Aqueous pigment dispersion for inkjet recording

Abstract

To provide an aqueous pigment dispersion for inkjet recording which offers superior storage stability, and exhibits high print density and superior fixability in inkjet recording on high water-absorbing recording media, and a method for producing the same, as well as to provide an inkjet recording ink using the aqueous pigment dispersion.SOLUTION: The present invention provides an aqueous pigment dispersion for inkjet recording that comprises: a self-dispersing pigment (A); a resin-dispersed pigment (B); a salt (C); and water, and a method for producing the same, as well as an inkjet recording ink using the aqueous pigment dispersion.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous pigment dispersion for inkjet recording, a method for producing the same, and an inkjet recording ink using the aqueous pigment dispersion.

Background Art

[0002] The inkjet recording method is a recording method in which ink droplets are directly ejected from very fine nozzles onto a recording medium and adhered to obtain a printed matter on which characters and images are recorded. This method has many advantages such as being easy to full-colorize, inexpensive, being able to use plain paper as a recording medium, and being non-contact with the object to be printed, so it has become extremely popular. Recently, in order to impart weather resistance and water resistance to printed matter, inkjet recording inks using pigments as colorants have been widely used, and studies have been made on pigment aqueous dispersions and inkjet recording inks to be blended in the inks.

[0003] For example, in Patent Document 1, for the purpose of providing a method for producing a pigment aqueous dispersion excellent in continuous ejection stability, printing density, and fixing property, a step of mixing an aqueous dispersion in which a pigment is dispersed with a crosslinked water-dispersible polymer and an aqueous dispersion of a self-dispersing pigment to obtain an aqueous dispersion, and a step of heat-treating the aqueous dispersion obtained in the step at 40°C or higher to obtain a pigment aqueous dispersion are disclosed. In Patent Document 2, for the purpose of providing an ink that can achieve both the reliability of the ink, such as suppression of ink retention in the cap and excellent storage stability, and the image characteristics, such as excellent image density and bleeding resistance, an inkjet ink containing a self-dispersing pigment, a salt, a polyoxyethylene alkyl ether, and a water-soluble organic solvent is disclosed. In Patent Document 3, for the purpose of providing an inkjet ink that can suppress repulsion on a recording medium and suppress ejection sag when ejected from a nozzle, it contains an aqueous medium, a pigment, and a predetermined compound. The predetermined compound is at least one compound selected from phosphoric acid, citric acid, salts thereof, and alkyl esters thereof. An inkjet ink is disclosed in which the ratio of the mass of the phosphoric acid moiety or citric acid moiety of the predetermined compound to the mass of the pigment is within a predetermined range. It is disclosed that the pigment is a self-dispersing pigment or a resin-dispersed pigment.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the inkjet recording method, in order to obtain high ejection reliability, it is necessary to use a dispersion of a pigment dispersed with a resin having good redispersibility. However, since the hydrophilicity of the pigment increases, when such a pigment dispersion is used as an ink, the pigment tends to penetrate into a highly absorbent recording medium such as plain paper together with the ink medium, resulting in a decrease in printing density. On the other hand, in the case of self-dispersing pigments, the balance due to charge repulsion is easily destroyed by calcium carbonate contained as a filler in a highly absorbent recording medium such as plain paper, so it tends to remain on the surface of the recording medium and a high printing density can be obtained. However, on the contrary, the fixing property tends to be poor. In the method described in Patent Document 1, a pigment dispersion using a dispersion of a pigment dispersed with a crosslinked water-dispersible polymer and a dispersion of a self-dispersible pigment has been proposed, but it has been found that the printing density is not sufficient. Further, in the method described in Patent Document 2, the fixing property has not been improved at all. Further, in the method described in Patent Document 3, no study has been made on the printing density, and no example of using a combination of a self-dispersible pigment and a resin-dispersed pigment has been given. Further, it has also been found that in the method described in Patent Document 3, the storage stability as an aqueous pigment dispersion may not be sufficient. Therefore, along with the improvement of the storage stability of the aqueous pigment dispersion, further improvement is required in achieving both high printing density and excellent fixing property when using the aqueous pigment dispersion for inkjet recording on a highly water-absorbent recording medium. An object of the present invention is to provide an aqueous pigment dispersion for inkjet recording, a method for producing the same, and an ink for inkjet recording using the aqueous pigment dispersion, which have excellent storage stability, have a high printing density in inkjet recording on a highly water-absorbent recording medium, and have excellent fixing property. [Means for Solving the Problems]

[0006] The present inventors have focused on the fact that an aqueous pigment dispersion for inkjet recording containing a self-dispersible pigment, a resin-dispersed pigment, a salt, and water can improve storage stability and achieve both high printing density and excellent fixing property in inkjet recording on a highly water-absorbent recording medium, and have found that the above problems can be solved. That is, the present invention relates to the following [1] to [3]. [1] An aqueous pigment dispersion for inkjet recording containing a self-dispersible pigment (A), a resin-dispersed pigment (B), a salt (C), and water. [2] An ink for inkjet recording containing the aqueous pigment dispersion according to [1] and a water-soluble organic solvent. [3] A method for producing the aqueous pigment dispersion for inkjet recording according to [1], including the following Step 1 and Step 2. Step 1: A step of mixing an aqueous dispersion (II) of a resin-dispersed pigment (B) and a salt (C) to obtain an aqueous dispersion (II’). Step 2: A step of obtaining an aqueous pigment dispersion by mixing the aqueous dispersion (II’) obtained in Step 1 with the aqueous dispersion (I) of the self-dispersing pigment (A).

Advantages of the Invention

[0007] According to the present invention, there can be provided an aqueous pigment dispersion for inkjet recording, a method for producing the same, and an ink for inkjet recording using the aqueous pigment dispersion, which have excellent storage stability, have a high printing density in inkjet recording on a highly water-absorbent recording medium, and have excellent fixing properties.

Embodiments for Carrying Out the Invention

[0008] [Aqueous Pigment Dispersion for Inkjet Recording] The aqueous pigment dispersion for inkjet recording of the present invention (hereinafter, also simply referred to as "the aqueous pigment dispersion of the present invention") contains a self-dispersing pigment (A), a resin-dispersed pigment (B), a salt (C), and water. In the present invention, "containing Component X" also means "composed of Component X". Further, "aqueous" means that water occupies the largest proportion by mass in the medium. In addition, in this specification, "recording" is a concept including printing and printing for recording characters and images, and "recorded matter" is a concept including printed matter and printed matter on which characters and images are recorded. Further, "high water absorbency" is a concept including high liquid absorbency, and the water absorption amount of the recording medium at a contact time of 100 msec between the recording medium and pure water is 10 g / m 2 The above refers to, and "low water absorbency" is a concept including low liquid absorbency and non-liquid absorbency, and the water absorption amount of the recording medium at a contact time of 100 msec between the recording medium and pure water is 0 g / m 2 10 g / m or more 2 Less than this. The water absorption amount can be measured as the transfer amount at a contact time of 100 msec of pure water under the conditions of 23°C and a relative humidity of 50% using an automatic scanning liquid absorber (for example, KM500win manufactured by Kumagai Riki Kogyo Co., Ltd.).

[0009] According to the present invention, it is possible to obtain a recording material that has excellent storage stability in an aqueous pigment dispersion, has a high printing density in inkjet recording on a highly water-absorbent recording medium, and has excellent fixing properties. The reason for such an effect is not clear, but it is considered as follows. In the aqueous pigment dispersion of the present invention, the self-dispersing pigment is dispersed in an aqueous medium by the charge repulsive force of the functional groups on the pigment surface. In an ink containing such an aqueous pigment dispersion, the self-dispersing pigment that is dispersed is rapidly aggregated by calcium ions derived from calcium carbonate contained as a filler in a highly water-absorbent recording medium such as plain paper, so that a recording material having a high printing density can be obtained. Further, in the aqueous pigment dispersion of the present invention, due to the decrease in the charge repulsive force of the self-dispersing pigment by further containing a salt, the aggregation rate of the self-dispersing pigment after landing on a highly water-absorbent recording medium such as plain paper is further accelerated, so that a recording material having a higher printing density can be obtained. And, in the aqueous pigment dispersion of the present invention, a resin-dispersed pigment is further contained. Therefore, when the self-dispersing pigment aggregates, aggregation occurs so as to also entrap the resin-dispersed pigment present in the vicinity of the self-dispersing pigment, and it is considered that a high printing density is maintained and the fixing property can also be improved. Further, in the aqueous pigment dispersion of the present invention, since a resin-dispersed pigment that is stable to salts is further contained, aggregation of the self-dispersing pigment by the salt in the aqueous pigment dispersion is suppressed, and it is considered that the storage stability can be improved.

