JP2021102668A - Pigment aqueous dispersion - Google Patents

Abstract

To provide a pigment aqueous dispersion capable of maintaining excellent storage stability of ink when being blended with the ink, and, in an inkjet recording system, improving continuous ejection stability by suppressing occurrence of kogation in a heater part of a thermal head in particular, its manufacturing method, and an inkjet recording aqueous ink containing the pigment aqueous dispersion.SOLUTION: In a pigment aqueous dispersion, an organic pigment A is dispersed with a crosslinked polymer, the organic pigment A is one or more selected from a disazopyrazolone pigment, perinone pigment, dioxazine pigment and copper phthalocyanine pigment, and the crosslinked polymer is a polymer crosslinked with a specific crosslinking agent. There are also provided a manufacturing method of the pigment aqueous dispersion, and an inkjet recording aqueous ink containing the pigment aqueous dispersion.SELECTED DRAWING: None

Description

The present invention relates to an aqueous pigment dispersion, a method for producing the same, and a water-based ink for inkjet recording containing the aqueous pigment dispersion.

The inkjet recording method is a recording method in which ink droplets are directly ejected from a very fine nozzle onto a recording medium by heat or mechanical vibration and adhered to obtain a printed matter on which characters and images are recorded. This method is remarkably popular because it is easy to make full color, inexpensive, can use plain paper as a recording medium, and has many advantages such as non-contact with the printed matter.
In particular, a thermal inkjet recording device that boils water by heating a heater and ejects ink at the foaming pressure can produce inkjet heads using MEMS (micro electro mechanical system) technology, which enables inexpensive and high-speed printing. Since it is possible, it is widely used. In recent years, inks that use pigments as colorants have been widely used in order to impart weather resistance and water resistance to printed matter.
In the case of ink jet recording pigment ink, the pigment is dispersed in the vehicle using a dispersant, but with the remarkable improvement in printing speed in recent years, the thermal and mechanical stress on the ink increases, and it continues. Improvement of discharge stability (continuous discharge stability) for stable discharge is being studied. In particular, in the case of a thermal inkjet recording device, the temperature of the discharge heater of the thermal head momentarily becomes high at 300 ° C. or higher, and ink components such as pigments are scorched on the heater and deposits are deposited. So-called kogation occurs, which reduces the foaming pressure and results in poor ejection properties. Therefore, in order to suppress the aggregation and accumulation of colloids in the vicinity of the surface of the heater, improvement of the thermal stability of the colloids has also been attempted.

For example, Patent Document 1 describes a pigment aqueous dispersion having excellent thermal stability when mixed with ink and printing, particularly suppressing the occurrence of crosslinks in the heater portion of the thermal head, and having excellent continuous ejection stability. A pigment aqueous dispersion containing crosslinked polymer particles containing a pigment, wherein the crosslinked polymer contained in the particles has a specific chain length of ethyleneoxy group or propyleneoxy group. Described is a pigment aqueous dispersion or the like, which is a polymer crosslinked with a compound represented by the above, and the pigment is carbon black.

JP-A-2017-165965

In a general inkjet recording method, inks using the three basic primary colors of yellow, magenta, and cyan and black coloring materials are adopted, and various colors are reproduced by subtractively mixing the inks of the three basic primary colors on a recording medium. However, so-called special color inks using color materials having hues other than the three basic primary colors such as orange, red, violet, green, and blue may be added to expand the color reproducibility region.
However, although the technique described in Patent Document 1 improves the thermal stability and continuous ejection stability of carbon black, it has been found that it is not sufficient for organic pigments such as those used in spot color inks.
According to the present invention, when blended with ink, while maintaining excellent storage stability of the ink, in the inkjet recording method, it is possible to suppress the occurrence of cogation, especially in the heater portion of the thermal head, and improve the continuous ejection stability. It is an object of the present invention to provide a pigment aqueous dispersion capable of producing an ink jet, a method for producing the same, and an inkjet recording water-based ink containing the pigment aqueous dispersion.

The present inventors have made a pigment aqueous dispersion in which an organic pigment is dispersed with a cross-linked polymer, the organic pigment is a specific pigment, and the cross-linked polymer is a polymer cross-linked with a specific cross-linking agent. , Have found that the above problems can be solved.
That is, the present invention provides the following [1] to [3].
[1] An aqueous pigment dispersion in which the organic pigment A is dispersed with a crosslinked polymer.
The organic pigment A is one or more selected from dysazopyrazolone-based pigments, perinone-based pigments, dioxazine-based pigments, and copper phthalocyanine-based pigments.
An aqueous pigment dispersion in which the crosslinked polymer is a polymer crosslinked with 1,4-butanediol diglycidyl ether as a crosslinking agent.
[2] An inkjet recording water-based ink containing the pigment aqueous dispersion according to the above [1] and a solvent.
[3] A method for producing an aqueous pigment dispersion in which an organic pigment A is dispersed in a crosslinked polymer.
The organic pigment A is one or more selected from dysazopyrazolone-based pigments, perinone-based pigments, dioxazine-based pigments, and copper phthalocyanine-based pigments.
A method for producing an aqueous pigment dispersion, which comprises the following steps 1 and 2.
Step 1: Disperse the water-dispersible polymer, the organic pigment A, and the pigment mixture containing water to obtain a pigment aqueous dispersion. Step 2: The pigment aqueous dispersion obtained in Step 1 and as a cross-linking agent. A step of mixing 1,4-butanediol diglycidyl ether and reacting the water-dispersible polymer with the cross-linking agent to form a cross-linked polymer to obtain a pigment aqueous dispersion.

According to the present invention, when blended with ink, while maintaining excellent storage stability of the ink, in the inkjet recording method, in particular, the occurrence of cogation in the heater portion of the thermal head is suppressed, and continuous ejection stability is maintained. It is possible to provide an aqueous pigment dispersion that can be improved, a method for producing the same, and a water-based ink for inkjet recording containing the aqueous pigment dispersion.

[Pigment aqueous dispersion]
The pigment aqueous dispersion of the present invention is a pigment aqueous dispersion in which an organic pigment A is dispersed with a crosslinked polymer, and the organic pigment A is a disazopyrazolone-based pigment, a perinone-based pigment, a dioxazine-based pigment, and a copper phthalocyanine-based pigment. One or more selected from pigments, the cross-linked polymer is a polymer cross-linked with 1,4-butanediol diglycidyl ether as a cross-linking agent.
Here, 1,4-butanediol diglycidyl ether is represented by the following formula (1).

In the pigment aqueous dispersion of the present invention, water occupies the maximum proportion of the medium in which the organic pigment A is dispersed by the crosslinked polymer. That is, the medium is mainly composed of water, but may contain components other than water. Examples of components other than water include alcohol solvents such as methanol, ethanol, isopropanol and butanol; ketone solvents such as acetone and methyl ethyl ketone; and organic solvents such as ether solvents such as tetrahydrofuran.
The content of water in the medium is preferably 80% by mass or more, more preferably 90% by mass or more, and preferably 100% by mass, from the viewpoint of dispersion stability and environmental safety of the pigment aqueous dispersion. It is as follows.

