples 17 to 18 In Example 16, the amount of reactive group-containing compound (R2) was changed as shown in Table 4, and the crosslink density (q2) of shell resin A2 was changed. In the same manner as in Example 16, however, aqueous dispersions of core-shell type resin particles A-17 to A-18 in which a crosslinked structure was introduced into shell resin A2 were obtained. Next, water-based inks I-17 to I-18 were obtained in the same manner as in Example 1, except that the water dispersion of the core-shell type resin particles A-17 to A-18 was used instead of the water dispersion of the core-shell type resin particles A-1.

[0093] Examples 19 to 22 In Example 1, the aqueous dispersion of anionic polymer P1 was replaced with aqueous dispersions of anionic polymers P8 to P11, as shown in Table 4, respectively, and the same procedure as in Example 1 was repeated to obtain aqueous dispersions of core-shell type resin particles A-19 to A-22, respectively. Next, water-based inks I-19 to I-22 were obtained in the same manner as in Example 1, except that the water dispersion of the core-shell type resin particles A-1 was replaced with the water dispersion of the core-shell type resin particles A-19 to A-22.

[0094] Comparative Examples 1-2 In Example 1, the aqueous dispersion of anionic polymer P1 was replaced with aqueous dispersions of anionic polymers P6 to P7, as shown in Table 4, respectively, and the same procedure as in Example 1 was repeated to obtain aqueous dispersions of core-shell type resin particles A-23 to A-24, respectively. Next, water-based inks I-23 to I-24 were obtained in the same manner as in Example 1, except that the water dispersion of the core-shell type resin particles A-23 to A-24 was used instead of the water dispersion of the core-shell type resin particles A-1.

[0095] Comparative Example 3 Aqueous dispersions of core-shell type resin particles A-25 were obtained in the same manner as in Example 1, except that the amount of monomer (a1) constituting the core resin A1 was changed as shown in Table 4. Next, a water-based ink I-25 was obtained in the same manner as in Example 1, except that the water dispersion of the core-shell type resin particles A-1 was replaced with the water dispersion of the core-shell type resin particles A-25.

[0096] Comparative Example 4 In the same manner as in Example 1, except that in Example 1, no crosslinked structure was introduced into the core resin A1 as shown in Table 4, an aqueous dispersion of the core-shell type resin particles A-26 was obtained. Next, a water-based ink I-26 was obtained in the same manner as in Example 1, except that the water dispersion of the core-shell type resin particles A-26 was used instead of the water dispersion of the core-shell type resin particles A-1.

[0097] <Evaluation> In an environment with a temperature of 25±1°C and a relative humidity of 30±5%, ink was filled into the cartridge of a printing evaluation device (Seiko Epson Corporation, inkjet printer, model number: PX-105, piezoelectric type), an A4-sized film heater (Kawai Electric Works Co., Ltd.) was attached to the recording medium ejection section so that the recording medium could be heated, and a corona-discharge-treated OPP film (Futamura Chemical Co., Ltd., product number: FOR-AQ, film thickness: 20 μm) cut to A4 size was set in the paper holder as a low-absorbency recording medium. Next, each of the water-based inks of the Examples and Comparative Examples was filled into the printing evaluation device, and the intermittent ejection property and image bleeding were evaluated by the following methods. The results are shown in Tables 3 and 4.

[0098] (Intermittent ejection) Using the printing evaluation device, 10 solid images of 20 mm x 20 mm were printed with 100% ink duty, and then left for 5 minutes without printing. Then, one solid image of 20 mm x 20 mm was printed. The solid image formation surface of the obtained solid record just before leaving for 5 minutes (i.e., the 10th record of the solid record obtained by the command to print 10 sheets) and the solid record just after leaving for 5 minutes (i.e., the solid record obtained by the command to print one sheet just after leaving) was captured with a portable magnifying camera "PIAS-II" (manufactured by QEA) at 640 x 480 pixels, and the ejection area was calculated using image analysis software "Image-J", and the ejection recovery rate (%) was calculated by the following formula to evaluate intermittent ejection properties. In this evaluation, no current was applied to the film heater. Discharge recovery rate (%)=[(discharge area of ​​solid printed matter immediately after being left for 5 minutes) / (discharge area of ​​solid printed matter immediately before being left for 5 minutes)]×100 The closer the ejection recovery rate is to 100%, the better the intermittent ejection performance is.