[0010] <Self-dispersing pigment (A)> The self-dispersing pigment (A) means a pigment that can be dispersed in an aqueous medium without using a surfactant or resin by bonding one or more hydrophilic functional groups such as an anionic hydrophilic group and a cationic hydrophilic group directly or via another atomic group to the surface of the pigment. Here, "dispersible" means that a state in which it is dispersed to a concentration of 10% by mass in water can be visually confirmed to stably exist even after storage at 25 °C for one month. Examples of the other atomic groups include an alkanediyl group having 1 to 24 carbon atoms, preferably 1 to 12 carbon atoms, a phenylene group which may have a substituent, or a naphthylene group which may have a substituent. Note that a plurality of hydrophilic functional groups may be present as long as they do not inhibit the object of the present invention, and they may be the same or different.

[0011] As the anionic hydrophilic group, any group can be used as long as it has sufficiently high hydrophilicity to stably disperse the pigment in an aqueous medium. Specific examples thereof include a carboxy group (-COOM 1 ), a sulfonic acid group (-SO3M 1 ), -SO2NH2, -SO2NHCOR 1 , a phosphonic acid group (-PO3M 1 2), or their dissociated ionic forms (-COO - , -SO3 - , -PO3 2- , -PO3 - M 1 ), etc. Acidic groups are exemplified. In the above chemical formula, M 1 may be the same or different, and specifically includes a hydrogen atom; an alkali metal such as lithium, sodium, or potassium; ammonium; a monomethylammonium group, a dimethylammonium group, a trimethylammonium group; a monoethylammonium group, a diethylammonium group, a triethylammonium group; an organic ammonium such as a monomethanolammonium group, a dimethanolammonium group, or a trimethanolammonium group. Further, in the above chemical formula, R 1 is an alkyl group having 1 to 12 carbon atoms, a phenyl group which may have a substituent, or a naphthyl group which may have a substituent. Examples of the cationic hydrophilic group include an ammonium group and an amino group. Among these, an ammonium group is preferable, and a quaternary ammonium group is more preferable. Among these hydrophilic functional groups, an anionic hydrophilic group is preferable from the viewpoint of miscibility with other components in the aqueous ink, and a carboxy group (-COOM is preferable from the viewpoints of improving the storage stability of the aqueous pigment dispersion and the ejection reliability of the ink.1 ) and a sulfonic acid group (-SO3M 1 ) or more selected from the group consisting of is more preferable.

[0012] Examples of the pigment of the self-dispersing pigment (A) include inorganic pigments, organic pigments, and extender pigments. Among these, in the black ink, the pigment of the self-dispersing pigment (A) is preferably carbon black. Specific examples of commercially available self-dispersing pigments (A) include CAB-O-JET 200, 300, 352K, 250C, 260M, 270Y, 450C, 465M, 470Y, 480V (above, manufactured by Cabot Corporation), BONJET BLACK CW-1, CW-2, CW-3, CW-4 (above, manufactured by Orient Chemical Industries Co., Ltd.), Aqua-Black 162 (manufactured by Tokai Carbon Co., Ltd.), and SDP-100, SDP-1000, SDP-2000 (above, manufactured by Sensient). The self-dispersing pigment (A) can be used alone or in combination of two or more in any ratio.

[0013] <Resin-dispersed pigment (B)> The resin-dispersed pigment (B) according to the present invention is particles of a pigment dispersed in an aqueous medium with a resin (b).

[0014] (Pigment) The pigment of the resin-dispersed pigment (B) may be either an organic pigment or an inorganic pigment. Examples of the organic pigment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. Examples of the inorganic pigment include carbon black and metal oxides. Particularly in the black ink, carbon black is preferable. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. In achromatic inks, achromatic pigments such as white, black, and gray can be used, and in chromatic inks, chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used. Among these, in black ink, the pigment of the resin-dispersed pigment (B) is preferably carbon black. Specific examples of commercially available carbon blacks include the "MONARCH" series, "REGAL" series, and "MOGUL L" manufactured by Cabot Corporation; the "NIPex" series manufactured by Orion Engineered Carbons; and the "Mitsubishi Carbon Black" series manufactured by Mitsubishi Chemical Corporation. The pigments of the resin-dispersed pigment (B) can be used singly or in combination of two or more in any ratio.

[0015] The color combinations of the pigments of the self-dispersing pigment (A) and the resin-dispersed pigment (B) may be the same or different, but from the viewpoint of printing density, it is preferable that the colors of the pigments of the self-dispersing pigment (A) and the resin-dispersed pigment (B) are the same, and it is more preferable that the pigments of both the self-dispersing pigment (A) and the resin-dispersed pigment (B) are carbon black.

[0016] (Resin (b)) The resin (b) according to the present invention is a resin having the ability to disperse a pigment in an aqueous medium as a dispersant. As the resin (b), from the viewpoint of dispersing the pigment in an aqueous medium, a resin having a hydrophilic functional group having an affinity for water is preferable, and a hydrophilic resin having more hydrophilic functional groups having an affinity for water is more preferable. Examples of the hydrophilic functional group contained in the resin (b) include anionic hydrophilic groups such as carboxy groups and sulfonic acid groups, and cationic hydrophilic groups such as quaternary ammonium groups. Anionic hydrophilic groups are preferable, and carboxy groups are more preferable. When having an anionic hydrophilic group as the hydrophilic functional group, the hydrophilic resin used as the resin (b) is preferably a resin having an acid value of 40 mgKOH / g or more and 800 mgKOH / g or less. When the resin (b) is a hydrophilic resin, the aqueous pigment dispersion of the present invention contains, together with the self-dispersing pigment (A), a resin-dispersed pigment (B) dispersed with a hydrophilic resin having a hydrophilic functional group as the resin (b). As a result, in the aqueous medium, the salt (C) is surrounded by the abundant hydrophilic functional groups of the hydrophilic resin, or is taken into the surface or interior of the resin-dispersed pigment (B), weakening the influence of the salt (C) on the self-dispersing pigment (A), and it is considered that good storage stability of the aqueous pigment dispersion is ensured.

[0017] Examples of the resin (b) include vinyl resins, polyester resins, and polyurethane resins. From the viewpoints of improving the dispersion stability of the pigment and the storage stability of the aqueous pigment dispersion, and improving the printing density and fixability, vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds) are preferred, vinyl resins having a carboxy group are more preferred, and vinyl resins containing a structural unit derived from a carboxy group-containing monomer (b-1) and a structural unit derived from a hydrophobic monomer (b-2) are even more preferred. Further, the resin (b) may further contain a structural unit derived from a nonionic monomer (b-3) from the viewpoints of improving the dispersion stability of the pigment and the storage stability of the aqueous pigment dispersion, and improving the printing density and fixability. When the vinyl resin is a copolymer, it may be any of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer. The vinyl resin is preferably a vinyl resin obtained by copolymerizing raw material monomers including a carboxy group-containing monomer (b-1), a hydrophobic monomer (b-2), and, if necessary, a nonionic monomer (b-3).

[0018] 〔Carboxy Group-Containing Monomer (b-1)〕 Examples of the carboxy group-containing monomer (b-1) include, preferably, one or more selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid. From the viewpoint of improving the dispersion stability of the pigment and the storage stability of the aqueous pigment dispersion, and from the viewpoint of improving the printing density and fixing property, more preferably, it is one or more selected from the group consisting of acrylic acid and methacrylic acid.

[0019] [Hydrophobic monomer (b-2)] The "hydrophobicity" of the hydrophobic monomer (b-2) means that when the monomer is dissolved until saturated in 100 g of ion-exchanged water at 25°C, the dissolved amount is less than 10 g. Examples of the hydrophobic monomer (b-2) include, preferably, one or more selected from aromatic group-containing monomers, (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol, and macromers, and more preferably, one or more selected from aromatic group-containing monomers and macromers. In this specification, "(meth)acrylate" means one or more selected from the group consisting of acrylate and methacrylate. "(meth)acrylate" hereinafter has the same meaning.

[0020] The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group with 6 to 22 carbon atoms, and more preferably, one or more selected from styrene-based monomers and aromatic group-containing (meth)acrylates. The molecular weight of the aromatic group-containing monomer is preferably less than 500. The styrene-based monomer is preferably one or more selected from styrene and 2-methylstyrene. The aromatic group-containing (meth)acrylate is preferably one or more selected from benzyl (meth)acrylate and phenoxyethyl (meth)acrylate, and more preferably benzyl (meth)acrylate.

[0021] (Meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol preferably has a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms, more preferably has an alkyl group having 1 to 22 carbon atoms, and still more preferably has an alkyl group having 6 to 18 carbon atoms. For example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, amyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, tertiary butyl (meth)acrylate, isoamyl (meth)acrylate, isooctyl (meth)acrylate, isodecyl (meth)acrylate, isododecyl (meth)acrylate, isostearyl (meth)acrylate can be mentioned.