Since the pigment aqueous dispersion of the present invention can obtain a good printed matter when blended with an aqueous ink and printed, it is suitably used as a pigment aqueous dispersion for flexographic printing, gravure printing, or inkjet recording. be able to. The pigment aqueous dispersion of the present invention is preferably used as a pigment aqueous dispersion for inkjet recording because it is excellent in continuous ejection stability in an inkjet recording method when it is blended with an aqueous ink and printed. It is more preferable to use it as a thermal ink jet recording pigment aqueous dispersion.

The pigment aqueous dispersion of the present invention maintains excellent storage stability of the ink when blended with the ink, and suppresses the occurrence of cogation, especially in the heater portion of the thermal head, in the inkjet recording method, and continuously ejects the ink. Stability can be improved. The reason is not clear, but it can be considered as follows.
In the pigment aqueous dispersion of the present invention, the organic pigment type is one or more selected from a specific type, that is, a disazopyrazolone-based pigment, a perinone-based pigment, a dioxazine-based pigment, and a copper phthalocyanine-based pigment, and further, as a cross-linking agent, 1 Contains organic pigment particles dispersed and atomized by a polymer crosslinked with 4-butanediol diglycidyl ether. It is presumed that the crosslinked polymer has a crosslinked structure derived from the crosslinking agent and can efficiently exist in the vicinity of the pigment because it has a strong affinity specific to the above-mentioned specific type of organic pigment. .. Therefore, even if the liquid medium evaporates in the heater portion of the thermal inkjet printer and the pigments are close to each other, the dispersion stability is excellent, the pigment aggregation can be suppressed, and the pigment in the liquid medium can be suppressed. Since it is possible to reduce the amount of the coarse-grained crosslinked polymer floating without being adsorbed on the surface, it is considered that the occurrence of cogging can be suppressed and the continuous discharge stability is improved.
Further, in the pigment aqueous dispersion, by having the crosslinked structure derived from the crosslinking agent in the crosslinked polymer in which the organic pigment is dispersed, the organic pigment particles dispersed in the crosslinked polymer and the water of the pigment aqueous dispersion are the main components. It is thought that the affinity with the liquid medium will also increase. Therefore, even if the ink is maintained at a high temperature for a long period of time, the organic pigment dispersed by the crosslinked polymer having a crosslinked structure derived from the crosslinking agent can maintain high dispersion stability and is excellent in storage. It is presumed that stability can be maintained.

<Organic Pigment A>
In the present invention, the organic pigment A is contained in the pigment aqueous dispersion as the organic pigment A dispersed by the crosslinked polymer, and the crosslinked polymer particles containing the organic pigment A are contained from the viewpoint of improving continuous discharge stability and storage stability. It is preferably contained as (hereinafter, also simply referred to as “pigment A-containing crosslinked polymer particles”).

The organic pigment A according to the present invention is one or more selected from disazopyrazolone-based pigments, perinone-based pigments, dioxazine-based pigments, and copper phthalocyanine-based pigments.
Examples of the disazopyrazolone pigment include C.I. I. Pigment Orange 34, 13 and other disazopyrazolone orange pigments; C.I. I. Examples thereof include dysazopyrazolone red pigments such as Pigment Red 37, 38, 41, and 111. Of these, disazopyrazolone orange pigments are preferable from the viewpoint of improving continuous discharge stability.
Examples of perinone pigments include C.I. I. Perinone orange pigments such as Pigment Orange 43; C.I. I. Examples thereof include perinone red pigments such as Pigment Red 194. Of these, perinone orange pigments are preferable from the viewpoint of improving continuous discharge stability.
Examples of dioxazine pigments include C.I. I. Examples thereof include dioxazine violet pigments such as Pigment Violet 23.
Examples of the copper phthalocyanine pigment include C.I. I. Pigment Green 7 (Copper Phthalocyanine Green), C.I. I. Pigment Green 36 (Copper Phthalocyanine Green) and other copper phthalocyanine green pigments; I. Examples thereof include copper phthalocyanine blue pigments such as Pigment Blue 15 (copper phthalocyanine blue). Of these, copper phthalocyanine green pigments are preferable from the viewpoint of improving continuous discharge stability.
The above pigments can be used alone or in admixture of two or more at any ratio.
The organic pigment A is preferably one or more selected from disazopyrazolone orange pigments, perinone orange pigments, dioxazine violet pigments, and copper phthalocyanine green pigments from the viewpoint of improving continuous discharge stability. ..

<Crosslinked polymer>
The cross-linked polymer according to the present invention is a polymer cross-linked with the cross-linking agent (1,4-butanediol diglycidyl ether) and has a cross-linked structure derived from the cross-linking agent.
The crosslinked polymer may contain a crosslinked product of the water dispersible polymer with the crosslinking agent from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion, suppressing the occurrence of cogging, and improving the continuous discharge stability. It is more preferable that the crosslinked product of the water-dispersible polymer is crosslinked by the crosslinking agent.

[Water-dispersible polymer]
In the present invention, the "water-dispersible polymer" means a polymer before cross-linking, and the water-dispersible polymer is a polymer having an ability to disperse an organic pigment in water or a medium containing water as a main component at room temperature. means.
Examples of the water-dispersible polymer include polyester, polyurethane, vinyl-based polymer and the like. The water-dispersible polymer may be used alone or in combination of two or more.
The water-dispersible polymer is preferably a vinyl-based polymer obtained by addition polymerization of a vinyl monomer from the viewpoint of improving continuous discharge stability.
The water-dispersible polymer has a reactive group (crosslinkable functional group) capable of reacting with the crosslinking agent. Examples of the reactive group include a carboxy group, a sulfonic acid group, a phosphoric acid group, an amino group and a hydrophilic functional group of a hydroxyl group, and from the viewpoint of reaction stability, a carboxy group is preferable. Examples of the vinyl-based polymer having a carboxy group used in the water-dispersible polymer include (meth) acrylic acid-based polymers.
In addition, in this specification, "(meth) acrylic acid" means "one or more kinds selected from acrylic acid and methacrylic acid". "(Meta) acrylic acid" in the following is also synonymous.

The water-dispersible polymer is preferably a structural unit derived from an ionic monomer, from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion, suppressing the occurrence of cogging, and improving the continuous discharge stability and the storage stability. And a vinyl-based polymer containing a structural unit derived from a hydrophobic monomer. The vinyl-based polymer may further have a structural unit derived from a nonionic monomer. The vinyl-based polymer is obtained by copolymerizing an ionic monomer, a hydrophobic monomer, and a raw material monomer containing a nonionic monomer, if necessary (hereinafter, also referred to as "raw material monomer according to the present invention").

(Ionic monomer)
The water-dispersible polymer is preferably an ionic monomer from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion, suppressing the occurrence of cogging, improving the continuous discharge stability, and improving the storage stability. Includes building blocks of origin.
The ionic monomer is a monomer having a group that can be an ion under any of acidic, neutral and alkaline conditions.
The ionic monomer has a reactive group capable of reacting with the cross-linking agent from the viewpoint of improving continuous discharge stability and storage stability. Examples of the reactive group include those mentioned above, and examples of the ionic monomer include an anionic monomer and a cationic monomer having the reactive group. Among these, an anionic monomer having the reactive group is preferable from the viewpoint of improving continuous discharge stability and storage stability.
Examples of the anionic monomer having a reactive group include a carboxylic acid monomer, a sulfonic acid monomer, and a phosphoric acid monomer. Of these, the carboxylic acid monomer is more preferable.
Examples of the carboxylic acid monomer include (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2-methacryloyloxymethylsuccinic acid and the like. Among them, (meth) acrylic acid is more preferable.