[0099] (Image Bleeding) Using the print evaluation device, an image was formed with a 10mm x 10mm area inside a 20mm x 20mm area, with the print duty of the 10mm x 10mm area being 100% and the print duty of the area surrounding the 10mm x 10mm area being 40%, and then dried to obtain a recorded matter. The area of ​​the area of ​​the obtained recorded matter where the print duty was 100% was calculated using the image analysis software "Image-J" by setting the threshold value to a print duty of 70%, and the bleeding rate (%) was calculated using the following formula to evaluate the suppression of bleeding of the image. In this evaluation, the film heater was heated to 50° C. and records were produced. Bleed rate (%) = [(area of ​​area with print duty of 70% or more) / (10mm x 10mm)] x 100 The closer the bleeding rate is to 100%, the better the bleeding suppression of the image is.

[0100] [Table 3]

[0101] [Table 4]

[0102] From Tables 3 and 4, it is clear that, compared with Comparative Examples 1 to 4, Examples 1 to 22 are excellent in intermittent ejection properties, and can provide recorded matter with suppressed image bleeding.

Claims

1. The ink contains a pigment, resin particles A having a core-shell structure, a water-soluble organic solvent, and water, a core resin A1 constituting a core of the resin particle A has a crosslinked structure derived from a compound (R1) having a plurality of reactive groups in the molecule, and has a glass transition temperature of 25° C. or higher as calculated by Fox's formula from the mass ratio of monomer components other than the compound (R1) constituting the core resin A1; the shell resin A2 constituting the shell of the resin particle A contains a structural unit derived from a carboxylic acid monomer (a2-1) and has an acid value of 90 mgKOH / g or more and 350 mgKOH / g or less.

2. 2. The water-based ink for ink-jet printing according to claim 1, wherein the shell resin A2 is a resin which may have a crosslinked structure derived from a compound (R2) having a plurality of reactive groups in the molecule, and the shell resin A2 has a crosslink density (q2) represented by the following formula of 0 mmol / g or more and 1.0 mmol / g or less. Crosslink density (q2) (mmol / g)=[[(number of moles of structural units derived from the compound (R2) in the shell resin A2)×(number of reactive groups possessed by the compound (R2)] / (mass of the shell resin A2 in the resin particle A)]×1000

3. 3. The water-based ink for ink-jet printing according to claim 1, wherein the shell resin A2 is a resin having no crosslinked structure, and the weight average molecular weight of the shell resin A2 is 5,000 or more and 150,000 or less.

4. The water-based ink for ink-jet printing according to any one of claims 1 to 3, wherein the core resin A1 has a crosslink density (q1) represented by the following formula of 0.2 mmol / g or more and 3.0 mmol / g or less. Crosslink density (q1) (mmol / g)=[[(number of moles of structural units derived from the compound (R1) in the core resin A1)×(number of reactive groups possessed by the compound (R1)] / (mass of the core resin A1 in the resin particle A)]×1000

5. The water-based ink for ink-jet printing according to any one of claims 1 to 4, wherein the core resin A1 is a resin having a crosslinked structure derived from 1,6-hexanediol di(meth)acrylate as the compound (R1).

6. The water-based ink for ink-jet printing according to any one of claims 1 to 5, wherein the core part resin A1 has a glass transition temperature of 110°C or lower, calculated from a mass ratio of monomer components other than the compound (R1) constituting the core part resin A1 according to Fox's formula.

7. The water-based ink for ink-jet printing according to any one of claims 1 to 6, which is substantially free of anionic surfactants.

8. 8. The water-based ink for ink-jet printing according to claim 1, wherein a ratio of the mass of the core portion resin A1 to the total mass of the core portion resin A1 and the shell portion resin A2 [core portion resin A1 / (core portion resin A1+shell portion resin A2)] is 0.50 or more and 0.90 or less.

9. The water-based ink for ink-jet printing according to any one of claims 1 to 8, wherein the pigment is dispersed in a polymer dispersant B, and a mass ratio of a content of the pigment to a total content of the resin particles A and the polymer dispersant B [pigment / (resin particles A+polymer dispersant B)] is 0.2 or more and 4.5 or less.

10. 10. The water-based ink for ink-jet printing according to claim 9, wherein a mass ratio of the resin particles A to a total content of the resin particles A and the polymer dispersant B [resin particles A / (resin particles A+polymer dispersant B)] is 0.4 or more and 0.98 or less.

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