[0022] As the hydrophobic monomer (b-2), a macromer may be used. The macromer is a compound having a number average molecular weight of 500 or more and 100,000 or less and having a polymerizable functional group at one end. From the viewpoints of improving the dispersion stability of the pigment and the storage stability of the aqueous pigment dispersion, and improving the printing density and fixability, it is preferably a compound having a number average molecular weight of 1,000 or more and 10,000 or less. The number average molecular weight is a value measured by gel permeation chromatography using chloroform containing 1 mmol / L of dodecyl dimethylamine as a solvent and using polystyrene as a standard substance. The polymerizable functional group present at one end of the macromer is preferably a methacryloyloxy group and an acryloyloxy group, and more preferably a methacryloyloxy group. From the viewpoints of improving the dispersion stability of pigments and the storage stability of aqueous pigment dispersions, as well as improving printing density and fixing properties, the macromer is preferably at least one selected from aromatic group-containing monomer-based macromers and silicone-based macromers, and more preferably an aromatic group-containing monomer-based macromer. Examples of the aromatic group-containing monomer that constitutes the aromatic group-containing monomer-based macromer include the aforementioned aromatic group-containing monomers, and at least one selected from the group consisting of styrene and benzyl (meth) acrylate is preferred, and styrene is more preferred. Specific examples of commercially available styrene-based macromers include AS-6(S), AN-6(S), HS-6(S) (manufactured by Toagosei Co., Ltd.). Examples of the silicone-based macromer include organopolysiloxane having a polymerizable functional group at one end.

[0023] The nonionic monomer (b-3) is a monomer having a high affinity for water and water-soluble organic solvents, and is, for example, a monomer containing a hydroxy group or a polyalkylene glycol chain. Examples of the nonionic monomer (b-3) include polyalkylene glycol mono (meth) acrylates such as polyethylene glycol mono (meth) acrylate and polypropylene glycol mono (meth) acrylate; alkoxypolyalkylene glycol mono (meth) acrylates such as methoxypolyethylene glycol mono (meth) acrylate and octoxypolyethylene glycol mono (meth) acrylate. Specific examples of commercially available nonionic monomers (b-3) include the "NK Ester" series manufactured by Shin-Nakamura Chemical Co., Ltd. and the "Blemmer" series manufactured by NOF Corporation. Each monomer of the vinyl-based resin can be used alone or in combination of two or more.

[0024] ​The content of the structural unit derived from the carboxy group-containing monomer (b-1) in all the structural units of the resin (b) is preferably 5% by mass or more, more preferably 8% by mass or more, still more preferably 10% by mass or more, from the viewpoints of improving the dispersion stability of the pigment and the storage stability of the aqueous pigment dispersion, and improving the printing density and the fixing property, and from the same viewpoints as above, it is preferably 45% by mass or less, more preferably 40% by mass or less, still more preferably 35% by mass or less. The content of the structural unit derived from the hydrophobic monomer (b-2) in all the structural units of the resin (b) is preferably 50% by mass or more, more preferably 55% by mass or more, still more preferably 60% by mass or more, even more preferably 65% by mass or more, from the viewpoints of improving the dispersion stability of the pigment and the storage stability of the aqueous pigment dispersion, and improving the printing density and the fixing property, and from the same viewpoints as above, it is preferably 90% by mass or less, more preferably 85% by mass or less, still more preferably 80% by mass or less. When the resin (b) further contains a structural unit derived from a nonionic monomer (b-3), the content of the structural unit derived from the nonionic monomer (b-3) in all the structural units of the resin (b) is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 8% by mass or more, from the viewpoints of improving the dispersion stability of the pigment and the storage stability of the aqueous pigment dispersion, and improving the printing density and the fixing property, and from the same viewpoints as above, it is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 12% by mass or less.

[0025] When the resin (b) has a carboxy group, the carboxy group is preferably neutralized with a neutralizing agent. Examples of the neutralizing agent include hydroxides of alkali metals, ammonia, and organic amines, but preferably hydroxides of alkali metals, and more preferably sodium hydroxide. The neutralizing agent can be used singly or in combination of two or more. The equivalent amount of the neutralizing agent is preferably 10 mol% or more, more preferably 20 mol% or more, still more preferably 30 mol% or more, from the viewpoint of improving the dispersion stability of the pigment and the storage stability of the aqueous pigment dispersion, and from the same viewpoint as described above, it is preferably 120 mol% or less, more preferably 90 mol% or less, still more preferably 70 mol% or less. The equivalent amount of the neutralizing agent can be determined by the following formula. When the equivalent amount of the neutralizing agent is 100 mol% or less, it is synonymous with the degree of neutralization. When the equivalent amount of the neutralizing agent exceeds 100 mol% in the following formula, it means that the neutralizing agent is in excess with respect to the carboxy groups of the resin (b), and the degree of neutralization of the resin (b) at this time is regarded as 100 mol%. Equivalent amount of neutralizing agent (mol%) = {[Mass of neutralizing agent added (g) / Equivalent weight of neutralizing agent (g / mol)] / [(Acid value of resin (b) before neutralization (mgKOH / g) × Mass of resin (b) before neutralization (g)) / (56.1 × 1,000)]} × 100

[0026] From the viewpoint of improving the storage stability of the aqueous pigment dispersion, the resin (b) preferably has a structure crosslinked with a crosslinking agent. Here, in this specification, the resin (b) having a structure crosslinked with a crosslinking agent is also referred to as "crosslinked resin (b)". The crosslinked resin (b) preferably has a structure containing a constituent component of a polymer having a linear two-dimensional structure which may have a branched chain and a constituent component derived from the crosslinking agent. Such a crosslinked structure is considered to be a three-dimensional structure formed by a polymer having a linear two-dimensional structure which may have a branched chain and a constituent component derived from the crosslinking agent. Examples of the polymer having a linear two-dimensional structure which may have a branched chain include vinyl resins, polyester resins, and polyurethane resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds), and the vinyl resin having the aforementioned carboxy groups is preferred. Among them, from the viewpoint of improving the storage stability of the aqueous pigment dispersion, the crosslinked resin (b) is preferably a resin obtained by crosslinking a vinyl resin containing a structural unit derived from a carboxy group-containing monomer (b-1) and a structural unit derived from a hydrophobic monomer (b-2) with a crosslinking agent.

[0027] The crosslinking agent is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule from the viewpoint of improving the storage stability of the aqueous pigment dispersion, more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group with 3 to 8 carbon atoms, and still more preferably trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6 - hexanediol diglycidyl ether, 1,4 - butanediol diglycidyl ether, 1,4 - cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and still more preferably trimethylolpropane polyglycidyl ether. When the crosslinking agent is a polyfunctional epoxy compound, the epoxy equivalent of the crosslinking agent is preferably 90 g / eq. or more, more preferably 100 g / eq. or more, still more preferably 110 g / eq. or more, and preferably 300 g / eq. or less, more preferably 200 g / eq. or less, still more preferably 150 g / eq. or less. The crosslinking rate of the crosslinked resin (b) is preferably 10 mol% or more, more preferably 30 mol% or more, still more preferably 50 mol% or more from the viewpoint of improving the storage stability of the aqueous pigment dispersion, and from the same viewpoint as above, preferably 85 mol% or less, more preferably 80 mol% or less, still more preferably 75 mol% or less. The crosslinking rate (mol%) of the crosslinked resin (b) is a value calculated by the following formula from the acid value of the resin (b) before crosslinking and the epoxy equivalent of the crosslinking agent. Crosslinking rate = {[Mass of crosslinking agent added (g) / Epoxy equivalent of crosslinking agent (g / eq.)] / [(Acid value of resin (b) before crosslinking (mgKOH / g) × Mass of resin (b) before crosslinking (g)) / (56.1 × 1000)]}

[0028] The acid value of resin (b) is preferably 25 mgKOH / g or more, more preferably 30 mgKOH / g or more, still more preferably 40 mgKOH / g or more, even more preferably 50 mgKOH / g or more, even more preferably 60 mgKOH / g or more, even more preferably 70 mgKOH / g or more, from the viewpoint of improving the dispersion stability of the pigment and the storage stability of the aqueous pigment dispersion. And from the same viewpoint as above, it is preferably 800 mgKOH / g or less, more preferably 500 mgKOH / g or less, still more preferably 300 mgKOH / g or less. The acid value of resin (b) can be determined by the method described in the examples, but can also be calculated from the mass ratio of the constituent monomers. Further, the acid value of the crosslinked resin (b) can also be calculated by the following formula. Acid value of crosslinked resin (b) (mgKOH / g) = Acid value of resin (b) before crosslinking (mgKOH / g) × [(100 - crosslinking rate (mol%)) / 100]

[0029] The weight average molecular weight of resin (b) is preferably 5,000 or more, more preferably 7,000 or more, still more preferably 10,000 or more, from the viewpoint of improving the dispersion stability of the pigment and the storage stability of the aqueous pigment dispersion. And from the same viewpoint as above, it is preferably 300,000 or less, more preferably 100,000 or less, still more preferably 50,000 or less, even more preferably 30,000 or less. Also, the weight average molecular weight of resin (b) is preferably 10,000 or more, more preferably 50,000 or more, still more preferably 100,000 or more, from the viewpoint of improving the printing density and the fixing property. And from the same viewpoint as above, it is preferably 500,000 or less, more preferably 300,000 or less, still more preferably 200,000 or less. Incidentally, the weight average molecular weight can be determined by the method described in the examples.