(Hydrophobic monomer)
The water-dispersible polymer preferably contains a structural unit derived from a hydrophobic monomer from the viewpoint of adsorbability of the polymer to the pigment surface. The "hydrophobicity" of a monomer means that when the monomer is dissolved in 100 g of ion-exchanged water at 25 ° C. until it is saturated, the amount of the monomer dissolved is less than 10 g. The amount of the hydrophobic monomer dissolved in 100 g of ion-exchanged water at 25 ° C. is preferably 5 g or less, more preferably 1 g or less, from the viewpoint of the adsorptivity of the polymer to the pigment surface.
The hydrophobic monomer is preferably one or more selected from an aromatic group-containing monomer and a (meth) acrylate having a hydrocarbon group derived from an aliphatic alcohol.
As used herein, the term "(meth) acrylate" means "one or more selected from acrylates and methacrylates".

The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group having 6 or more and 22 or less carbon atoms, and more preferably one or more 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.
The styrene-based monomer is preferably one or more selected from styrene and 2-methylstyrene, and more preferably styrene. 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.
Among these, styrene-based monomers are preferable, and styrene is more preferable, from the viewpoint of the adsorptivity of the polymer to the pigment surface.

The (meth) acrylate having a hydrocarbon group derived from an aliphatic alcohol preferably has a hydrocarbon group derived from an aliphatic alcohol of 1 or more and 22 or less, and more preferably an alkyl group having 1 or more and 22 or less carbon atoms. It is more preferably one having an alkyl group having 6 or more and 18 or less carbon atoms.
For example, a (meth) acrylate having a linear alkyl group, a (meth) acrylate having a branched chain alkyl group, a (meth) acrylate having an alicyclic alkyl group, and the like can be mentioned.

As the hydrophobic monomer, a macromonomer can also be used.
Macromer is a compound having a polymerizable functional group at one end and having a number average molecular weight of 500 or more and 100,000 or less, and preferably has a number average molecular weight of 1,000 or more and 10 or more from the viewpoint of improving continuous discharge stability and storage stability. It is a compound of 000 or less. The number average molecular weight is a value measured by gel permeation chromatography using chloroform containing 1 mmol / L dodecyldimethylamine as a solvent and polystyrene as a standard substance.
The polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, and more preferably a methacryloyloxy group.
The macromonomer is preferably one or more selected from an aromatic group-containing monomer-based macromonomer and a silicone-based macromonomer from the viewpoint of polymer adsorption to the pigment surface, and more preferably an aromatic group-containing monomer-based macromonomer. It is a monomer.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromonomer include the aromatic group-containing monomer described in the hydrophobic monomer, and styrene and benzyl (meth) acrylate are preferable, and styrene is more preferable.
Specific examples of the styrene-based macromer include AS-6 (S), AN-6 (S), HS-6 (S) (these are trade names manufactured by Toagosei Co., Ltd.) and the like.
Examples of the silicone-based macromonomer include organopolysiloxane having a polymerizable functional group at one end.

The hydrophobic monomer is preferably aromatic from the viewpoint of improving the dispersion stability of the aqueous pigment dispersion, suppressing the occurrence of hydrocarbons, improving the continuous ejection stability of the ink, and improving the storage stability. One or more selected from a group-containing monomer, a (meth) acrylate having a hydrocarbon group derived from an aliphatic alcohol, and an aromatic group-containing monomer-based macromer, more preferably an aromatic group-containing monomer, and further preferably. One or more selected from styrene-based monomers and aromatic group-containing (meth) acrylates, and even more preferably styrene-based monomers.

(Nonionic monomer)
The nonionic monomer does not have the above-mentioned ionic group and has a dissolution amount of 10 g or more in 100 g of ion-exchanged water at 25 ° C.
Examples of the nonionic monomer include a monomer having at least one of a hydroxyl group and a polyalkyleneoxy group.
Examples of the nonionic monomer include hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate and 3-hydroxypropyl (meth) acrylate; polyethylene glycol (n = 2 to 30, n is the average addition of oxyethylene groups). The number of moles is shown. The following n indicates the average number of moles of the oxyalkylene group added.) Polyalkylene glycol (meth) acrylate such as (meth) acrylate; methoxypolyethylene glycol (n = 1 to 30) (meth) acrylate. , Octoxypolyethylene glycol (n = 1-30) (meth) acrylate and other alkoxy polyethylene glycol (meth) acrylate; phenoxy (ethylene glycol / propylene glycol copolymerization) (n = 1-30, ethylene glycol in it: n = 1-29) Examples thereof include (meth) acrylate.
Specific examples of commercially available nonionic monomers include NK ester M-20G, 40G, 90G, NK ester EH-4E (above, trade name manufactured by Shin-Nakamura Chemical Industry Co., Ltd.), and Blemmer PE-. 90, 200, 350; Blemmer PME-100, 200, 400; Blemmer PP-500, 800; Blemmer AP-150, 400, 550; Blemmer 50 PEP-300, 50 POEP-800B, 43 PAPE -600B (above, trade name manufactured by NOF CORPORATION) and the like can be mentioned.

The above-mentioned ionic monomer, hydrophobic monomer and nonionic monomer can be used alone or in combination of two or more.
As described above, the water-dispersible polymer according to the present invention preferably contains a structural unit derived from one or more ionic monomers selected from acrylic acid and methacrylic acid, and carbonization derived from an aromatic group-containing monomer and an aliphatic alcohol. A vinyl-based polymer containing a structural unit derived from one or more hydrophobic monomers selected from (meth) acrylates having a hydrogen group, and more preferably one or more carboxylic acid monomers selected from acrylic acid and methacrylic acid. A vinyl-based polymer containing a derived structural unit and a structural unit derived from an aromatic group-containing monomer, more preferably a structural unit derived from one or more carboxylic acid monomers selected from acrylic acid and methacrylic acid, and styrene. It is a vinyl-based polymer containing a structural unit derived from a based monomer, and is even more preferably an acrylic acid / styrene copolymer.

When a vinyl-based polymer is used as the water-dispersible polymer, the contents of the structural unit derived from the ionic monomer and the structural unit derived from the hydrophobic monomer in the vinyl-based polymer are as follows.
The content of the ionic monomer improves the dispersion stability of the pigment aqueous dispersion, suppresses the occurrence of cogging, improves the viewpoint of improving the continuous ejection stability of the ink, and improves the storage stability. From the viewpoint of making the ink, it is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 25% by mass or more, and preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 40% by mass. It is mass% or less.
The content of the hydrophobic monomer is preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 60% by mass or more, and preferably from the viewpoint of the adsorptivity of the crosslinked polymer to the pigment surface. Is 90% by mass or less, more preferably 80% by mass or less, still more preferably 75% by mass or less.
The total content of the structural unit derived from the ionic group-containing monomer and the structural unit derived from the hydrophobic monomer in the vinyl polymer is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass. The above, and preferably 100% by mass or less.
The content of the structural unit derived from each monomer in the above vinyl polymer can be measured by analysis such as NMR. Further, the preferable range of the content (content as an unneutralized amount) of each monomer in the raw material monomer according to the present invention at the time of producing a vinyl polymer is the structural unit derived from each monomer in the vinyl polymer. It can be regarded as the same as the preferable range of the content.