[0030] Examples of commercially available products of the resin (b) include, for example, polyacrylic acid such as "Aron AC-10SL" (manufactured by Toagosei Co., Ltd.); styrene / acrylic resins such as "Joncryl 67", "Joncryl 611", "Joncryl 678", "Joncryl 680", "Joncryl 690", "Joncryl 819" (all of the above are manufactured by BASF Japan Ltd.).

[0031] As the form of the resin-dispersed pigment (B) in the aqueous pigment dispersion of the present invention, the form of resin particles containing a pigment (hereinafter, also referred to as "pigment-containing resin particles") is preferable. Here, the form of the pigment-containing resin particles is not particularly limited as long as the particles are formed by at least the pigment and the resin (b), and the particles are those in which the resin (b) is adsorbed to the pigment in the aqueous pigment dispersion. Examples of the form of the pigment-containing resin particles include, for example, a particle form in which the pigment is encapsulated in the resin (b), a particle form in which the pigment is uniformly dispersed in the resin (b), a particle form in which the pigment is exposed on the surface of the resin (b) particles, etc., and mixtures thereof are also included. As will be described later, the resin-dispersed pigment (B) can be obtained as an aqueous dispersion (II) by subjecting a pigment, the resin (b), a neutralizing agent, a surfactant, etc., if necessary, to a dispersion treatment by a known method. Further, when the resin (b) has a structure crosslinked with a crosslinking agent, it is preferable to add a crosslinking agent to the aqueous dispersion (II) and perform a crosslinking treatment by a known method. From the viewpoint of the storage stability of the aqueous pigment dispersion, the average particle diameter of the resin-dispersed pigment (B) in the aqueous dispersion (II) is preferably 30 nm or more, more preferably 50 nm or more, still more preferably 70 nm or more, and from the same viewpoint as above, it is preferably 600 nm or less, more preferably 550 nm or less, still more preferably 500 nm or less, and even more preferably 450 nm or less. The average particle diameter of the resin-dispersed pigment (B) in the aqueous dispersion (II) is measured by the same method as the method for measuring the average particle diameter of the particles contained in the ink for inkjet recording described in the examples.

[0032] <Salt (C)> From the viewpoint of improving the printing density and fixing property, at least one selected from the group consisting of salts of inorganic acids and salts of organic acids is preferably mentioned as the salt (C). Examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid, carbonic acid, and phosphoric acid. Examples of the organic acid include monocarboxylic acids such as formic acid, acetic acid, propionic acid, and benzoic acid; dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, and phthalic acid; polycarboxylic acids such as polyglutamic acid; hydroxycarboxylic acids such as glycolic acid, lactic acid, hydroxyacrylic acid, glyceric acid, malic acid, tartaric acid, and citric acid; acidic amino acids such as glutamic acid and aspartic acid; sulfonic acids such as methanesulfonic acid, N-methyltaurine, sulfamic acid, xylenesulfonic acid, p-toluenesulfonic acid, and benzenesulfonic acid; sulfuric esters such as lauryl sulfate; and organic phosphate esters such as methyl phosphate and ethyl phosphate. From the viewpoint of improving the printing density and fixing property, the salt (C) is preferably a salt containing at least one selected from the group consisting of alkali metal ions, metal ions of Group 2 elements, and ammonium ions as constituent ions, more preferably a salt containing at least one selected from the group consisting of alkali metal ions and metal ions of Group 2 elements, still more preferably a salt containing alkali metal ions, even more preferably a salt containing at least one selected from the group consisting of sodium ions and potassium ions, and even more preferably a salt containing sodium ions. Among these, from the viewpoint of improving the printing density and fixing property, the salt (C) is preferably at least one selected from the group consisting of polyvalent acids and their salts, more preferably at least one selected from the group consisting of phosphoric acid, phthalic acid, citric acid, and their salts, still more preferably at least one selected from the group consisting of phosphoric acid, phthalic acid, and their salts, even more preferably at least one selected from the group consisting of phosphates and phthalates, and even more preferably phosphates.

[0033] Examples of the phosphate include orthophosphates such as potassium phosphate (K3PO4), dipotassium hydrogen phosphate (K2HPO4), potassium dihydrogen phosphate (KH2PO4), sodium phosphate (Na3PO4), disodium hydrogen phosphate (Na2HPO4), sodium dihydrogen phosphate (NaH2PO4), diammonium hydrogen phosphate ((NH4)2HPO4), and ammonium dihydrogen phosphate (NH4H2PO4); phosphites (phosphonates) such as potassium phosphite (K2HPO3) and sodium phosphite (Na2HPO3); hypophosphites such as potassium hypophosphite (KH2PO2), sodium hypophosphite (NaH2PO2), and ammonium hypophosphite (NH4H2PO2); and dehydrated condensed phosphates such as tetrasodium pyrophosphate, disodium dihydrogen pyrophosphate, sodium tripolyphosphate, sodium tetrapolyphosphate, and sodium hexametaphosphate. Among these, from the viewpoint of improving the printing density and fixing property, the phosphate is preferably a salt of phosphoric acid and sodium, more preferably at least one selected from the group consisting of sodium orthophosphate and dehydrated condensed sodium phosphate, still more preferably at least one selected from the group consisting of disodium hydrogen phosphate, tetrasodium pyrophosphate, disodium dihydrogen pyrophosphate, sodium tripolyphosphate, sodium tetrapolyphosphate, and sodium hexametaphosphate, and even more preferably disodium hydrogen phosphate. The phosphate may have water of hydration in the raw material form. The salt (C) can be used alone or in combination of two or more.

[0034] <Water> The aqueous pigment dispersion of the present invention contains water. As the water used in the aqueous ink of the present invention, pure water or ion-exchanged water is preferable from the viewpoint of preventing contamination with unintended substances.

[0035] [Method for producing aqueous pigment dispersion for inkjet recording] The aqueous pigment dispersion of the present invention is preferably produced by mixing an aqueous dispersion (I) of a self-dispersing pigment (A), an aqueous dispersion (II) of a resin-dispersed pigment (B), and a salt (C). There is no particular limitation on the mixing order of the aqueous dispersion (I) of the self-dispersing pigment (A), the aqueous dispersion (II) of the resin-dispersed pigment (B), and the salt (C). However, among them, from the viewpoint of the storage stability of the aqueous pigment dispersion and the improvement of printing density and fixing property, the aqueous pigment dispersion of the present invention is obtained by mixing the aqueous dispersion (II) of the resin-dispersed pigment (B) with at least a part of the salt (C) to obtain an aqueous dispersion, and then mixing the aqueous dispersion with the aqueous dispersion (I) of the self-dispersing pigment (A) and the remainder of the salt (C) to be blended as necessary to obtain an aqueous pigment dispersion. It is more preferably included, and it is further preferably produced by a method including the following Step 1 and Step 2. Step 1: A step of mixing the aqueous dispersion (II) of the resin-dispersed pigment (B) and the salt (C) to obtain an aqueous dispersion (II') Step 2: A step of mixing the aqueous dispersion (II') obtained in Step 1 with the aqueous dispersion (I) of the self-dispersing pigment (A) to obtain an aqueous pigment dispersion

[0036] <Step 1> Step 1 is a step of mixing the aqueous dispersion (II) of the resin-dispersed pigment (B) and the salt (C) to obtain an aqueous dispersion (II'). In the present invention, from the viewpoint of sufficiently refining the pigment and improving the printing density and fixing property, it is preferable to include the following Step 1-1 before Step 1. Step 1-1: A step of subjecting a mixture of a pigment and an aqueous dispersion of a resin (b) to a dispersion treatment to obtain an aqueous dispersion (II) of a resin-dispersed pigment (B)

[0037] In Step 1-1, from the viewpoint of improving the dispersion stability of the pigment and improving the storage stability of the aqueous pigment dispersion, it is preferable to use the above-mentioned neutralizing agent for the preparation of the aqueous dispersion of the resin (b). When using a neutralizing agent, it is preferable to neutralize so that the pH of the obtained aqueous dispersion (II) is 7 or more and 11 or less. In the dispersion treatment in Step 1-1, although the pigment can be atomized to a desired particle size only by this dispersion due to shear stress, from the viewpoint of obtaining a uniform aqueous dispersion, it is preferable to perform further dispersion after preliminary dispersion. As the disperser used for preliminary dispersion, a commonly used mixing and stirring device such as an anchor blade or a dispersing blade can be used. As means for applying the shear stress used for this dispersion, for example, kneaders such as a roll mill and a kneader; high-pressure homogenizers such as a microfluidizer; and media-type dispersers such as a paint shaker and a bead mill can be mentioned. Among these, from the viewpoint of reducing the particle size of the pigment, it is preferable to use a high-pressure homogenizer or a bead mill. When performing the dispersion treatment using a high-pressure homogenizer, the average particle size of the pigment can be adjusted by controlling the treatment pressure and the number of passes. From the viewpoints of productivity and economy, the treatment pressure is preferably 60 MPa or more and 300 MPa or less, and the number of passes is preferably 3 or more and 30 or less. Also, for the purpose of removing coarse particles and the like, it is preferable to obtain, as the aqueous dispersion (II), something that has passed through a filter or the like.

[0038] In Step 1-1, from the viewpoint of improving the storage stability of the aqueous pigment dispersion, it is preferable to further add a crosslinking agent and react the crosslinking agent with the resin (b) to obtain an aqueous dispersion (II) of a resin-dispersed pigment (B) in which the pigment is dispersed with the resin (b) crosslinked by the crosslinking agent. The temperature of the crosslinking reaction is preferably 40°C or more and 95°C or less, the time of the crosslinking reaction is preferably 0.5 hour or more, more preferably 1 hour or more, and preferably 10 hours or less, more preferably 7 hours or less.

[0039] In Step 1, the method of mixing the aqueous dispersion (II) and the salt (C) is not particularly limited, and for example, it can be mixed using a conventionally known mixing device such as a homomixer, a homodisper, a wave rotor, a homogenizer, a disperser, a paint conditioner, a ball mill, a magnetic stirrer, a mechanical stirrer, etc. There are no particular restrictions on the method of adding salt (C), but it is preferable to add an aqueous solution of salt (C) to the aqueous dispersion (II) all at once or in portions.

[0040] <Step 2> Step 2 is a step of mixing the aqueous dispersion (II’) obtained in Step 1 with the aqueous dispersion (I) of the self-dispersing pigment (A) to obtain an aqueous pigment dispersion. The aqueous dispersion (I) is obtained by dispersing the solid content of the self-dispersing pigment (A) in an aqueous medium. As the commercially available aqueous dispersion (I), the specific examples of the commercially available products of the aforementioned self-dispersing pigment (A) can be used. In Step 2, there are no particular restrictions on the method of mixing the aqueous dispersion (II’) obtained in Step 1 with the aqueous dispersion (I), but they can be mixed using a conventionally known mixing device in the same manner as in Step 1. In Step 2, there are no particular restrictions on the method of adding the aqueous dispersion (I), but it is preferable to add the aqueous dispersion (I) to the pigment aqueous dispersion obtained in Step 1 all at once or in portions.

[0041] (Composition and Physical Properties of Aqueous Pigment Dispersion) The content of the self-dispersing pigment (A) in the aqueous pigment dispersion of the present invention is preferably 3% by mass or more, more preferably 4% by mass or more, still more preferably 5% by mass or more from the viewpoint of improving the printing density, and preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less from the viewpoints of improving the storage stability and fixing property of the aqueous pigment dispersion. The content of the resin-dispersed pigment (B) in the aqueous pigment dispersion of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, still more preferably 2% by mass or more from the viewpoints of improving the storage stability and fixing property of the aqueous pigment dispersion, and preferably 10% by mass or less, more preferably 8% by mass or less, still more preferably 6% by mass or less, even more preferably 4% by mass or less from the viewpoint of improving the printing density. The total content of the pigments of the self-dispersing pigment (A) and the resin-dispersed pigment (B) in the aqueous pigment dispersion of the present invention, that is, the pigment concentration, is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 7% by mass or more, from the viewpoints of improving the storage stability of the aqueous pigment dispersion and improving the printing density and fixability, and is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less. The mass ratio of the content of the self-dispersing pigment (A) to the content of the resin-dispersed pigment (B) [self-dispersing pigment (A) / resin-dispersed pigment (B)] in the aqueous pigment dispersion of the present invention is preferably 40 / 60 or more, more preferably 45 / 55 or more, still more preferably 50 / 50 or more, even more preferably 55 / 45 or more, even more preferably 60 / 40 or more, even more preferably 65 / 35 or more, from the viewpoint of improving the printing density, and is preferably 90 / 10 or less, more preferably 85 / 15 or less, still more preferably 80 / 20 or less, even more preferably 75 / 25 or less, from the viewpoints of improving the storage stability of the aqueous pigment dispersion and improving the fixability.

[0042] The content of the salt (C) in the aqueous pigment dispersion of the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, still more preferably 0.3% by mass or more, even more preferably 0.4% by mass or more, from the viewpoint of improving the printing density, and is preferably 3% by mass or less, more preferably 2% by mass or less, still more preferably 1% by mass or less, even more preferably 0.5% by mass or less, from the viewpoint of improving the storage stability of the aqueous pigment dispersion. The content of the salt (C) with respect to 100 parts by mass of the content of the self-dispersing pigment (A) in the aqueous pigment dispersion of the present invention is preferably 0.2 part by mass or more, more preferably 0.5 part by mass or more, still more preferably 1 part by mass or more, even more preferably 3 part by mass or more, even more preferably 5 part by mass or more, from the viewpoint of improving the printing density, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, still more preferably 10 parts by mass or less, even more preferably 8 parts by mass or less, from the viewpoint of improving the storage stability of the aqueous pigment dispersion. The content of the salt (C) with respect to 100 parts by mass of the resin-dispersed pigment (B) in the aqueous pigment dispersion of the present invention is preferably 0.2 part by mass or more, more preferably 0.5 part by mass or more, still more preferably 1 part by mass or more, even more preferably 4 parts by mass or more, even more preferably 8 parts by mass or more, and even more preferably 10 parts by mass or more from the viewpoint of improving the printing density, and preferably 25 parts by mass or less, more preferably 20 parts by mass or less, still more preferably 17 parts by mass or less, and even more preferably 15 parts by mass or less from the viewpoint of improving the storage stability of the aqueous pigment dispersion.

[0043] The mass ratio [(pigment of the resin-dispersed pigment (B)) / resin (b)] of the content of the pigment of the resin-dispersed pigment (B) to the content of the resin (b) of the resin-dispersed pigment (B) in the aqueous pigment dispersion of the present invention is preferably 40 / 60 or more, more preferably 50 / 50 or more, still more preferably 60 / 40 or more, even more preferably 70 / 30 or more, and even more preferably 80 / 20 or more from the viewpoints of improving the storage stability of the aqueous pigment dispersion and improving the printing density, and preferably 98 / 2 or less, more preferably 95 / 5 or less, and still more preferably 92 / 8 or less from the same viewpoints as above. The mass ratio [salt (C) / resin (b)] of the content of the salt (C) to the content of the resin (b) of the resin-dispersed pigment (B) in the aqueous pigment dispersion of the present invention is preferably 0.1 or more, more preferably 0.2 or more, still more preferably 0.6 or more, even more preferably 1.0 or more, and even more preferably 1.2 or more from the viewpoint of improving the printing density, and preferably 3.0 or less, more preferably 2.5 or less, still more preferably 2.0 or less, and even more preferably 1.7 or less from the viewpoint of improving the storage stability of the aqueous pigment dispersion. The water content in the aqueous pigment dispersion of the present invention is preferably 75% by mass or more, more preferably 80% by mass or more, and still more preferably 85% by mass or more, and preferably 95% by mass or less, more preferably 93% by mass or less.

[0044] The aqueous pigment dispersion of the present invention may further contain additives such as water-soluble organic solvents such as wetting agents and penetrants commonly used in aqueous inks, surfactants, viscosity modifiers, defoamers, rust inhibitors, preservatives, and fungicides.

[0045] [Ink for inkjet recording] The ink for inkjet recording of the present invention (hereinafter, also referred to as "the ink of the present invention") preferably contains an aqueous pigment dispersion and a water-soluble organic solvent. That is, the ink of the present invention contains a self-dispersing pigment (A), a resin-dispersed pigment (B), a salt (C), water, and a water-soluble organic solvent. Since the ink of the present invention contains the above-mentioned aqueous pigment dispersion, it contains a resin-dispersed pigment that is stable with respect to the salt, and aggregation of the self-dispersing pigment due to the salt in the ink is suppressed, so it is considered to be excellent in storage stability and ejection reliability. The ink of the present invention is preferably an aqueous ink. Here, the "aqueous ink" means an ink in which water occupies the largest proportion by mass in the medium contained in the ink. As a method for producing the ink of the present invention, the method (i) of mixing the above-mentioned aqueous pigment dispersion and a water-soluble organic solvent may be used, or the aqueous dispersion (I) of the self-dispersing pigment (A), the aqueous dispersion (II) of the resin-dispersed pigment (B), the salt (C), and a water-soluble organic solvent may be mixed. In the method (ii), the mixing of the aqueous dispersion (I) of the self-dispersing pigment (A), the aqueous dispersion (II) of the resin-dispersed pigment (B), the salt (C), and the water-soluble organic solvent may be simultaneous or separate, but it is preferable to mix them in the order of the aqueous dispersion (II) of the resin-dispersed pigment (B), the salt (C), the aqueous dispersion (I) of the self-dispersing pigment (A), and the water-soluble organic solvent.