As the water-dispersible polymer, a synthetic polymer may be used, or a commercially available product may be used.
When the water-dispersible polymer is obtained by synthesis, it can be produced by copolymerizing the raw material monomer according to the present invention by a known polymerization method such as a massive polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. .. Further, the mode of chaining the polymerization monomers is not limited, and any polymerization mode such as random, block, and graft may be used.
Examples of commercially available water-dispersible polymers include acrylic acid / styrene copolymers such as John Krill 67, 611, 678, 680, 690, and 819 (manufactured by BASF Japan Ltd.).

The weight average molecular weight of the water-dispersible polymer is preferably 3,000 or more, more preferably 5,000 or more, still more preferably 10,000 or more, and from the viewpoint of improving continuous discharge stability and storage stability. It is preferably 100,000 or less, more preferably 50,000 or less, still more preferably 30,000 or less.
The weight average molecular weight can be determined by the method described in Examples.

The acid value of the water-dispersible polymer is preferably 150 mgKOH / g or more, more preferably 180 mgKOH / g or more, still more preferably 200 mgKOH / g or more, still more preferably 200 mgKOH / g or more, from the viewpoint of improving continuous discharge stability and storage stability. It is 220 mgKOH / g or more, and preferably 320 mgKOH / g or less, more preferably 300 mgKOH / g or less, still more preferably 280 mgKOH / g or less.
The acid value of the water-dispersible polymer can be calculated from the mass ratio of each monomer constituting the water-dispersible polymer.

[Crosslinking agent]
In the present invention, 1,4-butanediol diglycidyl ether is used as the cross-linking agent.
Examples of commercially available products of the cross-linking agent include "Denacol EX-214L" (manufactured by Nagase ChemteX Corporation). Since the cross-linking agent is usually produced using epichlorohydrin, chlorine (as an impurity in the cross-linking agent) ( Chloride ion) is included. However, from the viewpoint of suppressing corrosion of recording devices such as inkjet recording devices and suppressing cogation in the heater portion of the thermal head when the ink ejection method in the inkjet recording method is the thermal system, the continuous ejection stability is improved. , It is preferable to use a cross-linking agent having a reduced chlorine content. From this point of view, the content of chloride ions (chloride content) of the impurities of the cross-linking agent is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 1% by mass or less, still more preferably 0. It is 0.7% by mass or less, and from the viewpoint of productivity of the cross-linking agent, it is 0% by mass or more, preferably 0.1% by mass or more.
Chlorine in the cross-linking agent is considered to exist as ^{an impurity chlorine ion (Cl −).} The content of chloride ions in the cross-linking agent can be determined from the chlorine ion concentration measured by a titration method or an ion chromatograph method.

The ratio of the number of moles of the epoxy group of the cross-linking agent to the number of moles of the crosslinkable functional group of the water-dispersible polymer improves the dispersion stability of the pigment aqueous dispersion, suppresses the generation of cogging, and continues the ink. From the viewpoint of improving discharge stability and storage stability, it is preferably 1 mol% or more, more preferably 2 mol% or more, further preferably 3 mol% or more, and preferably 20 mol% or more. Below, it is more preferably 17 mol% or less, still more preferably 15 mol% or less.

[Manufacturing method of aqueous pigment dispersion]
The aqueous pigment dispersion of the present invention is preferably efficiently produced by a production method including the following steps 1 and 2.
Step 1: Disperse the water-dispersible polymer, the organic pigment A, and the pigment mixture containing water to obtain a pigment aqueous dispersion. Step 2: The pigment aqueous dispersion obtained in Step 1 and as a cross-linking agent. A step of mixing 1,4-butanediol diglycidyl ether and reacting the water-dispersible polymer with the cross-linking agent to form a cross-linked polymer to obtain a pigment aqueous dispersion.

<Step 1>
Step 1 is a step of dispersing a water-dispersible polymer, an organic pigment A, and a pigment mixture containing water to obtain a pigment aqueous dispersion.
In step 1, a water-dispersible polymer, organic pigment A, water, and if necessary, a neutralizing agent, a surfactant, and the like are added and mixed to obtain a pigment mixture, and then the mixture is dispersed to obtain a pigment. The step of obtaining an aqueous dispersion is preferable. The order of addition is not limited, but it is preferable to add a pigment to an aqueous solution of a water-dispersible polymer prepared by using a neutralizing agent, if necessary, to obtain a pigment mixture.

In step 1, it is preferable to use a neutralizing agent from the viewpoint of improving the dispersion stability of the aqueous pigment dispersion and improving the continuous discharge stability and the storage stability. When a neutralizing agent is used, it is preferable to neutralize the pigment aqueous dispersion so that the pH is 7 or more and 11 or less.
Examples of the neutralizing agent used include alkali metal hydroxides, ammonia, and organic amines, which are alkaline from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion and improving the continuous discharge stability and the storage stability. One or more selected from metal hydroxides and ammonia is preferable, alkali metal hydroxides are more preferable, and sodium hydroxide is even more preferable.
The neutralizing agent is preferably used as an aqueous solution of the neutralizing agent from the viewpoint of sufficiently promoting neutralization. The neutralizing agent may be used alone or in combination of two or more.
The mass ratio of the organic pigment A to the mass of the water-dispersible polymer used in step 1 [organic pigment A / water-dispersible polymer] improves the dispersion stability of the pigment aqueous dispersion, and improves continuous discharge stability and storage stability. From the viewpoint of improvement, it is preferably 1 or more, more preferably 1.5 or more, still more preferably 2 or more, still more preferably 2.5 or more, and preferably 5 or less, more preferably 4 in the pigment mixture. It is 5.5 or less, more preferably 4 or less, and even more preferably 3.5 or less.

In step 1, the method of dispersion treatment is not particularly limited. The average particle size of the particles of the organic pigment A can be atomized to a desired particle size only by the main dispersion due to the shear stress, but after the pre-dispersion, the main dispersion is further performed to average the particles of the organic pigment A. The particle size may be controlled to be a desired particle size.
Examples of the means for applying the shear stress of this dispersion include a media type disperser such as a paint shaker and a bead mill; a kneader such as a roll mill and a kneader, and a high pressure homogenizer such as a microfluidics (trade name).
The non-volatile component concentration (solid content concentration) of the pigment aqueous dispersion obtained in step 1 is preferably 10 from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion and facilitating the preparation of the pigment aqueous dispersion. It is by mass% or more, more preferably 15% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less.

<Process 2>
Step 2 is a step of mixing the pigment aqueous dispersion obtained in step 1 with the cross-linking agent and reacting the water-dispersible polymer with the cross-linking agent to form a cross-linked polymer to obtain a pigment aqueous dispersion. Is.
In step 2, the ratio of the number of moles of the epoxy group of the cross-linking agent to the number of moles of the cross-linking functional group of the water-dispersible polymer is as described above.
The temperature of the cross-linking reaction is preferably 40 ° C. or higher, more preferably 60 ° C. or higher, and preferably 95 ° C. or lower, more preferably 80 ° C. or lower. The time of the cross-linking reaction is preferably 1 hour or more and 10 hours or less.