[0046] In the present invention, the "water solubility" of the water-soluble organic solvent means the property of being miscible with water in any proportion. The boiling point of the water-soluble organic solvent is, in terms of the weighted average value, preferably 90°C or higher, more preferably 150°C or higher, still more preferably 180°C or higher, and preferably 250°C or lower, more preferably 240°C or lower, still more preferably 230°C or lower. Examples of the water-soluble organic solvent include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, from the viewpoint of improving the printing density and fixing property, one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers are preferable. 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, and triethylene glycol, glycerin, and trimethylolpropane. Among these, one or more selected from the group consisting of propylene glycol, 1,2-hexanediol, triethylene glycol, and glycerin are preferable.

[0047] Examples of the polyhydric alcohol alkyl ether 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, and triethylene glycol monoisobutyl ether. As the water-soluble organic solvent, it is preferable to use 1,2-hexanediol and propylene glycol as the polyhydric alcohol and triethylene glycol monobutyl ether as the polyhydric alcohol alkyl ether in combination. The water-soluble organic solvent can be used alone or in combination of two or more.

[0048] The ink of the present invention may contain various additives such as a surfactant, a humectant, a wetting agent, a wetting and penetrating agent, a viscosity modifier, an antifoaming agent, a preservative, a fungicide, and a rust preventive agent, if necessary. Examples of the surfactant include nonionic surfactants, anionic surfactants, and amphoteric surfactants. Among these, nonionic surfactants are preferable. Examples of nonionic surfactants include polyoxyalkylene alkyl ether type surfactants, acetylene glycol based surfactants, polyhydric alcohol type surfactants, fatty acid alkanolamides, silicone based surfactants, and fluorine based surfactants.

[0049] From the viewpoint of improving printing density, the blending amount of the above-mentioned aqueous pigment dispersion in the ink of the present invention is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less, even more preferably 8% by mass or less, as the total content of the pigments of the self-dispersing pigment (A) and the resin-dispersed pigment (B) in the ink. From the viewpoints of improving the storage stability of the ink and improving the printing density, the mass ratio [(pigment of resin-dispersed pigment (B)) / resin (b)] of the pigment content of the resin-dispersed pigment (B) to the resin (b) content in the resin-dispersed pigment (B) in the ink of the present invention is preferably 40 / 60 or more, more preferably 50 / 50 or more, still more preferably 60 / 40 or more, even more preferably 70 / 30 or more, even more preferably 80 / 20 or more, and from the same viewpoints as above, preferably 98 / 2 or less, more preferably 95 / 5 or less, still more preferably 92 / 8 or less. From the viewpoint of improving printing density, the content of the salt (C) in the ink of the present invention is preferably 0.02% by mass or more, more preferably 0.05% by mass or more, still more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and preferably 1.5% by mass or less, more preferably 1.0% by mass or less, still more preferably 0.7% by mass or less, even more preferably 0.5% by mass or less, even more preferably 0.3% by mass or less. The content of the water-soluble organic solvent in the ink of the present invention is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less, even more preferably 15% by mass or less. The water content in the ink of the present invention is preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 60% by mass or more, even more preferably 70% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less.

[0050] The viscosity of the ink of the present invention at 20 °C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, still more preferably 3.5 mPa·s or more, and preferably 15 mPa·s or less, more preferably 10 mPa·s or less, still more preferably 8 mPa·s or less, even more preferably 6 mPa·s or less. The viscosity of the aqueous ink can be measured by the method described in the examples using an E-type viscometer.

[0051] (Inkjet recording method) When the ink of the present invention is used for inkjet recording, the inkjet recording method is not particularly limited, and it can be used for any ejection method such as an electro-mechanical conversion method such as a piezo method or an electro-thermal conversion method such as a thermal method. Examples of the recording medium to which the ink of the present invention is applied include ordinary paper with high water absorbency, coated paper with low water absorbency, and resin films. Examples of the coated paper include general-purpose glossy paper and multicolor form gloss paper. Examples of the resin film include, for example, polyester film, polyvinyl chloride film, polypropylene film, and polyethylene film. The resin film may be a biaxially stretched film, a uniaxially stretched film, or an unstretched film. Among these, from the viewpoints of printing density and fixing property, a recording medium with high water absorbency is preferable, and ordinary paper is more preferable.

Examples

[0052] In the following examples, comparative examples, and production examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The measurement methods for each physical property are as follows.

[0053] (1) Measurement of the weight average molecular weight of resin (b) It was determined by gel permeation chromatography. The measurement conditions are shown below. GPC apparatus: "HLC-8320GPC" manufactured by Tosoh Corporation Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", "TSKgel guardcolumn SuperAW-H" manufactured by Tosoh Corporation Eluent: A solution prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively Flow rate: 1 mL / min Standard substances: Monodisperse polystyrene kits with known molecular weights, "PStQuick B (F-550, F-80, F-10, F-1, A-1000)", "PStQuick C (F-288, F-40, F-4, A-5000, A-500)" manufactured by Tosoh Corporation

[0054] (2) Measurement of acid value of resin (b) Using an automatic potentiometric titrator (manufactured by Kyoto Electronics Industry Co., Ltd., motor-driven burette, model number: APB-610), in the case of resin (b) having no cross-linked structure, resin (b) having no cross-linked structure was dissolved in a titration solvent obtained by mixing toluene and acetone (toluene:acetone = 2:1 (volume ratio)), and in the case of cross-linked resin (b), an aqueous pigment dispersion was dispersed in the titration solvent and titrated with a 0.1 N potassium hydroxide / ethanol solution by potentiometric titration, and the inflection point on the titration curve was taken as the end point. The acid value (mgKOH / g) was calculated from the titration volume up to the end point of the potassium hydroxide solution.

[0055] (3) Measurement of solid content concentration Weighed 10.0 g of sodium sulfate, which had been made constant in a desiccator, into a 30 mL polypropylene container (φ = 40 mm, height = 30 mm), added approximately 1.0 g of the sample thereto, mixed it, then weighed it accurately, maintained it at 105°C for 2 hours to remove the volatile matter, left it in the desiccator for an additional 15 minutes, and measured the mass. The mass of the sample after removing the volatile matter was taken as the solid content, and divided by the mass of the added sample to obtain the solid content concentration (%).

[0056] (4) Measurement of the average particle size of the particles contained in the ink for inkjet recording Cumulant analysis was performed using a laser particle analysis system ("ELS-8000" manufactured by Otsuka Electronics Co., Ltd.), and the obtained cumulant average particle size was measured as the average particle size of the resin-dispersed pigment (B) in the aqueous dispersion. As the measurement sample, a dispersion diluted with water so that the concentration of the particles to be measured was 5 × 10 -3 % (in terms of solid content concentration) was used. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and an integration number of 100 times, and the refractive index of water (1.333) was input as the refractive index of the dispersion medium.

[0057] (5) Viscosity of the ink for inkjet recording The viscosity at 20°C was measured using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., model number: TV-25, using a standard cone rotor of 1°34’×R24, rotation speed of 100 rpm).

[0058] <Production of resin (b)> Production Example 1 30.8 parts of acrylic acid, 59.2 parts of styrene, and 10.0 parts of α-methylstyrene were mixed to prepare a raw material monomer mixture. 10 parts of methyl ethyl ketone (hereinafter referred to as "MEK"), 0.3 part of 2-mercaptoethanol as a polymerization chain transfer agent, and 10% (10.0 parts) of the above raw material monomer mixture were placed in a reaction vessel, mixed, and sufficiently purged with nitrogen gas. On one hand, into a dropping funnel, a mixed solution of the remaining 90% (90.0 parts) of the raw material monomer mixture, 0.27 part of 2-mercaptoethanol, 40 parts of MEK, and 1.1 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) ("V-65" manufactured by Fuji Film Wako Pure Chemical Corporation) as an azo radical polymerization initiator was put. While stirring the raw material monomer mixture in the reaction vessel under a nitrogen atmosphere, the temperature was raised to 65°C, and the raw material monomer mixture in the dropping funnel was dropped over 3 hours. After stirring for 2 hours from the end of dropping, a solution prepared by dissolving 0.15 part of the azo radical polymerization initiator (V-65) in 2.5 parts of MEK was added, and it was aged at 65°C for 2 hours and further at 70°C for 2 hours to obtain a solution of a resin (b1) having a carboxy group (weight average molecular weight: 16,000, acid value: 240 mgKOH / g).

[0059] Production Example 2 13.8 parts of methacrylic acid, 56.2 parts of benzyl acrylate, 40.0 parts (20.0 parts as solids) of a styrene macromer ("AS-6S" manufactured by Toagosei Co., Ltd., number average molecular weight: 6,000, solid content concentration 50%), and 10.0 parts of polypropylene glycol monomethacrylate ("Blemmer PP-800" manufactured by NOF Corporation, average number of moles of propylene oxide added 13, terminal: hydroxyl group) were mixed to prepare a raw material monomer mixture. Into the reaction vessel, 10 parts of MEK, 0.3 part of 2-mercaptoethanol, and 10% (12.0 parts) of the raw material monomer mixture were put and mixed, and sufficient nitrogen gas substitution was performed. On one hand, into a dropping funnel, a mixed solution of the remaining 90% (108.0 parts) of the raw material monomer mixture, 0.27 part of 2-mercaptoethanol, 40 parts of MEK, and 1.1 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) ("V-65" manufactured by Fuji Film Wako Pure Chemical Corporation) as an azo radical polymerization initiator was put. Thereafter, in the same manner as in Production Example 1, a solution of a resin (b2) having a carboxy group (weight average molecular weight: 150,000, acid value: 90 mgKOH / g) was obtained.

[0060] <Production of Aqueous Solution (P) of Resin (b)> Production Example 1-1 After drying the solution of the resin (b1) obtained in Production Example 1 under reduced pressure, it was pulverized using a coffee mill to obtain the resin (b1). 80.0 parts of the resin (b1), 287.2 parts of ion-exchanged water, and 32.4 parts of a 5N aqueous sodium hydroxide solution (reagent manufactured by Fujifilm Wako Pure Chemical Corporation) as a neutralizing agent (an amount such that the ratio of the number of moles of sodium hydroxide to the number of moles of carboxy groups of the resin (b1) is 40 mol%) were added to a heat-resistant bottle. Neutralization and dispersion were carried out by heating at 90°C for 5 hours while stirring at 150 rpm to obtain an aqueous dispersion (P1) of the resin (b1) (degree of neutralization: 40 mol%, solid content concentration: 20.0%).

[0061] Production Example 1-2 In Production Example 1-1, an aqueous dispersion (P2) of the resin (b2) (degree of neutralization: 60 mol%, solid content concentration: 20.0%) was obtained in the same manner as Production Example 1-1 except that the type of the solution of the resin (b), the addition amount of the 5N aqueous sodium hydroxide solution, and the addition amount of ion-exchanged water were changed as shown in Table 1.

[0062]

Table 1

[0063] <Production of Aqueous Dispersion (II) of Resin Dispersed Pigment (B) Having No Crosslinked Structure> Production Example 2-1 To 39.2 parts of the aqueous dispersion (P1) of the resin (b1) obtained in Production Example 1-1, 373.9 parts of ion-exchanged water and 100.0 parts of carbon black (「Monarch880」manufactured by Cabot Corporation) as a black pigment were added, and using a disper (「Ultra Disper」manufactured by Asada Iron Works Co., Ltd.), stirring was carried out at 20°C for 60 minutes under the condition that the disper blade was rotated at 7,000 rpm. The obtained mixture was subjected to a dispersion treatment of 10 passes at a pressure of 200 MPa using a high-pressure homogenizer (「Microfluidizer」manufactured by Microfluidics Corporation, model name: M-110EH) to obtain a dispersion-treated product. The obtained dispersion was filtered through a 25 mL syringe without a needle (manufactured by Terumo Corporation) equipped with a syringe filter with a pore size of 5 μm ("Minisart" manufactured by Sartorius, model number: S7594-FMOSK) to remove coarse particles, thereby obtaining an aqueous dispersion (II-1) (solid content concentration: 21.0%) of a black pigment (B1) dispersed with a resin (b1) (hereinafter also referred to as "resin-dispersed pigment (B1)").

[0064] Production Example 2-2 In Production Example 2-1, an aqueous dispersion (II-2) (solid content concentration: 21.0%) of a black pigment (B2) dispersed with a resin (b2) (hereinafter also referred to as "resin-dispersed pigment (B2)") was obtained in the same manner as in Production Example 2-1, except that the type and addition amount of the aqueous dispersion (P) of the resin (b) and the addition amount of ion-exchanged water were changed as shown in Table 2.

[0065]

Table 2

[0066] <Production of Aqueous Dispersion (II) of Crosslinked Resin-Dispersed Pigment (B)> Production Example 2-3 100.0 parts (solid content concentration: 21.0%) of the aqueous dispersion (II-1) of the resin-dispersed pigment (B1) obtained above was placed in a glass bottle with a screw cap, and 0.64 part of trimethylolpropane polyglycidyl ether ("Denacol EX-321" manufactured by Nagase ChemteX Corporation, epoxy equivalent: 139 g / eq., water solubility rate: 27%) (an amount capable of crosslinking 70 mol% of all carboxyl groups contained in the resin (b1) (crosslinking rate 70 mol%)) as a crosslinking agent and 43.9 parts of ion-exchanged water were added, and the bottle was sealed. While stirring with a stirrer, it was heated at 70°C for 5 hours. Then, the temperature was lowered to room temperature, and it was filtered through a 25 mL syringe without a needle equipped with the syringe filter with a pore size of 5 μm, thereby obtaining an aqueous dispersion (II-3) (solid content concentration: 15.0%) of a black pigment (B1) dispersed with a crosslinked resin (b1) (mass ratio [pigment / crosslinked resin (b)]: 90 / 10, acid value of the crosslinked resin (b): 72 mgKOH / g) (hereinafter also referred to as "resin-dispersed pigment (B1')").

[0067] Production Example 2-4 Next, in Production Example 2-3, as shown in Table 3, except that the type and addition amount of the aqueous dispersion of the resin-dispersed pigment (B), the addition amount of trimethylolpropane polyglycidyl ether as a crosslinking agent (the amount capable of crosslinking 70 mol% of all carboxyl groups possessed by the resin (b2) (crosslinking rate 70 mol%)), and the addition amount of ion-exchanged water were changed, in the same manner as in Production Example 3-1, a black pigment (B2) dispersed with the crosslinked resin (b2) (mass ratio [pigment / crosslinked resin (b)]: 70 / 30, acid value of the crosslinked resin (b): 27 mgKOH / g) (hereinafter also referred to as "resin-dispersed pigment (B2')") aqueous dispersion (II-4) (solid content concentration: 15.0%) was obtained.

[0068] <Production of Aqueous Dispersion (II') of Crosslinked Resin-Dispersed Pigment (B)> Production Example 2-5 To the aqueous dispersion (II-3) of the resin-dispersed pigment (B1') obtained in Production Example 2-3, 27.1 parts of an aqueous solution of disodium hydrogen phosphate dodecahydrate (manufactured by Fujifilm Wako Pure Chemical Corporation) (solid content concentration at the time of charging: 10%) was further added to obtain an aqueous dispersion (II'-5) of the resin-dispersed pigment (B1') (solid content concentration: 14.2%).

[0069]

Table 3

[0070] Example 1 (Production of Aqueous Pigment Dispersion) As the aqueous dispersion (I-1) of the self-dispersing pigment (A1), a modified carbon black aqueous dispersion ("BONJET BLACK CW-4" manufactured by Orient Chemical Industries Co., Ltd.) was diluted with ion-exchanged water to a pigment concentration of 10.0%, and 63.00 parts of the solution was taken. To this, 20.00 parts of the aqueous dispersion (II-3) of the resin-dispersed pigment (B1') obtained in Production Example 2-3 (mass ratio [pigment / crosslinked resin (b)]: 90 / 10) (solid content concentration: 15.0%) was added. Further, 3.75 parts of an aqueous solution of disodium hydrogen phosphate dodecahydrate (reagent, manufactured by FUJIFILM Wako Pure Chemical Corporation) as the salt (C) (solid content concentration at the time of charging: 10%) was added, and then it was adjusted with ion-exchanged water to obtain an aqueous pigment dispersion (D1) with a pigment concentration of 9.0%. (Production of Inkjet Recording Ink) The aqueous pigment dispersion obtained above was blended so that the pigment concentration in the ink was 6.0%, and 4.0 parts of triethylene glycol monobutyl ether (hereinafter referred to as "BTG"), 4.0 parts of 1,2-hexanediol (hereinafter referred to as "1,2-HD"), 4.0 parts of propylene glycol (hereinafter referred to as "PG"), 0.5 part of "Surfinol 104PG-50" (propylene glycol solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, active ingredient 50%) manufactured by Nissin Chemical Industry Co., Ltd. as an acetylene glycol-based surfactant (hereinafter referred to as "Surfinol 104PG-50") as it is, and ion-exchanged water were added and adjusted so that the total amount was 100.0 parts. The obtained mixed solution was filtered through a filter with a pore size of 1.2 μm ("Minisart" manufactured by Sartorius, model number: SM17593K) to obtain Ink I-1.