The pigment aqueous dispersion of the present invention is obtained by dispersing pigment A-containing crosslinked polymer particles in a medium containing water as a main component. Here, the form of the pigment A-containing crosslinked polymer particles in the pigment aqueous dispersion is not particularly limited, and at least the particles may be formed by the organic pigment A and the crosslinked polymer. For example, a particle form in which the organic pigment A is encapsulated in the crosslinked polymer, a particle form in which the organic pigment A is uniformly dispersed in the crosslinked polymer, a particle form in which the organic pigment A is exposed on the particle surface of the crosslinked polymer, and the like are included. , A mixture of these is also included.

(Composition and physical properties of aqueous pigment dispersion)
The content of the organic pigment A is the pigment water dispersion from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion, suppressing the occurrence of cogging, improving the continuous discharge stability, and improving the storage stability. In the body, preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, still more preferably 13% by mass or more, and preferably 25% by mass or less, more preferably 20% by mass or more. It is mass% or less, more preferably 18 mass% or less.
The content of the crosslinked polymer is a pigment aqueous dispersion from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion, suppressing the occurrence of cogging, improving the continuous discharge stability, and improving the storage stability. Among them, preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, and preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 7% by mass. It is as follows.
The water content is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more in the pigment aqueous dispersion from the viewpoint of improving continuous discharge stability and storage stability. And, preferably 95% by mass or less, more preferably 90% by mass or less, still more preferably 85% by mass or less.
The mass ratio of the organic pigment A to the crosslinked polymer in the aqueous pigment dispersion [organic pigment A / crosslinked polymer] is preferably 1 or more from the viewpoint of improving continuous ejection stability and storage stability, and from the viewpoint of improving the printing density. , More preferably 1.5 or more, still more preferably 2 or more, even more preferably 2.5 or more, and preferably 5 or less, more preferably 4.5 or less, still more preferably 4 or less, even more preferably. Is 3.5 or less.

The average particle size of the organic pigment A particles (pigment A-containing crosslinked polymer particles) dispersed in the crosslinked polymer in the pigment aqueous dispersion of the present invention is preferably from the viewpoint of improving continuous discharge stability and storage stability. It is 40 nm or more, more preferably 80 nm or more, further preferably 120 nm or more, and preferably 300 nm or less, more preferably 250 nm or less, still more preferably 200 nm or less. The average particle size can be measured by the method described in Examples described later.

The viscosity of the aqueous pigment dispersion of the present invention at 25 ° C. is preferably 1 mPa · s or more, more preferably 2 mPa · s or more, still more preferably 3 mPa · s or more, from the viewpoint of improving continuous discharge stability and storage stability. It is preferably 10 mPa · s or less, more preferably 8 mPa · s or less, and further preferably 6 mPa · s or less.
The viscosity at 25 ° C. can be measured by the method described in Examples described later.

The pigment aqueous dispersion of the present invention contains additives such as solvents, penetrants, dispersants, surfactants, viscosity modifiers, defoaming agents, rust preventives, preservatives, and antifungal agents that are usually used for water-based inks. It may be contained, and can be used as it is as a water-based ink for flexographic printing, gravure printing, or inkjet recording, preferably as a water-based ink for inkjet recording.

[Water-based ink for inkjet recording]
The water-based ink for inkjet recording of the present invention preferably contains the pigment aqueous dispersion and a solvent. In addition to the solvent, a penetrant, a dispersant, a surfactant, a viscosity modifier, a defoaming agent, a rust preventive, a preservative, a fungicide, etc. are added to the water-based ink, and further filtered with a filter or the like. be able to.

<Solvent>
In the present invention, the "solvent" means something other than water.
The solvent preferably contains an organic solvent from the viewpoint of suppressing an excessive increase in viscosity due to the crosslinked polymer, preventing the ink from drying, and improving continuous ejection stability and storage stability.
The organic solvent contains a monohydric alcohol having 1 to 4 carbon atoms, a polyhydric alcohol, a polyhydric alcohol alkyl ether, a ketone, a cyclic ether, a nitrogen-containing heterocyclic compound, an amide, an amine, a sulfur-containing compound and the like. be able to. The organic solvent is preferably one or more selected from polyhydric alcohols, polyhydric alcohol alkyl ethers and nitrogen-containing heterocyclic compounds from the viewpoint of improving continuous discharge stability and storage stability.

Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4 butanediol, and 3-methyl-. 1,3-Butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, 1,2,6-hexanetriol, 1,2,4-butanetriol, Examples thereof include 1,2,3-butanetriol, petriol, triethylene glycol, tripropylene glycol and glycerin.
Examples of the polyhydric alcohol alkyl ether include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoisobutyl ether, and tetraethylene glycol. Examples thereof include monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, and triethylene glycol monobutyl ether.
Examples of the nitrogen-containing heterocyclic compound include N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethylimidazolidinone, ε-caprolactam and the like.
The above-mentioned organic solvent may be used alone or in combination of two or more.

The solvent is preferably a polyhydric alcohol, more preferably one or more selected from propylene glycol and polyethylene glycol, and further preferably polyethylene glycol, from the viewpoint of improving continuous discharge stability and storage stability.
The average molecular weight of polyethylene glycol is preferably 300 or more, more preferably 400 or more, and preferably 1,000 or less, more preferably 800 or less.

<Surfactant>
The water-based ink of the present invention may further contain a surfactant from the viewpoint of improving continuous ejection stability and storage stability. As the surfactant, a nonionic surfactant is preferable.
Nonionic surfactants include (1) saturated or unsaturated, linear or branched higher alcohols, polyhydric alcohols, or aromatic alcohols having 8 to 22 carbon atoms, and ethylene oxide, to these alcohols. Polyoxyalkylene alkyl ethers, alkenyl ethers, alkynyl ethers or aryl ethers to which propylene oxide or butylene oxide (hereinafter collectively referred to as "alkylene oxide") is added, (2) Saturation or unsaturation of 8 to 22 carbon atoms. Esters of saturated, linear or branched hydrocarbon groups with higher alcohols and polyhydric fatty acids, (3) Polyoxys with 8 to 20 carbon atoms, linear or branched, alkyl or alkenyl groups. Examples thereof include alkylene aliphatic amines, (4) higher fatty acids having 8 to 22 carbon atoms, ester compounds of polyhydric alcohols, and compounds to which alkylene oxides are added.
Commercially available nonionic surfactants include, for example, the Surfinol series manufactured by Nissin Chemical Industry Co., Ltd., the acetylenol series manufactured by Kawaken Fine Chemical Co., Ltd., and the Emargen 120 (polyoxyethylene lauryl ether) manufactured by Kao Corporation. And so on.

The content of each component of the water-based ink of the present invention and the physical characteristics of the ink are as follows.
The total content of the organic pigment A and the crosslinked polymer in the water-based ink of the present invention is preferably 1% by mass or more in the water-based ink from the viewpoint of printing density and improving continuous ejection stability and storage stability. More preferably 3% by mass or more, further 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, still more preferably 8% by mass. It is as follows.

The content of the solvent in the water-based ink of the present invention is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 8% by mass or more, from the viewpoint of improving continuous ejection stability and storage stability. Yes, and preferably 30% by mass or less, more preferably 20% by mass or less, still more preferably 15% by mass or less.
The content of water in the water-based ink of the present invention is preferably 55% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, from the viewpoint of improving continuous ejection stability and storage stability. Yes, and preferably 95% by mass or less, more preferably 90% by mass or less, still more preferably 87% by mass or less.

The content of the surfactant in the water-based ink of the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, from the viewpoint of improving continuous ejection stability and storage stability. It is more preferably 0.3% by mass or more, and preferably 3% by mass or less, more preferably 2% by mass or less, still more preferably 1% by mass or less.

The particles of the organic pigment A (pigment A-containing crosslinked polymer particles) dispersed in the crosslinked polymer in the water-based ink of the present invention preferably do not swell or shrink, or agglomerate between the particles, and are contained in the water-based ink. It is more preferable that the average particle size of the particles of the organic pigment A in the above is the same as the average particle size of the particles of the organic pigment A in the aqueous pigment dispersion. The preferred mode of the average particle size of the particles of the organic pigment A in the water-based ink is the same as the preferred mode of the average particle size of the particles of the organic pigment A in the pigment aqueous dispersion described above. The average particle size of the particles of the organic pigment A in the water-based ink can be measured by the method described in Examples described later.

The static surface tension of the water-based ink at 20 ° C. is preferably 23 mN / m or more, more preferably 25 mN / m or more, and preferably 45 mN / m from the viewpoint of improving continuous ejection stability and storage stability. Below, it is more preferably 40 mN / m or less.
The static surface tension at 20 ° C. can be measured by the method described in Examples described later.

The viscosity of the water-based ink at 25 ° C. is preferably 1.0 mPa · s or more, more preferably 1.5 mPa · s or more, still more preferably 2.0 mPa · s, from the viewpoint of improving continuous ejection stability and storage stability. The above, and preferably 10 mPa · s or less, more preferably 7.0 mPa · s or less, still more preferably 5.0 mPa · s or less.
The viscosity at 25 ° C. can be measured by the method described in Examples described later.

Inkjet recording methods include a piezo method that uses mechanical energy and a thermal method that uses thermal energy as ink ejection methods. Since the pigment aqueous dispersion of the present invention can suppress the occurrence of cogation particularly in the heater portion of the thermal head and improve the continuous ejection stability, it is suitable for the thermal inkjet recording method in which the ink ejection method is the thermal method. It is preferable to use it. The thermal method is a method in which an ink subjected to the action of thermal energy undergoes a sudden volume change, and the ink is ejected from a nozzle by the acting force due to this state change. For example, US Pat. No. 4,723,129, US Pat. No. It is preferably carried out using the basic principles disclosed in 4740796. More specifically, the method described in Japanese Patent Publication No. 61-59911 can be mentioned.
The water-based ink containing the pigment aqueous dispersion of the present invention can achieve stable continuous ejection stability even when the ink ejection method is the thermal method, and can be suitably used for inkjet recording by the thermal method. it can. The reason for this is that the pigment aqueous dispersion of the present invention has a strong affinity specific to the polymer crosslinked by the cross-linking agent and the organic pigment A of a specific type, and the heater portion of the thermal inkjet printer. Even if the liquid medium evaporates and the pigments are close to each other, the dispersion stability is excellent, the pigments can be agglomerated, and the pigments are suspended without being adsorbed on the pigments in the liquid medium. Since the amount of the crosslinked polymer that has been atomized can be reduced, it is possible to suppress the occurrence of cogging and improve the continuous discharge stability.

In the following examples and comparative examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified.
The various physical properties were measured by the following methods.

(1) Gel permeation chromatography using a solution prepared by dissolving phosphoric acid and lithium bromide in N, N-dimethylformamide, which have a weight average molecular weight of an aqueous dispersible polymer, at concentrations of 60 mmol / L and 50 mmol / L, respectively, as an eluent. Graffiti method [GPC device (model: HLC-8320GPC, manufactured by Tosoh Corporation), column (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guard polymer AW-H, above, trade name manufactured by Tosoh Corporation), flow velocity: 0. 5 mL / min], as a standard substance, a monodisperse polystyrene kit [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-1000), whose molecular weight is known. 40, F-4, A-5000, A-500), above, trade name manufactured by Tosoh Corporation].
For the measurement sample, 0.1 g of water-dispersible polymer was mixed with 10 mL of the eluent in a glass vial, stirred at 25 ° C. for 10 hours with a magnetic stirrer, and a syringe filter (trade name: DISMIC-13HP, membrane filter material) was used. : Hydrophilic PTFE, pore size 0.2 μm, manufactured by Advantech Co., Ltd.) was used.

(2) Measurement of solid content concentration In a 30 ml polypropylene container (φ = 40 mm, height = 30 mm), 10.0 g of sodium sulfate homogenized in a desiccator was weighed, and about 1.0 g of a sample was added thereto. After mixing, the mixture was accurately weighed, maintained at 105 ° C. for 2 hours to remove volatile matter, and further left in a desiccator for 15 minutes to measure 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.

(3) Average particle size of organic pigment A particles (pigment A-containing crosslinked polymer particles) dispersed with the crosslinked polymer in the pigment aqueous dispersion and the aqueous ink Laser particle analysis system "ELS-8000" (Otsuka Electronics Co., Ltd.) ) (Cumulland analysis) was used as the average particle size of the pigment A-containing crosslinked polymer particles in the pigment aqueous dispersion or the water-based ink. The measurement conditions were a temperature of 25 ° C., an angle of 90 ° between the incident light and the detector, and 100 times of integration, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measured concentration was 5 × 10 ^-3 %.

(4) Static surface tension of water-based ink Using a surface tension meter "CBVP-Z" (manufactured by Kyowa Interface Science Co., Ltd.), a platinum plate is placed in a cylindrical polyethylene container (3.6 cm in diameter) containing 5 g of water-based ink. It was immersed in a depth of 1.2 cm), and the static surface tension of the pigment aqueous dispersion or the aqueous ink was measured at 20 ° C.

(5) Viscosity of pigment aqueous dispersion and water-based ink E-type viscometer (manufactured by Toki Sangyo Co., Ltd., model number: TV-25, standard cone rotor 1 ° 34'x R24 used, rotation speed: 50 rpm) at 25 ° C. The viscosity of the pigment aqueous dispersion or the aqueous ink was measured in.