[0071] Examples 2 to 17 In Example 1, as shown in Table 4, except that the type and amount of the aqueous dispersion (I) of the self-dispersing pigment (A), the type and amount of the aqueous dispersion (II) of the resin-dispersed pigment (B), the type and amount of the aqueous solution of the salt (C), and the amount of ion-exchanged water were changed, aqueous pigment dispersions (D2) to (D17) were obtained in the same manner as in Example 1. Next, in Example 1, except that the aqueous pigment dispersion (D1) was changed to the aqueous pigment dispersions (D2) to (D17), Inks I-2 to I-17 were obtained in the same manner, respectively. Details of the components other than those used in Example 1 are as follows. Aqueous dispersion (I-2) of self-dispersing pigment (A2): A liquid obtained by diluting a modified carbon black aqueous dispersion ("BONJET BLACK CW-4" manufactured by Orient Chemical Industries, Ltd.) with ion-exchanged water to a pigment concentration of 10.0%. Sodium pyrophosphate: Manufactured by Merck KGaA Sodium polyphosphate: Manufactured by Fujifilm Wako Pure Chemical Corporation Potassium phthalate: Manufactured by Kanto Chemical Co., Inc.

[0072] Example 18 To 63.00 parts of a liquid obtained by diluting a modified carbon black aqueous dispersion ("BONJET BLACK CW-4" manufactured by Orient Chemical Industries, Ltd.) with ion-exchanged water to a pigment concentration of 10.0% as the aqueous dispersion (I-1) of self-dispersing pigment (A1), 23.77 parts of the aqueous dispersion (II'-5) (solid content concentration: 14.2%) of the resin-dispersed pigment (B1') obtained in Production Example 2-5 (mass ratio [pigment / crosslinked resin (b)]: 90 / 10) was added, and the mixture was adjusted with ion-exchanged water to obtain an aqueous pigment dispersion (D18) having a pigment concentration of 9.0%. Next, in Example 1, Ink I-18 was obtained in the same manner except that the aqueous pigment dispersion (D1) was changed to the aqueous pigment dispersion (D18).

[0073] Comparative Examples 1 to 3 As shown in Table 5, aqueous pigment dispersions (DC1) to (DC3) were obtained in the same manner as in Example 1 except that the amounts of the aqueous dispersion (I) of self-dispersing pigment (A), the aqueous dispersion (II) of resin-dispersed pigment (B), the aqueous solution of salt (C), and the amount of ion-exchanged water were changed. Next, in Example 1, Inks I-C1 to I-C3 were obtained in the same manner except that the aqueous pigment dispersion (D1) was changed to the aqueous pigment dispersions (DC1) to (DC3).

[0074] [Evaluation] Using each of the aqueous pigment dispersions and each of the aqueous inks obtained in the examples and comparative examples, the evaluation was carried out according to the following (1) to (3). The results are shown in Tables 4 and 5. (1) Evaluation of storage stability of aqueous pigment dispersion The obtained aqueous pigment dispersion was stored at 70 °C, and after one week, the average particle size and viscosity were measured. The particle size retention rate and viscosity retention rate were calculated by the following formulas respectively and used as indicators of storage stability. The closer the particle size retention rate and viscosity retention rate are to 100%, the better the storage stability. Particle size retention rate (%) = [Average particle size of the aqueous pigment dispersion after storage / Average particle size of the aqueous pigment dispersion before storage] × 100 Viscosity retention rate (%) = [Viscosity of the aqueous pigment dispersion after storage / Viscosity of the aqueous pigment dispersion before storage] × 100

[0075] (2) Evaluation of printing density The printing density was evaluated using an inkjet printer ("PX-105" manufactured by Seiko Epson Corporation). Using the obtained aqueous ink, a solid image with a size of 5 cm × 5 cm and a Duty of 100% was printed on ordinary paper P paper (manufactured by Fujifilm Business Innovation Corporation) as a highly absorbent recording medium. After leaving it in an environment of 23 °C and 50% relative humidity for one day, the printing density at five locations, namely the center and four corners, was measured using a spectrophotometer / colorimeter "X-Rite eXact" (manufactured by X-Rite) under the conditions of an observation light source D50 and an observation field angle of 2°. The average value of the printing density at the five locations was calculated as the printing density of the printed matter. The higher the numerical value of the printing density, the better the image on the highly absorbent recording medium.

[0076] (3) Evaluation of fixability The fixability was evaluated using an inkjet printer ("PX-105" manufactured by Seiko Epson Corporation). Using the obtained aqueous ink, a solid image with a size of 5 cm × 5 cm and a Duty of 100% was printed on ordinary paper P paper (manufactured by Fujifilm Business Innovation Corporation) as a highly absorbent recording medium. After leaving it in an environment of 23 °C and 50% relative humidity for one day, the fixability was evaluated. A cellulose non-woven fabric ("Bencott (registered trademark) M3-II" manufactured by Asahi Kasei Corporation) was pressed against the solid image part, and the bottom surface of the weight (the area of the bottom surface is 50 cm 2) A load of 200 gf was applied using [equipment name] to rub the solid image portion. The stain of the ink transferred to the cellulose nonwoven fabric was visually judged, and the fixing property was evaluated by the number of rubbing times at which the stain occurred. The larger the value of the number of rubbing times, the better the fixing property. In addition, if no stain was observed even after 20 rubs, the evaluation was terminated.

[0077]

Table 4

[0078]

Table 5

[0079] From Table 4 and Table 5, it can be seen that the aqueous pigment dispersions of Examples 1 to 18 are superior in storage stability compared to Comparative Example 3, and the inkjet recording inks using the aqueous pigment dispersions of Examples 1 to 18 have a high printing density and can obtain a recording material with excellent fixing property compared to Comparative Examples 1 to 3. Also, in inkjet recording on a highly absorbent recording medium such as plain paper, it is very difficult to increase the numerical value of the printing density by 0.02 without sacrificing other performances such as cost, and the difference in printing density between Example 1 to 18 and Comparative Example 1 can be said to be a significant difference.

Industrial Applicability

[0080] According to the present invention, since it is not necessary to make a special capital investment and a part of the expensive self-dispersing pigment can be replaced with an inexpensive resin-dispersed pigment, it is excellent in storage stability, and in inkjet recording on a highly absorbent recording medium, it is possible to provide an aqueous pigment dispersion capable of obtaining a recording material having a high printing density and excellent fixing property and an ink using the aqueous pigment dispersion at an unprecedentedly low cost.

Claims

1. An aqueous pigment dispersion for inkjet recording, containing a self-dispersing pigment (A), a resin-dispersed pigment (B), a salt (C), and water.

2. The aqueous pigment dispersion for inkjet recording according to Claim 1, wherein the salt (C) is at least one selected from the group consisting of phosphates and phthalates.

3. The aqueous pigment dispersion for inkjet recording according to Claim 1 or 2, wherein the salt (C) is a salt containing sodium ions.

4. The aqueous pigment dispersion for inkjet recording according to any one of Claims 1 to 3, wherein the salt (C) is a salt of phosphoric acid and sodium.

5. The aqueous pigment dispersion for inkjet recording according to any one of Claims 1 to 4, wherein the content of the salt (C) relative to 100 parts by mass of the content of the self-dispersing pigment (A) is 0.5 parts by mass or more and 15 parts by mass or less.

6. The aqueous pigment dispersion for inkjet recording according to any one of Claims 1 to 5, wherein the content of the salt (C) relative to 100 parts by mass of the content of the resin-dispersed pigment (B) is 1 part by mass or more and 25 parts by mass or less.

7. The aqueous pigment dispersion for inkjet recording according to any one of Claims 1 to 6, wherein the pigments of the self-dispersing pigment (A) and the resin-dispersed pigment (B) are both carbon black.

8. The aqueous pigment dispersion for inkjet recording according to any one of Claims 1 to 7, wherein the mass ratio [self-dispersing pigment (A) / resin-dispersed pigment (B)] of the content of the self-dispersing pigment (A) to the content of the resin-dispersed pigment (B) is 40 / 60 or more and 90 / 10 or less.

9. The mass ratio [(pigment of the resin-dispersed pigment (B)) / resin (b)] of the content of the pigment of the resin-dispersed pigment (B) to the content of the resin (b) of the resin-dispersed pigment (B) is 40 / 60 or more and 95 / 5 or less. The aqueous pigment dispersion for inkjet recording according to any one of claims 1 to 8.

10. The mass ratio [salt (C) / resin (b)] of the content of the salt (C) to the content of the resin (b) of the resin-dispersed pigment (B) is 0.1 or more and 3.0 or less. The aqueous pigment dispersion for inkjet recording according to any one of claims 1 to 9.

11. An ink for inkjet recording containing the aqueous pigment dispersion according to any one of claims 1 to 10 and a water-soluble organic solvent.

12. The content of the salt (C) is 0.02% by mass or more and 1.5% by mass or less. The ink for inkjet recording according to claim 11.

13. A method for producing an aqueous pigment dispersion for inkjet recording, comprising the following steps 1 and 2. Step 1: A step of mixing an aqueous dispersion (II) of a resin-dispersed pigment (B) and a salt (C) to obtain an aqueous dispersion (II'). Step 2: A step of mixing the aqueous dispersion (II') obtained in Step 1 and an aqueous dispersion (I) of a self-dispersing pigment (A) to obtain an aqueous pigment dispersion.

Images