<Manufacturing of aqueous pigment dispersion>
Example 1-1
(Step 1)
As the organic pigment A, C.I. I. 165 parts of Pigment Orange 34 (disazopyrazolone orange pigment), acrylic acid / styrene copolymer "John Krill 690" as an aqueous dispersible polymer (weight average molecular weight: 16,500, acid value: 240 mgKOH / g) (BASF) Aqueous solution (concentration 20%) of 55 parts as a solid content and 33 parts of a 5N sodium hydroxide aqueous solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., reagent) as a neutralizing agent for water-dispersible polymer are mixed and pigmented. After obtaining the mixture, the pigment mixture was dispersed and treated using zirconia beads to obtain a pigment aqueous dispersion having a solid content concentration of 22%.
(Step 2)
Denacol EX-214L (manufactured by Nagase ChemteX Corporation, 1,4-butanediol diglycidyl ether, epoxy equivalent: 120, chlorine content: 120) as a cross-linking agent with respect to 795 parts of the pigment aqueous dispersion obtained in step 1. 0.4%) Add 4.0 parts (ratio of the number of moles of epoxy group of the cross-linking agent to the number of moles of carboxy group of the water-dispersible polymer: 14 mol%) and 12.2 parts of ion-exchanged water, and stir It was heated at 70 ° C. for 6 hours.
Then, after cooling to room temperature, it is filtered through a filter "Mini Sartorius Filter" (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, and pigment aqueous dispersion containing crosslinked polymer particles containing pigment A. Body (I-1) was obtained.
The solid content concentration of the aqueous pigment dispersion (I-1) was 22% by mass (pigment content: 16.2%, crosslinked polymer content: 5.8%). Table 1 shows the characteristics of the aqueous pigment dispersion (I-1).

Example 1-2
In step 2 of Example 1-1, 2.0 parts of Denacol EX-214L 4.0 parts as a cross-linking agent (ratio of the number of moles of epoxy groups of the cross-linking agent to the number of moles of carboxy groups of the water-dispersible polymer: 7) A pigment aqueous dispersion (I-2) containing crosslinked polymer particles containing pigment A was obtained in the same manner as in Example 1 except that 12.2 parts of ion-exchanged water was changed to 10.2 parts. Table 1 shows the characteristics of the aqueous pigment dispersion (I-2).

Examples 1-3 to 1-5 and Comparative Examples 1-1, 1-2, 1-7
In step 1 of Example 1-2, C.I. I. Pigment aqueous dispersions (I-3) to (I-5) and (I) containing pigment A-containing crosslinked polymer particles in the same manner as in Example 1-1 except that Pigment Orange 34 was replaced with the pigment shown in Table 1. -C1), (IC2), and (IC7) were obtained. Table 1 shows the characteristics of each pigment aqueous dispersion.

Comparative Example 1-3
In step 2 of Example 1-1, 4.0 parts of Denacol EX-214L was added as a cross-linking agent to Denacol 810 (manufactured by Nagase ChemteX Corporation, ethylene glycol diglycidyl ether, epoxy equivalent: 113, chlorine content: 0.6. %) Pigment A was contained in the same manner as in Example 1-1 except that it was replaced with 3.8 parts (ratio of the number of moles of the epoxy group of the cross-linking agent to the number of moles of the carboxy group of the water-dispersible polymer: 14%). An aqueous pigment dispersion (IC3) containing crosslinked polymer particles was obtained. Table 1 shows the characteristics of each pigment aqueous dispersion (IC3).

Comparative Example 1-4
In step 2 of Example 1-1, 4.0 parts of Denacol EX-214L as a cross-linking agent was used as Denacol EX-850L (diethylene glycol diglycidyl ether manufactured by Nagase ChemteX Corporation, epoxy equivalent: 145, chlorine content: 0.6. %) The pigment A was contained in the same manner as in Example 1-1 except that it was replaced with 4.8 parts (ratio of the number of moles of the epoxy group of the cross-linking agent to the number of moles of the carboxy group of the water-dispersible polymer: 14%). An aqueous pigment dispersion (IC4) containing crosslinked polymer particles was obtained. Table 1 shows the characteristics of each pigment aqueous dispersion (IC4).

Comparative Example 1-5
In step 2 of Example 1-1, 4.0 parts of Denacol EX-214L as a cross-linking agent was added to 5.0 parts (water) of Epolite 70P (manufactured by Kyoeisha Chemical Co., Ltd., propylene glycol diglycidyl ether, epoxy equivalent: 140 to 160). A pigment aqueous dispersion containing crosslinked polymer particles containing pigment A in the same manner as in Example 1-1 except that the ratio of the number of moles of epoxy group to the number of moles of carboxy group of the dispersible polymer was replaced with (14 mol%). I-C5) was obtained. Table 1 shows the characteristics of each pigment aqueous dispersion (IC5).

Comparative Example 1-6
In step 2 of Example 1-1, 4.0 parts of Denacol EX-214L was added as a cross-linking agent to Denacol EX-321L (manufactured by Nagase ChemteX Corporation, trimethylolpropane polyglycidyl ether, epoxy equivalent: 130, chlorine content: 0.3%) Pigment A in the same manner as in Example 1-1 except that it was replaced with 4.3 parts (ratio of the number of moles of epoxy group to the number of moles of carboxy group of the water-dispersible polymer: 14 mol%). An aqueous pigment dispersion (IC6) containing the crosslinked polymer particles contained therein was obtained. Table 1 shows the characteristics of each pigment aqueous dispersion (IC6).

Comparative Example 1-8
In step 2 of Example 1-1, 4.0 parts of Denacol EX-214L as a cross-linking agent was used as Denacol EX-212L (manufactured by Nagase ChemteX Corporation, 1,6-hexanediol diglycidyl ether, epoxy equivalent: 135, chlorine. Content: 0.4%) The same method as in Example 1-1 except that it was replaced with 4.6 parts (ratio of the number of moles of epoxy group to the number of moles of carboxy group of the water-dispersible polymer: 14 mol%). A pigment aqueous dispersion (IC8) containing the crosslinked polymer particles containing pigment A was obtained. Table 1 shows the characteristics of each pigment aqueous dispersion (IC8).

Each notation in Table 1 is as follows.
(Organic pigment)
PO34: C.I. I. Pigment Orange 34 (Disazopyrazolone orange pigment, manufactured by Dainichiseika Kogyo Co., Ltd.)
PO43: C.I. I. Pigment Orange 43 (Perinone orange pigment, manufactured by Dainichiseika Kogyo Co., Ltd.)
PV23: C.I. I. Pigment Violet 23 (dioxazine violet pigment, manufactured by Dainichiseika Kogyo Co., Ltd.)
PG7: C.I. I. Pigment Green 7 (Copper Phthalocyanine Green, manufactured by Clariant Japan Co., Ltd.)
PV19: C.I. I. Pigment Violet 19 (quinacridone pigment) (manufactured by Dainichiseika Kogyo Co., Ltd.)
PR122: C.I. I. Pigment Red 122 (quinacridone pigment) (manufactured by Dainichiseika Kogyo Co., Ltd.)
M717: Carbon black (manufactured by Cabot Specialty Chemicals, trade name "Monarch 717 carbon black")
(Water-dispersible polymer)
J690: John Krill 690
(Crosslinking agent)
Denacol EX-214L: 1,4-butanediol diglycidyl ether Denacol EX-810: Ethylene glycol rudiglycidyl ether Denacol EX-850L: Diethylene glycol diglycidyl ether Denacol EX-321L: Trimethylol propanepolyglycidyl ether Denacol EX-212L: 1 , 6-Hexanediol Diglycidyl Ether Epolite 70P: Propropylene Glycol Diglycidyl Ether

<Manufacturing of water-based ink>
Example 2-1
24.8 parts of the aqueous pigment dispersion (I-1) obtained in Example 1-1, polyethylene glycol 400 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., reagent, number average molecular weight 360-440 (catalog value)) 10 Part, Surfinol 104PG-50 (manufactured by Nissin Chemical Industry Co., Ltd., propylene glycol solution of acetylene glycol-based surfactant, effective content: 50%) 1 part, Emargen 120 (manufactured by Kao Co., Ltd., ether-based nonionic surfactant) After adding ion-exchanged water to make 0.5 parts of the activator and 100 parts of the ink and stirring the ink, the ink is filtered with a 0.3 μm filter “20L-MBP-003XS” (manufactured by ROKI). The water-based ink (II-1) of Example 2-1 (total content of pigment and crosslinked polymer in the water-based ink: 5.46%) was obtained.

Examples 2-2-2-5 and Comparative Examples 2-1-2-8
In Example 2-1 the water-based inks (II-2) to (II-5) and Comparative Examples (II-C1) to (II) were subjected to the same procedure except that the pigment aqueous dispersion was changed as shown in Table 1. -C8) water-based ink was obtained.

The following evaluations were carried out using the water-based inks obtained in Examples and Comparative Examples. The results are shown in Table 2. Each notation shown in Table 2 is the same as in Table 1.
<Evaluation of continuous discharge stability>
Obtained in Examples and Comparative Examples on a printing machine modified so that a liquid feeding tube of an inkjet recording device "LPP-6010N" (manufactured by LG Electronics Co., Ltd.) having a thermal head is pulled out and the tube is put into an ink tank for printing. Filled with water-based ink, in an environment of temperature 25 ± 1 ° C. and relative humidity 30 ± 5%, A4 size normal printing conditions with a resolution of 1,600 dpi x 1,600 dpi in the best mode and 100% duty. Continuous printing is performed on paper "All-in-One paper" (manufactured by Office Max), and the number of sheets that can be printed until the value becomes 0.05 lower than the print density of the first sheet is measured, and the following evaluation criteria are used. evaluated.
The print density is measured by using a spectrophotometer / densitometer "Spectroeye" (manufactured by X-Light Co., Ltd.) to measure the print density (value output as the optical density of black) of the obtained printed matter. A total of 5 points were measured with (observation viewing angle: 2 degrees, observation light source: D65, white standard: Abs, polarization filter: none, density standard: DIN), and the average value was used as the print density of the printed matter. If it is the following evaluation standard A, it is suitable as a water-based ink. There is a practical problem with the following evaluation criteria B or C.
(Evaluation criteria)
A: 15,000 or more sheets of A4 paper B: 10,000 or more sheets of A4 paper and less than 15,000 sheets C: Less than 10,000 sheets of A4 paper

<Evaluation of storage stability>
40 g of water-based ink obtained in Examples and Comparative Examples was sealed in a 50 cc screw tube (manufactured by Maruemu Corporation, screw tube bottle No. 7), and the temperature was set to 70 ° C. (no humidity setting). It was stored in a product manufactured by Co., Ltd., model: PR-3FT) for 2 weeks, and the average particle size change before and after storage was evaluated as the particle size change rate calculated from the following formula. The closer the particle size change rate is to 100%, the better the storage stability.
Particle size change rate (%) = | [(Average particle size of pigment A-containing crosslinked polymer particles in water-based ink after storage / Initial average particle size of pigment A-containing crosslinked polymer particles in water-based ink) -1] × 100 ｜
The "initial average particle size" is the average particle size of the crosslinked polymer particles containing pigment A in the water-based ink before storage, and the pigment A in the water-based ink obtained in Examples and Comparative Examples shown in Table 2 is used. It is the average particle size of the contained crosslinked polymer particles. If it is the following evaluation standard A, it is suitable as a water-based ink. If it is the evaluation standard B, there is no practical problem, but if the evaluation standard C is, there is a practical problem.
(Evaluation criteria)
A: Particle size change rate is less than 5% B: Particle size change rate is 5% or more and less than 10% C: Particle size change rate is 10% or more

From Table 2, the water-based ink containing each pigment aqueous dispersion of Examples 1-1 to 1-5 uses a specific organic pigment and 1,4-butanediol diglycidyl ether as a cross-linking agent. It can be seen that, as compared with the water-based ink containing each pigment aqueous dispersion of Comparative Examples 1-1 to 1-8, cogging is sufficiently suppressed and the continuous ejection stability is excellent.
Since the water-based ink containing the respective pigment aqueous dispersions of Comparative Examples 1-1 and 1-2 and Comparative Example 1-7 uses quinacridone pigment or carbon black as the organic pigment, the continuous ejection stability is inferior.
Since the water-based ink containing each pigment aqueous dispersion of Comparative Examples 1-3 to 1-6, 1-8 uses a cross-linking agent other than 1,4-butanediol diglycidyl ether as the cross-linking agent, it is continuously ejected. Poor stability.

The present invention can improve the continuous ejection stability of the ink while maintaining the excellent storage stability of the ink when blended with the ink, and therefore, for flexographic printing, gravure printing, or inkjet recording. Since it can be suitably used as a pigment aqueous dispersion, cogation can be sufficiently suppressed, and continuous ejection stability is excellent, it can be particularly suitably used as a pigment aqueous dispersion for thermal inkjet recording. ..

Claims (7)

An aqueous pigment dispersion in which the organic pigment A is dispersed with a crosslinked polymer.
The organic pigment A is one or more selected from dysazopyrazolone-based pigments, perinone-based pigments, dioxazine-based pigments, and copper phthalocyanine-based pigments.
An aqueous pigment dispersion in which the crosslinked polymer is a polymer crosslinked with 1,4-butanediol diglycidyl ether as a crosslinking agent. The crosslinked polymer is a vinyl polymer containing a crosslinked product of the water-dispersible polymer by the cross-linking agent, and the water-dispersible polymer contains a structural unit derived from a hydrophobic monomer and a structural unit derived from an ionic monomer. The pigment aqueous dispersion according to 1. The pigment aqueous dispersion according to claim 2, wherein the water-dispersible polymer is a vinyl-based polymer having a carboxy group. The pigment aqueous dispersion according to claim 2 or 3, wherein the acid value of the water-dispersible polymer is 150 mgKOH / g or more and 320 mgKOH / g or less. The pigment according to any one of claims 2 to 4, wherein the ratio of the number of moles of the epoxy group of the crosslinking agent to the number of moles of the crosslinkable functional group of the water-dispersible polymer is 1 mol% or more and 20 mol% or less. Water dispersion. An inkjet recording water-based ink containing the pigment aqueous dispersion according to any one of claims 1 to 5 and a solvent. A method for producing an aqueous pigment dispersion in which an organic pigment A is dispersed in a crosslinked polymer.
The organic pigment A is one or more selected from dysazopyrazolone-based pigments, perinone-based pigments, dioxazine-based pigments, and copper phthalocyanine-based pigments.
A method for producing an aqueous pigment dispersion, which comprises the following steps 1 and 2.
Step 1: Disperse the water-dispersible polymer, the organic pigment A, and the pigment mixture containing water to obtain a pigment aqueous dispersion. Step 2: The pigment aqueous dispersion obtained in Step 1 and as a cross-linking agent. A step of mixing 1,4-butanediol diglycidyl ether and reacting the water-dispersible polymer with the cross-linking agent to form a cross-linked polymer to obtain a pigment aqueous dispersion.